Steel for rare earth rock drilling tool and preparation method thereof

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to steel for a rare earth rock drilling tool and a preparation method thereof. Comprising a matrix and doping elements, the doping amount of the doping elements accounts for 0.008 wt.%-0.01 wt.% of a matrix system, the doping elements are cerium and yttrium, and the matrix comprises the chemical components of C, Si, Mn, S, P, O, Al, Cr, Ni, Mo, Cu and the balance Fe and inevitable impurities. The rare earth elements cerium and yttrium are used for jointly modifying matrix steel, the rare earth elements cerium and yttrium are used for modifying large-size brittle inclusions to generate fine and dispersed rare earth inclusions, the rare earth inclusions are mainly RE-O type and RE-O-S type, grains in a steel structure for the rock drilling tool are refined, the crack nucleation effect is weakened, and the mechanical property of the rock drilling tool is improved. And uneven steel structure distribution caused by segregation of impurity elements at the grain boundary is reduced, so that the impact toughness of the steel for the rock drilling tool is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and particularly relates to a steel for rare earth rock drilling tools and a preparation method thereof. Background Art

[0002] With the exploitation of mineral resources, energy construction, transportation and urban subway construction, rock drilling tools play an indispensable and important role in them. Therefore, the demand for rock drilling tool products is also continuously increasing. In addition, the harsh working environments such as high-frequency impact, strong torsion, and high wear during the rock drilling process also pose new challenges to rock drilling tool products.

[0003] In China, due to the existence of many infrastructure construction projects that need to be constructed every year, the quantity of rock drilling tool products required for project development is continuously increasing. Affected by this situation, not only large rock drilling tool production enterprises have started to increase production and expand production scale, but also a large number of private small enterprises have started to produce rock drilling tool products driven by interests. As a result, the output of rock drilling tool products has continued to increase in recent years. However, the increased rock drilling tool products mainly meet the domestic market demand. Therefore, the overall quality level of the products is not high and the technical content is relatively low, which has intensified the domestic market competition. At the same time, due to the unreasonable structure of domestic rock drilling tool products, there is a phenomenon of overcapacity caused by excessive production of low-end drill tool products, while relatively high-end rock drilling tool products need to rely on imports. This is also an urgent problem that needs to be faced in the research and development of rock drilling tools.

[0004] The existing steel for rock drilling tools used in mineral exploration and mining has high plasticity, high toughness and high fatigue strength. However, during the forging process, impurity elements segregate at grain boundaries, resulting in uneven distribution of the steel structure, which causes the impact toughness of the steel for rock drilling tools to be relatively low and the service life to be relatively short. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a steel for rare earth rock drilling tools and a preparation method thereof. Rare earth cerium and yttrium are doped in the matrix, and the large-size brittle inclusions are modified by rare earth cerium and yttrium to generate fine and dispersed rare earth inclusions. The rare earth inclusions are mainly of the RE-O type and the RE-O-S type. The refinement of grains in the matrix structure weakens the crack nucleation effect and reduces the uneven distribution of the steel structure caused by the segregation of impurity elements at grain boundaries, thereby greatly improving the impact toughness of the steel for rock drilling tools.

[0006] The present invention solves the above technical problems through the following technical solutions.

[0007] The first object of the present invention is to provide a steel for rare earth rock drilling tools, including a matrix and doping elements. Among them, the doping amount of the doping elements is 0.008 wt.% - 0.01 wt.% of the matrix system, the doping elements are cerium and yttrium, and the chemical composition of the matrix is as follows by mass percentage: C: 0.3% - 0.35%, Si: 0.29% - 0.3%, Mn: 0.35% - 0.45%, S: 0.001% - 0.002%, P: 0.010% - 0.020%, O: 0.0007% - 0.0015%, Al: 0.03% - 0.032%, Cr: 1.05% - 1.25%, Ni: 3.9% - 3.92%, Mo: 0.359% - 0.37%, Cu: 0.05 - 0.15%, and the balance is Fe and inevitable impurities.

