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Temperature-supported gas forming of ferritic stainless steel tubes

: Schieck, Frank; Drossel, Welf-Guntram; Albert, Andre

Korean Society for Technology of Plasticity:
6th International Conference on Tube Hydroforming, TUBEHYDRO 2013 : August 25-28, 2013, Jeju, Korea
Jeju, 2013
ISBN: 978-89-98950-00-2
International Conference on Tube Hydroforming (TUBEHYDRO) <6, 2013, Jeju/Korea>
Fraunhofer IWU ()
gas forming; temperature; ferritic stainless steel; tubes

Lightweight design in passenger cars is gaining more and more importance. Besides the whole body in white also the suspension, chassis and powertrain components are in the focus of weight reduction. Especially in exhaust system components, casting design is been substituted increasingly by thin-walled stainless steel blanks and tubes. Today there is a wide field of applications for using austenitic stainless steels such as X5CrNi18-10 (DIN 1.4301). Due to the need to increase the exhaust temperature required for more effective exhaust cleaning and the pressure to reduce the costs, ferritic stainless steels such as X2CrTiNb18 (DIN 1.4509) becomes more and more important.
Unfortunately, the elongation (A5) of X2CrTiNb18 (DIN 1.4509) is only approximately 18% at room temperature. Compared to X5CrNi18-10 (DIN 1.4301) with an elongation (A5) of about 42% at room temperature. The achievable deformation rate of ferritic stainless steel is thus significantly lower. Based on this fact, manufacturing of complex exhaust components by hydroforming is much more difficult. That means more forming steps including annealing steps between are required in order to reach the final geometry. The increased production effort also causes an increase of production costs. Investigations show that when using X2CrTiNb18 (DIN 1.4509), an increase in the forming temperature also causes an increase in elongation (A5). At a temperature of 800 the elongation (A5) is above 50% and at 1050 it lies above 100%. The focus of this investigation was to determine a feasible process window for relevant part geometries together with the corresponding devices and tools. It was shown that, in order to reach comparable part geometries the hydroforming technology used for X5CrNi18-10 (DIN 1.4301) at room temperature could be substituted by a gas forming technology for X2CrTiNb18 (DIN 1.4509) at temperatures above 800.