JPS62205202A - Production of stock for superplastic forging having fine crystal grains - Google Patents

Abstract

PURPOSE:To produce a sintered material which has a fine crystal and permits superplastic forging by specifying temp. and pressure to specific conditions at the time of subjecting heat-resistant superalloy powder to pressurizing, molding and sintering by a hot hydrostatic pressing method. CONSTITUTION:The pulverized superalloy powder sized <=80mum is packed into a cylinder made of a stainless steel sheet and the inside of the cylinder is evacuated to a vacuum state at the time of producing a stock for superplastic forging by subjecting the powder of the superalloy made by a gaseous Ar atomization method to pressurizing, molding and sintering by the hot hydrostatic pressing (HIP) method. The raw material is subjected to the HIP treatment at the temp. lower by 250 deg.C than the melting temp. of the superalloy which is the raw material and under 1,000-2,000kg/cm<2> pressure at the time of subjecting the powder to pressurizing, molding and sintering by the HIP method. The treatment is so executed that the temp. in the central part of the superalloy molding which is the material to be treated is maintained at the above-mentioned temp. for at least >=30 minutes. The sintered superalloy stock of the fine crystal suitable for superplastic forging is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a material having fine crystal grains suitable for superplastic forging.

(Conventional technology) When superplastically forging a heat-resistant superalloy material and processing it into various shapes, if the crystal grains are made finer, superplastic behavior will occur.
It is a well-known fact in the art that complex shapes can be easily obtained, and for this reason, various methods have been tried in the past to make crystal grains finer.

That is, one of them is powder obtained by gas atomization, which is subjected to cold pre-straining treatment such as rolling by passing through rollers, attritor treatment, impact using a ball mill, and other cold pre-straining treatments. The other method is to fill a capsule with the powder and compact it at a temperature slightly lower than the recrystallization temperature using a hot isostatic pressing (hereinafter abbreviated as HIP) process to obtain fine grains. The molten alloy flow is made to fall through a tundish into a gas atomization chamber using argon gas, etc., and the droplets are pulverized, and this powder is filled into a case and hot extruded to compact the powder. This method simultaneously applies strain to refine crystal grains.

However, in each of these methods, in the former method, in order to give pre-strain to the powder? It is necessary to perform triter treatment and cold rolling, which not only lengthens the process and increases costs, but also eliminates gas components (0, N, etc.) and foreign substances that adversely affect the properties of the final product. There is a problem that it gets mixed into the powder during processing. Particularly, the problem of foreign matter getting mixed in during processing is, for example, when processing by passing through a rolling roll, the fine powder particles adhere to the circumferential surface of the roll.
It is necessary to scrape off this with a brush or other means, and at this time, troubles such as contamination of the powder due to the mixing of debris from the brush etc. are likely to occur. Since it is used in high-heat, high-load equipment and parts such as turbines, contamination with substances other than powder can cause serious accidents.

Therefore, a preferred form is to obtain fine crystal grains without performing the above-mentioned pre-strain addition process.

Therefore, from this point of view, the latter method of putting clean powder in a case and extruding it under hot conditions is a preferable method. Since a cross-sectional area ratio of 3 to 5 or more is required, in order to obtain a material for forging, it is required to bend a 200 to 400 mm diameter core. A press will be required.

Moreover, this extrusion method has restrictions on the shape of the material, and not only is it difficult to manufacture materials with relatively complex shapes other than cylindrical shapes, but also distortion occurs on the outer periphery and inside when extruding with a conventional press for grain refinement. There is a problem that a homogeneous microstructure cannot be obtained because the amount of heat is different and the amount of heat generated during processing is also different due to this.

As described above, the conventionally known methods have many problems in quality and increase in cost when used industrially, and have not yet reached a fully satisfactory method.

