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Understanding Stress Corrosion Cracking in Duplex Stainless Steel

by Feb 28, 2018News

stainless steelDuplex stainless steel has become more and more popular for its combination of strength and affordability. Not only can duplex stainless steel hold up reliably through trauma impact, but through corrosion as well.

To understand the corrosion resistance properties of duplex stainless steel, you must also understand the concept of stress corrosion cracking. Let’s discuss what it entails, and how it relates to duplex. 

What is Stress Corrosion Cracking?

Stress corrosion cracking – sometimes shortened to SCC – refers to the manner in which metals crack in corrosive conditions. SCC occurs not only under corrosive conditions, but under conditions in which tensile stress is continuously applied as well.

A slow, gradual process, stress corrosion cracking does not include instances in which metals are cracked by sudden trauma.

Cracking from SCC does not present itself as one long crack, but as a series of interconnected cracks. These cracks could most accurately be described as looking like a bare tree with limbs and branches extending to and fro.

All different metals can experience stress corrosion cracking, but some of them experience it much easier than others. Of course, the conditions under which these metals exist will also have a lot to do with whether or not stress corrosion cracking occurs.

Austenitic Stainless Steel and Corrosion Cracking

Duplex stainless steel is an alloy made out of both austenitic steel and ferritic steel. These two forms of steel combine to give duplex stainless steel the great versatility that it possesses.

Austenitic steel contains a great deal of nickel, giving it the ability to withstand a great deal of corrosion. However, when introduced to chlorides, it tends to suffer stress corrosion cracking fairly quickly. This makes it insufficient for purposes in which excess amounts of chloride are present.

Ferritic Stainless Steel and Corrosion Cracking

While its tensile strength is not at the level of austenitic stainless steel, ferritic stainless steel is much more resistant to corrosion than is austenitic. However, ferritic steel is still fairly vulnerable to stress corrosion cracking.

In essence, on their own, ferritic stainless steel and austenitic stainless steel don’t handle stress corrosion cracking admirably. For this reason, they can’t be used to serve a number of different functions.

Duplex Stainless Steel and Corrosion Cracking

It’s when austenitic stainless steel and ferritic stainless steel are put together that they become truly resistant to stress corrosion cracking.

This can be seen in the PREN (pitting resistance equivalent number) of duplex stainless steel as well as in its tensile strength.

In general, PREN is a good way to gauge a steel’s resistance to corrosion. Most duplex stainless steels have a PREN of around 35. This PREN outpaces lone austenitic stainless steels by about 10 points. At the same time, duplex stainless has shown that it’s much stronger than lone ferritic stainless steel.

In essence, duplex stainless steel is the best of both worlds. It combines the corrosion resistance of ferritic stainless with the strength of austenitic stainless to make a steel that is highly-resistant to stress corrosion cracking. 

Have Further Questions About Duplex Stainless Steel?

Do you feel as though you’ve got a good understanding of stress corrosion cracking in duplex stainless steel? Are you interested in more information on the subject. If so, we here at Great Plains Stainless are the people to talk to.

We manufacture and distribute duplex stainless steel all across the world. If anybody understands its benefits and characteristics, it’s us.

Contact us today to chat!