Advanced high-strength steels and improved designs will play an important role as North American auto producers strive to reduce weight and meet projected mandates to improve mileage and reduce carbon dioxide emissions. Those were among the highlights of a “Great Designs in Steel” conference held by the American Iron and Steel Institute March 7 in Southfield, MI. The AISI named the engineering team for the Pontiac Solstice for its inaugural Great Designs in Steel Automotive Excellence Award. Use of advanced high-strength steels in the Solstice “clearly demonstrates how recent advances in material and processing technology enable steel to offer significant advantages in structural efficiency, quality and cost for new vehicle designs,” commented Brian Aranha, chairman of the AISI Automotive Applications Committee.
Solstice Takes Honors
The Pontiac Solstice roadster is the first vehicle to incorporate dual-phase steel, an advanced high-strength steel grade, into its hydroformed structure, consisting of 600-grade tubes. The hydroformed tubular rails form the underbody structure extending from the front to the rear bumper and provide an efficient way of improving structural performance and stiffness. The hydroformed rails also significantly reduce the weight of the vehicle without incurring cost penalties. Hydroforming is a type of die forming employing a high-pressure hydraulic fluid to press material (at room temperature) into a die. GM’s Sanjay Shah says that hydroforming can be used to reduce mass of parts, as well as costs. In one example he cited in a conference presentation, mass can be reduced by almost 40 percent.
Dual Phase on the Sebring
The Chrysler Sebring uses dual-phase 590 steel for key structural components that must be crash worthy, including the front rails, sills, tunnel reinforcement and cross-car beams. Dual-phase steels are leading the charge in new steel applications because they can be tuned to meet specific requirements for strength and processing. Structures with dual-phase steel are as much as three times stronger than low carbon or “mild” steel. Dual-phase steels, such as 590 strength level, allow downgaging and weight reduction. Features include good stampability and weldability.
Safety First at Honda
Half of the body structure in the Honda Civic advanced compatibility engineering (ACE) design relies on high-strength steels to meet stringent safety requirements. Use of advanced high-strength steel will grow from 149 lbs per light vehicle in North America this year to 403 lbs in 2015, according to a report from Ducker Worldwide. The shift will come at the expense of low carbon steel, which recently constituted 41 percent of car body structures, according to a presentation by Curt D. Horvath, a technical fellow at GM. Future car body structures will consist of only about 12 percent of low carbon steel.