Wear-resistant cast steel and its manufacturing method

Abstract

To provide a wear-resistant cast steel that can ensure toughness and hardness without a tempering step and a method for producing the same.SOLUTION: A wear-resistant cast steel contains, in mass%, C: 0.27%-0.36%, Si: 0.10%-0.50%, Mn: 0.30%-0.70%, P: 0.04% or less, S: 0.04% or less, Ni: 1.4%-1.9%, Cr: 0.4%-1.0%, Mo: 0.2%-0.3%, Al: 0.1% or less, with the balance being Fe and impurities. The wear-resistant cast steel has the sections that have a product thickness equal to or greater than one inch. The wear-resistant cast steel has an HB hardness of 421-560 and a Charpy impact value of 20-40 J / cm2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wear-resistant cast steel used for crusher parts and the like. [Background technology]

[0002] Crushers are known for crushing scrap metal, crushed stone, bulky waste, etc. Crushers, for example, roughly crush materials by rotating breakers at high speed inside a shell, and then finely crush materials with a rotating grinder. These components require wear resistance and impact resistance, so high-hardness and high-toughness materials are used.

[0003] As one such material, Patent Document 1 discloses a wear-resistant cast steel consisting of, in mass%, 0.30% to 0.35% C, 0.30% to 0.60% Si, 0.90% to 1.50% Mn, 0.91% to 1.50% Cr, 1.60% to 1.90% Ni, 0.20% to 0.30% Mo, 0.05% or less P, 0.05% or less S, and the balance being Fe and impurities. This wear-resistant cast steel has a product thickness of 1 inch or more, an HRC of 45 to 53 (HBW 421 to 525), and a Charpy impact value (U notch) of 20 to 40 J / cm. 2 is.

[0004] In order to achieve the desired hardness and Charpy impact value, the wear-resistant cast steel of Patent Document 1 requires three essential processes: a homogenization process in which the prepared cast steel ingot is heated and held at 1000°C to 1100°C and then furnace cooled; a quenching process in which the ingot is heated and held at 850°C to 950°C and then water cooled; and a tempering process in which the ingot is heated and held at 150°C to 280°C and then furnace cooled to room temperature. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-246564 Summary of the Invention [Problem to be solved by the invention]

[0006] The high-temperature homogenization process and tempering process are costly. Furthermore, the tempering process is performed to restore the toughness lost by quenching, but tempering also reduces hardness. Therefore, there is a need to develop a cast steel material with excellent toughness without reducing hardness.

[0007] An object of the present invention is to provide a wear-resistant cast steel that can ensure toughness and hardness without carrying out a tempering process, and a method for producing the same. [Means for solving the problem]

[0008] The wear-resistant cast steel of the present invention is The alloy contains, in mass%, C: 0.27% to 0.36%, Si: 0.10% to 0.50%, Mn: 0.30% to 0.70%, P: 0.04% or less, S: 0.04% or less, Ni: 1.4% to 1.9%, Cr: 0.4% to 1.0%, Mo: 0.2% to 0.3%, Al: 0.1% or less, and the remainder being Fe and impurities; The product has a wall thickness of 1 inch or more, HB hardness 421~560, Charpy impact value: 20~40J / cm 2 is.

[0009] Si+Mn: 1.0% or less is desirable.

[0010] More preferably, Si is 0.10% to 0.30%, Mn is 0.50% to 0.65%, and Cr is 0.7% or more.

[0011] Average grain size of martensite: desirably 50 μm to 300 μm.

[0012] Further, the method for producing wear-resistant cast steel of the present invention comprises the steps of: A cast steel ingot containing, by mass%, C: 0.27% to 0.36%, Si: 0.10% to 0.50%, Mn: 0.30% to 0.70%, P: 0.04% or less, S: 0.04% or less, Ni: 1.4% to 1.9%, Cr: 0.4% to 1.0%, Mo: 0.2% to 0.3%, Al: 0.1% or less, with the remainder being Fe and impurities; A homogenization process in which the material is heated to 900°C to 960°C and then cooled in the furnace. A quenching process is carried out in which the material is heated and held at 800°C to 950°C, and then water quenched.

[0013] After the quenching step, the tempering step may not be carried out.

