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Article

Microstructure Formation and Carbon Partitioning with Austenite Decomposition during Isothermal Heating Process in Fe-Si-Mn-C Steel Monitored by In Situ Time-of-Flight Neutron Diffraction

1
Frontier Research Center for Applied Atomic Sciences, Ibaraki University, 162-1 Shirakata, Tokai 319-1106, Ibaraki, Japan
2
Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi 316-8511, Ibaraki, Japan
3
Nippon Steel Research Institute Corporation, 1-8 Fuso-Cho, Amagasaki 660-0891, Hyogo, Japan
4
Advanced Technology Research Labs., R&D Laboratories, Nippon Steel Corporation, 20-1 Shintomi, Futtsu 293-8511, Chiba, Japan
*
Author to whom correspondence should be addressed.
Academic Editor: Atef Saad Hamada
Metals 2022, 12(6), 957; https://doi.org/10.3390/met12060957
Received: 28 March 2022 / Revised: 22 May 2022 / Accepted: 30 May 2022 / Published: 2 June 2022
Retained austenite is a key feature used to realize the transformation-induced plasticity in bainitic high strength steels. In this study, the authors focused on the formation of metastable austenite in Fe-0.61C-1.9Si-0.98Mn (mass%) during isothermal heating processes using in situ neutron diffraction techniques. Quantitative discussion of carbon partitioning processes is enabled by applying an in situ phase fraction analysis considering crystallographic textures, in addition to the carbon concentration estimation based on the lattice parameter of austenite. The carbon partitioning behavior is inhomogeneous, resulting in a bimodal carbon concentration distribution in austenite. The carbon enriched, high carbon austenite is stable during isothermal heating at 673 K and is retained even after cooling to room temperature. The remainder is low carbon austenite, which is gradually consumed by bainite transformation. Above 723 K, the high carbon austenite also decomposes to ferrite and cementite due to the fast diffusion of Si. Conversely, below 623 K, cementite is stabilized even without the diffusion of Si. These cementite formation mechanisms prevent the formation and retention of high carbon austenite. The inhomogeneous carbon distribution and cementite formation must be carefully considered to precisely predict the microstructure formation in Si-added bainitic steels. View Full-Text
Keywords: TRIP steel; bainite transformation; neutron diffraction; Rietveld texture analysis; iMATERIA TRIP steel; bainite transformation; neutron diffraction; Rietveld texture analysis; iMATERIA
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MDPI and ACS Style

Onuki, Y.; Umemura, K.; Fujiwara, K.; Tanaka, Y.; Tomida, T.; Kawano, K.; Sato, S. Microstructure Formation and Carbon Partitioning with Austenite Decomposition during Isothermal Heating Process in Fe-Si-Mn-C Steel Monitored by In Situ Time-of-Flight Neutron Diffraction. Metals 2022, 12, 957. https://doi.org/10.3390/met12060957

AMA Style

Onuki Y, Umemura K, Fujiwara K, Tanaka Y, Tomida T, Kawano K, Sato S. Microstructure Formation and Carbon Partitioning with Austenite Decomposition during Isothermal Heating Process in Fe-Si-Mn-C Steel Monitored by In Situ Time-of-Flight Neutron Diffraction. Metals. 2022; 12(6):957. https://doi.org/10.3390/met12060957

Chicago/Turabian Style

Onuki, Yusuke, Kazuki Umemura, Kazuki Fujiwara, Yasuaki Tanaka, Toshiro Tomida, Kaori Kawano, and Shigeo Sato. 2022. "Microstructure Formation and Carbon Partitioning with Austenite Decomposition during Isothermal Heating Process in Fe-Si-Mn-C Steel Monitored by In Situ Time-of-Flight Neutron Diffraction" Metals 12, no. 6: 957. https://doi.org/10.3390/met12060957

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