Vol 48, No 11 (2018)

The use of low-temperature quartz modifications in pulverized form creates additional risks in the manufacture of molds, since polymorphic transformations decrease their crack resistance. In practice, individual layers of the shell wall or the mold as a whole often crack and even disintegrate. In many casting shops, the lining is preliminarily roasted. That may somewhat improve the consequences of polymorphic transformations in the quartz, but steady heating of the molds through the filler to reduce the odds of cracking prolongs the process and increases the energy consumption. The best-known approach to minimizing the cracking and disintegration of shell molds on roasting is to replace the filler: instead of quartz dust, it is possible to use disperse quartz sand of polyfractional composition, sillimanite, pulverized alumosilicate, globular corundum, or fused quartz. However, those materials are expensive and their use is inconsistent with the requirements of resource conservation in casting. A possible material might be silica-based ceramic cullet from the shells used in steel and aluminum investment casting. At present, such cullet is not recycled. It is dumped or used as filler in the flasks used for shaping shells. Chemical and phase analysis shows that the ceramic cullet formed after removing the steel and aluminum castings contains not only quartz and high-temperature tridymite and cristobalite phases (the base) but also 5–10% iron and iron scale and 3–5% aluminum and its oxides. The use of such ceramic cullet in shell production eliminates repeated polymorphic transformation of the quartz in roasting and sealing the molds, which would change the volume, density, and crystal lattice of the material. That increases the crack resistance and strength of the shells and minimizes the waste of the castings produced. Residual iron and aluminum and their oxides improve the utility of the mold. Tests of this recycling method in production conditions confirm its effectiveness.

Analysis of literature and production data shows that, despite significant gains in rail quality made possible in the past decade by the reequipment of Russian rail plants, the rejection rate of rails due to surface defects is still high. Research on the composition of rail steel shows that increase in copper content in the range 0.07–0.15% and in sulfur content in the range 0.006–0.011% in Э76XФ electrosteel at AO EVRAZ ZSMK significantly increases the rejection rate of rails due to surface defects. The mechanism by which the copper and sulfur concentration in the steel affects the rail quality is established. The ratio of iron and scrap in the metal batch is found to determine the copper and sulfur content in the rail steel: increase in the hotmetal content from 20 to 50% decreases the copper concentration and increases the sulfur content. To establish the optimal composition of the metal batch in the electrosmelting of rail steel, taking account of the relation between rail quality and the production economics, the influence of the ratio of iron (in liquid and solid forms) and scrap in the metal batch on electrofurnace performance is assessed. It is found that increasing the content of hot metal and pig iron in the metal batch results in linear decrease in power consumption, parabolic increase in oxygen consumption, and linear decrease in manganese content of the steel discharged from the furnace. The dependence of the smelting time on the proportion of batch components includes a minimum when the hot-metal content is 35–40% and the pig-iron content is 30–35%. On the basis of regression equations, we formulate a statistical model describing how the composition of the metal batch affects the overall performance of the electrosmelting shop in rail-steel production. Optimization is based on two factors: the total costs corresponding to the composition of the metal batch; and the productivity of the shop in terms of continuous-cast billet. This model permits recommendations regarding the optimal iron content in the metal batch at current prices of the batch materials and power, taking account of the change in shop productivity.

Flux-cored wire of Fe–C–Si–Mn–Cr–Ni–Mo composition (type A in the International Institute of Welding classification) is developed for the surfacing of abrasively worn parts. In the laboratory, multiple surface layers are applied to plate samples, with preliminary heating to 350°C and subsequent (after surfacing) slow cooling. An ASAW-1250 welding tool with the new wire is used for surfacing: six layers are applied to a 09Г2С steel plate. Instead of amorphous carbon, the wire consists of dust containing carbon and fluorine, with the following composition: 21–46% Al2O3, 18–27% F, 8–15% Na2O, 0.4–6.0% K₂O, 0.7–2.3% CaO, 0.5–2.5% SiO2, 2.1–3.3% Fe₂O₃, 12.5–30.2% Ctot, 0.07–0.90% MnO, 0.06–0.90% MgO, 0.09–0.19% S, and 0.10–0.18% P. The filler is a powder: PZhV1 iron powder (State Standard GOST 9849–86); FS75 ferrosilicon powder (State Standard GOST 1415–93); FKh900A high-carbon ferrochrome powder (State Standard GOST 4757–91); FMn78(A) carbon ferromanganese powder (State Standard GOST 4755–91); PNK-1L5 nickel powder (State Standard GOST 9722–97); FMo60 ferromolybdenum powder (State Standard GOST 4759–91); FV50U0.6 ferrovanadium powder (State Standard GOST 27130–94); PK-1U cobalt powder (State Standard GOST 9721–79); and PVN tungsten powder (Technical Specifications TU 48-19-72–92). Analysis of the applied layer shows that, within the ranges studied, carbon, chromium, molybdenum, nickel, manganese and, to a small extent, vanadium both increase the surface hardness and slow sample wear. Increasing the tungsten concentration somewhat increases the surface hardness but decreases the wear resistance. The low ductility of the matrix prevents the retention of tungsten carbides at the surface and so, rather than uniform surface wear, what is observed is crumbling of strong carbide particles from the matrix, with the formation of cracks that facilitate additional wear. The introduction of cobalt in the batch does not markedly affect the hardness and surface wear: the matrix obtained is more ductile but less hard. With no hard carbide particles in the matrix, the introduction of cobalt is deleterious. Multifactorial correlation analysis yields dependences of the hardness and wear resistance of the applied layer on the content of elements in the Fe‒C–Si–Mn–Cr–Mo–Ni–V–Co flux-cored wire.

Optimization of the lining life in converters is considered. The relation between the converter productivity and the lining life is established. With long lining life, the time for lining maintenance is greatly increased, with corresponding decrease in converter productivity. The optimal lining life is calculated for the converter shop at AO EVRAZ NTMK.

A new approach is proposed to preventing the brittle failure of steel parts and structural elements associated with embrittlement by stress concentrators such as cracks. This approach applies when alloys with insufficient margin of plasticity are used. The strength of parts with stress concentrators may be ensured by optimizing their strength and plasticity so as to maintain ductile failure in the given stress–strain state. The mechanical properties of the optimized metal are calculated on the basis of the correlations established in tests of standard samples and tests of parts with the specified stress–strain state.

Alternative methods of producing thin metal strip by melt solidification are considered, including the use of a two-roller system.