ArcelorMittal has invested heavily to produce AHSS for the automotive industry. Chris Wright visits the company’s Sagunto plant, Spain, which is ramping up to produce 150,000 tons of Usibor per year from 2016

ArcelorMittal has collaborated with OEMs to develop steel solutions that meet critical requirements in terms of weight reduction as well as safety. The results are the company’s proprietary S-in motion steel solutions, which provide 19% weight savings for the body-in-white (BIW) of a typical C-Segment vehicle. The company has also introduced new advanced high-strength steels (AHSS) such as the proprietary Usibor for hot stamping and Fortiform for cold stamping, tailored specifically for automotive applications.

The steel giant has been producing galvanised steel for the automotive industry at Sagunto, near Valencia in Spain, since 1976. The huge plant is now ramping up its production of aluminium-silicone-coated Usibor. The €9m ($9.9m) Usibor Alusi project was started last year and will reach full rate by the second quarter of 2016, producing around 150,000 tons of Usibor. In addition to Europe, ArcelorMittal also produces Usibor Alusi in Brazil, China, and the US.

Plant director Pablo Avello Martinez says that Sagunto is fully oriented to the automotive sector, supplies all the carmakers in Spain, and is strategically placed to do so. “We are a finishing plant with no primary assets and fully integrated in terms of supply, with steel coils coming from ArcelorMittal plants in northern Spain and Marseilles in France,” he states. “Sagunto also supplies Fiat Group factories in Italy and the new Renault operation in Morocco. “Seventy-six per cent of our production is for the auto industry... 65% of auto production goes to domestic manufacturers in Spain, 15% to Italy and 10% goes to other markets including China, South America and Canada.”

Sagunto receives 2,500 tons of coils every day by rail from northern Spain while a ship from Marseilles arrives every two to three days. Each supplies around 50% of Sagunto’s requirements.

ArcelorMittal Sagunto schematic

Hot and cold rolling
One line remains purely as a cold rolling mill for conventional zinc galvanised steel, while the second mill uses hot-dip galvanising for three weeks of the month and in the fourth week it produces aluminium-silicon-coated Usibor boron steel. The coils are pickled and cleaned before entering the tandem mill to be cold rolled. The line has a maximum speed of 1,500 metres a minute and the rolling process hardens it. Most of this steel is then sent to OEMs or sub contractors to form the ‘skin’ of vehicles.

Hot rolling in the other mill produces an altogether different form of steel, with the heat and rolling process producing changes to the molecular structure. This steel is then used by OEMs and sub contractors in the production of BIW and tailored blanks. Maintaining the heat and the line speed is vital for the production of hot-rolled steel, and Sagunto uses a 50-metre high tower, or accumulator, which can be raised or lowered to achieve this, and is able to take up to nearly 1km of ‘slack’ in the system.

While the steel is heated to around 460°C, Usibor Alusi requires an even higher temperature of 680°C, and here a second accumulator is used on the line to prevent any bottlenecks. Switching once a month between the two processes takes around 12 hours. The Sagunto site covers 2,044 sq.m and the buildings account for 193,204 sq.m. Despite the size and scale of operation, there are few environmental issues, claims Martinez. “We are not a primary process like a blast furnace so there are no emissions. Our main concern is water management. All wastewater is treated and sent back into the sea,” he says.

Safety is a key consideration, however. “We are constantly moving extremely heavy loads, up to 40-ton coils of steel, and we carry out some 3,500 safety actions a year in terms of talks and seminars,” he adds.

What is Usibor?

Usibor is a press-hardenable, boron-alloyed steel with an aluminium-silicon coating. It is used in automotive components when high strength is required. The coating protects the steel from oxidation during heating and provides corrosion protection for the component. Manufacturing is done in a press-hardening line, where a steel blank is heated to 900°C and formed, then rapidly cooled (quenched) to room temperature in a water-cooled forming tool. The result is a hardened part with an ultimate tensile strength of 1,500MPa.

Usibor is used for many structural car parts such as:

• Front and rear bumper beams
• Door reinforcements
• Windscreen upright reinforcements
• B-pillar reinforcements
• Floor and roof reinforcements.

Pressing for weight and cost improvements
Philippe Baudon, CEO, Europe and Asia, for ArcelorMittal Tailored Blanks, explains that laser welding allows the company to put together steels of different grades or thicknesses to increase strength and improve crash performance. “We can also lower a car’s production cost, reduce weight and eliminate the need for reinforced parts.” he states. “Hot stamping produces high-strength steel with no reinforcement needed. We have found that a hot-stamped car part is nearly 30% lighter than baseline car parts and 17.7% lower on cost, and it is also 17.5% lighter than cold-stamped car parts.

“Rather than just being a materials supplier, we now work with OEMs at the very earliest stages of a vehicle’s development. Obviously we are not designers, but we can [offer] support in terms of the validation of design and identify potential improvements in terms of cost, mass and performance.”

Following an ambitious investment programme in Europe and the Americas, the Fortiform range of AHSS for cold stamping could lead to further weight savings of up to 20% in vehicle parts, compared with the weight savings already offered by ArcelorMittal’s current AHSS. Fortiform is able to absorb more energy in a crash, with less steel. This makes it suitable for use in many structural parts of the vehicle that may be affected during impact, including front and rear chassis members and windscreen A- and B-pillars.

ArcelorMittal spends around $260m annually on R&D, 30% of which is devoted to the automotive market. “Steel remains the most cost-effective material as well as the most commonly used metal in vehicles,” says Greg Ludkovsky, vice-president, global R&D. “While carbon fibre and aluminium are often proposed as alternatives to steel, these materials cost significantly more than the latest advanced high-strength steels.

“Steel remains the most cost-effective and most environmentally friendly material for automotive applications. Thanks to steel’s 100% recyclability and the lightweighting potential of AHSS steels, vehicles made with steel are also gentle on the environment.”

ArcelorMittal Sagunto

ArcelorMittal Sagunto has been producing steel for automotive uses since 1976 and is now ramping up for Usibor
Philippe Aubron, chief marketing officer for ArcelorMittal Automotive Europe, says there will be an increase in cars made on global platforms from 46% last year to 63% by 2020. “We need to demonstrate that we can supply all over the world as well as meet regulatory requirements that see ever decreasing limits on greenhouse gas emissions,” he adds. “Two-thirds of our research and development budget goes on ways we can help the auto industry reduce emissions with new products and solutions and adding more value to our products.

“For example, we can demonstrate that we can reduce body-in-white weight by 20% with existing steel grades such as Usibor high-strength steel, and 23% on a US large pick-up. Steel is taken for granted, but most of our customers recognise that ArcelorMittal is the technology leader. It is less costly to lose weight with steel than with aluminium, carbon fibre or magnesium. Steel is not a commodity, it’s a sophisticated and technical material.

“It is our belief that carbon fibre will not be relevant before 2030, while aluminium is still too expensive, plus steel is also 100% recyclable. High-strength steel is replacing mild strength [steel] and the next step will see ultra-high-strength steel having the potential to substitute aluminium parts. We are already seeing some manufacturers reverting back to steel from aluminium on next-generation models.”