Basic oxygen steelmaking

“ The air is then turned on, and the converter is raised to a perpendicular position. The air passes up through the entire charge of iron; consequently the metal is thoroughly189 acted upon, while in the open-hearth process it is not. The Bessemer process is based on oxidation; it produces a very high temperature and keeps the charge in a liquid state during the time of blowing. This is continued until the sulphur and phosphorus are removed or the charge becomes decarbonized,—a condition termed burned steel, owing to the presence of dissolved oxygen. ”

“ The best fire for perfect heating is a reducing one, that is, one in which the combustion of the fuel is rapid enough to use entirely the oxygen in the air which is supplied. An oxidizing fire is one that does not use all the oxygen in the blast for the combustion of the fuel. The surplus oxygen will produce, on the surface of the metal, oxide of iron, or a black scale, which is extremely injurious. This scale will prevent welding, so all possible precautions should be taken to avoid its forming. ”

“ Heating in an open fire is very injudicious, because the carbon which enters the steel as an element combines with the oxygen of the air to the detriment of the quality of the steel. Usually steel goods are heated in an iron oven with charcoal powder, or placed in the heart of hot cinders, so as to exclude all air and oxy gen. ”

“ Internal studs are so arranged as to keep the ore agitated; and spiral flanges convey it to the outlet end continually, shooting it across the cylinder. The cylinder is encased in a brick furnace. The firing is provided from outside, the inventor maintaining that the products of combustion are inimical to rapid oxidisation, to specially promote which he introduces an excess of oxygen produced in a small retort set in the roof of the furnace and fed from time to time with small quantities of nitrate of soda and sulphuric acid. Ores containing much sulphur virtually calcine themselves. ”

“ Oxygen unites with almost every other element, this union often taking place with great heat and much light, producing flame. Steel and iron will burn rapidly when placed in this gas if the combustion is started with a flame of high heat playing on the metal. If the end of a wire is heated bright red and quickly plunged into a jar containing this gas, the wire will burn away with a dazzling light and be entirely consumed except for the molten drops that separate themselves. This property of oxygen is used in oxy-acetylene cutting of steel. ”

“ In electric smelting, the high temperature of the arc (3600° C.) may be used for the reduction of certain metallic oxides, which at the lower temperature of furnaces heated by coal, coke, gas, &c. (2000° C.) , will not give up their oxygen to carbon; other ores are also sometimes smelted by electrical means, especially in localities where current is cheap and fuels are dear. The production of refined steel, special alloy steels, and certain non-ferrous alloys is also carried out in electric furnaces of various types. ”

“ In the wrought iron process most of it was furnished by the iron ore or scale which was stirred into the metal, or by the slag which covered the “bath.” In the Bessemer, or as it was first known in America, “Kelly’s air blowing process,” the oxygen of the air blown through the molten metal directly oxidizes or burns out the carbon, silicon, and manganese. The extremely rapid oxidation of these furnishes the heat. ”

“ At present, not only the cutting but also the welding of iron and steel is accomplished by means of such a flame; every machine shop is provided with an oxygen apparatus, and soon every garage will be similarly equipped, as it has been observed that the carbon collected in the cylinders of gas engines for automobiles, etc., can be easily removed by burning it out with the oxygen-flame. ”

“ Steel, of whatever kind, should never be heated in a thin fire, especially in one having a forced blast, such as an ordinary blacksmith's or iron rivet furnace fire. The reason for this is that more air passes through the fire than is needed for combustion, and in consequence there is a considerable quantity of free oxygen in the fire which will oxidize the steel, or in other words, burn it. If free oxygen is excluded steel cannot burn; if the temperature is high enough it can be melted and will run down through the fire, but burning is impossible in a thick fire with a moderate draught. ”

“ It will be noticed that the neutral flame assumes a more bluish color, is a little pointed, and a very noticeable hissing sound is in evidence. This is what is called an oxidizing flame and will be again referred to. Too much oxygen is used. Operators who attempt to turn on the oxygen first and then light it, will find that it does not burn, and their efforts will be useless. In picking up a torch for the first time, any operator can turn on one valve and detect by the odor of the gas, whether it is oxygen or the fuel gas, and can light it in accordance. ”

“ The rod must be kept constantly in contact with the work and should not be added until the edges are thoroughly melted. The flux may or may not be used. If one is wanted, it may be made from three parts iron filings, six parts borax and one part sal ammoniac.
It will be noticed that the steel runs from the flame, but tends to hold together. Should foaming commence in the molten metal, it shows an excess of oxygen and that the metal is being burned. ”

“ High carbon steels are very difficult to handle. It is claimed that a drop or two of copper added to the weld will assist the flow, but will also harden the work. An excess of oxygen reduces the amount of carbon and softens the steel, while an excess of acetylene increases the proportion of carbon and hardens the metal. High speed steels may sometimes be welded if first coated with semi-steel before welding. ”

“ The very ore, the coal, the presence of oxygen, the excess of it, all vary the quality of the material. An excess of carbon is more detrimental than a scarcity; for where carbon has once been, it leaves an indelible mark, and though extracted to as great an extent as practicable, it leaves a residue that possesses an affinity to absorb carbon again equal to the original quantity: thus, steel once made will never, by any process yet known, be reconverted back to iron of the same nature it was originally. ”

“ An important feature in the process is, that by stopping it at a particular stage, immediately following the boil, before the whole of the carbon has been abstracted by the oxygen, the crude iron will be found to have passed into the condition of cast-steel of ordinary quality. By continuing the process, the metal losing its carbon, it passes from hard to soft steel, thence to steely iron, and last of all to very soft iron ”

