Steel material with uniformly finely divided carbon particles with an excellent machinability, cold-forming property and curing properties and its production method

摘要

This invention provides a fine graphite uniform dispersion steel material excellent in cold workability, cuttability and hardenability by particularly dispersing graphite finely and uniformly, and a production method thereof, this steel comprising 0.30 to 1.0% of C, 0.4 to 1.3% of Si, 0.3 to 1.0% of Mn, 0.0003 to 0.006% of B, 0.002 to 0.010% of N and 0.05 to 0.20% of Mo as the basic components and contains graphite having a mean grain diameter of not more than 4.0 mu m and a number of grains of at least 3,000 pcs/mm2, and the production method comprising cooling the steel having these components at a cooling start temperature of not less than an Ar1 point, a cooling end temperature of not more than an Ms point and a mean cooling rate of 5 to 100 DEG C/s.