Wear-resistant alloy dual-phase steel lining plate for semi-autogenous mill and manufacturing method of wear-resistant alloy dual-phase steel lining plate

Abstract

The invention belongs to the technical field of metal wear-resistant materials, and particularly relates to a wear-resistant alloy dual-phase steel lining plate for a semi-autogenous mill and a manufacturing method of the wear-resistant alloy dual-phase steel lining plate. Alloy components are optimized, air cooling and fog cooling are matched with a phase change window in a precise temperature control mode, and it is guaranteed that the bainite-martensite double-phase proportion is uniform; the rare earth core-spun yarn is used for feeding, burning loss is inhibited, uniform distribution is promoted, and the purification and refining effects are maximized; a high-intensity magnetic field is adopted for promoting nucleation, a low-intensity magnetic field is adopted for conducting growth, the double-phase structure steel lining plate with 45%-55% of lath-shaped bainite, 40%-50% of acicular martensite and 3%-5% of retained austenite is manufactured, the hardness of the double-phase structure steel lining plate reaches HRC50-55, the tensile strength is 1520-1530 MPa, the impact toughness is good, the wear rate is low, the interface bonding strength is larger than or equal to 850 MPa, and the double-phase structure steel lining plate has high reliability and durability in the high-stress and high-wear environment.

Description

Technical Field

[0001] This invention belongs to the field of metal wear-resistant materials technology, specifically relating to a wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill and its manufacturing method. Background Technology

[0002] Semi-autogenous grinding mills are widely used grinding equipment in industries such as mining, cement, and chemicals. During operation, the ore and steel balls inside the mill exert strong impacts, abrasion, and corrosion on the mill cylinder. Ordinary cylinder materials cannot withstand this harsh working environment and are prone to wear, deformation, or even damage, leading to mill malfunction. Liners are installed on the inner wall of the mill cylinder to protect it. Furthermore, properly designed and manufactured liners can optimize the movement trajectory of the grinding media, enhance grinding efficiency, and improve the mill's production capacity and product quality. Therefore, to improve the overall performance of a semi-autogenous grinding mill, suitable liners need to be manufactured.

[0003] Currently, the lifespan of semi-autogenous mill liners on the market is generally 3-5 months, requiring frequent replacement of the cylinder. This not only increases the purchase cost of the equipment but also causes production interruptions due to equipment downtime for maintenance, resulting in significant economic losses. Manufacturing durable and efficient liners can extend their lifespan, reduce replacement frequency, lower equipment maintenance costs and downtime, thereby improving the economic efficiency of enterprises.

[0004] Martensite, due to its extremely high hardness and strength, can significantly improve the wear resistance of materials. While bainite is slightly less hard than martensite, it still possesses high strength. Furthermore, bainite's high toughness effectively absorbs impact energy and prevents crack propagation. This high toughness allows the material to exhibit excellent crack resistance under high stress and impact loads. By rationally controlling the ratio of bainite to martensite, a balance between hardness and toughness can be achieved, enabling the material to exhibit excellent comprehensive performance under complex working conditions. In recent years, bainitic-martensitic dual-phase steels have become a research hotspot. However, existing technologies still have the following problems: Traditional processes control bainite transformation through a single cooling rate, which struggles to precisely match the dual-stage requirements of nucleation and growth. This results in low aspect ratios and poor parallel alignment of lath bainite, limiting its impact resistance. Insufficient interfacial bonding between bainite and martensite makes it prone to crack initiation under impact loads, leading to premature liner failure. Furthermore, the significant differences in cooling rates across different parts of the workpiece during quenching cause microstructure inhomogeneity. The lack of active means to control atomic diffusion leads to random precipitation of carbides between bainite laths, weakening interlaminar bonding. Existing technologies extend the bainite transformation window by increasing Cr and Mo content (>3%), but this increases costs and can lead to coarse as-cast microstructure. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a wear-resistant alloy duplex steel liner for semi-autogenous grinding mills and its manufacturing method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention proposes a wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill. The chemical composition, by mass percentage, includes: C: 0.35%-0.5%, Si: 0.8%-1.2%, Mn: 0.2%-0.6%, Cr: 1.8%-2.5%, Mo: 0.2%-0.6%, Cu: 0.3%-0.6%, RE: 0.2%-0.4%, Ti: 0.03%-0.05%, Nb: 0.02%-0.03%, B: 0.002%-0.005%, with the balance being Fe and unavoidable impurities.

[0007] The microstructure of the wear-resistant alloy duplex steel liner for a semi-autogenous mill consists of 45%-55% lath bainite, 40%-50% acicular martensite and 3%-5% retained austenite; the lath bainite has an aspect ratio ≥15:1 and a parallel arrangement ≥85%.

[0008] The functions of each element and the basis for their selection are as follows: C: Carbon is the most basic strengthening element in steel, which can improve the hardness and strength of steel. However, excessive carbon content will reduce the toughness of steel. This invention controls the carbon content at 0.35%-0.5%, balancing hardness and toughness.

