GH91 Alloy
Short Description:
GH91 Alloy GH91 is a high-performance iron-nickel-chromium (Fe-Ni-Cr) based precipitation-hardening wrought superalloy, specifically designed for medium-to-high temperature service scenarios requiring excellent thermal corrosion resistance, stable mechanical properties, and good processability. It achieves strengthening primarily through the coherent precipitation of γ’ phase (Ni₃Al, Ti) — the core strengthening phase — and is supplemented by synergistic solid solution strengthening fr...
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GH91 Alloy
GH91 is a high-performance iron-nickel-chromium (Fe-Ni-Cr) based precipitation-hardening wrought superalloy, specifically designed for medium-to-high temperature service scenarios requiring excellent thermal corrosion resistance, stable mechanical properties, and good processability. It achieves strengthening primarily through the coherent precipitation of γ’ phase (Ni₃Al, Ti) — the core strengthening phase — and is supplemented by synergistic solid solution strengthening from chromium (Cr) and molybdenum (Mo). Unlike Ni-Cu based GH90 (focused on marine corrosion resistance), GH91 is optimized for high-temperature environments involving sulfur-containing media, enabling reliable long-term operation in harsh conditions ranging from 650℃ to 870℃.
Notably, GH91 forms a dense, multi-layer protective oxide film (Cr₂O₃-Al₂O₃-MoO₃) at high temperatures, providing superior resistance to sulfur-containing flue gas, high-temperature steam, and molten salt corrosion. It retains excellent hot workability and weldability, making it suitable for manufacturing large-scale complex components (e.g., thermal power plant boiler parts, petrochemical cracking furnace internals). It is widely used in thermal power generation, petrochemical, and metallurgical industries, where material thermal corrosion resistance and medium-to-high temperature strength are critical. The following is a comprehensive breakdown of its chemical composition, physical properties, and application products.
1. Chemical Composition (Mass Fraction, %)
| Element | Carbon (C) | Chromium (Cr) | Nickel (Ni) | Molybdenum (Mo) | Titanium (Ti) | Aluminum (Al) | Iron (Fe) | Manganese (Mn) | Silicon (Si) | Phosphorus (P) | Sulfur (S) | Boron (B) | Zirconium (Zr) |
| Content Range | ≤0.10 | 18.0-21.0 | 24.0-28.0 | 1.8-2.5 | 2.3-2.8 | 0.3-0.8 | Balance | ≤0.50 | ≤0.50 | ≤0.020 | ≤0.015 | ≤0.010 | ≤0.10 |
| Function Note | Controls grain growth; forms fine MC carbides at grain boundaries to enhance intergranular strength and creep resistance | Enhances high-temperature oxidation and thermal corrosion resistance; forms Cr₂O₃ protective film to isolate corrosive media | Forms stable γ’ phase with Ti/Al; improves alloy ductility and toughness at 650-870℃ | Enhances medium-to-high temperature strength; improves resistance to sulfur-induced corrosion and hydrogen embrittlement | Core element for γ’ phase precipitation; determines γ’ phase content (≈15-20%) and high-temperature strength | Assists Ti in forming γ’ phase; optimizes γ’ particle size (0.12-0.25μm) for balanced strength and ductility | Matrix element; balances alloy cost, density, and processability for large components | Improves hot workability; strictly controlled to avoid low-melting-point inclusions | Enhances deoxidation effect; strictly limited to avoid reducing high-temperature mechanical properties | Strictly limited to prevent intergranular corrosion in sulfur-containing environments | Strictly limited to avoid hot cracking during forging/welding | Refines grain boundaries; improves intergranular strength and thermal fatigue resistance |
2. Physical Properties
2.1 Basic Physical Parameters
- Density: Approximately 7.95g/cm³ at room temperature (25℃), lower than Ni-Cu based GH90 (8.25g/cm³) and 8-10% lower than high-Ni superalloys such as GH4738 (8.45g/cm³). This low-density advantage is critical for weight-sensitive medium-to-high temperature components (e.g., thermal power plant superheater tubes), reducing equipment overall weight by 4-9% compared to corrosion-resistant alloys like Incoloy 800H.
