Mg处理X100管线钢的焊接CCT曲线及其组织

Welding CCT Curve and Microstructure of the Magnesium Treated X100 Pipeline Steel

采用焊接热模拟技术和显微组织分析等方法,对Mg处理X100管线钢在连续冷却转变下的显微组织的变化规律进行了研究。通过对Mg处理X100管线钢CCT曲线的建立和显微组织分析结果表明:对比焊接CCT模拟工艺和常规950℃保温的CCT工艺,前者AC1、AC3相变点要分别高于后者25℃,奥氏体晶粒显著大于后者,冷却相变点要低于后者50～80℃。在焊接热模拟工艺下,当冷却速度在0.1～3℃/s之间时,组织以准多边形铁素体(QF)和粒状贝氏体为主;在3～30℃/s的冷却速度范围,主体组织为粒状贝氏体(GB)和针状铁素体(BF);当冷却速度为30～50℃/s,组织以贝氏体铁素体(BF)为主;大于50℃/s的冷却速度,将形成马氏体(M)组织。

Microstructure in a continuously cool of magnesium treated X100 high strength pipeline steel was investigated by means of heat simulation technique with a DIL805A simulator, optical microscopy （OM） and scanning electron microscopy （SEM）. The results show that comparing the welding simulation CCT with 950℃ insulated CCT process, the AC1 and ACa temperatures of the former are 25℃ higher than those of the latter, and the austenite grain size is also significantly larger than that of the latter too, but the temperature of cooling phase is 30-50℃ lower than that of the latter. Microstructure of X100 high strength pipeline steel is mainly composed of quasi-polygonal ferrite（QF） and granular bainite （GB） when the cooling rate is in the range of 0.1-3℃/s. Acicular ferrite and granular ferrite （GB＋BF） prevail in the steel when the cooling rate is in the range of 3-30℃/s. Martensite（M） forms in the steel when the cooling rate is higher than 50℃/s.