STEEL:
A MANUAL FOR STEEL-USERS.

BY
WILLIAM METCALF.

FIRST EDITION.
FIRST THOUSAND.

NEW YORK:
JOHN WILEY & SONS.
London: CHAPMAN & HALL, Limited.
1896.

Copyright, 1896,
BY WILLIAM METCALF.

ROBERT DRUMMOND,
ELECTROTYPER AND PRINTER,
NEW YORK.

INTRODUCTION.

Twenty-seven years of active practice in the manufacture of steel brought the author in daily contact with questions involving the manipulation of steel, its properties, and the results of any operations to which it was subjected.

Blacksmiths, edge-tool makers, die-makers, machine-builders, and engineers were continually asking questions whose answers involved study and experiment.

During these years the Bessemer and the open-hearth processes were developed from infancy to their present enormous stature; and the shadows of these young giants, ever menacing to the expensive and fragile crucible, kept one in a constant state of watching, anxiety, and more study.

The literature of steel has grown with the art; its books are no longer to be counted on the fingers, they are to be weighed in tons.

Then why write another?

Because there seems to be one little gap. Metallurgists and scientists have worked and are still working; they have given to the world much information for which the world should be thankful.

Engineers have experimented and tested, as they never did before, and thousands of tables and results are recorded, providing coming engineers with a mine of invaluable wealth. Steel-workers and temperers have written much that is of great practical value.

Still the questions come, and they are almost always those involving an intimate acquaintance with the properties of steel, which is only to be gained by contact with both manufacturers and users. In this little manual the effort is made to fill this gap and to give to all steel-users a systematic, condensed statement of facts that could not be obtained otherwise, except by travelling through miles of literature, and possibly not then. There are no tables, and no exact data; such would be merely a re-compilation of work already done by abler minds.

It is a record of experiences, and so it may seem to be dogmatic; the author believes its statements to be true—they are true as far as his knowledge goes; others can verify them by trial.

If the statements made prove to be of value to others, then the author will feel that he has done well to record them; if not, there is probably nothing said that is likely to result in any harm.

CONTENTS.

STEEL:
A MANUAL FOR STEEL USERS.

I.
GENERAL DESCRIPTION OF STEEL AND
OF MODES OF ITS MANUFACTURE.

Steel may be grouped under four general heads, each receiving its name from the mode of its manufacture; the general properties of the different kinds are the same, modified to some extent by the differences in the operations of making them; these differences are so slight, however, that after having mentioned them the discussion of various qualities and properties in the following pages will be general, and the facts given will apply to all kinds of steel, exceptions being pointed out when they occur.

The first general division of steel is cemented or converted steel, known to the trade as blister-steel, German, shear, and double-shear steel.

This is probably the oldest of all known kinds of steel, as there is no record of the beginning of its manufacture. This steel is based upon the fact that when iron not saturated with carbon is packed in carbon, with all air excluded, and subjected to a high temperature,—any temperature above a low red heat,—carbon will be absorbed by the iron converting it into steel, the steel being harder or milder, containing more or less carbon, determined by the temperature and the time of contact.

Experience and careful experiment have shown that at a bright orange heat carbon will penetrate iron at the rate of about one eighth of an inch in twenty-four hours. This applies to complete saturation, above 100 carbon; liquid steel will absorb carbon with great rapidity, becoming saturated in a few minutes, if enough carbon be added to cause saturation.

MANUFACTURE OF BLISTER-STEEL.

Bars of wrought iron are packed in layers, each bar surrounded by charcoal, and the whole hermetically sealed in a fire-brick vessel luted on top with clay; heat is then applied until the whole is brought up to a bright orange color, and this heat is maintained as evenly as possible until the whole mass of iron is penetrated by carbon; usually bars about three quarters of an inch thick are used, and the heat is required to be maintained for three days, the carbon, entering from both sides, requiring three days to travel three eighths of an inch to the centre of the bar. If the furnace be running hot, the conversion may be complete in two days, or less. The furnace is then cooled and the bars are removed; they are found to be covered with numerous blisters, giving the steel its name.

The bars of tough wrought iron are found to be converted into highly crystalline, brittle steel. When blister-steel is heated and rolled directly into finished bars, it is known commercially as german steel.

When blister-steel is heated to a high heat, welded under a hammer, and then finished under a hammer either at the same heat or after a slight re-heating, it is known as shear-steel, or single-shear.

When single-shear steel is broken into shorter lengths, piled, heated to a welding-heat and hammered, and then hammered to a finish either at that heat or after a slight re-heating, it is known as double-shear steel.

Seebohm gives another definition of single-shear, and double-shear; probably both are correct, being different shop designations.

Until within the last century the above steels were the only kinds known in commerce. There was a little steel made in India by a melting process, known as Wootz. It amounted to nothing in the commerce of the world, and is mentioned because it is the oldest of known melting processes.

Although converted steel is so old, and so few years ago was the only available kind of steel in the world, nothing more need be said of it here, as it has been almost superseded by cast steel, superior in quality and cheaper in cost, except in crucible-steel.

Inquiring readers will find in Percy, and many other works, such full and detailed accounts of the manufacture of these steels that it would be a waste of space and time to reprint them here, as they are of no more commercial importance.

In the last century Daniel Huntsman, of England, a maker of clocks, found great difficulty in getting reliable, durable, and uniform springs to run his clocks. It occurred to him that he might produce a better and more uniform article by fusing blister-steel in a crucible. He tried the experiment, and after the usual troubles of a pioneer he succeeded, and produced the article he required. This founded and established the great Crucible-cast-steel industry, whose benefits to the arts are almost incalculable; and none of the great inventions of the latter half of this nineteenth century have produced anything equal in quality to the finer grades of crucible-steel.

crucible-cast steel is the second of the four general kinds of steel mentioned in the beginning of this chapter.

Although Huntsman succeeded so well that he is clearly entitled to the credit of having invented the crucible process, he met with many difficulties, from porosity of his ingots mainly; this trouble was corrected largely by Heath by the use of black oxide of manganese. Heath attempted to keep his process secret, but it was stolen from him, and he spent the rest of a troubled life in trying to get some compensation from the pilferers of his process. An interesting and pathetic account of his troubles will be found in Percy.

Heath’s invention was not complete, and it was finished by the elder Mushet, who introduced in addition to the oxide of manganese a small quantity of ferro-manganese, an alloy of iron and manganese; and it was now possible, with care and skill, to make a quality of steel which for uniformity, strength, and general utility has never been equalled.

Crucible-steel was produced then by charging into a crucible broken blister-steel, a small quantity of oxide of manganese, and of ferro-manganese, or Spiegel-eisen, covering the crucible with a cap, and melting the contents in a coke-furnace, a simple furnace where the crucible was placed on a stand of refractory material, surrounded by coke, and fired until melted thoroughly.

The first crucibles used, and those still used largely in Sheffield, were made of fire-clay; a better, larger, and more durable crucible, used in the United States exclusively, and in Europe to some extent, is made of plumbago, cemented by enough of fire-clay to make it strong and tough. As the demands for steel increased and varied it was found that the carbon could be varied by mixing wrought iron and blister-bar, and so a great variety of tempers was produced, from steel containing not more than 0.10% of carbon up to steel containing 1.50% to 2% of carbon, and even higher in special cases.

It was soon found that the amount of carbon in steel could be determined by examining the fractures of cold ingots; the fracture due to a certain quantity of carbon is so distinct and so unchanging for that quantity that, once known, it cannot be mistaken for any other. The ingot is so sensitive to the quantity of carbon present that differences of .05% may be observed, and in everyday practice the skilled inspector will select fifteen different tempers of ingots in steels ranging from about 50 carbon to 150 carbon, the mean difference in carbon from one temper to another being only .07%. And this is no guess-work;—no chemical color determination will approach it in accuracy, and such work can only be checked by careful analysis by combustion.

This is the steel-maker’s greatest stronghold, as it is possible by this means for a careful, skilful man to furnish to a consumer, year after year, hundreds or thousands of tons of steel, not one piece of which shall vary in carbon more than .05% above or below the mean for that temper.

The word “temper” used here refers to the quantity of carbon contained in the steel, it is the steel-maker’s word; the question, “What temper is it?” answered, No. 3, No. 6, or any other designation, means a fixed, definite quantity of carbon.

When a steel-user hardens a piece of steel, and then lets down the temper by gentle heating, and he is asked, “What temper is it?” he will answer straw, light brown, brown, pigeon-wing, light blue, or blue, as the case may be, and he means a fixed, definite degree of softening of the hardened steel.

It is an unfortunate multiple meaning of a very common word, yet the uses have become so fixed that it seems to be impossible to change them, although they sometimes cause serious confusion.

