Cast steel products and methods for manufacturing cast steel products

Abstract

This enables the creation of thick-walled cast steel products that achieve both hardness and toughness. [Solution] The cast steel product contains, by mass%, C: 0.27% to 0.37%, Si: 0.20% to 0.80%, Mn: 0.60% to 1.10%, P: greater than 0.0% and less than 0.04%, S: greater than 0.0% and less than 0.04%, Ni: 1.2% to 2.0%, Cr: 1.5% to 2.0%, Mo: 0.0% to 0.2%, and Al: 0.0% to 0.1%, with the remainder being Fe and unavoidable impurities, and has a wall thickness of 1 inch or more, and the impact value in the Charpy impact test measured in accordance with JIS Z 2242 is 20 J / cm². 2 That's all.

Description

[Technical Field]

[0001] This invention relates to cast steel products and methods for manufacturing cast steel products. [Background technology]

[0002] Traditionally, crushers have been used in recycling facilities and other similar facilities to crush materials such as waste materials containing various metals, construction waste materials such as concrete, and various types of bulky waste. Among the crushers, vertical crushers are known, which coarsely crush the material to be crushed with a breaker that rotates at high speed inside the shell, and then finely crush it with a grinder. Vertical crushers have many advantages, such as high processing efficiency because the input material is crushed while falling naturally, and good maintainability. However, wear and damage to various parts that directly contribute to crushing (cast steel parts such as shell liners, breaker liners, and grinders) are still unavoidable, and since these parts are consumables, they need to be replaced periodically.

[0003] To improve the wear resistance of cast steel used in parts of such crushers, for example, Japanese Patent Publication No. 2012-246564 (Patent Document 1) describes a cast steel composition by mass%, consisting of C: 0.30%~0.35%, Si: 0.30%~0.60%, Mn: 0.90%~1.50%, Cr: 0.91%~1.50%, Ni: 1.60%~1.90%, Mo: 0.20%~0.30%, P: 0.05% or less, S: 0.05% or less, with the remainder being Fe and unavoidable impurities, with a product wall thickness of 1 inch or more, a hardness of HRC 45~53, and a Charpy impact value (U-notch) of 20~40 J / cm². 2 A wear-resistant low-alloy cast steel has been proposed. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-246564 [Overview of the project] [Problems that the invention aims to solve]

[0005] When a product has a large wall thickness, such as 1 inch or more, it is difficult to ensure sufficient hardenability in the interior of the product, such as in the center of the wall thickness. As a result, the hardness and impact resistance in the interior of the product are lower than on the exterior, and consequently, wear resistance tends to decrease. For this reason, the wear-resistant low-alloy cast steel described in Patent Document 1 requires three steps: a homogenization process in which the cast product is heated and held at 1000°C to 1100°C and then furnace-cooled; a quenching process in which the product is heated and held at 850°C to 950°C, then immersed in water and water-cooled; and a tempering process in which the product is heated and held at 150°C to 280°C and then furnace-cooled to room temperature. Therefore, manufacturing costs tend to increase, and there is also a risk of reduced hardness due to the tempering process. There is still room for improvement in the production of thick-walled cast steel products that achieve both impact resistance and hardness. Furthermore, from the viewpoint of toughness of cast steel products, it is desirable for them to have excellent strength (tensile strength, etc.) in addition to impact resistance, as this would make them even less prone to breakage.

[0006] Thus, there is a need to create thick-walled cast steel products that achieve both hardness and toughness. [Means for solving the problem]

[0007] The cast steel product according to the present invention contains, by mass%, C: 0.27% to 0.37%, Si: 0.20% to 0.80%, Mn: 0.60% to 1.10%, P: greater than 0.0% and less than 0.04%, S: greater than 0.0% and less than 0.04%, Ni: 1.2% to 2.0%, Cr: 1.5% to 2.0%, Mo: 0.0% to 0.2%, and Al: 0.0% to 0.1%, with the remainder being Fe and unavoidable impurities, having a wall thickness of 1 inch or more, and an impact value of 20 J / cm in a Charpy impact test measured in accordance with JIS Z 2242. 2 The above is the characteristic feature.

