X120管线钢激光电弧复合焊热模拟热影响区的组织转变

Microstructure Transformation of Laser-Arc Hybrid Welding Thermal Simulate Heat Affected Zone of X120 Pipeline Steel

X120管线钢具有优异的综合力学性能。采用金相显微镜和透射电镜研究了X120管线钢连续冷却转变(CCT)组织,采用热模拟设备建立了常规热处理条件下的CCT曲线和激光电弧复合焊条件下的模拟热影响区连续冷却转变(SHCCT)曲线。试验结果表明,在激光电弧复合焊条件下,随着冷却速度的增加,热模拟粗晶区组织依次为粒状贝氏体、贝氏体铁素体和板条马氏体,激光电弧复合焊条件下的快速加热使A_(c1)和A_(c3)相变线有所提升,高温停留时间短使得奥氏体来不及长大,使组织细化,激光电弧复合焊条件下的M_(s)转变温度提高,马氏体转变温度区间扩大,使得形成的板条马氏体能够发生自回火,从而减小淬火应力,改善强度和韧性,提高抗开裂能力。

X120 pipeline steel has excellent comprehensive mechanical properties.The continuous cooling transformation(CCT)microstructure of X120 pipeline steel was studied using optical microscope and transmission electron microscope.The CCT curve under conventional heat treatment and SHCCT curve of coarse grain heat affected zone under laser-arc hybrid welding were established by thermal simulation equipment.The experimental results show that with the increase of cooling rate,the microstructures of the thermal simulated coarse grain region are granular bainite,bainite ferrite and lath martensite in turn under the condition of laser-arc hybrid welding.The rapid heating during the laser-arc hybrid welding increases the phase change lines of A_(c1) and A_(c3).The short residence time at high temperature inhibits austenite grain growth,therefore,the formed microstructure is refined.The M_(s)transformation temperature under the condition of laser-arc hybrid welding increases and the transformation temperature range of martensite is expanded.Thus,the formed lath martensite undergoes self tempering and the quenching stress reduces,which can improve the strength and toughness,and enhence the crackingresistance.