| 摘要 |
A case hardening steel, which has excellent cold forgeability and excellent crystal grain coarsening prevention characteristics after carburization, contains, in mass%, 0.05-0.20% of C, 0.01-0.1% of Si, 0.3-0.6% of Mn, 0.03% or less of P (excluding 0%), 0.001-0.02% of S, 1.2-2.0% of Cr, 0.01-0.1% of Al, 0.010-0.10% of Ti, 0.010% or less of N (excluding 0%), and 0.0005-0.005% of B, with the balance made up of iron and unavoidable impurities. The density of Ti-based precipitates having circle-equivalent diameters less than 20 nm in the case hardening steel is 10-100 pieces/µm2; the density of Ti-based precipitates having diameters of 20 nm or more in the case hardening steel is 1.5-10 pieces/µm2; and the case hardening steel has a Vickers hardness of 130 HV or less. |