[0008] Furthermore, the method for manufacturing a cast steel product according to the present invention is characterized by comprising: a casting step to obtain a first intermediate casting having a wall thickness of 1 inch or more, comprising, by mass%, C: 0.27% or more and 0.37%, Si: 0.20% or more and 0.80%, Mn: 0.60% or more and 1.10%, P: greater than 0.0% and 0.04%, S: greater than 0.0% and 0.04%, Ni: 1.2% or more and 2.0%, Cr: 1.5% or more and 2.0%, Mo: 0.0% or more and 0.2%, and Al: 0.0% or more and 0.1%, with the remainder being Fe and unavoidable impurities; a homogenization step to obtain a second intermediate casting by heating and holding the first intermediate casting at 900°C or more and 960°C or less, followed by furnace cooling; and a quenching step to obtain a cast steel product by heating and holding the second intermediate casting at 800°C or more and 950°C or less and then oil cooling.

[0009] These configurations enable the creation of thick-walled cast steel products that achieve both hardness and toughness. In particular, since tensile strength can be improved in addition to wear resistance and impact resistance, cast steel products that are less prone to breakage than conventional products can be realized.

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

[0011] The cast steel product according to the present invention is preferably heat-treated at a temperature of 800°C or higher but less than 1000°C.

[0012] This configuration allows for a homogenized structure, making it easier to release stresses generated during casting and thus increasing hardness.

[0013] The cast steel product according to the present invention preferably has a tensile strength of 1700 MPa or more, as measured in accordance with JIS Z 2241.

[0014] This configuration offers excellent tensile strength in addition to impact resistance, and makes it easier to further improve toughness.

[0015] The cast steel product according to the present invention has a Shore hardness (HS) of 60 to 74, and an impact value in the Charpy impact test measured in accordance with JIS Z 2242 is 28 J / cm 2 or more, which is preferable.

[0016] According to this configuration, it is excellent in hardness and toughness, and it is easy to improve the balance of physical properties as a product.

[0017] The cast steel product according to the present invention is preferably a part for a crusher.

[0018] Since the cast steel product according to the present invention has improved tensile strength in addition to wear resistance and impact resistance, it is easy to apply to parts for crushers.

[0019] Further features and advantages of the present invention will become clearer from the following description of exemplary and non-limiting embodiments described with reference to the drawings.

Brief Description of Drawings

[0020] [Figure 1] It is a schematic view of a blade for a crusher according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view taken along line II-II of FIG. 1. [Figure 3] It is a view showing the shape of a keel block for a casting test created in an example, (a) is a front view, and (b) is a side view.

Modes for Carrying Out the Invention

[0021] Hereinafter, embodiments of a cast steel product and a method for manufacturing a cast steel product according to the present invention will be described with reference to the drawings.

[0022] In this specification, "cast steel" means Fe-C alloy used in casting before it is shaped into a product, and "cast steel product" refers to a product made by pouring molten cast steel into a mold to form a required shape. "Cast steel product" includes not only products that have been shaped into a final product by machining such as cutting, but also intermediate products in the manufacturing process before machining. The cast steel product according to the present invention has portions with a wall thickness of 1 inch or more.

[0023] First, the composition of each component of the cast steel product will be described. Unless otherwise specified in this specification, "%" refers to "mass%".

[0024] [Component composition of cast steel products] C: 0.27% or more and 0.37% or less Carbon (C) is the main element contributing to hardenability, ensuring hardness by forming a martensite structure. Therefore, C is included at a concentration of 0.27% or more. Hardenability is related to both the hardening ability, which is the ability to increase the hardness of the hardened area, and the depth to which the hardening occurs. Since the cast steel products of the present invention have a wall thickness of 1 inch or more, C alone is insufficient to ensure hardness in the thick interior, and the addition of elements such as Cr is necessary. On the other hand, the C content is kept at 0.37% or less to maintain an appropriate toughness range and prevent cracking during hardening (quench cracking).

[0025] Si: 0.20% or more and 0.80% or less Silicon (Si) is an essential element for deoxidation and ensuring molten metal flow, contributing to the suppression of gas defects and poor molten metal flow, and consequently to the soundness of cast steel products. Therefore, Si is included at a concentration of 0.20% or more. On the other hand, the Si content is kept below 0.80% to maintain an appropriate level of toughness. Since Si is consumed during casting as a deoxidizing agent, it is preferable to add approximately 1.5 to 2 times the final composition during casting.

