Alloy 32750 (UNS S32750)
Alloy 32750 is a super duplex stainless steel supplied in the solution annealed condition. As a super duplex stainless steel, it combines the desirable aspects of both austenitic and ferritic grades. The higher chromium, molybdenum and nitrogen contents result in a Pitting Resistance Equivalent number (PREN) of >41, providing pitting and crevice corrosion resistance superior to austenitic and duplex stainless steels in almost all corrosive media, and a Critical Pitting Temperature exceeding 50°C.
Supplied in the annealed condition, it achieves yield strengths of 80ksi (550Mpa), greater than most austenitic and duplex stainless steel grades. It cannot be hardened by heat treatment but can be strengthened by cold working. It also exhibits a low coefficient of thermal expansion and higher heat conductivity than austenitic steels and is suitable for working temperatures up to 300°C. Alloy 32750 is listed in NACE MR 0175 for sour service and having gained ASME Approval for Pressure Vessel applications it can be used in a wide variety of applications.
Chemical Composition
| Cr | Ni | Mo | Co | Nb (+Ta) | Ti | V | W | Cu | C | Mn | N | Si | P | S | Fe | Al | |
| Min | 24.50 | 6.00 | 3.00 | 0.50 | 0.24 | 0.10 | |||||||||||
| Max | 26.00 | 8.00 | 5.00 | 0.50 | 0.03 | 1.20 | 0.32 | 0.80 | 0.035 | 0.020 | Bal |
Mechanical Properties:
| 0.2% Proof Stress | 550 N/mm2 | 79.8 ksi |
| Tensile Strength | 800 N/mm2 | 116 ksi |
| Elongation, 5.65√S0 | 25% | |
| Reduction of area | 45% | |
| Hardness (Brinell) | <270 | |
| Impact Strength (Room Temp) | 80J | |
| Impact Strength (-46oC) | Longitidinal 45J (35J min) | |
| Transverse 45J (35J min) | ||
Notes:
- Testing shall be carried out in accordance with ASTM A370 or EN ISO 6892-1 (tensile), EN ISO 6506-1 (hardness)
- Minimum properties quoted (tested at room temperature in a longitudinal direction)
- Testing performed on each melt of material per heat treatment batch
- Hardness shall be in accordance with NACE MR 1075 with a maximum HRC of 25
- ASTM G48A corrosion test (at 50°C) No pitting and < 3.0g/m2 weight loss (ASTM specification < 4.0g/m2)
- Ferrite content 35-55%
- Microstructure certified free from grain boundary carbides, sigma, chi and laves phases
Physical Properties:
| Density (Kg/m3) | 7810 |
| Magnetic Permeability (20°C) | 33 |
| Young’s Modulus (kN/mm2) | 199 |
| Specific Electrical Resistance, 20°C (µΩ.m) | 0.8 |
| Mean coefficient of thermal expansion, 20-300°C (m/m/oC) | 11.1 x 10-6 |
| Specific Heat, 20°C (J/kg.K) | 475 |
| Thermal conductivity, 20°C (W/m.K) | 14.2 |