Heat-resistant alloy having superior corrosion resistance and impact resistance, member for lime calcination furnace, and incinerator grate

Abstract

To provide a heat-resistant alloy having superior corrosion resistance to corrosive substances derived from fuel discharged from a burner produced during lime calcination and having superior impact resistance so that chipping or the like is unlikely to occur, and to provide a member for a lime calcination furnace and an incinerator grate manufactured from the heat-resistant alloy.SOLUTION: A heat-resistant alloy comprises, in mass%, C: 0.35-0.55%, Si: 1.0-2.5%, Mn: 1.5% or less, Cr: 27.0-30.0%, and Ni: 47.0-50.0%, with the balance being Fe and unavoidable impurities, and contains neither W nor Co, wherein the heat-resistant alloy is preferably used for a member for a lime calcination furnace or an incinerator grate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heat-resistant alloy having excellent corrosion resistance and impact resistance, and to a lime kiln component and an incinerator grate made from the alloy. [Background technology]

[0002] Lime kilns are calcination facilities used to produce quicklime for use in industries such as steel, chemicals, and paper. Rotary kilns (also called rotary kilns) are preferably used as such lime kilns. A rotary kiln is a calcination furnace in which materials to be treated are loaded into a horizontal, cylindrical heating furnace body with a slight slope, which rotates slowly. The materials are then heated and discharged from the outlet while moving toward the outlet using the slope of the heating furnace body. In a lime kiln using a rotary kiln, carbon dioxide escapes from the loaded limestone and dolomite, turning them into quicklime and lightly burned dolomite. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2021 / 132350 Summary of the Invention [Problem to be solved by the invention]

[0004] In lime kilns, a preheating chamber and a burner are located on either side of a rotary kiln. Washed limestone and dolomite are loaded into the preheating chamber, and the burner heats the rotary kiln. Powdered limestone accumulates in the preheating chamber. These deposits are heated by the hot air generated by the rotary kiln, generating gas. Because these deposits and gases contain corrosive substances derived from the fuel emitted from the burner, there is a demand for improved corrosion resistance in lime kiln components. Furthermore, components with excellent impact resistance are required because chipping due to impact requires replacement. Meeting these demands will extend the life of components and contribute to cost reduction. While not intended for lime kiln applications, Patent Document 1 proposes an example of a Ni-based alloy that can be used as heat- and corrosion-resistant parts for rotary kilns used in the production of electrode materials for lithium-ion batteries, solid-state batteries, and other devices.

[0005] In addition to the lime kilns mentioned above, grates used in incinerators such as stoker-type incinerators (hereinafter referred to as incinerator grates) are also required to be corrosion-resistant and impact-resistant. Heat-resistant steels such as SCH2, SCH11, and SCH13 are used for such incinerator grates, but when high-calorie waste is incinerated, the incinerator grates are subject to wear, so a material with excellent corrosion resistance is required.

[0006] The present invention has been made to solve the above-mentioned problems, and its object is to provide a heat-resistant alloy that has excellent corrosion resistance against high-temperature oxidation in lime kilns and refuse incinerators, and also has excellent impact resistance that makes it less likely to chip or break when subjected to impact, as well as lime kiln components and incinerator grates made from this heat-resistant alloy. [Means for solving the problem]

[0007] In the course of research to solve the above problems, the inventors have discovered a novel heat-resistant alloy that exhibits the excellent corrosion resistance required for components of lime kilns by varying the alloy composition based on heat-resistant steel, and have completed the present invention. They have also discovered that by manufacturing grates (also called incinerator grates) used in incinerators such as stoker-type incinerators from the heat-resistant alloy of the present invention, it is possible to obtain incinerator grates that have excellent corrosion resistance and impact resistance.

[0008] The heat-resistant alloy according to the present invention is characterized by containing, by mass%, C: 0.35-0.55%, Si: 1.0-2.5%, Mn: 1.5% or less, Cr: 27.0-30.0%, Ni: 47.0-50.0%, the balance being Fe and unavoidable impurities, and not containing W or Co.

