Hard alloy wear-resistant steel ball suitable for mine grinding and preparation method thereof

Abstract

The present application belongs to the field of metal materials, and provides a hard alloy wear-resistant steel ball suitable for mine grinding and a preparation method thereof.The present application adopts scrap pig iron as a basic raw material, and the chemical composition of the present application is C2.1-2.2%, Cr9.8-10.0%, V0.10-0.20%, and Ti0.03-0.06%.The present application is melted by a medium-frequency induction furnace, a V-Ti-C-N microalloy system is established by controlled nitrogen introduction, bottom pouring and solidification, and austenitizing quenching and tempering heat treatment processes are used, so that a core-shell precipitated phase microstructure design is formed, in which MN / MCN is used as a hard core, and carbonitrided chromium is used as a gradient self-passivation shell layer.The present application realizes the performance indexes of a surface hardness of HRC60-63 and a core hardness of HRC54-58, the average grain size of the core-shell precipitated phase is 20-200nm, the shell layer thickness is 5-50nm, and the present application has excellent wear resistance and corrosion resistance under the condition of high impact and high wear in wet grinding, solves the problem of insufficient wear resistance and corrosion resistance of traditional alloy steel balls, and has wide application value in mine grinding.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, specifically to a cemented carbide wear-resistant steel ball suitable for mining grinding and its preparation method. Background Technology

[0002] In mining and mineral processing, grinding is a core step in mineral processing, placing extremely stringent demands on the performance of grinding media. Steel balls, as the primary grinding media, need to operate stably for extended periods under high-intensity impact, continuous friction, and complex chemical environments. Their performance directly impacts grinding efficiency, product quality, and production costs. Modern mining grinding processes face the challenges of increasingly harder ores and more stringent requirements for grinding fineness. This necessitates that steel balls possess excellent wear resistance to withstand prolonged, high-frequency mechanical impact and abrasion, while also exhibiting superior corrosion resistance to cope with the chemical erosion of acidic or alkaline media during wet grinding. The wear resistance of steel balls directly determines their service life and grinding efficiency, while corrosion resistance relates to the stability of the grinding process and product purity. Meeting these key performance requirements can not only significantly reduce grinding costs and improve production efficiency but also drive overall progress in mineral processing technology, creating greater economic value for mining enterprises. Therefore, developing grinding steel balls with excellent wear and corrosion resistance has significant engineering application value and broad market prospects.

[0003] Currently, the research and development of grinding steel balls mainly includes technical systems such as high-chromium cast iron balls, medium-chromium alloy steel balls, and low-alloy steel balls. However, there are still significant shortcomings in the synergistic improvement of wear resistance and corrosion resistance. For example, Chinese patent CN104561761B discloses a high-chromium wear-resistant steel ball, but it suffers from insufficient corrosion resistance. Although high-chromium cast iron balls have good wear resistance, their coarse eutectic carbide structure leads to poor toughness and brittle fracture, while their corrosion resistance in acidic environments is limited. Medium-chromium alloy steel balls improve toughness by reducing chromium content, but sacrifice wear resistance and lack an effective surface passivation mechanism. Low-alloy steel balls have lower costs but severely insufficient wear resistance, making it difficult to meet the requirements of high-intensity grinding operations. The core problem of existing technologies lies in the lack of refined microalloying design, making it impossible to achieve precise control of the nanoscale dispersion distribution and gradient microstructure of the hard phase. Traditional alloying methods mainly rely on carbide strengthening, but carbides are large in size and unevenly distributed, which affects the overall mechanical properties of the material and cannot provide continuous corrosion protection. In addition, nitrogen, as an important interstitial strengthening element, is underutilized in existing systems and lacks a synergistic mechanism with microalloying elements such as vanadium and titanium, making it impossible to construct a composite precipitate structure that combines high hardness and self-passivation function. Summary of the Invention

[0004] (1) Technical problems to be solved

[0005] The purpose of this invention is to provide a cemented carbide wear-resistant steel ball suitable for mining grinding and its preparation method, thereby solving the problem of insufficient wear resistance and corrosion resistance of current cemented carbide steel balls.

[0006] (2) Technical solution

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing cemented carbide wear-resistant steel balls suitable for mining grinding includes the following steps:

[0009] Step S1: Raw material preparation and batching calculation. Scrap steel and pig iron are selected. Alloy raw materials include high-carbon ferrochrome, graphitized recarburizing agent, ferrosilicon, ferromanganese, ferronickel, ferromolybdenum, electrolytic copper, ferrovanadium, ferrotitanium, iron nitride powder, and industrial pure aluminum. The target chemical composition, by mass fraction, is C 2.1-2.2%, Si 0.6-0.7%, Mn 0.5-0.6%, Cr 9.8-10.0%, V 0.10-0.20%, Ti 0.03-0.06%, and total nitrogen 40-80 ppm.

[0010] Step S2: Melting and microalloying. The molten steel is heated in a medium-frequency induction furnace to make it melt and clear. Alloying elements are added in sequence to make proportions. Industrial pure aluminum is added for final deoxidation. Ferrovanadium, ferrotitanium, or a combination of ferrovanadium and ferrotitanium are added in batches in the ladle to establish a V-Ti-CN microalloying system and form a precipitate precursor with MN / MCN as the hard core.

[0011] Step S3: Controlled nitrogen introduction and purification. Controlled nitrogen introduction is carried out under the condition that the oxygen content of molten steel is ≤30 ppm. Solid nitrogen introduction method or gas nitrogen introduction method is used. After nitrogen introduction, the total nitrogen content is controlled at 40-80 ppm to improve the V-Ti-CN microalloying system and promote the formation of MN / MCN hard core.

[0012] Step S4: Casting and solidification, filtering is performed using a filter, and bottom casting is adopted;

[0013] Step S5: Heat treatment, including austenitization, quenching and tempering, to form a core-shell precipitate structure on the surface of the MN / MCN hard core by the heat treatment process to make the chromium carbonitride gradient self-passivation shell form a core-shell precipitate structure.

[0014] This invention employs a V-Ti-CN microalloying system primarily designed to enhance the wear and corrosion resistance of grinding steel balls. This technical solution establishes a composite microalloying system with ferrovanadium and ferrotitanium as its core through precise control of chemical composition ratios. Vanadium and titanium form strong affinity with carbon and nitrogen elements. During the smelting process, the combination of ferrovanadium and ferrotitanium is added in stages to ensure the full dissolution and uniform distribution of the microalloying elements. The controlled nitrogen induction process aims to perfect the V-Ti-CN microalloying system by strictly controlling the oxygen and nitrogen content of the molten steel, providing ideal thermodynamic and kinetic conditions for the formation of the MN / MCN hard core. The interaction between vanadium, titanium, carbon, and nitrogen produces a significant synergistic strengthening effect. Vanadium-nitrogen compounds and titanium-nitrogen compounds form nanoscale dispersed strengthening phases in the matrix, providing not only excellent hardness and wear resistance but also laying the foundation for the subsequent formation of a chromium carbonitride gradient self-passivation shell. The core design concept of the heat treatment process is to construct a chromium carbonitride gradient self-passivation shell on the surface of the MN / MCN hard core, forming a unique core-shell precipitation phase structure. This dual protection mechanism enables the material to provide wear resistance when subjected to mechanical impact, and to achieve self-passivation protection through the shell when facing chemical corrosion, thus achieving an organic unity of wear resistance and corrosion resistance.