[0008] The present invention uses cerium and yttrium, rare earth elements, to jointly modify the matrix. Among them, the reaction products of cerium and yttrium elements in the molten matrix steel are all rare earth oxysulfides. The rare earth inclusions are mainly of the RE - O type and the RE - O - S type. The refinement of the grains in the matrix structure significantly reduces the average grain size of the steel for rock drilling tools, and the grain boundaries also increase accordingly, which can better hinder the propagation of cracks during plastic deformation. Therefore, the force resisting deformation of the steel for rock drilling tools will be improved. In addition, the atomic radius of yttrium is smaller than that of lighter rare earths, which can more effectively reduce the inclusion content, improve the inclusion distribution, reduce the inclusion size, refine and spheroidize the inclusions, thereby improving the steel properties, reducing the uneven distribution of the steel structure caused by the segregation of impurity elements at the grain boundaries, and eliminating the phenomenon of larger inclusions and carbide segregation originally distributed along the grain boundaries, thus improving the impact toughness of the matrix.

[0009] In some specific embodiments, the mass ratio of cerium to yttrium is 3 - 4:6 - 7. Through the rare earth elements cerium and yttrium in a specific mass ratio, the impact performance of the steel for rock drilling tools is improved from 55.3 J to 77.8 J - 90.2 J, an increase of 40.7% - 63.1%.

[0010] In some specific embodiments, the doping amount of the doping elements is 0.009 wt.% of the matrix system. Cerium and yttrium, rare earth elements, jointly modify the matrix, making the brittle inclusions with large sizes in the large matrix generate fine and dispersed rare earth inclusions, weakening the crack nucleation effect, thereby greatly improving the impact toughness of the steel for rock drilling tools. When the rare earth content in the steel is within a suitable range, the comprehensive performance of the steel for rock drilling tools can be improved. However, when the rare earth content is too high, a large number of flocculent rare earth inclusions generated in the steel for rock drilling tools will instead reduce the impact toughness of the steel for rock drilling tools.

[0011] Furthermore, the matrix is prepared from chemical components with the following mass percentages: C: 0.31%, Si: 0.29%, Mn: 0.42%, S: 0.001%, P: 0.016%, O: 0.0007%, Al: 0.03%, Cr: 1.15%, Ni: 3.9%, Mo: 0.37%, Cu: 0.08%, and the balance is Fe and unavoidable impurities. The doping elements are mixed with cerium and yttrium in a mass ratio of 3.5:6.5. Rare earth cerium and yttrium form RE-O type and RE-O-S type in the matrix, refining the matrix grains.

[0012] The addition of rare earth elements cerium and yttrium can react with sulfur and oxygen in the steel to form rare earth compounds, thereby purifying the molten steel. It can also refine the grains, making the carbides more finely and dispersedly distributed in the matrix. Yttrium is mainly Y-O-S composite inclusions with a density of about 4.25, and cerium is mainly Ce-O-S composite inclusions with a density of about 6.0. This weakens the crack nucleation effect and reduces the segregation of impurity elements at the grain boundaries, resulting in uneven distribution of the steel structure. Thus, it greatly improves the impact toughness of the steel for rock drilling tools. When the content of rare earth cerium is 0.009 wt.%, the impact energy of the steel for rock drilling tools increases the most, by 32.38%. The fine and dispersed rare earth inclusions formed by rare earth cerium modifying large-size brittle inclusions weaken the crack nucleation effect, thereby greatly improving the impact toughness of the steel for rock drilling tools.

[0013] The second object of the present invention is to provide a preparation method of the above rare earth steel for rock drilling tools, including the following steps: S1. After formulating the raw materials according to the components and ratios, vacuum smelt the matrix until it is completely melted, then add the doping elements, stir, and keep the melt at a certain temperature.

[0014] S2. After the melting is completed, cast the molten metal into an ingot by die casting.

[0015] S3. Perform a forging process on the ingot to obtain the rare earth steel for rock drilling tools.

[0016] The present invention adopts the method of vacuum smelting. The vacuum environment can effectively remove air and other impurities, significantly improving the purity of the smelting materials. And under vacuum conditions, the heating speed is fast, the heat loss is small, and the production efficiency is improved.

[0017] In some specific embodiments, the temperature of vacuum smelting is 1580 °C to 1620 °C, and the time is 68 min to 72 min.

[0018] In some specific embodiments, the time for keeping the melt at a certain temperature is 2 min to 3 min.

[0019] In some specific embodiments, during the forging process, the starting forging temperature is 1150 °C to 1200 °C, and the final forging temperature is 940 °C to 980 °C.

[0020] In some specific embodiments, the dimensions of the steel for rare earth rock drilling bits are (25 mm - 35 mm) × (120 mm - 140 mm) × (430 mm - 460 mm).

