Influence of rolling of TRIP steel in the intercritical region on the stability of retained austenite

Basuki, Arif; Aernoudt, Etienne

doi:10.1016/s0924-0136(99)00037-0

Cited by 75 publications

(54 citation statements)

References 14 publications

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“…Bhadeshia and Singh's theory 2-4) seems clearly not convincing unless it is assumed that no bainite can form in the highly deformed area. Basuki and Aernoudt 6,7) suggested that deformation bands formed during the simulated intercritical rolling divided the austenite grains into several parts, which suppressed the bainite growth since bainite is only allowed to grow within austenite. But they seemed to lack the clear experimental proof for deformation bands.…”

Section: Mechanism For Influence Of Intercritical Deformation On Bainmentioning

confidence: 99%

“…deformation performed in the austenite plus ferrite dual phase region, has been done. Basuki and Aernoudt 6,7) found that intercritical rolling results in an acceleration of ferrite formation and suppression of bainite formation, and refined the retained austenite grains. They suggested that deformation bands, formed during the deformation, divided the austenite grains and effectively refined the retained austenite grains.…”

Section: Introductionmentioning

confidence: 99%

“…Contrastively, such etching can reveal ferrite as light gray, bainite/martensite as black and retained austenite (if preserved) as white. 6,7) In addition, nital and saturated picric acid were also used to reveal the prior austenite grain boundaries and ferrite subgrain boundaries. Image analysis software of Leica was used to quantify the volume fractions of ferrite in the quenched specimens and austenite grain sizes achieved from the solution at 950 and 1 100°C.…”

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confidence: 99%

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Effect of Intercritical Deformation on Bainite Formation in Al-containing TRIP Steel

Luo¹,

Zhao²,

Kruijver³

et al. 2003

ISIJ International

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The Influence of intercritical deformation, cooling rate and prior austenite grain size on bainite formation were investigated by dilatometry tests. Intercritical deformation (0-40 %) performed in steels with a prior austenite grain size of 15-28 mm leads to formation of more ferrite during the cooling and less bainite during the subsequent isothermal stage, and even almost no bainite is formed after 40 % strain. Fast cooling after deformation can suppress ferrite transformation. Relaxation following deformation can significantly, but not completely, reduce such effect of deformation due to the occurrence of recovery and recrystallization, particularly for the finer prior austenite grain size. When the prior austenite grain size was changed from 26.8 to 16.8 mm, bainite formation was suppressed. The mechanism for influence of deformation on bainite formation was discussed on the basis that deformation could refine the austenitic microstructure. Further, it is suggested that there is a critical size of austenite grains or subunits after deformation for the formation of bainite.KEY WORDS: TRIP steels; bainite formation; intercritical deformation; austenite grain size; cooling rate; relaxation.by relaxation for either 0 or 60 s; next, cooled to the bainitic stage (400°C) at 20 or 50°C/s and held for 10 min. Finally, they were quenched to room temperature by helium gas.The quenched samples were cut through cross-sections in the middle of deformed samples, and polished as normal, then etched with 5 % nital and rinsed with water followed by etching in a 10 % sodium metabisulphite solution. This etching is intended to better distinguish between upper bainite and ferrite for quantification of phase fractions because both of them will appear as a light color under the optical microscope after nital etching. Contrastively, such etching can reveal ferrite as light gray, bainite/martensite as black and retained austenite (if preserved) as white. 6,7) In addition, nital and saturated picric acid were also used to reveal the prior austenite grain boundaries and ferrite subgrain boundaries. Image analysis software of Leica was used to quantify the volume fractions of ferrite in the quenched specimens and austenite grain sizes achieved from the solution at 950 and 1 100°C. There are three points in the process at which austenite fractions is determined to follow transformations taking place during the whole process, as shown in Fig. 1. Intercritical austenite fraction before the deformation, i.e. f v 1 g , is derived from the optical measurement of the ferrite fractions of interruptedly quenched samples. Similarly, the austenite fraction before bainite formation, i.e. f v 2 g in Fig.1, is also calculated from the measurements on the ferrite fractions of samples after the whole processing. The remained austenite fraction just after bainite formation, i.e. f v 3 g , is calculated from the dilation signals which will be discussed later. X-ray diffractometry is used to measure the quantity of retained austenite in some quenched spe...

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Section: Mechanism For Influence Of Intercritical Deformation On Bainmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Effect of Intercritical Deformation on Bainite Formation in Al-containing TRIP Steel

Luo¹,

Zhao²,

Kruijver³

et al. 2003

ISIJ International

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“…[2][3][4] The demand for ultra-high-strength steels can be satisfied when a soft ferritic matrix is replaced by harder bainite. Hence, a growing importance of the AHSSs containing increased bainite amounts can be observed in [4][5][6][7][8][9] . The desired ductility can be only obtained in advanced carbide-free bainitic steels, achieved with Si, Al, or Si-Al alloying.…”

Section: Introductionmentioning

confidence: 99%

“…5,6,10,14 However, there are only few reports on the microstructure-property relationships in hot-rolled medium-C, carbide-free bainitic steels. 4,7 It is known that thermomechanical processing requires a detailed time-temperature regime during a sheet's cooling. 13,15 It is especially important for multiphase steels because austenite retention requires one or two isothermal holding steps upon cooling.…”

Section: Introductionmentioning

confidence: 99%

Microstructure evolution of advanced high-strength TRIP-aided bainitic steel

Grajcar¹

2015

Mater. Tehnol.

