(Photo by Fischer Feritscope® FMP30C - Link: https://www.verniersales.com/ferrite-content ) To convert from ferrite % to FN, the following can be used: For 22 % Cr duplex stainless steel, ferrite % = 0.7 × FN; For 25 % Cr duplex and super duplex stainless steels, ferrite % = 0.65 × FN. Refer to API RP 582 2016 Section 11.3.4.3 Weld metal: 30 to 65% HAZ: 40 to 65 % Base metal: 40 to 60%