JP2018051583A - Hot-forging die and method for producing forged product using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot-forging die that is made of an Ni-based superalloy and resists corrosion caused by a glass lubricant and a method for producing a forged product using the same.SOLUTION: A hot-forging die has a base material having a composition composed of an Ni-based superalloy containing, in mass%, W: 10.3-11.0%, Mo: 9.0-11.0%, and Al: 5.8-6.8%, with the balance being Ni and inevitable impurities. On at least one of a mold face and a side face of the hot-forging die, provided is an oxide coating layer predominantly composed of Si, and between the base material and the oxide coating layer, provided is an aluminum oxide layer of 1.0-5.0 μm in thickness.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a hot forging die having excellent oxidation resistance and a method for producing a forged product using the same.

In forging a product made of a heat-resistant alloy, the forging material is heated to reduce deformation resistance. However, since heat-resistant alloys have high strength even at high temperatures, hot forging dies used for forging require high mechanical strength at high temperatures.
Further, in hot forging, when the temperature of the hot forging die is lower than that of the forging material, the workability of the forging material is reduced due to heat removal. Is performed by heating and forging a die for hot forging (hereinafter sometimes simply referred to as a die) together with the material. Therefore, the hot forging die must have a high mechanical strength at a high temperature similar to or close to that of the forging material. As a hot forging die that satisfies this requirement, Ni-based superalloys that can be used for hot forging at a die temperature of 1000 ° C. or higher in the atmosphere have been proposed (see, for example, Patent Documents 1 to 3).
The hot forging referred to in the present invention includes hot die forging in which the temperature of the hot forging die is brought close to the temperature of the forging material and isothermal forging in which the temperature is the same as that of the forging material.

JP 62-50429 A Japanese Patent Publication No. 63-21737 U.S. Pat. No. 4,740,354

The Ni-base superalloy described above is advantageous in that it has high high temperature compressive strength. By the way, when hot forging the difficult-to-work material, the surface of the difficult-to-work material is coated with a glass lubricant to reduce the forging load or prevent the temperature of the forged material from being lowered. is there. However, it has been found that this glass lubricant causes corrosion of the above-mentioned Ni-based superalloy alloy hot forging die. If the die for hot forging corrodes due to glass lubrication, the engraved shape formed on the work surface of the hot forging die may change, and corrosion due to this glass lubrication can be prevented. Wanted.
An object of the present invention is to provide a hot forging die in which corrosion due to a glass lubricant is prevented and a method for producing a forged product using the same in the above-described Ni-based super heat-resistant alloy die for hot forging. That is.

The present invention has been made in view of the above-described problems.
That is, the present invention is mass%, W: 10.3-11.0%, Mo: 9.0-11.0%, Al: 5.8-6.8%, and the balance is Ni and A hot forging die provided with a base material having a composition made of a Ni-based superalloy that is an inevitable impurity,
At least one of the molding surface and the side surface of the hot forging die has an oxide coating layer mainly composed of Si,
A hot forging die having an aluminum oxide layer having a thickness of 1.0 to 5.0 μm between the base material and the oxide coating layer.
The present invention also relates to a method for producing a forged product in which a heated forging material is hot forged with an upper die and a lower die, wherein the forged product uses the hot forging die as the upper die and the lower die. It is a manufacturing method.

  The hot forging die of the present invention can prevent corrosion due to a glass lubricant, and can more reliably enable hot forging of difficult-to-work materials in the atmosphere.

It is the external appearance photograph which showed the effect which prevents oxidation and the scale scattering accompanying it. It is the external appearance photograph which showed suppression of the oxidation-resistant fall with respect to repetition of a heating and cooling. It is a cross-sectional photograph which shows the reflection electron image of the electron microscope which shows the aluminum oxide layer by the self-oxidation film of this invention, the elemental map of Al, and the elemental map of O (oxygen). It is the external appearance photograph which showed the corrosion phenomenon of the base material by a glass lubricant. It is an appearance photograph showing the suppression of corrosion by the coating layer It is a cross-sectional photograph which shows the reflected-electron image of a comparative example, the element map of Al, and the element map of O (oxygen). It is a cross-sectional photograph which shows the reflected electron image of the electron microscope of the example of this invention, the elemental map of Al, and the elemental map of O (oxygen). It is the external appearance photograph before and after the constant temperature forging of the metal mold | die for hot forging which coat | covered the molding surface with the coating layer.

