Chemicals Used in Steel Industry J . L. GREGG, Assistant to Vice President, Bethlehem Steel Co., Bethlehem, Pa. Few appreciate the variety of chemicals employed in the manufacture of steels and the vast tonnage of many of these materials. Producers of these products will find this authoritative survey most illuminating in evaluating the market possibilities for chemicals in America's steel industry. ALL figures quoted on consumption of chemicals in the steel industry are for t h e year 1943, and are given in net tons; that is, tons of 2,000 pounds. Some are only estimates, and may, therefore, be somewhat in error. It should also b e realized that 1943 was a superboom year with respect to steel production, as about 90,000,000 tons of steel ingots were pro duced, which may be compared with t h e production of 52,500,000 tons of ingots in 1939. In the recovery and treatment of by products from the coke ovens, sulfuric acid is used for the production of ammo nium sulfate and for washing light oils. T h e consumption of sulfuric acid by the steel industry in 1943 is estimated at 1,580,000 tons, of which something of the order of 280,000 tons were probably used at t h e coke ovens. Relatively small amounts of caustic soda are used at the coke ovens for neutralizing and for the removal of phenol; this consumption may be of the order of 10,000 tons. At the blast furnace, coke, iron ore, and limestone are the constituents of the bur den. In 1943, the use of limestone
amounted to 29,337,000 tons. The calcium oxide from the limestone charged serves to flux the gangue in the ore. I t is necessary t o burden with the proper amount of stone to yield a slag having the required melting point and viscos ity, but especially is it necessary to have enough lime to keep the sulfur con tent of the iron produced at a reasonably low value. It is possible, but usually not considered desirable, to use less stone in the burden, and to obtain a high-sulfur pig iron, which is subsequently treated with soda ash to remove part of the sulfur. Soda ash has not found wider use because of the fumes produced when the molten iron is mixed with the soda ash, because of the attack of the molten soda ash on refractories and the difficulty of making a complete separation of the molten iron and the reaction products after the treatment. Soda ash has been used as a standard practice at one plant in England for desulfurizing at the blast furnace, and it is used sporadically in this country for desulfurizing an occasional cast of highsulfur iron at the blast furnace. I t is used to a greater extent for desulfurizing cupola
PHOTO BY B E T H L E H E M STEEL CO.
General view of blast furnaces
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The author, Missouri School οf Mines graduate, has been research engineer with several steel companies, as well as at Battelle Memorial Institute.
metal, where the quantities of metal to be treated are much smaller than the normal cast from a blast furnace. Approximately 85 per cent of the steel made in this country is made by the basic open-hearth process. Most of this steel is made by charging limestone, ore, and scrap in the order named, partially melting and then adding liquid pig iron. After, or just before, all of the scrap is melted, it may be found necessary to add more lime, usually as calcined stone. In 1943, the industry used 931,600 tons of burnt lime. The lime, both that resulting from the calcination of the stone in the charge and that added as burnt lime, frequently does not dissolve readily in the slag and fluor spar is added to hasten its solution. The consumption of fluorspar in 1943 was 223,000 tons. The amount of spar used varies from shop t o shop, and there is even a great variation in the amounts used by different helpers in the same shop. T h e general practice is "to season to taste". It has been difficult to obtain sufficient spar during the past two years, and all steel producers have tried to keep the con sumption at a minimum. Mill scale, either alone or mixed with spar, has helped in saving spar. Bauxite has been reported to b e a satisfactory substitute, but there is a better use for bauxite. Some pro ducers have tried common salt as a sub stitute, but this may be poor practice, be cause of the fluxing action of the salt on the refractories. We have used a few cars of topaz, obtained from a deposit of the m a s sive mineral, and the results with this material were rather encouraging. Spar is also used in the manufacture of electricfurnace steel, but the amount used is much smaller than that used in the open-hearth, because of the relatively small production of electric-furnace steel as compared with that of open-hearth steel. With t h e exception of the latter stages in t h e making of electric-furnace steel, all steel is melted and worked under an ox idizing slag, and i n an oxidizing atmos phere. If we consider a heat of steel in basic open-hearth furnace shortly before
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Right. Charging a 5 0 - t o n electric arc furnace used i n the p r o d u c t i o n of a l l o y steels, at Bethlehem Steel C o . Below. R o l l i n g an ingot on b l o o m i n g m i l l
ALL PHOTOS ON THIS PAGE BY B E T H L E H E M STEEL CO
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Above Tapping open hearth steel furnace at Bethlehem plant. Left. Rolling rod on two-strand, continuous rod mill. Roughing stands on right, intermediate stands at left
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CHEMICAL
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PHOTO BY B E T H L E H E M S T E E L CO.
