Stainless Steel CN7MS
ASTM CN7MS · UNS J94650
CN7MS (J94650, ASTM A351/A743, A744) is a silicon-modified cast austenitic Ni-Cr-Mo-Cu stainless steel developed from CN7M to further improve resistance in concentrated sulfuric acid duty.
Reference datasheet — CN7MS is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the SA condition
CN7MS tempers and conditions
CN7MS is supplied in 3 conditions, soft to hard. SA is the default FabDigit quotes; the values on this page are for it.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
SADefault Solution annealed (≈1120 °C, water quenched) per ASTM A743 | The only condition supplied to standard — full solution treatment puts carbides and Cu/Mo into solution for maximum sulfuric-acid resistance. | 210 | 470 | 42 | 150 HB | 1.8 % IACS |
solution annealed casting for severe corrosive service | Same heat treatment as A743 but ordered to ASTM A744 with tighter foundry practice/inspection for pumps and valves in severe acid duty. | 210 | 470 | 42 | 150 HB | 1.8 % IACS |
Spheroidize annealed | Only seen on rough/unfinished castings before solution treatment; interdendritic carbides and segregation sharply reduce acid resistance — not for service. | 230 | 450 | 25 | 165 HB | 1.8 % IACS |
What is CN7MS?
CN7MS (J94650, ASTM A351/A743, A744) is a silicon-modified cast austenitic Ni-Cr-Mo-Cu stainless steel developed from CN7M to further improve resistance in concentrated sulfuric acid duty. Engineers specify it as solution-annealed or as-cast pump casings, valve bodies and fittings, with 210 MPa yield, 470 MPa tensile, 42 % elongation and 150 HB in the default condition. The trade-offs are poor machinability (score 30), abrasive high-silicon structure, and hot-cracking sensitivity in both weld metal and HAZ, so major repairs need re-solution treatment. CN7M remains the alternative for less aggressive or dilute acid service. CN7MS has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 65% of stainless steel grades. It melts at 1,350°C (2,462 °F). CN7MS has a yield strength of 210 MPa (30.5 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 100% of stainless steel grades. Elongation at break is 42% and the elastic modulus is 190 GPa (27.6 Msi).
What is CN7MS used for?
- concentrated sulfuric acid pumps
- chemical process valves
- acid piping fittings
Advantages
- Good corrosion resistance — 85/100, better than 92% of stainless steel grades
Limitations
- Low strength — 210 MPa (30.5 ksi), worse than 100% of stainless steel grades
- Poor heat conductor — 12.5 W/m·K (7.22 BTU/hr·ft·°F), worse than 90% of stainless steel grades
- Low electrical conductivity — 1.8 % IACS, worse than 87% of stainless steel grades
- Difficult to weld — 35/100, worse than 86% of stainless steel grades
- Limited formability — 20/100, worse than 86% of stainless steel grades
CN7MS properties
Typical room-temperature values for CN7MS-SA; bars are the position among stainless steel grades.
Physical3
CN7MS has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 65% of stainless steel grades. It melts at 1,350°C (2,462 °F).
Mechanical16
CN7MS has a yield strength of 210 MPa (30.5 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 100% of stainless steel grades. Elongation at break is 42% and the elastic modulus is 190 GPa (27.6 Msi).
Thermal6
CN7MS is rated for continuous service to 500°C (932 °F). It conducts heat at 12.5 W/m·K (7.22 BTU/hr·ft·°F), worse than 90% of stainless steel grades. Thermal expansion is 16.2 µm/m·K (9 µin/in·°F).
Electrical3
CN7MS conducts electricity at 1.8 % IACS, worse than 87% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is excellent (85/100), better than 92% of stainless steel grades.
Sustainability4
Producing a kilogram of CN7MS takes about 60 MJ of energy and emits 5.2 kg of CO₂ — more than 70% of stainless steel grades. Typical recycled content is 65%.
Manufacturability7
CN7MS's machinability is poor (30/100, worse than 70% of stainless steel grades); weldability fair (35/100); formability poor (20/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. CN7MS is highlighted; hover a dot for its name, or open the interactive family chart.
Working with CN7MS
Is CN7MS easy to machine?
