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Technical Paper

New Microstructural Approaches for Improved Mechanical Properties of Multiphase Steels with Emphasis on TRIP Steels

The newly developed multiphase high-strength steels with improved formability characteristics mainly owe their beneficial properties to their special microstructural composition. The multiphase structure can in general be classified as a mixture of varying amounts of soft steel phases and distinctly harder ones. As introduction the variety of nowadays multiphase steels is mentioned concerning the process strategy and the resulting range of strength. Focussing on the concept of TRIP steels (TRIP = transformation induced plasticity) the retained metastable austenite as one special steel phase plays an additional role. A microstructural model, which was originally applied to dualphase steels, was successfully used to explain the work hardening of TRIP steels at higher strain rates. The multiphase structure is also interesting in terms of void nucleating mechanisms. As indicated by microstructural observations austenite particles play a double role depending on the grain size.
Technical Paper

Production of Autobody Components with Hydromechanical Sheet Forming (AHU®)

The lightweight construction strategies that are demanded by the automobile industry are being employed more and more. These strategies lead to the increasing importance of the forming method and types of materials used. Especially forming technologies based on liquid media have the potential to meet these demands. These forming technologies make it possible to produce parts that have both, more complex geometries and optimized characteristics. This forming technology constitutes an intelligent process management including the significant materials parameters and behavior, the simulation and some new developments especially for the optimization of the quality and the cycle time. Hydromechanical sheet forming (AHU®) is an alternative production (forming) process, with very interesting results and developments for the manufacture of specific automobile components.
Technical Paper

How the Modeling of Virtual Materials Can Secure Part Feasibility

The paper describes a method applied to show how to perform a steel sheet metal sensitivity analyses while the material is subjected to stretch forming and deep drawing. It is shown that the sensitivity analysis provides meaningful results. Simulations were run with simplified laboratory geometries and extended for the most complex automotive parts. The variety of likely numerical runs are dramatically reduced by means of a statistical design of experiments, minimizing the number of simulations required for daily use. As a result it is possible to choose the optimal material for a specific forming process and part, as well as to assess the expected scattering in the material properties.
Technical Paper

Steel Battles Plastic for Fuel Tank Application: - Forming - Joining - Corrosion Resistance

Worldwide regulations for environmental issues are forcing the automotive industries to evaluate new materials for compliance. Future requirements for automotive recycling and stricter automotive emission standards are causing the industry to look for steel fuel tanks, which are inherently impermeable and 100% recyclable. Challenges to steel as a fuel tank material are to achieve a minimum of 15 years of corrosion life with a cost effective product demonstrating weight and complex shapes comparable to plastic. The paper will discuss the impact of the future regulations on steel fuel tanks and the product actions what have been taken to meet these regulations. Specific data will be presented on the test and development of a pre-painted aluminized steel fuel tank material designed to exceed the 15 year corrosion life requirement.
Technical Paper

Tailored Hybrid Blanks in Steel and Aluminium

Thyssen Tailored Hybrid Blanks (THB) are cold-formable combinations of steel and aluminium sheets. They include linear lap joints fabricated by means of a laser-assisted roll bonding technique. The initial development work has meanwhile progressed to the stage where a pilot line is set to start up operation and fabricate hybrid blanks in shapes and sizes required for automotive engineering applications. The present state of development, a possible spectrum of products, and main process parameters are discussed. Research into the forming behaviour of hybrid blanks is looked at, citing practical examples, added with findings from metallographic analyses and corrosion testing.
Technical Paper

Hydromechanical Sheet Forming (AHU®) -an Innovative Process for the Production of Autobody Parts of New and Further Developed Steel Materials

Hydromechanical sheet forming (AHU®) is an innovative production process with interesting applications, possibilities and potential for the cost-effective manufacture of automobile body parts, particularly with regard to the use of new and improved steels. The targeted, component-specific use of hydro-mechanical sheet forming in automobile construction promises to deliver outstanding results from both a technological and economic point of view.
Technical Paper

Numerical Modelling of Tailored Blank Applications for Autobody Components

Tailored Blank applications have become more and more important for the advanced light weight and cost effective steel automobile body. During the last decade, the production of Tailored Blanks with a straight weldline has been constantly increasing because their technical and economical advantages are well accepted by automobile manufacturers /1, 2, 3, 4/. But, now the body engineers prefer to have an even more flexible product with specific weldline design, according to the engineering design needs. Thyssen Krupp Stahl AG reacted quickly on this demand and now offers the new product called, Thyssen Engineered Blanks (TEB®s), which meets almost all the needs for the design of components concerning weld-line geometry and weld-line positioning. With our new production line, both single and multiple steel sheets can now be joined together with linear weld-lines, angled weld-lines and curved laser beam weld-lines, Figure 1.
Technical Paper

Hot Dip Aluminized Steel Sheet - An Excellent Material for Fuel Tank Application

In 1989 Daimler Benz AG, Stuttgart, introduced hot dip aluminized steel sheet for this application in passenger vehicles. By now, after 10 years' experience, most of this manufacturer's current models are equipped with fuel tanks made from aluminized steel sheet. This material incorporates a combination of a specially designed deep drawing IF steel with the excellent corrosion protection properties of Al coatings. The two methods for joining the upper and lower halves of the tank body are resistance roller seam welding with an additional wire or laser beam welding. The first method was applied to the fuel tank bodies illustrated in this paper. In laboratory corrosion test series, aluminized steel sheet performed very well with regard to fuel resistance, including resistance to fuels containing methanol and rape-methyl-ester (bio diesel). Attempts to improve external corrosion resistance by in-line chromate treatment were successful.