GH2903 is a nickel-based low expansion high-temperature alloy, with its composition precisely controlled to achieve an extremely low thermal expansion coefficient. The high nickel content gives GH2903 excellent oxidation resistance and corrosion resistance, while the addition of elements such as chromium, titanium, and aluminum enhances the alloy's high-temperature strength and stability. This alloy is mainly used to manufacture components that require low expansion and high strength in high-temperature environments.

2. Chemical Composition and Requirements

The chemical composition of GH2903 alloy must be strictly controlled to ensure that the content of each element is within the specified range, guaranteeing the performance of the alloy. The main elements in the alloy include nickel, chromium, and iron, with a high nickel content to provide excellent oxidation and corrosion resistance. The addition of other elements must also be precisely controlled to meet specific performance requirements.

3. Performance Characteristics

Low thermal expansion coefficient: The thermal expansion coefficient of GH2903 is extremely low in the range from room temperature to 600°C, which is particularly important in high-precision mechanical structures, effectively preventing dimensional changes and deformations caused by thermal expansion and contraction.

High-temperature strength: At high temperatures, the tensile strength and yield strength of GH2903 remain at a high level, especially in the range of 300°C to 600°C, allowing it to be used in harsh temperature environments without losing stability.

Good oxidation and corrosion resistance: Thanks to the content of nickel and chromium, GH2903 exhibits excellent resistance in oxidizing and corrosive environments, making it suitable for use in corrosive gases and liquids.

High toughness and fatigue strength: Even in low and high-temperature environments, GH2903 shows good toughness and fatigue performance, making it suitable for use in complex stress environments.

4. Manufacturing Process and Heat Treatment

Melting and Casting: Vacuum induction melting (VIM) or vacuum arc remelting (VAR) processes are used to ensure uniform alloy composition and reduce impurity content. By controlling the cooling rate of the alloy, a more uniform microstructure can be obtained.

Forging and Rolling: After initial shaping, the alloy is forged into bars and hot-rolled to improve the material's density and tensile strength.

Cold Drawing and Straightening: Multiple cold drawing and straightening processes are performed according to size requirements to ensure the dimensional accuracy and surface finish of the bars.

Heat Treatment:

Solution Treatment: This process homogenizes the material's grains, eliminates residual stress, and improves the material's high-temperature strength and oxidation resistance. The temperature is controlled at 1000-1050°C, with a holding time of 1-2 hours, and cooling can be done by water cooling or air cooling.

Aging Treatment: This process precipitates strengthening phases (such as γ' phase), further enhancing the material's high-temperature strength and hardness, and stabilizing its microstructure to control thermal expansion. The temperature is controlled at 700-750°C, with a holding time of 8-16 hours, and cooling is done by furnace cooling.

5. Mechanical Properties and Low Expansion Performance

Under the above heat treatment specifications, the mechanical properties and low expansion performance of GH2903 bars reach optimal conditions. Its main performance parameters include:

Tensile Strength: Approximately 600-700 MPa at room temperature (some data indicate that the tensile strength at room temperature is usually between 1000 MPa and 1300 MPa, and specific values may vary due to different batches or manufacturing processes).

Yield Strength: 450-550 MPa at room temperature (the yield strength at room temperature is generally between 700 MPa and 900 MPa).

Elongation: Approximately 20% (some data indicate that elongation is between 30% and 40%).

Thermal Expansion Coefficient: 5.5-7.5 × 10⁻⁶ /°C in the range from room temperature to 600°C.

6. Application Fields

GH2903 low expansion high-temperature alloy bars have a wide range of applications in the following fields due to their excellent low thermal expansion coefficient, high-temperature strength, and corrosion resistance:

Aerospace: Used to manufacture engine components, such as seals and heat-resistant structural parts for gas turbines, ensuring stability under extreme temperatures.

Electronic Instruments: Used to manufacture fixed structural parts and supports to prevent dimensional changes due to temperature fluctuations from affecting instrument accuracy.

Nuclear Industry: In high-radiation environments such as nuclear reactors, GH2903 is used to manufacture irradiated materials and support structures due to its corrosion resistance, radiation resistance, and low expansion characteristics.

Precision Machinery: The low expansion characteristics of GH2903 make it an ideal material for high-precision optical instruments and measuring instruments.

7. Precautions

Machining: GH2903 alloy can be processed using traditional metal cutting methods, but hard alloy tools should be used, and cutting speed and feed should be appropriately controlled.

Welding: It has excellent welding performance and can be welded using methods such as TIG (Tungsten Inert Gas), MIG (Metal Inert Gas), and electroslag welding.

Protective Measures: In some high-temperature applications, protective coatings may be required to prevent oxidation or corrosion of the alloy.