Investigation of Thermal and Mechanical Properties of Quenchable High-Strength Steels in Hot Stamping
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demand for reductions in vehicular weight and higher levels of safety, compared to current levels, has led to an increase in the use of ultra-high-strength steels (UHSS) in the manufacture of new structural components. Hot stamping technology can be used for A- and B-pillar reinforcements, roof rails, side-wall members, and beams for crash management structures. Compared with cold-formed parts, hot-stamped parts exhibit better formability at high temperatures, without the occurrence of springback on the final part (Merklein and Lechler).[1] This technology has significant potential for minimizing the weight of components by reducing the sheet thickness and the number of body in white (BIW) components. This reduction can be achieved by integrating two or three parts into one, through the use of quenchable steels during the hot stamping process. In order to meet this requirement, careful control of the mechanical, metallurgical, and thermal aspects of the process is essential. Abdulhay et al.[2] designed an experimental device to estimate the thermal contact ANTON GORRIN˜O and CARLOS ANGULO, Associate Professors, are with the Department of Mechanical Engineering, University of the Basque Country (UPV/EHU), Bilbao, Spain. Contact e-mail: [email protected] MAIDER MURO and JULIAN IZAGA, Researchers, are with the Metallurgy Research Centre IK4 AZTERLAN, Durango, Spain. Manuscript submitted December 9, 2015. Article published online April 5, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
resistance at the part/tool interface in hot stamping experiments under different contact pressures (10 to 30 MPa). Hu et al.[3] analyzed the effects of temperature, pressure, and oxide scale thickness on interfacial heat transfer coefficient (IHTC) in the cooling process. Nishibata and Kojima[4] investigated the effect of the cooling rate on the hardness and microstructure of the hot-stamped boron steel containing 0.2 mass pct carbon. The number of steel parts manufactured by hot stamping (also known as the press hardening process) has increased significantly in recent years (Karbasian and Tekkaya).[5] However, compared with that needed for cold stamping, the design and optimization of the hot stamping process require considerable knowledge of heat transfer, metallurgy, and mechanical behavior. Merklein et al.[6] investigated the characterization of the cooling behavior of boron manganese steel blanks with respect to partial press hardening. Bardelcik et al.[7] investigated the effect of cooling rate on the high strain rate behavior of hardened boron steel. Naderi et al.[8] hot stamped four high-strength non-boron alloyed steels using water and nitrogen cooling media, and performed microstructural analyses, lateral and surface hardness profiling, as well as tensile tests of these hot-stamped samples. Bosetti et al.[9] developed an experimental apparatus with a cooling water system to identify the dependence of IHTC on the applied contact pressure. Determination of the link between this design and optimization and the IHTC values is therefore
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