[0021] The present invention has the following beneficial effects compared with the prior art: (1) For the steel for rare earth rock drilling bits provided by the present invention, the matrix is modified by rare earth elements cerium and yttrium. The reaction products of cerium and yttrium elements in the molten matrix steel are both rare earth oxysulfides. The rare earth elements purify the molten steel and refine the grains, making the carbides more finely and dispersedly distributed in the matrix. The rare earth inclusions are mainly of the RE - O type and the RE - O - S type, which significantly reduces the average grain size of the steel for rock drilling bits, increases the corresponding grain boundaries, and can better hinder the propagation of cracks during plastic deformation, weakens the crack nucleation effect, reduces the segregation of impurity elements at the grain boundaries, resulting in uneven distribution of the steel structure, and improves the force resistance of the steel for rock drilling bits to deformation. In addition, the atomic radius of yttrium is smaller than that of lighter rare earths, which can more effectively reduce the inclusion content, improve the inclusion distribution, reduce the inclusion size, refine and spheroidize the inclusions, thereby improving the steel properties, reducing the segregation of impurity elements at the grain boundaries, resulting in uneven distribution of the steel structure, eliminating the phenomenon of larger inclusions and carbide segregation originally distributed along the grain boundaries, and thus improving the impact toughness of the matrix.

[0022] (2) The present invention uses rare earth elements cerium and yttrium to jointly modify the matrix. The rare earth elements modify the large - sized brittle inclusions to form fine and dispersed rare earth inclusions. The yttrium - based inclusions are mainly Y - O - S composite inclusions with a density of about 4.25, while the cerium - based inclusions are mainly Ce - O - S composite inclusions with a density of about 6.0. For the refinement of grains in the structure of the steel for rock drilling bits, the average grain size is reduced, and the corresponding grain boundaries are increased. When rare earth cerium and rare earth yttrium are doped in the matrix in a ratio of 3.5:6.5 and the doping content is 0.009 wt.%, the impact energy of the steel for rock drilling bits is 90.2 J, which is an increase of 63.1% compared to the impact energy of the undoped matrix, improving the comprehensive performance of the steel for rock drilling bits. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a room - temperature impact performance diagram of the steel for rock drilling bits in Examples 1 - 3 and Comparative Examples 1 - 5 of the present invention.

[0024] Figure 2 It is a microscopic morphology diagram of the impact fracture surface of the rock drilling bits in Examples 1 - 3 of the present invention. Among them, Figure 2Among them, (a) is Example 1, (b) is Example 2, and (c) is Example 3.

[0025] Figure 3 This is the microstructural morphology diagram of the impact fracture of the steel for rock drilling tools in Example 1 of the present invention and Comparative Examples 1 to 5. Among them, Figure 3 Among them, (a) is Example 1, (b) is Comparative Example 1, (c) is Comparative Example 2, (d) is Comparative Example 3, (e) is Comparative Example 4, and (f) is Comparative Example 5. Detailed implementation manners

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0027] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the following embodiments of the present invention can be obtained through the market or prepared by existing methods.

[0028] The existing steel for rock drilling tools used in mineral exploration and mining has high plasticity, high toughness, and high fatigue strength. However, during the forging process, impurity elements segregate at the grain boundaries, resulting in uneven distribution of the steel structure, low impact toughness of the steel for rock drilling tools, and short service life.

[0029] Based on the above problems, the present invention provides a rare earth steel for rock drilling tools, including a matrix and doping elements. Among them, the doping amount of the doping elements is 0.008 wt.% to 0.01 wt.% of the matrix system, the doping elements are cerium and yttrium, and the matrix is prepared from the following chemical components by mass percentage: C: 0.3% to 0.35%, Si: 0.29% to 0.3%, Mn: 0.35% to 0.45%, S: 0.001% to 0.002%, P: 0.010% to 0.020%, O: 0.0007% to 0.0015%, Al: 0.03% to 0.032%, Cr: 1.05% to 1.25%, Ni: 3.9% to 3.92%, Mo: 0.359% to 0.37%, Cu: 0.05 to 0.15%, and the balance is Fe and inevitable impurities.

