Steel A372 Grade L QT-40-44HRC
Hardness band
ASTM A372 Grade L
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.
Values for the QT-40-44HRC condition
Other A372 Grade L tempers and conditions
A372 Grade L is listed in 6 conditions; see the grade overview at A372 Grade L.
- A
- F
- N+T
- QT-32-36HRC
- QT-HS
- QT-40-44HRC
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 | — |
QT-40-44HRCThis page 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 QT-40-44HRC?
A372 Grade L QT-40-44HRC is A372 Grade L heat treated to QT-40-44HRC — 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. A372 Grade L QT-40-44HRC has a yield strength of 1,170 MPa (170 ksi) and a tensile strength of 1,310 MPa (190 ksi) — stronger than 94% of steel grades. Elongation at break is 13% and the elastic modulus is 205 GPa (29.7 Msi). A372 Grade L QT-40-44HRC 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). QT-HS is the default condition FabDigit quotes; QT-40-44HRC is available on request or by drawing note.
Advantages
- High strength — 1,170 MPa (170 ksi), better than 94% 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 — 15/100, worse than 91% of steel grades
- Low fracture toughness — 55 MPa·√m (50.1 ksi·√in), worse than 82% of steel grades
- Difficult to machine — 38/100, worse than 80% of steel grades
- Limited ductility — 13%, worse than 78% of steel grades
A372 Grade L QT-40-44HRC properties
Typical room-temperature values for A372 Grade L QT-40-44HRC; 12 are specific to this condition. Other listed values are A372 Grade L reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A372 Grade L QT-40-44HRC 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 QT-40-44HRC has a yield strength of 1,170 MPa (170 ksi) and a tensile strength of 1,310 MPa (190 ksi) — stronger than 94% of steel grades. Elongation at break is 13% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Grade L QT-40-44HRC 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 QT-40-44HRC 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 QT-40-44HRC 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 QT-40-44HRC's machinability is fair (38/100, worse than 80% of steel grades); weldability poor (15/100); formability not recommended (12/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A372 Grade L QT-40-44HRC
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.
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.
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 | — |
A372 Grade L QT-40-44HRC — frequently asked
What is A372 Grade L QT-40-44HRC used for?
A372 Grade L QT-40-44HRC 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 QT-40-44HRC?
A372 Grade L QT-40-44HRC has a typical yield strength of 1,170 MPa (170 ksi) and a tensile strength of 1,310 MPa (190 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is A372 Grade L QT-40-44HRC 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 QT-40-44HRC be welded?
Not readily — weldability is rated poor (15/100). 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 QT-40-44HRC?
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 QT-40-44HRC 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 QT-40-44HRC?
A372 Grade L QT-40-44HRC 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.