Micro Plastic Deformation Behavior of Carbide-Free Bainitic Steel during Tensile Deformation Process.

Ming Zhang,Fucheng Zhang,Xiaowu Yang,Jie Kang,Zhinan Yang

doi:10.3390/ma13214703

Ming Zhang, Fucheng Zhang + Show 3 more

Open Access

https://doi.org/10.3390/ma13214703

Copy DOI

Abstract

The microstructure of carbide-free bainitic steel has been widely reported because of its excellent mechanical properties. However, no work has explored the deformation behavior of each phase in the microstructure, namely, retained austenite (RA) and bainitic ferrite (BF). In this paper, the deformation behavior of RA and BF during tension was investigated through the in situ electron backscatter diffusion method. The results showed that the RA surrounded by BF with a high Schmid factor (SF) was accelerated towards being transformed into martensite, but the surrounding BF with low SF value retarded the transformation. The kernel average misorientation (KAM) findings revealed that the strain of the RA and BF rapidly increased initially, slowed down after the critical points of 0.25 and 0.54, respectively, and then increased again. The calculated result for the KAM fraction indicated that the contribution of RA to the total plastic deformation gradually decreased throughout the total tensile process, whereas that of BF increased in the presence of RA.

Highlights

Carbide-free bainitic steel is mainly composed of bainitic ferrite (BF) and carbon-rich retained austenite (RA) [1,2]
The evolution of the soft RA in bainitic steel is the main focus of researchers, with minimal concern for harder phases, such as BF or martensite [3,7,8]
Specimens were austenitized at 930 ◦ C for 45 min, subjected to isothermal transformation at 350 ◦ C for 2 h to obtain the carbide-free bainitic microstructure, and air cooled to room temperature

Summary

Introduction

Carbide-free bainitic steel is mainly composed of bainitic ferrite (BF) and carbon-rich retained austenite (RA) [1,2]. RA is distributed between BF lathes and/or sheaves, possessing different stabilities, and the two phases coordinate with each other during deformation, thereby guaranteeing an excellent balance of strength and toughness, especially when the coarse, blocky RA is eliminated. RA is a metastable phase that can transform into martensite because of stress concentration [3,4,5,6]. The stability of RA is influenced by several factors, such as morphology, grain size, carbon content, distribution, and crystalline orientation [7,8]. The evolution of the soft RA in bainitic steel is the main focus of researchers, with minimal concern for harder phases, such as BF or martensite [3,7,8]

Methods

Results

Conclusion