| 摘要 |
PROBLEM TO BE SOLVED: To provide case hardened steel with no crack occurring at cold-forging, and with an excellent crystal grain coarsening prevention characteristic in a surface-hardening heat treatment such as a carburization treatment or a carbonitriding treatment.SOLUTION: Case hardened steel includes 0.05-0.40% of C, 0.01-2.0% of Si, 0.3-2.0% of Mn, 0.030% or less (not including 0%) of P, 0.030% or less (not including 0%) of S, 0.50-2.5% of Cr, 0.010-0.10% of Al, 0.0010-0.050% of N, respectively, and the balance includes iron and inevitable impurities. An area ratio of pearlite clusters is 2.0% or lower, and a ratio (D/d) of a mean diameter D of largest pearlite clusters and a mean diameter d of pearlite grains is 5.5 or less. |
