Formation of Widmanstätten ferrite at very high temperatures in the austenite phase field

Grewal, Rupanjit; Aranas, Clodualdo; Chadha, Kanwal; Shahriari, D.; Jahazi, Mohammad; Jonas, John J.

doi:10.1016/j.actamat.2016.02.062

Cited by 53 publications

(65 citation statements)

References 27 publications

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“…Under these conditions, an equivalent strain of one is again consistent with the experimental data, as shown below for the present steel, as well as for the other steels that have been examined to date [7]. C. Aranas Jr. et al: A metastable phase diagram for the dynamic transformation of austenite above the Ae 3 [3]. This was calculated using the FSstel database of the FactSage thermodynamic software [11].…”

Section: The Driving Force For Dynamic Transformationsupporting

confidence: 63%

“…It was shown in earlier work [3] that dynamic transformation can be initiated up to 480 8C above the paraequilibrium C. Aranas Jr. et al: A metastable phase diagram for the dynamic transformation of austenite above the Ae 3 The total accommodation work represented by the sum of Fig. 5a and b plotted against temperature.…”

Section: Metastable Fe-c Binary Phase Diagrammentioning

confidence: 99%

“…More recently, this temperature range has been extended to 1 350 8C, i. e. to 480 8C above the paraequilibrium Ae 3 [3,4]. The observation that Widmanstätten ferrite [4 -7] can be formed throughout the austenite phase field indicates that the conventional Fe-C phase diagram does not apply when austenite is being deformed.…”

Section: Introductionmentioning

confidence: 99%

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A metastable phase diagram for the dynamic transformation of austenite at temperatures above the Ae₃

Aranas

Jung

Yue

et al. 2016

International Journal of Materials Research

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A metastable phase diagram for the dynamic transformation of austenite at temperatures above the Ae 3 A method is proposed for calculation of the pseudobinary phase diagram associated with the dynamic transformation of austenite to ferrite. Here the driving force is taken as the difference between the austenite flow stress at the moment of initiation and the yield stress of the fresh Widmanstätten ferrite that takes its place. The energy opposing the transformation consists of the Gibbs energy difference between austenite and ferrite at temperatures above the Ae 3 and the work of accommodating the shear displacements and dilatation associated with the phase change. A metastable phase diagram is calculated for a 0.30 wt.% Mn-0.01 wt.% Si steel by balancing the driving force against the three obstacles. The results show that, under dynamic conditions, the ferrite phase field extends all the way from room temperature to that for the formation of delta ferrite.Keywords: Dynamic transformation; Austenite; Ferrite; Fe-C phase diagrams; Thermomechanical processing IntroductionIn the early work on dynamic transformation (DT), it was shown that DT takes place at temperatures up to 166 8C above the Ae 3 [1, 2]. More recently, this temperature range has been extended to 1 350 8C, i. e. to 480 8C above the paraequilibrium Ae 3 [3,4]. The observation that Widmanstätten ferrite [4 -7] can be formed throughout the austenite phase field indicates that the conventional Fe-C phase diagram does not apply when austenite is being deformed. It is the aim of this paper to propose an approach for the derivation of phase diagrams that applies to 'dynamic' conditions and to provide an example of such a diagram for a particular steel.In order to deal with the effect of deformation on the phases present, three quantities must be evaluated that play particularly important roles, the first of which is totally absent under conventional 'static' conditions. In the latter case, the driving force is the free energy difference between the original and the replacement phase, the latter being of lower energy. In the dynamic case, however, the free energy difference is of opposite sign, so that it becomes a barrier to the transformation instead. Under these conditions, it is the flow stress difference between the work hardened austenite and the much softer ferrite that replaces it that provides the driving force [8,9].The other quantities are the work of dilatation and of shear accommodation [10]. Unlike the situation at ambient temperatures, at which these energies are stored elastically, the high temperature versions are not stored reversibly, but involve dissipation by means of plastic work. It is shown below how these three quantities can be evaluated over the experimental temperature range and expressed algebraically. These expressions can then be introduced into the Fe-C database of the FactSage thermodynamic software [11]. A metastable phase diagram is in turn generated employing the modified database and valid over the temperature range an...

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Section: The Driving Force For Dynamic Transformationsupporting

confidence: 63%

Section: Metastable Fe-c Binary Phase Diagrammentioning

confidence: 99%

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A metastable phase diagram for the dynamic transformation of austenite at temperatures above the Ae₃

Aranas

Jung

Yue

et al. 2016

International Journal of Materials Research

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“…[1][2][3][4][5][6][7] This has been shown to occur throughout the austenite phase field. 8,9) In earlier publications, the present authors have reported that the amounts of ferrite formed per pass increase with decreasing temperature. 9,10) Subsequently, the metastable ferrite tends to retransform to austenite to an extent that increases with the length of the interpass interval.…”

Section: Introductionmentioning

confidence: 94%

Retransformation Behavior of Dynamically Transformed Ferrite during the Simulated Plate Rolling of a Low C and an X70 Nb Steel

2017

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Plate rolling simulations were carried out on an X70 Nb and a low C steel by means of torsion testing. A seven-pass rolling schedule was employed where the last pass was always applied above the respective Ae 3 temperature of the steel. Interpass intervals of 10 and 30 s were employed, which corresponded to cooling rates of 1.5 and 0.5 C/s. The mean flow stresses (MFS`s) applicable to each schedule increased less rapidly than expected from the decreases in temperature due to the dynamic transformation (DT) that took place during straining. The amounts of ferrite that retransformed into austenite during holding were determined by optical metallography. These increased with length of the interpass intervals and were reduced in the X70 steel due to the presence of Nb. The holding times after rolling required to increase the amount of austenite available for microstructure control on subsequent cooling were also determined for the two steels.

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“…3) More recently Basabe et al, 4) conducted torsion tests on a 0.036% Nb microalloyed steel and reported that both the forward and the reverse transformation were retarded by the addition of niobium. In some follow-up experiments, Grewal et al 5) showed that ferrite can be formed everywhere within the austenite phase field.…”

Section: Introductionmentioning

confidence: 99%

Dynamic Transformation of an X70 Steel under Plate Rolling Conditions

et al. 2017

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Formation of Widmanstätten ferrite at very high temperatures in the austenite phase field

Cited by 53 publications

References 27 publications

A metastable phase diagram for the dynamic transformation of austenite at temperatures above the Ae₃

A metastable phase diagram for the dynamic transformation of austenite at temperatures above the Ae₃

Retransformation Behavior of Dynamically Transformed Ferrite during the Simulated Plate Rolling of a Low C and an X70 Nb Steel

Dynamic Transformation of an X70 Steel under Plate Rolling Conditions

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Formation of Widmanstätten ferrite at very high temperatures in the austenite phase field

Cited by 53 publications

References 27 publications

A metastable phase diagram for the dynamic transformation of austenite at temperatures above the Ae3

A metastable phase diagram for the dynamic transformation of austenite at temperatures above the Ae3

Retransformation Behavior of Dynamically Transformed Ferrite during the Simulated Plate Rolling of a Low C and an X70 Nb Steel

Dynamic Transformation of an X70 Steel under Plate Rolling Conditions

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A metastable phase diagram for the dynamic transformation of austenite at temperatures above the Ae₃

A metastable phase diagram for the dynamic transformation of austenite at temperatures above the Ae₃