P92钢正火均温性控制

Control of thermal homogeneity of normalizing process for P92 steel

正火工艺对P92钢的性能影响较大,某台热处理炉对P92钢进行处理常出现金相不合格问题,对此,本文对该热处理炉的有效加热区进行了检定,同时通过控温精确的小加热炉模拟工业热处理炉低温加热区,并采用光学显微镜、扫描电子显微镜及透射电子显微镜对2种热处理后的P92钢试样进行组织观察。结果表明:正火过程中炉膛内温度存在偏差和炉膛底部温度明显偏低是造成P92钢金相不合格的主要原因;970℃正火与1 070℃正火后的P92钢性能基本无差异,金相组织均为细小的板条马氏体,属于合格金相组织;随着正火温度升高,微观组织的马氏体板条的宽度逐渐增加,强化相析出明显,持久强度提高,最小蠕变速率下降。

Working zone of the industrial heat treatment furnace was checked, and the small-scale heating furnace with accurate temperature control was applied to simulate the low temperature heating zone of the industrial heat treatment furnace. Moreover, the optical microscope, scanning electron microscope and transmission electron microscope were used to observe the microstructure of the samples which have suffered different heat treatment processes. The results show that, the positive deviation of temperature in the furnace and the obvious low temperature at the bottom of furnace were the main reasons for metallographic ＂unqualified＂ for P92 steel. The mechanical properties of the samples after normalizing at 970℃ and 1 070℃ nearly had no difference,the microstructure of both the samples were fine tempered martensite, which is qualified. With an increase in normalizing temperature, the width of martensite laths increased, the strengthening phases precipitated obviously,the persistent strength increased and the minimum creep rate decreased.