Steel is synonymous with strength: hard, durable, and resistant to much of what nature can throw at it. But modern life demands materials that are also light, ductile and eco-friendly.
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Now, thanks to two pioneering European Union (EU) projects, researchers have forged a steel that hits all those marks: an ultra-strong alloy with deformation properties can be manufactured with improved energy efficiency, offering a huge industrial potential.
The two EU projects, PROMS and EAF-PROMS, looked at ways of producing novel ultra strong steel grades with high manganese content.
A PROM ran from 2003 to 2006, and was backed by € 560,693 from the European Commission. Its follow-up, EAF-PROMS ran from 2006 to 2008, with € 391,661 in Commission backing and had a particular focus on steel production in electric arc furnaces (EAF).
High-strength steel alloys are particularly interesting for carmakers, allowing them to reduce car weights through thinner sheets. They also help conserve resources: lighter, fuel-efficient vehicles mean less overall steel use and ultimately less fuel consumption (by some estimates, up to 0.2 litres per 100 km) and carbon emissions.
There are other areas where these ultra-strong steels could be used, like high temperature energy production, where they resist oxidation and corrosion while maintaining ductility. “There is a whole range of industrial applications where these high strength steels could be used,” says Karl-Heinz Spitzer, one of the project leaders.
Manganese is crucial for the alloy, increasing depth of hardening and improving strength and toughness by up to three times. While most steels contain up to 1.2% manganese (and much smaller amounts of silicon, nickel, chromium, aluminium, molybdenum and copper), manganese steel alloys have around 13% manganese. However these projects looked at manganese proportions of between 10 and 25%.
But producing such high-manganese steels is tricky and requires a delicate balance of other elements to ensure the final alloys retains its qualities. Spitzer, a process metallurgy professor at the Clausthal University of Technology in the German town of Clausthal-Zellerfeld, says the key challenge was to develop a production process that brought all the elements together. “This high strength steel cannot be cast by conventional continuous casting,” he says. “It needs new production technologies. The projects showed that with the right combinations of elements, mass production of high-manganese steel grades is possible using either the blast furnace-basic oxygen converter route or the electric arc furnace route.”
Indeed, on the back of PROMS and EAF-PROMS, the projects’ industrial partner, Salzgitter AG steel group, decided to build the world‘s first line for production of high-manganese steel grades based on the electric arc furnace route. Salzgitter is using a strip casting production process, which means less energy and carbon dioxide use than traditional technologies: the low casting thickness – 8 to 15 mm compared to 200 to 250 mm for conventional continuous casting - means it is possible to save up to 75% during casting, heating and rolling.
The projects could thus transform the steelmaking, helping Europe develop light but strong metals through energy efficient production. “Europe’s steel industry can only survive with innovative products and technologies. We hope we can contribute to this challenge with our projects,” says Spitzer.