Forging an armor plate in 14,000-ton press Forge is ready to be tapped from the furnace, we find: (1) that by proper operations it is hot enough for t h e m o l t e n metal to be tapped from t h e furnace into a ladle, and that from minutes to a n hour later the molten metal will flow through a nozzle about 2 inches i n diameter into the molds ; (2) t h a t by using the proper charge and correct operation of the furnace, and by additions of either ore or pig iron, t h e carbon content is as desired ; (3) that by charging the proper materials and producing a good slag containing sufficient lime, the phosphorus and sulfur contents are below certain maximum values—say 0.04 per cent maximum phosphorus and 0.05 per cent maximum sulfur; (4) the metal contains a superabundance of oxygen, and on cooling, this oxygen will react with carbon in the steel, which reaction continues while the metal is solidifying, and thereby prevents the formation of a solid ingot or casting. In order t o obtain satisfactory ingots or castings, the m e t a l must be at least partially deoxidized. I t is deoxidized t o different degrees, depending o n the grade of steel being m a d e . Such deoxidization is brought about b y adding metals or metalloids, either as pure materials or as ferroalloys, and such deoxidizers are added t o either the furnace, ladle, or molds. Lowcarbon steels m a y b e treated with but a very small quantity of deoxidizers to yield what i s known as rimmed steel. In such a practice, the carbon-oxygen reaction takes place vigorously i n the molds for several minutes, during w h i c h time a case of rather pure iron, almost free from blow holes, i s formed. When t h e rimming subsides, a cap is placed on t h e ingot, and the molten metal remaining tends to freeze without the formation of a large shrinkage cavity; but this core contains m a n y blow holes, V O L U M E
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which are welded shut i n rolling. The behavior of the solidifying rimming steel in the mold is generally controlled by adding a small amount of metallic aluminum. Sometimes sodium fluoride is added to the steel in the mold, for the purpose of influencing t h e rimming action in a manner that will yield a thicker and more solid rim. At t h e other end of the scale, certain steels are deoxidized t o such a n extent that no evolution of gas occurs on freezing. These are said to b e "killed", and unless they cast in hot-topped molds, t h e y tend t o form a shrinkage cavity or pipe that extends alm o s t t o t h e bottom of t h e ingot. Steels partly deoxidized are said to be semikilled; they freeze in t h e mold, when properly made, without pipe; but are filled with blow holes, which weld shut when rolled. T h e principal deoxidizers used in steel making are manganese, silicon, and aluminum, and their deoxidizing power increases in t h e order named. Manganese, being closely related t o iron in its chemical properties, i s a weak deoxidizer, and there is some justification for not even considering i t as a deoxidizer. I t is, however, an essential ingredient of steel, because of its ability t o combine w i t h sulfur and thereby prevent the steel from being h o t short. Without manganese the sulfur in the steel is found as iron sulfide, which, a t the rolling or forging temperature, occurs as a liquid phase. Manganese is usually added in t h e form of blast-furnace ferromanganese, containing approximately 80 per cent manganese and 6 per cent carbon. I n 1943, the production of ferromanganese was 655,000 tons. Manganese, together w i t h silicon, is sometimes added t o the furnace in the form of silicomanganese, which contains a b o u t 67 per cent man-
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ganese, and from 12 to 25 per cent silicon. T h e consumption of silicomanganese in 1943 was 49,670 tons. Silicon is usually used as ferrosilicon, containing 50 per cent silicon, and 441,500 tons of this alloy were used in 1943. It is generally added t o the ladle, rarely t o the molds. When silicon is added t o the furnace, it is usually contained in silicon pig, containing 14 per cent silicon, or silicomanganese. A product newly on the market for adding silicon to steel in the ladle consists of a mixture of ferrosilicon and sodium nitrate. The reaction between the sodium nitrate and a portion of the ferrosilicon yields enough heat to melt all of the material in the mixture, and it is claimed that the resulting slag tends t o help remove the silica on deoxidizing the steel. A similar product for the addition of chromium has been on the market for several years. Aluminum is generally added as the commercially pure