Bar and Rod
Plate and Sheet
Strip
Pipe and Tube
Wire
Welding
Powder Material
Cast Products
Forged Products
Fittings
Fastening
Round Bar:
φ2–500 mm, 1–6 m length
Flat/Square Bar:
4–100 mm thickness/width
Hex Bar:
A/F 3–100 mm
Hollow Bar:
OD 20–300 mm
Sheet:
0.3–6 mm thickness
Medium Plate:
6–25 mm thickness
Heavy Plate:
25–100 mm thickness
Standard Strip:
0.05–3 mm thick,
10–600 mm wide
Precision strip:
0.01–0.5 mm thick,
tight tolerance ±0.005 mm
Foil:
0.005–0.1 mm thick
Seamless Tube:
OD 6–450 mm,
WT 1–50 mm,
1–12 m length
Welded Tube:
OD 10–600 mm,
WT 1–20 mm
Capillary Tube:
OD 1–10 mm,
WT 0.1–2 mm
Wire Form:
Cold Drawn Wire,
Bright Wire,
Spring Wire,
Fine Wire,
Ultra-fine Wire
General Diameter:
φ0.1–10 mm
Coil Weight:
50–500 kg,
customizable tolerance
Solid Wire:
φ0.8–4.0 mm
Flux-cored Wire:
φ1.2–4.0 mm
Welding Rod:
φ2.0–5.0 mm
Powder Form:
AM 3D Printing Powder,
Spherical Powder,
Gas-atomized Powder,
Water-atomized Powder
Particle Size:
10–150 μm
Sphericity:
≥90% for AM grade
Cast Ingot:
φ200–800 mm
Precision Casting:
min wall 0.5 mm
Cast Pipe:
OD 100–600 mm,
WT 10–50 mm
Forged Bar:
Φ35–500 mm
Forged Ring:
OD 200–2000 mm
Forging Weight:
1–5000 kg
Fittings Form:
Elbow, Tee, Reducer, Flange, Cap, Outlet, Lap Joint
Size range:
1/2''–24'' (DN15–DN600)
Wall thickness:
Sch10–Sch160, STD, XS, XXS
Pressure Class:
150–2500 LB
Fastening Form:
Bolt, Nut, Screw, Stud, Washer, Pin, Rivet
Metric: M3–M64
Imperial: #4–2.5''
Length: 6–500 mm
Alloy 751 is a precipitation-hardenable nickel-chromium alloy developed for the exhaust valves of internal-combustion engines. This datasheet presents the material within the American (ASTM / ASME / UNS) standard system.
A modified version of alloy X-750, Alloy 751 has essentially the same composition and the same excellent physical, mechanical and corrosion-resistance properties, but with increased aluminium and titanium content for greater precipitation hardening. Strength is developed by ageing through precipitation of the gamma-prime (γ′, Ni₃(Al,Ti)) phase together with some carbides; the alloy offers high strength and hot hardness, good creep and stress-rupture resistance, and excellent resistance to oxidation and to exhaust-stream impurities such as lead oxide, sulfur, bromine and chlorine up to about 980 °C (1800 °F). Its excellent hot hardness usually makes hard-facing of valve-seat areas unnecessary. It is used in the solution-treated and aged condition.
Typical applications include exhaust valves for heavy-duty diesel and gasoline engines, and other high-temperature components requiring strength, hot hardness and oxidation resistance.
| Property | Value | Unit |
|---|---|---|
| Density | 8.28 | g/cm³ |
| Melting range | 1390–1430 | °C |
| Elastic modulus | 213 | GPa |
| Coefficient of thermal expansion (20–100 °C) | 12.6 | µm/m·°C |
| Thermal conductivity (20 °C) | 12.0 | W/m·K |
| Specific heat (20 °C) | 431 | J/kg·K |
| Structure | Austenitic (FCC) | — |
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Nickel + Cobalt | Ni (+Co) | 70.0 | — | Base element; γ′ matrix |
| Chromium | Cr | 14.0 | 17.0 | Oxidation / corrosion resistance |
| Iron | Fe | 5.0 | 9.0 | Solid-solution element |
| Titanium | Ti | 2.0 | 2.6 | γ′ (Ni₃(Al,Ti)) precipitation strengthening |
| Aluminium | Al | 0.9 | 1.5 | γ′ precipitation strengthening |
| Niobium | Nb (+Ta) | 0.70 | 1.20 | Carbide / γ′ strengthening |
| Manganese | Mn | — | 1.00 | Deoxidiser |
| Silicon | Si | — | 0.50 | Deoxidiser |
| Carbon | C | — | 0.10 | Carbide formation |
Solution-treated and aged condition, typical values for UNS N07751.