[0026] Mn: 0.60% or more and 1.10% or less Manganese (Mn) is an essential element for deoxidation, contributing to the suppression of gas defects and, consequently, to the integrity of cast steel products. Therefore, Mn should be included at a concentration of 0.60% or more. On the other hand, the Mn content should be kept below 1.10% to maintain an appropriate level of toughness. Since Mn is also consumed during casting as a deoxidizing agent, it is preferable to add approximately 1.5 to 2 times the final composition of Mn during casting.

[0027] P: Greater than 0.0% and less than or equal to 0.04% The phosphorus (P) content is kept below 0.04% to prevent embrittlement and casting cracking.

[0028] S: Greater than 0.0% and less than or equal to 0.04% Sulfur (S) content is kept below 0.04% to prevent embrittlement and casting cracking.

[0029] Ni: 1.2% or more and 2.0% or less Nickel (Ni) is an element necessary for ensuring the toughness and strength of cast steel products. Since the cast steel products of the present invention have a wall thickness of 1 inch or more, Ni is contained at a concentration of 1.2% or more to ensure hardness and toughness within the thick walls. On the other hand, in order to keep costs down, the Ni content is kept at 2.0% or less.

[0030] Cr:1.5% or more and 2.0% or less Cr (chromium), along with C, is an important element for ensuring hardenability. Since the cast steel products of the present invention have a wall thickness of 1 inch or more, the interior of the thick wall cannot be rapidly cooled and is difficult to harden, so it is important to ensure hardness in the interior of the thick wall with Cr. For this reason, Cr is included in a range of 1.5% or more. In the present invention, by setting the Cr content in the range of 1.5% to 2.0%, not only hardness but also toughness (impact resistance and tensile strength) can be achieved, resulting in an excellent balance of physical properties. Furthermore, by setting the Cr content to 2.0% or less, it is possible to suppress costs and ensure manufacturability such as formability and weld repairability. The Cr content is preferably in the range of 1.5% to 1.73%.

[0031] Mo: 0.0% or more and 0.20% or less Mo (molybdenum), like Cr, contributes to ensuring hardenability and hardness. It also contributes to improving mechanical properties and toughness. Mo does not need to be included (i.e., it can be 0%). On the other hand, the Mo content is kept below 0.20% to control costs.

[0032] Al: 0.0% or more and 0.1% or less Aluminum (Al) is an element necessary for deoxidation, contributing to the suppression of gas defects and, consequently, to the integrity of cast steel products. While Al does not necessarily have to be present (i.e., it can be 0%), it is preferable to have a content of 0.02% or more. On the other hand, the Al content is kept at 0.1% or less to maintain an appropriate level of toughness.

[0033] The remainder is Fe and unavoidable impurities. The remainder consists of unavoidable impurities that are introduced during the process of melting Fe into raw materials such as ore and scrap, as well as various factors in the manufacturing process. Examples of unavoidable impurities include O, S, N, and H, but are not limited to these. 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.

[0034] [Cast steel products] The cast steel product having the above components and component ratios has a portion with a wall thickness of 1 inch (2.54 cm) or more. Conventional cast steel products are difficult to harden near the center of the wall thickness, resulting in low internal hardness and impact resistance. However, the cast steel product according to this embodiment has the above-described component composition, which suppresses the decrease in internal hardness and impact resistance. The cast steel product according to this embodiment is assumed to have been heat-treated at 800°C or higher and less than 1000°C, but the heat treatment will be described later.

[0035] The cast steel product according to this embodiment exhibits excellent wear resistance and impact resistance, and also has improved tensile strength, making it suitable for use as, for example, a component for a crusher. Specifically, the cast steel product has a portion with a wall thickness of 1 inch or more and possesses the following physical properties, resulting in a well-balanced product in terms of physical properties.

[0036] 1) Shore stiffness (HS) The Shore hardness (HS) of a randomly selected sample 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 using tungsten carbide spheres. In other words, the cast steel product according to this embodiment has sufficient hardness not only on the outer surface of the product but also in the center in the thickness direction. Preferably, the Shore hardness (HS) is 65 to 73.

