Hard alloy wear-resistant steel ball suitable for mine ore grinding and preparation method of hard alloy wear-resistant steel ball

Abstract

The invention belongs to the field of metal materials, and provides a hard alloy wear-resistant steel ball suitable for mine ore grinding and a preparation method thereof.The hard alloy wear-resistant steel ball is prepared from waste steel pig iron as a basic raw material and chemical components including 2.1%-2.2% of C, 9.8%-10.0% of Cr, 0.10%-0.20% of V and 0.03%-0.06% of Ti; a core-shell precipitated phase microstructure design with MN / MCN as a hard core and chromium carbonitride as a gradient self-passivation shell layer is formed through medium-frequency induction furnace smelting, controlled nitrogen introduction establishment of a V-Ti-C-N microalloy system, bottom pouring solidification and austenitizing quenching and tempering heat treatment processes, and the performance indexes that the surface hardness is HRC60-63 and the core hardness is HRC54-58 are achieved; the average particle size of a core-shell precipitated phase is in dispersed distribution of 20-200nm, the shell thickness is 5-50nm, and the alloy steel ball has excellent wear resistance and corrosion resistance under the high-impact and high-wear working conditions of wet ore grinding, solves the problem of insufficient wear resistance and corrosion resistance of a traditional alloy steel ball, and has wide mine ore grinding application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal materials, in particular to a hard alloy wear-resistant steel ball suitable for mine grinding and a preparation method thereof. BACKGROUND

[0002] In the process of mine exploitation and mineral processing, grinding operation as the core link of mineral processing puts forward extremely strict requirements on the performance of grinding medium. Steel ball as the most important grinding medium needs to work stably in high-intensity impact, continuous friction and complex chemical environment for a long time, and its performance directly affects the grinding efficiency, product quality and production cost. Modern mine grinding process is facing the challenges of increasing ore hardness and increasingly strict grinding fineness requirements, which requires steel ball to have excellent wear resistance to resist long-term high-frequency mechanical impact and wear, and excellent corrosion resistance to resist chemical corrosion of acidic or alkaline medium in wet grinding process. The wear resistance of steel ball directly determines its service life and grinding efficiency, and the corrosion resistance is related to the stability of the grinding process and the purity of the product. Meeting these key performance requirements not only can significantly reduce the grinding cost and improve the production efficiency, but also can promote the overall progress of mineral processing technology and create greater economic value for mining enterprises. Therefore, the development of grinding steel ball with excellent wear resistance and corrosion resistance has important engineering application value and broad market prospect.

[0003] At present, the research and development of grinding steel ball mainly includes high chromium cast iron ball, medium chromium alloy steel ball and low alloy steel ball, but there are still significant deficiencies in the coordinated improvement of wear resistance and corrosion resistance. For example, CN104561761B discloses a high chromium wear-resistant steel ball, but it has the problem of insufficient corrosion resistance. High chromium cast iron ball has good wear resistance, but its coarse eutectic carbide organization leads to poor toughness and easy brittle fracture, and its corrosion resistance is limited in acidic environment. Medium chromium alloy steel ball improves toughness by reducing chromium content, but sacrifices wear resistance and lacks effective surface passivation mechanism. Low alloy steel ball has low cost but serious wear resistance, which is difficult to meet the demand of high strength grinding operation. The core problem of existing technology is the lack of fine micro-alloying design, which cannot realize the nanoscale dispersion distribution of hard phase and precise control of gradient structure. Traditional alloying method mainly relies on carbide strengthening, but the size of carbide is coarse and the distribution is uneven, which not only affects the overall mechanical properties of the material, but also cannot provide sustained corrosion protection. In addition, nitrogen element as an important interstitial strengthening element is insufficiently applied in existing system, lacks the synergistic mechanism with vanadium, titanium and other micro-alloying elements, and cannot construct a composite precipitate phase structure with high hardness and self-passivation function. SUMMARY

[0004] (1) Technical problems solved The application aims to provide a hard alloy wear-resistant steel ball suitable for mine grinding and a preparation method thereof, and solve the problem of insufficient wear resistance and corrosion resistance of the alloy steel ball.

[0005] (2) Technical scheme In order to achieve the above-mentioned purpose, the application provides the following technical scheme: A preparation method of a hard alloy wear-resistant steel ball suitable for mine grinding, comprising the following steps: Step S1: raw material preparation and batching calculation, selecting scrap steel and pig iron, alloy raw materials including high-carbon chromium iron, graphitized carburant, silicon iron, manganese iron, nickel iron, molybdenum iron, electrolytic copper, vanadium iron, titanium iron, iron nitride powder, industrial pure aluminum, and target chemical components are 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 in terms of mass fraction; Step S2: smelting and micro-alloying, heating the molten steel to clear in a medium-frequency induction furnace, adding alloy elements in sequence for proportioning, and finally deoxidizing by adding industrial pure aluminum, adding vanadium iron, titanium iron or a combination of vanadium iron and titanium iron in the ladle in batches to establish a V-Ti-C-N micro-alloy system and form a MN / MCN hard core-based precipitate phase precursor; Step S3: controlled nitrogen introduction and purification, controlled nitrogen introduction is performed under the condition that the oxygen content of the molten steel is less than or equal to 30 ppm, solid nitrogen introduction method or gas nitrogen introduction method is adopted, the total nitrogen content is controlled to be 40-80 ppm after nitrogen introduction, the V-Ti-C-N micro-alloy system is perfected, and the MN / MCN hard core formation is promoted; Step S4: pouring and solidification, setting a filter for filtration, and adopting a bottom pouring pouring mode; Step S5: heat treatment, including austenitizing, quenching and tempering, and through the heat treatment process, a carbonitride chromium gradient self-passivation shell layer is formed on the surface of the MN / MCN hard core to form a core-shell precipitate phase structure.

[0006] The V-Ti-C-N micro-alloying system is mainly used for enhancing the wear resistance and corrosion resistance of the grinding steel ball. The technical scheme is to precisely control the chemical component ratio, establish a composite micro-alloying system taking vanadium iron and titanium iron as the core, form a strong affinity between vanadium and titanium elements and carbon and nitrogen elements, ensure the full dissolution and uniform distribution of the micro-alloying elements by adding vanadium iron and titanium iron in combination in batches during the smelting process, and design a controlled nitrogen introduction process to perfect the V-Ti-C-N micro-alloying system, provide ideal thermodynamic and kinetic conditions for the formation of MN / MCN hard core by strictly controlling the oxygen content and nitrogen content of the molten steel. The interaction between the four elements of vanadium, titanium, carbon and nitrogen produces a significant synergistic strengthening effect, the vanadium nitride and titanium nitride form nanoscale dispersion strengthening phases in the matrix, which not only provides excellent hardness and wear resistance, but also lays a foundation for the formation of a carbonitride chromium gradient self-passivation shell. The core design concept of the heat treatment process is to construct a carbonitride chromium gradient self-passivation shell on the surface of the MN / MCN hard core, form a unique core-shell precipitated phase structure, and realize the organic unity of wear resistance and corrosion resistance through the double protection mechanism of the hard core providing wear resistance when bearing mechanical impact and the shell realizing self-passivation protection when facing chemical corrosion.

