Thermal induced residual stress and microstructural constituents of dissimilar S690QT high-strength steels and 316L austenitic stainless steel weld joints

Abstract

Abstract The effect of thermal cycle on the residual stress, microstructural constituents, and alloying elements composition of dissimilar S690QT and 316L austenite stainless steel was studied. Finite element model (FEM) using ANSYS 19.1 software and an experimental investigation using gas metal arc welding (GMAW) process with fully austenite filler wire were applied to developed thermal cycle and evaluate residual stress in the heat-affected zone of both materials. The experimental data were recorded using a thermal-cycle sensor (TCS) and x-ray diffraction technique. A microstructural investigation was done using Scanning electron microscopy (SEM) and Energy-Dispersive x-ray Spectroscopy (EDS). The thermal cycle showed the maximum temperature (T max) in the HAZ of 316L side (850 °C) at a distance of 7 mm away from the centreline of the weld compare to S690QT side. The magnitude of tensile residual stresses in the 316L side decreased as welding heat input increased. The maximum residual stresses were observed on the S690QT side (700 MPa). Microstructural investigations revealed the formation of Bainite, and some retained of austenite at the temperature of 800 °C in the coarse grain heat-affected zone (CGHAZ) of S690QT. On 316L side, some grain boundary austenite (GBA), intragranular austenite (IGA), and carbides were observed in the CGHAZ. Compared to the initial microstructure of both materials, a slightly increase of Mn, Cr, and Si were observed at the respective values of 1.90%, 1.25%, and 0.40% on the S690QT side compared to the BM. For 316L side, it indicated an increase of Cr (26%), Mo (5.69%), and Ni (17%) in the alloying element composition compared to the BM. Applying 10 kJ cm−1 of heat input produced an excellent mechanical property and reduced the formation of carbide, inter-granular corrosion in the microstructure of 316L side.