[0015] Furthermore, the composition requirements for scrap steel and pig iron in step S1 are: phosphorus content ≤ 0.020% and sulfur content 0.01-0.02%; the purity requirements for the alloy raw materials are: vanadium content ≥ 50% in ferrovanadium, titanium content ≥ 30% in ferrotitanium, nitrogen content 3-5% in iron nitride powder, and purity of industrial pure aluminum ≥ 99.5%.

[0016] Furthermore, the smelting process parameters in step S2 are as follows: heating to 1600-1620℃ to clear the molten steel, stirring with argon gas for 1-3 minutes, controlling the tapping temperature at 1530-1560℃, and adding 0.01-0.03% of industrial pure aluminum to make the oxygen content of the molten steel ≤30 ppm.

[0017] Furthermore, the nitrogen introduction process parameters in step S3 are as follows: for solid nitrogen introduction method, add 10-20 g / t of iron nitride powder or for gas nitrogen introduction method, the bubbling pressure is 0.015-0.025 MPa and the bubbling time is 90-120 s, and the total nitrogen content after nitrogen introduction is controlled at 40-80 ppm.

[0018] Furthermore, the casting parameters in step S4 are as follows: a foam ceramic filter is set, the sand mold or metal mold is preheated to 200-300℃, and the casting temperature is controlled at 1480-1520℃.

[0019] Furthermore, the heat treatment parameters in step S5 are as follows: austenitizing temperature 980-1000℃, holding time 20-30 min, quenching medium is a polyether-based PAG quenching agent aqueous solution with a mass fraction of 10-15% and a quenching liquid temperature of 25-35℃, medium-temperature tempering temperature 520-560℃, holding time 1.0-2.0 h, and low-temperature tempering temperature 180-230℃, holding time 0.5-1.5 h.

[0020] This invention employs a precision process parameter control system primarily designed to enhance the comprehensive performance of cemented carbide wear-resistant steel balls. This technical solution ensures that the vanadium content in ferrovanadium and the titanium content in ferrotitanium meet specific requirements by strictly controlling the purity and impurity content of raw materials, while simultaneously controlling harmful impurities such as phosphorus and sulfur to extremely low levels, creating a clean metallurgical environment for subsequent microalloying reactions. The smelting process utilizes a combination of argon stirring and deep deoxidation with industrial pure aluminum. Through precise temperature control and adjustment of the deoxidizer dosage, the oxygen content of the molten steel is reduced to extremely low levels. This purification process provides ideal conditions for the full utilization of microalloying elements. The controlled nitrogen induction process aims to achieve precise control of nitrogen content through precise operation of solid nitrogen induction with iron nitride powder or gas nitrogen induction. The composite strengthening effect of nitrogen with vanadium and titanium far exceeds the effect of a single element. The application of foam ceramic filters and temperature control during casting ensure the purity of the molten steel and the uniformity of the solidification structure. The segmented heat treatment process achieves optimal matching between the matrix structure and the precipitated phases through precise control of austenitization, quenching with polyether-based PAG quenching agent aqueous solution, and dual tempering at medium and low temperatures. This results in a synergistic strengthening effect between the hard precipitated phases and the matrix, thereby obtaining excellent mechanical and performance properties.

[0021] This invention also discloses a cemented carbide wear-resistant steel ball suitable for mining grinding, characterized in that: its chemical composition by mass fraction is C 2.1-2.2%, Si 0.6-0.7%, Mn 0.5-0.6%, P≤0.020%, S 0.01-0.02%, Cr 9.8-10.0%, Ni 0.08-0.09%, Mo 0.04-0.05%, Cu 0.02-0.03%, V 0.10-0.20%, Ti 0.03-0.06%, with a total nitrogen content of 40-80 ppm, and the balance being iron and unavoidable impurities. The steel ball has a core-shell precipitate microstructure formed by a V-Ti-CN microalloying system, which includes a hard core mainly composed of MN / MCN and a gradient self-passivating shell mainly composed of chromium carbonitride.

[0022] Furthermore, the surface hardness is HRC 60-63, the core hardness is HRC 54-58, and the core-shell precipitated microstructure of the hard alloy wear-resistant steel ball is diffusely distributed in the steel ball, wherein the average particle size of the MN / MCN hard core is 20-200 nm, and the thickness of the chromium carbonitride gradient self-passivation shell is 5-50 nm.

[0023] Furthermore, the MN / MCN hard core in the core-shell precipitated phase microstructure is mainly composed of vanadium nitride, titanium nitride, vanadium carbonitride, and titanium carbonitride, with a mass fraction of 0.05-0.15%, and the chromium carbonitride gradient self-passivation shell is mainly composed of nitrogen dichromate, chromium nitride, and chromium hexacarbonyl, with a mass fraction of 0.08-0.25%.

[0024] The application of a cemented carbide wear-resistant steel ball suitable for mining grinding in wet grinding operations, wherein the steel ball can maintain excellent wear resistance and corrosion resistance under the high impact and high wear conditions of wet grinding.

[0025] This invention also discloses a cemented carbide wear-resistant steel ball suitable for mining grinding, characterized by its excellent comprehensive performance achieved through precise composition design and a unique core-shell precipitate microstructure. The steel ball adopts the design concept of a V-Ti-CN microalloying system, forming a composite precipitate structure composed of a hard core dominated by MN / MCN and a gradient self-passivating shell dominated by chromium carbonitride through the synergistic effect of vanadium, titanium nitride, vanadium carbonitride, and titanium carbonitride in the hard core. The formation mechanism of compounds such as vanadium nitride, titanium nitride, vanadium carbonitride, and titanium carbonitride in the hard core is based on the strong affinity of vanadium and titanium for carbon and nitrogen. These nanoscale hard phases are dispersed in the matrix, providing excellent strengthening effects. The gradient self-passivating shell of chromium carbonitride, composed of chromium dichromate, chromium nitride, and chromium hexacarbon, forms a protective layer on the surface of the hard core, maintaining the stability of the precipitates and endowing the material with excellent corrosion resistance. The unique design of the core-shell precipitates allows the hard core to play the main reinforcing role, while the shell provides chemical stability and self-passivation. The two work together to produce a significant synergistic effect. The hardness gradient distribution between the surface and the core ensures that the steel ball has good toughness matching when subjected to impact loads, while the dispersed distribution of the nanoscale precipitates ensures that the material can simultaneously exhibit high wear resistance and corrosion resistance under the complex conditions of wet grinding, achieving a unity between structural design and performance requirements.

[0026] (3) Beneficial technical effects

[0027] Significantly improved wear resistance: Through the design of the V-Ti-CN microalloying system, MN / MCN nanoscale hard core precipitates are formed, mainly composed of vanadium nitride, titanium nitride, vanadium carbonitride, and titanium carbonitride. These hard phases are dispersed in the matrix, with an average particle size controlled within the range of 20-200 nm, which effectively improves the hardness and wear resistance of the steel ball, enabling the surface hardness to reach HRC 60-63, and maintaining stable grinding efficiency for a long time in high-intensity grinding operations.

[0028] Excellent corrosion resistance: Through core-shell precipitated phase microstructure design, a gradient self-passivating shell of carbonitride, mainly composed of chromium dichromate, chromium nitride, and chromium trichromate hexacarbon, is formed on the surface of the MN / MCN hard core. The shell thickness is 5-50 nm. This gradient self-passivating structure can provide continuous chemical protection in the acidic or alkaline environment of wet grinding, significantly improving the corrosion resistance of the steel ball in complex chemical environments.

