Capability of New High Strength ADI-Materials for Automotive Components under Crash Loading

The development of new high strength ADI (Austempered Ductile Iron) materials and their evaluation for light weight design purposes are parts of the German research project LEA. The Fraunhofer IWM is investigating the capabilities of ADI materials under crash loading situations by conducting high rate tensile tests which quantify the material's strain rate sensitivity. These investigations result in a reduction of the austenitic phase content of initially about 35%, decreasing to 5–10% after fracture (as characterized by X‐ray diffraction), indicating a phase transformation comparable to a TRIP effect. Several ADI 1000 and ADI 1200 samples show an increase in strength of about 100 MPa up to crash‐relevant strain rates of 100 s−1, and the elongation at fracture is constant or increasing, in some cases up to more than 20%. Thus, the newly developed high strength ADI materials exhibit good potential for crash loaded automotive components. High strength properties and large elongations at fracture are determined for two ADI materials by high rate tensile tests. The reason for this good crash performance might be a significant reduction of the austenite phase as detected with EBSD after the tests. This indicates a phase transformation comparable to a TRIP effect.