Steel A372 Grade K-NT
Heat-treated state
ASTM A372 Grade K
Alternative treatment for heavier or geometrically awkward forgings where full quenching is impractical; lower strength and more scatter than Q&T.
Values for the NT condition
Other A372 Grade K tempers and conditions
A372 Grade K is listed in 5 conditions; see the grade overview at A372 Grade K.
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 |
NTThis page 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-NT?
A372 Grade K-NT is A372 Grade K heat treated to NT — alternative treatment for heavier or geometrically awkward forgings where full quenching is impractical; lower strength and more scatter than Q&T. A372 Grade K-NT has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 720 MPa (104 ksi) — stronger than 67% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi). A372 Grade K-NT 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). QT is the default condition FabDigit quotes; NT is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
A372 Grade K-NT properties
Typical room-temperature values for A372 Grade K-NT; 23 are specific to this condition. Other listed values are A372 Grade K reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A372 Grade K-NT 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-NT has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 720 MPa (104 ksi) — stronger than 67% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
A372 Grade K-NT is rated for continuous service to 425°C (797 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
A372 Grade K-NT conducts electricity at 9 % IACS, better than 71% 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-NT 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-NT's machinability is good (55/100, better than 62% of steel grades); weldability fair (52/100); formability fair (36/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A372 Grade K-NT
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.
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.
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 | — |
A372 Grade K-NT — frequently asked
What is A372 Grade K-NT used for?
A372 Grade K-NT 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-NT?
A372 Grade K-NT has a typical yield strength of 520 MPa (75.4 ksi) and a tensile strength of 720 MPa (104 ksi) — stronger than 67% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is A372 Grade K-NT easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% 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-NT be welded?
With care — weldability is rated fair (52/100). 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-NT?
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-NT 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-NT?
A372 Grade K-NT is rated for continuous use to about 425°C (797 °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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.