[0037] 2) Impact value The impact value (U-notch) in the Charpy impact test, measured in accordance with JIS Z 2242, for a randomly selected sample from the cast steel product according to this embodiment was 20 J / cm². 2 This concludes the explanation. In other words, the cast steel product according to this embodiment has impact resistance not only on the outer surface of the product but also in the center of the thickness direction. The upper limit of the impact value in the Charpy impact test is not particularly limited, but is 50 J / cm². 2 The following applies: The impact value (U-notch) is preferably 28 J / cm². 2 More preferably, 29-50 J / cm² 2 That is the case.

[0038] 3) Tensile strength The tensile strength of a randomly selected sample from the cast steel product according to this embodiment, measured in accordance with JIS Z 2241, is 1700 MPa or higher. In other words, the cast steel product according to this embodiment has sufficient strength not only on the outside of the product but also in the center in the thickness direction. Preferably, the tensile strength is 1750 MPa or higher. The upper limit of the tensile strength is not particularly limited, but it is 2000 MPa or lower.

[0039] Figures 1 and 2 show the cast steel product according to this embodiment applied to a crusher blade (an example of a crusher component).

[0040] The crusher blade 1 is a crusher component used in a vertical crusher, and is a gear-shaped component (grinder) that finely crushes the material to be crushed after it has been coarsely crushed by the breaker. In this embodiment, the crusher blade 1 has an inner diameter D1 of 130 mm, an outer diameter D2 of 320 mm, a wall thickness T of 65 mm (i.e., 1 inch or more), a width W1 of 95 mm, and a width W2 of 75 mm, but the dimensions are not limited to these.

[0041] As described above, even with a large wall thickness, the cast steel product of this embodiment exhibits excellent wear resistance due to suppressed reduction in hardness within the product, and also has excellent impact resistance, making it suitable for use as a crusher part such as the crusher blade 1. Due to these excellent wear resistance and impact resistance, the crusher blade 1 has excellent durability, and the frequency of parts replacement can be reduced compared to conventional products.

[0042] Next, we will describe a method for manufacturing a crusher blade 1 as an example of a cast steel product.

[0043] [Manufacturing method for cast steel products (breaker blades)] ≪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 material steel billets (steel slabs, steel blooms, etc.) having the same composition as the above-mentioned cast steel product are melted to form molten steel, which is then poured into a mold (for example, a sand mold) to produce a first intermediate casting in the shape of the crusher blade 1. The casting temperature is preferably set to the melting point + approximately 100°C, and in this embodiment, it is set to 1550°C or higher and 1630°C or lower. Setting the casting temperature within this range makes it less likely for molten metal to flow poorly, and oxidation and casting cracks are also easily suppressed.

[0044] 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 and less than 1000°C. In detail, the heat treatment consists of a homogenization process and a quenching process, and can optionally include a tempering process. The following describes each step of the heat treatment.

[0045] <<Homogenization Process>> The homogenization process involves heating the first intermediate casting obtained in the casting process to 900°C or higher and holding it at 960°C or lower, and then cooling it in a furnace (furnace cooling) to obtain a second intermediate casting. Specifically, the homogenization process is performed to remove non-uniform structures such as segregation of coarse dendrite structures present in the first intermediate casting and to obtain an austenitic structure. Casting stress generated in the first intermediate casting during the casting process is also removed during the homogenization process. The temperature of the homogenization process can be less than 1000°C. If the temperature of the homogenization process is less than 1000°C, oxidation is less likely to progress and surface irregularities are less likely to occur. As a result, dimensional accuracy is easier to maintain. Preferably, the temperature of the homogenization process is between 900°C and 960°C. If the temperature of the homogenization process is above 900°C, carbides are more likely to solid dissolve in the matrix, and a homogenized structure is more easily obtained. The holding time for the homogenization treatment varies depending on the thickness of the casting, but is preferably 2 to 8 hours, more preferably 3 to 6 hours. After holding at the predetermined temperature for the predetermined time as described above, it is desirable to slowly cool (furnace cooling) in the furnace to prevent residual stress. 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, thereby obtaining a second intermediate casting with improved mechanical properties.

[0046] After the homogenization process, the second intermediate casting is subjected to machining, cutting, or other processes as needed.

