Heat-resistant cast steel and grates

Abstract

The objective of this disclosure is to provide heat-resistant cast steel and grates with improved wear resistance and corrosion resistance while suppressing manufacturing costs. [Solution] The present invention provides a heat-resistant cast steel or a grate manufactured by casting, characterized in that its chemical composition includes C: 1.00 to 1.71% by weight, Cr: 16.10 to 31.20% by weight, Si: 1.00 to 2.50% by weight, Mn: 0.50 to 1.00% by weight, Al: 4.00% by weight or less, with the remainder being Fe and impurities.

Description

Technical Field

[0001] The present invention relates to heat-resistant cast steel and fire grates.

Background Art

[0002] Generally, heat-resistant cast steel used as a fire grate in a waste incinerator is required to have properties such as heat resistance, corrosion resistance (anti-corrosion property), and wear resistance.

[0003] For example, Patent Document 1 discloses a technique for improving the above properties by containing a certain amount or more of Cr. Also, Patent Document 1 discloses containing a certain amount or more of Ni for the purpose of improving toughness. Patent Document 2 discloses a technique for improving the above properties by containing a large amount of Cr.

[0004] However, elements such as Cr and Ni are relatively expensive, and there is a problem that the manufacturing cost increases due to the addition of these elements. That is, a material with a balance between the properties such as heat resistance, corrosion resistance, and wear resistance required for heat-resistant cast steel used as a fire grate in a waste incinerator and the cost has been desired. Therefore, the inventors of the present invention have intensively studied heat-resistant cast steel that satisfies the properties required for a fire grate of a waste incinerator, such as heat resistance, corrosion resistance (anti-corrosion property), and wear resistance, while suppressing the manufacturing cost.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] This disclosure aims to provide heat-resistant cast steel and grates with improved wear resistance and corrosion resistance while suppressing manufacturing costs. [Means for solving the problem]

[0007] A heat-resistant cast steel according to one aspect of the present invention is In terms of chemical composition, C: 1.00~1.71% by weight, Cr:16.10~31.20wt%, Si: 1.00~2.50% by weight, Mn: 0.50~1.00% by weight, Al: 4.00% by weight or less, Includes, The remainder contains Fe and impurities. It is characterized by the following: [Effects of the Invention]

[0008] According to the present invention, it is possible to provide heat-resistant cast steel and grates with improved wear resistance and corrosion resistance while suppressing manufacturing costs. [Brief explanation of the drawing]

[0009] [Figure 1] This graph shows the relationship between the ratio of carbon (C) content to chromium (Cr) content and the resulting carbides. [Figure 2] This graph shows the relationship between the volume fraction of carbides and their hardness (Hv). [Figure 3] This graph shows the relationship between the Al or Ni content (weight %) and corrosion loss (g). [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described below with reference to examples, but it is obvious that this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of the invention according to this disclosure are obtained. In addition, each component of the embodiments described below can be combined with one another. Furthermore, in this specification, numerical ranges represented by "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits. In this specification, the term "step" is included not only in the sense of an independent process, but also in the sense of a process that cannot be clearly distinguished from other processes, as long as the intended purpose of that process is achieved.

[0011] [First Embodiment] The heat-resistant cast steel according to this embodiment has a chemical composition of C: 1.00 to 1.71% by weight, Cr: 16.10 to 31.20% by weight, and Al: 4.00% by weight or less. The remainder of the chemical composition of the heat-resistant cast steel includes Fe (iron) and impurities. The chemical composition is described below.

[0012] (C:1.00~1.71wt%) Carbon (C) is an important element for obtaining hardness. By forming carbides with chromium (Cr) and other elements, C contributes to increasing the hardness of heat-resistant cast steel. This increased hardness improves the wear resistance of the heat-resistant cast steel. A certain hardness can be obtained by having a carbon content of 1.00% by weight or more. This certain hardness is, for example, 150 Hv. Here, hardness is a value obtained by measuring the Vickers hardness test.

[0013] A certain level of toughness can be obtained by having a carbon content of 1.71% by weight or less. When used as a grate for a waste incinerator, it is preferable that the heat-resistant cast steel has a certain level of toughness. For this reason, it is more preferable that the carbon content be 1.5% by weight or less.

