Steel for rare earth rock drilling tools and preparation method thereof

Abstract

The present invention belongs to the field of metallurgy technology and specifically relates to a rare earth steel for rock drill tools and a preparation method thereof. The steel comprises a matrix and a doping element, wherein the doping amount of the doping element is 0.008 wt.% to 0.01 wt.% of the matrix system, the doping elements are cerium and yttrium, and the chemical composition of the matrix comprises: C, Si, Mn, S, P, O, Al, Cr, Ni, Mo, and Cu, with the remainder being Fe and unavoidable impurities. The present invention uses the rare earth elements cerium and yttrium to modify the matrix steel. The rare earth elements cerium and yttrium modify large-sized brittle inclusions to generate fine and dispersed rare earth inclusions, which are primarily RE-O and RE-O-S types. These rare earth inclusions refine the grains in the rock drill tool steel structure, weaken crack nucleation, and reduce 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 rock drill tool steel.

Description

Technical Field

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

[0002] With the development of mineral resources, energy construction, transportation, and urban subway construction, rock drilling tools play an indispensable role in all of these areas, resulting in a continuously growing demand for rock drilling tools. Furthermore, the harsh working environment during rock drilling, such as high-frequency impact, strong torsion, and high wear, also poses new challenges to rock drilling tools.

[0003] In China, the demand for rock drilling tools continues to grow due to the numerous infrastructure projects urgently needed each year. This has driven not only large rock drilling tool manufacturers to increase output and expand production, but also a large number of small private enterprises, driven by profit, have begun producing rock drilling tools. As a result, rock drilling tool production has continued to increase in recent years. However, this increase primarily serves domestic market demand, resulting in low overall quality and technological content, intensifying competition in the domestic market. Furthermore, due to an irrational domestic rock drilling tool product structure, the production of low-end tools is excessive, leading to overcapacity and a reliance on imports for higher-end products. This presents a pressing challenge for the research and development of rock drilling tools.

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

[0005] In order to solve the above problems, the present invention provides a rare earth steel for rock drilling tools and a preparation method thereof, wherein rare earth cerium and yttrium are doped into a matrix, and rare earth cerium and yttrium modify large-sized brittle inclusions to generate fine and dispersed rare earth inclusions, wherein the rare earth inclusions are mainly of RE-O type and RE-OS type, which refine the grains in the matrix structure, weaken the crack nucleation effect, and reduce the uneven distribution of the steel structure caused by the segregation of impurity elements at the 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, comprising a matrix and a doping element, wherein the doping amount of the doping element is 0.008 wt.% to 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% 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: 0.05~0.15%, the balance is Fe and inevitable impurities.

[0008] The present invention uses the rare earth elements cerium and yttrium to modify the matrix. The reaction products of cerium and yttrium in the matrix steel liquid are both rare earth oxysulfides. The rare earth inclusions are primarily RE-O and RE-OS types. This refines the grain size in the matrix structure, significantly reducing the average grain size of the rock drill steel and correspondingly increasing the number of grain boundaries. This effectively hinders crack propagation during plastic deformation, thereby increasing the deformation resistance of the rock drill steel. Furthermore, yttrium, with a smaller atomic radius than lighter rare earth elements, can more effectively reduce the inclusion content, improve inclusion distribution, reduce inclusion size, refine and spheroidize inclusions, and thus improve steel performance. It also reduces the uneven distribution of steel structure caused by impurity element segregation at grain boundaries and eliminates the segregation of larger inclusions and carbides along grain boundaries, thereby increasing the impact toughness of the matrix.

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

[0010] In some specific embodiments, the doping amount of the doping element is 0.009 wt.% of the matrix system. The rare earth elements cerium and yttrium jointly modify the matrix, so that the small and dispersed rare earth inclusions generated from the large brittle inclusions in the matrix weaken the crack nucleation effect, thereby greatly improving the impact toughness of the rock drilling tool steel. When the rare earth content in the steel is within an appropriate range, the overall performance of the rock drilling tool steel can be improved. However, when the rare earth content is too high, the large amount of flocculent rare earth inclusions generated in the rock drilling tool steel can reduce the impact toughness of the rock drilling tool steel.

[0011] Furthermore, the matrix is ​​prepared according to the following chemical composition in mass percentage: 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 remainder 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-OS type in the matrix, which refines the matrix grains.

