Kinetics of austenite transformation during thermomechanical processes

Khlestov, V. M.; Konopleva, E. V.; McQueen, H.J.

doi:10.1016/s0008-4433(97)00030-x

Cited by 25 publications

(9 citation statements)

References 11 publications

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“…pseudo eutectoid transformation occurs 7. The influence of the high temperature deformation on perlitic transformation in isothermal process or continuous cooling process is the same as it on ferritic transformation, which speeds up the dynamic process of the transformation 15. For the steel whose carbon content is 0.77% or similar with this value, the deformation increases the nucleation sites, that is to say, the nucleation rate is improved, and perlitic transformation is stimulated in turn.…”

Section: Discussionmentioning

confidence: 95%

Effect of Deformation on Continuous Cooling Phase Transformation Behaviors of 780 MPa Nb‐Ti Ultra‐High Strength Steel

Wang

Xie

et al. 2011

steel research int.

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For the purpose of achieving the reasonable rolling technology of 780 MPa hot‐rolled Nb‐Ti combined ultra‐high strength steel, the effect of deformation and microalloy elements Nb and Ti on phase transformation behaviors was investigated by thermal simulation experiment. The results indicated: the deformation promoted ferritic transformation; due to the carbon content of the experimental steel was lower (<0.12% wt), the deformation indirectly impacted perlitic transformation through promoting ferritic transformation; the effect of the deformation on bainitic transformation was subject to condition whether proeutectoid ferrite precipitated before bainitic transformation. At low cooling rate of 0.5 °C/s, Nb and Ti promote transformation process γ → α, but that not good for refining the ferrite grain; at high cooling rate of 25 °C/s, Nb and Ti to a certain extent promote bainitic transformation. The recrystallization stop temperature of experimental steel was greater than 1000 °C, and phase transformation point Ar3 was 764 °C. In order to obtain the fully bainite microstructure in the practical rolling process, the cooling rate should be controlled above 15 °C/s, the start finish rolling temperature between 950–980 °C, the finishing temperature between 830–850 °C, the coiling temperature between 450–550 °C.

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Section: Discussionmentioning

confidence: 95%

Effect of Deformation on Continuous Cooling Phase Transformation Behaviors of 780 MPa Nb‐Ti Ultra‐High Strength Steel

Wang

Xie

et al. 2011

steel research int.

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“…This effect of controlled rolling can play both a positive and a negative role. If steel of the ferrite-pearlite class such as 09Mn2VNb is rolled, the effect should be positive, 1 Effect of deformation on the CCT diagram of 09Mn2VNb steel: 1, after heating at 920uC for 10 min and furnace cooling to 820uC; 2, after heating at 920uC for 10 min and furnace cooling to 740uC with soaking 30 s; 3, after heating at 1150uC for 30 min, furnace cooling to 1000uC, rolling by a 35% reduction in two passes, cooling at 0 . 5 K s 21 to 740uC and rolling at the same temperature in three passes by a 53% reduction; cooling rates: 0 .…”

Section: Resultsmentioning

confidence: 99%

“…[1][2][3][4][5][6] The most significant feature of the phenomenon is the great increase in initial nucleation rates associated with very fine nuclei that are generated through the activation of the elongated austenite boundaries by dense dislocation walls. 7 The effect appears to be relatively independent of the metallic alloying content, being maximum at 0 .…”

Section: Introductionmentioning

confidence: 99%

“…2%C at a level one-fifth the peak value of 4-5 times after 40% reduction at the nose of the pearlite transformation. 1 The objective of the present study is to understand the transformation rates after rolling in the intercritical range to 50-55% ferrite. The remaining austenite has a higher carbon content than the original homogeneous one but also has a much higher density of substructure owing to the reduced temperature compared with rolled stable austenite.…”

Section: Introductionmentioning

confidence: 99%

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Transformation of austenite remaining after intercritical rolling to ferrite

Khlestov¹,

Konopleva²,

McQueen³

2006

Materials Science and Technology

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The impact of austenite deformation in the intercritical range on the rate of transformation in continuous cooling to ferrite, pearlite, bainite or martensite has been studied. The austenite associated with the rolled ferrite is much higher in carbon content, which does not influence the pearlite transformation but retards bainite and martensite. Furthermore, in comparison with rolling of stable austenite the increased strain hardening of the intercritically cooled austenite accelerates the formation of ferrite and pearlite (z10-30uC) and refines them but retards the bainite and martensite transformations (220-40uC). At the intermediate cooling rate near 16 K s 21 , these several influences combined with near doubling of the ferrite production give rise to the suppression of bainite formation and to maximum increased delay of martensite start.

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“…Indeed, it is well known that carbon is the only alloying element which decreases substantially the activation energy for both dynamic (DRX) and static (SRX) recrystallization. As pointed out by Khlestov et al, [19] the deformation is often not homogenous and the strain level can be higher at the grain boundaries, which favors locally the nucleation process. Consequently, DRX takes places by nucleation of new grains at the grain boundaries which grow progressively into the deformed matrix and can be classified as discontinuous dynamic recrystallization (dDRX).…”

Section: Hot Rolling Behavior and Strain Induced Transformationmentioning

confidence: 95%

Strain‐Induced Development of Very Fine Ferrite‐Cementite Structures in Eutectoid Steels

Caruso

Godet

2012

Adv Eng Mater

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The development of duplex microstructures consisting of very fine ferrite grains and spheroidized cementite particles during concurrent hot deformation has been investigated by hot torsion in a eutectoid steel. It is shown that the hot deformation of the undercooled austenite at temperatures close to Ar1 induces and accelerates significantly the γ‐to‐pearlite transformation. Further deformation of the transforming pearlite does not lead only to the instantaneous spheroidization of the cementite lamellae but also refines the ferrite orientations units from 15 to 3 µm. Microstructures consisting of very fine ferrite grains (3 µm) and submicron cementite particles are produced at strain levels larger than ε = 1.5. The initial grains undergo progressive fragmentation by the generation of low angle boundaries (LABs) by dynamic recovery that progressively transform into high angle boundaries (HABs). The progressive increase of LABs misorientation is attributed to the presence of cementite particles and is referred to as continuous dynamic recrystallization (cDRX). Fine prior austenite grain size and moderate strain rates are found to promote the occurrence of cDRX. The resulting torsion textures consist of a strong 〈111〉 fiber dominated by the D {112} 〈111〉 component. During the subsequent annealing step, cementite particles coarsen preferentially at the triple junctions whereas the very fine ferrite grain are stable due to the strong pinning effect exerted by the cementite particles.

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Kinetics of austenite transformation during thermomechanical processes

Cited by 25 publications

References 11 publications

Effect of Deformation on Continuous Cooling Phase Transformation Behaviors of 780 MPa Nb‐Ti Ultra‐High Strength Steel

Effect of Deformation on Continuous Cooling Phase Transformation Behaviors of 780 MPa Nb‐Ti Ultra‐High Strength Steel

Transformation of austenite remaining after intercritical rolling to ferrite

Strain‐Induced Development of Very Fine Ferrite‐Cementite Structures in Eutectoid Steels

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