加热参数对T122高铬耐热钢奥氏体晶粒异常长大的影响

Effect of Austenitizing Condition on Abnormal Grain Growth in T122 Heat-Resistant Steel

12Cr-2W—Mo—Nb—V—Cu-N-B钢（简称T122钢）是一种新开发、用于超超临界火电机组的马氏体耐热钢。在奥氏体化过程中，发现该钢种有异常晶粒长大现象。为此，研究了950～1250℃奥氏体化温度下，保温时间和加热速率对奥氏体晶粒长大的影响，同时热力学计算的平衡相转变被用于更好了解加热过程中组织的演变。为了检测异常晶粒长大，系统研究了晶粒尺寸分布，并采用晶粒尺寸相对差（RD）比较了不同加热参数下奥氏体晶粒长大行为。结果表明，加热速率对奥氏体化晶粒长大有显著影响。当加热速率大于临界值时，存在一个异常晶粒长大的温度范围，此温度范围为1000～1100℃；加热速率小于临界值时，则不会出现异常晶粒长大现象。随着保温时间的增加，异常晶粒长大所造成的晶粒不均匀程度逐渐降低。

12Cr-2W-Mo-Nb-V-Cu-N-B （T122） is newly developed martensitic heat-resistant steel used in Ultra Super Critical fossil power plants. The grain growth at temperature from 950℃ to 1250℃ was systemically investigated for heating Rate ranging from 0.1 to 10℃/s and holding time from 15 min to 60 min. Phase equilibrium calculation was presented as a contribution to better understanding of microstructure evolution during heating. A method of assessing grain size distribution in order to detect abnormal grain growth was proposed. The results showed that the heating rate plays a key role in affecting austenite grain growth. When heating rate is higher than a critical value, there is a temperature range from 1 000 ℃ to 1 100℃, in which austenite grain grows abnormally. When heating rate is less than the critical value, no abnormal growth occurs. With the increase of holding time during heating, grains tend to be uniform.