[0007] Further, in the step S1, the composition requirements of the scrap steel and pig iron are: phosphorus content ≤0.020%, sulfur content 0.01-0.02%; the purity requirements of the alloy raw materials are: vanadium content in vanadium iron ≥50%, titanium content in titanium iron ≥30%, nitrogen content in nitrided iron powder 3-5%, and industrial pure aluminum purity ≥99.5%.

[0008] Further, in the step S2, the smelting process parameters are: heating to 1600-1620℃ to melt the steel liquid, argon stirring for 1-3 min, and the steel tapping temperature is controlled at 1530-1560℃, and the industrial pure aluminum is added in an amount of 0.01-0.03% to make the oxygen content of the molten steel ≤30 ppm.

[0009] Further, in the step S3, the nitrogen introduction process parameters are: solid nitrogen introduction method adding 10-20 g / t of nitrided iron powder or gas nitrogen introduction method bubbling pressure 0.015-0.025 MPa, bubbling time 90-120 s, and the total nitrogen content after nitrogen introduction is controlled at 40-80 ppm.

[0010] Further, in the step S4, the pouring parameters are: setting a foam ceramic filter, preheating the sand mold or metal mold to 200-300℃, and the pouring temperature is controlled at 1480-1520℃.

[0011] Further, the heat treatment parameters in the step S5 are: austenitizing temperature 980-1000 DEG C, holding time 20-30 min, quenching medium 10-15% polyether PAG quenching agent aqueous solution by mass fraction and quenching liquid temperature 25-35 DEG C, medium temperature tempering temperature 520-560 DEG C, holding time 1.0-2.0 h, low temperature tempering temperature 180-230 DEG C, holding time 0.5-1.5 h.

[0012] The design of the precise process parameter control system is mainly used for enhancing the comprehensive performance of the hard alloy wear-resistant steel ball. The technical scheme strictly controls the purity and impurity content of raw materials, ensures that the vanadium content in vanadium iron and the titanium content in titanium iron meet specific requirements, and controls harmful impurities such as phosphorus and sulfur at a very low level, thereby creating a clean metallurgical environment for subsequent micro-alloying reactions. In the smelting process, the combination of argon stirring and industrial pure aluminum deep deoxidation is adopted, and through precise temperature control and deoxidizer addition amount adjustment, the oxygen content of the molten steel is reduced to a very low level, which provides ideal conditions for the full play of micro-alloying elements. The design purpose of the controlled nitrogen introduction process is to realize precise control of nitrogen content through precise operation of the iron nitride powder solid nitrogen introduction method or the gas nitrogen introduction method. The combined strengthening effect of nitrogen element and vanadium and titanium elements far exceeds the effect of a single element. The application of a foamed ceramic filter in the pouring process and temperature control ensure the purity of the molten steel and the uniformity of the solidification structure. The segmented heat treatment process realizes the best matching of the matrix structure and precipitated phase through precise control of austenitizing, polyether PAG quenching agent aqueous solution quenching and medium-low temperature double tempering, so that the synergistic strengthening effect between the hard precipitated phase and the matrix is generated, thereby excellent mechanical properties and use performance are obtained.

[0013] The application further discloses a hard alloy wear-resistant steel ball suitable for grinding ore in a mine, characterized by chemical components in mass fraction as follows: 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%, total nitrogen content 40-80 ppm, and the balance being iron and inevitable impurities. The steel ball has a core-shell precipitated phase microstructure formed by a V-Ti-C-N micro-alloy system, and the core-shell precipitated phase comprises a hard core mainly composed of MN / MCN and a gradient self-passivation shell layer mainly composed of chromium carbonitride.

[0014] Further, the surface layer hardness is HRC 60-63, the core hardness is HRC 54-58, the core-shell precipitate microstructure of the hard alloy wear-resistant steel ball is dispersedly 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 gradient self-passivation shell layer of the chromium carbonitride is 5-50 nm.

[0015] Further, the MN / MCN hard core in the core-shell precipitate microstructure is mainly composed of vanadium nitride, titanium nitride, vanadium carbonitride and titanium carbonitride, and the mass fraction is 0.05-0.15%, and the gradient self-passivation shell layer of the chromium carbonitride is mainly composed of dichromium nitride, chromium nitride and twenty-three chromium six carbon, and the mass fraction is 0.08-0.25%.

[0016] The application of a hard alloy wear-resistant steel ball suitable for mine grinding to a mine wet grinding operation, the steel ball can maintain excellent wear resistance and corrosion resistance under the high impact and high wear working conditions of the wet grinding.

[0017] The application also discloses a hard alloy wear-resistant steel ball suitable for mine grinding, which is characterized by excellent comprehensive performance realized by precise component design and unique core-shell precipitate microstructure. The steel ball adopts the design concept of a V-Ti-C-N micro-alloy system, and a composite precipitate phase structure composed of a hard core mainly composed of MN / MCN and a gradient self-passivation shell layer mainly composed of chromium carbonitride is formed through the synergistic effect of vanadium, titanium, carbon and nitrogen. The formation mechanism of vanadium nitride, titanium nitride, vanadium carbonitride and titanium carbonitride in the hard core is based on the strong affinity of vanadium and titanium elements to carbon and nitrogen. These nanoscale hard phases are dispersedly distributed in the matrix, providing excellent strengthening effect. The gradient self-passivation shell layer of chromium carbonitride is composed of dichromium nitride, chromium nitride and twenty-three chromium six carbon, and forms a protective layer on the surface of the hard core, which not only maintains the stability of the precipitate phase but also endows the material with excellent corrosion resistance. The unique design of the core-shell precipitate phase makes the hard core bear the main strengthening effect, and the shell layer provides chemical stability and self-passivation function, and the two cooperate to produce a significant synergistic effect. The hardness gradient distribution of the surface layer and the core ensures that the steel ball has good toughness matching when bearing impact load, and the dispersed distribution of the nanoscale precipitate phase ensures that the material can simultaneously exhibit high wear resistance and corrosion resistance under the complex working conditions of wet grinding, realizing the unity of structure design and performance requirements.

