超超临界机组转子钢FB2持久性能和组织演变研究

An Investigation on Stress Rupture Property and Microstructure Evolution for FB2 Rotor Steel Used in Ultra-Supercritical Units

摘要:

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转子钢在高温630℃作用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M23C6相。持久应力作用下,随着时间延长,马氏体板条发生分解逐渐变宽,位错密度下降,M23C6相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转子钢最长断裂点能满足630℃、10_⁵h持久应力不小于100 MPa的要求。

Abstract:

In present work the stress rupture property and related microstructure evolution of FB2 rotor steel are investigated by metallographic analysis, scanning electron microscope and transmission electron microscope. The investigation shows that the microstructure of FB2 rotor steel is composed of tempered martensite. Large amount of fine M23C6 carbides precipitates on original austenite grain boundary and in matrix. Decomposition and broaden of martensite lath can be found with prolonging stress rupture duration. The dislocation density decreases at the same time. Meanwhile, the M23C6 carbides located at grain boundary and martensite lath boundary grows. Laves phase gradually grows at original austenite grain boundary and aggregates into a chain distribution. The microstructure evolution at high temperature can apparently influence high temperature stress rupture property. While the FB2 roto steel can still meet the requirement that the stress is higher than 100 MPa after 630℃stress rupture test for 105h.