A WORD FOR THE WORKMAN.
Give him a chance. A steel-worker to be expert must have a well-trained eye and know how to use it. He must work with delicate tints, ranging in the yellows from creamy yellow to dark orange or orange red as extremes, and most of his work must be done between bright lemon and medium orange in forging, and between rather dark to medium orange, or possibly nearly light orange, when hardening and tempering.
Probably in no other business is there such ridiculous waste as is often found in steel-working where the manufacturer economizes in his blacksmiths.
A large, wealthy railroad condemns a brand of steel. The steel-maker goes to the shop and is informed by a bright, intelligent blacksmith that the steel will not make a track-chisel. It is a hot summer day; the smith is working over a huge fire with a large piece of work in the middle of the fire and a number of small pieces of steel stuck in the edge of the fire.
He is welding large iron frog-points, and in the interval he is filling a hurried order for four dozen track-chisels for which the trackmen are waiting. He is not merely forging the chisels, he is hardening and tempering them. The glare of the welding-work makes him color-blind, the hurry gives him no time for manipulation, and the trackmen have no chisels.
After a thorough expression of sympathy for the smith the steel-maker turns upon the foreman and master mechanic, and gives them such a tongue-lashing that they turn away silenced and ashamed.
Page after page of such cases could be written, but one should be enough.
A steel-maker has a thoroughly skilled and expert steel-worker; he rushes into the shop and says, “Mike, refine this right away, please; I want to know what it is.”
Mike replies, “I will do that to-morrow; I am welding to-day.”
That is entirely satisfactory; those men understand one another, and they know a little something about their business.
A temperer should do no other work when he is heating for hardening, and he should always be allowed to use as much time about it as he pleases, assuming that he is a decently honest man who prefers good work to bad; and as a rule such honest men are in the majority, if they are given a fair chance.
IX.
ON THE SURFACE.
The condition of the surface of steel has much to do with its successful hardening and working.
A slight film adherent to the surface of steel will prevent its hardening properly; the steel may harden under such a film and not be hard upon the immediate surface, and, as in almost every case a hard, strong surface is necessary to good work, it is important that a piece of steel to harden well should have a clean surface of sound steel.
It has been stated already that all bars and forgings of steel have upon the surface a coat of oxide of iron, and immediately beneath this a thin film of decarbonized iron.
Neither of these substances will harden, and in every case where a hard-bearing surface or a keen cutting-edge is desired these coatings must be removed. Polished drill-wire and cold-rolled spring-steel for watches, clocks, etc., should have perfect surfaces, and it is the duty of steel-makers to turn them out in that condition. All black steel, or hot-finished steel, contains these coatings.
In the manufacture of railroad, wagon, and carriage springs it is not necessary or customary to pay any attention to these coatings; the body of the steel hardens well, giving the required resilience and elasticity, so that an unhardened coat of .01 to .001 inch thick does no harm. To all bearing-surfaces and cutting-edges such coatings are fatal.
The ordinary way of preparing steel is to cut the skin off, and this is sufficient if enough be taken off; it happens often that a purchaser, in pursuit of economy and unaware of the importance of this skin, orders his bars or forgings so close to size that when they are finished the decarbonized skin is not all removed, and the result is an expensive tap, reamer, milling-cutter, or some tool of that sort with the points of the teeth soft and worthless.
In small tools ¹/₁₆ inch, in medium-size tools, say up to two or three inches in diameter, ⅛ inch cut off should be plenty; in large tools and dies, especially in shaped forgings, it would be wiser to cut away ³/₁₆ inch.
In many cases sufficient hardness can be obtained by pickling off the surface-scale, but this will not do where thorough hardening is required, because the acid does not remove the thin decarbonized surface. It seems to be impracticable to remove the decarbonized skin by the action of acid, for if the steel be left in the acid long enough to accomplish this the acid will penetrate deeper, oxidizing and ruining the steel as it advances.
Grinding is frequently resorted to, being quicker and cheaper than turning, planing, or milling.
When grinding is used, care must be taken not to glaze the surface of the steel, or if it should be glazed the glaze must be removed by filing or scraping.
In the manufacture of files it is customary to grind the blanks after they are forged and before the teeth are cut.
After the blanks are ground they are held up to the light and examined carefully for glaze. Every blank that shows by the flash of light that it is glazed is put to one side; then these glazed blanks are taken by other operatives and filed until all traces of glaze are removed. The file-maker will explain that if this be not done the files when hardened will be soft at the tips of the teeth over the whole of the glazed surface. This inspection and filing of blanks involves considerable expense, and it is certain that such an expense would not be incurred if it were not necessary.
This glaze does not appear to be due to burning, at least the stones are run in water; the blanks are handled by the bare hands of the grinders, and do not appear to be hot.
After pieces are hardened and tempered they frequently require grinding to bring them to exact dimensions. This is usually done on emery-wheels with an abundance of water, and as no temper colors are developed indicating heat it is assumed that no harm can be done.