- Magnetic Properties: Weakly magnetic at room temperature (magnetic permeability μᵣ ≈ 1.005-1.012); magnetic property gradually fades as temperature rises, becoming nearly non-magnetic (μᵣ ≈ 1.002-1.003) in the service temperature range (650-870℃). This makes it suitable for applications near general electromagnetic equipment, though caution is needed for high-precision magnetic sensors (e.g., power plant flowmeters).
- Melting Temperature Range: 1330-1390℃ (liquidus: ~1390℃; solidus: ~1330℃). The narrow and stable melting range ensures uniform solidification during casting and consistent deformation during forging, reducing internal defects (e.g., shrinkage porosity, segregation) and improving structural integrity—critical for large-scale welded components such as boiler headers.
- Thermal Expansion Coefficient (CTE):
2.2 Thermal Properties
◦ 20-100℃: ~12.5×10⁻⁶/℃
◦ 20-600℃: ~14.0×10⁻⁶/℃
◦ 20-800℃: ~15.3×10⁻⁶/℃
◦ 20-870℃: ~15.7×10⁻⁶/℃
The gradual CTE increase minimizes thermal stress during frequent temperature cycling (e.g., power plant boiler start-stop, petrochemical furnace load adjustment), reducing thermal fatigue cracking risk by 45-55% compared to Fe-Cr-Ni alloys like 316H stainless steel.
- Thermal Conductivity (λ):
◦ 100℃: ~15.8W/(m·K)
◦ 500℃: ~19.2W/(m·K)
◦ 800℃: ~22.5W/(m·K)
◦ 870℃: ~23.2W/(m·K)
The temperature-dependent conductivity improvement promotes efficient heat transfer in medium-to-high temperature components, avoiding localized overheating (a major cause of creep acceleration) and extending part service life by 30-35% compared to conventional Fe-Cr-Ni alloys.
2.3 Mechanical Properties (After Standard Heat Treatment: 1080-1120℃ solid solution for 1h, water cooling + 720-750℃ aging for 12h, air cooling)
| Property | Room Temperature (25℃) | 650℃ | 750℃ | 800℃ | 870℃ |
| Yield Strength (σ₀.₂, MPa) | ≥720 | ≥650 | ≥580 | ≥420 | ≥330 |
| Tensile Strength (σᵦ, MPa) | ≥920 | ≥850 | ≥750 | ≥550 | ≥450 |
| Elongation (δ₅, %) | ≥17 | ≥15 | ≥13 | ≥11 | ≥9 |
| Reduction of Area (ψ, %) | ≥24 | ≥22 | ≥20 | ≥17 | ≥14 |
| Creep Rupture Strength (1000h, MPa) | - | ≥500 | ≥400 | ≥250 | ≥180 |
Key Notes:
- The high room-temperature strength (σᵦ ≥920MPa) meets the load-bearing requirements of thermal power plant high-pressure boiler tubes and petrochemical high-temperature valves, with strength 25-30% higher than Incoloy 800H;
- At 750℃ (a typical service temperature for petrochemical cracking furnace internals), the creep rupture strength (≥400MPa) is 30-35% higher than that of GH90, ensuring long-term structural stability under medium-to-high temperature load;
- Even at 870℃ (near its upper service limit), the retained elongation (≥9%) prevents brittle fracture during emergency shutdowns, making it suitable for components with frequent thermal cycling (e.g., metallurgical furnace rolls).
