Determination of the Critical Strains for the Initiation of Dynamic Transformation and Dynamic Recrystallization in Four Steels of Increasing Carbon Contents

Ghosh, Chiradeep; Basabe, Vladimir V.; Jonas, John J.

doi:10.1002/srin.201200188

Cited by 45 publications

(39 citation statements)

References 21 publications

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“…As ferrite is softer than austenite at a given temperature, the formation of strain-induced ferrite from work hardened austenite reduces the flow stress of the specimen. As mentioned earlier, the critical strain for dynamic transformation determined by the double differentiation method is about 0.20, 31) which is almost always less than the critical strain for dynamic recrystallization (DRX), the second softening mechanism.…”

Section: Stress-strain Curvesmentioning

confidence: 84%

“…From Ref. 31), it is clear that the critical strain for DT to occur in this particular steel is about 0.20, below which no appreciable phase transformation takes place (see inset). The rate of transformation is highest in the strain interval from 0.6 to 2.0 and decreases with temperature.…”

Section: Effect Of Strain On Phase Proportionsmentioning

confidence: 85%

“…31) and found to be in the range 0.35-0.45. The initiation of DT does not, however, lead to the immediate presence of a stress peak, i.e.…”

Section: Stress-strain Curvesmentioning

confidence: 99%

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Dynamic Transformation Behavior of a Deformed High Carbon Steel at Temperatures Above the Ae3

et al. 2013

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The dynamic transformation behavior of deformed austenite was studied in a 0.79%C high carbon steel over the temperature range 743-823°C. The experiments were carried out in torsion under an atmosphere of argon and 5% H2. All these temperatures are above the orthoequilibrium Ae3 temperature of the steel. Strains of 0.25-4 were applied at a strain rate of 4 s -1 . The experimental parameters were varied in order to determine the effects of strain and temperature on the formation of strain-induced ferrite and cementite. The critical strain for dynamic transformation was about 0.20. The volume fractions of the transformed phases increased with strain and decreased with temperature. The observed ferrite structures are Widmanstätten in nature and appear to have formed displacively. The carbon diffusion times required for formation of the observed spheroidal cementite particles were calculated; these are consistent with the occurrence of interstitial diffusion during deformation. Similar calculations indicate that substitutional diffusion does not play a role during dynamic transformation.

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Section: Stress-strain Curvesmentioning

confidence: 84%

Section: Effect Of Strain On Phase Proportionsmentioning

confidence: 85%

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Dynamic Transformation Behavior of a Deformed High Carbon Steel at Temperatures Above the Ae3

et al. 2013

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“…19,20) As in the case of steel 1, the nucleation of DT ferrite took place at both austenite grain boundaries and within the grains. At a strain of 0.4, both Widmanstätten plates and polygonal grains were present (see Figs.…”

Section: Steelmentioning

confidence: 94%

“…The critical strain for the formation of DT ferrite in the 0.06% C steel was 0.08, as determined by the double differentiation method. 19,20) A typical optical microstructure of a sample deformed to a strain of ε = 0.2 is illustrated in Fig. 2.…”

Section: Steelmentioning

confidence: 99%

Formation of Strain-induced Ferrite in Low Carbon Steels at Temperatures Above the Ae3

2013

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The formation of strain-induced ferrite was investigated in two low carbon steels and in a 0.036% Nb microalloyed low carbon steel at temperatures above the Ae3. Two distinct stages were observed, the first of which was characterized by the formation of Widmanstätten colonies with very fine plates of similar orientation. In the second stage, observed after further straining, the initial plates coalesced into polygonal ferrite grains. The transition from stage I to stage II was retarded by additions of carbon and niobium and slightly by an increase in strain rate. EBSD analysis revealed that the small misorientations (<1.5°) between Widmanstätten plates allow them to coalesce into grains. The 60° misorientations between some of the colonies suggest that they form from twinned regions of the parent austenite. A common characteristic of the polygonal grains is the presence of planar high angle boundaries, a feature inherited from the original Widmanstätten microstructure.

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Dynamic Transformation Mechanism for Producing Ultrafine Grained Steels

et al. 2018

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Ultrafine grained (UFG) steels with grain sizes around 1 micron exhibit an excellent strength‐ductility combination and have been extensively studied worldwide. Among the different grain refinement strategies, thermomechanical controlled processing (TMCP) employing dynamic transformation (DT), that is, ferrite transformation during deformation of austenite, is considered as the simplest and commercially exploitable approach to produce ultrafine ferrite (UFF) with grain size of a couple of microns or below. The present paper reviews the research history of DT and highlights the major aspects of continuous interest including the methods and evidences for identifying DT, thermodynamics and kinetics of DT, mechanism for UFF formation and the effects of some key thermomechanical parameters on DT (and UFF formation), together with an outlook for the future research, and new TMCP design for industrial application. This paper also discusses some areas remaining under debate such as the diffusional or displacive mechanism, thermodynamic modeling, and the mechanism for UFF formation, etc.

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Determination of the Critical Strains for the Initiation of Dynamic Transformation and Dynamic Recrystallization in Four Steels of Increasing Carbon Contents

Cited by 45 publications

References 21 publications

Dynamic Transformation Behavior of a Deformed High Carbon Steel at Temperatures Above the Ae3

Dynamic Transformation Behavior of a Deformed High Carbon Steel at Temperatures Above the Ae3

Formation of Strain-induced Ferrite in Low Carbon Steels at Temperatures Above the Ae3

Dynamic Transformation Mechanism for Producing Ultrafine Grained Steels

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