Steel HP9-4-30-QT590
Heat-treated state
UNS K91972
QT590 = q&T, double temper 565–595 °C
Choose when fracture toughness and damage tolerance outweigh peak strength.
Values for the QT590 condition
Other HP9-4-30 tempers and conditions
HP9-4-30 is listed in 5 conditions; see the grade overview at HP9-4-30.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Pick for rough machining of large forgings before final austenitize-quench-temper. | 790 | 1,000 | 18 | 31 HRC | — |
Normalized and tempered | Mill delivery condition for bar/plate that will be re-heat-treated by the part maker. | 1,000 | 1,200 | 16 | 38 HRC | 3.9 % IACS |
QT590This page Q&T, double temper 565–595 °C | Choose when fracture toughness and damage tolerance outweigh peak strength. | 1,310 | 1,520 | 15 | 45 HRC | — |
QT540Default Q&T, austenitize 830–860 °C, oil quench, −73 °C refrigerate, double… | Standard aerospace condition — best strength/toughness balance for landing gear and structural forgings. | 1,400 | 1,655 | 13 | 48 HRC | — |
Q&T, double temper 480–510 °C | Use only where maximum strength is required and section/stress state tolerates reduced toughness. | 1,520 | 1,790 | 11 | 51 HRC | — |
What is HP9-4-30-QT590?
HP9-4-30-QT590 is HP9-4-30 heat treated to QT590 — choose when fracture toughness and damage tolerance outweigh peak strength. HP9-4-30-QT590 has a yield strength of 1,310 MPa (190 ksi) and a tensile strength of 1,520 MPa (220 ksi) — stronger than 95% of steel grades. Elongation at break is 15% and the elastic modulus is 200 GPa (29 Msi). HP9-4-30-QT590 has a density of 7.84 g/cm³ (0.283 lb/in³), lighter than 78% of steel grades. It melts at 1,420°C (2,588 °F). QT540 is the default condition FabDigit quotes; QT590 is available on request or by drawing note.
Advantages
- High strength — 1,310 MPa (190 ksi), better than 95% of steel grades
- Tough — resists crack growth — 130 MPa·√m (118.3 ksi·√in), better than 89% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- High embodied carbon — 3.4 kg CO₂/kg, worse than 93% of steel grades
- Difficult to machine — 28/100, worse than 91% of steel grades
- Poor heat conductor — 24 W/m·K (13.9 BTU/hr·ft·°F), worse than 90% of steel grades
- Limited formability — 15/100, worse than 87% of steel grades
- Low electrical conductivity — 3.8 % IACS, worse than 84% of steel grades
HP9-4-30-QT590 properties
Typical room-temperature values for HP9-4-30-QT590; 12 are specific to this condition. Other listed values are HP9-4-30 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
HP9-4-30-QT590 has a density of 7.84 g/cm³ (0.283 lb/in³), lighter than 78% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
HP9-4-30-QT590 has a yield strength of 1,310 MPa (190 ksi) and a tensile strength of 1,520 MPa (220 ksi) — stronger than 95% of steel grades. Elongation at break is 15% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
HP9-4-30-QT590 is rated for continuous service to 425°C (797 °F). It conducts heat at 24 W/m·K (13.9 BTU/hr·ft·°F), worse than 90% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
HP9-4-30-QT590 conducts electricity at 3.8 % IACS, worse than 84% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (20/100), better than 87% of steel grades.
Sustainability4
Producing a kilogram of HP9-4-30-QT590 takes about 45 MJ of energy and emits 3.4 kg of CO₂ — more than 93% of steel grades. Typical recycled content is 15%.
Manufacturability8
HP9-4-30-QT590's machinability is poor (28/100, worse than 91% of steel grades); weldability fair (45/100); formability poor (15/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with HP9-4-30-QT590
Is HP9-4-30 easy to machine?
Rough machine in the annealed condition; at 46–50 HRC use rigid setups, negative-rake carbide or CBN, low speed/high feed, and avoid grinding burn (temper etch inspect).
