CD4MCu Duplex Stainless Steel Castings: What You Need to Know

What is CD4MCu?

A Casting-Only Duplex Stainless Steel

CD4MCu is a duplex stainless steel composed of ferrite and austenite phases, produced to ASTM A890 specification as a casting alloy grade, with Alloy 255 (Ferralium 255 / UNS S32550) serving as its wrought counterpart.

What distinguishes this casting alloy is its copper content, a deliberate compositional choice that brings distinct advantages in both corrosion resistance and mechanical performance.

CD4MCu Chemical Composition

The performance of CD4MCu comes from its carefully balanced chemistry—with copper being the key element that sets it apart from other casting materials.

CD4MCu Mechanical Properties

These values are what make CD4MCu a high-strength alternative to standard austenitic grades:

Key Features of CD4MCu Castings

High Strength & Hardness

CD4MCu delivers yield strength approximately twice that of 316L stainless steel, with hardness ranging from 230–280 HB. For your cast components, this means greater resistance to high-pressure loads and abrasive wear.

Superior Corrosion Resistance

With a PREN (pitting resistance equivalent number) of 30–34, CD4MCu offers you strong resistance to chloride pitting. Its duplex structure also provides inherent resistance to stress corrosion cracking (SCC), a common failure mode in chloride-rich environments that standard austenitic grades cannot withstand.

Copper-Enhanced Performance

The copper content (2.75–3.25%) distinguishes CD4MCu from other duplex grades, providing unique resistance to reducing acids such as dilute sulfuric acid and phosphoric acid—a capability you won’t find in copper-free duplex grades like 2205.

CD4MCu Equivalent Material: Grade Cross-Reference

CD4MCu is known under different designations across standards. If you’re sourcing castings or cross-referencing a drawing, here are the equivalents you’ll most likely encounter.

Comparison with Other Casting Materials

CD4MCu vs. CF8M

You know CF8M—it’s the standard austenitic grade that most foundries cast every day. It handles general corrosion well, but it lacks the strength for high-pressure or abrasive service without heavy sections. CD4MCu steps in with roughly double the yield strength, so you can design thinner walls and lighter castings without sacrificing part life.

CD4MCu vs. CD3MN

If you’re familiar with 2205, you already know CD3MN is its casting equivalent—great for chloride environments, good strength, plenty of applications. But when abrasion or erosive slurries enter the picture, CD3MN’s wear resistance starts to fall short. CD4MCu delivers higher hardness and better surface protection, so your castings last longer in the tough stuff.

CD4MCu vs. CD4MCuN

You might still see CD4MCu on old drawings, but the standard has moved on. The modern replacement is CD4MCuN—which adds nitrogen (0.10–0.25%) to the original copper-bearing chemistry, significantly improving toughness, weldability, and pitting resistance. If your drawing says CD4MCu, we’ll cast it as CD4MCuN to give you a more reliable final part.

CD4MCu vs. CN7M (Alloy 20)

CN7M, is known as the cast equivalent of Alloy 20—the go-to choice for hot sulfuric acid service. But as an austenitic grade, it doesn’t handle stress corrosion cracking or abrasive wear well. CD4MCu delivers both, plus resistance to reducing acids, at a more economical price—so you get longer service life in erosive conditions without the premium cost.

Common Applications for CD4MCu Custom Castings

Thanks to these combined properties—high strength, corrosion resistance, and wear protection—CD4MCu is widely used in the following demanding applications:

Pumps

When your pump handles chloride-laden seawater or abrasive slurries, CD4MCu gives you a casting that fights both corrosion and wear at once. That’s why we routinely produce these components for demanding fluid-handling applications:

• Pump bodies and casings
• Impellers
• Volutes
• Wear rings
• Back liners

Valves

For valve applications where CF8M fails from stress cracking or pitting, CD4MCu provides a proven upgrade. Our castings hold up where standard austenitic grades simply cannot:

• Valve bodies
• Bonnets
• Discs
• Seats
• Plugs

Other Key Components

Beyond pumps and valves, we supply CD4MCu castings for equipment that sees both corrosion and mechanical abuse:

• Mixing shafts and impellers
• Flanges and fittings
• FGD system components
• Slurry handling parts

How We Control Quality in Your CD4MCu Castings

Process Selection Tailored to Your Part

CD4MCu work-hardens rapidly, making extensive CNC milling extremely costly. We select casting methods that achieve near-net shapes to save your machining budget:

• Investment Casting (Silica Sol): Ideal for intricate, thin-walled parts like impellers and valve discs. It produces smooth surfaces (Ra 3.2 – 6.3 μm) directly out of the mold, eliminating expensive profile machining.
• Resin Sand Casting: Best suited for large pump casings(>50 kg). To counteract CD4MCu’s high volumetric shrinkage (1.5–2.0%), we engineer custom gating systems with exothermic risers to prevent internal shrinkage cavities.

Metallurgical Controls That Preserve Performance

CD4MCu’s corrosion resistance and strength come from its balanced ferrite-austenite structure—but that structure is easy to lose if cooling isn’t controlled. That’s why we’re careful about two things:

• Heat treatment: We solution-anneal every casting at 1100–1140°C and transfer to the quench tank in under 30 seconds—so the alloy doesn’t linger in the temperature range where embrittlement occurs. This protects your casting’s long-term integrity.
• Phase balance: We adjust chromium and nickel during melting to target a 50:50 ferrite-austenite mix. That balance is what gives your castings both high strength and stress-corrosion resistance in service.

Quality Verification You Can Rely On

Every batch is tested—not sampled, not assumed. Here’s what we verify on your castings:

• Chemistry & ferrite: We check copper (2.75–3.25%), molybdenum (1.75–2.25%), and ferrite content (40–60%) using calibrated instruments and metallographic cross-section checks—so your material meets the specification you ordered.
• NDT: Liquid penetrant inspection on all critical flow passages. Radiography on high-stress sections upon request. Pressure testing on valve and pump bodies. We run these, so you don’t have to worry about hidden defects.
• Full traceability: Every casting is stamped with a heat number. You get a complete test certificate with your order—so you have documentation you can trace back to the melt.

Conclusion

CD4MCu gives you the strength and corrosion resistance that standard castings simply don’t offer—whether you’re handling seawater, acids, or abrasive slurries. At YTD Casting, we specialize in turning this alloy into reliable custom components. Send us your drawings, and we’ll help you get the right solution for your project.