metal, either t o the ladle or to the molds. In addition t o deoxidizing the steel, the hardenability of steel of a given composition can be varied b y the amount of aluminum added. The consumption of aluminum in 1943 was 26,800 tons. Several alloys especially made for deoxidization and containing aluminum in addition to one or more other deoxidizers, are on the market, but the bulk of the aluminum additions are made by means of the simple metal. Titanium is used to a limited extent as a deoxidizer, and it is added as a ferro-alloy. Calcium and alloys containing calcium have been tried out as deoxidizers, but these have not found general application. Although such elements as manganese, silicon, and aluminum are usually used as deoxidizers, or for obtaining sound steel that is not hot short, greater amounts than are required for these purposes may be added to take advantage of the effects of these elements as alloys. As examples, a tough and abrasion-resistant steel contains 12 per cent manganese; steels for transformer sheets contain as much as 5 or 6 per cent silicon, and nitriding steels may contain somewhat over 1 per cent aluminum. A general aim in steel making is t o produce steels with low phosphorus and low sulfur; yet, for some special steels, these elements are intentionally added. Phosphorus m a y be added as a ferro-alloy t o increase either or both the strength and t h e corrosion resistance. It's use now is confined to a few grades of tin plate, and t o some of the proprietary lowalloy, high-strength steels. Sulfur is added as the element to certain steels t o increase their machinability, and such steels are known as free-machining steels. T h e use of sulfur in 1943 amounted t o 1,600 tons. The metals nickel, chromium, molybdenum, and vanadium are used in a number of alloy steels, where their function is 1557
to make it possible to obtain stronger and tougher components than can be produced from simple carbon steels. Such steels are practically always quenched and tempered. Nickel is usually added as the commercially pure metal and the consumption of nickel in 1943 was 102,500 tons. Chromium is added as ferro-chromium. In 1943 the steel industry consumed about a million tons of chrome ore, much of which was used for refractory purposes. Molybdenum is sometimes used as ferromolybdenum, but the usual practice is to add it as an oxide or molybdate to the steel-making furnace. The consumption of vanadium contained in the ferro-alloy was probably 1,700 tons. Both chromium and nickel are used in so-called stainless steels, all of which contain at least 12 per cent chromium, and only some of which contain nickel. Molybdenum is also used in some of these steels. Chromium, molybdenum and vanadium are used in certain tool and die steels. The principal use of tungsten is in tool steels, and in many of such steels it may be replaced by molybdenum. Tungsten is used as the ferro-alloy, and in 1943 the consumption of tungsten in ferrotungsten was 8,600 tons. Cobalt is used as the commercially pure metal, and the consumption in 1943 was 2,300 tons. Some steel producers are now using zirconium, both as a deoxidizer and alloying element in constructional steels. It is used as a ferroalloy containing 35 to 40 per cent zirconium, and in 1943 the consumption of ore was 23,500 tons. Copper is added to some steels in small amounts to improve the resistance to atmospheric corrosion, and in larger amounts t o increase strength. Scrap copper is usually employed, and the consumption of copper in 1943 has been estimated as 3,800 tons. Lead is added to a small tonnage of steel t o improve machinability. Because t h e boiling point of lead is near the melting point of steel, it is added to the mold, and t h e loss by volatilization is large. In 1943, t h e consumption of lead in the industry for all purposes was about 5,600 tons. A relatively small quantity of Columbian or titanium is used in austenitic stainl e s s steels to prevent weld decay. I t has recently been found that extremely small amounts of boron increase t h e hardenability of steel, and a use for boron-containing alloys seems to be developing. Where scale must be removed by pickling, the usual practice at steel plants is to remove it by pickling in hot dilute sulfuric acid, and the pickling solutions may or may not contain a n inhibitor. Some muriatic is used in pickling prior t o galvanizing. T h e usual materials pickled are rods and bars prior to drawing; hot-rolled strip prior t o cold-rolling; wire, sheet, and pipe prior t o galvanizing, and back plate prior t o tinning. In some instances billets may b e pickled, in order t o locate and remove seams by chipping.
