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GH2747 (formerly GH747) is a precipitation-hardenable, iron–nickel–chromium wrought superalloy classified under GB/T 14992. It is supplied in the solution-annealed condition and serves continuously at 1100–1250 °C, with short-term excursions to 1300 °C; its nominal density is 7.78 g/cm³. The grade was engineered around oxidation resistance rather than load-bearing capacity at intermediate temperature: a high aluminum content of 2.9–3.9 %, chromium at 15–17 % and a controlled cerium addition together produce a dense alumina–chromia scale that remains adherent through repeated thermal cycling. This article consolidates the composition, physical and mechanical data, heat-treatment practice, applicable standards and selection boundaries of GH2747, and reconciles several property values that circulate inconsistently in public sources.
Attribute | Value |
|---|---|
Designation | GH2747 (former designation GH747) |
Material family | Iron-based Fe–Ni–Cr, precipitation-hardenable, wrought |
Governing designation standard | GB/T 14992 |
Density | 7.78 g/cm³ |
Continuous service temperature | 1100–1250 °C |
Short-term service temperature | up to 1300 °C |
Delivery condition | Solution annealed; normally no aging treatment |
Typical product forms | Hot-rolled bar, forging, plate, cold-rolled sheet and strip, seamless tube, wire |
Key takeaways
GH2747 is an iron-based (Fe–Ni–Cr) grade, not a nickel-based one, although its nickel content reaches 44–46 %.
Oxidation resistance depends on aluminum as much as on chromium; chromium alone is insufficient above roughly 1200 °C.
Its useful strength is low by superalloy standards, and the 1000 °C tensile minimum must never be treated as an allowable design stress.
The grade is specified for thin-wall, oxidation-limited components, not for rotating or highly stressed parts.
In the Chinese designation system, "GH" is the pinyin abbreviation for wrought high-temperature alloy (gao wen he jin), and 2747 is a sequential number within that series. The earlier form GH747 still appears in drawings, legacy specifications and export quotations, and both designations refer to the same composition and property requirements. The closest documented foreign analogue is the Russian grade ЭП747; the "Haynes 747" designation frequently encountered in trade listings is a commercial search alias without a corresponding standard specification, and should not be used as the basis for acceptance.
GB/T 14992 classifies the grade as an iron-based, precipitation-hardenable wrought superalloy, a classification that reflects the balance of the composition rather than the nickel level alone. The apparent contradiction between a "precipitation-hardenable" family and "solution-annealed" service is resolved by distinguishing the alloy system from the delivery condition. The system is capable of forming γ′ (Ni₃Al) because of its aluminum content, whereas the delivered condition keeps that precipitate largely in solution so that the material retains formability and weldability. High-temperature strength therefore derives from solid-solution strengthening, residual γ′ and the integrity of the oxide scale rather than from a peak-aged microstructure.
This positioning defines the grade's limits. Compared with precipitation-hardened nickel-based grades such as GH4169 or GH4141, which are designed for load-bearing service at 650–950 °C, GH2747 has a markedly lower strength level; its advantage lies in oxidation life and structural stability above 1100 °C. Where a component is a rotating disk, a highly stressed fastener or a pressure-retaining structural member, a medium-strength nickel-based grade should be selected instead.
The composition is controlled to the following ranges under GB/T 14992 (mass fraction, %).