[0014] After the quenching step, After heating and holding at 150℃~250℃, return to room temperature air-cooled A tempering step can also be carried out. [Effects of the Invention]

[0015] The wear-resistant cast steel of the present invention can ensure toughness by reducing the Si and Mn contents, so that the tempering process for recovering toughness can be omitted. Since the tempering process can be omitted, a decrease in hardness due to tempering does not occur, and therefore a wear-resistant cast steel with high toughness and high hardness can be obtained. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is an explanatory diagram of the test grinder used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Reason for limiting ingredients> The reasons for limiting the components of the wear-resistant cast steel of the present invention are as follows: In the following, unless otherwise specified, "%" means "mass %".

[0018] C: 0.27% to 0.36% C is a major element that contributes to hardenability, and is contained in an amount of 0.27% or more to transform the structure into martensite and ensure hardness. Hardenability includes both the hardenability, which increases the hardness of the hardened portion, and the hardening depth. Since the wear-resistant cast steel of the present invention has a thickness of 1 inch or more, C alone is insufficient to ensure the hardness inside the thick wall, and the addition of elements such as Cr is necessary. On the other hand, a high C content can lead to a decrease in toughness and cracking during hardening (quench cracking), so the upper limit is set to 0.36%.

[0019] Si: 0.10% to 0.50% Si is an element necessary for deoxidization and ensuring melt flow. It suppresses gas defects and poor melt flow, thereby contributing to the soundness of the cast steel, and therefore should be contained in an amount of 0.10% or more. On the other hand, a high Si content leads to a decrease in toughness, and the decreased toughness is difficult to recover even by tempering, so the upper limit is set to 0.50%, preferably 0.30%, and more preferably less than 0.30%. Note that Si is consumed as a deoxidizer during casting, so it is preferable to add Si in an amount 1.5 to 2 times the final composition during casting.

[0020] Mn: 0.30% to 0.70% Mn is also an element necessary for deoxidation, suppressing gas defects and thereby contributing to the soundness of cast steel, so it should be contained in an amount of 0.30% or more, preferably 0.50% or more. On the other hand, a high Mn content leads to a decrease in toughness, so the upper limit is set to 0.70%, preferably 0.65%. 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.

[0021] P: 0.04% or less, S: 0.04% or less P and S are impurities that cause embrittlement and casting cracks, so the upper limit is set at 0.04%.

[0022] Ni: 1.4% to 1.9% Ni is an element necessary for ensuring the toughness and strength of cast steel, and is contained in an amount of 1.4% or more. In particular, since the wear-resistant cast steel of the present invention has a thickness of 1 inch or more, Ni is essential for ensuring the hardness and toughness inside the thick wall. However, if the Ni content is too high, these effects will saturate and costs will increase, so the upper limit is set to 1.9%.

[0023] Cr: 0.4% to 1.0% Cr, along with C, is an important element for ensuring hardenability. In particular, since the wear-resistant cast steel of the present invention has a thickness of 1 inch or more, the thick-wall interior cannot be rapidly cooled and is difficult to harden, so Cr must be used to ensure the hardness of the thick-wall interior. For this reason, Cr is contained in an amount of 0.4% or more, preferably 0.7% or more. On the other hand, a high Cr content not only increases costs but also reduces manufacturability, such as formability and weld repairability, so the upper limit is set to 1.0%, preferably 0.9%.

[0024] Mo: 0.2% to 0.3% Like Cr, Mo contributes to ensuring hardenability and hardness. It also contributes to improving mechanical properties and toughness. For this reason, Mo should be contained in an amount of 0.2% or more. However, a high Mo content increases costs, so the upper limit is set at 0.3%.

[0025] Al: 0.1% or less Al is an element necessary for deoxidation, suppressing gas defects and thereby contributing to the soundness of cast steel, so it is added. On the other hand, a high Al content leads to a decrease in toughness, so the upper limit is set to 0.1%.

[0026] Remainder: Fe and impurities The balance consists of Fe and impurities that are mixed in due to various factors during the melting process, raw materials such as ore and scrap, and the manufacturing process. Examples of impurities include, but are not limited to, O, S, N, and H. The total amount of impurities should be 0.5% or less, preferably 0.1% or less.

