Stainless Steel CN7MS-AC (Spheroidize annealed)
Heat-treated state
ASTM CN7MS · UNS J94650
Only seen on rough/unfinished castings before solution treatment; interdendritic carbides and segregation sharply reduce acid resistance — not for service.
Values for the AC condition
Other CN7MS tempers and conditions
CN7MS is listed in 3 conditions; see the grade overview at CN7MS.
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 |
ACThis page 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-AC?
CN7MS-AC is CN7MS heat treated to AC — only seen on rough/unfinished castings before solution treatment; interdendritic carbides and segregation sharply reduce acid resistance — not for service. CN7MS-AC has a yield strength of 230 MPa (33.4 ksi) and a tensile strength of 450 MPa (65.3 ksi) — weaker than 99% of stainless steel grades. Elongation at break is 25% and the elastic modulus is 188 GPa (27.3 Msi). CN7MS-AC 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). SA is the default condition FabDigit quotes; AC is available on request or by drawing note.
Limitations
- Low strength — 230 MPa (33.4 ksi), worse than 99% of stainless steel grades
- Difficult to weld — 25/100, worse than 92% of stainless steel grades
- Limited formability — 15/100, worse than 91% 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
- Difficult to machine — 25/100, worse than 88% of stainless steel grades
CN7MS-AC properties
Typical room-temperature values for CN7MS-AC; 22 are specific to this condition. Other listed values are CN7MS reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
CN7MS-AC 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-AC has a yield strength of 230 MPa (33.4 ksi) and a tensile strength of 450 MPa (65.3 ksi) — weaker than 99% of stainless steel grades. Elongation at break is 25% and the elastic modulus is 188 GPa (27.3 Msi).
Thermal6
CN7MS-AC is rated for continuous service to 425°C (797 °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-AC conducts electricity at 1.8 % IACS, worse than 87% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (65/100), better than 56% of stainless steel grades.
Sustainability4
Producing a kilogram of CN7MS-AC 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-AC's machinability is poor (25/100, worse than 88% of stainless steel grades); weldability poor (25/100); formability poor (15/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with CN7MS-AC
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.
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.
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 | — |
CN7MS-AC — frequently asked
What is CN7MS-AC used for?
CN7MS-AC 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-AC?
CN7MS-AC has a typical yield strength of 230 MPa (33.4 ksi) and a tensile strength of 450 MPa (65.3 ksi) — weaker than 99% of stainless steel grades. Strength varies by condition: see the 3 listed tempers.
Is CN7MS-AC easy to machine?
Not especially — machinability is rated poor (25/100, worse than 88% 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-AC be welded?
Not readily — weldability is rated poor (25/100). 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-AC?
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-AC 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-AC?
CN7MS-AC is rated for continuous use to about 425°C (797 °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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.