JPH0617486B2 - Method for forging powder-made Ni-base superalloy - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forging a powder-made Ni-base superalloy for use in heat-resistant and high-strength members such as gas turbines.

(Prior Art) Conventionally cast or cast / forged materials have been used for blades and disks of gas turbines. However, in order to improve efficiency, high temperature combustion has been promoted, and turbine disk materials, etc., have become extremely highly alloyed, and as a result, the conventional casting and forging methods obtain the desired characteristics due to segregation of alloy elements. Not only could it not be observed, but even cracks were sometimes seen during processing. Therefore, recently, powder metallurgical means which does not cause segregation of alloying elements has come to be used.

On the other hand, the above-mentioned cast materials such as IN100 of high strength Ni-based alloy
A method has been developed to make alloys that have been regarded as unforgeable as described above, forgeable by utilizing superplasticity (Japanese Patent Publication No. 51-38665).

Forging of IN100 alloy by the same method, first, 1093 ~ 1149 ℃
It is compressed at a drawing ratio of 5: 1 or more at a temperature below the recrystallization temperature and within 250 ° C from that to give high ductility by refining the crystal grains, and then isothermal forging (die and material temperature Forging using superplasticity while heating to the same temperature to prevent material temperature drop is performed at 1038 to 1093 ° C (range below recrystallization temperature to 194 ° C) at strain rate of 0.5 cm / cm / min. After that, as a heat treatment for returning the forged product to a high strength state, a solution treatment at 1190 ° C. is followed by a stabilization and precipitation treatment or an age hardening treatment.

A similar forging method has also been developed for powder metallurgy materials (see Japanese Patent Laid-Open No. 54-2220), and the method for forging powder-improved IN100 alloy by the same method is to perform hot isostatic treatment (HIP treatment) on the raw material powder. ) Sinters the powders and densifies them to a theoretical density at a temperature not higher than the recrystallization temperature and not higher than 195 ° C., and the thickness reduction rate is at least 10% or more (about 15 to 35%). %) Is performed at a strain rate of 0.1 cm / cm / min or less to give a high ductility by constant temperature forging, and then a strain rate of 0.1 cm at the same temperature as in the first step.
/ Cm / min or more (0.3 to 0.75 cm / cm / min) second-stage constant temperature forging is carried out, whereby a thickness reduction rate of 50% or more can be achieved. The forged product is made into a product with its strength recovered by solution treatment at 1121 ° C and stabilization and precipitation treatment.

(Problems to be Solved by the Invention) The above isothermal forging has an advantage that it can be formed into a shape very close to the final product. However, in general, superplasticity is exhibited in a region where the strain rate is 0.5 to 1.25% / sec at the maximum, and is not exhibited when the strain rate exceeds that.

Therefore, it takes a long time for forging, and the temperature is required to be as high as 1000 to 1100 ° C., so that there is a problem that an expensive mold material such as Mo alloy is required.

The present invention has been made in view of the above problems, Ni
In the powder Ni-based super heat-resistant alloy containing ≧ 30%, the relationship between the microstructure related to its hot workability and the processing conditions (strain rate and temperature) was investigated and investigated, and die forging under the high strain rate was possible. The purpose of this study is to clarify the alloy manufacturing method and forging conditions and establish the forging method.

(Means for Solving the Problems) The means of the present invention for achieving the above-mentioned object is, in terms of weight percentage, in the production of a powder-made Ni-base superheat-resistant alloy containing Ni ≧ 30%, the raw material powder is After solidifying to a theoretical density by hot isostatic pressing, the alloy is extruded at an extrusion ratio of 1.5 or more at a temperature not higher than its recrystallization temperature and within 250 ° C of the same temperature, and then the γ'phase is completely removed. The point is that high-speed die forging is performed below the solid solution temperature and within 200 ° C of the temperature.

(Examples) The present invention will be described in detail with reference to various investigation results using a powdered Ni-base superalloy having the composition shown in Table 1 below as an example.

First, the HIP process will be described. For HIP treatment, thoroughly mixed raw material powder is processed at 950 to 1250 ° C × 1000 to 2000 kgf / cm ²
The HIP treatment is carried out for 1 to 5 hours to substantially solidify it to the theoretical density. The above treatment conditions are ordinary conditions. The alloys exemplified in Table 1 are solidified at 1180 ° C. × 1000 kgf / cm ² × 2
I went at h.

FIG. 1 is a microstructure photograph of the above alloy, which is substantially densified to the theoretical density, and the interface of the original powder is embossed by the precipitation of carbide. The carbide is M called PPB
It is a C carbide.

