JP2599729B2 - Ingot making method for alloy articles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ingot making method using a powder as a starting material to obtain a large-diameter steel ingot with little segregation without using HIP (hot isostatic pressing).

[Conventional technology]

In ordinary melting methods such as high-speed steel, high-C cold tool steel, and superalloys, to refine the microstructure of highly segregated metallic materials, a pre-alloyed powder is prepared by gas atomization and compacted by HIP. Has been implemented.

This method can produce an ingot or a NNS product with a fine structure without segregation by densifying the rapidly solidified microingot without segregation under high pressure in the solid phase temperature range where the structure does not coarsen. It is a feature of.

[Problems to be solved by the invention]

However, since this method uses HIP equipment, despite the fact that this equipment is expensive production equipment, the productivity is low,
In addition, since Ar gas is used as a consolidation medium, there is a disadvantage that it is expensive in principle.

Although the HIP method and its device with a fast cycle time have been proposed, the cost is still unavoidable when compared with the usual ingot making method.

Furthermore, when this process is applied to high-speed steel and other tool steels, the carbide particle size is too fine, wear resistance deteriorates, and other than tools and other applications where toughness is very important, There is a disadvantage that its merit is small.

The present invention is different from the conventional method in that it uses a technique of densifying alloy powder under normal pressure without using HIP at all, thereby providing a compacted "ingot" (hereinafter referred to as the present invention method). Is referred to as "ingot"), the degree of fineness of the composition is slightly coarser than that obtained by the conventional HIP method, but it is much more fine than that obtained by ingot casting by the smelting method. Is found to be able to be manufactured.

By performing normal hot forging and rolling after the "ingot", it is possible to produce various forms of products such as bars and plates.

[Means for solving the problem]

In the present invention, a metal or alloy powder having a desired composition after sintering is filled in a ceramic container, and is then kept in a vacuum or a non-oxidizing atmosphere. Sintering is performed partially in order from the lower part of the container to the upper part, and after the density ratio after sintering is made 96% or more, the true density is made by hot forging or rolling. Lump method.

The present invention is most effective when applied to an alloy that forms a eutectic. After the alloy powder is filled in a ceramic container, the powder in the container is placed in a vacuum atmosphere at a temperature just above a temperature at which a partial liquid phase occurs (SL), and By maintaining the temperature below the temperature (ML) at which the whole becomes a liquid phase, it sinters using the melt diffusion of the powder particles to create an "ingot", which is then formed during hot forging or rolling in the next process. Densify, normal bars, conditions, wires,
A plate material or the like is obtained.

The density ratio after sintering needs to be 96% or more. If the density is lower than this, it is difficult to obtain a true density by hot forging or rolling in a subsequent step.

Sintering is performed one by one from the bottom of the container, and a kind of pressure sintering effect is also added by its own weight.

In a temperature region where a partial liquid phase exists, the material is sufficiently deformed even with a small stress, and contracts by sintering, so that it is possible to prevent a space from being generated between the container and the sintered body. From the macroscopic viewpoint, the present invention is similar to the gradual solidification progressing from the bottom of the steel ingot in the case of directional solidification, but in the present invention, it is fundamental that the gradual semi-melting progresses from the bottom. There are differences. The inside of the container may be kept in a non-oxidizing atmosphere, but the inside of the container is connected to a vacuum exhaust device, and while the half-dissolution gradually proceeds, the inside of the container including the semi-dissolved portion is kept in a vacuum state. Even better.

In this case, a degassing effect similar to vacuum melting acts on the semi-dissolved portion, and after solidification, gas components such as O ₂ and N ₂ can be almost completely removed. In this case, a degassing effect by vacuum or a reducing effect by generated Co gas or the like acts, so that oxides on the powder surface or oxides contained in the powder can be almost completely removed.

By gradually moving the semi-dissolved portion toward the upper part of the container, the semi-dissolved portion solidifies, and finally, the powder in the entire container is semi-dissolved and then solidified. The appearance change during this time is schematically shown in FIG.

By limiting the semi-melted part to the narrowest possible range or by forcibly cooling the lower part of the container after solidification, the semi-melted part completes solidification relatively quickly. The structure is much finer and segregation due to movement of the molten metal, concentration of alloying elements at the solidification interface, and the like hardly occurs.

FIG. 1 (c) shows a state in which the work is almost completed, and a space corresponding to the packing density of the powder in the container is formed in the upper part of the container.
Coagulation is completed. No extra portion such as a riser is required, and the whole "ingot" is sound, and the yield when hot working in the subsequent process is completed is significantly increased.

For the local heating of the container, existing industrial methods can be adopted. For example, various methods such as a method using high-frequency power, immersion in a salt bath, or movement in a furnace having a temperature difference, or a combination thereof can be applied.

