I recently had the opportunity to showcase our automotive solutions at the Global Automotive Lightweight Materials Summit North America. Annually held in Detroit, the event was virtual in 2020. I joined a panel of steel industry leaders, organized in partnership with the American Iron and Steel Institute, to make the material case for steel to technical leaders and chief engineers from leading OEMs and autonomous and electric vehicle start-ups.
Innovation is always in practice at ArcelorMittal as we continue to develop technical solutions for our customers, targeting improvements in crash energy management and lightweighting. In addition to a broad product portfolio, we are the global leader in the development of both press-hardened steels (PHS) and martensitic steels.
Compared to traditional stamping done at room temperature, also known as cold stamping, PHS or hot-stamped steels achieve their high strength through heating the incoming steel to austenitic temperatures, and then quenching it in a water-cooled die – producing a martensitic microstructure. Forming at elevated temperatures allows for more complex geometry, resulting in no springback and more uniform mechanical properties in the final part.
In the late 1990s, ArcelorMittal introduced the first aluminum-silicon (Al-Si) coated PHS product, Usibor® 1500. Launched in Europe, we now offer it globally and have plants manufacturing PHS products in Europe, North America, South America and Asia. Our goal is to be a global supplier that offers global solutions to our customers.
Following Usibor 1500, we developed several additional products to address OEM requirements, such as Ductibor® 500 and 1000, and Usibor® 2000.
Usibor® 1500 and 2000 are very high strength products ideal for anti-intrusion applications, such as front and rear bumper beams, B-pillars, floor, door and roof reinforcements, as well as roof and dash panel crossmembers.
Ductibor® products are lower strength, more formable and are designed to absorb crash energy. Ductibor® is often combined with Usibor® in the form of laser-welded blanks, enabling hot-stamped parts with more ductile properties. Some applications for Usibor®/Ductibor® laser-welded blanks are front and rear rails, and B-pillar reinforcements, with the upper section in Usibor®, and lower section in Ductibor®. Door rings are also a growing market.
Example of potential applications of Usibor®/Ductibor® steels
These products and processes are proprietary, but we have expanded the supply chain through various licensing agreements.
Despite 20 years of tremendous global growth for these products, ArcelorMittal still sees significant potential. We continue to push the envelope and work with our customers to understand their technical issues and where we should focus our research.
For example, we have recently developed Thermoboost®, a proprietary coating applied after the pot on top of the standard Al-Si coating. This coating increases the emissivity of the surface, thereby increasing the heating rate and decreasing the cycle time, which can contribute to higher hot stamping process efficiency. This also widens the heating window for laser-welded blanks making it possible to have a larger difference between the thinnest and thickest sections of the blank.
We have developed another proprietary coating called Ultraprotect®, designed to improve the corrosion performance in wet areas, reducing and potentially eliminating the use of waxes and sealers. These coating products are available in Europe today and market interest is being investigated in North America.
All advanced high-strength steels (AHSS) need a strong stamper community to convert these products into assembly-ready parts. ArcelorMittal has invested in lab-based equipment to simulate a production environment. We also work with industrial partners to simulate a wider range of conditions. The goal is continuous improvement in our collective understanding of a wide range of topics, such as dimensional performance and the need to laser trim – a significant input to net cost.
Complementary to our press-hardenable steels, ArcelorMittal offers a full range of coatings and surface treatments to protect our steels for automotive applications.
Martensitic steels are also very high strength and enable lightweight structural elements to be manufactured, usually via roll forming. These grades are primarily for anti-intrusion, such as front and rear bumper beams, door beams, side sill reinforcements and roof crossmembers.
Typical automotive parts for MartINsite® steels
ArcelorMittal is a pioneer in developing this family of steels and has been manufacturing and supplying these products for over 35 years, starting with the 1983 commissioning of the No. 3 continuous annealing line at our Indiana Harbor plant. Since then, we have worked with our customers to develop many cost-effective lightweight steel solutions using these products.
Existing products include our proprietary MartINsite® 900, 1100, 1200, 1300, 1500, 1700 – and we are developing a 2000 product.
New product development is a very high priority within ArcelorMittal, but it’s not only about new products. It is also about continuous improvement to our existing portfolio. For example, in 2018 we completed a $34 million-dollar upgrade to the #3 continuous annealing facility. This included a new tension leveler, quench system and a strip transport control system. The result is significantly improved shape and product uniformity.
This upgrade was done to support existing business but is also key to our ability to supply the battery electric vehicle (BEV) community, and, especially the battery enclosure, where higher strength martensitic grades such as 1500 and 1700 play a significant role in ArcelorMittal design solutions.
The packaging space available for the battery pack structure in a BEV is limited. The design is driven more by anti-intrusion than stiffness. In limited package space, AHSS designs are more efficient than aluminum. Our internal studies show that with this limited space, an optimized aluminum battery box is only about 10% lighter than steel. This small weight penalty is more than offset by steels significant cost advantage.
Early battery enclosures made from aluminum tended to be for high end, lower volume, performance vehicles. Multiple studies have concluded that the need for lightweighting is lower with BEV and we are beginning to see OEM design strategies that reflect this with more designs exploring steel.
We believe martensitic steels will play a significant role in cost-effective lightweighting for these applications, maximizing packaging space and protecting the enclosure in a crash.
PHS and martensitic products were the main topic for my presentation, but I encourage you to check out our global site at automotive.arcelormittal.com. It summarizes the availability of all products on different continents. It also includes a wealth of information on our global portfolio, including the latest information on Generation 3 AHSS steels, and our battery pack designs for BEVs.