[0030] In the present invention, the matrix is modified by rare earth elements cerium and yttrium. The reaction products of cerium and yttrium elements in the molten matrix steel are all rare earth oxysulfides. The rare earth elements purify the molten steel and refine the grains, making the carbides more finely and dispersedly distributed in the matrix. The rare earth inclusions are mainly of the RE-O type and the RE-O-S type, which significantly reduces the average grain size of the steel for rock drilling tools, increases the grain boundaries accordingly, and can better hinder the propagation of cracks during plastic deformation, weakens the crack nucleation effect, reduces the segregation of impurity elements at the grain boundaries, resulting in uneven distribution of the steel structure, and improves the force resistance of the steel for rock drilling tools against deformation. In addition, the atomic radius of yttrium is smaller than that of lighter rare earths, which can more effectively reduce the inclusion content, improve the inclusion distribution, reduce the inclusion size, refine and spheroidize the inclusions, thereby improving the steel properties, reducing the segregation of impurity elements at the grain boundaries, resulting in uneven distribution of the steel structure, eliminating the phenomenon of larger inclusions and carbide segregation originally distributed along the grain boundaries, and thus improving the impact toughness of the matrix.

[0031] The following is further illustrated by specific examples.

[0032] Example 1 A steel for rare earth rock drilling tools includes a matrix and doping elements. Among them, the chemical composition of the matrix by mass percentage is as follows: C: 0.31%, Si: 0.29%, Mn: 0.42%, S: 0.001%, P: 0.016%, O: 0.0007%, Al: 0.03%, Cr: 1.15%, Ni: 3.9%, Mo: 0.37%, Cu: 0.08%, and the balance is Fe and inevitable impurities. The doping amount of the doping elements is 0.009 wt.% of the matrix system. The doping elements are cerium and yttrium, and the mass ratio of cerium to yttrium is 3.5:6.5.

[0033] The preparation method of the above-mentioned steel for rare earth rock drilling tools includes the following steps: S1. After the raw materials are prepared according to the components and ratios, the matrix is placed in the crucible of a 25 kg vacuum induction melting furnace, and then the vacuum is pumped and the temperature is raised to 1600 °C for vacuum smelting for 70 min until completely melted. Then, a mixture formed by mixing rare earth cerium with a purity of 99.9% and rare earth yttrium with a purity of 99.9% is added to the crucible through a bunker. To ensure the uniformity of the steel for rock drilling tools, electromagnetic stirring is performed on the molten steel, and finally, it is kept warm for 2 min.

[0034] S2. After the smelting is completed, the molten steel is cast into an ingot through die casting.

[0035] S3. Forge the ingot. The forging is carried out at an initial forging temperature of 1180 °C and a final forging temperature of 950 °C to forge it into a slab with dimensions of 30 mm × 130 mm × 450 mm, obtaining the steel for rare earth rock drilling bits.

[0036] Example 2 A steel for rare earth rock drilling bits includes a matrix and doping elements. Among them, the chemical composition of the matrix is as follows by mass percentage: C: 0.3%, Si: 0.29%, Mn: 0.42%, S: 0.001%, P: 0.016%, O: 0.0001%, Al: 0.03%, Cr: 1.15%, Ni: 3.91%, Mo: 0.359%, Cu: 0.08%, and the balance is Fe and unavoidable impurities. The doping amount of the doping elements is 0.009 wt.% of the matrix system. The doping elements are cerium and yttrium, and the mass ratio of cerium to yttrium is 3:7.

[0037] The preparation method of the above-mentioned steel for rare earth rock drilling bits includes the following steps: S1. After preparing the raw materials according to the components and ratios, place the matrix in the crucible of a 25 kg vacuum induction melting furnace, then evacuate and heat up to 1600 °C for vacuum smelting for 70 min until completely melted. Then, a mixture formed by mixing rare earth cerium with a purity of 99.9% and rare earth yttrium with a purity of 99.9% is added to the crucible through a bunker. To ensure the uniformity of the steel for rock drilling bits, electromagnetic stirring is carried out on the molten steel, and finally, heat preservation is carried out for 2 min.

[0038] S2. After the smelting is completed, the molten steel is cast into an ingot through die casting.

[0039] S3. Forge the ingot. The forging is carried out at an initial forging temperature of 1180 °C and a final forging temperature of 950 °C to forge it into a slab with dimensions of 30 mm × 130 mm × 450 mm, obtaining the steel for rare earth rock drilling bits.

