High-wear-resistance impact-resistance semi-autogenous mill Cr-Mo alloy steel lining plate and preparation method thereof

Abstract

The invention discloses a high-wear-resistance impact-resistance semi-autogenous mill Cr-Mo alloy steel lining plate and a preparation method. The high-wear-resistance impact-resistance semi-autogenous mill Cr-Mo alloy steel lining plate comprises the following chemical components: 0.2-0.6% of C, 0.5-1.5% of Cr, 0.2-0.5% of Mo, 0.5-1.0% of V, 0.5-1.5% of Ni, 0.5-1.5% of Si, less than or equal to 0.003% of P, less than or equal to 0.005% of S, 1.5-2.0% of Ti and the balance of Fe and inevitable impurities. By controlling the microscopic gradient structure distribution of the Cr-Mo alloy steel lining plate, the hardness, impact toughness, impact wear and other properties of the alloy steel lining plate are remarkably improved, and the lining plate does not deform or break in the using process.

Description

Technical Field

[0001] This invention relates to the field of metal material casting technology, and in particular to a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous grinding mill and its preparation method. Background Technology

[0002] Cr-Mo alloy steel liners are high-hardness alloy steel liners with superior wear resistance unmatched by other materials. However, Cr-Mo steel liners have poor overall stability, and casting defects are prone to occur in the thicker sections during manufacturing. This ultimately leads to the liner breaking under conditions of high-hardness abrasives and high impact stress, thus failing to fully utilize its wear resistance.

[0003] Currently, due to the severe working conditions such as strong impact and abrasive wear that affect the liners of large semi-autogenous grinding mills used in metallurgy and mining, the performance of traditional Cr-Mo steel is no longer able to meet the actual application requirements. Therefore, this application provides a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for semi-autogenous grinding mills and its preparation method to meet the requirements. Summary of the Invention

[0004] This invention addresses the problems of Cr-Mo steel liners being prone to fracture under conditions of high-hardness abrasives and high impact stress, as well as their poor wear resistance, by providing a high-wear-resistant and impact-resistant Cr-Mo alloy steel liner for semi-autogenous grinding mills and its preparation method.

[0005] To achieve the above objectives, this application provides the following technical solution: a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous mill, characterized in that it contains the following chemical components by mass percentage:

[0006] C: 0.2-0.6%, Cr: 0.5-1.5%, Mo: 0.2-0.5%, V: 0.5-1.0%, Ni: 0.5-1.5%, Si: 0.5-1.5%, P: ≤0.003%, S: ≤0.005%, Ti: 1.5-2.0%, with the remainder being Fe and unavoidable impurities.

[0007] A method for preparing a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous grinding mill includes the following steps:

[0008] S1. Smelting: Add each raw material according to the mass percentage, melt, remove slag, and refine to obtain refined molten steel;

[0009] S2. Modification treatment: The refined molten steel is modified to obtain modified molten steel.

[0010] S3. Casting: The modified steel molten material is poured into the mold cavity at the casting temperature, left to stand, the mold is opened, and the mold is cleaned to obtain the precast casting.

[0011] S4. Heat treatment: The precast casting is subjected to normalizing, quenching and tempering operations in sequence. First, the casting is normalized, then quenched to room temperature, and then tempered to obtain the high wear-resistant and impact-resistant semi-autogenous mill Cr-Mo alloy steel liner.

[0012] In a preferred embodiment of this example, during normalizing in step S4, the temperature is first raised to 400-500°C at a rate of 60-100°C / h and held for 6-8 hours. Then, the temperature is raised to 900-950°C at a rate of 60-100°C / h and held for 6-8 hours. Finally, the temperature is cooled to 400-650°C by air.

[0013] After casting, the liner plate is subject to casting stress (caused by uneven cooling of thick sections) and has a coarse structure and compositional segregation. Direct quenching can easily lead to cracking and uneven structure.

[0014] 400-500℃ low temperature heat preservation (stress relief preheating): Under the premise of no structural transformation, heat preservation for 6-8 hours allows the surface layer of the liner and the base layer to have a uniform temperature, releases residual casting stress, and avoids stress superposition during subsequent high temperature heating, which can lead to cracking.

[0015] High-temperature holding at 900-950℃ (complete austenitization): 30-50℃ higher than the Ac3 critical temperature of Cr-Mo steel, ensuring that the coarse pearlite and ferrite in the as-cast state are completely transformed into austenite, while allowing alloying elements such as Cr, Mo, and V to be fully dissolved and eliminating compositional segregation;

[0016] Air cooling to 400-650℃: The cooling rate is between air cooling and water cooling, which can obtain fine and uniform pearlite + ferrite (refining the grains and improving the uniformity of the subsequent quenching structure) while avoiding the generation of new thermal stress due to excessive cooling.

