Tensile Response of Two Nanoscale Bainite Composite-Like Structures

Morales-Rivas, Lucía; Yen, Hung‐Wei; Huang, Bo-Ming; Kuntz, M.; Caballero, Francisca G.; Yang, Jer−Ren; García‐Mateo, C.

doi:10.1007/s11837-015-1562-x

Cited by 48 publications

(30 citation statements)

References 87 publications

(110 reference statements)

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“…(2) Two austenite C contents, 0.6 and 1 wt %. This covers a range of concentrations in good agreement with the values detected by XRD for the nanobainitic structures examined in the mentioned reference [54].…”

Section: Retained Austenite Evolution and Mechanical Partitioningsupporting

confidence: 88%

“…There is no correlation between the elongation and the strength of the material (yield strength and UTS, separately) either, as seen in Figure 5b,c, with data from reference [53]. On the other hand, it has been reported that the samples with a high ductility present a stronger damage resistance [54]. This can be evaluated with another parameter, UTS·e t , , which is a measure of the toughness, as in Figure 5d, with data from reference [53], where the correlation is confirmed.…”

Section: Ductility: Work-hardening and Fracture Mechanisms In Nanostrmentioning

confidence: 59%

“…Regarding the fracture analyses of the tensile-tests of nanostructured bainite, Figure 7, tear ridges are revealed, which converge at a unique site within the specimen section, closer or further from its center, but beneath the surface, ruling out influence of the machining process. There are always signs of intermixed fracture mechanisms, both ductile and brittle: voids, cleavage facets and intergranular fracture at prior austenite grain (PAG) boundaries [54], Figure 7. Cracks in low-ductility tensile specimens have not been found to originate at inclusions or coarse precipitates, but there seems to be a prevalence of fragile fracture, from the observation of large extensions of PAG boundaries on the fracture surface (as in Figure 7c, corresponding to a microstructure with a total elongation of 7%) [54].…”

Section: Ductility: Work-hardening and Fracture Mechanisms In Nanostrmentioning

confidence: 99%

“…There are always signs of intermixed fracture mechanisms, both ductile and brittle: voids, cleavage facets and intergranular fracture at prior austenite grain (PAG) boundaries [54], Figure 7. Cracks in low-ductility tensile specimens have not been found to originate at inclusions or coarse precipitates, but there seems to be a prevalence of fragile fracture, from the observation of large extensions of PAG boundaries on the fracture surface (as in Figure 7c, corresponding to a microstructure with a total elongation of 7%) [54]. In quenching and partitioning (Q&P) steels, which consist of a matrix of tempered martensite plus C-enriched retained austenite, it has been reported that the transformation of retained austenite into high-C martensite may lead to the decohesion of PAG boundaries.…”

Section: Ductility: Work-hardening and Fracture Mechanisms In Nanostrmentioning

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: Retained Austenite Evolution and Mechanical Partitioningsupporting

confidence: 88%

Section: Ductility: Work-hardening and Fracture Mechanisms In Nanostrmentioning

confidence: 59%

Section: Ductility: Work-hardening and Fracture Mechanisms In Nanostrmentioning

confidence: 99%

Section: Ductility: Work-hardening and Fracture Mechanisms In Nanostrmentioning

confidence: 99%

See 2 more Smart Citations

Ductility of Nanostructured Bainite

Morales-Rivas

García‐Mateo

Sourmail³

et al. 2016

Metals

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“…One of the most effective approaches to increase both strain hardening and ductility is the transformation-induced plasticity, i.e. the TRIP effect, which is observed in dual-/multi-phase steels [11e13,16e18], TRIP steels [11,12,19e23], bainite steels [15,24], etc. In these steels, the phase-specific deformation mechanism takes effect at different stress or strain levels and therefore, the global plastic response is composite-like, which critically depends on the evolution of stress transfer and dynamic strain partitioning among different phases [11,12].…”

Section: Introductionmentioning

confidence: 99%

Combining gradient structure and TRIP effect to produce austenite stainless steel with high strength and ductility

et al. 2016

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a b s t r a c tWe report a design strategy to combine the benefits from both gradient structure and transformationinduced plasticity (TRIP). The resultant TRIP-gradient steel takes advantage of both mechanisms, allowing strain hardening to last to a larger plastic strain. 304 stainless steel sheets were treated by surface mechanical attrition to synthesize gradient structure with a central coarse-grained layer sandwiched between two grain-size gradient layers. The gradient layer is composed of submicron-sized parallelepiped austenite domains separated by intersecting ε-martensite plates, with increasing domain size along the depth. Significant microhardness heterogeneity exists not only macroscopically between the soft coarse-grained core and the hard gradient layers, but also microscopically between the austenite domain and ε-martensite walls. During tensile testing, the gradient structure causes strain partitioning, which evolves with applied strain, and lasts to large strains. The g / a 0 martensitic transformation is triggered successively with an increase of the applied strain and flow stress. Importantly, the gradient structure prolongs the TRIP effect to large plastic strains. As a result, the gradient structure in the 304 stainless steel provides a new route towards a good combination of high strength and ductility, via the co-operation of both the dynamic strain partitioning and TRIP effect.

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Fatigue Properties at Elevated Temperatures of Secondary Tempered Nanostructured Bainite: A Study of Deformation Mechanisms

Kuntz,

Wicks,

Sourmail

et al. 2024

steel research int.

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Nanostructured bainitic steel obtained through austempering or bainitic transformation of high Si steels consists of bainitic ferrite and carbon‐enriched retained austenite. Secondary tempering of those microstructures tailors their mechanical properties through its unique nanostructure and austenite stability. Herein, fatigue and tensile properties of a nanobainitic steel in different secondary tempering conditions are presented and the results are discussed based on the deformation mechanisms taking place due to the microstructure evolution during secondary tempering. Influence of secondary tempering and elevated testing temperature on tensile and fatigue properties at room temperature and 250 °C is presented. Based on the present deformation, mechanism results are discussed supported by microstructure evolution results obtained through dilatometry, X‐ray diffraction, and microscopy. Depending on secondary tempering temperature, main influencing mechanisms are martensite formation after secondary tempering during cooling, transformation‐induced plasticity effect, and precipitation hardening obtained by secondary tempering.

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Tensile Response of Two Nanoscale Bainite Composite-Like Structures

Cited by 48 publications

References 87 publications

Ductility of Nanostructured Bainite

Ductility of Nanostructured Bainite

Combining gradient structure and TRIP effect to produce austenite stainless steel with high strength and ductility

Fatigue Properties at Elevated Temperatures of Secondary Tempered Nanostructured Bainite: A Study of Deformation Mechanisms

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