The quantity of carbon contained in steel, and indeed of all ingredients, as a rule, is designated in one hundredths of one per cent; thus ten (.10) carbon means ten one hundredths of one per cent; nineteen (.19) carbon means nineteen one hundredths of one per cent; one hundred and thirty-five (1.35) carbon means one hundred and thirty-five one hundredths of one per cent, and so on. So also for contents of silicon, sulphur, phosphorus, manganese and other usual ingredients.

This enumeration will be used in this work, and care will be taken to use the word “temper” in such a way as not to cause confusion.

It has been stated that crucible-cast steel is made from ten carbon up to two hundred carbon, and that its content of carbon can be determined by the eye, from fifty carbon upwards, by examining the fracture of the ingots. The limitation from fifty carbon upwards is not intended to mean that ingots containing less than fifty carbon have no distinctive structures due to the quantity of carbon; they have such distinctive structures, and the difficulty in observing them is merely physical.

Ingots containing fifty carbon are so tough that they can only be fractured by being nicked with a set deeply, and then broken off; below about fifty carbon the ingots are so tough that it is almost impossible to break open a large enough fracture to enable the inspector to determine accurately the quantity of carbon present; therefore it is usual in these milder steels, when accuracy is required, to resort to quick color analyses to determine the quantity of carbon present. Color analyses below fifty carbon may be fairly accurate, above fifty carbon they are worthless.

As the properties and reliability of crucible-steel became better known the demand increased, and the requirements varied and were met by skilful manufacturers, until, by the year 1860, ingots were produced weighing many tons by pouring the contents of many crucibles into one mould; in this way the more urgent demands were met, but the material was very expensive and the risks in manufacturing were great. About this time, stimulated by the desire of enlightened governments to increase their powers of destruction in war by the use of heavy guns of greater power than could be obtained by the use of cast iron, and for heavier ship-armor to be used in defence, Mr. Bessemer, of England, now Sir Henry Bessemer, reasoned that if melted cast iron was reduced to wrought iron by puddling, or boiling, by the mere oxidation, or burning out, of the excess of carbon and silicon from the cast iron, that the same cast iron might be reduced to steel in large masses by blowing air through a molten mass in a close vessel, retaining enough heat to keep the mass molten so that the resulting steel could be poured into ingots as large as might be desired. At about the same time, or a little earlier, Mr. Kelly, of the United States, devised and patented the same method. Both of these gentlemen demonstrated the potencies of their invention, and neither brought it to a successful issue.

To persistent and intelligent iron-masters of Sweden must be given the credit of bringing the process of Bessemer to a commercial success, and so they gave to the world pneumatic or Bessemer steel, the latter name holding, properly, as a just tribute to the inventor, and this inaugurated the third general division:

BESSEMER STEEL.

Bessemer steel is made by pouring into a bottle-shaped vessel lined with refractory material a mass of molten cast iron, and then blowing air through the iron until the carbon and silicon are burned out. The gases and flame resulting escape from the mouth of the vessel.

The combustion of carbon and silicon produce a temperature sufficient to keep the mass thoroughly melted, so that the steel may be poured into moulds making ingots of any desired size.

In the beginning, and for many years, the lining of the vessel was of silicious or acid material, and it was found that all of the phosphorus and sulphur contained in the cast iron remained in the resulting steel, so that it was necessary to have no more of these elements in the cast iron than was allowable in the steel. The higher limit for phosphorus was fixed at ten points (.10%), and that is the recognized limit the world over. When Bessemer pig is quoted, or sold and bought, it means always a cast iron containing not more than ten phosphorus.

In regard to sulphur, it was found that if too much were present the material would be red-short, so that it could not be worked conveniently in the rolls or under the hammer, and that when the amount of sulphur present was not enough to produce red-shortness it was not sufficient to hurt the steel.

As red-short material is costly and troublesome to the manufacturer, it was not found necessary to fix any limit for sulphur, because the makers could be depended upon to keep it within working limits.

Later investigations prove this to be a fallacy, as much as ten or even more sulphur has been found in broken rails and shafts, the steel having made workable by a percentage of manganese. (See the results of Andrews’s investigation given in [Chap. X].)

During the operation of blowing Bessemer steel the flame issuing from the vessel is indicative of the elimination of the elements, and it is found that while the combustion is partially simultaneous the silicon is all removed before the carbon, and the characteristic white flame towards the end of the blow is known as the carbon flame; when the carbon is burned out, this flame drops suddenly and the operator knows that the blow is completed. Any subsequent blowing would result in burning iron only. During the blow the steel is charged heavily with oxygen, and if this were left in the steel it would be rotten, red-short, and worthless. This oxygen is removed largely by the addition of a predetermined quantity of ferro-manganese, usually melted previously and then poured into the steel.

The manganese takes up the greater part of the oxygen, leaving the steel free from red-shortness and easily worked.

The fact that the phosphorus of the iron remained in the steel notwithstanding the active combustion and high temperature led to the dictum that at high temperatures phosphorus could not be eliminated from iron. This conclusion was credited because in some of the so-called direct processes of making iron where the temperature was never high enough to melt steel all, or nearly all, of the phosphorus was removed from the iron.

For many years steel-makers the world over worked upon this basis, and devoted themselves to procuring for their work iron containing not more than ten (.10) phosphorus, now universally known and quoted as Bessemer iron.

Two young English chemists, Sidney Gilchrist Thomas and Percy C. Gilchrist, being careful thinkers, concluded that the question was one of chemistry and not one of temperature; accordingly they set to work to obtain a basic lining for the vessel and to produce a basic slag from the blow which should retain in it the phosphorus of the iron. After the usual routine of experiment, and against the doubtings of the experienced, they succeeded, and produced a steel practically free from phosphorus. For the practical working of their process it was found better, or necessary, to use iron low in silicon and high in phosphorus, using the phosphorus as a fuel to produce the high temperature that is necessary instead of the silicon of the acid process. In the acid process it is found necessary to have high silicon—two percent or more—to produce the temperature necessary to keep the steel liquid; in the Thomas-Gilchrist process phosphorus takes the place of silicon for this purpose.

In this way the basic Bessemer process was worked out and became prominent.

The basic Bessemer process is of great value to England and to the continent of Europe by enabling manufacturers to use their native ores, which are usually too high in phosphorus for the acid process, so that before this invention nearly all of the ores for making Bessemer steel were imported from Sweden, Spain, and Africa.

The basic process has found little development in the United States, because the great abundance of pure ore keeps the acid process the cheaper, except in one or two special localities. Where the basic process is profitable in the United States, it is worked successfully.

At about the time that Bessemer made his invention William Siemens, afterward Sir William, invented the well-known regenerative gas-furnace. A Frenchman named Martin utilized this furnace to melt steel in bulk in the hearth of the furnace, developing what was known for some years as Siemens-Martin steel, or open-hearth steel; the latter name has prevailed, and open-hearth steel is the fourth of the general kinds of steel mentioned in the beginning of this chapter.

At first open-hearth steel was made upon a specially prepared sand bottom, by first melting a bath of cast iron and then adding wrought iron to the bath until by the additions of wrought iron and the action of the flame the carbon and silicon of the cast iron were reduced until the whole became a mass of molten steel. Sometimes iron ore is used instead of wrought iron as the reducing agent; this is called the pig and ore process. Now in general practice wrought iron, steel scrap, and iron ore are used, sometimes alone and sometimes together, as economy or special requirements make it convenient.

It was found as in the Bessemer, so in the open-hearth, the sulphur and the phosphorus of the charge remained in the steel, making it necessary to see that in the charge there was no more of these elements than the steel would bear.

This is known now as the acid open-hearth process.

After the success of the basic Bessemer process was assured the same principle was tried in the open-hearth; a basic bottom of dolomite or of magnesite was substituted for the acid sand bottom, and care was taken to secure a basic slag in the bath.

Success was greater than in the Bessemer; phosphorus was eliminated and a better article in every way was made by this process, now used extensively over the whole civilized world.

This is the basic open-hearth process.

Neither the basic Bessemer process nor the basic open-hearth removed sulphur, so that this element must still be kept low in the original charge, until some way shall be found for its sure and economical elimination.

The four general divisions, then, are:

Converted or Cemented Steel.
Crucible-cast Steel.
Bessemer		Acid		Cast Steel.
		Basic
Open-hearth		Acid		Cast Steel.
		Basic

Little or nothing more will be said of the first kind, as it has been so thoroughly superseded by the cast steels. After a statement of the most patent applications and uses of the different cast steels the discussions which follow will apply to all, because practically they are all governed by the same general laws.