[0014] (Cr:16.10~31.20wt%) Cr (chromium) is an important element for improving the corrosion resistance of heat-resistant cast steel. Cr in the matrix of heat-resistant cast steel contributes to the improvement of corrosion resistance. When the Cr content is 16.10 wt% or more, good corrosion resistance can be obtained. More preferably, the Cr content is 26.30 wt% or more. Adding Cr improves the corrosion resistance of heat-resistant cast steel, but since Cr is an expensive element, controlling the Cr content to 31.20 wt% or less can suppress the manufacturing cost.

[0015] (Cr / C) Regarding the chemical composition of heat-resistant cast steel, by controlling (Cr / C), the hardness further increases. Here, Fig. 1 shows a graph representing the relationship between the C content, the ratio of the Cr content, and the carbides formed. The horizontal axis of the graph in Fig. 1 is the C content (wt%), and the vertical axis is the Cr content (wt%). The range of carbides formed according to the ratio of the C content and the Cr content is shown. As can be seen from Fig. 1, the type of carbide changes depending on the ratio of the C content and the Cr content. In the range where (Cr / C) is small, M7C3 is likely to be formed. Among the carbides, M 23 M7C3 has a high effect of increasing the hardness of heat-resistant cast steel compared to M6C. Therefore, it is preferable that more M7C3 is formed.

[0016] At least in the range where the C content is 1.00 wt% or more, it is preferable that (Cr / C) is 15 or less. When (Cr / C) is 15 or less, the hardness of heat-resistant cast steel further increases. More preferably, (Cr / C) is 5 or more and 15 or less. The dotted line in the graph of Fig. 1 represents the straight line of (Cr / C) = 15.

[0017] (Al: 4.00 wt% or less) Aluminum (Al) is an important element for improving corrosion resistance. Al improves the corrosion resistance of heat-resistant cast steel by forming Al oxides such as Al2O3. In particular, this oxide layer is dense and chemically stable, maintaining its corrosion-inhibiting properties over long periods. Furthermore, Al has the advantage of being less expensive than chromium (Cr). The effect of adding aluminum to improve corrosion resistance saturates beyond a certain amount; therefore, from a cost perspective, the aluminum content is 4.00% by weight or less.

[0018] The Al content is preferably 1.00 to 2.00% by weight. By ensuring an Al content of 1.00% by weight or more, stable corrosion resistance can be achieved. Corrosion resistance can be ensured by adding Al without adding expensive materials such as Ni. By limiting the Al content to 2.00% by weight or less, stable corrosion resistance can be ensured while keeping costs down.

[0019] The corrosion inhibition effect per unit of additive is maximized when the Al content is 1.00% by weight or less. In other words, an Al content of 1.00% by weight or less is technically and economically optimized from the standpoint of corrosion inhibition effect and cost.

[0020] Heat-resistant cast steel contains silicon (Si). Si improves the corrosion resistance of heat-resistant cast steel by forming Si oxides. From the viewpoint of improving castability, corrosion resistance, and ensuring toughness, the Si content is 1.00% to 2.50% by weight.

[0021] Heat-resistant cast steel contains manganese (Mn). The Mn content is between 0.50% and 1.00% by weight, serving to remove impurities during casting.

[0022] (Remainder) The remainder of the chemical composition of heat-resistant cast steel consists of Fe (iron) and impurities. Impurities refer to components present in the raw materials or those introduced during the manufacturing process, and not intentionally included. Generally, the presence or absence of impurities depends on the degree of refinement of the raw materials. Impurities refer to elements such as P and S. It is preferable to limit these impurities to 0.01% or less in order to fully exhibit the effects of the present invention. Furthermore, since a low impurity content is preferable, there is no need to limit the lower limit, and the lower limit of impurities may be 0%. The remainder of the chemical composition of the heat-resistant cast steel may consist of Fe and impurities.

[0023] The chemical composition may include nickel (Ni) as an impurity. This includes unavoidable impurities that are present in the raw materials or inevitably introduced during the manufacturing process.

[0024] The chemical composition may include molybdenum (Mo) as an impurity.