Element | Range | Function |
|---|---|---|
Ni | 44.0–46.0 | Stabilizes the face-centered cubic austenitic matrix; governs ductility and structural stability |
Cr | 15.0–17.0 | Forms the inner Cr₂O₃ layer; provides oxidation and hot-corrosion resistance |
Al | 2.90–3.90 | Forms the outer Al₂O₃ scale; the principal source of oxidation resistance at 1000–1300 °C |
Ce | ≤ 0.030 | Rare-earth microalloying; improves scale density and adherence, limiting spallation under cycling |
C | ≤ 0.10 | Controls carbide volume; balances strength against ductility |
Si | ≤ 1.00 | Residual from deoxidation; excess impairs hot workability |
Mn | ≤ 1.00 | Residual from deoxidation; must be kept within limit |
S | ≤ 0.020 | Deleterious impurity affecting hot workability and weldability |
P | ≤ 0.025 | Deleterious impurity affecting toughness |
Fe | Balance | Matrix constituent; reduces alloy cost relative to nickel-based grades |
Oxidation resistance is not simply a function of chromium. At 15.0–17.0 %, the chromium level is moderate by nickel-alloy standards; a chromia-only scale would begin to volatilize and spall above roughly 1200 °C. GH2747 raises aluminum to 2.9–3.9 %, so that service exposure generates a duplex scale with an Al₂O₃ outer layer over a Cr₂O₃ inner layer, while the cerium addition improves scale adherence and self-healing. The result is a low oxidation mass gain across the 1000–1300 °C range. By contrast, austenitic heat-resistant stainless steels such as 310S (UNS S31008) contain no aluminum and rely on chromia alone; above approximately 1050 °C in continuous service, scale spallation and section loss become the life-limiting mechanisms.
The aluminum window is also the principal processing constraint. If aluminum runs low, the γ′ fraction is insufficient and high-temperature strength and stress-rupture life fall; if it runs high, coarse precipitation and segregation impair hot workability and cold-roll formability. Heat-level chemistry should therefore be verified against the mill certificate and, where required, by optical emission spectrometry, rather than assumed from nominal values.
Property | Value | Condition |
|---|---|---|
Density | 7.78 g/cm³ | Room temperature |
Thermal conductivity | 10.5–24.3 W/(m·K) | 100–900 °C; rises with temperature |
Coefficient of thermal expansion | 17.07 × 10⁻⁶/K | Mean value, 20–800 °C |
Elastic modulus | 218 GPa | 20 °C |
Elastic modulus | 177 GPa | 500 °C |
Elastic modulus | 159 GPa | 600 °C |
Elastic modulus | 146 GPa | 700 °C |
Elastic modulus | 128 GPa | 800 °C; approximately 41 % below the room-temperature value |
Density warrants a specific note, because two values are in circulation: 7.78 g/cm³ and 8.26 g/cm³. Applying a rule-of-mixtures calculation to the specified composition (Ni 44–46 %, Cr 15–17 %, Al 2.9–3.9 %, Fe balance) yields 7.7–7.8 g/cm³, consistent with 7.78 g/cm³. A value of 8.26 g/cm³ exceeds what this composition can support and corresponds to a different grade. Because the two figures differ by roughly 6 %, using the higher value in weight-per-piece calculations and quotations introduces a material pricing error that becomes significant at batch scale.
Each of these properties has a direct design consequence. Thermal conductivity is lower than that of austenitic stainless steel, so thick sections develop steeper through-thickness gradients during heating and cooling, and both soak times and welding heat input require adjustment. The expansion coefficient is close to that of austenitic stainless steels but differs substantially from ferritic and low-alloy steels, so dissimilar joints should be checked for thermally induced stress. The elastic modulus falls by more than 40 % between room temperature and 800 °C; stiffness calculations that use the ambient value will underestimate deflection and buckling risk in service.
Typical tensile properties in the standard heat-treatment condition are given below; values are specification minimums.
Product form | Test temperature | Tensile strength Rm | Elongation A | Reduction of area Z |
|---|---|---|---|---|
Hot-rolled bar | 20 °C | ≥ 550 MPa | ≥ 15 % | ≥ 20 % |
Hot-rolled bar | 1000 °C | ≥ 40 MPa | ≥ 30 % | ≥ 30 % |
Cold-rolled sheet | 20 °C | ≥ 600 MPa | ≥ 30 % | — |
The 40 MPa minimum at 1000 °C is frequently misread as evidence of an inadequate grade. It is better understood as a statement of function: at ultra-high temperature the value of this alloy lies in scale integrity, resistance to grain coarsening and dimensional stability, not in carrying mechanical load. For that reason the short-time tensile figure at 1000 °C must not be adopted as an allowable stress. Where a component carries sustained stress above 900 °C, creep and stress-rupture data should be evaluated separately, or a more heavily precipitation-hardened nickel-based grade should be considered.
