Steel A372 Grade G
ASTM A372 Grade G
A372 Grade G is an intermediate-strength class of ASTM A372 quenched-and-tempered alloy steel forging, specified for thin-walled seamless pressure vessels and supplied in Class 55, 65 and 70 as well as annealed and normalized-and-tempered conditions.
Reference datasheet — A372 Grade G 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 QT-CL70 condition
A372 Grade G tempers and conditions
A372 Grade G is supplied in 5 conditions, soft to hard. QT-CL70 is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Soft intermediate condition used for rough machining and cold straightening before the mandatory quench and temper; not a deliverable A372 condition. | 380 | 620 | 25 | 180 HB | — |
Normalized and tempered | Used only by agreement for very heavy sections where full quenching is impractical; strength falls below the Class 55 minimum in thick walls. | 400 | 640 | 22 | 12 HRC | 8 % IACS |
Class 55 | Lowest-strength class of Grade G — pick when toughness, weldability and wall-thickness tolerance matter more than pressure rating. | 430 | 640 | 23 | 190 HB | — |
Class 65 | Balanced class: higher pressure rating than Class 55 while keeping good Charpy energy in moderate wall thicknesses. | 495 | 700 | 21 | 16 HRC | — |
QT-CL70Default Class 70 | Highest-strength Grade G class and the usual stock condition for thin-walled cylinders and accumulator shells; keep hardness ≤22 HRC for sour service. | 530 | 740 | 19 | 19 HRC | — |
What is A372 Grade G?
A372 Grade G is an intermediate-strength class of ASTM A372 quenched-and-tempered alloy steel forging, specified for thin-walled seamless pressure vessels and supplied in Class 55, 65 and 70 as well as annealed and normalized-and-tempered conditions. Default Q&T values are 530 MPa yield, 740 MPa tensile, 19% elongation and about 220 HB (19 HRC), with service to 400 °C, in backward-extruded or closed-die forged cylinder bodies. It carries a higher minimum tensile strength than Grade F, but has no corrosion resistance, low cold formability and restricted weldability requiring low-hydrogen practice and post-weld tempering. Grade H is the next composition class in the same specification. A372 Grade G 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). A372 Grade G has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 740 MPa (107 ksi) — stronger than 69% of steel grades. Elongation at break is 19% and the elastic modulus is 205 GPa (29.7 Msi).
What is A372 Grade G used for?
- pressure vessel forgings
- high-pressure gas cylinders
- rocket motor case forgings
A372 Grade G properties
Typical room-temperature values for A372 Grade G-QT-CL70; bars are the position among steel grades.
Physical3
A372 Grade G 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
A372 Grade G has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 740 MPa (107 ksi) — stronger than 69% of steel grades. Elongation at break is 19% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Grade G is rated for continuous service to 400°C (752 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
A372 Grade G conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of A372 Grade G takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
A372 Grade G's machinability is fair (48/100, worse than 57% of steel grades); weldability fair (42/100); formability poor (28/100).
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. A372 Grade G is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A372 Grade G
Is A372 Grade G easy to machine?
Machine rough in the annealed state and finish after Q&T; at 200–250 HB use rigid setups, coated carbide, 90–150 m/min, and generous coolant to avoid work-hardened skins.
Can A372 Grade G be welded?
Low-hydrogen process only; preheat 150–250 °C depending on section, interpass control, and post-weld temper below the original tempering temperature — then re-verify hardness for sour service.
Can A372 Grade G be formed, bent or molded?
Formed hot as a closed-die or backward-extruded forging (1050–1200 °C) then fully quenched and tempered; cold forming of the Q&T material is limited to light straightening.
A372 Grade G 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 |
|---|---|---|
| Cmaximum per A372 alloy grades; heat analysis | ≤ 0.35 | 0.3 |
| Mn | 0.6 – 1.1 | 0.85 |
| Si | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| NiNi-Cr-Mo alloy type; verify exact limits against the current ASTM A372 Table 1 edition | 0.4 – 1.1 | 0.7 |
| Crverify against current ASTM A372 edition | 0.4 – 1.1 | 0.8 |
| Moverify against current ASTM A372 edition | 0.15 – 0.3 | 0.22 |
| Fe | balance |
What surface finishes work on A372 Grade G?
No anodizing — protect with shot blast + zinc phosphate and epoxy paint, or Zn/Ni electroplating with a 200 °C hydrogen bake-out; internal surfaces of gas cylinders are typically left bare and inspected.
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 A372 Grade G in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Also called
- A372-G
How much does A372 Grade G cost?
A372 Grade G is a standard-cost steel ($$), cheaper than about 71% 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.
A372 Grade G — frequently asked
What is A372 Grade G used for?
A372 Grade G is typically used for pressure vessel forgings, high-pressure gas cylinders and rocket motor case forgings. In short: thin-wall pressure vessel forging; 740 MPa Q&T strength; gas cylinder forging grade.
What is the yield strength of A372 Grade G?
A372 Grade G has a typical yield strength of 530 MPa (76.9 ksi) and a tensile strength of 740 MPa (107 ksi) — stronger than 69% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is A372 Grade G easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Machine rough in the annealed state and finish after Q&T; at 200–250 HB use rigid setups, coated carbide, 90–150 m/min, and generous coolant to avoid work-hardened skins.
Can A372 Grade G be welded?
With care — weldability is rated fair (42/100). Low-hydrogen process only; preheat 150–250 °C depending on section, interpass control, and post-weld temper below the original tempering temperature — then re-verify hardness for sour service.
What surface finishes work on A372 Grade G?
No anodizing — protect with shot blast + zinc phosphate and epoxy paint, or Zn/Ni electroplating with a 200 °C hydrogen bake-out; internal surfaces of gas cylinders are typically left bare and inspected.
Can A372 Grade G be formed, bent or molded?
Formed hot as a closed-die or backward-extruded forging (1050–1200 °C) then fully quenched and tempered; cold forming of the Q&T material is limited to light straightening.
What is the maximum service temperature of A372 Grade G?
A372 Grade G is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A372 Grade G QT-CL70 and A372 Grade G-ANN?
QT-CL70 is the default condition — highest-strength Grade G class and the usual stock condition for thin-walled cylinders and accumulator shells; keep hardness ≤22 HRC for sour service. ANN: soft intermediate condition used for rough machining and cold straightening before the mandatory quench and temper; not a deliverable A372 condition. Yield strength is 530 MPa in QT-CL70 versus 380 MPa in ANN.
How much does A372 Grade G cost?
A372 Grade G is a standard-cost steel ($$), cheaper than about 71% 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 A372/A372M — Carbon and Alloy Steel Forgings for Thin-Walled Pressure Vessels — ASTM International (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- ASTM A370 — Mechanical Testing of Steel Products (hardness conversions) — ASTM International (2022)
- NACE MR0175 / ISO 15156-2 — hardness limits for sour service — NACE/ISO (2020)
- 40CrNiMo/ — Mysteel / 1688 (2026)
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.