[0027] Cast steel ingots of the above composition are produced by casting. Casting is performed by sand casting, and the casting temperature can be set to the melting point plus approximately 100°C (for example, 1500°C to 1620°C). If the casting temperature is low, poor molten metal flow occurs, while if the casting temperature is high, there is a risk of oxidation or casting cracks. Cast steel ingots are used, for example, for crusher parts. Crusher parts have parts that are 1 inch (2.54 cm) or more in thickness, so the area near the center of the wall thickness cannot be rapidly cooled and is difficult to harden. For this reason, cast steel ingots are subjected to heat treatment.

[0028] The heat treatment includes the homogenization process and the quenching process described below, and may optionally include a tempering process.

[0029] <Homogenization process> The homogenization process is performed to remove inhomogeneous structures, such as the segregation of coarse dendrite structures, present in the cast steel ingot, to relieve casting stress, and to obtain an austenitic structure. The homogenization temperature can be less than 1000°C. Homogenization temperatures above 1000°C increase costs and promote oxidation, resulting in severe surface irregularities and reduced dimensional accuracy. The homogenization temperature is preferably 900°C to 960°C. Homogenization temperatures below 900°C prevent carbides from dissolving in the matrix, making feeder cutting and grinder maintenance difficult. The holding time for the homogenization process varies depending on the thickness of the cast steel ingot, but is typically 2 to 8 hours, preferably 3 to 6 hours. After holding at the specified temperature for the specified time, furnace cooling is desirable to prevent residual stress. The austenitic structure transforms into a ferrite structure during furnace cooling. This homogenization treatment homogenizes the structure in the cast ingot and removes casting stress, thereby improving the mechanical properties.

[0030] After the homogenization process, the cast steel ingot is subjected to machining, fusion cutting, etc. as needed.

[0031] <Quenching process> After the homogenization treatment step, the cast steel ingot is quenched. Quenching is performed to transform the austenite state into a martensite structure by rapidly cooling it, thereby increasing hardness. Quenching is preferably performed so that the average grain size of the martensite is 50 μm to 300 μm, and more preferably 100 μm to 200 μm. The average grain size of the martensite can be the average grain size of the prior austenite. Since the cast steel ingot has thick portions with a thickness of 1 inch or more, the average grain size of the martensite in the thick portions is relatively coarse.

[0032] Specifically, the quenching temperature can be 800°C to 950°C. If the quenching temperature is less than 800°C, the structure becomes non-uniform, resulting in reduced hardness and wear resistance. If the quenching temperature exceeds 950°C, the crystal grains become coarse, resulting in reduced mechanical properties. The quenching holding time varies depending on the thickness of the cast steel ingot, but is 2 to 6 hours, preferably 3 to 4 hours.

[0033] When the thickness of a cast steel ingot exceeds 60 mm, the hardening may not reach the center of the wall. However, the composition of the present invention contains 0.4% to 1.0% Cr, which allows for a large hardening depth and hardening up to the center of the wall.

[0034] If the tempering step described below is not carried out after the quenching step, the cast steel ingot after the quenching step is polished as necessary to produce a finished product.

[0035] <Tempering process (optional)> The tempering process after the quenching process is carried out to restore toughness, even at the expense of some hardness. In the present invention, the cast steel ingot has low Si and Mn, which reduce toughness, so that the cast steel ingot has high toughness even after quenching. Therefore, since there is no need to restore toughness, the tempering process can be omitted, and the reduction in hardness due to the tempering process can also be avoided. Therefore, the cast steel after the quenching process can have high toughness and hardness.

[0036] Although it will increase costs, a tempering process may be carried out as necessary. Tempering reduces hardness, but it can restore the toughness lost by quenching. If tempering is carried out, a low-temperature tempering temperature of 150°C to 280°C is sufficient, and the holding time varies depending on the thickness of the cast steel ingot, but should be 1 to 3.5 hours, preferably 1.5 to 3 hours. To obtain the desired tempering effect, the Larson-Miller parameter [LogT*(20+log(t), where T is the tempering temperature (K) and t is the tempering time (h)] must be 9460 or greater, preferably 9543 or greater. As the tempering temperature x time increases, toughness improves but hardness decreases significantly. Therefore, it is preferable to keep the tempering temperature x time value at 9717 or less, and preferably 9686 or less. Table 1 shows the relationship between the tempering time t and the Larson-Miller parameter when the tempering temperature T is 200°C (473K).