[0017] In a preferred embodiment of this example, during quenching in step S4, the temperature is increased to 600-700℃ at a rate of 60-100℃ / h (after normalizing, the liner temperature drops to 400-650℃; directly increasing the temperature to 850-900℃ can easily cause thermal stress due to the large temperature difference between the surface and the base layer; preheating to 600-700℃ ensures uniform liner temperature, releases residual stress, and reduces the risk of quenching cracking; moreover, this temperature is close to the Ac1 critical temperature (Ac1 for Cr-Mo steel is approximately 720-750℃). Preheating before increasing the temperature to the quenching temperature results in more complete and uniform austenitization, avoiding... (Due to excessively rapid heating leading to microstructure segregation), hold at that temperature for 6-8 hours, then heat at a rate of 60-100℃ / h to 850-900℃ (lower limit 850℃: higher than the Ac3 critical temperature of Cr-Mo steel, ensuring that the as-cast microstructure (pearlite + ferrite) is completely transformed into austenite, and that alloying elements such as Cr, Mo, and V are fully dissolved; upper limit 900℃: to avoid austenite grain growth leading to coarse martensite laths and decreased toughness, while also reducing alloying element burn-off and ensuring compositional stability), hold at that temperature for 6-8 hours, and then perform three-stage water quenching only on the upper outer surface layer of the casting, as detailed below:

[0018] The first stage of uniform water spraying: initial water pressure 1.2-1.8MPa, water flow rate 15-25L / min·m², lasting 12-18min, to reduce the surface temperature of the casting to 600-700℃;

[0019] The purpose of the first stage of uniform water spraying quenching is to form a fine-grained martensite structure on the surface of the alloy liner to ensure wear resistance.

[0020] High water pressure (1.2-1.8MPa) + large flow rate (15-25L / min·m²) achieves a cooling rate of ≥18℃ / min, exceeding the critical cooling rate for martensitic transformation of Cr-Mo steel (approximately 15℃ / min), thus preventing austenite from decomposing into pearlite / bainite and ensuring a martensitic transformation rate of ≥95%. Furthermore, rapid cooling inhibits the coarsening of martensite laths, prevents surface embrittlement, and enhances impact resistance.

[0021] High pressure (1.2-1.8MPa) breaks the surface vapor film (a vapor film easily forms on the surface of high-temperature castings, hindering heat exchange), allowing the cooling rate to quickly exceed the critical value, ensuring that the surface austenite undergoes a "diffusion-free phase transformation" into martensite, avoiding surface softening (pearlification) due to insufficient cooling rate, and laying the foundation for wear resistance.

[0022] High flow rate (15-25L / min·m²) quickly breaks the surface "vapor film", ensuring that the surface austenite undergoes "diffusion-free phase transformation" into martensite. Moreover, the water flow distribution is more uniform under high flow rate (especially when combined with high-pressure spraying), and the surface temperature drop rate fluctuates less, ensuring uniform martensite structure and consistent surface hardness.

[0023] The temperature is reduced to 600-700℃; this temperature is the "starting range" of martensitic transformation (approximately 310-370℃ at the Ms point of Cr-Mo steel). When cooled to 600-700℃, the surface layer has completed the martensitic transformation (the martensitic transformation starts at the Ms point and ends at the Mf point). At the same time, it avoids excessively low temperatures (<600℃) that could lead to a large temperature difference between the surface layer and the transition layer, resulting in thermal stress.

[0024] The second stage involves uniform water spraying: adjust the water pressure to 0.3-0.5MPa, the water flow rate to 6-10L / min·m², and continue for 8-12 minutes to reduce the surface temperature of the casting to 450-550℃.

[0025] The purpose of the second stage of uniform water spraying quenching is to form a "martensite + bainite" composite structure in the transition layer, so as to achieve a smooth transition of properties between the surface layer and the base layer.

[0026] Low water pressure (0.3-0.5MPa) + small flow rate (6-10L / min·m²) achieves a cooling rate of 5-15℃ / min, which is between the cooling rates of martensite and pearlite transformation, promoting the synergistic formation of the two structures. The slow cooling process reduces the accumulation of thermal stress and reduces the risk of deformation and cracking of the liner.

[0027] Low pressure (0.3-0.5MPa) reduces water flow impact and heat exchange efficiency, and the cooling rate is reduced to the bainite transformation range, allowing some austenite to retain martensite (maintaining hardness) and some to transform into bainite (improving toughness). If high pressure is still used here, the transition layer will become fully martensitic (indistinguishable from the surface layer), losing its "buffering" function. If atmospheric pressure (lower water pressure) is used, the cooling rate will be too slow, forming full pearlite (the transition layer is soft and tough), resulting in an excessively large hardness step between the surface layer and the matrix layer (≥15HRC), making it prone to cracking.