[0012] The addition of rare earth elements cerium and yttrium can react with sulfur and oxygen in steel to form rare earth compounds and thus purify the molten steel. It can also refine the grains, making the carbides more finely dispersed in the matrix. Yttrium is mainly in the form of YOS composite inclusions with a density of about 4.25, and cerium is mainly in the form of Ce-OS composite inclusions with a density of about 6.0. This weakens the crack nucleation effect and reduces the uneven distribution of steel tissue caused by the segregation of impurity elements at grain boundaries, thereby greatly improving the impact toughness of rock drilling tool steel. When the rare earth cerium content is 0.009 wt.%, the impact energy of rock drilling tool steel increases the most, which is 32.38%. The fine and dispersed rare earth inclusions generated by the rare earth cerium modification of large-sized brittle inclusions weaken the crack nucleation effect, thereby greatly improving the impact toughness of rock drilling tool steel.

[0013] A second object of the present invention is to provide a method for preparing the above-mentioned rare earth rock drilling tool steel, comprising the following steps:

[0014] S1. After the raw materials are prepared according to the components and proportions, the base is smelted in a vacuum until it is completely melted, and then the doping elements are added, stirred, and then smelted and kept warm.

[0015] S2. After smelting, the ingot is obtained by mold casting.

[0016] S3. Forging the ingot to obtain steel for rare earth rock drilling tools.

[0017] The present invention adopts a vacuum smelting method, wherein the vacuum environment can effectively exclude air and other impurities, significantly improving the purity of the smelting material. In addition, the heating speed under vacuum conditions is fast, heat loss is small, and production efficiency is improved.

[0018] In some specific embodiments, the vacuum smelting temperature is 1580° C. to 1620° C., and the time is 68 min to 72 min.

[0019] In some specific embodiments, the melting and holding time is 2 min to 3 min.

[0020] In some specific embodiments, during the forging process, the start forging temperature is 1150°C to 1200°C, and the final forging temperature is 940°C to 980°C.

[0021] In some specific embodiments, the dimensions of the steel for rare earth rock drilling tools are (25 mm to 35 mm)×(120 mm to 140 mm)×(430 mm to 460 mm).

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The rare earth rock drill steel provided by the present invention uses rare earth elements cerium and yttrium to modify the matrix. The reaction products of cerium and yttrium in the matrix steel liquid are rare earth oxysulfides. The rare earth elements purify the steel liquid and refine the grains, so that the carbides are more finely dispersed in the matrix. The rare earth inclusions are mainly RE-O type and RE-OS type, which significantly reduces the average grain size of the rock drill steel and increases the grain boundaries accordingly, which can better hinder the expansion of cracks during plastic deformation and weaken the crack nucleation effect. It reduces the uneven distribution of steel tissue caused by the segregation of impurity elements at the grain boundaries, and improves the force of steel used for rock drilling tools to resist deformation; in addition, the atomic radius of yttrium is lighter and smaller than that of rare earth, which can more effectively reduce the inclusion content, improve the inclusion distribution, reduce the size of inclusions, refine and spheroidize inclusions, thereby improving the performance of steel, reducing the uneven distribution of steel tissue caused by the segregation of impurity elements at the grain boundaries, eliminating the phenomenon of large inclusions and carbide segregation originally distributed along the grain boundaries, thereby improving the impact toughness of the matrix.

[0024] (2) The present invention adopts rare earth elements cerium and yttrium to jointly modify the matrix. The rare earth elements modify large-sized brittle inclusions to generate fine dispersed rare earth inclusions. The yttrium is mainly in the form of YOS composite inclusions with a density of about 4.25, while the cerium is mainly in the form of Ce-OS composite inclusions with a density of about 6.0. The invention refines the grains in the structure of the steel for rock drilling tools, reduces the average grain size, and increases the corresponding grain boundaries. 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 0.009wt.%, the impact energy of the steel for rock drilling tools is 90.2J, which is 63.1% higher than that of the undoped matrix, thereby improving the comprehensive performance of the steel for rock drilling tools. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a room temperature impact performance diagram of steel for rock drilling tools of Examples 1 to 3 of the present invention and Comparative Examples 1 to 5.

[0026] Figure 2 These are microstructure morphologies of the impact fracture of rock drilling tools according to Examples 1 to 3 of the present invention, wherein: Figure 2(a) is Example 1, (b) is Example 2, and (c) is Example 3.

[0027] Figure 3 The microstructure morphology of the impact fracture of the steel for rock drilling tools of Example 1 and Comparative Examples 1 to 5 of the present invention is shown in FIG. Figure 3 (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 DESCRIPTION

[0028] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0029] 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 scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0030] The existing steel used for rock drilling tools in mineral exploration has high plasticity, high toughness and high fatigue strength. However, during the forging process, impurity elements are concentrated at the grain boundaries, resulting in uneven distribution of the steel structure, resulting in low impact toughness and short service life of the steel for rock drilling tools.

