Investigation of the microstructure of laser-deposited layers on cast-iron parts

The gas-powder laser surfacing process of the cast-iron parts' surfaces with the aim of increasing the wear resistance is investigated. Obtaining a coating with specified parameters (chemical composition, dimensions and quality of the rollers being deposited) depends on the irradiation regimes: power, processing speed, dimensions of the focal spot, powder consumption and the method of its delivery. St3 steel was used as a base material. Self-fluxing powders PG-C3R2, PG-PBH-6-2 and PG-US25-20Fe and their mixtures were used as a material for surfacing. The powders had a particle size of 50-160 microns. During laser heating, the structure is refined: the size of graphite plates is reduced from 150-200 mu m to 20-40 mu m in the melted zone, then their depth increases to the initial value. In the melted zone, graphite partially dissolves, partially burns out, forming pores. In the areas with the most complete dissolution of graphite plates, an austenite-martensitic structure with a hardness of up to 8.0-9.5 GPa is formed. In areas with a lower degree of dissolution of graphite, a martensite-sorbitol structure is formed with a hardness of 6.5-7.0 GPa. In the area of laser exposure, the hardness of the cast-iron welded parts increases by 3-4 times, which provides a significant increase in wear resistance.