Carbon partitioning into austenite after martensite transformation
TL;DR: In this paper, a model is developed to describe the endpoint of carbon partitioning between quenched martensite and retained austenite, in the absence of carbide formation.
About: This article is published in Acta Materialia.The article was published on 2003-05-23. It has received 1240 citations till now. The article focuses on the topics: Bainite & Austenite.
Citations
More filters
TL;DR: In this article, the authors review the current knowledge about the relationship between the micro-structure of cold rolled intercritically annealed low-alloy TRIP-aided sheet steels and their mechanical properties from a materials engineering point of view.
Abstract: The purpose of the present contribution is to review the current knowledge about the relationship between the micro-structure of cold rolled intercritically annealed low alloy TRIP-aided sheet steels and their mechanical properties from a materials engineering point of view. The focus is on their production in existing industrial lines and on their application in the manufacture of passenger cars with a body-in-white which offers an improved passive safety. The review aims to make clear that although low alloy TRIP-aided sheet steel is by now starting to be an established structural material in BIW manufacturing, there is still room for the further optimization of the composition and the processing. In addition, there are still a number of problems related to their physical metallurgy that require a better fundamental understanding.
753 citations
TL;DR: The deformed and partitioned (D and P) process produced dislocation hardening but retained high ductility, both through the glide of intensive mobile dislocations and by allowing us to control martensitic transformation.
Abstract: A wide variety of industrial applications require materials with high strength and ductility. Unfortunately, the strategies for increasing material strength, such as processing to create line defects (dislocations), tend to decrease ductility. We developed a strategy to circumvent this in inexpensive, medium manganese steel. Cold rolling followed by low-temperature tempering developed steel with metastable austenite grains embedded in a highly dislocated martensite matrix. This deformed and partitioned (D and P) process produced dislocation hardening but retained high ductility, both through the glide of intensive mobile dislocations and by allowing us to control martensitic transformation. The D and P strategy should apply to any other alloy with deformation-induced martensitic transformation and provides a pathway for the development of high-strength, high-ductility materials.
673 citations
25 Nov 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a novel concept for the heat treatment of martensite, different to customary quenching and tempering, is described, which can be used to generate microstructures with martensites/austenite combinations giving attractive properties.
Abstract: A novel concept for the heat treatment of martensite, different to customary quenching and tempering, is described. This involves quenching to below the martensite-start temperature and directly ageing, either at, or above, the initial quench temperature. If competing reactions, principally carbide precipitation, are suppressed by appropriate alloying, the carbon partitions from the supersaturated martensite phase to the untransformed austenite phase, thereby increasing the stability of the residual austenite upon subsequent cooling to room temperature. This novel treatment has been termed ‘quenching and partitioning’ (Q&P), to distinguish it from quenching and tempering, and can be used to generate microstructures with martensite/austenite combinations giving attractive properties. Another approach that has been used to produce austenite-containing microstructures is by alloying to suppress carbide precipitation during the formation of bainitic structures, and interesting comparisons can be made between the two approaches. Moreover, formation of carbide-free bainite during the Q&P partitioning treatment may be a reaction competing for carbon, although this could also be used constructively as an additional stage of Q&P partitioning to form part of the final microstructure. Amongst the ferrous alloys examined so far are medium carbon bar steels and low carbon formable TRIP-assisted sheet steels.
618 citations
TL;DR: In this paper, X-ray diffraction and transmission electron microscopy experiments are employed to investigate the mechanical stability of retained austenite in a quenching and partitioning steel.
482 citations
TL;DR: In this article, a model for carbon partitioning between supersaturated ferrite and retained austenite is presented, where the process involves quenching the remaining austenites below the martensite-start temperature, followed by a partitioning treatment to enrich the remaining Austenite with carbon.
