Niobium-containing hypereutectoid wear-resistant alloy steel, preparation method and application of niobium-containing hypereutectoid wear-resistant alloy steel in large rod mill lining plate

Abstract

The invention discloses niobium-containing hypereutectoid wear-resistant alloy steel, a preparation method and application of the niobium-containing hypereutectoid wear-resistant alloy steel in a large rod mill lining plate, and relates to the technical field of alloy steel. According to the alloy steel, a component system is designed according to the specific mass percent, during preparation, fine processes such as medium-frequency induction furnace smelting, converter bottom oxygen and argon blowing, medium-frequency induction furnace alloying and composite slagging treatment and steel ladle further calcification treatment are performed, and the prepared alloy steel has excellent wear resistance, obdurability, corrosion resistance and the like after quenching and tempering. The material is used for a large-scale rod mill lining plate, greatly prolongs the service life, reduces the cost, has an application prospect in the industrial wear-resistant field, and provides a high-performance material solution for related industries.

Description

Technical Field

[0001] The invention relates to the technical field of alloy steels, and in particular to a niobium-containing hypereutectoid wear-resistant alloy steel, a preparation method and application thereof in a large rod mill liner. Background Art

[0002] 1. Hypereutectoid steel

[0003] Hypereutectoid steel is a carbon steel with a carbon content higher than 0.77%. Its microstructure is mainly composed of pearlite and pre-precipitated cementite distributed in a network along the austenite grain boundary. After heat treatment, this steel can obtain higher strength and hardness. During quenching, usually all cementite is not dissolved, but some undissolved cementite is retained and distributed in the martensite matrix in a granular form, which can effectively improve the wear resistance of the steel.

[0004] Hypereutectoid steel needs to rely on heat treatment to show its comprehensive performance advantages, and there are specific requirements for its quenching heating temperature. Generally speaking, the quenching heating temperature cannot be lower than Ac1 (the starting temperature of hypoeutectoid transformation), otherwise the steel cannot complete the austenitization process. If the heating temperature is slightly higher than Ac1, the pearlite will be partially transformed into austenite, and a small amount of cementite will be dissolved into the austenite, and the mass fraction of carbon will increase, which will increase the tendency of quenching deformation, increase the number of microcracks, and increase the brittleness. Therefore, the quenching heating temperature of hypereutectoid steel should be above Ac1, and it should not be too high to prevent adverse effects on the mechanical properties and wear resistance of the steel.

[0005] 2. Main problems in the production of eutectoid steel

[0006] (1) Component segregation

[0007] In the production process of hypereutectoid steel, segregation of components in different parts is a key problem that needs to be solved urgently. For hypereutectoid steel containing alloy components, this problem is more prominent.

[0008] (2) Inclusions

[0009] Non-metallic inclusions are an important factor affecting the performance of hypereutectoid steel. With the development of the industry, the requirements for the cleanliness of hypereutectoid steel liquid are becoming more and more stringent.

[0010] (3) Gas content

[0011] Too high nitrogen content in steel will cause the steel to deteriorate. Nitrogen can enhance the age hardening of steel and increase the strength and hardness of steel, but at the same time, the plasticity, impact resistance and toughness will be significantly reduced.

[0012] The presence of oxygen in steel will also have a negative impact on the mechanical properties of steel, and the extent of the impact is closely related to the oxygen content, the type, distribution and number of oxygen-containing inclusions.

[0013] Hydrogen is extremely harmful to steel, especially in high-carbon steels such as hypereutectoid steel. As the hydrogen content in the steel increases, the plasticity and toughness will decrease significantly. This negative effect is more significant during the processing and cooling stage. Therefore, in hypereutectoid steel, the hydrogen content should be controlled as much as possible to avoid affecting the steel quality due to excessive hydrogen content.

[0014] 3. Problems that need to be solved when hypereutectoid steel is used in wear-resistant steel

[0015] (1) Insufficient comprehensive mechanical properties

[0016] When hypereutectoid steel is used for wear-resistant steel, it faces the dilemma that the comprehensive mechanical properties cannot meet the requirements, and it is difficult to take into account both strength and toughness at the same time.

