Residual Stresses Induced by Welding in High Performance Steel

Abstract: Today, high performance steel as a construction material is treated as conventional steel in the European standards. Referring to the Eurocodes, the buckling curves for dimensioning of steel constructions only presents values up to steel grade S460, meaning that the full potential of high performance steel is not considered. If the amplitude of the residual stresses in high performance steel can be confirmed to be smaller than in conventional steel, more slender cross sections could be obtained when using high performance steel, HPS. One challenge with the residual stress patterns for HPS is its variation obtained in different studies, where new resulting residual stress patterns are found depending on plate thickness and manufacturing methods for the steel.   Residual stresses in steel are stresses not associated with external forces. The stresses are instead caused by internal forces, such as differencing temperature. Residual stresses can therefore be connected to stresses due to welding. Considering HPS, it is distinctive from conventional steel in the way that it has higher performance in tensile strength, toughness, weldability, corrosion and cold formability.   This study has been performed by Finite Element Modelling in the software Abaqus and by performing an experiment. The objective of this study was to find residual stress patterns and to compare the results with existing residual stress patterns according to the European Convention for Constructional Steel (ECCS) and the Swedish handbook for steel constructions provided by Boverket (BSK 07), but also to compare the results with previous studies.   The influence of temperature changes due to welding was studied for a L-section made of steel S690QL, where only the longitudinal stresses were considered during the research. The numerical analysis in Abaqus was performed using a DFlux subroutine, which is written in Fortran language. Furthermore, the analysis was divided into subparts; one heat transfer analysis and two three-dimensional stress analyses for two different boundary conditions, with the purpose of obtaining results in terms of temperature and stresses for further analysis. The experimental work was performed on three specimens using Gas Metal Arc Welding, where thermocouples and strain gages were used for measuring temperature and strains respectively.   Conclusions of this study were that the resulting residual stress pattern obtained the experiment was similar to the stress pattern for a L-section in BSK 07, while the resulting residual stress pattern obtained in the numerical analysis was mostly comparable to ECCS, but with similarities to BSK 07 and a previous study by Cherenenko & Kennedy (1990).  Moreover, the resulting residual tensile stresses obtained in the study had the same amplitude or lower than what is specified in BSK 07.