Nanostructured steel industrialisation: Plausible reality

García‐Mateo, C.; Sourmail, Thomas; Caballero, Francisca G.; Smanio, Véronique; Kuntz, M.; Ziegler, C.; Leiro, Alejandro; Vuorinen, Esa; Elvira, Roberto; Teeri, T.

doi:10.1179/1743284713y.0000000428

Cited by 73 publications

(59 citation statements)

References 33 publications

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“…A recent work [9,42] on a large set of nanobainitic structures from different steels and heat treatments clearly revealed that there is no overall correlation between the initial austenite content and either the uniform elongation or the total elongation, Figure 8. A recent work [9,42] on a large set of nanobainitic structures from different steels and heat treatments clearly revealed that there is no overall correlation between the initial austenite content and either the uniform elongation or the total elongation, Figure 8.…”

Section: Ductility and Retained Austenite Contentmentioning

confidence: 98%

Section: Ductility and Retained Austenite Contentmentioning

confidence: 98%

“…Considering the whole microstructure, the yield strength (YS) has been found to be mainly controlled by the amount and scale of the bainitic ferrite [10,42]. In this sense, the yield strength correlates well with the ratio Vα/tα see Figure 3) where Vα is the volume fraction of ferrite and tα the mean bainitic plate thickness (tα is Lα after stereological correction [43,44]).…”

Section: Mechanical Properties Of Nanostructured Bainitementioning

confidence: 99%

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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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Section: Ductility and Retained Austenite Contentmentioning

confidence: 98%

Section: Ductility and Retained Austenite Contentmentioning

confidence: 98%

Section: Mechanical Properties Of Nanostructured Bainitementioning

confidence: 99%

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Ductility of Nanostructured Bainite

Morales-Rivas

García‐Mateo

Sourmail³

et al. 2016

Metals

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“…First, as the same theory used for the design of such alloys predicts, the transformation slows down dramatically as the transformation temperature is reduced, and it may take as long as 10 to 20 h to fully transform to bainite [4,5]. Second, due to their high carbon content, the steels are difficult to weld because of the formation of untempered, brittle martensite in the coarse grained heat affected zones of the joints.…”

Section: Nanostructured Bainitementioning

confidence: 99%

“…%) high silicon (1.5-3 wt. %) steels were designed to produce incredibly fine plates of bainitic ferrite, 20-40 nm thick, separated by a percolating network of retained austenite after transformation at 200-350 • C [4,5]. The scale of this structure is such that it contains a remarkably large density of interfaces, making it very strong even without the presence of a substantial fraction of carbide precipitates.…”

Section: Nanostructured Bainitementioning

confidence: 99%

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

García‐Mateo

Paul

Somani

et al. 2017

Metals

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Abstract:The major strengthening mechanisms in bainitic steels arise from the bainitic ferrite plate thickness rather than the length, which primarily determines the mean free slip distance. Both the strength of the austenite from where the bainite grows and the driving force of the transformation, are the two factors controlling the final scale of the bainitic microstructure. Usually, those two parameters can be tailored by means of selection of chemical composition and transformation temperature. However, there is also the possibility of introducing plastic deformation on austenite and prior to the bainitic transformation as a way to enhance both the austenite strength and the driving force for the transformation; the latter by introducing a mechanical component to the free energy change. This process, known as ausforming, has awoken a great deal of interest and it is the object of ongoing research with two clear aims. First, an acceleration of the sluggish bainitic transformation observed typically in high C steels (0.7-1 wt. %) transformed at relatively low temperatures. Second, to extend the concept of nanostructured bainite from those of high C steels to much lower C contents, 0.4-0.5 wt. %, keeping a wider range of applications in view.Keywords: bainite; ausforming; kinetics; plate thickness Structural Refinement of Bainitic Steels: General ConsiderationsBainitic steels can be designed on the basis of the theory that predicts the highest temperature at which bainite (Bs) and martensite (Ms) can start to form in a steel of a given composition. These two temperatures constitute the upper and lower limits at which the isothermal heat treatment can be performed to generate bainite.It has been reported that bainitic ferrite plate thickness depends primarily on three parameters, i.e., (1) the strength of the austenite at the transformation temperature, (2) the dislocation density in the austenite and (3) the chemical free energy change accompanying transformation [1][2][3]. In accord, a strong austenite possessing a high dislocation density and a large driving force results in finer plates. Austenite strength and dislocation density refine the structure by increasing the resistance to interface motion, and the thermodynamic driving force refines the structure by increasing the nucleation rate. All three factors-austenite strength, dislocation density and driving force-increase

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Understanding the Mechanical Properties of Nanostructured Bainite

García‐Mateo

Caballero

2015

Handbook of Mechanical Nanostructuring

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Nanostructured steel industrialisation: Plausible reality

Cited by 73 publications

References 33 publications

Ductility of Nanostructured Bainite

Ductility of Nanostructured Bainite

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

Understanding the Mechanical Properties of Nanostructured Bainite

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