Influence of Multiple Post Weld Repairs on Mechanical and Microstructural Properties of Butt Weld Joint Utilized in Structural Members

Abstract

Developed countries are distinguished by their large-scale infrastructure, including bridges, towers, and power plants, most of which are constructed using various types of steel, such as mild and stainless steel. Strength and durability of steel in low budget make it an ultimate choice. In the construction of these structures, welding plays a crucial role, utilizing various joint configurations such as butt, T, and lap joints. This study examines the effect of multiple weld repairs on mild steel, using a welding speed of 150 mm/min and a current of 100 amperes for 3 mm thick sheets. Initially, the weld’s microstructure exhibited several cracks within the Weld Zone due to inadequate weld material filling. After the first repair, significant changes were observed, with elongated and distorted grains and an increase in hardness due to pearlite formation and Sulfur segregation. A second repair further highlighted the effects of repeated thermal cycles, causing increased brittleness and Sulfur segregation. The hardness of the weld joints increased by 16% and 24% after the first and second repairs, respectively, when compared to the base mild steel material. However, the Ultimate Tensile Strength (UTS) decreased to 48%, and the Yield Strength (YS) fell to approximately 54% after the second repair. Interestingly, the weld joint showed improved tensile properties after the first repair, attributed to the effective filling of cracks that appeared after the initial welding pass. This resulted in a slight increase in UTS and YS. However, the percent elongation of the material decreased due to the repeated thermal cycles involved in the welding repairs, with reductions of 44.3% and 63.6% after the first and second repairs, respectively. This increase in hardness and decrease in ductility after repairs suggest that the weld joints became more brittle.