Steel A372 Grade M
ASTM A372 Grade M
A372 Grade M is the highest-strength class defined by ASTM A372, a fully quenched-and-tempered alloy steel forging supplied as QT-CL85 and QT-CL100 plus annealed and normalized conditions.
Reference datasheet — A372 Grade M 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-CL100 condition
A372 Grade M tempers and conditions
A372 Grade M is supplied in 4 conditions, soft to hard. QT-CL100 is the default FabDigit quotes; the values on this page are for it.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Non-code intermediate condition supplied for further machining or forging; must be re-austenitized, quenched and tempered before the forging can be certified to A372 Grade M. | 400 | 660 | 24 | 197 HB | — |
Normalized | Grain-refining condition after forging, used before final quench and temper; not a deliverable A372 Grade M class on its own. | 530 | 830 | 20 | 24 HRC | 7.8 % IACS |
Class 85 | Pick when somewhat lower strength is acceptable in exchange for better ductility, toughness and easier weld/repair behaviour, or for heavier sections where full hardenability is uncertain. | 620 | 790 | 18 | 21 HRC | — |
QT-CL100Default Class 100 | Pick for the thinnest possible wall / highest strength-to-weight in high-pressure cylinders where notch toughness and weld repair are less critical. | 725 | 860 | 16 | 26 HRC | — |
What is A372 Grade M?
A372 Grade M is the highest-strength class defined by ASTM A372, a fully quenched-and-tempered alloy steel forging supplied as QT-CL85 and QT-CL100 plus annealed and normalized conditions. Default values are 725 MPa yield, 860 MPa tensile, 16 % elongation and 262 HB (26 HRC), with service to 400 °C. It is used where maximum strength-to-weight ratio is required in thin-walled pressure vessels. Machinability (40), weldability (28), formability (20) and corrosion resistance (12) are all low, so plan on machining before final temper and full protective coating; Grade K is the easier-to-fabricate option. A372 Grade M 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 M has a yield strength of 725 MPa (105 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 82% of steel grades. Elongation at break is 16% and the elastic modulus is 205 GPa (29.7 Msi).
What is A372 Grade M used for?
- high-performance pressure vessels
- rocket motor cases
- ordnance forgings
Advantages
- High strength — 725 MPa (105 ksi), better than 82% of steel grades
Limitations
- Limited formability — 20/100, worse than 80% of steel grades
- Difficult to machine — 40/100, worse than 77% of steel grades
A372 Grade M properties
Typical room-temperature values for A372 Grade M-QT-CL100; bars are the position among steel grades.
Physical3
A372 Grade M 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 M has a yield strength of 725 MPa (105 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 82% of steel grades. Elongation at break is 16% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Grade M 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 M 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 M takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability6
A372 Grade M's machinability is fair (40/100, worse than 77% of steel grades); weldability poor (28/100); formability poor (20/100).
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 M is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A372 Grade M
Is A372 Grade M easy to machine?
Machine in the annealed/normalized state where possible; at 250–290 HB use rigid setups, carbide inserts, ~60–90 m/min and heavy flood coolant, and finish-machine after final temper to control distortion.
Can A372 Grade M be welded?
Low-hydrogen processes only, preheat 200–300 °C, interpass control and mandatory post-weld temper below the original tempering temperature; avoid weld hardness above NACE limits in sour service.
Can A372 Grade M be formed, bent or molded?
Hot forge at 1050–1200 °C with finish above ~950 °C, then normalize, austenitize, water/oil quench and temper; essentially no cold forming in the delivered condition.
A372 Grade M 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 Ni-Cr-Mo hardenable base; verify exact limits against the current ASTM A372 chemical-requirements table | 0.35 – 0.5 | 0.42 |
| Mn | 0.55 – 1 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Nihardenability/toughness; range covers the Ni-Cr-Mo chemistry family permitted for this grade | 0.6 – 2 | 1.2 |
| Cr | 0.55 – 1.2 | 0.85 |
| Motemper-embrittlement resistance | 0.15 – 0.4 | 0.25 |
| Fe | balance |
What surface finishes work on A372 Grade M?
No natural corrosion resistance — shot blast plus paint, zinc/phosphate or electroless nickel; avoid electroplating that charges hydrogen unless baked (190–210 °C) immediately after plating.
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 M in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Also called
- A372-M
How much does A372 Grade M cost?
A372 Grade M 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 M — frequently asked
What is A372 Grade M used for?
A372 Grade M is typically used for high-performance pressure vessels, rocket motor cases and ordnance forgings. In short: maximum strength-to-weight A372 class; lowest machinability in family; no inherent corrosion resistance.
What is the yield strength of A372 Grade M?
A372 Grade M has a typical yield strength of 725 MPa (105 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 82% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is A372 Grade M easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Machine in the annealed/normalized state where possible; at 250–290 HB use rigid setups, carbide inserts, ~60–90 m/min and heavy flood coolant, and finish-machine after final temper to control distortion.
Can A372 Grade M be welded?
Not readily — weldability is rated poor (28/100). Low-hydrogen processes only, preheat 200–300 °C, interpass control and mandatory post-weld temper below the original tempering temperature; avoid weld hardness above NACE limits in sour service.
What surface finishes work on A372 Grade M?
No natural corrosion resistance — shot blast plus paint, zinc/phosphate or electroless nickel; avoid electroplating that charges hydrogen unless baked (190–210 °C) immediately after plating.
Can A372 Grade M be formed, bent or molded?
Hot forge at 1050–1200 °C with finish above ~950 °C, then normalize, austenitize, water/oil quench and temper; essentially no cold forming in the delivered condition.
What is the maximum service temperature of A372 Grade M?
A372 Grade M 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 M QT-CL100 and A372 Grade M-A?
QT-CL100 is the default condition — pick for the thinnest possible wall / highest strength-to-weight in high-pressure cylinders where notch toughness and weld repair are less critical. A: non-code intermediate condition supplied for further machining or forging; must be re-austenitized, quenched and tempered before the forging can be certified to A372 Grade M. Yield strength is 725 MPa in QT-CL100 versus 400 MPa in A.
How much does A372 Grade M cost?
A372 Grade M 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 — Standard Specification for 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)
- ASM Handbook Vol.13B — Corrosion: Materials — ASM International (2005)
- ASTM A370 — Mechanical Testing of Steel Products (hardness conversions) — ASTM International (2022)
- / 34CrNiMo6 40CrNiMoA — 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.