Method makes stronger steel

Researchers from Oak Ridge National Laboratory and the University of Tennessee have found a way to cast relatively large structures from a type of steel whose atomic structure is amorphous, like glass, rather than the usual orderly crystalline structure of metal.

Amorphous metal alloys are generally stronger and harder than their crystalline cousins; they enable light sports equipment and strong medical implants. Amorphous metals are also not magnetic.

Current amorphous alloys are relatively expensive because they are made from metals like zirconium and palladium. The new steel alloy is around seven times cheaper than these, and is also stronger and has higher resistance to corrosion and heat, according to the researchers.

The trick to making structures from amorphous metal is keeping the metal atoms from arranging themselves into an orderly crystalline form as it turns from liquid to solid. Past research efforts ran into trouble when casting amorphous steel objects more than 4 millimeters across.

The researchers used a mix of metals that allows them to drop-cast their alloy to produce glassy steel rods as large as 12 millimeters. Steel is a mix of iron and carbon and often contains small amounts of other elements. The researchers' iron alloy contains chromium, manganese, molybdenum, carbon, boron and yttrium.

Key to the researchers' mix is the rare earth metal yttrium, which allowed the mix to remain molten at lower temperatures, and slowed the growth of crystals.

The new materials can be used for practical applications within one to two years, according to the researchers. The work appeared in the June 18, 2004 with issue of Physical Review Letters.