First, the chemical composition of the hot forging die of the present invention will be described. The Ni-base superalloy having the following alloy composition defined in the present invention has a high-temperature compressive strength superior to other mold materials for hot forging, and heat such as isothermal forging and hot die forging in the atmosphere. Inter-forging can be performed. The unit is mass%.
<W: 10.3-11.0%>
W forms a solid solution in the austenite matrix and also forms a solid solution in the gamma prime phase based on Ni ₃ Al as a precipitation strengthening phase, thereby increasing the high temperature strength of the alloy. In addition, W crystallizes a body-centered cubic α- (Mo, W) phase consisting of a solid solution of W and Mo at the grain boundary, thereby enhancing the grain boundary strength of the alloy and at the same time enhancing the machinability of the alloy. There is. On the other hand, W also has an effect of lowering the oxidation resistance, and if it is added in excess of 11.0%, cracking is likely to occur. The content of W in the Ni-base superalloy in the present invention is 10.3 to 11.0% from the viewpoint of increasing the high temperature strength, suppressing the decrease in oxidation resistance, and further suppressing the occurrence of cracks. To do. The preferable lower limit for obtaining the effect of W more reliably is 10.4%, and the preferable upper limit of W is 10.7%.

<Mo: 9.0 to 11.0%>
Mo dissolves in the austenite matrix and also dissolves in the gamma prime phase based on Ni ₃ Al, which is a precipitation strengthening phase, to increase the high temperature strength of the alloy. On the other hand, Mo has the effect | action which reduces oxidation resistance. From the viewpoint of increasing the high temperature strength and further suppressing the decrease in oxidation resistance, the content of Mo in the Ni-base superalloy according to the present invention is set to 9.0 to 11.0%. A preferable lower limit for obtaining the effect of Mo more reliably is 9.5%, and more preferably 9.8%. Moreover, the upper limit of preferable Mo is 10.5%, More preferably, it is 10.2%.

<Al: 5.8 to 6.8%>
Al binds to Ni and precipitates a gamma prime phase composed of Ni ₃ Al, thereby increasing the high temperature strength of the alloy, forming an alumina coating on the surface of the alloy, and imparting oxidation resistance to the alloy. On the other hand, when the content of Al is too large, an eutectic gamma prime phase is excessively generated, and the high temperature strength of the alloy is lowered. From the viewpoint of enhancing the oxidation resistance and the high temperature strength, the Al content in the Ni-base superalloy according to the present invention is set to 5.8 to 6.8% by mass. A preferable lower limit for obtaining the effect of Al more surely is 6.0%, and more preferably 6.1%. Moreover, the upper limit of preferable Al is 6.6%, More preferably, it is 6.4%.

The alloy is basically composed of Al, W, and Mo, which are essential components, and Ni with the remainder excluding inevitable impurities. In the Ni-base superalloy according to the present invention, Ni is a main element constituting a gamma phase and constitutes a gamma prime phase together with Al, Mo and W.
The Ni-base superalloy according to the present invention can contain components other than Ni, Mo, W, and Al as inevitable impurities.

<Oxide coating layer>
In this invention, the oxide coating layer which has Si as a main component is formed in the base material of the metal mold | die for hot forging which has said alloy composition.
The purpose of forming an oxide coating layer containing Si as a main component on a hot forging die having the above alloy composition is to prevent peeling of the scale. The Ni-based superalloy described above is advantageous in that it has a high high temperature compressive strength, but in terms of oxidation resistance, a fine scale of nickel oxide scatters from the mold surface during cooling after heating in the atmosphere. Therefore, there is a problem that there is a risk of deterioration of the working environment and shape. The problem of oxidation of the mold surface and the accompanying scattering of the scale is a big problem in maximizing the effect that it can be used in the atmosphere.
Therefore, by covering the surface of the hot forging die with a dense protective coating (coating layer), direct contact between oxygen in the atmosphere at high temperatures and the die base material is blocked, and the die surface is oxidized. Is to prevent. Therefore, in this invention, the oxide which has Si as a main component is coat | covered in layer shape, and it is set as an oxide coating layer, and prevents the oxidation of the metal for hot forging.

