Steel A372 Grade C-QT (Quenched and tempered)
Heat-treated state
ASTM A372 Grade C
Choose when maximum allowable stress / thinnest wall is required; gives the highest and most uniform strength through section, with tempering set to keep hardness below sour-service limits.
Values for the QT condition
Other A372 Grade C tempers and conditions
A372 Grade C is listed in 4 conditions; see the grade overview at A372 Grade C.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Soft intermediate condition used between forging operations or for heavy machining before final normalizing/quenching; not a final vessel-service condition. | 315 | 565 | 26 | 163 HB | 9 % IACS |
Normalized | Simplest A372 heat treatment for thicker, lower-stress vessel forgings where the specified minimums are met without tempering. | 415 | 655 | 20 | 197 HB | 9 % IACS |
N+TDefault Normalized and tempered | Most commonly stocked A372 Grade C condition: balanced strength, ductility and residual-stress relief for thin-walled vessel and cylinder forgings. | 420 | 625 | 22 | 187 HB | — |
QTThis page Quenched and tempered | Choose when maximum allowable stress / thinnest wall is required; gives the highest and most uniform strength through section, with tempering set to keep hardness below sour-service limits. | 550 | 725 | 20 | 20 HRC | — |
What is A372 Grade C-QT?
A372 Grade C-QT is A372 Grade C heat treated to QT — choose when maximum allowable stress / thinnest wall is required; gives the highest and most uniform strength through section, with tempering set to keep hardness below sour-service limits. A372 Grade C-QT has a yield strength of 550 MPa (79.8 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 71% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi). A372 Grade C-QT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). N+T is the default condition FabDigit quotes; QT is available on request or by drawing note.
Advantages
- Conducts heat well — 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades
A372 Grade C-QT properties
Typical room-temperature values for A372 Grade C-QT; 12 are specific to this condition. Other listed values are A372 Grade C reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A372 Grade C-QT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
A372 Grade C-QT has a yield strength of 550 MPa (79.8 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 71% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Grade C-QT is rated for continuous service to 400°C (752 °F). It conducts heat at 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
A372 Grade C-QT conducts electricity at 9 % IACS, better than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of A372 Grade C-QT takes about 25 MJ of energy and emits 2.1 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
A372 Grade C-QT's machinability is good (55/100, better than 62% of steel grades); weldability fair (40/100); 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 C-QT
Is A372 Grade C easy to machine?
Machines like 1045-class C-Mn steel at ~55–60 % of 1212; rough-machine in annealed/normalized state, finish after final heat treatment with rigid setups and carbide tooling.
Can A372 Grade C be welded?
Weldable with low-hydrogen SMAW/SAW consumables but CE is high — use 150–250 °C preheat, control interpass, and apply PWHT at ~600–650 °C; avoid welding on quenched-and-tempered vessel walls without requalification.
Can A372 Grade C be formed, bent or molded?
Designed for hot forging/hot spinning of vessel bodies and closures (typ. 1100–1230 °C); cold formability is limited by the medium carbon content — bend radii should be generous.
What surface finishes work on A372 Grade C?
No anodizing; protect with shot blast + epoxy/zinc-rich paint, phosphate + oil, or galvanizing, and use internal coatings/liners for wet or sour gas service.
A372 Grade C 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 |
|---|---|---|
| Chigher C than Grades A/B for increased strength | ≤ 0.48 | 0.42 |
| Mn | 0.6 – 1.65 | 1.2 |
| Sikilled steel | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.03 | 0.02 |
| Fe | balance | — |
A372 Grade C-QT — frequently asked
What is A372 Grade C-QT used for?
A372 Grade C-QT is typically used for high-pressure gas cylinders, pressure vessel forgings and aerospace bottle shells. In short: higher-carbon A372 forging; hot-spun cylinder grade; stronger than A372 Grade A.
What is the yield strength of A372 Grade C-QT?
A372 Grade C-QT has a typical yield strength of 550 MPa (79.8 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 71% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is A372 Grade C-QT easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machines like 1045-class C-Mn steel at ~55–60 % of 1212; rough-machine in annealed/normalized state, finish after final heat treatment with rigid setups and carbide tooling.
Can A372 Grade C-QT be welded?
With care — weldability is rated fair (40/100). Weldable with low-hydrogen SMAW/SAW consumables but CE is high — use 150–250 °C preheat, control interpass, and apply PWHT at ~600–650 °C; avoid welding on quenched-and-tempered vessel walls without requalification.
What surface finishes work on A372 Grade C-QT?
No anodizing; protect with shot blast + epoxy/zinc-rich paint, phosphate + oil, or galvanizing, and use internal coatings/liners for wet or sour gas service.
Can A372 Grade C-QT be formed, bent or molded?
Designed for hot forging/hot spinning of vessel bodies and closures (typ. 1100–1230 °C); cold formability is limited by the medium carbon content — bend radii should be generous.
What is the maximum service temperature of A372 Grade C-QT?
A372 Grade C-QT 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 C N+T and A372 Grade C-QT?
N+T is the default condition — most commonly stocked A372 Grade C condition: balanced strength, ductility and residual-stress relief for thin-walled vessel and cylinder forgings. QT: choose when maximum allowable stress / thinnest wall is required; gives the highest and most uniform strength through section, with tempering set to keep hardness below sour-service limits. Yield strength is 420 MPa in N+T versus 550 MPa in QT.
Sources
- ASTM A372/A372M — Carbon and Alloy Steel Forgings for Thin-Walled Pressure Vessels — ASTM International (2020)
- ASME BPVC Section II Part D — Material Properties — ASME (2023)
- 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)
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.