后热温度对1000MPa级高强钢焊缝组织与性能的影响

Effect of the Temperature of Post Weld Heat Treatment on Microstructure and Performance of Weld Metal for 1000 MPa Grade High Strength Steel

采用GHS90高强焊丝为填充材料对1 000 MPa级工程机械用高强钢进行熔化极活性气体保护(Metal active gas,MAG)焊,并对接头进行250℃、480℃、600℃保温2 h的焊后热处理。通过拉伸试验、显微硬度测试、光学显微镜(Optical microscope,OM)、扫面电镜(Scanning electron microscope,SEM)、透射电镜(Transmission electron microscopy,TEM)及电子背散射衍射(Electron back-scattered diffraction,EBSD)观察不同热处理温度后的焊缝微观组织及力学性能进行对比研究。结果表明,随后热温度从250℃升高到600℃,接头抗拉强度从1 014.5 MPa降低到934.5 MPa;焊缝平均冲击吸收能量从66 J降低到24 J;随后热温度升高,焊缝板条组织粗化,碳化物析出长大且连续分布是导致焊缝韧性降低的原因之一;同时焊缝有效晶粒尺寸变大和大角度晶界密度降低也是导致其韧性降低的原因。

1 000 MPa high-strength steel plates for construction machinery are welded by metal active gas（MAG） welding method with GHS90 welding wire as filler material and the weld joints are treated at 250 ℃, 480 ℃, 600 ℃ for 2 h, respectively. Microstructure and mechanical properties of welded joints with different post weld heat treatment （PWHT） is analyzed by tensile test, microhardness measurement, optical microscope（OM）, scanning electron microscope（SEM）, transmission electron microscopy（TEM） and electron back-scattered diffraction（EBSD）. The results show that with the increase of PWHT temperature from 250 ℃ to 600℃, the average strength of welded joint reduces from 1 014.5 MPa to 934.5 MPa and the average–20 ℃ impact absorbing energy of weld metals decreases from 66 J to 24 J. With higher PWHT temperature, larger bainitic lath and coarser carbide precipitates result in lower toughness of weld metal. Meanwhile, the size of effective grains becomes larger and the density of high-angle grain boundary is decreased, which led to the degradation of impact property of weld metal.