Stabilization of retained austenite by the two-step intercritical heat treatment and its effect on the toughness of a low alloyed steel |
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| Affiliation: | 1. School of Materials Science and Engineering, University of Science and Technology, Beijing, China;2. Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan;1. The State Key Laboratory of Rolling and Automation Northeastern University, Shenyang 110819, China;2. Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical and Materials Engineering,University of Texas at El Paso, TX 79968-0521, USA;1. Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, 3 Wenhua Road, Shenyang 110004, China;2. Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352, USA;3. Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996, USA;4. Max-Planck-Institut fuer Eisenforschung, Max-Planck-Str. 1, 8, 40237 Düsseldorf, Germany;1. State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, People''s Republic of China;2. School of Materials and Metallurgy, Northeastern University, Shenyang 110819, People''s Republic of China;1. School of Materials Science and Engineering, University of Science & Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing 100083, PR China;2. Qingzhou Construction Quality and Safety Supervision Station, Shandong 262500, PR China;1. Engineering Research Institute, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China;2. Beijing Laboratory of Metallic Materials and Processing for Modern Transportation, Beijing 100083, People’s Republic of China;3. National Engineering Research Center of Advanced Rolling, Beijing 100083, People’s Republic of China |
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| Abstract: | Fine film-like stable retained austenite was obtained in a Fe–0.08C–0.5Si–2.4Mn–0.5Ni in weight percent (wt.%) steel by the two-step intercritical heat treatment. The first step of intercritical annealing creates a mixed microstructure of preliminary alloy-enriched martensite and lean alloyed intercritical ferrite, which is called as “reverted structure” and “un-reverted structure”, respectively. The second step of intercritical tempering is beneficial for producing film-like stable reverted austenite along the reverted structure. The stabilization of retained austenite was studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), dilatometry and X-ray diffraction (XRD) analysis. The two-step austenite reverted transformation associated with intercritical partition of C, Mn and Ni is believed to be the underlying basis for stabilization of retained austenite during the two-step intercritical heat treatment. Stable retained austenite is not only beneficial for high ductility, but also for low temperature toughness by restricting brittle fracture. With 10% (volume fraction) of retained austenite in the steel, high low temperature toughness with average Charpy impact energy of 65 J at −80 °C was obtained. |
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| Keywords: | Retained austenite Low temperature toughness Intercritical partition Austenite reverted transformation |
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