Steel A372 Grade M-A (Solution annealed)
Temper
ASTM A372 Grade M
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.
Values for the A condition
Other A372 Grade M tempers and conditions
A372 Grade M is listed in 4 conditions; see the grade overview at A372 Grade M.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AThis page 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-A?
A372 Grade M-A is A372 Grade M in the A temper — 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. A372 Grade M-A has a yield strength of 400 MPa (58 ksi) and a tensile strength of 660 MPa (95.7 ksi) — weaker than 60% of steel grades. Elongation at break is 24% and the elastic modulus is 205 GPa (29.7 Msi). A372 Grade M-A 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). QT-CL100 is the default condition FabDigit quotes; A is available on request or by drawing note.
A372 Grade M-A properties
Typical room-temperature values for A372 Grade M-A; 11 are specific to this condition. Other listed values are A372 Grade M reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A372 Grade M-A 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-A has a yield strength of 400 MPa (58 ksi) and a tensile strength of 660 MPa (95.7 ksi) — weaker than 60% of steel grades. Elongation at break is 24% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Grade M-A 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-A 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-A 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-A's machinability is good (58/100, better than 75% of steel grades); weldability fair (45/100); formability fair (40/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A372 Grade M-A
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.
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.
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 | — |
A372 Grade M-A — frequently asked
What is A372 Grade M-A used for?
A372 Grade M-A 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-A?
A372 Grade M-A has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 660 MPa (95.7 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is A372 Grade M-A easy to machine?
Reasonably — machinability is rated good (58/100, better than 75% 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-A be welded?
With care — weldability is rated fair (45/100). 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-A?
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-A 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-A?
A372 Grade M-A 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.