Steel C12A
ASTM A217 Grade C12A
C12A is the cast equivalent of wrought P91 (9Cr-1Mo-V-Nb) to ASTM A217 Grade C12A, with vanadium and niobium additions that raise creep strength well above C12.
Reference datasheet — C12A 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
C12A tempers and conditions
C12A is supplied in 6 conditions, soft to hard. N+T is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Intermediate softening condition only — castings must be re-normalized and tempered before service. | 360 | 560 | 26 | 9 HRC | 3 % IACS |
N+T high temper | Choose when weld-repair ductility, toughness or a ≤210 HB hardness cap is more important than peak strength. | 435 | 610 | 24 | 13 HRC | — |
N+T plus post-weld heat treatment 750–770 °C | Condition of production/repair-welded castings after mandatory PWHT; slightly softer HAZ than the base N+T state. | 450 | 630 | 21 | 17 HRC | 2.9 % IACS |
N+TDefault Normalized and tempered | Standard mandatory ASTM A217 delivery condition for all C12A castings in creep service. | 470 | 650 | 21 | 19 HRC | — |
Quenched and tempered | Used on very heavy valve bodies where air cooling would not fully transform the core to martensite. | 520 | 700 | 19 | 22 HRC | — |
Spheroidize annealed | Reference only: the raw casting is hard, brittle and crack-prone and must never be shipped or welded in this state. | 800 | 1,150 | 5 | 43 HRC | 2.6 % IACS |
What is C12A?
C12A is the cast equivalent of wrought P91 (9Cr-1Mo-V-Nb) to ASTM A217 Grade C12A, with vanadium and niobium additions that raise creep strength well above C12. Normalized and tempered it gives 470 MPa yield, 650 MPa tensile, 21 % elongation and 215 HB (19 HRC), with service to 600 °C, and is cast into large pressure-retaining shapes for ultra-supercritical power plants. The martensitic matrix means tightly controlled welding — preheat, controlled cooling and PWHT are mandatory — and machinability remains modest (42/100). Where creep strength is not the driver, C12 or C5 is simpler to fabricate. C12A has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 92% of steel grades. It melts at 1,420°C (2,588 °F). C12A has a yield strength of 470 MPa (68.2 ksi) and a tensile strength of 650 MPa (94.3 ksi) — stronger than 57% of steel grades. Elongation at break is 21% and the elastic modulus is 218 GPa (31.6 Msi).
What is C12A used for?
- Ultra-supercritical steam valve bodies
- Turbine casings
- High-temperature power plant castings
Advantages
- High service temperature — 600°C (1,112 °F), better than 98% of steel grades
- Good corrosion resistance — 33/100, better than 97% of steel grades
- Tough — resists crack growth — 130 MPa·√m (118.3 ksi·√in), better than 89% of steel grades
Limitations
- Limited formability — 10/100, worse than 95% of steel grades
- 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
C12A properties
Typical room-temperature values for C12A-N+T; bars are the position among steel grades.
Physical3
C12A has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 92% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
C12A has a yield strength of 470 MPa (68.2 ksi) and a tensile strength of 650 MPa (94.3 ksi) — stronger than 57% of steel grades. Elongation at break is 21% and the elastic modulus is 218 GPa (31.6 Msi).
Thermal6
C12A 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 10.8 µm/m·K (6 µin/in·°F).
Electrical3
C12A conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (33/100), better than 97% of steel grades.
Sustainability4
Producing a kilogram of C12A takes about 33 MJ of energy and emits 2.4 kg of CO₂ — more than 76% of steel grades. Typical recycled content is 80%.
Manufacturability7
C12A's machinability is fair (42/100, worse than 73% of steel grades); weldability fair (38/100); formability not recommended (10/100).
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. C12A is highlighted; hover a dot for its name, or open the interactive family chart.
Working with C12A
Is C12A easy to machine?
Machine in the tempered condition with rigid setups, carbide inserts and moderate speed (≈60–100 m/min); the martensitic matrix work-hardens and scale from heat treatment is very abrasive, so take the first cut under the scale.
Can C12A be welded?
