回火温度和冷却方式对T91钢组织性能的影响

 结合现场实际情况，为改善T91组织性能而利于后期加工，利用金相观察、扫描电镜及显微硬度试验等手段，研究分析300～780 ℃不同回火温度及回火冷却速度下T91钢的组织及硬度变化规律。试验结果表明，300～400 ℃回复程度低，硬度难以降低；500～600 ℃为碳化物析出敏感区间，大量碳化物在基体弥散析出，在此区间硬度较高且有上升趋势；随着温度从600升高到780 ℃，碳化物沿晶界充分析出，硬度降低。随着回火冷却速度的增加，硬度逐渐降低，以5 ℃/min缓慢冷却经过500～600 ℃敏感区间，碳化物弥散析出，基体硬度较高；以780 ℃回火保温和较快冷却速度（50 ℃/min）进行冷却处理后，快速通过碳化物析出敏感区间，碳化物在基体析出少，硬度明显降低，综合性能满足后续加工。

Effect of temper temperature and cooling rate on the microstructure and properties of T91 alloy steel

Based on the actual situation ，in order to improve the structure property of T91，be benefit for later processing，the effects of temper temperature within the range of 300- 780 ℃ and cooling rate on the microstructural evolution and hardness change of T91 steel have been analyzed and compared by means of metallographic analysis，scanning electron microscopy and hardness measurement，and to provide some practical reference significance. The results show low degree of tempering to reply at 300- 400 ℃，hardness is difficult to be reduced. Under the condition of tempering at 500- 600 ℃，large amount of fine dispersed granular carbides precipitate in the matrix microstructure of T91 steel，and the Vicker hardness remains high. As the temperature increases at 600- 780 ℃，carbides precipitate along the grain boundary adequately，hardness decreases obviously. With the increase of tempering cooling speed，hardness gradually decreases. A large number of carbides precipitate at the sensitive range from 500 to 600 ℃ under the condition of furnace cooling (5 ℃/min)，and the hardness of T91 steel is high. In the way of tempering at 780 ℃ and cooling rate(50 ℃/min)，getting through the sensitive interval quickly，the carbides precipitate less in the matrix，and the hardness decreases obviously，comprehensive properties meet the processing requirement.