SURFACE HARDENING BY NITRATION

The properties on surface of part can be changed by diffusioning nitrogen to steel surface in nitration heat treatment. The diffusion of nitrogen is very fast in high tempertures in ostenite phase. But massing the nitrure on surface causes very brittle layer on surface. Tht’s why nitrogen is not diffused to ostenitic structure (except more alloyed ostenitic steel), it is diffused to ferritic structure. So it is formed very thin and brittle layer and nitrures settle in this layer contains nitrogen.

The hardened layer that is obtained by gas nitration in 510°C, is very thin. Although this, with alloy elements which can constitute nitrure, it can be obtained both thick hardened layer and homogen and much hardness. Most important elements which can be constitute nitrure, is chromium, titanium and aluminium.

In nonalloyed and low alloyed steels, it is reached to very much hardness level at diffusion temperatures under 590°C. Even the temperatures under 530°C are suitable. It has the problem of diffusioning very slow at low nitration temperatures.