Cold-rolled sheet retains a tensile strength of at least 600 MPa with elongation of at least 30 %, which indicates sufficient forming reserve for stamping, spinning, bending and roll-forming of thin-wall components. The alloy work-hardens rapidly, however, so intermediate annealing is required between forming passes to restore ductility.
GH2747 is delivered in the solution-annealed condition. The purpose of the treatment is not to develop peak strength but to dissolve γ′ and carbides and obtain a uniform supersaturated structure that preserves formability and weldability.
For hot-rolled bar, forged bar and forgings, the standard solution treatment is 1000–1200 °C followed by water quenching, with soaking time determined by section thickness. Cold-rolled sheet and strip are usually solution treated at approximately 1150–1200 °C and rapidly cooled, and the treatment must be carried out under a hydrogen or vacuum atmosphere. Because aluminum reaches 2.9–3.9 %, the surface oxidizes readily above 1150 °C, and selective oxidation of aluminum depletes the surface layer. An aluminum-depleted zone cannot precipitate sufficient γ′ and therefore loses both high-temperature strength and oxidation resistance exactly where the component first meets combustion gas and corrosive media, which makes depletion more consequential than any cosmetic discoloration.
Welding behavior is favorable. Gas tungsten arc welding, spot welding, seam (roller) welding and electron beam welding all produce sound joints, and matching-composition filler wire or parent-metal wire may be used for dissimilar joints. Given the low thermal conductivity and comparatively high expansion coefficient, heat input should be controlled, and thick sections or highly restrained joints should be welded symmetrically with backstep sequencing to limit hot cracking and distortion. Post-weld heat treatment is generally not required, although joints subject to severe thermal cycling should be qualified by procedure testing.
Aerospace propulsion is the principal application. The grade is used for combustor liners and barrels, afterburner components, heat shields, flame tubes and high-temperature oxidation-resistant static parts in aero and rocket engines. These components share a common profile: thin walls, complex geometry and continuous exposure to combustion gas above 1100 °C, where oxidation life and structural stability matter far more than room-temperature strength.
In industrial thermal processing, GH2747 serves as furnace rollers, radiant tubes, hearth fixtures, retorts, muffle liners, high-temperature baffles and thermocouple protection sheaths. In continuous annealing, carburizing and sintering furnaces its advantage over 310S and the Incoloy 800 series lies in a higher service ceiling and a lower tendency to shed scale, which reduces shutdowns for descaling and roller refinishing.
In process industries the grade is applied to ethylene cracking furnace internals, incinerator linings and oxidation-resistant components in nuclear and metallurgical plant. One limitation should be stated plainly: the alloy contains no molybdenum or tungsten and therefore offers limited resistance to chloride pitting and wet corrosion. Its domain is high-temperature dry oxidation and sulfur-bearing flue gas, not high-chloride aqueous service.
GH2747 is covered by a designation standard and by a set of product specifications.
Standard | Title | Scope |
|---|---|---|
GB/T 14992 | Classification and designation of superalloys and intermetallic high-temperature materials | Grade classification and composition system |
Q/GYB 511 | GH2747 alloy hot-rolled and forged bar | Hot-rolled and forged bar |
Q/GYB 512 | GH2747 alloy cold-drawn (rolled) seamless tube | Seamless tube |
GB/T 15062 | Superalloy tube for general purposes | General-purpose tube |
GJB 1952A | Specification for cold-rolled superalloy sheet for aviation | Cold-rolled sheet |
GJB 3165A | Specification for hot-rolled and forged superalloy bar for aviation load-bearing parts | Bar for load-bearing parts |
GJB 3317A / 3318A | Specifications for hot-rolled superalloy plate and strip for aviation | Plate and strip |
HB/Z 140 | Heat treatment of superalloys for aviation | Heat-treatment practice |
Product forms include hot-rolled bar, forgings, hot-rolled plate, cold-rolled sheet, cold-rolled strip, seamless tube and wire, all supplied in the solution-annealed condition. Purchase specifications should state the grade and condition, dimensions and tolerances, mechanical property criteria, grain size requirements and inspection items, so that acceptance can be verified against the mill certificate and, where specified, by spectrometric re-check on receipt.