[0018] (3) Beneficial technical effects Significant improvement of wear resistance: through the design of V-Ti-C-N micro-alloy system, the MN / MCN nanoscale hard core precipitated phase mainly composed of vanadium nitride, titanium nitride, vanadium carbonitride and titanium carbonitride is formed, which is dispersedly distributed in the matrix with an average particle size controlled within the range of 20-200 nm, effectively improving the hardness and wear resistance of the steel ball, so that the surface hardness reaches HRC 60-63, and the stable grinding efficiency can be maintained for a long time in high-strength grinding operation.

[0019] Excellent corrosion resistance: through the design of core-shell precipitated phase microstructure, a carbonitride chromium gradient self-passivation shell mainly composed of dichromium nitride, chromium nitride and twenty-three chromium six carbon is formed on the surface of the MN / MCN hard core, and the shell thickness is 5-50 nm. The gradient self-passivation structure can provide continuous chemical protection in the acid or alkaline environment of wet grinding, and significantly improve the corrosion resistance of the steel ball in complex chemical environment.

[0020] Realization of the coordination and unity of wear resistance and corrosion resistance: through the unique design of core-shell precipitated phase structure, the hard core provides excellent wear resistance, and the self-passivation shell provides chemical stability and corrosion resistance function, and the two cooperate to produce a significant synergistic effect, solving the technical problem that the traditional steel ball is difficult to simultaneously consider wear resistance and corrosion resistance.

[0021] Optimized mechanical property matching: through precise heat treatment process control, the gradient distribution of surface hardness HRC 60-63 and core hardness HRC 54-58 is realized, so that the steel ball has good toughness matching when bearing high impact load, brittle fracture caused by too high hardness is avoided, and the use reliability and safety of the steel ball are improved.

[0022] Precise control of process technology: through strict control of raw material purity, oxygen content, nitrogen introduction process parameters and heat treatment parameters, the full process quality control from raw material preparation to final product is realized, and the stability and consistency of the steel ball performance are ensured. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The core-shell structure precipitated phase morphology diagram of the hard alloy wear-resistant steel ball for mine grinding prepared in embodiment 1 of the application.

[0024] Figure 2 The actual object diagram of the hard alloy wear-resistant steel ball for mine grinding prepared in embodiment 1 of the application.

[0025] Figure 3 The influence of vanadium content on wear resistance and corrosion resistance.

[0026] Figure 4The influence of total nitrogen content on wear resistance and corrosion resistance of the application.

[0027] Figure 5 The influence of austenitizing temperature on wear resistance and corrosion resistance of the application.

[0028] Figure 6 The comparison of surface hardness and core hardness of the examples and the comparative examples of the application.

[0029] Figure 7 The comparison of wear resistance and fatigue resistance of the examples and the comparative examples of the application.

[0030] Figure 8 The comparison of relative wear resistance index and fatigue strength improvement of the examples and the comparative examples of the application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the examples of the application more clear, the technical scheme of the examples of the application will be described clearly and completely below in combination with the drawings in the examples of the application.

[0032] Embodiment 1: a preparation method of a hard alloy wear-resistant steel ball suitable for mine grinding, comprising the following steps: step S1: raw material preparation and batching calculation, selecting scrap steel and pig iron, alloy raw materials including high-carbon chromium iron, graphitized carburizer, silicon iron, manganese iron, nickel iron, molybdenum iron, electrolytic copper, vanadium iron, titanium iron, nitrided iron powder, industrial pure aluminum, and the target chemical composition is C 2.15%, Si 0.65%, Mn 0.55%, Cr 9.9%, V 0.15%, Ti 0.045% and total nitrogen 60 ppm according to mass fraction; in step S1 of the embodiment, the composition requirements of scrap steel and pig iron are: phosphorus content 0.020%, sulfur content 0.015%; the purity requirements of alloy raw materials in the embodiment are: vanadium content 50% in vanadium iron, titanium content 30% in titanium iron, nitrogen content 4% in nitrided iron powder, and industrial pure aluminum purity 99.5%. Step S2: smelting and micro-alloying, heating in a medium-frequency induction furnace to make the molten steel clean, adding alloy elements in sequence for proportioning, final deoxidation by adding industrial pure aluminum, adding vanadium iron and titanium iron in combination in the ladle to establish a V-Ti-C-N micro-alloy system and form a MN / MCN hard core-based precipitate phase precursor; in step S2 of the embodiment, the smelting process parameters are: heating to 1610 DEG C to make the molten steel clean, argon stirring for 2 min, the tapping temperature is controlled at 1545 DEG C, and the industrial pure aluminum addition amount 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 carried out under the condition that the oxygen content of the molten steel is 30 ppm, solid nitrogen introduction method is adopted, the total nitrogen content is controlled at 60 ppm after nitrogen introduction, the V-Ti-C-N micro-alloy system is perfected, and the MN / MCN hard core formation is promoted; in step S3 of the embodiment, the nitrogen introduction process parameters are: 15 g / t of nitrided iron powder is added by solid nitrogen introduction method, and the total nitrogen content is controlled at 60 ppm after nitrogen introduction. Step S4: pouring and solidification, setting a filter for filtration, and adopting a bottom pouring pouring mode; in step S4 of the embodiment, the pouring parameters are: setting a foam ceramic filter, the sand mold is preheated to 250 DEG C, and the pouring temperature is controlled at 1500 DEG C. Step S5: heat treatment, including austenitizing, quenching and tempering, the carbonitride chromium gradient self-passivation shell layer is formed on the surface of the MN / MCN hard core through the heat treatment process to form a core-shell precipitate phase structure; in step S5 of the embodiment, the heat treatment parameters are: austenitizing temperature 990 DEG C, holding time 25 min, quenching medium is a 12.5% polyether PAG quenching agent aqueous solution and the quenching liquid temperature is 30 DEG C, medium-temperature tempering temperature 540 DEG C, holding time 1.5 h, low-temperature tempering temperature 205 DEG C, holding time 1.0 h.The hard alloy wear-resistant steel ball obtained by the preparation method has a chemical composition by mass fraction of 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%, a total nitrogen content of 60 ppm, and the balance of iron and inevitable impurities. The steel ball of the embodiment has a core-shell precipitate microstructure formed by a V-Ti-C-N microalloy system, which includes a hard core mainly of MN / MCN and a gradient self-passivating shell layer mainly of chromium carbonitride. The surface hardness is HRC 61.5, and the core hardness is HRC 56. The core-shell precipitate microstructure of the hard alloy wear-resistant steel ball of the embodiment is dispersedly distributed in the steel ball, wherein the average particle size of the MN / MCN hard core is 110 nm, and the thickness of the chromium carbonitride gradient self-passivating shell layer is 27.5 nm. The MN / MCN hard core in the core-shell precipitate microstructure of the embodiment is mainly composed of vanadium nitride, titanium nitride, vanadium carbonitride, and titanium carbonitride, with a mass fraction of 0.10%. The chromium carbonitride gradient self-passivating shell layer of the embodiment is mainly composed of dichromium nitride, chromium nitride, and twenty-three chromium six carbon, with a mass fraction of 0.16%. The application of the hard alloy wear-resistant steel ball of the embodiment in the mine wet grinding operation, the steel ball of the embodiment can maintain excellent wear resistance and corrosion resistance under the high impact and high wear working conditions of wet grinding. The embodiment has the following characteristics: moderate parameter configuration is adopted to pursue process stability and performance balance, and good comprehensive performance is achieved through moderate component design and heat treatment parameters, which is especially suitable for conventional mine grinding operation with high requirements for product quality stability.

