APM 2327 is a powder metallurgical super duplex stainless steel. Compared to conventional duplex steels the grade has improved mechanical properties, corrosion resistance and superior corrosion fatigue performance.
The chemical composition is optimized for manufacturing large components with high wall thickness and is very similar to ASTM A182-F61 (UNS S32550) which requires max. 0.25% nitrogen. The corresponding European norm, W.Nr 1.4507, allows 0.30% nitrogen. APM 2327 has a nitrogen content of 0.25-0.30% which gives improved corrosion and mechanical properties.
Standards
- ASTM: A988
- UNS: S32505
- EN Number: 1.4410
Approvals
- Qualified according to NORSOK M650 (D52 eller D54). Maximum thickness 200 mm
Chemical composition (nominal)
| C | Cr | Mo | Ni | Cu | N |
|---|---|---|---|---|---|
| <0.03 | 26 | 3 | 7 | 2 | 0.27 |
Balance Fe.
Forms of supply
Components can be supplied in a wide range of dimensions and shapes because of the flexibility provided by powder metallurgy and near net shape technology. The products are supplied in the solution annealed and water quenched condition.
Applications
Thanks to its excellent corrosion properties, APM 2327 is a highly suitable material for service in environments containing chlorides and hydrogen sulphide. The material is suitable for use for topside and subsea offshore components, such as valve bodies, manifolds, swivels and headers. The steel is also suitable for use in dilute sulphuric acid solutions and for handling organic acids, e.g. acetic acid and mixtures.
The high strength of APM 2327 makes the material an attractive alternative to austenitic steels in structures subjected to heavy loads. good mechanical and corrosion properties make APM 2327 an economical choice in many applications by reducing the life cycle cost of equipment.
Mechanical properties
Hot isostatic pressed components have isotropic properties, meaning the mechanical properties are similar in all directions.
| Minimum* | Typical | |
| Proof strength, Rp0.2, MPa (ksi) | 550 (80) | 620 (90) |
| Tensile strength, Rm, MPa (ksi) | 800 (116) | 860 (125) |
| Elongation, A | 30% | 40% |
| Reduction of area, Z | 65% | 70% |
| Impact strength CVN at -46ºC, J (ft lb) | ≥45 (33) | |
| Hardness, HRC | <32 |
* Minimum values according to ASTM 988. Impact toughness values valid for wall thicknesses up to 200mm (round bar) at T/4.
| Temperature | Rp0.2 | |
|---|---|---|
| Minimum | Typical | |
| ºC | MPa (ksi) | MPa (ksi) |
| 50 | 530 (77) | 580 (84) |
| 100 | 480 (69) | 520 (75) |
| 150 | 420 (61) | 485 (70) |
| 200 | 405 (58) | 450 (65) |
Physical properties
Density: 7.8 g/cm3, 0.28 lb/in3
Mean coefficient of thermal expansion, 20-100°C: 13.5x10-6/°C
| Temperature, ºC | MPa | Temperature, ºF | ksi |
|---|---|---|---|
| 20 | 190 | 68 | 27.6 |
* (x103)
Microstructure
Hot isostatic pressed components have isotropic properties, meaning the mechanical properties are similar in all directions.
Fine isotropic microstructure of HIPed material vs. forged bar.
Corrosion resistance
In most media, APM 2327 possesses better resistance to general corrosion than steel of type ASTM 316L and 317L.
Pitting corrosion
Thanks to the high content of chromium, molybdenum and nitrogen, APM 2327 has good pitting and crevice corrosion resistance. A parameter for comparing the resistance of different steels to pitting corrosion is the PRE number (Pitting Resistance Equivalent). The PRE is defined as, in weight %: PRE = % Cr + 3.3 x % Mo + 16 x % N.
The critical pitting temperature of APM 2327 according to testing by ASTM G48A is 50°C.
Stress corrosion cracking
Duplex stainless steels are far less prone to stress corrosion cracking in chloride-bearing solutions at temperatures above 60°C (140°F) than for instance standard austenitic steels ASTM 304L and ASTM 316L.
In aqueous solutions containing hydrogen sulphide and chlorides, stress corrosion cracking can also occur on stainless steels at temperatures below
60°C (140°F). The corrosivity of such solutions is affected by acidity and chloride content.
APM 2327 possesses good resistance to stress corrosion cracking in environments containing chlorides as well as in those containing both chlorides and hydrogen sulphide. This has also been confirmed by available operating experience.
Hydrogen induced stress cracking (HISC)
Powder metal based, hot isostatic pressed duplex stainless steels generally have better resistance to hydrogen induced stress corrosion cracking than forged or cast material duplex stainless steel. One reason for this is smaller austenite spacing of the hot isostatic pressed material that is typically below 15 µm.
Heat treatment
Products are delivered in the heat-treated condition. If additional heat treatment is needed after further processing, the following is recommended:
Solution annealing 1050-1125oC (1920-2060°F) plus quenching in water.
Welding
The weldability of APM 2327 is good. Suitable welding methods are manual metal-arc welding with covered electrodes or gas shielded arc welding. Welding should be undertaken within the heat input range 0.5-2.5 kJ/mm. Max. interpass temperature is 150°C (482°F), depending on the application. Preheating or post-weld heat treatment is normally not necessary.
Matching filler metals are recommended in order to obtain a weld metal with optimum corrosion resistance and mechanical properties. For gas-shielded arc welding we recommend Sandvik 22.8.3.L or Sandvik 22.8.3.LSi, developed to give improved welding properties by gas metal arc welding (MIG/MAG).
For manual metal-arc welding, covered electrode Sandvik 22.9.3.LR is recommended and can also be used for welding APM 2327 to both carbon steels and stainless steels. Covered electrode Sandvik 23.12.2.LR and welding wire Sandvik 22.15.3.L, both of type AWS 309 Mo with low carbon content, can also be used. Contact Sandvik for further information on welding.
Fabrication
Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials. Tooling and work surfaces must be thoroughly cleaned before use. These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolor the surface of the fabricated product.
Machining
Being a two-phase (austenitic-ferritic) material, APM 2327 will present a different tool wear profile from that of single phase steels of types ASTM 304/304L and 316/316L. The cutting speed must therefore be lower than that recommended for ASTM 304/304L and 316/316L. Built-up edges and chipping are to be expected. It is recommended that a tougher insert grade is used than when machining austenitic stainless steel. For more information on machining APM 2327, please visit Sandvik Coromant.