高镍铬含氮奥氏体耐热钢在高温渗碳环境中的蜕变

应用SEM，EDS及X射线衍射等方法分析研究了高镍铬含氮奥氏体型耐热钢Cr30Ni20NRE在长期高温渗碳环境运行中的蜕变。试验结果表明，长期在高温条件下服役，铸态Cr30Ni20NRE耐热钢中沿奥氏体晶界的珠光体首先融入奥氏体；长期高温单边渗碳形成大量富铬碳化物，促使镍富集并起泡形成瘤状物，催化含碳气体的分解；表层瘤状物使辐射管表层疏松，表面积扩张，加快了碳向基体的渗入，提供了碳化物持续长大的条件，并引起沿碳化物周边开裂和奥氏体基体严重萎缩；合金元素的重新分布造成主合金元素铬和镍产生两极分化，镍和硅的富集促使石墨化，与侵入的氧形成内部氧化空洞和膨胀疏松，最终导致构件穿孔失效。因此，对高温渗碳环境中长期使用的高合金耐热钢，迎渗碳面的抗渗碳性能和其内壁面的抗氧化性能十分重要。

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 longterm and high-temperature service condition, and that a number of Cr-richened carbides were formed due to unilateral 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.