Mild steel

“ Of recent years, mild steel has been the great competitor of wrought iron. With marvelous energy, skill, and much capital the manufacturers of Bessemer and open-hearth steels have adapted their products very well to the needs of the iron user, while the enormous tonnages turned out in short time by use of ingenious furnaces and other devices has resulted in a low cost of production. ”

“ Mild steel is manufactured extensively, and some crucible cast steel is made. In addition to brass foundries there are works for the extraction of copper and the smelting of lead and zinc. With such resources every branch of engineering is well represented. ”

“ Although a certain make of material may vary in composition from time to time the products of a manufacturer of good steel can be generally relied upon, and it is better to deal directly with him than with others.
In most cases the case-hardening steels can be chosen from the following: (1) Case-hardening mild steel of 0.20 per cent carbon; (2) case-hardening 31⁄2 per cent nickel steel; (3) case-hardening nickel-chromium steel; (4) case-hardening chromium vanadium. ”

“ But future historians may well be tempted to substitute the word steel for iron, for it is an undoubted fact that improved processes of manufacture, and the resulting easy and cheap production, are causing steel to be widely substituted for its parent metal. In railways, steel rails are now almost entirely replacing iron ones, and that modification of the metal known as ‘mild steel’ is finding great favour just now among shipbuilders. ”

“ But since modern methods of manufacturing have been adopted, tons of metal, which would have been classed as iron if judged by the cooling test, are at present known as mild or soft steel.
Steel may properly be defined as an alloy of iron with carbon, the latter not exceeding 1.8 per cent; the materials are completely fused and poured into molds, allowed to cool, and then rolled into shape. In the processes of making wrought iron the materials are only partly fused and are not cast into molds, but are taken out of the furnace in a soft, pasty condition suitable for immediate working. ”

“ It will resist great shock and can be severely battered and bent without breaking. It has about 75 per cent or more of the tensile strength of mild steel and because of the cheapness of its castings the malleable iron industry has developed wonderfully. About a million tons of this product are produced here each year.
Naturally malleable iron castings are used where a material with properties intermediate between cast iron and steel will suffice. Such are castings for railroad cars, for reapers, binders, and other agricultural machines, pipe fittings, and the cheaper grades of tools. ”

“ E. Windsor Richards it has been made a great success, while in Germany there are several works also using the process largely. Mild steel is now being used to a great extent for the construction of steam boilers as well as of ships, and in steel castings for a variety of purposes, such as spur wheels, frames of portable engines, manhole door frames, etc., etc. Among the uses to which steel may be put is the manufacture of steel sleepers in place of wood. ”

“ V, it will be seen that the change in volume due to differences of temperature is much less in mild steel than in high steel. This fact does not rest upon the evidence of this table alone; it is a fact of common knowledge to all steel-makers that mild steel is much more inert than high steel; therefore differences of heat and working that produce serious results in high steel are hardly appreciable in mild steel. As a rule all structural steels are comparatively mild, therefore they are generally in a fit condition for use when they leave the rolls or forge. ”

“ It appeared then as the “free” carbon (crystalline graphite) which remained distributed throughout the alloy and may be seen as the jet black flakes in photomicrograph No. 198.
Every pure metal is supposed to be composed of crystals or grains which would have been of the true cubic form if the severe internal pressure during solidification and cooling had not distorted them.
Photomicrograph No. 99b represents quite well a pure metal. It is that of an extremely mild steel made by special methods in the open-hearth steel furnace. ”

“ As fortune has withheld from Kelly and from this country credit which was deserved, it is desirable to tell briefly the part which he had in the development of this process that with a single furnace converts pig iron into steel at the rate of a thousand tons in 24 hours and first made mild steel available as a building material. ”

“ Cast steel is used for many of the same purposes as cast iron, but more particularly for those purposes where castings of great strength are required. Wrought iron is forged into various shapes for special purposes, and is rolled into bars, plates, beams, rails, and structural shapes. Extra hard steels are used for tools, hard steel for piston-rods and other parts of machines, medium steel for rails and guns, and the mild and soft steels for beams and structural purposes. ”

“ The physical properties of steel depend upon the chemical composition and method of manufacture, and they vary so greatly, both relatively and absolutely, that no effort will be made to define them here. The mild and soft structural steels for bridges and buildings have tensile strengths of from 60,000 pounds to 70,000 pounds per square inch, with a limit of elasticity of from 30,000 pounds to 40,000 pounds per square inch. The hard steels have a much greater strength. The compressive strength of steel is always greater than the tensile strength. ”

“ Alloying Elements.—Commercial steels of even the simplest types are therefore primarily alloys of iron and carbon. Impurities and their "remedies" are always present: sulphur, phosphorus, silicon and manganese—to say nothing of oxygen, nitrogen and carbon oxide gases, about which we know very little. It has been found that other metals, if added to well-made steel, produce definite improvements in certain directions, and these "alloy steels" have found much use in the last ten years. ”

“ The steels that will harden (we will call them “carbon tool steels”) , range ordinarily from the .60 per cent carbon variety, used for hammers, cold chisels, etc., to those containing 1.50 per cent of carbon which are selected for razors, scalpels, and other tools requiring high temper. Each one of these many grades is susceptible of a wide variety of temper in the hands of a capable man, who must select his steel and give to it the most desirable temper for the work for which the tool is designed. ”

“ The old varieties of wrought iron, steel and cast iron preserve their old names; the new class is called steel by main force. As a result, certain varieties, such as blister steel, are called “steel” solely because they have the hardening power, and others, such as low-carbon steel, solely because they are free from slag. But the former lack the essential quality, slaglessness, which makes the latter steel, and the latter lack the essential quality, the hardening power, which makes the former steel. “Steel” has come gradually to stand rather for excellence than for any specific quality. ”

