Rock drilling brazing steel and preparation method thereof

Abstract

The invention relates to rock drilling brazing steel and a preparation method, and belongs to the technical field of steel manufacturing. The brazing steel comprises the following chemical components in percentage by mass: 0.19 percent to 0.30 percent of C, 0.15 percent to 0.40 percent of Si, 1.0 percent to 1.70 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.025 percent of S, 2.20 percent to 2.70 percent of Cr, 0.10 percent to 0.30 percent of Ni, 0.30 percent to 0.60 percent of Mo, 0.10 percent to 0.30 percent of V, 0.01 percent to 0.03 percent of Al and a matrix element Fe, the microstructure of the brazing steel comprises bainite and martensite. By optimizing the alloy component design, Mo and V are comprehensively utilized to improve the wear resistance, Mo is utilized to improve the heat resistance, and Mn and Si are utilized to synergistically optimize the obdurability. Meanwhile, the hardenability, the tempering stability and the corrosion resistance of the rock drilling brazing steel are enhanced under the composite action of Cr and Mo, so that the brazing steel with good obdurability is obtained, and the production cost and the process difficulty are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel manufacturing, and particularly relates to a rock drill steel and a preparation method thereof. BACKGROUND

[0002] The rock drill is a core tool in mining, tunneling and rock breaking engineering, and the performance of the rock drill directly determines the engineering efficiency and cost. At present, mainstream drill materials such as 55SiMnMo, 40CrNiMoV and 27SiMnNi2CrMo have certain advantages in wear resistance, toughness and heat treatment process adaptability, but still have problems such as difficult to balance wear resistance and impact resistance, complex heat treatment process and high cost, and insufficient corrosion resistance.

[0003] In recent years, in order to meet the needs of higher rock drilling life and automatic rock drilling machines, the industry has begun to use 23CrNi3Mo carburized bainite steel. The 23CrNi3Mo carburized bainite steel can obtain a composite structure of "hard surface and tough core" through carburizing treatment, the surface is high-carbon martensite, and the core is bainite with good toughness, which shows good application effect. However, 23CrNi3Mo steel still has obvious limitations, the solid solution strengthening effect of alloy elements of 23CrNi3Mo carburized bainite steel is weak, the pinning inhibition effect on grain boundary is limited, and the rolling temperature and time need to be strictly controlled in the production process, the process window is narrow and the production is difficult. In addition, the high cost of Ni element also increases the cost, thereby limiting the wider application of 23CrNi3Mo carburized bainite steel.

[0004] Therefore, it is urgent to develop a new type of rock drill steel with low cost, easy processing and high wear resistance, excellent toughness and high tempering stability. SUMMARY

[0005] The present application provides a rock drill steel and a preparation method thereof, to solve the technical problem of how to reduce the production cost of the rock drill steel. In a first aspect, the embodiments of the present application provide a rock drill steel, the chemical composition of the drill steel includes, in mass fraction: C: 0.19% to 0.30%, Si: 0.15% to 0.40%, Mn: 1.0% to 1.70%, P≤0.025%, S≤0.025%, Cr: 2.20% to 2.70%, Ni: 0.10% to 0.30%, Mo: 0.30% to 0.60%, V: 0.10% to 0.30%, Al: 0.01% to 0.03%, and base element Fe. The microstructure of the drill steel includes bainite and martensite.

[0006] Optionally, the volume fraction of the bainite is 90% to 95%, and the volume fraction of the martensite is 5% to 10%.

[0007] Optionally, the reticular carbide organization of the steel is ≤1 level, the residual austenite organization of the steel is ≤1 level, and the martensite organization of the steel is ≤1 level.

[0008] Optionally, the austenite grain size of the steel is 5-8 levels.

[0009] Optionally, the steel satisfies at least one of the following properties: the surface hardness is 55-58 HRC, and the matrix hardness is 38-42 HRC.

