Suppression of δ-ferrite formation on Al-Si coated press-hardened steel during laser welding

Mechanical properties of Al-Si coated press-hardened steel laser welded joint can not meet requirement due to the presence of delta-ferrite. This study investigated the suppression mechanism of delta-ferrite using a nickel interlayer during fiber laser welding. The fraction of primary solidification delta-ferrite was reduced to 57% with a 5.85% Ni in welding pool, and completely transformed into austenite during peritectic reaction (L + delta -> gamma) and solid phase transformation (delta -> gamma). Full martensite microstructure was obtained in welded seam and fusion line without Al-segregation. Tensile strength of welded joint had a similar to 17.1% improvement compared to as-received welded, similar to that of removing Al-Si coating. (C) 2019 Elsevier B.V. All rights reserved.