USAMP team gives update on development of third-generation advanced high-strength steels

A project team led by the United States Automotive Materials Partnership (USAMP), a wholly owned subsidiary of the U.S. Council for Automotive Research representing FCA US, Ford Motor Co. and General Motors, is nearing completion of a multiyear effort to develop an Integrated Computational Materials Engineering (ICME) model for third-generation advanced high-strength steels (3GAHSS). When complete, the ICME model is expected to aid the development of 3GAHSS alloys for use in lightweighting automotive vehicle components and assemblies.

Engaging experts from Pacific Northwest National Laboratory, Clemson University, AK Steel Corp., the Advanced Photon Source (APS) at Argonne National Laboratory, Colorado School of Mines and the Auto/Steel Partnership (A/SP), USAMP’s ICME 3GAHSS team has successfully produced small volume heats (or sample casts) of two 3GAHSS alloys with mechanical properties close to those targeted by the U.S. Department of Energy (DOE) for an exceptional-strength, high-ductility alloy and a high-strength, exceptional-ductility alloy. 

Specifically, the team produced sufficient quantities of two 3GAHSS alloys for testing, model calibration and model validation. The first, a medium manganese (10 weight percent) 3GAHSS alloy, achieved 1,200 MPa (megapascal) ultimate tensile strength and 37 percent tensile elongation, which exceeded DOE targets for a high-strength/exceptional-ductility steel. The second 3GAHSS alloy of a 3 percent manganese steel achieved 1,538 MPa tensile strength and 19 percent tensile elongation, which exceeded the strength target and was close to the ductility target for the DOE’s exceptional-strength/high-ductility steel.  

These results enabled the development and calibration of a functional ICME model for 3GAHSS, which integrates material and forming models. The project leveraged DOE National Laboratories to produce, test and characterize the alloys. It also developed 3D representative volume elements of the microstructures and a 3GAHSS ICME model for steel alloys that previously did not exist.  

The 3GAHSS alloys are complex multiphase materials with a metastable phase (austenite) that transforms (to martensite) when deformed. In the past, this has made modeling a challenge as the material phase composition and resulting mechanical properties change when being formed into components or during vehicle impact. 

To effectively model the complex behavior of these alloys, the team developed a new lab procedure for dynamically measuring the retained austenite volume fraction as a function of deformation mode (e.g., tension, bending, plane strain) and strain path. The lab procedure uses a high energy synchrotron x-ray diffraction technique coupled with digital image correlation, which is a whole field optical strain measurement technique. This new experimental methodology provides an unprecedented look at both the materials science of the austenite transformation and the extent to which it impacts strength and ductility.

Since the ICME model produces a forming prediction that relates stress, strain and strain rate, it can be used in forming and vehicle performance codes. The model also captures the relevant details of the microstructure.

In addition, a baseline automotive AHSS side structure was used to determine the potential performance and mass savings that could be provided by the two 3GAHSS alloys.  The results demonstrated the potential for significant weight reduction in automotive body and chassis components with an equal or better change in performance.     

This year, the project team is validating the 3GAHSS ICME model through forming trials, working to improve model accuracy, and preparing its final report. The team expects the delivered models to aid the steel industry in developing 3GAHSS alloys that could be used in manufacturing lightweight steel components to meet automotive mass savings, performance and safety requirements.  

The USAMP 3GAHSS project, managed in collaboration with A/SP, was funded in part by a competitively solicited $6 million award from the U.S. Department of Energy in 2013.  The project also was supported by ArcelorMittal, Nucor Corp., Brown University and the University of Illinois Urbana-Champaign.