[0031] Based on the above problems, the present invention provides a steel for rare earth rock drilling tools, comprising a matrix and a doping element, wherein the doping amount of the doping element is 0.008 wt.% to 0.01 wt.% of the matrix system, the doping elements are cerium and yttrium, and the matrix is ​​prepared according to the following chemical composition in 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% %, the balance being Fe and inevitable impurities.

[0032] In the present invention, the matrix is ​​modified by rare earth elements cerium and yttrium. The reaction products of cerium and yttrium in the matrix steel liquid are rare earth oxysulfides. The rare earth elements purify the steel liquid and refine the grains, so that the carbides are more finely dispersed in the matrix. The rare earth inclusions are mainly RE-O type and RE-OS type, which significantly reduces the average grain size of the steel for rock drilling tools and increases the grain boundaries accordingly, which can better hinder the expansion of cracks during plastic deformation, weaken the crack nucleation effect, and reduce the impurity The segregation of impurity elements at the grain boundaries causes uneven distribution of steel tissue, thereby increasing the force of steel used for rock drilling tools to resist deformation; in addition, the atomic radius of yttrium is lighter than that of rare earth, which can more effectively reduce the inclusion content, improve the inclusion distribution, reduce the size of inclusions, refine and spheroidize inclusions, thereby improving the performance of steel, reducing the uneven distribution of steel tissue caused by the segregation of impurity elements at the grain boundaries, eliminating the phenomenon of large inclusions and carbide segregation originally distributed along the grain boundaries, thereby improving the impact toughness of the matrix.

[0033] The following is further described through specific examples.

[0034] Example 1

[0035] A steel for rare earth rock drill tools comprises a matrix and doping elements. The matrix's chemical composition, 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%, with the remainder being 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, with a mass ratio of cerium to yttrium of 3.5:6.5.

[0036] The method for preparing the rare earth rock drilling tool steel comprises the following steps:

[0037] S1. After the raw materials are prepared according to their components and proportions, the matrix is ​​placed in a crucible of a 25 kg vacuum induction melting furnace. The furnace is then vacuumed and heated to 1600°C for 70 minutes until completely melted. A mixture of 99.9% pure rare earth cerium and 99.9% pure rare earth yttrium is then added to the crucible through a hopper. To ensure the uniformity of the steel for rock drill tools, the molten steel is electromagnetically stirred and finally kept warm for 2 minutes.

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

[0039] S3. The ingot is forged at an initial forging temperature of 1180°C and a final forging temperature of 950°C to be forged into a slab of 30 mm × 130 mm × 450 mm to obtain steel for rare earth rock drilling tools.

[0040] Example 2

[0041] A rare earth rock drill steel comprises a matrix and doping elements. The matrix's chemical composition, by mass percentage, is as follows: 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%, with the remainder being 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, with a mass ratio of cerium to yttrium of 3:7.

[0042] The method for preparing the rare earth rock drilling tool steel comprises the following steps:

[0043] S1. After the raw materials are prepared according to their components and proportions, the matrix is ​​placed in a crucible of a 25 kg vacuum induction melting furnace. The furnace is then vacuumed and heated to 1600°C for 70 minutes until completely melted. A mixture of 99.9% pure rare earth cerium and 99.9% pure rare earth yttrium is then added to the crucible through a hopper. To ensure the uniformity of the steel for rock drill tools, the molten steel is electromagnetically stirred and finally kept warm for 2 minutes.

[0044] S2. After smelting, the molten steel is cast into an ingot by die casting.

[0045] S3. The ingot is forged at an initial forging temperature of 1180°C and a final forging temperature of 950°C to be forged into a slab of 30 mm × 130 mm × 450 mm to obtain steel for rare earth rock drilling tools.

[0046] Example 3

[0047] A steel for rare earth rock drill tools comprises a matrix and doping elements. The matrix's chemical composition, 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%, with the remainder being 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, with a mass ratio of cerium to yttrium of 4:6.

[0048] The method for preparing the rare earth rock drilling tool steel comprises the following steps:

[0049] S1. After the raw materials are prepared according to their components and proportions, the matrix is ​​placed in a crucible of a 25 kg vacuum induction melting furnace. The furnace is then vacuumed and heated to 1600°C for 70 minutes until completely melted. A mixture of 99.9% pure rare earth cerium and 99.9% pure rare earth yttrium is then added to the crucible through a hopper. To ensure the uniformity of the steel for rock drill tools, the molten steel is electromagnetically stirred and finally kept warm for 2 minutes.