[0010] In a second aspect, the embodiments of the present application provide a preparation method of the steel as described in the first aspect, and the method comprises: obtaining a billet with the following chemical composition: C: 0.19%-0.30%, Si: 0.15%-0.40%, Mn: 1.0%-1.70%, P≤0.025%, S≤0.025%, Cr: 2.20%-2.70%, Ni: 0.10%-0.30%, Mo: 0.30%-0.60%, V: 0.10%-0.30%, Al: 0.01%-0.03%, and matrix element Fe; carburizing, quenching and tempering the billet in sequence to obtain the steel.

[0011] Optionally, the holding temperature of the heating is 1150-1220°C, the holding time of the heating is 2-3 hours, and the out-furnace temperature of the heating is 1080-1120°C.

[0012] Optionally, the opening rolling temperature of the rough rolling is 960-1050°C, and the total deformation of the rough rolling is 30%-40%.

[0013] Optionally, the opening rolling temperature of the finish rolling is 900-1000°C, and the total deformation of the finish rolling is 40%-60%.

[0014] Optionally, the carburized layer thickness of the steel is 1.0-1.5 mm, and the hardened layer thickness of the steel is 0.7-1.2 mm.

[0015] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art: The embodiment of the present application provides a rock drill steel, and the chemical composition of the rock drill steel comprises, in mass fraction, C: 0.19%-0.30%, Si: 0.15%-0.40%, Mn: 1.0%-1.70%, P: 0.025% or less, S: 0.025% or less, Cr: 2.20%-2.70%, Ni: 0.10%-0.30%, Mo: 0.30%-0.60%, V: 0.10%-0.30%, Al: 0.01%-0.03%, and base element Fe; and the microstructure of the rock drill steel comprises bainite and martensite. Through component optimization and structure design, the problems of high cost, narrow production process window and difficult balanced performance of the traditional rock drill steel caused by the dependence on valuable alloy elements are systematically solved. The core principle is that through accurate control of the proportion of C and Cr, Mo and V and other multi-alloy elements, under the premise of not depending on expensive nickel elements, the synergistic effect of Mo-V compound carbide strengthening and Mn-Si solid solution strengthening and other elements is utilized to improve the hardenability, tempering stability and fine grain strengthening effect of the rock drill steel. This makes the rock drill steel obtain a complex structure mainly composed of bainite and supplemented by martensite under the condition of air cooling, and the expensive and complex heat treatment step is omitted, so that the production difficulty and energy cost are greatly reduced. Meanwhile, the harmful elements such as P and S are strictly controlled in the component design, and a small amount of Al is added for deoxidization and grain refinement, so that the cleanliness and toughness of the rock drill steel are effectively improved.

[0016] In conclusion, the scheme can ensure that the rock drill steel has high hardness, high wear resistance and sufficient toughness, reduce the alloy cost and the dependence on harsh process conditions, and realize the unity of low cost, high performance and easy preparation. BRIEF DESCRIPTION OF DRAWINGS

[0017] The drawings incorporated into the specification and constituting a part of the specification show embodiments consistent with the present application and, together with the specification, serve to explain the principles of the present application.

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0019] Figure 1 A flow chart of a rock drill steel and a preparation method provided by the embodiment of the present application is shown in the figure. Figure 2 A metallographic chart of a rock drill steel provided by the embodiment 1 of the present application is shown in the figure. Figure 3 A metallographic chart of a rock drill steel provided by the comparative example 1 of the present application is shown in the figure. Figure 4A metallographic phase diagram of the rock drill steel provided for Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0020] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0021] The range descriptions described herein, such as numerical range, ratio range, etc., include all possible sub-ranges and single values within the range, for example, the range description of "1 to 6" or "1~6" covers all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single values (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "include", "contain" and the like used herein mean "include but not limited to"; the relationship terms "first", "second" and the like are only used to distinguish different entities or operations, and do not imply actual sequence or relationship. "And / or" means that multiple situations can exist independently or simultaneously. "At least one", "multiple", "at least one" and the like refer to any combination of the corresponding objects, including single or multiple combinations of the objects. The ratio relationships involved herein, such as mass ratio, molar ratio, etc., should be understood as the corresponding relationship between the front and the rear in the ratio according to the sequence of description. The raw materials, reagents, instruments and equipment used herein can be purchased or prepared by existing methods.

