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

Zhenjia Xie,Xuelin Wang,Chengjia Shang,Gang Han,Lin Xiong

doi:10.3390/met8100807

Zhenjia Xie, Xuelin Wang + Show 3 more

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https://doi.org/10.3390/met8100807

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Journal: Metals	Publication Date: Oct 9, 2018
Citations: 6	License type: CC BY 4.0

Affiliation: University of Science and Technology Beijing

Abstract

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.

Highlights

It has been recognized that steels with retained austenite processes a good combination of strength and ductility due to the transformation-induced plasticity (TRIP) effect of retained austenite [1,2,3].Retained austenite has become an essential component in the development of new-generation, advanced, high-strength steels in the automobile industry
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
Stable retained austenite has been suggested to be helpful for the improvement of low-temperature toughness by lowering ductile–brittle transition temperature (DBTT)

Summary

Introduction

It has been recognized that steels with retained austenite processes a good combination of strength and ductility due to the transformation-induced plasticity (TRIP) effect of retained austenite [1,2,3]. A high yield strength (~500–700 MPa) with excellent ductility and high toughness at low temperatures was obtained with a multi-phase microstructure containing a stable film-like retained austenite [10,11], which has great potential for structural engineering. Retained is inevitably exposed to high temperatures in certain about riskssuch dueas togalvanization, the deteriorated of retained austenite This suggests that retained austenite processes, thestability heat effect zone during welding, and fire-resistant applications [12]. Decomposes into thermodynamically stable ferrite and cementite, leading to a sudden deterioration This brings about risks due to the deteriorated stability of retained austenite. Austenite decomposes into thermodynamically ferrite and cementite, leading to a sudden understandinginthe thermal and stability of retained austenite upon an essential topic to deterioration toughness an increase in DBTT, known as tempering tempering is embrittlement design low-carbon, low-alloy withstability retainedofaustenite. The effect of the stability of retained austenite on properties was investigated

Experimental Material and Procedure

Schematic

Discussion

Conclusions