Nickel-based heat-resistant casting alloy, vacuum carburizing furnace components and incinerator grates using the same

Abstract

To more economically provide a nickel group heat-resistant casting alloy which maintains a predetermined component composition and is excellent in corrosion resistance, high temperature strength and abrasion resistance without using a high-cost device using vacuum melting and vacuum casting, and a member for a vacuum carburization furnace and an incinerator fire grate using the same.SOLUTION: A nickel group heat-resistant casting alloy contains, by mass%, 0.05-0.15% C, 0.25-0.75% Si, 0.30-1.00% Mn, 20.00-24.00% Cr, 1.00-3.00% Mo, 13.00-15.00% W, 4-35 ppm H, 15-300 ppm O, and the Ni with inevitable impurities.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a nickel-based heat-resistant cast alloy, and a vacuum carburizing furnace component and an incinerator grate each using the same. [Background technology]

[0002] The vacuum carburizing heat treatment method is becoming increasingly popular as an excellent method for manufacturing high-performance carburized heat-treated products such as gears, shafts, etc. The vacuum carburizing heat treatment method is characterized by its high heat treatment temperature of 980°C, which has the advantage of shortening the heat treatment time compared to the conventional gas carburizing heat treatment method, which has a heat treatment temperature of about 930°C, thereby increasing productivity.

[0003] The increase in heat treatment temperature during vacuum carburizing heat treatment affects the heat resistance of the heat treatment components (such as tray components) used in vacuum carburizing heat treatment, and conventional heat-resistant steels (heat-resistant steels defined by JIS) such as SCH13 and SCH21 are likely to cause operational troubles such as deformation, cracks, and breakage even after short periods of use, as well as increased operating costs. To solve these problems, nickel-based heat-resistant casting alloys have come to be used.

[0004] There are various types of nickel-based heat-resistant casting alloys, and when used for vacuum carburizing heat treatment, nickel-based heat-resistant casting alloys with a composition that contains a lot of Al, an active alloying element, have been adopted to take advantage of Ni3Al's role in increasing heat resistance strength. However, nickel-based heat-resistant casting alloys that contain a lot of Al must be produced using expensive equipment such as vacuum melting and vacuum casting because they need to be isolated from oxygen, which means that the productivity is low and the material is expensive, and the final products such as heat treatment components manufactured are inevitably expensive.

[0005] Meanwhile, the grates of stoker-type combustion furnaces are also made of heat-resistant steels such as SCH2, SCH11, and SCH13, but due to the demand for longer grate life and lower maintenance costs, importance is being placed on corrosion resistance in high-temperature corrosive atmospheres. For this reason, the use of nickel-based heat-resistant cast alloys is being considered.

[0006] The argon gas shielding during casting is described in Patent Document 1 and the like. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2012-528943 A Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above-mentioned background art, an object of the present invention is to provide a nickel-base heat-resistant cast alloy which maintains a predetermined component composition and is excellent in corrosion resistance, high-temperature strength, wear resistance, etc., without using high-cost equipment such as vacuum melting or vacuum casting, and to provide a vacuum carburizing furnace component and an incinerator grate which use the same in a more economical manner. [Means for solving the problem]

[0009] In the course of research to solve the above problems, the present inventors focused on the amount of gas components contained in nickel-based heat-resistant cast alloys, and discovered that by setting the amount of contained gas components within a predetermined range, nickel-based heat-resistant cast alloys having excellent corrosion resistance, high-temperature strength, wear resistance, etc. can be produced more inexpensively, and thus completed the present invention.

[0010] (1) A nickel-base heat-resistant casting alloy according to the present invention is characterized by containing, by mass%, C: 0.05-0.15%, Si: 0.25-0.75%, Mn: 0.30-1.00%, Cr: 20.00-24.00%, Mo: 1.00-3.00%, W: 13.00-15.00%, H: 4-35 ppm, O: 15-300 ppm, and the balance being Ni and unavoidable impurities.

