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1. Alloy GH99 Overview
GH99 (GH4099) is a wrought nickel-base superalloy that combines tungsten-molybdenum-cobalt solid solution strengthening with aluminum-titanium γ’ precipitation hardening. Consequently, it delivers long-term stable service up to 900°C, with a short-term maximum temperature of 1000°C.
In addition, this alloy offers an exceptional balance of high-temperature load-bearing capacity, oxidation resistance and process adaptability. For instance, cold-rolled sheets can be directly formed and welded in the solution-treated condition, whereas bars and forgings gain substantially higher strength through aging treatment. Therefore, it has become a classic high-temperature structural material for aerospace, gas turbines and industrial heating equipment.
2. Chemical Composition & Strengthening Mechanism
| Element | Fe | C | Si | Mn | P | S | Cr | Co | Cu | Mo | W | Ti | Al |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min | – | – | – | – | – | – | 17 | 5.0 | – | 3.5 | 5 | 1.0 | 1.7 |
| Max | 2 | 0.08 | 0.5 | 0.4 | 0.015 | 0.015 | 20 | 8.0 | 0.25 | 4.5 | 7 | 1.5 | 2.4 |
Nickel matrix. High chromium provides oxidation resistance; tungsten, molybdenum and cobalt deliver solid solution strengthening; aluminum and titanium form nano-sized γ’ precipitates for elevated-temperature strength.
Notably, compared with standard solid-solution strengthened superalloys, GH4099 achieves higher strength and longer stress rupture life. On the other hand, relative to high-strength age-hardened alloys with higher Al+Ti content, it demonstrates superior formability and weldability. As a result, it is particularly suitable for thin-plate welded load-bearing structures exposed to cyclic thermal stresses.
3. Physical Properties of GH99
| Density (g/cm³) | Melting Range (°C) | CTE (20~900°C, μm/m·K) | Thermal Conductivity (RT, W/m·K) | Elastic Modulus (RT, GPa) | Relative Permeability (RT) |
|---|---|---|---|---|---|
| 8.32 | 1340~1390 | 14.7 | 12.1 | 206 | ≈1.008 (non-magnetic) |
Thanks to its steady thermal expansion coefficient, thermal stress remains predictable under frequent start-stop cycling. Furthermore, the moderate thermal conductivity makes it a reliable choice for heat exchange components.
4. GH4099 Mechanical Properties
4.1 Room Temperature Properties
| Product Form | Condition | Rm (MPa) | Rp₀.₂ (MPa) | A (%) | Z (%) |
|---|---|---|---|---|---|
| Cold-rolled sheet (δ1.5~5.0mm) | Solution-treated | ≥780 | ≥350 | ≥35 | ≥35 |
| Hot-rolled bar / forging | Solution + aged | ≥1180 | ≥780 | ≥18 | ≥20 |
Solution-treated sheets exhibit high ductility for deep stamping and bending, while aged bars provide the strength required for high-stress structural components.
4.2 High-Temperature Properties (900°C)
| Product Form | Condition | Rm (MPa) | Rp₀.₂ (MPa) | A (%) | Z (%) |
|---|---|---|---|---|---|
| Cold-rolled sheet (δ1.5~5.0mm) | Solution-treated | ≥320 | ≥150 | ≥20 | —* |
| Hot-rolled bar / forging | Solution + aged | ≥420 | ≥250 | ≥10 | ≥15 |
5. GH99 (GH4099) Core Performance Advantages
5.1 Exceptional Strength and Creep Resistance at Temperature
Dual solid-solution and precipitation hardening rank GH99 among the strongest 900°C-class superalloys. Consequently, it maintains a stable matrix, low creep rate and long rupture life under sustained load. In effect, it resists plastic deformation failure, making it a primary choice for critical high-temperature load-bearing components.
5.2 Superior Oxidation and Hot Corrosion Resistance
High chromium (17–20%) rapidly forms a dense, adherent Cr₂O₃ scale that resists spalling during thermal cycling up to 950°C. Additionally, the alloy tolerates sulfur- and carbon-containing flue gases, performing reliably in both open-atmosphere and industrial exhaust environments.
6. Heat Treatment Guidelines
First, for solution treatment (sheets), heat to 1140–1160°C, hold per section thickness (8–15 min for 1.5–5mm sheet), then air cool. This produces a uniform austenitic matrix with maximum formability.
Next, for aging treatment (bars/forgings), heat to 750–850°C, hold 8–16 h, and air cool. This step precipitates the γ’ phase, significantly improving strength and hardness.
For bars and forgings, solution treatment can be performed at 1120–1150°C followed by air cooling or rapid air cooling. (Water quenching may be applicable under controlled conditions; please consult our technical team.) Following this, aging can be optimized to meet specific property targets.
7. Welding Recommendations
Gas tungsten arc welding (GTAW/TIG), electron beam welding and resistance welding are all recommended. Generally, preheating is unnecessary. However, to restore joint properties, post-weld aging or stress relief can be effectively applied.
8. Typical Applications
- Aerospace: Combustion chambers, afterburner casings, guide vane supports, nozzle flaps and flame holders — all core hot-section structural components.
- Heat treatment & industrial equipment: Furnace rollers, radiant tubes, heat treatment fixtures and conveyor rollers. As a result, their service life far exceeds that of conventional heat-resistant stainless steels.
- Petrochemical & energy: High-temperature reaction furnace internals, heat exchange tubes and hydrogenation unit components that require both temperature strength and medium corrosion resistance.
C&N Supply & Support
To sum up, C&N offers GH99 (GH4099) in hot/cold rolled sheets, bars, seamless pipes, forgings and custom machined parts. Non-standard sizes and special performance requirements are always available upon request.
All batches are produced to strict specifications and shipped with original Material Test Certificates (MTC). Beyond products, we also provide material selection guidance, heat treatment process design and welding engineering support — covering your project from initial selection to on-site application. Contact us today with your requirements.
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