| 摘要 |
PURPOSE:To improve mechanism properties, particularly toughness, of the titled steel to be obtained, by limiting a cooling velocity to a specific temp. range after casting at the time of manufacturing ingots, etc., from a molten steel in which steel composition is specified. CONSTITUTION:In a process for manufacturing ingots or billets from the molten steel having a composition mentioned below, the cast steel is cooled from 1,400-1,000 deg.C at a cooling rate of >=2 deg.C/min to be formed into the titled steel. The composition of the above steel consists of, by weight, 0.1-0.6% C, 0.02-2.0% Si, 0.1-3.0% Mn, <=0.05% P, <=0.05% S, 0.001-0.3% Zr, 0.001-0.1% Al, 0.001-0.02% N, one or more kinds among 0.01-3.0% Cr, 0.01-1.0% Cu, 0.01-2.0% Ni, 0.01-1.0% Mo, 0.001-1.0% V, 0.001-0.30% Nb, and 0.001-0.30% Ti, and the balance Fe with inevitable impurities.
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