P91厚壁钢管混晶组织分析

P91厚壁钢管经金相检验时出现混晶现象，导致钢管的高温性能降低.对钢管热处理工艺、坯料种类和热轧过程中组织变化进行分析，结果表明:P91锻坯和连铸坯的种类不同并不会导致组织差异；钢管热轧后出现明显的混晶组织，仅通过传统正火+回火热处理工艺不能得到最优组织形态.将钢管的非平衡组织先转变为平衡组织，然后进行合理的热处理可有效优化组织均匀性;在同样的热轧工艺参数下，毛管中未出现混晶，而荒管中晶粒却发生了异常长大，则皮尔格轧制阶段为混晶的萌生阶段和改善组织均匀性的重要阶段.

Analysis of Mixed-Grain Microstructure of P91 Thick-Walled Steel Pipes

A mixed-grain phenomenon was observed in the P91 thick-walled steel pipes， which would reduce the high-temperature properties of the pipes. Heat treatment process， the category of ingot and the microstructural evolution during hot rolling were analyzed. The results indicated that the difference of the categories for the P91 forging ingot and continuous casting ingot did not lead to microstructure difference. The pipes appeared obvious mixed-grain microstructure after hot rolling and the optimal microstructure could not be achieved only through the conventional normalizing and tempering treatment. The pipes’ microstructure uniformity can be optimized effectively by transforming from non-equilibrium microstructure to equilibrium one and rational heat treating process. The mixed-grain microstructure was not discovered in the steel pipes under the hot rolling process with the same processing parameters. However， abnormal grains growth was observed in the pipes after Pilger rolling.Therefore， the Pilger rolling process was the stage of mixed-grain initiation and improvement of microstructure uniformity.