Therefore, the inventors of the present invention have made extensive research efforts to find an industrially viable manufacturing method, and have found that the superplastic deformability necessary for forming can be secured with only HIP treatment, and the cost required for material preparation is low. , focused on obtaining a forging material with less contamination, considered the particle size of the powder and the crystal grain size after HIP, and proposed the particle size of the powder to be used, its arrangement, and the relationship between the powder particle size and heating temperature. did. (Special application 1986-1
(No. 09330, No. 109331) (Problems to be Solved by the Invention) The present invention is based on the above-mentioned actual situation, and furthermore, it solves the problem of H I when obtaining a material suitable for superplastic forging using HIP processing.
This paper considers the P condition as a problem and attempts to solve it.

That is, the factors when performing HIP treatment on superalloy powder are temperature for 1 hour and pressure, and the HIP treatment conditions are determined by a combination of these. Among these, temperature has the greatest influence on the size of crystal grains, which is a problem in obtaining the above-mentioned material, but, of course, the pressure for one hour also has an influence in parallel.

(Means for Solving the Problems) Therefore, the feature of the manufacturing method of the present invention that corresponds to and solves the above-mentioned problems is that superalloy powder made by argon gas atomization etc.) (I P This is a method of manufacturing a superplastic forging material by forming and solidifying it through processing, and at the same time, the HIP treatment at that time is performed at a processing temperature 250°C lower than the melting temperature of the superalloy and at a pressure of lO00 to 2000k.
g/cIl! After at least the center reaches the above temperature, it is held for 30 minutes or more and then subjected to HIP treatment.

Hereinafter, to further specifically explain the present invention, the present inventors first manufactured three types of representative Ni-based superalloy powders shown in Table 1, and fixed the particle size of the powder at 80 μm. i(
Molding was carried out by varying the temperature of the IP treatment.

Table 1 Ni-based superalloy composition (tVt%)
The results are shown in Figure 1, and the deformation resistance of the material, which is the most important problem in superplastic forging, is that the HIP treatment temperature (T HIF ) of the three types of superalloys is 250% from the melting temperature (T, ) of the superalloy. ℃ is lower, that is, the difference between the two temperatures (TRIP
The lowest value was shown when TM = ΔT) was 250°C.

In addition, the pressure of HIP treatment at this time is 1500 kg/c
rA, but it was found that this pressure is preferably as high as possible from the powder molding surface.

However, at present, the pressure of commercially available HIP equipment is around 2,000 yen.
up to kg/-. On the other hand, as for the lower limit of pressure, as a result of another test, below 1000 kg/- the powder does not solidify completely and a material with several percent porosity is obtained.
As a result of superplastic forging of this, cracking occurred in a part of the porosity, and a good forged product could not be obtained, so 1000 kg/cjl is not suitable.

Therefore, the pressure range is 1000 to 2000 kg/Cl1
1 is valid.

Further, although the holding time cannot necessarily be determined uniformly depending on the size of the product, at least 30 minutes or more after the center reaches the HIP treatment temperature is necessary for diffusion bonding of the particles.

Thus, based on these results, it can be said that the HIP treatment conditions in the production method of the present invention are important.

Note that superalloy powder is most commonly produced by argon gas atomization, but is not limited thereto.

However, since it is preferable for the particle size to be small, the above-mentioned argon gas atomization method is very advantageous, and in the present invention, preferably, powder with a particle size of 80 μm or less is used.

(Example 1) Fine powder sprayed by argon gas atomization was directly filled into a metal capsule, solidified by H[P treatment, and then tensile tested to examine the influence of HIP treatment conditions on superplastic properties. did.

The test piece was a Ni-based superalloy as shown in Figure 2 (rl), in which a pair of cylindrical pieces were connected by a small-diameter cylinder. The small diameter cylindrical part was 4Φ Tsuru and 16 m long.

In order to consider the influence of powder particle size on superplastic properties, powders with three types of particle sizes, 30 μm, 40 μm, and 80 μm, were used.

After filling this powder into a stainless steel container with a diameter of 17.3 fins,
It was degassed in vacuum and subjected to HIP treatment to obtain the above-mentioned test piece. At this time, the HIP conditions are such that the true density is obtained and the coarsening of crystal grains is suppressed.

