New Steel Alloy as Strong as Titanium

New Steel Alloy as Strong as Titanium
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If human society had a backbone, it would probably be composed of steel. Alloys of iron and carbon, steels are manufactured to the tune of 1.3 billion tons annually, and put to work in buildings, tools, automobiles, machines, and weapons, among many other places.

The reasons for steel's success are simple: it is cheap, strong, relatively easy to mass-produce, and generally ductile, meaning that it can be stretched and bent without fracturing.

But steel's dominance has been slightly waning of late. For example, the proportion of steel and iron in an average light vehicle decreased from 68.1% in 1995 to 60.1% in 2011. Materials with higher ratios of strength to weight are increasingly being used instead.

Today, a team of researchers reporting in Nature has provided a recipe that could return steel to its top form. Sang-Heon Kim, Hansoo Kim, and Nack J. Kim, based out of South Korea's Graduate Institute of Ferrous Technology, describe a new alloy of steel bolstered with aluminum and augmented with nickel that matches or outperforms titanium alloys on measures of strength and ductility.

The formula is key, but the process is just as important. The authors described their methods in detail and noted that they're readily "compatible with existing commercial processes of the steel industry."

The steel under investigation here was produced using an induction melting furnace. About 40 kg was melted in a protective argon atmosphere and cast to a rectangular ingot. After homogenization treatment at 1,150 C for 2 h, the ingot was hot-rolled with a starting temperature of 1,050 C to hot strips 3 mm in thickness. Then, the hot-rolled strips were cold-rolled to final sheets 1 mm in thickness. The cold-rolled sheets were annealed at 870–900 C for 2–60 min and immediately water-quenched or continuously cooled down to 25 C at the rate of 30 C.

After creating their new steel, which they dubbed high-specific-strength steel (HSSS), the researchers put it to the test, comparing it to two top, widely-used alloys of steel (PHS and TRIPLEX), one of titanium (Ti6Al4V), and one of aluminum (AA2000). They found that HSSS matched titanium's strength, while proving more ductile at those strengths. The aluminum and steel alloys were soundly beaten.

If adopted, the new steel could be applied in a host of settings, from buildings, to bridges, to cars.

(Top Image: Hansoo Kim)

Source: Sang-Heon Kim, Hansoo Kim, and Nack J. Kim. "Brittle intermetallic compound makes ultrastrong low-density steel with large ductility." 5 FEBRUARY 2015 | VOL 518 | NATURE | 77

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