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The present work is focused on monitoring the microstructure evolution of the thermomechanically rolled medium-C steel containing Si and Al to prevent the precipitation of carbides. The initial microstructure consists of carbide-free bainite, polygonal ferrite and blocky-type and interlath retained austenite. To monitor the transformation behaviour of the retained austenite transforming into strain-induced martensite, tensile tests were interrupted at particular strains (5 %, 10 %, 15 %, 18.4 %). The amount of the retained austenite determined with XRD and EBSD techniques decreased from 17 % to 6.8 % upon straining, which was related to the transformation-induced plasticity effect. The identification of the retained austenite and strain-induced martensite was carried out using an electron scanning microscope equipped with EBSD (electron backscatter diffraction). It was found that sheet samples are strongly strengthened by the transformation of the blocky retained austenite, whereas the layers and films of the g phase are over-stabilized and they do not transform into martensite. Keywords: AHSS, bainitic steel, retained austenite, thermomechanical treatment, TRIP effect, strain-induced martensite Delo obravnava pregled razvoja mikrostrukture pri termomehanskem valjanju srednje oglji~nega jekla s Si in Al, ki prepre~ita izlo~anje karbidov. Za~etna mikrostruktura je bila iz bainita brez karbidov, poligonalnega ferita ter zaostalega avstenita kockaste oblike in zaostalega avstenita med lamelami. Za spremljanje vedenja zaostalega avstenita pri pretvorbi v deformacijsko induciran martenzit so bili natezni preizkusi prekinjeni pri posameznih raztezkih (5 %, 10 %, 15 %, 18,4 %). Dele`zaostalega avstenita, dolo~en z XRD in EBSD, se je zmanj{al po natezni deformaciji iz 17 % na 6,8 %, kar je posledica vpliva z deformacijo povzro~ene pretvorbe na plasti~nost. Identifikacija zaostalega avstenita in napetostno induciranega martenzita je bila izvr{ena z vrsti~nim elektronskim mikroskopom, opremljenim z EBSD (difrakcija odbitih elektronov). Ugotovljeno je, da se vzorci plo~evine bolj utrjujejo s pretvorbo kockastega zaostalega avstenita, medtem ko so plasti in sloji g-faze bolj stabilizirani in se ne pretvorijo v martenzit.

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A Micromechanical Study of the Deformation Behavior of TRIP‐Assisted Multiphase Steels as a Function of the Microstructural Parameters of the Retained Austenite

et al. 2009

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Steels assisted by transformation-induced plasticity (TRIP steels) are a class of multiphase carbon steels that have interesting mechanical characteristics due to the presence of metastable grains of austenite in their microstructure at room temperature (retained austenite). Upon application of thermal and/or mechanical loading, the grains of retained austenite may transform into martensite, which strongly influences the overall mechanical performance of the steels. Consequently, the stability of retained austenite against transformation is considered to be an important factor in the mechanical performance of this class of steels. Experimental investigations show that the stability of retained austenite is influenced by various microstructural parameters, such as the initial phase volume fractions (phase morphology), [1][2][3] the austenite carbon concentration [1,[4][5][6][7] and the austenitic grain size. [8][9][10] However, in most cases it is difficult to directly measure the individual contributions of these parameters to the stability of retained austenite since, during the processing of experimental samples, microstructural parameters typically cannot be varied independently.In the present work, the overall mechanical behavior of a discrete aggregate of ferritic and austenitic grains, representative of a microstructure of TRIP-assisted steels, is simulated numerically. The goal is to elucidate by means of a parametric study the specific effect of each microstructural parameter on the effective mechanical response, i.e., the effective stressstrain response and the evolution of martensitic transformation. Previous work by the authors was concerned with analyzing the influence of the initial phase volume fractions and carbon concentration [11] and grain size [12] for multiphase TRIP steels with high-yield austenitic phases (which do not deform plastically prior to transformation). In the present analysis, employing the constitutive model presented in Tjahjanto et al., [13] the influence of possible plastic deformations in austenite prior to transformation is taken into account.The results provide important information for further development of the mechanical performance of TRIP steels as well as for the optimization of TRIP steel processing routes. Micromechanical Models, Sample Geometries, and Boundary ConditionsThe type of multiphase steels considered in the present analysis consist of isolated grains of retained austenite embedded in a ferritic matrix. For simplicity, the behavior of the bainitic phase is combined with the effective behavior of the matrix. The constitutive model presented in Tjahjanto et al. [13] is applied to simulate the elastic, plastic, and transformation mechanisms in the austenitic grains and the elasto-plastic response of the ferritic matrix. This model combines the transformation model of Turteltaub and Suiker [14][15][16] [used to simulate the transformation of facecentered cubic (FCC) austenite into body-centered tetragonal (BCT) martensite] with a crystal plasticity model (used...

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Influence of rolling of TRIP steel in the intercritical region on the stability of retained austenite

Cited by 75 publications

References 14 publications

Effect of Intercritical Deformation on Bainite Formation in Al-containing TRIP Steel

Effect of Intercritical Deformation on Bainite Formation in Al-containing TRIP Steel

Microstructure evolution of advanced high-strength TRIP-aided bainitic steel

A Micromechanical Study of the Deformation Behavior of TRIP‐Assisted Multiphase Steels as a Function of the Microstructural Parameters of the Retained Austenite

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