超超临界机组转子钢FB2持久性能和组织演变研究

Stress Rupture Property and Microstructure Evolution of FB2 Rotor Steel Used in Ultra-Supercritical Units

以FB2转子钢为研究对象,通过高温持久试验、金相显微镜、扫描电镜及透射电镜等研究手段,研究了FB2转子钢在630℃下的持久性能及组织演变规律。结果表明:FB2转子钢为回火马氏体组织,原奥氏体晶界与晶内均析出了大量细小M_(23)C_(6)碳化物。持久实验中在应力作用下,随时间延长,马氏体板条发生分解逐渐变宽,位错密度下降,M_(23)C_(6)碳化物在原奥氏体晶界和马氏体板条边界上逐渐长大,Laves相逐渐在原奥氏体晶界上析出长大,并聚集成链状分布。微观组织结构的变化会显著影响高温持久性能,但FB2转子钢最长断裂点仍能满足630℃、105h持久应力不小于100 MPa的要求。

The stress rupture property and related microstructure evolution of FB2 rotor steel were investigated by metallographic analysis,scanning electron microscope and transmission electron microscope.The results show that the microstructure of FB2 rotor steel is composed of tempered martensite.A large amount of fine M_(23)C_(6) carbides precipitate on original austenite grain boundary and in grains.Decomposition and broadening of martensite lath can be found with prolonging stress rupture duration.The dislocation density decreases at the same time.Meanwhile,the M_(23)C_(6) carbides located at grain boundary and martensite lath boundary grow.Laves phase gradually grows at original austenite grain boundary and aggregates into a chain.The microstructure evolution at high temperature can apparently influence high temperature stress rupture property.While the longest breaking point of the FB2 rotor steel can still meet the requirement that the stress is higher than 100 MPa after the stress rupture test at 630℃ for 105 h.