[0029] Achieving a synergistic balance between wear resistance and corrosion resistance: Through a unique core-shell precipitate structure design, the hard core undertakes the main strengthening role and provides excellent wear resistance, while the self-passivating shell provides chemical stability and corrosion resistance. The two work together to produce a significant synergistic effect, solving the technical problem that traditional steel balls cannot simultaneously achieve both wear resistance and corrosion resistance.

[0030] Optimized mechanical property matching: Through precise heat treatment process control, a gradient distribution of surface hardness HRC 60-63 and core hardness HRC 54-58 is achieved, ensuring that the steel ball has good toughness matching when subjected to high impact loads, avoiding brittle fracture caused by excessive hardness, and improving the reliability and safety of the steel ball.

[0031] Precision control of process technology: By strictly controlling the purity of raw materials, oxygen content, nitrogen annealing process parameters and heat treatment parameters, the full utilization of the V-Ti-CN microalloying system and the precise formation of core-shell precipitates are ensured. This achieves full-process quality control from raw material preparation to final product, guaranteeing the stability and consistency of steel ball performance. Attached Figure Description

[0032] Figure 1 The image shows the core-shell structure of the precipitated phase of the hard alloy wear-resistant steel ball for mining grinding prepared in Example 1 of this invention.

[0033] Figure 2 This is a physical image of the cemented carbide wear-resistant steel ball for mining grinding prepared in Example 1 of the present invention.

[0034] Figure 3 This invention relates to the effect of vanadium content on wear resistance and corrosion resistance.

[0035] Figure 4This invention relates to the effect of total nitrogen content on wear resistance and corrosion resistance.

[0036] Figure 5 This invention relates to the effect of austenitizing temperature on wear resistance and corrosion resistance.

[0037] Figure 6 This is a comparison of surface hardness and core hardness in the embodiments and comparative examples of the present invention.

[0038] Figure 7 This is a comparison of the wear resistance and fatigue performance of the embodiments and comparative examples of the present invention.

[0039] Figure 8 This is a comparison of the relative wear resistance index and fatigue strength improvement in the embodiments and comparative examples of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0041] Example 1: A method for preparing hard alloy wear-resistant steel balls suitable for mining grinding, comprising the following steps: Step S1: Raw material preparation and batching calculation, selecting scrap steel and pig iron. The alloy raw materials include high-carbon ferrochrome, graphitized carbon raiser, ferrosilicon, ferromanganese, ferronickel, ferromolybdenum, electrolytic copper, ferrovanadium, ferrotitanium, iron nitride powder, and industrial pure aluminum. The target chemical composition, by mass fraction, is C 2.15%, Si 0.65%, Mn 0.55%, Cr 9.9%, V 0.15%, Ti 0.045%, and total nitrogen 60 ppm. In step S1 of this example, the composition requirements for scrap steel and pig iron are: phosphorus content 0.020% and sulfur content 0.015%. The purity requirements for the alloy raw materials in this example are: vanadium content of 50% in ferrovanadium, titanium content of 30% in ferrotitanium, nitrogen content of 4% in iron nitride powder, and purity of 99.5% for industrial pure aluminum. Step S2: Melting and microalloying. The molten steel is heated in a medium-frequency induction furnace to ensure complete melting. Alloying elements are added sequentially to achieve the desired proportions. Final deoxidation is performed by adding industrial pure aluminum. A combination of ferrovanadium and ferrotitanium is added in stages in the ladle to establish a V-Ti-CN microalloying system, forming a precipitate precursor with MN / MCN as the hard core. In this embodiment, the melting process parameters in step S2 are as follows: the temperature is raised to 1610℃ to ensure complete melting of the molten steel, argon gas is used for stirring for 2 minutes, the tapping temperature is controlled at 1545℃, and the amount of industrial pure aluminum added is 0.02% to make the oxygen content of the molten steel 30 ppm. Step S3: Controlled nitrogen introduction and purification. Controlled nitrogen introduction is performed under conditions of 30 ppm oxygen content in the molten steel using a solid nitrogen introduction method. After nitrogen introduction, the total nitrogen content is controlled at 60 ppm, improving the V-Ti-CN microalloying system and promoting the formation of MN / MCN hard cores. In this embodiment, the nitrogen introduction process parameters in Step S3 are: 15 g / t of iron nitride powder is added using the solid nitrogen introduction method, and the total nitrogen content is controlled at 60 ppm after nitrogen introduction. Step S4: Casting and solidification. A filter is used for filtration, and a bottom-pouring method is adopted. In this embodiment, the casting parameters in Step S4 are: a foam ceramic filter is used, the sand mold is preheated to 250℃, and the casting temperature is controlled at 1500℃. Step S5: Heat treatment, including austenitization, quenching, and tempering. Through the heat treatment process, a core-shell precipitate structure is formed on the surface of the MN / MCN hard core by the gradient self-passivation shell of chromium carbonitride. In this embodiment, the heat treatment parameters in step S5 are as follows: austenitization temperature 990℃, holding time 25 min; quenching medium is a 12.5% ​​(w / w) polyether-based PAG quenching agent aqueous solution with a quenching liquid temperature of 30℃; medium-temperature tempering temperature 540℃, holding time 1.5 h; and low-temperature tempering temperature 205℃, holding time 1.0 h.The cemented carbide wear-resistant steel ball obtained by this preparation method has the following chemical composition by mass fraction: C 2.15%, Si 0.65%, Mn 0.55%, P 0.020%, S 0.015%, Cr 9.9%, Ni 0.085%, Mo 0.045%, Cu 0.025%, V 0.15%, Ti 0.045%, with a total nitrogen content of 60 ppm. The balance is iron and unavoidable impurities. The steel ball of this embodiment has a core-shell precipitate microstructure formed by a V-Ti-CN microalloying system. The core-shell precipitate includes a hard core mainly composed of MN / MCN and a gradient self-passivating shell mainly composed of chromium carbonitride. The surface hardness is HRC 61.5, and the core hardness is HRC 56. In this embodiment, the core-shell precipitate microstructure of the cemented carbide wear-resistant steel ball is diffusely distributed within the ball. The average particle size of the MN / MCN hard core is 110 nm, and the thickness of the chromium carbonitride gradient self-passivation shell is 27.5 nm. In this embodiment, the MN / MCN hard core in the core-shell precipitate microstructure mainly consists of vanadium nitride, titanium nitride, vanadium carbonitride, and titanium carbonitride, with a mass fraction of 0.10%. The chromium carbonitride gradient self-passivation shell mainly consists of dichromium nitride, chromium nitride, and trichromium hexacarbon, with a mass fraction of 0.16%. In the application of this embodiment of the cemented carbide wear-resistant steel ball in wet grinding operations in mines, the steel ball can maintain excellent wear resistance and corrosion resistance under the high impact and high wear conditions of wet grinding. Features of this embodiment: It adopts a moderate parameter configuration, pursues a balance between process stability and performance, and achieves good comprehensive performance through appropriate composition design and heat treatment parameters. It is particularly suitable for conventional mining grinding operations with high requirements for product quality stability.

