Characteristics of High Temperature Tensile Properties and Residual Stresses in Weldments of High Strength Steels

In this study, high temperature tensile properties of high strength steels, POSTEN60 and POSTEN80, whose tensile strengths were 600 and 800 MPa respectively, were investigated through the elevated temperature tensile test. Residual stress measurements were also carried out to estimate the residual stress relaxation due to phase transformation (martensite transformation) in the process of cooling after welding. A finite element (FE) model which was able to include the volumetric changes due to the austenite (right arrow) martensite phase transformation was developed on the basis of the experimental results. The three-dimensional thermal elastic-plastic FE analyses using the FE model were conducted to determine residual stresses in weldments of the high strength steels. The results show that the extents of residual stress relaxation due to the austenite (right arrow) martensite phase transformation in the process of cooling after welding are approximately 0.85 (sigma)x/(sigma)Y0 and 0.75 (sigma)x/(sigma)Y0 in the FZ and HAZ of POSTEN60 and POSTEN80, respectively. And residual stresses of weld line direction in the base metal (BM) which is adjacent to HAZ, therefore, do not undergo martensitic transformation increase (655 MPa<870 MPa) with increasing tensile strength of the high strength steels (POSTEN60 < POSTEN80).