[0040] Example 3 A steel for rare earth rock drilling bits includes a matrix and doping elements. Among them, the chemical composition of the matrix is as follows by mass percentage: C: 0.32%, Si: 0.3%, Mn: 0.42%, S: 0.001%, P: 0.016%, O: 0.0007%, Al: 0.03%, Cr: 1.15%, Ni: 3.92%, Mo: 0.363%, Cu: 0.08%, and the balance is Fe and unavoidable impurities. The doping amount of the doping elements is 0.009 wt.% of the matrix system. The doping elements are cerium and yttrium, and the mass ratio of cerium to yttrium is 4:6.

[0041] The preparation method of the above-mentioned steel for rare earth rock drilling tools comprises the following steps: S1. After preparing the raw materials according to the components and proportions, place the matrix in the crucible of a 25 kg vacuum induction melting furnace, then evacuate and heat up to 1600 °C for vacuum smelting for 70 min until completely melted. Then, add the mixture formed by mixing rare earth cerium with a purity of 99.9% and rare earth yttrium with a purity of 99.9% into the crucible through a bunker. To ensure the uniformity of the steel for rock drilling tools, perform electromagnetic stirring on the molten steel, and finally keep it warm for 2 min.

[0042] S2. After the smelting is completed, obtain an ingot by casting the molten steel through die casting.

[0043] S3. Perform a forging process on the ingot, and forge it under the conditions that the starting forging temperature is 1180 °C and the final forging temperature is 950 °C to forge it into a slab with dimensions of 30 mm × 130 mm × 450 mm, thus obtaining the steel for rare earth rock drilling tools.

[0044] Comparative Example 1 A steel for rare earth rock drilling tools includes a matrix. The chemical composition of the matrix by mass percentage is as follows: C: 0.31%, Si: 0.3%, Mn: 0.42%, S: 0.002%, P: 0.016%, O: 0.0015%, Al: 0.023%, Cr: 1.15%, Ni: 3.92%, Mo: 0.363%, Cu: 0.08%, and the balance is Fe and unavoidable impurities.

[0045] The preparation method of the above-mentioned steel for rare earth rock drilling tools comprises the following steps: S1. After preparing the raw materials according to the components and proportions, place the matrix in the crucible of a 25 kg vacuum induction melting furnace, then evacuate and heat up to 1600 °C for vacuum smelting for 70 min until completely melted to obtain molten steel.

[0046] S2. After the smelting is completed, obtain an ingot by casting the molten steel through die casting.

[0047] S3. Perform a forging process on the ingot, and forge it under the conditions that the starting forging temperature is 1180 °C and the final forging temperature is 950 °C to forge it into a slab with dimensions of 30 mm × 130 mm × 450 mm, thus obtaining the steel for rare earth rock drilling tools.

[0048] Comparative Example 2 A steel for rare earth rock drilling tools, comprising a matrix and doping elements. Among them, the chemical composition of the matrix is as follows by mass percentage: C: 0.32%, Si: 0.3%, Mn: 0.42%, S: 0.001%, P: 0.016%, O: 0.0007%, Al: 0.03%, Cr: 1.15%, Ni: 3.92%, Mo: 0.363%, Cu: 0.08%, and the balance is Fe and inevitable impurities. The doping amount of the doping element is 0.009 wt.% of the matrix system, and the doping element is cerium.

[0049] The preparation method of the above-mentioned steel for rare earth rock drilling tools includes the following steps: S1. After formulating the raw materials according to the components and ratios, put the matrix into the crucible of a 25 kg vacuum induction melting furnace, then evacuate and heat up to 1600 °C for vacuum smelting for 70 min until completely melted, and then add rare earth cerium with a purity of 99.9% into the crucible through a bunker. To ensure the uniformity of the steel for rock drilling tools, electromagnetic stirring is carried out on the molten steel, and finally heat preservation is carried out for 2 min.

[0050] S2. After the smelting is completed, the molten steel is cast into an ingot through die casting.

[0051] S3. Carry out a forging process on the ingot. Forge at an initial forging temperature of 1180 °C and a final forging temperature of 950 °C to forge into a slab with dimensions of 30 mm×130 mm×450 mm to obtain the steel for rare earth rock drilling tools.

