High-hardness and high-toughness cast steel bucket tooth and preparation method thereof

Abstract

The invention relates to a high-hardness and high-toughness cast steel bucket tooth and a preparation method thereof, and belongs to the technical field of bucket tooth preparation. The cast steel bucket tooth comprises 0.27%-0.30% of C, 1.80%-2.20% of Si, 1.20%-1.50% of Mn, 0.50%-0.80% of Cr, less than or equal to 0.01% of P, less than or equal to 0.01% of S and the balance Fe. Under the cooperation of component adjustment and a heat treatment process, the prepared bucket tooth material is low in cost, economical and practical, and has high strength, high hardness and better low-temperature toughness at the same time. The mechanical properties of the cast steel bucket tooth are as follows: Rm is greater than or equal to 1600MPa, the hardness is greater than or equal to 450HB, and the impact absorbing energy Akv at-40 DEG C is greater than or equal to 30J.

Description

Technical Field

[0001] This invention relates to the field of bucket tooth manufacturing technology, and in particular to a high-hardness, high-strength and high-toughness cast steel bucket tooth and its manufacturing method. Background Technology

[0002] With the increasing number of dredging projects and the growing ban on underwater blasting, the use of rock-drilling bucket vessels is becoming more prevalent, leading to a continuous increase in the demand and consumption of buckets. Bucket teeth are the first parts of a dredging vessel bucket to come into contact with materials such as sand, rock, and minerals. Their primary function is to separate and excavate materials, operating under extremely harsh conditions. Upon contact with materials, the rapid movement of the material subjects the bucket teeth to powerful impacts. The tips of the teeth experience wear and tear due to the strong impact and sliding of the material, making them prone to surface wear and chipping. Therefore, the lifespan of bucket teeth is often short, resulting in significant consumption. Currently, dredging vessel bucket teeth are mainly imported, primarily made of CrNiMo wear-resistant steel. With the continuous development of dredging vessels, the requirements for the service life of bucket teeth are becoming increasingly stringent. Therefore, exploring and developing high-hardness, high-strength, and high-toughness cast steel bucket tooth materials to replace imported products and reduce wear-related losses has significant social and economic implications.

[0003] In the patent CN102383038A, titled "Battery Tooth Material and Its Production Method," rare earth elements are used to replace alloying elements such as molybdenum and nickel, significantly reducing production costs. Simultaneously, rare earth elements have strong purifying effects, refine grain size, and reduce microstructure segregation, significantly improving the plasticity and impact toughness of cast steel. However, the addition of rare earth elements requires precise control of the timing; otherwise, it can be counterproductive. Excessive addition can lead to the formation of large inclusions in the steel, negatively impacting its mechanical properties. Adding rare earth elements when deoxidation is incomplete can cause them to react with oxygen, sulfur, and other elements to produce complex compounds, affecting the purity of the molten steel.

[0004] In patent CN105838987B, titled "A Preparation Method of High-Strength and High-Toughness Low-Alloy Wear-Resistant Steel for Bucket Teeth," the chemical composition is ordinary low-alloy wear-resistant steel with added rare earth elements. Bainitic microstructure is formed through a heat treatment process involving salt bath quenching followed by isothermal transformation, resulting in high-hardness, high-strength, and high-toughness low-alloy wear-resistant steel. However, the process control of bainitic steel is highly sensitive. The formation of bainite depends on precise cooling rates and isothermal transformation temperatures, resulting in a narrow process window and high requirements for production equipment and process stability. Furthermore, to form a stable bainitic microstructure, quenching in a medium such as a salt bath furnace is necessary, which can cause environmental pollution.