[0009] Silicon (Si): Silicon can strengthen ferrite through solid solution, improving the strength and hardness of steel. It also inhibits the precipitation of carbides during the bainite transformation process and promotes the formation of lath bainite. However, excessive silicon content can lead to a decrease in the weldability of steel; therefore, it is controlled within the range of 0.8%-1.2%.

[0010] Mn: Manganese can improve the hardenability of steel and promote the formation of bainite and martensite. However, excessive manganese content will lead to coarse grains and reduced toughness, so it should be controlled at 0.2%-0.6%.

[0011] Cr: Chromium significantly improves the hardenability and wear resistance of steel, while also delaying pearlite formation and expanding the bainite transformation zone during the bainite transformation process. This invention controls the chromium content at 1.8%-2.5%, which, in synergy with a magnetic field, prolongs the bainite transformation time and inhibits pearlite formation.

[0012] Mo: Molybdenum can further improve the hardenability of steel, refine grains, and reduce the activation energy of bainite nucleation. This effect of molybdenum is even more pronounced under the influence of a magnetic field, which can further reduce the activation energy of bainite nucleation by 15%. Excessive molybdenum content increases costs, so it is controlled at 0.2%-0.6%.

[0013] Cu: strengthens ferrite, does not form carbides, expands the γ region; improves corrosion resistance (including cavitation resistance); shifts the isothermal transformation diagram of austenite to the right, improving hardenability; lowers the Ms point; does not change temper brittleness, content should be controlled at 0.3%-0.6%.

[0014] Rare earth elements (RE): Rare earth elements can purify grain boundaries, refine grains, and improve the toughness and fatigue resistance of steel. This invention uses a composite rare earth element of La and Ce (La:Ce=2:1), with the content controlled at 0.2%-0.4%. Under the action of a magnetic field, the segregation effect of rare earth elements at grain boundaries is enhanced (concentration increased by 40%), further refining austenite grains to ≤30μm, providing more grain boundary nucleation sites for the directional growth of bainite laths.

[0015] Ti and Nb: Titanium and niobium can form fine carbonitrides, which prevent austenite grains from growing at high temperatures, refine the grains, and improve the strength and toughness of the steel. In this invention, the titanium content is controlled at 0.03%-0.05%, and the niobium content is controlled at 0.02%-0.03%.

[0016] B: Boron can significantly improve the hardenability of steel. Even trace amounts of boron (0.002%-0.005%) can segregate at grain boundaries, reducing the bainite nucleation work and promoting bainite nucleation. Under the influence of a magnetic field, the distribution of boron becomes more uniform (segregation ≤10%), further increasing the bainite nucleation density.

[0017] This invention also proposes a method for manufacturing the aforementioned wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill, specifically including the following steps: (1) Molding: The V-method molding process is adopted, and a 0.12-0.15mm thick polyethylene film is used for heating riser feeding. The riser neck diameter is 1.3-1.6 times the casting wall thickness; Utilizing the principle of vacuum sealing, a vacuum is created to ensure the plastic film covering the sand mold adheres tightly to the sand grains, forming a compact sand mold. The polyethylene film acts as an isolation and sealant. The heating riser generates heat during pouring, compensating for the volume shrinkage of the casting and preventing defects such as shrinkage cavities and porosity. The riser neck diameter is 1.3-1.6 times the casting wall thickness to ensure effective feeding. If the riser neck diameter is too small, the feeding capacity is insufficient; if it is too large, it increases the riser volume, wasting material and hindering operation.

[0018] (2) Smelting: The medium-frequency furnace is heated to 1660-1680℃, and pig iron, scrap steel and alloy materials are added for melting; composite purifying agent is added at 1600-1620℃; then ferrosilicon pre-deoxidation and aluminum wire final deoxidation are used, and after stirring for 15 minutes, the slag is removed, controlling the oxygen content ≤12ppm and the sulfur content ≤0.008%; then heating is stopped, the furnace temperature is lowered to 1520-1550℃, rare earth cored wire and Ti-Nb-B composite compression block are added, and argon is blown and stirred: 1.0-1.2m 3 / h, ≥10 minutes; The medium-frequency furnace rapidly melts pig iron, scrap steel, and alloy materials through induction heating to reach the required smelting temperature. The composite purifying agent reacts with impurities in the molten steel at high temperatures to form a slag phase. Stirring allows the impurities to float to the surface, and slag removal removes them, improving the purity of the molten steel. Pre-deoxidation of ferrosilicon and final deoxidation of aluminum wire are to remove oxygen from the molten steel, preventing oxygen from combining with alloying elements to form oxide inclusions that affect the steel's performance. The cored wire uses a low-carbon steel strip as its outer shell, encapsulating rare earth powder within. When fed into the molten steel, the outer shell melts first, and the rare earth powder is slowly released in an inert atmosphere (argon stirring environment), avoiding direct exposure to a high-temperature oxidizing atmosphere and increasing the rare earth utilization rate to over 80%.

