Determining Individual Phase Flow Properties in a Quench and Partitioning Steel with In Situ High-Energy X-Ray Diffracti
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VEHICLE lightweighting can be achieved with the use of lighter materials such as aluminum[1] and magnesium[2] sheets as body panels, or by down-gauging through the introduction of higher strength steels with high ductility. The latter option has led to the advent of advanced high-strength steels (AHSS) that can be categorized into three generations. The first-generation AHSS includes dual-phase (DP) and transformation-induced plasticity (TRIP) steels,[3] and the second-generation includes twinning-induced plasticity (TWIP) steel.[4] TWIP steel is fully austenitic and has a superior strength and plasticity combination due to deformation twinning-induced plasticity and hardening mechanisms. TWIP steel, however, is more expensive than first-generation AHSS due to its high manganese content. The XIAOHUA HU and KYOO SIL CHOI, Scientists, and XIN SUN, Laboratory Fellow, are with the Pacific Northwestern National Laboratory, Richland, WA 99354. Contact e-mail: xiaohua.hu@pnnl. gov YANG REN, Scientist, is with the Argonne National Laboratory, Argonne, IL 60439. YANGDONG WANG, Professor, is with The State Key Laboratory for Advanced Metals and Materials, University of Science and Technology, Beijing 100083, China. X.H. Hu, K.S. Choi, and X. Sun are employed by Pacific Northwest National Laboratory. Y. Ren is employed by Argonne National Laboratory. U.S. Government work is not protected by U.S. Copyright. Manuscript Submitted October 29, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
recent development of third-generation AHSS, hence, has two routes: (1) Reduce the amount of manganese to lower the cost of TWIP steel or (2) modify the thermomechanical processing parameters with first-generation AHSS chemistry to make the material stronger and more ductile. The latter case can be accomplished by a material heat treatment process such as quenching and partitioning (Q&P),[5,6] which can create a desired microstructure and the associate constituent phase properties to achieve the overall strength and ductility of the third-generation AHSS target. The steel produced by the Q&P process is called Q&P steel, and various Q&P processing parameters, including the quench and partitioning temperatures and time, would generate a variety of materials with different properties. If the relationship between the processing parameters and final material properties can be established, such a relationship can be used as guidance for material design for various applications. The link between materials thermomechanical processing parameters, i.e., the Q&P temperature and time, and its performances is the specific microstructures and constituent phase properties in the microstructure. Obtaining the material microstructure-property/performance relationship is one of the most important tasks in new materials and process development. Mechanism-based dislocation theories[7] and empirical or phenomenological models have been developed to relate the material microstructural characteristics, such as gain size[8,9] for granular materials and lamellar
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