Iron-based alloy

Abstract

To provide an iron-based alloy which endures, over a long term, high-temperature corrosion conditions to which a grate of a waste incinerator is subjected.SOLUTION: An iron-based alloy is used which contains, in mass%, C: 0.3 mass% or more and 1.5 mass% or less, Si: 0.3 mass% or more and 2.0 mass% or less, Mn: 0.6 mass% or more and 4.0 mass% or less, Ni: 5.0 mass% or more and 35.0 mass% or less, Cr: 15.0 mass% or more and 45.0 mass% or less, and Al: 0.005 mass% or more and 0.5 mass% or less, optionally further containing Mo: 3.0 mass% or less and Nb: 1.5 mass% or less, with the balance being Fe and inevitable impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to iron-based alloys used in high-heat environments such as waste incinerators. [Background technology]

[0002] In waste incineration plants, high-temperature incineration is recommended to prevent the generation of dioxins during incineration, resulting in harsh operating conditions within the plant. In particular, grates come into contact with various chemical components derived from the waste, the incineration flame, and the combustion gases produced during incineration, which causes molten salt corrosion, high-temperature oxidation, and high-temperature abrasion, resulting in rapid wear and the need for frequent replacement. For this reason, iron-based materials with excellent corrosion resistance, heat resistance, and strength are required.

[0003] Patent Document 1 proposes a high-carbon alloy steel for use in grates of waste incinerators, which contains, by weight, 0.70 to 1.10 C, 0.5 to 1.5 Si, 0.3 to 1.5 Mn, 22 to 28 Cr, 0.5 to 1.5 Ni, 0.5 or less Ti, 0.5 or less V, and the balance being Fe and impurity elements, with the ferrite to austenite ratio in the base structure being within a specified range, and which is excellent in resistance to thermal shock and high-temperature wear.

[0004] Furthermore, Patent Document 2 proposes an iron-based alloy for waste incinerators that ensures corrosion resistance (anti-corrosion properties) by using a high-chromium cast steel composition containing 1.0 to 2.0 wt% C, 0.5 to 4.0 wt% Si, 0.3 to 1.5 wt% Mn, 31 to 37 wt% Cr, 0.5 to 3.0 wt% Ni, with the remainder being Fe and unavoidable impurities. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 4-187744 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-262462 Summary of the Invention [Problem to be solved by the invention]

[0006] However, for the continued use of incinerators, durability, including corrosion resistance, even higher than that of the alloy in Patent Document 2 is required. Even if a material has sufficient durability at the time of manufacture, its durability will decrease over the long term as corrosion due to ash progresses inside the incinerator. Therefore, ensuring corrosion resistance can contribute to long-term durability.

[0007] Therefore, an object of the present invention is to provide an iron-based material that can be used for fire grates and that can withstand use in an incinerator environment for a longer period of time than conventional materials. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides, as a first solution, The above problem was solved by an iron-based alloy containing 0.3 to 1.5 mass% C, 0.3 to 2.0 mass% Si, 0.6 to 4.0 mass% Mn, 5.0 to 35.0 mass% Ni, 15.0 to 45.0 mass% Cr, 0.005 to 0.5 mass% Al, and optionally 3.0 mass% or less Mo and 1.5 mass% or less Nb, with the balance being Fe and unavoidable impurities.

[0009] Furthermore, the present invention provides a second solution that further limits the first solution, as follows: An iron-based alloy containing 0.7% by mass or more and 0.9% by mass or less of C, 1.0% by mass or more and 1.5% by mass or less of Si, 0.6% by mass or more and 2.0% by mass or less of Mn, 15.0% by mass or more and 20.0% by mass or less of Ni, 30.0% by mass or more and 40.0% by mass or less of Cr, and 0.01% by mass or more and 0.5% by mass or less of Al can be selected.

[0010] Furthermore, the present invention provides a third solution that further limits the first solution, as follows: An iron-based alloy containing 0.9% by mass or more and 1.2% by mass or less of C, 1.0% by mass or more and 1.5% by mass or less of Si, 0.6% by mass or more and 1.0% by mass or less of Mn, 15.0% by mass or more and 20.0% by mass or less of Ni, 30.0% by mass or more and 40.0% by mass or less of Cr, and 0.01% by mass or more and 0.5% by mass or less of Al can be selected.

[0011] The present invention allows selection of incinerator components using iron-based alloys, which are the first to third means of solving the problems described above.

