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Open AccessArticle

Effect of C2H2/H2 Gas Mixture Ratio in Direct Low-Temperature Vacuum Carburization

1
Dongnam Regional Division, Korea Institute of Industry Technology (KITECH), Namyangsan 1-gil 14, Yangsan 50635, Korea
2
Department of Materials Science and Engineering, Pusan National University, Busandaehak-ro 63beon-gil 2, Busan 46241, Korea
3
Department of Materials Science and Engineering, Inha University, Inha-ro 100, Incheon 22212, Korea
*
Authors to whom correspondence should be addressed.
Metals 2018, 8(7), 493; https://doi.org/10.3390/met8070493
Received: 29 May 2018 / Revised: 20 June 2018 / Accepted: 25 June 2018 / Published: 28 June 2018
(This article belongs to the Special Issue Surface Treatment Technology of Metals and Alloys)
The effect of the acetylene and hydrogen gases mixture ratios in direct low-temperature vacuum carburization was investigated. The gas ratio is an important parameter for producing free radicals in carburization. The free radicals can remove the natural oxide film by strong reaction of the hydrocarbons, and then thermodynamic activity can be increased. When the gas ratio was below one, carbon-supersaturated expanded austenite layers were formed on the surface of the AISI 316L stainless steel, which had a maximum carbon solubility up to 11.5 at% at 743 K. On the other hand, when the gas ratio was above one, the carbon concentration of the layers was low even if the process time was increased enough to reach the maximum carbon solubility. As a result, the carbon concentration underneath the surface was determined to be highly dependent on the gas mixture ratio of acetylene and hydrogen. In conclusion, it is necessary to restrict the ratio of acetylene and hydrogen gases in the total mixture of gases to form an expanded austenite layer with high carbon concentration in direct low-temperature vacuum carburization. View Full-Text
Keywords: direct surface activation; low-temperature vacuum carburization; expanded austenite; supersaturation; acetylene direct surface activation; low-temperature vacuum carburization; expanded austenite; supersaturation; acetylene
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Song, Y.; Kim, J.-H.; Kim, K.-S.; Kim, S.; Song, P.K. Effect of C2H2/H2 Gas Mixture Ratio in Direct Low-Temperature Vacuum Carburization. Metals 2018, 8, 493.

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