[0022] In a first aspect, the embodiments of the present application provide a rock drill steel, the chemical composition of the drill steel includes, in mass fraction: C: 0.19%~0.30%, Si: 0.15%~0.40%, Mn: 1.0%~1.70%, P≤0.025%, S≤0.025%, Cr: 2.20%~2.70%, Ni: 0.10%~0.30%, Mo: 0.30%~0.60%, V: 0.10%~0.30%, Al: 0.01%~0.03%, and base element Fe; Positive effects of limiting the mass fraction of C to 0.19% to 0.30%: C elements can improve the strength of the drill steel by forming solid solution structure, and promote the generation of carbides, thereby enhancing the hardness and wear resistance of the drill steel. To ensure the formation of bainite structure with good strength and toughness in the matrix, the mass fraction of C needs to be controlled within a reasonable range. Too high mass fraction of C will lead to too high hardness of the matrix, and the toughness of the drill steel will decrease, and the drill steel is prone to breakage during the drilling process; too low mass fraction of C cannot provide sufficient strength for the drill steel, which may cause the long rod product to bend during use, affecting the service life of the drill steel. For example, the mass fraction of C can be 0.19%, 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, etc.

[0023] Positive effects of limiting the mass fraction of Si to 0.15% to 0.40%: Si mainly plays a role in assisting deoxidization and improving cleanliness in steel, and can also improve the strength of the drill steel through solid solution strengthening, and cooperates with Mn to enhance the strength and toughness of the drill steel. However, too high mass fraction of Si will reduce the plasticity and toughness of the drill steel, and increase the cold brittle transition temperature, which will adversely affect the service performance of the drill steel. Therefore, the mass fraction of Si needs to be controlled within a reasonable range to ensure sufficient deoxidization of the molten steel and certain strengthening effect, while minimizing the damage to the toughness of the drill steel. Too high mass fraction of Si will lead to a decrease in the plasticity and toughness of the drill steel, and too low mass fraction of Si will affect the deoxidization effect of the molten steel and the strength improvement of the drill steel. For example, the mass fraction of Si can be 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, etc.

[0024] Positive effects of limiting the mass fraction of Mn to 1.0% to 1.70%: Mn can effectively improve the strength of the steel, and improve the hot working performance and cold brittle tendency of the drill steel, without damaging the plasticity and impact toughness of the drill steel. Mn can also eliminate the hot brittleness problem caused by elements such as S and O, and cooperates with Si to further improve the strength and toughness of the drill steel. During the smelting process, Mn also plays a deoxidizing role, and can combine with S to form manganese sulfide inclusions, thereby optimizing the performance of the drill steel. However, it should be noted that too high mass fraction of Mn will lead to the embrittlement of the drill steel, the increase in hardness, and the decrease in corrosion resistance and weldability; and too low mass fraction of Mn will result in insufficient strength of the drill steel, and cannot effectively suppress the hot brittle tendency. For example, the mass fraction of Mn can be 1.0%, 1.10%, 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, etc.

[0025] The positive effects of limiting the phosphorus (P) mass fraction to ≤0.025%: While phosphorus generally reduces the plasticity and toughness of drill steel, it can also improve machinability and corrosion resistance in certain special steel grades. To suppress the adverse effects of P on the toughness of drill steel, the P mass fraction should be strictly controlled to maintain a low level. The lower the P mass fraction, the better it is for ensuring the plasticity and toughness of the drill steel. For example, the P mass fraction can be 0.005%, 0.010%, 0.015%, 0.020%, 0.025%, etc.

[0026] The positive effects of limiting the sulfur (S) mass fraction to ≤0.025%: S is a harmful element in most steels, causing hot brittleness and reducing the steel's ductility and toughness. While it can be used to improve machinability in some steels with specific processing requirements, machinability is not a primary consideration in drill steel. Furthermore, since the desulfurization and deoxidation processes are thermodynamically closely related, controlling the S mass fraction at a low level not only helps avoid hot brittleness in drill steel but also improves the cleanliness of the molten steel, thereby optimizing the overall performance of the drill steel. Therefore, the S mass fraction should be reduced as much as possible to maximize the toughness and reliability of the drill steel. For example, the S mass fraction can be 0.005%, 0.010%, 0.015%, 0.020%, 0.025%, etc.