[0019] (3) Casting: Bottom pouring ladle casting, pouring temperature 1530-1540℃, argon blowing inside the ladle: 0.3-0.5m³ / h, heat insulation agent is low carbon graphite and Al2O3; (4) Magnetic field-assisted targeted heat treatment: S1 diffusion annealing: Cool the furnace to 1020-1050℃ and hold for 3-4 hours; S2 segmented quenching: Austenitizing: Cool the furnace to 920-950℃ and hold for 2-2.5 hours; Bainite transformation: air cool to 600-650℃ at a cooling rate of 50-80℃ / s, then mist cool to 400-450℃ at a cooling rate of 15-20℃ / s, and hold at 400-450℃ isothermally for 5-10 minutes while applying a low-frequency alternating magnetic field. Martensitic transformation: oil cooling to 150-200℃, cooling rate 25-30℃ / s; S3 Low-temperature tempering: Hold at 200-250℃ for 1.5-2 hours, then air cool to room temperature.

[0020] The theoretical basis of diffusion annealing is the principle of solid-state diffusion. At high temperatures, the diffusion rate of alloying elements (such as Cr and Mo) in steel increases. Heating at this temperature allows for a more uniform distribution of these elements, reducing segregation. The austenitizing process is based on the principle of phase transformation. Heating the steel to the austenitic phase region (920-950℃) completely austenitizes it, preparing it for subsequent phase transformations. The selection of the austenitizing temperature is based on the iron-carbon phase diagram and the influence of alloying elements. The bainitic transformation process is based on the principle of non-diffusional phase transformation. By controlling the cooling rate (air cooling to 600-650℃, mist cooling to 400-450℃), the steel undergoes a bainitic transformation at 600-650℃, forming lath bainite. During the mist cooling stage, the water mist flow rate and air pressure control the cooling rate at 15-20℃ / s to avoid pearlite formation and ensure bainite formation. The martensitic transformation process is also based on the principle of non-diffusional phase transformation. Oil cooling to 150-200℃ induces a martensitic transformation in the steel, forming acicular martensite. The selection of the martensitic transformation temperature is based on the critical cooling rate of the steel and the influence of alloying elements; the theoretical basis of low-temperature tempering is the phase transformation and stress relaxation principle during the tempering process. Holding at 200-250℃ for 1.5-2 hours can eliminate quenching stress, stabilize the microstructure, and improve the toughness and wear resistance of the steel. The selection of the tempering temperature is based on the tempering stability curve of the steel and the influence of alloying elements.

[0021] Preferably, in a method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous mill, the furnace cooling refers to controlling the cooling rate to 10-15℃ / min by finely adjusting the power of the medium-frequency furnace.

[0022] Preferably, in a method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill, The composite purifying agent used in the smelting process (2) is a silicon-aluminum-calcium ternary alloy, with an addition amount of 6‰-8‰ of the total weight of the molten steel. It is formed into regular particles with a diameter of 10-50mm through high-pressure forming technology. It can form low-melting-point compounds (CaO-Al2O3-SiO2 system) with oxygen and sulfur, of which silicon ≥20%, aluminum ≥7%, and calcium ≥15%. The amount of ferrosilicon added in the pre-deoxidation of ferrosilicon is 0.4%-0.6% of the total weight of the molten steel; The amount of aluminum wire added in the final deoxidation of the aluminum wire is 0.15%-0.25% of the total weight of the molten steel; The rare earth cored wire is formed by wrapping rare earth oxides (RE) in steel, wherein the RE is a mixture of La and Ce in a mass ratio of 2:1. It is fed into the smelting induction furnace at a feeding speed of 2.5-3 m / min. The feeding speed (2.5-3 m / min) is synchronized with the stirring of the molten steel (argon flow rate 1.0-1.2 m). 3 ( / h) synergistic effect, rare earth powder diffuses evenly with the airflow, ensuring that the number of rare earth inclusions in each cubic centimeter of molten steel is ≥10. 5 Number of samples, with a standard deviation of ≤15%; The Ti-Nb-B composite compression block is obtained by compressing Ti-Nb-B alloy material according to the amount of Ti, Nb and B added in the chemical composition of the aforementioned wear-resistant alloy duplex steel liner for a semi-autogenous mill, and then drying it by heating at >300℃.

[0023] Preferably, in a method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous mill, the mass ratio of low-carbon graphite to Al2O3 insulation agent in the casting process (3) is 7:3.

[0024] Preferably, in a method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous mill, in the bainitic transformation stage of the magnetic field-assisted targeted heat treatment in (4), the water mist flow rate is 0.5-1.0 L / h and the air pressure is 0.3-0.5 MPa in the mist cooling stage.