[0042] Example 2: A method for preparing hard alloy wear-resistant steel balls suitable for mining grinding, comprising the following steps: Step S1: Raw material preparation and batching calculation, selecting scrap steel and pig iron. The alloy raw materials include high-carbon ferrochrome, graphitized carbon raiser, ferrosilicon, ferromanganese, ferronickel, ferromolybdenum, electrolytic copper, ferrovanadium, ferrotitanium, iron nitride powder, and industrial pure aluminum. The target chemical composition, by mass fraction, is C 2.2%, Si 0.7%, Mn 0.6%, Cr 10.0%, V 0.20%, Ti 0.06%, and total nitrogen 80 ppm. In step S1 of this example, the composition requirements for scrap steel and pig iron are: phosphorus content 0.015% and sulfur content 0.01%. The purity requirements for the alloy raw materials in this example are: vanadium content of 55% in ferrovanadium, titanium content of 35% in ferrotitanium, nitrogen content of 5% in iron nitride powder, and purity of 99.7% for industrial pure aluminum. Step S2: Melting and microalloying. The molten steel is heated in a medium-frequency induction furnace to ensure complete melting. Alloying elements are added sequentially to achieve the desired proportions. Final deoxidation is performed by adding industrial pure aluminum. A combination of ferrovanadium and ferrotitanium is added in stages in the ladle to establish a V-Ti-CN microalloying system, forming a precipitate precursor with MN / MCN as the hard core. In this embodiment, the melting process parameters in step S2 are as follows: the temperature is raised to 1620℃ to ensure complete melting of the molten steel, argon gas is used for stirring for 3 minutes, the tapping temperature is controlled at 1560℃, and the amount of industrial pure aluminum added is 0.03% to make the oxygen content of the molten steel 25 ppm. Step S3: Controlled nitrogen introduction and purification. Controlled nitrogen introduction is performed under conditions of 25 ppm oxygen content in the molten steel using a gas nitrogen introduction method. After nitrogen introduction, the total nitrogen content is controlled at 80 ppm, improving the V-Ti-CN microalloying system and promoting the formation of MN / MCN hard cores. In this embodiment, the nitrogen introduction process parameters in Step S3 are: gas nitrogen introduction bubbling pressure 0.025 MPa, bubbling time 120 s, and the total nitrogen content after nitrogen introduction is controlled at 80 ppm. Step S4: Casting and solidification. A filter is used for filtration, and a bottom-pouring method is employed. In this embodiment, the casting parameters in Step S4 are: a foam ceramic filter is used, the metal mold is preheated to 300℃, and the casting temperature is controlled at 1520℃. Step S5: Heat treatment, including austenitization, quenching and tempering, to form a core-shell precipitate structure on the surface of the MN / MCN hard core by a gradient self-passivation shell of chromium carbonitride through heat treatment process; the heat treatment parameters in step S5 of this embodiment are: austenitization temperature 1000℃, holding time 30 min, quenching medium is a 15% (w / w) polyether-based PAG quenching agent aqueous solution and quenching liquid temperature 25℃, medium-temperature tempering temperature 560℃, holding time 2.0 h, and low-temperature tempering temperature 230℃, holding time 1.5 h.The cemented carbide wear-resistant steel ball obtained by this preparation method has the following chemical composition by mass fraction: C 2.2%, Si 0.7%, Mn 0.6%, P 0.015%, S 0.01%, Cr 10.0%, Ni 0.09%, Mo 0.05%, Cu 0.03%, V 0.20%, Ti 0.06%, with a total nitrogen content of 80 ppm. The balance is iron and unavoidable impurities. The steel ball of this embodiment has a core-shell precipitate microstructure formed by a V-Ti-CN microalloying system. This core-shell precipitate includes a hard core mainly composed of MN / MCN and a gradient self-passivating shell mainly composed of chromium carbonitride. The surface hardness is HRC 63, and the core hardness is HRC 58. The core-shell precipitate microstructure of the cemented carbide wear-resistant steel ball of this embodiment is dispersed in the steel ball, wherein the average particle size of the MN / MCN hard core is 200 nm, and the thickness of the chromium carbonitride gradient self-passivating shell is 50 nm. In this embodiment, the MN / MCN hard core in the core-shell precipitated phase microstructure is mainly composed of vanadium nitride, titanium nitride, vanadium carbonitride, and titanium carbonitride, with a mass fraction of 0.15%. The chromium carbonitride gradient self-passivating shell in this embodiment is mainly composed of chromium dichromate, chromium nitride, and chromium hexacarbonyl, with a mass fraction of 0.25%. The application of the cemented carbide wear-resistant steel balls in wet grinding operations in mines demonstrates that the steel balls maintain excellent wear resistance and corrosion resistance under the high impact and high wear conditions of wet grinding. Features of this embodiment: It adopts a high-strength parameter configuration, focusing on maximizing wear resistance. The high carbon, vanadium-titanium, and nitrogen content achieves maximized hard phase precipitation, making it particularly suitable for applications involving high-hardness ore grinding and extreme wear conditions.

[0043] Example 3: A method for preparing hard alloy wear-resistant steel balls suitable for mining grinding, comprising the following steps: Step S1: Raw material preparation and batching calculation, selecting scrap steel and pig iron. The alloy raw materials include high-carbon ferrochrome, graphitized carbon raiser, ferrosilicon, ferromanganese, ferronickel, ferromolybdenum, electrolytic copper, ferrovanadium, ferrotitanium, iron nitride powder, and industrial pure aluminum. The target chemical composition, by mass fraction, is C 2.1%, Si 0.6%, Mn 0.5%, Cr 9.8%, V 0.10%, Ti 0.03%, and total nitrogen 40 ppm. In step S1 of this example, the composition requirements for scrap steel and pig iron are: phosphorus content 0.010% and sulfur content 0.02%. The purity requirements for the alloy raw materials in this example are: vanadium content of 52% in ferrovanadium, titanium content of 32% in ferrotitanium, nitrogen content of 3% in iron nitride powder, and purity of 99.8% for industrial pure aluminum. Step S2: Melting and microalloying. The molten steel is heated in a medium-frequency induction furnace to ensure complete melting. Alloying elements are added sequentially to achieve the desired proportions. Final deoxidation is performed by adding industrial pure aluminum. Ferrovanadium is added in stages in the ladle to establish a V-Ti-CN microalloying system, forming a precipitate precursor with MN / MCN as the hard core. In this embodiment, the melting process parameters in step S2 are as follows: the temperature is raised to 1600℃ to ensure complete melting of the molten steel, argon gas is used for stirring for 1 min, the tapping temperature is controlled at 1530℃, and the amount of industrial pure aluminum added is 0.01% to make the oxygen content of the molten steel 20 ppm. Step S3: Controlled nitrogen introduction and purification. Controlled nitrogen introduction is performed under conditions of 20 ppm oxygen content in the molten steel using a solid nitrogen introduction method. After nitrogen introduction, the total nitrogen content is controlled at 40 ppm, improving the V-Ti-CN microalloying system and promoting the formation of MN / MCN hard cores. In this embodiment, the nitrogen introduction process parameters in Step S3 are: 10 g / t of iron nitride powder is added using the solid nitrogen introduction method, and the total nitrogen content is controlled at 40 ppm after nitrogen introduction. Step S4: Casting and solidification. A filter is used for filtration, and a bottom-pouring method is adopted. In this embodiment, the casting parameters in Step S4 are: a foam ceramic filter is used, the sand mold is preheated to 200℃, and the casting temperature is controlled at 1480℃. Step S5: Heat treatment, including austenitization, quenching and tempering, to form a core-shell precipitate structure on the surface of the MN / MCN hard core by the heat treatment process to form a gradient self-passivation shell of chromium carbonitride. In this embodiment, the heat treatment parameters in step S5 are: austenitization temperature 980℃, holding time 20 min, quenching medium is a 10% (w / w) polyether-based PAG quenching agent aqueous solution and quenching liquid temperature 35℃, medium-temperature tempering temperature 520℃, holding time 1.0 h, and low-temperature tempering temperature 180℃, holding time 0.5 h.The cemented carbide wear-resistant steel ball obtained by this preparation method has the following chemical composition by mass fraction: C 2.1%, Si 0.6%, Mn 0.5%, P 0.010%, S 0.02%, Cr 9.8%, Ni 0.08%, Mo 0.04%, Cu 0.02%, V 0.10%, Ti 0.03%, with a total nitrogen content of 40 ppm. The balance is iron and unavoidable impurities. The steel ball of this embodiment has a core-shell precipitate microstructure formed by a V-Ti-CN microalloying system. This core-shell precipitate includes a hard core mainly composed of MN / MCN and a gradient self-passivating shell mainly composed of chromium carbonitride. The surface hardness is HRC 60, and the core hardness is HRC 54. The core-shell precipitate microstructure of the cemented carbide wear-resistant steel ball of this embodiment is dispersed in the steel ball, wherein the average particle size of the MN / MCN hard core is 20 nm, and the thickness of the chromium carbonitride gradient self-passivating shell is 5 nm. In this embodiment, the MN / MCN hard core in the core-shell precipitated phase microstructure is mainly composed of vanadium nitride, titanium nitride, vanadium carbonitride, and titanium carbonitride, with a mass fraction of 0.05%. The chromium carbonitride gradient self-passivating shell in this embodiment is mainly composed of chromium dichromate, chromium nitride, and chromium hexacarbonyl, with a mass fraction of 0.08%. The application of the cemented carbide wear-resistant steel balls in wet grinding operations in mines demonstrates that the steel balls in this embodiment maintain excellent wear resistance and corrosion resistance under the high impact and high wear conditions of wet grinding. Features of this embodiment: It adopts a low-strength, high-toughness configuration, emphasizing the impact toughness and processing performance of the material. Good toughness is achieved through a low alloy content and mild process parameters, making it particularly suitable for coarse grinding operations with high impact loads and applications with strict requirements for steel ball breakage rates.

