Cast steel product and method for producing cast steel product

Abstract

To provide a cast steel product in which a decrease in internal hardness is suppressed even when the wall thickness is large, and which possesses wear resistance and impact resistance.SOLUTION: A cast steel product comprises, in mass%, C: 0.28% or more and 0.36% or less, Si: 0.10% or more and 0.50% or less, Mn: 0.60% or more and 1.20% or less, P: more than 0.0% and 0.04% or less, S: more than 0.0% and 0.04% or less, Ni: 1.0% or more and 1.5% or less, Cr: 0.8% or more and 1.2% or less, Mo: 0.0% or more and 0.35% or less, B: 0.001% or more and 0.007% or less, and Al: 0.0% or more and 0.1% or less, with the balance being Fe and unavoidable impurities, and has a portion with a wall thickness of 1 inch or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a steel casting and a method for manufacturing the steel casting. [Background technology]

[0002] Conventionally, recycling facilities and the like have used crushers to crush materials to be crushed, such as various types of metal-containing waste, construction waste such as concrete, and various types of bulky waste. A well-known type of crusher is a vertical crusher, which roughly crushes materials to be crushed using a breaker that rotates at high speed inside a shell, and then finely crushes them using a grinder. Vertical crushers have many advantages, such as high processing efficiency because the materials fed into them are crushed as they fall naturally, and easy maintenance. However, wear and tear on the various parts that directly contribute to crushing (cast steel parts such as shell liners, breaker liners, and grinders) are still unavoidable, and these parts become consumables and require regular replacement.

[0003] In order to improve the wear resistance of cast steel used in such crusher parts, for example, Japanese Patent Application Laid-Open No. 2012-246564 (Patent Document 1) discloses a steel sheet containing, in mass %, C: 0.30% to 0.35%, Si: 0.30% to 0.60%, Mn: 0.90% to 1.50%, Cr: 0.91% to 1.50%, Ni: 1.60% to 1.90%, Mo: 0.20% to 0.30%, P: 0.05% or less, S: 0.05% or less, the balance being Fe and unavoidable impurities, with a product thickness of 1 inch or more, a hardness of HRC 45 to 53, and a Charpy impact value (U notch) of 20 to 40 J / cm. 2 A wear-resistant low-alloy cast steel has been proposed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-246564 Summary of the Invention [Problem to be solved by the invention]

[0005] When the thickness of a product is large, for example, 1 inch or more, it is difficult to ensure sufficient hardenability inside the product, such as at the center in the thickness direction. As a result, the hardness and impact resistance inside the product become lower than those on the outside of the product, and as a result, wear resistance is likely to decrease. The wear-resistant low-alloy cast steel of Patent Document 1 requires three processes: a homogenization process in which the cast product is heated and held at 1000°C to 1100°C and furnace-cooled; a quenching process in which the product is heated and held at 850°C to 950°C, then immersed in water for water cooling; and a tempering process in which the product is heated and held at 150°C to 280°C, then furnace-cooled to room temperature. In addition, in order to ensure the toughness inside a thick-walled cast steel product, a quenching temperature of 20 to 40 J / cm is particularly required. 2 In order to secure the Charpy impact value of 1.6 mass %, it is necessary to include 1.6 mass % or more of expensive Ni. Therefore, the manufacturing cost tends to increase, and there is still room for improvement in cast steel products that combine impact resistance and hardness inside the product.

[0006] Therefore, there is still a demand for a cast steel product that has wear resistance and impact resistance and in which the decrease in hardness inside the product is suppressed even when the wall thickness is large. [Means for solving the problem]

[0007] The cast steel product according to the present invention is characterized by containing, in mass%, C: 0.28% or more and 0.36% or less, Si: 0.10% or more and 0.50% or less, Mn: 0.60% or more and 1.20% or less, P: more than 0.0% and 0.04% or less, S: more than 0.0% and 0.04% or less, Ni: 1.0% or more and 1.5% or less, Cr: 0.8% or more and 1.2% or less, Mo: 0.0% or more and 0.35% or less, B: 0.001% or more and 0.007% or less, and Al: 0.0% or more and 0.1% or less, with the remainder being Fe and unavoidable impurities, and having a portion with a wall thickness of 1 inch or more.

