PHASE TRANSFORMATION AND Fe DIFFUSION CONDITIONS OF A Fe-Zn COATED STEEL AD APPLICATION IN HOT STAMPING

Abstract

Hot stamping hardened steels have played a significant role in enabling the automotive industry to comply with increasingly stringent regulations aimed at reducing fuel consumption and greenhouse gas emissions, while simultaneously enhancing passenger safety through the production of lightweight car body components. Fe-Zn coatings are a viable alternative for preventing corrosion or even improving the corrosion resistance of these steels. However, Fe-Zn coatings are susceptible to liquid metal embrittlement (LME) during the hot forming process. To mitigate LME, it is essential that the coating be fully transformed into a solid solution prior to the forming operation, thereby preventing contact between the liquid zinc phase and the steel substrate. The primary objective of this study was to determine the phase transformation temperatures and the critical cooling rate necessary to define the processing window for Fe-Zn coated boron steel sheets subjected to higher heating rates than those used in conventional direct hot forming processes. As a complementary objective, X-ray diffraction analysis was performed on a hot-stamped component heated by Joule effect.