[0028] Low flow rate (6-10 L / min·m²): Reduces the water supply per unit area, lowers the heat exchange intensity, and allows the cooling rate to naturally drop to the bainitic transformation range, avoiding excessively fast cooling rate leading to full martensite formation in the transition layer, or excessively slow cooling rate leading to full pearlite formation; Lower limit (6 L / min): Ensures that the water flow can cover the transition layer area, avoiding localized low cooling rates that could form pearlite "soft bands"; Upper limit (10 L / min): Prevents excessive flow rate from causing the cooling rate to rise back to the martensite transformation range, ensuring a stable composite structure ratio.

[0029] Temperature drops to 450-550℃: This temperature is the core range of bainite transformation (the bainite transformation temperature of Cr-Mo steel is about 350-550℃). When cooled to this range, the composite structure of the transition layer is fully transformed. If the temperature is too high (>550℃), the bainite transformation is insufficient (too much retained austenite); if the temperature is too low (<450℃), some austenite will be transformed into pearlite, and the toughness of the transition layer will decrease.

[0030] The third stage involves uniform water spraying: readjust the water pressure to 1.0-1.5MPa, the water flow rate to 12-18L / min·m², continue for 6-10 minutes, and finally turn off the water spray to allow the casting to cool to 200-250℃.

[0031] The purpose of the third stage of uniform water spraying quenching is to form a fine-grained pearlite structure in the matrix layer, taking into account both impact resistance and toughness as well as basic strength.

[0032] Medium and high pressure (1.0-1.5MPa) + medium flow rate (12-18L / min·m²) achieve a cooling rate of 3-8℃ / min, which avoids the formation of martensite due to excessive cooling rate and the formation of coarse pearlite due to excessive cooling rate;

[0033] When cooled to 200-250℃, there is no residual austenite, and the microstructure is more stable and the performance fluctuation is smaller after subsequent tempering;

[0034] The cooling rate of medium-high pressure (1.0-1.5MPa) is between that of the first two stages. It can both inhibit the growth of pearlite grains in the matrix layer (fine grain strengthening) and avoid the formation of martensite. If low pressure is used here, the cooling rate will be too slow, which will lead to coarse pearlite (grains ≥20μm) and a decrease in the impact toughness of the matrix layer (fracture elongation ≤10%). If the same high pressure as the first stage is used, the cooling rate will be too fast, which will lead to martensite (hardness ≥45HRC), which is hard, brittle and easy to break.

[0035] Medium flow rate (12-18 L / min·m²): The heat exchange intensity is moderate, and the cooling rate is neither too fast, which would cause martensite to form in the matrix layer, nor too slow, which would cause coarse pearlite grains.

[0036] Temperature should be reduced to 200-250℃: This temperature is below the pearlite transformation completion temperature (approximately 200℃) to ensure complete transformation of austenite into pearlite, with no residual austenite (residual austenite will transform into martensite during subsequent use, leading to liner deformation and performance fluctuations); avoid excessively low temperatures (<200℃): excessive cooling will exacerbate stress accumulation between the matrix layer and the surface layer, increasing the risk of deformation; avoid excessively high temperatures (>250℃): excessive residual austenite will result in poor microstructure stability after tempering.

[0037] As a preferred embodiment of this example, the spray water temperature is 20-25℃ during the first stage of uniform water spraying.

[0038] If the temperature is below 20℃: Although the temperature difference is greater, the rapid cooling rate will cause microcracks on the surface (Cr-Mo steel has poor thermal conductivity and is prone to thermal stress when cooled quickly); If the temperature is above 25℃: The temperature difference will be smaller and the cooling rate will drop to below 15℃ / min, the martensite transformation rate will be less than 80%, and the surface will be prone to defects.

[0039] During the second stage of uniform water spraying, the spray water temperature should be 40-50℃. The transition layer needs to be cooled at a rate of 5-15℃ / min to form a composite structure of "40-50% martensite + 50-60% bainite". If the temperature is below 40℃, the temperature difference is too large and the cooling rate rises to above 15℃ / min, the bainite content will be less than 30%. If the temperature is above 50℃, the temperature difference is too small and the cooling rate is below 5℃ / min, the martensite content will be less than 20%, and neither of these conditions can achieve "strong and tough synergy".

[0040] During the third stage of uniform water spraying, the spray water temperature is 25-35℃. If the temperature is below 25℃: the cooling rate exceeds 8℃ / min, the martensite content is ≥30%, and the impact toughness is ≤10J / cm². If the temperature is above 35℃: the cooling rate is below 3℃ / min, the pearlite grains are ≥25μm, and the tensile strength is ≤900MPa. Neither of these conditions can meet the impact resistance and deformation resistance requirements of the lining plate.

[0041] In a preferred embodiment of this example, during the first and third stages of uniform water spraying, the spray water is modified water with nano-ZrO2-nano-SiC composite particles, wherein the mass fraction of the composite particles is 0.05-0.08%, and the particle size of both nano-ZrO2 and nano-SiC is controlled at 30-80nm, with a mass ratio of 3:2. During the second stage of uniform water spraying, the spray water is tap water.

