| Title |
Effect of Hot-stamping Heat Treatment on the Microstructure of Al-Segregated Zone in TWB Laser Joints of Al-Si-coated Boron Steel and Zn-coated DP Steel |
| Authors |
정병훈(Byung Hun Jung); 공종판(Jong Pan Kong); 강정윤(Chung Yun Kang) |
| DOI |
https://doi.org/10.3365/KJMM.2012.50.6.455 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
metals; joining; phase transformation; transmission electron microscopy; Al-segregated zone |
| Abstract |
Al-Si coated boron steel and Zn coated DP steel plates were laser-welded to manufacture a Tailor Welded Blank (TWB) for a car body frame. Hot-stamping heat treatment (900℃, 5 min) was applied to the TWB weld, and the microstructural change and transformation mechanism were investigated in the Al-rich area near the bond line of the Al-Si coated steel side. There was Al-rich area with a single phase, Fe3(Al,Si), which was transformed to α-Fe (Ferrite) after the heat treatment. It could be explained that the Fe3(Al,Si) phase was transformed to α-Fe during heat treatment at 900℃ for 5 min and the resultant α-Fe phase was not transformed by rapid cooling. Before the heat treatment, the microstructures around the Fe3(Al,Si) phase consisted of martensite, bainite and α-Fe while they were transformed to martensite and δ-Fe after the heat treatment. Due to the heat treatment, Al was diffused to the Fe3(Al,Si) and this resulted in an increase of Al content to 0.7 wt% around the Al-rich area. If the weld was held at 900℃ for 5 min it was transformed to a mixture of austenite (γ) and δ-Fe, and only γ was transformed to the martensite by water cooling while the δ-Fe was remained unchanged. |