Duplex can form intermetallic phases such as sigma, which cut its toughness and corrosion resistance, when it is held between about 600 and 1750 °F (320 and 955 °C) or cooled too slowly. Meeting the chemistry and strength of the product specification does not prove these phases are absent, which is why the ASTM A923 tests exist. The bar and bolting specifications set no ferrite range and do not require A923 by default: the range and the method come from the purchaser's specification, and a requirement placed on bar while the mill makes it costs less than testing stock afterwards.
On duplex, a magnetic ferrite gauge has limited reliability unless it is checked against reference pieces of the same shape whose ferrite was measured by point count, and it cannot find sigma, which is non-magnetic. The point count can also be made by image analysis to ASTM E1245. For austenitic parts that must be non-magnetic, the limit is on relative permeability instead, measured to ASTM A342.
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model dataFerrite fraction by systematic manual point count to ASTM E562; the first field and its 9 × 5 grid match the drawing on the test page, and every microstructure is schematic. 2205 is typically 40 to 50% ferrite (IMOA, Practical Guidelines for the Fabrication of Duplex Stainless Steels, 2014). The intermetallic temperature range and Methods A, B and C from ASTM A923; the Method C rate, time and temperature from IMOA. The Charpy specimen is drawn to ASTM A370; no impact energy is given because A923 sets it per steel type. Permeability by a low-mu indicator to ASTM A342, and 1.05 at 100 oersteds from ASTM F837 S3, on a 1/2-13 socket head cap screw drawn to ASME B18.3 proportions. The furnace, microscope, polisher, Charpy machine, balance and indicator are generic; the furnace hold, the counts in the later fields, the corrosion results and the indicator reading are for illustration.
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