[0025] Air cooling stage (600-650℃, 5-8 seconds): The cooling rate is relatively fast (about 50-80℃ / s), serving only as a "transitional cooling" to rapidly reduce the temperature from the austenitizing temperature (920-950℃) to the "preparatory temperature zone" (600-650℃) for bainite transformation. This avoids prolonged exposure to the high-temperature zone (>650℃) which could lead to pearlite nucleation (the pearlite nose temperature is about 550℃; excessively rapid cooling will skip this zone). Fogging stage (400-450℃, 15-20℃ / s): The cooling rate is moderate and precisely controllable, falling precisely within the critical cooling rate range for bainite transformation—faster than the critical rate for pearlite transformation (<12℃ / s), preventing pearlite formation; and slower than the critical rate for martensite transformation (>25℃ / s), allowing time for bainite nucleation and growth. Meanwhile, air cooling relies on natural air convection, resulting in a small temperature difference between the surface and core of thick parts (≤20℃), thus avoiding localized overcooling; mist cooling, through the spraying of a mixture of water mist and air, achieves high cooling uniformity.

[0026] Preferably, in a method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous mill, a low-frequency alternating magnetic field is applied during the bainitic transformation stage of the magnetic field-assisted targeted heat treatment in step (4). For the first 0-3 minutes: a strong magnetic field of 0.4T with a frequency of 50-100Hz; for the 3rd-10th minutes: the magnetic field is reduced to a weak magnetic field of 0.2T with a frequency of 50-100Hz. The magnetic field device used in the magnetic field-assisted targeted heat treatment includes: two sets of symmetrical Helmholtz coils with an inner diameter of 2-3 times the maximum size of the workpiece and a controller with a frequency of 50-100Hz that can output a low-frequency alternating magnetic field of 0.2-0.4T. Each coil has ≥20 turns and is made of pure copper.

[0027] The Lorentz force generated by a low-frequency alternating magnetic field (50-100Hz) can accelerate charged particles (such as carbon) in steel. 4+ 、Fe 2+The directional migration of carbon atoms increases the enrichment rate of carbon atoms at austenite grain boundaries by 30%, rapidly enriching them to form a "carbon pool" that provides ample carbon source for bainite nucleation, increasing nucleation density by 40%-50%. The crystal structure of bainitic ferrite is body-centered cubic (BCC), consistent with ferrite, with a Curie point close to 770℃. Therefore, it exhibits distinct ferromagnetism at 400-450℃. The easy magnetization direction of bainitic ferrite aligns with the long axis of the laths. Under a 0.2T magnetic field, the laths spontaneously adjust their orientation, reducing crossing and twisting, and increasing parallelism by 5%-10%. Simultaneously, the magnetic field suppresses disordered precipitation of carbides between laths, promoting uniform distribution along the long axis and enhancing inter-laminar bonding. Precise control of "strong magnetic field promoting nucleation - weak magnetic field guiding growth" is achieved through stepped magnetic field strength (0.4T→0.2T). Compared to a constant magnetic field, the length-to-diameter ratio of the slab is improved, and the problem of "less bainite at the edges and corners and more bainite in the core" in traditional processes is solved, so that the difference in the proportion of bainite in the core and edges of the workpiece is ≤±1.5%.

[0028] The beneficial effects of this invention are: 1. This invention optimizes the alloy composition by adding appropriate amounts of elements such as Cr, Mo, and Ti, and precisely controls the heat treatment process. Air cooling and mist cooling are used to precisely match the phase transformation window, ensuring the bainite-martensite dual-phase ratio and uniformity. Rare earth cored wire is used to suppress burn-off and promote uniform distribution, maximizing the purification and refining effect of rare earth elements and providing a high-quality matrix for high-performance microstructure. Furthermore, precise control of strong magnetic field-induced nucleation and weak magnetic field-guided growth achieves a dual-phase microstructure of 45%-55% lath bainite, 40%-50% acicular martensite, and 3%-5% retained austenite, resulting in a liner hardness of HRC50-55. This ensures the reliability and durability of the liner under high stress and high wear environments.

[0029] 2. This invention controls the ratio and properties of the bainite + martensite dual-phase microstructure. Lathar bainite accumulates at the lath interface through high-density dislocation accumulation, generating a Koch pinning effect. Residual austenite between laths absorbs crack energy through the TRIP effect (transformation-induced plasticity). Under load, the hard phase martensite (hardness approximately 580 HV) bears the main stress, while the soft phase bainite (hardness approximately 450 HV) coordinates the stress through plastic deformation. The interfacial bonding strength ≥850 MPa ensures effective load transfer. This achieves a balance between high strength and good toughness. Simultaneously, it exhibits good impact toughness, and the liner demonstrates excellent crack resistance and impact resistance under complex working conditions. Attached Figure Description

[0030] Figure 1 This is a metallographic image of the duplex steel liner prepared in Example 2 of the present invention at magnification of 1000. Figure 2This is a metallographic image of the duplex steel liner prepared in Example 2 of the present invention at magnification of 10,000. Figure 3 This is the metallographic structure of the alloy steel liner plate, which is widely used in the market today, in Comparative Example 4, at 1000x magnification. Figure 4 This is the metallographic structure of the alloy steel liner plate, which is widely used in the market today, in Comparative Example 4, magnified at 5000x. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0032] Example 1: Composition (wt%): C: 0.38%, Si: 0.9%, Mn: 1.1%, Cr: 1.9%, Mo: 0.2%, Cu: 0.4%, RE (La:Ce=2:1): 0.25%, Ti: 0.035%, Nb: 0.022%, B: 0.003%, balance Fe.

