Nitriding of iron and steel parts in salt bath having improved corrosion resistance

Abstract

A new nitriding process by using a salt bath to produce iron and steel parts having excellent abrasion resistance and corrosion resistance includes forming an iron lithium complex oxide layer at the outermost surface of the iron part by immersing the iron and steel parts in a salt bath containing cationic component of Li, Na and K and anionic components of CNOand CO, where hydroxide compound selected from lithium hydroxide, sodium hydroxide and potassium hydroxide are added to the salt bath. Materials being in a hydrated state or in a free water containing state can be used for preparation or replenishing of the salt bath. Moistened air of (1×10kg·HO)/(1 kg dry air) can be used for mixing the salt bath. Containing ratio of Li, Na, K is preferable where a solidifying temperature of the mixture of carbonates of Li, Na, K in that ratio is lower than 500° C. It is preferable that the mol ratio of Na and K is to be 2:8˜8:2, the content of CNOis to be 5˜35 wt %, the content of CNin the salt bath is less than 2 wt % and the temperature of the salt bath is to be 450˜650° C.