Post-weld heat treatment of API 5L X70 high strength low alloy steel welds
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Date
2020-12-18
Journal Title
Journal ISSN
Volume Title
Publisher
MDPI
Abstract
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. © 1996-2021 MDPI
Description
Keywords
Alloys, Steels, Heat treatments, Arc welding, Phase transformations, Transmission electron microscopy, Microstructure, Yield strength, Tensile properties
Citation
Alipooramirabad, H., Paradowska, A., Nafisi, S., Reid, M., & Ghomashchi, R. (2020). Post-weld heat treatment of API 5L X70 high strength low alloy steel welds. Welding and Joining Processes of Materials, 3(24): 5801. doi:10.3390/ma13245801