[0005] Existing dredging vessel bucket teeth materials mainly consist of CrNiMo wear-resistant steel and low-alloy wear-resistant steel. CrNiMo wear-resistant steel has a high Cr, Ni, and Mo content, resulting in high manufacturing costs. Low-alloy wear-resistant steel is primarily prepared by adding rare earth elements to replace Ni and Mo alloying elements, improving the microstructure, and altering heat treatment methods to form bainitic microstructure. Materials prepared using these methods exhibit good strength and toughness, but process control is difficult, requiring high stability of production equipment and processes. This invention optimizes composition design, employs mature heat treatment processes, optimizes heat treatment parameters, and saves manufacturing costs, thereby obtaining a high-hardness, high-strength, and high-toughness low-alloy wear-resistant steel. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide a high-hardness, high-strength, and high-toughness cast steel bucket tooth and its preparation method, thereby obtaining a low-alloy wear-resistant steel bucket tooth with high hardness and high strength.

[0007] On the one hand, the present invention provides a high-hardness, high-strength and high-toughness cast steel bucket tooth, the chemical composition of which, by mass percentage, includes: C: 0.27% to 0.30%, Si: 1.80% to 2.20%, Mn: 1.20% to 1.50%, Cr: 0.50% to 0.80%, P: ≤0.01%, S: ≤0.01%, with the balance being Fe.

[0008] Furthermore, the chemical composition of the cast steel bucket teeth, by mass percentage, includes: C: 0.28%–0.30%, Si: 1.90%–2.10%, Mn: 1.40%–1.50%, Cr: 0.60%–0.80%, P: ≤0.01%, S: ≤0.01%, with the balance being Fe.

[0009] Furthermore, the carbon equivalent in the cast steel bucket teeth is 0.57% to 0.71%.

[0010] Furthermore, the microstructure of the cast steel bucket teeth consists of tempered martensite and retained austenite.

[0011] Furthermore, the grain size grade of the cast steel bucket teeth is level 5.

[0012] Furthermore, the cast steel bucket teeth have a tensile strength Rm≥1600MPa, a hardness HB≥450HB, and an impact absorption energy Akv≥30J at -40℃.

[0013] On the other hand, the present invention provides a method for preparing high-hardness, high-strength and high-toughness cast steel bucket teeth, which involves obtaining a cast steel blank through smelting and casting, followed by normalizing, quenching and low-temperature tempering.

[0014] Furthermore, in the first normalizing process, the cast steel blank is heated to 650-750°C and held at that temperature. After holding at that temperature, the temperature is further increased to 880-930°C and held at that temperature before being air-cooled.

[0015] Furthermore, during quenching, the cast steel blank after one normalizing is heated to 650-750℃ and held at that temperature. After holding at that temperature, the temperature is further increased to 860-910℃ and held at that temperature before water quenching.

[0016] Furthermore, in low-temperature tempering, the quenched cast steel blank is heated to 150-250℃ and held at that temperature before furnace cooling.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0018] 1. This invention precisely controls the C, Mn, and Cr composition of the high-hardness, high-strength, and high-toughness bucket tooth material, achieving a balance between strength, hardness, and toughness through carbon equivalent control, with the carbon equivalent controlled at 0.57%–0.71%. It increases the Si content, suppressing carbide precipitation and promoting carbon enrichment in austenite to increase the content and stability of retained austenite, thereby improving toughness. Furthermore, it reduces the content of high-cost elements such as Ni and Mo, controlling them according to residual element requirements, thus saving manufacturing costs.

[0019] 2. The heat treatment process of this invention includes one normalizing, quenching, and low-temperature tempering. The microstructure of the cast steel bucket teeth consists of tempered martensite plus less than 5% retained austenite. Excessive retained austenite can lead to decreased material hardness, dimensional instability, or deterioration of fatigue performance. The cast steel bucket teeth have a uniform microstructure, fine grains, and a grain size of grade 5, exhibiting both high strength and hardness as well as good low-temperature toughness. Furthermore, the preparation method of this invention is simple to control.

[0020] 3. With the combination of composition adjustment and heat treatment processes, the bucket tooth material prepared by this invention is low-cost, economical, and practical, while also possessing high strength, high hardness, and good low-temperature toughness. The mechanical properties of the cast steel bucket teeth of this invention are as follows: Rm≥1600MPa, hardness≥450HB, impact absorption energy Akv≥30J at -40℃.