[0025] (Method for measuring chemical composition) The chemical composition of heat-resistant cast steel is measured using an emission spectrometer (JIS standard) in accordance with JIS G0320.

[0026] The heat-resistant cast steel according to this embodiment is a heat-resistant cast steel that has improved wear resistance and corrosion resistance while suppressing manufacturing costs.

[0027] The heat-resistant cast steel according to this embodiment can be preferably used as a material for constituting a grate. The grate is, for example, a grate for a waste incinerator. The waste incinerator is, for example, a melting furnace or a stoker furnace. The shape of the grate is not limited in any way, and the heat-resistant cast steel according to this embodiment can be applied to various known grates. For example, it can be used in both air-cooled and water-cooled grates, and in both movable and fixed grates.

[0028] [Second Embodiment] The grate according to this embodiment is A grate manufactured by casting, In terms of chemical composition, C: 1.00~1.71% by weight, Cr:16.10~31.20wt%, Si: 1.00~2.50% by weight, Mn: 0.50~1.00% by weight, Al: 4.00% by weight or less, Includes, The remainder contains Fe and impurities.

[0029] The chemical composition of the grate according to this embodiment is the same as that of the heat-resistant cast steel described in the first embodiment, so a detailed explanation is omitted here.

[0030] The method for manufacturing a grate according to this embodiment is not limited to the following methods. The grates may be manufactured by common manufacturing methods. Common manufacturing methods include, for example, casting. Casting means melting metal and pouring it into a mold to create the desired shape.

[0031] The grate according to this embodiment is a grate that has improved wear resistance and corrosion resistance while suppressing manufacturing costs.

[0032] The grate according to this embodiment is, for example, a grate for a waste incinerator. A waste incinerator is, for example, a melting furnace or a stoker furnace. For a melting furnace grate, corrosion resistance is particularly required, so the grate according to this embodiment can be preferably used. For a stoker furnace grate, wear resistance is particularly required, so the grate according to this embodiment can be preferably used. The shape of the grate is not limited in any way, and the grate according to this embodiment can be applied to various known types of grates. For example, it can be used as either an air-cooled or water-cooled grate, and can be used as either a movable or fixed grate.

[0033] (Note) The heat-resistant cast steel and grate according to the above embodiment can be understood, for example, as follows. (1) In terms of chemical composition, C: 1.00~1.71% by weight, Cr:16.10~31.20wt%, Si: 1.00~2.50% by weight, Mn: 0.50~1.00% by weight, Al: 4.00% by weight or less, Includes, The remainder contains Fe and impurities. Heat-resistant cast steel characterized by the following features. (2) The C content is 1.00 to 1.50% by weight. The heat-resistant cast steel according to (1), characterized in that it is a heat-resistant cast steel. (3) The Cr / C ratio is 15 or less. The heat-resistant cast steel according to (1) or (2), characterized in that it is a heat-resistant cast steel according to (1) or (2). (4) The Al content is 1.00 to 2.00% by weight. A heat-resistant cast steel according to any one of (1) to (3), characterized in that (5) The Al content is 1.00% by weight or less. A heat-resistant cast steel according to any one of (1) to (3), characterized in that

[0034] (6) A grate manufactured by casting, In terms of chemical composition, C: 1.00~1.71% by weight, Cr:16.10~31.20wt%, Si: 1.00~2.50% by weight, Mn: 0.50~1.00% by weight, Al: 4.00% by weight or less, Includes, The remainder contains Fe and impurities. A fire grate characterized by the following features. (7) The C content is 1.00 to 1.50% by weight. The fire grate according to (6), characterized in that it is a fire grate. (8) The Cr / C ratio is 15 or less. A grate according to (6) or (7), characterized in that it is a grate. (9) The Al content is 1.00 to 2.00% by weight. A fire grate according to any one of (6) to (8), characterized in that (10) The Al content is 1.00% by weight or less. A heat-resistant cast steel according to any one of (6) to (8), characterized in that... (11) Used as a grate for waste incinerators, A grate according to any one of (6) to (10), characterized in that it is a grate. [Examples]

[0035] The invention described herein will be explained in detail below with reference to examples, but the invention is not limited thereto.

