Patent ID: 9127342
Filing Date: 2015-09-08
Classification: C21D,C23C

Abstract:
1. A method of manufacturing a high-strength transmission gear, comprising the steps of: machining a nitriding steel having a composition including iron (Fe) as a main component, 0.25˜0.40 wt % of carbon (C), 0.50˜1.0 wt % of manganese (Mn), 2.0˜3.0 wt % of chromium (Cr), 0.3˜1.0 wt % of molybdenum (Mo), 0.2˜0.7 wt % of copper (Cu), 0.03˜0.1 wt % of niobium (Nb), 0.03˜0.1 wt % of aluminum (Al), 0.05˜0.15 wt % of vanadium (V), 0.001˜0.005 wt % of boron (B) and other inevitable impurities in a shape of a gear; and gas-nitriding the nitriding steel, wherein the nitriding steel is heated in steps and a ratio of nitrogen gas in the nitriding steel is decreased in steps, to form a nitrogen compound layer that provides high toughness to the nitriding steel, wherein, while gas-nitriding the nitriding steel, the temperature is maintained in steps at 450˜500° C., for 4˜5 hours, at 480˜530° C. for 4˜5 hours and at 510˜540° C. for 8˜10 hours, and the nitrogen gas is reduced at a ratio of 8˜10:4˜6:1˜2 in steps.