S21800, often known by its AK Steel brand name of Nitronic 60®, is a galling and wear resistant nitrogen-bearing austenitic stainless steel. It has superior corrosion resistance to 316L.
Approximate Composition – 17% Cr, 8.0% Mn, 4.0% Si, 8.0% Ni, 0.15% N. There is no equivalent in the EN system.
This grade combines the following characteristics:
- Good pitting and crevice corrosion resistance (better than 316L) based on a wide range of applications, despite its low Pitting Resistance Equivalent Number (PREN)
- High wear resistance. Weight loss reduced by 80% compared to 304 in abrasion test
- Cavitation erosion resistance better than standard austenitic and duplex grades
- Excellent galling resistance in contact with itself and other stainless steels
- 0.2% PS 50% higher than standard austenitic grades 304 and 316 in annealed condition
- High work hardening rate allows 0.2% PS of 600 MPa minimum by cold drawing
- Good weldability
- More difficult to machine than standard austenitic grades due to its high wear resistance
Stainless steels in general are prone to cold welding or galling when rubbed together under stress. The typical situation occurs in the threads of a bolt and nut or tapped hole. This is due to local breakdown of the passive film on the surface of the steel. S21800 was specifically developed to combat this problem. It uses a combination of Mn, Si, Ni and N to produce a highly stable and adherent passive oxide film. The high wear resistance is also a key feature of the grade.
Applications which illustrate these features include:
Fasteners, bridge pins, bridge bearings, valve stems, bearings, chain drives, impellers, wear rings, space research, surgical instruments.