| 摘要 |
PROBLEM TO BE SOLVED: To obtain a tool steel improved in machinability by containing a specified quantity in each of C, Si, Mn, Cr, Mo and V, making the balance to be Fe with inevitable impurities, and specifying a value of Rockwell hardness after quenching/tempering. SOLUTION: The content is, by weight, 1.20-1.35% C, 0.20-0.30% Si, >=0.3% Mn, 9.0-11.0% Cr, 1.10-1.35 Mo, 0.20-0.45% V. A Rockwell hardness after quenching/tempering is 55-60 HRC, a wear resistance machinability index preferably satisfies the formula of 1,800<25,329-0.325×(Rockwell hardness)<3> +15.9×(residual austenite %)<2> -329.9×(residual austenite %). A tempering treatment temp. after quenching is >=505 deg.C and the steel is treated by repeating twice or more to be a Rockwell hardness of 55-60 HRC, further preferably, a tempering treatment temp. is >=550 deg.C and a Rockwell hardness is 56-59 HRC.
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