complex heat treated gear having excellent machinability and low deformability for heat treatment and method for manufacturing the same

摘要

The present invention relates to a gear for an automobile with reduced heat treatment deformation compared to an existing carburized heat treated gear, high durability, and excellent machinability and a gear manufacturing method, wherein the gear for an automobile has a hardened layer along the contour of the gear surface by performing high-frequency contour quenching after nitriding heat treatment. The gear manufacturing method comprises: a step of hot-forging carburized steel or nitriding steel of SCr420H material of JIS standard, which comprises 0.17-0.23% of carbon (C), 0.15-0.35% of silicon (Si), 0.55-0.90% of manganese (Mn), 0.85-1.25% of chromium (Cr), and the remainder consisting of iron (Fe) and inevitable impurities, and performing nitriding heat treatment for the machined gear in NH_3+CO_2+N_2 gas atmosphere condition within 3 hours at 570°C, so the gear surface is composed of an epsilon phase (Fe2-3N) in which a fraction of a nitriding compound layer is 90% or more. After the nitriding heat treatment, the gear is manufactured by heating the high-frequency contour quenching for less than 50 seconds.