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

[0051] S3. The ingot is forged at an initial forging temperature of 1180°C and a final forging temperature of 950°C to be forged into a slab of 30 mm × 130 mm × 450 mm to obtain steel for rare earth rock drilling tools.

[0052] Comparative Example 1

[0053] A steel for rare earth rock drilling tools includes a matrix, wherein the chemical composition of the matrix is, by mass percentage, 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.

[0054] The method for preparing the rare earth rock drilling tool steel comprises the following steps:

[0055] S1. After the raw materials are prepared according to the components and proportions, the matrix is ​​placed in a crucible of a 25 kg vacuum induction melting furnace, and then vacuum-heated to 1600 °C and vacuum-smelted for 70 min until all the steel is melted to obtain molten steel.

[0056] S2. After smelting, the molten steel is cast into an ingot by die casting.

[0057] S3. The ingot is forged at an initial forging temperature of 1180°C and a final forging temperature of 950°C to be forged into a slab of 30 mm × 130 mm × 450 mm to obtain steel for rare earth rock drilling tools.

[0058] Comparative Example 2

[0059] A steel for rare earth rock drill tools comprises a matrix and a doping element. The matrix has the following chemical composition, 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%, with the remainder being Fe and unavoidable impurities. The doping amount of the doping element is 0.009 wt.% of the matrix system, and the doping element is cerium.

[0060] The method for preparing the rare earth rock drilling tool steel comprises the following steps:

[0061] S1. After the raw materials are prepared according to their components and proportions, the matrix is ​​placed in a crucible of a 25 kg vacuum induction melting furnace. The furnace is then vacuum-heated to 1600°C and smelted in vacuum for 70 minutes until it is completely melted. Rare earth cerium with a purity of 99.9% is then added to the crucible through a hopper. To ensure the uniformity of the steel used for rock drill tools, the molten steel is electromagnetically stirred and finally kept warm for 2 minutes.

[0062] S2. After smelting, the molten steel is cast into an ingot by die casting.

[0063] S3. The ingot is forged at an initial forging temperature of 1180°C and a final forging temperature of 950°C to be forged into a slab of 30 mm × 130 mm × 450 mm to obtain steel for rare earth rock drilling tools.

[0064] Comparative Example 3

[0065] A rare earth rock drill steel comprises a matrix and a doping element. The matrix comprises, by weight percentage, 0.32% C, 0.3% Si, 0.42% Mn, 0.001% S, 0.016% P, 0.0007% O, 0.03% Al, 1.15% Cr, 3.92% Ni, 0.363% Mo, and 0.08% Cu, with the remainder being Fe and unavoidable impurities. The doping amount of the doping element is 0.0038% by weight of the matrix, and the doping element is yttrium.

[0066] The method for preparing the rare earth rock drilling tool steel comprises the following steps:

[0067] S1. After the raw materials are prepared according to their components and proportions, the matrix is ​​placed in a crucible of a 25 kg vacuum induction melting furnace. The temperature is then raised to 1600°C and vacuum smelted for 70 minutes until it is completely melted. A mixture of 99.9% pure rare earth yttrium is then added to the crucible through a hopper. To ensure the uniformity of the steel for rock drill tools, the molten steel is electromagnetically stirred and finally kept warm for 2 minutes.

[0068] S2. After smelting, the molten steel is cast into an ingot by die casting.

[0069] S3. The ingot is forged at an initial forging temperature of 1180°C and a final forging temperature of 950°C to be forged into a slab of 30 mm × 130 mm × 450 mm to obtain steel for rare earth rock drilling tools.

[0070] Comparative Example 4

[0071] A rare earth rock drill steel comprises a matrix and a doping element. The matrix comprises, by mass percentage, 0.32% C, 0.3% Si, 0.42% Mn, 0.001% S, 0.016% P, 0.0007% O, 0.03% Al, 1.15% Cr, 3.92% Ni, 0.363% Mo, and 0.08% Cu, with the remainder being Fe and unavoidable impurities. The doping amount of the doping element is 0.009% by weight of the matrix, and the doping element is yttrium.

