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H. K. D. H. Bhadeshia - One of the best experts on this subject based on the ideXlab platform.
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The Bainite Reaction
Steels, 2020Co-Authors: H. K. D. H. Bhadeshia, R. W. K. HoneycombeAbstract:Bainites can be of two types, upper and lower Bainite. The microstructure of upper Bainite consists of fine plates of ferrite, each of which is about 0.2 μm thick, and about 10 μm long. The plates grow in clusters called “sheaves.” The individual plates in a sheaf are often called the “sub-units” of Bainite. They are usually separated by low-misorientation boundaries or by cementite particles. Lower Bainite has a microstructure and crystallographic features, similar to those of upper Bainite. The major distinction is that cementite particles precipitate inside the plates of ferrite. Bainite forms at somewhat higher temperatures, where the carbon can escape out of the plate within a fraction of a second. The bainitic reaction has several of the recognized features of a nucleation and growth process. “Granular Bainite” is a term used to describe the Bainite that occurs during continuous cooling transformation. There are significant differences in the tempering behavior of Bainite and martensite, the most prominent being that there is little carbon in solid solution in Bainite. Consequently, bainitic microstructures are much less sensitive to tempering, since there is hardly any loss of strength due to the removal of the small quantity of dissolved carbon. Major changes in strength occur only when the Bainite plate microstructure coarsens or recrystallizes into one consisting of equi-axed grains of ferrite. Minor changes in strength are due to the cementite particle coarsening and a general recovery of the dislocation substructure. Bainitic steels containing strong carbide-forming elements tend to exhibit secondary hardening phenomena rather like those observed in martensitic steels, which depends on the precipitation of fine alloy carbides.
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The Nature, Mechanism and Properties of Strong Bainite
2020Co-Authors: H. K. D. H. BhadeshiaAbstract:Consistent with the wishes of the Conference Organisers, the basic theory of the Bainite re- action including the crystallographic, thermodynamic and kinetic framework is described, together with the development of fine Bainite and its properties.
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designing low carbon low temperature Bainite
Materials Science and Technology, 2008Co-Authors: Hongseok Yang, H. K. D. H. BhadeshiaAbstract:AbstractThe possibility of producing Bainite at low temperatures by suppressing transformation using substitutional solutes has been investigated, as an alternative to using large carbon concentrations to achieve the same purpose. It is found that although transformation temperatures can indeed be suppressed in this way, the difference between the Bainite and martensite start temperatures diminishes. This, combined with the relatively low carbon concentration of the steels studied, promotes the coarsening of the microstructure via a coalescence of fine Bainite plates, which may have detrimental consequences on the properties although this remains to be demonstrated. The study also reveals the need for a better interpretation of the Bainite start temperature to cover circumstances where the transformation times are unusually long.
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low temperature Bainite
Journal De Physique Iv, 2003Co-Authors: C Garciamateo, F. G. Caballero, H. K. D. H. BhadeshiaAbstract:It is demonstrated that Bainite can be obtained by isothermal transformation at a temperature which is so low that the calculated diffusion distance of an iron atom, over the time scale of the experiment, is many orders of magnitude less than an interatomic spacing; and yet, it is possible to obtain plates of Bainite which are a few micrometers in length. Bainite has been obtained by isothermal transformation at 400 K. The time taken for nucleation at this temperature can be many days, but the transformation results in the growth of extremely thin platelets of Bainite, so thin that the hardness of the resulting steel can be greater than 600HV.
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Bainite in steels
2001Co-Authors: H. K. D. H. BhadeshiaAbstract:The mechanism of the Bainite transformation in steels is reviewed, beginning with a summary of the early research and finishing with an assessment of the transformation in the context of the other reactions which occur as austenite is cooled to temperatures where it is no longer the stable phase. The review includes a detailed account of the microstructure, chemistry, and crystallography of bainitic ferrite and of the variety of carbide precipitation reactions associated with the Bainite transformation. This is followed by an assessment of the thermodynamic and kinetic characteristics of the reaction and by a consideration of the reverse transformation from Bainite to austenite. It is argued that there are useful mechanistic distinctions to be made between the coherent growth of ferrite initially supersaturated with carbon (Bainite), coherent growth of Widmanstatten ferrite under paraequilibrium conditions, and incoherent growth of ferrite under local equilibrium or paraequilibrium conditions. The nature of the so-called acicular ferrite is also discussed.