[0008] The method for producing a cast steel product according to the present invention comprises, in mass%, C: 0.28% or more and 0.36% or less, Si: 0.10% or more and 0.50% or less, Mn: 0.60% or more and 1.20% or less, P: more than 0.0% and 0.04% or less, S: more than 0.0% and 0.04% or less, Ni: 1.0% or more and 1.5% or less, Cr: 0.8% or more and 1.2% or less, Mo: 0.0% or more and 0.35% or less, and B: 0.001% or more and 0.007% or less , Al: 0.0% or more and 0.1% or less, with the balance being Fe and unavoidable impurities, and having a portion with a thickness of 1 inch or more; a homogenization treatment process in which the first intermediate casting is heated and held at 900°C or more and 960°C or less, and then furnace-cooled to obtain a second intermediate casting; and a quenching process in which the second intermediate casting is heated and held at 800°C or more and 950°C or less, and then water-cooled to obtain a cast steel product.

[0009] According to these configurations, by having the above composition, even if the product has a portion with a wall thickness of 1 inch or more, a decrease in hardness inside the product is suppressed, and a cast steel product with wear resistance and impact resistance can be realized.

[0010] Preferred embodiments of the present invention will be described below, but the scope of the present invention is not limited to the preferred embodiments described below.

[0011] The steel casting according to the present invention is preferably heat treated at a temperature of 800°C or higher and lower than 1000°C.

[0012] This configuration homogenizes the structure, making it easier to release stress generated during casting and to increase hardness.

[0013] The cast steel product according to the present invention has an impact test value of 30 J / cm in a Charpy impact test according to JIS Z 2242. 2 It is preferable that the above is true.

[0014] Cast steel products having the above composition tend to have good impact resistance.

[0015] In the cast steel product according to the present invention, the difference in Shore hardness (HS) between two samples taken at random from two locations is preferably 5 or less.

[0016] A steel casting having the above composition can easily suppress the difference in hardness between the interior and exterior of the steel casting, and can easily provide excellent wear resistance.

[0017] In the cast steel product according to the present invention, it is preferable that the Shore hardness (HS) of each sample is 60-74.

[0018] A steel casting having the above composition tends to have hardness extending to the interior of the steel casting, and to have excellent wear resistance.

[0019] The steel casting according to the present invention is preferably a part for a crusher.

[0020] Cast steel products having the above composition are suitable for use as crusher parts because they are wear-resistant and impact-resistant.

[0021] Further features and advantages of the present invention will become more apparent from the following description of exemplary and non-limiting embodiments, which is given with reference to the drawings. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram of a grinder according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a steel casting and a method for manufacturing a steel casting according to the present invention will be described with reference to the drawings.

[0024] In this specification, "cast steel" refers to an Fe-C alloy used for casting before being formed into a product shape, and "cast steel product" refers to a product formed by pouring molten steel into a mold and forming it into a desired shape. "Cast steel product" includes not only products formed into the shape of a final product by machining such as cutting, but also intermediate products in the manufacturing process before machining. The cast steel product of the present invention has a portion with a wall thickness of 1 inch or more.

[0025] First, the composition of each component of the cast steel product will be described. Unless otherwise specified, "%" in this specification indicates "mass %."

[0026] [Composition of cast steel products] C: 0.28% or more and 0.36% or less Carbon (C) is the main element that contributes to hardenability, transforming the structure into martensite to ensure hardness. Therefore, the C content is set to 0.28% or more. Hardenability is related to both the hardenability, which is the ability to increase the hardness of the hardened portion, and the depth of hardening. Because the cast steel product of the present invention has a wall thickness of 1 inch or more, C alone is insufficient to ensure the hardness inside the thick wall; therefore, the addition of elements such as Cr is necessary. Meanwhile, the C content is set to 0.36% or less to ensure an appropriate range for impact resistance (toughness) and to prevent cracking during hardening (quench cracking).

[0027] Si: 0.10% or more and 0.50% or less Silicon (Si) is an element necessary for deoxidization and ensuring melt flow, and contributes to suppressing gas defects and poor melt flow, thereby contributing to the soundness of cast steel products. For this reason, the Si content is set to 0.10% or more. On the other hand, the Si content is set to 0.50% or less to ensure an appropriate range for impact resistance (toughness). Since Si is consumed as a deoxidizer during casting, it is preferable to add about 1.5 to 2 times the final composition during casting.

