Micromechanical Characterization of Multilayered Steel Composites
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Micromechanical Characterization of Multilayered Steel Composites K. Hirashita1, M. Matsuda1, M. Otsu1, K. Takashima1 1 Department of Materials Science and Engineering, Kumamoto University, 2-39-1, Kurokami, Kumamoto, Japan ABSTRACT The mechanical properties and deformation behavior of each constituent layer of multilayered steel composites were examined using microtensile testing. Three-layered integrated steels consisting of SUS420 and SPCC (cold-reduced carbon steel sheets) were fabricated by a cold-rolling process. Different heat treatment processes were used to prepare three types of specimens (as-rolled, 823K-2 min heat-treated, and 823K-500 min heat-treated), and the effect of heat treatment on their mechanical properties was investigated. In the as-rolled specimens, the average tensile strengths in the SUS420 and SPCC layers were 1063 and 606 MPa, respectively, while in the specimens heat-treated for 500 min, they were 680 and 451 MPa, respectively. The tensile strength decreased with the increase in the heat treatment time. The tensile strength of the specimens was also calculated by using the rule of mixture. For the as-rolled specimens and the 823K-2 min heat-treated specimens, the calculated value was consistent with the measured value; however, for the 823K-500 min heat-treated specimens, the calculated value was lower than the measured value. This result suggests that the necking of this layered structure was effectively obstructed by the outer ductile layer. The micromechanical characterization technique used in this study is useful not only for investigating deformation behavior but also for designing multilayered steel composites with superior mechanical properties. INTRODUCTION Recently, the weight reduction of transportation systems has been desired to reduce energy consumption owing to the issues of global warming and depletion of fossil fuel. Today, high-strength steels have been used extensively as the structural material of automobiles to attain low weight; however, they have low shock absorption and workability. Therefore, multilayered steel composites alternately accumulated with high-strength steel and high-ductility steel by a rolling process have been developed. These composites are promising materials for reducing the weight and improving the safety of transportation systems. The mechanical behavior of such multilayered metal composites has been extensively studied [1, 2], but the achieved improvement in ductility is not yet sufficient. Several studies have been conducted to achieve both high strength and high ductility of multilayered steel composites [3, 4]. As a result, 1300-MPa tensile strength and 25% elongation were achieved in SUS420J2/SUS301 multilayered composites. The properties of these multilayered materials depend on the mechanical properties of each constituent layer and the interfaces between the layers; hence, the measurement of these mechanical properties is essential for realizing high-performance multilayered steel composites. It is, however, rather difficult to measur
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