[0072] The method for preparing the rare earth rock drilling tool steel comprises the following steps:

[0073] S1. After the raw materials are prepared according to their components and proportions, the matrix is ​​placed in a crucible of a 25 kg vacuum induction melting furnace. The temperature is then raised to 1600°C and vacuum smelted for 70 minutes until it is completely melted. A mixture of 99.9% pure rare earth yttrium is then added to the crucible through a hopper. To ensure the uniformity of the steel for rock drill tools, the molten steel is electromagnetically stirred and finally kept warm for 2 minutes.

[0074] S2. After smelting, the molten steel is cast into an ingot by die casting.

[0075] S3. The ingot is forged at an initial forging temperature of 1180°C and a final forging temperature of 950°C to be forged into a slab of 30 mm × 130 mm × 450 mm to obtain steel for rare earth rock drilling tools.

[0076] Comparative Example 5

[0077] A rare earth rock drill steel comprises a matrix and a doping element. The matrix comprises, by weight percentage, 0.32% C, 0.3% Si, 0.42% Mn, 0.001% S, 0.016% P, 0.0007% O, 0.03% Al, 1.15% Cr, 3.92% Ni, 0.363% Mo, and 0.08% Cu, with the remainder being Fe and unavoidable impurities. The doping amount of the doping element is 0.0018% by weight of the matrix, and the doping element is yttrium.

[0078] The method for preparing the rare earth rock drilling tool steel comprises the following steps:

[0079] S1. After the raw materials are prepared according to their components and proportions, the matrix is ​​placed in a crucible of a 25 kg vacuum induction melting furnace. The temperature is then raised to 1600°C and vacuum smelted for 70 minutes until it is completely melted. A mixture of 99.9% pure rare earth yttrium is then added to the crucible through a hopper. To ensure the uniformity of the steel for rock drill tools, the molten steel is electromagnetically stirred and finally kept warm for 2 minutes.

[0080] S2. After smelting, the molten steel is cast into an ingot by die casting.

[0081] S3. The ingot is forged at an initial forging temperature of 1180°C and a final forging temperature of 950°C to be forged into a slab of 30 mm × 130 mm × 450 mm to obtain steel for rare earth rock drilling tools.

[0082] The performance and microstructure of the rock drilling tool steels prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were analyzed, and the results are as follows:

[0083] The location, orientation, and number of impact specimens were determined in accordance with the standard GB / T2975-2018, "Steel and Steel Products Mechanical Properties Sampling Location and Preparation," or in accordance with the agreed protocol. The impact test was conducted using a Charpy impact testing machine. Three U-shaped specimens measuring 55 mm × 10 mm × 10 mm were machined according to the national standard GB / T229-2007, "Metallic Materials Charpy Pendulum Impact Test Method." The average of these three measurements was used to determine the room temperature impact strength.

[0084] According to GB / T 13298-2015, a 10 mm × 10 mm × 15 mm metallographic specimen was cut at one-quarter the width of the horizontal interface of the rock drill steel perpendicular to the forging direction. The specimen was first ground and polished using a grinder-polish machine with 600-3000 grit metallographic sandpaper in a stepwise manner. The specimen was then cleaned with alcohol and dried to ensure a smooth surface free of scratches and rust. The specimen was then corroded with a pre-prepared 4 wt% nitric acid alcohol solution for approximately 15 seconds. The corrosive solution was then immediately rinsed with distilled water and dried. The microstructure of the specimen was observed using a MIRA3 LMH emission scanning electron microscope at a magnification of more than 1000x.

[0085] Figure 1 The room temperature impact performance diagram of the steel used for rock drilling tools in Examples 1 to 3 and Comparative Examples 1 to 5 of the present invention is shown. Figure 1 As shown in the figure, when the mass ratio of rare earth cerium and yttrium is 3.5:6.5, the room temperature impact resistance of rock drilling tool steel is the best, reaching 90.2 J, which is 63.1% higher than that of rock drilling tool steel without rare earth doping.

[0086] Figure 2 These are microstructure morphologies of the impact fracture of rock drilling tools according to Examples 1 to 3 of the present invention, wherein: Figure 2 (a) is Example 1, (b) is Example 2, and (c) is Example 3. Figure 2As shown, when the mass ratio of cerium to yttrium doped with rare earth elements is 3.5:6.5, as in Example 1, the fracture surface of the rock drilling fiber steel exhibits significantly more dimples, significantly increases the depth of the dimples, and contains small inclusions at the bottom of the dimples. Furthermore, when subjected to high stress, the inclusions easily become crack sources, leading to crack initiation and growth. However, the strong cohesive force between the rare earth inclusions and their interfaces increases the capacity to absorb crack propagation, thereby improving the impact performance of the rock drilling fiber steel. When the mass ratio of cerium to yttrium doped with rare earth elements is 4:6, as in Example 3, and 3:7, as in Example 2, the plastic deformation at the bottom of the dimples in the fracture surface of the rock drilling fiber steel is significantly reduced. Since the dimple size is closely related to the size of the inclusions and second-phase particles, this indicates that the inclusions have a significantly weaker effect in resisting crack propagation. Therefore, the impact toughness of Examples 2 and 3 is reduced compared to that of the rock drilling fiber steel in Example 1.

