Stainless steel · cast
CN7M
ASTM A351 Grade CN7M · Alloy 20
A cast alloy with high nickel, molybdenum and copper. The classic valve material for hot sulphuric acid service.
- Rp0.2 · MPa
- ≥ 170
- Rm · MPa
- ≥ 425
- TEMPERATURE
- ≤ +425 °C
- COST
Chemical composition
C≤ 0.07
Si≤ 1.50
Mn≤ 1.50
P≤ 0.04
S≤ 0.04
Cr19.0–22.0
Ni27.5–30.5
Mo2.0–3.0
Cu3.0–4.0
%, single values are maximums.
Mechanical properties
| STANDARD · CONDITION | Rp0.2 MPa | Rp1.0 MPa | Rm MPa | A % | KV J |
|---|---|---|---|---|---|
| ASTM A351 · CN7M | 170 | — | ≥ 425 | 35 | — |
Room temperature, solution annealed (ASTM A351).
Service temperature
+425 °C−200−1000100200300400500600700800
This is the limit of the material itself. A valve's service temperature is usually set by the seal and seat materials; product pages give it for each seal option.
Media suitability GENERAL TREND
Fresh water
Seawater
Steam
Hydrocarbons, oil
Dilute acid
Caustic
Air, gas
Low temperature
Emsal assessment. The final choice is made from corrosion tables, taking concentration, temperature, chloride content and flow velocity into account.
Strengths and weaknesses
Strengths
- Very good resistance in sulphuric acid
- High nickel: resistant to chloride stress corrosion cracking
Weaknesses
- Low proof strength
- Expensive and difficult to cast (hot tearing)
- Falls behind super duplex in seawater
Manufacturing and use
- ECONOMY
- High.
- MANUFACTURING METHODS
- Sand casting · Investment casting
- TYPICAL VALVE PARTS
- Body · Disc, ball (acid service)
Source: ASTM A351. Values compiled and verified by Emsal Vana; for binding values, refer to the current edition of the standard and the material certificate.