Kinetics of Microstructure Evolution during Gaseous Thermochecical Surface Treatment

The incorporation of nitrogen or carbon in steel is widely applied to provide major improvements in-materials performance with respect to fatigue, weaif tribology, and atmospheric corrosion. These improvements rely on a modification of the surface-adjacent region of the materiat by tl.re (internalf precipitation 6f ailoying element nitrides/carbides"or by thE development of a continuo_us laye_r of iron-based (carbo-) nitrides. The evolution of the microstructure during thermochemical treatme_nts is not only determined by solid-state diffusion, but in many cases also by the kinetics of the surface reactions and the interptay with mechanical stress.'In the present arlicle a few examplesr_co_ve_ring-research on the inleraction of carbon and,/or nitrogen with iron-based metals, are included to illustrate the various aspects of gas-metal interactidns.