What Is ASTM A995?
When to Specify ASTM A995
ASTM A995 covers cast duplex and super duplex stainless steel for pressure-containing components: valve bodies, pump casings, fittings, and manifolds exposed to chloride-bearing, corrosive, or erosive environments. These castings combine high strength with excellent pitting and stress corrosion cracking resistance that standard austenitic grades (CF8M/316) cannot match.
| Grade | UNS | Alloy Type | PREN (min) | Wrought Equivalent |
|---|---|---|---|---|
| 1B | J93372 | Duplex (CD4MCuN) | ~38 | - |
| 4A | J92205 | Duplex 2205 | ~34 | A182 F51 |
| 5A | J93404 | Super duplex 2507 | ~41 | A182 F53 |
| 6A | J93380 | Super duplex (Zeron 100) | ~41 | A182 F55 |
Duplex Microstructure
Duplex stainless steels contain approximately equal proportions of austenite and ferrite (typically 40-60% ferrite). This two-phase microstructure delivers roughly double the yield strength of austenitic grades while maintaining excellent toughness and corrosion resistance. The ferrite phase resists chloride stress corrosion cracking; the austenite phase provides toughness and general corrosion resistance.
| Property | CF8M (Cast 316) | A995 4A (Cast 2205) | A995 5A (Cast 2507) |
|---|---|---|---|
| Tensile (min) | 485 MPa | 620 MPa | 690 MPa |
| Yield (min) | 205 MPa | 450 MPa | 485 MPa |
| Elongation (min) | 30% | 25% | 25% |
| PREN | ~26 | ~34 | ~41 |
| Max service temp | 538°C | 315°C | 315°C |
| SCC resistance | Moderate | Excellent | Excellent |
Applications
- Offshore oil and gas: subsea valve bodies, topside piping valves, manifolds, and Christmas trees
- Seawater systems: fire water, cooling water, and ballast system valves
- Chemical processing: chloride-bearing acid, brine, and caustic service
- Desalination plants: high-pressure pump casings and valve bodies
- Pulp and paper: chlorine dioxide bleaching circuit valves
A995 castings pair with A182 F51/F53/F55 forged flanges and fittings and A790 S31803/S32750 seamless pipe.
Testing and Quality
ASTM A995 requires solution annealing (typically 1020-1120°C followed by water quench) and ferrite content verification (30-60% for most grades). Ferrite is measured per ASTM E562 (point count) or calibrated ferritescope. Mill test certificates must report chemistry, mechanical properties, ferrite content, and heat treatment condition. Radiographic and liquid penetrant examination follow ASME B16.34. Hydrostatic testing is per the applicable valve standard. Corrosion testing per ASTM A923 (detects sigma phase) and ASTM G48 (pitting test at specified temperatures) is commonly required for critical service.
The maximum continuous service temperature for duplex grades is approximately 315°C (600°F). Above this, sigma phase precipitation degrades toughness and corrosion resistance. The casting process requires tight control of solidification conditions to achieve the balanced austenite-ferrite ratio.
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