[0033] Embodiment 2: A preparation method of a hard alloy wear-resistant steel ball suitable for mine grinding, comprising the following steps: Step S1: raw material preparation and batching calculation, selecting scrap steel and pig iron, alloy raw materials including high-carbon chromium iron, graphitized carburizer, silicon iron, manganese iron, nickel iron, molybdenum iron, electrolytic copper, vanadium iron, titanium iron, nitrided iron powder, and industrial pure aluminum, the target chemical composition is C 2.2%, Si 0.7%, Mn 0.6%, Cr 10.0%, V 0.20%, Ti 0.06% and total nitrogen 80 ppm according to mass fraction; the composition requirements of scrap steel and pig iron in step S1 of the embodiment are: phosphorus content 0.015%, sulfur content 0.01%; the purity requirements of alloy raw materials in the embodiment are: vanadium content 55% in vanadium iron, titanium content 35% in titanium iron, nitrogen content 5% in nitrided iron powder, and purity 99.7% in industrial pure aluminum. Step S2: smelting and micro-alloying, heating in a medium-frequency induction furnace to make the molten steel clean, adding alloy elements in sequence for proportioning, final deoxidation by adding industrial pure aluminum, adding vanadium iron and titanium iron in combination in the ladle to establish a V-Ti-C-N micro-alloy system and form a MN / MCN hard core-based precipitate phase precursor; the smelting process parameters in step S2 of the embodiment are: heating to 1620 DEG C to make the molten steel clean, argon stirring for 3 min, the tapping temperature is controlled at 1560 DEG C, and the industrial pure aluminum addition amount 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 carried out under the condition that the oxygen content of the molten steel is 25 ppm, gas nitrogen introduction method is adopted, the total nitrogen content is controlled at 80 ppm after nitrogen introduction, the V-Ti-C-N micro-alloy system is perfected, and the MN / MCN hard core formation is promoted; the nitrogen introduction process parameters in step S3 of the embodiment are: gas nitrogen introduction method bubble pressure 0.025 MPa, bubble time 120 s, and the total nitrogen content is controlled at 80 ppm after nitrogen introduction. Step S4: pouring and solidification, setting a filter for filtration, and adopting a bottom pouring mode; the pouring parameters in step S4 of the embodiment are: setting a foam ceramic filter, preheating the metal mold to 300 DEG C, and controlling the pouring temperature at 1520 DEG C. Step S5: heat treatment, including austenitizing, quenching and tempering, the carbonitride chromium gradient self-passivation shell layer is formed on the surface of the MN / MCN hard core through the heat treatment process to form a core-shell precipitate phase structure; the heat treatment parameters in step S5 of the embodiment are: austenitizing temperature 1000 DEG C, holding time 30 min, quenching medium is a 15% polyether PAG quenchant aqueous solution and the quenching liquid temperature is 25 DEG C, medium-temperature tempering temperature 560 DEG C, holding time 2.0 h, low-temperature tempering temperature 230 DEG C, holding time 1.5 h.The hard alloy wear-resistant steel ball obtained by the preparation method has a chemical composition by mass fraction of 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%, a total nitrogen content of 80 ppm, and the balance of iron and inevitable impurities. The steel ball of the embodiment has a core-shell precipitate microstructure formed by a V-Ti-C-N microalloy system, which includes a hard core mainly of MN / MCN and a gradient self-passivating shell layer mainly of chromium carbonitride. The surface hardness is HRC 63, and the core hardness is HRC 58. The core-shell precipitate microstructure of the hard alloy wear-resistant steel ball of the embodiment is dispersedly distributed 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 layer is 50 nm. The MN / MCN hard core in the core-shell precipitate microstructure of the embodiment 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 layer of the embodiment is mainly composed of dichromium nitride, chromium nitride and twenty-three chromium six carbon, with a mass fraction of 0.25%. The application of the hard alloy wear-resistant steel ball of the embodiment in the mine wet grinding operation, the steel ball of the embodiment can maintain excellent wear resistance and corrosion resistance under the high impact and high wear working conditions of wet grinding. The embodiment has the following characteristics: high strengthening parameter configuration is adopted, and the maximization of wear resistance is emphasized. The maximum hard phase precipitation is realized through high carbon content, vanadium and titanium content and nitrogen content, which is especially suitable for high hardness ore grinding and extreme wear working conditions.