[0036] Heat-resistant cast steels with the chemical compositions shown in Table 1 were prepared. The chemical composition of the cast steel was measured using an emission spectrometer in accordance with JIS G 0320. In Table 1, a dash ("-") indicates that the value was below the detection limit of the instrument.

[0037] The molten raw material was poured into a mold, and casting was carried out.

[0038] (Evaluation of wear resistance) High-temperature hardness tests were conducted on each casting to investigate its wear resistance. Specifically, hardness (HV) was measured under a certain load condition in an Ar gas atmosphere at 600°C. Measurements were performed with n=3, and the arithmetic mean was used as the hardness value. Higher hardness indicates greater wear resistance. The results are shown in Table 1.

[0039] (Evaluation of corrosion resistance) High-temperature corrosion tests were conducted on each casting to investigate its corrosion resistance. Specifically, the test involved burying the test specimens in ash simulating the environment of a waste incinerator and holding them at 600°C for 100 hours. The amount of corrosion was measured from the change in weight before and after the test. The results are shown in Table 1.

[0040] [Table 1]

[0041] As can be seen from the results in Table 1, castings No. 1-4, 6, 7, 10, 11, and 14-18 according to the present invention have a hardness of 150 Hv or higher. Such castings can be preferably used as heat-resistant cast steel for grates.

[0042] Furthermore, higher hardness was achieved in samples No. 1 and 2. This is thought to be due to the Cr / C ratio being 15 or less. Figure 2 shows a graph illustrating the relationship between the volume fraction of carbides and hardness (Hv). As can be seen from Figure 2, samples No. 1-4, 6, 7, 10, 11, and 14-18 (circular plots), which have a carbon content of 1.00 wt% or more, have a hardness of 150 Hv or more. Furthermore, samples No. 1 and 2 (triangular plots), which have a Cr / C ratio of 15 or less, exhibit even higher hardness.

[0043] Figure 3 shows a graph illustrating the relationship between the Al or Ni content (weight %) and corrosion loss (g) for samples No. 14-17. It can be seen that the corrosion loss of samples No. 15 and No. 16, which have only Al added, is similar to that of sample No. 18, which has only Ni added. Furthermore, the Al or Ni content (weight %) in these samples is similar. Therefore, from a manufacturing cost perspective, it is preferable to add less expensive Al rather than more expensive Ni. [Industrial applicability]

[0044] According to the present invention, it is possible to provide heat-resistant cast steel and grates with improved wear resistance and corrosion resistance while suppressing manufacturing costs. Therefore, the invention described herein is extremely useful in the industry.

Claims

1. In terms of chemical composition, C: 1.00 to 1.71% by weight, Cr: 16.10 to 31.20% by weight, Si: 1.00 to 2.50% by weight, Mn: 0.50 to 1.00% by weight, Al: 4.00% by weight or less, Includes, The remainder consists of Fe and impurities. Heat-resistant cast steel characterized by the following features.

2. The content of C is 1.00 to 1.50% by weight. The heat-resistant cast steel according to feature 1.

3. When the Cr content is Cr and the C content is C, the Cr / C ratio is 15 or less. The heat-resistant cast steel according to feature 1.

4. The Al content is 1.00 to 2.00% by weight. The heat-resistant cast steel according to feature 1.

5. The Al content is 1.00% by weight or less. The heat-resistant cast steel according to feature 1.

6. A grate manufactured by casting, In terms of chemical composition, C: 1.00 to 1.71% by weight, Cr: 16.10 to 31.20% by weight, Si: 1.00 to 2.50% by weight, Mn: 0.50 to 1.00% by weight, Al: 4.00% by weight or less, Includes, The remainder consists of Fe and impurities. A fire grate characterized by the following features.

7. The content of C is 1.00 to 1.50% by weight. The grate according to claim 6.

8. When the Cr content is Cr and the C content is C, the Cr / C ratio is 15 or less. The grate according to claim 6.

9. The Al content is 1.00 to 2.00% by weight. The grate according to claim 6.

10. The Al content is 1.00% by weight or less. The grate according to claim 6.

11. Used as a grate for waste incinerators, A grate according to any one of claims 6 to 10, characterized by the features described herein.

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