[0047] ≪Heat treatment process≫ The quenching process is an oil quenching process in which the second intermediate casting is heated and held at 800°C to 950°C, and then cooled in oil (oil quenching). The oil quenching process is performed after the homogenization process to increase the hardness of the second intermediate casting. In the oil quenching process, the austenitic state is transformed into a martensitic structure by cooling at a slightly slower rate, and it is preferable to perform the process so that the average grain size of the martensite in the martensite structure after the quenching process is 50 μm to 300 μm. Oil quenching allows for slower cooling compared to water quenching, and the structure tends to become more uniform compared to water quenching, which can suppress the occurrence of cracks, etc. An average grain size of martensite in this range tends to have excellent impact resistance. It is more preferable to perform the process so that the average grain size of the martensite is 100 μm to 200 μm. Since cast steel products have thick-walled parts with a wall thickness of 1 inch or more, the average grain size of the martensite structure becomes relatively coarser in the thick-walled parts. In this specification, the average grain size of martensite is determined by the average grain size of prior austenite.

[0048] The quenching temperature can be between 800°C and 950°C. If the quenching temperature is 800°C or higher, the structure tends to become more uniform, and the hardness and wear resistance do not decrease easily. If the quenching temperature is 950°C or lower, the grains do not coarse easily, and the mechanical properties do not decrease easily. The holding time at the above quenching temperature varies depending on the thickness of the casting, but is preferably 2 to 6 hours, more preferably 3 to 4 hours. Furthermore, the oil quenching process is preferably carried out with quenching oil at 40 to 80°C, and it is preferable that the temperature of the quenching oil is controlled to a constant temperature in the range of 50 to 60°C, for example. As the quenching oil used in the oil quenching process, a general type of quenching oil can be used, and there are no particular limitations on its type, but for example, oil such as re-distilled refined oil may be used.

[0049] When the wall thickness of a casting is 1 inch or more, it can be difficult to harden the material to the center of the wall thickness. However, in this invention, since the material contains 1.5% to 2.0% Cr and 1.2% to 2.0% Ni, the hardening depth can be increased, allowing the material to harden to the center of the wall thickness. As a result, the decrease in hardness in the center of the wall thickness can be suppressed. Furthermore, by using oil cooling instead of water cooling during the hardening process, cracking during cooling can be prevented, improving impact resistance and tensile strength.

[0050] If the tempering process described below is not performed after the quenching process, the cast steel product will be cleaned, polished, etc. as needed to become the final product (cast steel product). The tempering process shown below may be performed at the discretion of the manufacturer.

[0051] ≪Tempering process≫ The tempering process is a further heat treatment process for cast steel products after the quenching process. Tempering is usually performed to restore toughness, even at the expense of some hardness. In this embodiment, the cast steel product has the above-mentioned proportions of components that can reduce toughness (C, Si, Mn, P, S, Al) and the above-mentioned proportions of components that contribute to improving toughness (Cr, Ni), and is further oil-quenched. As a result, the cast steel product has high impact resistance and tensile strength (toughness) after quenching. Therefore, there is no need to restore toughness, and the tempering process can be omitted. Omitting the tempering process also reduces the reduction in hardness caused by the tempering process, and the cast steel product after quenching can possess high toughness and hardness.

[0052] Furthermore, a tempering process may be performed as needed. If a tempering process is performed, the tempering temperature can be low-temperature tempering between 150°C and 280°C, and the holding time will vary depending on the thickness of the cast steel product, but it should be 1 to 3.5 hours, preferably 1.5 to 3 hours.

[0053] [Other embodiments] Other embodiments of the cast steel product and the method for manufacturing the cast steel product according to the present invention will be described below. Note that the configurations disclosed in each of the following embodiments can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise.

[0054] In the above embodiment, a configuration in which the cast steel product is a crusher component (crusher blade) was described as an example. However, in the present invention, the cast steel product may be applied not only to crusher components but also to other products such as pulverizers that require wear resistance and impact resistance. Furthermore, although the above embodiment described a configuration in which the crusher component is a crusher blade as an example, the crusher component may be a shell liner, a breaker liner, etc. Moreover, it is not limited to components of vertical crushers, but may be components of various types of crushers, such as horizontal crushers.

[0055] In the above embodiment, a configuration was described in which the wall thickness of the cast steel crusher blade was 65 mm (Figure 2). However, the wall thickness of the cast steel product of the present invention does not need to be more than 1 inch, and the wall thickness is not limited to that extent.