Generally, there is an oxide film on the surface of the raw material powder, and HIP
As described above, depending on the material, PPB reduces the toughness and ductility precipitated at the grain boundaries, and also has a large effect on hot workability, which was also a cause of cracking during forging.

Therefore, it is desirable that the HIP treatment condition is such that MC carbide formation is suppressed.

Fig. 2 shows the test piece with the structure of Fig. 1 at ε at 1075 ℃.
= 200% / sec. A photograph showing a state of fracture due to high-speed tension, and the drawing after fracture is almost zero.

However, even with such a material, when it is extruded, it has a fine structure as shown in the microstructure photograph of the extruded material in Fig. 3, and PPB is dispersed, and the test piece of the extruded material is fractured by high-speed tension. As shown in Fig. 4, the aperture of more than 85% was obtained. The above extrusion was performed at 1100 ° C. with an extrusion ratio of 7.2. High-speed tension is 1075 ℃
The strain rate is 200% / sec.

However, it is known that the HIP solidified powder material exhibits superplasticity if the strain rate is about 0.1% / sec, under appropriate conditions below the recrystallization temperature, even if it is not the above extruded material, The HIP material shown in Fig. 1 is 1050 ℃, ε = 0.1%
Superplasticity due to grain boundary slip appears when pulled at a rate of 99 / sec, 99%
Aperture (elongation 660%) was obtained. Under such conditions, so-called constant temperature forging is possible.

Therefore, as shown below, the extrusion conditions (temperature,
The extrusion ratio) and the processing conditions (temperature, strain rate) of the extruded material were evaluated by focusing on the drawing value of the tensile test, and the high-efficiency forging method of the powder-made Ni-base superheat-resistant alloy was investigated and studied.

First, FIG. 5 shows the results of the investigation of hot workability when the extrusion ratio was kept constant at 7.2 and various extrusion temperatures were changed, that is, the influence of the extrusion temperature on the breaking reduction.

In the tensile test, a tensile test piece with a parallel section of 6φ × 15l was cut out from each extruded material, and this was cut at 1075 ° C., strain rate ε = 200% /
The sample was stretched under a constant condition of seconds, and the hot workability was evaluated by the drawing value at that time.

In FIG. 5, in the extrusion temperature range of 1025 to 1125 ° C., the aperture value exceeding 70% was obtained. This is because a fine recrystallized structure can be obtained by extrusion.

The squeeze decreases sharply after extrusion at 1150 ℃ or higher. This is because recrystallization progresses and a part of γ'in the precipitation phase forms a solid solution to cause crystal coarsening.

The squeeze is reduced even when extruding at 1000 ° C or less. This is because recrystallization is not performed only by the processing heat at the time of extrusion and relatively coarse crystal grains are present. In this case, it is possible to obtain a fine recrystallized grain structure by reheating to around 1100 ° C. Further, the decrease in extrusion temperature causes an increase in deformation resistance during extrusion, making it impossible to secure a predetermined extrusion ratio.

Therefore, depending on the pressing capacity, the extrusion temperature should be based on the recrystallization temperature determined by the material, and the temperature range in which a fine recrystallization structure can be obtained by extrusion should be selected. Was recognized as appropriate.

Next, FIG. 6 shows the results of an examination of the influence of the extrusion ratio and the strain rate during the tensile test of the extruded material on the breaking reduction value. However, the extrusion temperature of the extruded material is 1070 ° C.

Examination of this figure shows that when the strain rate is as low as 0.2% / sec, a drawing close to 100% is obtained regardless of the extrusion ratio. This is because the strain rate is within the superplasticity developing region.

It has been shown that superplasticity is no longer exhibited at high strain rates of 20% / sec and 200% / sec, and the drawing value greatly changes depending on the strain rate or the extrusion ratio that determines the microstructure.

Figures 7 and 8 are photographs showing the microstructures of extruded materials (extrusion temperature: 1070 ° C) with extrusion ratios of 1.6 and 3.6, respectively. In the case of an extrusion ratio of 1.6, the dendrite structure of the raw material powder is In contrast to the remaining part, a complete recrystallized structure is obtained in FIG. 8 when the extrusion ratio is 3.6.

FIG. 9 is a graph of the result of investigation on the influence of the tensile test temperature on the breaking reduction value.

