Steel A266
ASTM A266
A266 is an ASTM specification for carbon steel forgings used in pressure vessel and piping components, issued in Grades 1, 2, 3 and 4 with increasing strength (also cross-referenced to grade 20).
Reference datasheet — A266 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 GR2 condition
A266 tempers and conditions
A266 is supplied in 7 conditions, soft to hard. GR2 is the default FabDigit quotes; the values on this page are for it.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Grade 1 | Lowest-strength, most ductile class; pick for low-pressure flanges and fittings where machinability and forming ease matter more than strength. | 240 | 470 | 29 | 140 HB | — |
ASTM A266 Grade 1 | Lowest-strength A266 forging grade (60–85 ksi class), annealed or normalized, used for flanges, nozzles and pressure-vessel fittings where formability and weldability outrank strength. | 250 | 515 | 28 | 143 HB | 10.5 % IACS |
GR2Default Grade 2 | The standard stock class for pressure-vessel flanges, nozzles and tubesheets — best balance of strength, toughness and price. | 290 | 550 | 26 | 160 HB | — |
ASTM A266 Grade 2 | The workhorse A266 forging grade (70–95 ksi class) for boiler and pressure-vessel flanges, tubesheets and valve bodies; roughly the Chinese 20/16Mn forging equivalent. | 290 | 550 | 26 | 160 HB | 10 % IACS |
ASTM A266 Grade 4 | 70–95 ksi A266 forging grade heat-treated for higher ductility and notch toughness than Grade 2 at the same strength level, favoured for impact-tested pressure components. | 290 | 550 | 28 | 160 HB | 10 % IACS |
Grade 4 | Q&T version at Grade 2 strength but with finer structure, higher reduction of area and better low-temperature notch toughness — choose for impact-tested or cold-service pressure boundaries. | 305 | 555 | 27 | 170 HB | — |
Grade 3 | Highest tensile class of A266; use where wall thickness or bolt-load must be reduced and slightly lower ductility is acceptable. | 310 | 585 | 24 | 175 HB | 10 % IACS |
What is A266?
A266 is an ASTM specification for carbon steel forgings used in pressure vessel and piping components, issued in Grades 1, 2, 3 and 4 with increasing strength (also cross-referenced to grade 20). It is specified for flanges, nozzles and forged fittings because it delivers guaranteed notch toughness and pressure-boundary integrity with high weldability (score 88); the reference condition gives 290 MPa yield, 550 MPa tensile, 26 % elongation, 160 HB and service to 425 °C. It has no inherent corrosion resistance and heavy sections can vary in hardness from surface to core. Where low-temperature impact values are required, A350 LF2 is the usual alternative. A266 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). A266 has a yield strength of 290 MPa (42.1 ksi) and a tensile strength of 550 MPa (79.8 ksi) — weaker than 88% of steel grades. Elongation at break is 26% and the elastic modulus is 200 GPa (29 Msi).
What is A266 used for?
- pressure vessel flanges
- nozzles
- forged fittings
- piping components
Advantages
- Conducts heat well — 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades
- Easy to machine — 62/100, better than 89% of steel grades
- Readily welded — 88/100, better than 87% of steel grades
- High electrical conductivity — 10 % IACS, better than 83% of steel grades
- Ductile — tolerates forming and impact — 26%, better than 82% of steel grades
Limitations
- Low strength — 290 MPa (42.1 ksi), worse than 88% of steel grades
- Hard to polish — 45/100, worse than 84% of steel grades
A266 properties
Typical room-temperature values for A266-GR2; bars are the position among steel grades.
Physical3
A266 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
A266 has a yield strength of 290 MPa (42.1 ksi) and a tensile strength of 550 MPa (79.8 ksi) — weaker than 88% of steel grades. Elongation at break is 26% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
A266 is rated for continuous service to 425°C (797 °F). It conducts heat at 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades. Thermal expansion is 11.9 µm/m·K (6.61 µin/in·°F).
