超超临界机组用P92钢焊接细晶区高温蠕变行为研究

High-temperature Creep Behaviour of Fine Grained Heat-affected Zone in P92 Weldment Used in Ultra Supercritical Units

用热模拟方法制备了P92钢的焊接细晶区(fine grained heat-affected zone,FGHAZ)试样,观察细晶区的显微组织,研究比较细晶区与母材在650℃、90～120MPa蠕变行为的差异。研究结果表明,与母材相比,细晶区的蠕变性能出现劣化现象,稳态蠕变速率明显增大,蠕变断裂寿命缩短。可用幂律蠕变定律来描述细晶区稳态蠕变速率与应力之间的关系。当应力≥100MPa时,n为15.1;应力小于100MPa时,n降低为8.64。高应力(≥100MPa)下,细晶区蠕变断裂主要受晶内空位和裂纹形成与扩展所控制,且其断裂数据遵循Monkman-Grant规律。与母材相比,细晶区M23C6相数量和尺寸差别不大,但其基体组织有显著改变,板条亚结构特征不明显。FGHAZ蠕变性能的劣化可能与基体组织改变有关。

Welding thermal cycle was given to the specimens to simulate fine grained heat-affected zone （FGHAZ） in P92 weldment. The microstructures of FGHAZ was examinated and the high-temperature creep behavior of FGHAZ was investigated at 650 ℃ under the applied stress of 90-120 MPa. The results show that the creep properties of FGHAZ is strongly degraded compared with the base memtal, which exhibits the higher steady creep-rate and shorter time to creep fracture. The power law equation can describe the steady creep-rate dependent on applied stress. The stress exponent n of FGHAZ is distinguished between two regions with n=15.1 at high stresses （more than 100 MPa） and n=8.64 at lower stresses. At high stresses, it is found that the creep fracture of FGHAZ is controlled by the nucleation and propagation of microvoids and cracks, and the creep rupture data obey the Monkman-Grant relationship. Although the difference in the amount and size of M23C6 precipitates is smaller for the FGHAZ and base metal, the matrix of FGHAZ shows no lath substructure, which is probably attributed to the degradation of its creep properties.