Steel A372 Gr E CL55-QT
Heat-treated state
ASTM A372 Gr E
CL55-QT = class 55
Lowest strength class — pick for thicker walls, best toughness and easiest machining/welding.
Values for the CL55-QT condition
Other A372 Gr E tempers and conditions
A372 Gr E is listed in 5 conditions; see the grade overview at A372 Gr E.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Soft intermediate condition supplied for rough boring/machining before final quench and temper — not a certified A372 delivery class. | 370 | 590 | 26 | 170 HB | — |
Normalized and tempered | Used where section size prevents effective liquid quenching; gives Class 55-level properties with more uniform through-thickness structure. | 415 | 640 | 23 | 12 HRC | 8 % IACS |
CL55-QTThis page Class 55 | Lowest strength class — pick for thicker walls, best toughness and easiest machining/welding. | 420 | 630 | 24 | 187 HB | — |
Class 65 | Intermediate strength/toughness balance for medium-wall cylinders and rings. | 485 | 700 | 22 | 18 HRC | — |
CL70-QTDefault Class 70 | Most commonly ordered class — highest strength of Grade E for thin-wall, high-pressure gas cylinders and accumulators. | 515 | 725 | 20 | 20 HRC | — |
What is A372 Gr E CL55-QT?
A372 Gr E CL55-QT is A372 Gr E heat treated to CL55-QT — lowest strength class — pick for thicker walls, best toughness and easiest machining/welding. A372 Gr E CL55-QT has a yield strength of 420 MPa (60.9 ksi) and a tensile strength of 630 MPa (91.4 ksi) — weaker than 53% of steel grades. Elongation at break is 24% and the elastic modulus is 205 GPa (29.7 Msi). A372 Gr E CL55-QT 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). CL70-QT is the default condition FabDigit quotes; CL55-QT is available on request or by drawing note.
Advantages
- Easy to machine — 62/100, better than 89% of steel grades
- Tough — resists crack growth — 115 MPa·√m (104.7 ksi·√in), better than 77% of steel grades
A372 Gr E CL55-QT properties
Typical room-temperature values for A372 Gr E CL55-QT; 16 are specific to this condition. Other listed values are A372 Gr E reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A372 Gr E CL55-QT 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).
Mechanical17
A372 Gr E CL55-QT has a yield strength of 420 MPa (60.9 ksi) and a tensile strength of 630 MPa (91.4 ksi) — weaker than 53% of steel grades. Elongation at break is 24% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Gr E CL55-QT is rated for continuous service to 425°C (797 °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 Gr E CL55-QT conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of A372 Gr E CL55-QT takes about 34 MJ of energy and emits 2.3 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 25%.
Manufacturability7
A372 Gr E CL55-QT's machinability is good (62/100, better than 89% of steel grades); weldability fair (50/100); formability poor (30/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A372 Gr E CL55-QT
Is A372 Gr E easy to machine?
Bore and turn in the annealed or as-Q&T condition with carbide tooling, ~120–180 m/min, rigid setups; finish machine after heat treatment to hold cylinder wall tolerance.
Can A372 Gr E be welded?
Weldable with low-hydrogen E80xx-B2/ER80S-D2 consumables, 200–300 °C preheat and 620–680 °C PWHT; pressure-boundary welds on cylinders are generally avoided by design.
Can A372 Gr E be formed, bent or molded?
Hot forged/pierced at 1050–1200 °C then liquid quenched and tempered; cold forming is impractical at these strength levels.
What surface finishes work on A372 Gr E?
Shot blast, then phosphate + paint, zinc or electroless-Ni plating; avoid hydrogen-charging plating without bake-out, and keep hardness ≤22 HRC for wet H2S service.
A372 Gr E 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 |
|---|---|---|
| CCr-Mo grade, 4130/4135-type carbon level | 0.28 – 0.35 | 0.32 |
| Mn | 0.75 – 1.05 | 0.9 |
| Si | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Cr | 0.8 – 1.15 | 0.95 |
| Mo | 0.15 – 0.25 | 0.2 |
| Febalance; verify exact ranges against current ASTM A372 edition | balance | — |
A372 Gr E CL55-QT — frequently asked
What is A372 Gr E CL55-QT used for?
A372 Gr E CL55-QT is typically used for high-pressure gas cylinders, forged pressure vessel rings and compressor components. In short: high-strength forged pressure steel; Q&T in three strength classes; better machining than P91/P92.
What is the yield strength of A372 Gr E CL55-QT?
A372 Gr E CL55-QT has a typical yield strength of 420 MPa (60.9 ksi) and a tensile strength of 630 MPa (91.4 ksi) — weaker than 53% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is A372 Gr E CL55-QT easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% of steel grades). Bore and turn in the annealed or as-Q&T condition with carbide tooling, ~120–180 m/min, rigid setups; finish machine after heat treatment to hold cylinder wall tolerance.
Can A372 Gr E CL55-QT be welded?
With care — weldability is rated fair (50/100). Weldable with low-hydrogen E80xx-B2/ER80S-D2 consumables, 200–300 °C preheat and 620–680 °C PWHT; pressure-boundary welds on cylinders are generally avoided by design.
What surface finishes work on A372 Gr E CL55-QT?
Shot blast, then phosphate + paint, zinc or electroless-Ni plating; avoid hydrogen-charging plating without bake-out, and keep hardness ≤22 HRC for wet H2S service.
Can A372 Gr E CL55-QT be formed, bent or molded?
Hot forged/pierced at 1050–1200 °C then liquid quenched and tempered; cold forming is impractical at these strength levels.
What is the maximum service temperature of A372 Gr E CL55-QT?
A372 Gr E CL55-QT 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 A372 Gr E CL70-QT and A372 Gr E-A?
CL70-QT is the default condition — most commonly ordered class — highest strength of Grade E for thin-wall, high-pressure gas cylinders and accumulators. A: soft intermediate condition supplied for rough boring/machining before final quench and temper — not a certified A372 delivery class. Yield strength is 515 MPa in CL70-QT versus 370 MPa in A.
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 ratings) — Industrial Press (2020)
- ANSI/NACE MR0175 / ISO 15156 — Materials for H2S-containing environments — NACE/ISO (2015)
- 35CrMo/42CrMo — 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.