Weld with matching 9Cr-1Mo-V filler (AWS E9015-B9 / ER90S-B9), 200–250 °C preheat, ≤300 °C interpass, cool to 80–120 °C to complete martensite transformation, then PWHT 750–770 °C — never leave the joint untempered.
Can C12A be formed, bent or molded?
Cast to shape only; use generous risers and chills for the long freezing range, control nitrogen and avoid hot tearing in section changes, and always re-normalize + temper after any upgrading weld.
C12A 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 | 0.08 – 0.12 | 0.1 |
| MnMn+Ni often limited to ≤1.0 % to keep Ac1 high | 0.3 – 0.6 | 0.45 |
| Si | 0.2 – 0.5 | 0.35 |
| P | ≤ 0.02 | 0.01 |
| S | ≤ 0.01 | 0.01 |
| Cr | 8 – 9.5 | 8.8 |
| Mo | 0.85 – 1.05 | 0.95 |
| VMX carbonitride former | 0.18 – 0.25 | 0.21 |
| Nblisted as Cb in ASTM A217 | 0.06 – 0.1 | 0.08 |
| Nessential for VN precipitation strengthening | 0.03 – 0.07 | 0.05 |
| Ni | ≤ 0.4 | 0.2 |
| Almax; low Al preserves free N | ≤ 0.02 | 0.01 |
| Ti | ≤ 0.01 | 0 |
| Zr | ≤ 0.01 | 0 |
| Fe | balance |
What surface finishes work on C12A?
Shot blast to remove heat-treat scale; parts are painted or aluminized for external protection, and no anodizing applies — internal steam surfaces rely on the Cr oxide formed in 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 C12A in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- A217 Grade C12A
How much does C12A cost?
C12A 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.
C12A — frequently asked
What is C12A used for?
C12A is typically used for ultra-supercritical steam valve bodies, turbine casings and high-temperature power plant castings. In short: cast P91 equivalent; highest creep strength here; ultra-supercritical steam grade.
What is the yield strength of C12A?
C12A has a typical yield strength of 470 MPa (68.2 ksi) and a tensile strength of 650 MPa (94.3 ksi) — stronger than 57% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is C12A easy to machine?
Not especially — machinability is rated fair (42/100, worse than 73% of steel grades). Machine in the tempered condition with rigid setups, carbide inserts and moderate speed (≈60–100 m/min); the martensitic matrix work-hardens and scale from heat treatment is very abrasive, so take the first cut under the scale.
Can C12A be welded?
With care — weldability is rated fair (38/100). Weld with matching 9Cr-1Mo-V filler (AWS E9015-B9 / ER90S-B9), 200–250 °C preheat, ≤300 °C interpass, cool to 80–120 °C to complete martensite transformation, then PWHT 750–770 °C — never leave the joint untempered.
What surface finishes work on C12A?
Shot blast to remove heat-treat scale; parts are painted or aluminized for external protection, and no anodizing applies — internal steam surfaces rely on the Cr oxide formed in service.
Can C12A be formed, bent or molded?
Cast to shape only; use generous risers and chills for the long freezing range, control nitrogen and avoid hot tearing in section changes, and always re-normalize + temper after any upgrading weld.
What is the maximum service temperature of C12A?
C12A 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 C12A N+T and C12A-AC?
N+T is the default condition — standard mandatory ASTM A217 delivery condition for all C12A castings in creep service. AC: reference only: the raw casting is hard, brittle and crack-prone and must never be shipped or welded in this state. Yield strength is 470 MPa in N+T versus 800 MPa in AC.
How much does C12A cost?
C12A 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 at High Temperature — ASTM International (2021)
- ASME BPVC Section II Part D — Properties (Materials) — ASME (2023)
- ASM Handbook Vol. 1: Properties and Selection — Irons, Steels, and High-Performance Alloys — ASM International (1990)
- The Grade 91 Steel Handbook / EPRI Guidelines for Grade 91 Fabrication and Service — EPRI (2015)
- GB/T 16253 / DL/T (ZG1Cr9Mo1VNbN) (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.