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Thermal Stability of Retained Austenite and Properties of A Multi-Phase Low Alloy Steel

Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing 100083, China
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Metals 2018, 8(10), 807; https://doi.org/10.3390/met8100807
Received: 16 September 2018 / Revised: 26 September 2018 / Accepted: 29 September 2018 / Published: 9 October 2018
(This article belongs to the Special Issue TRIP Steels)
In this work, we elucidate the effects of tempering on the microstructure and properties in a low carbon low alloy steel, with particular emphasis on the thermal stability of retained austenite during high-temperature tempering at 500–700 °C for 1 h. Volume fraction of ~14% of retained austenite was obtained in the studied steel by two-step intercritical heat treatment. Results from transmission electron microscopy (TEM) and X-ray diffraction (XRD) indicated that retained austenite had high thermal stability when tempering at 500 and 600 °C for 1 h. The volume fraction was ~11–12%, the length and width remained ~0.77 and 0.21 μm, and concentration of Mn and Ni in retained austenite remained ~6.2–6.6 and ~1.6 wt %, respectively. However, when tempering at 700 °C for 1 h, the volume fraction of retained austenite was decreased largely to ~8%. The underlying reason could be attributed to the growth of austenite during high-temperature holding, leading to a depletion of alloy contents and a decrease in stability. Moreover, for samples tempered at 700 °C for 1 h, retained austenite rapidly transformed into martensite at a strain of 2–10%, and a dramatic increase in work hardening was observed. This indicated that the mechanical stability of retained austenite decreased. View Full-Text
Keywords: thermal stability; retained austenite; multi-phase microstructure; low alloy steel thermal stability; retained austenite; multi-phase microstructure; low alloy steel
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Xie, Z.; Xiong, L.; Han, G.; Wang, X.; Shang, C. Thermal Stability of Retained Austenite and Properties of A Multi-Phase Low Alloy Steel. Metals 2018, 8, 807.

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