Understanding Forming Characteristics of Different Microstructure Steels within 980MPa and 1180MPa

For electrical vehicle (EV) automotive body-in-white (BIW) structures, protection of passengers and battery in crash event becomes equally important. In addition to energy absorption, intrusion protection for battery and vehicle becomes extremely important and GPa advanced high strength steels (AHSS) including press hardened steels (PHS), DP/MP/CP/GEN3 steels have become material of choice for design for those components. Higher yield strength materials especially in 980/1180MPa MP and CP category are chosen for part design over conventional low yield strength DP. In this study, the forming characteristics including both global and local formability are evaluated and compared among 980 DP/MP grades. Formability test such as forming limit curve (FLC), true fracture strain, V bend, half dome, and hole expansion tests are conducted. Microstructure analysis to understand the effect of different grain structure and phases of DP/MP grades is also accomplished. A T-shape laboratory die trials are carried out to compare and understand the global formability of these steels. Experimental results indicate MP grades tend to have better local and equivalent global formability than DP steels. Some best practices are recommended when AHSS (MP) is used to form 980DP type parts in terms of both global and local formability performances.