Welding behavior of an ultrahigh-strength quenching and partitioning steel by fusion and solid-state welding methods

Abstract

How the quenching and partitioning (Q&P) steel with an ultrahigh strength (>1 GPa) behaves during the welding process is a considerable issue for its practical application, but the systematical evaluation on the welding behavior of this new steel has not yet been concerned. Here the structure-property relationships of three typical Q&P 1180 steel joints were comparatively studied by using laser welding (LW), tungsten inert gas (TIG) welding, and friction stir welding (FSW). Weld metal (WM) region and heat-affected zone were generated in the welded joints and their widths were mainly related to the welding linear energy (LW < FSW < TIG welding). During LW and TIG welding, the parent metal (PM) was totally destroyed and coarsened in the WMs whereas ultrafine microstructures with high hardness were obtained after FSW by means of the low peak temperature and severe plastic deformation. The TIG welding produced serious material softening, while the softening degree could be alleviated via LW and FSW. Excellent tensile strength as high as that of the PM was achieved in both the LW and FSW joints by means of the suppressed material softening as well as small soft zone width. However, dramatic losses of strength and ductility were found in the TIG welded joint owing to the premature strain localization and fracture in the soft zone.