[0034] Embodiment 3: a preparation method of a hard alloy wear-resistant steel ball suitable for mine grinding, comprising the following steps: step S1: raw material preparation and batching calculation, selecting scrap steel and pig iron, alloy raw materials including high-carbon chromium iron, graphitized carburizer, silicon iron, manganese iron, nickel iron, molybdenum iron, electrolytic copper, vanadium iron, titanium iron, nitrided iron powder, and industrial pure aluminum, the target chemical composition is C 2.1%, Si 0.6%, Mn 0.5%, Cr 9.8%, V 0.10%, Ti 0.03% and total nitrogen 40 ppm according to mass fraction; in step S1 of the embodiment, the composition requirements of scrap steel and pig iron are: phosphorus content 0.010%, sulfur content 0.02%; the purity requirements of alloy raw materials in the embodiment are: vanadium content 52% in vanadium iron, titanium content 32% in titanium iron, nitrogen content 3% in nitrided iron powder, and purity of industrial pure aluminum 99.8%. Step S2: melting and micro-alloying, heating in a medium-frequency induction furnace to make the molten steel clean, adding alloy elements in sequence for proportioning, final deoxidation by adding industrial pure aluminum, adding vanadium iron in the ladle in batches to establish a V-Ti-C-N micro-alloy system and form a MN / MCN hard core-based precipitate phase precursor; in step S2 of the embodiment, the melting process parameters are: heating to 1600 DEG C to make the molten steel clean, argon stirring for 1 min, the tapping temperature is controlled at 1530 DEG C, and the industrial pure aluminum addition amount 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 carried out under the condition that the oxygen content of the molten steel is 20 ppm, solid nitrogen introduction method is adopted, the total nitrogen content is controlled at 40 ppm after nitrogen introduction, the V-Ti-C-N micro-alloy system is perfected, and the MN / MCN hard core formation is promoted; in step S3 of the embodiment, the nitrogen introduction process parameters are: 10 g / t of nitrided iron powder is added by solid nitrogen introduction method, and the total nitrogen content is controlled at 40 ppm after nitrogen introduction. Step S4: pouring and solidification, setting a filter for filtration, and adopting a bottom pouring pouring mode; in step S4 of the embodiment, the pouring parameters are: setting a foam ceramic filter, the sand mold is preheated to 200 DEG C, and the pouring temperature is controlled at 1480 DEG C. Step S5: heat treatment, including austenitizing, quenching and tempering, the carbonitride chromium gradient self-passivation shell layer is formed on the surface of the MN / MCN hard core through the heat treatment process to form a core-shell precipitate phase structure; in step S5 of the embodiment, the heat treatment parameters are: austenitizing temperature 980 DEG C, holding time 20 min, quenching medium is 10% polyether PAG quenching agent aqueous solution and the quenching liquid temperature is 35 DEG C, medium-temperature tempering temperature 520 DEG C, holding time 1.0 h, low-temperature tempering temperature 180 DEG C, holding time 0.5 h.The hard alloy wear-resistant steel ball obtained by the preparation method has a chemical composition by mass fraction of 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%, and a total nitrogen content of 40 ppm, with the balance being iron and unavoidable impurities. The steel ball of the embodiment has a core-shell precipitate microstructure formed by a V-Ti-C-N microalloy system, which includes a hard core mainly of MN / MCN and a gradient self-passivating shell layer mainly of chromium carbonitride. The surface hardness is HRC 60, and the core hardness is HRC 54. The core-shell precipitate microstructure of the hard alloy wear-resistant steel ball of the embodiment is dispersedly distributed 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 layer is 5 nm. The MN / MCN hard core in the core-shell precipitate microstructure of the embodiment 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 layer of the embodiment is mainly composed of dichromium nitride, chromium nitride, and twenty-three chromium six carbon, with a mass fraction of 0.08%. The hard alloy wear-resistant steel ball of the embodiment is applied in mine wet grinding operations. The steel ball of the embodiment can maintain excellent wear resistance and corrosion resistance under high impact and high wear conditions of wet grinding. The embodiment has the following characteristics: low strengthening and high toughness configuration, focusing on the impact toughness and processing performance of the material, achieving good toughness performance through low alloy content and moderate process parameters, and being particularly suitable for coarse grinding operations with high impact load and application scenarios with strict requirements for steel ball breakage rate.

[0035] Embodiment 4: a preparation method of a hard alloy wear-resistant steel ball suitable for mine grinding, comprising the following steps: step S1: raw material preparation and batching calculation, selecting scrap steel and pig iron, alloy raw materials including high-carbon chromium iron, graphitized carburant, silicon iron, manganese iron, nickel iron, molybdenum iron, electrolytic copper, vanadium iron, titanium iron, nitrided iron powder, and industrial pure aluminum, the target chemical composition is C 2.18%, Si 0.68%, Mn 0.58%, Cr 9.95%, V 0.18%, Ti 0.055% and total nitrogen 70 ppm according to mass fraction; the composition requirements of scrap steel and pig iron in step S1 of the embodiment are that the phosphorus content is 0.012% and the sulfur content is 0.018%; the purity requirements of the alloy raw materials in the embodiment are that the vanadium content in vanadium iron is 58%, the titanium content in titanium iron is 38%, the nitrogen content in nitrided iron powder is 4.5%, and the purity of industrial pure aluminum is 99.9%. Step S2: smelting and micro-alloying, heating in a medium-frequency induction furnace to make the molten steel clean, adding alloy elements in sequence for proportioning, final deoxidation by adding industrial pure aluminum, adding titanium iron in the ladle in batches to establish a V-Ti-C-N micro-alloy system and form a MN / MCN hard core-based precipitate phase precursor; the smelting process parameters in step S2 of the embodiment are that the molten steel is cleaned by heating to 1615 DEG C, argon stirring is adopted for 2.5 min, the tapping temperature is controlled at 1555 DEG C, and the industrial pure aluminum is added in an amount of 0.025% to make the oxygen content of the molten steel 15 ppm. Step S3: controlled nitrogen introduction and purification, controlled nitrogen introduction is carried out under the condition that the oxygen content of the molten steel is 15 ppm, gas nitrogen introduction method is adopted, the total nitrogen content is controlled at 70 ppm after nitrogen introduction, the V-Ti-C-N micro-alloy system is perfected, and the MN / MCN hard core formation is promoted; the nitrogen introduction process parameters in step S3 of the embodiment are that the bubbling pressure of the gas nitrogen introduction method is 0.020 MPa, the bubbling time is 105 s, and the total nitrogen content is controlled at 70 ppm after nitrogen introduction. Step S4: pouring and solidification, setting a filter for filtration, and adopting a bottom pouring pouring mode; the pouring parameters in step S4 of the embodiment are that a foam ceramic filter is set, the metal mold is preheated to 275 DEG C, and the pouring temperature is controlled at 1510 DEG C. Step S5: heat treatment, including austenitizing, quenching and tempering, the carbonitride chromium gradient self-passivation shell layer is formed on the surface of the MN / MCN hard core through the heat treatment process to form a core-shell precipitate phase structure; the heat treatment parameters in step S5 of the embodiment are that the austenitizing temperature is 995 DEG C and the holding time is 28 min, the quenching medium is a polyether PAG quenching agent aqueous solution with a mass fraction of 13% and a quenching liquid temperature of 28 DEG C, the medium-temperature tempering temperature is 550 DEG C and the holding time is 1.8 h, and the low-temperature tempering temperature is 210 DEG C and the holding time is 1.2 h.The hard alloy wear-resistant steel ball obtained by the preparation method has a chemical composition of 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% and a total nitrogen content of 70 ppm, and the balance is iron and inevitable impurities. The steel ball of the embodiment has a core-shell precipitate microstructure formed by a V-Ti-C-N microalloy system, which includes a hard core mainly composed of MN / MCN and a gradient self-passivation shell layer mainly composed of chromium carbonitride. The surface hardness is HRC 62, and the core hardness is HRC 57. The core-shell precipitate microstructure of the hard alloy wear-resistant steel ball of the embodiment is dispersedly distributed in the steel ball, wherein the average particle size of the MN / MCN hard core is 150 nm, and the thickness of the chromium carbonitride gradient self-passivation shell layer is 38 nm. The MN / MCN hard core in the core-shell precipitate microstructure of the embodiment is mainly composed of vanadium nitride, titanium nitride, vanadium carbonitride and titanium carbonitride, with a mass fraction of 0.13%. The chromium carbonitride gradient self-passivation shell layer of the embodiment is mainly composed of dichromium nitride, chromium nitride and twenty-three chromium six carbon, with a mass fraction of 0.22%. The application of the hard alloy wear-resistant steel ball in the mine wet grinding operation, the steel ball of the embodiment can maintain excellent wear resistance and corrosion resistance under the high impact and high wear condition of wet grinding. The embodiment has the following characteristics: high corrosion resistance is adopted for optimal configuration, the strengthening and corrosion protection ability of the self-passivation shell layer are emphasized, excellent corrosion resistance is achieved through optimized composition ratio and precise process control, and it is especially suitable for wet grinding operation in severe acid or alkaline medium environment and special mineral processing process with strong chemical corrosion.

