TY - JOUR
T1 - Effect of carbon content on bainite transformation start temperature in middle–High carbon fe–9Ni–C alloys
AU - Kawata, Hiroyuki
AU - Manabe, Toshiyuki
AU - Fujiwara, Kazuki
AU - Takahashi, Manabu
N1 - Funding Information:
The authors would like to express their sincere thanks to Dr. Goro Miyamoto (Tohoku University, Japan) and Dr. Tadashi Maki (Honorary Professor of Kyoto University, Japan) for their valuable comments and stimulating discussions.
Publisher Copyright:
© 2018 ISIJ.
PY - 2018
Y1 - 2018
N2 - Bainite in steel is an industrially useful structure. However, the controlling factor of its transformation start point is not clearly known. In this study, we measured the bainite transformation start temperature (Bs) in Fe–9Ni–C alloys containing 0.3–0.9 mass%C via microstructure observation of the specimens held isothermally between 600 K and 798 K. Bs existed between 758 K and 773 K in all alloys used, and was independent of carbon content. Especially, Bs was higher than T0, at which fcc and bcc of the same composition have the same free energy, at more than 0.3 mass%C. This result was completely different from that of our previous study on low carbon Fe–9Ni–C alloys, in which Bs decreased with the increase in carbon and kept the certain driving force of partitionless transformation from fcc to bcc. Bs in middle–high carbon alloys corresponded to the temperature of the intersection point between T0, at which the driving force is 400 J/mol, and the /( + ) phase boundary. This suggests that the nucleation and growth of bainitic ferrite in austenite containing solute carbon higher than T0 is promoted by the precipitation of cementite in austenite.
AB - Bainite in steel is an industrially useful structure. However, the controlling factor of its transformation start point is not clearly known. In this study, we measured the bainite transformation start temperature (Bs) in Fe–9Ni–C alloys containing 0.3–0.9 mass%C via microstructure observation of the specimens held isothermally between 600 K and 798 K. Bs existed between 758 K and 773 K in all alloys used, and was independent of carbon content. Especially, Bs was higher than T0, at which fcc and bcc of the same composition have the same free energy, at more than 0.3 mass%C. This result was completely different from that of our previous study on low carbon Fe–9Ni–C alloys, in which Bs decreased with the increase in carbon and kept the certain driving force of partitionless transformation from fcc to bcc. Bs in middle–high carbon alloys corresponded to the temperature of the intersection point between T0, at which the driving force is 400 J/mol, and the /( + ) phase boundary. This suggests that the nucleation and growth of bainitic ferrite in austenite containing solute carbon higher than T0 is promoted by the precipitation of cementite in austenite.
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U2 - 10.2355/isijinternational.ISIJINT-2017-387
DO - 10.2355/isijinternational.ISIJINT-2017-387
M3 - Article
AN - SCOPUS:85040738777
SN - 0915-1559
VL - 58
SP - 165
EP - 172
JO - Transactions of the Iron and Steel Institute of Japan
JF - Transactions of the Iron and Steel Institute of Japan
IS - 1
ER -