A New Physical Model for the Kinetics of the Bainite Transformation

Gaude-Fugarolas, Daniel; Jacques, Pascal

doi:10.2355/isijinternational.46.712

Cited by 36 publications

(24 citation statements)

References 30 publications

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“…These observations are in agreement with the results obtained elsewhere. [6][7][8][9][10][11][12][13][14][15][16][17][18] The lower the austempering temperature, the lower the ferrite free energy relative to that of the austenite. Therefore, the X T0 concentration (Figure 9) increases.…”

Section: B Analysis Of the Resultsmentioning

confidence: 99%

“…The hc-c does not transform to martensite after rapid cooling because the martensite start temperature (M S ) at high carbon content decreases to low values, even below room temperature, [12] as shown schematically in Figure 10. The austenite to ferrite transformation occurs as a displacive transformation, [13][14][15][16][17][18] which results in the formation of carbon supersaturated ferrite needles, followed by carbon diffusion from the ferrite needles into the surrounding austenite. This results in an increase in the carbon content in the austenite.…”

Section: A the C Fi A Transformation Characteristicsmentioning

confidence: 99%

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Influence of Copper Addition and Temperature on the Kinetics of Austempering in Ductile Iron

Amran

Katsman

Schaaf

et al. 2010

Metall Mater Trans B

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Austempered ductile iron (ADI) is a material that exhibits excellent mechanical properties because of its special microstructure, combining ferrite and austenite supersaturated with carbon. Two ADI alloys, Fe-3.5 pct C-2.5 pct Si and Fe-3.6 pct C-2.7 pct Si-0.7 pct Cu, austempered for various times at 623 K (350°C) and 673 K (400°C) followed by water quenching, were investigated. The first ferrite needles nucleate mainly at the graphite/austenite interface. The austenite and ferrite weight fractions increase with the austempering time until stabilization is reached. The increase in the lattice parameter of the austenite during austempering corresponds to an increase of carbon content in the austenite. The increase in the ferrite weight fraction is associated with a decrease in microhardness. As the austempering temperature increases, the ferrite weight fraction decreases, the high carbon austenite weight fraction increases, but the carbon content in the latter decreases. Copper addition increases the high carbon austenite weight fraction. The results are discussed based on the phases composing the Fe-2Si-C system.

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Section: B Analysis Of the Resultsmentioning

confidence: 99%

Section: A the C Fi A Transformation Characteristicsmentioning

confidence: 99%

Influence of Copper Addition and Temperature on the Kinetics of Austempering in Ductile Iron

Amran

Katsman

Schaaf

et al. 2010

Metall Mater Trans B

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“…Different steels require different coefficients in Eq. (1), whereas, the driving force is proportional to the IBT temperature [12,45,46]. With a decrease in IBT temperature, the critical driving force decreases.…”

mentioning

confidence: 99%

Microstructure and mechanical properties of strip cast TRIP steel subjected to thermo-mechanical simulation

Xiong

Kostryzhev

Liang

et al. 2016

Materials Science and Engineering: A

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Instead of hot rolling and cold rolling followed by annealing, strip casting is a more economic and environmentally friendly way to produce transformation-induced plasticity (TRIP) steels. According to industrial practice of strip casting, rapid cooling in this work was achieved using a dip tester, and a Gleeble 3500 thermo-mechanical simulator was used to carry out the processing route. A typical microstructure of TRIP steels, which included ~0.55 fraction of polygonal ferrite with bainite, retained austenite and martensite, was obtained. The effects of deformation (0.41 reduction) above non-recrystallisation temperature, isothermal bainite transformation temperature and the size of second phase region on microstructure and mechanical properties were studied. The steel isothermally transformed at 400 °C had the best combination of ultimate tensile strength (UTS) and total elongation (TE), whether deformation was applied or not. The deformation resulted in the improvement of mechanical properties after holding at 400 °C: the UTS increased from 590 to 696 MPa and TE decreased from 0.27 only to 0.26. It was predominantly ascribed to grain size refinement and dislocation strengthening. The studied TRIP steel had comparable mechanical properties with TRIP 690 produced commercially. Abstract: Instead of hot rolling and cold rolling followed by annealing, strip casting is a more economic and environmentally friendly way to produce transformation-induced plasticity (TRIP) steels. According to industrial practice of strip casting, rapid cooling in this work was achieved using a dip tester, and a Gleeble 3500 thermo-mechanical simulator was used to carry out the processing route. A typical microstructure of TRIP steels, which included ~ 0.55 fraction of polygonal ferrite with bainite, retained austenite and martensite, was obtained. The effects of deformation (0.41 reduction) above non-recrystallisation temperature, isothermal bainite transformation temperature and the size of second phase region on microstructure and mechanical properties were studied. The steel isothermally transformed at 400 °C had the best combination of ultimate tensile strength (UTS) and total elongation (TE), whether deformation was applied or not. The deformation resulted in the improvement of mechanical properties after holding at 400 °C: the UTS increased from 590 to 696 MPa and TE decreased from 0.27 only to 0.26. It was predominantly ascribed to grain size refinement and dislocation strengthening. The studied TRIP steel had comparable mechanical properties with TRIP 690 produced commercially.

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“…Although not explicitly stated, a pivotal e ect of the strain, which favors the autocatalytic nucleation at the tip of the subunit, is acknowledged and even implemented in some of these works [20,17]. In the present analysis, these energetically favored spots for the autocatalytic events are quantitatively described.…”

Section: Other Frameworkmentioning

confidence: 90%

“…(6), di erent activation energies, Q GB and Q A , are correspondingly adopted for grain boundary and α γ-interface nucleation. Moreover, the interaction between the di erent activation energies, particularly during the autocatalytic nucleation, is implicitly considered in this formulation [17]. In Eqn.…”

Section: Generalized Framework For the Estimation Of The Transformatimentioning

confidence: 99%

Influence of stress-free transformation strain on the autocatalytic growth of bainite: A multiphase-field analysis

et al. 2020

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Analytical treatments, formulated to predict the rate of the bainite transformation, de ne autocatalysis as the growth of the subunits at the bainite-austenite interface. Furthermore, the role of the stress-free transformation strain is o en translated to a thermodynamic criterion that needs to be ful lled for the growth of the subunits. In the present work, an elastic phase-eld model, which elegantly recovers the sharp-interface relations, is employed to comprehensively explicate the e ect of the elastic energy on the evolution of the subunits. e primary nding of the current analysis is that the role of eigenstrains in the bainite transformation is apparently complicated to be directly quanti ed as the thermodynamic constraint. It is realized that the inhomogeneous stress state, induced by the growth of the primary subunit, renders a spatially dependent ill-and well-favored condition for the growth of the secondary subunits. A favorability contour, which encloses the sections that facilitate the elastically preferred growth, is postulated based on the elastic interaction. rough the numerical analyses, the enhanced growth of the subunits within the favorability-contour is veri ed. Current investigations show that the morphology and size of the elastically preferred region respectively changes and increases with the progressive growth of the subunits.

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A New Physical Model for the Kinetics of the Bainite Transformation

Cited by 36 publications

References 30 publications

Influence of Copper Addition and Temperature on the Kinetics of Austempering in Ductile Iron

Influence of Copper Addition and Temperature on the Kinetics of Austempering in Ductile Iron

Microstructure and mechanical properties of strip cast TRIP steel subjected to thermo-mechanical simulation

Influence of stress-free transformation strain on the autocatalytic growth of bainite: A multiphase-field analysis

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