[0042] Nano-ZrO2-nano-SiC composite particles serve as the heterogeneous nucleation core. The first stage of uniform water spraying reduces the spacing between surface martensite laths to 0.6-0.9μm, while the third stage of uniform water spraying refines the pearlite grains in the matrix layer to 8-12μm, thereby improving strength, toughness, and wear resistance.

[0043] The high thermal conductivity of the composite particles will cause the cooling rate of the transition layer to exceed 15℃ / min, making it impossible to form a "martensite + bainite" composite structure. It will either be all martensite (without buffer) or all pearlite (hardness fracture). Therefore, in the second stage, water modified with nano ZrO2-nano SiC composite particles is not used as spray water.

[0044] As a preferred embodiment of this example, in S4, during tempering, the temperature is raised to 300-350°C at a heating rate of 60-100°C / h, held for 10-15h, and then cooled to room temperature under natural conditions. At this time, the microstructure from the surface of the casting to the matrix layer is martensite, martensite + bainite, and pearlite.

[0045] After quenching, the surface layer of the liner plate is martensitic, with extremely high internal stress (caused by the difference in cooling rate of the thick section), making it prone to breakage if used directly.

[0046] Tempering at medium and low temperatures of 300-350℃: Without significantly reducing hardness, martensite is decomposed into tempered troostite and sorbite (fine carbides are dispersed in the ferrite matrix), which greatly releases the quenching internal stress.

[0047] 10-15h long-term heat preservation: For thick lining substrate layers, it ensures that internal stress is fully conducted and released, avoiding deformation and cracking during use due to residual stress;

[0048] Stable gradient structure: stabilizes the structure of surface martensite, martensite + bainite, and matrix pearlite to avoid performance fluctuations caused by microstructure transformation during subsequent use;

[0049] Natural cooling is extremely slow (1-3℃ / min), which allows residual stress to be released slowly, ensuring the dimensional accuracy of the liner (deformation ≤0.5%), while further stabilizing the gradient structure and avoiding performance fluctuations during use.

[0050] In a preferred embodiment of this example, in S1, the raw materials include scrap steel, ferroniobium, ferromolybdenum, ferrochrome, and ferrovanadium.

[0051] The melting process involves heating the temperature to 1500-1580℃ and then holding it at that temperature for 2-5 minutes.

[0052] Lower temperature limit (1500℃): Allows scrap steel, ferroniobium, ferromolybdenum, ferrochrome, ferrovanadium and other raw materials to be completely melted, avoiding the residue of "unmelted particles" (unmelted particles will cause uneven as-cast structure, and subsequent heat treatment is prone to local hard and brittle or soft and tough areas, affecting the wear resistance and impact resistance of the liner).

[0053] Upper temperature limit (1580℃): To avoid excessive burning of alloying elements (such as Cr, Mo, V) (Cr is easily oxidized at high temperatures to form Cr2O3 inclusions, and Mo is easily volatilized).

[0054] Add a slag-forming agent before the slag removal process;

[0055] The refining process is argon blowing refining.

[0056] In a preferred embodiment of this example, in S2, the temperature of the modification treatment is 1480-1560℃; the modification treatment uses a niobium-containing rare earth alloy as the modifier, and the amount of modifier added is 0.05-0.15% of the total mass of the refined Cr-Mo steel liquid.

[0057] In a preferred embodiment of this example, in step S3, the pouring temperature is 1450-1500℃ and the settling time is 1-2 hours.

[0058] Lower limit of temperature (1450℃): Ensure that the modified molten steel has sufficient fluidity to fill the mold cavity (the liners of semi-autogenous grinding mills are mostly thick cross sections (15-35cm). Insufficient fluidity will lead to "incomplete filling" (local incomplete filling) or "cold shut" (layer solidification of molten steel), forming a weak area in the structure, which is prone to subsequent fracture).

[0059] Upper temperature limit (1500℃): to avoid overheating of the mold (high temperature molten steel will burn the surface of the mold, causing sand to stick to the surface of the casting, affecting subsequent cleaning and dimensional accuracy), and to shorten the solidification time (to prevent excessive grain growth).

[0060] The Cr-Mo alloy steel liner with a gradient microstructure prepared using this formula and process, from top to bottom (e.g.) Figure 5 (As shown) It is divided into a surface layer, a transition layer, and a matrix layer. The surface layer has a microstructure of martensite, the transition layer has a microstructure of martensite and bainite composite, and the matrix layer has a microstructure of pearlite.

