将25MnV石油套管用钢通过直接淬水与水冷→空冷→水冷的双介质淬火冷却工艺分别处理成全马氏体组织与下贝氏体/马氏体复相组织,对比研究了不同淬火工艺下的微观组织特征及回火工艺参数对试验钢强韧性的影响.结果表明:双介质淬火所得下贝氏体/马氏体复相组织具有明显的强韧化效果,可以降低应力集中,有利于材料韧性的改善和阻止微裂纹的产生与扩展;力学性能测试表明,试验钢大约在400℃左右出现韧性低谷,呈现出低温回火脆性的特征,因此,该复相组织适合于在高温回火状态下使用,此时复相组织提高材料韧性的作用更为显著.
The full martensite (M) microstructure and lower bainite/martensite duplex microstructure of 25MnV steel for oil casing were obtained respectively by direct water quenching and water-air-water double medium quenching process,the effect of microstructure under different quenching processes and tempering processes on the strength and toughness of the tested steel was studied.The results show that the lower bainite/martensite duplex microstructure treated by double medium quenching process has obvious strengthening and toughening effect,which can reduce the stress concentration and prevent micro-crack initiation and propagation,and is benificial to the improvement of the toughness.The mechanical properties tests show that the tested steel presents lower toughness at about 400 ℃,showing the characteristics of low temperature temper brittleness.Therefore,the duplex microstructure is suitable to be used in the form of high temperature tempering state,in which the effect of duplex microstructure on improving the toughness of the material is more significant.
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