| 摘要 |
PROBLEM TO BE SOLVED: To produce a cold forging steel in which deterioration in ductility due to work hardening is prevented and deformability is maintained and also the occurrence of blue brittleness is prevented and deformation resistance is reduced, even in the case where material temp. is increased as a result of cold forging at high draft and particularly cold forging at high draft of >=90% compressibility. SOLUTION: This steel is (1) a cold forging steel having a composition which consists of, by weight, 0.10-0.60% C, >0.05-0.10% Al, <=0.35% Si, <=1.2% Mn, <=0.5% Cr, <=0.07% Ti, <=0.003% B, and the balance Fe with inevitable impurities and in which the contents of P, S, and N among the impurities are limited to <0.01%, <0.01%, and <0.005%, respectively, and [(N(%)/Al(%)]<=0.05 is satisfied and also the value of (ρ) represented byρ=30×Si(%)+10×Mn(%)+300×P(%)+500×N(%) is regulated to <20; (2) a cold forging steel having a composition prepared by replacing the <=0.07% Ti] of the composition of the above cold forging steel (1) with [Ti+0.5Zr<=0.10%]; (3) a cold forging steel of the above (1) or (2), containing <=0.40% Cu and <=0.40% Ni.
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