“ Steel cannot be burnt unless some portion of it has been oxidized. The carbon would of course be attacked first, its affinity for oxygen being greatest; but we find nothing wanting in a piece of burnt steel. It can, by careful heating, hammering and hardening, be returned to its former excellence. Then what change has taken place? I should say that two modifications have been made, one physical, the other chemical. The change chemically is that of a chemical compound to a mixture of carbon and iron, so that in a chemical sense it resembles cast iron. ”

“ The open-hearth process does this by two distinct steps: (1) by oxidizing and removing these elements by means of the flame of the furnace, usually aided by the oxygen of light charges of iron ore, and (2) by diluting them with scrap steel or its equivalent. The “pig and ore” or “Siemens” variety of the process works chiefly by oxidation, the “pig and scrap” or “Siemens-Martin” variety chiefly by dilution, sometimes indeed by extreme dilution, as when 10 parts of cast iron are diluted with 90 parts of scrap. ”

“ Pouring Charge of Molten Pig Iron into Converter
130Technically speaking, the metalloids are “oxidized.” Oxidation is the chemical uniting of oxygen, generally from the air, which has 21 per cent of this element, with another element or material such as iron, silicon, carbon, wood, coal, etc. If the oxidation is slow as in the “rusting” of iron, the resulting heat dissipates as fast as it is generated and the change is hardly noticeable. ”

“ Up to this point, the oxygen has been utilised in removing iron, sulphur, etc., which are eliminated as oxides, so that but little of the oxygen is retained in the metal, but after the boiling stage is passed, oxygen is actually absorbed, the copper now [Pg 222] becoming oxidised, and the oxygen contents of the metal rapidly increase. As in the analogous instance of steel bessemerising, it appears essential to introduce some excess of oxygen into the metal in order to ensure the complete removal of the oxidisable impurities, so in copper-refining, an excess which amounts to about 0·7 per cent. ”

“ This light is dangerous to observe at close range without colored glasses. The burning of the metal can be maintained for hours, without any other source of heat except that caused by the combustion of the iron. The oxy-acetylene cutting process is based upon this principle, in that a neutral flame is applied in order to heat the part being cut to the desired temperature. Once the melting-point is reached, pure oxygen under pressure is applied to maintain oxidation and force out the burned portion. ”

“ The combination of oxygen with other substances does not necessarily cause great heat, in fact the combination may be so slow and gradual that the change of temperature can not be noticed. An example of this slow combustion, or oxidation, is found in the conversion of iron into rust as the metal combines with the active gas. ”

“ In hearths the fuel is burned in direct contact with the iron, and the chief source of oxygen is the atmosphere; in the reverberatory furnace the oxygen is obtained from special oxidizing materials added for the purpose, and the fuel is burned in a chamber separate from, but communicating with, the chamber in which the charge is placed. With this outline of the methods of producing wrought iron from cast iron, attention will be turned to the process which is chiefly employed. ”

“ 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. ”

“ Acetylene gas, when burned with a proper portion of oxygen gas, produces an extremely hot flame, in fact, the hottest flame known. Its temperature is over 6000 degrees Fahrenheit. With this flame it is possible to bring any of the so-called commercial metals, namely: cast iron, steel, copper, and aluminum, to a molten state and cause a fusion of two pieces of like metals in such a manner that the point of fusion will very closely approach the strength of the metal fused. If more metal of like nature is added, the union is made even stronger than the original. ”

“ The flame must be much larger than for the same thickness of steel and neutral in character. A slight excess of acetylene would be preferable to an excess of oxygen, and in all cases the molten metal should be kept enveloped with the flame. The welding rod is of copper which contains phosphorus; and a flux, also containing phosphorus, should be spread for about an inch each side of the joint. These assist in preventing oxidation, which is sure to occur with heated copper. ”

“ Vanadium steel furnishes our modern tools, which are distinguished by extreme hardness, and here a war on a small scale is going on between structural steel and steel for tools with which to work the former. Every improvement in the hardness of structural steel must of necessity bring about the manufacture of a still harder steel for tools, exactly as in the case of armor plates and armor piercing projectiles.
German militarism has also benefited the industries in a field where its activities could hardly have been expected. We refer to the manufacture of hydrogen and oxygen. ”

“ Many times part of the scale or metal will pop up against the tip and cause the oxygen jet to flicker. This slight variation may cause an excessive pressure of oxygen to be introduced into the preheating flame momentarily, by backing up the oxygen in the cutting jet. This lean mixture of gas will generally flash back instantaneously and will deposit a layer of carbon on the inside of the tip, which causes much annoyance to the operator. ”

“ Scores of millions of cubic feet of oxygen are used every year in the wonderfully efficient33 process of welding metals with the oxyacetylene blowpipe, the flame of which has a temperature of about 6,000° Fahrenheit. Most of the supply now comes from liquid air. An equally large amount is used in a recently introduced method of cutting metal. The object to be cut is first heated to incandescence, after which a jet of oxygen is played upon it. The metal actually burns away in the stream, and a clean cut is made like that of a saw. ”

“ Best carbon is heated with coal or charcoal, in some works on the refining hearth, in others upon the bed of the puddling furnace. The oxygen burnt off the excess of carbon from the iron and steel is left. Payen says that when the iron contains slag, the ferrous silicate present in this takes part in the reaction.
The steel obtained by this method is called natural steel. It is afterwards subjected to forging, and being of inferior quality is employed in the manufacture of springs for machinery, railway carriages, wheel tyres, ploughs, and other farming implements. ”