| High-manganese austenitic transformation- and twinning-induced plasticity (TRIP/TWIP) steels are a new class of advanced high strength steels (AHSSs) that have received significant research interest over the last decade owing to their superior combination of strain-hardening, strength and ductility compared to other types of steel [1] [2] [3] [4] [5] [6] [7] [8] (see Figure 1-1). The automotive industry is highly interested in these steels as a means to reduce vehicle weight (through down gauging), increase crash worthiness and improve manufacturing efficiency through better room temperature formability. The performance requirements of structural automotive components are largely being driven by more stringent fuel economy and safety requirements. New corporate average fuel economy (CAFE) standards will require the average fuel economy of a manufacturer's fleet of cars and light trucks to be 54.5 miles per gallon (MPG) by 2025 [9]. Increasingly rigorous crash requirements, like the Insurance Institute for Highway Safety (IIHS) offset frontal impact test [10], require materials that can dissipate large amounts of energy during crashes in order to protect vehicle occupants. While lighter-weight materials such as Aluminum and Magnesium will play a role in meeting these requirements, AHSSs currently offer substantial cost savings over the aforementioned materials and are the preferred material to meet these targets [11]. Figure 1-2 shows the estimated production costs/savings associated with reducing vehicle mass with several types of material solutions. AHSSs are currently the only material which can reduce vehicle mass and production costs simultaneously. In fact, several automotive manufacturers, such as Volkswagen [12], have begun replacing aluminum with thinner gauge AHSS to retain weight savings while lowering costs. The multinational steel manufacturer POSCO has recently produced the first commercially available high-Mn TWIP steel [13] proving that these materials have the potential to play an important part in automotive design in the coming years. However, there are still many aspects of these steels and their unique deformation mechanisms that are not well understood. Further research is necessary to ensure TRIP and TWIP steels become a major part of the solution to the challenges of the automotive community. |
