Carbide-free bainite in medium carbon steel

Long, Xiaoyan; Kang, Jie; Lv, Bo; Zhang, F.C.

doi:10.1016/j.matdes.2014.07.055

Cited by 116 publications

(40 citation statements)

References 38 publications

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“…The obtained microstructure was indeed a fine mixture of bainitic ferrites plates interwoven with thin films of retained austenite, see results of the measured bainitic ferrite plate and retained austenite film thickness, tBF and tAr respectively, in Figure 2. Wang et al [22] and Long et al [23] investigated an alloy (34MnSi-CrAlNiMo) containing 0.35C-1.5Si-1.5Mn-0.8Al-1.15Cr-0.4Mo all in wt. %.…”

Section: Chemical Composition Modificationmentioning

confidence: 99%

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Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

García‐Mateo

Paul

Somani

et al. 2017

Metals

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Abstract:The major strengthening mechanisms in bainitic steels arise from the bainitic ferrite plate thickness rather than the length, which primarily determines the mean free slip distance. Both the strength of the austenite from where the bainite grows and the driving force of the transformation, are the two factors controlling the final scale of the bainitic microstructure. Usually, those two parameters can be tailored by means of selection of chemical composition and transformation temperature. However, there is also the possibility of introducing plastic deformation on austenite and prior to the bainitic transformation as a way to enhance both the austenite strength and the driving force for the transformation; the latter by introducing a mechanical component to the free energy change. This process, known as ausforming, has awoken a great deal of interest and it is the object of ongoing research with two clear aims. First, an acceleration of the sluggish bainitic transformation observed typically in high C steels (0.7-1 wt. %) transformed at relatively low temperatures. Second, to extend the concept of nanostructured bainite from those of high C steels to much lower C contents, 0.4-0.5 wt. %, keeping a wider range of applications in view.Keywords: bainite; ausforming; kinetics; plate thickness Structural Refinement of Bainitic Steels: General ConsiderationsBainitic steels can be designed on the basis of the theory that predicts the highest temperature at which bainite (Bs) and martensite (Ms) can start to form in a steel of a given composition. These two temperatures constitute the upper and lower limits at which the isothermal heat treatment can be performed to generate bainite.It has been reported that bainitic ferrite plate thickness depends primarily on three parameters, i.e., (1) the strength of the austenite at the transformation temperature, (2) the dislocation density in the austenite and (3) the chemical free energy change accompanying transformation [1][2][3]. In accord, a strong austenite possessing a high dislocation density and a large driving force results in finer plates. Austenite strength and dislocation density refine the structure by increasing the resistance to interface motion, and the thermodynamic driving force refines the structure by increasing the nucleation rate. All three factors-austenite strength, dislocation density and driving force-increase

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Section: Chemical Composition Modificationmentioning

confidence: 99%

“…Wang et al [22] and Long et al [23] investigated an alloy (34MnSi-CrAlNiMo) containing 0.35C-1.5Si-1.5Mn-0.8Al-1.15Cr-0.4Mo all in wt. %.…”

Section: Chemical Composition Modificationmentioning

confidence: 99%

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

García‐Mateo

Paul

Somani

et al. 2017

Metals

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“…It was claimed that axial stress increases bainite transformation amount and accelerates bainite transformation kinetics [1][2][3][4][5][6]. Carbide-free bainite steel, which has excellent strength and toughness combination, is a new generation of advanced high strength steels [6][7][8][9][10][11]. Authors' previous studies confirmed the acceleration of stress on bainite transformation in a carbide-free bainite steel and found that the acceleration of stress on bainite transformation varies nonlinearly with the stress [12][13][14][15].…”

Section: Introductionmentioning

confidence: 96%

Effects of Plastic Stress on Transformation Plasticity and Microstructure of a Carbide-Free Bainite Steel

Liu

et al. 2019

Metallogr. Microstruct. Anal.

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Thermal simulation experiments were conducted, the microstructures were observed by scanning electron microscope (SEM) and transmission electron microscopy (TEM), and the bainite orientation was examined by electron backscattering diffraction (EBSD). The effects of plastic stress on transformation plasticity (TP) strain were investigated. The results show that the TP strain increases nonlinearly with the applied stress. It increases slowly versus the stress in the elastic region, and there is a sharp increase in TP strain if the stress exceeds the parent austenite yield strength because of the combined effect of prior deformation and stress. As the stress continues to increase, the bainite transformation amount decreases, leading to a slower increasing rate of TP strain. In addition, it is confirmed by EBSD that the TP strain is accompanied by the variant selection in microstructures, so that the occurrence of TP is consistent with the Magee mechanism. Moreover, the TP strain is more obvious at lower transformation temperatures due to the increased bainite transformation amount and more organized bainite structure.

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“…Research on the transformation behavior, microstructure evolution and mechanical property of ultra-fine bainite steels has attracted much attention [6][7][8][9][10][11]. Ultra-fine bainite rail steel has been developing in recent years.…”

Section: Introductionmentioning

confidence: 99%

Effects of Tempering on the Microstructure and Properties of a High-Strength Bainite Rail Steel with Good Toughness

Zhu

Zhou

et al. 2018

Metals

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An advanced bainite rail with high strength-toughness combination was produced in a steel mill and the effects of tempering on the microstructure and properties of the bainite rail steel were investigated by optical microscopy, transmission electron microscopy, electron back-scattering diffraction and X-ray diffraction. Results indicate that the tensile strength, elongation and impact toughness were about 1470 MPa, 14.5% and 83 J/cm 2 , respectively, after tempering at 400 • C for 200 min. Therefore, a high-strength bainite rail steel with good toughness was developed. In addition, the amount of retained austenite (RA) decreased due to bainite transformation after low-temperature tempering (300 • C) and RA almost disappeared after high-temperature tempering (500 • C). Moreover, as the tempering temperature increased, the tensile strength of the rail head first decreased due to the decreased dislocation density and carbon content in bainite ferrite and the coarseness of bainite ferrite, and then increased because of carbide precipitation at high-temperature tempering. Furthermore, RA played a significant role in the toughness of bainite rail. The elongation and toughness of the rail obviously decreased after tempering at 500 • C for 200 min because of the disappearance of RA and appearance of carbides.

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Carbide-free bainite in medium carbon steel

Cited by 116 publications

References 38 publications

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

Effects of Plastic Stress on Transformation Plasticity and Microstructure of a Carbide-Free Bainite Steel

Effects of Tempering on the Microstructure and Properties of a High-Strength Bainite Rail Steel with Good Toughness

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