Deformation-Induced Microstructural Banding in TRIP Steels
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RODUCTION
TRANSFORMATION-INDUCED plasticity (TRIP) steels are one class of advanced high-strength steels (AHSS) that have been developed for applications in the automotive industry in recent years.[1,2] Their combination of high strength and increased uniform and total elongation, even compared to dual-phase (DP) steels, enables the forming of complex-shaped components where stretchability is a key formability characteristic. Additionally, this combination of properties can enhance the energy absorption capacity, giving better crashworthiness and thus, improved passenger safety. However, this new class of material exhibits microstructural banding, a common detrimental microstructural feature found in many steel types. These bands in general consist of alloying addition (e.g., C, Mn) enriched microstructural constituents, usually pearlite or martensite, as layers parallel to the rolling plane.
S. CELOTTO is with Tata Steel R&D, IJmuiden, 1970 CA, The Netherlands. H. GHADBEIGI and C. PINNA are with the Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK. B.A. SHOLLOCK and P. EFTHYMIADIS are with the WMG, University of Warwick, Coventry CV4 7AL, UK. Contact e-mail: P.Efthymiadis@warwick. ac.uk Manuscript submitted December 18, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
They form as a consequence of the processing at both casting and rolling deformation stages.[3] This study, like others, shows that these bands have an important effect on mechanical properties.[4–6] There have been previous studies to investigate and control the formation of microstructural bands during processing.[7,8] It has been reported that the thermomechanical processing required to avoid the formation of microstructural bands can be sometimes economically impractical[7] or physically impossible due to the thermodynamics and kinetics governing the formation of such bands.[8] Nevertheless, a better understanding of the effects of such bands on the microstructural behavior of TRIP steels can lead to the development of new processing routes aimed at improving the mechanical properties of these materials by optimizing the geometric characteristics of these bands.[3,9] Furthermore, some optimizations can be realized through economically feasible thermomechanical processes.[3,9] For example, it has been suggested that increasing the cooling rate during the hot rolling process leads to a significant decrease of martensite banding in the microstructure of dual-phase steels for sheets used in the automotive industry.[9] The influence of microstructural bands on the global material behavior of banded and un-banded microstructures has been widely investigated in the literature with differing conclusions. The effect of such bands on local deformation and damage has been reported to be both
microstructural bands on the local deformation and damage mechanisms in the microstructure of TRIP steels. Unlike other studies which are usually focused on evaluating the influence of the major strain component, the minor str
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