以使用线性摩擦焊工艺连接的S31042钢接头为研究对象,在700 ℃下对其进行长期时效和力学性能测试。通过OM、SEM、TEM和拉伸实验研究高温时效对S31042钢线性摩擦焊接头组织和力学性能的影响。结果表明,在700 ℃长期时效过程中,线性摩擦焊中形成的再结晶晶粒和纳米级NbCrN相的稳定性较好,细晶强化和析出强化的综合作用使接头保持优异的高温性能。而焊缝区、热力影响区及热影响区中不同类型的M₂₃C₆相在时效过程中均发生粗化。在时效500 h样品的热力影响区中初次观察到σ相,随着时效时间的延长,σ相的析出数量增加且尺寸增大,导致摩擦焊接头的高温力学性能急剧降低。

S31042 steels with 25%Cr (mass fraction) and 20%Ni have been served as super-heaters and re-heaters in ultra-super critical (USC) plants, owing to their outstanding corrosion resistance and creep rupture strength. And the reliability of joints at high temperature has attracted much attention since the S31042 steels have been joined successfully by linear friction welding. In this work, the microstructures and mechanical properties of linear friction welded S31042 steel joint subjected to ageing treatment were investigated by using OM, SEM, TEM and mechanical test at 700 ℃. The recrystallized grains and nanoscale NbCrN particles have been stable during the high-temperature ageing, and the joint exhibited excellent performance due to the grain refinement strengthening and precipitation strengthening. The average size of M₂₃C₆ phase in weld zone, thermo-mechanically affected zone and heat affected zone increased with the ageing time. After ageing treatment at 700 ℃ for 500 h, σ phase precipitated at boundary junctions in thermo-mechanically affected zone. The average size of σ phase increased with the ageing time, as well as the volume fraction of the σ-phase. With the formation of σ phase, the fracture site of joints shifted from the parent material to the areas adjacent to the weld zone, and the high-temperature mechanical properties of joints were sharply decreased.