II.
APPLICATIONS AND USES OF THE
DIFFERENT KINDS OF STEEL.

Where exact uniformity of composition is not a necessity, and where welding is required, cemented or converted steel may be preferred to cast steel, because the converted bar retains the occluded layers of slag which give to wrought iron its peculiar welding properties, and for this reason blister- or shear-steel may be welded more easily and surely than cast steel. For tires, composite dies, and many compound articles this steel will do very well, and it may be worked with good results by almost any smith of ordinary skill; however, owing to the more uniform structure and the greater durability of the cast steels, they have, even for these purposes, almost entirely displaced the more easily worked, but less durable, cemented steels.

CRUCIBLE-CAST STEEL.

For all purposes crucible-steel has proved to be superior to all others; it is well known to all experienced and observing workers in steel that, given an equal composition, crucible is stronger and more reliable in every way than any of the other kinds of steel.

This may read like a mere dictum, and it might be asked properly, What are the proofs?

The proofs are wanting for two reasons: first, because crucible-steel is so expensive that except for gun parts, armor, and such uses where expense could be ignored, crucible-steel never came into extensive use for structural purposes; second, that while thousands upon thousands of tests of the cheaper steels are recorded and available to engineers very few of such tests have been made on crucible-steel, simply because it has not been used for structural purposes.

On the other hand, intelligent makers of crucible-steel have for self-preservation made careful study of the relative properties of the different steels in order that they might know what to expect from the cheaper processes. In this way they have surrendered boiler-steel, spring-steel, machinery-steel, battering-tool steel, cheap die-steel, and many smaller applications; not because they could not produce a better article, but because the cheaper steels met the requirements of consumers satisfactorily, and therefore they could not be expected to pay a higher price for an article whose superiority was not a necessity in their requirements.

Still this stated superiority is proven best by the fact that many careful consumers who have special reasons for studying durability as against first cost adhere to the higher priced crucible-steel for such uses as, for instance, parts of mining- and quarrying-drills, high-speed spindles, in cotton-mills, and in expensive lathes and machines of that kind.

This sort of testimony should be more conclusive than that of interested steel-makers, because these men pay their own money for the higher priced material, and because men who are most careful of the quality of their produce and of their reputation are the most clear-headed and most sensible men of their class; they have the best business and the greatest success. Such men are not fools; they may be depended upon to try everything of promise with the greatest care, and to use only that thing which pays them best. In fact such men do use the cheaper steels freely wherever they can do so safely.

A good car-spring, carriage-spring, or wagon-spring is made from Bessemer or open-hearth steel, a spring that will wear out the car or carriage; it would be stupid then to buy more expensive steel for such purposes, for even if crucible-steel would wear out two cars or two wagons the owner never expects to take the springs out of an old wagon to put them under a new one.

On the other hand, the watch-spring maker or the clock-spring maker will find a great advantage in using the very best crucible-steel that can be made.

A sledge, a maul, or a hammer can be made of such excellent quality from properly selected Bessemer or open-hearth steel that it would be foolish for makers of such tools to continue to buy crucible-steel, even though they knew it to be superior, for lower first cost in such cases outweighs superiority that cannot be shown for a number of years.

Locomotive-boilers, crank-pins, slide-rods, connecting-rods, and springs can be made of such good quality of Bessemer or open-hearth steel that, like the “one-horse shay,” the whole machine will wear out at the same time practically, and that a good long time; there would be no reason in this case for using crucible-steel for one or more of these parts, although twenty-five years ago it was by means of crucible-steel that engineers learned to use steel for these purposes.

A good cam for an ordinary machine, such as a shear or punch, may be made of Bessemer or open-hearth steel where greater strength and endurance are required than can be had in cast iron; on the other hand, makers of cams for delicately adjusted high-speed machines where intricacy and accuracy are necessary will touch nothing but the very best crucible-steel of fine-tool quality for their work. It is of no use to suggest the greater cheapness of the other steels; they have tried them thoroughly, and they know that in their case the highest priced is the cheapest.

This superiority of crucible-steel has been doubted, because the claim appeared to rest solely upon the statements of steel-makers, and not to have any scientific basis; there is, however, a scientific basis for the fact. Given three samples of steel of say the following composition:

Why should there be any difference in the strength of the three? In mere tensile strength in an untempered bar the difference might not be very great, although all experienced persons would expect the crucible to show the highest; but it is not necessary to make the claim, because we have not enough tests of crucible-steel to enable us to establish a mean, and one or two tests are insufficient to establish a rule in any case.

There have been made, however, hundreds of tests of hardened and tempered samples by the most expert persons, with one invariable result: the crucible-steel is incomparably finer and stronger than the others, and the open-hearth is almost invariably stronger and finer than the Bessemer.

Unfortunately for the argument these tests cannot be recorded so as to be intelligible to the non-expert, because we cannot tabulate the result of the touch of the expert hand or the observation of the experienced eye.

For a time it was popular to call these differences mysteries, and so let them pass; this, however, was not satisfactory, and the question was studied carefully for the physical reasons which must exist.

Much thought led to the conclusion that the reason lay with the three elements oxygen, nitrogen, and hydrogen; they are known to exist in greater or less quantity in all iron and steel.

It is known that the presence of oxygen beyond certain small limits produces red-shortness and general weakness; it is probably a much more hurtful element than phosphorus or sulphur, but no quantitative method for its determination has been worked out; there is an effort now being made to develop a simple and expeditious oxygen determination, and it is to be hoped that it will be successful.

In the crucible no more oxygen, hydrogen, or nitrogen can get into the steel than is contained in the material charged and in the atmosphere of the crucible, or than may penetrate the walls of the crucible during melting. In the open hearth the process is an oxidizing one, and besides the charge is swept continuously by hot flames containing all of these elements.

In the Bessemer process the conditions are worse still, as these elements are all blown through the whole mass of the steel.

We know the effect of oxygen and how to eliminate it practically.

Percy gives the effects of nitrogen as causing hardness and extreme brittleness, and giving to iron or steel a brassy lustre. Such a brassy lustre may be seen frequently in open-hearth or Bessemer steel, and occasionally in crucible-steel. When seen in crucible-steel it is known to be due to the fact that the cap of the crucible became displaced, exposing the contents to the direct action of the flame. Of the effect of hydrogen we know less; there is no reason apparent why it may not be as potent as the others.

Ammonia in sufficient quantity to be detected by the nose has often been observed in open-hearth and Bessemer steel.

To settle the nitrogen question Prof. John W. Langley developed some years ago a very delicate and accurate process for the determination of nitrogen even in minute quantities; the process was tedious and expensive, so that it was not adapted for daily use; it involved the careful elimination of nitrogen from all of the reagents to be used, requiring several days’ work, in each case to prepare for only a few nitrogen determinations.

By this process it was found, in every one of many trials, that crucible-steel contained the least amount of nitrogen, open-hearth steel the next greater quantity, and Bessemer steel the greatest amount. He found no exceptions to this. For many years great efforts had been made both in Europe and in the United States to make by the Bessemer or the open-hearth process a cheap melting-product to be used in the crucible instead of the expensive irons which so far have proved to be necessary to give the best results.

There appeared to be no difficulty in making a material as pure chemically, or purer, than the most famous irons in the world, and this material was urged upon the crucible-steel makers. Careful tests of such material failed to produce the required article; in fact it was demonstrated over and over again that an inferior wrought iron would produce a stronger steel than this very pure steel melting-material, and crucible-steel makers were compelled to adhere to the more costly irons to produce their finer grades.

Prof. Langley determined the nitrogen in a given quantity of open-hearth and Bessemer steel; this same material was then melted in a crucible, and it was found that the resulting ingots contained nearly as much nitrogen as the original charge. The quantity was reduced slightly; still this steel contained more nitrogen than any other sample of crucible-steel that he had tested. The physical test of this trial steel showed the usual weakness of the Bessemer or open-hearth steel, as compared to crucible-steel.

The next step was to try to get rid of nitrogen by the use of some affinity, as oxygen is removed by manganese. Boron and titanium seemed to be the most feasible elements; boron appeared to offer less chance of success, and titanium was selected. A ferro-titanium containing six per cent of titanium was imported from Europe at some expense. As the most careful and exacting analyses of this material failed to reveal a trace of titanium, it was not used.

After many futile efforts Langley succeeded, by means of electric heat, in reducing rutile and producing a small quantity of an alloy of iron and titanium. A trial of this alloy, although not conclusive, led to the belief that such an alloy could be used successfully to eliminate nitrogen; but as its cost, about two dollars a pound, was prohibitory of any commercial use, the subject was not pursued farther.

