Hot Stamping of Boron Steel Using Partition Heating for Tailored Properties: Experimental Trials and Numerical Analysis
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WITH the increasing demand for vehicle weight reduction and passenger safety improvement, hot stamping of boron steel has been becoming popular in the automobile industry. The hot stamping process improves the formability of sheet blank, decreases the springback, and guarantees the high strength by heating the boron steel to austenitization and then forming and quenching it simultaneously in cool dies.[1,2] Hot stamping of boron steel has been studied by many researchers, who mainly focused on phase transformation,[3] constitutive modeling,[4] formability,[5] and interface contact.[6,7] Traditional hot-stamped components own the same tensile strength up to 1500 MPa in each section; however, the further requirement that the auto-body parts should be produced with different mechanical properties in various regions to enhance crashworthiness
YANHONG MU, BAOYU WANG, JING ZHOU and XU HUANG are with the School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China. Contact e-mail: [email protected] XUETAO LI is with the Shougang Research Institute of Technology, Shougang Group, Beijing 100041, China. Manuscript submitted January 23, 2017. Article published online August 16, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
has been put forward in recent years.[8] Taking B pillars, for example, the upper segment should possess high strength to enhance intrusion resistance, whereas the bottom segment should be manufactured with high elongation in order to improve the energy buffering capacity.[9] With respect to producing the parts with tailored properties, various new process variants, based on traditional hot stamping, have been introduced lately. Tailored welded blanks (TWBs) and tailored rolled blanks (TRBs) can be used to manufacture the parts of graded properties by choosing varying materials or thicknesses.[10] Qiu and Chen[11] and Lee et al.,[12] respectively, investigated the formability of the tailored laser-welded blanks and friction stir-welded blanks and analyzed the influence of the weld seam. Urban et al.[13] studied the high-pressure sheet metal forming of TRBs using numerical analysis and optimized the entire process chain. These two methods achieving tailored properties rarely need much modification in the forming process but complicate the sheet production and tool design. Intrinsic tailored blank is another approach to produce the parts with tailored properties, which changes the microstructure of components using the specifically arranged strategies of cooling or annealing. Merklein and Sevc[14] analyzed the effect of tool temperature and contact pressure on the heat-transfer coefficient, and a hat-profile geometry with tailored VOLUME 48A, NOVEMBER 2017—5467
properties was manufactured and calculated numerically. George et al.[15] produced a B pillar with tailored properties in a lab using a segmented die with local heating and cooling. They analyzed the effect of die temperature and quenching duration on the mechanical properties of tailored parts by experiment and s
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