[0052] Comparative Example 3 A steel for rare earth rock drilling tools, comprising a matrix and doping elements. Among them, the chemical composition of the matrix is as follows by mass percentage: C: 0.32%, Si: 0.3%, Mn: 0.42%, S: 0.001%, P: 0.016%, O: 0.0007%, Al: 0.03%, Cr: 1.15%, Ni: 3.92%, Mo: 0.363%, Cu: 0.08%, and the balance is Fe and inevitable impurities. The doping amount of the doping element is 0.0038 wt.% of the matrix system, and the doping element is yttrium.

[0053] The preparation method of the above-mentioned steel for rare earth rock drilling tools includes the following steps: S1. After formulating the raw materials according to the components and proportions, place the matrix into the crucible of a 25 kg vacuum induction melting furnace, then evacuate and heat up to 1600 °C for vacuum smelting for 70 min until completely melted. Then, add the mixture formed by mixing rare earth yttrium with a purity of 99.9% into the crucible through a bunker. To ensure the uniformity of the steel for rock drilling tools, perform electromagnetic stirring on the molten steel, and finally keep it warm for 2 min.

[0054] S2. After the smelting is completed, cast the molten steel into an ingot through die casting.

[0055] S3. Perform a forging process on the ingot. Forge it at an initial forging temperature of 1180 °C and a final forging temperature of 950 °C to obtain a slab with dimensions of 30 mm × 130 mm × 450 mm, thus obtaining the steel for rare earth rock drilling tools.

[0056] Comparative Example 4 A steel for rare earth rock drilling tools, comprising a matrix and doping elements. Among them, the chemical composition of the matrix by mass percentage is as follows: C: 0.32%, Si: 0.3%, Mn: 0.42%, S: 0.001%, P: 0.016%, O: 0.0007%, Al: 0.03%, Cr: 1.15%, Ni: 3.92%, Mo: 0.363%, Cu: 0.08%, and the balance is Fe and unavoidable impurities. The doping amount of the doping element is 0.009 wt.% of the matrix system, and the doping element is yttrium.

[0057] The preparation method of the above-mentioned steel for rare earth rock drilling tools includes the following steps: S1. After formulating the raw materials according to the components and proportions, place the matrix into the crucible of a 25 kg vacuum induction melting furnace, then evacuate and heat up to 1600 °C for vacuum smelting for 70 min until completely melted. Then, add the mixture formed by mixing rare earth yttrium with a purity of 99.9% into the crucible through a bunker. To ensure the uniformity of the steel for rock drilling tools, perform electromagnetic stirring on the molten steel, and finally keep it warm for 2 min.

[0058] S2. After the smelting is completed, cast the molten steel into an ingot through die casting.

[0059] S3. Perform a forging process on the ingot. Forge it at an initial forging temperature of 1180 °C and a final forging temperature of 950 °C to obtain a slab with dimensions of 30 mm × 130 mm × 450 mm, thus obtaining the steel for rare earth rock drilling tools.

[0060] Comparative Example 5 A steel for rare earth rock drilling tools includes a matrix and doping elements. Among them, the chemical composition of the matrix is as follows by mass percentage: C: 0.32%, Si: 0.3%, Mn: 0.42%, S: 0.001%, P: 0.016%, O: 0.0007%, Al: 0.03%, Cr: 1.15%, Ni: 3.92%, Mo: 0.363%, Cu: 0.08%, and the balance is Fe and unavoidable impurities. The doping amount of the doping element is 0.0018 wt.% of the matrix system, and the doping element is yttrium.

[0061] The preparation method of the above-mentioned steel for rare earth rock drilling tools includes the following steps: S1. After preparing the raw materials according to the components and ratios, put the matrix into the crucible of a 25 kg vacuum induction melting furnace, then evacuate and heat up to 1600 °C for vacuum smelting for 70 min until completely melted. Then, add the mixture formed by mixing 99.9% pure rare earth yttrium into the crucible through a bunker. To ensure the uniformity of the steel for rock drilling tools, electromagnetic stirring is carried out on the molten steel, and finally, heat preservation is carried out for 2 min.

[0062] S2. After the melting is completed, pour the molten steel into a mold for casting to obtain an ingot.

[0063] S3. Perform a forging process on the ingot. Forge it at an initial forging temperature of 1180 °C and a final forging temperature of 950 °C to forge it into a slab of 30 mm×130 mm×450 mm to obtain the steel for rare earth rock drilling tools.

