EFFECT OF SUBSTRATE STRUCTURE ON PROPERTIES OFNITRIDED LAYERS FORMED ON PURE IRON

In the present paper the structure and scratch resistance properties of gas nitrided pure iron samples were investigated. The effects of material strain hardening and amount of grain boundaries exposed on nitriding surface were evaluated by cold rolling the starting samples to different reduction levels before gas nitriding. Nitriding without any prior cold rolling produced a comparatively wide compound layer with a large fraction of porous zone featuring low scratch hardness values but no evidence of damage. On the contrary, cold rolling before nitriding led to a more irregular and thinner compound layer with reduced amount of porous zone and much finer nitrides in the diffusion zone. Scratch hardness was increased but failure mechanism changed by generation of conformal cracks within the track groove and the appearance of discontinuous spallation at high loads.