Stainless Steel Casting Grades Guide

Q: What is the difference between CF8 and CF8M?

The main difference is molybdenum content. CF8 has no intentional Mo (304 equivalent); CF8M contains 2–3% Mo (316 equivalent), raising PRE from ~20 to ~28 for significantly better pitting and crevice corrosion resistance.

Q: How do I choose between 17-4PH H900 and H1150?

H900 delivers maximum strength (≥1310 MPa) with lower toughness — suited to high-stress wear service. H1150 reduces strength (≥930 MPa) but improves toughness and SCC resistance — better when corrosion exposure is higher.

Q: What heat treatment does cast 17-4PH require?

Standard practice is solution treatment at 1040°C (air or oil quench) followed by aging. H900 (482°C / 1 h) maximizes strength; H1150 (620°C / 4 h) trades strength for improved toughness.

Direct answer: Stainless steel castings are near-net-shape parts poured from austenitic (CF8/CF8M, ASTM A351), martensitic, or precipitation-hardening (17-4PH) alloys — most often by investment (lost-wax) casting; grade selection matches alloy class to media, temperature, and strength, with ASTM A351 governing chemistry and mechanical minimums.

What Are Stainless Steel Castings?

Stainless steel castings are near-net-shape components produced by pouring molten stainless alloy into a refractory mould — most commonly via stainless steel casting investment casting (lost-wax) for complex valve, pump, and machinery parts. Cast grades span three families used in industry: austenitic (CF8, CF8M per ASTM A351), martensitic, and precipitation-hardening alloys such as 17-4PH. For pressure-containing and general corrosion-service castings, ASTM A351 is the primary specification governing chemistry, heat treatment, and mechanical minimums. Selecting among stainless steel casting grades starts with matching alloy class to media, temperature, and strength — then confirming pour feasibility with your foundry’s investment casting process.

Chemical Composition Comparison

The tables below summarize key elemental ranges for the three most specified cast stainless grades in valve, pump, and industrial programs. Full mill certificates should be referenced for lot-specific values; use our CF8 and CF8M data sheet for extended property tables.

CF8 (304 Equivalent)

Standard: ASTM A351 CF8 (UNS J92600) | Wrought equivalent: ASTM A240 Type 304 / UNS S30400

Element	Range (%)	Role
C	≤0.08	Low carbon limits intergranular corrosion risk
Cr	18.0–21.0	Provides corrosion resistance
Ni	8.0–11.0	Stabilizes austenite structure
Si	≤2.00	Deoxidation
Mn	≤1.50	Deoxidation / hot workability
Fe	Balance	—

CF8M (316 Equivalent)

Standard: ASTM A351 CF8M (UNS J92900) | Wrought equivalent: ASTM A240 Type 316 / UNS S31600

Element	Range (%)	Role
C	≤0.08	Low carbon limits intergranular corrosion risk
Cr	18.0–21.0	Corrosion resistance
Ni	9.0–12.0	Slightly higher than CF8 — stabilizes austenite
Mo	2.0–3.0	Enhances pitting and crevice corrosion resistance
Si	≤1.50	Deoxidation
Mn	≤1.50	Deoxidation
Fe	Balance	—

17-4PH (Precipitation Hardening)

Standard: ASTM A747 (cast) / UNS S17400 | European designation: X5CrNiCuNb16-4 / 1.4542

Element	Range (%)	Role
C	≤0.07	—
Cr	15.0–17.5	Corrosion resistance
Ni	3.0–5.0	Austenite former / matrix balance
Cu	3.0–5.0	Precipitation strengthening
Nb+Ta	0.15–0.45	Carbide / nitride hardening

Stainless steel casting grades CF8 CF8M 17-4PH chemical composition comparison table per ASTM A351

Mechanical Properties Comparison

Values below reflect typical ASTM minimums and industry ranges for as-cast or heat-treated conditions. Always verify final design against certified MTRs and your pressure-equipment code. For trim and body pairing in valves, see our valve materials guide.

Grade	R_m (MPa)	R_p0.2 (MPa)	A%	HBW	Impact (J)
CF8 (304)	≥485	≥205	≥30	150–190	>80
CF8M (316)	≥485	≥205	≥30	150–190	>80
17-4PH H900	≥1310	≥1170	≥10	380–420	15–25
17-4PH H1150	≥930	≥725	≥16	260–300	45–80

17-4PH achieves its property window through precipitation hardening. H900 (482°C / 1 h) maximizes tensile and yield strength but reduces toughness and impact energy. H1150 (620°C / 4 h) sacrifices peak strength for improved ductility, Charpy values, and stress-corrosion cracking resistance — the usual trade-off when specifying high-strength cast trim for corrosive duty.