Can HP9-4-30 be welded?
Best of the UHS steel family for fusion welding — GTAW/EB with matching 9Ni-4Co filler, clean low-hydrogen practice, then re-temper (or full re-heat-treat) the weldment.
Can HP9-4-30 be formed, bent or molded?
Hot forge 1050–1200 °C with controlled finish temperature; cold forming is impractical at strength level — bend/straighten only in the annealed state.
What surface finishes work on HP9-4-30?
Cannot be anodized; use Zn-Ni or Cd plate, IVD aluminium, or phosphate + epoxy primer, with 190 °C/23 h hydrogen-relief bake after plating and shot peening of fillets.
HP9-4-30 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 |
|---|---|---|
| C | 0.29 – 0.34 | 0.31 |
| Ni | 7 – 8 | 7.5 |
| Co | 4.25 – 4.75 | 4.5 |
| Cr | 0.9 – 1.1 | 1 |
| Mo | 0.9 – 1.1 | 1 |
| V | 0.06 – 0.12 | 0.09 |
| Mn | 0.1 – 0.35 | 0.22 |
| Si | ≤ 0.2 | 0.1 |
| P | ≤ 0.01 | — |
| S | ≤ 0.01 | — |
| Fe | balance | — |
HP9-4-30-QT590 — frequently asked
What is HP9-4-30-QT590 used for?
HP9-4-30-QT590 is typically used for landing gear forgings, arresting gear components and rocket motor cases. In short: weldable 9Ni-4Co steel; thick-section toughness; rocket case forging grade.
What is the yield strength of HP9-4-30-QT590?
HP9-4-30-QT590 has a typical yield strength of 1,310 MPa (190 ksi) and a tensile strength of 1,520 MPa (220 ksi) — stronger than 95% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is HP9-4-30-QT590 easy to machine?
Not especially — machinability is rated poor (28/100, worse than 91% of steel grades). Rough machine in the annealed condition; at 46–50 HRC use rigid setups, negative-rake carbide or CBN, low speed/high feed, and avoid grinding burn (temper etch inspect).
Can HP9-4-30-QT590 be welded?
With care — weldability is rated fair (45/100). Best of the UHS steel family for fusion welding — GTAW/EB with matching 9Ni-4Co filler, clean low-hydrogen practice, then re-temper (or full re-heat-treat) the weldment.
What surface finishes work on HP9-4-30-QT590?
Cannot be anodized; use Zn-Ni or Cd plate, IVD aluminium, or phosphate + epoxy primer, with 190 °C/23 h hydrogen-relief bake after plating and shot peening of fillets.
Can HP9-4-30-QT590 be formed, bent or molded?
Hot forge 1050–1200 °C with controlled finish temperature; cold forming is impractical at strength level — bend/straighten only in the annealed state.
What is the maximum service temperature of HP9-4-30-QT590?
HP9-4-30-QT590 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 HP9-4-30-QT540 and HP9-4-30-ANN?
QT540 is the default condition — standard aerospace condition — best strength/toughness balance for landing gear and structural forgings. ANN: pick for rough machining of large forgings before final austenitize-quench-temper. Yield strength is 1,400 MPa in QT540 versus 790 MPa in ANN.
Sources
- AMS 6526 — Steel Bars, Forgings and Tubing 7.5Ni-4.5Co-1.0Cr-1.0Mo (0.29-0.34C), Consumable Electrode Melted — SAE International (2017)
- AMS 6523 — Steel Sheet, Strip and Plate, 9Ni-4Co-0.30C — SAE International (2016)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (Ultrahigh-Strength Steels) — ASM International (1990)
- MMPDS / MIL-HDBK-5 — Metallic Materials Properties Development and Standardization, 9Ni-4Co steels — Battelle / FAA (2023)
- ASM Handbook Vol. 19 — Fatigue and Fracture — ASM International (1996)
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.