焊接热循环对Ni-Fe基合金高温力学性能的影响

采用焊接热模拟试验,分析了焊接热循环对一种700℃超超临界火电机组高温部件候选材料——Ni-Fe基高温合金组织和高温性能的影响.结果表明,焊接热循环过程使合金中γ'相以及MC碳化物大量固溶.700℃持久试验中HAZ试样在400 MPa的持久断裂时间低于母材,300和350 MPa的持久断裂时间与母材相当.随着持久试验进行,HAZ组织中的晶界逐渐析出M₂₃C₆,晶内重新析出大量γ'相,使HAZ的持久性能逐渐恢复.高温焊接热循环使MC发生部分溶解,为M₂₃C₆在后续持久试验时效中的析出提供了C元素.

Effect of welding thermal cycle on high temperature mechanical property of Ni-Fe base superalloy

The weldability of a Ni-Fe base superalloy, one of the candidate materials for high temperature components of 700℃ ultra-supercritical coal plant, was studied in this paper.Based on welding thermal simulator experiments, the variation and evolution of microstructure and mechanical properties were analyzed for this Ni-Fe base superalloy under welding thermal cycle treatment condition. The microstructure analysis showed thatγ phase and MC carbide in Ni-Fe base superalloy dissolved during high temperature welding thermal simulation process. The creep rupture time of welding thermal cycled sample was severely shorter than that of base solutioned sample at 700℃/400 MPa, and was similar to that of base solutioned sample at 700℃/350 MPa and 700℃/300 MPa, respectively. During creep test at 700℃, M₂₃C₆ gradually precipitated at the grain boundaries of HAZ, while γ precipitated in the HAZ matrix. The precipitated M₂₃C₆ and γ resulted in an improvement of 700℃ creep rupture property of HAZ. The precipitation of M₂₃C₆ at grain boundaries during creep test was mainly due to the supply of the carbon from MC which was dissolved partially during former welding thermal cycle.