[0061] In summary, the technical effects and advantages of this invention are as follows:

[0062] This invention controls the micro-gradient structure distribution of Cr-Mo alloy steel liner, which significantly improves the hardness, impact toughness, and impact wear properties of the alloy steel liner. Moreover, the liner does not deform or break during use and has a long service life. Attached Figure Description

[0063] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0064] Figure 1 Here is a metallographic image of the microstructure of Example 1;

[0065] Figure 2 Metallographic image of the microstructure of Example 2;

[0066] Figure 3 Metallographic image of the microstructure of Comparative Example 1;

[0067] Figure 4 Metallographic image of the microstructure for Comparative Example 2;

[0068] Figure 5 This is a structural diagram of a Cr-Mo alloy steel liner with a gradient microstructure. Detailed Implementation

[0069] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0070] Example 1

[0071] The chemical composition of a method for preparing a high wear-resistant and impact-resistant semi-autogenous mill Cr-Mo alloy steel liner with a gradient microstructure, by mass percentage, is as follows:

[0072] C: 0.4%, Cr: 1.0%, Mo: 0.3%, V: 0.5%, Ti: 1.6%, Ni: 1.0%, Si: 1.0%, P: 0.002%, S: 0.002%, with the remainder being Fe and unavoidable impurities.

[0073] The specific preparation steps are as follows:

[0074] S1. Smelting: Smelting is carried out using an electric arc furnace. During the smelting process, scrap steel is added first. After the scrap steel melts, ferroniobium, ferromolybdenum, ferrochrome, and ferrovanadium are added sequentially. After complete melting, samples are taken for analysis, and the composition is adjusted until it meets the mass percentage requirements of the chemical composition of the Cr-Mo steel. A slagging agent is added, and after two slag removals, the temperature is raised to the smelting temperature of 1550℃ and held for 4 minutes. Then, argon blowing is used for refining to obtain refined high-manganese steel molten steel.

[0075] S2. Tapping and Modification Treatment: The refined Cr-Mo steel liquid is poured into a ladle and treated with a niobium-containing rare earth alloy modifier by wire feeding at a modification temperature of 1490℃ to obtain modified Cr-Mo steel liquid.

[0076] S3. Pouring, casting and cleaning: The modified Cr-Mo steel molten steel is poured into the pre-prepared hollow mold cavity at a pouring temperature of 1480℃, and after standing for 2 hours, the mold is opened. The riser and gating gate are removed by impact, the flash and burrs are cleaned by hand, and the remaining roots of the riser and gating gate are ground to obtain the precast casting.

[0077] S4. Heat Treatment: After the castings are packed into the trolley furnace, they are heated to 500℃ at a heating rate of 60℃ / h and held for 8 hours. Then, they are heated to 900℃ at a heating rate of 60℃ / h and held for 8 hours. After that, they are air-cooled to 400℃. Based on the above, during quenching, the castings are heated to 600℃ at a heating rate of 60℃ / h and held for 8 hours. Then, they are heated to 850℃ at a heating rate of 60℃ / h and held for 8 hours. Finally, only the upper outer surface layer of the castings is subjected to three-stage water spray quenching. The specific operation is as follows: First stage: uniform water spraying: initial water pressure 1.2M. The first stage involves uniform water spraying: 1. Water pressure is adjusted to 0.3 MPa, water flow rate is 22 L / min·m², spray water temperature is 23℃, and spraying continues for 18 minutes to reduce the surface temperature of the casting to 620℃; 2. Uniform water spraying: water pressure is adjusted to 0.3 MPa, water flow rate is 6 L / min·m², spray water temperature is 40℃, and spraying continues for 12 minutes to reduce the surface temperature of the casting to 450℃; 3. Uniform water spraying: water pressure is adjusted again to 1 MPa, water flow rate is 12 L / min·m², spray water temperature is 25℃, and spraying continues for 8 minutes. Finally, the spraying is turned off to allow the casting to cool to 250℃.

[0078] Based on the above, the casting was heated to 300℃ at a heating rate of 60℃ / h, held at that temperature for 15h, and then cooled to room temperature under natural conditions. At this point, the microstructure from the surface of the casting to the matrix layer consisted of martensite, martensite + bainite, and pearlite. The microstructure of different parts of the liner is shown in the figure. Figure 1 (Surface martensite, transition layer martensite + bainite, matrix layer pearlite).

[0079] Example 2

[0080] The chemical composition of a method for preparing a high wear-resistant and impact-resistant semi-autogenous mill Cr-Mo alloy steel liner with a gradient microstructure, by mass percentage, is as follows:

[0081] C: 0.45%, Cr: 1.1%, Mo: 0.35%, V: 0.6%, Ti: 1.7%, Ni: 1.1%, Si: 1.2%, P: 0.002%, S: 0.002%, with the remainder being Fe and unavoidable impurities.

[0082] S1. Smelting: Smelting is carried out using an electric arc furnace. During the smelting process, scrap steel is added first. After the scrap steel melts, ferroniobium, ferromolybdenum, ferrochrome, and ferrovanadium are added sequentially. After complete melting, samples are taken for analysis, and the composition is adjusted until it meets the mass percentage requirements of the chemical composition of the Cr-Mo steel. A slagging agent is added, and after two slag removals, the temperature is raised to the smelting temperature of 1550℃ and held for 4 minutes. Then, argon blowing is used for refining to obtain refined high-manganese steel molten steel.

