碳含量对5Cr2MoV系列钢的连续冷却转变行为的影响

通过测定不同碳含量的钢种在不同冷速下的相变点曲线、金相组织和显微硬度，得到了不同碳含量的钢种的过冷奥氏体连续冷却转变曲线(CCT曲线)及其相变点和组织形貌演变；比较分析了不同碳含量下5Cr 2Mo V系列钢CCT曲线的关系。结果表明：随着碳含量的增加，3种钢Ac1点变化不大，Ac3点略有降低，Ms点降低幅度较大；当冷却速度为0.04 ℃/s和0.06 ℃/s时，0.35%C、0.47%C和0.71%C钢的组织由“贝氏体+少量马氏体”构成；0.35%C和0.47%C在大于0.14 ℃/s冷速以上时，贝氏体完全转变为马氏体；0.71%C钢在大于1 ℃/s冷速时，贝氏体完全转变成马氏体；随着碳含量增加，5Cr 2Mo V系列钢的贝氏体转变相区发生左移现象，这与碳在组织转变过程中的扩散有关。

Effect of carbon content on continuous cooling transformation

By measuring the transformation point curve, metallographic structure and microhardness of steels with various carbon content at different cooling rates, the continuous cooling transformation curves (CCT curves) of undercooled austenite of steel with different carbon content as well as transformation point and structure morphology evolution were obtained. The relationships of CCT curves of 5Cr 2Mo V series steels with different carbon content were compared and analyzed. The results showed that with the increase of carbon content, the Ac1 point of three steels had little change, the Ac3 point slightly decreased, and the Ms point greatly decreased. When the cooling rate was 0.04 ℃/s and 0.06 ℃/s, the microstructure of 0.35%, 0.47% C and 0.71% C steels was composed of "Bainite + a small amount of martensite". When the cooling rate of 0.35% C and 0.47% C was higher than 0.14 ℃/s, the bainite was completely transformed into martensite. When the cooling rate of 0.71% C steel was higher than 1 ℃/s, the bainite was completely transformed into martensite. With the increase of carbon content, the bainite transformation phase region of 5Cr 2Mo V series steel showed left shift, which was related to the diffusion of carbon in the process of microstructure transformation.