[0011] According to the present invention, since the nickel-based heat-resistant casting alloy contains hydrogen and oxygen within the above ranges, it can be said that this nickel-based heat-resistant casting alloy is not produced by vacuum melting and vacuum casting (where the hydrogen and oxygen contents are extremely small), but is produced by air melting and casting in an oxygen-blocked environment. Such a nickel-based heat-resistant casting alloy is excellent in corrosion resistance, high-temperature strength, wear resistance, etc., and can be produced by a low-cost method that contains hydrogen and oxygen within a specified range. The balance, Ni content, is within the range of 56.1 to 65.4% by mass.

[0012] A preferred example of the nickel-base heat-resistant casting alloy according to the present invention contains, by mass%, 0.07-0.13% C, 0.27-0.73% Si, 0.42-0.65% Mn, 20.50-23.00% Cr, 1.20-2.80% Mo, 13.20-14.80% W, 4-35 ppm H, 15-300 ppm O, and the balance being Ni and unavoidable impurities. The Ni content, which is the balance, is within the range of 57.9-64.3% by mass.

[0013] The nickel-base heat-resistant casting alloy according to the present invention contains, by mass %, Co: 0-5.00%, Al: 0-0.50%, and Fe: 0-3.00%, and the inevitable impurities are P, S, Ti, V, Nb, and the like.

[0014] (2) A vacuum carburizing furnace component according to the present invention is characterized in that it is manufactured from the nickel-base heat-resistant cast alloy according to the present invention. Examples of the vacuum carburizing furnace component include components used in vacuum carburizing furnaces and components repeatedly placed in vacuum carburizing furnaces, such as trays and base members.

[0015] (3) An incinerator grate according to the present invention is characterized in that it is manufactured from the nickel-base heat-resistant cast alloy according to the present invention.

[0016] (4) A method for producing a nickel-base heat-resistant cast alloy according to the present invention comprises, by mass%, 0.05-0.15% C, 0.25-0.75% Si, 0.30-1.00% Mn, 20.00-24.00% Cr, 1.00-3.00% Mo, 13.00-15.00% W, 4-35 ppm H, 15-300 ppm O, and the balance being Ni and unavoidable impurities, The method comprises the steps of: preparing raw materials for a nickel-base heat-resistant casting alloy; blending the prepared raw materials and melting the raw materials in air while shielding the surface of the molten metal with an inert gas to block the atmosphere; and casting the molten metal in air directly from a melting furnace without using a ladle.

[0017] According to the present invention, the alloy is melted while being shielded from the atmosphere by inert gas shielding, and is cast directly from the melting furnace without using a ladle, so that it is possible to produce a nickel-base heat-resistant cast alloy having the above composition containing hydrogen and oxygen within a predetermined range. This production method is less expensive than the expensive methods of vacuum melting and vacuum casting, and it is possible to more economically produce a nickel-base heat-resistant cast alloy having the above composition and excellent corrosion resistance, high-temperature strength, wear resistance, etc. Effect of the Invention

[0018] According to the present invention, it is possible to provide a nickel-based heat-resistant casting alloy having excellent corrosion resistance, high-temperature strength, wear resistance, etc., and a vacuum carburizing furnace component and an incinerator grate using the same in a more economical manner. In particular, since the nickel-based heat-resistant casting alloy contains hydrogen and oxygen within the above-mentioned ranges, it can be said that the nickel-based heat-resistant casting alloy is not produced by vacuum melting and vacuum casting, but is produced by atmospheric melting and casting in an oxygen-blocked state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the nickel-based heat-resistant cast alloy according to the present invention, and the vacuum carburizing furnace component and the incinerator grate using the same will be described in detail based on the embodiments. Note that the following embodiment is merely an example according to the present invention, and the present invention should not be interpreted as being limited to the embodiment.

