Microstructure-tensile strength correlation of salt bath nitrocarburised engineering steels

A commonly used engineering steel (En8) and a hot working die steel (H11) w ere salt bath nitrocarburised in the ferritic and austenitic range and stud ied for their microstructure and tensile properties. Compound layer thickne ss and hardness increased with increasing treatment temperature. There was a marginal improvement in the tensile strength after ferritic nitrocarburis ing due to the hardness increase in the compound layer and diffusion zone. There was marginal drop in the tensile properties of specimens treated in t he austenitic range, but these values were comparable to those obtained aft er blank treatment at the same temperature. The tests showed that the compo und layer had good cohesion with the underlying zone despite the precipitou s hardness drop at their interlace.