High-temperature creep properties of fine grained heat-affected zone in P92 weldment

The simulated fine grained heat-affected zone (FGHAZ) specimens for P92 welded joints were prepared by heat treatment, then the creep tests were carried out at 650 ℃ under the applied stress of 90-120 MPa to investigate high-temperature creep behavior of FGHAZ. The results show that the creep property of FGHAZ is much inferior to that of the base metal, which exhibits the much higher steady creep rate and shorter time to creep fracture. The power law equation can describe the steady creep rate dependence on applied stress, indicating that 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. Based on Monkman-Grant equation, the relationship between the secondary creep rate and time to rupture is obtained to evaluate the creep life of FGHAZ with the applied stress above 100 MPa.

超超临界机组用P92钢焊接细晶区高温蠕变行为研究

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。

P91铁素体耐热钢细晶热影响区蠕变过程中组织演化

高铬铁素体耐热钢存在的一个问题是其焊接试样的蠕变强度远低于母材,为了从组织演化角度分析其产生机制,对P91铁素体耐热钢焊接试样在600℃、100 MPa应力条件下进行了中断蠕变试验,利用扫描电镜与EBSD对蠕变过程中不同区域的微观组织进行观察,分别计算不同区域的核心平均取向差(KAM),结果表明:细晶热影响区的KAM值随着蠕变时间的增加发生显著降低,蠕变断裂后与试验前相比下降约25%,而母材的KAM值虽然有所降低,但幅度远小于细晶热影响区。经过2 000 h蠕变试验后,在细晶热影响区已经形成大量的蠕变孔洞,而相同试验条件下母材中则没有观察到蠕变孔洞。上述结果表明细晶热影响区的高温组织稳定性明显劣于母材,而引起其组织劣化的原因可能与碳化物的析出行为有关。