Stress and crack propagation in the surface layer of carburized stable austenitic alloys during cooling

Abstract

While operating in furnaces for thermal-chemical treatment, the furnace equipment cast from stable austenitic steel is exposed to many unfavourable factors that contribute to the formation of cracks and deformations, ultimately resulting in withdrawal of this equipment from further use. This study discusses the issue of microstresses formation in the carburized, surface layer of cast steel caused, during temperature changes, by different coefficients of thermal expansion of the structural constituents – carbides and austenitic matrix, of this steel and impact of the stresses on the development of cracks running from the surface to the core of the material. To study this problem a model of carbides network at the austenite grain boundary, for the carburized Fe-Ni-Cr alloy, with an oxides layer on its surface has been developed. It was used in the simulation analysis of the influence of carbides network depth and oxides layer thickness on stresses generated on the casts surface and in the subsurface zone during rapid cooling.

Keywords:

• Austenitic alloys
• carburized layer
• thermal shock
• structural stresses
• crack initiation