Coalesced bainite by isothermal transformation of reheated weld metal

Pak, Junhak; Bhadeshia, H. K. D. H.; Karlsson, Leif; Keehan, Enda

doi:10.1179/136217108x338926

Cited by 36 publications

(25 citation statements)

References 26 publications

(30 reference statements)

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“…Unfortunately, the theory indicates that the level of substitutional solute required would prevent completely the formation of bainite because the difference between the bainite and the martensite start temperatures then vanishes (Bhadeshia 2005a). There is another difficulty discovered experimentally (Yang & Bhadeshia 2008), which is that, at low carbon concentrations, the thin platelets of bainite that do form tend to coalesce into coarse grains which are detrimental to toughness (Keehan et al 2006;Pak et al 2008). The prospects therefore do not look promising for the design of a low-carbon nanostructured bainite.…”

Section: Low-carbon Nanostructured Bainitementioning

confidence: 99%

Nanostructured bainite

2009

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An alloy system based on iron is described in which it has been possible to create a high density of interfaces by heat treatment alone. The resulting structure consists of a mixture of slender platelets of bainitic ferrite, just 20-40 nm in thickness, embedded in a matrix of carbon-enriched austenite. The rate at which this structure evolves is slow by conventional standards, but this permits components to be made which are large in all three dimensions, with uniform properties throughout. The fundamental mechanisms behind this novel nanostructured steel are reviewed, along with the factors determining its strength, ductility and fracture toughness. It is argued that, although reasonable toughness can be achieved in the context of strength levels exceeding 2000 MPa, the impact toughness remains poor and that it may not be possible to improve this particular parameter.

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Section: Low-carbon Nanostructured Bainitementioning

confidence: 99%

Nanostructured bainite

2009

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“…Microstructural evolution was studied using samples 2 × 3 × 10 mm on a dilatometer described elsewhere (Pak et al 2008). X-ray diffraction was done on metallographically prepared samples etched using 2 per cent nital in order to remove any deformed surface, with CuK a radiation with the data subjected to Rietveld analysis (Hill & Howard 1987) and refinement (Rietveld 1967(Rietveld , 1969.…”

Section: Alloys and Experimental Methodsmentioning

confidence: 99%

Extraordinary ductility in Al-bearing δ-TRIP steel

Lee

Bhadeshia

2010

Proc. R. Soc. A.

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An iron-based alloy system has been developed that exhibits impressive combinations of tensile strength and elongation that are not available with current steels used in the manufacture of automobiles. Furthermore, the heat treatments required to achieve these properties are consistent with practical production processes. The alloys rely on significant concentrations of ferrite-stabilizing solutes so that d-ferrite which forms during solidification is retained in the microstructure.

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“…This coalescence counteracts the advantage of refining the bainite plates by their formation at low temperatures. The consequences of this coalescence on toughness are detrimental, but the influence on other properties requires further investigation [12][13][14][15][16][17].…”

Section: Chemical Composition Modificationmentioning

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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Coalesced bainite by isothermal transformation of reheated weld metal

Cited by 36 publications

References 26 publications

Nanostructured bainite

Nanostructured bainite

Extraordinary ductility in Al-bearing δ-TRIP steel

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

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