XDB620焊接热影响区连续冷却相变研究

Research on Continuous Cooling Phase Transformation of XDB620 Steel in Welding Heat Affected Zone

低焊接裂纹敏感性CF型XDB620钢板采用调质工艺生产,为了解其焊接热影响区在连续冷却过程中的相转变行为,在MMS-200热力模拟实验机及C-Strain传感器上进行了不同冷却速率下的相变温度区间测试,并且利用Imager D1m型金相显微镜和JSM-6490LV扫描电子显微镜对相变组织进行观察,分析了冷却速度对相变组织的影响。研究结果表明:在实验冷速范围内,获得的金相组织为贝氏体,在冷速为1℃/s以下时组织含极少量退化珠光体,并且随着冷速的增加,贝氏体内部结构呈现细化趋势。在实验冷速范围内,随着冷速的增加,相变开始温度/结束温度缓慢降低,分别由0.2℃/s时的610℃/510℃下降到30℃/s时的550℃/450℃。用膨胀法测得该实验钢的临界点温度为A_(c1)=726℃,A_(c3)=899℃。

CF type XDB620 steel plate with low welding crack sensitivity was produced by quenching and tempering process.To know about its continuous cooling phase transformation behavior in simulated welding heat affected zone,the phase transition temperature ranges at different cooling rates were investigated by means of the MMS-200 thermal simulation machine and C-Strain sensor.The phase transformation microstructure was observed by Imager D1m metallographic microscope and JSM-6490LV scanning electron microscope.The effect of cooling rate on phase transformation microstructure was analyzed.The results show that the microstructure obtained is bainite in the range of experimental cooling rate,the microstructure contains very little degenerated pearlite when the cooling speed is under 1 ℃/s,and with the increase of cooling speed,the interior structure of bainite is becoming more refined.In the range of experimental cooling rate,the beginning temperature/ending temperature of phase transition decreases slowly from 610 ℃/510℃ at 0.2 ℃/s to 550℃/450℃ at 30 ℃/s with the increase of cooling speed.A critical temperature of the steel is A_(c1)=726℃ and A_(c3)=899℃ by the expansion method.