Abstract: A model is reviewed, that describes the endpoint of carbon partitioning between supersaturated ferrite and retained austenite. A new process, quenching and partitioning (Q&P), has been developed recently to intentionally employ such partitioning in creating useful ferrous microstructures containing retained austenite. The process involves quenching austenite below the martensite-start temperature, followed by a partitioning treatment to enrich the remaining austenite with carbon, thereby stabilizing it to room temperature. Recent experimental studies have confirmed that Q&P provides a viable means to create microstructures containing carbon-enriched retained austenite, and attractive property combinations have been achieved in a variety of materials, while opportunities remain for further optimization. Furthermore, some implications of the partitioning model with respect to fundamentals of the bainite transformation are discussed, including the possibility of displacive growth under carbon diffusion control, with an austenite composition at the α/γ interface represented by the (adjusted) T0 composition. It is suggested that individual movements of iron atoms are likely during growth of Widmanstatten ferrite, and that there may be a need for further consideration of thermally activated iron-related processes in general.
465 citations
References
More filters
Book•
01 Jan 1982
TL;DR: In this article, the authors studied the effects of alloying elements in iron-carbon alloys and the formation of martensite, bainite reaction and acicular ferrite reaction.
Abstract: Iron and its interstitial solid solutions * The strengthening of iron and its alloys * The iron-carbon equilibrium diagram and plain carbon steels * The effects of alloying elements in iron-carbon alloys * Formation of martensite * The bainite reaction * Acicular ferrite * The heat treatment of steels - hardenability * The tempering of martensite * Commercial Steels: New material to include Nanostructured Steels, Steels for the Energy and Automobile Industries * The embrittlement and fracture of steels * Stainless steel * Weld microstructures * Modelling of microstructure and properties *
1,613 citations
Book•
[...]
TL;DR: The mechanism of the bainite transformation in steels is reviewed in this paper, with a summary of the early research and concluding 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.
Abstract: 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.
1,162 citations
Book•
01 Jan 1990
TL;DR: Steels: Processing, Structure, and Performance as mentioned in this paper is a comprehensive guide to the broad, dynamic physical metallurgy of steels, including chemistry, processing, structure, and performance.
Abstract: Steels: Processing, Structure, and Performance is a comprehensive guide to the broad, dynamic physical metallurgy of steels. The volume is an extensively revised and updated edition of the classic 1990 book Steels: Heat Treatment and Processing Principles. Eleven new chapters expand the coverage in the previous edition, and other chapters have been reorganized and updated. This volume is an essential reference for anyone who makes, uses, studies, or designs with steel. The interrelationships between chemistry, processing, structure, and performance--the elements of physical metallurgy--are integrated for all the types of steel discussed.
512 citations
Abstract: An experimental silicon steel has been used in a detailed kinetic and structural study of the bainite transformation in an attempt to resolve some of the controversies concerning the reaction mechanism. Distinct reaction ‘C’ curves and transformation mechanisms were observed for the upper and lower bainite reactions. The observed set of three minima in transformation kinetics were found to be incompatible with the solute drag explanation of the kinetic Bs temperature. Transmission electron microscopy indicated the growth of both upper and lower bainite by the propagation of displacive subunits, with adjacent nucleation in the latter case. Definite evidence for carbon supersaturation was obtained for the lower bainitic ferrite. The results are best explained in terms of a shear mechanism for the ferritic component of bainite rather than a ledge mechanism (as is observed in Widmanstatten ferrite growth). Carbide precipitation events were also characterized and the evidence suggested that precipitation resulted from the aging of a supersaturated matrix in lower bainite. The evidence also suggests that carbide precipitation events are of secondary importance to the essence of bainite formation. It was further proven that the concept of a metastable equilibrium1 controlling the transition from upper to lower bainite was not applicable to the present steel and indeed, if any metastable equilibrium does exist in any other steel, it does not constitute a general phenomenon and hence is not essential to the bainite transformation mechanism.
477 citations
TL;DR: In this article, microstructural evidence, together with a thermodynamic analysis, of the bainite reaction in steels are presented in support of a growth mechanism involving the propagation of displacive sub-units.
455 citations