| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile strength hot rolled steel sheet which is suitable for applications in which various machine parts and automobile parts are produced by performing precision blanking, has excellent dimensional precision in the precision blanking-worked face, also has extremely high surface hardness in the blanked face after the working, further has excellent red scale flaw resistance, and has a tensile strength of≥490 MPa and a local elongation of≥10%. SOLUTION: The steel sheet has a composition comprising≤0.10% C, <0.01% Si,≤1.5% Mn and≤0.20% Al, further comprising Ti and Nb in the range satisfying (Ti+Nb)/2:0.05 to 0.50%, and comprising≤0.005% S,≤0.005% N and≤0.004% O so as to control the total of S, N and O to≤0.0100%, and has a microstructure substantially consisting of a ferrite single phase structure of≥95%. COPYRIGHT: (C)2004,JPO
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