CD4MCu Duplex Stainless Castings: Strength Plus Chloride Resistance

Quick Answer

CD4MCu is a cast duplex stainless steel — roughly half ferrite, half austenite — that delivers about twice the yield strength of CF8M together with better chloride pitting and stress-corrosion resistance. It is the step buyers take when 316-class castings either corrode (pitting in brines) or wear and flex too much (pump internals). Typical homes: pump casings and impellers in mining, desalination, chemical and marine service.

Composition (ASTM A995 Gr. 1A / A744 CD4MCu type)

High chromium with moderate nickel produces the balanced two-phase structure; copper adds resistance in acidic and brine media.

Properties: The Duplex Advantage

The yield-strength gap is the headline: 485 vs 205 MPa lets designers thin walls, resist pressure pulsation and survive abrasive slurries that peen soft austenitics.

Applications Where CD4MCu Earns Its Cost

• Slurry and process pump casings, impellers and wear parts in mining and FGD systems
• Desalination and seawater handling components
• Valve bodies and internals in chloride-bearing chemical streams
• Marine hardware where 316 pits at crevices

The Specification Pitfalls (Read Before Ordering)

• Solution annealing is critical and less forgiving than for austenitics. Wrong cooling through 700–950°C precipitates sigma phase — a brittle intermetallic that wrecks toughness and corrosion resistance. Require the anneal cycle on the certificate.
• Ferrite balance matters. Ask for a ferrite measurement (point count or feritscope) on qualification castings; 40–60% is the healthy window.
• Welding needs duplex procedure discipline — matched filler, controlled interpass temperature. Casual repair welding is where duplex reputations die.
• Machining is harder than CF8M — plan roughly 30–50% more machining effort; another argument for near-net investment casting with minimal stock.

Where CD4MCu is over-kill and CF8M under-kill, modern 2205-type cast duplex (CD3MN, A995 Gr. 4A) sits between — worth a line in your RFQ if sourcing flexibility helps. Grade-family context is in the cast stainless overview.

Engineering & Sourcing Tools: Use our ASTM vs EN/DIN vs JIS vs GB Casting Grade Cross-Reference Calculator and ISO 8062 CT4–CT12 Casting Tolerance & RMA Chart to verify specifications, or explore YCUMETAL’s precision investment casting, 3/4/5-axis CNC machining, automotive & drivetrain castings, and full foundry services (request a 24h DFM quote).

FAQ

Is CD4MCu magnetic?

Noticeably, yes — about half the structure is ferrite. Unlike with CF8M’s faint pull, a magnet grips duplex firmly. Normal, not a defect.

CD4MCu vs CD3MN (2205) — which duplex?

CD4MCu: higher chromium and copper, long track record in acids and mining. CD3MN: tougher, easier to weld, broader mill familiarity. Media chemistry and your industry’s habit usually decide.

Can CD4MCu be used at high temperature?

Keep continuous service below roughly 250–300°C — above that, embrittlement mechanisms activate. Duplex is a wet-corrosion family, not a heat-resistant one.

For production DFM, tooling, and batch inspection on these components, explore our marine and shipbuilding corrosion-resistant castings capabilities at YCUMETAL’s 34,000㎡ Pingdu facility.

For production DFM, tooling, and batch inspection on these components, explore our industrial hardware and fluid control castings capabilities at YCUMETAL’s 34,000㎡ Pingdu facility.