| 摘要 |
PROBLEM TO BE SOLVED: To provide a case-hardened steel superior in grain-coarsening resistance compared to a conventional steel even when the steel material contains bainite. SOLUTION: The case-hardened steel superior in grain-coarsening resistance for carburized parts includes, by mass%, 0.10% to 0.35% C, 0.05% to 2.0% Si, less than 0.60% Mn, 0.030% or less P, 0.10% or less S, 1.5% to 3.0% Cr, 0.005% to 0.050% Al, 0.0030% or less O and the balance Fe with unavoidable impurities, while controlling [Mn/Cr] to less than 0.35 by mass% ratio; has 20% or more of bainite by fraction of a structure; and can inhibit crystal grains from being coarsened even when having been carburizing-heat-treated after having been hot-forged. COPYRIGHT: (C)2009,JPO&INPIT
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