| 摘要 |
PURPOSE: To produce a fine graphite uniformly dispersed bar steel excellent in toughness after quench-and-temper treatment by dispersing graphite, in particular, finely and uniformly. CONSTITUTION: This fine graphite uniformly dispersed bar steel excellent in toughness is composed of a steel where 0.30-1.0% C, 0.6-1.3% Si, 0.4-1.0% Mn, <=0.020% P, 0.015-0.055% S, 0.01-0.10% Al, 0.001-0.004% B, 0.002-0.008% N, and 0.05-0.20% Mo are added as essential components and also the average grain size and the number of grains of 0.3-1.0% graphite are regulated to <=4.0μm and <=3000pieces/mm<2> , respectively. The bar steel having this composition, immediately after hot rolling, is cooled while regulating initial cooling temp., cooling finishing temp., and average cooling rate to a temp. not lower than the Ar1 point, a temp. not higher than the Ms point, and (30 to 100) deg.Cps, respectively.
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