Advantages in Performance Duplex Stainless Steel
	There is no such thing as an all-purpose material for corrosion resistance, just as there is not just one corrosion type. Duplex alloys are in a class with several other materials for various types of corrosion resistance. Some of the corrosive environments listed below depict these differences. There are many more types of corrosive conditions but these are some for which stainless and nickel alloys are suitable. Environment Problem Poor Good Best Chlorides Pitting, crevice corrosion 300 Series SS Duplex alloys 317LXN® Alloy 276 AL6XN® Chlorides/Halides Stress corrosion cracking 300 Series SS Duplex alloys Alloy 600/625 AL6XN® Hydrochloric Acid Pitting, crevice corrosion Titanium, Duplex, 20 Cb-3 Alloy 22, 276 Zirconium, Tantalum Hydrofluoric Acid Pitting, crevice corrosion Duplex Alloys Silver, Gold Copper, Alloy 400 Sulfuric Acid Pitting, crevice corrosion Copper-Nickel (MONEL®) Alloy 601 20 Cb-3 Alloy 622 HASTELLOY® C-22 General Acidic Attack Critical Pitting 300 Series SS 317LNMo Duplex Alloys Alloy 25-6 Mo Alloy 625 ® AL6XN and 317LXN are Trademarks of Allegheny Ludlum Steel. ® MONEL and HASTELLOY are trademarks of Allegheny Ludlum Steel. ® Nitronic is a trademark of U.S. Steel. As the table shows, some alloys outperform duplex alloys in many environments. Duplex is better than the 300 series in nearly every category. The consideration in the case of chlorides and halides must include costs. Duplex alloys are nearly equal in strength to the C276 and AL6XN alloys. The pitting and crevice corrosion resistance of C276 and AL6XN are only slightly superior to the duplex alloys'. The corrosion rate for duplex is 23 mil/year; AL6XN is 17 mil/year. (Boiling NaOH, 290 degrees F for 48 hours.) Duplex alloys are much more readily available than higher-nickel alloys. The elements that provide the strength and corrosion resistance in duplex are much more common than those found in some high-nickel alloys. For instance C276 contains tungsten. Carpenter 20Cb contains columbium and tantalum. The 625 alloy contains columbium, tantalum, cobalt, and titanium. Chromium, nickel, molybdenum, and nitrogen are common elements that provide the strength and corrosion resistance in the duplex alloys. The nitrogen is used in much the same way as it is used to protect the surface of Nitronic® 30.