1. What Are 316L Stainless Steel Castings?

316L (cast grade CF3M) is a low-carbon version of 316 stainless steel. The "L" means maximum 0.03% carbon, which reduces the risk of carbide precipitation and intergranular corrosion after welding or heat treatment.

Typical properties of CF3M (316L) investment castings:

Tensile strength: ≥ 485 MPa

Yield strength: ≥ 205 MPa

Elongation: ≥ 30%

Chromium 17–21%, Nickel 9–13%, Molybdenum 2–3%

316L is the workhorse material for marine hardware, food machinery and pump/valve parts in moderately corrosive environments. It is easy to machine, easy to weld, and offers good value for most seawater-adjacent applications.

2. What Are Duplex Stainless Steel Castings?

Duplex stainless steel has a mixed austenitic-ferritic microstructure, roughly 50/50. That structure gives roughly double the yield strength of 316L plus far better resistance to chloride stress corrosion cracking.

Two common casting grades:

2205 duplex (cast grade CD3MN):

Tensile strength: ≥ 620 MPa

Yield strength: ≥ 450 MPa

Elongation: ≥ 25%

Chromium 21–23.5%, Nickel 4.5–6.5%, Molybdenum 2.5–3.5%, Nitrogen 0.12–0.20%

2507 super duplex (cast grade CE3MN):

Tensile strength: ≥ 690 MPa

Yield strength: ≥ 515 MPa

Elongation: ≥ 18%

Chromium 24–26%, Nickel 6–8%, Molybdenum 3.5–5%, Nitrogen 0.20–0.30%

Both grades are produced by the silica sol investment casting process with solution annealing (≥1040°C water quench) to restore the duplex microstructure.

3. Side-by-Side Comparison

4. Which One Should You Choose?

Choose 316L (CF3M) when:

The part operates in mild to moderate marine splash or food processing environments

The design needs complex machining or extensive welding

You want proven, widely available material with lower cost

Example parts: glass clamps, railing fittings, valve trim, pump housings for fresh water

Choose duplex 2205 (CD3MN) when:

The part is exposed to seawater, chloride or acidic media

You need higher strength to reduce wall thickness and weight

You need resistance to stress corrosion cracking

Example parts: seawater pump bodies, impellers, shaft sleeves, heat exchanger components

Choose super duplex 2507 (CE3MN) when:

The application is offshore, desalination or high-chloride chemical service

Maximum pitting and crevice corrosion resistance is required

Example parts: offshore valve bodies, subsea connectors, high-pressure pump casings

5. Why Investment Casting for These Materials?

Silica sol investment casting (lost-wax) is ideal for both 316L and duplex stainless steel because:

Dimensional accuracy up to CT4–CT6 (GB/T 6414), surface finish Ra 3.2–6.3 µm

Near-net shape for complex geometries such as impellers, volutes and valve bodies

Reduced machining cost compared with sand casting or forging

Full material certificates (MTC) with chemical composition and mechanical test data per batch, with heat-lot traceability

Our foundry produces 316L (CF3M), duplex 2205 (CD3MN), super duplex 2507 (CE3MN), 304/316, carbon steel and alloy steel castings under IATF 16949 quality management, all made to customer drawings with custom tooling.

Send Us Your Drawings

Not sure which grade fits your part? Send your drawings (PDF / 2D / 3D) with the working conditions - our engineering team will recommend the right material and reply within 48 hours with a quotation.