[0028] Mn: 0.60% or more and 1.20% or less Manganese (Mn) is an element necessary for deoxidation, and contributes to suppressing gas defects, thereby contributing to the soundness of cast steel products. Therefore, the Mn content is set to 0.60% or more. On the other hand, the Mn content is set to 1.20% or less to keep the impact resistance (toughness) within an appropriate range. Note that Mn is also consumed as a deoxidizer during casting, so it is preferable to add about 1.5 to 2 times the final composition during casting.

[0029] P: More than 0.0% and less than 0.04% P (phosphorus) is set to 0.04% or less to prevent embrittlement and casting cracks.

[0030] S: Over 0.0% and 0.04% or less S (sulfur) content is set to 0.04% or less to prevent embrittlement and casting cracks.

[0031] Ni: 1.0% or more and 1.5% or less Ni (nickel) is an element necessary for ensuring the toughness and strength of cast steel products, and is contained in an amount of 1.0% or more. Because the cast steel products of the present invention have a wall thickness of 1 inch or more, Ni is an essential component for ensuring the hardness and toughness inside the thick wall. On the other hand, in the present invention, the strength and toughness inside the product are ensured by other components such as B, so the Ni content is set to 1.5% or less. By keeping the Ni content to 1.5% or less, costs can be reduced. Furthermore, if the Ni content is too high, the above-mentioned effects will saturate.

[0032] Cr: 0.8% or more and 1.2% or less Cr (chromium) is an important element, along with C, for ensuring hardenability. Because the cast steel product of the present invention has a wall thickness of 1 inch or more, the thick-wall interior cannot be rapidly cooled and is difficult to harden, so it is important to ensure the hardness of the thick-wall interior by using Cr. For this reason, the Cr content is set to 0.8% or more, preferably 0.82% or more. On the other hand, by setting the Cr content to 1.2% or less, costs can be reduced and manufacturability, such as formability and weld repairability, can be ensured. The Cr content is preferably 1.1% or less.

[0033] Mo: 0.0% or more and 0.35% or less Mo (molybdenum), like Cr, contributes to ensuring hardenability and hardness. It also contributes to improving mechanical properties and toughness. Mo may not be contained (i.e., 0%), but is preferably contained in an amount of 0.01% or more. On the other hand, the Mo content is set to 0.35% or less, preferably 0.30% or less, and more preferably 0.25% or less, in order to reduce costs and ensure impact resistance.

[0034] B: 0.001% or more and 0.007% or less Like Cr, B contributes to ensuring hardenability and hardness. It also contributes to improving mechanical properties and toughness. For this reason, the B content is set to 0.001% or more, preferably 0.002% or more. Thus, even a small amount of B exerts the above-mentioned effects. On the other hand, the B content is set to 0.007% or less, preferably 0.005% or less, in order to keep the impact resistance (toughness) in an appropriate range.

[0035] Al: 0.0% or more and 0.1% or less Aluminum (Al) is an element necessary for deoxidation, contributes to suppressing gas defects, and as a result contributes to the soundness of cast steel products. Aluminum may not be contained (i.e., 0%), but is preferably contained at 0.02% or more. On the other hand, the Al content is set to 0.1% or less to maintain an appropriate range for impact resistance (toughness).

[0036] The balance is Fe and unavoidable impurities The balance is made up of Fe and unavoidable impurities that are mixed in during the process up to the smelting stage, such as raw materials like ore and scrap, and various factors in the manufacturing process. Examples of unavoidable impurities include, but are not limited to, O, S, N, and H. The amount of unavoidable impurities is not limited, but the total amount is preferably 0.5% or less, and more preferably 0.1% or less.

[0037] [Cast steel products] A cast steel product having the above-mentioned composition and proportions has a portion with a wall thickness of 1 inch (2.54 cm) or more. Conventional cast steel products cannot be rapidly cooled near the center of the wall thickness, making it difficult to harden, resulting in low internal hardness and impact resistance. However, the cast steel product of the present invention has the above-mentioned composition, which prevents the internal hardness and impact resistance from decreasing. The cast steel product of this embodiment is heat-treated at a temperature of 800°C or higher but lower than 1000°C, and the heat treatment will be described later.

