【正文】 ，陳煒，王曉璐， 彭華. 基于數(shù)值模擬的覆蓋件沖壓成形工藝研究. 新技術(shù)新工藝，2004.[17] 黃慶寶，陳玉全，楊大宇，李金宇，付仲偉， 柴邦林. 汽車覆蓋件沖壓數(shù)值模擬分析及參數(shù)優(yōu)選. 鍛壓技術(shù)，2006.[18] 陳小芳，扶名福，袁志軍. Dynaform數(shù)值模擬技術(shù)在汽車覆蓋件成形中的應(yīng)用. 模具制造，2009附錄1：英文資料Analysis of microstructure and mechanical properties of different high strength carbon steels after hot stampingM. Naderia,?, M. Ketabchia, M. Abbasia, W. Bleckba Department of Mining and Metallurgy, Amirkabir University of Technology, Tehran, Iranb Department of Ferrous Metallurgy, RWTH Aachen University, Aachen, GermanyAbstractUsage of high strength steels may reduce the weight of automobiles and improve the crash safety and lowdown the gas emissions. Besides cold forming, hot stamping has gained much interest for the production of car body ponents. Boron alloyed steels have been the point of focus for the materials choice in hot stamping. In this paper, four high strength nonboron alloyed steels were hot stamped using water and nitrogen cooling media. Microstructural analyses, lateral and surface hardness prowling as well as tensile tests of hot stamped samples were performed. These steels provided yield strength (.) values of600–1100 MPa and ultimate tensile strength (.) values of 900–1400 MPa. Increasing cooling rates, using nitrogen cooled punch (NCP) during hot stamping resulted in mostly martens tic microstructure and maximum strength, while hot stamping using water cooled punch (WCP) resulted in maximum formability index due to presence of some ferrite phase.169。 2011 Elsevier . All rights reserved.1. IntroductionAlong with the development of automobile industry for lightweight car bodies, more and more advanced high strength and ultrahigh strength steels have been used to produce automotive parts. Making use of the mentioned steels not only reduces the weight of automobiles, but also improves crash safety and decreases gas emissions. Difficulties such as large forming forces, low formability and occurrence of spring back during cold stamping of these steels, have made manufacturers to look for new solutions. The possibility to perform stamping operations at elevated temperatures represents a solution to these problems, allowing lower loads on tools and higher accuracy of formed measurements (197。kerstr246。m, 2006). Additionally as the part remains in the die during the cooling stage, spring back is totally waned. According to Naderi et al. (2008) hot stamping is a nonisothermal hightemperature forming process, in which plex ultrahigh strength parts are produced, with the goal of no spring back. In hot stamping process, the blanks are austenitized and subsequently formed and quenched in the die. During quenching, the austenitic microstructure transforms into a martens tic one because of rapid cooling. The marten site evolution during quenching causes an increased tensile strength of up to 1500 MPa, which is veri?ed in different works using tensile tests (Naderi, 2007) and hardness. Corresponding author at: Department of Mining and Metallurgy, AmirKabir University of Technology (Tehran Polytechnic), PO Box 158754413, 424 Hafez Ave.,Tehran, Iran. Tel.: +98 21 64542978。 fax: +98 21 66405846.Email addresses: mnaderi@, mmzz52@ (M. Naderi).09240136/$ – see front matter 169。 2011 Elsevier . All rights reserved.doi:(2007) represented an ef?cient methodology which made it possible to optimize the geometrical design of the cooling ducts for a given set of boundary conditions and parameters. The objective was to quench the hot part effectively and at a constant rate and to provide a cooling rate of at least 27 K/s while marten site was formed. The method was successfully applied for a test tool. Kolleck et al. (2009) developed a twostep inductive heating system as an effective concept to decrease energy consumption of conventional heating methods. Tremendous reduction of heating time and consequently lower investment costs as well as reduced ?oor space for the heating device were some results of using thenew presented technology. Bariani et al. (2008) presented an innovative experimental procedure based on Nakazima test for evaluating the formability limits of high strength steels during hot stamping. The procedure generated formability data suitable for an FE modeling of the hot stamping process. They provided the formability data in the formof binations of strains that caused the onset of necking and fracture for given temperatures and average strain rates in the metastable austenitic phase. Xing et al. (2009) set up a material model under hot stamping condition of quenchable steel, based on the experimental data of mechanical and physical properties. They also simulated the whole hot stamping process by ABAQUS.M. Naderi et al. / Journal of Materials Processing Technology 211 (2011) 1117–1125The main objective of the present research is focused on investigation into microstructure and mechanical properties of different nonboron alloyed steel grades after being hot stamped. This objective was followed by selection of four different highstrength uncoated carbon steel sheets. Microstructural evaluation, lateral and surface hardness measurements and tensile tests after hot stamping were performed and considered.2. Materials and methods. Chemical positionThe investigated materials were different nonboron alloyed Fig. 1. An overview of the hot stamping process sequence (Altan, 2007). steel grades with carbon contents between and wt%.The chemical analyses as well as carbon equivalent values of theinvestigated steels are given in Table 1. Carbon equivalent (Ceq) of investigated steels was calculated according to the equation presented by Patchett (2003) for carbon steels. SteelsA, B, C and D show an increasing trend in their carbon equivalent value in order.As seen in Table 1, carbon equivalent ranges from in steelA to in steelD. Accordingly, all the investigated steels are listed in the low carbon steel grades..