Effects of Concentrations of Micro-alloying Elements and Hot-forging Temperature on Austenite Grain Structure Formed during Carburization of Case-hardening Steel
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- Saito Genki
- Faculty of Engineering, Hokkaido University
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- Sakaguchi Norihito
- Faculty of Engineering, Hokkaido University
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- Ohno Munekazu
- Faculty of Engineering, Hokkaido University
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- Matsuura Kiyotaka
- Faculty of Engineering, Hokkaido University
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- Takeuchi Masayoshi
- Mitsubishi Steel MFG. Co., Ltd.
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- Sano Taichi
- Mitsubishi Steel MFG. Co., Ltd.
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- Minoguchi Koki
- Mitsubishi Steel MFG. Co., Ltd.
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- Yamaoka Takuya
- Mitsubishi Steel MFG. Co., Ltd.
抄録
<p>Effects of fine precipitates on the austenite (γ) grain structures were investigated in JIS SCM420-based case-hardening steels with several different concentrations of the micro-alloying elements and hot-forging temperatures. Micro-alloyed steels of 18Al (0.018 mass% Al) and 35Al–32Nb (0.035 mass% Al, 0.032 mass% Nb) were forging-simulated at 1150°C or 1250°C, normalized at 1070°C, and carburized at 1050°C. When the as-received 18Al steel was normalized and carburized without forging-simulated heating, a uniform γ grain structure was observed with the distribution of fine AlN precipitates. However, coarsening of AlN occurred when the forging-simulated temperature was 1150°C and it caused abnormal grain growth during carburization. In 35Al–32Nb steel, the same heating did not induce the abnormal grain growth owing to the AlN–Nb(C,N) combined particles. The size of these particles increase with an increase in the forging-simulated temperature. The high forging-simulated temperature caused the dissolution of the fine precipitates, followed by reformation and coarsening of the precipitates during the subsequent cooling and the normalization heating, which resulted in a decreased pinning force and γ grain coarsening. Furthermore, TEM observations revealed that a considerable amount of Nb(C,N) particles exist near large eutectic MnS particles. Thermodynamic calculations based on the Scheil’s condition showed that the formation of these Nb(C,N) particles was due to segregation during solidification. It was suggested that such local concentration of the precipitate particles in the last solidifying region leads to ununiform distribution of the pinning force that may induce the abnormal grain growth.</p>
収録刊行物
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- ISIJ International
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ISIJ International 60 (11), 2549-2557, 2020-11-15
一般社団法人 日本鉄鋼協会
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詳細情報 詳細情報について
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- CRID
- 1390849376464791424
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- NII論文ID
- 130007940416
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- ISSN
- 13475460
- 09151559
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- 本文言語コード
- en
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- データソース種別
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- JaLC
- Crossref
- CiNii Articles
- KAKEN
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- 抄録ライセンスフラグ
- 使用不可