Just here much valuable work is destroyed. The tempered piece is put on the wheel, in a “flood of water”; the work is rushed, and the piece comes out literally covered with little surface-cracks running in every direction, perfectly visible to the naked eye. Until the steel-worker learns better he blames and condemns the steel.
This result is very common in the manufacture of shear-knives, scissors, shear-blades, dies, etc.
Sometimes too a round bearing or expander-pin is hardened; examined by means of a file it appears perfectly hard; it is then ground, not quite heavily enough to produce surface-cracks, but still heavily, and on a glazed wheel. It is found now that the surface is soft; only a thousandth of an inch or so has been cut off, and the steel is condemned at once because it will harden only skin deep. Let the file be drawn heavily over the surface and it will be found that the soft surface is only about a thousandth of an inch thick, and underneath the steel is perfectly hard.
Now grind slightly on a sharp, clean wheel and re-harden; the surface will be found to be perfectly hard. Ground heavily again on the glazed wheel, it will become soft, as before. These operations can be repeated with unvarying results until the whole piece is ground away.
These difficulties occur more with emery-wheels than with grindstones, either because emery-wheels glaze more easily than grindstones, or because, owing to their superior cutting powers under any circumstances, they are more neglected than grindstones.
Experience shows that these bad results occur almost invariably on glazed wheels. It is rare to find any bad work come off from a clean, sharp wheel, unless the pressure has been so excessive as to show that the operator is either foolish or stupid.
The remedy is simple: Keep the wheels clean and sharp.
Many grinders who understand this matter will not run any wheel more than one day without dressing, nor even a whole day if the work is continuous and they have reason to apprehend danger.
A FEW WORDS IN REGARD
TO PICKLING.
Pickling is the placing of steel in a bath of dilute acid to remove the scale. It is a necessary operation in wire-making and for many other purposes, and it may be hastened by having the acid hot.
Sulphuric acid is used generally; it is efficient and cheap. When thin sheets are to be pickled, the acid should not be too hot, or it will raise a rash all over the sheet in many cases. This indicates some unsoundness in the steel, the presence probably of innumerable little bubbles of occluded gases. This is possibly true, yet the same sheets pickled properly and brought out smooth will polish perfectly, or if cut up will make thousands of little tools that will show no evidence of unsoundness.
Steel should never be left in the pickling-bath any longer than is necessary to remove the scale; it seems unnecessary to warn readers that the acid will continue to act on the steel, eat the steel after the scale is removed. When taken from the pickle, the steel should be washed in limewater and plenty of clean running water; but this does not take out all of the acid. It should then be baked for several hours at a heat of 400° to 450° F. to decompose the remaining acid. This is just below a bluing heat, and it does not discolor or oxidize the surface. It is known as the sizzling-heat, the heat that the expert laundry-woman gets on her flat-iron which she tests with her moistened finger.
Acid if not taken off completely will continue to act upon and rot the steel; how far this will go on is not known exactly; for instance, it is not known whether if a block six inches cube were pickled and merely washed, the remaining acid would penetrate and rot the whole mass or not. There must be some relation between the mass of the steel and the power of a small amount of acid to penetrate.
The power of acid can be illustrated on the other extreme: A lot of watch-spring steel is finished in long coils and .010 inch thick; when last pickled, the baking was neglected; the steel is tough, it hardens well, and when tempered it is springy and strong; by all of the tests it is just right in every coil. It is shipped away and in three or four weeks the spring-maker begins work on it. He reports at once that it is rotten and worthless, it will not make a spring at all, and he is angry. The steel is returned to the maker and he finds the report true: the steel is rotten and worthless. Then by diligent inquiry he finds that the last baking was omitted, and he pockets his loss, sending an humble apology to the irate spring-maker.
Whether the residual acid can ruin a large piece of steel or not need not be considered when the simple operation of baking will remove the possibility of harm.
X.
IMPURITIES IN STEEL.
Any elements in steel which reduce its strength or durability in any way may be classed as impurities.
A theoretical ideal of pure steel is a compound of iron and carbon; it is an ideal that is never reached in practice, but it is one that is aimed at by many manufacturers and consumers, because experience shows that, especially in high steels, the more nearly it is attained the more reliable and safe is the product.
All steel contains silicon, phosphorus, sulphur, oxygen, hydrogen, and nitrogen, none of which add any useful property to the material. It is admitted that, starting with very small quantities of silicon or phosphorus in mild steel, small additions of either element will increase the tensile strength of the steel perceptibly up to a given amount, and that then the addition of more of either one will cause a reduction of strength. The same increase of strength can be obtained by the addition of a little carbon, producing a much more reliable material. It is not known that even such slight apparent gain in strength can be made by using oxygen, nitrogen, or hydrogen.
Manganese is present in all steel as a necessary ingredient, it gives an increase in strength in the same way as phosphorus, and when increased beyond a small limit it causes brittleness. Hadfield’s manganese steel is a unique material, not to be considered in connection with the ordinary steel of commerce.