[0033] Preparation steps: (1) Molding: V-shaped molding, with a 0.13mm thick polyethylene film, and the riser neck diameter is 1.4 times the casting wall thickness.

[0034] (2) Smelting: The medium-frequency furnace is heated to 1670℃ to melt the raw materials. At 1610℃, 6.5‰ of the total weight of the molten steel is added as a CaO-Al2O3-SiO2 composite purifying agent. After stirring for 15 minutes, the slag is removed. 0.45% ferrosilicon is used for pre-deoxidation and 0.18% aluminum wire is used for final deoxidation. The oxygen content is controlled to be ≤12ppm and the sulfur content is controlled to be ≤0.008%. Heating is stopped, and the temperature is reduced to 1530℃ at 12℃ / min. Rare earth cored wire (feeding speed 2.6m / min) and Ti-Nb-B composite compression block are added. Argon is blown and stirred (1.1m). 3 / h) 11 minutes.

[0035] (3) Casting: Bottom-pouring ladle casting, pouring temperature 1535℃, argon blowing 0.4m inside the ladle. 3 / h, the insulation agent is low carbon graphite and Al2O3 (mass ratio 7:3).

[0036] (4) Magnetic field-assisted targeted heat treatment: S1 diffusion annealing: cooling to 1030℃ at a rate of 12℃ / min and holding for 3.2h; S2 segmented quenching: cooling to 930℃ at 12℃ / min and holding for 2.2h for austenitization; air cooling to 620℃ (6 seconds), then mist cooling to 420℃ (water mist flow rate 0.6L / h, air pressure 0.35MPa, cooling rate 16℃ / s), isothermal at 420℃ for 7 minutes (0.4T / 60Hz for the first 3 minutes, 0.2T / 60Hz for the last 4 minutes); oil cooling to 170℃ (cooling rate 27℃ / s). S3 Low-temperature tempering: Hold at 220℃ for 1.6 hours, then air cool to room temperature.

[0037] Example 2: Composition (wt%): C: 0.42%, Si: 1.0%, Mn: 1.3%, Cr: 2.2%, Mo: 0.4%, Cu: 0.5%, RE (La:Ce=2:1): 0.3%, Ti: 0.04%, Nb: 0.025%, B: 0.004%, balance Fe.

[0038] Preparation steps: (1) Molding: V-shaped molding, with a 0.14mm thick polyethylene film, and the riser neck diameter is 1.5 times the casting wall thickness.

[0039] (2) Smelting: The medium-frequency furnace is heated to 1670℃ to melt the raw materials. At 1610℃, 7‰ of the total weight of the molten steel is added as a CaO-Al2O3-SiO2 composite purifying agent. After stirring for 15 minutes, the slag is removed. 0.5% ferrosilicon is used for pre-deoxidation and 0.2% aluminum wire is used for final deoxidation. The oxygen content is controlled to be ≤12ppm and the sulfur content is controlled to be ≤0.008%. Heating is stopped, and the temperature is reduced to 1535℃ at 13℃ / min. Rare earth cored wire (feeding speed 2.8m / min) and Ti-Nb-B composite compression block are added. Argon is blown and stirred (1.1m). 3 / h) 12 minutes.

[0040] (3) Casting: Bottom-pouring ladle casting, pouring temperature 1535℃, argon blowing 0.4m inside the ladle. 3 / h, the insulation agent is low carbon graphite and Al2O3 (mass ratio 7:3).

[0041] (4) Magnetic field-assisted targeted heat treatment: S1 diffusion annealing: cooling to 1035℃ at 13℃ / min and holding for 3.5h; S2 segmented quenching: cooling to 935℃ at 13℃ / min and holding for 2.3h for austenitization; air cooling to 630℃ (7 seconds), then mist cooling to 430℃ (water mist flow rate 0.7L / h, air pressure 0.4MPa, cooling rate 18℃ / s), isothermal at 430℃ for 8 minutes (0.4T / 80Hz for the first 3 minutes, 0.2T / 80Hz for the last 5 minutes); oil cooling to 180℃ (cooling rate 28℃ / s). S3 Low-temperature tempering: Hold at 230℃ for 1.7 hours, then air cool to room temperature.

[0042] Metallographic images of the duplex steel liner prepared in Example 2 of this invention at different magnifications are shown below. Figure 1 As shown, it exhibits a dual-phase microstructure with uniformly distributed lath bainite and acicular martensite.

[0043] Example 3: Composition (wt%): C: 0.48%, Si: 1.1%, Mn: 1.4%, Cr: 2.4%, Mo: 0.6%, Cu: 0.5%, RE (La:Ce=2:1): 0.35%, Ti: 0.045%, Nb: 0.028%, B: 0.004%, balance Fe.

[0044] Preparation steps: (1) Molding: V-shaped molding, with a 0.14mm thick polyethylene film, and the riser neck diameter is 1.5 times the casting wall thickness.