[0020] [Nickel-based heat-resistant casting alloy] The nickel-base heat-resistant casting alloy according to the present invention is characterized by containing, by mass%, C: 0.05-0.15%, Si: 0.25-0.75%, Mn: 0.30-1.00%, Cr: 20.00-24.00%, Mo: 1.00-3.00%, W: 13.00-15.00%, H: 4-35 ppm, O: 15-300 ppm, and the balance being Ni and unavoidable impurities.

[0021] Since this nickel-based heat-resistant casting alloy contains hydrogen and oxygen within the above ranges, it can be said that this nickel-based heat-resistant casting alloy is not produced by vacuum melting and vacuum casting, but by atmospheric melting and casting in which oxygen is blocked. This nickel-based heat-resistant casting alloy is excellent in corrosion resistance, high-temperature strength, wear resistance, etc., and can be produced by a low-cost method that contains hydrogen and oxygen within a specified range. The balance, Ni content, is within the range of 56.1 to 65.4% by mass.

[0022] Each component will be described below. Note that "%" in expressing the composition means mass % (weight %).

[0023] (C: 0.05~0.15%) C (carbon) is an element necessary for the formation of carbides and for increasing the hardness of the matrix, and is an essential component for improving wear resistance and castability through solid solution hardening and precipitation hardening of chromium carbides. On the other hand, since the formation of chromium carbides promotes intergranular corrosion, it is preferable that the amount of carbon is small from the viewpoint of corrosion resistance, and in the present invention, the C content is in the range of 0.05 to 0.15%. If the C content is less than 0.05%, the amount of carbides generated is too small and the hardness of the matrix is ​​reduced, so that the wear resistance may be insufficient. On the other hand, if the C content exceeds 0.15%, the amount of carbides increases, intergranular corrosion increases, and the corrosion resistance may be insufficient. The preferred C content is 0.07 to 0.13%. Typically, the C content is about 0.10%.

[0024] (Si: 0.25~0.75%) Silicon (Si) exerts a deoxidizing effect during melting and refining, and improves the fluidity of the molten metal during casting. On the other hand, when the Si content exceeds a certain amount, the effect is saturated, and when the Si content is contained in excess, the toughness of the nickel-based heat-resistant casting alloy decreases. For this reason, in the present invention, the upper limit of the Si content is set to 0.75%. The preferred Si content is 0.27 to 0.73%. Typically, the preferred embodiment has a Si content of about 0.50%.

[0025] (Mn: 0.3-1.00%) Manganese (Mn) acts as a deoxidizing agent and a desulfurizing agent, and is an element that improves castability and hardenability, and has the effect of suppressing the formation of δ-ferrite. On the other hand, if a large amount of Mn is contained, high temperature oxidation resistance decreases, creep rupture strength deteriorates, and wear resistance decreases. For this reason, in the present invention, the upper limit of the Mn content is set to 1.00%. The preferred Mn content is 0.42 to 0.65%. Typically, the preferred embodiment has a Mn content of about 0.50%.

[0026] (Cr:20.00~24.00%) Cr (chromium) is an essential element for improving high-temperature corrosion resistance. It reacts with oxygen in the atmosphere to form a protective chromium oxide film against corrosion on the alloy surface, suppressing corrosion of the base material. However, if the content is excessive, toughness may decrease. For this reason, in the present invention, the lower limit of the Cr content is set to 20.00% and the upper limit is set to 24.00%. The preferred Cr content is 20.50 to 23.00%. Typically, the preferred embodiment has a Cr content of about 22.0%.

[0027] (Mo:1.00~3.00%) Mo (molybdenum) is a carbide-forming element and is essential for imparting corrosion resistance and maintaining high-temperature strength. At high temperatures, it easily reacts with S, C, or Si to increase the amount of MoS2, Mo2C, and MoSi2, which increases the effect, but on the other hand, it also causes embrittlement of the alloy. Mo also oxidizes rapidly at temperatures above 500°C, which is likely to deteriorate corrosion resistance. In addition, since it is a rare metal, it is expensive, and from an economical point of view, it is preferable that its content is small. For this reason, in the present invention, the lower limit of the Mo content is 1.00% and the upper limit is 3.00%. The preferred Mo content is 1.20 to 2.80%. Typically, it is desirable that the Mo content is about 2.0%.

