Alipooramirabad Houman, Paradowska Anna, Nafisi Shahrooz, Reid Mark, Ghomashchi Reza
School of Engineering, University of British Columbia, Okanangan, BC V1V 1V7, Canada.
School of Mechanical Engineering, the University of Adelaide, Adelaide, SA 5005, Australia.
Materials (Basel). 2020 Dec 18;13(24):5801. doi: 10.3390/ma13245801.
High Strength Low Alloy (HSLA) steels are the materials of choice in pipeline construction with the API X70 grade as the steel for the majority of pipeline networks constructed during the late 20th and early this century. This paper reports on the influence of Post-Weld Heat Treatment (PWHT) on the reduction of residual stresses, resulting changes in the microstructure, and mechanical properties of a multi-pass, X70 HSLA steel, weld joints made by a combined Modified Short Arc Welding (MSAW) and Flux Cored Arc Welding (FCAW) processes. Neutron diffraction results highlighted high magnitude of tensile residual stresses, in excess of yield strength of both parent and weld metal, in the as-welded specimen (650 MPa), which were decreased substantially as a result of applying PWHT (144 MPa). Detailed microstructural studies are reported to confirm the phase transformation during PWHT and its interrelationship with mechanical properties. Transmission Electron Microscopy (TEM) analysis showed polygonization and formation of sub-grains in the PWHT specimen which justifies the reduction of residual stress in the heat-treated weld joints. Furthermore, microstructural changes due to PWHT justify the improvement in ductility (increase in the elongations) with a slight reduction in yield and tensile strength for the PWHT weld joint.
高强度低合金（HSLA）钢是管道建设中的首选材料，API X70级钢是20世纪末和本世纪初建造的大多数管道网络所使用的钢材。本文报道了焊后热处理（PWHT）对多道次X70 HSLA钢焊接接头残余应力降低、微观结构变化以及力学性能的影响，该焊接接头由改进型短弧焊（MSAW）和药芯焊丝电弧焊（FCAW）组合工艺制成。中子衍射结果表明，焊态试样（约650MPa）中的拉伸残余应力水平很高，超过了母材和焊缝金属的屈服强度，而通过进行PWHT（约144MPa），残余应力大幅降低。本文还报告了详细的微观结构研究，以证实PWHT过程中的相变及其与力学性能的相互关系。透射电子显微镜（TEM）分析表明，PWHT试样中出现了多边形化和亚晶粒形成，这解释了热处理焊接接头中残余应力降低的原因。此外，PWHT引起的微观结构变化说明了PWHT焊接接头的延展性有所改善（伸长率增加），同时屈服强度和抗拉强度略有降低。
