Structural Performance Comparison between 980MPa Generation 3 Steel and Press Hardened Steel Applied in the Body-in-White A and B-Pillar Parts 2020-01-0537
Commercially available Generation 3 (GEN3) advanced high strength steels (AHSS) have inherent capability of replacing press hardened steels (PHS) using cold stamping processes. 980 GEN3 AHSS is a cold stampable steel with 980 MPa minimum tensile strength that exhibits an excellent combination of formability and strength. Hot forming of PHS requires elevated temperatures (> 800ºC) to enable complex deep sections. 980 GEN3 AHSS presents similar formability as 590 DP material, allowing engineers to design complex geometries similar to PHS material; however, its cold formability provides implied potential process cost savings in automotive applications. The increase in post-forming yield strength of GEN3 AHSS due to work and bake hardening contributes strongly toward crash performance in energy absorption and intrusion resistance. The viability of using cold stamped 980 GEN3 AHSS as a replacement for PHS has often been challenged due to concerns about formability and capability to meet final crash performance targets. To address these concerns, A-pillar and B-pillar parts were successfully cold stamped using U. S. Steel 980 GEN3 AHSS and assembled in a prototype mid-size sedan. Advanced computer simulations were carried out to emulate the crash events and predict the crash behavior of 980 GEN3 AHSS. The crash performance of these vehicles were physically validated in roof crush, side impact and side pole impact tests. This paper gives an overview of 980 GEN3 AHSS formability and crash simulation, using a fracture criterion that includes the plastic strain and thickness mapped from the formability analysis. Crash simulations confirm that 980 GEN3 AHSS exhibits comparable performance when compared to the baseline PHS for structural deformation and occupant safety.
Vasant Pednekar, Andre Pereira, Adam Ballard, Guofei Chen, Rajmouli Komarivelli, Haoming Li
United States Steel Corp., General Motors LLC