| 摘要 |
PROBLEM TO BE SOLVED: To provide a non-tempered steel material, excellent in fatigue resistance and machinability and applicable to general purposes, at a low cost by specifying a composition, consisting of C, Si, Mn, S, Cr, Ti, Al, N, and Fe, and a structure, respectively. SOLUTION: This steel material has a composition, consisting of, by weight, 0.2-0.6% C, 0.05-1.0% Si, 0.4-2.0% Mn, 0.01-0.1% S, 0.03-2.0% Cr, 0.04-0.25% Ti, 0.005-0.05% Al, <=0.008% N, and the balance Fe with inevitable impurities and satisfying fn1>0 and fn2>0 (where fn1 and fn2 represent Ti-10N and Al-1.95N, respectively), and also has a ferritic-pearlitic structure consisting of ferrite of JIS grain size number 6 or above and pearlite of <=0.2μm interlamellar spacing. This non-tempered steel material can be obtained by subjecting a steel with the prescribed composition to heating up to 1,100-1,300 deg.C, to hot working at >=900 deg.C, and then to cooling at 5 to 30 deg.C/min cooling rate.
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