Swagelok Improves Stainless Steel Hardness

Swagelok Co., well known for its products in fluid systems, is now commercializing an interesting process for treating the surface of austenitic stainless steel that makes the material act like much more expensive alloys.

According to the first patent issued for the development, the surface of the metal is activated and is then carburized at a temperature that is low enough that carbides are not formed. In effect, the enrichment of carbon on the surface makes the stainless harder. This is generally done by a process called case hardening, which is done at higher temperatures that promote formation of carbides. The beauty of the new Swagelok process, called SAT12, is that corrosion resistance of the stainless is not compromised by the hardening process.

"Hardness and corrosion resistance are known to be tradeoffs," says Swagelok. "Typically, when carbon enters the crystal structure, chromium moves in from surrounding areas to form chromium carbides." This reduces corrosion resistance, the reason stainless is often used. Meanwhile, the hardness for a thin layer around a treated part is about four to five times greater than the hardness for bulk 316L.

Hardness can be increased through additional carburization treatments. Hardness depths of 10 mum to 50 mum have been reached.

According to Swagelok, the process "enables ordinary stainless steel to adopt certain performance characteristics of expensive alloys like Hastelloy or titanium."

Swagelok, based in Solon, OH, is not a steel producer, but has done extensive research on metal treatment. In fact, its partner for the development and commercialization of the process is the Case Western Reserve University Center for Surface Analysis and Materials, just renamed the Swagelok Center. Swagelok and CWRU received a $5.5 million grant from the State of Ohio to develop the new surface hardening process.

Swagelok has been using the process internally since 2000 to improve the operation of the rear ferrule on a tube fitting. SAT12 makes the ferrule harder without compromising its corrosion resistance. Earlier this year, Swagelok Technical Services Co. was formed to commercialize SAT12. The company is considering licensing, but a specific go-to-market plan is still under development.

Potential markets are commercial pumps and circulation systems; fasteners; bearings, clutch plates and other industrial parts subject to heavy wear; military applications; aerospace, automotive; and medical devices, such as hip implants.

Key Properties of SAT12-Treated Stainless