[0009] According to this invention, since the heat-resistant alloy is composed of the above-mentioned composition, it has excellent corrosion resistance against high-temperature oxidation in lime kilns and refuse incinerators. Furthermore, it has excellent impact resistance, making it less likely to chip due to impact. As a result, the life of the components can be extended, contributing to cost reduction. Note that Fe is the balance other than C, Si, Mn, Cr, Ni, and unavoidable impurities. In this application, "not containing W and Co" is understood to include a range of 0% (not containing) to 0.50% (substantially not containing).

[0010] The heat-resistant alloy according to the present invention is preferably used for components for lime kilns, such as components for a preheating chamber for preheating raw materials in a rotary kiln, and components for the rotary kiln.

[0011] A lime kiln component according to the present invention is characterized in that it is manufactured from the corrosion-resistant heat-resistant alloy according to the present invention.

[0012] The heat-resistant alloy according to the present invention is preferably used for incinerator grates. According to this invention, by manufacturing an incinerator grate for use in an incinerator such as a stoker-type incinerator from the heat-resistant alloy according to the present invention, the incinerator grate can have excellent corrosion resistance and impact resistance.

[0013] The incinerator grate according to the present invention is characterized in that it is made of the corrosion-resistant heat-resistant alloy according to the present invention. [Effects of the Invention]

[0014] The present invention provides a heat-resistant alloy that is highly resistant to corrosion caused by high-temperature oxidation in lime kilns and refuse incinerators, and also has excellent impact resistance that makes it less susceptible to chipping due to impact, as well as lime kiln components and incinerator grates made from the heat-resistant alloy, which can extend the service life of the components and contribute to cost reduction. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing an example of a lime burning furnace to which a member made of a heat-resistant alloy according to the present invention is preferably applied. [Figure 2] FIG. 1 is an explanatory diagram of a corrosion test method. DETAILED DESCRIPTION OF THE INVENTION

[0016] The heat-resistant alloy according to the present invention, and the lime kiln component and incinerator grate using the same will be described below. Note that the following embodiment is merely an example of the present invention, and the present invention should not be construed as being limited to this embodiment.

[0017] [Heat-resistant alloy] The heat-resistant alloy according to the present invention is characterized by containing, by mass%, 0.35-0.55% C, 1.0-2.5% Si, 1.5% or less Mn, 27.0-30.0% Cr, and 47.0-50.0% Ni, with the balance being Fe and unavoidable impurities, and containing no W or Co. Preferably, the alloy contains, by mass%, 0.40-0.50% C, 1.4-2.1% Si, 0.8-1.2% Mn, 27.5-29.0% Cr, and 47.5-48.5% Ni, with the balance being Fe and unavoidable impurities. Because this heat-resistant alloy has the above composition, it has excellent corrosion resistance against high-temperature oxidation in lime kilns and waste incinerators. Furthermore, it has excellent impact resistance, making it less susceptible to chipping due to impact. As a result, the life of components can be extended, contributing to cost reduction.

[0018] Each component will be explained below. Note that "%" in the composition indicates mass % (weight %).

[0019] (C: 0.35 to 0.55%) Carbon (C) is an element necessary for the formation of carbides and the hardening of the matrix. It is an essential component for improving mechanical properties (impact resistance and wear resistance) and castability through solid solution hardening and precipitation hardening of chromium carbides. However, because the formation of chromium carbides promotes intergranular corrosion, from the viewpoint of corrosion resistance, it is desirable that the carbon content not be too high. Addition of less than 0.35% results in a small amount of carbide formation and a tendency for the matrix hardness to decrease, which may result in insufficient mechanical properties (impact resistance and wear resistance) in the lime kiln components and incinerator grates that are preferably used in the present invention. Addition of more than 0.55% results in a large amount of carbide, which may increase intergranular corrosion and result in insufficient corrosion resistance. Therefore, in the present invention, the lower limit of the C content is set to 0.35% and the upper limit to 0.55%. The preferred range of the C content is 0.40 to 0.50%.

