Steel A372 Grade L
ASTM A372 Grade L
A372 Grade L is a very high strength quenched-and-tempered class of ASTM A372 forged pressure vessel steel, supplied as QT-HS, in 32–36 HRC and 40–44 HRC tempers, and also normalized-and-tempered, annealed or as-forged.
Reference datasheet — A372 Grade L 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-HS condition
A372 Grade L tempers and conditions
A372 Grade L is supplied in 6 conditions, soft to hard. QT-HS is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softened stock for rough machining or cold sizing before final quench and temper; not a service condition for pressure parts. | 415 | 655 | 25 | 197 HB | — |
As fabricated | Mill-supplied rough forging before heat treatment — properties are non-uniform and it is not acceptable for A372 acceptance testing. | 500 | 800 | 18 | 25 HRC | 8.1 % IACS |
Normalized and tempered | Lower-cost, lower-strength route for heavy sections where full hardenability cannot be achieved or peak strength is not needed. | 520 | 760 | 20 | 20 HRC | — |
intermediate strength temper | Pick when toughness and Charpy requirements outrank peak strength, or where welding/repair is anticipated. | 930 | 1,055 | 17 | 34 HRC | — |
QT-HSDefault Q&T | Standard supply condition: oil/water quenched and tempered to the upper strength classes of A372 for thin-wall pressure vessels and ordnance forgings. | 1,030 | 1,170 | 15 | 38 HRC | — |
maximum strength temper | Top of the specification range for thin-wall high-pressure cylinders and gun-tube type parts; notch sensitivity and hydrogen embrittlement risk are highest here. | 1,170 | 1,310 | 13 | 42 HRC | — |
What is A372 Grade L?
A372 Grade L is a very high strength quenched-and-tempered class of ASTM A372 forged pressure vessel steel, supplied as QT-HS, in 32–36 HRC and 40–44 HRC tempers, and also normalized-and-tempered, annealed or as-forged. The default condition reaches 1030 MPa yield, 1170 MPa tensile, 15 % elongation and 352 HB (38 HRC), with service to 400 °C. It is used near the top of the specification's strength range for demanding pressure vessel and ordnance service. Toughness margin, weldability and formability are all reduced at this hardness; Grade K is the more fabricable alternative. A372 Grade L has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F). A372 Grade L has a yield strength of 1,030 MPa (149 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 93% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
What is A372 Grade L used for?
- high-strength gas cylinders
- rocket motor forgings
- artillery breech components
Advantages
- High strength — 1,030 MPa (149 ksi), better than 93% of steel grades
- Polishes to a fine finish — 68/100, better than 83% of steel grades
Limitations
- Limited formability — 12/100, worse than 92% of steel grades
- Difficult to weld — 22/100, worse than 81% of steel grades
- Difficult to machine — 38/100, worse than 80% of steel grades
A372 Grade L properties
Typical room-temperature values for A372 Grade L-QT-HS; bars are the position among steel grades.
Physical3
A372 Grade L has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F).
Mechanical16
A372 Grade L has a yield strength of 1,030 MPa (149 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 93% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Grade L 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 L conducts electricity at 7.8 % IACS, worse than 57% 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 L takes about 32 MJ of energy and emits 2.3 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 30%.
Manufacturability6
A372 Grade L's machinability is fair (38/100, worse than 80% of steel grades); weldability poor (22/100); formability not recommended (12/100).
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 L is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A372 Grade L
Is A372 Grade L easy to machine?
Rough machine annealed, finish after Q&T with rigid setups, negative-rake carbide and 60–100 m/min; grind or hone bores at 38+ HRC.
Can A372 Grade L be welded?
Weld only with low-hydrogen consumables, 250–350 °C preheat and immediate PWHT below the tempering temperature; avoid welding in the highest-hardness temper.
Can A372 Grade L be formed, bent or molded?
Hot forge 1150–1230 °C, finish above 900 °C, slow cool then normalize/anneal before quench and temper; no meaningful cold forming in the Q&T state.
A372 Grade L 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 |
|---|---|---|
| Calloy classes of A372; exact range is producer/class specific | 0.35 – 0.5 | 0.42 |
| Mn | 0.6 – 1 | 0.85 |
| Si | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | 0.01 |
| S | ≤ 0.03 | 0.01 |
| CrCr-Mo hardenability base (4140/4340 family) | 0.8 – 1.15 | 0.95 |
| Mo | 0.15 – 0.35 | 0.22 |
| Niadded for heavy sections / low-temperature toughness | ≤ 1.85 | 0.3 |
| Fe | balance |
What surface finishes work on A372 Grade L?
Phosphate-and-oil, paint or electroless nickel; bake 190–220 °C for 8–24 h after any acid pickling or electroplating to relieve hydrogen.
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 L in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Also called
- A372-L
How much does A372 Grade L cost?
A372 Grade L 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 L — frequently asked
What is A372 Grade L used for?
A372 Grade L is typically used for high-strength gas cylinders, rocket motor forgings and artillery breech components. In short: highest-hardness A372 class; 1030 MPa yield forging steel; weld before final temper.
What is the yield strength of A372 Grade L?
A372 Grade L has a typical yield strength of 1,030 MPa (149 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 93% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is A372 Grade L easy to machine?
Not especially — machinability is rated fair (38/100, worse than 80% of steel grades). Rough machine annealed, finish after Q&T with rigid setups, negative-rake carbide and 60–100 m/min; grind or hone bores at 38+ HRC.
Can A372 Grade L be welded?
Not readily — weldability is rated poor (22/100). Weld only with low-hydrogen consumables, 250–350 °C preheat and immediate PWHT below the tempering temperature; avoid welding in the highest-hardness temper.
What surface finishes work on A372 Grade L?
Phosphate-and-oil, paint or electroless nickel; bake 190–220 °C for 8–24 h after any acid pickling or electroplating to relieve hydrogen.
Can A372 Grade L be formed, bent or molded?
Hot forge 1150–1230 °C, finish above 900 °C, slow cool then normalize/anneal before quench and temper; no meaningful cold forming in the Q&T state.
What is the maximum service temperature of A372 Grade L?
A372 Grade L 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 L QT-HS and A372 Grade L-A?
QT-HS is the default condition — standard supply condition: oil/water quenched and tempered to the upper strength classes of A372 for thin-wall pressure vessels and ordnance forgings. A: softened stock for rough machining or cold sizing before final quench and temper; not a service condition for pressure parts. Yield strength is 1,030 MPa in QT-HS versus 415 MPa in A.
How much does A372 Grade L cost?
A372 Grade L 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)
- ASTM A370 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)
- 42CrMo/35CrMo — Mysteel / 1688 (2025)
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.