Steel A372 Grade F-CL55
Heat-treated state
ASTM A372 Grade F
CL55 = class 55
Lowest-strength class: choose when maximum ductility, reduction of area and toughness matter more than wall-thickness savings.
Values for the CL55 condition
Other A372 Grade F tempers and conditions
A372 Grade F is listed in 3 conditions; see the grade overview at A372 Grade F.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
CL55This page Class 55 | Lowest-strength class: choose when maximum ductility, reduction of area and toughness matter more than wall-thickness savings. | 415 | 640 | 23 | 190 HB | — |
Class 65 | Mid strength class: balanced compromise between wall thickness and toughness for accumulator and cylinder shells. | 485 | 690 | 21 | 16 HRC | — |
CL70Default Class 70 | Highest class of Grade F: choose for the thinnest practical vessel wall while retaining ductile behaviour. | 520 | 720 | 20 | 18 HRC | — |
What is A372 Grade F-CL55?
A372 Grade F-CL55 is A372 Grade F heat treated to CL55 — lowest-strength class: choose when maximum ductility, reduction of area and toughness matter more than wall-thickness savings. A372 Grade F-CL55 has a yield strength of 415 MPa (60.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 56% of steel grades. Elongation at break is 23% and the elastic modulus is 205 GPa (29.7 Msi). A372 Grade F-CL55 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 is the default condition FabDigit quotes; CL55 is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- Easy to machine — 62/100, better than 89% of steel grades
- Tough — resists crack growth — 120 MPa·√m (109.2 ksi·√in), better than 81% of steel grades
A372 Grade F-CL55 properties
Typical room-temperature values for A372 Grade F-CL55; 17 are specific to this condition. Other listed values are A372 Grade F reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A372 Grade F-CL55 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 Grade F-CL55 has a yield strength of 415 MPa (60.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 56% of steel grades. Elongation at break is 23% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Grade F-CL55 is rated for continuous service to 400°C (752 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
A372 Grade F-CL55 conducts electricity at 9 % IACS, better than 71% 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 F-CL55 takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability6
A372 Grade F-CL55's machinability is good (62/100, better than 89% of steel grades); weldability good (60/100); formability fair (42/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A372 Grade F-CL55
Is A372 Grade F easy to machine?
Machines like Q&T medium-carbon steel at 190–235 HB; use rigid setups, coated carbide, ~100–160 m/min, and rough before final tempering where tolerances are tight.
Can A372 Grade F be welded?
Weldable with low-hydrogen consumables but CE ≈ 0.5: preheat 150–250 °C, control interpass, and PWHT/re-heat-treat to restore Q&T properties in pressure-retaining welds.
Can A372 Grade F be formed, bent or molded?
Hot forged/pierced or flow-formed into the vessel shell, then austenitised, quenched and tempered; cold forming in the Q&T state is limited to minor straightening.
What surface finishes work on A372 Grade F?
No corrosion resistance of its own — shot-blast then paint, zinc-rich primer, phosphate or internal coating; avoid electroplating processes that risk hydrogen embrittlement without bake-out.
A372 Grade F 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 |
|---|---|---|
| Cheat analysis, ASTM A372/A372M Grade F; verify against current edition | ≤ 0.35 | 0.3 |
| MnC-Mn hardenability base | 0.6 – 1.35 | 1 |
| Sideoxidation; fully killed, fine grain | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.03 | 0.01 |
| Febalance; residual Cr/Ni/Mo/Cu limited by purchaser agreement | balance | — |
A372 Grade F-CL55 — frequently asked
What is A372 Grade F-CL55 used for?
A372 Grade F-CL55 is typically used for gas cylinder forgings, pressure vessel shells, gun tube blanks and high-pressure component forgings. In short: thin-wall pressure vessel forging; Q&T strength with toughness; lower-strength A372 class.
What is the yield strength of A372 Grade F-CL55?
A372 Grade F-CL55 has a typical yield strength of 415 MPa (60.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 56% of steel grades. Strength varies by condition: see the 3 listed tempers.
Is A372 Grade F-CL55 easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% of steel grades). Machines like Q&T medium-carbon steel at 190–235 HB; use rigid setups, coated carbide, ~100–160 m/min, and rough before final tempering where tolerances are tight.
Can A372 Grade F-CL55 be welded?
Yes — weldability is rated good (60/100). Weldable with low-hydrogen consumables but CE ≈ 0.5: preheat 150–250 °C, control interpass, and PWHT/re-heat-treat to restore Q&T properties in pressure-retaining welds.
What surface finishes work on A372 Grade F-CL55?
No corrosion resistance of its own — shot-blast then paint, zinc-rich primer, phosphate or internal coating; avoid electroplating processes that risk hydrogen embrittlement without bake-out.
Can A372 Grade F-CL55 be formed, bent or molded?
Hot forged/pierced or flow-formed into the vessel shell, then austenitised, quenched and tempered; cold forming in the Q&T state is limited to minor straightening.
What is the maximum service temperature of A372 Grade F-CL55?
A372 Grade F-CL55 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 F-CL70 and A372 Grade F-CL55?
CL70 is the default condition — highest class of Grade F: choose for the thinnest practical vessel wall while retaining ductile behaviour. CL55: lowest-strength class: choose when maximum ductility, reduction of area and toughness matter more than wall-thickness savings. Yield strength is 520 MPa in CL70 versus 415 MPa in CL55.
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 — Materials for H2S-containing environments — NACE/ISO (2015)
- Mysteel / 1688 — Mysteel (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.