[0020] (Si: 1.0 to 2.5%) Silicon (Si) exerts a deoxidizing effect during melting and refining, and improves the flow of molten metal during casting. However, when the Si content exceeds a certain level, this effect saturates, and if the Si content is excessive, the toughness of the heat-resistant alloy may decrease. For this reason, in the present invention, the lower limit of the Si content is set to 1.0% and the upper limit to 2.5%. The preferred range of Si content is 1.4 to 2.1%.

[0021] (Mn:1.5% or less) Manganese (Mn) acts as a deoxidizing agent and a desulfurizing agent, and is also 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 mechanical properties (impact resistance and wear resistance) decrease. For this reason, in the present invention, the upper limit of the Mn content is set to 1.5%. The lower limit can be set to 0.8%. The preferred Mn content is 0.8 to 1.2%.

[0022] (Cr: 27.0 to 30.0%) 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 on the alloy surface, suppressing corrosion of the base material. However, if added in excess, toughness may decrease. For this reason, in the lime kiln components and incinerator grates applications that are preferably applied in the present invention, the lower limit of the Cr content is set to 27.0% and the upper limit to 30.0%. The preferred Cr content is 27.5 to 29.0%.

[0023] (Ni: 47.0 to 50.0%) Ni (nickel) is a preferred heat-resistant alloy component, and is excellent in corrosion resistance, high-temperature strength, wear resistance, etc. In lime kiln components and incinerator grates, which are preferably used in the present invention, the Ni content is in the range of 47.0 to 50.0%. The preferred Ni content is 47.5 to 48.5%. Note that if the Ni content exceeds 50%, costs tend to increase and the effects of each property become less pronounced, so the Ni content is set to 50% or less.

[0024] (Remainder and unavoidable impurities) Fe (iron) is the base metal that constitutes the remainder of this heat-resistant alloy. Fe-based heat-resistant steels are used as kiln components, but the present invention uses an Fe-based alloy containing the above-mentioned components, making it suitable as a heat-resistant alloy material for lime kilns and incinerator grates, and it has excellent corrosion resistance and impact resistance. In the present invention, the Fe content as the remainder is the content remaining after subtracting the main elements (C, Si, Mn, Cr, Ni) and inevitable impurities, and can be said to be in the range of, for example, approximately 14.4 to 24.7%.

[0025] Inevitable impurities are elements that may be unavoidably introduced due to the conditions of raw materials, materials, manufacturing equipment, etc., and the type and content of these elements are not particularly limited. Examples of such inevitable impurities include P, S, Sn, As, Pb, Al, Ti, Mo, V, and Nb, each of which may be present in a range of 0 (absent) to 0.5%. It is assumed that these inevitable impurities and their contents do not impair the effects of the present invention. Among these inevitable impurities, P and S are not particularly limited, but it is desirable to keep them within the ranges normally contained, such as P: 0.04% or less and S: 0.04% or less, to ensure castability. As with ordinary heat-resistant steels, the presence of inevitable impurity elements other than P and S within the range normally contained as inevitable impurities is also acceptable to ensure castability.

[0026] The heat-resistant alloy according to the present invention is characterized by being free of or substantially free of W and Co. W and Co may be present in small amounts (substantially free amounts) that do not impair the effects of the present invention, for example, 0 to 0.50%. However, if the W content exceeds this amount, particularly 4.0% or more, the impact resistance deteriorates, as can be seen from the results of Comparative Example 4 described below, and the intended objective of the present invention cannot be achieved. Furthermore, if the Co content exceeds this amount, particularly 4.0% or more, it is undesirable because it increases costs. For these reasons, the heat-resistant alloy according to the present invention does not contain W or Co (0%) or substantially does not contain W or Co (0.50% or less).

[0027] (Manufacturing method) The heat-resistant alloy according to the present invention is obtained by preparing raw materials having the above-described composition, blending the prepared raw materials, melting them in air, and air-casting the resulting molten metal. The raw materials can be prepared by preparing raw materials whose respective component compositions are known, and then weighing them to achieve the target component composition. The melting is performed by blending the prepared raw materials and melting them in air. The melting temperature and other conditions are not particularly limited, and known methods suitable for the heat-resistant alloy can be employed. The casting is performed by air-casting the melted metal. The casting temperature, heat treatment, slow cooling, and other conditions are not particularly limited, and known methods suitable for the heat-resistant alloy can be employed.