Although we know these elements only as gases, there is no reason to suppose that their atoms may not be as potent, when added to steel, as atoms of carbon, silicon, phosphorus, or any other substance.

Such are the facts for crucible-steel as far as they are known; it is vastly more expensive than any other kind of steel, yet for the present it holds its own unique and valuable place in the arts.

For all tools requiring a fine edge for cutting purposes, such as lathe-tools, drills, taps, reamers, milling-cutters, axes, razors, pocket-knives, needles, graving-tools, etc.; for fine dies where sharp outline and great endurance are required; for fine springs and fine machinery parts and fine files and saws, and for a hundred similar uses, crucible-cast steel still stands pre-eminent, and must remain so until some genius shall remove from the cheaper steels the elements that unfit them for these purposes.

As stated before, crucible-steel is divided into fifteen or more different tempers, ranging in carbon from .50 to 1.50. Each of these tempers has its specific uses, and a few will be pointed out in a general way.

.50 to .60 carbon is best adapted for hot work and for battering-tools.

.60 to .70 carbon for hot work, battering-tools, and tools of dull edge.

.70 to .80 carbon for battering-tools, cold-sets, and some forms of reamers and taps.

.80 to .90 carbon for cold-sets, hand-chisels, drills, taps, reamers, and dies.

.90 to 1.00 carbon for chisels, drills, dies, axes, knives, and many similar purposes.

1.00 to 1.10 carbon for axes, hatchets, knives, large lathe-tools, and many kinds of dies and drills if care be used in tempering them.

1.10 to 1.50 carbon for lathe-tools, graving-tools, scribers, scrapers, little drills, and many similar purposes.

The best all-around tool-steel is found between .90 and 1.10 carbon; steel that can be adapted safely and successfully to more uses than any other temper.

At somewhere from .90 to 1.00 carbon, iron appears to be saturated with carbon, giving the highest efficiency in tools and the highest results in the testing-machine except for compressive strains. More will be said upon this point in treating of the carbon-line.

Much more could be said about the uses for the different tempers of steel; it would be easy to write out in great detail the exact carbon which experience has shown to be best adapted to any one of hundreds of different uses, but it would only be confusing and misleading to a great many people.

It is within the experience of every steel-maker that men are just as variable as steel, and the successful steel-maker must familiarize himself with the personal equations of his patrons. One man on the sunny side of a street may be making an excellent kind of tool from a certain grade and temper of steel, and be perfectly happy and prosperous in its use. His competitor on the shady side of the street may fail in trying to use the same steel for the same purpose and condemn it utterly.

The know it all agent will condemn the latter man with an intimation that his ears are too long, and so lose his trade. The tactful agent will supply him with steel a temper higher or a temper lower, until he hits upon the right one, and so will retain both men on his list; and both men will turn out equally good products.

Few men know their own personal equations, and the best way for a steel-user to do is to tell the steel-maker what he wants to accomplish, and put upon him the responsibility of selecting the best temper.

It costs no more to make and to provide one temper than another; therefore the one inducement of the steel-maker is to give his patron that which is best adapted to his use. This plan puts all of the responsibility upon the steel-maker, just where it ought to be, because he should know more about the adaptability of his steel than any other person.

BESSEMER STEEL.

Bessemer steel is probably the cheapest of all grades of steel; that is to say, it can be made so rapidly, so continuously, and in such enormous quantities that a greater output per dollar invested can be made than by either of the other processes. Again, the work is controlled and operated by machinery to a much greater extent than in the other processes; therefore the cost of labor per ton of product both for skilled and unskilled labor is less than in the crucible or the open-hearth method.

This being the case, it might be inferred that the result would be the eventual driving out of all other steels by this, the cheapest. This would be the inevitable result if Bessemer steel were as well adapted to all purposes as either of the other kinds of steel; there are limitations which prevent this.

The source of heat in the Bessemer process is in the combustion of the elements of the charge, there is no extraneous source of heat; therefore, if the heat be too cold, there is no way to remedy it unless it be by the addition of ferro-silicon and more blowing; if it be too hot, it may be allowed to stand a few minutes to cool. Still in either case the remedy is somewhat doubtful. This limitation must not be taken as being fatal to good work, for in skilful hands such cases are rare, and the product is generally fully up to the standard of good work.

As there is no known sure way of stopping the blow at a given point in the operation to produce a steel of required carbon, it is usual to blow clear down, that is, to burn out all of the carbon practically and then to re-carbonize by the addition of spiegel-eisen or ferro-manganese. It is necessary, also, to add the manganese in one of these forms to remove the oxygen introduced during the blow; this must be done quickly, and all accomplished before the metal becomes too cold for pouring into ingots.

So little time for reactions is available that it is doubtful if the material is ever quite as homogeneous as it can be made by either of the other processes.

Notwithstanding these limitations, which are not mentioned to throw doubt upon the process, but merely to inform readers fully so as to enable them to judge rightly as to what may be expected, enormous quantities of good, reliable Bessemer steel are made to meet many requirements.

For good, serviceable, cheap rails Bessemer steel stands pre-eminent, and if it found no other use it would be difficult to overestimate the benefit to the world of this one great success.

Bessemer steel is used largely for a great number of purposes, Bessemer billets being now as regular an article of commerce as pig iron.

For wire for all ordinary purposes; for skelp to be worked into butt-welded and lap-welded tubing; for wire nails, shafting, machinery-steel, tank-plates, and for many other uses, Bessemer steel has absorbed the markets almost entirely.

For common cutlery, files, shovels, picks, battering-tools, and many such uses it contests the market with open-hearth steel; and while many engineers now specify that their structural shapes, plates, beams, angles, etc., must be of open-hearth steel, there are many eminent engineers who see no need for this discrimination, they being satisfied that if their requirements are met the process by which they are met is a matter of indifference.

OPEN-HEARTH STEEL.

As in the Bessemer process, so in the open-hearth, carbon and silicon are burned out, phosphorus is removed on the basic hearth, and the sulphur of the charge remains in the steel. During the operation oxygen and nitrogen are absorbed by the steel, although not quite so largely as in the Bessemer process, so that practically the chemical limitations are the same in each.

The open-hearth reductions are much slower than in the Bessemer, each heat requiring from five to eight hours for its completion; the furnace must be operated by a skilled man of good judgment, so that more time and more skilled labor per ton of product are required than in the Bessemer, and the making of an equal quality as cheaply in the open hearth is problematical. The open hearth has extraneous sources of heat at the command and under the control of the operator, and there need be no cold heats, and no too hot heats.

The time for reactions is much longer, and for this reason they ought to be more complete, and they are so in good hands; yet it is a fact that, as the operation is a quiet one compared to the Bessemer, and not nearly so powerful and energetic, a careless or unskilful operator may produce in the open hearth an uneven result that is quite as bad as anything that can be brought out of a Bessemer converter. The process that eliminates the human factor has not yet been invented.

For fine boiler-plates, armor-plates, and gun parts open-hearth steel has won its place as completely as has the crucible for fine-tool steel or the Bessemer for rails.

For all intermediate products there is a continued race and keen competition, so that it is impossible to draw any hard and fast line between the products of the three processes where they approach each other; the only clear distinctions are at the other extremes.

Owing to the power to hold and manipulate a heat in the open-hearth it is safe to say that it is superior to the Bessemer in the manufacture of steel castings; and owing to its much greater cheapness it is difficult for the crucible to compete with it at all in this branch of manufacture.

In conclusion of this chapter it is safe to say that in good hands these processes are all good, and each has its own special function to perform.

III.
ALLOY STEELS AND THEIR USES.

In addition to the four general kinds of steel treated of in the last chapter there are a number of steels in the market which contain other metals, and which may be termed properly alloy steels, to distinguish them from carbon steel, or the regular steels of world-wide use which depend upon the quantity of carbon present for their properties. The most generally known of the alloy steels is the so-called Self-hardening steel.

Self-hardening steel is so called because when it is heated to the right temperature,—about a medium orange color,—and is then allowed to cool in the air, it becomes very hard. This steel is so easily strained that it is impossible, as a rule, to quench it in water without cracking it. It may be quenched in a blast of air without cracking, and so be made much harder than if it be allowed to cool more slowly in a quiet atmosphere. If it be quenched in oil or water, it will become excessively hard, much harder than when quenched in air, and it will almost invariably be cracked, or if it be not cracked it will be so excessively brittle as to be of little use.

Self-hardened steel is so hard in what may be called its natural condition, that is, in ordinary bars, that it cannot be machined, drilled, planed, or turned in a lathe.

