Gh4738 / Waspaloy (USA) / Nc20K14 (France) / Nickel-Based Superalloy / Gh738 /

GH738 is a nickel-based superalloy reinforced by γ' phase precipitation. It has good gas corrosion resistance, high yield strength and fatigue performance, good process plasticity and stable structure. It is widely used in rotating parts of aero-engine, and the operating temperature is not higher than 815ºC. Cold-rolled and hot-rolled sheet, tube, strip, wire and forgings, castings, fasteners can be produced.

Material introduction

Heat treatment system 1080ºC±10ºC, 4h, air cooling +840ºC, 24h, air cooling +760ºC, 16h, air cooling.

Variety Specifications and Status

It can produce bars, profiles, forging billets, rings, thick plates, thin plates, strips, pipes, wires, sand castings, precision castings and fasteners, etc. Usually delivered without heat treatment, and the plates are delivered after solution treatment. goods.

Melting and casting process

The alloy adopts vacuum induction and vacuum arc remelting process.

Application overview and special requirements

The alloy is widely used in aero-engine gas turbines in China, mainly used for rotating parts such as turbine blades and turbine disks, and has mature experience in use. Due to the high cobalt content of this alloy, it is rarely used in China.

1.1, material grade
GH738

1.2, similar grades
Waspaloy (USA), NC20K14 (France)

1.3. Technical standards of materials

Q/6S1035-1992 "GH738 alloy bars for high temperature fasteners"


1.4, Chemical composition
Table 1-1
       C                Cr             Ni           Co           Mo          Al             Ti
0.03~0.10   18.0~21.0   margin  12.0~15.0  3.5~5.0  1.2~1.6  2.75~3.25

        B                 Zr           Fe     Mn       Si         P           S         Cu
0.003~0.01   0.02~0.08   ≤2.0  ≤0.10  ≤0.15  ≤0.015   ≤0.015   ≤0.1
Note: Trace impurities are ω(Pb)≤0.001%, ω(As)≤0.0025%, ω(Sn)≤0.0012%, ω(Sb)≤0.0025%, ω(Bi)≤0.0001%.

Physical and chemical properties

2.1. Thermal performance

2.1.1. Melting temperature range 1330~1360ºC

2.1.2. Thermal conductivity

Table 2-1

θ/°C                  360   460   545   640   770   855   985
λ/(W/(m·C))      16.8  18.3  20.2  22.4  24.1  25.3  28.0

2.1.3. Specific heat capacity

Table 2-2

θ/°C                360  460  545  640  770  855  985
c/(J/(kg·C))     515  540  573  603  640  665  707

2.1.4. Linear expansion coefficient

Table 2-3

θ/°C             20~100   20~200  20~300  20~400  20~500  20~600  20~700  20~800  20~900
α/10-6C-1     12.47      12.73     13.04     13.53     13.97     14.47    15.05       15.68     15.95

2.2. Density ρ=8.22g/cm3

2.3. Electrical resistivity

2.4, magnetic energy type

The alloy is non-magnetic.

2.5, chemical properties

2.5.1 Oxidation resistance The oxidation rate of the alloy after 100h in the air medium

Table 2-4

Test time/h                          900   1000
Oxidation rate/(g/(m2.h))  0.083   0.226

2.5.2. Corrosion resistance The alloy has good resistance to salt spray corrosion.

metallographic structure

The structure of the alloy in the standard heat treatment state is composed of γ matrix, Ti(C, N), Nb(C, N), M23C6 carbide and γ'[Ni3(Al, Ti, Nb)] phase, and the γ' content is about 14.5% , is the main strengthening phase of the alloy.

Process performance

1. The forging temperature of the alloy is easy to form between 1220 and 950 °C. The alloy is solution treated after the vigorous forming process.

2. The average grain size of the alloy is closely related to the deformation degree and final forging temperature of the forging.

3. The alloy has good welding performance and can be welded in various ways. Aging treatment after welding can obtain approximately the strength of the fully heat-treated state.

4. The heat treatment of parts is carried out in a neutral or reducing atmosphere without sulfur to avoid vulcanization.

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