焊接热循环对1000 MPa级焊缝金属组织性能的影响

Effects of weld thermal cycle on microstructure and properties of 1 000 MPa grade weld metal

为研究多层多道焊对1 000 MPa级焊缝金属组织性能的影响,采用热模拟试验对末道焊缝金属进行一次及二次焊接热循环,并通过冲击、硬度试验,利用金相显微镜、扫描电镜、透射电子显微镜和电子背散射衍射技术分析热循环后焊缝金属组织性能的变化规律.结果表明:单次热循环下,随着峰值温度(Tp)的升高,冲击韧性逐渐下降,显微硬度先上升后下降;TP为800℃时出现了软化现象,显微硬度326 HV,冲击韧性较高为64 J;TP为950℃时,其奥氏体晶粒相对细小,具有良好的综合力学性能;TP为1 350℃时,显微硬度最高为383 HV,冲击吸收功只有19 J,其脆化原因是冷却时获得粗大原奥氏体晶粒以及粗大的、且方向性较为一致的板条马氏体和贝氏体硬脆组织;经800℃的二次循环后,再次出现软化现象,显微硬度为313 HV,并且焊缝热影响区中残余奥氏体体积分数为1.39%,冲击韧性得到改善为59 J.

The influence of welding thermal cycle on the microstructures and mechnical properties of 1 000 MPa grade weld metal was investigated by means of welding thermal simulation,metallography,transmission electron microscope（ TEM）,scanning electron microscope（ SEM）,electron backscatter diffraction（ EBSD）,Charpy impact toughness test and hardness test. With the increase of peak temperature,the impact toughness decreased,and the hardness increased first and then decreased under single-pass thermal cycling. When peak temperature is800 ℃,softened zone appeared with low microhardness of 326 HV and high impact toughness of 64 J. When peak temperature increased to 900 ℃,the prior-austenite grains were refined,resulting in good comprehensive mechanical properties at HAZ. Highest microhardness of 383 HV,yet with lowest impact toughness of 19 J,was achieved at peak temperature of 1 350 ℃. The reason for the embrittlement was the coarsed prior-austensite grain and oriented coarsed bainite / martensite. When the re-heating peak temperature of twice welding thermal cycle is800 ℃,which is in the α-γ two phase region,softened zone can be found in the CGHAZ after two-pass welding thermal cycle. The microhardness is 313 HV,and residual austensite is about 1.39%,which can improve the impact toughness（ 59 J）.