By keeping it in an annealing-furnace at about bright orange heat for about twenty-four to thirty-six hours, and then covering it with hot sand or ashes in the furnace, and allowing about the same time for it to cool, it may be annealed pretty thoroughly so that it may be machined readily.

When annealed in this way and formed into cutters of irregular shape, or dies, it has been found so far not to be economical or well adapted to such work, so that up to the present time annealing is more of a scientific than a useful fact.

Self-hardened steel has the useful property of retaining its hardness when heated almost to redness; therefore it may be used as a lathe or similar cutter upon hard work, such as cutting cast iron and other metals, at a much higher speed than is possible with ordinary steel, which would be softened by the heat generated by the high speed. This property makes self-hardened steel very useful and economical for many purposes.

Self-hardened steel is an alloy of iron, carbon, tungsten, and manganese, and some brands contain chromium in addition to these, and it is claimed, and probably truly, that the chromium improves the quality of the steel.

It was supposed for a long time that tungsten was the hardener that gave to self-hardened steel its peculiar properties. By means of an open hearth, steel was produced containing about 3% tungsten and little carbon and manganese. This steel worked like any mild steel, except that it was hot-short and difficult to forge. It was not hard and had no hardening properties; that is, it did not harden in the ordinary sense when quenched in water. The addition of carbon to this steel, keeping the manganese low, produced a steel very difficult to work, which would harden like ordinary steel when quenched, and which had no self-hardening properties whatever. The addition of 2½% to 3% of manganese to this steel produced self-hardening steel having the usual properties.

Manganese, then, is the metal that gives the self-hardening property, and this might have been anticipated by considering the properties of Hadfield’s manganese steel, which, when it contains above 7% manganese, cannot be annealed so that it can be machined or drawn into wire. From this it might be inferred that tungsten is not a necessary constituent of self-hardened steel; that it performs an important function will be shown presently. Tests of the iron-tungsten alloy low in carbon gave only a small increase in strength above ordinary low cast steel containing little carbon; it was difficult and troublesome to work, and more expensive than the common steels, so that its production presented no advantages. When carbonized, it was fine-grained and could be made exceedingly hard; it was brittle, and compared to very ordinary cast steel comparatively worthless.

In self-hardened steel tungsten is the mordant that holds the carbon in solution and enables the steel to retain its hardness at comparatively high temperatures. That it does hold the carbon in solution may be proved in a moment by a beautiful test, first observed by Prof. John W. Langley.

When a piece of carbon steel is pressed against a rapidly running emery wheel, there is given off a shower of brilliant sparks which flash out in innumerable white, tiny stars of great beauty; it is accepted that this brilliancy is due to the explosive combustion of particles of carbon.

When a steel containing as much as three per cent of tungsten is pressed against the wheel, the entire absence of these brilliant flashes is at once noticeable, and if there be an occasional little flash it only serves to emphasize the absence of the myriads.

Instead there is an emission of a comparatively small number of dull particles, and there is clinging to the wheel closely a heavy band of a deep, rich red color. This red streak is distinctive of the presence of tungsten.

By testing various pieces it was soon observed that different quantities of tungsten gave different sizes of red streaks; as tungsten decreased the width of the band diminished and the number and brilliancy of carbon sparks increased. As little as .10 tungsten will show a fine red line amidst a brilliant display of sparks, and it soon became possible to determine so closely by the streak the quantity of tungsten present that the ordinary analyses for tungsten became unnecessary, except in occasional important cases where analysis was used merely to confirm the testimony of the wheel.

Self-hardening steel, then, is a steel which, owing to the presence of manganese and tungsten, hardens when quenched in quiet air, and which retains its hardness almost up to a red heat.

It may be forged between the temperatures from orange to bright orange; it cannot be worked safely outside of this range. The more quickly it is quenched the harder it will be; and it may be annealed so that it can be machined readily. Therefore it is not self-hardening; it simply has all of the properties of carbon steel modified profoundly by tungsten and manganese. If a piece of this steel will not harden sufficiently by cooling in the air quietly, that difficulty may be remedied by cooling it in an air-blast; if quenching in an air-blast will not give sufficient hardness, the steel had better be rejected, for quenching in oil or water means almost certain destruction.

As stated before, the range of temperature in which self-hardened steel can be forged safely is much smaller than for a high-carbon steel; it is harder at this heat than carbon steel and not so plastic, so that it requires more care and more heats in working it to tool-shapes.

This steel is so sensitive that it often occurs in redressing it that it will crumble at a heat that was all right in the first working. This difficulty may be remedied by first cutting off the shattered part with a sharp tool,—it must be cut hot,—then heating the piece up to nearly a lemon color, heating it through without soaking it in the fire, and then allowing it to cool slowly in a warm, dry place. After this treatment the steel may be heated and worked as at first. This treatment does not anneal the steel soft, because the heat is not continued long enough, and the cooling is not sufficiently slow; it does relieve the strains in the steel, so that it is plastic and malleable.

This treatment is good in any high steel which has become refractory from previous working.

Self-hardened steel is not as strong in the hardened condition as good high-carbon steel; it has not been used successfully for cutting chilled cast iron, for instance. If made hard enough to cut a chill, it is so brittle that the cutting-edge will crumble instead of cutting; if the temper be let down enough to stop the crumbling, the steel will be softer than the chill, and the edge will curl up instead of cutting.

Owing to the retention of hardness at a higher temperature than carbon steel will bear this steel is capable of doing a great amount of work at high speed, so that for much lathe-work it is cheap at almost any price.

Owing to its brittle, friable nature its use is limited to the simpler forms of tools, and to a narrower range of work than is possible with carbon steel.

CHROME STEEL.

An alloy of chromium with carbon steel has been before the public for many years, and greater claims have been made for it than experience seems to justify. Chrome steel is fine-grained and very hard in the hardened state, and it will do a large amount of work at the first dressing; upon redressing it deteriorates much more rapidly than carbon steel and becomes inferior; it is believed that this is due to a rapid oxidation of the chromium.

It is claimed for it that it will endure much higher heats without injury than carbon steels of the same temper. Intending purchasers will do well to satisfy themselves upon these points before investing too heavily.

SILICON STEEL.

Steel containing two to three per cent of silicon was put upon the markets, and great claims were made for it.

It is exceedingly fine-grained and hardens very hard; it is brittle, much more liable to crack in hardening than ordinary steel, and it is not nearly so strong as carbon steel.

It is made cheaply enough as far as melting goes, but it may not be melted dead, and therefore sound, because long-continued high heat will destroy it; therefore the ingots are more honeycombed than well-melted carbon steel ingots. The steel will not bear what is known as a welding-heat in steel-working; it is hot-short; for this reason the bars are more seamy than is usual in carbon steel. Added to this the hot-shortness makes it so difficult to work that the labor cost is high. Altogether, then, silicon steel is expensive, and it presents no extra good qualities in compensation.

MANGANESE STEEL.

The glassy hardness, brittleness, and friability of ferro-manganese and of spiegel-eisen are well known; these are products of the blast-furnace, and the manganese ranges all the way from say 10% up to 80%.

Steel containing from 1% to 3% of manganese is about as brittle and almost as unworkable as spiegel-eisen, and a fair deduction would be that manganese above very small limits will not form any useful alloy with iron. Many a general law of nature has been based upon much more meagre data and has been announced with a great flourish of trumpets; such discoveries are usually heard of no more after the first blare has died away.

R. A. Hadfield, of Sheffield, England, is an inquirer who wants to know, and who is willing to travel the whole road in order to find out. Hadfield discovered that an alloy of iron and manganese containing from 7% to 20% of manganese was a compound possessing many remarkable properties. This alloy is now known as manganese steel.

Manganese steel is both hard and tough to a degree not found in any other metal or alloy.

It is so hard and strong that it cannot be machined with the best of tools made of the finest steel. Castings made of it may be battered into all sorts of shapes as completely as if they were made of the mildest dead-soft steel; still they are too hard to be machined.

The ordinary hardening process toughens this steel instead of hardening it to brittleness.

This steel is non-magnetic, and this property alone would give it exceedingly great value if the steel could only be worked into the required shapes.

Up to this time all attempts to anneal this steel have failed, and this persistent hardness is the best proof that manganese is the real hardener in self-hardened steel. So far carbon and manganese have not been separated in this steel or in any other. Persistent attempts have been made to produce manganese steel low in carbon, but all have been failures, because any operation that burned out the carbon took the manganese with it. The hope was that a non-magnetic alloy might be produced that would be soft enough to work. This may yet be accomplished, and if it should be another great step in the arts will have been taken.

Hard, tough, strong, non-magnetic—what great things may not come out of this when it has been worked out finally?

