Effect of carbon content of substrate on alloying layer in double glow plasma surface alloying

Abstract

Surface age-hardening high-speed steel has been formed on the surface of different substrates by double glow plasma surface alloying (DGPSA) technique, which possesses many excellent properties such as high hardness, high anti-temper stability, high wear resistance, etc. The hardness of the surface alloying layer is mainly determined by the construction of alloying layer as thickness, element distribution, structure and constituent phases of the alloying layer. In this paper, composition of the alloying layer and its constituent phases were studied for different substrates after the plasma surface alloying with W, Mo and Co. The results showed that the thickness, distribution of elements, structure and constituent phases of alloying layer were influenced greatly by the carbon content of the substrate. It is found the increase in the carbon content in the sample substrate decreases the depth of the surface compound layer. The constituent phases of the surface layer were (FeCo) 7 (WMo) 6-type μ phase, (FeCo) 2 (WMo)-type laves phase and W (Mo) solid solution for the ingot and 20 steel and MC-type carbide and M 6C-type carbide for the 45 steel and the T8 steels, respectively. The surface alloying layer exhibited high hardness of 1200–1400 HV 0.2.The thickness of the surface alloying layer was 120 μm for ingot, 50–95 μm for 20, 45, T8 steels. The advantage of the DGPSA is that thick alloying layer is formed without adhesion problem, almost every metal including W, Mo can be surface-alloyed without environment contamination problem.