[0064] Analyze the performance and microstructure of the steel for rock drilling tools prepared in Examples 1 to 3 and Comparative Examples 1 to 5. The results are as follows: Determine the cutting position, direction, and quantity of the impact specimen according to the provisions of the standard GB / T2975-2018 "Sampling Positions and Specimen Preparation for Mechanical Properties of Steel and Steel Products" or the agreement. The equipment used for the impact test is a Charpy impact testing machine. The impact specimen is processed into three U-shaped specimens of 55 mm×10 mm×10 mm according to the requirements of the national standard GB / T229-2007 "Metallic Materials - Charpy Pendulum Impact Test Method", and the average value of the three measurement data is taken as the room temperature impact strength.

[0065] According to GB / T 13298-2015, a metallographic specimen of 10 mm×10 mm×15 mm is intercepted at the 1 / 4 of the cross-sectional width of the steel for rock drilling tools in the vertical forging direction. First, it is ground step by step with metallographic sandpaper of 600 mesh to 3000 mesh on a grinding and polishing machine and then polished. Then, it is cleaned with alcohol and dried to ensure that the surface of the specimen is smooth, free of scratches and rust spots. After the specimen is corroded with a pre-prepared 4wt% nitric acid alcohol solution for about 15 s, the corrosion solution on the surface of the specimen is immediately rinsed with distilled water and dried. The microstructure of the specimen at more than 1000 times is observed by using a MIRA3 LMH type emission scanning electron microscope.

[0066] Figure 1 This is the room temperature impact performance diagram of the steel for rock drilling tools in Examples 1 to 3 and Comparative Examples 1 to 5 of the present invention. As Figure 1 shown, when the mass ratio of doped rare earth cerium and yttrium is 3.5:6.5, the room temperature impact performance of the steel for rock drilling tools is the best, reaching 90.2 J, which is 63.1% higher than that of the steel for rock drilling tools without doping rare earth.

[0067] Figure 2 This is the microscopic structure morphology diagram of the impact fracture of the steel for rock drilling tools in Examples 1 to 3 of the present invention. Among them, Figure 2 in (a) is Example 1, (b) is Example 2, and (c) is Example 3. As Figure 2 shown, when the mass ratio of doped rare earth cerium and yttrium is 3.5:6.5 as in Example 1, there are significantly more dimples in the fracture surface of the steel for rock drilling tools, and the depth of its dimples also increases significantly, and there are fine inclusions at the bottom of the dimples. In addition, when subjected to greater stress, the position where the inclusions are located is extremely likely to become the crack source, resulting in crack initiation and growth. However, due to the large cohesive force between the rare earth inclusions and their interfaces, the ability to absorb energy required for crack propagation is increased, thereby improving the impact performance of the steel for rock drilling tools. When the mass ratio of doped rare earth cerium and yttrium is 4:6 as in Example 3 and 3:7 as in Example 2, the plastic deformation at the bottom of the dimples of the steel for rock drilling tools is significantly reduced. Since the dimple size is closely related to the size of the inclusions and the second-phase particles, it shows that the role of the inclusions in resisting crack propagation is significantly weaker. Therefore, compared with the steel for rock drilling tools in Example 1, the impact toughness of Examples 2 and 3 is reduced.

[0068] Figure 3 This is the microscopic structure morphology diagram of the impact fracture of the steel for rock drilling tools in Example 1 and Comparative Examples 1 to 5 of the present invention. Among them, Figure 3 in (a) is Example 1, (b) is Comparative Example 1, (c) is Comparative Example 2, (d) is Comparative Example 3, (e) is Comparative Example 4, and (f) is Comparative Example 5. As Figure 3As shown, the impact fracture surface of Example 1 consists of dimples, and there are petal-shaped fracture surfaces between the dimples, indicating that the steel for rock drilling tools under this composition has experienced significant plastic deformation before fracture. However, for Comparative Examples 1 to 5, the amount of plastic deformation at the bottom of the dimples has decreased to varying degrees, and the existence of a cleavage plane-like structure has appeared, resulting in a reduction in their impact performance.

