Strength and deformation in HAZ-softened welded joints

The softening in the HAZ(heat-affected zone) of the weldment of fine-grained steels is an ubiquitous problem. Using the finite element analysis, both yield strength and tensile strength in the HAZ-softened welded joints are evaluated, and the stress distribution and deformation behaviors were analyzed. An calculation results show that an increase of the softened HAZ width and a decrease of yield stress in it can lower slightly yield strength in HAZ-softened joints, and reduced significantly the tensile strength in HAZ-softened joints. Increasing of the yield stress of weld metal can improve the yield strength and tensile strength in HAZ-softened welded joints. Analyses demonstrate that as applied stress is higher the yield stress of the softened HAZ, a triaxial stress state occurs in HAZ and its adjacent zones. At the boundaries of zones with different yield stresses, the principal stresses and the Mises equivalent stresses change in the step wise. The Mises equivalent stresses decrease in the softened HAZ and increase in its adjacent zones correspondingly. Utilizing these analyses results, the mechanism of the effect of width and softened degree of softened-HAZ on the strength of such joints can be explained.