Application of Metal Ceramics for the Manufacture of Chill Molds
Abstract Generated abstract
The paper examines the use of cermets made from fine steel powder or steel powder waste as a material for manufacturing permanent molds for casting high-speed-steel tools. It argues that casting in metal molds improves tool performance by accelerating crystallization and producing a more favorable distribution of alloying elements between solid solution and carbide phases, but that conventional complex permanent molds are costly and often insufficiently durable. The authors propose pressing steel powder at high pressure to form split or complex cermet molds without binders, or using inorganic binders when pressureless molding is required. Comparative wedge-casting tests indicate that pressed cermet permanent molds provide cooling rates nearly identical to those of ordinary metal permanent molds.
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APPLICATION OF CERMETS FOR MANUFACTURING PERMANENT MOLDS
V. T. Svishchenko and N. D. Tyuteva
From a number of research works carried out at factories and in the laboratories of institutes \[1; 2; 3\], it is known that a cast high-speed-steel tool cast in rotating metal molds (permanent molds) works more productively than a tool cast in sand molds. The teeth of end mills cast in a permanent mold under pressure are characterized by higher red hardness in comparison with teeth cast in sand molds.
With accelerated cooling, we have special conditions for crystallization of the alloy. The phase state of an alloy crystallizing in a metal mold (permanent mold) does not at all correspond to the equilibrium diagram of the alloy’s state. The faster the cooling during crystallization of the ingot, the farther the system is from the equilibrium state.
During crystallization of a cast high-speed-steel tool in a permanent mold, the nature of the phases is different and the distribution of alloying elements between the phases is entirely different, sharply differing from that which we have during crystallization in sand molds. The distribution of alloying elements between the phases during crystallization in a permanent mold is far more favorable than during crystallization in sand molds. Phase analysis, determination of microhardness, and testing of cutting properties have proved a more favorable distribution of alloying elements between the solid solution and the carbide phase in a cast tool, cast in metal molds, made of modified steel.
The favorable redistribution of alloying elements between the phases of cast high-speed steel significantly improves the cutting properties of the cast tool. However, the manufacture of a complex permanent mold is expensive, which entails large overhead costs for the production of the cast tool.
Permanent molds made from accidentally selected materials are not durable; they often have to be replaced. The problem of selecting the material (steel) for manufacturing durable permanent molds cannot yet be considered solved. It seems rational to us to use cermets for manufacturing permanent molds from ordinary fine steel powder (for this purpose, production wastes of fine steel powder may be used). In this case the metal powder is used as a molding material.
A permanent mold for a tool of complex shape can be made as follows: mold the pattern of the tool to be cast with steel powder under a press at high pressure. Such a form pressed from metal powder can replace an ordinary permanent mold. The permanent mold may be split. The cooling rate of the casting is determined by the mass of the permanent mold, which can be made as desired by using one or another quantity of molding material (steel chips). When manufacturing a permanent mold under high pressure, the need to use binders is eliminated. When molding without pressure, ordinary binders may be recommended, preferably inorganic ones. Organic binders ...
may produce a gas phase, which will lead to porosity in the casting. A comparison of the cooling rate provided by an ordinary permanent mold with the cooling rate of a casting in a cermet permanent mold showed that a pressed cermet permanent mold gives, during casting, a cooling rate almost identical to that of an ordinary permanent mold.
The cooling rates were compared by the hardenability of wedges cast in ordinary and cermet permanent molds of identical dimensions.
REFERENCES
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Dobrovidov A. N., Rozenberg A. M., Yakovlev G. M. Cast cutting tool. “Stanki i instrument,” No. 1, 1943.
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Tyuteva N. D. Cast cobalt steels. Bulletin of the Tomsk Polytechnic Institute, vol. 68, 1951.
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Tyuteva N. D. and Tikhonov I. T. Investigation of the structure and properties of cast high-speed steels. Bulletin of the Tomsk Polytechnic Institute, vol. 68, 1951.