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However, they will not be supplied under the name of TRIP steel. After all, the new generation of superstrength TRIP steels behaves quite differently than conventional TRIP steel, with which they now have little in common. Salzgitter AG will launch them on the market as HSD (high strength and ductility) steels.

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Tensile test: Georg Frommeyer examines a sheet that was drawn into a hollow dome shape until the first crack appeared.... [more]

Tensile test: Georg Frommeyer examines a sheet that was drawn into a hollow dome shape until the first crack appeared. The black gridlines show where the strain is strongest. [less]

Tensile test: Georg Frommeyer examines a sheet that was drawn into a hollow dome shape until the first crack appeared. The black gridlines show where the strain is strongest.

© Frank Vinken

© Frank Vinken

“In addition to the excellent mechanical properties, these steels are 5 to 6 percent less dense,” says Dr. Matthias Niemeyer, who heads Salzgitter Mannes­mann Forschungs GmbH, the research company of the Salzgitter Group. Automotive manufacturers will have a very new lightweight material to work with. After all, the car body accounts for a quarter or more of the total vehicle weight.

Niemeyer cannot yet say how much weight will be saved in the end. It depends on how the carmakers use the material. “At the moment, I’m assuming weight savings of between 10 and 20 percent; it might even be as much as 30 percent for some components,” he says.

Recently, another lightweight steel – triplex steel – was developed at the Max Planck Institute for Iron Research, Düsseldorf, for which the researchers received an award in the category “Steel in Research and Development” as part of the Steel Innovation Prize 2009 granted by the Steel Institute VDEh.

Triplex steel consists of three phases: austenite, ferrite and nano-sized carbides, which are finely and homo­geneously dispersed throughout the austenitic matrix. Georg Frommeyer’s former colleague Udo Brüx, who now works with Ford Research Center in Aachen, made a significant contribution to the development of this steel.

Triplex steel is even lighter than its TWIP/TRIP cousins, by 10 to 16 percent – but it has some very impressive properties. It is harder than TWIP steel and more ductile than TRIP. This is mainly due to the finely distributed carbides, which allow the austenite and ferrite phases to deform easily, even at a high strength level. The material and the manufacturing process still need to be optimized, but in all likelihood, Triplex steel will be a bestseller in automotive manufacturing in a few years.

GLOSSARY

TRIP effect
Transformation-induced plasticity: Under stress, the crystal structure changes – for instance from austenite to martensite – increasing the ductility.

TWIP effect
Twinning-induced plasticity: Under stress, the crystal structure folds at a stacking fault, and a twin is formed. The process absorbs a very large amount of impact energy.

Stacking fault
Irregularity in the order of the layers of atoms in a crystal.

Crystal twin
Occurs when the order of the crystal layers is reversed at a stacking fault – for example from ABC to CBA. Two crystals are formed that grow symmetrically from a common layer.