[0017] (2) Heat treatment specifications are not compatible

[0018] The conventional heat treatment specification (quenching) of hypereutectoid steel is carried out at a temperature that is not completely austenitized. Under this temperature condition, part of the cementite is not completely dissolved. After cooling, the structure is mainly martensite. Although it has a certain hardness, the toughness is poor and it cannot meet the requirements of wear-resistant alloy steel structure.

[0019] (3) Production conditions lead to poor performance

[0020] Under normal atmospheric conditions, the hypereutectoid steel produced in a medium frequency furnace has a high content of non-metallic inclusions and gases, which directly leads to poor mechanical properties of the steel.

[0021] 4. Application of hypereutectoid wear-resistant alloy steel containing niobium

[0022] In the mining, cement and other industries, the requirements for the preparation of materials for powder making equipment such as liners in ball mills, various sprockets, hammer heads and wall panels of hammer crushers, especially liners in large rod mills, are extremely strict. Ordinary high manganese steel materials are difficult to meet the needs of actual application scenarios due to their easy rheology, and general alloy steel materials cannot ensure both wear resistance and toughness, resulting in low efficiency. In addition, iron powder needs to be selected in the magnetic separation link of the powder making process. Since high manganese steel materials are non-magnetic and cannot be used, ordinary alloy steel materials are also difficult to meet the use requirements. Therefore, it is of great significance to develop materials with both high wear resistance and toughness. Niobium-containing hypereutectoid wear-resistant alloy steel has emerged, which is expected to solve these problems. Summary of the invention

[0023] The present invention aims to provide a niobium-containing hypereutectoid wear-resistant alloy steel, a preparation method and its application in a large rod mill liner, so as to overcome the defects of existing liner materials and apply them to large rod mill liner, thereby improving the comprehensive performance of the liner, extending the service life and reducing the production cost.

[0024] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0025] A method for preparing niobium-containing hypereutectoid wear-resistant alloy steel comprises the following steps:

[0026] (1) Design the composition system according to the chemical composition in terms of mass percentage;

[0027] (2) adding raw materials including scrap steel into a medium frequency induction furnace and melting and heating to 1500-1550°C;

[0028] (3) Then raise the temperature to 1580-1650°C and let stand for 10-15 minutes;

[0029] (4) After standing still, the converter is quickly transferred to the converter, which uses an alkaline lining. Oxygen is blown quickly at the bottom of the converter for 3-10 minutes. After stopping the oxygen blowing, argon is blown for 5-10 minutes, and then the converter is allowed to stand still for 5-10 minutes.

[0030] (5) After the converter molten steel is left to stand, it is quickly transferred to a medium frequency induction furnace, and ferrochromium alloy, ferroniobium alloy, and nickel are added for alloying treatment and composite slag treatment. After sampling and analysis are qualified, the molten steel temperature is adjusted to 1500-1550° C. The composite slag treatment method is to add a slag-forming agent to the molten steel after the alloying treatment is completed and then perform composite slag treatment;

[0031] (6) Then raise the temperature to 1580-1650°C and let stand for 5-10 minutes;

[0032] (7) Add calcium iron alloy into the ladle for calcification treatment for 5-10 minutes, and control the tapping temperature at 1570-1600°C;

[0033] (8) Adjust the temperature of the molten steel to 1520-1550°C according to the size of the casting, and then cast the casting;

[0034] (9) Cleaning the casting and producing niobium-containing hypereutectoid wear-resistant alloy steel after heat treatment.

[0035] Preferably, in step (2), ferrochromium alloy, ferroniobium alloy and nickel are not added to the raw materials including scrap steel.

[0036] Preferably, in step (4), the argon gas flow rate is controlled at 6-14 L / min.

[0037] Preferably, the method for preparing the slag-forming agent in step (5) comprises the following steps: weighing the raw materials in proportion, premixing at 520-490°C for 1-1.5h, heating to 1900-2300°C for smelting for 2-3h, and finally cooling and crushing to obtain the slag-forming agent.

