高アルミニウムおよび高リン耐候性鋼FSW継手の疲労性能評価

抄録

The increasing contents of alloy elements, such as P and Cu, can lead to cracks in the welded joints of weathering steel during conventional welding processes. Friction stir welding (FSW) provides an effective method to join weathering steel at a lower heat input. In the present study, two high-strength weathering steels, high aluminum weathering steel (S-AL) and high phosphorus weathering steel (S-P), were joined using FSW at a relatively low temperature, below 700°C. The microstructure of the welded joints was observed by scanning electron microscope (SEM) and EBSD, the micro-hardness was also measured across the various weld regions. The mechanical properties were then assessed by digital image correlation (DIC). The results suggest that the joints with no defects were obtained for both materials (S-AL and S-P). The microhardness results show slight softening in the stir zone (SZ) of S-AL. Conversely, for S-P, there is noticeable softening in the thermal-mechanical affected zone (TMAZ) and hardening in the SZ. The joint efficiency of the S-AL and S-P reached 100% and 97.1%, respectively. The fatigue strengths of S-AL base metal (S-AL-BM) and its FSW joints (S-AL-FSW) are nearly identical with only a 0.7% difference. Although the fatigue strength of S-P-FSW is 4.7% lower than that of S-P-BM due to softening, the effect is not significant, which also indicates good welding performance.