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For galvanizing, ammonium chloride, zinc chloride, or a mixture of these two compounds may be used as a flux. For hot-dipped tinning, zinc ammonium chloride is used as a flux. In 1943 the consumption of ammonium chloride was 11,000 tons, and that of zinc chloride 4,300 tons. The consumption of zinc was 290,000 tons, and that of tin 42,000 tons. In the cold-rolling of hot bands, which are ultimately to be sheet or tin plate, the material is coated with either oil or a water-oil emulsion. For sheets, a light mineral oil is used; but for the thinner tin plate, palm oil is generally used. In 1943 the industry used 14,500 tons of palm oil. The major amount was probably used in hot-dip tinning, where the hot oil floats on the molten tin, so that the plate coated with a layer of molten tin passes through the palm oil as it is leaving the tinning pot. The excess palm oil may be removed from the tin plate by a wet cleaner, either silicate with caustic, or trisodium phosphate; it may also be removed by branning. If it is removed by wet cleaning, some oil, either palm oil or cottonseed oil, is usually added b y means of a branner. Alkaline cleaners are also used for removing the oil from the cold-rolled strip that is to become tin plate. The usual cleaner is orthosilicate, plus caustic soda. For a number of years we have produced zinc-coated wire which is sold to the trade under the trade name "Bethanized". In the making of this wire, we have used the Tainton electroplating process, in which insoluble anodes are employed and the zinc is extracted from roasted concentrates. As the plating solution becomes richer in sulfuric acid and poorer in zinc, i t is sent to the leach plant, and used for leaching. I n purifying the electrolyte, manganese dioxide is used for oxidizing, and zinc dust is used for final purification.
Silicic acid and cresylic acid are added to the electrolyte to help form a blanket of foam on the cells. I n some cases the wire to be plated isdescaled electrolytically in molten caustic; otherwise, it is pickled in muriatic acid. Much of the tin plate now being produced is made by electrode position of the tin. Several different electrolytes are used, both acid and alkaline, but soluble anodes are used in all processes. The large-scale manufacture of electrolytictin plate is comparatively new, and the details of all the processes are not available. With the alkaline process, the electrolyte is made from sodium stannate and caustic soda. Caustic soda must be added periodically to maintain the alkalinity, and it is sometimes necessary t o add stannate. After the tin has been plated on the steel, it is melted by one of several methods; and, after melting, a practice now general is to pass through a solution of chromic acid, which tends to improve the adherence of lacquers. T h e plate is finally oiled by branning, spraying, or passing through an emulsion. Materials used for oiling are palm oil, cottonseed oil, and dibutyl sebacate. The amount of oil left on the plate amounts t o only 0.15 or 0.20 gram per base box, a base box having 435 square feet of surface. The electrolytic tin plate now being made is coated with 0.5 pound of tin per base box, as compared with over twice as much tin on hot-dip plate, in which 1.25 pounds of tin are now being used to coat a base box of plate; and electrolytic plate is used chiefly to conserve tin. As a further step in tin conservation, the can companies are using some tin-free bonderized plate. In bonderizing, the steel is passed through a proprietary phosphate bath which contains a strong oxidizing CONTINUED ON PAGE 1612
PHOTO BY BETHLEHEM STEEL CO.
Finishing stands and continuous strip mill.
CHEMICAL
Slab is rolled to strip in a continuous operation
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SOMETHING NEW IN
Rotameter DESIGN
Ν THE SERÏES-iOO ROTAMETERS, the g u i d e rod IS ichored to and centered in thr metering tube by means of precision-made discs which fit snugly into the ends of the tube. This makes certain that the metering float is always in the exact center of the tapered metering tube throughout the entire length of the tubeIn oîder constructions, the guide rod was anchored to the end fittings by means of discs which were sealed in the drain plug cavities. In such Rotameters, the packing in the stuffing box becomes set after use, requiring tightening of the sruffing boxes. This, however, will draw the end fittings together, decreasing the tension in the guide rod so that the float no longer moves in the exact center of the tube. In the Series-100 Rotameters, adjusting the stuffing box in no way affects the guide rod tension.
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