“ When the carbon has been put in, the retort is closed. The molten metal absorbs the alloy, and the product is Bessemer steel. In fifteen minutes pig iron can be transformed into ingot steel. The invention made possible the use of steel in the construction of bridges, high buildings, and ships. It made this age of the world the Age of Steel. ”

“ If the die is for a forging which is machined all over and does not have to be especially close to size, where a variation of 1/16 in. is not considered excessive, a low grade steel will be perfectly satisfactory.
In cases of fine work, however, where the variation cannot be over 0.005 to 0.01 in. we must use a fine steel and prevent its going out of shape in the heating and quenching. A high quality crucible steel is suggested with about the following analysis: Carbon 0.75 per cent, manganese 0.25 per cent, silicon 0.15 per cent, sulphur 0.015 per cent, and phosphorus 0.015 per cent. ”

“ I wish to call the attention of the meeting to some of the peculiarities which distinguish cast steel from all other forms of iron, viz., the perfectly homogeneous character of the metal, the entire absence of sand-cracks or flaws, and its greater cohesive force and elasticity, as compared with the blister steel from which it is made,—qualities which it derives solely from its fusion and formation into ingots, all of which properties malleable iron acquires in like manner by its fusion and formation into ingots in the new process ”

“ It will be observed,
'The primary object of my invention is to provide means for rendering the product of steel works uniform in chemical composition. In practice it is found that metal tapped from different blast furnaces is apt to vary considerably in chemical composition, particularly in silicon and sulphur; and such lack of uniformity is observable in different portions of the same cast, and even in different portions of the same pig. [Here follows table of analyses said to have been made of metal contained in different ladle charges from one cast of a blast furnace.] ”

“ When the steel made from such iron is wrought into a tool and ground, the edge is uneven, serrated, softer in one place than another. This amounts to a fatal defect in those articles where great and uniform hardness is required, as in screw-taps, wire-drawers, plates, dies, and stamps for coining and engraving. It is evident, as the carbon is introduced from the surface, that there will be less in the middle than at the outside of the bars; thus the steel is not of a uniform character. ”

“ Of the degrees of heat workmen judge by the change of colour on its surface. Steel, like crude iron, is capable of being melted without losing its properties. It is then called cast steel, and is of a more uniform texture. Iron acquires some little weight by being [Pg 109] converted into steel; and when dissolved in acid, it yields more plumbago. Steel has something less specific gravity than iron. If the cementation be continued too long, the steel acquires a darkish fracture, it is more fusible, and incapable of welding. Steel heated in contact with earthy matters, is reduced to iron. ”

“ However, during the melting down of the charge the steel scrap becomes molten and its constituents merge with those 186of the other iron materials charged. We get out of the cupola, then, a mixture which, disregarding the losses and gains due to the air of the blast, the fuel, etc., is an average of the materials charged. We, therefore, no longer have any steel, but a cast iron which has a somewhat lower silicon, phosphorus and carbon than the softer cast irons. The greater strength of the alloy is due to its composition and only indirectly to the fact that steel was used in its production. ”

“ By the continuation of the process the steel so produced gradually loses its small remaining portion of carbon, and passes successively from hard to soft steel, and from soft steel to steely iron, and eventually to very soft iron; hence, at a certain period of the process, any quality of metal may be obtained. There is one in particular which by way of distinction I call semi-steel, being in hardness about midway between ordinary cast steel and soft malleable iron. This metal possesses the advantage of much greater tensile strength than soft iron ”

“ Whenever we have the good fortune to intersect India with railroads, steel-iron will be among the number of our enlarged imports.
The hard and elastic qualities of steel, known as “temper,” are obtained by heating and then cooling rapidly. For this purpose baths of mercury and of boiling oil are used. Some waters are supposed to have peculiar virtues for tempering steel.
Case-hardening, a process much used for tools and plough-shares, consists in superficially hardening cast iron or wrought iron by heating it in a charcoal crucible, and so converting it into steel. ”

“ Ordinary steel contains certain other chemicals, such as silicon, manganese, sulphur, and phosphorus, but these are mere natural impurities existing in the metal. The essential ingredients are iron and carbon. Steel is hardened by being heated to a high temperature and then suddenly cooled by contact with cold water, or in other like ways. Fixing the degree of hardness in a piece of steel is called tempering. The degree of hardness is dependent upon the suddenness of cooling. ”

“ The provocation came from his claims that the product of the first stage of the conversion was the equivalent of charcoal iron, the processes following the smelting being conducted without contact with, or the use of, any mineral fuel; and that further blowing could be used to produce any quality of metal, that is, a steel with any desired percentage of carbon. ”

“ Iron, when first melted from its ore, has little malleability, and the vessels and other implements that are made of it in that state, by casting into moulds, are easily broken. It acquires toughness and malleability by forging, which is done by beating it when red-hot with heavy hammers, till it becomes ductile and flexible. Steel, again, is made by heating small bars of iron with charcoal, bone, and horn shavings, or other inflammable matters, by which it acquires a finer grain and more compact texture, and becomes harder, and more elastic. ”

“ For the production of natural steel, a white cast iron is preferred, which contains little carbon, which does not flow thin, and which being cemented over or above the wind, falls down at once through the blast to the bottom of the hearth in the state of steel. With this view, a very flat fire is used; and should the metal run too fluid, some malleable lumps are introduced to give the mass a thicker pasty consistence. ”