[0028] [Lime kiln components] The lime kiln component according to the present invention is manufactured from the heat-resistant alloy according to the present invention. Examples of lime kiln components include components used in lime kilns. In particular, components that may be affected by corrosive substances derived from the fuel released from the burner, such as components of the furnace body and inner wall of a rotary kiln, components of the preheating chamber and inner wall, and components of the burner and inner wall, can be mentioned. Manufacturing such components from the heat-resistant alloy according to the present invention can extend the life of the lime kiln component, contributing to cost reduction.

[0029] Fig. 1 is a schematic diagram showing an example of a lime kiln 1 to which members made of the heat-resistant alloy according to the present invention are preferably applied. The shape of the lime kiln 1 is not particularly limited, but one example is one in which a preheating chamber 3 and a burner section 4 are installed on either side of a rotary kiln 2, as shown in Fig. 1.

[0030] The illustrated rotary kiln 2 has a cylindrical heating furnace body 2a around which roll members 2b are mounted, and these roll members 2b are placed on rotating rollers 2c, with the heating furnace body 2a rotated by a drive unit (not shown). The raw materials to be calcined in the rotary kiln 2 are continuously supplied to the heating furnace body 2a by a raw material charging device 5, such as a screw conveyor. As the heating furnace body 2a rotates, the raw materials are heated as they move downstream within the furnace, and undergo heat treatments such as calcination, pre-calcination, roasting, and reduction. The processed quicklime is discharged from a discharge port.

[0031] In this example of lime kiln 1, washed limestone and dolomite are charged into preheating chamber 3, and burner section 4 heats rotary kiln 2. Powdered limestone accumulates in preheating chamber 3, and the deposits are heated by the hot air generated when rotary kiln 2 is heated, generating gas. The lime kiln components according to the present invention are made of a heat-resistant alloy that has excellent corrosion resistance against high-temperature oxidation in the lime kiln and also excellent impact resistance, thereby achieving a longer service life for the components and contributing to cost reduction.

[0032] [Incinerator grate] The incinerator grate is manufactured from the heat-resistant alloy according to the present invention. Examples of the incinerator grate include grates used in stoker-type refuse incinerators and industrial waste incinerators (also called industrial waste incinerators). The shape and type of the incinerator grate are not limited, and various known incinerator grates can be used. For example, the grate may be not only a typical air-cooled type but also a water-cooled type, and may be not only a movable grate but also a fixed grate. [Example]

[0033] The present invention will be explained in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0034] [Example 1] A raw material was prepared so that the alloy obtained after casting would have a composition, in mass%, of C: 0.49%, Si: 1.7%, Mn: 1.3%, Cr: 28.5%, Ni: 48.4%, and the remainder Fe. The raw material was air-melted and then air-cast (casting temperature: 1500°C) to obtain the alloy of Example 1. The alloy composition obtained was consistent with the composition described above. Note that this alloy did not contain W or Co.

[0035] [Example 2] A raw material was prepared so that the alloy obtained after casting would have a composition, in mass%, of C: 0.52%, Si: 1.8%, Mn: 1.0%, Cr: 28.4%, Ni: 47.4%, and the remainder Fe. The raw material was melted in the same manner as in Example 1 and then cast to obtain the alloy of Example 2. The alloy composition obtained was consistent with the composition described above. Note that this alloy did not contain W or Co.

[0036] [Example 3] A raw material was prepared so that the alloy obtained after casting would have a composition, in mass%, of C: 0.47%, Si: 1.8%, Mn: 1.1%, Cr: 27.2%, Ni: 49.5%, and the remainder Fe. The raw material was melted in the same manner as in Example 1 and then cast to obtain the alloy of Example 3. The alloy composition obtained was consistent with the composition described above. Note that this alloy did not contain W or Co.

[0037] [Comparative Examples 1 to 4] Alloys of Comparative Examples 1 to 4 having the component compositions shown in Table 1 were obtained in the same manner as in Examples 1 to 3.