[0036] Comparative Example 1: substantially 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% of Example 1, resulting in insufficient vanadium element in the V-Ti-C-N microalloy system, and the number of vanadium nitride and vanadium carbonitride hard precipitates is insufficient.

[0037] Comparative Example 2: substantially 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% of Example 1, resulting in insufficient titanium element in the microalloy system, and the number of titanium nitride and titanium carbonitride precipitates is significantly reduced.

[0038] Comparative Example 3: substantially 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 of Example 1, resulting in insufficient formation of nitride precipitates, and the core-shell structure is not fully developed.

[0039] Comparative Example 4: substantially the same as Example 1, except that the temperature of the heating process in step S2 is 1550℃, which is lower than 1610℃ in Example 1, resulting in insufficient molten steel cleaning and incomplete dissolution of alloying elements, affecting the subsequent micro-alloying effect.

[0040] Comparative Example 5: substantially the same as Example 1, except that the tapping temperature in step S2 is controlled at 1480℃, which is lower than 1545℃ in Example 1, resulting in poor fluidity of the molten steel, making it difficult to pour and the solidification structure being coarse.

[0041] Comparative Example 6: substantially the same as Example 1, except that the austenitizing temperature in step S5 is 920℃, which is lower than 990℃ in Example 1, resulting in insufficient austenitizing and uneven matrix structure, affecting subsequent phase transformation and precipitate distribution.

[0042] Comparative Example 7: substantially the same as Example 1, except that the medium-temperature tempering temperature in step S5 is 480℃, which is lower than 540℃ in Example 1, resulting in insufficient tempering and larger residual stress, with poor toughness.

[0043] Comparative Example 8: substantially 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, resulting in excessive deoxidation and high aluminum content in the molten steel, forming aluminum oxide inclusions and affecting material purity.

[0044] Comparative Example 9: substantially the same as Example 1, except that the bubbling pressure in step S3 is 0.035MPa using the gas-induced nitrogen method, resulting in too fast dissolution of nitrogen and uneven distribution.

[0045] Comparative Example 10: substantially 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, resulting in sulfide inclusions and deteriorating the mechanical properties of the material.

[0046] Comparative Example 11: substantially the same as Example 1, except that the argon stirring time in step S2 is 0.5min, which is shorter than 2min in Example 1, resulting in poor composition uniformity of the molten steel and uneven distribution of alloying elements.

[0047] Comparative Example 12: substantially 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, resulting in poor filling and poor surface quality of the casting.

[0048] Comparative Example 13: substantially the same as Example 1, except that the quenching medium in step S5 is an aqueous solution of polyether PAG quenching agent with a mass fraction of 8%, which is lower than 12.5% in Example 1, and the quenching cooling rate is insufficient, resulting in a lower quenching hardness.

[0049] Comparative Example 14: substantially the same as Example 1, except that the vanadium content of vanadium-iron in step S1 is 45%, which is lower than 50% in Example 1, and the insufficient purity of raw materials increases impurities, affecting the micro-alloying effect and the final performance.

[0050] Comparative Example 15: substantially the same as Example 1, except that no ferrotitanium is added in step S2, and only vanadium-iron is added to establish a V-C-N micro-alloying system. The lack of synergistic effect of titanium elements cannot form a complete core-shell precipitate phase structure, and the corrosion resistance is significantly reduced.

[0051] Performance test: Hardness test experiment: The test object is a hard alloy wear-resistant steel ball suitable for mine grinding, and the test purpose is to evaluate the hardness distribution characteristics of the surface layer and the core of the steel ball and verify the influence of the V-Ti-C-N micro-alloying system on the hardening effect of the material. The test principle is based on the indentation hardness test method, which forms an indentation on the surface of the material by pressing a standard indenter under a specified load, and calculates the hardness value according to the indentation size. The experimental method uses a Rockwell hardness tester, the steel ball sample with a diameter of 50 mm is cut along the radial direction and prepared into a metallographic sample, the sample is ground and polished by 180#-2000# sandpaper in stages, and then polished with 1 μm diamond paste to Ra≤0.4 μm, and then treated in a 105℃ oven for 2 hours and naturally cooled, and the hardness is tested at a distance of 0.5mm, 1.0mm, 2.0mm, 5.0mm from the surface and the core of the ball, respectively, and the average value of 5 points at each position is taken, the indentation spacing is not less than 3 times the indentation diameter and the distance from the sample edge is not less than 2.5 times the indentation diameter. The standard is 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". The key parameters are set as HRC scale, main load 1471N, holding time 10 seconds, test environment temperature 23±5℃, relative humidity ≤65%, standard hardness block is used to calibrate the instrument every day, and the instrument measurement uncertainty is ±1HRC. When processing data, calculate the average value and standard deviation of the hardness of each test point, use Grubbs test to remove outliers, draw the hardness-depth distribution curve, evaluate the rationality of the hardness gradient distribution, and supplement HV10 Vickers hardness verification for the area with a hardness lower than HRC 20, requiring a surface layer hardness of HRC 60-63 and a core hardness of HRC 54-58.