[0027] The positive effects of limiting the Cr mass fraction to 2.20%~2.70% include: Cr effectively improves the strength and hardness of drill steel and enhances its hardenability. Simultaneously, the carbides formed by Cr and C also exhibit good wear resistance. Controlling the Cr mass fraction within a reasonable range helps to form a high-hardness martensitic structure on the surface of the drill bit after carburizing, while the core retains a tough bainitic structure, thus achieving excellent wear resistance on the surface and improving the drill steel's wear resistance during rock drilling. Furthermore, Cr can also have a synergistic effect with Mo, further improving the strength and toughness of the drill steel and enhancing its corrosion resistance. However, an excessively high Cr mass fraction leads to excessive matrix hardness and excessive carbides, resulting in a decrease in the drill steel's toughness; conversely, if the Cr mass fraction is too low, it is difficult to achieve the required strength improvement and microstructure optimization. For example, the Cr mass fraction can be 2.20%, 2.30%, 2.40%, 2.50%, 2.60%, 2.70%, etc.

[0028] The positive effects of limiting the Ni mass fraction to 0.10%~0.30% include: the addition of Ni can effectively improve the strength of the drill steel while maintaining good plasticity and toughness, which helps to improve fatigue performance and reduce notch sensitivity. Controlling the Ni mass fraction within a suitable range can, to some extent, reduce the carbon activity in the drill steel, thereby optimizing the strength-toughness balance. However, an excessively high Ni mass fraction increases the cost of the drill steel, while an excessively low Ni mass fraction cannot effectively improve the strength and toughness of the drill steel. For example, the Ni mass fraction can be 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, etc.

[0029] The positive effects of limiting the Mo mass fraction to 0.30%~0.60% include: Mo can significantly shift the precipitation of ferrite in the isothermal transformation curve of the brazing steel to the right, thereby promoting the formation of bainite under air cooling conditions. Mo also helps refine the grains, improves the hardenability and hot strength of the brazing steel, and can effectively suppress temper brittleness. To ensure that the matrix structure of the brazing steel is dominated by bainite and to enhance the performance stability of the brazing steel during subsequent quenching and tempering processes, the Mo mass fraction needs to be controlled within a reasonable range. Too high a Mo mass fraction will increase costs, while too low a Mo mass fraction will not be able to exert the alloying effect that Mo should have. For example, the Mo mass fraction can be 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, etc.

[0030] The positive effects of limiting the V mass fraction to 0.10%~0.30% include: the addition of V can effectively refine the grains and produce precipitation strengthening, thereby improving the strength, wear resistance, and hydrogen embrittlement resistance of the brazing steel, while suppressing temper brittleness and reducing the susceptibility to hot working cracks. The MC-type carbides formed by V and C can inhibit grain growth in austenite and precipitate dispersed carbonitrides during cooling, refining the microstructure and simultaneously improving the strength and toughness of the brazing steel. To fully utilize the strengthening effect of V and avoid adverse effects, the V mass fraction must be controlled within an appropriate range: too high a V mass fraction can easily form coarse carbonitrides, impairing the toughness of the brazing steel; while too low a V mass fraction will result in insufficient precipitation, failing to achieve effective strengthening. For example, the V mass fraction can be 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, etc.

[0031] The positive effects of limiting the Al mass fraction to 0.01%~0.03% include: Al is mainly used as a deoxidizer in drill steel, effectively improving the cleanliness of molten steel; simultaneously, Al can also improve the impact toughness of drill steel by refining grains. To balance the deoxidation effect and microstructure optimization during smelting, the Al mass fraction must be controlled within an appropriate range. Al can combine with N to form aluminum nitride, further enhancing grain refinement and toughening effects; however, if the Al mass fraction is too high, it can easily cause nozzle blockage during continuous casting, affecting production stability; while if the Al mass fraction is too low, it will lead to insufficient deoxidation of molten steel, decreased cleanliness, and weakened grain refinement effect. For example, the Al mass fraction can be 0.01%, 0.02%, 0.03%, etc.