[0012] Furthermore, in the present invention, it is possible to select incinerator components cast using the iron-based alloys according to the first to third solving means described above. [Effects of the Invention]

[0013] The iron-based alloy of the present invention exhibits high-temperature oxidation resistance due to Cr, and exhibits a significant effect mainly due to Ni, and exhibits molten salt corrosion resistance that can be adjusted by the amounts of Si, Mn, C, and Cr added, and also exhibits high-temperature wear resistance due to chromium carbide. Furthermore, by converting the matrix to austenite, it is possible to prevent a decrease in high-temperature matrix hardness.

[0014] These combined effects result in an iron-based alloy that can withstand the harsh environments that grates and other components in current incinerators are exposed to for a long period of time, making it possible to provide highly durable incinerator components, which can extend the replacement cycle of incinerator components and lengthen the maintenance intervals for the incinerator, thereby improving the operating rate. [Brief explanation of the drawings]

[0015] [Figure 1] Outline drawing of the sand mold used to produce the ingots used in the verification example [Figure 2] A perspective view showing the shape of the ingot used in the verification example [Figure 3] Graph showing the amount of corrosion for each verification example [Figure 4](a) A photograph showing the underside of the upper mold of the spiral test sand mold used in the examples on the left and the upper side of the lower mold on the right, (b) A photograph showing the underside of the upper mold in (a) superimposed on the upper side of the lower mold, viewed from the spout on the upper side of the upper mold. [Figure 5] Photographs of test pieces obtained by pouring molten metal into spiral test sand molds for Reference Example 2 and Examples 7-9 DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the iron-based alloy according to the present invention is an iron-based alloy containing C, Si, Mn, Ni, Cr, and Al, and may also contain Mo and Nb, with the balance being Fe and unavoidable impurities. Here, the iron-based alloy is an alloy in which Fe is the most abundant element by mass. This iron-based alloy can be suitably used for incinerator components. Incinerator components refer to components that are exposed to high heat, such as fire grates, incinerator inner walls, flue gas ducts, and chimneys, among other components of an incinerator.

[0017] The iron-based alloy according to the present invention contains 0.3 to 1.5 mass% C, 0.3 to 2.0 mass% Si, 0.6 to 4.0 mass% Mn, 5.0 to 35.0 mass% Ni, 15.0 to 45.0 mass% Cr, 0.005 to 0.5 mass% Al, 3.0 mass% or less Mo, 1.5 mass% or less Nb, with the balance being Fe and unavoidable impurities. This configuration ensures corrosion resistance and provides an iron-based alloy with excellent long-term durability.

[0018] The iron-based alloy must contain 0.3% by mass or more of C, preferably 0.4% by mass or more. C contributes to wear resistance, which is linked to strength, and if the C content is less than 0.3% by mass, the decrease in wear resistance becomes significant. On the other hand, the C content must be 1.5% by mass or less, preferably 1.1% by mass or less. If the C content exceeds 1.5% by mass, it becomes difficult to achieve the sufficient strength and corrosion resistance required for incinerator components such as fire grates.

[0019] The iron-based material must contain at least 0.3% by mass of Si, preferably at least 1.0% by mass. Si acts as a deoxidizer and is necessary when manufacturing incinerator components such as fire grates as castings. However, if the Si content is less than 0.3% by mass, the deoxidizing effect is insufficient, and the presence of oxides as impurities may become significant. On the other hand, the Si content must be 2.0% by mass or less, preferably 1.5% by mass or less. If the Si content exceeds 2.0% by mass, the embrittlement of the alloy becomes significant.

[0020] The iron-based alloy must contain 0.6% by mass or more of Mn. Mn also acts as a deoxidizer, so it is necessary when producing incinerator components such as fire grates as castings. However, if the content is less than 0.6% by mass, the deoxidizing effect is insufficient, and the presence of oxides as impurities may become significant. On the other hand, the Mn content must be 4.0% by mass or less. If the content exceeds 4.0% by mass, the deoxidizing effect reaches its upper limit, making its addition meaningless. Furthermore, if the content exceeds 4% by mass, the viscosity of the molten metal becomes too high, making it difficult to cast.

[0021] The iron-based alloy must contain 5.0% by mass or more of Ni, preferably 10.0% by mass or more. Ni contributes significantly to corrosion resistance, and if the Ni content is less than 5.0% by mass, this effect becomes insufficient. Furthermore, by incorporating an appropriate amount of Ni in accordance with the Cr content, it also contributes to high-temperature oxidation resistance. On the other hand, the Ni content must be 35.0% by mass or less, preferably 25.0% by mass or less. Even if the Ni content exceeds 35.0% by mass, the improvement in high-temperature oxidation resistance combined with Cr reaches a plateau. Furthermore, the increased cost burden makes it difficult to introduce incinerator components such as grates, which are durable but consumable.