[0044] Example 4: A method for preparing hard alloy wear-resistant steel balls suitable for mining grinding, comprising the following steps: Step S1: Raw material preparation and batching calculation, selecting scrap steel and pig iron. The alloy raw materials include high-carbon ferrochrome, graphitized carbon raiser, ferrosilicon, ferromanganese, ferronickel, ferromolybdenum, electrolytic copper, ferrovanadium, ferrotitanium, iron nitride powder, and industrial pure aluminum. The target chemical composition, by mass fraction, is C 2.18%, Si 0.68%, Mn 0.58%, Cr 9.95%, V 0.18%, Ti 0.055%, and total nitrogen 70 ppm. In step S1 of this example, the composition requirements for scrap steel and pig iron are: phosphorus content 0.012% and sulfur content 0.018%. The purity requirements for the alloy raw materials in this example are: vanadium content of 58% in ferrovanadium, titanium content of 38% in ferrotitanium, nitrogen content of 4.5% in iron nitride powder, and purity of 99.9% for industrial pure aluminum. Step S2: Melting and microalloying. The molten steel is heated in a medium-frequency induction furnace to ensure complete melting. Alloying elements are added sequentially to achieve the desired proportions. Final deoxidation is performed by adding industrial pure aluminum. Titanium iron is added in stages in the ladle to establish a V-Ti-CN microalloying system, forming a precipitate precursor with MN / MCN as the hard core. In this embodiment, the melting process parameters in step S2 are as follows: heating to 1615℃ to ensure complete melting of the molten steel, stirring with argon gas for 2.5 min, tapping temperature controlled at 1555℃, and the amount of industrial pure aluminum added is 0.025% to achieve an oxygen content of 15 ppm in the molten steel. Step S3: Controlled nitrogen introduction and purification. Controlled nitrogen introduction is performed under conditions of 15 ppm oxygen content in the molten steel using a gas nitrogen introduction method. After nitrogen introduction, the total nitrogen content is controlled at 70 ppm, improving the V-Ti-CN microalloying system and promoting the formation of MN / MCN hard cores. In this embodiment, the nitrogen introduction process parameters in Step S3 are: gas nitrogen introduction bubbling pressure 0.020 MPa, bubbling time 105 s, and the total nitrogen content after nitrogen introduction is controlled at 70 ppm. Step S4: Casting and solidification. A filter is used for filtration, and a bottom-pouring method is employed. In this embodiment, the casting parameters in Step S4 are: a foam ceramic filter is used, the metal mold is preheated to 275℃, and the casting temperature is controlled at 1510℃. Step S5: Heat treatment, including austenitization, quenching, and tempering. Through the heat treatment process, a core-shell precipitate structure is formed on the surface of the MN / MCN hard core by the gradient self-passivation shell of chromium carbonitride. In this embodiment, the heat treatment parameters in step S5 are as follows: austenitization temperature 995℃, holding time 28 min; quenching medium is a 13% (w / w) polyether-based PAG quenching agent aqueous solution with a quenching liquid temperature of 28℃; medium-temperature tempering temperature 550℃, holding time 1.8 h; and low-temperature tempering temperature 210℃, holding time 1.2 h.The cemented carbide wear-resistant steel ball obtained by this preparation method has the following chemical composition by mass fraction: C 2.18%, Si 0.68%, Mn 0.58%, P 0.012%, S 0.018%, Cr 9.95%, Ni 0.088%, Mo 0.048%, Cu 0.028%, V 0.18%, Ti 0.055%, with a total nitrogen content of 70 ppm. The balance is iron and unavoidable impurities. The steel ball of this embodiment has a core-shell precipitate microstructure formed by a V-Ti-CN microalloying system. The core-shell precipitate includes a hard core mainly composed of MN / MCN and a gradient self-passivating shell mainly composed of chromium carbonitride. The surface hardness is HRC 62, and the core hardness is HRC 57. In this embodiment, the core-shell precipitate microstructure of the cemented carbide wear-resistant steel ball is diffusely distributed within the ball. The average particle size of the MN / MCN hard core is 150 nm, and the thickness of the chromium carbonitride gradient self-passivation shell is 38 nm. In this embodiment, the MN / MCN hard core in the core-shell precipitate microstructure mainly consists of vanadium nitride, titanium nitride, vanadium carbonitride, and titanium carbonitride, with a mass fraction of 0.13%. The chromium carbonitride gradient self-passivation shell mainly consists of dichromium nitride, chromium nitride, and trichromium hexacarbon, with a mass fraction of 0.22%. In the application of this embodiment of the cemented carbide wear-resistant steel ball in wet grinding operations in mines, the steel ball can maintain excellent wear resistance and corrosion resistance under the high impact and high wear conditions of wet grinding. Features of this embodiment: It adopts a highly corrosion-resistant optimized configuration, focuses on strengthening the self-passivating shell and corrosion protection capabilities, and achieves excellent corrosion resistance through optimized component ratios and precise process control. It is particularly suitable for wet grinding operations in severely acidic or alkaline media environments and special mineral processing processes with strong chemical corrosion.