That is, it is a graph obtained by obtaining the change in the drawing when the test pieces with a constant extrusion ratio were pulled at different test temperatures with a constant strain rate. According to the figure, the extrusion ratio R = 3.
In the case of 6, even if the strain rate is as large as ε = 200% / sec, it is possible to draw in any of the tensile test temperatures of 1000 to 1100 ° C.
80% or more, R = 1.6, ε = 20% / s drawing in any test between 1000 ~ 1100 ℃ 75% pulling 75
% Or more. However, when R = 1.6 and ε = 200% / sec, the aperture shows only 70% at 1050 ° C.

That is, the larger the extrusion ratio, the wider the temperature range in which the drawing becomes larger.

This means that the appropriate forging temperature region under the strain rate is widened to the extent that the extrusion ratio is increased and the structure is refined, and as a result, constant temperature forging is not required.

Considering the above points, and based on the above survey results, it is recognized that an extrusion ratio of 1.5 or more is necessary.

Further, for high-speed die forging, it is necessary to carry out at a temperature equal to or lower than the temperature where the γ'phase complete solution temperature is higher than the complete solution temperature because the crystal grains abruptly coarsen and the deformation resistance increases.
As can be seen from the effect of the tensile test temperature on the maximum deformation resistance in Fig. 10, the lower the forging temperature, the larger the maximum deformation resistance. When the deformation resistance becomes large, the die life becomes short, and in the case of forging with a press having the same ability, the larger the deformation resistance becomes, the smaller the size of the forged product becomes, and the lower the productivity becomes. From the above, it was confirmed that high-speed die forging is appropriate at temperatures below the complete solution temperature of the γ'phase but within 200 ° C, depending on the capabilities of the forging press.

In addition, FIG. 10 is a graph in which the maximum deformation resistance is obtained when a test piece with an extrusion ratio of 3.6 is pulled at a tensile strain rate of 200% / sec at each test temperature.

In the case of the Ni-base superalloy according to the present embodiment, the complete solid solution temperature of the γ'phase is about 1200 ° C, so the high temperature die forging temperature is 10
It is better to set it to about 00 ° C or higher, and at such a temperature
From the figure, the maximum deformation resistance is also about 50 kgf / mm ² or less, and plastic deformation is relatively easy.

(Effects of the Invention) The present invention has conducted various experiments on powdered Ni-based alloys having the compositions shown in Table 1, found conditions for improving the hot workability of the raw material and appropriate forging conditions, and follows the same conditions. It is possible to forge with high efficiency (high strain rate) by processing,
The forging method of the present invention is not limited to the alloys exemplified above, but Ni ≧ 30
It is also applicable to other powdered Ni-base superalloys containing 100% by weight, the present invention may improve the quality of members made of these difficult-to-forge materials, or may be applied to new members of these materials. The industrial value of the present invention is enormous.

[Brief description of drawings]

FIG. 1 is a photograph of a micro-metallographic microstructure of an example material of the present invention (the same applies to the following HIP material), FIG. 2 is a drawing showing a fractured state of a test piece of a material example of the present invention by a tensile test, and FIG. 3 is an embodiment of the present invention. Micro metallographic micrograph of extruded example material, FIG. 4 is a drawing showing a fractured state of a test piece of extruded material of an example of the present invention by a tensile test. FIG. 5 is a graph showing the influence of the extrusion temperature on the breaking reduction in the material of Example of the present invention. FIG. 6 is a graph showing the influence of the extrusion ratio and the strain rate on the breaking reduction value of the material of the present invention. FIG. 7 is a micro-metallographic micrograph of the extruded material of the present invention (extrusion ratio 1.6), FIG. 8 is a micro-microscopic microscopic photograph of the extruded material (extrusion ratio of 3.6), and FIG. 10 is a graph showing the influence of the tensile test temperature on the breaking reduction value of the material, and FIG. 10 is a graph showing the influence of the tensile test temperature on the maximum deformation resistance of the extruded material of the present invention.

Continuation of the front page (56) References JP-A-62-96604 (JP, A) JP-A-61-73851 (JP, A) JP-A-52-50908 (JP, A) JP-B-52-26721 (JP , B2)

Claims (1)

[Claims] 1. In the production of a powder-made Ni-base superalloy containing Ni ≧ 30% by weight, the raw material powder is solidified to a substantially theoretical density by hot isostatic pressing, and then the alloy is reprocessed. Extrusion ratio below the crystallization temperature and within 250 ℃ of the same temperature
A method for forging a powder-made Ni-base superalloy, which comprises performing an extrusion process of 1.5 or more, and then performing high-speed die forging at a temperature not higher than the temperature of the complete solid solution of the γ'phase and within 200 ° C of the temperature.