In the present invention, the oxide coating layer contains Si as a main component. This is because the effect of preventing oxidation of the mold surface is particularly excellent. In the present invention, the Si-based oxide coating layer is naturally formed on the outermost surface of the hot forging die during heating or hot forging, such as a self-oxidizing film. It refers to what is formed by coating, spraying, vapor deposition, etc., not an oxide film to be formed. The above-mentioned “oxide coating layer containing Si oxide as a main component” is other than the auto-oxidized film naturally formed during the hot forging process. The oxide coating layer does not include so-called glass lubrication. The “oxide coating layer” of the present invention does not include a glass lubricant whose effect is substantially impaired by one hot forging.
In addition, the “main component” refers to an oxygen covering layer that is detected when an oxide coating layer is subjected to quantitative analysis by surface analysis using, for example, an energy dispersive X-ray analyzer (hereinafter referred to as EDX). It means that the ratio of Si is the largest among components excluding gas components such as nitrogen and nitrogen. The result of quantitative analysis excluding gas components is approximately 30% by mass or more. Preferably it is 50 mass% or more.
In addition, as a coating method of the oxide coating layer containing Si as a main component, there are methods such as vapor deposition, spraying, and coating. Among these, coating and spraying are advantageous in terms of cost, and are preferable coating methods because an oxide coating layer mainly composed of Si can be formed over a wide range.

The reason why the coating layer of the inorganic material is formed on either or both of the molding surface and the side surface in the present invention is that these two surfaces are usually exposed to a high-temperature atmosphere. In the present invention, an inorganic material coating layer is formed on either or both of the molding surface and the side surface. However, in order to ensure the effect of scale peeling, an inorganic material coating layer is formed on both the molding surface and the side surface. Good to do. The “molding surface” in the present invention refers to a surface that presses the forged material in order to hot forge the material to be forged. For example, the surface shape may be flat like a so-called anvil. However, a mold-sculpted surface may be formed.
In the present invention, in order to further ensure the effect of scale peeling, it is preferable to form a coating layer of an inorganic material on all surfaces (molding surface, side surface, bottom surface) of the hot forging die. Thereby, oxidation of the mold surface due to contact between oxygen in the atmosphere at high temperature and the mold base material and scale scattering associated therewith can be more reliably prevented, and deterioration of the working environment and shape deterioration can be prevented.

<Aluminum oxide layer>
In the present invention, an aluminum oxide layer having a thickness of 0.5 to 5.0 μm is formed between the base material and the oxide coating layer. The aforementioned oxide coating layer is formed, for example, by coating or spraying, and the aluminum oxide layer is an Al self-oxidation coating contained in the mold base material (base material) having the above composition. By forming the aluminum oxide layer by this self-oxidized film, the mold is prevented from being corroded by the glass lubricant. The aluminum oxide layer is not preferably in a discontinuous state in which a missing portion of the aluminum oxide layer partially exists, and is preferably formed continuously.
In other words, for example, when a forged material is coated with a glass lubricant, the glass lubricant may cause a phenomenon that the oxide coating layer or the oxide coating layer and the base material are corroded. When the self-oxidized film is present at the interface with the base material, it functions as a barrier layer that hinders the progress of corrosion of the glass lubricant. The self-oxidized film can be formed by performing a preliminary oxidation treatment after forming an oxide coating layer on the mold surface.
The Al self-oxidation film can be formed, for example, by performing preliminary oxidation at 900 to 1100 ° C. for 3 to 5 hours. When the pre-oxidation conditions are different from the pre-heating conditions of the hot forging die performed before hot forging, it is necessary to perform special pre-oxidation in order to form a self-oxidized film.

Moreover, the thickness of the said aluminum oxide layer shall be 1.0-5.0 micrometers. If the thickness of the aluminum oxide layer is less than 1.0 μm, a sufficient effect as a barrier layer that prevents the progress of corrosion by the glass lubricant cannot be obtained. Moreover, it becomes easy to be in a discontinuous state in which an aluminum oxide layer that is partially effective as a barrier layer is not formed. The discontinuous aluminum oxide layer cannot provide a sufficient effect as a barrier layer that prevents the progress of corrosion by the glass lubricant. On the other hand, even if the thickness of the aluminum oxide layer exceeds 5.0 μm, the effect as a barrier layer is saturated and it takes only a long time to form the self-oxidized film. Therefore, the thickness of the aluminum oxide layer is 1.0 to 5.0 μm.
As described above, when hot forging is performed using the hot forging die of the present invention described above as an upper die and a lower die, for example, even in the constant temperature forging in the atmosphere, oxidation of the die surface and accompanying scale scattering It is possible to suppress the above problem and the progress of corrosion by the glass lubricant.

