Glow discharge nitriding of nanobainitic X37CrMoV5-1 steel

Abstract

One of the methods of improving mechanical properties of steels is nanostructuring via austempering, which leads to formation of a nanobainitic microstructure - a fine carbide-free bainitic ferrite plates with retained austenite. Due to high density of grain and interphase boundaries, this microstructure provides high tensile strength. Moreover, high amount of retained austenite guarantees high ductility and fracture toughness. However, retained austenite may also decrease hardness and wear resistance. Thus, to improve the properties of the surface an additional process is necessary. There are several methods of surface engineering which allow to produce hard diffusive layer, however most them are usually carried out at a temperature, in which nanobainite decomposes and loses its high properties. The purpose of the present work was to produce hard and wear-resistant nitrided diffusion layers on nanobainitic X37CrMoV5-1 steel surface during glow discharge nitriding, while keeping microstructure in core of the sample almost intact. Two temperatures of a nitriding were chosen. Obtained results were compared to the layers produced at quenched and tempered substrate to determine the influence of the microstructure of the substrate on the kinetics of the layer’s growth. The microstucture of the layers were described and their properties such as microhardness and wear resistance were investigated.