Density, Melting Point & Physical Properties of GH698 Alloy

GH698 is the old drawing name; the current GB/T 14992-2005 designation is GH4698 (ISC H46980), Russian equivalent ЭИ698 / ХН73МБТЮ. It is a Ni-Cr base, γ′ precipitation-hardened wrought superalloy — Cr 13–16%, Ni balance, Al 1.3–1.7%, Ti 2.35–2.75%, Nb 1.8–2.2%, Mo 2.8–3.2%. Physical properties below are for the solution + aged condition​ (canonical 1120℃×8h AC + 1000℃×4h AC + 775℃×16h AC) unless stated otherwise; cold-drawn or over-aged stock shifts E and CTE by a few percent, not the density or melt range.

1. Density

• ρ = 8.31–8.32 g/cm³​ (8.31 from Ningdan/SMI-handbook tables, 8.32 from GB/T 14992 derivative datasheets; both sit inside mill tolerance)

• Nonmagnetic (FCC γ matrix, no ferromagnetic phase)

• For rotor mass calculation: use 8.32 g/cm³; centrifugal stress ∝ ρ, so a 0.01 g/cm³ slip is ~0.1% on rim stress — small but not zero on a 750℃ disk.

2. Melting Range

• Solidus ≈ 1340℃

• Liquidus ≈ 1365℃

• Useful forge window: ingot 1120℃±20℃ heat, start >980℃, finish ≥900℃; never soak above 1150℃ on finished forgings (γ′ solvus ~1000–1020℃, grain runaway above 1150℃).

The 1340–1365℃ range is the alloy's own melt, not a service number. Service redline for stressed parts is 800℃, skin-only transient 850℃.

3. Elastic Modulus

Linear-ish drop, ~0.06 GPa/℃ average. For blade/disk frequency calculation at 750℃ use E ≈ 178 GPa, not room-temp value.

Shear modulus G ≈ 84 GPa at 20℃ (from ν=0.40). Bulk modulus K ≈ 183 GPa.

4. Poisson's Ratio

• ν = 0.40​ (20℃, typical Ni-base γ′ alloy value; some mills quote 0.39–0.41 depending on γ′ fraction after aging)

5. Coefficient of Thermal Expansion (CTE)

• 20–100℃: 12.1×10⁻⁶ /K​ (Ningdan table) — alternate GB derivative datum 12.7×10⁻⁶/K at 20–100℃, both within scatter

• 20–200℃: ~12.5×10⁻⁶/K

• 20–500℃: ~13.4×10⁻⁶/K

• 20–750℃: ~14.0×10⁻⁶/K

• 20–800℃: ~14.1×10⁻⁶/K

GH4698 tracks Waspaloy's CTE within ~3%; mating to GH4169 (α~13.2×10⁻⁶/K at 20–650℃) gives a small but real differential that matters on shrink-fit disks.

6. Thermal Conductivity

• 50℃: λ ≈ 23.5 W/(m·K)​ (Ningdan direct table value)

• 100℃: ~10.2 W/(m·K)​ (GB derivative datum — note the apparent drop vs 50℃ is a table-source mismatch; the 23.5 figure is the widely cited handbook number, 10.2 appears in simplified datasheets and is likely a transposed low-temp/low-confidence point)

Practically: GH4698 is a poor conductor​ like all γ′ Ni-base alloys. At 750℃ working estimate λ ≈ 23–26 W/(m·K)​ interpolating from the 23.5 W/(m·K) at 50℃ and known Ni-base trends; do not use 10.2 for FEA thermal maps. If your code needs a single input, 23.5 W/(m·K) at low temp, rising to ~26 at 800℃​ is the defensible line.

7. Specific Heat

• c ≈ 422 J/(kg·K)​ at room temp (Ningdan table)

• c ≈ 410 J/(kg·K) at 100℃​ (GB derivative datum)

• 750℃ estimate: ~520–540 J/(kg·K)

Heat capacity is not a design gate for this alloy; thermal inertia in a disk transient is dominated by ρ·c ≈ 3.5×10⁶ J/(m³·K) at 20℃, ~4.3×10⁶ at 750℃.

8. Electrical Resistivity

• ρ_e = 0.332 μΩ·m (332 μΩ·mm²/m)​ at 20℃

• Equivalent: 1.32×10⁻⁶ Ω·m quoted in some GB derivative sheets (same number, 0.332 Ω·mm²/m = 0.332×10⁻⁶ Ω·m — watch unit slip; correct is 0.332 μΩ·m = 332 μΩ·mm²/m)

• Positive TCR, rises ~0.5 μΩ·m over 20→800℃

Not a resistive-heating alloy; resistivity only matters for eddy-current UT calibration and weld parameter setting.

9. Physical Property Summary Block

These numbers are what you put into a disk FE model: ρ for centrifugal load, E(750℃)=178 GPa for rim deflection and modal freq, CTE=14.0×10⁻⁶/K for 20→750℃ growth against the shaft, λ≈23.5 W/(m·K) for the thermal gradient. They are not sensitive to heat-treat route (aging moves E by <2%), so one physical table serves bar, plate, and forged disk of GH4698/GH698 from any VIM+VAR heat.