The time was kept constant at 1500 kg/cni and 1 hour, respectively, and the temperature was changed to examine the effects.

Table 2 shows the conditions on the ridges.

Figure 2 (a) shows that the strain rate is 5×10− based on the above considerations.
The relationship between deformation resistance and HIP treatment temperature in 'S is shown.

As is clear from the figure, the three types of powders A, B, and C all exhibit the minimum deformation resistance when the HIP treatment temperature is 100'C. This is because recrystallization is occurring at this temperature.

Since the melting temperature of the superalloy powder used here is 1250°C, the temperature at which the above deformation resistance is minimum is T.

-250℃.

In addition, in the temperature range of 1000° C. or lower in FIG. 2, the lower the HIP temperature, the greater the deformation resistance.

This is because the lower the HIP temperature, the higher the proportion of dendrites that are unrecrystallized Mi textures. On the other hand, when the temperature exceeds 1000° C., the deformation resistance increases again, but this is because the recrystallized grains become coarser. Jutte, TM 25
It is understood that HIPing at a temperature of 0'C(7) is best.

(Example 2) The same powder as in Example 1 was used at various temperatures, i.e. 9
00'c, 950℃, 1000℃, 1050℃, 1io
Materials were molded by HIP treatment at various temperatures of 0.degree. C., and their elongation at break was examined. The results are shown in FIG. 3, and as in FIG. 2(a), when the H[P treatment temperature was 1000'c, that is, Ts-250°C, it exhibited the best superplastic properties and elongated well.

FIG. 4 shows the longitudinal cross-sectional microstructure of this test piece sample after elongation fracture. This has a particle size of 30μm and is HI-Ped at 1100℃.
The specimens were treated and tested at a temperature of 1050°C and a strain rate of 5 x 10-'/S.

This is a case where the elongation is as small as 96%, and in this case, a large number of voids are generated from the powder interface, which maintains its original shape. It can be seen from the state near the fracture that the fracture was caused by the connection of such voids. Under such conditions, it is clear that the microstructure immediately after the HIP treatment becomes a major influencing factor.

On the other hand, when the elongation was large, a fine crystalline structure with dynamic recrystallization was observed, and powder that maintained its original shape was hardly found.

(Effects of the Invention) The present invention is a method of manufacturing a material having fine crystals suitable for superplastic forging by selecting the HIP processing conditions as described above, and solves the problems of the conventional extrusion method. , superplastic properties can be imparted through a simple process of only HIP treatment, the cost required for superplastic forging materials can be significantly reduced, cost reduction can be achieved, and the same remarkable effects can be achieved in industry.

Moreover, the present invention achieves homogenization with no strain difference between the outer periphery and the center of the material due to the processing conditions, and there is no restriction on the shape of the material, and there is no need to add prestrain, so the prestrain addition step However, it is an extremely effective method for producing superplastic forging materials, and is expected to be put to practical use in the future.

[Brief explanation of drawings]

Figure 1 is a chart showing the relationship between temperature and deformation resistance in Ni-based super-superalloy powder HIP treatment, and Figure 2 (a) is Example 1.
Deformation resistance and HI at strain rate 5 x 10-'/S
A chart showing the relationship with the P treatment temperature, Figure 2 (b) is an explanatory diagram showing the shape of the test piece, and Figure 3 is the HI in Example 2.
A graph showing the relationship between P treatment temperature and elongation at break, and FIG. 4 is a 400x microscopic photograph showing the microstructure of a longitudinal section of a break test piece. Patent Applicant Institute of Technology VZ Diagram of Long Rod 1st Eye (A) HI P gL) L(') 3rd Eye Flower 4th Eye (×toty)

Claims (1)

[Claims] 1. When solidifying superalloy powder by hot isostatic pressing to produce a superplastic forging material having fine crystal grains,
50℃ lower processing temperature, pressure range 1000~2000
production of a superplastic forging material having fine crystal grains, characterized in that the temperature is maintained at least 30 minutes or more after the center of the object to be processed reaches the above temperature, and hot isostatic pressing is performed. Method.