[0083] S2. Tapping and Modification Treatment: The refined Cr-Mo steel liquid is poured into a ladle and treated with a niobium-containing rare earth alloy modifier by wire feeding at a modification temperature of 1490℃ to obtain modified Cr-Mo steel liquid.

[0084] S3. Pouring, casting and cleaning: The modified Cr-Mo steel molten steel is poured into the pre-prepared hollow mold cavity at a pouring temperature of 1480℃, and after standing for 2 hours, the mold is opened. The riser and gating gate are removed by impact, the flash and burrs are cleaned by hand, and the remaining roots of the riser and gating gate are ground to obtain the precast casting.

[0085] S4. Heat Treatment: After the castings are packed into the trolley furnace, they are heated to 500℃ at a heating rate of 100℃ / h and held for 6 hours. Then, they are heated to 900℃ at a heating rate of 100℃ / h and held for 6 hours. Afterward, they are air-cooled to 400℃. For quenching, the castings are heated to 700℃ at a heating rate of 100℃ / h and held for 6 hours. Then, they are heated to 900℃ at a heating rate of 100℃ / h and held for 6 hours. Finally, only the upper outer surface layer of the casting is subjected to three-stage water spray quenching. The specific operation is as follows: First stage: uniform water spraying: initial water pressure 1.8MPa, water flow rate 25L / min·m², spray water temperature 25℃, lasting 12 minutes, to make the surface of the casting... The surface temperature was reduced to 600℃; the second stage involved uniform water spraying: adjusting the water pressure to 0.5MPa, the water flow rate to 10L / min·m², and the spray water temperature to 50℃ for 8 minutes, reducing the surface temperature of the casting to 550℃; the third stage involved uniform water spraying: again adjusting the water pressure to 1.5MPa, the water flow rate to 18L / min·m², and the spray water temperature to 35℃ for 6 minutes, finally stopping the spray to allow the casting to cool to 200℃. Based on the above, the temperature was increased to 300℃ at a rate of 100℃ / h, held for 15 hours, and then cooled to room temperature under natural conditions. At this point, the microstructure from the surface to the matrix layer of the casting consisted of martensite, martensite + bainite, and pearlite. The microstructure of different parts of the liner is shown in the figure. Figure 2 (The surface layer is martensite, the transition layer is martensite + bainite, and the matrix layer is pearlite).

[0086] Comparative Example 1

[0087] The chemical composition of a method for preparing a high wear-resistant and impact-resistant semi-autogenous mill Cr-Mo alloy steel liner with a gradient microstructure, by mass percentage, is as follows:

[0088] C: 0.45%, Cr: 1.1%, Mo: 0.35%, V: 0.6%, Ti: 1.7%, Ni: 1.1%, Si: 1.2%, P: 0.002%, S: 0.002%, with the remainder being Fe and unavoidable impurities.

[0089] S1. Smelting: Smelting is carried out using an electric arc furnace. During the smelting process, scrap steel is added first. After the scrap steel melts, ferroniobium, ferromolybdenum, ferrochrome, and ferrovanadium are added sequentially. After complete melting, samples are taken for analysis, and the composition is adjusted until it meets the mass percentage requirements of the chemical composition of the Cr-Mo steel. A slagging agent is added, and after two slag removals, the temperature is raised to the smelting temperature of 1550℃ and held for 4 minutes. Then, argon blowing is used for refining to obtain refined high-manganese steel molten steel.

[0090] S2. Tapping and Modification Treatment: The refined Cr-Mo steel liquid is poured into a ladle and treated with a niobium-containing rare earth alloy modifier by wire feeding at a modification temperature of 1490℃ to obtain modified Cr-Mo steel liquid.

[0091] S3. Pouring, casting and cleaning: The modified Cr-Mo steel molten steel is poured into the pre-prepared hollow mold cavity at a pouring temperature of 1480℃, and after standing for 2 hours, the mold is opened. The riser and gating gate are removed by impact, the flash and burrs are cleaned by hand, and the remaining roots of the riser and gating gate are ground to obtain the precast casting.

[0092] S4. Heat Treatment: After the castings are packed into the trolley furnace, they are heated to 600℃ at a heating rate of 100℃ / h and held for 6 hours. Then, they are heated to 900℃ at a heating rate of 100℃ / h and held for 6 hours. They are then air-cooled to 400℃. Based on the above process, they are heated to 700℃ at a heating rate of 100℃ / h and held for 6 hours. Then, they are heated to 850℃ at a heating rate of 100℃ / h and held for 6 hours. They are then cooled in water to 200℃. Based on the above process, they are heated to 300℃ at a heating rate of 100℃ / h and held for 15 hours. Finally, they are cooled to room temperature under natural conditions. The microstructure of different parts of the lining plate is shown in the figure. Figure 3 (The surface layer, transition layer, and matrix layer are all martensite).

