Papers by Keyword: High Strength Steel (HSS)

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Authors: R.K. Dutta, R.M. Huizenga, M. Amirthalingam, H. Gao, A. King, M.J.M. Hermans, I.M. Richardson
Abstract: The effect of plastic deformation of austenite at elevated temperatures on the kinetics ofphase transformations during continuous cooling was studied in a high strength quenched and tem-pered structural steel S690QL1 (Fe-0.16C-0.2Si-0.87Mn-0.33Cr-0.21Mo (wt.%)) by means of in-situsynchrotron diffraction. The steel was heated to 900 C (above Ac3) in the austenite region and elon-gated by 6% followed by quenching to room temperature. Time-temperature-load resolved 2D syn-chrotron diffraction patterns were recorded and used to calculate the local d-spacings between latticeplanes. The plane specific diffraction elastic constants of austenite at 900 C in the steel were deter-mined from the local d-spacings. The effect of the deformation of austenite on the phase transforma-tion kinetics was studied. The evolution of lattice parameters and the phase fraction of the bcc phasesduring the quenching process were calculated.The calculated plane specific elastic constants of austenite at 900 C varied between 32 GPa to140 GPa for the different fhklg reflections of austenite. The deformation of austenite at 900 C re-sulted in the formation of a mixture of 38 % bainite, 59 % martensite and 3 % retained austenite afterquenching to room temperature. Without hot deformation, austenite transformed to 9 % bainite and88 % martensite with 3 % retained austenite. The presence of the bainitic and the martensitic phaseswas observed fromthe change in the slopes of the lattice parameters of the bcc phase during quenchingand confirmed by microscopy.
Authors: P. Hein
Abstract: The use of quenched boron steel components is an economic way to achieve significant improvements in terms of weight saving and crash performance. The material and process knowledge on the hot stamping of boron steels (e.g. Arcelor’s USIBOR 1500 P®) by the stampers needs to be extended and accurate simulation tools must be developed to support the growth of this forming technology. This paper simultaneously addresses the specific requirements of the hot stamping simulation and the current state of the art in this field. A specific approach is presented for the detection of the process limits within the simulation tool. A software chain has been set up with the target to decrease the computation times.
Authors: Karin Yvell, Michael Lindgren, Ulf Bexell
Abstract: Due to high production rates and the possibility to form complex geometries roll forming has become an increasingly popular forming process for sheet metal. Increasing quantities of high strength steels are used today but can be difficult to form due to their low ductility. One way to partly overcome this problem is to heat the steel in the forming area thus locally increasing the ductility. In the present study partially heated cold rolled high strength AISI 301 type austenitic stainless steel was investigated using electron backscattered diffraction (EBSD), and the results were compared to microhardness measurements. The results show that partial heating will give an almost complete reverse martensite transformation, i.e. martensite (α ́) transforms to austenite (γ), close to the surfaces and grain growth in the middle of the steel sheet. The extension of the heat affected zone can be determined using either microhardness or EBSD measurements. Both these measurements can be used to determine the position of the neutral layer after roll forming. The hardness measurement cannot distinguish between microstructural features but the results are in good agreement with the EBSD results for volume fraction of α ́-martensite. A major advantage of using EBSD is the possibility to characterize and follow the microstructural development when heating and roll forming.
Authors: Zhi Jie Jiao, Jian Ping Li, Jie Sun
Abstract: High strength steels, such as austenitic stainless steel, Transformation Induced Plasticity (TRIP) steel and silicon steel, have significant work hardening during cold rolling, which in turn induces a quickly increased rolling force. Tension plays a very important role in the reduction of the rolling force. However, coiler tension control system used in the classic experimental rolling mill requires long-scale strip, which cannot be satisfied for most experimental cases. To overcome this drawback, a new pilot rolling mill has been developed. The horizontally located hydraulic cylinders and clamps have been used to apply tension to the rolled short-scale strip. With this rolling mill, the austenitic stainless steel strip, TRIP steel strip and other high strength strips have been studied.