[0045] (2) Smelting: The medium-frequency furnace is heated to 1680℃ to melt the raw materials. At 1620℃, 7.5‰ of the total weight of the molten steel is added as a CaO-Al2O3-SiO2 composite purifying agent. After stirring for 15 minutes, the slag is removed. 0.55% ferrosilicon is used for pre-deoxidation and 0.22% aluminum wire is used for final deoxidation. The oxygen content is controlled to be ≤12ppm and the sulfur content is controlled to be ≤0.008%. Heating is stopped, and the temperature is reduced to 1540℃ at 14℃ / min. Rare earth cored wire (feeding speed 2.9m / min) and Ti-Nb-B composite compression block are added. Argon is blown and stirred (1.15m). 3 / h) 12 minutes.

[0046] (3) Casting: Bottom-pouring ladle casting, pouring temperature 1538℃, argon blowing 0.45m inside the ladle. 3 / h, the insulation agent is low carbon graphite and Al2O3 (mass ratio 7:3).

[0047] (4) Magnetic field-assisted targeted heat treatment: S1 diffusion annealing: cooling to 1040℃ at 14℃ / min and holding for 3.8h; S2 segmented quenching: cooling to 940℃ at 14℃ / min and holding for 2.4h for austenitization; air cooling to 640℃ (7 seconds), then mist cooling to 440℃ (water mist flow rate 0.9L / h, air pressure 0.45MPa, cooling rate 19℃ / s), isothermal at 440℃ for 9 minutes (0.4T / 90Hz for the first 3 minutes, 0.2T / 90Hz for the next 6 minutes); oil cooling to 190℃ (cooling rate 29℃ / s). S3 Low-temperature tempering: Hold at 240℃ for 1.9 hours, then air cool to room temperature.

[0048] Comparative Example 1: The composition is the same as in Example 2, except that a low-frequency alternating magnetic field is not applied during the bainitic transformation stage, and the rest of the preparation steps are the same.

[0049] Comparative Example 2: The composition is the same as in Example 2, except that the rare earth cored wire is replaced with an equal amount of blocky rare earth directly added during smelting, and the rest of the preparation steps are the same.

[0050] Comparative Example 3: The composition is the same as in Example 2, but the cooling method during the bainite transformation stage is changed to "oil cooling to 620°C → water cooling to 430°C", and the rest of the preparation steps are the same.

[0051] Comparative Example 4: As a widely used alloy steel liner in today's market, its surface metallographic structure is as follows Figure 3 and Figure 4 As shown, its metallographic structure is pearlite + tempered sorbite.

[0052] Performance testing: 1. Bainite / martensite ratio, aspect ratio, and arrangement Test methods: Observation was performed using a metallurgical microscope (OM) and a scanning electron microscope (SEM, such as ZEISS Sigma300).

[0053] step: The sample size was 10mm×10mm×5mm, and after grinding and polishing, it was etched with 4% nitric acid alcohol solution; The area ratio of each phase (bainite / martensite / retained austenite) was statistically analyzed using Image-ProPlus image analysis software. Measure the major and minor axis dimensions of more than 50 bainitic laths and calculate the length-to-diameter ratio; Calculate the angle between the axial direction of the slats and the direction of the magnetic field, and determine the degree of parallelism (the percentage of slats with an angle ≤ 15°).

[0054] 2. Residual austenite content Test method: X-ray diffractometer (XRD, such as Bruker D8 Advance), using Cu-Kα target, scanning range 40°-100°.

[0055] Principle: The volume fraction of retained austenite is calculated by combining the ratio of the diffraction peak intensity of austenite (200), (220), and (311) crystal planes to the peak intensity of ferrite / martensite (200) and (211) crystal planes with Rietveld full spectrum fitting.

[0056] 3. Hardness (HRC) Test method: Rockwell hardness tester (such as HR-150A), according to GB / T230.1-2018 standard.

[0057] Steps: Select 5 points evenly on the surface of the sample (avoiding the edge by 2mm), apply a main load of 150kgf, and take the average value.

[0058] 4. Tensile strength and elongation Test method: Universal testing machine (such as Instron 5982), according to GB / T228.1-2010 standard.

[0059] Specimen: Prepare a circular tensile specimen with a diameter of 10 mm × 50 mm (gauge length 30 mm). Steps: Loading rate 2 mm / min, record the maximum load at fracture (to calculate tensile strength) and the elongation of the gauge length (to calculate elongation).

[0060] 5. Impact toughness (U-notch / unnotch) Test method: Pendulum impact testing machine (such as ZBC 2452), according to GB / T229-2020 standard.

[0061] Samples: U-notched sample dimensions are 10mm×10mm×55mm (notch depth 2mm, radius 1mm), unnotched sample dimensions are the same; Procedure: After keeping the sample at -20℃ for 30 minutes, test and record the impact absorption energy (average of 3 samples).

[0062] 6. Interface bonding strength Test method: Tensile shear test (refer to GB / T6396-2008).

