Page 60 - MetalForming-Apr-2018-issue

New Steels
produced small-volume heats of two 3rd-Gen-AHSS alloys with mechanical properties that met DOE targets for a high-strength, exceptional-ductility 3rd-Gen AHSS, and nearly met targets for exceptional strength and high duc- tility. The first, a medium manganese (10 percent by weight) 3rd-Gen-AHSS alloy, achieved 1200-MPa ultimate ten- sile strength and 37-percent tensile elongation, which met the DOE target for high strength and exceeded the 30- percent exceptional-ductility target. The second 3rd-Gen-AHSS alloy with 3-percent manganese achieved 1500- MPa tensile strength and 19-percent tensile elongation, which met the strength target and fell short of the 25- percent ductility target.
With insufficient time to develop and produce an exceptional-strength, high-elongation steel meeting DOE tar- gets for both strength and ductility, the project team employed the ICME mate- rial model to predict a steel microstruc- ture that would do so. In addition, the
project team designed and built a dieset to validate the forming model with respect to geometry and thickness, and material models with respect to post-forming microstructure and mechanical properties. Data obtained from the medium-manganese 3rd- Gen-AHSS T-components enabled the project team to better predict post- forming microstructure and subse- quent mechanical properties.
Yields Improved Side-Structure Design
The project also simulated the appli- cation of 3rd-Gen AHSS into a baseline automotive side structure shown in Fig. 2. The side-structure design was optimized to take advantage of improved 3rd-Gen-AHSS mechanical properties, resulting in a final design that reduced the number of compo- nents from 46 to 28 and achieved 30- percent mass savings. This optimized design met vehicle-crash (pole intru- sion, side impact, rear impact, roof
crush) and stiffness (torsional and bending) requirements—significant considering that steel thicknesses for the side-structure components ranged from 0.5 to 2 mm. Even with such reduced thickness, the optimized final side-structure design showed improved crash performance versus the baseline design.
Economical Path Forward
The project developed a process- driven model to compare costs of the baseline side-structure assembly against the final 3rd-Gen-AHSS side structure. Costs, based on industry esti- mates, are not specific to any OEM or steel provider. The model estimated a cost increase of between $0.32 and $1.26/lb. of weight saved for the 3rd Gen AHSS side-structure assembly. This totaled much lower than DOE’s target of $3.18/lb. of weight saved, thus sug- gesting that 3rd Gen AHSS can provide a cost-effective solution to meet OEM lightweighting goals. MF
58 MetalForming/April 2018
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