[0038] The steel casting according to this embodiment has excellent hardness and impact resistance both inside and outside the product, and excellent wear resistance, and is therefore suitable for use as a crusher part, for example. Specifically, the steel casting has a portion with a product wall thickness of 1 inch or more and has the following physical properties:

[0039] 1) Hardness The Shore hardness (HS) of a sample taken at random from the cast steel product according to this embodiment is 60 to 74. This corresponds to a Shore hardness (HB) of 421 to 560 and a Rockwell hardness (HRC) of 45 to 55 measured with a tungsten carbide ball. The Shore hardness (HS) is preferably 65 to 73. Furthermore, the cast steel product according to this embodiment is prevented from losing hardness inside the product, and the difference in Shore hardness (HS) of samples taken at random from two locations is 5 or less.

[0040] 2) Impact test value The impact test value (U notch) of a sample taken from the cast steel product according to this embodiment in a Charpy impact test measured in accordance with JIS Z 2242 was 30 J / cm 2 The upper limit of the impact test value in the Charpy impact test is not particularly limited, but is 50 J / cm 2 Preferably, the impact test value (U notch) is 32 to 50 J / cm 2 is.

[0041] 1 and 2 show a steel casting according to this embodiment applied to a grinder (one example of a part for a crusher).

[0042] The grinder 1 is a crusher component used in vertical crushers, and is a gear-shaped component that finely crushes the material to be crushed that has been roughly crushed by the breaker. The grinder 1 according to this embodiment has an inner diameter D1 of 130 mm, an outer diameter D2 of 320 mm, and a wall thickness T of 65 mm (i.e., 1 inch or more).

[0043] As described above, the cast steel product of this embodiment has excellent wear resistance and impact resistance because the decrease in hardness inside the product is suppressed even if the wall thickness is large, and therefore can be suitably used as a part for a crusher such as the grinder 1. Such excellent wear resistance and impact resistance allows the frequency of part replacement to be reduced compared to conventional products.

[0044] Next, a method for manufacturing the grinder 1 as an example of a steel casting will be described.

[0045] [Manufacturing method for cast steel products (grinders)] <Casting process> The casting process is a process for obtaining a first intermediate casting having a portion with a wall thickness of 1 inch or more. Specifically, raw steel billets (steel slabs, steel blooms, etc.) having the same composition as the above-mentioned steel cast are melted to produce molten steel, which is then poured into a mold (e.g., a sand mold) to produce a first intermediate casting having the shape of the grinder 1. The pouring temperature is preferably the melting point plus approximately 100°C, and in this embodiment is set to 1550°C or higher and 1630°C or lower. If the pouring temperature is within this range, poor running is less likely to occur and oxidation and casting cracks are also easily suppressed.

[0046] Next, the first intermediate casting is heat-treated. The cast steel product according to this embodiment is heat-treated at a temperature of 800°C or higher but lower than 1000°C. Specifically, the heat treatment includes a homogenization step and a quenching step, and can optionally include a tempering step. Each step of the heat treatment will be described below.

[0047] <Homogenization process> The homogenization process involves heating and holding the first intermediate cast obtained in the casting process at a temperature between 900°C and 960°C, followed by cooling in a furnace (furnace cooling) to obtain a second intermediate cast. Specifically, the homogenization process is carried out to remove inhomogeneous structures, such as the segregation of coarse dendritic structures, present in the first intermediate cast, and to obtain an austenitic structure. The homogenization process also removes the casting stress generated in the first intermediate cast during the casting process. The homogenization process can be performed at a temperature below 1000°C. A homogenization process below 1000°C reduces oxidation and reduces the occurrence of surface irregularities. As a result, dimensional accuracy is easily maintained. Preferably, the homogenization process is performed at a temperature between 900°C and 960°C. A homogenization process at 900°C or higher facilitates the solid solution of carbides into the matrix, making it easier to obtain a homogenized structure. The holding time for the homogenization treatment varies depending on the wall thickness of the casting, but is preferably 2 to 8 hours, more preferably 3 to 6 hours. After holding at the above-mentioned predetermined temperature for the predetermined time, it is desirable to slowly cool the casting in a furnace (furnace cooling) to prevent residual stress. The furnace cooling transforms the austenite structure into a ferrite structure. This homogenization treatment homogenizes the structure in the first intermediate casting and removes casting stress, resulting in a second intermediate casting with improved mechanical properties.

[0048] After the homogenization treatment step, the second intermediate casting is subjected to machining, fusion cutting, and the like, as required.