[0063] Sample preparation: Prepare a bainite-martensite interface shear sample (overlap area 10mm×10mm). Steps: Apply shear load using a universal testing machine, record the maximum load during interface separation, and calculate the strength per unit area.

[0064] 7. Machine service life (days) Three liners of the same specification (three for the example and three for the comparative example) were installed in the same compartment of the mill to ensure consistent operating conditions (stable speed, ore flow, etc.). The mill was shut down for inspection every 7 days, and the remaining thickness, weight loss, and damage were recorded. The failure criteria were defined as "remaining thickness reaching 50% of the initial thickness" or "the appearance of critical cracks / sparging," and the cumulative operating time was converted to days (based on actual operating procedures). The average value of the three liners was taken, and the lifespan differences between the groups were compared to verify durability.

[0065] The test results are shown in Table 1.

[0066] Table 1 Performance test results of embodiments and comparative examples of the present invention Data Analysis: 1. Comparing Example 2 with Comparative Example 1, the key role of magnetic field assistance can be observed: Microstructure control: After applying a magnetic field, the aspect ratio of bainite increased from 12:1 to 16:1, and the parallel alignment increased from 72% to 88%. This indicates that the magnetic field achieved directional optimization of bainite through "strong magnetic field promoting nucleation + weak magnetic field guiding growth," solving the problem of disordered bainite arrangement in traditional processes. Figure 1 and Figure 2 As shown; Performance improvements: Tensile strength increased from 1450MPa to 1525MPa, and U-notch impact energy increased from 20J / cm². 2 Increased to 32J / cm 2 The interfacial bonding strength increased from 780 MPa to 860 MPa. The core reason is that the magnetic field-induced directional arrangement of bainite enhanced the tissue's ability to withstand stress and suppressed the disordered precipitation of carbides.

[0067] 2. Comparing Example 2 and Comparative Example 2, the advantages of rare earth cored wires can be observed: Uniformity of structure: When cored wire is used for feeding, the bainite arrangement is increased from 75% to 88%, avoiding local agglomeration caused by blocky rare earth. For example, there is a rare earth enrichment area in Comparative Example 2, while in Example 2, the isolation and protection of the cored wire reduces the loss of rare earth, and the utilization rate is increased from 50% to 80%, achieving uniform distribution.

[0068] Improved toughness: Unnotched impact energy increased from 200 J / cm 2 Increased to 260J / cm 2 This confirms that rare earth elements can purify grain boundaries by reducing oxygen and sulfur content, refining austenite grains from 50μm to 30μm, thereby refining grains and improving toughness.

[0069] 3. Comparing Example 2 and Comparative Example 3, the precise temperature control value of air cooling + mist cooling can be demonstrated: Phase transformation window matching: Air cooling + mist cooling increased the bainite ratio from 42% to 52%, while the oil cooling + water cooling in Comparative Example 3, due to the fluctuation of the cooling rate, exceeded the critical range of bainite, resulting in an excessively high martensite ratio, reaching more than 55%. This shows that the air cooling + mist cooling in Example 2 can stably control the cooling rate of 15-20℃ / s, accurately falling within the bainite transformation range.

[0070] Stress control: Comparative Example 3 experienced a drop in elongation to 2.9% and the appearance of microcracks due to intense cooling. In contrast, the slow cooling and precise mist cooling in Example 2 reduced thermal stress and ensured that the elongation was maintained at 3.6%, verifying the role of this cooling method in ensuring the uniformity of the microstructure of thick parts (60-80mm).

[0071] 4. Parameter coordination rules among implementation examples Composition and performance balance: Example 1 product of low C low alloy has slightly better toughness and elongation of 3.6%; Example 3 product of high C high alloy has higher hardness of HRC54; indicating that the composition can be finely adjusted within the limited range according to the working conditions, and can meet the core indicators of HRC50-54 and tensile strength ≥1520MPa.

[0072] Process stability: The bainite ratio in the three sets of examples was 48%-54% and the retained austenite ratio was 3%-5%, both within the target range. The difference in microstructure between the core and the edges was ≤±1.5%, which proves the stability and repeatability of process parameters such as magnetic field frequency and mist cooling rate.

[0073] This invention achieves precise matching of "composition-process-structure-performance" through a synergistic design of magnetic field assistance, rare earth cored wire, and air-cooled mist cooling: all core properties reach the target range (hardness HRC50-54, tensile strength 1520-1530MPa, impact energy 26-36J / cm). 2 Compared to Comparative Examples 1-4, the key performance indicators have improved by 10%-60%, with significant advantages in toughness and interfacial bonding strength, fully meeting the requirements of semi-autogenous mill liners under high stress and high wear conditions. Its overall performance far surpasses that of the wear-resistant alloy steel liner widely used in the market for Comparative Example 4. Field application has increased its service life from 95 days to over 154 days, an increase of over 60%. The higher wear resistance, longer service life, and better grinding efficiency of this liner make its market benefits considerable.

