Surface modification of carbon steel by vacuum AIH-FPP treatment using mixed shot particles of chromium and high speed steel

We developed a new surface treatment system, a vacuum atmospheric-controlled induction heating fine particle peening (AIH-FPP) treatment system. The system is able to shoot fine particles at high speed in a controlled atmosphere with less than 10 ppm of oxygen concentrations. In the treatment, the substrate is heated to higher temperature by high frequency induction heating. In order to investigate the effects of treatment temperature and shot of mixed particles of Chromium (Cr) and high speed steel (AISI M42) on the formation of the surface modified layer, carbon steel was treated by vacuum AIH-FPP treatment using Cr particles and mixed shot particles of Cr and AISI M42 (Cr75, 50 and 25 mass%) at 800°C and 1000°C in nitrogen atmosphere. The surface modified layer was characterized by a scanning electron micro scope (SEM) and an energy dispersive X-ray spectrometer (EDX). In the case of the specimen treated with mixed shot particles of Cr and AISI M42 (Cr50 and 25 mass%) at 1000°C, a Cr diffused layer was formed at the surface. This was because the diffusion of Cr was accelerated by higher temperature and using mixed shot particles of Cr and AISI M42. Moreover, we revealed that the increase in flow velocity at the point of FPP nozzle accelerated the transfer of Cr.