Corrosion Resistance

Pitting Resistance Equivalent (PRE) offers a quick screen for chloride-bearing service. PRE = %Cr + 3.3×%Mo + 16×%N (nitrogen term often negligible in cast certs).

Grade	PRE Calculation	PRE Value
CF8 (304)	19.0 + 0 + 0.8	~20
CF8M (316)	19.0 + 8.25 + 0.8	~28
17-4PH	16.0 + 0 + 0.48	~17

CF8M’s molybdenum raises PRE roughly 40% above CF8, materially improving resistance to pitting and crevice attack in chlorides and many chemical streams. 17-4PH delivers the highest strength of the three but the lowest PRE — best reserved for moderate-corrosion, high-mechanical-load applications such as stems and fasteners rather than long-term seawater immersion.

Stress corrosion cracking (SCC): Austenitic CF8 and CF8M can be susceptible in 50–150°C chloride environments. 17-4PH in H900 is the most SCC-sensitive condition; H1150 aging significantly improves performance. Intergranular corrosion (IGC): Even at C ≤0.08%, heavy sections and weld HAZs may require low-carbon CF3 / CF3M (304L / 316L cast equivalents) in strongly oxidizing or nitric-acid service. Broader alloy context is in our stainless steel materials hub.

Corrosion resistance comparison chart — PRE values, SCC sensitivity, IGC resistance for CF8 CF8M 17-4PH

Typical Applications by Grade

Industry	Recommended Grade	Typical Parts
Food processing	CF8 (304)	Pump housings, valve bodies, pipe fittings
Chemical / marine	CF8M (316)	Chemical valve bodies, seawater pump casings
Aerospace / valve trim	17-4PH	Valve stems, seat rings, fasteners
Pharma / biotech	CF8 / 316L	Sanitary valve bodies, CIP system components
Pulp & paper	CF8M (316)	Bleach-line valve hardware

Matson Foundry produces these grades through silica-sol and water-glass investment casting lines, with integrated CNC machining from casting blank to finished sealing surfaces. Align wall thickness, fillet radii, and machining datums early using our casting design guide. End-market examples appear in valve casting by industry, oil & gas applications, and related OEM programs.

Stainless steel casting application matrix — food processing, chemical, marine, aerospace per grade

Cost Reference

Relative indices help budget material at RFQ stage; actual quotes depend on section size, alloy surcharge, heat treatment, and machining scope.

Material	Relative Cost Index	Notes
CF8 (304)	1.0×	Baseline austenitic cast grade
CF8M (316)	1.3–1.5×	Molybdenum alloy premium
17-4PH	1.8–2.5×	Copper / niobium + heat-treat cost
Casting vs forging	Casting ≈ 60–80% of forging	Near-net shape saves metal and machining

Frequently Asked Questions

What is the difference between CF8 and CF8M?

The main difference is molybdenum. CF8 has no intentional Mo (304 equivalent); CF8M contains 2–3% Mo (316 equivalent), raising PRE from ~20 to ~28 for significantly better pitting and crevice corrosion performance. See CF8/CF8M specifications for certified limits.

How do I choose between 17-4PH H900 and H1150?

H900 provides maximum strength (≥1310 MPa) with lower toughness — ideal for high-stress wear components. H1150 reduces strength (≥930 MPa) but improves toughness and SCC resistance — preferred when corrosive exposure is more severe.

Is cast stainless steel better than forged stainless steel?

Casting uses near-net shaping for complex geometries at roughly 60–80% of forging cost by saving material and machining. Forging offers denser microstructure and more uniform mechanical properties. Choose based on part complexity, batch size, and performance requirements.

When should I use CF3 or CF3M instead of CF8 or CF8M?

CF3 (304L) and CF3M (316L) limit carbon to ≤0.03%, reducing carbide precipitation and intergranular corrosion in heavy sections or weld heat-affected zones — critical in strong oxidizing acids and hot nitric acid.

What tolerance can investment-cast stainless steel achieve?

Silica-sol investment casting typically achieves CT5–CT7 (±0.13–0.25 mm). With CNC finishing, critical features can reach ±0.025 mm when datums are planned per the casting design guide.

What heat treatment does cast 17-4PH require?

Standard practice: solution treatment at 1040°C (air or oil quench) followed by aging. H900 (482°C / 1 h) maximizes strength; H1150 (620°C / 4 h) improves toughness.

What surface treatments are available for stainless steel castings?

Options include shot blasting, pickling/passivation, electropolishing, mechanical polishing, and coatings (PTFE, nylon, epoxy). Pickling and passivation is standard to restore the passive chromium oxide film.