长期高温服役后S31042奥氏体耐热钢的微观组织

Microstructure of S31042 austenite heat resistant steel after long-term service under high temperature

利用光学显微镜、扫描电镜及能谱仪和X-射线衍射分析仪,研究了1000 MW超超临界机组用S31042奥氏体耐热钢服役50000 h后的微观组织变化。结果表明,经长期高温服役后,S31042钢组织由奥氏体基体和M_(23)C_6、NbCrN和Nb(C,N)析出相组成,服役过程中析出相不断发生析出、聚集和长大。M_(23)C_6碳化物在奥氏体晶界、孪晶界等位置形成链条状,在晶内析出为细小颗粒状,并随着服役时间的延长发生聚集长大,而在晶界附近区域则为细小颗粒状。NbCrN和Nb(C,N)主要分布于奥氏体晶粒内部,尺寸细小的NbCrN、Nb(C,N)和M_(23)C_6碳化物可有效提高S31042钢的蠕变强度,而尺寸较大的M_(23)C_6碳化物以及初始Nb(C,N)将对材料的蠕变强度产生不利影响。

Microstructural change of S31042 austenitic heat resistant steel used in 1000 MW ultra-supercritical unit after serving for 50 000 h was studied by means of optical microscope,scanning electron microscope,energy spectrometer and X-ray diffractometer.The results show that S31042 steel after long-term service at high temperature consists of austenite and M23C6,NbCrN and Nb(C,N)precipitated phases.In the service processes,the precipitated phases constantly precipitated out,aggregated and grew up.At the austenite grain boundary and twin boundary M23C6 carbide formed in chain shape,inside grain M23C6 formed as small granular particles then gathered and grew up with the extension of service time,while in the vicinity of grain boundaries it is seen fine grainy.NbCrN and Nb(C,N)are mainly distributed in the austenite grains.NbCrN,Nb(C,N)and M23C6 carbide with small size can effectively improve the creep strength of S31042 steel.However,M23C6 carbide and initial Nb(C,N)with larger size will adversely affect the creep strength of the steel.