[0032] Fe is a matrix element, and the specific content / range of Fe can be obtained through the upper and lower limit formulas of the component, that is: The sum of the percentages of all components in a composition should equal 100%, and the content ranges of several components should meet the following conditions: the upper limit of a certain component + the lower limit of other components ≤ 100; the lower limit of a certain component + the upper limit of other components ≥ 100. Furthermore, the specific content of Fe is made up to 100% by the actual detected values ​​of the other chemical components mentioned above, together with any unlisted active elements and / or impurity elements, and Fe must constitute the absolute proportion as a matrix element.

[0033] The microstructure of the drill steel includes bainite and martensite.

[0034] Bainite: A non-lamellar structure formed by the decomposition of supercooled austenite in the intermediate temperature range. In the drill steel of this application, it forms a tough matrix to withstand impact loads and prevent fracture. Martensite: A supersaturated solid solution of carbon in α-Fe. In the drill steel of this application, it is mainly distributed in the surface layer, providing high hardness and wear resistance, thereby extending drilling life.

[0035] In some embodiments, the volume fraction of bainite is 90% to 95%, and the volume fraction of martensite is 5% to 10%.

[0036] The volume fraction of bainite is between 90% and 95%. Bainite is the main source of strength and toughness in drill bit steel. Too high a volume fraction of bainite will lead to increased strength but insufficient toughness, while too low a volume fraction will result in insufficient strength. Examples of bainite volume fractions include 90%, 91%, 92%, 93%, 94%, and 95%. The volume fraction of martensite is between 5% and 10%. It can adjust the strength and toughness of the drill bit steel. Too high a volume fraction of martensite will lead to excessive strength but compromised toughness, while too low a volume fraction will result in insufficient stiffness. Examples of martensite volume fractions include 5%, 6%, 7%, 8%, 9%, and 10%.

[0037] In some embodiments, the brazing steel has a network carbide structure ≤ grade 1, a retained austenite structure ≤ grade 1, and a martensite structure ≤ grade 1.

[0038] The brazing drill steel has a network carbide structure ≤ grade 1, eliminating continuous network carbides to prevent grain boundary brittleness and brittle fracture or chipping during rock drilling. For example, the network carbide structure of the drill steel can be grade 0.2, 0.4, 0.6, 0.8, or 1. The brazing drill steel has a retained austenite structure ≤ grade 1, controlling the unstable retained austenite content to an extremely low level to ensure high surface hardness, dimensional stability, and fatigue resistance. For example, the retained austenite structure of the drill steel can be grade 0.2, 0.4, 0.6, 0.8, or 1. The brazing drill steel has a martensite structure ≤ grade 1, obtaining fine cryptocrystalline or fine acicular martensite, providing high hardness and strength to the surface of the drill steel while retaining good toughness. For example, the martensite structure of the drill steel can be grade 0.2, 0.4, 0.6, 0.8, or 1.

[0039] In some embodiments, the austenite grain size of the brazing steel is grade 5 to grade 8.

[0040] The austenite grain size of the drill steel is between grade 5 and 8. Fine-grained strengthening optimizes its microstructure and properties: on the one hand, after heat treatment, fine austenite grains can form finer and more uniform martensite and bainite structures, significantly improving the balance between surface hardness and core toughness; on the other hand, fine grains increase the number of grain boundaries, hindering crack propagation, improving the drill steel's impact resistance and wear resistance, and ultimately extending its service life during rock drilling. For example, the austenite grain size of the drill steel can be grade 5, 6, 7, or 8.

[0041] In some embodiments, the brazing steel satisfies at least one of the following properties: surface hardness of 55HRC~58HRC and matrix hardness of 38HRC~42HRC.

