Investigation on Laser Weldability of a 2.1 GPa-Grade Hot Stamping Steel with Medium Carbon Content

• Published in: Metals (Basel ) Vol. 15; no. 2; p. 198
• Main Authors: Huang, Jiming, Shang, Xuekun, Li, Liejun, Liang, Zhiyuan
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.02.2025
• Subjects: Automobile industry; Baking; Base metal; Boron; Butt welding; Carbon content; Carbon steel; Diamond pyramid hardness; Ductility; Electron back scatter; Hardness; Heat treating; Heat treatment; Heterogeneity; Hot stamping; hot stamping steel; Investigations; Laser beam welding; laser welding; Lasers; lath martensite; Low temperature; Martensite; Mechanical properties; medium carbon content; Medium carbon steels; Metal industry; Microcracks; Microstructure; Optical microscopy; Solid solutions; Ultimate tensile strength; ultrahigh strength; Weld defects; Weldability; Welding; China
• ISSN: 2075-4701; 2075-4701
• DOI: 10.3390/met15020198

This investigation aimed at evaluating the weldability of a 2.1 GPa-grade hot stamping steel (HSS) containing 0.40 wt.% carbon using laser butt welding. It is shown that the subject HSS can be properly joined by laser welding without welding defects, such as voids and micro-cracks. The mechanical properties of joints before and after hot stamping were examined using cross-weld uniaxial tension and Vickers hardness, while microstructure was systematically characterized using optical microscopy and electron backscatter diffraction. The experimental results demonstrate that fresh martensite was formed in the weld nugget after welding, leading to a hardness much higher than that of the base metal. Nevertheless, such cross-weld microstructural heterogeneity was erased after hot stamping and low-temperature baking heat treatments, resulting in a uniform microstructure of lath martensite across the weld. As a result, the joint after hot stamping and baking exhibited an ultimate tensile strength of 2140 MPa and a total elongation of 12.03%, with the fracture occurring in the base metal. Such excellent mechanical properties of the joint demonstrate the great weldability of the present 2.1 GPa-grade HSS during laser welding.