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Processing routes, resulting microstructures, and strain rate dependent deformation behaviour of advanced high strength steels for automotive applications

Nanda Tarun, Singh Vishal, Singh Gurpreet, Singh Manpreet, Kumar B. Ravi

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 1

112--135

Automobile industry is continuously striving to obtain light body-in-white structures to meet tightened regulations on flue-gas emissions/crash-testing parameters. ‘Advanced high strength steels (AHSS)’ find increased applications in the automotive industry because of improved crashworthiness/formability at reasonably low costs. AHSS category mainly includes transformation induced plasticity (TRIP) steels, twinning induced plasticity (TWIP) steels, dual phase (DP) steels, complex-phase (CP) steels, and quenching-partitioning (Q&P) steels. AHSSs provide superior strength-ductility combination than conventional high-strength steels by virtue of their multi-phase microstructures. Mechanical properties of AHSSs are greatly influenced by processing routes/derived microstructures. Furthermore, mechanical properties/tensile deformation behavior are also strain rate dependent. During an automobile crash, deformation occurs at strain rates which are exceedingly higher than quasi-static conditions. So, investigation of AHSS properties under both quasi-static as well as high strain rates conditions is important to check applicability for superior crash-resistance. The present work critically reviews details of processing routes, room temperature microstructures, mechanical properties, and finally strain rate dependence of tensile deformation behaviour of AHSSs. Finally, main gaps in existing literature/scope for future research with regards to high strain rate deformation dependent properties of this steel category are presented.

Correlation between Lüders band formation and precipitation kinetics behaviour during the industrial processing of interstitial free high strength steels

Singh Gurpreet, Nanda Tarun, Miadad Sk. Jabed, Gorain Nemai Chandra, Venugopalan T., Kumar B. Ravi

Archives of Civil and Mechanical Engineering

2019

Vol. 19, no. 2

469--483

Lüders band formation in steels is critical to surface finish during automobile panel manufacturing. This research reports on the problem of Lüders band formation in interstitial free high strength steel compositions (IFHS-steels). The study investigates the effect of chemical composition and processing parameters on the formation of Lüders bands in IFHS-steels. It correlates the problem of Lüders band formation with precipitation kinetics behaviour during the industrial processing of IFHS-steels. Four different compositions viz. Ti-stabilized, Ti-Nb stabilized, low Ti-low Nb, and high Ti-low Nb with high Al were investigated. Annealing parameters were similar to industrial practice followed for batch and continuous annealing lines in steel manufacturing plants. Stabilized IFHS-steel compositions possessing excess of stabilizing elements (Ti, Nb, etc.) for stabilization of interstitial elements (C, N) also showed the problem of Lüders band formation. The new type of IFHS composition containing high Al, investigated in this research, showed no Lüders band formation during batch annealing cycles along with adequate mechanical properties (YS: 190–202 MPa; Δr-value: 0.25). Thus, steel compositions with high Al content processed through batch annealing cycle offer a practical solution to the problem of Lüders band formation in IFHS-steels.