T23钢再热裂纹敏感性的改善及其组织

 T23钢较高的再热裂纹敏感性严重危害了超超临界火电厂的安全运行。为了改进T23钢再热裂纹敏感性,主要通过改变其碳、钨等元素的质量分数,并且采用Gleeble热模拟及等温缓慢拉伸方法评判T23钢和改进型T23钢焊接热影响区粗晶区(CGHAZ)的再热裂纹敏感性。利用光学显微镜(OM)、扫描电镜(SEM)和透射电镜(TEM)研究两者CGHAZ的微观组织,探讨了微观组织对改进型T23钢再热裂纹敏感性的影响。结果表明,改进型T23钢的再热裂纹敏感性得到极大的改善,且其常规力学性能均达到ASME规范要求。与T23钢相比,改进型T23钢CGHAZ晶界M₂₃C₆相和晶内MX相数量均较少,同时,其固溶强化元素碳、钨质量分数较低。因此,改进型T23钢CGHAZ晶内晶界的强度差降低,再热裂纹敏感性改善。另外,较小的CGHAZ晶粒尺寸及较少的M-A组元也有助于降低改进型T23钢的再热裂纹敏感性。改进型T23钢晶界较少的M₂₃C₆相还使得晶界上孔洞连接和裂纹扩展的速率降低。设计的改进型T23钢成分可以为以后进一步改善T23钢再热裂纹敏感性提供参考。

Improvement of reheat-cracking susceptibility and microstructure of T23 steel

The high reheat-cracking susceptibility of T23 severely endangers the safety of Ultra-super critical power plants. In order to decrease the reheat-cracking susceptibility of T23,the mass percent of elements such as C and W was optimized. The simulated coarse-grained heat-affected zone (CGHAZ) in T23 and modified T23 was produced via thermal simulation of welding,and the reheat-cracking susceptibility was evaluated by isothermal slow strain rate tensile test on Gleeble. The microstructure of CGHAZ in T23 and modified T23 was investigated by optical microscope (OM),scanning electron microscope (SEM) and transmission electron microscope (TEM). The effect of microstructure on the reheat-cracking susceptibility of modified T23 was discussed. The result shows that the reheat-cracking susceptibility of modified T23 is greatly decreased,and the mechanical properties meet the requirements of ASME specification. Compared with T23,there are less intergranular M₂₃C₆ precipitates and intragranular MX particles in modified T23. At the same time,the mass percent of C and W in the grain interiors is decreased in modified T23. Therefore,the difference between intergranular and intragranular strength is small in modified T23,leading to the improved reheat-cracking susceptibility. In addition,smaller grains and fewer M-A constituents in modified T23 help to decrease the reheat-cracking susceptibility. The decreased number of M₂₃C₆ at grain boundaries slows down the micro-void connection and crack propagation. The composition of modified T23 steel can provide reference for further improving the reheat-cracking susceptibility of T23 steel.