[0049] <Quenching process> The quenching process is a process in which the second intermediate cast is heated and held at a temperature of 800°C to 950°C and then cooled in water (water cooling). The quenching process is performed after the homogenization process to increase the hardness of the second intermediate cast. In the quenching process, the austenite is transformed into a martensite structure by rapid cooling, and the quenching process is preferably performed so that the average grain size of the martensite in the martensite structure after the quenching process is 50 μm to 300 μm. When the average grain size of the martensite is within this range, excellent impact resistance is likely to be achieved. It is more preferable to perform the quenching process so that the average grain size of the martensite is 100 μm to 200 μm. Since cast steel products have thick portions with a wall thickness of 1 inch or more, the average grain size of the martensite structure in the thick portions is relatively coarse. In this specification, the average grain size of the martensite is determined based on the average grain size of the prior austenite.

[0050] The quenching temperature can be 800°C or higher and 950°C or lower. When the quenching temperature is 800°C or higher, the structure tends to become uniform, and hardness and wear resistance are less likely to decrease. When the quenching temperature is 950°C or lower, crystal grains are less likely to coarsen, and mechanical properties are less likely to decrease. The holding time at the above quenching temperature varies depending on the wall thickness of the casting, but is preferably 2 to 6 hours, more preferably 3 to 4 hours.

[0051] When the thickness of a casting is 1 inch or more, it can be difficult to harden it all the way to the center of the wall. However, the present invention contains 0.8% to 1.2% Cr, 1.0% to 1.5% Ni, and a small amount of B (0.001% to 0.007%), which allows for a large hardening depth and hardening all the way to the center of the wall. As a result, the decrease in hardness in the center of the wall can be suppressed, and impact resistance can be improved.

[0052] If the tempering step described below is not carried out after the quenching step, the cast steel product after the quenching step is polished as necessary to form a finished product (cast steel product). The tempering step described below may be carried out optionally.

[0053] ≪Tempering process≫ The tempering process is a further heat treatment of the cast steel product after the quenching process. The tempering process is usually performed to restore impact resistance (toughness), even at the expense of some hardness. In the present invention, the cast steel product has the above-mentioned blending amounts of components (C, Si, Mn, P, S, Al) that may reduce impact resistance (toughness) and the above-mentioned blending amounts of components (Cr, B, Ni) that contribute to improving toughness. Therefore, the cast steel product after quenching has high impact resistance (toughness). Therefore, there is no need to restore impact resistance (toughness), and the tempering process can be omitted. If the tempering process is omitted, the decrease in hardness due to the tempering process is less likely, and the cast steel product after quenching can have high impact resistance (toughness) and hardness.

[0054] If necessary, a tempering step may be carried out. When the tempering step is carried out, the tempering temperature may be low, at 150°C or higher and 280°C or lower, and the holding time may be 1 to 3.5 hours, preferably 1.5 to 3 hours, depending on the thickness of the cast steel product.

[0055] [Other embodiments] Other embodiments of the steel cast product and the method for manufacturing the steel cast product according to the present invention will be described below. Note that the configurations disclosed in the following embodiments can be applied in combination with the configurations disclosed in other embodiments, as long as no contradiction occurs.

[0056] In the above embodiment, the steel castings are described as crusher parts (grinders) by way of example. However, in the present invention, the steel castings may be applied not only to crusher parts but also to other products such as crushers that require wear resistance and impact resistance. Furthermore, in the above embodiment, the steel castings are described as crusher parts by way of example, but the crusher parts may also be shell liners, breaker liners, etc. Furthermore, the steel castings are not limited to parts for vertical crushers, but may also be parts for various types of crushers, such as horizontal crushers.

[0057] In the above embodiment, the wall thickness of the steel casting is 65 mm. However, the wall thickness of the steel casting of the present invention is not limited as long as it is 1 inch or more.

[0058] In the above embodiment, the cast steel product has been described as being heat-treated at a temperature of 800°C or higher but lower than 1000°C. However, the cast steel product of the present invention also includes a product that has not been heat-treated at the above temperature. For example, it may be an intermediate product that has not been heat-treated.

[0059] In the above embodiment, the impact test value in the Charpy impact test according to JIS Z 2242 is 30 J / cm 2 The above configuration has been described as an example. However, in the present invention, the numerical value of the impact test value in the Charpy impact test is not limited. For example, 20 J / cm 2 It may be more than that.

[0060] In the above embodiment, the difference in Shore hardness (HS) between two samples randomly taken from two locations is 5 or less. However, the present invention does not limit the difference in Shore hardness (HS) between the two samples. For example, when the wall thickness is large, the difference in Shore hardness (HS) may be 10 or more.