[0037] [Table 1]

[0038] The obtained cast steel product has high hardness and toughness, and is suitable for use as, for example, crusher parts. Specifically, the cast steel product has a portion with a product thickness of 1 inch or more, an HB hardness of 421 to 560 (tungsten carbide ball) (hardness HRC: 45 to 55, hardness HS: 60 to 74), and a Charpy impact value (U notch) of 20 to 40 J / cm 2 Preferably, the HB hardness is 450 to 480, and the Charpy impact value (U notch) is 30 to 40 J / cm 2 is. [Example]

[0039] Two test grinders 10, which are crusher parts shown in Fig. 1, were prepared from the cast steel ingots of the invention example, reference example 1, and comparative example, each having the composition shown in Table 2, and various tests were carried out. The test grinder 10 had a diameter of 340 mm, a thickness of 65 mm (2.56 inches), and a mass of approximately 29 kg.

[0040] [Table 2]

[0041] The compositions of Examples 1 and 2 and Reference Example 1 are all within the range of the present invention. Comparative Example 1 is an example in which the Mn and Si+Mn contents are higher than the range of the present invention, and Comparative Example 2 is an example in which the Si, Mn, Si+Mn, and Ni contents are higher than the range of the present invention.

[0042] The test grinder 10 was produced by obtaining a cast steel ingot by sand casting, and then subjecting the cast steel ingot to a homogenization process, machining, quenching, and optional tempering process as shown in Table 3. The heat treatment conditions are shown in Table 3, but Inventive Example 1 and Comparative Examples 1 and 2 are all examples without tempering, while Inventive Example 2 and Reference Example 1 are examples with tempering.

[0043] [Table 3]

[0044] The homogenization treatment involved heating at 930°C followed by furnace cooling, and the quenching treatment involved heating at 880°C followed by water cooling. Tempering for Example 2 and Reference Example 1 involved holding at 200°C for 2 hours followed by air cooling for Example 2, and air cooling for Reference Example 1, which was the same as Example 2, at 200°C for 4 hours.

[0045] As shown in FIG. 1, test pieces 11, 12, and 13 were cut out from one of the two test grinders 10 thus fabricated. Reference numeral 11 denotes tensile test pieces (two pieces) for a tensile test. Reference numeral 12 denotes impact test pieces (three pieces x three sets) for an impact test, with the outer periphery of the grinder 10 serving as the notch side. Reference numeral 13 denotes a hardness test piece (one piece) for a hardness test.

[0046] Another test grinder 10 was used for wear tests using an actual machine.

[0047] The test pieces 11, 12, and 13 were subjected to various tests in the following manner.

[0048] The tensile test was carried out on 11 tensile test pieces in accordance with JIS Z2241 to measure the tensile strength (N / mm 2 ) and 0.2% yield strength (N / mm 2 ), elongation (%) and reduction in area (%) were measured.

[0049] The impact test was performed on impact test pieces 12 formed with a 2 mm U-notch according to JIS X2202, and the Charpy impact values ​​were measured in accordance with JIS Z2242. The Charpy impact values ​​were measured at three locations on each test piece 12, and the average value was calculated.

[0050] In the hardness test, the Brinell hardness (HB hardness) of the hardness test piece 13 was measured in accordance with JIS Z2243.

[0051] The results of the above tests are shown in Table 4.

[0052] [Table 4]

[0053] First, comparing non-tempered Example 1 with Comparative Examples 1 and 2, Example 1 exhibits the same tensile strength and 0.2% proof stress as Comparative Examples 1 and 2, but exhibits higher elongation and reduction of area. It also exhibits a higher Charpy impact value than the comparative examples. This is the result of reducing Si, Mn, and Si+Mn in Example 1, and it is clear that Example 1 possesses high toughness. Comparative Examples 1 and 2 have high Si, Mn, or Si+Mn contents, resulting in poor elongation, reduction of area, and Charpy impact value, and therefore insufficient toughness. While the hardness of Example 1 is slightly lower than that of Comparative Examples 1 and 2, there is no significant difference between Example 1 and Comparative Examples 1 and 2, and they are comparable.

[0054] Comparing the invention examples, invention example 1 and invention example 2 have the same composition, but they have higher elongation, reduction of area, and Charpy impact value than invention example 1, demonstrating superior toughness. This is because tempering restored the toughness that had been reduced by quenching. On the other hand, invention example 2 showed a decrease in hardness due to tempering.