[0021] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0022] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0023] Figure 1 This is a microstructure diagram of the cast steel bucket teeth of Embodiment 1 of the present invention;

[0024] Figure 2 This is a microstructure diagram of the cast steel bucket teeth of Embodiment 2 of the present invention;

[0025] Figure 3 This is a microstructure diagram of the cast steel bucket teeth of Embodiment 3 of the present invention;

[0026] Figure 4 This is a microstructure diagram of the cast steel bucket teeth in Embodiment 4 of the present invention;

[0027] Figure 5 This is a microstructure diagram of the cast steel bucket teeth of Comparative Example 1 of the present invention;

[0028] Figure 6 This is a microstructure diagram of the cast steel bucket teeth of Comparative Example 2 of the present invention;

[0029] Figure 7 This is a microstructure diagram of the cast steel bucket teeth of Comparative Example 3 of the present invention. Detailed Implementation

[0030] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0031] Dredging vessel bucket teeth come into direct contact with sand, soil, rock, and minerals during operation, suffering severe abrasive wear. Therefore, these teeth must be wear-resistant as well as possess sufficient strength and impact toughness. Currently, dredging vessel bucket teeth are mainly imported, primarily made of CrNiMo series wear-resistant steel. This material relies on alloying elements such as Cr and Ni to provide strength, hardness, and low-temperature toughness. However, these alloying elements are expensive, leading to high manufacturing costs. In contrast, low-alloy wear-resistant steels, due to their excellent comprehensive properties, low alloy content, low cost, and flexible production methods, hold great promise in the current field of wear-resistant materials.

[0032] Currently, the microstructures of low-alloy wear-resistant steels are mainly bainitic and martensitic. Bainitic steel, due to its combination of high strength and high toughness, has become a research focus in the field of wear-resistant materials. However, bainitic steel is highly sensitive to process control; the formation of bainite depends on precise cooling rates and isothermal transformation temperatures, resulting in a narrow process window and high requirements for production equipment and process stability. Moreover, to form a stable bainitic structure, quenching in media such as salt bath furnaces is required, which can cause environmental pollution. In contrast, martensitic steel has higher strength and hardness than bainitic steel, and its heat treatment process, quenching (water quenching or oil quenching) + tempering, offers strong process control. However, martensitic steel has poor low-temperature toughness and high residual stress during the quenching process.

[0033] Therefore, the present invention provides a high-hardness, high-strength and high-toughness cast steel bucket tooth, the chemical composition of which, by mass percentage, includes: C: 0.27% to 0.30%, Si: 1.80% to 2.20%, Mn: 1.20% to 1.50%, Cr: 0.50% to 0.80%, P: ≤0.01%, S: ≤0.01%, with the balance being Fe.

[0034] Compared with existing technologies, this invention precisely controls the C, Mn, and Cr composition of the high-hardness, high-strength, and high-toughness bucket tooth material, achieving a balance between strength, hardness, and toughness through carbon equivalent control, with the carbon equivalent controlled at 0.57%–0.71%. It increases the Si content, suppresses carbide precipitation, and promotes carbon enrichment in austenite to increase the content and stability of retained austenite, thereby improving toughness. Furthermore, by optimizing the alloy composition design, without adding high-cost elements such as Ni and Mo, and controlling only the content of residual elements, it achieves cost savings in manufacturing. The mechanical properties of the cast steel bucket teeth are as follows: Rm≥1600MPa, hardness≥450HB, and impact absorption energy Akv≥30J at -40℃.

[0035] The following details the function and dosage selection of the components contained in this invention:

[0036] C: Carbon is the most important element determining the mechanical properties of steel. As the carbon content increases, the strength and hardness of the steel increase; however, excessive carbon content will form coarse carbides, increasing brittleness and reducing ductility and toughness. Therefore, in order to ensure that the bucket tooth material of the present invention has both high strength and high hardness as well as a certain degree of low-temperature toughness, the C content in the present invention is controlled at 0.27% to 0.30%.

