Experimental to study the effect of multiple weld-repairs on microstructure, hardness and residual stress for a stainless steel clad plate

Abstract

This paper presents an experimental study of multiple repair welds in a stainless steel clad plate. Four weld samples with one, two, three and four repairs in the same area were prepared, respectively, to determine the changes in microstructure, residual stress and micro hardness. Neutron diffraction measurement was used to determine the weld residual stress. The results show that the repair weld contains nine zones with different microstructures. Around weld-base metal interface, a diffusion layer is formed because of the diffusion of C, Cr, Ni and Fe elements. The diffusion layer, which contains martensite with larger hardness than the adjacent metals, should be removed completely before re-repair. Around the weld–clad metal interface, short ferrite is generated along the fusion zone. As the repair number increases, the fusion zone becomes thicker, and the content of short ferrite also increases, which leads to some voids in the third and fourth repair welds. In the fusion zone of the sample with four repairs, massive ferrite is generated because more Cr element is diffused to the fusion zone. Residual stress increases gradually from the weld center and reaches the maximum at heat affected zone (HAZ) and then decreases far away. The residual stress in the sample with four repairs decreases because the hardness is decreased. Based on the comprehensive considerations of microstructure, residual stress and hardness, it proposes that the clad plate cannot be repaired more than 2 times.