Content area
Full Text
Advanced high-strength steels (AHSS) are of great interest to the transportation industry to help meet increasingly restrictive fuel economy and emissions regulations. Since the mid-1990s, the properties of steels used in automotive structures have changed dramatically, and in some cases the tensile strength levels have increased more than fivefold: current press-hardened grades achieve strengths of 1500 MPa or more relative to mild steel sheets with strengths of less than 300 MPa. New AHSS grades have a wide variety of sophisticated microstructures carefully designed to produce a desired combination of mechanical properties. As such, there are significant challenges in the understanding of microstructure effects on mechanical response of these steels during manufacturing and in service. To give a few examples, the effects of strain rate, predictions of springback, measurements of phase stability, and assessments of stretch flangeability have all become more challenging with increasing microstructural complexity. In addition, there are continuous efforts to further improve the properties of steel sheets, and density modification via alloying may allow for materials with similar strengths but decreased weight, further improving the specific strengths of sheet materials. Here, we have selected a set of articles that address some of the challenges associated with current AHSS, and also look into possible pathways for future grades.
In the first article, "Strain Rate Effect on Tensile Flow Behavior and Anisotropy of a Medium Manganese TRIP Steel," by Rakan Alturk et al., the authors evaluate the effects of strain rates from quasi-static (0.005/s) to crash-relevant (500/s) in AHSS sheets that exhibit transformation-induced plasticity (TRIP) and yield point elongation. In addition, the relative effects of strain rate as a function of test orientation in the sheet are probed. They have found significant orientation effects on the strength, planar anisotropy, and normal anisotropy, showing the need to incorporate these effects into analyses of forming operations, in order to accurately predict material response and material condition after forming. Discussion of...