A new class of lightweight, stainless steels with ultra-high strength and large ductility

Stainless steels, invented more than 100 years ago, enable many sustainable applications: 1) they are among the most corrosion-resistant commodity alloys (corrosion being one of the biggest sustainability problems, destroying annually about 3.4% of the GDP (2.5 trillion Euros )).
2) they have with about 75% one of the highest end-of-life recycling rates of all mass-produced materials is use, averaged over all stainless steel grades.
However, there are 2 drawbacks: (a) high and expensive alloying content. (b) high weight.
We tackled both challenges: In a team effort we developed a new family of low-density stainless steels with ultra-high strength (> 1 GPa) and high ductility (> 35%).

The alloys are based on the Fe–(20–30)Mn–(11.5–12.0)Al–1.5C–5Cr (wt%) system and are strengthened by dispersions of nano-sized Fe3AlC-type kappa-carbide. Alloying with Cr enhances the ductility without sacrificing strength, by suppressing the precipitation of κ-carbide and thus stabilizing the austenite matrix. The formation of a protective Al-rich oxide film on the surface lends the alloys outstanding resistance to pitting corrosion similar to ferritic stainless steels. The new alloy class has thus the potential to replace commercial stainless steels as it has much higher strength at similar formability, 17% lower mass density and lower environmental impact, qualifying it for demanding lightweight, corrosion resistant, high-strength structural parts.

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