3. Application Products & Industry Scenarios
3.1 Thermal Power Generation Field
As a core material for medium-to-high temperature components in thermal power plants, GH91 is used for:
- Boiler Superheater & Reheater Tubes: Tubes in ultra-supercritical (USC) power plant boilers (operating temperature: 650-750℃, steam pressure: 25-30MPa), resisting high-temperature steam oxidation and sulfur-induced corrosion; the alloy’s creep resistance extends tube service life by 36-42 months compared to 12Cr1MoV steel;
- Boiler Headers: High-temperature headers (680-720℃) connecting superheaters, where its excellent weldability allows for large-diameter header manufacturing (maximum diameter ≥1200mm) without welding defects;
- Turbine Blades: Low-pressure turbine blades (operating temperature: 600-650℃), withstanding centrifugal forces and high-temperature steam erosion; its low density reduces turbine rotational inertia and energy consumption.
3.2 Petrochemical Field
In large-scale petrochemical and coal-to-olefins units (operating temperature: 700-850℃), GH91 is applied to:
- Cracking Furnace Internals: Catalyst support grids and furnace tube liners in ethylene cracking furnaces, resisting hydrocarbon gas pyrolysis corrosion and high-temperature sulfur-containing media; compared to Incoloy 800H, it extends service life by 50-60% and reduces maintenance costs by 40-45%;
- High-temperature Valves: Gate valves and control valves in high-temperature syngas pipelines (pressure: 18-22MPa), withstanding medium corrosion and cyclic thermal stress; its creep resistance ensures seal integrity for over 100,000 hours;
- Heat Exchanger Tubes: Tubes in waste heat boilers for petrochemical plants, resisting 750-800℃ flue gas corrosion and improving heat recovery efficiency by 18-25%.
3.3 Metallurgical Industry Field
In metallurgical plants (especially stainless steel and non-ferrous metal smelting), GH91 is used for:
- High-temperature Furnace Rolls: Rolls in continuous annealing furnaces (working temperature: 750-850℃), withstanding high-temperature air oxidation and metal melt splashing; the alloy’s wear resistance extends roll service life by 70-80% compared to 310S stainless steel;
- Vacuum Smelting Furnace Components: Crucible liners and heating element supports in vacuum induction melting furnaces, resisting 800-870℃ high-temperature oxidation and ensuring uniform metal melting;
- Continuous Casting Machine Parts: Guide rollers and segment frames in continuous casting machines (operating temperature: 650-700℃), withstanding high-temperature molten steel radiation and mechanical wear.
- Waste Incineration Power Generation: Flue gas heat exchanger tubes (operating temperature: 700-780℃) in waste incineration plants, resisting chlorine- and sulfur-containing flue gas corrosion; the alloy’s corrosion resistance reduces tube replacement frequency by 60-70% compared to 316L stainless steel;
- Solar Thermal Power Generation: Heat absorber tube supports in tower-type solar thermal power plants (operating temperature: 550-600℃), resisting outdoor UV radiation and high-temperature heat transfer fluid erosion;
- High-temperature Test Equipment: Sample holders for medium-to-high temperature creep testing (650-870℃) and high-load fixture components, providing stable support for long-term tests (up to 8,000 hours) and ensuring accurate test data for superalloy research.
- Hot Working: Forging temperature range: 1120-1180℃; initial forging temperature should not exceed 1180℃ to avoid γ’ phase dissolution and grain coarsening, and final forging temperature should not be lower than 980℃ to prevent work hardening and cracking;
- Cold Working: Cold rolling, stamping, or bending can be performed at room temperature, with intermediate annealing (1020-1060℃, 1h) recommended after 20-30% deformation to restore ductility—cold workability is significantly better than high-Ni superalloys like GH4738;
- Heat Treatment: The two-step process (solid solution + aging) must be strictly controlled—over-aging (above 780℃) will cause γ’ phase coarsening (particle size >0.5μm) and significant strength degradation, while under-aging (below 700℃) will result in insufficient precipitation strengthening and reduced high-temperature performance.
3.4 Other High-temperature Industrial Fields
4. Processing & Heat Treatment Recommendations
This comprehensive performance and application profile makes GH91 a cost-effective, corrosion-resistant superalloy for medium-to-high temperature industrial manufacturing, perfectly balancing thermal corrosion resistance, high-temperature strength, and processability for large-scale, complex-shaped components in power generation, petrochemical, and metallurgical industries.
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