[0087] Figure 3 The microstructure morphology of the impact fracture of the steel for rock drilling tools of Example 1 and Comparative Examples 1 to 5 of the present invention is shown in FIG. Figure 3 (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. Figure 3 As shown, the impact fracture surface of Example 1 is composed of dimples, with petal-shaped fractures between the dimples, indicating that the rock drilling fiber steel with this composition experienced significant plastic deformation before fracture. However, in Comparative Examples 1 to 5, the plastic deformation at the bottom of the dimples decreased to varying degrees, and cleavage-like planes appeared, resulting in reduced impact performance.

[0088] As shown above, when rare earth cerium and rare earth yttrium are doped in the matrix at a ratio of 3.5:6.5 and a doping content of 0.009 wt.%, the impact energy of the rock drill steel reaches 90.2 J, a 63.1% increase compared to the undoped matrix. This is because the rare earth cerium and yttrium co-modify large brittle inclusions to form fine, dispersed rare earth inclusions, which weaken crack nucleation and significantly improve the impact toughness of the rock drill steel. When the rare earth content in the steel is within an appropriate range, the overall performance of the rock drill steel can be improved. However, when the rare earth content is too high, the large number of rare earth inclusions generated in the rock drill steel will concentrate at the grain boundaries, which will actually reduce the impact toughness of the rock drill steel. The main reasons for the improved toughness of the rock drill steel are as follows: First, the rare earth elements cerium and yttrium refine the grains in the rock drill steel structure. The addition of the rare earth elements cerium and yttrium significantly reduces the average grain size of rock drill steel, resulting in an increase in grain boundaries. This effectively hinders crack propagation during plastic deformation and hinders dislocation movement, thereby increasing the rock drill steel's resistance to deformation. Furthermore, the addition of cerium and yttrium effectively purifies and strengthens the grain boundaries by eliminating harmful impurities there. Furthermore, the addition of cerium and yttrium modifies the non-metallic inclusions in the rock drill steel, eliminating the larger inclusions and carbide segregation that were previously distributed along the grain boundaries, thereby improving the impact toughness of the matrix.

[0089] It should be noted that when numerical ranges are mentioned in the present invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints may be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes preferred embodiments. Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they understand the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0090] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A steel for rare earth rock drilling tools, characterized in that: The invention comprises a matrix and doping elements, wherein 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 according to the following chemical composition in 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% and Cu: 0.05% to 0.15%, and the remainder 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 cerium to 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 element 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 according to the following chemical composition in mass percentage: 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 remainder is Fe and unavoidable impurities, totaling 100%; the doping elements are mixed with cerium and yttrium in a mass ratio of 3.5:6.

5.

5. A method for preparing steel for rare earth rock drilling tools according to any one of claims 1 to 4, characterized in that: The following steps are involved: After the raw materials are prepared according to the components and proportions, the base is smelted in a vacuum until it is completely melted, and then the doping elements are added, stirred, and then smelted and kept warm; After smelting, the ingot is obtained by mold casting; The ingot is subjected to a forging process to obtain steel for rare earth rock drilling tools.

6. The method for preparing steel for rare earth rock drilling tools according to claim 5, characterized in that: The vacuum smelting temperature is 1580 ℃ ~ 1620 ℃, and the time is 68 min ~ 72 min.

7. The method for preparing steel for rare earth rock drilling tools according to claim 5, characterized in that: The melting and holding time is 2 min to 3 min.

8. The method for preparing steel for rare earth rock drilling tools according to claim 5, characterized in that: During the forging process, the start forging temperature is 1150 ℃ ~ 1200 ℃, and the final forging temperature is 940 ℃ ~ 980 ℃.

9. The method for preparing steel for rare earth rock drilling tools according to claim 5, characterized in that: The dimensions of steel for rare earth rock drilling tools are (25 mm to 35 mm) × (120 mm to 140 mm) × (430 mm to 460 mm).

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