The present invention exerts this effect as the diameter of the manufactured “ingot” increases. In the “ingot” state, the microstructure is slightly coarser than that of the HIP ingot which is consolidated in the solid state, but after sufficient hot working, the microstructure corresponding to the HIP material is obtained due to the effect of microstructure refinement by processing. Organizations can be acquired.

Further, since O ₂ and N ₂ in the product are reduced and the inclusions are almost reduced, the mechanical properties particularly in the radial direction can be more excellent than those of the HIP material.

The type of ceramic used must, of course, be inexpensive and readily available for the purposes of the present invention.

Since a large size is required, a refractory or a brick usually used for a steelmaking operation is preferable. It is required to have the strength to withstand the hydrostatic pressure of a large volume of molten steel and not to react with the molten steel. Of course, it is necessary to be conductive. In terms of strength, from the viewpoint of cost, the inner wall is made of a material such as a furnace material that can withstand a single use and has high heat resistance, and the outer wall uses a high-strength refractory that can withstand repeated use even with low heat resistance.
Double structures are preferred.

It is preferable to remove the ingot that has been ingot by tilting or removing the floor and dropping it together with the inner wall.

It is close to the work of tilting and removing solidified metal blocks in a high-frequency melting furnace.

The inner wall material is preferably an unburnt brick or a castable method.
Molding by adding a binder that expresses bonding strength at low temperature,
It is formed by assembling the brick inside the outer wall to the extent that it is slightly cured.

Castables are a type of refractory concrete, and are built using a cast iron.

In any case, since the thermal conductivity of the wall is lower than that of the metal, the improvement of the cooling rate of the steel ingot by reducing the wall thickness cannot be expected. Rather, it is preferable to increase the heat capacity by increasing the thickness, and to cool by an endothermic effect.

Examples of the material of the inner wall include synthetic mullite, corundum, electroformed mullite, electroformed alumina, and the like. All of these materials are mainly composed of Al ₂ O _{3 and} have a softening point under load T ₁ ° C of 1 ° C.
700 ° C or higher.

On the other hand, the material of the outer wall is chamotte bricks and the softening point under load is
It is about 1400 ° C, but this level is sufficient. Regarding these air permeability, since they are put in a vacuum vessel or connected to a vacuum exhaust system, there is no particular problem. This corresponds to the relationship between a vacuum layer and a melting furnace in a normal vacuum melting furnace.

〔Example〕

 Next, the present invention will be described in detail based on examples.

Example 1 A ceramic container is a commercially available chamotte brick having an outer diameter of 600 m.
mφ, 420mmφ inside diameter, 1200mml depth of the outer wall is manufactured, as the inner wall inside this outer wall, the outer diameter 420mmφ, the inner diameter 400mmφ,
The inner wall having a height of 1200 mml was formed using a commercially available alumina brick.

C: 1.31%, Cr: 4.0%, W: 6.1%, Mo: 5.2% by weight ratio,
An alloy powder of high-speed steel consisting of V: 3.0%, Co: 8.2%, balance iron and unavoidable impurities was prepared by N ₂ gas atomization. The average particle size was 300 μm, and the O ₂ content was 70 ppm.

This powder was vibration-filled into the above-mentioned ceramic container.
Weight is about 850kg including the container, after filling, the density ratio is 68%
Met.

A degassing pipe was attached to the upper part of this vessel, and the vessel was evacuated and placed in a furnace where the entire vessel was kept at 1000 ° C. At the bottom of the vessel, a coil connected to an annular high-frequency power supply was placed. Placed around. When 150kW, 180Hz power is supplied to this coil, the height of about 75mm at the bottom of the container is 1250 ℃
The temperature rose. When the high-frequency coil was pulled upward at a speed of 20 mm / min from this state, the coil was separated from the upper part of the container in a required time of 58 minutes.

Next, the ceramic container filled with the sintered powder (ingot) was tilted and tilted until almost inverted, and the ingot was dropped together with the inner wall and taken out, and the inner wall was mechanically hit and broken and removed.

Thereafter, the "ingot" was annealed and cut into two pieces in the vertical direction. A gap of about 390 mm was formed in the upper part of the container, but the upper end surface was almost flat.

From each part of the "ingot", cut out TP of 15mmφ,
The density and microstructure were investigated. Table 1 shows the measurement results of the density ratio.

At the top of the "ingot" the density ratio is slightly lower,
It was found that the upper part also had a density ratio of 98% or more. There is almost no significant difference between internal and external comparisons. FIG. 2 shows the microstructure of the central portion of the "ingot" in comparison with the same steel type having a diameter of 400 mm and made by a normal melting method. It is clear that the structure is extremely fine as compared with the ordinary ingot.

