| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for hot-forging non-heat-treated parts, which can reliably acquire high strength, high toughness and adequate machinability, and is suitable for a process of manufacturing the non-heat-treated parts for automobiles. SOLUTION: A steel material for the parts comprises 0.15-0.5% C, 0.6-1.0% Si, 0.6-1.5% Mn, 0.03% or less P, 0.03-0.2% S, 0.008-0.025% N, 0.003-0.1% Ti, 0.1-0.5% V, 0.2-0.8% Cr, 0.002-0.1% Al, while satisfying [%C]/[%V]≥0.5, (wherein [%C] and [%V] represent contents of C and V in the steel by mass% respectively), and the balance Fe with unavoidable impurities. The method for hot-forging the non-heat-treated parts comprises the steps of: heating the steel material to 1,100 to 1,250°C; forging it into a shape of the parts in a temperature range between (T+50) and (T+100)°C, wherein T represents a temperature (°C) of 1,000°C or lower calculated from the expression of Log[%C][%V]=(-9,500/t)+6.72 and the expression of T=t-273; and then cooling it at a cooling rate of 0.2 to 5.0°C/second in a range of 800 to 500°C. COPYRIGHT: (C)2007,JPO&INPIT
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