[0037] Silicon (Si) plays a role in solid solution strengthening in martensitic steel, improving its strength and hardness. Silicon can also inhibit carbide precipitation, improving resistance to tempering softening. Simultaneously, silicon promotes carbon enrichment in austenite, increasing the content and stability of retained austenite and improving toughness; however, the content of retained austenite cannot exceed 5%, otherwise it will reduce the hardness of the teeth. Therefore, in this invention, the Si content is controlled between 1.80% and 2.20%.

[0038] Mn: Manganese is an essential element for ensuring the strength and toughness of steel. Adding Mn can compensate for the strength loss caused by the reduction of C content. Simultaneously, manganese can improve the hardenability of martensitic steel, lower the martensitic transformation temperature (Ms point), and enhance the strength and toughness of martensitic steel. However, excessive manganese content can lead to component segregation and increase the risk of temper brittleness. To comprehensively improve strength and toughness, the Mn content in this invention is controlled at 1.20%–1.50%.

[0039] Cr: Chromium increases the hardenability of steel and has a secondary hardening effect, thus improving its strength. Simultaneously, chromium can combine with carbon to form fine, stable carbides, improving the steel's resistance to tempering softening. However, excessive chromium leads to coarse carbides, reducing the steel's toughness. Therefore, this invention controls the Cr content to be 0.50%–0.80%.

[0040] P: Phosphorus is an impurity in steel and reduces its toughness. Therefore, the P content in this invention is controlled to be ≤0.010%.

[0041] S: Sulfur can severely degrade the toughness of steel. Therefore, the S content in this invention is controlled to be ≤0.010%.

[0042] Preferably, the chemical composition of the high-hardness, high-strength and high-toughness cast steel bucket teeth, by mass percentage, includes: C: 0.28% to 0.30%, Si: 1.90% to 2.10%, Mn: 1.40% to 1.50%, Cr: 0.60% to 0.80%, P: ≤0.01%, S: ≤0.01%, with the balance being Fe.

[0043] Specifically, the carbon equivalent in the cast steel bucket teeth is 0.57% to 0.71%.

[0044] It should be noted that this invention achieves a balance between strength, hardness, and toughness by precisely controlling the composition of the high-hardness, high-strength, and high-toughness cast steel bucket tooth material, using a carbon equivalent range to precisely control the chemical composition. The carbon equivalent calculation formula is as follows: At the same time, increasing the Si content inhibits the precipitation of carbides and promotes the enrichment of carbon in austenite to increase the content and stability of residual austenite and improve toughness.

[0045] This invention provides a method for preparing high-hardness, high-strength and high-toughness cast steel bucket teeth, including smelting and casting to obtain cast steel blanks, followed by normalizing, quenching and low-temperature tempering.

[0046] Specifically, the steps include the following:

[0047] Step 1: After smelting and casting, a cast steel blank is obtained;

[0048] Step 2, First normalizing: Heat the cast steel blank to 650-750℃ and hold it at that temperature. After holding, continue to raise the temperature to 880-930℃ and hold it at that temperature before air cooling.

[0049] Step 3, Quenching: Heat the cast steel blank after the first normalizing to 650-750℃ and hold it at that temperature. After holding at that temperature, continue to raise the temperature to 860-910℃ and hold it at that temperature before water quenching.

[0050] Step 4, Low-temperature tempering: Heat the quenched cast steel blank to 150-250℃ and hold for a period of time, then furnace cool; to obtain high-hardness, high-strength and high-toughness cast steel bucket teeth.