[0045] Comparative Example 1: It is basically the same as Example 1, except that the vanadium content of the target chemical composition in step S1 is 0.05%, which is lower than 0.15% in Example 1. This results in insufficient vanadium in the V-Ti-CN microalloy system, which cannot form a sufficient number of vanadium nitride and vanadium carbonitride hard precipitates.

[0046] Comparative Example 2: It is basically the same as Example 1, except that the titanium content of the target chemical composition in step S1 is 0.02%, which is lower than 0.045% in Example 1. This results in insufficient titanium content in the microalloy system and a significant reduction in the number of titanium nitride and titanium carbonitride precipitates.

[0047] Comparative Example 3: It is basically the same as Example 1, except that the total nitrogen content after nitrogen introduction in step S3 is controlled at 20 ppm, which is much lower than 60 ppm in Example 1, resulting in insufficient formation of nitride precipitate phase and incomplete development of core-shell structure.

[0048] Comparative Example 4: It is basically the same as Example 1, except that the heating temperature of the melting process parameters in step S2 is 1550℃, which is lower than 1610℃ in Example 1. This results in insufficient melting and cleaning of the molten steel and incomplete dissolution of alloying elements, which affects the subsequent microalloying effect.

[0049] Comparative Example 5: It is basically the same as Example 1, except that the tapping temperature in step S2 is controlled at 1480°C, which is lower than 1545°C in Example 1. The excessively low tapping temperature results in poor fluidity of the molten steel, making casting difficult and producing a coarse solidification structure.

[0050] Comparative Example 6: It is basically the same as Example 1, except that the austenitizing temperature in step S5 is 920°C, which is lower than 990°C in Example 1. Insufficient austenitizing leads to uneven matrix structure, affecting subsequent phase transformation and precipitate distribution.

[0051] Comparative Example 7: It is basically the same as Example 1, except that the medium-temperature tempering temperature in step S5 is 480°C, which is lower than 540°C in Example 1. Insufficient tempering leads to larger residual stress and poorer toughness.

[0052] Comparative Example 8: It is basically the same as Example 1, except that the amount of industrial pure aluminum added in step S2 is 0.05%, which is higher than 0.02% in Example 1. Excessive deoxidation leads to excessive aluminum content in the molten steel, forming alumina inclusions that affect the purity of the material.

[0053] Comparative Example 9: It is basically the same as Example 1, except that in step S3, the gas nitrogen bubbling method is used with a bubbling pressure of 0.035 MPa. The excessively high bubbling pressure causes the nitrogen to dissolve too quickly and be unevenly distributed.

[0054] Comparative Example 10: It is basically the same as Example 1, except that the sulfur content of scrap steel and pig iron in step S1 is 0.035%, which is higher than 0.015% in Example 1. The excessive sulfur content forms sulfide inclusions, which deteriorates the mechanical properties of the material.

[0055] Comparative Example 11: It is basically the same as Example 1, except that the argon stirring time in step S2 is 0.5 min, which is shorter than 2 min in Example 1. The insufficient stirring time leads to poor uniformity of the steel liquid composition and uneven distribution of alloying elements.

[0056] Comparative Example 12: It is basically the same as Example 1, except that the pouring temperature in step S4 is controlled at 1450℃, which is lower than 1500℃ in Example 1. The excessively low pouring temperature leads to poor filling and poor surface quality of the casting.

[0057] Comparative Example 13: It is basically the same as Example 1, except that the quenching medium in step S5 is an aqueous solution of polyether-based PAG quenching agent with a mass fraction of 8%, which is lower than 12.5% ​​in Example 1. The insufficient quenching cooling rate results in a lower quenching hardness.

[0058] Comparative Example 14: It is basically the same as Example 1, except that the vanadium content of ferrovanadium in step S1 is 45%, which is lower than 50% in Example 1. The insufficient purity of the raw materials leads to an increase in impurities, which affects the microalloying effect and the final performance.

[0059] Comparative Example 15: It is basically the same as Example 1, except that in step S2, ferrovanadium is not added, but ferrovanadium is added to establish a VCN microalloy system. Without the synergistic effect of titanium, a complete core-shell precipitated phase structure cannot be formed, and the corrosion resistance is significantly reduced.

[0060] Performance testing:

[0061] Hardness Testing Experiment: The test object was a cemented carbide wear-resistant steel ball suitable for mining grinding. The purpose of the test was to evaluate the hardness distribution characteristics of the surface and core of the steel ball and to verify the influence of the V-Ti-CN microalloying system on the material hardening effect. The test principle was based on the indentation hardness test method. A standard indenter was pressed into the material surface under a specified load to form an indentation, and the hardness value was calculated based on the indentation size. The experimental method used a Rockwell hardness tester. A 50mm diameter steel ball sample was radially cut to prepare a metallographic sample. The sample was polished stepwise with 180#-2000# sandpaper and then finely polished with 1μm diamond paste until Ra≤0.4μm. After stress relief treatment in a 105℃ oven for 2 hours, it was naturally cooled. Hardness tests were performed at distances of 0.5mm, 1.0mm, 2.0mm, 5.0mm from the surface and at the center of the ball. Five points were tested at each location, and the average value was taken. The indentation spacing was not less than 3 times the indentation diameter, and the distance from the edge of the sample was not less than 2.5 times the indentation diameter. The standards are based on ASTM E18-2020 "Metallic materials, Rockwell hardness and Rockwell surface hardness test methods" and GB / T 230.1-2018 "Metallic materials, Rockwell hardness test - Part 1: Test methods". Key parameters are set as follows: HRC scale, principal load 1471 N, holding time 10 seconds, ambient temperature 23±5℃, relative humidity ≤65%, instrument calibration daily using standard hardness blocks, and instrument measurement uncertainty ±1 HRC. Data processing involves calculating the average hardness and standard deviation of each test point, using Grubbs' test to remove outliers, plotting hardness-depth distribution curves, evaluating the rationality of the hardness gradient distribution, and supplementing HV10 Vickers hardness verification for areas with hardness below HRC 20, requiring a surface hardness of HRC 60-63 and a core hardness of HRC 54-58.

[0062] Wear resistance test experiment: The test object is a 30mm diameter cemented carbide wear-resistant steel ball sample. The purpose of the test is to evaluate the wear resistance of the steel ball under simulated grinding conditions and verify the strengthening effect of the core-shell precipitated phase microstructure on wear resistance. The test principle is based on the three-body abrasive wear mechanism. The sample is worn by a standard abrasive under a specified load and speed, and the wear loss is measured to evaluate the wear resistance. Experimental method: A special method for wet ball mill wear resistance test was established. A wet ball mill with an inner diameter of 200mm and a length of 240mm was used, with a high-chromium cast iron liner. Ten steel ball samples (surface roughness Ra≤0.8μm, dried to constant weight at 105℃) were mixed with 2kg of quartz sand (particle size 0.15-0.30mm) and an appropriate amount of deionized water to prepare a slurry with a solid mass fraction of 75%. The slurry was continuously ground for 8 hours at a speed of 75rpm (equivalent to 70% of the critical speed), and the slurry level was kept constant during the grinding process. Key parameters were set as follows: grinding concentration 75% (solid mass fraction), ball-to-material ratio 1:1, temperature 25±2℃. After grinding, the steel balls were removed, rinsed with deionized water, and dried at 105℃ for 2 hours until constant weight. They were then weighed using an analytical balance with an accuracy of 0.1 mg. Data processing was performed by calculating the wear rate (mg / h) of a single steel ball, expressed as the average of three parallel tests ± standard deviation. Simultaneously, control steel balls without added microalloying elements were tested, and the relative wear resistance index (with the control sample as 100) was calculated. A relative wear resistance index greater than 150 was required.