[0042] The surface hardness, between 55 HRC and 58 HRC, provides the drill steel with extremely high wear resistance, directly resisting rock abrasion and cutting, thus extending the life of the drill bit. For example, the surface hardness can be 55 HRC, 56 HRC, 57 HRC, 58 HRC, etc. The matrix hardness, between 38 HRC and 42 HRC, imparts good toughness to the drill steel to absorb impact energy and provides strong support for the hardened surface, preventing fracture or collapse under high impact loads. For example, the matrix hardness can be 38 HRC, 39 HRC, 40 HRC, 41 HRC, 42 HRC, etc.

[0043] Figure 1 This is a flowchart illustrating a rock drilling steel and its preparation method, provided as an embodiment of this application. Please see Figure 1 Secondly, this application provides a method for preparing the drill steel described in the first aspect, the method comprising: S1. Obtain a steel billet having the following chemical composition: C: 0.19%~0.30%, Si: 0.15%~0.40%, Mn: 1.0%~1.70%, P≤0.025%, S≤0.025%, Cr: 2.20%~2.70%, Ni: 0.10%~0.30%, Mo: 0.30%~0.60%, V: 0.10%~0.30%, Al: 0.01%~0.03%, and the base element Fe; S2. The steel billet is sequentially heated, rough rolled, finish rolled, carburized, quenched and tempered to obtain brazing steel.

[0044] In the above technical solution, the steel billet is a hollow steel billet obtained by smelting, having a central hole drilled, and inserting a core material into the hole.

[0045] In some embodiments, the holding temperature for heating is 1150℃~1220℃, the holding time for heating is 2h~3h, and the exit temperature for heating is 1080℃~1120℃.

[0046] The heating and holding temperature is between 1150℃ and 1220℃ to ensure the billet is fully austenitized and its composition is homogenized, providing an ideal initial microstructure for subsequent hot working. For example, the heating and holding temperatures can be 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, 1210℃, 1220℃, etc. The heating and holding time is between 2h and 3h to ensure that the alloying elements are fully dissolved and diffused to obtain austenite with uniform composition and microstructure. For example, the heating and holding time can be 2h, 3h, etc. The furnace exit temperature is between 1080℃ and 1120℃ to control the billet within a suitable hot working window to prevent abnormal grain growth and ensure smooth subsequent rolling. For example, the furnace exit temperatures can be 1080℃, 1090℃, 1100℃, 1110℃, 1120℃, etc.

[0047] In some embodiments, the initial rolling temperature of the roughing roll is 960°C to 1050°C, and the total deformation of the roughing roll is 30% to 40%.

[0048] The initial rolling temperature of the roughing mill is between 960℃ and 1050℃ to ensure that the drill steel has suitable plasticity in the austenitic region, facilitating large deformation processing, while avoiding cracking due to excessively low temperatures or coarse grains due to excessively high temperatures. For example, the initial rolling temperature can be 960℃, 970℃, 980℃, 990℃, 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, or 1050℃. The total deformation of the roughing mill is between 30% and 40% to ensure uniform microstructure of the drill steel during rolling deformation and to avoid rolling stress affecting the quality of the finished product. For example, the total deformation of the roughing mill can be 30%, 32%, 34%, 36%, 38%, or 40%.

[0049] In some embodiments, the initial rolling temperature of the finishing mill is 900°C to 1000°C, and the total deformation of the finishing mill is 40% to 60%.

[0050] The initial rolling temperature of the finish rolling is between 900℃ and 1000℃ to ensure that the drill steel undergoes plastic deformation within a suitable austenitic temperature range. This avoids both excessively high temperatures leading to coarse grains and excessively low temperatures causing work hardening and a sudden increase in rolling force. For example, the initial rolling temperature of the finish rolling can be 900℃, 920℃, 940℃, 960℃, 980℃, or 1000℃. The total deformation of the finish rolling is between 40% and 60%. By applying sufficient multi-pass cumulative deformation, the austenite grains are sufficiently refined, optimizing the uniformity and density of the drill steel microstructure, thus laying the foundation for the final mechanical properties of the product. For example, the total deformation of the finish rolling can be 40%, 45%, 50%, 55%, or 60%.

