Chapter XV: Conclusions 164 (1)

GLOSSARY.
DEFINITIONS OF SHOP TERMS USED 167

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 }
{Basic} Cast Steel.

Open-hearth {Acid }
{Basic} Cast Steel.

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:

Crucible. Open-hearth. Bessemer.
Carbon 1.00 1.00 1.00
Silicon .10 .10 .10
Phosphorus .05 .05 .05
Sulphur .02 .02 .02
Copper, arsenic, etc. traces

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.