Example 1
The following examples further illustrate the present invention. Ingots of Ni-base superalloys shown in Table 1 were produced by vacuum melting. The alloy having the composition of the produced ingot has excellent high temperature compressive strength characteristics as shown in Table 2, and has sufficient characteristics as a hot forging die. The high temperature compressive strength (compression strength) was performed at 1100 ° C.

  A disk-shaped test piece having a diameter of 50 mm and a height of 10 mm was cut out from the above ingot, and one of the circular surfaces of the test piece was polished to the equivalent of No. 500, and then the Si shown in Table 3 was mainly contained on the polished surface. A test piece was prepared by forming an oxide coating layer (hereinafter referred to as an oxide coating layer) of about 100 to 150 μm by coating. Using this test piece, the effect of preventing the oxidation of the mold surface and the scattering of the scale due to the formation of the coating layer was evaluated. The test piece produced this time simulates the surface of a hot forging die that is not subjected to stress. Moreover, the coating layer was formed only on one side of the circular surface. As a result of quantitative analysis of the surface of the oxide layer with an energy dispersive X-ray analyzer (EDX), an oxide layer mainly composed of Si with Si exceeding 50% by mass in the components excluding the gas component was obtained. I confirmed that there was.

Using the test piece having the oxide coating layer and the comparative material not forming the oxide coating layer, the sample was put into a furnace heated to 1100 ° C., held at 1100 ° C. for 3 hours, then taken out of the furnace and air-cooled. A heating test was performed. The heating test was repeated by cooling and re-charging in order to evaluate the decrease in oxidation resistance due to repeated use. When the coating layer was completely peeled off, the test was stopped for the test piece and repeated up to 10 times. In addition, the used comparative material is the same shape as the test piece in which the said oxide coating layer was formed, and gave the same grinding | polishing.
FIG. 1 shows a photograph of the appearance of the test result after heating once. The black scale on the surface of the test piece on which the oxide coating layer is not formed is a peeled fine scale. From this, it can be seen that in the test piece in which the oxide coating layer is not formed, surface oxidation and accompanying scale scattering occur. On the other hand, in the test piece in which the oxide coating layer is formed, it can be seen that the coating layer suppresses the oxidation of the surface and prevents the oxidation of the mold base material on the evaluation surface and the accompanying scattering of the scale.
FIG. 2 shows an appearance photograph after the 10th heating test. In the test piece on which the oxide coating layer was formed, no peeling of the scale was confirmed even when heating and cooling were repeated 10 times. On the other hand, in the test piece in which the oxide coating layer was not formed, the oxidation of the surface and the accompanying scattering of the scale were similarly observed from the 1st to the 10th time.
FIG. 3A shows an FE-EPMA reflected electron image observed from the cross-sectional direction after the 10th heating test of the test piece on which the oxide coating layer is formed, FIG. 3B shows an Al element map, and FIG. 3C shows an O element. Show the map. The shading in the element map image corresponds to the concentration of the element to be measured, and the whiter the concentration is. FIG. 3 shows that Al and O are concentrated on the surface of the base material on the coating layer side, and an aluminum oxide layer is formed here. This aluminum oxide layer is a layer of an Al self-oxidation film having a thickness of 1.0 to 2.5 μm formed during application for 3 hours at 1100 ° C. after applying a paint having the composition shown in Table 3. It was confirmed that the test piece having the layer structure defined in the present invention has excellent oxidation resistance.

(Example 2)
Next, an experiment was conducted to confirm the corrosion of the base material by the glass lubricant.
When forging a forged material coated with a glass lubricant using a hot forging die formed with an oxide coating layer, the glass coating agent corrodes the oxide coating layer or the oxide coating layer and the base material. May occur.
First, in order to evaluate the phenomenon that the base material is corroded by the glass lubricant, three test pieces were prepared in which 400 to 500 mg of glass lubricant was applied in the vicinity of the center on the sample processed in the same manner as the comparative material. The prepared test piece was put into a heated furnace, held for 3 hours, and then taken out from the furnace and air-cooled, and a heating test was performed once for 900, 1000, and 1100 ° C., which are temperatures assumed in an actual machine. . Note that the atmosphere in the heating test is air, and all the atmospheres in the tests after this test are also air. Table 4 shows the composition of the glass lubricant used.
FIG. 4A shows a photograph of the sample before the 900 ° C. heating test, and FIG. 4D shows the sample after the 900 ° C. heating test. FIG. 4B shows a photograph of the sample before the 1000 ° C. heat test, (e) after the 1000 ° C. heat test, (c) before the 1100 ° C. heat test, and (f) after the 1100 ° C. heat test. It can be seen that the base metal is corroded by the glass lubricant at 900, 1000 and 1100 ° C., and the reaction becomes more intense as the temperature rises.

