| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel improved in machinability without damaging the advantage of an excellent balance of strength and ductility which is the characteristics of steel essentially consisting of a martensitic structure and capable of producing a die as a preharden material, particularly, high strength steel usable as steel for a plastic molding die. SOLUTION: This steel is the one contg., by weight, 0.05 to 0.1% C, <=1.5% Si, <=2.0% Mn, 3.0 to <8.0% Cr, <=4.0% Ni, 0.1 to 2.0% Al and <=3.5% Cu and having a structure consisting essentially of martensite, and in which the contents of N and O which are inevitably present are controlled to <=0.02% N and <=0.003% O. By controlling the value of the formula: 7.7[%C]+2.2[%Si]+271.2[%S] to >=2.5, preferably to <=6, its machinability by heavy cutting, and moreover, its precision discharge machinability and high- class polishability can be improved.
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