Han Zhang - One of the best experts on this subject based on the ideXlab platform.
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concurrent enhancement of ductility and toughness in an ultrahigh strength lean alloy steel treated by Bainite based quenching partitioning tempering process
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Baifeng An, Han ZhangAbstract:Abstract A low-carbon Mn-Si-Cr-Mo alloyed steel was treated by two different heat treatment routes, namely Bainite-based quenching plus tempering (BQ-T) and Bainite-based quenching- partitioning- tempering (BQ-P-T). The strength, ductility and toughness were enhanced concurrently after BQ-P-T treatment (i.e., ultimate tensile strength: 1416 MPa, the PSE: ~ 25.5 GPa%, the CVN impact energy at 20 °C and − 40 °C: ~ 95 J cm −2 and ~ 45 J cm −2 , respectively). These enhanced mechanical properties were attributed to the refined ductile Bainite/martensite and the filmy retained austenite multiphase microstructure. The microstructural characterization were carried out by conducting scanning electron microscopy, X-ray diffraction, electron backscatter diffraction, transmission electron microscopy and dilatometry. The carbon partitioning between Bainite/martensite and austenite can not only stabilize the austenite films but also hinder the coalescence of the bainitic plates and promote the formation of ultrafine bainitic plates. Besides, both the carbon partitioning and the enhanced tempering of martensite/Bainite in the BQ-P-T condition contribute to generating the ductile Bainite/martensite. Finally, the microstructural factors in controlling the strength, ductility as well as impact toughness were investigated through the analyses of the fracture surface morphology and the retained austenite evolution beneath the fracture surface.
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enhanced ductility and toughness in an ultrahigh strength mn si cr c steel the great potential of ultrafine filmy retained austenite
Acta Materialia, 2014Co-Authors: Han ZhangAbstract:Three heat-treatment routes incorporating Bainite formation, namely Bainite-based quenching plus tempering, Bainite austempering and Bainite-based quenching plus partitioning (BQP total elongation: 25.2%; U-notch impact toughness at � 40 C: 48 J cm � 2 ). The enhanced mechanical properties were attributed to an increased amount of refined filmy retained austenite (22 vol.%, nanometer width range: <100 nm and submicron width range: 100–500 nm). The formation process of the bainitic microstructure as well as martensite and retained austenite was revealed by conducting dilatometry, X-ray diffraction, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy (TEM). The effect of the retained austenite on mechanical properties was discussed in terms of its size and morphology. 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Wen Hsiung Wang - One of the best experts on this subject based on the ideXlab platform.
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Crystallographic and Fractographic Analysis of Upper Bainite
Materials Transactions, 2008Co-Authors: Meng Yin Tu, Wen Hsiung WangAbstract:This study investigates the relationship between the morphology and the fracture behavior of upper Bainite in JIS SK5 steel. The cleavage crack path was found to lie on f001g� , f112gor f123gusing electron backscatter diffraction (EBSD) from the fracture surface. Additionally, most of the Bainite sheaf boundaries were found to be high-angle boundaries. If the cleavage planes are presumed to lie uniquely on f001g� , then most of the deviations of the angles between two K-S variants in a given austenite grain are high-angle deviations. According to TEM diffraction analysis, the orientation relationship of cementite/bainitic ferrite satisfies the Bagaryatskii relation, and the habit plane of cementite precipitated in the Bainite sheaf locates on ð0�Þ� kð 100Þ� . Cementite does not significantly affect the propagation of a cleavage crack. Hence, cleavage cracking deflects at grain boundaries or Bainite sheaf boundaries, but only reinitiates at the cementite/bainitic ferrite interface. (doi:10.2320/matertrans.MRA2007204)
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comparison of microstructure and mechanical behavior of lower Bainite and tempered martensite in jis sk5 steel
Materials Chemistry and Physics, 2008Co-Authors: Meng Yin Tu, Wen Hsiung WangAbstract:Abstract This study investigated the microstructures and mechanical properties of lower Bainite and tempered martensite in JIS SK5 steel. At equivalent hardness, the toughness and ductility of lower Bainite are superior to those of tempered martensite. However, the lower Bainite has a lower yield strength owing to that the Bainite sheaf is larger than the tempered martensite plate. The fracture surface of lower Bainite exhibits transgranular cleavage and differs considerably from that of tempered martensite. Tempered martensite embrittlement (TME) occurred in the tempered martensite, which is dominated by intergranular failure. It is caused by grain boundary segregation of phosphorus and grain boundary precipitation of carbide during tempering. Additionally, the size of the cleavage facet of lower Bainite was demonstrated to be correlated with the width of the Bainite sheaf. The results of electron back-scatter diffraction (EBSD) analysis indicates not only that the sheaf boundary is a high-angle boundary, but also that the cleavage crack travels along the {0 0 1} ferrite plane, whose surface energy is low.
