What Is ASTM A217 WC6?
ASTM A217 WC6 is a 1-1/4 chromium, 1/2 molybdenum cast alloy steel grade used for valve bodies, bonnets, and pressure-containing parts in high-temperature service up to 565°C (1050°F). It is the cast counterpart of ASTM A182 F11 forged steel and pairs with ASTM A335 P11 seamless pipe.
| Property | Value |
|---|---|
| Specification | ASTM A217 / ASME SA-217 |
| Grade | WC6 |
| Material type | Cast alloy steel (Cr-Mo) |
| Carbon | 0.05-0.20% |
| Chromium | 1.00-1.50% |
| Molybdenum | 0.45-0.65% |
| Manganese | 0.50-0.80% |
| Silicon | 0.60% max |
| Sulfur | 0.045% max |
| Phosphorus | 0.04% max |
| Tensile strength (min) | 485 MPa (70 ksi) |
| Yield strength (min) | 275 MPa (40 ksi) |
| Elongation (min) | 20% |
| Reduction of area (min) | 35% |
| Hardness | 241 HBW max |
| Max service temp | 565°C (1050°F) |
| Heat treatment | Normalize + temper, or quench + temper |
Why WC6 Over Carbon Steel?
Standard ASTM A216 WCB carbon steel castings lose creep strength above 425°C. The 1.25% chromium in WC6 provides oxidation and sulfidation resistance at elevated temperatures, while 0.5% molybdenum increases creep rupture strength. This combination extends reliable service to 565°C, covering the bulk of refinery and power plant high-temperature piping.
WC6 occupies the first rung of the chrome-moly ladder within the ASTM A217 specification. For higher temperatures or more aggressive sulfidation environments, WC9 (2.25Cr-1Mo) and C5 (5Cr-0.5Mo) are specified.
Applications
WC6 dominates cast valve specifications for moderate high-temperature service:
- Refinery units: FCC main fractionator, crude/vacuum distillation overhead systems, reformer piping
- Power plants: superheater and reheater header drain valves, main steam isolation valves up to 565°C
- Petrochemical: ethylene cracker transfer line valves, high-temperature reactor circuits
Cast WC6 valve bodies pair with A182 F11 forged flanges and fittings, A234 WP11 buttweld fittings, and A335 P11 seamless pipe. All components in a 1-1/4Cr-1/2Mo piping class must match to avoid dissimilar-metal weld issues.
Testing and Quality
ASTM A217 requires chemical analysis, tensile testing, and mandatory heat treatment for all castings. Normalize and temper is the standard cycle; quench and temper is permitted for thicker sections. Mill test certificates per EN 10204 3.1 document chemistry, mechanical properties, and heat treatment records.
Supplementary requirements include radiographic examination per ASME B16.34, magnetic particle inspection, and Charpy impact testing when specified. Hydrostatic testing follows the applicable API or ASME valve standard. The casting process for chrome-moly grades demands tighter foundry controls than carbon steel to manage alloy segregation during solidification.
Welding WC6 castings requires preheat (150-200°C minimum), matching E/ER 8018-B2 filler metals, and PWHT at 690-750°C to restore toughness in the heat-affected zone.
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