Steel-intensive vehicles driven by physics and collaboration

Sept. 2, 2019
Steel has two major advantages over competing automotive structural materials: physics and collaboration.

A few years after fuel economy standards increased, Ford announced the 2015 model year F-150 pickup truck would be aluminum-intensive. It debuted at the 2014 North American International Auto Show and went on sale a few months later. In that same year, Ducker Worldwide completed a vehicle materials content study and concluded, “Within the decade… Seven out of 10 new pickup trucks produced in North America will be aluminum-bodied[1].” Although this forecast was a wake-up call for the steel industry, it was not a big surprise to the automotive industry. After all, vehicle manufacturers, suppliers and all those involved in automotive, were well informed of the changing fuel economy regulations including the final target of 54.5 mpg by 2025, based on the vehicle mix in 2011, with more than half of the market represented by cars.

Automakers began to address the challenges by using technology that was on the shelf and ready to use but hadn’t been needed yet. It was also known these technologies would only achieve a portion of the required fuel economy improvements and more innovations were necessary. Powertrain, aerodynamics and lightweighting represent the top three categories most impactful to fuel economy so many developments began happening quickly in these segments. The body and closures make up almost one-third of the mass of a vehicle so debates started about what materials yield the best mass reduction and would the cost justify use of these materials to achieve fractional improvements in miles per gallon.

It’s been five years since this forecast and several new fully-redesigned, steel-intensive pickup trucks have been introduced over that span: 2015 Chevrolet Colorado/ GMC Canyon, 2016 Toyota Tacoma, 2016 Nissan Titan, 2018 Chevrolet Silverado/ GMC Sierra, 2019 Jeep Wrangler, 2019 Jeep/Gladiator, 2019 Ram 1500 and the 2019 Ford Ranger. How could the Ducker forecast be so far off, when their information came directly from the automakers who design, engineer and build the vehicles? Let’s take a look at why steel remains the dominant material for automotive body structures and closures.

Steel has two major advantages over competing automotive structural materials: physics and collaboration.

Steel is composed of iron and a very small amount of carbon, adding small amounts of other alloying elements (such as silicon, manganese, etc.) and certain material processing yields a wide variety of grades ranging in strength from approximately 200 to2,000 MegaPascals (29-290 ksi). The steel industry provides more than 200 grades of automotive sheet steel to give the right combination of properties for each of the hundreds of parts that make up a vehicle’s body. Each part has its own design and manufacturing requirements, which vary by vehicle and automaker. With pressure to maximize lightweighting and be competitive, automakers can benefit from the flexibility offered by this wide variety of steel grades and properties.

How did the steel industry increase steel’s strength ten times over what was available in the 1970’s and earlier? Simple: through innovation by collaboration. Combine the technical leaders in the steel industry with the best in automotive engineering and encourage them to develop pre-competitive automotive steel solutions to help the industry meet new fuel economy standards and vehicle collision performance improvements. Focusing on what the customers (automakers) need to meet their challenges as a collaborative steel industry, rather than as individual steel companies, leads to timely, cost-effective, synergistic innovation not achievable if tackled by individual companies, automotive or steel.

The properties delivered by the basic physics of iron and carbon along with innovation by collaboration allow steel to provide the most cost-effective automotive structural material in vehicles today. Automakers choose steel for its performance benefits in strength, stiffness and noise abatement, as well as durability and ease of manufacturing. But what about the future?

Future Mobility (FM) is a rapidly growing area in the automotive industry. It is defined as vehicles which are autonomous, connected (talking with each other and the infrastructure), electric (powered by batteries, fuel cells or hybrid technologies) and shared (owned and operated by fleet companies –mobility service providers, MSPs).  Although powertrain systems are changing dramatically in vehicles, moving people and goods from place to place remains very similar to today. Vehicles will need to provide appropriate space for passengers and cargo, including ease of ingress and egress. The vehicle will need to provide a safe, comfortable ride, as well as be durable and reliable. In addition, MSPs will be interested in a low total cost of ownership to help their business models. The price of the vehicle is greatly influenced by the cost of its materials and cost to manufacture, so this is important to automakers as well as MSPs. It would also be beneficial to society as a whole if the vehicle’s content was fully recyclable and environmentally friendly with the lowest carbon footprint.

Many critical requirements were discussed above. However, there are three main differences where steel provides the optimal solution: ingress/egress, battery packaging and protection, and optimized lightweighting.

Most FM autonomous vehicle (AV) designs do not show a B-pillar to allow for easy and quick ingress and egress to the vehicle and a living room style seating arrangement. This is challenging to the auto industry, as the B-pillar plays a significant role in structural stiffness as well as collision protection. Although the goal of FM is to eliminate collisions, industry experts agree this will take decades to achieve as several challenges will need to be addressed. Some of these include optimizing technology to reliably handle all external situations, such as animals running into a vehicle’s path, high winds taking down a tree, cybersecurity to avoid intentional collisions and older non-AVs on the road.

Image courtesy of Yanfeng Automotive Interiors

The exceptional strength, stiffness and formability of steel give automotive designers a mass efficient solution to eliminating the B-pillar.

These same properties assist designers with packaging batteries or other powertrain components. Using steel in the structure yields more space to package additional batteries through thinner sections as compared with materials of lower strength and/or stiffness. Using more batteries means driving farther on a charge. Good protection means not stranding passengers in the event of a minor collision.

Distance on a charge is already a major concern for consumers, and battery technology is constantly improving. Electric propulsion systems are typically more efficient than conventional powertrains today. This, coupled with higher power density batteries and advanced energy recovery technologies (e.g., regenerative brakes) means the amount of energy consumed to move battery electric vehicles is much less sensitive to change in vehicle weight than in gasoline powered vehicles. This is not to say lightweighting is not important. But, it means the cost of lightweighting plays a bigger role. Why pay hundreds or thousands of dollars more for a vehicle to get five percent or less additional miles on a charge?

The combination of exceptional strength, stiffness and formability along with cost-effectiveness and a low carbon footprint – through basic physics – makes steel a mainstay in the automotive structure materials toolbox today and for the future. It is hard to beat basic physics, especially when you have a great team collaborating to fully understand and exploit what the physics can deliver.

[1] Ducker Worldwide, 2014

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