| 摘要 |
PROBLEM TO BE SOLVED: To provide a bar steel for cold forging superior in cold workability, a cold-forged article, and a manufacturing method therefor. SOLUTION: The bar steel has a ferrite single-phase structure after being rolled, and has a composition comprising, by mass%, 0.15% or less C, 0.3% or less Si, 2% or less Mn, 0.03-0.35% Ti, 0.05-0.8% Mo, further one or more elements of 0.08% or less Nb, 0.15% or less V, and 1.5% or less W, one or more elements of 0.03-0.1% S, 0.2% or less Pb, 0.005% or less Ca, and 0.02% or less B, preferably so as to satisfy 0.5≤(C/12)/ä(Ti/48)+(Mo/96)+(Nb/93)+(V/51)+(W/192)}≤1.5, and the balance Fe with unavoidable impurities. The manufacturing method comprises steps for heating the steel at 950-1,250°C or higher, rolling it at a finishing temperature of 800°C, subsequently cooling it to 700-550°C at a higher rate than 0.5°C/sec, then cold-forging it into a predetermined shape, and then holding it at 550-700°C for 10 minutes or longer to precipitate fine precipitates having particle sizes of less than 10 nm. COPYRIGHT: (C)2004,JPO
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