[0038] Preferably, the particle size of the slag-forming agent is 5-10 mm.

[0039] Preferably, the amount of slag-forming agent added in step (6) is in the range of 8.2-9.5 kg / t.

[0040] Preferably, the qualified components of the sample analysis in step (5) are as follows: carbon: 0.8-1.2%, silicon: 0.6-1.0%, manganese: 0.6-1.0%, chromium: 0.8-3.5%, nickel: 0.1-0.8%, niobium: 0.05-0.15%, phosphorus less than 0.05%, sulfur <0.04%, and the balance is iron and unavoidable impurities.

[0041] Preferably, the heat treatment method after cleaning the casting in step (9) is as follows: during quenching treatment, the quenching temperature is 920-1000°C, and the insulation time is 6-8h according to the thickness and size of the casting; during tempering treatment, the tempering temperature is 220-550°C, and the insulation time is 6-8h.

[0042] The present invention also provides an application of niobium-containing hypereutectoid wear-resistant alloy steel in a large rod mill lining plate, wherein the thickness of the lining plate is 50-150 mm.

[0043] Compared with the prior art, the present invention has the following technical advantages:

[0044] (1) The present invention adopts a combination of medium frequency induction furnace-converter-medium frequency induction furnace, making full use of the advantages of medium frequency induction furnace melting, alloy composition control and converter slag removal, and maximizing the high wear resistance of hypereutectoid steel.

[0045] In the selection of the high-alloy hypereutectoid wear-resistant steel smelting process, the present invention creatively adopts a combined process of medium frequency induction furnace-converter-medium frequency induction furnace. This combination cleverly integrates the advantages of different equipment and realizes high efficiency and precision in the production process.

[0046] First of all, the medium frequency induction furnace, with its excellent melting capacity, can melt the raw materials quickly and evenly, laying a solid foundation for the subsequent adjustment of alloy composition. Its unique heating method not only improves the melting efficiency, but also ensures the purity of the melt, providing a strong guarantee for the production of high-quality steel.

[0047] Then, the introduction of the converter gave full play to its excellent slag removal capabilities. During the smelting process, the converter effectively removed impurities and inclusions in the melt through efficient physical and chemical reactions, further improving the purity and quality of the steel.

[0048] Finally, the medium frequency induction furnace is used again for refining and alloy composition adjustment. With the precision of the medium frequency induction furnace in controlling the alloy composition, the present invention can accurately adjust the proportion of key alloy elements such as carbon, chromium, and manganese in the steel, thereby maximizing the high wear resistance advantage of hypereutectoid steel.

[0049] This combined process not only improves production efficiency, but also significantly enhances the comprehensive performance of steel, making the final product outstanding in high strength and high wear resistance. It is widely used in machinery manufacturing, mining and other fields, meeting the market's urgent demand for high-quality steel.

[0050] (2) The slag-making agent of the present invention can effectively reduce the content of harmful impurity elements such as hydrogen and oxygen in molten steel, and significantly improve the mechanical properties of the produced alloy steel

[0051] In the production process of the hypereutectoid steel of the present invention, the slag-forming agent plays a key role, and the development of the slag-forming agent of the present invention is of great significance. The content of harmful elements such as hydrogen and oxygen in the molten steel has a profound impact on the performance of the alloy steel finally generated, and the slag-forming agent of the present invention can effectively reduce the content of harmful elements such as hydrogen and oxygen in the molten steel.

[0052] From the perspective of hydrogen, as described in the background technology, hydrogen in steel will cause a significant decrease in plasticity and toughness, especially for high-carbon steels such as hypereutectoid steel. The gas generated by the decomposition of lithium carbonate in the slag-making agent of the present invention at high temperature can play a role in stirring the molten steel, making the composition of the molten steel more uniform, and the lithium element can react with the hydrogen in the molten steel to fix the hydrogen, thereby reducing the free hydrogen content in the molten steel, thereby reducing the hydrogen content of the steel, effectively alleviating the risk of hydrogen embrittlement, and laying a foundation for improving the toughness of alloy steel.

