EFFECT OF PACVD TIN ON PITTING CORROSION OF HIGH ALLOYED TOOL STEEL

PACVD TiN layers formed on pre-nitrided tool steel considerably decrease the active dissolution, hinder the pit nucleation, and eliminate the deterioration of the steel surface in chlorine containing acid solution. Pre-nitriding of tool steel under glow discharge conditions providing the formation of a diffusion zone only, affects the structure and properties of the TiN deposit. The boundaries of grains and grain conglomerates serve as sites for pitting attack on TiN covered steel. Increase in the grain size and formation of conglomerates decrease the corrosion susceptibility, however, if the conglomerate size overlaps the layer thickness, the possibility of corrosion attack increases.