Evaluation of Carbon Partitioning in New Generation of Quench and Partitioning (Q&P) Steels |
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Authors: | Ariza Edwan Anderson Poplawsky Jonathan Guo Wei Unocic Kinga Ramirez Antonio J. Tschiptschin André P. Babu Sudarsanam Suresh |
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Affiliation: | 1.Department of Metallurgical and Materials Engineering, University of São Paulo, Av. Prof. Mello Moraes, 2463, São Paulo, SP, 05508-030, Brazil ;2.Mechanical Technology Program, Technological University of Pereira, Cra. 27 No. 10-02, Barrio Álamos, Pereira, Risaralda, Colombia ;3.Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN, 37831-6064, USA ;4.Materials Science and Technology Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN, 37831-6139, USA ;5.Department of Materials Science and Engineering, Ohio State University, Columbus, OH, 43221, USA ;6.Department of Mechanical, Aerospace and Biomedical Engineering, The University of Tennessee, Knoxville, TN, 37996-2210, USA ; |
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Abstract: | Quenching and partitioning (Q&P) and a novel combined process of hot straining (HS) and Q&P (HSQ&P) treatments have been applied to a TRIP-assisted steel in a Gleeble®3S50 thermomechanical simulator. The heat treatments involved intercritical annealing at 800 °C and a two-step Q&P heat treatment with a partitioning time of 100 seconds at 400 °C. The “optimum” quench temperature of 318 °C was selected according to the constrained carbon equilibrium (CCE) criterion. The effects of high-temperature deformation (isothermal and non-isothermal) on the carbon enrichment of austenite, carbide formation, and the strain-induced transformation to ferrite (SIT) mechanism were investigated. Carbon partitioning from supersaturated martensite into austenite and carbide precipitation were confirmed by means of atom probe tomography (APT) and scanning transmission electron microscopy (STEM). Austenite carbon enrichment was clearly observed in all specimens, and in the HSQ&P samples, it was significantly greater than in Q&P, suggesting an additional carbon partitioning to austenite from ferrite formed by the deformation-induced austenite-to-ferrite transformation (DIFT) phenomenon. By APT, the carbon accumulation at austenite/martensite interfaces was observed, with higher values for HSQ&P deformed isothermally (≈ 11 at. pct), when compared with non-isothermal HSQ&P (≈ 9.45 at. pct) and Q&P (≈ 7.6 at. pct). Moreover, a local Mn enrichment was observed in a ferrite/austenite interface, indicating ferrite growth under local equilibrium with negligible partitioning (LENP). |
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