| Condition | Property | Value |
|---|---|---|
| Solution treated & aged | Tensile strength (UTS) | ≥1200 MPa (174 ksi) |
| Solution treated & aged | 0.2% yield strength | ≥800 MPa (116 ksi) |
| Solution treated & aged | Elongation at break | ≥20 % |
| At 649 °C (1200 °F) | Tensile strength (UTS) | ~1100 MPa (160 ksi) |
| — | Elastic modulus | 213 GPa |
Confirm against the mill test report. Properties are typically developed by a direct age (for example 732 °C / 2 h); strength and hot hardness are retained to high temperature.
| Environment | Performance | Notes |
|---|---|---|
| High-temperature oxidation | Excellent | To about 980 °C |
| Exhaust-stream impurities | Excellent | Resists lead oxide, S, Br, Cl attack |
| Stress-corrosion cracking | Very Good | High resistance |
| Aqueous / general | Good | Chromium-bearing |
| Elevated-temperature strength | Excellent | Primary design advantage |
The alloy resists high-temperature oxidation and attack by exhaust-stream impurities (notably lead oxide, sulfur, bromine and chlorine) to about 980 °C, with high resistance to stress-corrosion cracking — the combination that makes it a leading exhaust-valve material.
A γ′ precipitation-hardenable nickel-chromium alloy; strengthened by solution treatment followed by ageing.
Solution Treatment Solution anneal at approximately 1090–1150 °C and cool, placing the aluminium and titanium in solid solution. Material may also be supplied hot-finished and direct-aged.
Precipitation Hardening (Ageing) Age to precipitate γ′ (Ni₃(Al,Ti)); a direct age of approximately 732 °C (1350 °F) for 2 hours gives the optimum combination of properties with economy, while longer or multi-step ageing may be used to enhance specific properties. A slight permanent contraction (~0.0003 in/in) occurs during precipitation.
Joined mainly by flash-butt and inertia (friction) welding in valve manufacture; weldable in the solution-annealed condition with post-weld ageing to develop properties.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| Flash-butt welding | Excellent | Standard for valve manufacture |
| Inertia / friction welding | Excellent | Used for valve heads to stems |
| GTAW / TIG | Good | Matching filler; post-weld age |
Weld in the solution-annealed condition where fusion welding is used; apply post-weld ageing to develop properties.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Preferred sequence | Machine slightly oversize, age, then finish to size |
| Machinability | Difficult; rigid setups, carbide tooling, slow speeds |
| Coolant | Water-based coolant for grinding/milling/turning |
Forming Processes
| Process | Notes |
|---|---|
| Cold forming | In the annealed condition; work-hardens |
| Hot forming | Readily forged; solution and age afterward |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Automotive / diesel | Exhaust valves (heavy-duty engines) | Hot hardness + oxidation resistance |
| Internal combustion | Valves for locomotive, marine, power | Strength + corrosion resistance |
| Aerospace | High-temperature components | Strength + creep resistance |
| Industrial gas turbine | Hot-section parts | Strength + oxidation resistance |
| Product Form | Standard / Designation | Notes |
|---|---|---|
| Bar and rod (valve stock) | UNS N07751 | Special Metals product |
| Bar and wire | AMS 5668 | — |
| Hot-finished / direct-aged | UNS N07751 | Common valve route |
| Material designation | UNS N07751 | High-Ti X-750 variant |
Nickel-chromium precipitation-hardenable alloy. UNS N07751.
| Alloy | Cr % | Ti % | Al % | Best Used For |
|---|---|---|---|---|
| Alloy 751 | 14–17 | 2.0–2.6 | 0.9–1.5 | High-Ti X-750 variant; exhaust valves, hot hardness to ~980 °C |
| Alloy X-750 | 14–17 | 2.25–2.75 | 0.4–1.0 | Springs, bolts, high-temperature fasteners |
| Alloy 600 | 14–17 | — | — | General-purpose Ni-Cr-Fe alloy (base) |
| Alloy 718 | 17–21 | 0.65–1.15 | 0.2–0.8 | Most-used high-strength superalloy |
| Alloy 80A (Nimonic) | 18–21 | 1.8–2.7 | 1.0–1.8 | Gas-turbine components, fasteners |
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