Vehicle manufacturers worldwide are increasingly facing the need to make their vehicles lighter than ever, in order to meet stricter emissions standards. At the same time, there is an increasing requirement to deliver vehicles with higher fuel mileage.
Such requirements have seen OEMs and suppliers turn to newer materials, such as aluminium alloys and carbon fibre reinforced plastics (CFRP), to achieve weight reductions. Each of these materials has its own advantages and disadvantages, and in most cases, a common disadvantage has been that of cost.
Steel still holds an advantage when costs come into play, and while aluminium and carbon fibre composites feature in premium and sports cars, the mass market still relies on steel. However, with the emergence of aluminium as a key lightweighting material in the global automotive industry, manufacturers of conventional automotive steel have had to up their ante.
Steel suppliers now contend that steel automotive body structures can, in the near future, be as light as today’s aluminium bodies. Advanced high-strength steels (AHSS) are a step in this direction, and the industry has now seen several generations of these steels.
Some OEMs, like Nissan, have turned to AHSS to reduce overall vehicle weight. The OEM eventually wants AHSS to account for up to 25% of all of a vehicle’s parts, by weight, for new production models. The OEM will start working towards this in 2017, and reaching this target will translate into a 15% weight reduction in Nissan’s vehicles.
Steel manufacturer ArcelorMittal has been working on, and investing in, AHSS. One of its key product lines for the automotive sector is Usibor, a press-hardened boron steel, featuring an aluminium-silicon coating. Usibor was developed specifically for the metal forming technique known as hot stamping, and it has strength of 1,500 MPa after being hot stamped. As a result, it is used mainly for the production of structural parts including A-pillars, B-pillars, frontal and rear bumpers, various types of rails, and the tunnel floor.
Megatrends spoke with Dr. Blake Zuidema, Director of Automotive Product Applications at ArcelorMittal, about the supplier’s investments in automotive body structure design technology.
“This has allowed us to look at each part of the automobile body structure, both individually as well as holistically,” explained Zuidema, “and helped us to understand what kinds of material properties are required to make each part as light and safe and fuel efficient, and as low cost, as possible.”
Lessons learned
ArcelorMittal’s involvement in internal body structure design programmes has resulted in the company turning this understanding inwards, into its own product development system.
“We’ve used what we’ve learned about the properties that are needed to make each part as light and safe and low cost as possible, and have developed a whole new family of products around that understanding,” explains Zuidema. “So, today you’ll see a number of advanced products, like the Usibor press hardened steel that was a feature in the Acura MDX door ring; you’ll also see things like higher strength dual-phase steels, the new high formability steels, even some higher strength exposed steels for use in other body panels.”
The use of Usibor in the Acura MDX’s door ring has been well received, says Zuidema, with numerous OEMs expressing interest in the concept. This three-way collaboration between ArcelorMittal, Honda and Magna’s Cosma International, involved replacing the Acura MDX door ring components with the Usibor-based lightweight laser-welded hot-stamped door ring. The result was a 14% weight reduction.
Global products, local markets
North America and Europe already have more stringent fuel and emissions standards in effect than many other markets, especially emerging markets. Megatrends asked Zuidema whether ArcelorMittal develops automotive products for North America and Europe, and then adapts them for emerging markets as necessary, or if emerging markets required the development of specific products, for reasons of cost, for instance.
“While the regulations in North America and in Europe are particularly challenging today, we see a movement all around the world towards ever-increasing fuel economy and CO2 tailpipe emissions standards,” said Zuidema. “Virtually all developed and developing countries around the world are enacting some sort of CO2 and fuel economy legislation. So, these lightweighting solutions are going to become increasingly important, not just in North America and Europe, but all over the world.”
Another important trend shaping the industry is that of vehicle manufacturers’ rising use of global platforms. Fewer platforms or architectures now underpin more cars globally than ever before. “In terms of imports and exports, there are a number of instances where an automaker may wish to produce vehicles in one region and ship them to another, because of the economies of scale.”
For those reasons, explains Zuidema, “it is extremely important that we have these advanced lightweight, cost effective, low carbon footprint steel solutions available in all of the markets that we participate in around the world.”
Other materials
There are, at present, many kinds of steels being used by OEMs worldwide, with varying degrees of strength, stiffness and weight. However, there is also a growing enthusiasm for aluminium, as demonstrated by Ford’s latest generation F-150 pick-up, which features significant quantities of aluminium. Other new materials, such as CFRP, are both light and strong.
According to Zuidema, the levels of weight reduction that are now possible with advanced steels, combined with the advancements made in powertrain technologies, mean the fleet of vehicles in North America can reach future fuel economy goals without going to other lightweight materials.
“Aluminium is, obviously, much more expensive, so, if an OEM can get a vehicle to its prescribed fuel economy with steel, it would be at a much lower cost. Carbon fibre is substantially more expensive. Obviously, we’re continuing to watch developments, but we’re not seeing the advancement in cost in some of these carbon fibre materials to really allow them to break into the mainstream of automobiles that most of us buy and drive every day.
“The other thing that we’re watching very carefully is the total lifecycle of carbon footprint that is provided by each of these vehicles,” adds Zuidema. “We’ve shown, through our CO2 emissions models, that cars built of steel have a much lower total lifecycle carbon footprint than vehicles made with aluminium or carbon fibre.”
The reason for this is that while aluminium is light and is an advantage when it comes to vehicular emissions and fuel economy, production of a component out of aluminium, or carbon fibre, results in more CO2 emissions than if the part were made of steel.
“The result is that the small differences in the use phase of fuel economy between the two do not make up for the difference in the manufacturing phase. And the steel cars, we’ve shown, provide a much lower overall lifecycle carbon footprint when all of the phases – manufacturing, use and recycling – are considered.”
Looking to the future
Zuidema identifies two key megatrends driving automotive product development: fuel economy and the need for global solutions. Fuel economy is, in Zuidema’s view, the key automotive megatrend, but it needs to be delivered in automotive products that are also safe and affordable. “One of the things we don’t want to do is to achieve lower tailpipe emissions and end up putting more carbon into the environment over the entire life of the vehicle,” he explains. “So these overall global challenges are driving the steel industry as much as anything right now. And, obviously, you can see that they’re also having a profound influence on the automotive industry.”
The growing importance of global solutions is thanks to the rise of the aforementioned global platforms, off which OEMs are building an increasing number of global vehicles. As a result, the need is also growing for solutions, support, and products in all regions of the world.
To fulfil the demands of these automotive megatrends, ArcelorMittal is developing Martensite 2,000 MPa strength products, and a next-generation version of Usibor, which could provide a minimum of 1,800 MPa.
The use of hot stamping is already increasing across the automotive industry, but Zuidema sees further significant opportunities for that technology and for higher strength, higher formability grades of steel. “Usibor products enable the carmaker to get the highest strength possible into very complicated geometry parts, particularly within the passenger compartment,” he explains. “The growth of Usibor will increase over that time frame.”
Zuidema says ArcelorMittal has looked at the long-term trends in advanced steel applications, and, both in terms of the current trajectory, as well as advanced solutions for 54.5 mpg cars that will be required in the US by 2025. “We see the total advanced steel content in the body and structure rising to something in the 60% to 65% range, which is a considerable increase from where it is today.”
With BMW leading the field in terms of high-volume carbon fibre production, and Ford committing to aluminium for its best-selling pick-up, the race is on for the strongest, lightest, cheapest and ‘greenest’ material for automotive applications.