[0056] In the above embodiment, a configuration in which the cast steel product is heat-treated at 800°C or higher but less than 1000°C was described as an example. However, in the present invention, the cast steel product may also include products that have not been heat-treated at the above temperature. For example, it may be an unheat-treated intermediate product.

[0057] In the above embodiment, a configuration in which the tensile strength measured in accordance with JIS Z 2241 (2011) is 1700 MPa or more was described as an example. However, the numerical value of the tensile strength is not limited in the present invention.

[0058] In the above embodiment, a configuration with a Shore hardness (HS) of 60 to 74 was described as an example. However, the value of the Shore hardness (HS) is not limited in the present invention.

[0059] With regard to other configurations, the embodiments disclosed herein are illustrative in all respects, and it should be understood that the scope of the present invention is not limited thereto. Those skilled in the art will readily understand that modifications can be made as appropriate without departing from the spirit of the invention. Therefore, other embodiments modified without departing from the spirit of the invention are naturally included within the scope of the present invention. [Examples]

[0060] The present invention will be further described below with reference to examples. However, the following examples are not intended to limit the present invention.

[0061] (Examples 1-4, Comparative Examples 1-10) Steel billets (steel slabs) of each composition shown in Table 1 were melted to produce molten steel, which was then poured into sand molds at a casting temperature of 1600°C to produce keel blocks 2 (first intermediate castings) for test casting. The shape of the produced keel blocks 2 is shown in Figure 3 (a) front view and (b) right side view. The rear view is the same as the front view, and the left side view is the same as the right side view. Each side of the keel block 2 is tapered. The dimensions of the produced keel blocks 2 are L1 = 260 mm, L2 = 80 mm, L3 = 100 mm, L4 = 110 mm, H1 = 50 mm, and H2 = 150 mm.

[0062] For each example and comparative example, the keel block 2 was cut from the bottom end at a height of H1 to obtain a plate-shaped block 21 with a wall thickness of 50 mm. Next, heat treatment was carried out under the conditions shown in Table 1 to obtain a cast steel product with a wall thickness of 50 mm. In detail, the homogenization process in Table 1 was performed by heating and holding the first intermediate casting of each example and comparative example in a 930°C furnace for 3 hours, followed by furnace cooling. The quenching process was performed by heating and holding the homogenized second intermediate casting of each example and comparative example in a 900°C furnace for 3 hours, followed by oil cooling in Examples 1-4 and Comparative Examples 1-8, and water cooling in Comparative Examples 9 and 10. Oil cooling was performed using JIS K 2242 Type 1 heat treatment oil for general quenching (oil temperature at 60°C). The tempering process was not performed in any of the examples or comparative examples.

[0063] <<Preparation of test specimens>> Test specimens were prepared by cutting out pieces from the center of the 50 mm thick cast steel products obtained through the above process for each example and comparative example. Each test specimen was cut from the cast steel product manufactured from the plate-shaped block 21, avoiding both ends of 30 mm in the L1 direction and both ends of 12 mm in the L2 and L3 directions.

[0064] (Test specimen for hardness testing) Three cube-shaped test pieces, each measuring 10mm x 10mm x 10mm on each side, were cut from the central part of the cast steel's wall thickness.

[0065] (Test specimen for impact testing) Three test specimens were prepared with a cross-section of 10 mm x 10 mm and a length of 55 mm, with the L1 direction being the longitudinal direction. A 2 mm U-shaped notch was formed in the longitudinal center of each test specimen.

[0066] (Test specimen for tensile strength testing) Two test specimens (No. 14A) with a parallel section cross-section of 10 mm in diameter and 200 mm in length were prepared in accordance with JIS Z 2241, with the L1 direction being the longitudinal direction.

[0067] The following tests were conducted using the methods described below.

[0068] ≪Shore hardness test≫ Hardness testing was performed by measuring Rockwell hardness (HRC) in accordance with JIS Z 2245 (2021), and then converting it to Shore hardness (HS) using a conversion table. For each example and comparative example, Shore hardness testing was performed on three test specimens prepared for hardness testing, and the average value was used to determine the Shore hardness (HS).

