High-strength hot rolled steel sheet
AssigneeJfe Steel Corporation
InventorsYoshimasa Funakawa, Tetsuo Yamamoto, Hiroshi Uchomae, Hiroshi Nakano, Taro Kizu
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Abstract
A high-strength hot rolled steel sheets with excellent stretch flangeability has small variations in mechanical properties in individual coils. Variations in strength from place to place in a coil are decreased by minimally reducing the Si and Mn contents to suppress the occurrence of problems such as segregation. Further, the microstructure of the steel sheets is configured such that a ferrite phase represents an area ratio of not less than 95%, the ferrite crystal grains have an average grain size of not less than 1 μm, and the ferrite crystal grains contain TiC with an average particle size of not more than 7 nm dispersed in the crystal grains.
Claims12
A high-strength hot rolled steel sheet with a yield strength of not less than 530 MPa, the steel sheet having a chemical composition including, by mass %:
- C:
- more than 0.010% and not more than 0.06%,
- Si:
- not more than 0.3%,
- Mn:
- not more than 0.48%,
- P:
- not more than 0.03%,
- S:
- not more than 0.02%,
- Al:
- not more than 0.1%,
- N:
- not more than 0.01% and Ti:
- 0.05 to 0.10%,
- the balance comprising Fe and inevitable impurities, the steel sheet comprising a metal microstructure including a ferrite phase with an area ratio of not less than 95%, the ferrite crystal grains having an average grain size of not less than 1 μm, the ferrite crystal grains containing TiC precipitate particles dispersed in the crystal grains, the TiC precipitate particles having an average particle size of not more than 7 nm, and the steel sheet having a ΔYS of 20 MPa or less.
Dependencies are inferred from the claim text.