[0028] (W:13.00~15.00%) W (tungsten) is an element effective in improving high-temperature strength. In the present invention, the lower limit of the W content is set to 13.00%, and the upper limit is set to 15.00%, to achieve high-temperature strength. The W content is preferably 13.20 to 14.80%. Typically, the W content is preferably about 14.0%.

[0029] (H: 4-35 ppm) H (hydrogen) is 4 to 35 ppm. Since the H content is 35 ppm or less, members made of this nickel-based heat-resistant casting alloy can suppress the occurrence of cracks during use in a high-temperature atmosphere. On the other hand, in order to make the H content less than 4 ppm, the manufacturing process such as melting and mixing of raw materials must be performed in a high-cost vacuum, which increases the manufacturing cost. However, since the H content of this nickel-based heat-resistant casting alloy is 4 ppm or more, it can be manufactured at low cost by melting and casting in an oxygen-blocked atmosphere. The preferred H content is 4 to 32 ppm.

[0030] (O: 15-300 ppm) O (oxygen) is 15 to 300 ppm. Since the O content is 300 ppm or less, members made of this nickel-based heat-resistant cast alloy can suppress the occurrence of blowholes during welding repair. On the other hand, in order to make the O content less than 15 ppm, the manufacturing process such as melting and mixing of raw materials must be performed in a high-cost vacuum, which increases the manufacturing cost. However, since this nickel-based heat-resistant cast alloy has an O content of 15 ppm or more, it can be manufactured at low cost by melting and casting in an oxygen-blocked atmosphere. The preferred O content is 20 to 250 ppm.

[0031] (Ni: remainder) Ni (nickel) is the base metal constituting the remainder of this nickel-based heat-resistant casting alloy. A nickel-based alloy containing each component element in a predetermined range is preferable as a heat-resistant casting alloy, and is excellent in corrosion resistance, high-temperature strength, wear resistance, etc. In the present invention, the Ni content is within the range of 56.1 to 65.4%.

[0032] (Co, Al, Fe) Co, Al, and Fe may be contained as necessary. The Co content is 0 to 5.00%, the Al content is 0 to 0.50%, and the Fe content is 0 to 3.00%. The preferred contents of Co, Al, and Fe are Co: 0.50 to 2.00%, Al: 0.20 to 0.40%, and Fe: 0.20 to 1.00%.

[0033] (Inevitable impurities) Inevitable impurities are elements that are inevitably introduced depending on the conditions of raw materials, supplies, manufacturing equipment, etc., and examples of such impurities include P, S, Ti, V, and Nb. Each of these is contained in a range of 0 (not included) to 0.05%, preferably 0 to 0.02%.

[0034] (Manufacturing method) The method for producing a nickel-base heat-resistant cast alloy contains, by mass%, 0.05-0.15% C, 0.25-0.75% Si, 0.30-1.00% Mn, 20.00-24.00% Cr, 1.00-3.00% Mo, 13.00-15.00% W, 4-35 ppm H, 15-300 ppm O, and the balance being Ni and unavoidable impurities. In detail, the method includes the steps of preparing raw materials for the nickel-base heat-resistant cast alloy, blending the prepared raw materials and melting them in air while shielding the molten metal surface with an inert gas to block the atmosphere, and casting the molten metal directly from a melting furnace without using a ladle when casting the molten metal in air.

[0035] This manufacturing method involves melting while blocking the atmosphere with an inert gas shield and casting directly from the melting furnace without using a ladle, so that it is possible to manufacture at low cost the nickel-base heat-resistant cast alloy having the above composition containing hydrogen and oxygen within the specified ranges. This manufacturing method is less expensive than the expensive methods of vacuum melting and vacuum casting, and can more economically manufacture the nickel-base heat-resistant cast alloy having the above composition and excellent corrosion resistance, high-temperature strength, wear resistance, etc.