[0093] Comparative Example 2

[0094] The chemical composition of a method for preparing a high wear-resistant and impact-resistant semi-autogenous mill Cr-Mo alloy steel liner with a gradient microstructure, by mass percentage, is as follows:

[0095] C: 0.45%, Cr: 1.1%, Mo: 0.35%, V: 0.6%, Ti: 1.7%, Ni: 1.1%, Si: 1.2%, P: 0.002%, S: 0.002%, with the remainder being Fe and unavoidable impurities.

[0096] S1. Smelting: Smelting is carried out using an electric arc furnace. During the smelting process, scrap steel is added first. After the scrap steel melts, ferroniobium, ferromolybdenum, ferrochrome, and ferrovanadium are added sequentially. After complete melting, samples are taken for analysis, and the composition is adjusted until it meets the mass percentage requirements of the chemical composition of the Cr-Mo steel. A slagging agent is added, and after two slag removals, the temperature is raised to the smelting temperature of 1550℃ and held for 4 minutes. Then, argon blowing is used for refining to obtain refined high-manganese steel molten steel.

[0097] S2. Tapping and Modification Treatment: The refined Cr-Mo steel liquid is poured into a ladle and treated with a niobium-containing rare earth alloy modifier by wire feeding at a modification temperature of 1490℃ to obtain modified Cr-Mo steel liquid.

[0098] S3 casting, mold opening and cleaning: The modified Cr-Mo steel molten steel is poured into the pre-prepared hollow mold cavity at a casting temperature of 1480℃, and after standing for 2 hours, the mold is opened, the riser and gating gate are removed by impact, the flash and burrs are cleaned by hand, and the remaining roots of the riser and gating gate are ground to obtain the precast casting.

[0099] S4. Heat Treatment: After the castings are packed into the trolley furnace, they are heated to 600℃ at a heating rate of 100℃ / h and held for 6 hours. Then, they are heated to 900℃ at a heating rate of 100℃ / h and held for 6 hours. Afterward, they are air-cooled to 400℃. Based on the above, they are heated to 700℃ at a heating rate of 100℃ / h and held for 6 hours. Then, they are heated to 850℃ at a heating rate of 100℃ / h and held for 6 hours. Afterward, they are air-cooled to 200℃. Based on the above, they are heated to 300℃ at a heating rate of 100℃ / h and held for 15 hours. Finally, they are cooled to room temperature under natural conditions. The microstructure of different parts of the lining plate is shown in [the diagram]. Figure 4 (The surface layer, transition layer, and matrix layer are all pearlite).

[0100] Effect verification

[0101] The Cr-Mo steel liners prepared in Examples 1-2 and Comparative Examples 1-2 were used for mechanical property testing. The mechanical property tests included surface hardness, transition layer hardness, matrix hardness, tensile strength, elongation at break, and service life. The sample dimensions for tensile strength were obtained according to GB6397-86 standard; the service life was determined using a semi-autogenous grinding mill (Φ10x3.2m, cylinder speed 30 r / min, filling rate 50%, daily ore processing capacity 12000 tons). The test results are shown in Table 1.

[0102] Table 1 Mechanical Performance Test Table

[0103]

[0104] As can be seen from the data in Examples 1 and 2 in the table, a gradient distribution of "high surface hardness, medium hardness of transition layer, and low hardness of matrix" is presented. The surface hardness is 58.6 HRC and 58.1 HRC, respectively, which is contributed by martensite structure. The transition layer hardness is 54.6 HRC and 53.5 HRC, respectively, which is contributed by martensite / bainite composite structure. The matrix hardness is 31.5 HRC and 32.6 HRC, respectively, which is contributed by pearlite structure. This gradient ensures the wear resistance of the surface layer and provides toughness support through the low hardness of the matrix.

[0105] The tensile strengths are 1000.6 MPa and 1050.1 MPa, respectively, and the elongation at break is 12.6% and 12.3%, respectively, achieving a balance of "high strength + high toughness". The core reason is the synergistic effect of the gradient structure: the surface martensite ensures the strength, and the composite structure of pearlite in the matrix layer and marbainite in the transition layer ensures the toughness, avoiding the problems of "hard and brittle" or "tough but not wear-resistant".

[0106] The service life is 3850h and 3812h respectively, which is 2.4-2.8 times that of the comparison ratio. The key lies in the synergy of gradient structure and strength-toughness balance: the high hardness of the surface layer resists wear, and the high toughness of the matrix absorbs impact energy, avoiding failure of the liner due to excessive wear or impact fracture.

[0107] As can be seen from the data in Comparative Example 1 in the table: there is no effective hardness gradient, and the matrix hardness is as high as 49.6 HRC (close to the transition layer hardness). The reason is that the quenching stage adopts "full water cooling". The cooling rate is too fast, which causes a large amount of martensite to form in the matrix layer, thus losing the toughness buffering effect of the matrix.

[0108] With a service life of only 1566 hours, although the surface hardness is similar to that of the example, it is prone to cracking due to impact during use due to the lack of gradient structure and insufficient toughness, thus failing prematurely.

