Patent ID: 9452792
Filing Date: 2016-09-27
CPC Classification: B21D,B62D,C21D,C22C,Y10T

Claim Text:
1. A vehicle collision energy absorbing member formed by shaping a high strength thin steel sheet, wherein the high strength thin steel sheet has a tensile strength TS of at least 980 MPa, and has an n-value and a limit bending radius Rc satisfying Formula (1) below: where Rc: limit bending radius (mm), t: sheet thickness (mm), and n: n-value obtained for a true strain is 5% to 10%, the high strength thin steel sheet includes a chemical composition containing, by mass %: C: 0.14% to 0.30%; Si: 0.01% to 1.6%; Mn: 3.5% to 10%; P: 0.060% or less; S: 0.0050% or less; Al: 0.01% to 1.5%; N: 0.0060% or less; Nb: 0.01% to 0.10%; and the balance being Fe and incidental impurities, and the high strength thin steel sheet has a microstructure including a ferrite phase by 30% to 70% in volume fraction with respect to the entire microstructure and a secondary phase other than the ferrite phase, the ferrite phase having an average grain size of 1.0 μm or smaller, the secondary phase at least containing a retained austenite phase by at least 10% in volume fraction to the entire microstructure, the retained austenite phase having an average spacing of 1.5 μm or less.