Manganese Substitution Grades of Stainless Steel

During World War II when nickel shortages were severe, the stainless steel industry turned to manganese as a substitute.  Manganese is about half as effective in forming austenite as is nickel, so for every 1% reduction in nickel content, roughly 2% of manganese must be substituted.

Because the broadly named 18-8 stainless (301, 304 types) constituted the largest consumption of stainless, it was the first to be targeted for nickel substitution and the result was Type 201.  Generic Type 301 stainless is essentially 16% Cr/6% Ni while Type 201 is 16% Cr/3.5% Ni and 5.5% Mn (5.5*0.5 + 3.5 = 6.25 nickel equivalent).  These alloys have similar corrosion resistance and similar mechanical properties. Their forming and fabrication characteristics are also nearly the same. In recent times when nickel prices have soared, there was a significant move in the appliance and food equipment industries to switch to Type 201 as a cost saving measure.  Most recently, nickel prices have returned to more historic levels, but that is a topic for another time. (see the Surcharge topic, May 12, 2014).

Armco Steel expanded on this concept and developed the Nitronic® series of alloys.  A side benefit of higher manganese is the ability to absorb more nitrogen.  Nitrogen can act as a strengthener and can also enhance pitting resistance.  This opened the opportunity to develop alloys with high strengths and improved corrosion resistance without costly alloying additions. One of the more widely used of this series is Nitronic 50 (UNS S20910, XM-19) which has a nominal 22% Cr, 13% Ni and 5% Mn composition.  Its corrosion resistance and strength is comparable to duplex alloy 2205, but this alloy remains non-magnetic even after severe cold work.  This means the alloy is useful in both the annealed and strain hardened condition.

Nitronic 30 (S20400, 16% Cr-2% Ni-8% Mn) and Nitronic 40 (S21900, 21% Cr-6% Ni-9% Mn) have been used in the aerospace and chemical process industries.  Although the Nitronic tradename now belongs to AK Steel, the alloys are in the public domain.  Another widely used alloy from this series is the Nitronic 60 (S21800, 17% Cr-8.5% Ni-8% Mn-4%Si) galling resistant alloy.  Also used in both the annealed and strain hardened conditions, this alloy has been used for wear and fastener applications requiring moderate corrosion resistance.

Other manganese substitution or high manganese grades exist including Carpenter’s Gall-Tough® alloy (S20161, 16% Cr-5% Ni-5% Mn-3.5% Si) and 15-15LC® Modified (16% Cr-3% Ni-15% Mn).  Outokumpu invented a lean duplex alloy that also reduces nickel content through manganese substitution.  This LDX2101® alloy (S32101) contains only 1.5% Ni, with 21% Cr and 5% Mn.  The corrosion resistance of LDX2101 is comparable to that of 304 stainless which has five times the nickel content. With the duplex austenite/ferrite microstructure, LDX2101 also resists chloride stress corrosion cracking.

Additional technical information on S20910 (XM-19) and S21800 can be found elsewhere on the Rolled Alloys website.