Since this was written carbonless manganese has been produced which is claimed to contain 98% + of manganese and no carbon, but at present it is sold at $1 per pound. If it can be produced more cheaply, it may lead to a workable non-magnetic alloy of iron and manganese which may prove to be of great value to electricians and to watchmakers.

The uses of manganese steel are large and growing, and it must be regarded as having an established and a prominent place.

It has been stated that in self-hardened steel and in manganese steel manganese is the hardener; it should be borne in mind that carbon is always present, that it is the one great hardener, but its hardening property in the absence of manganese depends directly upon rapidity of cooling. By rapid cooling steel containing carbon is made harder than glass, and by slow cooling it may be made softer and more ductile than ordinary wrought iron.

Self-hardened steel may be annealed so that it can be machined, but it is by no means as soft and ductile as well-annealed carbon steel. Manganese steel has not been annealed at all; it cannot be annealed by any of the well-known annealing processes; some new way of doing it must be discovered. Therefore it is proper to say that the peculiar hardening properties of these two steels are due to manganese.

NICKEL STEEL.

The addition of a few per cent of nickel to mild steel adds greatly to its strength—so much so that nickel steel is now world-renowned as used in armor-plate for navy vessels, and for great guns. Recent reports from the ordnance bureaus indicate that it will also be of great use in the barrels of small arms, by means of which they may be made lighter, and still of sufficient strength. Nickel is so expensive and it adds so much to the cost of steel that its use for ordinary structural purposes, bridges, etc., has not been found to be economical.

Some years ago careful experiments were made with nickel alloy in a fine grade of high-carbon tool-steel to find out whether such steel would be improved as much as are the mild steels.

In such case the expense would not count, for if the best steel can be made better there are many users who would gladly pay a higher price for a better service.

The results were not encouraging. The high-carbon nickel steel was not as strong as the same quality of steel without nickel; the mixture seemed to be imperfect, containing little dark specks, supposed to be carbon thrown into the graphitic state. The steel did not refine as well and was not as strong as the carbon steel.

All of this applies to high-carbon tool-steel, hardened and tempered; no tests were made of the steel unhardened, for they would have been of no practical use.

ALUMINUM STEEL.

When a heat of steel is boiling violently, is wild, and unfit to be poured, the addition of a minute quantity of aluminum will have the effect of quieting it quickly. Half an ounce to an ounce of aluminum to a ton of steel will be enough usually, and for this purpose aluminum has become useful to steel-makers. If a little too much aluminum be added, the ingots will pipe from end to end; therefore the use of aluminum is restricted to small quantities. Experiments have shown that a considerable percentage of aluminum adds no good properties to steel; therefore aluminum steel so called may be treated later under a different heading.

IV.
CARBON.

Of all of the abundant elements of nature carbon is presented in the greatest variety of forms, and admits of the greatest number of useful applications.

In the form of the diamond it is the hardest of substances, and is the base used in determining the comparative hardness of all others.

In the form of graphite it is soft and smooth, and is one of the best and most durable of lubricants.

In the form of soot it is probably the softest of solids.

In the form of coal it is the one great and abundant fuel of the world, while as graphite again it is one of the best of refractory materials.

Hard, soft, highly combustible, almost infusible, refractory, it lends itself to the greatest variety of useful applications. To the iron- and steel-maker or worker it is simply indispensable; as charcoal or coke it is the fuel of the smelter; as gas, either carbon monoxide or as a hydrocarbon, it is the cheapest and most manageable fuel for melting and for all operations requiring heat.

As graphite, plumbago, mixed with a little fire-clay as a binder, it is the best material for crucibles in which to melt metals; as soot it forms the best coating for moulds into which metals are to be cast.

Durable beyond almost any other substance, it would make the very best paint for metal structures if there were any known way to make it adhere.

CARBON IN IRON.

Carbon may be introduced into iron in any quantity from a few hundredths of one per cent as usually found in wrought iron, and in what is known as dead-soft steel, up to about four per cent as found in cast iron. By the addition of manganese as high as six or seven per cent of carbon has been introduced into iron. Carbon does not form a true alloy with iron, neither does it form any stable chemical compound. Its condition in iron seems to be as variable as it is in nature, and sometimes it has been supposed to be as capricious as it is variable. It is hoped that the reader of these pages will find that there is no caprice about it, that its action is governed by as sure laws as any in nature, and that certain results may be predicated upon any treatment to which it is subjected.

The theories of its actions are as numerous and variable as are the actions themselves, and they will be treated in a separate chapter, this chapter being confined to a statement of known facts.

As stated in [Chap. I], carbon may be introduced into iron by heating carbon and iron in contact when air is excluded; and, conversely, carbon is burned out of cast iron by the Bessemer and open-hearth processes to reduce the cast iron to cast steel.

In the crucible any quantity of carbon may be obtained in steel by melting a mixture of high blister-steel and wrought iron, or cast iron and wrought iron, or by charging with wrought iron the necessary quantity of coke or charcoal. When using plumbago crucibles, the iron takes up some carbon from the crucible; also the spiegel-eisen or ferro-manganese used adds some carbon; and for these two sources of carbon the melter allows when he decides upon the quantity of charcoal needed.

Results from crucible-melting are not strictly uniform; even if every charge were weighed in a chemical balance accurately the product would not be uniform, because one crucible gives off more carbon than another; in one crucible a little more charcoal may be burned and escape as gas than in another; and most variable of all, unless the charcoal has been dried thoroughly, is the quantity of moisture in the charcoal. One charge of charcoal may be dry, and the next may contain as much as twenty-five per cent of moisture; obviously equal weights in such a case would not give equal quantities of carbon to the steel.

In crucible steel this is no disadvantage; a skilful mixer will get from 75% to 90% of his ingots of the desired temper; the other ingots will all be in demand for other uses, and as he can separate them all with absolute certainty by ocular inspection, as described before, he labors under no fear of bad results.

In the Bessemer process it is usual to burn out all of the carbon and then to add the required amount in the spiegel; for structural steels and for rails this method is satisfactory. For high steel—from fifty to a hundred or more carbon—the spiegel method does not answer so well, because it increases the quantity of manganese to too great an amount; higher carbon is then sometimes put in by the addition of a given quantity of pure pig iron previously melted, or by putting coke in the ladle, but this is very uncertain on account of the tendency of the coke to float, and be dissipated as a gas instead of entering the steel.

The Darby method is to place in the way of the stream of steel as it is poured from the vessel to the ladle a refractory-lined, funnel-shaped vessel filled with finely divided, but not powdered, coke. As the stream rushes through the coke it absorbs carbon with great rapidity, and it is asserted that the currents and eddies formed in the ladle by the rush of the stream cause an even distribution of carbon. That carbon will be taken up in this way is certain; that a required amount, evenly distributed, can be obtained is not so certain.

In the acid open-hearth as in the Bessemer process for milder steels it is usual to burn the carbon out almost entirely, and then to add the desired amount with the spiegel. Higher carbon may be obtained by the addition of pure pig iron, or by using carbon bricks pasted together with tar and weighted with iron turnings; these bricks may be pushed under the surface in different parts of the bath, and in this way the carbon can be distributed pretty evenly. In good practice now the melt is stopped at the carbon desired with great success, thus saving time and expense. In the basic open-hearth the melter, by the use of a little care and good judgment, stops his melt at the required carbon, and so avoids any additional operations, unless his charge is excessively high in phosphorus and his steel is to be very low in the same; in that case he may have to melt clear down and re-carbonize.

Steel of 130 carbon with phosphorus <.05 may be made on the basic hearth from a charge containing 10 to 12 phosphorus without melting below 130 carbon.

If high-carbon Bessemer steel is not uniform, it is not to be wondered at, but as a matter of fact it is usually found to be fairly uniform, sufficiently so to work well.

If open-hearth steel of high carbon is not uniform, it is clearly because the maker would not take a little trouble to have it so.

Assuming that for convenience cast steel is graded for carbon content by even tens, and that the different tempers are separated half-way between the tens, we have:

This covers the usual commercial range from what is known as dead-soft steel up to a high, lathe-temper steel.

Higher steels are used sometimes, even up to 225 carbon, but they are so exceptional that it is not worth while to continue the list above 150.

This list allows a variation of .05 carbon above and below the datum of each temper; some margin must be had of course, and this is sufficient in the hands of a careful steel-maker; it is found in practice to be satisfactory to the user. Even in the highest lathe-steel where the strains from hardening are the greatest, because the change in volume due to a degree of temperature is the greatest, a variation of three or four points above and below the mean does not make enough difference in the results to throw a skilful temperer off from his desired conditions.