[0061] In the above embodiment, an example has been described in which the Shore hardness (HS) of each of two samples randomly taken from two locations is 60 to 74. However, the Shore hardness (HS) value is not limited in the present invention.

[0062] Regarding other configurations, it should be understood that the embodiments disclosed in this specification are illustrative in all respects and that the scope of the present invention is not limited thereby. Those skilled in the art will easily understand that appropriate modifications are possible without departing from the spirit of the present invention. Therefore, other embodiments modified within the spirit of the present invention are naturally included in the scope of the present invention. [Example]

[0063] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0064] (Examples 1 to 6, Comparative Examples 1 to 10) Two grinders each having the shape shown in FIG. 1 were produced by the manufacturing method described below.

[0065] <Casting manufacturing process> A steel billet (steel slab) having the composition shown in Table 1 was melted to form molten steel, which was then poured into a sand mold to produce a casting (first intermediate casting) in the shape of grinder 1. The casting temperature was 1590°C.

[0066] [Table 1]

[0067] <Homogenization process> The obtained first intermediate castings of the examples and comparative examples were heated and held in a furnace at 930°C for 3 hours, and then furnace cooled. The second intermediate castings obtained by the homogenization treatment step were subjected to machining such as cutting and polishing to adjust the surface shape.

[0068] <Quenching process> Next, the homogenized second intermediate castings of the Examples and Comparative Examples were heated and held in a furnace at 900°C for 3 hours, and then water-cooled to obtain the cast steel products (grinders) of the Examples and Comparative Examples. No tempering process was performed in any of the Examples and Comparative Examples.

[0069] Using the above manufacturing method, two grinders 1 shown in Fig. 1 were produced for each example. The grinders of Examples 1 to 4 and Comparative Examples 1 to 10 had an inner diameter D1 of 130 mm, an outer diameter D2 of 320 mm, a width W1 of 95 mm, a width W2 of 75 mm, a thickness T of 65 mm (2.56 inches), and a mass of 28 kg ± 1 kg. As shown in Table 2, the grinder of Example 5 had a thickness of 30 mm (mass 14 kg), and the grinder of Example 6 had a thickness of 50 mm (mass 22 kg).

[0070] <Preparation of test specimen> As shown in FIGS. 1 and 2, impact test specimens 2 and hardness test specimens 3 were cut from one of the two grinders used in each of the Examples and Comparative Examples. The impact test specimens 2 were obtained by cutting three sets of specimens, the inner, middle, and outer, in the radial direction from the inner periphery to the outer periphery of the grinder 1. The impact test specimens 2 were 55 mm long (25 mm in Example 5 and 45 mm in Example 6) with a longitudinal direction in the thickness direction of the grinder, and had a cross-section of 10 mm × 10 mm. To ensure that the length of the impact test specimens 2 was 55 mm, 15 mm long square pieces with the same cross-sectional area (10 mm × 10 mm) were brazed to both ends of the impact test specimens 2 in Example 5. Similarly, 5 mm long square pieces with the same cross-sectional area (10 mm × 10 mm) were brazed to both ends of the impact test specimens 2 in Example 6. Three sets of such impact test specimens 2 were prepared from one grinder 1. For each test specimen, the center of the outer periphery of the grinder 1 (the center in the direction of thickness T) was set as the notch side. For the hardness test specimens 3, as shown in Figures 1 and 2, cube-shaped specimens each measuring 10 mm x 10 mm x 10 mm in thickness were cut out into a total of nine pieces: three in the direction of thickness T and three in the direction of width W2. Each set consisted of nine test specimens, and three sets were cut out from one grinder for each example and comparative example.

[0071] Various tests were carried out using the following methods.

[0072] <Impact test using Charpy impact test> The impact test was conducted in accordance with JIS Z 2242 (2005). A 2 mm U-notch was formed in the impact test specimen 2 of each example and comparative example, and the impact test value was measured. The impact test was conducted on three sets of impact test specimens 2, with each set consisting of the inner, middle, and outer radial locations. The average value was calculated for each location. As mentioned above, the U-notch at each location of the impact test specimen 2 was located at the center of the grinder in the thickness direction.

