Automakers face conflicting constraints when designing new body structures:
- With escalating concerns about human-induced green-house gases, global legislators have passed increasingly stringent vehicle emissions regulations, with even more aggressive targets planned for the coming years. Lighter weight body structures promote reduced vehicle emissions.
- Fuel price increases lead to greater consumer sensitivity to vehicle fuel economy. Lighter weight body structures also promote improved fuel economy.
- One of the easiest ways to reduce vehicle weight is to use thinner metal. To maintain crash performance, this thickness reduction must be accompanied by an increase in the strength of the sheet metal grade. Since thickness and stiffness are related, decreases in thickness must be accompanied by other methods to increase stiffness: either using a high-modulus material like steel, and/or using design features like darts or beads to lock in the shape. The chosen grade must be sufficiently formable to successfully incorporate these features.
- Automaker marketing departments highlight spacious interiors. Greater room can be accomplished by making larger vehicles, but the extra weight does not support mass reduction. On the other hand, use of more formable steels is a cost-effective way to increase packaging efficiency. New vehicle designs with complex geometries are aesthetically pleasing, but are difficult to form and join unless the chosen alloy has the necessary balance between strength and ductility.
- Global crash and safety regulations must be contemplated, especially if one body architecture will be used as the basis for vehicles intended for sale in multiple regions around the world. Increasing sheet metal thickness improves crash performance, so any reduction in thickness must be paired with using high strength grades where the deformation characteristics can be tuned to optimize crash energy management.
- All of these challenges must be addressed with sustainability in mind.
The global steel industry continues to develop new grades of steel defined by ever-increasing strength and ductility, continually reinventing this diverse material to address these challenges faced by automakers. Advanced High-Strength Steels (AHSS) are characterized by unique microstructures and metallurgical properties that allow OEMs to meet the diverse functional requirements of today’s vehicles.
Worldwide working groups within WorldAutoSteel member companies created the AHSS Application Guidelines to explain how and why AHSS steels are different from traditional higher strength steels in terms of press-forming, fabrication and joining for automotive underbody, structural, and body panel applications. This website provides in-depth current information on a wide range of topics related to successful application of these steels.
Automotive companies around the world have adopted different specification criteria. Steel companies have different production capabilities and commercial availability. As a result, the typical mechanical properties provided on this website simply illustrate the broad range of AHSS grades that may be available worldwide.
In addition, regional test procedures will cause a systematic variation in some properties measured on the same steel sample. One example is total elongation, where both measurement gauge length and gauge width are a function of the standard to which the test is conducted (ASTM, DIN, or JIS, also known as ISO I, II, or III), with these differences impacting the measured value. In addition, property requirements can be defined relative to either the rolling direction or transverse direction. Therefore, communication directly with individual steel companies is imperative to determine grade availability along with specific test procedures, associated parameters, and steel properties.