Degradation of the Cr-Ni-N Austenite Refractory Steel at High Temperature Carburizing Atmosphere

By means of SEM,EDS and XRD, the degradation of austenitic refractory steel Cr30Ni20NRE in the enviroment of long-term and high-temperature unilateral carburizing was investigated. The expermental results denoted that the finer pearlite along the austenite boundaries in the as-cast Cr30Ni20NRE steel disappeared first under long-term and high-temperature service condition, and that a number of Cr-richened carbides were formed due to unila-teral carburizing at long-term and high-temperature, consequently causing Ni to concentrate, bulging and calalyzing decomposition of the carburizing gas. The bulged surface expanded carburizing area and pormoted the carbon atoms to penetrate into the steel, thus allowing the carbides to continuously grow, forming cracks around the carbieds and causing the austenite to shrivel. The redistribution of alloy elements caused Cr and Ni to respectively concentrate into carbied and austenite. The concentration of Ni and Si resulted in formation of graphite which was burnt by oxygen penetrating in reverse direction, thus producing oxidized cavities and porosities, and finally resulting in failure of the structural component because of holing.Therefore, it is most important for the radiant tube to obtain anti-carburizing preformance in order to extend the service life under high temperature carburizing enviromment.