[0055] Comparing Example 2 and Reference Example 1, both of which were tempered, Reference Example 1 had the same toughness as Example 2, but the hardness was even lower. This was because the tempering time was long and excessive tempering was performed.

[0056] For reference, the average grain size of martensite in the test grinder 10 from which the test specimens were taken was measured, and as shown in Table 4, the size was approximately the same in the invention example, comparative example, and reference example 1.

[0057] Next, the test grinder 10 was attached to a crusher at an actual plant, and the wear loss during operation was measured. The crusher used was a KE-600 manufactured by Kubota Environmental Engineering Co., Ltd. The test grinder 10 rotated at 300 rpm, and the materials to be crushed were printed circuit boards and metal scraps. The wear test was performed by operating the crusher for a total of 891 hours, and the test grinder 10 was evaluated based on the weight loss before and after the test. The results are shown in Table 4.

[0058] Referring to Table 4, invention examples 1 and 2 have reduced wear loss and are superior in wear resistance compared to comparative examples 1 and 2. This is because invention examples 1 and 2 have the same or slightly lower hardness than comparative examples 1 and 2, but have higher toughness. The reduction in wear loss makes it possible to achieve a longer life for the grinder.

[0059] Comparing Inventive Examples 1 and 2 with Reference Example 1, Reference Example 1 exhibits a large abrasion loss. This is because the hardness of Reference Example 1 is significantly reduced due to excessive tempering.

[0060] In a crusher, the grinder may become hydrogen embrittled and peel off due to moisture contained in the material to be crushed or in the atmosphere. This peeling occurs starting from white tissue formed on the surface of the grinder. For this reason, the test grinder 10 was examined for the presence or absence of white tissue after the wear test. As a result, as shown in Table 4, white tissue was observed in all examples. The amount of white tissue in Invention Examples 1 and 2 and Comparative Examples 1 and 2 was relatively light, while the amount of white tissue in Reference Example 1 was severe. In Reference Example 1, a large amount of white tissue was formed, which led to tissue peeling during the wear test, and this is thought to be one of the reasons for the large abrasion loss.

[0061] The above description is for the purpose of explaining the present invention, and should not be construed as limiting the invention described in the claims or narrowing its scope. Furthermore, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications are possible within the technical scope described in the claims.

[0062] For example, in the above description, the wear-resistant cast steel of the present invention is applied to crusher parts, but the present invention is not limited to this and can also be applied to crushers and the like.

Claims

1. The alloy contains, in mass %, C: 0.27% to 0.36%, Si: 0.10% to 0.50%, Mn: 0.30% to 0.70%, P: 0.04% or less, S: 0.04% or less, Ni: 1.4% to 1.9%, Cr: 0.4% to 1.0%, Mo: 0.2% to 0.3%, Al: 0.1% or less, with the balance being Fe and impurities; The product has a part with a wall thickness of 25.4 mm (1 inch) or more, an HB hardness of 421 to 560, and a Charpy impact value of 20 to 40 J / cm ２ That is, Wear-resistant cast steel.

2. Si + Mn: 1.0% or less, The wear-resistant cast steel according to claim 1.

3. Si: 0.10% to 0.30%, Mn: 0.50% to 0.65%, Cr: 0.7% or more; The wear-resistant cast steel according to claim 2.

4. Average grain size of prior austenite: 50 μm to 300 μm. The wear-resistant cast steel according to claim 1.

5. A method for producing the wear-resistant cast steel according to claim 1, a cast steel ingot containing, by mass%, C: 0.27% to 0.36%, Si: 0.10% to 0.50%, Mn: 0.30% to 0.70%, P: 0.04% or less, S: 0.04% or less, Ni: 1.4% to 1.9%, Cr: 0.4% to 1.0%, Mo: 0.2% to 0.3%, Al: 0.1% or less, with the balance being Fe and impurities; a homogenization treatment step of heating and holding the material at 900°C to 960°C and then furnace cooling; A quenching process is carried out in which the material is heated and held at 800°C to 950°C, and then water quenched. Manufacturing method for wear-resistant cast steel.

6. After the quenching step, no tempering step is performed. A method for producing the wear-resistant cast steel according to claim 5.

7. After the quenching step, A tempering process is carried out by heating and holding at 150°C to 250°C for 1 to 3.5 hours, and then air-cooling to room temperature. A method for producing the wear-resistant cast steel according to claim 5.

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