[0051] In some embodiments, the carburized layer thickness of the drill steel is 1.0 mm to 1.5 mm, and the hardened layer thickness of the drill steel is 0.7 mm to 1.2 mm.

[0052] The carburized layer thickness of the drill bit is between 1.0 mm and 1.5 mm, providing a sufficiently deep high carbon concentration gradient on the drill bit surface to ensure excellent wear resistance and contact fatigue resistance. For example, the carburized layer thickness can be 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, etc. The hardened layer thickness of the drill bit is between 0.7 mm and 1.2 mm, ensuring the formation of a sufficiently deep effective reinforcement zone on the drill bit surface, providing reliable load-bearing strength and crush resistance, and preventing plastic deformation and premature failure. For example, the hardened layer thickness can be 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, etc.

[0053] The product prepared by the method of preparing rock drilling steel is the rock drilling steel described above. Since the method of preparing rock drilling steel adopts some or all of the technical solutions of the rock drilling steel embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0054] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0055] The chemical composition (mass percentage / %) of the examples and comparative examples is shown in Table 1.

[0056] Table 1

[0057] Example 1 The steel billet with the chemical composition described in Example 1 of Table 1 was obtained; The steel billet is heated to a holding temperature of 1200℃ for 2.5 hours, and then exits the furnace at 1090℃. Next, the billet undergoes rough rolling at an initial rolling temperature of 1000℃, with a total deformation of 35%. Finally, the billet undergoes finish rolling at an initial rolling temperature of 950℃, with a total deformation of 50%. Subsequently, the billet is sequentially carburized, quenched, and tempered to obtain drill steel. The carburized layer thickness of the drill steel is 1.2 mm, and the hardened layer thickness is 1.1 mm.

[0058] Figure 2 This is a metallographic image of the rock drilling drill steel provided in Embodiment 1 of this application. According to... Figure 2 It can be seen that Example 1 has a uniform and refined microstructure, and its network carbides, retained austenite and martensite structure all meet the design requirements of ≤1 level.

[0059] Example 2 A steel billet with the chemical composition described in Example 2 of Table 1 was obtained; The steel billet is heated to a holding temperature of 1190℃ for 2.6 hours, and then exits the furnace at 1100℃. Next, the billet undergoes rough rolling at an initial rolling temperature of 1030℃, with a total deformation of 34%. Finally, the billet is finished rolled at an initial rolling temperature of 980℃, with a total deformation of 45%. Subsequently, the billet is subjected to carburizing, quenching, and tempering to obtain brazing steel. The carburized layer thickness of the brazing steel is 1.15 mm, and the hardened layer thickness is 1.1 mm.

[0060] Example 3 The steel billet with the chemical composition described in Example 3 of Table 1 was obtained; The steel billet is heated to a holding temperature of 1200℃ for 2.5 hours and then removed from the furnace at a temperature of 1090℃. The billet is then subjected to rough rolling at an initial rolling temperature of 1000℃ and a total deformation of 35%. Finally, the billet is subjected to finish rolling at an initial rolling temperature of 950℃ and a total deformation of 50%. The billet is then sequentially carburized, quenched, and tempered to obtain brazing steel.

[0061] Comparative Example 1 The steel billet with the chemical composition described in Comparative Example 1 in Table 1 was obtained; The steel billet is heated to a holding temperature of 1250℃ for 3.2 hours and then removed from the furnace at 1150℃. The billet is then rough-rolled at an initial rolling temperature of 1080℃ with a total deformation of 28%. Finally, it is finish-rolled at an initial rolling temperature of 1020℃ with a total deformation of 40%. The billet is then sequentially carburized, quenched, and tempered to obtain brazing steel.

[0062] Figure 3 Metallographic image of the rock drill bit provided in Comparative Example 1 of this application. According to Figure 3 It can be seen that the microstructure of Comparative Example 1 is coarse and uneven, with obvious continuous network carbides and coarse martensite, which does not meet the microstructure design requirements of ≤1 grade.