[0073] The impact test values ​​were evaluated according to the following criteria. A: The average of the three points on the inside, middle, and outside is 30 J / cm2 End B: The average of the three points on the inside, middle, and outside is 20 J / cm 2 More than 30J / cm 2 less than C: The average of the three points on the inside, middle, and outside is 20 J / cm 2 less than

[0074] <Shore hardness test> The hardness test was performed on three sets of hardness test specimens 3, each consisting of nine specimens per set, obtained for one Example and Comparative Example. The Rockwell hardness (HRC) of each specimen was measured in accordance with JIS Z 2245 (2021) and converted to Shore hardness (HS) using a conversion table. The average value of the three sets of Shore hardness (HS) was calculated for each of the nine locations. The maximum and minimum values ​​were calculated from the average Shore hardness (HS) values ​​for each of the nine locations, and the difference between the maximum and minimum values ​​was determined.

[0075] The Shore hardness (HS) was evaluated according to the following criteria. A: (Maximum value - Minimum value) is 4 or less B: (Maximum value - minimum value) is greater than 4 and less than or equal to 5 C: (Maximum value - Minimum value) is greater than 5

[0076] <Heat treatment cracks> During the homogenization treatment and quenching processes, the occurrence of cracks was visually observed. Those in which no cracks were observed visually were evaluated as "absent," and those in which cracks were observed were evaluated as "present."

[0077] <Abrasion test> The grinders of the Example and Comparative Examples were attached to a vertical crusher of an actual plant, and the grinders were operated in the actual plant to carry out a wear test. The reduction rate of the grinder's weight before and after the test was calculated as the wear reduction rate. The test conditions were as follows: (Test conditions) Crusher: "KE-600" manufactured by Kubota Environmental Engineering Co., Ltd. Grinder speed: 300 rpm Materials to be crushed: printed circuit boards, metal scraps Operating hours: 484 hours in total

[0078] The abrasion test was evaluated according to the following criteria: If the grinder was broken during the abrasion test and the weight could not be measured after the test, the test was deemed "unable to test." A: Wear reduction rate is 7% or less B: Wear reduction rate is over 7% and 8% or less C: Wear reduction rate exceeds 8% or evaluation is not possible

[0079] Furthermore, the prior austenite grain size and transformation thermal expansion coefficient were measured by the following methods.

[0080] <Prior austenite grain size> The grinders of the examples and comparative examples were mirror-polished and then immersed in an etching solution (nital) for 2 minutes, and the prior austenite grain boundaries of the metal structure were observed with an optical microscope. Approximately 70 points were observed for each, and the average values ​​were calculated.

[0081] <Transformation thermal expansion coefficient> Test pieces (φ3 mm × length 10 mm) separately cut from the grinders of the Examples and Comparative Examples were heated to 900°C in a Formaster testing machine (manufactured by Fuji Electric Industrial Co., Ltd., product name "formaster-EDP-FTM-100"), and the transformation thermal expansion coefficient was measured from 350°C to room temperature (25°C) at a cooling rate of 2°C / sec. The transformation thermal expansion coefficient was evaluated according to the following criteria. A: Transformation thermal expansion coefficient is 0.2% or less B: Transformation thermal expansion coefficient exceeds 0.2%

[0082] The results of the above tests are shown in Table 2.

[0083] [Table 2]

[0084] Examples 1 to 6 had no heat treatment cracks, were all rated A in the impact test, had a Shore hardness (HS) rating of B or higher, and were also rated B or higher in the abrasion test, and thus had both impact resistance and abrasion resistance and were excellent in abrasion resistance. In contrast, Comparative Examples 1 to 10 were all rated C in the impact test, and were unable to achieve both sufficient impact resistance and abrasion resistance.

[0085] In detail, in Examples 1 to 6, the impact test values ​​were all 32 J / cm 2 or more (evaluation A), whereas in Comparative Examples 1 to 10, 2 or less (rating C), and Examples 1 to 6 were superior in impact resistance to Comparative Examples 1 to 10. Furthermore, Examples 1 to 6, which contained a predetermined amount of B, had a difference between the maximum and minimum Shore hardness (HS) values ​​of 5 or less (rating A or B), whereas Comparative Examples 2, 4 to 7, which did not contain B, all had a difference between the maximum and minimum Shore hardness (HS) values ​​of 6 or more (rating C), resulting in variations in Shore hardness (HS). Comparative Examples 2, 4 to 7, which did not contain B, all received a rating of C in the abrasion test, and were inferior in abrasion resistance to Examples 1 to 6.