Grade | Matrix and strengthening | Continuous service | Oxidation resistance | Selection note |
|---|---|---|---|---|
GH2747 | Fe–Ni–Cr, γ′ precipitation-hardenable, used solution annealed | 1100–1250 °C | High (Al₂O₃ + Cr₂O₃ duplex scale) | Ultra-high-temperature oxidation-limited thin-wall parts, furnace hardware |
GH3030 | Ni–Cr, solid-solution strengthened | up to 800 °C | Moderate | Moderate temperature; favors formability and welding |
GH3044 | Ni–Cr–W, solid-solution strengthened | up to 900 °C | Good | 900 °C class combustor components |
GH3536 | Ni–Cr–Fe–Mo, solid-solution strengthened | approximately 900 °C | High | Good cold formability; requires protection against chromium depletion |
GH2132 | Fe–Ni–Cr, γ′ precipitation-hardened | approximately 650 °C | Moderate | Fasteners and moderate-temperature load-bearing parts |
310S | Austenitic stainless steel | approximately 1000 °C, oxidation-limited | Moderate | Cost-efficient; scale spallation above about 1050 °C |
Selection reduces to three rules. Where service temperature exceeds 1100 °C and oxidation is the controlling failure mode, GH2747 has no practical substitute in this family. Where service is around 900 °C and formability and weldability dominate, a solid-solution-strengthened grade is more economical. Where load bearing is the governing requirement, the specification should return to the precipitation-hardened nickel-based series rather than raising design stress on GH2747.
Is GH2747 an iron-based or a nickel-based alloy? Under GB/T 14992 it is classified as an iron-based Fe–Ni–Cr precipitation-hardenable wrought superalloy. Although nickel reaches 44–46 %, classification follows the matrix element and the standard's own taxonomy, so nickel content alone does not make it a nickel-based grade.
Are GH2747 and GH747 the same grade? Yes. GH747 is the former designation; GH2747 is the current one, with identical composition and property requirements. Specifications should cite GH2747 and note the former designation for searchability.
What is the density of GH2747? 7.78 g/cm³. The 8.26 g/cm³ figure that appears in some sources is inconsistent with the specified composition and should not be used for weight or quotation calculations.
Can GH2747 be used continuously at 1300 °C? No. 1300 °C is a short-term excursion limit; continuous service is 1100–1250 °C. Above 1250 °C under sustained load, neither scale stability nor structural stability can be assured.
Does GH2747 require post-weld heat treatment? Generally not. The alloy welds readily and joints meet the requirements of most oxidation-resistant components. For joints under severe thermal cycling or high restraint, a qualified local stress-relief treatment may still be advisable.
How does GH2747 compare with Inconel 601? Both rely on an alumina-forming surface, but they belong to different systems: GH2747 is iron-based with 44–46 % Ni, while Inconel 601 is nickel-based with roughly 60 % Ni and higher chromium. Selection should follow the governing design code and the required creep data rather than oxidation resistance alone.
Shanghai Bozhong Metal Group holds stock of GH2747 in plate, bar, tube, strip, wire and forgings, sourced through both domestic mill direct supply and imported original stock. Material is available in full mill lengths or cut to size, including small-lot and prototype quantities. Each consignment is accompanied by a mill test certificate covering heat number, chemical analysis and mechanical properties, and spectrometric verification reports can be provided on request.
Technical support covers grade comparison for a given temperature and atmosphere, guidance on solution treatment and bright annealing, welding procedure and filler metal selection, and machining recommendations for a work-hardening austenitic grade. For combustor liners, furnace rollers and thermocouple sheaths, supply can be aligned with the drawing, delivery condition and inspection requirements agreed in the purchase specification.
Data note. Composition ranges follow GB/T 14992; physical and mechanical values are taken from established material data and specification minimums. Actual heat-level chemistry, mechanical properties and delivery condition are governed by the mill certificate and the agreed purchase specification. Density, elastic modulus and high-temperature strength are quoted with their applicable conditions and should be cited with those conditions retained.
