Comparative study on strength of TMCP and QT high-strength steel butt-welded joints

Abstract

The strength of high-strength steel butt-welded joints with a similar steel grade may be quite different due to their discrepancies in the processing methods of high-strength steel. The process methods mainly include quenching and tempering (QT) and thermo-mechanically controlled process (TMCP). These differences in the strength of high-strength steel butt-welded joints with different processing methods of steel have not been quantitatively determined and considered in several design codes, which may lead to the unsafe design for the high-strength steel butt-welded joints. This research demonstrated a comparative and quantitative study on the strength of double-V butt-welded joints made of QT550, QT690, TMCP 550, and TMCP690. The true stress-strain behavior of various zones within these welded joints, including the hardened heat affected zone (HHAZ), softened HAZ (SHAZ), weld metal (WM), and base metal (BM), were investigated based on the test and simulation results of the round notched specimens and the flat grooved specimens in tension. The developed true stress-strain models were validated against the test results of high-strength steel butt-welded joints. The strength of QT and TMCP high-strength steel butt-welded joints were then numerically analyzed considering the effect of different heat inputs of 1.0, 1.5 and 1.9 kJ/mm. The results show that strength ratios of SHAZ to BM of butt-welded joints made of TMCP steel were lower than those made of QT steel when the heat input was <1.9 kJ/mm. The strength of each zone in the TMCP high-strength steel butt-welded joint may not necessarily decrease with increasing heat inputs.