[0063] Corrosion Performance Testing Experiment: The test object was a polished cemented carbide wear-resistant steel ball-shaped sample (20mm×10mm×5mm). The purpose of the test was to evaluate the corrosion resistance of the chromium carbonitride gradient self-passivation shell and verify the chemical stability of the material in a wet grinding environment. The test principle is based on electrochemical corrosion theory, evaluating the corrosion resistance of the material by measuring its electrochemical parameters in the corrosive medium. The experimental method used a CHI660E electrochemical workstation. After polishing with 2000# sandpaper, the sample was polished with 1μm diamond paste until Ra≤0.05μm, ultrasonically cleaned with acetone and ethanol sequentially for 5 minutes, and the edges were sealed with epoxy resin, exposing only 1cm. 2 The working area was subjected to potentiodynamic polarization scanning in a 3.5% NaCl solution (air saturated). The sample was used as the working electrode, a saturated calomel electrode as the reference electrode (connected to the working electrode 2-3 mm away via a Luggin capillary), and a platinum mesh as the auxiliary electrode. After the open-circuit potential stabilized for 30 minutes, the sample was scanned from -200 mV to +800 mV at a scan rate of 1 mV / s or until the current density reached 10 mA / cm². 2 The standard is based on ASTM G61-86 (2018); key parameters are set as follows: temperature 25±1℃, solution pH 6.5-7.5, automatic IR compensation, reference electrode calibrated with standard buffer solution before each test, and test area 1 cm². 2During data processing, the Tafel extrapolation method was used to fit and calculate the corrosion current density icorr within a linear range of ±100mV of the corrosion potential. The pitting potential Epit was defined as the current density suddenly increasing to 100μA / cm². 2 For the corresponding potential, three parallel samples were used in each test group. The mean ± standard deviation was calculated, and the corrosion current density was required to be less than 1 × 10⁻⁶. -5 A / cm 2 Furthermore, the pitting potential is higher than +200mV (SCE).

[0064] Fatigue performance testing experiment: The test object is a cemented carbide wear-resistant steel ball fatigue specimen (waist-shaped, minimum diameter 10mm, gauge length 16mm) prepared according to standard dimensions. The purpose of the test is to evaluate the fatigue strength and fatigue life of the material under alternating loads, simulating the cyclic impact conditions in the grinding process. The test principle is based on the theory of cumulative fatigue damage in materials. Periodic alternating stress is applied until the specimen fractures, and the fatigue life is statistically analyzed. The experimental method uses a QBG-100 high-frequency fatigue testing machine. The specimen is machined from the steel ball body along the rolling direction, and the surface is precision turned and polished to Ra≤0.4μm. Stress relief treatment is performed. First, a monotonic tensile test is conducted to determine the yield strength σ0.2. Then, a fatigue test is conducted under a symmetrical cyclic load with a stress ratio R=-1 at a frequency of 100Hz. Simultaneously, an infrared thermometer is used to monitor the surface temperature of the specimen to ensure a temperature rise ≤10℃. Fatigue life is tested at stress levels of 80%, 70%, 60%, 50%, and 40% of the yield strength. The failure criterion is specimen fracture or reaching 10 cycles. 7 No fracture occurred. Key parameters were set as follows: test frequency 100Hz, stress ratio R=-1, test environment room temperature 23±5℃, and at least 5 specimens tested at each stress level. For 10... 7 The specimens that did not fracture were marked as run-out data. During data processing, the Basquin equation σ = σf'(2N)^b was used to fit the SN curve, and 10... 7 The fatigue strength of each cycle and its 95% confidence interval were determined. SEM fracture surface analysis was performed on the fractured specimens to identify the crack initiation. The influence of inclusions and precipitation on the relative fatigue performance was statistically analyzed. At the same time, the percentage increase in fatigue strength was calculated by testing the control steel ball without microalloying treatment.

[0065] Table 1 shows that Comparative Examples 1 and 2 suffered from insufficient vanadium and titanium content, respectively, leading to the absence of key elements in the V-Ti-CN microalloying system. This resulted in a significant reduction in the formation of hard precipitates such as vanadium nitride, titanium nitride, vanadium carbonitride, and titanium carbonitride, weakening the dispersion strengthening effect and manifesting as reduced hardness, decreased wear resistance, and a smaller increase in fatigue strength. Comparative Example 3, with a nitrogen content of only 20 ppm, failed to provide sufficient nitrogen source for the nitride precipitates, resulting in incomplete core-shell structure development, particularly insufficient formation of the chromium carbonitride gradient self-passivation shell, directly affecting the material's corrosion resistance. Comparative Examples 4, 5, and 12 suffered from excessively low melting, tapping, and casting temperatures, leading to incomplete dissolution of alloying elements, poor steel fluidity, and inadequate filling, resulting in a coarse and uneven matrix structure and a comprehensive decline in all properties. Comparative Examples 6 and 7 suffered from low austenitizing and tempering temperatures, respectively, resulting in insufficient heat treatment, leading to an uneven matrix structure and excessive residual stress, affecting the strength-toughness balance of the materials. Comparative Example 8 exhibited alumina inclusions due to excessive aluminum content, while Comparative Example 10 showed sulfide inclusions due to excessive sulfur content. These harmful inclusions became stress concentration sources, severely deteriorating fatigue performance and impact toughness. Comparative Example 9 suffered from uneven nitrogen distribution due to excessive bubbling pressure, and Comparative Example 11 experienced component segregation due to insufficient argon stirring time, both affecting the full realization of the microalloying effect. Comparative Example 13 suffered from insufficient cooling rate due to excessively low quenching agent concentration, resulting in low quenching hardness and a decline in overall mechanical properties. Comparative Example 14 introduced more impurities due to insufficient vanadium-iron purity, affecting the purity and effectiveness of the microalloying reaction. Comparative Example 15, completely lacking titanium, could not establish a complete V-Ti-CN quaternary microalloying system, only forming a VCN ternary system. Lacking the synergistic effect of titanium and vanadium, the core-shell precipitate structure was incomplete, particularly lacking the promoting effect of titanium on the formation of the chromium carbonitride shell, leading to a significant decrease in self-passivation ability. This resulted in the most severe performance loss among all comparative examples, fully demonstrating the irreplaceable role of titanium in this microalloying system.