Electrical3
A266 conducts electricity at 10 % IACS, better than 83% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of A266 takes about 25 MJ of energy and emits 2 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 28%.
Manufacturability7
A266's machinability is good (62/100, better than 89% of steel grades); weldability excellent (88/100); formability good (65/100).
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. A266 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A266
Is A266 easy to machine?
Machines like normalized 1025–1030: use carbide at 120–180 m/min, sharp tooling and good chip control since gummy at low hardness; heavy sections may vary in hardness core-to-surface.
Can A266 be welded?
P-No.1 material, weldable by SMAW/SAW/GTAW with E70xx-class consumables; preheat 100–150 °C for thick sections and PWHT per ASME Sec.VIII when thickness or service demands.
Can A266 be formed, bent or molded?
Supplied as open-die or closed-die forgings finished 1050–1250 °C with a minimum forging reduction; cold forming limited to mild bending — re-normalize after severe hot or cold work.
A266 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 |
|---|---|---|
| C0.35 max for Grades 1 and 3; 0.30 max for Grades 2 and 4 | ≤ 0.35 | 0.25 |
| Mn | 0.4 – 1.05 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | 0.01 |
| S | ≤ 0.03 | 0.01 |
| Curesidual element | ≤ 0.4 | |
| Niresidual element | ≤ 0.4 | |
| Crresidual element | ≤ 0.3 | |
| Moresidual element | ≤ 0.12 | |
| Vsum of Cu+Ni+Cr+Mo+V generally limited to ~1.00 % | ≤ 0.05 | |
| Fe | balance |
What surface finishes work on A266?
No anodizing; protect with shop primer, epoxy paint, zinc/electroless-Ni plating, or stainless/Inconel weld overlay on wetted seal faces.
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 A266 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- 20
How much does A266 cost?
A266 is a budget-cost steel ($), cheaper than about 90% 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.
A266 — frequently asked
What is A266 used for?
A266 is typically used for pressure vessel flanges, nozzles, forged fittings and piping components. In short: code forging for vessels; four strength grades; P-No.1 easy welding.
What is the yield strength of A266?
A266 has a typical yield strength of 290 MPa (42.1 ksi) and a tensile strength of 550 MPa (79.8 ksi) — weaker than 88% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is A266 easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% of steel grades). Machines like normalized 1025–1030: use carbide at 120–180 m/min, sharp tooling and good chip control since gummy at low hardness; heavy sections may vary in hardness core-to-surface.
Can A266 be welded?
Yes — weldability is rated excellent (88/100). P-No.1 material, weldable by SMAW/SAW/GTAW with E70xx-class consumables; preheat 100–150 °C for thick sections and PWHT per ASME Sec.VIII when thickness or service demands.
What surface finishes work on A266?
No anodizing; protect with shop primer, epoxy paint, zinc/electroless-Ni plating, or stainless/Inconel weld overlay on wetted seal faces.
Can A266 be formed, bent or molded?
Supplied as open-die or closed-die forgings finished 1050–1250 °C with a minimum forging reduction; cold forming limited to mild bending — re-normalize after severe hot or cold work.
What is the maximum service temperature of A266?
A266 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 A266-GR2 and A266-GR1?
GR2 is the default condition — the standard stock class for pressure-vessel flanges, nozzles and tubesheets — best balance of strength, toughness and price. GR1: lowest-strength, most ductile class; pick for low-pressure flanges and fittings where machinability and forming ease matter more than strength. Yield strength is 290 MPa in GR2 versus 240 MPa in GR1.
How much does A266 cost?
A266 is a budget-cost steel ($), cheaper than about 90% 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 A266/A266M — Carbon Steel Forgings for Pressure Vessel Components — ASTM International (2021)
- ASME BPVC Section II Part A / Part D (SA-266 allowable stresses and physical properties) — ASME (2023)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
- Forged carbon steel flange and tubesheet mill certificates (SA-266 Cl.2) — various forging producers (2023)
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.