[0074] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill, characterized in that, The chemical composition, by mass percentage, includes: C: 0.35%-0.5%, Si: 0.8%-1.2%, Mn: 0.2%-0.6%, Cr: 1.8%-2.5%, Mo: 0.2%-0.6%, Cu: 0.3%-0.6%, RE: 0.2%-0.4%, Ti: 0.03%-0.05%, Nb: 0.02%-0.03%, B: 0.002%-0.005%, with the balance being Fe and unavoidable impurities; The microstructure of the wear-resistant alloy duplex steel liner for a semi-autogenous mill consists of 45%-55% lath bainite, 40%-50% acicular martensite and 3%-5% retained austenite; the lath bainite has an aspect ratio ≥15:1 and a parallel arrangement ≥85%.

2. The method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill as described in claim 1, characterized in that, Includes the following steps: (1) Molding: The V-method molding process is adopted, and a 0.12-0.15mm thick polyethylene film is used for heating riser feeding. The riser neck diameter is 1.3-1.6 times the casting wall thickness; (2) Smelting: The medium-frequency furnace is heated to 1660-1680℃, and pig iron, scrap steel and alloy materials are added for melting; composite purifying agent is added at 1600-1620℃; then ferrosilicon pre-deoxidation and aluminum wire final deoxidation are used, and after stirring for 15 minutes, the slag is removed, controlling the oxygen content ≤12ppm and the sulfur content ≤0.008%; then heating is stopped, the furnace temperature is lowered to 1520-1550℃, rare earth cored wire and Ti-Nb-B composite compression block are added, and argon is blown and stirred: 1.0-1.2m 3 / h, ≥10 minutes; (3) Casting: Bottom-pouring ladle casting, pouring temperature 1530-1540℃, argon blowing inside the ladle: 0.3-0.5m 3 / h, the heat preservation agent is low carbon graphite and Al2O3; (4) Magnetic field-assisted targeted heat treatment: S1 diffusion annealing: Cool the furnace to 1020-1050℃ and hold for 3-4 hours; S2 segmented quenching: Austenitizing: Cool the furnace to 920-950℃ and hold for 2-2.5 hours; Bainite transformation: air cool to 600-650℃ at a cooling rate of 50-80℃ / s, then mist cool to 400-450℃ at a cooling rate of 15-20℃ / s, and hold at 400-450℃ isothermally for 5-10 minutes while applying a low-frequency alternating magnetic field. Martensitic transformation: oil cooling to 150-200℃, cooling rate 25-30℃ / s; S3 Low-temperature tempering: Hold at 200-250℃ for 1.5-2 hours, then air cool to room temperature.

3. The method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill according to claim 2, characterized in that, The in-furnace cooling refers to controlling the cooling rate to 10-15℃ / min by finely adjusting the power of the medium-frequency furnace.

4. The method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill according to claim 2, characterized in that, The composite purifying agent used in the smelting process (2) is a silicon-aluminum-calcium ternary alloy, with an addition amount of 6‰-8‰ of the total weight of the molten steel. It is formed into regular particles with a diameter of 10-50mm through high-pressure forming technology, wherein silicon ≥20%, aluminum ≥7%, and calcium ≥15%. The amount of ferrosilicon added in the pre-deoxidation of ferrosilicon is 0.4%-0.6% of the total weight of the molten steel; The amount of aluminum wire added in the final deoxidation of the aluminum wire is 0.15%-0.25% of the total weight of the molten steel; The rare earth cored wire is formed by wrapping RE with steel, wherein RE is a mixture of La:Ce in a mass ratio of 2:1, and is fed into the smelting induction furnace by wire feeding at a wire feeding speed of 2.5-3m / min; The Ti-Nb-B composite compression block is obtained by compressing Ti-Nb-B alloy material according to the amount of Ti, Nb and B added in the chemical composition of claim 1, and then drying it by heating at >300°C.

5. The method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill according to claim 2, characterized in that, The mass ratio of low-carbon graphite to Al2O3 insulation agent in casting (3) is 7:

3.

6. The method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill according to claim 2, characterized in that, In the bainite transformation stage of the magnetic field-assisted targeted heat treatment (4), the water mist flow rate is 0.5-1.0 L / h and the air pressure is 0.3-0.5 MPa.

7. The method for manufacturing a wear-resistant alloy duplex steel liner for a semi-autogenous grinding mill according to claim 2, characterized in that, In the bainitic transformation stage of the magnetic field-assisted targeted heat treatment (4), a low-frequency alternating magnetic field is applied. For the first 0-3 minutes: a strong magnetic field of 0.4T with a frequency of 50-100Hz; for the 3rd-10th minutes: the magnetic field is reduced to a weak magnetic field of 0.2T with a frequency of 50-100Hz. (4) The magnetic field device used in the magnetic field-assisted targeted heat treatment includes: two sets of symmetrical Helmholtz coils with an inner diameter of 2-3 times the maximum size of the workpiece and a controller with a frequency of 50-100Hz that can output a low-frequency alternating magnetic field of 0.2-0.4T; each coil has ≥20 turns and is made of pure copper.

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