球状黒鉛鋳鉄の熱処理時における連続冷却変態挙動
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概要
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The purpose of this study is to clarify the continuous cooling transformation behavior of the spheroidal graphite cast iron (FCD 700) during the heat treatment at various austenitized conditions. A high frequency induction heating was employed to heat and cool the specimens. The austenitized conditions were 1123 K × 420 s to 1323 K × 1800 s. The ranges of cooling time from the austenitized temperature to 773 K were about 6 s to 4000 s, respectively. The transformation temperature was measured by a thermal expansion method. As the austenitized temperature increased from 1123 K to 1323 K, ferrite and pearlite transformation regions were little affected by a austenitized temperature. Bainite transformation region did not exist in the CCT diagrams heated above 1223 K. Martensite transformation temperature dropped from 493 K to 458 K in these austenitized conditions. The nucleation sites of ferrite and pearlite in the spheroidal graphite cast iron were mainly not at austenite : austenite grain boundary, but at graphite : austenite boundary in austenite. It is considered that these came from a decrease of carbon content in austenite near graphite caused by a growth of graphite during cooling. The hardenability curves which obtained from CCT diagrams shifted a little to the longer cooling time with the increase of austenitized temperatue from 1123 K to 1173 K. But, that of more than 1173 K did not scarcely shift to the longer cooling time. Quenching cracks were observed in the martensite in the specimens heated at 1323 K.
- 日本鋳造工学会の論文
日本鋳造工学会 | 論文
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