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Energy savings are among the most important goals of steel users. Usinor proposes a wide range of very high strength steels (HSLA, DP, TRIP, etc.) for weight reduction and impact resistance. This text deals with the mechanical testing and different design solutions associated with these steel grades. Tensile and formability properties are presented first by means of basic tests (drawing, stretching, bending, etc.) in order to classify the different steels. A specific part of the text deals with a ultra high tensile strength pre-coated boron steel for hot forming. In addition to this, the crash resistance is investigated by using a dynamic axial compression test and a dynamic three point bending test on structural components with closed and open cross sections. For each steel grade, the estimated weight saving potential is compared with respect to parts manufactured in high drawability steel. Finally, two different designs are presented with steel solutions for safety parts.

Weight reduction, economy in the use of material and energy resources are among the most important goals of steel users. Usinor proposes a wide range of very high strength steels (HSLA, DP, TRIP, etc.) for weight reduction, fatigue considerations and impact resistance. This text deals with the mechanical testing and different design solutions associated with these steel grades. Tensile and mechanical properties are presented in order to classify the different steels. In addition to this, the crash resistance is investigated by using a dynamic axial compression test on structural components with closed cross sections. For each steel grade, the estimated weight saving potential is compared with respect to parts manufactured in deep drawing quality. The use of high strength steel like Dual Phase steel or TRIP steel improves crash and fatigue performance due to their great work hardening during the forming compared to HSLA or Complex Phase steel.

Tensile properties of sheet steels at dynamic conditions are becoming more important for automotives in recent years due to the positive strain rate effect of steels which significantly improves energy absorption capability during crash events. However, several testing techniques are used by different testing laboratories, no testing standards are available, and the quality of data generated by different laboratories is often not comparable. In order to improve the data quality at high strain rate testing conditions and thus to improve the accuracy of crash simulation results, The International Iron and Steel Institute (IISI) initiated a project to develop the “Recommendations for Dynamic Tensile Testing of Sheet Steels”. The document provides guidelines for key elements of high strain rate testing, testing techniques, input methods, specimen geometry and stress/strain measurement instrumentations.

Traditional constitutive models can only describe a parallel or divergent stress strain response at different strain rates. This paper presents a new constitutive model that can describe convergent, divergent or parallel stress strain patterns. The new model is a modification to the popular Johnson-Cook model. By comparison with the Johnson-Cook model using high strain rate data of seven high strength steels, the new model is evaluated. The results showed that the new model could adequately describe the stress strain relation at high strain rates for the seven steels. In addition, an empirical relationship between the parameters in the new constitutive model and quasi-static tensile data has been developed based on the analysis of several high strength steels. The equation requires only quasi-static data as the input and is capable of estimating flow stresses at high strain rates.

Energy savings are among the most important goals of steel users. But generally, the increase of Tensile Strength for a given metallurgy is obtained to the detriment of ductility. ARCELOR develops new ultra high strength steel with TWinning Induced Plasticity (TWIP) effect for weight reduction and impact resistance. This product based on a manganese (Mn) alloying metallurgy has a tensile stress higher than 1000 MPa for a total elongation superior to 50%. This text deals with mechanical testing, welding and different design solutions which could be associated with this new steel grade in comparison with conventional UHS steel (HSLA, DP, TRIP, etc.). Tensile and formability properties are presented first by means of basic tests (stretching, bending, etc.) in order to classify the different steels. Then welding parameters and mechanical behavior of spot weld are presented.