Duplex SS 32760

Duplex stainless steels are normally not used at elevated temperatures but when this grade is pushed at an increased temperature, it does not lose much yield strength. At a temperature of about 250°C, the yield strength of the grade remains about 400 MPa and UTS remains about 650 MPa. A high-pitting resistance is guaranteed by the grade in delivered condition. Pitting resistance number (PREN) of the grade is normally greater than 40, which is better than other austenitic and duplex grades. It also provides superior resistance to overall localized corrosion.

Tungsten is normally an impurity, but the addition of tungsten in the grade certainly enhances the pitting resistance and has its value in the PREN formula. A small addition of copper in 32760 makes sure that resistance to variable non-oxidizing and mineral acids is provided. The 25% chromium in the grade along with other alloying elements, gives the grade superior corrosion, oxidation resistance, better strength and better stress corrosion resistance to other 300 series alloys and many 22% Cr alloys. The grade has fine forming characteristics and can be appropriately forged around 1100-1250°C. Reheat might be required for complete forging, followed by cooling in air. The grade has significant impact strength and is used in many applications for the same purposes. Very less decrease in impact strength is obtained with a decrease in temperature.

The lost impact strength is retained post-welding. No ductile to brittle transition is obtained at lower temperatures, hence excellent ductility is one of its prime properties. Even at sub-zero temperatures, down to -50°C, ductility and mechanical properties are preserved.

Physical Properties

General Specification

Standards Specifications

Piping and tubing, fittings and flanges, washers.

Fittings & Flanges

Forms of Supply

Piping and tubing, fittings and flanges, washers.

[#corrosion-resistance]Corrosion Resistance[#corrosion-resistance]

This grade is commonly used in chloride stress cracking environments which require considerable resistance. Resistance to sulphide cracking is provided along with sour-gas cracking environments. It can effectively resist corrosion in seawater. The grade has exceptional pitting and crevice corrosion resistance, due to its chemical composition and has a critical pitting temperature of about 50°C. It retains its strength along with corrosion resistance in wide range of environments like organic and un-organic acids, strong alkalis, non-oxidizing acids, etc.

[#fabrication-and-heat-treatment]Heat Treatment[#fabrication-and-heat-treatment]

Annealing is done on the grade to remove internal stresses and restore its grain structure and ductility. It is done after the forming processes to restore its mechanical properties. Annealing is done around 1100-1150°C, followed by appropriate soaking through the sections.

• Time at temperature should be managed according to the sections.
• Sufficient time needs to be provided for the centre sections to reach the heat treatment temperature. Followed by water quenching.

[#weldability]Weldability[#weldability]

The grade is readily weldable using standard techniques. Electric arc welding techniques are normally used. Oxyacetylene welding is not recommended. The grade has a very low carbon content, hence carbide precipitation at the grain boundary of the heat affected zone is usually neglected. After welding, it retains most of its toughness and impact strength.

Machining

The grade is usually used in the annealed condition and can be conveniently machined using standard techniques. It has high strength and retains its strength at a wide range of temperatures. The grade needs to be machined with proper constraints; positive feed, rigid and sharp tooling, adequate lubrication, powerful machinery is recommended.

[#applications]Applications[#applications]

Oil and chemical tankers, Sewage treatment, Agrochemicals production, Oil & Gas industry pumps, valves, pipe, vessels, Subsea pipework systems, Flue gas desulphurisation (FGD) plants, Equipment handling organic & fatty acids, Centrifuges and agitators, Storage tanks and pressure vessels, Desalination plants, Food Industry applications including sugar cane centrifuges, corn and vegetable processing plant, Marine industry and shipbuilding propellers, shafts, rudders, shaft seals, pumps, bolts, fasteners, valves, instrumentation, Pollution control systems, fans and pumps, Seawater systems, Pulp & paper industry components, Process industry components.

Possible grade alternatives