| 摘要 |
PROBLEM TO BE SOLVED: To provide a composite-structured steel plate of high formability, excellent surface property and high strength of≥340 MPa. SOLUTION: The composite-structured steel plate contains≤0.03% C,≤1.0% Si,≤3.0% Mn,≤0.08% P,≤0.03% S, 0.01-0.10% Al and≤0.01% N, wherein the contents of Si, Mn and P and the tensile strength TS satisfy inequality: Si/12 + Mn/33 + P≤0.0008TS-0.243 (TS≥340 MPa). The steel plate may further contain one or more kinds of≤1.0% each of Cr, Mo and V,≤0.01% B, and≤0.1% each of Ti and Nb. In a manufacturing method for obtaining microscopic structures of the volume fraction of low-temperature transformation phase of below 10%, the hot-rolled steel plate is cold-rolled, annealed at Ac<SB>1</SB>to Ac<SB>3</SB>, cooled to 450-700°C at the cooling rate of > 4°C/second to <10°C/second, further cooled to Ms point or below at the cooling rate of≥10°C/second. COPYRIGHT: (C)2004,JPO
|