[0038] [Component composition] The component compositions of the alloys of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1. The elemental analysis of the alloys obtained was the result of measurement using an emission spectrometer. In Table 1, "%" stands for mass % (weight %). The symbols in the remarks column are JIS symbols that indicate known heat-resistant steels.

[0039] [Table 1]

[0040] [Corrosion resistance test] The corrosion resistance test was performed using the corrosion resistance test apparatus shown in Figure 2. Measurements were performed in accordance with JIS Z2293, "Salt Immersion and Salt Buried High-Temperature Corrosion Test Method for Metallic Materials." Test specimens (10 mm long, 10 mm wide, 2 mm thick) from Examples 1 to 3 and Comparative Examples 1 to 4 were buried in ash and heated (800°C, 120 hours) while a mixed gas was flowing through them. The ash used for the lime kiln corrosion test was powdered limestone deposited in the preheating chamber 3 of the lime kiln 1. Ash collected from an actual industrial waste kiln was also used for the industrial waste kiln corrosion test. After the test, the test specimens were cut in half, and the cross-sectional thickness was measured to calculate the amount of corrosion (μm). The results are shown in Table 2. The corrosion resistance was evaluated as follows: when the corrosion amount was 15 μm or less, it was marked with "◯" and evaluated as having excellent corrosion resistance; when the corrosion amount was more than 15 μm, it was marked with "△" and evaluated as having poor corrosion resistance.

[0041] [Impact resistance test] The impact resistance test was carried out using a Charpy impact tester in accordance with JIS Z2242 "Charpy impact test method for metallic materials" for the test pieces of Examples 1 to 3 and Comparative Examples 1 to 4. The results are shown in Table 2. The impact resistance was evaluated as follows: 2 The above items are marked with a "〇" and evaluated as having excellent impact resistance, with an impact value of 7J / cm 2 Those with a value of less than "B" were evaluated as not being excellent in impact resistance.

[0042] [Table 2]

[0043] [result] From the results in Table 2, the corrosion amounts of the alloys of Examples 1 to 3 in the lime kiln corrosion test were smaller than those of the alloys of Comparative Examples 1 to 3, indicating that the alloys of Examples 1 to 3 exhibit superior corrosion resistance in lime kilns compared to the alloys of Comparative Examples 1 to 3. Furthermore, the corrosion amounts of the alloys of Examples 1 to 3 in the industrial waste furnace corrosion test were smaller than those of the alloys of Comparative Examples 1 to 4, indicating that the alloys of Examples 1 to 3 exhibit superior corrosion resistance in incinerator grates used in industrial waste furnaces compared to the alloys of Comparative Examples 1 to 4. Furthermore, the impact values ​​of the alloys of Examples 1 to 3 were larger than those of the alloys of Comparative Examples 1, 2, and 4, indicating that the alloys of Examples 1 to 3 exhibit superior impact resistance compared to the alloys of Comparative Examples 1, 2, and 4. These results reveal that increasing the Ni content reduces the corrosion amount, but the inclusion of W reduces the impact value and makes the alloys more susceptible to cracking. [Explanation of symbols]

[0044] 1 Lime kiln 2. Rotary kiln 2a Furnace body 2b Roll member 2c Rotating roller 3 Preheating chamber 4 Burner section 5 Raw material input device

Claims

1. A corrosion-resistant heat-resistant alloy comprising, by mass%, 0.35 to 0.55% C, 1.0 to 2.5% Si, 1.5% or less Mn, 27.0 to 30.0% Cr, and 47.0 to 50.0% Ni, with the balance being Fe and unavoidable impurities, and not containing W or Co.

2. The corrosion-resistant heat-resistant alloy according to claim 1, which is used for components of a lime kiln.

3. A component for a lime kiln, characterized in that it is made of the corrosion-resistant heat-resistant alloy according to claim 1 or 2.

4. The corrosion-resistant, heat-resistant alloy according to claim 1, which is used for an incinerator grate.

5. An incinerator grate made of the corrosion-resistant heat-resistant alloy according to claim 1 or 4.

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