Steel A372 Grade J QT-CL70
Heat-treated state · default condition
ASTM A372 Grade J
QT-CL70 = class 70
Most commonly stocked balance of strength, toughness and fabricability for seamless forged cylinders.
Values for the QT-CL70 condition
Other A372 Grade J tempers and conditions
A372 Grade J is listed in 8 conditions; see the grade overview at A372 Grade J.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Soft intermediate state for rough machining or deep boring before final quench and temper. | 370 | 620 | 26 | 187 HB | — |
Class 55 | Lowest strength class — pick when toughness and weldability matter more than wall-thickness savings. | 420 | 620 | 24 | 180 HB | — |
Normalized and tempered | Alternative to Q&T for heavy sections or where the lower classes are acceptable without full quench. | 450 | 660 | 22 | 14 HRC | 8 % IACS |
Class 65 | Mid-low class for moderately loaded vessel shells with good notch toughness. | 490 | 690 | 22 | 16 HRC | — |
QT-CL70DefaultThis page Class 70 | Most commonly stocked balance of strength, toughness and fabricability for seamless forged cylinders. | 520 | 720 | 20 | 18 HRC | — |
Class 85 | Intermediate high-strength class where Class 70 walls are too thick but Class 110 toughness is insufficient. | 620 | 790 | 18 | 22 HRC | — |
Class 90 | High-strength class for weight-critical accumulator and gas-cylinder forgings. | 660 | 830 | 17 | 25 HRC | — |
Class 110 | Highest common class — maximum strength-to-weight, but lowest toughness and most sensitive to hydrogen/notches. | 800 | 930 | 15 | 30 HRC | — |
What is A372 Grade J QT-CL70?
A372 Grade J QT-CL70 is A372 Grade J heat treated to QT-CL70 — most commonly stocked balance of strength, toughness and fabricability for seamless forged cylinders. A372 Grade J QT-CL70 has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 720 MPa (104 ksi) — stronger than 67% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi). A372 Grade J 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 J QT-CL70 properties
Typical room-temperature values for A372 Grade J QT-CL70; 16 are specific to this condition. Other listed values are A372 Grade J reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A372 Grade J 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 J QT-CL70 has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 720 MPa (104 ksi) — stronger than 67% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Grade J 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 J QT-CL70 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of A372 Grade J QT-CL70 takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 25%.
Manufacturability8
A372 Grade J QT-CL70's machinability is good (55/100, better than 62% of steel grades); weldability fair (35/100); 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 J QT-CL70
Is A372 Grade J easy to machine?
Rough machine annealed, finish after Q&T; use rigid setups, carbide inserts and moderate speeds — chips get stringy above ~280 HB.
Can A372 Grade J be welded?
Low-hydrogen consumables with 200–300 °C preheat and mandatory PWHT; higher classes are best joined only if the standard's weld provisions allow.
Can A372 Grade J be formed, bent or molded?
Hot forge/pierce at 1100–1200 °C then quench and temper; cold forming is impractical in the hardened classes.
What surface finishes work on A372 Grade J?
No anodizing — protect with phosphate + paint, epoxy lining or zinc plating; bake after plating to avoid hydrogen embrittlement in Class 90/110.
A372 Grade J 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 |
|---|---|---|
| Cmedium-carbon Q&T forging grade; verify exact range against current ASTM A372 Table 1 | 0.35 – 0.5 | 0.42 |
| Mn | 0.6 – 1 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| NiNi-Cr-Mo alloy class | 0.4 – 1 | 0.7 |
| Cr | 0.7 – 1.2 | 0.95 |
| Mo | 0.15 – 0.3 | 0.22 |
| Fe | balance | — |
A372 Grade J QT-CL70 — frequently asked
What is A372 Grade J QT-CL70 used for?
A372 Grade J QT-CL70 is typically used for high-pressure vessel forgings, ordnance forgings and rocket casings. In short: mid-strength A372 forging class; widest class range in A372; needs preheat and PWHT.
What is the yield strength of A372 Grade J QT-CL70?
A372 Grade J QT-CL70 has a typical yield strength of 520 MPa (75.4 ksi) and a tensile strength of 720 MPa (104 ksi) — stronger than 67% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is A372 Grade J QT-CL70 easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Rough machine annealed, finish after Q&T; use rigid setups, carbide inserts and moderate speeds — chips get stringy above ~280 HB.
Can A372 Grade J QT-CL70 be welded?
With care — weldability is rated fair (35/100). Low-hydrogen consumables with 200–300 °C preheat and mandatory PWHT; higher classes are best joined only if the standard's weld provisions allow.
What surface finishes work on A372 Grade J QT-CL70?
No anodizing — protect with phosphate + paint, epoxy lining or zinc plating; bake after plating to avoid hydrogen embrittlement in Class 90/110.
Can A372 Grade J QT-CL70 be formed, bent or molded?
Hot forge/pierce at 1100–1200 °C then quench and temper; cold forming is impractical in the hardened classes.
What is the maximum service temperature of A372 Grade J QT-CL70?
A372 Grade J 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 J QT-CL70 and A372 Grade J-ANN?
QT-CL70 is the default condition — most commonly stocked balance of strength, toughness and fabricability for seamless forged cylinders. ANN: soft intermediate state for rough machining or deep boring before final quench and temper. Yield strength is 520 MPa in QT-CL70 versus 370 MPa in ANN.
Sources
- ASTM A372/A372M Standard Specification for Carbon and Alloy Steel Forgings for Thin-Walled Pressure Vessels — ASTM International (2021)
- ASTM A370 Standard Test Methods and Definitions for Mechanical Testing of Steel Products (hardness conversions) — ASTM International (2022)
- 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)
- Machinery's Handbook, machinability and heat-treatment data — Industrial Press (2020)
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.