[0053] Let's look at the oxygen element. Oxygen will also have an adverse effect on the mechanical properties of steel. The lime and calcium oxide in the slag-making agent of the present invention mainly play the role of slag-making and desulfurization. At the same time, they can also combine with oxygen in the molten steel to generate relatively stable oxides that enter the slag phase and are effectively removed, reducing the oxygen content in the molten steel; bauxite contains more aluminum oxide and has a strong ability to adsorb inclusions, some of which carry oxygen atoms on the surface of the inclusions. By adsorbing these inclusions, the oxygen content in the molten steel is indirectly reduced; rare earth oxides have a deoxidation function, and rare earth elements can be adsorbed on the surface of inclusions to make them spheroidized and refined, which not only reduces the adverse effects of inclusions on steel properties, but also consumes oxygen in the molten steel in this process, further purifying the molten steel.

[0054] The slag-making agent of the present invention, which is made by precisely mixing these raw materials, produces a synergistic effect, effectively reduces the hydrogen and oxygen contents in the molten steel, and reduces the damage of harmful impurities to the structure and performance of the hypereutectoid steel, so that the mechanical properties of the final alloy steel can be significantly improved in terms of strength, toughness, wear resistance, etc., and meets the stringent requirements of powder making equipment in the mining and cement industries for high-performance alloy steels, providing solid material support for the development of related industries.

[0055] (3) Excellent wear resistance

[0056] The niobium-containing hypereutectoid wear-resistant alloy steel of the present invention is designed with reasonable chemical composition, and carbon, chromium and other elements form a large number of carbides, especially chromium-containing carbides, which are extremely hard and dispersed in the steel matrix, effectively resisting the wear of the material. At the same time, the fine carbides and nitrides formed by the addition of niobium not only refine the grains, increase the grain boundary area, make the crack propagation path more tortuous, hinder the wear process, but also improve the matrix strength of the steel and further enhance the wear resistance. In the wear test simulating the working conditions of the rod mill, the alloy steel sample of the present invention is compared with the high manganese steel sample. Under the same abrasive, rotation speed and time conditions, the wear amount of the high manganese steel sample reaches 1.64g, while the wear amount of the alloy steel sample of the present invention is below 0.89g, and the wear rate is reduced by at least 45.7%, which fully demonstrates the excellent wear resistance, greatly prolongs the service life of the liner in a high-load grinding environment, and reduces the downtime and cost loss caused by frequent replacement of the liner.

[0057] (4) Good strength and toughness matching

[0058] In the design of alloy composition, elements such as manganese and nickel work together to improve toughness. Manganese refines the grains and reduces the brittleness of steel, while nickel improves the low-temperature toughness of steel and prevents low-temperature embrittlement. More importantly, niobium has a significant effect in refining grains. The fine grains enable the grain boundaries of steel to effectively hinder dislocation movement when subjected to impact loads, disperse stress concentration, and avoid rapid crack initiation and expansion. In the impact toughness test, the impact toughness value of the alloy steel of the present invention reaches 75J / cm 2 Compared with 51J / cm2 of ordinary low alloy steel 2 At least 47.1% improvement. Moreover, through a reasonable heat treatment process, the martensite structure after quenching is adjusted by tempering, and the toughness is further optimized while ensuring the hardness. For example, in the actual application of the rod mill, when encountering a large piece of ore impact, the high manganese steel liner is prone to cracking due to insufficient toughness, while the alloy steel liner of the present invention can effectively absorb the impact energy with good toughness, maintain the integrity of the structure, maintain the stable operation of the equipment, reduce the frequency of maintenance, and ensure production continuity.

[0059] (5) Excellent corrosion resistance

[0060] The addition of chromium is the key to improving corrosion resistance. It can form a dense chromium oxide protective film on the steel surface to prevent external corrosive media such as humid air, acidic or alkaline solutions from corroding the steel matrix. In the corrosion resistance test, the alloy steel of the present invention and ordinary low-alloy steel were immersed in a 5% sodium chloride solution for 30 days. Large-area rust appeared on the surface of the ordinary low-alloy steel, and the corrosion rate reached more than 0.402mm / year, while the alloy steel of the present invention only had slight rust spots, and the corrosion rate was as low as less than 0.088mm / year, and the corrosion rate was reduced by at least 78.1%. This allows the lining of the niobium-containing hypereutectoid wear-resistant alloy steel to maintain good surface conditions and mechanical properties for a long time in a working environment with humid or corrosive media such as mining and metallurgy, reduce material loss and performance degradation caused by corrosion, extend the overall service life, and reduce equipment maintenance costs.

