GH4049 is a high-temperature nickel-based superalloy (also classified as a "superalloy" or "high-performance alloy") developed and standardized in China, primarily designed for service in extreme high-temperature environments. It belongs to the GH series of nickel-based superalloys-a family of materials designated by China's national standards (e.g., GB/T 14992-2005 Nickel-Base and Cobalt-Base Superalloys for High Temperature) for high-temperature structural applications.
The core design goal of GH4049 is to maintain excellent mechanical properties (such as high tensile strength, creep resistance, and fatigue resistance) and chemical stability (oxidation and corrosion resistance) at temperatures ranging from 800°C to 1100°C (1472°F to 2012°F). This makes it particularly suitable for manufacturing key hot-end components in aerospace, energy, and industrial sectors, where materials must withstand prolonged exposure to high temperatures and mechanical loads.
Typical application scenarios include:
Aerospace: Turbine blades, turbine disks, and combustion chamber components for military and civil aero-engines (e.g., high-thrust jet engines).
Energy: Heat-resistant parts for gas turbines in power plants, and structural components for rocket engines.
Industrial: Heating elements, furnace liners, and high-temperature molds in metallurgical or chemical processing.
Notably, GH4049 is technologically analogous to some international nickel-based superalloys (e.g., Inconel 718, though with variations in composition and performance), but it follows China's independent material standardization system, ensuring compatibility with domestic manufacturing processes and engineering requirements.
GH4049 is a nickel (Ni)-based superalloy, with nickel as the matrix element, supplemented by key alloying elements (chromium, cobalt, molybdenum, tungsten, etc.) to enhance high-temperature strength, oxidation resistance, and microstructural stability. Its chemical composition is strictly regulated by Chinese national standards (e.g., GB/T 14992-2005 and GB/T 25820-2010), with allowable ranges for each element to ensure consistent performance across batches.
The following table outlines the typical and standard-specified chemical composition of GH4049:
Note: Minor variations in composition may exist between different manufacturers, but all must comply with the tolerance ranges specified in Chinese national standards to ensure qualification for high-temperature applications.
The hardness of GH4049 is not a fixed value-it depends primarily on its heat treatment state (a critical process for nickel-based superalloys that optimizes the formation of strengthening phases like γ'), as well as whether it undergoes post-processing (e.g., cold working). Unlike low-alloy steels, GH4049's hardness is closely linked to its high-temperature performance: the heat treatment is designed to balance hardness, strength, and ductility for service at extreme temperatures.
Below is a detailed breakdown of GH4049's typical hardness values across common heat treatment states, measured using standardized methods (Rockwell C, Brinell, or Vickers hardness testing):
Solution annealing is the first step in GH4049's heat treatment process, involving heating the alloy to a high temperature (typically 1100°C – 1150°C) and holding it for a period (1–4 hours) to dissolve precipitated phases (e.g., carbides, γ') into the nickel matrix, followed by rapid cooling (water quenching). This state maximizes ductility and prepares the alloy for subsequent aging.
Rockwell Hardness (HRC): Approximately 25 – 30 HRC
Brinell Hardness (HB): Approximately 240 – 280 HB
Vickers Hardness (HV): Approximately 250 – 290 HV
Purpose: This state is used for intermediate processing (e.g., forging, machining, or forming complex components) where high ductility is required to avoid cracking. It is not the final service state, as the alloy's high-temperature strength is not yet optimized.
Aging (also called "precipitation hardening") is the key heat treatment step for GH4049. After solution annealing, the alloy is heated to a lower temperature (typically 700°C – 850°C) and held for an extended period (8–24 hours), then cooled slowly or air-cooled. This process induces the uniform precipitation of fine γ' phase (Ni₃(Al,Ti)) particles in the matrix-these particles act as "barriers" to dislocation movement, significantly increasing the alloy's hardness and high-temperature strength.
The aging process is often performed in two stages (double aging) to further refine the γ' phase and balance properties:
First aging: 800°C – 850°C (4–8 hours) → Air cooling
Second aging: 700°C – 750°C (16–20 hours) → Air cooling
Typical hardness values after double aging (the most common final state for GH4049) are:
Rockwell Hardness (HRC): Approximately 38 – 45 HRC
Brinell Hardness (HB): Approximately 360 – 430 HB
Vickers Hardness (HV): Approximately 380 – 450 HV
Purpose: This is the standard service state for GH4049 components (e.g., turbine blades, gas turbine parts). The hardness in this state directly correlates with the alloy's ability to resist creep and mechanical deformation at temperatures up to 1100°C.
Cold working (e.g., rolling, drawing) is rarely used for GH4049, as the alloy is primarily designed for high-temperature applications where hot working and heat treatment are more effective for strengthening. However, if minor cold working is applied (e.g., to adjust dimensions of thin components), it may slightly increase hardness:
Hardness Increase: Typically 5 – 10 HRC above the solution-annealed state (e.g., 30 – 35 HRC)
Limitation: Cold working can introduce internal stresses and reduce ductility, which is undesirable for high-temperature service-thus, cold-worked GH4049 is almost always followed by stress-relief annealing (at ~600°C – 650°C) to restore ductility, which may reduce hardness back to near the solution-annealed level.
High-Temperature Hardness Retention: Unlike many materials that soften rapidly at high temperatures, GH4049 maintains significant hardness even at elevated temperatures. For example, at 800°C, its Vickers hardness remains at ~200 – 250 HV (compared to <100 HV for carbon steel at the same temperature)-this is critical for withstanding mechanical loads in hot-end components.
Batch Consistency: Hardness values may vary slightly between batches due to minor compositional differences or heat treatment process variations, but manufacturers must ensure values fall within the standard tolerance range (e.g., ±2 HRC for the aged state) to meet performance requirements.
In summary, GH4049's hardness is tailored to its application via heat treatment: the solution-annealed state prioritizes ductility for processing, while the aged state delivers the high hardness and strength needed for extreme high-temperature service.