[0051] Compared with existing technologies, this invention employs a heat treatment process of one-time normalizing + quenching + low-temperature tempering. The microstructure consists of tempered martensite plus less than 5% retained austenite. Excessive retained austenite can lead to decreased material hardness, dimensional instability, or deterioration of fatigue performance. The cast steel bucket teeth have a uniform microstructure, fine grains (grain size reaching grade 5), and possess both high strength and hardness as well as good low-temperature toughness. Furthermore, the preparation method of this invention is simple to control. The mechanical properties of the cast steel bucket teeth of this invention are as follows: Rm≥1600MPa, hardness≥450HB, and impact absorption energy Akv≥30J at -40℃.

[0052] Specifically, in step 1, the cavity is baked in a hot air furnace before pouring, with a baking temperature of 180-200℃ and a baking time of not less than 24 hours.

[0053] It should be noted that the mold cavity must be baked in a hot air furnace before pouring to ensure that the cavity surface is dry, reducing the risk of gas being drawn into the cast steel material during pouring and preventing porosity. Before pouring, the ladle must be externally drained to prevent slag formed after the molten steel solidifies at the ladle opening from entering the mold cavity.

[0054] Specifically, in step 2, the cast steel blank is heated to 650-750℃ and held at that temperature. After holding, the temperature is further increased to 880-930℃ and held at that temperature before air cooling. The holding time is calculated as 2-3 hours per 100mm.

[0055] It should be noted that, in this invention, the purpose or function of the first normalizing is to refine the microstructure and grains to provide a uniform matrix for subsequent quenching.

[0056] The primary normalizing temperature and holding time have a significant impact on the performance of cast steel bucket teeth. Temperatures can be 880℃, 890℃, 900℃, 910℃, 920℃, or 930℃. When the temperature is too high or the holding time is too long, austenite grains grow abnormally, resulting in coarse microstructure and grains after normalizing, reducing the material's strength and toughness. Simultaneously, excessively high temperatures and long holding times lead to severe oxidation and surface decarburization of the cast steel. Conversely, excessively low temperatures and short holding times result in incomplete austenitization of the cast steel bucket teeth, leading to uneven microstructure and anisotropy in mechanical properties. Furthermore, incomplete dissolution of carbides results in coarse particle distribution, reducing the hardness and wear resistance of the cast steel bucket teeth. Additionally, excessively low temperatures and short holding times can lead to incomplete elimination of original stress, increasing the risk of deformation during subsequent quenching. Therefore, the primary normalizing temperature for cast steel bucket teeth should be controlled between 880℃ and 930℃, with a holding time calculated at 2–3 hours per 100 mm.

[0057] Specifically, in step 3, the cast steel blank after the first normalizing is heated to 650-750℃ and held at that temperature. After holding, the temperature is further increased to 860-910℃ and held at that temperature before water quenching. The holding time is 2-3 hours per 100mm.

[0058] It should be noted that the purpose or function of quenching in this invention is to form lath martensite and less than 5% retained austenite, thereby obtaining high strength and wear resistance. Furthermore, water cooling must be used during the cooling process, rather than air cooling or oil cooling; otherwise, lath martensite cannot be obtained, or other structures, such as bainite, may appear, ultimately affecting the hardness and strength of the bucket teeth.

[0059] In this invention, the quenching temperature also has a significant impact on the microstructure and properties of the cast steel bucket teeth. The quenching temperature can be 860℃, 870℃, 880℃, 890℃, 900℃, or 910℃. When the temperature is too high or the holding time is too long, the high temperature causes abnormal growth of austenite grains, resulting in coarse martensite after quenching. This reduces grain boundaries, decreases crack propagation resistance, and leads to the superposition of high residual stress and structural stress, increasing the risk of cracking. Simultaneously, excessively high temperatures and long holding times result in severe oxidation of the cast steel surface and surface decarburization. Conversely, excessively low temperatures lead to incomplete austenitization of the cast steel bucket teeth, reducing the amount of martensite transformation after quenching and forming a mixed hard and soft microstructure. The anisotropy of this mixed microstructure results in insufficient hardness and large fluctuations in toughness in the cast steel bucket teeth. Insufficient holding time leads to the core not reaching the heating temperature, resulting in abnormal core microstructure and properties. Therefore, to ensure the performance of cast steel bucket teeth while preventing coarse grains, the quenching temperature is controlled at 860-910℃, and the holding time is calculated as 2-3h / 100mm.

