Effects of ausforming temperature on bainite transformation, microstructure and variant selection in nanobainite steel

Gong, Wu; Tomota, Yō; Adachi, Yoshitaka; Paradowska, Anna; Kelleher, Joe; Zhang, S.Y.

doi:10.1016/j.actamat.2013.03.041

Cited by 182 publications

(111 citation statements)

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“…Zhang et al [47] showed that ausforming decreased the Ms, thereby enabling isothermal transformation at lower temperatures, thus facilitating the formation of nanostructured bainite. Besides this, decreasing the ausforming temperature and increasing the An advantage of the low temperature process as compared with the higher temperature one is that the former can be employed to drastically reduce the number of bainite variants in a single austenite grain, leading to a reduction in the fraction of detrimental block-type retained austenite and an increase in the fraction of beneficial interlath films of retained austenite [48,50]. Gong et al [48,50] studied the effects of ausforming temperature on bainite transformation and variant selection in high-carbon nanobainitic steel.…”

Section: Deformation Of Austenite (Ausforming)mentioning

confidence: 99%

“…An advantage of the low temperature process as compared with the higher temperature one is that the former can be employed to drastically reduce the number of bainite variants in a single austenite grain, leading to a reduction in the fraction of detrimental block-type retained austenite and an increase in the fraction of beneficial interlath films of retained austenite [48,50]. Gong et al [48,50] studied the effects of ausforming temperature on bainite transformation and variant selection in highcarbon nanobainitic steel. Their results indicated that ausforming at a low temperature (300 °C) can accelerate bainite transformation and produce a strong variant selection, whereas ausforming at a high temperature (600 °C) has a weak influence.…”

Section: Deformation Of Austenite (Ausforming)mentioning

confidence: 99%

“…Zhang et al [47] showed that ausforming decreased the Ms, thereby enabling isothermal transformation at lower temperatures, thus facilitating the formation of nanostructured bainite. Besides this, decreasing the ausforming temperature and increasing the This same technique has received attention as a means of accelerating the sluggish bainitic transformation of (low temperature) nanostructured bainite and hence, different deformation routes have been tested, not only revealing accelerated transformation kinetics but also achieving an extra refinement of the microstructure [47][48][49][50][51][52][53][54][55][56][57][58][59]. While extensive work has been done on a single alloy containing 0.5 C wt.…”

Section: Deformation Of Austenite (Ausforming)mentioning

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: Deformation Of Austenite (Ausforming)mentioning

confidence: 99%

Section: Deformation Of Austenite (Ausforming)mentioning

confidence: 99%

“…Zhang et al [47] showed that ausforming decreased the Ms, thereby enabling isothermal transformation at lower temperatures, thus facilitating the formation of nanostructured bainite. Besides this, decreasing the ausforming temperature and increasing the This same technique has received attention as a means of accelerating the sluggish bainitic transformation of (low temperature) nanostructured bainite and hence, different deformation routes have been tested, not only revealing accelerated transformation kinetics but also achieving an extra refinement of the microstructure [47][48][49][50][51][52][53][54][55][56][57][58][59]. While extensive work has been done on a single alloy containing 0.5 C wt.…”

Section: Deformation Of Austenite (Ausforming)mentioning

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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“…However, the acceleration of the transformation must enlarge the application of nano-bainite steels. We have found that a small amount of low temperature ausforming (e.g., at 300˝C) [18,19] or partial quenching below Ms temperature [20] is effective to accelerate nano-bainite transformation. The dislocation structure introduced in austenite at low temperatures is found to assist bainite transformation with strong variant selection where partial dislocations introduced by ausforming play an important role for bainite transformation [19].…”

Section: Introductionmentioning

confidence: 99%

“…For studying microstructure evolution, in situ observations during processing using synchrotron X-ray [21,22] or neutron diffraction (ND) [19,20] have successfully been employed so far. Diffraction profiles provide the insights on volume fractions of constituents, which show good agreement with the results obtained by dilatometry [17], carbon contents in austenite [23], texture [19], and dislocation density [20].…”

Section: Introductionmentioning

confidence: 99%

Monitoring of Bainite Transformation Using in Situ Neutron Scattering

Nishijima

Tomota

et al. 2016

Metals

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Effects of Strain and Deformation Temperature on Bainitic Transformation in a Fe-C-Mn-Si Alloy

Wang

et al. 2016

steel research int.

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The relationship between the strain corresponding to the maximum amount of bainite (termed as peak value strain) and ausforming temperature is investigated by metallography, X-ray diffraction, and dilatometry. The results indicate that the peak value strain increases with the increase of ausforming temperature, whereas the corresponding maximum amount of bainitic transformation decreases. Ausforming has dual effects on bainitic transformation, i.e., the promoted nucleation and the retarded growth. However, the retardation of bainite growth increases more quickly with strain, whereas the promotion effect by nucleation increases slowly. When the ratio of the promoted factor to the negative factor reaches the maximum, the amount of bainite also reaches the maximum. The volume fraction of retained austenite increases with a lower ausforming temperature, which manifests that the stability of residual austenite is enhanced at a lower ausforming temperature. In addition, a critical strain corresponding to a certain ausforming temperature exists, depleting the previously increased bainite amount to the same degree as the undeformed austenite.

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Effects of ausforming temperature on bainite transformation, microstructure and variant selection in nanobainite steel

Cited by 182 publications

References 38 publications

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

Monitoring of Bainite Transformation Using in Situ Neutron Scattering

Effects of Strain and Deformation Temperature on Bainitic Transformation in a Fe-C-Mn-Si Alloy

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