Example 2 An “ingot” having the same size was manufactured under the same conditions as in Example 1. This "ingot" is forged at 4, 12, 24, 64
And 138 were obtained at 200, 115, 82, 50 and 34 mmφ, respectively. Longitudinally from each of these materials
A 5 mmφ × 70 mml bending test piece was cut out and the bending strength was measured. Table 2 shows the results. Conventional method of the same composition
The measurement results of the HIP material and the ingot material are also shown in comparison.

With a forging ratio of 4 already exceeded the strength of the ingot material, with a forging ratio of 24
It turned out to reach the same level as HIP material.

Next, a bending test specimen was similarly cut out from a direction perpendicular to the forging direction of the raw materials of 115 mmφ (forging ratio 12) and 50 mmφ (forging ratio 64), that is, the radial direction, and the bending strength was measured. The results are shown in Table 3 (Note: The length of the bending test piece is 45
mml).

It was confirmed that the radial bending strength exceeded the HIP material and the ingot material at both forging ratios 12 and 64.

With respect to the three types of manufacturing methods, the microstructures in the longitudinal direction at a forging ratio of 64 were compared and observed. As a result, the striped segregation of the eutectic carbide was minor compared to the ingot, and the grain size of the carbide was HI.
It was confirmed that it was at an intermediate level between P material and ingot material. Furthermore, there was almost no giant carbide of the primary crystal peculiar to the smelting material, and the method of the present invention showed that the striping segregation, which was the biggest defect of the high-speed steel by the conventional smelting method, almost disappeared.

Next, the gas contents in the test pieces shown in Table 3 were measured. Table 4 shows the results.

In the material of the present invention, both O ₂ and N ₂ show lower values than the HIP material and the ingot material. It is presumed that the reason for this is that vacuum sintering is performed in a state where a partial liquid phase is generated, so that the degassing effect is strongly exerted.

Since the HIP method is a solid phase bonding, the oxide film on the powder surface is not removed, and the film is mechanically broken as the processing proceeds, and the metal property becomes true metal contact, and the mechanical properties increase as the forging ratio increases However, at this time, since the degree of the metal contact progressing in the radial direction is smaller than that in the longitudinal direction, it is estimated that the strength is lower in the radial direction than in the longitudinal direction.

According to the method of the present invention, since the oxide film on the powder surface is removed by sintering during sintering, as shown in Table 3, the material of the present invention is considered to have a significantly high transverse rupture strength. .

Example 3 C: 0.88%, Cr: 4.20%, W: 6.02%, Mo: 5.80 by weight ratio
%, V: 1.92%, balance JI consisting of iron and unavoidable impurities
Water atomized powder of S SKH51 equivalent steel was prepared. The average particle size was 38 μm and the O ₂ content was 1800 ppm. 0.15% of graphite powder was added to and mixed with this powder, and light grinding was performed. The tap density ratio at this time was 51%.

After the powder was filled in the same container as in Example 1, vacuum sintering was performed at a power of 70 KW at a pulling rate of 30 mm / min and a vacuum evacuation degree of 10 ^-2 Torr. This "ingot" was rolled to 30 mmφ after casting.

 Further, a bending test was performed in the same manner as in Example 1.

Standard heat treatment of this steel (1200 ° C quenching, 560 ° C x 1 hour 3)
HRC65.2 that had been subjected to heat treatment and tempering) showed a bending strength of 480 kg / mm ² . A normal ingot of 30 mmφ had a bending strength of 420 kg / mm ² at the same hardness level, and the material of the present invention showed a superior toughness value.

〔The invention's effect〕

As described above, according to the method of the present invention, it is possible to produce an "ingot" in a time that does not require a HIP device and that is not much different from the ingot ingot making time by a normal melting method. The same ingot, forging, and rolling methods as in the past can be applied to the "ingot", and the mechanical properties of the product can be obtained at a strength level comparable to that of the gas atomizing HIP method.

In the examples, the case of high-speed tool steel was described,
Basically, it can be applied to a material that can achieve a high density of 96% or more by the vacuum sintering method. Since it can be widely applied to alloy systems having a partial liquid phase due to a eutectic reaction in the solidification process, the industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of the ingot making method according to the present invention, and FIG. 2 is a micro-metal structure photograph of an ingot made by the method of the present invention and a conventional method (usually a smelting method). 1: capsule, 2: powder, 3: semi-dissolved part, 4: solidified part, 5: space, 6: vacuum pump

Claims (2)

(57) [Claims] After filling a ceramic container with a metal or alloy powder having a desired composition after sintering, the container is held in a vacuum or a non-oxidizing atmosphere, and partial sintering is performed sequentially from the bottom to the top of the container. A method for ingot casting of an alloy article, comprising: setting the density ratio to 96% or more to obtain a true density by hot forging or rolling. 2. The alloy according to claim 1, wherein the alloy is a eutectic alloy, the atmosphere is vacuum, and the alloy is sintered in a range from a eutectic temperature to a solidification temperature of the alloy. Ingot making method for alloy articles.