[0061] (6) Advantages of precise composition and process control

[0062] The present invention precisely controls the chemical composition, and the content of each element is strictly limited to a specific range, ensuring that each element plays a full role and cooperates with each other, avoiding the overall performance being affected by an excessive or insufficient amount of a certain element. In terms of preparation technology, the process parameters of each link, from smelting, argon blowing, slag making to heat treatment, have been optimized through a large number of experiments. Such as the raw material ratio and preparation process of the slag-making agent, premixing, smelting at a specific temperature, and precise particle size control, ensure that the slag-making agent efficiently purifies the molten steel. Parameters such as the time and flow rate of oxygen and argon blowing in the converter not only ensure the uniform dissolution of alloy elements and the effective removal of impurities, but also prevent problems such as element burning and steel liquid aspiration. This precise control ensures that the quality of each furnace of molten steel is stable, and the performance of the finished alloy steel is highly consistent. In large-scale industrial production, it can stably provide high-quality liners for large rod mills, reduce production risks caused by product performance fluctuations, and improve production efficiency.

[0063] (7) Wide application adaptability and economy

[0064] The niobium-containing hypereutectoid wear-resistant alloy steel of the present invention has excellent comprehensive performance. It is not only suitable for large rod mill liners, but can also be expanded to other similar industrial fields with high wear, strong impact, and corrosion risks, such as ball mill liners, crusher hammers, excavator bucket teeth, etc., providing high-performance wear-resistant material solutions for multiple industries. From an economic point of view, although there is a certain investment in the addition of alloy raw materials and the refinement of the preparation process, compared with the frequent replacement of liners of traditional high-manganese steel, equipment maintenance and production stoppage losses caused by insufficient performance of ordinary low-alloy steel, and the high cost preparation of high-chromium cast iron and ceramic composite materials, the alloy steel of the present invention has obvious advantages in the cost of the whole life cycle. Taking a large rod mill as an example, after adopting the liner of the present invention (the thickness of the liner is 50-150mm), the liner replacement cycle is extended by 2-3 times, and the annual maintenance times of the equipment are reduced by more than 50%, which greatly reduces the equipment operation and maintenance costs of the enterprise, improves economic benefits, and promotes the sustainable development of the industry. DETAILED DESCRIPTION

[0065] The present invention will be further described in detail below in conjunction with specific embodiments. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope of the present invention and its application.

[0066] The technical solutions adopted in the embodiments of the present invention are as follows:

