Nickel Alloy X-750 3HT
Precip hard
UNS N07750 · EN 2.4669 · also Inconel X-750
3HT = triple heat treated
Choose for maximum creep-rupture life and notch ductility at 650–815 °C (turbine discs, hot bolting, nuclear internals).
Values for the 3HT condition
Other X-750 tempers and conditions
X-750 is listed in 8 conditions; see the grade overview at X-750.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Softest condition for forming, deep drawing and machining before age-hardening. | 345 | 830 | 45 | 180 HB | — |
Equalized | Intermediate stabilising treatment used on hot-rolled bar before ageing for bolting and springs. | 550 | 900 | 30 | 22 HRC | 1.4 % IACS |
Sheet/strip | Formed sheet parts (seals, bellows, diaphragms) aged after forming to reach service strength. | 700 | 1,140 | 26 | 28 HRC | 1.4 % IACS |
3HTThis page Triple heat treated | Choose for maximum creep-rupture life and notch ductility at 650–815 °C (turbine discs, hot bolting, nuclear internals). | 760 | 1,170 | 25 | 30 HRC | — |
STADefault Solution treated and aged | Standard stocked bar/forging condition: best all-round strength/ductility for bolts, shafts and fasteners to ~700 °C. | 815 | 1,200 | 24 | 32 HRC | — |
Equalized + aged | Highest room-temperature strength of the hot-finished bar conditions; typical for high-strength bolting and gas-turbine hardware below 650 °C. | 860 | 1,275 | 22 | 35 HRC | — |
No.1 Temper | As-supplied condition for coiling springs; wound cold then precipitation aged by the spring maker. | 1,240 | 1,450 | 6 | 42 HRC | 1.4 % IACS |
Spring temper + aged | Maximum strength and lowest relaxation — the standard condition for high-temperature springs and clips to ~650 °C. | 1,450 | 1,720 | 5 | 46 HRC | — |
What is X-750 3HT?
X-750 3HT is X-750 in the 3HT condition — choose for maximum creep-rupture life and notch ductility at 650–815 °C (turbine discs, hot bolting, nuclear internals). X-750 3HT has a yield strength of 760 MPa (110 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 83% of nickel alloy grades. Elongation at break is 25% and the elastic modulus is 214 GPa (31 Msi). X-750 3HT has a density of 8.28 g/cm³ (0.299 lb/in³), lighter than 55% of nickel alloy grades. It melts at 1,393°C (2,539 °F). STA is the default condition FabDigit quotes; 3HT is available on request or by drawing note.
Advantages
- High strength — 760 MPa (110 ksi), better than 83% of nickel alloy grades
Limitations
- High embodied carbon — 17.5 kg CO₂/kg, worse than 98% of nickel alloy grades
- Limited formability — 15/100, worse than 81% of nickel alloy grades
X-750 3HT properties
Typical room-temperature values for X-750 3HT; 10 are specific to this condition. Other listed values are X-750 reference data and may not represent this condition. Bars are the position among nickel alloy grades.
Physical3
X-750 3HT has a density of 8.28 g/cm³ (0.299 lb/in³), lighter than 55% of nickel alloy grades. It melts at 1,393°C (2,539 °F).
Mechanical16
X-750 3HT has a yield strength of 760 MPa (110 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 83% of nickel alloy grades. Elongation at break is 25% and the elastic modulus is 214 GPa (31 Msi).
Thermal6
X-750 3HT is rated for continuous service to 815°C (1,499 °F). It conducts heat at 12 W/m·K (6.93 BTU/hr·ft·°F), better than 65% of nickel alloy grades. Thermal expansion is 12.6 µm/m·K (7 µin/in·°F).
Electrical3
X-750 3HT conducts electricity at 1.4 % IACS, worse than 65% of nickel alloy grades.
Chemical & Environmental3
Corrosion resistance is very good (78/100), better than 51% of nickel alloy grades.
Sustainability4
Producing a kilogram of X-750 3HT takes about 290 MJ of energy and emits 17.5 kg of CO₂ — more than 98% of nickel alloy grades. Typical recycled content is 35%.
Manufacturability8
X-750 3HT's machinability is poor (18/100, worse than 61% of nickel alloy grades); weldability fair (40/100); formability poor (15/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with X-750 3HT
Is X-750 easy to machine?
