Steel A266-GR1
Grade
ASTM A266
GR1 = grade 1
Lowest-strength, most ductile class; pick for low-pressure flanges and fittings where machinability and forming ease matter more than strength.
Values for the GR1 condition
Other A266 tempers and conditions
A266 is listed in 7 conditions; see the grade overview at A266.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
GR1This page 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-GR1?
A266-GR1 is A266 in the GR1 grade — lowest-strength, most ductile class; pick for low-pressure flanges and fittings where machinability and forming ease matter more than strength. A266-GR1 has a yield strength of 240 MPa (34.8 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 96% of steel grades. Elongation at break is 29% and the elastic modulus is 200 GPa (29 Msi). A266-GR1 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). GR2 is the default condition FabDigit quotes; GR1 is available on request or by drawing note.
Advantages
- Easy to machine — 68/100, better than 95% of steel grades
- Conducts heat well — 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades
- Ductile — tolerates forming and impact — 29%, better than 91% of steel grades
- Readily welded — 90/100, better than 90% of steel grades
- Tough — resists crack growth — 130 MPa·√m (118.3 ksi·√in), better than 89% of steel grades
Limitations
- Low strength — 240 MPa (34.8 ksi), worse than 96% of steel grades
- Hard to polish — 45/100, worse than 84% of steel grades
A266-GR1 properties
Typical room-temperature values for A266-GR1; 17 are specific to this condition. Other listed values are A266 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A266-GR1 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-GR1 has a yield strength of 240 MPa (34.8 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 96% of steel grades. Elongation at break is 29% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
A266-GR1 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-GR1 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-GR1 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-GR1's machinability is good (68/100, better than 95% of steel grades); weldability excellent (90/100); formability very good (72/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A266-GR1
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.
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.
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 | — |
A266-GR1 — frequently asked
What is A266-GR1 used for?
A266-GR1 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-GR1?
A266-GR1 has a typical yield strength of 240 MPa (34.8 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 96% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is A266-GR1 easy to machine?
Reasonably — machinability is rated good (68/100, better than 95% 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-GR1 be welded?
Yes — weldability is rated excellent (90/100). 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-GR1?
No anodizing; protect with shop primer, epoxy paint, zinc/electroless-Ni plating, or stainless/Inconel weld overlay on wetted seal faces.
Can A266-GR1 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-GR1?
A266-GR1 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.