[0109] As can be seen from the data in Comparative Example 2 in the table: there is no hardness gradient and the overall hardness is low. The surface hardness is only 38.6 HRC, and the hardness difference between layers is very small (33.8-38.6 HRC). Because "air cooling" is used in the quenching stage, the cooling rate is too slow, the austenite has not been transformed into martensite, and pearlite structure is formed in the whole cross section, resulting in insufficient wear resistance.

[0110] With a minimum service life of 1389 hours, it suffers from low overall hardness, poor surface wear resistance, rapid wear failure, and insufficient strength, making it prone to deformation.

[0111] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous mill, characterized in that, It contains the following chemical components by weight percentage: C: 0.2-0.6%, Cr: 0.5-1.5%, Mo: 0.2-0.5%, V: 0.5-1.0%, Ni: 0.5-1.5%, Si: 0.5-1.5%, P: ≤0.003%, S: ≤0.005%, Ti: 1.5-2.0%, with the remainder being Fe and unavoidable impurities.

2. The method for preparing a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous mill according to claim 1, characterized in that: Includes the following steps: S1. Smelting: Add each raw material according to the mass percentage, melt, remove slag, and refine to obtain refined molten steel; S2. Modification treatment: The refined molten steel is modified to obtain modified molten steel. S3. Casting: The modified steel molten material is poured into the mold cavity at the casting temperature, left to stand, unpacked, and cleaned to obtain the precast casting; S4. Heat treatment: The precast casting is subjected to normalizing, quenching and tempering operations in sequence. First, the casting is normalized, then quenched to room temperature, and then tempered to obtain the high wear-resistant and impact-resistant semi-autogenous mill Cr-Mo alloy steel liner.

3. The method for preparing a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous mill according to claim 2, characterized in that: In S4, during normalizing, first heat to 400-500℃ at a heating rate of 60-100℃ / h, hold for 6-8h, then heat to 900-950℃ at a heating rate of 60-100℃ / h, hold for 6-8h, and then air cool to 400-650℃.

4. The method for preparing a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous mill according to claim 2, characterized in that: In S4, during quenching, the temperature is raised to 600-700℃ at a rate of 60-100℃ / h and held for 6-8 hours. Then, it is raised to 850-900℃ at a rate of 60-100℃ / h and held for 6-8 hours. Finally, only the upper outer surface layer of the casting is subjected to three-stage water spray quenching. The specific operation is as follows: The first stage of uniform water spraying: initial water pressure 1.2-1.8MPa, water flow rate 15-25L / min·m², lasting 12-18min, to reduce the surface temperature of the casting to 600-700℃; The second stage involves uniform water spraying: adjust the water pressure to 0.3-0.5MPa, the water flow rate to 6-10L / min·m², and continue for 8-12 minutes to reduce the surface temperature of the casting to 450-550℃. The third stage involves uniform water spraying: readjust the water pressure to 1.0-1.5MPa, the water flow rate to 12-18L / min·m², and continue for 6-10 minutes. Finally, turn off the water spraying to allow the casting to cool to 200-250℃.

5. The method for preparing a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous mill according to claim 4, characterized in that: During the first stage of uniform water spraying, the water temperature is 20-25℃; during the second stage of uniform water spraying, the water temperature is 40-50℃; and during the third stage of uniform water spraying, the water temperature is 25-35℃.

6. The method for preparing a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous mill according to claim 4, characterized in that: During the first and third stages of uniform water spraying, the spray water is water modified with nano-ZrO2-nano-SiC composite particles, wherein the mass fraction of the composite particles is 0.05-0.08%, and the particle size of both nano-ZrO2 and nano-SiC is controlled at 30-80nm, with a mass ratio of 3:

2. During the second stage of uniform water spraying, the spray water is tap water.

7. The method for preparing a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous mill according to claim 2, characterized in that: In S4, during tempering, the temperature is increased to 300-350℃ at a rate of 60-100℃ / h, held for 10-15h, and then cooled to room temperature under natural conditions.

8. The method for preparing a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous mill according to claim 2, characterized in that: In S1, the raw materials include scrap steel, ferroniobium, ferromolybdenum, ferrochrome, and ferrovanadium; The melting process involves heating the temperature to 1500-1580℃ and then holding it at that temperature for 2-5 minutes. Add a slag-forming agent before the slag removal process; The refining process is argon blowing refining.

9. The method for preparing a high wear-resistant and impact-resistant Cr-Mo alloy steel liner for a semi-autogenous mill according to claim 2, characterized in that: In S2, the temperature of the modification treatment is 1480-1560℃; the modification treatment uses a niobium-containing rare earth alloy as a modifier, and the amount of modifier added is 0.05-0.15% of the total mass of the refined Cr-Mo steel liquid.

10. The method for preparing a high wear-resistant and impact-resistant semi-autogenous mill Cr-Mo alloy steel liner according to claim 2, wherein in S3, the casting temperature is 1450-1500℃ and the settling time is 1-2h.

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