Randschichthärtung von rostfreiem stahl durch Gasnitrierung und Gascarburierung bei niedringen Temperaturen

In the present contribution an overview is given of new scientific and technological achievements on gaseous nitriding and carburizing of austenitic stainless steel at low temperature, i.e. below appr. 723 K for gaseous nitriding and below appr. 823 K for gaseous carburizing. These thermochemical treatments are enabled by a newly patented pretreatment, which replaces the passive chromium oxide layer by a very thin catalytic nickel layer. In the subsequent thermochemical treatment carbon and/or nitrogen containing species from the gas mixture dissociate at the Ni-surface. Simultaneously nitrogen and carbon atoms are incorporated in the substrate under the development of expanded austenite. Crystallographic data, absorption isotherms, diffusion coefficients and the thermal stability were investigated for homogeneous foils of expanded austenite with different nitrogen contents. Hardness and residual stress-depth profiles were measured on layers of expanded austenite, as obtained by gaseous nitriding and carburizing of austenitic stainless steels. It was concluded that a combination of gaseous nitriding preceded by gaseous carburizing provides the possibility of tailoring the hardness- and residual stress-depth profiles.