[0022] The iron-based alloy must contain 15.0% by mass or more of Cr, preferably 20.0% by mass or more. Cr, together with Ni, mainly contributes to high-temperature oxidation resistance, and if it is less than 15.0% by mass, this effect becomes insufficient. On the other hand, the Cr content must be 45.0% by mass or less, preferably 40.0% by mass or less. If it exceeds 45.0% by mass, the improvement in high-temperature oxidation resistance combined with Ni will plateau. Furthermore, the casting may crack, and the deterioration of castability will become significant. Furthermore, the Cr content must be less than the Fe content. If the Cr content is greater than the Fe content, it may be difficult to fully adjust the physical properties of the alloy.

[0023] The above iron-based alloy must contain 0.005% by mass or more of Al, and preferably 0.007% by mass or more. Al also acts as a deoxidizer, making it essential when manufacturing incinerator components such as fire grates as castings. If the Al content remaining in the alloy after manufacturing is less than 0.005% by mass, the deoxidizing effect is likely to be insufficient, and the presence of oxides as impurities may become significant. Furthermore, Al contributes to corrosion resistance, so it is preferable to include an amount that can exert its effect more effectively than an impurity. On the other hand, the content must be 0.5% by mass or less. If it exceeds 0.5% by mass, casting becomes difficult.

[0024] The iron-based alloy may contain 3.0% by mass or less of Mo. While Mo has almost no effect on corrosion resistance, it maintains the hardness of the alloy and contributes to high-temperature wear resistance. If Mo is added in excess of 3.0% by mass, the improvement in high-temperature wear resistance will not be commensurate with the amount added, and the addition will be wasted.

[0025] The iron-based alloy may contain 1.5 mass% or less of Nb. Although Nb has almost no effect on corrosion resistance, it bonds with carbon to form hard Nb carbides, thereby maintaining the hardness of the alloy and contributing to high-temperature wear resistance. Even if Nb is added in an amount exceeding 1.5 mass%, the improvement in high-temperature wear resistance is not commensurate with the amount added, and the added amount is wasted.

[0026] The iron-based alloy may contain unavoidable impurities in addition to the above elements. The unavoidable impurities are preferably less than 0.1% by mass, more preferably less than 0.01% by mass, and even more preferably below the detection limit. Examples of unavoidable impurities include P and S.

[0027] The iron-based alloy is an iron-based alloy containing Fe other than the above elements and unavoidable impurities, and contains Fe in the largest mass ratio among the elements contained therein.

[0028] Furthermore, the iron-based alloy contains 0.7 to 0.9 mass% C, 1.0 to 1.5 mass% Si, 0.6 to 2.0 mass% Mn, 15.0 to 20.0 mass% Ni, 30.0 to 40.0 mass% Cr, and 0.01 to 0.5 mass% Al in the ranges described above, making it an iron-based alloy according to one embodiment of the present invention that exhibits particularly excellent effects in corrosion resistance, castability, and high-temperature wear resistance. It is believed that the combination of these elements in these ranges exhibits these effects.

[0029] Furthermore, the iron-based alloy may contain C in the range of 0.9% by mass to 1.2% by mass, Si in the range of 1.0% by mass to 1.5% by mass, Mn in the range of 0.6% by mass to 1.0% by mass, Ni in the range of 15.0% by mass to 20.0% by mass, Cr in the range of 30.0% by mass to 40.0% by mass, and Al in the range of 0.01% by mass to 0.5% by mass, thereby achieving an iron-based alloy that exhibits excellent effects, particularly in corrosion resistance, castability, and wear resistance at high temperatures, among the iron-based alloys according to one embodiment of the present invention.

[0030] The incinerator component according to one embodiment of the present invention may be made of the above iron-based alloy, which has the advantage of providing an incinerator component with excellent corrosion resistance (molten salt corrosion resistance).

[0031] The incinerator component according to one embodiment of the present invention may be cast using the iron-based alloy. According to this configuration, the resulting incinerator component has the advantage of being easily castable because it is cast using the iron-based alloy, which has excellent fluidity.

[0032] The above iron-based alloy can be used to produce incinerator components, such as fire grates, incinerator inner walls, flue gas ducts, and chimneys, that can withstand high temperatures and molten salt exposure for extended periods of time. Compared to existing fire grates, fire grates cast from this iron-based alloy have higher corrosion resistance (molten salt corrosion resistance) and oxidation resistance. Furthermore, in incinerators where dioxin generation is suppressed, the fire grates are installed in environments of approximately 700°C. However, the iron-based alloy can ensure sufficient HV hardness and wear resistance in this temperature range, allowing for longer use than conventional alloys. Therefore, the iron-based alloy according to one embodiment of the present invention can also be used for fire grates.

