Martensitic transformation of individual grains in low-alloyed TRIP steels

Jimenez-Melero, Enrique; Dijk, Niels van; Zhao, L.; Sietsma, Jilt; Offerman, S.E.; Wright, Jonathan P.; Zwaag, Sybrand van der

doi:10.1016/j.scriptamat.2006.10.041

Cited by 247 publications

(147 citation statements)

References 14 publications

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“…15) This latter conclusion is questionable as these constituents differ strongly in grain size, dislocation density and C content. The authors also report that the austenite transformation is discrete, and that the autocatalytic effect is limited, a conclusion also reported previously by Samek et al 12) Using cryogenic cooling, Jimenez-Melero et al 17,18) made a detailed study of the athermal martensitic transformation of individual retained austenite grains in TRIP steel using high energy 80 keV synchrotron X-rays. The mechanism of martensitic transformation they observed was therefore very much below the M s s temperature, whereas the actual use of TRIP steels is above the M s s temperature.…”

Section: Introductionsupporting

confidence: 62%

Yielding Behavior of Nb Micro-alloyed C–Mn–Si TRIP Steel Studied by In-situ Synchrotron X-ray Diffraction

2010

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The stress and strain partitioning between the different micro-structural constituents, and the initiation of the martensitic transformation during the yielding of multi-phase transformation-induced plasticity steel were studied by in-situ synchrotron X-ray diffraction experiments under tensile tests. Position, intensity and width of retained austenite and ferrite diffraction peaks were used to determine lattice strain and phase fractions. At low tensile stress, small elastic lattice deformations were observed. Whereas the Poisson strains in the ferrite were found to be reduced at the macroscopic yield stress, the strain in the austenite increased. The results clearly show that at the elasto-plastic transition the transformation of some of the retained austenite is stress induced.KEY WORDS: TRIP; TWIP; IF steel; synchrotron radiation; mechanical properties. the presence of low stability austenite, with a larger island size and/or low carbon content, which undergoes stress-induced, rather than strain-induced, transformation. The yield strength of both bainitic ferrite and inter-critical ferrite was reported to be 695 MPa.15) This latter conclusion is questionable as these constituents differ strongly in grain size, dislocation density and C content. The authors also report that the austenite transformation is discrete, and that the autocatalytic effect is limited, a conclusion also reported previously by Samek et al. 12) Using cryogenic cooling, Jimenez-Melero et al. 17,18) made a detailed study of the athermal martensitic transformation of individual retained austenite grains in TRIP steel using high energy 80 keV synchrotron X-rays. The mechanism of martensitic transformation they observed was therefore very much below the M s s temperature, whereas the actual use of TRIP steels is above the M s s temperature. Their results have revealed some important features about the retained austenite. They observed that smaller austenite grains tended to have a higher C content. Very small grains with a volume smaller than 5 mm 3 , i.e. with a grain size of about 2 mm in diameter were found not to transform athermally. They reported the presence of two types of austenite grains, blocky austenite and film-type austenite, confirming an earlier transmission electron microscopy (TEM) observation of Samek et al. 12) In addition, they reported the presence of retained austenite with two distinct carbon contents. Size stabilization of the retained austenite was only observed when the particle volume was less than 15 mm 3 , i.e. with a grain size of 3 mm (f). Otherwise the stabilization by a higher carbon content dominated. They explained the large differences in M s temperature they observed by arguing that there was a distribution in stability from austenite grain to austenite grain.Streicher et al. 19) and Sugimoto et al. 20,21) explained the presence of internal stresses after the unloading of strained TRIP-assisted steel on the basis of strain partitioning between soft ferrite and hard austenite. Their results showed...

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Section: Introductionsupporting

confidence: 62%

Yielding Behavior of Nb Micro-alloyed C–Mn–Si TRIP Steel Studied by In-situ Synchrotron X-ray Diffraction

2010

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“…Therefore, several studies were carried out to reveal the deformation behavior of retained austenite in TRIP steels [7][8][9]. Experimental investigations showed that the austenite stability is affected by: (i) the constraining effect from the phases surrounding the retained austenite [10], (ii) the crystallographic orientation of grains with respect to the loading direction [11], (iii) the local carbon concentration in the austenite [12] and (iv) the grain volume of the retained austenite grains [14]. It has also been observed in these steels that the deformation behavior depends on the morphology of two types of retained austenite grains.…”

Section: Introductionmentioning

confidence: 99%

Deformation-induced austenite grain rotation and transformation in TRIP-assisted steel

et al. 2012

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Uniaxial straining experiments were performed on a rolled and annealed Si-alloyed TRIP (transformation-induced plasticity) steel sheet in order to assess the role of its microstructure on the mechanical stability of austenite grains with respect to martensitic transformation. The transformation behavior of individual metastable austenite grains was studied both at the surface and inside the bulk of the material using electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD) by deforming the samples to different strain levels up to about 20%. A comparison of XRD-and EBSD-results revealed that the retained austenite grains at the surface have a stronger tendency to transform than the austenite grains in the bulk of the material.The deformation-induced changes of individual austenite grains before and after straining were monitored with EBSD. Three different types of austenite grains can be distinguished that have different transformation behaviors: austenite grains at the grain boundaries between ferrite grains, twinned austenite grains, and embedded austenite grains that are completely surrounded by a single ferrite grain. It was found that twinned austenite grains and the austenite grains present at the grain boundaries between larger ferrite grains typically transform first, i.e. are less stable, in contrast to austenite grains that are completely embedded in a larger ferrite grain. In the latter case, straining leads to rotations of the harder austenite grain within the softer ferrite matrix before the austenite transforms into martensite. The analysis suggests that austenite grain rotation behavior is also a significant contributing factor for enhancement of the ductility.

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“…The concept of deformation-induced phase transformation has also been applied to polymers [5], brittle bulk metallic glasses [6] and very recently to titanium-based biomedical alloys [7]. In view of the technological importance there is a strong interest in understanding deformation-induced phase transformations, in particular to assess the role of various microstructural parameters such as the local chemical composition [8], grain size [9], crystal lattice orientation in relation to strain direction [10] and the location of the grain in relation to its surrounding grains [11]. An accurate understanding of all these factors and their interplay will allow fine tuning of phase transformations resulting in an enhanced control over the material properties [12].…”

mentioning

confidence: 99%

“…In the literature several factors affecting the martensitic transformation are given: (1) the local carbon concentration in austenite, [8] (2) the grain size of the austenite grains, [9] (3) the crystallographic orientation of austenite grains with respect to the loading direction, [10] and (4) the position of the austenite grains within the ferrite matrix [11]. The above four factors were also closely assessed for these grains with the help of EBSD and EPMA analysis.…”

mentioning

confidence: 99%

Unravelling the structural and chemical features influencing deformation-induced martensitic transformations in steels

Tirumalasetty¹,

Huis²,

Kwakernaak³

et al. 2014

Scripta Materialia

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Martensitic transformation of individual grains in low-alloyed TRIP steels

Cited by 247 publications

References 14 publications

Yielding Behavior of Nb Micro-alloyed C–Mn–Si TRIP Steel Studied by In-situ Synchrotron X-ray Diffraction

Yielding Behavior of Nb Micro-alloyed C–Mn–Si TRIP Steel Studied by In-situ Synchrotron X-ray Diffraction

Deformation-induced austenite grain rotation and transformation in TRIP-assisted steel

Unravelling the structural and chemical features influencing deformation-induced martensitic transformations in steels

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