ORCID Profile
0000-0002-3504-0788
Current Organisation
UNSW Sydney
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Publisher: Elsevier BV
Date: 10-2018
Publisher: Elsevier BV
Date: 09-2019
Publisher: Wiley
Date: 10-04-2021
Abstract: Low C microalloyed steels with a ferritic matrix are attractive for thin sheet applications, because they offer superior stretch formability. Previous approaches to overcome their poor yield strength apply warm deformation in the two‐phase region ( γ + α ), achieving ultrafine grain sizes. Single‐hit deformation studies of various microalloyed steels highlight the beneficial role of small Mo additions on enhancing ferritic yield strength via interphase nanoprecipitation. However, the detailed role of Mo on grain refinement and precipitation strengthening in industrial‐like schedules for low C microalloyed steels remains unclear. A computational approach for alloy and process design aims at improving ferrite yield strength through lowering finish rolling temperature, and Mo addition is attempted here. Based on modeling results, two compositions (Nb and NbMo) are cast and deformed under plane strain compression with two finish deformation conditions, in the single‐ and two‐phase regions, at 950 and 750 °C. Warm finishing at 750 °C results in an ultrafine polygonal ferrite grain sizes averaging of 1.6 μm (NbMo) and 2.1 μm (Nb). An ultimate tensile strength of MPa is found for the NbMo steel under both finishing conditions, with a maximum yield strength of 484 MPa. The role of Mo on the ferrite morphology and precipitation strengthening is assessed using electron microscopy.
Publisher: Springer Science and Business Media LLC
Date: 18-05-2022
DOI: 10.1007/S10853-022-07275-9
Abstract: Lath martensite substructures in as-quenched plain carbon steels exhibit dislocation-like contrast in the transmission electron microscope. More recent observations reported internal twins and nanoscale auto-tempered intra-lath carbides as additional lath substructures in ultra-low-C binary Fe–C steels. Modern microalloyed steels often have similar ultra-low C contents besides microalloying elements like Ti, Nb or V and, more recently, Mo, to achieve high strength, toughness and weldability. Nonetheless, little is known about the lath substructure evolution in the as-quenched state of microalloyed steels. This study investigates the hierarchical martensite substructure evolution post-quenching of microalloyed Nb and NbMo steels with 0.1 wt% C. Hierarchical microstructure characterization was done using scanning and transmission electron microscopy, and electron backscatter diffraction methods including parent grain reconstructions with MTEX. Thermokinetic simulations using MatCalc to determine the carbide evolution during auto-tempering were corroborated with site-specific transmission electron microscopy. Mo addition led to lowering of the martensite start temperature, yet the Nb steel showed a finer hierarchical microstructure. Finer laths with in-lath dislocations, short and long twins, and lath boundary decoration of carbides were found in the Nb steel. Conversely, laths in the NbMo were wider, with frequent intra-lath auto-tempered precipitates in the vicinity of dislocations, without twins.
Publisher: Informa UK Limited
Date: 14-04-2017
Publisher: SAGE Publications
Date: 12-08-2019
Abstract: The automobile industry is presently focusing on processing of advanced steels with superior strength–ductility combination and lesser weight as compared to conventional high-strength steels. Advanced high-strength steels are a new class of materials to meet the need of high specific strength while maintaining the high formability required for processing, and that too at reasonably low cost. First and second generation of advanced high-strength steels suffered from some limitations. First generation had high strength but low formability while second generation possessed both strength and ductility but was not cost effective. Amongst the different types of advanced high-strength steels grades, dual-phase steels, transformation-induced plasticity steels, and complex phase steels are considered as very good options for being extended into third generation advanced high-strength steels. The present review presents the various processing routes for these grades developed and discussed by different authors. A novel processing route known as quenching and partitioning route is also discussed. The review also discusses the resulting microstructures and mechanical properties achieved under various processing conditions. Finally, the key findings with regards to further research required for the processing of advanced high-strength steels of third generation have been discussed.
Publisher: Elsevier BV
Date: 10-2016
Publisher: MDPI AG
Date: 25-10-2022
DOI: 10.3390/MET12111808
Abstract: The effects of the combined addition of B and Ti, as well as the influence of different strain rates on the hot ductility behavior of low carbon, continuously cast, microalloyed steels were investigated in this work. Tensile tests, microstructure analyses, and thermokinetic simulations were performed with in situ melted s les. Furthermore, prior austenite grain evaluations were carried out for the two different microalloyed steels. Increasing the strain rate brought improvements to the ductility, which was more significant in the steel with the leanest composition. The steel containing more B and Ti presented a better hot ductility behavior under all conditions tested. The main causes for the improvements rely on the precipitation behavior and the austenite–ferrite phase transformation. The preferential formation of TiN instead of fine BN and AlN was seen to be beneficial to the ductility, as well as the absence of MnS. Grain boundary segregation of free B that did not form BN retarded the ferrite formation, avoiding the brittleness brought by the thin ferrite films at the austenite grain boundaries. Furthermore, it was revealed that for the steels in question, the prior austenite grains have less influence on the hot ductility behavior than the precipitates and ferrite formation.
Publisher: Informa UK Limited
Date: 18-12-2023
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