回火温度对改进型T23钢冲击吸收功的影响

 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。前期通过成分改进得到的改进型T23钢再热裂纹敏感性得到了较大的改善,但冲击吸收功较低。为了提高改进型T23钢的冲击吸收功,研究了回火温度对改进型T23钢显微组织、硬度和冲击吸收功的影响。测量改进型T23钢750~810 ℃回火后的硬度和冲击吸收功,并利用光学显微镜(OM)、扫描电镜(SEM)和透射电镜(TEM)分析显微组织。结果表明,随着回火温度升高,改进型T23钢硬度不断降低,冲击吸收功先升高后降低并在790 ℃回火后达到最大值。回火过程中基体组织软化、M-A组元分解和贝氏体板条宽化是造成改进型T23钢硬度不断下降的主要原因。与750 ℃回火相比,改进型T23钢790 ℃回火后的大尺寸M-A组元数量少且尺寸小,晶界仍存在一些尺寸较小的M₂₃C₆相,且贝氏体板条宽化程度较小,有效阻碍了裂纹的扩展,冲击吸收功最高。回火温度提高到810 ℃,小尺寸的M-A组元数量减少且M₂₃C₆相大量溶解,特别是贝氏体板条的严重宽化降低了对裂纹扩展的阻碍作用,冲击吸收功下降。

Effect of tempering temperature on impact absorbed energy of modified T23 steel

The safety of ultra-super critical power plants is severely endangered by the high reheat-cracking susceptibility of T23.Our former experimental results showed that the reheat cracking susceptibility of modified T23 steel was highly improved by modifying the composition,but the impact absorbed energy decreased.In order to improve the impact absorbed energy of modified T23 steel,the effect of tempering temperature on the microstructure,hardness and impact absorbed energy of modified T23 steel was investigated in this paper.The hardness and impact absorbed energy of modified T23 steel after tempering at 750-810 ℃ were measured,and the microstructure was analyzed by optical microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM).The result shows that with increasing tempering temperature,the hardness of modified T23 steel decreases,while the impact absorbed energy increases firstly and then decreases.After tempering at 790℃,the impact absorbed energy reaches the maximum value.The main reasons for the decrease of hardness are the softening of matrix,the decomposition of M-A constitutes and the widening of bainitic laths.Compared with tempering at 750 ℃,the number of M-A constitutes with large size in modified T23 steel after tempering at 790℃decreases,and the size is smaller.There are still some M23C6 carbides with small size at the grain boundaries,and the degree of bainitic lath widening is low.The crack propagation is hindered effectively,hence the impact absorbed energy is the highest.When the tempering temperature is increased to 810℃,the number of small M-A constitutes decreases and a large number of M23C6 carbides dissolve.In particular,the retarding effect of crack propagation is further reduced due to the severe widening of bainitic laths.Therefore,the impact absorbed energy decreases.