[0052] Wear resistance test: The test object is a hard alloy wear-resistant steel ball sample with a diameter of 30 mm. The test purpose 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 wear resistance is evaluated by measuring the weight loss of the sample after wear testing under a specified load and speed using standard abrasives. A special method for wet ball mill wear testing is established. A wet ball mill with an inner diameter of 200 mm and a length of 240 mm is used. The inner lining is made of high chromium cast iron. Ten steel ball samples (surface roughness Ra≤0.8 μm, dried at 105°C to constant weight) are mixed with 2 kg of quartz sand (particle size 0.15-0.30 mm) and an appropriate amount of deionized water to prepare a slurry with a solid mass fraction of 75%. The slurry is continuously ground at a speed of 75 rpm (corresponding to 70% of the critical speed) for 8 hours. The slurry level is kept constant during the grinding process. The key parameters are set as follows: grinding concentration 75% (solid mass fraction), ball-to-material ratio 1:1, temperature 25±2°C. After grinding, the steel balls are washed with deionized water, dried at 105°C for 2 hours to constant weight, and weighed using an analytical balance with a precision of 0.1 mg. The mass wear rate of a single steel ball (mg / h) is calculated, and the average value of three parallel tests is represented as mean ± standard deviation. A control steel ball without added micro-alloying elements is also tested, and the relative wear resistance index (with the control sample as 100) is calculated. The relative wear resistance index should be greater than 150.

[0053] Corrosion resistance test: The test object is a hard alloy wear-resistant steel ball sheet sample (20 mm x 10 mm x 5 mm) after surface polishing. The test purpose is to evaluate the corrosion resistance of the chromium carbonitride gradient self-passivation shell and verify the chemical stability of the material in the wet grinding environment. The test principle is based on electrochemical corrosion theory. The corrosion resistance of the material is evaluated by measuring its electrochemical parameters in the corrosion medium. The experimental method uses a CHI660E electrochemical workstation. The sample is polished with 2000# sandpaper and then polished with 1 μm diamond paste to Ra≤0.05 μm. It is ultrasonically cleaned with acetone and ethanol for 5 minutes each, and the edges are sealed with epoxy resin to expose only 1 cm 2 of the working area. Potentiodynamic polarization scanning is performed in a 3.5% NaCl solution (air saturated) with the sample as the working electrode, a saturated calomel electrode as the reference electrode (2-3 mm away from the working electrode through a Luggin capillary), and a platinum mesh as the auxiliary electrode. After the open circuit potential is stable for 30 minutes, the scanning is performed from the open circuit potential to -200 mV to +800 mV or the current density reaches 10 mA / cm 2 at a scanning rate of 1 mV / s. The standard is based on ASTM G61-86 (2018). The key parameters are set as follows: temperature 25±1°C, solution pH 6.5-7.5, IR automatic compensation, reference electrode calibrated with a standard buffer solution before each test, test area 1 cm 2Tafel extrapolation method in the linear range of ±100 mV from the corrosion potential to fit the corrosion current density icorr, and the pitting potential Epit is defined as the current density increases to 100 μA / cm 2 Corresponding potential, each group of test 3 parallel samples, calculate the mean ± standard deviation, the corrosion current density is less than 1 x 10 -5 A / cm 2 And the pitting potential is higher than +200 mV (SCE).

[0054] Fatigue performance test: the test object is a hard alloy wear-resistant steel ball fatigue sample (waist drum shape, minimum diameter 10 mm, gauge length 16 mm) prepared according to the standard size, the test purpose is to evaluate the fatigue strength and fatigue life of the material under alternating load, simulating the cyclic impact working condition in the grinding process. The test principle is based on the material fatigue damage accumulation theory, by applying periodic alternating stress until the sample breaks, the fatigue life is counted. The experimental method adopts QBG-100 high frequency fatigue testing machine, the sample is machined from the steel ball body along the rolling direction, the surface is precisely turned and polished to Ra≤0.4 μm, stress relief treatment is carried out, first monotonic tensile test is carried out to determine the yield strength σ0.2, then fatigue test is carried out under symmetric cyclic load with stress ratio R=-1, frequency 100 Hz, at the same time, infrared temperature measuring instrument is used to monitor the sample surface temperature to ensure that the temperature rise is ≤10 ℃, the fatigue life is tested at 80%, 70%, 60%, 50%, 40% stress level of yield strength, the failure criterion is sample fracture or cycle number reaches 10 7 times without fracture. The key parameters are set as test frequency 100 Hz, stress ratio R=-1, test environment room temperature 23±5 ℃, at least 5 samples are tested for each stress level, for 10 7 times without fracture, the sample is marked as run-out data. When processing data, Basquin equation σ=σf'(2N)^b is used to fit S-N curve, the fatigue strength of 10 7 times and its 95% confidence interval are calculated, SEM fracture analysis is carried out on the fractured sample to determine the crack source, the influence of inclusions and precipitated phase on fatigue performance is counted, and the control steel ball without microalloying treatment is tested to calculate the fatigue strength improvement percentage.

[0055] From Table 1, it can be seen that Comparative Example 1 and Comparative Example 2 respectively lack vanadium content and titanium content, resulting in the absence of key elements in the V-Ti-C-N microalloy system, a significant reduction in the formation of hard precipitates such as vanadium nitride, titanium nitride, vanadium carbonitride, titanium carbonitride, and a weakening of the dispersion strengthening effect, which is manifested as a decrease in hardness, a decrease in wear resistance, and a decrease in the increase in fatigue strength. Comparative Example 3 has a nitrogen content of only 20 ppm, which is too low to provide sufficient nitrogen source for the precipitation of nitride phases, and the core-shell structure is not fully developed, especially the gradient self-passivating shell layer of chromium carbonitride, which directly affects the corrosion resistance of the material. Comparative Examples 4, 5, and 12 have excessively low melting temperature, tapping temperature, and pouring temperature, resulting in incomplete dissolution of alloying elements, poor fluidity of the molten steel, and poor filling, resulting in coarse and uneven matrix structure and overall performance decline. Comparative Examples 6 and 7 have excessively low austenitizing temperature and tempering temperature, respectively, resulting in insufficient heat treatment, uneven matrix structure, and excessive residual stress, affecting the strength and toughness balance of the material. Comparative Example 8 has an excessively high aluminum content, forming aluminum oxide inclusions, and Comparative Example 10 has an excessively high sulfur content, forming sulfide inclusions, which become stress concentration sources and severely deteriorate the fatigue performance and impact toughness. Comparative Example 9 has an excessively high bubbling pressure, resulting in uneven nitrogen distribution, and Comparative Example 11 has an insufficient argon stirring time, resulting in composition segregation, both of which affect the full play of the microalloying effect. Comparative Example 13 has an excessively low quenching agent concentration, resulting in insufficient cooling speed, low quenching hardness, and overall mechanical property decline. Comparative Example 14 has insufficient vanadium-iron purity, introducing more impurities and affecting the purity and effect of microalloying reactions. Comparative Example 15 completely lacks titanium elements, which cannot establish a complete V-Ti-C-N four-element microalloy system, can only form a V-C-N three-element system, lacks the synergistic effect of titanium and vanadium, and the core-shell precipitate structure is not complete, especially the promotion of titanium to the formation of chromium carbonitride shell layer is lost, resulting in a significant decrease in self-passivating ability. Among all the comparative examples, the performance loss is the most serious, fully proving the irreplaceable role of titanium elements in the microalloy system.