  Next, in order to evaluate the corrosion phenomenon in the hot forging die having the layer structure defined in the present invention, after subjecting the test piece prepared in the same manner as the test piece of Example 1 to pre-oxidation treatment, A test piece was prepared by applying 400 to 500 mg of a glass lubricant having the composition shown in Table 4 near the center of the test piece on the coating layer. This test piece simulated the state in which the glass lubricant remained on the working surface (die-sculpture surface) of the die when hot forging using a hot forging die having a layer structure defined in the present invention. Is. Using this test piece, a heating test was performed once in which it was put into a furnace heated to 1100 ° C. where corrosion due to glass lubrication was most intense, held at 1100 ° C. for 3 hours, and then taken out from the furnace and air-cooled. Table 5 shows the heat treatment conditions for the preliminary oxidation treatment of the test piece and the film thickness of the oxide coating layer.

In FIG. Before the heating test of A, (c) shows a photograph after the heating test. Further, in FIG. A photograph after the heating test is shown in FIG. No. In A, the coating layer and the base material were corroded by the glass lubricant. It can be seen that the corrosion test is completely suppressed in the test piece of B.
In FIG. FE-EPMA reflected electron image observed from the cross-sectional direction after embedding the coating layer and base material after pre-oxidation of A in a resin and mirror polishing, (b) element map of Al, (c) element map of O Indicates. In addition, in FIGS. The observation result of B is shown.
No. In A, the thickness of the aluminum oxide layer was as thin as about 0.5 μm, which was insufficient as a corrosion barrier layer for the glass lubricant. On the other hand, no. In B, it can be seen that an aluminum oxide layer made of Al self-oxidized film having a thickness of 1.0 to 2.5 μm is formed to have a layer structure defined in the present invention. No. It was confirmed that the test piece B could prevent corrosion by the glass lubricant.

(Example 3)
As a base material, it has the composition shown in Table 6, and the oxide coating layer shown in Table 3 is formed on the molding surface (working surface) and a mold having a diameter of 300 mm and a height of 100 mm is used. The prevention effect of oxidation and scale scattering and the corrosion inhibition effect by the glass lubricant were evaluated.

The evaluation was constant temperature forging in which both the mold and the forging material were heated to 980 ° C. A Ni-based alloy was used as the forging material, and a glass lubricant shown in Table 4 was used as the lubricant, and isothermal forging in which a stress of about 150 MPa at the maximum was applied to the molding surface of the mold was performed twice. The pre-oxidation before forging is held at 980 ° C. for 1 hour after holding at 900 ° C. for 1 hour.
Fig. 8 (a) shows a photograph of the molding surface of the mold after the application of an oxide paint mainly composed of Si as an oxide coating layer, and Fig. 8 (b) shows the molding of the mold after the isothermal forging. A photograph of the surface is shown. It can be seen that the oxide coating layer formed on the molding surface of the mold was sufficiently maintained even though a slight peeling portion was confirmed in the mold carved surface by the constant temperature forging. Further, it can be seen that oxidation of the mold base material and the accompanying scattering of the scale are prevented on almost all the molding surfaces, and corrosion by the glass lubricant is suppressed.

From the above results, the hot forging die having the layer structure of the present invention has high oxidation resistance even when heating and cooling are repeated, and can prevent oxidation of the die surface and accompanying scale scattering. It was confirmed that the mold could be prevented from being corroded by the glass lubricant.
From this, in the hot (constant temperature) forging of difficult-to-work materials that require glass lubrication, it is possible to more reliably perform hot forging in the atmosphere.

Claims (2)

In mass%, W: 10.3-11.0%, Mo: 9.0-11.0%, Al: 5.8-6.8%, and the balance is Ni and inevitable impurities A hot forging die including a base material having a composition made of a Ni-base superalloy,
At least one of the molding surface and the side surface of the hot forging die has an oxide coating layer mainly composed of Si,
A hot forging die having an aluminum oxide layer having a thickness of 1.0 to 5.0 μm between the base material and the oxide coating layer. A forged product manufacturing method for hot forging a heated forging material with an upper die and a lower die, wherein the forged product uses the hot forging die according to claim 1 as the upper die and the lower die. Production method.