Webster’s experiments are perhaps the most complete of any that show the effects of small increases of silicon, phosphorus, sulphur, and manganese, but as these are not completed they are not quoted here, because Mr. Webster may reach additional and different results before these pages are printed.
The chief bad qualities of steel that are caused by these impurities are known as “red-shortness,” “cold-shortness,” and “hot-shortness.”
A steel is called red-short when it is brittle and friable at what is known commonly as a low red heat—“cherry red,” “orange red.”
Red-shortness is caused chiefly by sulphur or by oxygen; many other elements may produce the same effects; it seems probable that nitrogen may be one of these, but the real action of nitrogen is as yet obscure.
A red-short steel is difficult to work; it must be worked at a high heat—from bright orange up to near the heat of granulation—or it will crack. When hardened, it is almost certain to crack. When red-short steel is worked with care into a sound condition, it may when cold be reasonably strong, but hardly any engineer of experience would be willing to trust it.
Hot-short steel is that which cannot be worked at a high heat, say above a medium to light orange, but which is generally malleable and works soundly at medium orange down to dark orange, or almost black.
This is a characteristic of most of the so-called alloy steels, or steels containing considerable quantities of tungsten, manganese, or silicon. It is claimed that chrome steel may be worked at high heats and that it is less easily injured in the fire than carbon steel. This is not within the author’s experience. It is this property of hot-shortness that makes the alloy steels so expensive; the ingots cannot be heated hot enough nor worked heavily enough to close up porosities, and therefore, there is a heavy loss from seams.
The range of heat at which they can be worked is so small that many re-heatings are required, increasing greatly the cost of working.
As compared to good carbon steel they are liable to crack in hardening, and when hardened they are friable, although they may be excessively hard.
Cold-short steel is steel which is weak and brittle when cold, either hardened or unhardened. Of those which are always found in steel, phosphorus is the one well-known element which produces cold-shortness.
It is clear that no one can have any use for cold-short steel.
Red-short or hot-short steel may be of some use when worked successfully into a cold condition, but cold-short steel is to be avoided in all cases where the steel is used ultimately cold.
If the theoretically perfect steel is a compound of iron and carbon, it cannot be obtained in practice, and the only safeguard is to fix a maximum above which other elements are not to be tolerated.
In tool-steel of ordinary standard excellence such maximum should be .02 of one per cent; it may be worked to easily and economically, except perhaps in silicon, which element is generally given off to some extent by the crucible; it should be kept as low as possible, however, say well under 10, one tenth of one per cent. Some people claim that a little higher silicon makes steel sounder and better; but any expert temperer will soon observe the difference between steels of .10 and .01 silicon. For the highest and best grade of tool-steel the maximum should be the least attainable. Every one hundredth of one per cent of phosphorus, silicon, or sulphur will show itself in fine tool-steel when it is hardened. It is assumed, of course, that such impurities as copper, antimony, arsenic, etc., exist only as mere traces, or not at all.
As oxygen must be at a minimum, no one has yet succeeded in making a really fine tool-steel from the products of the Bessemer or of the open-hearth process.
The removal of the last fractions of these impurities is difficult and expensive; for instance, a steel melting iron of
| Silicon | .03 | to | .06 |
| Phosphorus | .03 | “ | .02 |
| Sulphur | .002 | or less | |
may be bought for 2 cents a pound or less, whereas an iron of
| Silicon | < .02 |
| Phosphorus | < .01 |
| Sulphur | trace |
can hardly be bought for less than 5 cents a pound.
This difference of three cents a pound is justifiable when the highest grade of tool-steel is to be made; and it would be silly to require any such material in any spring, machinery, or structural steel.
In addition to these impurities there are other difficulties to be guarded against, chief among which is an uneven distribution of elements.
In all steel there is some segregation; that is to say, as the liquid metal freezes, the elements are to some extent squeezed out and collected in that part of the ingot which congeals last. It is claimed that in the Bessemer and Open-hearth processes any ferro-silicon added to quiet a heat, or any ferro-manganese added to remove oxygen, are at once absorbed and distributed through the mass, and so when any serious irregularity is discovered it is charged to segregation.
A heat may produce billets of 75 carbon and 120 carbon, and again it is called segregation.
As a rule, inertia has more to do with such differences than segregation. One crucible of steel may produce an ingot containing 90 carbon and 130 carbon. Segregation has nothing to do with this: a careless mixer has put a heavy lump of 140- or 150-carbon steel in the bottom of the pot and covered it up with iron. The steel melted first and settled in the bottom of the pot, the iron melted later and settled on top of the steel, and they did not mix. The teeming was not sufficient to cause a thorough mixing.
Segregation covers a multitude of sins.
Exactly how much is sin and how much is segregation will not be known until analyses are made of the top, middle, and bottom of the bath, and of the contents of the ladle, these to be compared to analyses of the top, bottom, and middle of the ingots. There is certainly an unavoidable amount of segregation, and as equally certain an amount of curable irregularity due to inertia.