Improving the mechanical properties of PHS laser welded joints by adding Ni foil to suppress δ-ferrite
Xiaming Chen, Xiaonan Wang, Qian Sun, Zengrong Hu, Pengcheng Huan, Ge Yi, Nagaumi Hiromi, Hongshuang Di, Lining Sun
Abstract
Ni foils with various thickness were used as interlayer to achieve the laser tailored welding of 22MnB5 press-hardened steel (PHS) with Al-Si coating. The effect of Ni content on the microstructure, hardness and strength were studied. The results showed that Ni reduced the content of solidified primary δ phase in the fusion zone, and promoted the transformation from δ phase into γ phase. δ ferrite was absent with the Ni content of 4.7–19.5 wt.%. In addition, the fusion zone was in γ phase region during post-weld heat treatment at 950℃ because Ni can reduce the Ac3 temperature (the temperature at all ferrite was transformed into austenite). The microstructure of fusion zone after post-weld heat treatment was lath martensite with the Ni content of 4.7–11.2 wt.%. The average hardness was similar to base metal, and the tensile strength of welded joint was increased by ∼22% of as-received joint. Ni was effective to suppress the formation of δ ferrite in Al-rich fusion zone, which is potential to achieve the laser welding of PHS with Al-Si coating.