The Sweet Spot Between 316SS and High-Nickel Alloys
CD4MCuN (ASTM A890 Grade 1B) occupies a unique position in the ANSI process pump metallurgy spectrum. It offers significantly better corrosion resistance than 316 stainless steel — particularly against chloride stress corrosion cracking (Cl-SCC) — while costing roughly half as much as Alloy 20 and one-third as much as Hastelloy C.
What Is CD4MCuN?
CD4MCuN is a duplex (austenitic-ferritic) stainless steel — approximately 50% austenite and 50% ferrite. This dual-phase structure gives it properties superior to either phase alone:
| Property | CD4MCuN (Duplex) | 316SS (CF8M) |
|---|---|---|
| Tensile Strength | 100 ksi (690 MPa) | 70 ksi (485 MPa) |
| Yield Strength | 70 ksi (485 MPa) | 30 ksi (205 MPa) |
| Hardness (BHN) | 255-290 | 140-180 |
| PREN (Pitting Resistance) | 34-38 | 24-28 |
Key Alloying Elements
- Chromium (24.5-26.5%): Substantially higher than 316SS (18-20%)
- Nickel (4.7-6.0%): Much lower than 316SS (10-14%) — cost advantage
- Molybdenum (1.7-2.3%): Pitting resistance, especially against chlorides
- Copper (2.7-3.3%): Improves resistance to reducing acids
- Nitrogen (0.10-0.25%): Strengthens austenite, enhances pitting resistance
Why CD4MCuN Excels
1. Chloride SCC Resistance — The #1 Advantage
Austenitic stainless steels (304, 316) are notoriously susceptible to Cl-SCC above 140°F. The ferrite phase in duplex stainless steel effectively blocks crack propagation. CD4MCuN is virtually immune to Cl-SCC in conditions that would destroy 316SS within weeks.
2. High Strength
With yield strength more than double that of 316SS, CD4MCuN allows for higher pressure ratings or thinner wall sections.
3. Erosion-Corrosion Resistance
The higher hardness (255-290 BHN vs 140-180 BHN for 316SS) provides better resistance in services with entrained solids.
CD4MCuN vs. the Alternatives
| Application | 316SS | CD4MCuN | Alloy 20 | Hastelloy C |
|---|---|---|---|---|
| Chloride SCC risk (>140°F) | Poor | Excellent | Fair | Excellent |
| Dilute H₂SO₄ (<10%) | Fair | Good | Excellent | Excellent |
| Seawater / brine | Poor | Good | Fair | Excellent |
| Relative cost | 1.0× | 1.5× | 2.5× | 4.5× |
Typical CD4MCuN Applications
- Cooling tower water circulation (Cl-SCC resistance)
- Brackish water / produced water injection
- Flue gas desulfurization (FGD) slurry circulation
- Wet-process phosphoric acid (moderate fluoride levels)
- General chemical transfer with chloride contamination risk
Considering CD4MCuN for Your Next Rebuild?
Our CD4MCuN wet-end kits cost only 50% more than 316SS — but last 3-5× longer in chloride service. Send us your pump model and process conditions for a material-specific quote.