[0069] As can be seen from the above, when rare earth cerium and rare earth yttrium are doped in the matrix in a ratio of 3.5:6.5 and the doping content is 0.009 wt.%, the impact energy of the steel for rock drilling tools is 90.2 J, which is a 63.1% increase compared to the impact energy of the undoped matrix. This is because the fine and dispersed rare earth inclusions generated by the co-modification of large-sized brittle inclusions by rare earth cerium and yttrium weaken the crack nucleation effect, thus greatly improving the impact toughness of the steel for rock drilling tools. When the rare earth content in the steel is within a suitable range, the comprehensive performance of the steel for rock drilling tools can be improved. However, when the rare earth content is too high, a large number of rare earth inclusions generated in the steel for rock drilling tools will segregate at the grain boundaries, which will instead reduce the impact toughness of the steel for rock drilling tools. The reasons for the improvement of the toughness of the steel for rock drilling tools are mainly as follows: Firstly, the refinement of grains in the microstructure of the steel for rock drilling tools by rare earth elements cerium and yttrium. After adding rare earth elements cerium and yttrium, the average grain size of the steel for rock drilling tools significantly decreases, and the corresponding grain boundaries increase, which better hinders the propagation of cracks during plastic deformation and also causes difficulties for dislocation movement. Therefore, the force for the steel for rock drilling tools to resist deformation will increase. In addition, adding rare earth elements cerium and yttrium can purify the grain boundaries by removing harmful impurities at the grain boundaries, strengthening the grain boundaries; Secondly, after adding rare earth elements cerium and yttrium, the non-metallic inclusions in the steel for rock drilling tools are modified, eliminating the phenomenon of large-sized inclusions and carbide segregation distributed along the grain boundaries, thereby improving the impact toughness of the matrix.

[0070] It should be noted that when the present invention involves numerical ranges, it should be understood that any value between the two endpoints of each numerical range and either of the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to prevent repetition, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted to include the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0071] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A steel for rare earth rock drilling tools, characterized in that, It includes a matrix and doping elements. Among them, the doping amount of the doping elements is 0.008 wt.% - 0.01 wt.% of the matrix system. The doping elements are cerium and yttrium. The matrix is prepared from chemical components in the following mass percentages: C: 0.3% - 0.35%, Si: 0.29% - 0.3%, Mn: 0.35% - 0.45%, S: 0.001% - 0.002%, P: 0.010% - 0.020%, O: 0.0007% - 0.0015%, Al: 0.03% - 0.032%, Cr: 1.05% - 1.25%, Ni: 3.9% - 3.92%, Mo: 0.359% - 0.37% and Cu: 0.05 - 0.15%, and the balance is Fe and unavoidable impurities, totaling 100%.

2. The steel for rare earth rock drilling tools according to claim 1, characterized in that, The mass ratio of the cerium to the yttrium is 3 - 4:6 - 7.

3. The steel for rare earth rock drilling tools according to claim 1, characterized in that, The doping amount of the doping elements is 0.009 wt.% of the matrix system.

4. The steel for rare earth rock drilling tools according to claim 3, characterized in that, The matrix is prepared from chemical components in the following mass percentages: C: 0.31%, Si: 0.29%, Mn: 0.42%, S: 0.001%, P: 0.016%, O: 0.0007%, Al: 0.03%, Cr: 1.15%, Ni: 3.9%, Mo: 0.37% and Cu: 0.08%, and the balance is Fe and unavoidable impurities, totaling 100%; the doping elements are mixed in a mass ratio of cerium to yttrium of 3.5:6.

5.

5. A method for preparing the steel for rare earth rock drilling tools according to any one of claims 1 to 4, characterized in that, It includes the following steps: After the raw materials are formulated according to the components and ratios, the matrix is vacuum - smelted until completely melted, and then the doping elements are added, stirred and smelted for heat preservation; After the smelting is completed, ingots are obtained by die - casting pouring; The ingots are subjected to a forging process to obtain the steel for rare - earth rock - drilling tools.

6. The preparation method of the steel for rare earth rock drilling tools according to claim 5, characterized in that, The temperature of the vacuum smelting is 1580 °C - 1620 °C, and the time is 68 min - 72 min.

7. The preparation method of the steel for rare earth rock drilling tools according to claim 5, characterized in that, The time for smelting heat preservation is 2 min - 3 min.

8. The preparation method of the steel for rare earth rock drilling tools according to claim 5, characterized in that, During the forging process, the starting forging temperature is 1150 °C - 1200 °C, and the final forging temperature is 940 °C - 980 °C.

9. The preparation method of the steel for rare earth rock drilling tools according to claim 5, characterized in that, The size of the steel for rare - earth rock - drilling tools is (25 mm - 35 mm)×(120 mm - 140 mm)×(430 mm - 460 mm).

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