[0036] The raw material preparation step is a step of preparing raw materials for the nickel-based heat-resistant cast alloy having the above-mentioned composition. The raw materials can be prepared by preparing raw materials each having a known composition, and weighing them to obtain the target composition.

[0037] The melting process is a process in which the prepared raw materials are mixed and melted in air, and the raw materials are melted while blocking the air by shielding the molten metal surface with an inert gas. This process is characterized in that the molten metal surface is melted in air while blocking oxygen by an inert gas shielding method (e.g., gas shielding with helium, neon, argon, etc. belonging to Group 18 of the periodic table). The melting conditions, such as the melting temperature, are not particularly limited, and known methods suitable for the nickel-based heat-resistant casting alloy can be adopted.

[0038] The casting process is a process in which the molten metal is cast directly from the melting furnace without using a ladle when casting in air. This process is characterized by the fact that the time of exposure to air is shortened by casting directly from the melting furnace without using a ladle when casting in air. The conditions for casting, such as the melting temperature, casting temperature, heat treatment, and slow cooling, are not particularly limited, and known methods suitable for the nickel-based heat-resistant casting alloy can be used.

[0039] [Vacuum carburizing furnace components, incinerator grates] The vacuum carburizing furnace component is manufactured from the nickel-base heat-resistant cast alloy according to the present invention. Examples of the vacuum carburizing furnace component include components used in vacuum carburizing furnaces and components repeatedly inserted into vacuum carburizing furnaces, such as trays and base members. The vacuum carburizing furnace component manufactured from the nickel-base heat-resistant cast alloy according to the present invention has excellent corrosion resistance, high-temperature strength, wear resistance, etc., and can be used for a long period of time even when used repeatedly.

[0040] The incinerator grate is manufactured from the nickel-based heat-resistant cast alloy according to the present invention. An example of the incinerator grate is a grate used in a stoker-type waste incinerator. The shape, type, etc. of the incinerator grate are not limited, and various known grates can be used. For example, the grate includes not only a typical air-cooled type but also a water-cooled type, and includes not only a movable grate but also a fixed grate. EXAMPLES

[0041] The present invention will be explained more specifically with reference to examples, but the present invention is not limited to these examples in any way.

[0042] [Example 1] The prepared raw materials were blended to produce a nickel-based heat-resistant casting alloy (unavoidable impurities: P, S, Ti, V, Nb, etc.) with mass% of C: 0.10%, Si: 0.50%, Mn: 0.50%, Cr: 22.00%, Mo: 2.00%, W: 14.00%, Co: 0.60%, Al: 0.30%, Fe: 0.30%, and the balance Ni: 59.7%. When the blended raw materials were melted in air, the surface of the molten metal was shielded with argon gas to block the atmosphere while melting the raw materials (melting temperature: 1540°C). The argon gas shielding at this time was performed by continuously dripping liquefied argon onto the surface of the molten metal at a rate of 0.8 kg / min. The molten metal was then directly cast from the melting furnace without using a ladle when casting in air (casting temperature: 1540°C).

[0043] [Comparative Example 1] The raw materials were mixed to have the same composition as in Example 1. The mixed raw materials were vacuum melted (degree of vacuum: 0.1 Pa, melting temperature: 1500° C.). The molten metal was then vacuum cast (casting temperature: 1450° C.).

[0044] [Comparative Example 2] 100 kg of nickel-based heat-resistant cast alloy of Comparative Example 1 was prepared. When melting, the surface of the molten alloy was shielded with argon gas to shut out the atmosphere while melting the alloy (melting temperature: 1540°C). The argon gas shielding at this time was performed by continuously dropping liquefied argon onto the surface of the molten alloy at a rate of 0.8 kg / min. The molten alloy was then directly cast from the melting furnace without using a ladle when casting in the atmosphere (casting temperature: 1540°C).

