LAUSR

Use of high strength steel in car bodies has increased in an attempt to achieve improved passenger safety and fuel efficiency. The most efficient way to produce ultra-high strength steel (UHSS) with excellent formability is using a hot stamping process.1) During hot stamping, steel blanks are heated and kept above the Ac3 austenitization temperature. After heated steel blanks are transferred to the forming press, press forming and quenching are simultaneously carried out by water-cooled dies to obtain a full martensite microstructure, generally resulting in a yield strength (YS) of 1.0 GPa and ultimate tensile strength (UTS) of 1.5 GPa.2) Hot stamped steel parts were first used in automotive applications in 1984 when hot-stamped door intrusion beams were used in SAAB 9000 passenger cars.2,3) In 2002, the first pre-coated hot-stamped steel was used in Citroën C5.5) In current manufacturing processes, tailored properties of hot stamped automotive parts are obtained using tailor welded blanks (TWB), tailor rolled blanks (TRB), partial heating, differential cooling and other methods. Because of the continuous and innovative development of hot stamping technology, the number of hot -stamped components has increased considerably, reaching 250 million parts in 2015.6) When hot stamping technology was first implemented, bare steel was used. During the hot stamping heat treatment, iron oxide scale formed and decarburization occurred at the surface of steel sheets.7,8) Various coatings have therefore been developed to suppress both oxidation and decarburiFusion Zone Microstructural Evolution of Al-10% Si Coated Hot Stamping Steel during Laser Welding