Influence of the tool material on heat release in the process of mechanical-impulse hardening of steels

Abstract

In the zone of frictional contact (FC) between an article under treatment and a hardening tool, the surface layers of the article are heated with velocities of (104-105) K/sec and, at the same time, are deformed plastically, and afterwards they are cooled quickly [ 1 ]. Triboiogic and thermophysicai characteristics of the hardening tool strongly affect the temperature-force conditions in the FC zone. The temperature in this zone depends on the friction coefficients between the tool and article, and the generated heat is absorbed by the article, tool, and technological medium. In general, heat fluxes into the tool and article depend on thermal conductivities, and also on the ratio between their velocities [2]. Therefore, it was advisable to investigate the influence of the hardening tool material on heat release and distribution of heat fluxes in the FC zone. Maksymovych et al. [3] suppose that the optimal tool materials for mechanic-impulse treatment of steels are 40Kh and 40KhN steels, which have high endurance and give the necessary physicomechanical properties to the hardened metal. At the same time, the tool thermophysical characteristics must guarantee the direction of the main heat flux into the article under treatment.For comparison of tools of various materials, we calculated heat fluxes into the tool and article under hardening. Let a cylinder with a diameter of 20 ram, made of 45 normalized steel, be hardened in air. Materials of the tool-disk were 40Kh and 12Khl8N9T steels and VT6 titanium alloy. The disk diameter is 250 ram, and the length of contact line between the tool and article is equal to 5 mm. We assumed that the tool linear velocity was 70 m/sec, the article velocity was 33 mm/sec, the longitudinal tool feed was 1.2 mm/r, and the pressing force was 500kN/m.We determined the total heat fluxes by the formulas [4]