[0086] Comparative Example 1, which had a low Ni content of 0.08% and was outside the scope of the present invention, had a difference between the maximum and minimum Shore hardness (HS) of 10 (evaluation C), and was rated C for wear resistance, indicating that the wear resistance was inferior to Examples 1 to 6. Comparative Example 8, which had a high Mo content of 0.38% and was outside the scope of the present invention, had a difference between the maximum and minimum Shore hardness (HS) of 7 (evaluation C), and cracks occurred due to heat treatment. These phenomena are thought to be due to variations in Shore hardness (HS).

[0087] In Comparative Examples 3 and 9, which had a B content of 0.009% and were outside the scope of the present invention, the difference between the maximum and minimum Shore hardness (HS) values ​​was 5 (rating B), and the abrasion resistance was rated B or higher. However, the impact test rating was a low C, and the samples were unable to achieve both impact resistance and abrasion resistance.

[0088] Comparative Example 10, which is outside the scope of the present invention in that it contains 0.38% C and 0.2% Al, had a difference between the maximum and minimum Shore hardness (HS) values ​​of 4 (rating A), but received a low rating of C in the impact test, meaning that it was unable to achieve both impact resistance and strength.

[0089] Furthermore, Comparative Examples 5 and 6, which did not contain B, and Comparative Example 8, which had a high Mo content of 0.38%, received an impact test evaluation of C, and also received a Shore hardness (HS) evaluation of C, and cracks occurred during heat treatment. Comparative Examples 5 and 6 had severe cracks, and if they were subjected to an abrasion test, there would be a risk of accidents due to flying pieces, so the abrasion test could not be carried out. Comparative Example 8 also had cracks, so the abrasion test could not be carried out.

[0090] As shown in Table 2, the average grain size of prior austenite in Examples 1 to 6 and Comparative Examples 1 to 10 was in the range of 100 to 120 μm, and it was confirmed that the average grain size of martensite was approximately the same. Comparative Examples 5, 6, and 8, in which heat treatment cracking occurred, all had high transformation thermal expansion coefficients exceeding 0.2% (evaluation B). [Industrial Applicability]

[0091] The steel castings of the present invention can be used as various parts for crushers, pulverizers, etc. [Explanation of symbols]

[0092] 1: Crusher parts (crusher blades) 2: Impact test specimen 3: Hardness test specimen

Claims

1. A cast steel product comprising, by mass%, C: 0.28% or more and 0.36% or less, Si: 0.10% or more and 0.50% or less, Mn: 0.60% or more and 1.20% or less, P: more than 0.0% and 0.04% or less, S: more than 0.0% and 0.04% or less, Ni: 1.0% or more and 1.5% or less, Cr: 0.8% or more and 1.2% or less, Mo: 0.0% or more and 0.35% or less, B: 0.001% or more and 0.007% or less, and Al: 0.0% or more and 0.1% or less, with the balance being Fe and unavoidable impurities, and having a portion with a wall thickness of 1 inch or more.

2. 2. The steel casting according to claim 1, which has been heat treated at a temperature of 800°C or higher but lower than 1000°C.

3. Impact test value in Charpy impact test according to JIS Z 2242 is 30 J / cm ２ The steel casting according to claim 1 .

4. 4. The steel casting according to claim 3, wherein the difference in Shore hardness (HS) between two samples taken at random from two locations is 5 or less.

5. 5. The steel casting according to claim 4, wherein each of the samples has a Shore hardness (HS) of 60 to 74.

6. The steel casting according to any one of claims 1 to 5, which is a part for a crusher.

7. a casting step of obtaining a first intermediate casting containing, by mass%, C: 0.28% to 0.36%, Si: 0.10% to 0.50%, Mn: 0.60% to 1.20%, P: more than 0.0% to 0.04%, S: more than 0.0% to 0.04%, Ni: 1.0% to 1.5%, Cr: 0.8% to 1.2%, Mo: 0.0% to 0.35%, B: 0.001% to 0.007%, and Al: 0.0% to 0.1%, with the balance being Fe and unavoidable impurities, and having a portion with a thickness of 1 inch or more; a homogenization treatment step of heating and holding the first intermediate casting at 900°C or higher and 960°C or lower, and then furnace cooling the first intermediate casting to obtain a second intermediate casting; and a quenching step of heating and holding the second intermediate casting at a temperature of 800°C or higher but 950°C or lower, and then water-cooling the second intermediate casting to obtain a steel casting.

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