Experimental investigation of the influence of the HAZ on the strength of welded T-joints made of HSS

Abstract

The welding process introduces heat, which may cause softening in the heat-affected zone (HAZ) of high-strength steels (HSS). In welded components such as hollow section joints, this localised reduction in strength can reduce the load-bearing capacity by promoting early failure of the joint and decreasing plastic design strength. As part of this article, experimental investigations on single-sided welded T-joints were conducted to assess the impact of HAZ softening on the load-bearing capacity of brace–chord connections in HSS joints. The results should form a basis for improving the design guidelines for welded joints by taking better account of the HAZ influence. This article presents thermo-physical simulations for two S700MC steels, revealing tensile softening of up to 28.4 %. In addition, macro-section analysis of the welded T-joints shows that the HAZ expansion has a significant dependence on the cooling time t8/5. Furthermore, load-bearing capacity reductions of up to 16 % were observed, attributed to HAZ influences, when compared to the tensile strength of the unaffected base material. Additionally, the study shows that the HAZ interacts with the adjacent materials. In localised softening, the multiaxial stress state leads to an increase of the resistance. Therefore, not only the degree of softening in the heterogeneous HAZ but also the geometric expansion has an influence on the load-bearing capacity of a welded connection.