| 摘要 |
PROBLEM TO BE SOLVED: To produce a hot forged non-heat treated steel having fatigue strength higher than that of the conventional non-heat treated steel without deteriorating its machinability and furthermore having about 70 to 100kgf/mm<2> tensile strength. SOLUTION: The componental compsn. of this steel is composed of, by mass, 0.15 to 0.60% C, 0.05 to 2.5% Si, 0.3 to 2.5% Mn, 0.01 to 0.10% S, 0.05 to 2.5% Cr, 0.05 to 0.5% V, 0.01 to 0.060% Al, 0.005 to 0.030% N and 0.001 to 0.005% O, and the balance Fe with inevitable impurities. The structure obtd. after the steel is subjected to hot forging is formed of a ferritic-pearlitic one, and moreover, as for the pearlitic structure, the average grain size is regulated to >=3.0, the average colony size in the pearlite is regulated to <=20μm, and the average lamellar distance is regulated to <=0.30μm.
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