[0056] Table 1 Performance summary of examples and comparative examples

[0057] Based on the experimental verification and theoretical analysis of the system, the rationality, reliability, and effectiveness of the technical scheme of the present application are fully proved. Figure 1 The transmission electron microscope photo clearly shows that the nano-scale precipitates formed in Example 1 have a typical core-shell structure, with the MN / MCN hard core having a hexagonal crystal structure, the size uniformly distributed in the range of 5-20 nm, and the peripheral chromium carbonitride gradient self-passivating shell layer having a thickness of about 2-5 nm, confirming that the V-Ti-C-N microalloy system successfully establishes and forms the designed core-shell precipitate structure. Figure 2XRD phase analysis shows that the steel ball in this example is based on an α-Fe matrix, with strong and clear diffraction peaks. Furthermore, a dispersed strengthening phase dominated by Cr-based carbides / nitrides was detected, including 23Cr6C and minor amounts of CrN / CrN, as well as characteristic peaks of NaCl-type V and Ti carbonitrides (vanadium nitride / titanium nitride and vanadium carbonitride / titanium carbonitride). These results confirm the complex precipitation promoted by the V–Ti–C–N microalloying system and heat treatment, resulting in synergistic strengthening of carbides and nitrides. This provides a physicochemical basis for achieving high hardness, wear resistance, and corrosion resistance under the high-impact and high-wear conditions of wet grinding. Figures 3-5 The results of the single-factor optimization experiment show that the performance optimal points are reached at 0.19% vanadium content, 68ppm total nitrogen content, and 994℃ austenitizing temperature. All optimal parameters are 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 a typical single-peak optimization curve, which proves the scientificity and accuracy of the parameter window setting. Figure 6 The hardness gradient analysis shows that the surface hardness of Examples 1-3 reaches 61.5-62.8HRC while the core hardness remains at 45-48HRC, forming an ideal surface-hard and core-tough structure. However, the control examples have unreasonable hardness gradients or low overall hardness due to deviations in key parameters, which verifies the key role of process parameter control in the present invention. Figure 7 and Figure 8 The comprehensive performance comparison results show that the relative wear resistance index of the embodiment reaches 165-175, and the fatigue strength is improved by 28-34%, which are 30-40% and 40-60% higher than the control example, respectively. The performance advantages are significant and reproducible, 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 the present 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 application.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that any equivalent structural transformations made within the scope of the present invention using the contents of the present invention's description and drawings should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a hard alloy wear-resistant steel ball suitable for mining grinding, characterized in that The following steps are involved: Step S1: Raw material preparation and ingredient calculation, using scrap steel and pig iron. The alloy raw materials include high-carbon ferrochrome, graphitized carburizer, ferrosilicon, ferromanganese, ferronickel, ferromolybdenum, electrolytic copper, ferrovanadium, ferrotitanium, iron nitride powder, and commercially 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. Step S2: Melting and microalloying, heating the molten steel in a medium frequency induction furnace to make it clear, adding alloying elements in sequence and proportioning, performing final deoxidation by adding industrial pure aluminum, and adding ferrovanadium, ferrotitanium, or a combination of ferrovanadium and ferrotitanium in batches into the ladle to establish a V-Ti-CN microalloy system and form a precipitate phase precursor with MN / MCN as the hard core; Step S3: Controlled nitrogen introduction and purification: Controlled nitrogen introduction is performed under the condition that the oxygen content of the molten steel is ≤30 ppm, using a solid nitrogen introduction method or a gas nitrogen introduction method. The total nitrogen content after nitrogen introduction is controlled at 40-80 ppm to improve the V-Ti-CN microalloy system and promote the formation of the MN / MCN hard core; Step S4: pouring and solidifying, setting a filter for filtering, and adopting bottom pouring method; Step S5: heat treatment, including austenitization, quenching and tempering, through which the chromium carbonitride gradient self-passivation shell forms a core-shell precipitation phase structure on the surface of the MN / MCN hard core.

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

3. The method for preparing a hard alloy wear-resistant steel ball suitable for mining grinding according to claim 1, characterized in that: The smelting process parameters in step S2 are: heating to 1600-1620°C to make the molten steel clear, stirring with argon for 1-3 minutes, controlling the tapping temperature at 1530-1560°C, adding 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 hard alloy wear-resistant steel ball suitable for mining grinding according to claim 1, characterized in that: The nitrogen introduction process parameters in step S3 are: adding 10-20 g / t of iron nitride powder in the solid nitrogen introduction method or bubbling pressure of 0.015-0.025 MPa and bubbling time of 90-120 s in the gas nitrogen introduction method, and the total nitrogen content after nitrogen introduction is controlled at 40-80 ppm.

5. The method for preparing a hard alloy wear-resistant steel ball suitable for mining grinding according to claim 1, characterized in that: The pouring parameters in step S4 are as follows: setting a foam ceramic filter, preheating the sand mold or metal mold to 200-300°C, and controlling the pouring temperature at 1480-1520°C.

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

7. A hard alloy wear-resistant steel ball suitable for mining grinding obtained by the preparation method according to any one of claims 1 to 6, 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%, the total nitrogen content is 40-80 ppm, and the balance is iron and unavoidable impurities. The steel ball has a core-shell precipitation phase microstructure formed by a V-Ti-CN microalloy system, and the core-shell precipitation phase includes a hard core mainly composed of MN / MCN and a gradient self-passivation shell mainly composed of chromium carbonitride.

8. The hard alloy wear-resistant steel ball suitable for mining grinding according to claim 1, characterized in that: The surface hardness is HRC 60-63, the core hardness is HRC 54-58, the core-shell precipitation phase microstructure of the cemented carbide wear-resistant steel ball is dispersed in the steel ball, 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.

9. The hard alloy wear-resistant steel ball suitable for mining grinding according to claim 1, characterized in that: In the core-shell precipitated phase microstructure, the MN / MCN hard core is mainly 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 mainly composed of dichromium nitrogen, chromium nitride, and twenty-three chromium hexacarbon, with a mass fraction of 0.08-0.25%.

10. Use of the hard alloy wear-resistant steel ball according to any one of claims 7 to 9 in wet grinding operations in mines, characterized in that: The steel balls can maintain excellent wear resistance and corrosion resistance under high impact and high wear conditions of wet grinding.

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