Analysis on the Microstructure and Hardness Change After Carburizing of Chromium-Molybdenum Alloy Steel for Automobile Parts
Choon Yoo1, Sang-Jin Yoon2, Chang- Yeol Oh3, Bo-An Kang4
1Choon Yoo, Department of Mechanical Engineering, Nambu University, Gwang –Ju, Korea, East Asian.
2Sang-Jin Yoon, Department of Mechanical Engineering, Nambu University, Gwang –Ju, Korea, East Asian.
3Chang-Yeol Oh, Department of Mechanical Engineering, Nambu University, Gwang –Ju, Korea, East Asian.
4Bo-An Kang, Department of Mechanical Engineering, Nambu University, Gwang –Ju, Korea, East Asian.
Manuscript received on 10 June 2019 | Revised Manuscript received on 17 June 2019 | Manuscript Published on 22 June 2019 | PP: 857-864 | Volume-8 Issue-8S2 June 2019 | Retrieval Number: H11450688S219/19©BEIESP
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© The Authors. Blue Eyes Intelligence Engineering and Sciences Publication (BEIESP). This is an open-access article under the CC-BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Abstract: This study is to investigate the influence of gas carburizing heat treatment on an automatic transmission oil pump drive hub and an engine crankshaft sprocket, which are automotive parts using chrome-molybdenum alloy steel. The main focus is to investigate the effects of carbon potential, carburization time and diffusion time on surface hardness of automotive parts specimens. The test specimens used were made of actual models and sizes of automobile parts. Carrier gas was produced by introducing RX gas mixed with propane and air. The carburizing process was divided into two stages for carburization and diffusion. The results show that the lower the carbon content, the shorter the carburization time and diffusion time required to reach the required surface hardness and internal hardness. It is judged that this is related to the diffusion gradient of carbon on the surface and inside of the material. After the heat treatment, the surface structure was martensite and the internal structure showed a mixed structure of pearlite and ferrite. The hardness according to the carburizing depth of the heat treated parts was measured using a micro Vickers hardness (HV 550) tester. As a result of the analysis of the specimen which was carburized from carbon content 0.20% Oil pump drive hub and 0.15% Crankshaft sprocket prototype, the carbon potential was high, the carburization time was longer and the surface hardness was high. Also it was found that the Carburizing time and carbon potential were found to have a greater effect on carburization hardness than carbon content.
Keywords: Chromium-Molybdenum Alloy, Gas Carburizing, Crankshaft Sprocket, Oil Pump Drive Hub, Carbon Potential.
Scope of the Article: Mechanical Maintenance