| 摘要 |
PROBLEM TO BE SOLVED: To provide a case hardening steel combining excellent cold forgeability and crystal grain coarsening suppression performance.SOLUTION: Provided is a case hardening steel having a structure in which the structural fraction of ferrite and pearlite is 80% or higher, in which the number of precipitates including Nb and having a diameter below 50 nm is 30 pieces/μmand the number of precipitates including Nb and having a diameter of 50 to 100 nm is 3 pieces/μmor lower, and also, the number of precipitates including Nb and having a diameter below 50 nm (n) and the number of the precipitates including Nb and having a diameter of 50 to 100 nm (n) satisfy the relation of n-5nsatisfy the relation of n-5n>30. |