Machine in the annealed or solution-treated condition where possible; use rigid setups, positive-rake carbide or ceramic tooling, low speed/heavy feed and flood coolant — work hardens rapidly and notches tools like most γ′ superalloys.
Can X-750 be welded?
GTAW/EB weld in the solution-annealed condition with Inconel 69/718-type or matching filler, then re-solution and re-age; welding in the aged condition invites strain-age (post-weld heat-treat) cracking in the HAZ.
Can X-750 be formed, bent or molded?
Cold-form, deep-draw or coil springs in the annealed/spring-temper condition with generous bend radii and frequent interstage anneals; hot work 1150–1230 °C and finish above 950 °C.
What surface finishes work on X-750?
Not anodizable — finish by pickling/passivation, abrasive or electro-polishing; shot peening markedly improves fatigue and SCC life, and silver or dry-film lubricant coatings are used on hot bolting to prevent galling.
X-750 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 |
|---|---|---|
| Cr | 14 – 17 | 15.5 |
| Fe | 5 – 9 | 7 |
| Ti | 2.25 – 2.75 | 2.5 |
| Al | 0.4 – 1 | 0.7 |
| NbNb + Ta | 0.7 – 1.2 | 0.95 |
| Co | ≤ 1 | 0.3 |
| Mn | ≤ 1 | 0.3 |
| Si | ≤ 0.5 | 0.2 |
| Cu | ≤ 0.5 | 0.1 |
| C | ≤ 0.08 | 0.04 |
| S | ≤ 0.01 | 0 |
| NiNi + Co, balance | ≥ 70 (balance) | — |
X-750 3HT — frequently asked
What is X-750 3HT used for?
X-750 3HT is typically used for gas turbine blades and rings, springs, high-temperature bolts and reactor core components. In short: best spring superalloy; low relaxation to 700 °C; hot bolting standard.
What is the yield strength of X-750 3HT?
X-750 3HT has a typical yield strength of 760 MPa (110 ksi) and a tensile strength of 1,170 MPa (170 ksi) — stronger than 83% of nickel alloy grades. Strength varies by condition: see the 8 listed tempers.
Is X-750 3HT easy to machine?
Not especially — machinability is rated poor (18/100, worse than 61% of nickel alloy grades). Machine in the annealed or solution-treated condition where possible; use rigid setups, positive-rake carbide or ceramic tooling, low speed/heavy feed and flood coolant — work hardens rapidly and notches tools like most γ′ superalloys.
Can X-750 3HT be welded?
With care — weldability is rated fair (40/100). GTAW/EB weld in the solution-annealed condition with Inconel 69/718-type or matching filler, then re-solution and re-age; welding in the aged condition invites strain-age (post-weld heat-treat) cracking in the HAZ.
What surface finishes work on X-750 3HT?
Not anodizable — finish by pickling/passivation, abrasive or electro-polishing; shot peening markedly improves fatigue and SCC life, and silver or dry-film lubricant coatings are used on hot bolting to prevent galling.
Can X-750 3HT be formed, bent or molded?
Cold-form, deep-draw or coil springs in the annealed/spring-temper condition with generous bend radii and frequent interstage anneals; hot work 1150–1230 °C and finish above 950 °C.
What is the maximum service temperature of X-750 3HT?
X-750 3HT is rated for continuous use to about 815°C (1,499 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between X-750-STA and X-750 SPR-A?
STA is the default condition — standard stocked bar/forging condition: best all-round strength/ductility for bolts, shafts and fasteners to ~700 °C. SPR-A: maximum strength and lowest relaxation — the standard condition for high-temperature springs and clips to ~650 °C. Yield strength is 815 MPa in STA versus 1,450 MPa in SPR-A.
Sources
- INCONEL alloy X-750 technical bulletin — Special Metals Corporation (2004)
- ASTM B637 – Precipitation-Hardening and Cold Worked Nickel Alloy Bars, Forgings and Forging Stock for Moderate or High Temperature Service — ASTM International (2018)
- AMS 5667 / AMS 5668 / AMS 5670 / AMS 5698 – Alloy Bars, Wire and Springs, UNS N07750 — SAE International (2019)
- AMS 5542 – Nickel Alloy Sheet, Strip and Plate, Solution Heat Treated (UNS N07750) — SAE International (2018)
- ASM Handbook Vol.1 – Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.16 – Machining — ASM International (1989)
- High-Temperature Characteristics of Stainless Steels / Nickel Alloy Data — Nickel Institute (2020)
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.