Grade: Super Duplex stainless steel (UNS 32760, ASTM A182 grade F55) and (UNS32550, ASTM A182 grade F61)
Type: High alloy 25 % Cr (dual phase) stainless steel, usually delivered in the solution annealed conditionNominal CompositionElementUNS S32760, Wt % Zeron 100UNS S32550, Wt % Ferallium 255Carbon0.03 max0.04 maxSilicon1.0 max1.0 maxManganese1.0 max1.5 maxPhosphorus0.03 max0.04 maxSulphur0.01 max0.03 maxMolybdenum3.0 – 4.02.9 – 3.9Chromium24.0 – 26.024.0 – 27.0Nickel6.0 – 8.04.5 – 6.5Tungsten0.5 – 1.0–Copper0.5 – 1.01.5 – 2.5Nitrogen0.2 – 0.30.1 – 0.25
Notes The composition of super duplex varies depending on the manufacturer. Therefore other grades other than those shown above may be obtained.
Super duplex grades have PREN of 40 min. (see section 3.1)
Mechanical PropertiesPropertyValuesUltimate Tensile Strength110 min Ksi (760 Mpa)0.2 % Yield Strength *80 min Ksi (550 Mpa)Elongation *25 % minReduction of Area *45 % minCharpy Impact Toughness55 mean/40 min J at –46o CHardnessSee note below
Notes:
* There is no longer a maximum hardness value specified in ISO 15156/ NACE MR0175 for sour service applications. However many companies still impose the maximum hardness defined in NACE MR0175. This varies between 28 – 32 HRc max, depending on the grade and environmental conditions.
The impact toughness values shown are those typically specified for the grade
The grade consists of a ferrite – austenite phase balance, with typically ferrite being specified in the range 40 – 60 %.
Care is required when heat treating large sections, or welding this grade as deleterious precipitation (such as sigma) phase may occur. This results in a significant reduction in corrosion resistance and impact toughness.
The grade may be welded, however care is required to ensure the correct phase balance, and to avoid deleterious phases being formed.
The excellent corrosion resistance of these grades means that they are used in severe environments, for applications such as piping, valves, fasteners, F53 Flange and other pressure containing items.
Care is required when using the grade in conjunction with cathodic protection, due to concerns over hydrogen embrittlement, and it is advised that industry guidelines (such as those given in EEMUA 194) are followed in these applications.
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