Tough, work-hardening and abrasive from the high silicon — use rigid setups, sharp positive-rake carbide, heavy positive feed, low-to-moderate speed and flood coolant; never dwell.
Can CN7MS be welded?
Weld with GTAW/SMAW using matching CN7MS or Ni-base (ENiCrMo) filler, low heat input, no preheat and interpass below ~150 °C; high Si makes weld-metal and HAZ hot cracking the main risk, and re-solution treatment after major repair is preferred.
Can CN7MS be formed, bent or molded?
Cast only — good fluidity but high hot-tearing sensitivity, so use generous fillets, progressive-solidification gating and controlled shakeout; solution treat at ~1090–1150 °C and water quench.
CN7MS chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C | ≤ 0.07 | 0.05 |
| Mn | ≤ 1 | 0.7 |
| Sikey addition for concentrated H2SO4 resistance | 2.5 – 3.5 | 3 |
| P | ≤ 0.04 | |
| S | ≤ 0.03 | |
| Cr | 18 – 20 | 19 |
| Ni | 22 – 25 | 23.5 |
| Mo | 2.5 – 3 | 2.75 |
| Cu | 1.5 – 2 | 1.75 |
| Fe | balance |
What surface finishes work on CN7MS?
Pickle and passivate (nitric or nitric-HF) after grinding to restore the passive film; mechanical polishing is possible but casting porosity limits mirror finishes.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Passivation
Organic Coating
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel CN7MS in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- J94650
How much does CN7MS cost?
CN7MS is a high-cost stainless steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
CN7MS — frequently asked
What is CN7MS used for?
CN7MS is typically used for concentrated sulfuric acid pumps, chemical process valves and acid piping fittings. In short: silicon-modified CN7M; concentrated sulfuric acid service; cast alloy 20 family.
What is the yield strength of CN7MS?
CN7MS has a typical yield strength of 210 MPa (30.5 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 100% of stainless steel grades. Strength varies by condition: see the 3 listed tempers.
Is CN7MS easy to machine?
Not especially — machinability is rated poor (30/100, worse than 70% of stainless steel grades). Tough, work-hardening and abrasive from the high silicon — use rigid setups, sharp positive-rake carbide, heavy positive feed, low-to-moderate speed and flood coolant; never dwell.
Can CN7MS be welded?
With care — weldability is rated fair (35/100). Weld with GTAW/SMAW using matching CN7MS or Ni-base (ENiCrMo) filler, low heat input, no preheat and interpass below ~150 °C; high Si makes weld-metal and HAZ hot cracking the main risk, and re-solution treatment after major repair is preferred.
What surface finishes work on CN7MS?
Pickle and passivate (nitric or nitric-HF) after grinding to restore the passive film; mechanical polishing is possible but casting porosity limits mirror finishes.
Can CN7MS be formed, bent or molded?
Cast only — good fluidity but high hot-tearing sensitivity, so use generous fillets, progressive-solidification gating and controlled shakeout; solution treat at ~1090–1150 °C and water quench.
What is the maximum service temperature of CN7MS?
CN7MS is rated for continuous use to about 500°C (932 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between CN7MS-SA and CN7MS-AC?
SA is the default condition — the only condition supplied to standard — full solution treatment puts carbides and Cu/Mo into solution for maximum sulfuric-acid resistance. AC: only seen on rough/unfinished castings before solution treatment; interdendritic carbides and segregation sharply reduce acid resistance — not for service. Yield strength is 210 MPa in SA versus 230 MPa in AC.
How much does CN7MS cost?
CN7MS is a high-cost stainless steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM A743/A743M — Castings, Iron-Chromium, Iron-Chromium-Nickel, Corrosion Resistant, for General Application — ASTM International (2019)
- ASTM A744/A744M — Castings, Iron-Chromium-Nickel, Corrosion Resistant, for Severe Service — ASTM International (2021)
- ASM Specialty Handbook: Stainless Steels — ASM International (1994)
- Steel Castings Handbook, 6th ed. — Steel Founders' Society of America / ASM (1995)
- UNS J94650 alloy record — SAE/ASTM Unified Numbering System (2019)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.