[0069] ≪Impact testing using the Charpy impact test≫ Impact tests were conducted in accordance with JIS Z 2242 (2005). Impact tests were performed on three test specimens prepared for each example and comparative example, and the impact value was determined from the average value.

[0070] ≪Tensile Strength Test≫ The tensile strength test was carried out in accordance with JIS Z 2241 (2011). The tensile strength was performed on two tensile strength test pieces prepared for each of the examples and comparative examples, and the tensile strength was determined by the average value thereof.

[0071] Also, the prior austenite grain size was measured by the following method.

[0072] ≪Prior Austenite Grain Size≫ After mirror-polishing the cast steel products of the examples and comparative examples, they were immersed in a corrosion solution (nital) for 2 minutes, and the prior austenite grain boundaries of the metal structure were observed with an optical microscope. About 70 points were observed respectively, and the average value was determined.

[0073] The test results of each of the examples and comparative examples are shown in Table 1 together with their manufacturing conditions.

Table 1

[0074] As shown in Table 1, in Examples 1 to 4, the Shore hardness (HS) was all within the range of 60 to 74, the impact value was 28 J / cm 2 or more, the tensile strength was 1700 MPa, the hardness was high, the impact resistance and tensile strength were also excellent, and both hardness and toughness were excellent.

[0075] On the other hand, in Comparative Examples 1 to 8 where the Cr content was outside the scope of the present invention, the hardness and impact value were good, but the tensile strength was inferior to that of Examples 1 to 4. Among them, Comparative Examples 9 and 10 in which water cooling was performed instead of oil cooling in the homogenization process had an impact value of 19 J / cm 2 or less, the tensile strength was 1360 MPa or less, and the toughness was low. Also, as such, Comparative Examples 1 to 10 could not achieve both hardness, impact resistance and tensile strength.

[0076] Furthermore, as shown in Table 1, the average grain size of the prior austenite in Examples 1-4 and Comparative Examples 1-10 was all within the range of 100-120 μm, confirming that it was approximately the same size as the average grain size of the martensite. [Industrial applicability]

[0077] The cast steel products of the present invention can be used, for example, as various components for crushers, pulverizers, and the like. [Explanation of Symbols]

[0078] 1: Blades for crushers (parts for crushers) 2: Keelblock 21: Plate-shaped block

Claims

1. In mass%, the composition is as follows: C: 0.27% to 0.37%, Si: 0.20% to 0.80%, Mn: 0.60% to 1.10%, P: greater than 0.0% and less than 0.04%, S: greater than 0.0% and less than 0.04%, Ni: 1.2% to 2.0%, Cr: 1.5% to 2.0%, Mo: 0.0% to 0.2%, and Al: 0.0% to 0.1%, with the remainder being Fe and unavoidable impurities. The material has a wall thickness of 1 inch or more, and the impact value in the Charpy impact test, measured in accordance with JIS Z 2242, was 20 J / cm². ２ The above are cast steel products.

2. The cast steel product according to claim 1, which has been heat-treated at a temperature of 800°C or higher and less than 1000°C.

3. The cast steel product according to claim 2, wherein the tensile strength measured in accordance with JIS Z 2241 is 1700 MPa or more.

4. The Shore hardness (HS) is 60 to 74, and the impact value is 28 J / cm². ２ The cast steel product according to claim 3.

5. A cast steel product according to any one of claims 1 to 4, which is a component for a crusher.

6. A casting process to obtain a first intermediate casting having a portion with a wall thickness of 1 inch or more, comprising, by mass%, C: 0.27% to 0.37%, Si: 0.20% to 0.80%, Mn: 0.60% to 1.10%, P: greater than 0.0% and less than or equal to 0.04%, S: greater than 0.0% and less than or equal to 0.04%, Ni: 1.2% to 2.0%, Cr: 1.5% to 2.0%, Mo: 0.0% to 0.2%, and Al: 0.0% to 0.1%, with the remainder being Fe and unavoidable impurities, and the portion having a wall thickness of 1 inch or more, A homogenization process is performed to obtain a second intermediate casting by heating and holding the first intermediate casting at 900°C to 960°C, followed by furnace cooling. A method for manufacturing a cast steel product, comprising a quenching step of heating and holding the second intermediate casting at 800°C to 950°C, and then oil-cooling it to obtain a cast steel product.

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