Effect of Strengthening Mechanism on Strain-Rate Related Tensile Properties of Low-Carbon Sheet Steels for Automotive Ap
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Effect of Strengthening Mechanism on Strain-Rate Related Tensile Properties of Low-Carbon Sheet Steels for Automotive Application Anindya Das, Pinaki Biswas, S. Tarafder, D. Chakrabarti, and S. Sivaprasad (Submitted February 18, 2018; in revised form February 18, 2018) In order to ensure crash resistance of the steels used in automotive components, the ensile deformation behavior needs to be studied and predicted not only under quasi-static condition, but also under dynamic loading rates. In the present study, tensile tests have been performed on four different automobile grade sheet steels, namely interstitial free steel, dual-phase 600 and 800, and a carbon manganese steel over the strain rate regime of 0.001-800/s. Apart from the variation in strength (which always increased with strain rate), the effect of strengthening mechanism on strain rate sensitivity and strain hardening behavior has been evaluated. Strain rate sensitivity was found to increase at high-strain rate regime for all the steels. Contribution of solid solution hardening on strain rate sensitivity at lower plastic strains was found to be higher compared to dislocation strengthening and second-phase hardening. However, precipitation hardening coupled with solid solution hardening produced the highest strain rate sensitivity, in C-Mn-440 steel at high strain rates. Different strain-rate-sensitive models which take into account the change in yield stress and strain hardening behavior with strain rate for ductile materials were used to predict the flow behavior of these sheet steels at strain rates up to 800/s. Keywords
crashworthiness, high strain rate, strain rate sensitivity, strengthening mechanism, tensile test
1. Introduction Advancement in automotive industries demands steels that have high strength to weight ratio, good weldability, and excellent formability (Ref 1, 2). Some of these properties are achieved either through appropriate micro-alloy addition and/or by controlling phase constituent by a suitable heat treatment. One of the essential characteristics that these steels should posses during both the fabrication of components and in service is their ability to withstand the high rate of deformation. As the deformation, in general, is governed by the underlying strengthening mechanism and steels with different strengthening mechanisms are being employed in automotive applications, the role of strengthening mechanism on high-strain rate deformation behavior needs to be understood. This paper aims at providing such an understanding. Significant experimental data on high-strain rate behavior of automotive grade steels and constitutive models to predict their flow curves are available in the literature. For example, the variation of grain size on high-strain rate deformation has been
Anindya Das, S. Tarafder, and S. Sivaprasad, MTE Division, CSIRNML, Jamshedpur, Jharkhand 831007, India; Pinaki Biswas, R&D, Tata steel Limited, Jamshedpur, 831007, India; and D. Chakrabarti, Metallurgical and Materials Engi
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