Heat affected zone stress-strain relationship in high strength steel welds

Abstract

The use of high-strength steel (HSS) has increased significantly in recent years and their weldability has improved considerably. HSS can improve the profitability of the production process and end product by reducing materials and allowing designers to use less and thinner material in a specific design. Despite these benefits, certain restrictions are preventing the utilization of higher steel grades in applications, since to date, there is no universal welding specification for HSS welds. This thesis aims to study mechanical properties (yield strength, tensile strength, elongation, etc.,) of 4 mm thick SSAB’s S700 steel weldments with two different heat inputs (0.38 kJ/mm and 0.68 kJ/mm). The local behavior of three different zones of weldments: base metal (BM), heat affected zone (HAZ), and weld metal (WM) was studied by conducting tensile tests and using digital image correlation (DIC) techniques.

Both tensile test and 3D optical measurement (ARAMIS) were done simultaneously. True strain data for different zones of the weldment was obtained directly from ARAMIS 3D optical strain measurements. Using this data, true stress - true strain curves of weldments for three different zones were plotted and proposed to be used in Finite Element Method (FEM) simulation. Test result data comparison between the universal tensile testing machine with extensometer and ARAMIS from base metal show similar mechanical properties, thus increasing the reliability of the results. The experimental results show that the strength of the weldments is lower than that of the base material and fracture was initiated at WM zone for low heat input and at HAZ for high heat input.