[0060] Specifically, an intermediate heat preservation process is added during the normalizing and quenching process, with a heat preservation temperature of 650-750℃ and a heat preservation time of 1-1.5h / 100mm.

[0061] It should be noted that in this invention, heat preservation is required at 650-750℃, that is, heat preservation steps are added within the elastic-plastic transition range of the bucket tooth material. The purpose is to effectively reduce stress and deformation of the product (referring to cast steel bucket teeth) during the heating process. The heat preservation time is calculated as 1-1.5h / 100mm.

[0062] Specifically, the quenched cast steel blank is heated to 150-250℃ and held at that temperature, then furnace cooled; the holding time is 3-4 hours per 100mm.

[0063] It should be noted that in this invention, low-temperature tempering is performed after quenching. Its purpose is to eliminate quenching internal stress and reduce the risk of deformation and cracking. Simultaneously, low-temperature tempering can stabilize residual austenite, adjust the mechanical properties of the cast steel bucket teeth, and improve toughness.

[0064] The low-temperature tempering temperature and holding time have a significant impact on the performance of cast steel bucket teeth. The low-temperature tempering temperature of this invention can be 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃. When the temperature is too high, martensite decomposition accelerates, significantly reducing the material's hardness and wear resistance; simultaneously, excessively high temperatures cause retained austenite to transform into bainite or martensite, resulting in poor dimensional stability. When the temperature is too low, internal stress relief is insufficient, and the microstructure transformation is incomplete. Excessively long holding times cause fine carbides to coalesce into coarser ones, leading to a decrease in material strength and hardness; it also wastes resources. Insufficient holding times result in insufficient stress release, residual internal stress, and incomplete microstructure transformation; simultaneously, insufficient martensite decomposition leads to increased hardness and decreased toughness. Therefore, the low-temperature tempering temperature of cast steel bucket teeth is controlled at 150-250℃, and the holding time is calculated as 3-4h / 100mm.

[0065] To more clearly describe the present invention, the following embodiments and comparative examples are provided for further illustration.

[0066] Example 1

[0067] This embodiment provides a method for preparing high-hardness, high-strength and high-toughness bucket teeth, including the following steps:

[0068] Step 1: Smelting and casting to obtain a cast steel blank; its composition by mass percentage is: C: 0.30%, Si: 2.20%, Mn: 1.50%, Cr: 0.80%, P: ≤0.01%, S: ≤0.01%, balance Fe;

[0069] Step 2, First normalizing: Heat the cast steel blank to 650℃ and hold it at that temperature. After holding at that temperature, continue to raise the temperature to 900℃ and hold it at that temperature before air cooling.

[0070] Step 3, Quenching: Heat the cast steel blank after the first normalizing to 650℃ and hold it at that temperature. After holding at that temperature, continue to raise the temperature to 880℃ and hold it at that temperature before water quenching.

[0071] Step 4, Low-temperature tempering: Heat the quenched cast steel blank to 200℃ and hold it at that temperature, then furnace cool it to obtain high-hardness, high-strength and high-toughness cast steel bucket teeth.

[0072] Example 2

[0073] The preparation process of Example 2 is largely the same as that of Example 1, except that Example 2 includes the following steps:

[0074] Step 1: Smelting and casting to obtain a cast steel blank; its composition by mass percentage is: C: 0.30%, Si: 1.90%, Mn: 1.50%, Cr: 0.80%, P: ≤0.01%, S: ≤0.01%, balance Fe;

[0075] Step 2, First normalizing: Heat the cast steel blank to 650℃ and hold it at that temperature. After holding at that temperature, continue to raise the temperature to 900℃ and hold it at that temperature before air cooling.

