Steel A372 Grade G QT-CL70
Heat-treated state · default condition
ASTM A372 Grade G
QT-CL70 = 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.
Values for the QT-CL70 condition
Other A372 Grade G tempers and conditions
A372 Grade G is listed in 5 conditions; see the grade overview at A372 Grade G.
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-CL70DefaultThis page 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 QT-CL70?
A372 Grade G QT-CL70 is A372 Grade G heat treated to QT-CL70 — highest-strength Grade G class and the usual stock condition for thin-walled cylinders and accumulator shells; keep hardness ≤22 HRC for sour service. A372 Grade G QT-CL70 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). A372 Grade G QT-CL70 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 QT-CL70 properties
Typical room-temperature values for A372 Grade G QT-CL70; 17 are specific to this condition. Other listed values are A372 Grade G reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A372 Grade G QT-CL70 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 QT-CL70 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 QT-CL70 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 QT-CL70 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 QT-CL70 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 QT-CL70'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. Confirm any required mill or lot documentation when quoting.
Working with A372 Grade G QT-CL70
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.
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.
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 | — |
A372 Grade G QT-CL70 — frequently asked
What is A372 Grade G QT-CL70 used for?
A372 Grade G QT-CL70 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 QT-CL70?
A372 Grade G QT-CL70 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 QT-CL70 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 QT-CL70 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 QT-CL70?
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 QT-CL70 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 QT-CL70?
A372 Grade G QT-CL70 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.