Microarc surface alloying of tool steels

Abstract

A new method of accelerating of steel diffusion saturation during thermo-chemical treatment – microarc surface alloying is proposed. The steel product is placed in a metal container filled with coal powder, and heated by passing an electric current. Powder having microarcs, which are concentrated around the surface of the product with the formation of zones of local gas discharge. This significantly speeds up the diffusion saturation. After carburizing of steel 20Cr13 is formed a diffusion layer thickness of 13-15 μm microhardness of 10.5 to 12.5 HPa, located below the eutectoid area a thickness of 300 μm and a hardness of 6.5 GPA. After boriding of steel Cr12V1 after standard heat treatment, the surface layer with a thickness of 170-180 μm consists of a base with microhardness of 9.3-9.6 GPA with inclusions of microhardness of 14.5-15.0 GPA. After boriding of steel 5CrNiMo formed a layer thickness of 250-260 μm with a composite structure consisting of sections of the eutectoid structure of microhardness of 7.0-8.0 GPA, surrounded by boride eutectic microhardness 12.0-12.5 GPA. The composite structure provides the combination of very hard boride eutectic and eutectoid plastic mixture. After boriding of steel W6Mo5Co5 after standard heat treatment, the surface layer thickness of 230-240 μm consists of a base of microhardness 11,0-11,2 GPA with inclusions of microhardness 13,5-14,5 GPA. Given the high intensity of diffusion saturation, microarc surface alloying is recommended for surface hardening of tool steels.