[0033] When casting the above iron-based alloy, there is no particular limitation on the manufacturing procedure, and castings can be produced by a general procedure. Even without special treatment, when Ni is contained in the Fe matrix within the above range, the matrix is austenitized and the required hardness is obtained. [Example]

[0034] Below, verification examples for verifying the present invention and examples in which the invention is specifically implemented will be shown.

[0035] <Verification test> (Test piece manufacturing method) Iron and various alloy raw materials were melted to a total weight of 3000 g using the mass ratios shown in the tables below, and cast at 1500°C in a 35 mm square sand mold shown in Figure 1 to obtain an ingot with the shape shown in Figure 2. All measurements are in mm. The upper cylindrical portion of Figure 2 is the feeder, and the lower rectangular prism portion is the portion used for evaluation. The rectangular prism portion of this ingot was cut out to obtain a plate-shaped test piece measuring 15 mm long, 15 mm wide, and 3 mm thick.

[0036] (Molten salt corrosion resistance durability test) To replicate the environment experienced by incinerator grates, 50g of simulated ash was prepared by collecting and analyzing plant ash from an incinerator and mixing it with aggregate and corrosive salts. The aggregate components were 25% calcium carbonate, 15% silica sand, 8% alumina, and 2% gypsum, by mass. The corrosive salt components were 10% sodium carbonate, 10% potassium carbonate, 10% potassium chloride, 10% sodium chloride, and 10% potassium nitrate, by mass. 50g of this simulated ash was placed in a crucible, and one plate-shaped test piece, the mass of which had been measured, was immersed in the ash and left at 700°C for six hours. After the test, the plate-shaped test piece was removed and its mass was measured. Three test pieces were tested for each verification example, and the average of the corrosion amounts calculated using the following formula was used as the corrosion amount for each example.

[0037] The amount of corrosion (%) was calculated by (mass loss of test piece) / (initial mass of test piece)×100 (%).

[0038] The adjusted compositions of each verification example are shown in Table 1. Reference Example 1 is an alloy used in conventional grate materials, and the verification examples of each series are based on Reference Example 1, with the contents of the target elements for each verification being increased or decreased. However, due to the nature of the alloy raw materials, the contents of elements other than the target elements are also increased or decreased slightly. Verification Examples 1a to 1e in Table 1 are those in which the C content was increased or decreased as a target. Verification Examples 2a to 2d in Table 2 are those in which the Si content was increased or decreased as a target. Verification Examples 3a to 3b in Table 3 are those in which the Mn content was increased or decreased as a target. Verification Examples 4a to 4d in Table 4 are those in which the Cr content was increased or decreased as a target. Verification Examples 5a to 5b in Table 5 are those in which the Ni content was increased or decreased as a target. Verification Examples 6a to 6d in Table 6 are those in which the Mo content was increased or decreased. Verification Examples 7a to 7c in Table 7 are those in which the Nb content was increased or decreased as a target. Verification Examples 8a to 8b in Table 8 are those in which the Al content was increased or decreased as a target. The content in the table is in mass %, with the remainder consisting of Fe and unavoidable impurities. The corrosion amount shown in each table is the average value of data from three tests.

[0039]

Table 1

[0040]

Table 2

[0041]

Table 3

[0042]

Table 4

[0043]

Table 5

[0044]

Table 6

[0045]

Table 7

[0046]

Table 8

[0047] Figure 3 shows a graph for each verification example, with the content of the target element on the horizontal axis and the amount of corrosion (%) on the vertical axis. The legs in each example represent the range of three verification examples, and the dots indicate the average value. The amount of corrosion in Reference Example 1 was 40.9%, and changes in the amount of corrosion relative to this were verified. It was confirmed that there was a significant decrease in the amount of corrosion as the Ni and Cr content increased. On the other hand, it was confirmed that Si and Mo had little effect on the amount of corrosion within the verification range. For this reason, it was confirmed that by sufficiently increasing the Ni and Cr content within the verification range, sufficient corrosion resistance could be ensured even if there was a slight increase or decrease in the amounts of other elements.

[0048] (Examples 1 to 6, Comparative Example 1) Using the same procedures as in the verification example, test pieces according to Examples 1 to 6 listed in Table 9 were prepared as iron-based alloys according to the present invention that fully exhibit the corrosion amount suppression effect (corrosion resistance), and the corrosion amounts were similarly measured. A test piece according to Comparative Example 1, which is deficient in Ni, was also prepared, and the corrosion amounts were similarly measured. The results are shown in Table 9. Among the examples, Example 6 in particular had a small amount of corrosion, and it was confirmed that it exhibited excellent properties.

