| 摘要 |
PURPOSE: To provide a microalloyed steel for crankshaft of vehicle for improving forming property and strength by varying chemical composition for microalloyed steel and applying cooling conditions to the forged steel after forging the sheet, and a method for manufacturing the microalloyed steel for crankshaft of vehicle. CONSTITUTION: The microalloyed steel for crankshaft of vehicle comprises iron(Fe) as a principal constituent, 0.03 to 0.34 wt.% of carbon(C), 0.15 to 0.35 wt.% of silicon(Si), 1.35 to 1.75 wt.% of manganese(Mn), 0.03 wt.% or less of phosphorus(P), 0.03 to 0.34 wt.% of sulfur(S), 0.20 to 0.30 wt.% of vanadium(V), 0.25 to 0.40 wt.% of chromium(Cr), 0.06 to 0.10 wt.% of calcium(Ca) and 15 parts per million or less of oxygen(O2). The method for manufacturing the microalloyed steel for crankshaft of vehicle comprises a process of performing controlled cooling by a step of rapid cooling the forged microalloyed steel from a forging completion temperature and a step of slowly cooling the rapid cooled microalloyed steel at a rapid cooling completion time after forging the microalloyed steel for crankshaft of vehicle, wherein the forged microalloyed steel is cooled to 700 deg.C in a cooling rate of 180 to 220 deg.C/min in the rapid cooling section, and the rapid cooled microalloyed steel is cooled to an ordinary temperature from 700 deg.C in a cooling rate of 50 deg.C/min or less in the slow cooling section.
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