[0063] Comparative Example 2 The steel billet with the chemical composition described in Comparative Example 2 in Table 1 was obtained; The steel billet is heated to a holding temperature of 1200℃ for 2.5 hours and then removed from the furnace at a temperature of 1050℃. The billet is then subjected to rough rolling at an initial rolling temperature of 1000℃ and a total deformation of 35%. Finally, the billet is subjected to finish rolling at an initial rolling temperature of 900℃ and a total deformation of 60%. The billet is then carburized, quenched, and tempered to obtain brazing steel.

[0064] Figure 4 Metallographic image of the rock drill bit provided in Comparative Example 2 of this application. According to Figure 4 It can be seen that the microstructure of Comparative Example 2 is obviously coarse and uneven, with not only a large number of coarse acicular martensite, but also aggregated carbides; the network carbides, retained austenite and martensite of the microstructure do not meet the design requirements of ≤1 grade.

[0065] The experimental results of the examples and comparative examples are shown in Table 2.

[0066] Table 2

[0067] The data tables above provide a clear comparison of the differences between various embodiments and comparative examples. The following conclusions can be drawn: As can be seen from the data in Table 2, the brazing steel provided in this application embodiment has a surface hardness of 55HRC~57HRC, a matrix hardness of 38HRC~41HRC, a network carbide structure of grade 1.0, and a carburized layer thickness of 1.10mm~1.20mm.

[0068] As can be seen from Examples 1-5 and Comparative Examples 1-2, the surface hardness, matrix hardness, network carbides, and carburized layer thickness of Examples 1-5 are significantly better than those of Comparative Examples 1-2. Therefore, the rock drilling steel and its preparation method provided by the embodiments of the present invention can obtain bainitic steel with mechanical properties comparable to 23CrNi3Mo steel and good strength-toughness matching while reducing production costs and process difficulty.

[0069] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: The rock drilling steel provided in this embodiment of the invention achieves a good balance of hardness, toughness and wear resistance by optimizing the chemical composition and preparation process, thereby improving production stability and product service life.

[0070] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A rock drill steel, characterized in that The chemical composition of the steel in mass fraction includes: C: 0.19%-0.30%, Si: 0.15%-0.40%, Mn: 1.0%-1.70%, P≤0.025%, S≤0.025%, Cr: 2.20%-2.70%, Ni: 0.10%-0.30%, Mo: 0.30%-0.60%, V: 0.10%-0.30%, Al: 0.01%-0.03%, and base element Fe; The microstructure of the steel includes: bainite and martensite.

2. The steel for brazing according to claim 1, characterized by The volume fraction of the bainite is 90%-95%, and the volume fraction of the martensite is 5%-10%.

3. The steel according to claim 1, wherein The reticular carbide organization of the steel is ≤1 level, the residual austenite organization of the steel is ≤1 level, and the martensite organization of the steel is ≤1 level.

4. The steel according to claim 1, wherein The austenite grain size of the steel is 5-8 levels.

5. The steel according to claim 1, wherein The steel satisfies at least one of the following performances: surface hardness is 55HRC-58HRC, and base hardness is 38HRC-42HRC.

6. A method of producing the welding steel according to any one of claims 1 to 5, characterized in that, The method comprises: obtaining a billet with the chemical composition according to any one of claims 1-5; sequentially heating, rough rolling, finish rolling, carburizing, quenching and tempering the billet to obtain the steel.

7. The method of claim 6, wherein, The holding temperature of the heating is 1150°C-1220°C, the holding time of the heating is 2h-3h, and the furnace-out temperature of the heating is 1080°C-1120°C.

8. The method of claim 6, wherein, The rough rolling temperature is 960°C-1050°C, and the total deformation of the rough rolling is 30%-40%.

9. The method of claim 6, wherein, The finish rolling temperature is 900°C-1000°C, and the total deformation of the finish rolling is 40%-60%.

10. The method of claim 6, wherein, The carburized layer thickness of the steel is 1.0mm-1.5mm, and the hardened layer thickness of the steel is 0.7mm-1.2mm.

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