[0076] Step 3, Quenching: Heat the cast steel blank after the first normalizing to 650℃ and hold it at that temperature. After holding at that temperature, continue to raise the temperature to 880℃ and hold it at that temperature before water quenching.

[0077] Step 4, Low-temperature tempering: Heat the quenched cast steel blank to 200℃ and hold it at that temperature, then furnace cool it to obtain high-hardness, high-strength and high-toughness cast steel bucket teeth.

[0078] Example 3

[0079] The preparation process of Example 3 is largely the same as that of Example 1, except that Example 3 includes the following steps:

[0080] Step 1: Smelting and casting to obtain a cast steel blank; its composition by mass percentage is: C: 0.27%, Si: 2.20%, Mn: 1.20%, Cr: 0.80%, P: ≤0.01%, S: ≤0.01%, balance Fe;

[0081] Step 2, First normalizing: Heat the cast steel blank to 650℃ and hold it at that temperature. After holding at that temperature, continue to raise the temperature to 920℃ and hold it at that temperature before air cooling.

[0082] Step 3, Quenching: Heat the cast steel blank after the first normalizing to 650℃ and hold it at that temperature. After holding at that temperature, continue to raise the temperature to 910℃ and hold it at that temperature before water quenching.

[0083] Step 4, Low-temperature tempering: Heat the quenched cast steel blank to 200℃ and hold it at that temperature, then furnace cool it to obtain high-hardness, high-strength and high-toughness cast steel bucket teeth.

[0084] Example 4

[0085] The preparation process of Example 4 is largely the same as that of Example 1, except that Example 4 includes the following steps:

[0086] Step 1: Smelting and casting to obtain a cast steel blank; its composition by mass percentage is: C: 0.27%, Si: 2.20%, Mn: 1.20%, Cr: 0.80%, P: ≤0.01%, S: ≤0.01%, balance Fe;

[0087] Step 2, First normalizing: Heat the cast steel blank to 650℃ and hold it at that temperature. After holding at that temperature, continue to raise the temperature to 900℃ and hold it at that temperature before air cooling.

[0088] Step 3, Quenching: Heat the cast steel blank after the first normalizing to 650℃ and hold it at that temperature. After holding at that temperature, continue to raise the temperature to 880℃ and hold it at that temperature before water quenching.

[0089] Step 4, Low-temperature tempering: Heat the quenched cast steel blank to 250℃ and hold it at that temperature, then furnace cool it to obtain high-hardness, high-strength and high-toughness cast steel bucket teeth.

[0090] Comparative Example 1

[0091] The preparation process of Comparative Example 1 is largely the same as that of Example 1, except that the composition of the cast steel bucket teeth in Comparative Example 1, by mass percentage, includes: C: 0.30%, Si: 1.50%, Mn: 1.50%, Cr: 0.80%, P: ≤0.01%, S: ≤0.01%, with the balance being Fe.

[0092] Comparative Example 2

[0093] Comparative Example 2 is prepared in a manner largely the same as that of Example 1, except that the preparation method of Comparative Example 2 includes:

[0094] Step 1: Smelting and casting to obtain cast steel parts;

[0095] Step 2, First normalizing: Heat the cast steel to 650℃ and hold for a period of time. After holding at this temperature, continue to raise the temperature to 920℃ and hold for a period of time before air cooling.

[0096] Step 3, Secondary normalizing: Heat the cast steel part to 650℃ and hold it at that temperature. After holding, continue to raise the temperature to 900℃ and hold it at that temperature before air cooling.

[0097] Step 4, Low-temperature tempering: Heat the cast steel part to 200℃ and hold it at that temperature, then furnace cool it.

[0098] Comparative Example 3

[0099] Comparative Example 3 is prepared in a manner largely the same as that of Example 1, except that the preparation method of Comparative Example 3 includes:

[0100] Step 1: Smelting and casting to obtain cast steel parts;

[0101] Step 2, First normalizing: Heat the cast steel part to 650℃ and hold it at that temperature. After holding, continue to raise the temperature to 920℃ and hold it at that temperature before air cooling.