Authors: Chang Qing Zhang, Xi Jing Wang, Bo Qiang Li
Abstract: Friction stir blind riveting (FSBR) is a new joining process which eliminates the need to predrill a hole for rivet insertion. Lap joint friction stir blind riveting the plates made of high strength steel DP600 (1 mm) and magnesium alloys AZ31B(3 mm) with different technological parameters was carried out. This study experimented with the strength and the morphology of the joint with different rotation speed and feet rates of the spindle rivet, and which material on bottom or top. The main results obtained are as follows: FSBR’s process of steel and magnesium alloy plate was quickly and successfully achieved. The maximum shear strength of the joint reached about 6.3KN and the fracture path was along the shank of rivet. When Mg plate is on top of the other, the spindle speed is 2,200rpm, and along with the increase of the feed rates, the gap of plates is decreased, the strength of joint is increased. When steel plate is on top layer, the spindle speed at 2,200rpm, the rivet can then plug into the plates with a feed rate at least 600mm/min, and the joint shear strength will become higher.
Authors: Reimund Neugebauer, V. Kräusel, H. Bräunlich
Abstract: The application of high-tensile sheet metal materials in car body construction requires the development of new production strategies for preparing sheet metal part edges where laser welding operations have to be performed. Using up this sheet materials in cutting processes for car bodies lead to higher stressing of active tool parts. To arrive the same tool life quantities as is presently the standard in the production process using conventional materials it is necessary to modify the tool designs for cutting tools, to determine well adapted tool materials and coatings, to choose modified lubricants and to optimize the surface quality of tools for cutting operations.
Authors: M. Takahashi, A. Uenishi, H. Yoshida, H. Kuriyama
Abstract: There has been a big demand for increased vehicle safety and weight reduction of auto-bodies. An extensive use of high strength steels is one of the ways to answer the requirement. Since the crashworthiness is improved by applications of higher strength steels to crashworthiness conscious structural components, various types of advanced high strength steels have been developed. The crash energy during frontal collisions is absorbed by the buckling and bending deformations of thin wall tube structures of the crushable zone of auto-bodies. In the case of side collision, on the other hand, a limited length of crushable zone requires the components to minimize the deformation during the collision. The lower the strength during press forming, the better the press formability is expected. However, the higher the strength at a collision event, the better the crashworthiness can be obtained. It can, therefore, be concluded that steels with higher strain rate sensitivities are desired. Combinations of soft ferrite phase and other hard phases were found to improve the strain rate sensitivity of flow stresses. Bake hardening is also one of the ways to improve the strain rate sensitivity of flow stresses.
Authors: Miklós Tisza
Abstract: In this paper, some recent developments in materials applied in sheet metal forming processes will be overviewed mainly from the viewpoint of automotive industry as one of the most important application fields. If we consider the main requirements in the automotive industry we can state that there are very contradictory demands on developments. Better performance with lower consumption and lower harmful emission, more safety and comfort are hardly available simultaneously with conventional materials and conventional manufacturing processes. These requirements are the main driving forces behind the material and technological developments in sheet metal forming: application of high strength steels, low weight light alloys and the appropriate non-conventional forming processes are the main target fields of developments summarized in this paper.
Authors: Yong Joon Cho, In Sung Chang, Heui Bom Lee
Abstract: While resistance spot welding (RSW) has been the most successful sheet metal joining process in automotive industry, there are still certain quality and reliability issues due to the control system and its application process. Some weld spots have hard-to-reach areas and new materials make the process more complicated resulting in new challenges for quality welds. Recently, a new welding machine called one-sided RSW was introduced to make a weld of hard-to-reach areas in automotive application. Intelligent current regulation algorithm of welding machine timer helps to control welding current and time with more stablility than conventional constant current regulation. Newly developed RSW simulation tool is another advanced technology to improve weld quality and production stability. In this research, advanced RSW technologies, including one-sided RSW, intelligent adaptive control, and simulation of RSW process, are discussed with various automotive applications.
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