Formation mechanism of delta-ferrite and metallurgy reaction in molten pool during press-hardened steel laser welding

摘要

Al-Si coated press-hardened steel (PHS) welding was carried out using fiber laser with Ar and air atmospheres under different atmospheres. The formation mechanism of delta-ferrite in welded seam (WS) was: the melting Al-Si coating diffused into molten pool such that the stabilization of high-temperature I ferrite was improved as well as the phase transformation (delta -> gamma) was restrained by the effect of laser rapid cooling. Al-content in delta-ferrite of WS with Ar atmospheres was more than air atmospheres, leading to less delta-ferrite. A few of oxygen and nitrogen were ionized and droplet reaction zone with strong dissolution did not occur during laser lap welding, so welding defects were not obtained. Moreover, 0 element reacted with Al in the molten pool to form oxides of less than 1 mu m (Al2O3), it did not deteriorate the properties of WS. (C) 2017 Elsevier B.V. All rights reserved.