[0102] Step 3, Secondary normalizing: Heat the cast steel part to 650℃ and hold it at that temperature. After holding at that temperature, continue to heat it to 900℃ and hold it at that temperature before oil cooling.

[0103] Step 4, Low-temperature tempering: Heat the cast steel part to 200℃ and hold it at that temperature, then furnace cool it.

[0104] Performance testing

[0105] The above embodiments and comparative examples were subjected to performance tests, mainly including tensile strength, hardness, impact absorption energy at -40℃ and internal structure. The test results are shown in Table 1.

[0106] Table 1 Performance Test Results

[0107]

[0108] As can be seen from Examples 1-4 and Comparative Examples 1-3, and with reference to Table 1, the bucket teeth prepared using the component ratios and preparation method provided by this invention possess high hardness and high strength and toughness. The mechanical properties of the cast steel bucket teeth are as follows: tensile strength Rm≥1600MPa, hardness≥450HB, and impact absorption energy Akv≥30J at -40℃. The internal structure of the cast steel bucket teeth consists of tempered martensite and a small amount of retained austenite (less than 5%), with fine grains and a grain grade of 5.

[0109] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-hardness, high-strength, and high-toughness cast steel bucket tooth, characterized in that, Its chemical composition, by mass percentage, includes: C: 0.27%–0.30%, Si: 1.80%–2.20%, Mn: 1.20%–1.50%, Cr: 0.50%–0.80%, P: ≤0.01%, S: ≤0.01%, with the balance being Fe.

2. The high-hardness, high-strength, and high-toughness cast steel bucket tooth according to claim 1, characterized in that, Its chemical composition, by mass percentage, includes: C: 0.28%–0.30%, Si: 1.90%–2.10%, Mn: 1.40%–1.50%, Cr: 0.60%–0.80%, P: ≤0.01%, S: ≤0.01%, with the balance being Fe.

3. The high-hardness, high-strength, and high-toughness cast steel bucket tooth according to claim 1 or 2, characterized in that, The carbon equivalent in the cast steel bucket teeth is 0.57% to 0.71%.

4. The high-hardness, high-strength, and high-toughness cast steel bucket tooth according to claim 1 or 2, characterized in that, The microstructure of the cast steel bucket teeth consists of tempered martensite and retained austenite.

5. A high-hardness, high-strength, and high-toughness cast steel bucket tooth according to claim 1 or 2, characterized in that, The grain size grade of the cast steel bucket teeth is level 5.

6. The high-hardness, high-strength, and high-toughness cast steel bucket tooth according to claim 1 or 2, characterized in that, The cast steel bucket teeth have a tensile strength Rm≥1600MPa, a hardness HB≥450HB, and an impact absorption energy Akv≥30J at -40℃.

7. The method for preparing high-hardness, high-strength, and high-toughness cast steel bucket teeth according to any one of claims 1-6, characterized in that, After smelting and casting, the steel blanks are obtained, and then normalizing, quenching and low-temperature tempering are carried out.

8. The method for preparing high-hardness, high-strength, and high-toughness cast steel bucket teeth according to claim 7, characterized in that, In the first normalizing process, the cast steel blank is heated to 650-750°C and held at that temperature. After holding at that temperature, the temperature is further increased to 880-930°C and held at that temperature before being air-cooled.

9. The method for preparing high-hardness, high-strength, and high-toughness cast steel bucket teeth according to claim 7, characterized in that, In the quenching process, the cast steel blank after the first normalizing is heated to 650-750℃ and held at that temperature. After holding at that temperature, the temperature is further increased to 860-910℃ and held at that temperature before water quenching.

10. The method for preparing high-hardness, high-strength, and high-toughness cast steel bucket teeth according to claim 7, characterized in that, In low-temperature tempering, the quenched cast steel blank is heated to 150-250℃ and held at that temperature before furnace cooling.

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