Nanostructured steel industrialisation: Plausible reality (original) (raw)
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Industrialised nanocrystalline bainitic steels. Design approach
International Journal of Materials Research, 2014
Industrialised nanocrystalline bainitic steels. Design approach Nanostructured microstructures consisting of a mixture of very thin plates of bainitic ferrite separated by C-enriched austenite are the main characteristics of the so called NANOBAIN steel family. This paper shows the theoretical approach followed in the design of a new, industrially viable, generation of NANOBAIN steels, a process in which industrial demands such as simpler chemical compositions, faster transformation kinetics and sufficient hardenability have also been considered. The microstructural and mechanical characterization of the bainitic microstructures obtained by isothermal transformation at different temperatures, come to confirm and to validate the theoretical approach used.
Microstructural and Mechanical Characterization of a Nanostructured Bainitic Cast Steel
2020
Nanoscale bainite is a remarkable microstructure that exhibits a very promising combination of high strength with good ductility and toughness. The development of these types of microstructures has been focused on wrought materials, and very little information is available for steel castings. In this work, a specially designed cast steel with 0.76 wt % C was fabricated, and the heat treatment cycles to develop bainitic nanostructures were determined by studying the kinetics of the bainitic transformation using high-resolution dilatometry. The effects of isothermal holding temperature and time on the final microstructure and mechanical properties were thoroughly characterized in order to evaluate a future industrial implementation of the process in an effort to contribute to enhance and widen the potential applications for cast steels.
Novel Approach of Nanostructured Bainitic Steels’ Production with Improved Toughness and Strength
Materials, 2020
The tendencies of development within the field of engineering materials show a persistent trend towards the increase of strength and toughness. This pressure is particularly pronounced in the field of steels, since they compete with light alloys and composite materials in many applications. The improvement of steels’ mechanical properties is sought to be achieved with the formation of exceptionally fine microstructures ranging well into the nanoscale, which enable a substantial increase in strength without being detrimental to toughness. The preferred route by which such a structure can be produced is not by applying the external plastic deformation, but by controlling the phase transformation from austenite into ferrite at low temperatures. The formation of bainite in steels at temperatures lower than about 200 °C enables the obtainment of the bulk nanostructured materials purely by heat treatment. This offers the advantages of high productivity, as well as few constraints in regar...
The effect of bainite in producing nano/ultrafine grained steel by the martensite treatment
Materials Science and Engineering: A, 2011
The martensite treatment including cold rolling and subsequent annealing of microstructures with high percentage of martensite is one of the most effective thermo-mechanical methods for grain refinement in steels. In the present work, the effect of bainite phase on the formation of nano/ultrafine grained structure in a low alloy 0.2% C steel was investigated. The martensitic and bainitic-martensitic microstructures were first produced in the specimens by quenching in water and oil from the austenitizing temperature, respectively. The specimens were subjected to 90% reduction in thickness by cold rolling and subsequent annealing. The formation of the nano/ultrafine grained structure was discussed from the viewpoint of characteristics of the martensite and bainite starting structure. It was found that nano/ultrafine grained structures with similar hardness and mean ferrite grain size can be produced in both specimens by annealing 90% cold rolled specimens at 550 • C for 80 min. However, due to the lower hardness of the bainite phase, cold rolling of the bainitic-martensitic microstructure was much more facile than the martensitic one, resulting in no transverse cracks in the cold rolled specimen.
Characterization of Nano-Structured Bainitic Steel
International Journal of Modern Physics: Conference Series, 2012
A 0.79 C -1.5 Si -1.98 Mn -0.98 Cr -0.24 Mo -1.06 Al -1.58 Co ( wt %) steel was isothermally heat treated at 200°C for 10 days to produce a nano-structured bainitic steel. The microstructure consisted of nanobainitic ferrite laths with a high dislocation density and retained austenite films having extensive twins. The crystallographic analysis using TEM and EBSD revealed that the bainitic ferrite laths are close to the Nishiyama-Wassermann orientation relationship with their parent austenite. There was only one type of packet identified in a given transformed austenite grain. Each packet consisted of two different blocks having variants with the same habit plane, but different crystallographic orientations. Atom Probe Tomography (APT) revealed that the carbon content of nanobainitic ferrite laths was much higher than expected from the para-equilibrium level. This was explained due to the long heat treatment time, which led to the formation of fine Fe - C clusters on areas with high ...
Composition design of nanocrystalline bainitic steels by diffusionless solid reaction
Metals and Materials International, 2014
NANOBAIN is the term used to refer to a new generation of advanced steels capable of producing by isothermal transformation at low homologous temperatures, T/T m ∼ 0.25 where T m is the absolute melting temperature, a nanocrystalline microstructure, composed exclusively of two phases, thin plates of bainitic ferrite separated by C enriched austenite. Such alloys are exclusively designed on the basis of bainitic transformation theory and some physical metallurgy principles. In this work, by designing a new set of alloys capable of producing such microstructure, a further step toward the industrialization of NANOBAIN is taken. Some important industrial requirements, including circumventing the inclusion of expensive alloying elements and the need for faster transformations, are also considered. For all the alloys, the experimental results validate the design procedure and they illustrate that the NANOBAIN concept is a step closer to industrialization, probing that it is possible to obtain nanocristalline bainite in simpler alloy systems and in shorter times than those reported previously.
Computational metallurgy has grown rapidly over the last twenty years and the subject has been embraced by industry with remarkable enthusiasm, resulting in close collaborations and long term partnerships between industry and academic research laboratories. No longer are alloys designed from experience alone but calculations are used to reduce the task and to introduce creativity. There are now numerous examples of pro®table commercial products resulting from the application of this type of research.
Computational metallurgy has grown rapidly over the last twenty years and the subject has been embraced by industry with remarkable enthusiasm, resulting in close collaborations and long term partnerships between industry and academic research laboratories. No longer are alloys designed from experience alone but calculations are used to reduce the task and to introduce creativity. There are now numerous examples of pro®table commercial products resulting from the application of this type of research.
Development of Bainitic Steels for Engineering Applications
2014
Enormous efforts have been put in in an attempt to design steel with microstructure in the Nano range. Phase transformation theory has contributed to the successful design of these steels. This paper presents some of these developments, the physical metallurgy theory involved and areas where these materials have been destined.