| 摘要 |
PURPOSE: A non quenched and tempered steel composition is provided to improve strength by adding manganese and boron to low carbon steel and obtain non-heat treatment characteristics by adding titanium, niobium and vanadium, and a manufacturing method of connecting rod for large automobile engines using the same is provided. CONSTITUTION: The non quenched and tempered steel composition comprises iron (Fe) as a principal constituent, 0.10 to 0.20 wt.% of carbon (C), 0.30 wt.% or less of silicon (Si), 1.0 to 2.5 wt.% of manganese (Mn), 0.015 wt.% or less of phosphorus (P), 0.035 wt.% or less of sulfur (S), 0.01 to 0.03 wt.% of titanium (Ti), 0.10 to 0.20 wt.% of vanadium (V) and 0.02 to 0.05 wt.% of niobium (Nb), wherein the non quenched and tempered steel composition further comprises 10 to 20 ppm of boron (B). The manufacturing method of connecting rod comprises the steps of melting the alloy composition in converter under ordinary operating conditions; continuously casting the melt; hot forging the continuously cast alloy at a temperature of 1,200 deg.C when fabricating a connecting rod; and performing controlled water cooling on the hot forged alloy to the temperature range of 100 to 250 deg.C so that a matrix structure transforms to a lath martensite at an ordinary temperature, and composite carbide of vanadium, titanium and niobium is precipitation hardened inside grains.
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