SAE - Automotive Lightweighting Using Advanced High-Strength Steels

Organization: SAE
Publication Date: 13 June 2014
Page Count: 200


In the early 1990s, as a technical specialist at Ford Motor Company, I had a small support staff working for me to put together and solve large vehicle system computer-aided engineering (CAE) models. Though my work was primarily focused on steel, I also did some investigations on alternative materials (e.g., aluminum and magnesium). It was around this period that Al Gore spearheaded the Program for Next Generation Vehicles (PNGV) during the early years of the Clinton administration. Materials research played a big part in that program, and aluminum came to the forefront as the material of the future for automobiles. Most of the material focus was on the structural body of the vehicle, and the claim was made at that time that 50% of the weight could be saved by converting steel to aluminum; mid-sized concept vehicles were built by General Motors and Ford to prove that claim.

During the early PNGV days, through my own personal research, I came to believe that the claims for aluminum weight reduction were probably being exaggerated, but may not have been that far off, in that cars of that era had somewhat unoptimized architectures and were built out of fairly low-strength steels. The American Iron and Steel Institute (AISI) countered PNGV by building the Ultralight Steel Auto Body (ULSAB), which demonstrated that weight reductions close to what was claimed by PNGV could be achieved by extensive application of high-strength steels and accommodating architectures. This program also introduced advanced high-strength Steels (AHSS), primarily dual-phase steels, which were used to replace some of the previous generation mild steels and conventional high-strength steel (CHSS).

Though Corporate Average Fuel Economy (CAFE) requirements remained the same, during this period, the National Highway Traffic and Safety Administration (NHTSA) along with the Insurance Institute of Highway Safety (IIHS) were busy introducing new safety requirements along with test procedures, which became de facto requirements. This, along with pending fuel economy regulations in the United States and high fuel prices in other parts of the world, prompted a number of material initiatives by the International Iron & Steel Institute (IISI) (e.g., ULSAB-AVC and Future Steel Vehicle) and by PNGV, which morphed into Freedom Car under the Bush administration. Also, by this time, Freedom Car had become more material neutral and supported some amount of steel research. Steel research was also supported by the Auto/Steel Partnership (A/SP) in the United States and internally at the auto and steel companies.

Throughout this period, leading up to my retirement at the end of 2006, many materials engineers throughout the automotive industry still considered aluminum the material of the future for automobiles and still believed the weight reduction potential for aluminum to be about 45%, despite all of the steel research to the contrary. For this reason, I started to teach a seminar at the Society of Automotive Engineers on AHSS that would lay out the true technical case for how much weight could really be taken out of automobiles, using the different material alternatives. However, I believe that the course I'm teaching has hardly moved the needle for both the alternative materials engineer and the steel engineers. As evidence of this, AHSS account for less than 10% of the steel sheet metal volume used prior to the time of this writing (2013). However, the automobile industry is faced with the greatest hurdle, in terms of regulation, that it has ever faced. The Environmental Protection Agency (EPA) is now requiring that automobiles achieve a fleetwide average of 54.5 MPG by 2025 through a very aggressive fuel economy phase-in program. To meet this requirement, the auto industry is taking a very hard look at alternative materials, primarily aluminum, and is accelerating the application of AHSS. Meanwhile, the steel industry is starting to market second and third generation AHHS.

In support of the latest automotive challenges in terms of weight reduction, I wrote this book in an attempt to lay out the true opportunities for alternative material utility in automobiles and to offer the most up-to-date design guidance in efficient architectures supported with the application of AHSS while exploring weight savings and resulting fuel economy advantages of this strategy. Realistic comparisons with other alternative materials are made through detailed analysis. Many projects that I have been part of will be explored to demonstrate how AHSS technology has developed and to get us to the foothills of the mountain that we, as automobile design people, now must climb.