On the other hand, a difference of a full temper will throw the most skilful worker off from the track, and so that much variation is not allowable. For instance, if a man be working 130 carbon, and he should receive a lot of steel of 120 carbon, he would get his work too soft in following his regular methods; then if he doubted himself, as he would be apt to do, and raised his heat to correct his supposed aberration, he would get his work too hard, coarse-grained, and brittle; if he tried to correct this by drawing to a lower temper color, his tools would be too soft. Again, if he received a lot of steel of 140 carbon and proceeded in his regular way, he would get a lot of cracked tools. So that in either case the result would be confusion. It is probable that in almost any case either 120 or 140 carbon would make a thoroughly good tool if the temperer knew what he was working with and adapted his heats to the carbon. But he does not know of the variation, and even if he did he would say, very rightly, that he did not propose to make daily changes in his methods to suit the convenience or the carelessness of the steel-maker.

It must not be understood, however, that this narrow range for each temper limits the capacity of the steel; it merely gives the limit for regular easy working.

To illustrate: A good lathe-tool may be made of 100-carbon steel, and of 150 carbon; but no worker could use these tempers indiscriminately, nor even alternately, although he knew which was which, because he could not change all of his heats say every five minutes and turn out satisfactory work. A spring of given size, and to carry a given load, may be made equally good of 60-carbon steel or of 140 carbon, and such work is done frequently in shops that are attached to steel-works; but the spring-maker must be told beforehand what he is to work with, and he must be given enough of one kind of steel to make say a day’s work, so that he can go along regularly. The springs will be good, but the one containing 140 carbon will have the highest elasticity and the most life, although both will have the same modulus of elasticity. The spring-maker who buys his steel will not submit to any such variations, and he ought not to be asked to do it, because one temper of steel costs no more than another, and the selecting out and separating the tempers is only a matter of a little care.

Is it practicable to keep steel uniform in carbon within such narrow limits?

In crucible-steel practice it is very easy to do so. All ingots of 60 carbon upwards up to four or four and one half inches square may be broken completely off at the top, and then the clean fracture will indicate the quantity of carbon invariably, and after the ingot has been glanced at and marked properly it is as easy to put it on its proper pile as to put it on any other. In a good light a competent inspector will mark thirty or forty ingots per minute and do it correctly; it is as easy to the trained eye as it is to read a printed page.

This inspection is so important that it should never be neglected. It is not costly, much less than a dollar a ton.

With larger ingots only a piece can be broken off from the edge, but if the topper does his work properly, enough can be taken off to show the temper clearly. Large ingots containing the contents of a number of crucibles are liable to unevenness of temper from having uneven mixtures in the pots and from bad teeming into the moulds; this can be detected usually in the ingot inspection, and if not it can be found later during another inspection. Such variations are often called segregations. This question of segregation will be discussed in a future chapter.

In the Bessemer and the open-hearth practice ocular inspection of ingots to determine carbon is not used.

Enough examinations have been made to show that the fractures, although differing from those of crucible-steel, are quite as characteristic, and ocular inspection could be used. The ingots are large usually and to handle and top them would be expensive; but the heats are also large,—from five tons up to thirty tons in one heat,—and as they are supposed to be homogeneous, one chemical carbon analysis is enough for each heat.

Below 50 carbon a quick color analysis is accurate enough; above 50 carbon combustion should be used, for in high carbons the color test in the best hands is only the wildest guess-work.

The ten-point range of carbon is far more difficult to attain in high-carbon open-hearth practice than in the crucible. In one case where the limit fixed in a specification was 90 to 110 carbon, two full tempers, one of the most skilful and successful concerns in the world failed to meet the specification in twenty-ton and thirty-ton furnaces.

It was supposed at first that the trouble came from using different heats, and large lots of billets were sent out with the heat number stamped on each billet. The same variations were found in every heat, the carbon ranging from 80 to 120. The specification was met without any trouble in five-ton furnace.

This illustration should not lead to the conclusion that practically uniform steel cannot be obtained; there is little doubt that if the 30-ton heats had been stirred thoroughly in the furnace the required limits would have been obtained.

Neither is it to be understood that the same variation would occur in mild steel under 30 carbon. A call for 20 carbon would not result in steel ranging from below 10 to above 30,—such a result would show gross carelessness on the part of the melter,—the variation would go by percentage; thus the variation in the high steel is from 15% below to 15% above the mean of 100, or even as much as 20%.

If 20-carbon steel be required, a variation of 20% would give a range from 16 to 24 carbon, or well within the limits of one temper.

This matter will be considered farther under the head of Segregation.

The appropriate applications of the different tempers of steel have been stated in a general way, with the advice that for all tool purposes it is better to leave the selection of the temper to the steel-maker; also in structural work it may prove to be better to leave the question of temper, or carbon content, to the steel-maker, who should know how to meet any specification that is within the capacity of steel. On the other hand, every engineer should know what is attainable, and an effort to give this information in more definite form will be made in later chapters. A general view will now be taken of what may be called the carbon-line.

Let the horizontal line represent iron, the inclined line iron plus carbon, and the verticals physical properties.

We do not know the physical properties of pure iron. Assuming them to be uniform, let the vertical at .05 represent the tensile, torsional, transverse, or compressional strength of steel of 5 carbon; then for every increment of carbon up to 90 to 100 there will be an increase of strength to resist any of these strains, increasing in such regular amounts as to make the resulting carbon-line practically straight, as shown in the sketch. Above 100 carbon these resistances will all decrease, except resistance to compression.

So far as it is known, compressive strength increases slightly with the carbon, until cast iron is fairly reached; then the presence of silicon, and the fact that we are dealing with a casting instead of forged or rolled metal, causes a rapid fall in all resistances until the strength is below that of 5 carbon steel.

With increase of carbon there is a reduction of ductility, so that the extension of length and reduction of area decrease as the strength increases. In every case the engineer must decide how little ductility he can do with safely in securing the ultimate strength or the elastic limit he may require.

The highest strength and the greatest ductility cannot be had together; they are inverse functions one of the other.

If the exact resistances due to carbon were known along the whole line, it would be of great value to give them here but nearly all of the thousands of tests published are influenced by the quantities of silicon, phosphorus, sulphur, manganese, or oxides present, and an effort to determine the effects of the carbon-line exactly would be hazardous.

Kirkaldy’s tests of Fagerota steel, published in 1876, furnish a valuable guide in this direction.

Webster’s experiments on the effects of the different elements, phosphorus, manganese, etc., are interesting and valuable, but he has not yet tested a complete carbon-line with no other variables.

It has been stated time and again by experienced steel-makers that the best steel, the most reliable under all circumstances, is that which comes nearest to pure iron and carbon.

Some intelligent steel-makers, and engineers cast doubts upon this statement, and assert that because phosphorus up to a certain limit, or manganese, or silicon, or in fact it may be said almost any element, added to dead-soft steel will give an increase of strength, therefore the presence of one or more of these elements is not only not harmful, but beneficial.

As a matter of fact, however, every one of these elements is harmful, either in producing cold-shortness, or red-shortness, or brittleness, and not one of them will add any good quality to steel that may not be obtained better by the use of carbon. Given a uniform minimum content of these impurities, the carbon-line may be depended upon to furnish any desirable quality that is obtainable in steel; and it is certain, always sure, that that steel which is the nearest to pure carbon and iron will endure the most punishment with the least harm.

That is to say, that such a steel when overheated a little, or overworked, or subjected to any of the irregularities that are inevitable in shop practice, will suffer less permanent harm than a steel of equal strength where there is less carbon and the additional strength is given by any other known substance.

It is difficult to show this from testing-machine data, indeed it is doubtful if any such data exist, but experience in the steel-works, in the bridge- and machine-shops, and in the field proves it to be true. For further discussion of this question [see Chap. X].

The effects of a small difference in phosphorus or in silicon contents are shown plainly and unmistakably in high-carbon steel, and not so plainly in low-carbon steel; but as there is no known hard and fast line that divides low steel, medium steel, and high steel, so there is no marked difference in their properties. The same rules hold all along the line, the same laws govern all of the way through.

There is no set of properties peculiar to low steel and another set peculiar to high steel; the same laws govern all, and differences are those of degree and not of law.

Given three samples of steel of the following compositions:

A skilful worker, not knowing the composition of any, will pick them out invariably by tempering them and testing them with a hand-hammer and by inspecting the fractures.

He will pronounce No. 1 to be the best and the strongest in every way; No. 2 to be not quite as strong as No. 1, and more liable to crack from a little variation in heat; No. 3 to be not so strong as No. 1, and that it will not come quite as fine as either of the others, and, like No. 2, it will not stand as much variation in heat as No. 1.

