Microstructure, mechanical properties and fatigue behaviors of linear friction welded weathering steels

Abstract

The weathering steels SMA490AW and SPA-H with a high phosphorus content were successfully joined by linear friction welding (LFW) without welding defects and heat affected zone (HAZ) softening. The residual stress of the welded joints was measured by X-ray diffraction (XRD) after the welding. The microstructure characteristics were observed using a scanning electron microscope (SEM) and analyzed corresponding to the microhardness distribution in different regions. The mechanical properties and fatigue behaviors were assessed using the digital image correlation (DIC). The results suggest that the bainites were crystallized in the weld center zone (WCZ), and the area fraction of bainites was obviously decreased at a small distance from the WCZ, which illustrated a large welding temperature gradient. The ductile fracture of LFW joints occurred at the base metal part of the specimens, resulting in a joint efficiency close to 100%. The fatigue strength of LFW joints was close to that of base metals and the proposed S-N curves showed a much higher fatigue strength compared to the design curve FAT112.