| 摘要 |
PROBLEM TO BE SOLVED: To control crystal grains in a case hardening steel at a higher level, which is useful for manufacturing steel parts that are used in a motor vehicle, building site equipment and other industrial machinery after having been subjected to surface-hardening treatment such as carburization treatment. SOLUTION: The case hardening steel includes, 0.1-0.3% C (in which % means mass% and hereinafter equally means mass% when % is used for indicating a content of a chemical component), 1.5% or less Si (excluding 0%), 2% or less Mn (excluding 0%), 2.5% or less Cr (excluding 0%), 0.01-0.05% Nb and the balance iron with unavoidable impurities, while satisfying expression (1). The case hardening steel like this is superior in properties of reducing the size of the maximum crystal grain. (1): A/[Nb]≤0.7, wherein A represents an area rate (%) of Nb-based inclusions each having an area of 20 μm<SP>2</SP>or more; and [Nb] represents the Nb content (mass%) in the steel. COPYRIGHT: (C)2011,JPO&INPIT
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