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On the microstructure and fracture surface of Bainite in JIS SK5 steel
Solid State Phenomena, 2006Co-Authors: Meng Yin Tu, Wen Hsiung WangAbstract:The microstructure and fracture surface of Bainite in JIS SK5 steel have been investigated using transmission electron microscopy (TEM) and electron back-scatter diffraction (EBSD) in this study. Specimens were austenitized at 880 for 30 min and then austempered at 300 and 400 for 1hr, as a result, lower Bainite and upper Bainite were formed, respectively. The lower Bainite phase consists of plate-like bainitic ferrites and embedded cementite platelets, the cementite precipitated unidirectionally at an angle of 55 to 60 deg deviated from the long axes of the ferrites; in addition, the upper Bainite phase consists of a parallel array of ferrite laths and discrete cementite layers sandwiched between them. Both the Bainite structures have the same ferrite/cementite orientation relationship, which is close to that of the Bagaryatskii relation. The impact fractographs of lower and upper Bainite structures exhibit brittle failure with cleavage facets, of which the size is correlated with the width of the Bainite sheaves. Moreover, the crystallographic orientation of cleavage facets has been determined directly by EBSD. The results showed that the cleavage facet planes of lower Bainite structure are close to the {001} plane of ferrite, and they were close to the {001}, {112} and {123} planes of ferrite for the upper Bainite structure.
A Pineau - One of the best experts on this subject based on the ideXlab platform.
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austenite to Bainite phase transformation in the heat affected zone of a high strength low alloy steel
Acta Materialia, 2004Co-Authors: Astrid Lambertperlade, Annefrancoise Gourgues, A PineauAbstract:The austenite to Bainite phase transformation was investigated in a low alloy structural steel after simulated welding heat treatment, by means of light microscopy, electron backscatter diffraction and transmission electron microscopy. Upper Bainite packets result from the growth of groups of laths having close crystallographic orientations but highly misoriented habit planes. Self-accommodation of the transformation eigenstrain was evaluated for various Bainite configurations using a micromechanical model. The observed pairs of variants seem to help limiting plastic strain in the austenite phase, thus enhancing growth of the Bainite phase during cooling.
A J Clarke - One of the best experts on this subject based on the ideXlab platform.
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carbon partitioning to austenite from martensite or Bainite during the quench and partition q p process a critical assessment
Acta Materialia, 2008Co-Authors: John G Speer, D V Edmonds, A J Clarke, M K Miller, R E Hackenberg, David K Matlock, F C Rizzo, Kester D Clarke, E De MoorAbstract:Abstract The goal of the quench and partition (Q&P) process for steel heat treatment is to enrich austenite with carbon during a partitioning treatment after initial quenching below the martensite start temperature ( M s ). Two proposed mechanisms for austenite carbon enrichment during partitioning include carbon transport from martensite and/or the formation of carbide-free Bainite. Theoretical calculations show experimentally measured austenite fractions are difficult to explain based upon a mechanism involving solely Bainite formation. Carbon partitioning from martensite provides a more satisfactory explanation, although the formation of Bainite during partitioning cannot be completely excluded.
