Steel A372 Grade K
ASTM A372 Grade K
A372 Grade K is a higher-strength quenched-and-tempered class of the ASTM A372 seamless forged pressure vessel family, also held annealed, normalized, normalized-and-tempered and in a 22 HRC controlled-hardness temper.
Reference datasheet — A372 Grade K 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 condition
A372 Grade K tempers and conditions
A372 Grade K is supplied in 5 conditions, soft to hard. QT is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition; chosen for deep machining or cold sizing of the forging before final heat treatment. | 400 | 640 | 24 | 11 HRC | 8.5 % IACS |
Normalized | Grain-refining condition after forging, used before rough machining and final quench-and-temper. | 470 | 760 | 19 | 20 HRC | 8 % IACS |
normalized and tempered | Alternative treatment for heavier or geometrically awkward forgings where full quenching is impractical; lower strength and more scatter than Q&T. | 520 | 720 | 20 | 18 HRC | 9 % IACS |
Q&T, hardness-limited ≤22 HRC | Higher tempering temperature to cap hardness at 22 HRC for wet H2S / sour gas accumulators and vessels, at the cost of strength. | 620 | 760 | 21 | 21 HRC | 8 % IACS |
QTDefault Quenched and tempered | Standard delivery condition for the higher-strength A372 grades; use when the specified minimum yield/tensile combination and impact values must be met in the finished forging. | 725 | 860 | 18 | 25 HRC | — |
What is A372 Grade K?
A372 Grade K is a higher-strength quenched-and-tempered class of the ASTM A372 seamless forged pressure vessel family, also held annealed, normalized, normalized-and-tempered and in a 22 HRC controlled-hardness temper. Default properties are 725 MPa yield, 860 MPa tensile, 18 % elongation and 255 HB (25 HRC), with service to 400 °C. It is specified for thin-walled forged cylinders where wall thickness is set by minimum yield strength. Welding requires preheat and PWHT and the steel has no corrosion resistance; Grade J is the lower-strength option and Grade L the higher. A372 Grade K 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). A372 Grade K 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 18% and the elastic modulus is 205 GPa (29.7 Msi).
What is A372 Grade K used for?
- thin-wall high-pressure cylinders
- military ordnance forgings
- pressure vessel end closures
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High strength — 725 MPa (105 ksi), better than 82% of steel grades
A372 Grade K properties
Typical room-temperature values for A372 Grade K-QT; bars are the position among steel grades.
Physical3
A372 Grade K 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 K 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 18% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Grade K 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 K conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of A372 Grade K takes about 26 MJ of energy and emits 1.9 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 25%.
Manufacturability7
A372 Grade K's machinability is fair (48/100, worse than 57% of steel grades); weldability fair (42/100); formability poor (28/100).
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 K is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A372 Grade K
Is A372 Grade K easy to machine?
Rough machine annealed or normalized, finish after Q&T at ~255 HB with rigid setups, coated carbide and generous coolant; avoid grinding burns on finished bores.
Can A372 Grade K be welded?
Weldable with low-hydrogen consumables but requires 200–300 °C preheat, controlled interpass and PWHT at ~620–680 °C; most A372 vessels are seamless forgings with welding limited to attachments.
Can A372 Grade K be formed, bent or molded?
Hot forge/back-extrude at roughly 1100–1230 °C with finish above 900 °C, then normalize before hardening; cold forming is essentially limited to sizing.
A372 Grade K 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 hardenable base; verify exact limits against the current A372/A372M edition for Grade K | 0.3 – 0.5 | 0.4 |
| Mn | 0.6 – 1.05 | 0.85 |
| Si | 0.15 – 0.35 | 0.25 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Crchromium-molybdenum hardenability class | 0.75 – 1.2 | 0.95 |
| Mo | 0.15 – 0.3 | 0.2 |
| Fe | balance |
What surface finishes work on A372 Grade K?
No anodizing — protect by shot-blast plus epoxy/zinc-rich paint, phosphate, or zinc-nickel plating; bake plated high-strength parts to avoid hydrogen embrittlement.
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 K in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Also called
- A372-K
How much does A372 Grade K cost?
A372 Grade K 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 K — frequently asked
What is A372 Grade K used for?
A372 Grade K is typically used for thin-wall high-pressure cylinders, military ordnance forgings and pressure vessel end closures. In short: higher-strength A372 class; 22 HRC controlled-hardness option; thin-wall cylinder forgings.
What is the yield strength of A372 Grade K?
A372 Grade K 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 5 listed tempers.
Is A372 Grade K easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Rough machine annealed or normalized, finish after Q&T at ~255 HB with rigid setups, coated carbide and generous coolant; avoid grinding burns on finished bores.
Can A372 Grade K be welded?
With care — weldability is rated fair (42/100). Weldable with low-hydrogen consumables but requires 200–300 °C preheat, controlled interpass and PWHT at ~620–680 °C; most A372 vessels are seamless forgings with welding limited to attachments.
What surface finishes work on A372 Grade K?
No anodizing — protect by shot-blast plus epoxy/zinc-rich paint, phosphate, or zinc-nickel plating; bake plated high-strength parts to avoid hydrogen embrittlement.
Can A372 Grade K be formed, bent or molded?
Hot forge/back-extrude at roughly 1100–1230 °C with finish above 900 °C, then normalize before hardening; cold forming is essentially limited to sizing.
What is the maximum service temperature of A372 Grade K?
A372 Grade K 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 K-QT and A372 Grade K-A?
QT is the default condition — standard delivery condition for the higher-strength A372 grades; use when the specified minimum yield/tensile combination and impact values must be met in the finished forging. A: softest condition; chosen for deep machining or cold sizing of the forging before final heat treatment. Yield strength is 725 MPa in QT versus 400 MPa in A.
How much does A372 Grade K cost?
A372 Grade K 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)
- 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)
- NACE MR0175 / ISO 15156 — Materials for use in H2S-containing environments — NACE/ISO (2015)
- 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; 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.