[0045] [Comparative Example 3] 100 kg of the nickel-based heat-resistant cast alloy of Comparative Example 1 was prepared. It was melted in air without argon gas shielding. The molten alloy was then cast directly from the melting furnace (casting temperature: 1540°C) without using a ladle when casting in air.

[0046] [Table 1]

[0047] [Gas analysis] The hydrogen and oxygen contents in nickel-based heat-resistant casting alloys were measured. The analysis was performed using an oxygen, nitrogen and hydrogen analyzer (EMGA-930) manufactured by Horiba Ltd., in accordance with JIS G1239 ("Iron and steel - Oxygen determination method - Inert gas fusion - Near infrared absorption method"). The mass of the measurement sample was 1.0 g. The analysis results are shown in Tables 2 and 3.

[0048] [Table 2]

[0049] [Table 3]

[0050] [Examples 2 to 4] Examples 2 to 4 are the results of experiments carried out to confirm the preferred ranges of hydrogen and oxygen contents, in which the same raw materials as in Example 1 were blended, the blended raw materials were melted while blocking the air under the same conditions as in Example 1, and the molten metal was directly cast under the same conditions as in Example 1. Gas analysis was carried out in the same manner as above.

[0051] [Table 4]

[0052] [Table 5]

[0053] From the hydrogen and oxygen component results in Tables 2 to 5, the nickel-based heat-resistant cast alloys obtained in Examples 1 to 4 have H in the range of 4 to 35 ppm and O in the range of 15 to 300 ppm, and it is considered that the influence on the properties of the nickel-based heat-resistant cast alloy is small. In addition, the H content and O content in Examples 1 to 4 are larger than that in Comparative Example 1, but since they can be manufactured without using expensive equipment (vacuum melting, vacuum forging) as in Comparative Example 1, nickel-based heat-resistant cast alloys excellent in corrosion resistance, high-temperature strength, wear resistance, etc., and vacuum carburizing furnace members and incinerator grates using the same can be provided more economically.

Claims

1. A nickel-based heat-resistant casting alloy comprising, by mass%, 0.05-0.15% C, 0.25-0.75% Si, 0.30-1.00% Mn, 20.00-24.00% Cr, 1.00-3.00% Mo, 13.00-15.00% W, 0.50-2.00% Co, 0.20-0.40% Al, 0.20-1.00% Fe, 4-35 ppm H, 15-300 ppm O, and the balance being Ni and unavoidable impurities.

2. A nickel-based heat-resistant casting alloy comprising, by mass%, 0.07-0.13% C, 0.27-0.73% Si, 0.42-0.65% Mn, 20.50-23.00% Cr, 1.20-2.80% Mo, 13.20-14.80% W, 0.50-2.00% Co, 0.20-0.40% Al, 0.20-1.00% Fe, 4-35 ppm H, 15-300 ppm O, and the balance being Ni and unavoidable impurities.

3. 3. A vacuum carburizing furnace component, characterized in that it is made of the nickel-base heat-resistant cast alloy according to claim 1 or 2.

4. 3. An incinerator grate, characterized in that it is made of the nickel-base heat-resistant cast alloy according to claim 1 or 2.

5. A method for producing a nickel-base heat-resistant casting alloy comprising, by mass%, 0.05 to 0.15% C, 0.25 to 0.75% Si, 0.30 to 1.00% Mn, 20.00 to 24.00% Cr, 1.00 to 3.00% Mo, 13.00 to 15.00% W, 0.50 to 2.00% Co, 0.20 to 0.40% Al, 0.20 to 1.00% Fe, 4 to 35 ppm H, 15 to 300 ppm O, and the balance being Ni and unavoidable impurities, A method for producing a nickel-base heat-resistant cast alloy, comprising the steps of: preparing raw materials for the nickel-base heat-resistant cast alloy; blending the prepared raw materials and melting the raw materials in air while shielding a molten metal surface with an inert gas to block the atmosphere; and casting the molten metal directly from a melting furnace without using a ladle in air casting.

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