Production and properties of FeB-Fe2B-Fe3(B,C) surface layers formed on tool steel using combination of diffusion and laser processing

Abstract

The paper presents the study results of laser remelting diffusion boronized layers produced on CT90 tool steel. A diffusion boronized layer was produced at 950◦C in a powder mixture containing boron carbide as a source of boron. A needle-like microstructure of iron boride was obtained. After diffusion boronizing, the specimens were subjected to laser processing, which was carried out using a diode laser with a nominal power of 3 kW. Three laser beam power values were applied (600, 900, and 1200 W). The aim of the study was to investigate the microstructure, microhardness, chemical, and phase composition as well as the wear and corrosion resistance of newly formed FeB-Fe2B-Fe3(B,C) layers. As a result of the laser beam interaction, the needle-like borides occurring in the subsurface zone were remelted, and three characteristic areas were obtained: the remelted zone, the heat-affected zone, and the substrate. The properties of newly formed layers have improved in comparison to diffusion boronized layers (except for corrosion resistance). It should be noted that using the highest laser beam power contributed to a slight reduction in wear resistance. Both the reduced corrosion and wear resistance were caused by greater remelting of the steel substrate and thus by the increased iron content in the formed layer.