On measurement of carbon content in retained austenite in a nanostructured bainitic steel

García‐Mateo, C.; Caballero, Francisca G.; Miller, M.K.; Jiménez, José A.

doi:10.1007/s10853-011-5880-2

Cited by 93 publications

(72 citation statements)

References 35 publications

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“…The chemical compositions were designed based solely on bainitic phase transformation theory 11 and assisted by MUCG83™, a suite of software for modeling of the thermodynamics and kinetics of solid -state transformations in steels 31 . A recent review on the steps followed to design such type of alloys is given elsewhere [32][33][34][35] . Suffice to note that, the amount of Mn and Ni significantly varies in two alloys, as they were designed to have almost identical TTT and Tₒ diagrams 10,11 .…”

Section: Experimental Methodsmentioning

confidence: 99%

Characterisation of microstructure and mechanical properties in two different nanostructured bainitic steels

Avishan¹,

Yazdani²,

Caballero³

et al. 2015

Materials Science and Technology

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Recently, valuable combinations of mechanical properties with strength of 1.9 GPa accompanied by very decent ductility of 19 % and toughness of 31 J, have been achieved in a set of nanostructured bainitic steels. However, it is necessary to elucidate the significance of various microstructural features responsible of that extraordinary mechanical response in more detail.Thus, using two steels, with different Mn, Ni and V contents, and changing the nanostructured bainite isothermal transformation temperatures (200-300 ºC), has led to a plethora of subtle and essential microstructural variations, necessary to explain how the mechanical response of nanostructured bainite is attained.

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Section: Experimental Methodsmentioning

confidence: 99%

Characterisation of microstructure and mechanical properties in two different nanostructured bainitic steels

Avishan¹,

Yazdani²,

Caballero³

et al. 2015

Materials Science and Technology

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“…Intrinsic parameters are the chemical composition and the size/shape of the features. In these bainitic structures, the only alloying element whose content differs from one austenite feature to another is the C. In this sense, nanofilms of austenite are more enriched in C than submicron blocks of austenite [20,26]. This fact, together with the size/shape heterogeneity, results in a distribution of the stability of austenite within one microstructure, the finest austenite features being the most stable [27][28][29][30][31][32].…”

Section: Nanostructured Bainite: Heat-treatments and Microstructurementioning

confidence: 99%

Ductility of Nanostructured Bainite

Morales-Rivas

García‐Mateo

Sourmail³

et al. 2016

Metals

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Nanostructured bainite is a novel ultra-high-strength steel-concept under intensive current research, in which the optimization of its mechanical properties can only come from a clear understanding of the parameters that control its ductility. This work reviews first the nature of this composite-like material as a product of heat treatment conditions. Subsequently, the premises of ductility behavior are presented, taking as a reference related microstructures: conventional bainitic steels, and TRIP-aided steels. The ductility of nanostructured bainite is then discussed in terms of work-hardening and fracture mechanisms, leading to an analysis of the three-fold correlation between ductility, mechanically-induced martensitic transformation, and mechanical partitioning between the phases. Results suggest that a highly stable/hard retained austenite, with mechanical properties close to the matrix of bainitic ferrite, is advantageous in order to enhance ductility.Keywords: nanostructured bainite; ductility; microstructure; mechanical properties Nanostructured Bainite: Heat-Treatments and MicrostructureThere is an increasing interest in nanocrystalline steels because of their unique mechanical properties, achieving ultra-high strength while maintaining good values of ductility [1,2]. However, the manufacture of nanocrystalline steels is frequently very cost-consuming, involving the addition of expensive alloying elements, severe plastic deformation or complex thermomechanical routes in order to obtain the desired refinement of the microstructure during the material processing. A new generation of steels, nanostructured bainitic steels, is one promising solution because of the simplicity in terms of alloy design and processing. On the one hand, they are low-alloyed steels, with a typical chemical composition range being: (0.6-1)C-(≥1.5)Si-(0.7-2)Mn-(0.4-1.7)Cr-(0-0.2)Mo wt % [3]. On the other hand, the heat treatment consists of complete austenitization followed by isothermal holding at temperature T as low as T/T m < 0.25, where T m is the absolute melting temperature. The transformation itself leads to the nanocrystalline structure without further technological efforts, and has received much attention in recent years [4][5][6][7]. These novel microstructures have achieved the highest strength-toughness combinations ever recorded in bainitic steels (2.2 GPa-30 MPa·m 1/2 ) [8][9][10][11].The microstructure of nanostructured bainite consists basically of two phases: a hard matrix of bainitic ferrite and a carbon-enriched retained austenite, the second dispersed phase. It is characterized by the lack of coarse precipitates of cementite, due to the addition of Si with resulting content of near

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“…Supersaturated carbon is highly involved in several strengthening mechanisms of ultrahigh strength steels, regardless of the transformation kinetics [19][20][21]. In the transformation from austenite to martensite or bainite, carbon is known to diffuse from newly formed martensite or bainite to the parent austenite.…”

Section: Introductionmentioning

confidence: 99%

Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7

Luo

Kitchen

Abubakri

2017

Metals

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Ultrahigh strength steel 56NiCrMoV7 was austempered at 270 • C for different durations in order to investigate the microstructure evolution, carbon partitioning behaviour and hardness property. Detailed microstructure has been characterised using optical microscopy and field emission gun scanning electron microscopy. A newly developed X-ray diffraction method has been employed to dissolve the bainitic/martensitic ferrite phase as two sub-phases of different tetragonal ratios, which provides quantitative analyses of the carbon partitioning between the resultant ferrites and the retained austenite. The results show that, a short-term austempering treatment was in the incubation period of the bainite transformation, which resulted in maximum hardness being equivalent to the oil-quenching treatment. The associated microstructure comprises fine carbide-free martensitic and bainitic ferrites of supersaturated carbon contents as well as carbon-rich retained austenite. In particular, the short-term austempering treatment helped prevent the formation of lengthy martensitic laths as those being found in the microstructure of oil-quenched sample. When the austempering time was increased from 20 to 80 min, progressive decrease of the hardness was associated with the evolution of the microstructure, including progressive coarsening of bainitic ferrite, carbide precipitating inside high-carbon bainitic ferrite and its subsequent decarbonisation.

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On measurement of carbon content in retained austenite in a nanostructured bainitic steel

Cited by 93 publications

References 35 publications

Characterisation of microstructure and mechanical properties in two different nanostructured bainitic steels

Characterisation of microstructure and mechanical properties in two different nanostructured bainitic steels

Ductility of Nanostructured Bainite

Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7

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