Steel Melting

Lead and its alloys are generally melted, handled, and refined in cast-iron, cast-steel, welded-steel, or spun-steel melting ketdes without fear of contamination by iron (qv). Normal melting procedures require no dux cover for lead. Special reactive metal alloys require special alloying elements, duxes, or covers to prevent dross formation and loss of the alloying elements. 

Electric-Arc Furnace. The electric-arc furnace is by far the most popular electric steelmaking furnace. The carbon arc was discovered by Sir Humphry Davy in 1800, but it had no practical appHcation in steelmaking until Sir William Siemens of open-hearth fame constmcted, operated, and patented furnaces operating on both direct- and indirect-arc principles in 1878. At that early date, the avadabiHty of electric power was limited and very expensive. Furthermore, carbon electrodes of the quaHty to carry sufficient current for steel melting had not been developed (see Furnaces, electric). 

High density tungsten alloy machine chips are recovered by oxidation at about 850°C, foUowed by reduction in hydrogen at 700—900°C. Typically, the resultant powders are about 3-p.m grain size and resinter readily. There can be some pickup of refractory materials used in furnace constmction, which must be controUed. This process is important commercially. Eor materials that may be contaminated with other metals or impurities, the preferred recovery process is the wet chemical conversion process used for recovery of tungsten from ores and process wastes. Materials can always be considered for use as additions in alloy steel melting. 

Use of regenerators is limited to large steel-melting furnaces for example, an open-hearth furnace, and by-product coke ovens with fuel combustion systems only. 

The primary leachable hazardous constituents of EAF emission control dust/sludge are lead, cadmium, and hexavalent chromium. Generally, 20 to 40 lb of EAF dust per ton of steel are generated, depending on the mill s specific operating practices, with an average of about 35 lb/t of steel melted.1 Table 2.11 shows the typical ranges of concentration of each of these elements in EAF dust. 

If the thickness of the dissolved part of the solid specimen far exceeds the thickness of the ApBq layer formed at the solid-liquid interface in the course of dissolution, the error of determination of the mass loss by weighing the specimen before and after the experiment will be negligibly small. However, at low t and k0 > b the increase in the specimen mass due to the formation of the ApBq layer may prove greater than its decrease caused by dissolution. In such a case, instead of decreasing, the mass of the specimen will increase, as was observed, for example, by V.I. Zhalybin et al. during dissolution of titanium in the stainless-steel melt. 

Essentially the sensor comprises an YSZ element one side of which is in contact with the steel melt and the other with the metal—metal oxide reference mixture. The steel serves as one electrical contact to the zirconia and the... 

In European practice both coke and retort graphite have been admixed with the natural graphite for making crucibles. The practice is not desirable for steel melting,... 

The composition of graphite crucibles varies considerably with reference to whether they are to be used for brass or for steel melting. Some of the mixtures which have come to the knowledge of the writer are as follows, the first four being principally intended for melting brass and the last two for steel ... 

FIGURE 14.4 Schematic design of a direct arc electric furnace for steelmaking. The whole unit may be tilted to the side for emptying the finished steel melt. 

Tungsten in most cases is added to the steel melt as master alloy. The two usual types are ferrotungsten and melting base. Due to their lower melting point, master alloys dissolve and distribute more readily in the steel melt as pure tungsten. Moreover, they are cheaper because they are produced either directly fix)m ore concentrates in case of ferrotungsten or from scrap materials in case of melting base alloys. 

Tungsten Alloyed Steels. Tungsten addition to the steel melt. 

Timgsten sources which can be added to the steel melt are ... 

Loss by recycling dilution includes residues containing low tungsten concentrations as a result of recycling, and are not uneconomical to recover. For example, tungsten as trace constituent in recycling of tool steel, carbides, etc. is lost into the steel melt. 

Weyl, A., Tu, S.W. and Janke, D. (1994) Sensors based on new oxide electrolyte and oxygen reference materials for online measurement in steel melts. Steel Res., 65 (5), 167-72. 

L. and Daotze, L. (2000) A study of aluminum sensor for steel melt. Sens. Actuators B, 62, 31-4. 

Table 3. The Effect of Primary Battery Additions to a Typical Steel Melt...

The zinc component is an important addition for the steelmaker, both environmentally and economically. In all but the very fastest steel-melting imits, the majority of the zinc will vaporise into the furnace off-gases and add to the zinc oxide level in the filter plant dust. For most furnaces, the increased zinc content of the filter dust can be up to 6% or occasionally even more, for each 1% addition of batteries. 

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