| 摘要 |
PROBLEM TO BE SOLVED: To produce a low-cost steel having excellent fatigue strength and machinability as non-heat treated and suitable as the stock for parts of machine structures and to provide a method for producing the same. SOLUTION: This steel is the one having a compsn. contg., by weight, 0.2 to 0.6% C, 0.05 to 1.5% Si, 0.1 to 2.0% Mn, 0.01 to 0.07% P, 0.01 to 0.20% S, >0.25 to 1.0% Ti, 0.002 to 0.05% Al, <=0.008% N, 0 to 2.0% Cr, 0 to 0.3% V, 0 to 0.005% Nb, 0 to 0.5% Mo, 0 to 1.0% Cu, 0 to 0.1% Nd, 0 to 0.50% Pb, 0 to 0.01% Ca, 0 to 0.5% Se, 0 to 0.05% Te, 0 to 0.4% Bi, and the balance Fe with inevitable impurities and having a ferritic-pearlitic structure composed of ferrite having >=6 JIS size number and pearlite with <=0.2μm lamellar intervals. As to the method for producing it, after heating in the temp. range of 1,050 to 1,300 deg.C, hot working is executed in the temp. range of >=900 deg.C, and next, cooling is executed at a cooling rate of 5 to 30 deg.C/min.
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