[0049] [Table 9]

[0050] <Casting flowability test> Examples 7-9 Using the same procedure as in the verification example, 3000 g of an iron-based alloy according to the present invention, exhibiting sufficient corrosion resistance, was prepared with the mass ratios (mass%) of Examples 7-9 listed in Table 10. Additionally, an alloy with the same composition as Reference Example 1 was prepared and designated Reference Example 2. These alloys were poured into the spiral test sand mold shown in Figure 4 at 1500°C, and the spiral line lengths of the castings were compared. Specifically, the upper and lower molds shown in Figure 4(a) were stacked as shown in Figure 4(b), and the melt was poured from the central spout in Figure 4(a). The poured melt flowed through the central hole in the upper mold shown on the left in Figure 4(a) and into the groove on the upper surface of the lower mold shown on the right. The casting was cooled at room temperature and removed from the sand mold. The results are shown in Table 10 and Figure 5. While Example 7 also exhibited favorable melt flow, exceeding the 295 mm flow length of Reference Example 2, Examples 8 and 9 exhibited even better melt flow. Therefore, it was confirmed that the alloys of Examples 8 and 9 were particularly excellent in castability.

[0051] [Table 10]

[0052] <HV hardness test for wear resistance at high temperatures> Examples 10-12 Following the same procedures as in the verification examples, 3000 g of an iron-based alloy according to the present invention, exhibiting sufficient corrosion resistance, was prepared with the mass ratios (mass%) shown in Reference Example 2 and Examples 10-12 in Table 11. The alloy was poured into a sand mold at 1500°C to obtain a casting. Next, test specimens (5 mm x 5 mm x 10 mm) for HV hardness measurement were taken from the casting. One side (5 mm x 10 mm) of the test specimen was polished using waterproof paper and a buff, and the polished surface was used as the HV hardness measurement surface. The HV hardness test was performed using a hardness tester (Nikon Corporation QM-2) according to the JIS Z2252 high-temperature Vickers hardness test method. The HV hardness test was performed after heating the test specimen to 700°C at a heating rate of 20°C / min. The test load was 9.807 N (1 kg). The HV hardness of the polished surface was measured at 10 points, and the average of the six points, excluding the two highest and two lowest values, was designated as the "700°C HV hardness." The results are shown in Table 11. All of Examples 10-12 exhibited values greater than the 51.8 HV hardness at 700°C of Reference Example 2, an alloy used in incinerators. Furthermore, Examples 11 and 12 exhibited even better 700°C HV hardness than Example 10. Since the higher the HV hardness value at high temperatures, the better the wear resistance of an alloy at high temperatures. Therefore, it was revealed that the iron-based alloy according to one embodiment of the present invention has excellent wear resistance at high temperatures, and that the iron-based alloys of Examples 11-12 have particularly excellent wear resistance at high temperatures.

[0053] [Table 11]

Claims

1. An iron-based alloy containing 0.3 mass% to 1.5 mass% C, 0.3 mass% to 2.0 mass% Si, 0.6 mass% to 4.0 mass% Mn, 5.0 mass% to 35.0 mass% Ni, 15.0 mass% to 45.0 mass% Cr, 0.005 mass% to 0.5 mass% Al, and optionally containing 3.0 mass% or less Mo and 1.5 mass% or less Nb, with the balance being Fe and unavoidable impurities.

2. 2. The iron-based alloy according to claim 1, containing 0.7% by mass or more and 0.9% by mass or less of C, 1.0% by mass or more and 1.5% by mass or less of Si, 0.6% by mass or more and 2.0% by mass or less of Mn, 15.0% by mass or more and 20.0% by mass or less of Ni, 30.0% by mass or more and 40.0% by mass or less of Cr, and 0.01% by mass or more and 0.5% by mass or less of Al.

3. 2. The iron-based alloy according to claim 1, containing 0.9% by mass or more and 1.2% by mass or less of C, 1.0% by mass or more and 1.5% by mass or less of Si, 0.6% by mass or more and 1.0% by mass or less of Mn, 15.0% by mass or more and 20.0% by mass or less of Ni, 30.0% by mass or more and 40.0% by mass or less of Cr, and 0.01% by mass or more and 0.5% by mass or less of Al.

4. An incinerator member made of the iron-based alloy according to any one of claims 1 to 3.

5. An incinerator component cast using the iron-based alloy according to any one of claims 1 to 3.

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