Effect of Two-Step Austempering Process on Transformation Kinetics of Nanostructured Bainitic Steel.

Chunhe Chu,Zhinan Yang,Xuemei Li,Changhong Guo,Xiaoyan Long,Leilei You,Fucheng Zhang,Yuman Qin

doi:10.3390/ma12010166

Chunhe Chu, Zhinan Yang + Show 6 more

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https://doi.org/10.3390/ma12010166

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Abstract

The two-step austempering process has been reported to be an effective method to accelerate the bainitic transformation process by introducing martensite (Q-M-B). However, in this study, it was found that the Q-M-B process reduced the incubation time, but the transformation duration remained nearly unchanged. The notably reduced activation energy barrier for nucleation of bainitic ferrite on the preformed martensite should be responsible for the reduced duration time of the Q-M-B process. A process that both of the two steps were above, Ms (Q-B-B), has been demonstrated to increase transformation rate and improve the amount of bainitic ferrite, which probably results from the additional hysteresis free energy provided by the first quenching process.

Highlights

The bearing is a basic and key component in many mechanical parts, and bearings with the required properties are necessary for steady operation of the machinery
There is an abundance of cementite dispersed within the microstructure of all specimens, and statistic results reveal that the fraction of cementite is ~6.5% in all specimens for the same high temperature temper process and the subsequent
Ititcan be be seen that that therethere are bainitic ferrite plates from the preformed

Summary

Introduction

The bearing is a basic and key component in many mechanical parts, and bearings with the required properties are necessary for steady operation of the machinery. Nanostructured bainitic microstructure possesses excellent strength and toughness [1,2,3,4,5], but exhibits a high wear resistance and has a better rolling contact fatigue performance compared to the martensitic microstructure [6,7,8,9,10,11]. This material is suitable for the bearing application [12,13,14]. To accelerate kinetics of the bainitic phase transformation, researchers have developed methods such as adding Co and Al [16,17], or reducing

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