Give a ton of each to a skilful axe-maker, from which he will make one thousand axes of each, and he will be sure to report No. 1 all right; No. 2 good steel, more loss from cracked axes than in No. 1.

No. 3 good steel, some inclination to crack; it will not refine as well as No. 1 and is not as strong.

This is no guess-work, nor is it a fancy case; it is simple fact, borne out by long experience.

Give a skilful die-maker one hundred blocks of each to be made into dies. He will not break one of No. 1 in hardening them; he will probably break five to ten of No. 2; and if he breaks none of No. 3—a doubtful case—he will find in use that No. 1 will do from twice to twenty times as much work as either of the others. If he is making expensive dies,—many dies cost hundreds of dollars each for the engraving,—he will think No. 1 cheap at 25 cents a pound, and either of the others dear at 15 cents a pound.

In such steel, then, the absence of a few points of silicon, or of a point or two of phosphorus, is worth easily 10 cents a pound.

Now let the carbon in these three steels be reduced to 10, making them the mildest structural steel. The differences to be found in the testing-machine in tensile strength, elastic limit, extension, and reduction of area will be almost or altogether nothing; in forging, flanging, punching, etc., under ordinary conditions differences would not be observable; therefore there would be no practical difference in value. But let the silicon be raised to 30 or the phosphorus to 10,—the Bessemer limit,—or let both be raised together, and both the testing-machine and shop practice would show a marked difference.

This shows that in the absence of carbon the action of these elements is sluggish as compared to their effects in the presence of high carbon, or in the low-carbon steels their effects are not so observable. That their influence is there, there can be no doubt, but if it be not enough to endanger the material it is not worth while to take it into account.

Is it safe and wise, then, for steel-users to ignore composition?

Users of tool-steel may do so safely, because the smallest variations will manifest themselves so unmistakably that they give immediate warning, and the steel-maker must keep his product up to a rigid standard of excellence or lose his character and his trade. Many of the ablest users of structural steel take a similar ground, and say, We have nothing to do with method or composition if the material meets our tests.

It is believed that if these men knew how easy it is for a skilful worker to doctor temporarily an off heat by a little manipulation, and how dangerous the same may become by a little off practice in the field, they would be convinced that some limits should be put upon composition, especially if they could realize that a reasonable specification would add nothing to cost, as competition would take care of that.

The reader is referred again to [Chap. X] on impurities.

V.
GENERAL PROPERTIES OF STEEL.

Steel is very sensitive to heat. In general it may be stated that, starting with cold steel, every degree of heat added causes a change in size and in structure, until the limit is reached where disintegration begins. The changes are not continuous; there are one or two breaks in the line, notably at the point where we have what is called recalescence; this is a marked phenomenon and it will be considered later.

The effects of heat are permanent, so that it is a fact that every variation of temperature which is marked enough to be visible to the naked eye will leave a structure, due to that variation, when the steel is cold, which will be observable by the naked eye, and such structure, when not influenced by external force, such as by hammering or rolling, is as invariable and certain as is the structure of an ingot due to the quantity of carbon present.

This property furnishes what may be called the steel-maker’s and the steel-user’s thermometer. By its means the steel-maker can discover every irregularity in heating that may have been perpetrated by the operatives; so also the steel-user can decide whether the steel furnished him has been heated and worked uniformly and properly, and later he can tell whether those who have shaped this steel to its final forms have done their work properly. A thorough knowledge of this property is essential to a steel-maker; until he possesses it he is not fit to conduct his business. It is of great importance to the steel-user, and every engineer should try to acquire a knowledge of it in order that he may not be fooled by the carelessness or rascality of those who have preceded him. The steel-maker acquires this knowledge by daily contact with the facts; the engineer does not have it forced upon him in this way, but he should seek opportunities of observation, which will be abundant in his earlier practice when he is sent upon inspection duty. Like the structure of ingots, this heat-structure cannot be illustrated on paper, and an attempt to do so would be misleading; attempts at description will be made in the hope that by their means the engineer will have a pretty good idea what to look for, and to know when his suspicions should be aroused.

In addition to the ocular observations mentioned it has been shown by specific-gravity determinations, and by delicate electrical tests through small ranges of temperature, that steel is as truly thermometrical as mercury.

Steel passes through or into four general conditions due to heat. First, in the cold state, it is a crystalline solid of no uniform structure, for its structure is influenced by every element that enters into it, and by every irregularity of heat to which it has been subjected.

Good steel may be described as having a bluish-gray color, uniform grain as seen by the naked eye, and little lustre. But it should have some lustre and a silky appearance. When it is right, a steel-worker will say it is “sappy,” and that name, absurd as it may sound when applied to a metal, really expresses an appearance, and implies an excellence that it would be hard to find a better word for. If the structure be dull and sandy-looking, the steel-worker will say it is “dry,” and that term is as suggestive and appropriate as the word “sappy.”

If the fracture be granular with bright, flashing lustre, the steel-worker will say it is “fiery,” and again his term is expressive and proper.

It is perfectly safe to say that steel of a “sappy” appearance is good steel; but in order to know what it is it must be learned by observation, it cannot be described in exact terms.

It is equally certain that a “dry” fracture indicates a mean steel, a steel inherently mean,—too much phosphorus, or silicon, or oxides, or all combined,—and such a steel is incurable.

A “fiery” fracture indicates too much heat. It may be found in the best steel and in the poorest; it may be corrected by simply heating to a proper temperature. It shows that some one needs to be reprimanded for careless work.

If now an inquirer will take a piece of good steel of “sappy” fracture, and of “dry” steel of dull, sandy fracture of the same carbon, and will heat them say first to dark orange, then to bright orange, dark lemon, and so on, and examine the fractures after each heating, he will find a “fiery” fracture in the “dry” steel at a heat much below that which is necessary to make the “sappy” steel “fiery.” This is one proof that good steel will endure more punishment than poor steel.

Cold steel is not plastic in the common acceptance of the word; strictly speaking it has some plasticity, as shown in the extension noted in pulling it; this is its measure of ductility.

Also it may be drawn cold to fine wire of only a few thousandths of an inch in diameter, and it has been rolled cold to one five thousandth of an inch thick. But this work must be done with great care; the steel soon becomes brittle, and a little overdrawing or overrolling will crush the grain and ruin the steel; therefore the work must be done a little at a time, and be followed by a careful annealing.

To reduce a No. 5 wire rod to .005 inch diameter will require with high steel suitable for hair-springs about fourteen annealings.

A skilful hammerman will take a piece of mild cold steel, and by means of light, rapid blows he will heat it up to a bright lemon heat without fracturing it; then he will have it thoroughly plastic and malleable.

This has no practical commercial value; it is a beautiful scientific experiment exhibiting high manual skill, and showing that there is no hard and fast line between non-plasticity and plasticity.

The first condition, then, is cold steel, not plastic, not malleable.

When steel is heated, it begins to show color at about 700° to 800° F.; the first color is known as dark cherry red, or, better, orange red: above this color it turns to a distinct, rather dark, or medium orange color; this is the heat of recalescence, a good forging-heat, and the best annealing- and quenching-heat. At this heat and above it good steel is truly plastic and malleable; a roller or hammerman will say, “It works like wax,” and so it does.

This is the second or plastic condition.

Heated above this plastic condition to a bright lemon in high steel, or to a creamy, almost scintillating, heat in mild steel, steel will go to pieces under the hammer or in the rolls; the workman will probably say it is burned, but it is not burned necessarily; it is simply heated up to the third or granular condition; it is the beginning of disintegration and the end of plasticity.

This granular condition is important in several ways. It is made use of in Sweden, and has been demonstrated in the United States, to determine the quantity of carbon in steel. An intelligent blacksmith is given a set of rods of predetermined carbon, ranging from 100 carbon to zero, or through any range that may be necessary; each rod is marked to indicate its carbon. He takes the rods one by one and heats them until they scintillate, well up into the granular condition, then lays them on his anvil and hammers them, observing carefully the color at which each one becomes plastic as it cools slowly. After a little practice he is given rods that are not marked, and by treating them in the same way he will give them their proper numbers, rarely missing the carbon by as much as 10 points, or one temper.

It is a beautiful and useful illustration of the effect of carbon. The rule is, the higher the carbon the lower the granulating-point; or, as is well known, high steel will melt at a lower temperature than low steel.

This shows that every temper of steel has its disintegration temperature where it passes from plastic to granular, as fixed as its fusion-point or its point of recalescence.

Steel passes from the granular condition to the liquid or fourth form.

There is little of interest in the liquid condition of steel to any but the steel-maker; what there is to be said will be mentioned later.