Steel C12
EN C12 · ASTM A217 Grade C12
C12 is a 9Cr-1Mo cast alloy steel to ASTM A217 Grade C12, the cast counterpart of wrought P9, with the higher chromium level giving better oxidation and sulfidation resistance than C5.
Reference datasheet — C12 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 N+T condition
C12 tempers and conditions
C12 is supplied in 4 conditions, soft to hard. N+T is the default FabDigit quotes; the values on this page are for it.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Full annealed and tempered | Choose when maximum machinability and lowest residual stress are needed on complex castings; slightly lower strength than N+T. | 440 | 630 | 24 | 11 HRC | 2.9 % IACS |
N+TDefault Normalized and tempered | Standard supply condition for A217 C12 pressure castings; best balance of creep strength, toughness and hardness for valve bodies to ~600 °C. | 470 | 660 | 22 | 200 HB | — |
Quenched and tempered | Used on heavy-section castings where accelerated cooling is needed to obtain uniform tempered martensite and the highest yield strength. | 520 | 710 | 20 | 220 HB | — |
Spheroidize annealed | Intermediate foundry state only — hard, brittle untempered martensite; must be heat treated before machining and pressure use. | 760 | 1,050 | 6 | 38 HRC | 2.7 % IACS |
What is C12?
C12 is a 9Cr-1Mo cast alloy steel to ASTM A217 Grade C12, the cast counterpart of wrought P9, with the higher chromium level giving better oxidation and sulfidation resistance than C5. Normalized and tempered it delivers 470 MPa yield, 660 MPa tensile, 22 % elongation and about 200 HB, with service to 600 °C, and is used for pressure-retaining valve bodies and piping fittings in steam and refinery duty. Machinability is limited (40/100) and the martensitic structure demands preheat and PWHT for every weld. For higher creep strength at similar chemistry, use C12A (cast P91). C12 has a density of 7.79 g/cm³ (0.281 lb/in³), lighter than 90% of steel grades. It melts at 1,425°C (2,597 °F). C12 has a yield strength of 470 MPa (68.2 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 57% of steel grades. Elongation at break is 22% and the elastic modulus is 207 GPa (30 Msi).
What is C12 used for?
- High-temperature steam valve bodies
- Refinery process piping fittings
- Hot oil pump casings
- Cast elbows and tees for main steam lines
- Valve bonnets and yokes for high-pressure service
- Header connection castings
Advantages
- High service temperature — 600°C (1,112 °F), better than 98% of steel grades
- Good corrosion resistance — 32/100, better than 96% of steel grades
Limitations
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
- Poor heat conductor — 26 W/m·K (15 BTU/hr·ft·°F), worse than 87% of steel grades
- Limited formability — 15/100, worse than 87% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
- Difficult to machine — 40/100, worse than 77% of steel grades
C12 properties
Typical room-temperature values for C12-N+T; bars are the position among steel grades.
Physical3
C12 has a density of 7.79 g/cm³ (0.281 lb/in³), lighter than 90% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical17
C12 has a yield strength of 470 MPa (68.2 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 57% of steel grades. Elongation at break is 22% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
C12 is rated for continuous service to 600°C (1,112 °F). It conducts heat at 26 W/m·K (15 BTU/hr·ft·°F), worse than 87% of steel grades. Thermal expansion is 11.2 µm/m·K (6.22 µin/in·°F).
Electrical3
C12 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (32/100), better than 96% of steel grades.
Sustainability4
Producing a kilogram of C12 takes about 32 MJ of energy and emits 2.5 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 75%.
Manufacturability8
C12's machinability is fair (40/100, worse than 77% of steel grades); weldability fair (35/100); formability poor (15/100).
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 steel family
Yield strength against density for every steel grade FabDigit runs. C12 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with C12
Is C12 easy to machine?
Machine in the N+T or A+T condition at ~200 HB with rigid setups, carbide tooling and moderate speeds; work-hardening and gummy chips make sharp geometry and generous coolant important.
Can C12 be welded?
Weldable with matching E505/ER80S-B8 (9Cr-1Mo) consumables but requires 200–300 °C preheat/interpass, low-hydrogen practice and mandatory PWHT at 730–760 °C to avoid hard, crack-prone HAZ.
Can C12 be formed, bent or molded?
Supplied as sand castings — control feeding and slow post-pour cooling to prevent hot tears and quench cracks; no cold forming, and repair welding must be followed by full re-tempering.
C12 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 |
|---|---|---|
| C0.20 max per ASTM A217 | ≤ 0.2 | 0.12 |
| Si | ≤ 1 | 0.5 |
| Mn | 0.35 – 0.65 | 0.5 |
| P | ≤ 0.04 | 0.02 |
| S | ≤ 0.05 | 0.02 |
| Cr | 8 – 10 | 9 |
| Mo | 0.9 – 1.2 | 1 |
| Fe | balance |
What surface finishes work on C12?
Not anodizable; protect with phosphate + high-temperature aluminum/silicone paint, hard-facing on seats, or aluminizing for long-term oxidation service.
Surface treatments FabDigit runs on 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).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel C12 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- A217 Grade C12
How much does C12 cost?
C12 is a premium-cost steel ($$$), cheaper than about 51% 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.
C12 — frequently asked
What is C12 used for?
C12 is typically used for high-temperature steam valve bodies, refinery process piping fittings, hot oil pump casings, cast elbows and tees for main steam lines, valve bonnets and yokes for high-pressure service and header connection castings. In short: 9Cr cast valve steel; cast counterpart to P9; better oxidation resistance than C5.
What is the yield strength of C12?
C12 has a typical yield strength of 470 MPa (68.2 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 57% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is C12 easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Machine in the N+T or A+T condition at ~200 HB with rigid setups, carbide tooling and moderate speeds; work-hardening and gummy chips make sharp geometry and generous coolant important.
Can C12 be welded?
With care — weldability is rated fair (35/100). Weldable with matching E505/ER80S-B8 (9Cr-1Mo) consumables but requires 200–300 °C preheat/interpass, low-hydrogen practice and mandatory PWHT at 730–760 °C to avoid hard, crack-prone HAZ.
What surface finishes work on C12?
Not anodizable; protect with phosphate + high-temperature aluminum/silicone paint, hard-facing on seats, or aluminizing for long-term oxidation service.
Can C12 be formed, bent or molded?
Supplied as sand castings — control feeding and slow post-pour cooling to prevent hot tears and quench cracks; no cold forming, and repair welding must be followed by full re-tempering.
What is the maximum service temperature of C12?
C12 is rated for continuous use to about 600°C (1,112 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between C12 N+T and C12-AC?
N+T is the default condition — standard supply condition for A217 C12 pressure castings; best balance of creep strength, toughness and hardness for valve bodies to ~600 °C. AC: intermediate foundry state only — hard, brittle untempered martensite; must be heat treated before machining and pressure use. Yield strength is 470 MPa in N+T versus 760 MPa in AC.
How much does C12 cost?
C12 is a premium-cost steel ($$$), cheaper than about 51% 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 A217/A217M — Steel Castings, Martensitic Stainless and Alloy, for Pressure-Containing Parts, Suitable for High-Temperature Service — ASTM International (2021)
- ASME BPVC Section II Part D — Properties (Metric), 9Cr-1Mo materials — ASME (2023)
- ASME B16.34 — Valves, Flanged, Threaded and Welding End — ASME (2020)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Steel Castings Handbook, 6th ed. — Steel Founders' Society of America / ASM (1995)
- GB/T 16253 — (pressure-containing steel castings) — SAC (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.