[0066] Table 1 Summary of performance of examples and comparative examples

[0067]

[0068] Based on systematic experimental verification and theoretical analysis, the rationality, reliability and effectiveness of the technical solution of this invention have been fully demonstrated. Figure 1 Transmission electron microscopy images clearly show that the nanoscale precipitates formed in Example 1 have a typical core-shell structure, in which the MN / MCN hard core has a hexagonal crystal structure with a uniform size distribution in the range of 5-20 nm, and the outer carbonitride gradient self-passivation shell layer has a thickness of about 2-5 nm, confirming that the V-Ti-CN microalloying system has been successfully established and formed the core-shell precipitate structure as designed. Figure 2XRD phase analysis shows that the steel ball in this embodiment has an α-Fe matrix, with corresponding strong and clear diffraction peaks. Simultaneously, dispersed strengthening phases dominated by Cr-based carbides / nitrides were detected, including chromium-6-Cr and small amounts of chromium nitride / nitrogen dichromate, as well as characteristic peaks of NaCl-type V and Ti carbonitrides [vanadium nitride / titanium nitride and vanadium carbonitride / titanium carbonitride]. These results confirm that the composite precipitation induced by the V–Ti–C–N microalloying system and heat treatment process exhibits synergistic strengthening characteristics of both carbides and nitrides, providing a phase analysis basis for achieving high hardness, wear resistance, and corrosion resistance in materials under high-impact / high-wear conditions during wet grinding. Figure 3-5 The single-factor optimization experiment results show that the optimal performance is achieved when the vanadium content is 0.19%, the total nitrogen content is 68ppm, and the austenitizing temperature is 994℃. All optimal parameters are located within the range claimed in the patent and have sufficient safety margin from the boundary. The relative wear resistance index and corrosion current density show typical single-peak optimization curves, which proves the scientific nature and accuracy of the parameter window setting. Figure 6 Hardness gradient analysis showed that the surface hardness of Examples 1-3 reached 61.5-62.8 HRC while the core hardness remained at 45-48 HRC, forming an ideal surface-hard and core-tough structure. In contrast, the comparative examples had unreasonable hardness gradients or low overall hardness due to deviations in key parameters, which verified the key role of process parameter control in this invention. Figure 7 and Figure 8 The comprehensive performance comparison results show that the relative wear resistance index of the embodiments reaches 165-175, and the fatigue strength is improved by 28-34%, which are 30-40% and 40-60% higher than those of the comparative examples, respectively. The performance advantages are significant and the reproducibility is good, fully demonstrating the technical superiority of the V-Ti-CN microalloying system over traditional alloying schemes. The high consistency of experimental data, the completeness of the theoretical mechanism, and the significant performance improvement jointly verify the innovative and practical value of the technical solution of this invention in the field of preparing cemented carbide wear-resistant steel balls for mining grinding, providing a reliable technical foundation and theoretical support for industrial applications.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing cemented carbide wear-resistant steel balls suitable for mining grinding, characterized in that... Includes the following steps: Step S1: Raw material preparation and batching calculation. Scrap steel and pig iron are selected. Alloy raw materials include high-carbon ferrochrome, graphitized recarburizing agent, ferrosilicon, ferromanganese, ferronickel, ferromolybdenum, electrolytic copper, ferrovanadium, ferrotitanium, iron nitride powder, and industrial pure aluminum. The target chemical composition, by mass fraction, is C 2.1-2.2%, Si 0.6-0.7%, Mn 0.5-0.6%, P≤0.020%, S 0.01-0.02%, Cr 9.8-10.0%, Ni 0.08-0.09%, Mo 0.04-0.05%, Cu 0.02-0.03%, V 0.10-0.20%, Ti 0.03-0.06%, with a total nitrogen content of 40-80 ppm. The balance is iron and unavoidable impurities. Step S2: Melting and microalloying. The molten steel is heated in a medium-frequency induction furnace to make it melt and clear. Alloying elements are added in sequence to make proportions. Industrial pure aluminum is added for final deoxidation. Ferrovanadium, ferrotitanium, or a combination of ferrovanadium and ferrotitanium are added in batches in the ladle to establish a V-Ti-CN microalloying system and form a precipitate precursor with MN / MCN as the hard core. Step S3: Controlled nitrogen introduction and purification. Controlled nitrogen introduction is carried out under the condition that the oxygen content of molten steel is ≤30 ppm. Solid nitrogen introduction method or gas nitrogen introduction method is used. After nitrogen introduction, the total nitrogen content is controlled at 40-80 ppm to improve the V-Ti-CN microalloying system and promote the formation of MN / MCN hard core. Step S4: Casting and solidification, filtering is performed using a filter, and bottom casting is adopted; Step S5: Heat treatment, including austenitization, quenching and tempering, to form a core-shell precipitate structure on the surface of the MN / MCN hard core by the heat treatment process to make the chromium carbonitride gradient self-passivation shell form a core-shell precipitate structure. The steel ball has a core-shell precipitate microstructure formed by a V-Ti-CN microalloying system, which includes a hard core mainly composed of MN / MCN and a gradient self-passivating shell mainly composed of chromium carbonitride. The surface hardness of the steel ball is HRC 60-63, and the core hardness is HRC 54-58. The core-shell precipitated microstructure of the cemented carbide wear-resistant steel ball is dispersed in the steel ball, wherein the average particle size of the MN / MCN hard core is 20-200 nm, and the thickness of the chromium carbonitride gradient self-passivation shell is 5-50 nm. The MN / MCN hard core in the core-shell precipitated phase microstructure is composed of vanadium nitride, titanium nitride, vanadium carbonitride, and titanium carbonitride, with a mass fraction of 0.05-0.15%. The chromium carbonitride gradient self-passivation shell is composed of nitrogen dichromate, chromium nitride, and chromium hexacarbon, with a mass fraction of 0.08-0.25%.

2. The method for preparing a cemented carbide wear-resistant steel ball suitable for mining grinding as described in claim 1, characterized in that, The composition requirements for scrap steel and pig iron in step S1 are: phosphorus content ≤ 0.020% and sulfur content 0.01-0.02%; the purity requirements for the alloy raw materials are: vanadium content ≥ 50% in ferrovanadium, titanium content ≥ 30% in ferrotitanium, nitrogen content 3-5% in iron nitride powder, and purity of industrial pure aluminum ≥ 99.5%.

3. The method for preparing a cemented carbide wear-resistant steel ball suitable for mining grinding as described in claim 1, characterized in that, The smelting process parameters in step S2 are as follows: heat to 1600-1620℃ to clear the molten steel, stir with argon gas for 1-3 minutes, control the tapping temperature at 1530-1560℃, and add 0.01-0.03% of industrial pure aluminum to make the oxygen content of the molten steel ≤30 ppm.

4. The method for preparing a cemented carbide wear-resistant steel ball suitable for mining grinding as described in claim 1, characterized in that, The nitrogen introduction process parameters in step S3 are as follows: for solid nitrogen introduction, add 10-20 g / t of iron nitride powder or for gas nitrogen introduction, the bubbling pressure is 0.015-0.025 MPa and the bubbling time is 90-120 s. The total nitrogen content after nitrogen introduction is controlled at 40-80 ppm.

5. The method for preparing a cemented carbide wear-resistant steel ball suitable for mining grinding as described in claim 1, characterized in that, The casting parameters in step S4 are as follows: set a foam ceramic filter, preheat the sand mold or metal mold to 200-300℃, and control the casting temperature at 1480-1520℃.

6. The method for preparing a cemented carbide wear-resistant steel ball suitable for mining grinding as described in claim 5, characterized in that, The heat treatment parameters in step S5 are as follows: austenitizing temperature 980-1000℃, holding time 20-30 min; quenching medium is a polyether-based PAG quenching agent aqueous solution with a mass fraction of 10-15% and a quenching liquid temperature of 25-35℃; medium-temperature tempering temperature 520-560℃, holding time 1.0-2.0 h; and low-temperature tempering temperature 180-230℃, holding time 0.5-1.5 h.

7. The application of the cemented carbide wear-resistant steel balls obtained by the preparation method according to any one of claims 1-6 in wet grinding operations in mines, characterized in that: The steel balls can maintain excellent wear resistance and corrosion resistance under the high impact and high wear conditions of wet grinding.

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