[0067] (1) Chemical composition design

[0068] The niobium-containing hypereutectoid wear-resistant alloy steel of the present invention is designed with a component system according to a specific mass percentage, wherein carbon is 0.8-1.2%. Carbon is a key element to ensure that the steel has sufficient strength and hardness. An appropriate amount of carbon can form sufficient carbides during the subsequent heat treatment process to improve the wear resistance of the steel. The silicon content is 0.6-1.0%. Silicon can strengthen ferrite, improve the strength and hardness of steel, and improve the deoxidation effect of molten steel. The manganese content is 0.6-1.0%. Manganese can reduce the critical transition temperature of steel, refine grains, improve the toughness and strength of steel, and help deoxidation and desulfurization. The chromium content is 0.8-3.5%. Chromium can form stable carbides to improve the hardness, wear resistance and corrosion resistance of steel. The nickel content is 0.1-0.8%. Nickel can improve the toughness, corrosion resistance and hardenability of steel. The niobium content is 0.05-0.15%. Niobium is one of the key alloying elements of the present invention. Adding a certain amount of niobium alloying elements mainly plays the following roles: first, grain refinement and improvement of the comprehensive performance of hypereutectoid steel; second, niobium forms compounds with nitrogen to play a role in nitrogen fixation, thereby reducing the nitrogen content and achieving the purpose of improving the performance of hypereutectoid steel. Niobium added to steel as a microalloying element does not change the structure of iron, but combines with carbon, nitrogen and sulfur in steel to change the microstructure of steel. The strengthening effect of niobium on steel is mainly fine grain strengthening and dispersion strengthening. Niobium can generate stable carbides and carbonitrides with carbon and nitrogen in steel. In addition, carbides can be dispersed to form steel with fine grains. Niobium can also achieve dispersed distribution of precipitates by inducing precipitation and controlling the cooling rate. The toughness level of steel can be adjusted within a wide range. Therefore, adding niobium can not only improve the strength of steel, but also improve the toughness, high temperature oxidation resistance and corrosion resistance of steel, reduce the brittle transition temperature of steel, and obtain good welding performance and forming performance. Phosphorus is less than 0.05% and sulfur is less than 0.04% in the composition. Strict control of phosphorus and sulfur content is to reduce harmful impurities in steel, prevent hot brittleness and cold brittleness, and ensure the quality of steel. Oxygen content is less than 15ppm and hydrogen content is less than 5ppm. Reducing oxygen and hydrogen content as much as possible can reduce defects such as pores and cracks in steel, improve the density and mechanical properties of steel, and the balance is iron and unavoidable impurities.

[0069] (2) Preparation process

[0070] 1) Chemical composition design (step 1)

[0071] Carefully designing the composition system according to the mass percentage is the cornerstone of the entire preparation process. Determining the appropriate ratio of elements such as carbon, silicon, manganese, chromium, nickel, and niobium lays the foundation for the subsequent alloy to have excellent comprehensive properties such as wear resistance and strength. For example, the carbon content is controlled at 0.8-1.2%, which can ensure sufficient hardness to form a hypereutectoid structure without causing excessive brittleness due to excessive carbon content; niobium is added at a ratio of 0.05-0.15%, which can refine the grains and significantly improve the strength and toughness of the steel, and interact with elements such as carbon during the subsequent heat treatment process to further optimize the organizational structure. The synergy of various elements fundamentally determines the performance potential of alloy steel.

[0072] 2) Raw material melting (step 2)

[0073] Raw materials including scrap steel are added to a medium frequency induction furnace and melted to 1500-1550℃. It is considered that ferrochromium, ferroniobium and nickel are not added at this time. On the one hand, these alloy elements are prevented from being burned due to long-term high-temperature smelting and causing composition deviation. On the other hand, melting the scrap steel first can make the basic melt composition uniform and stable, creating conditions for subsequent precise alloying. This step provides a uniform and relatively pure basic steel liquid for subsequent processes.

[0074] 3) Heat up and let stand (step 3)

[0075] Then raise the temperature to 1580-1650℃ and let it stand for 10-15 minutes. High temperature standing helps to further remove inclusions in the melt, improve the purity of the molten steel, and reduce internal defect sources. Pure molten steel is the key to ensuring the consistency and reliability of alloy steel performance, providing a high-quality foundation for subsequent complex process treatment, and avoiding problems such as crack initiation and reduced wear resistance caused by excessive inclusions.

[0076] 4) Converter oxygen blowing and argon blowing treatment (step 4)

[0077] After standing still, it is quickly transferred to the converter. The converter uses an alkaline lining and oxygen is blown quickly from the bottom for 3-10 minutes. This can effectively decarburize and remove harmful impurities such as phosphorus in the molten steel, further purify the molten steel, and optimize the composition. After stopping the oxygen blowing, argon blowing is carried out for 5-10 minutes. The argon flow rate is controlled at 6-14L / min. Argon blowing can even out the composition and temperature of the molten steel, remove dissolved oxygen in the molten steel, and avoid the formation of oxide inclusions in the subsequent solidification process. The stirring effect of argon makes the composition of the molten steel more uniform and improves the overall quality stability. Finally, it is allowed to stand for 5-10 minutes to allow the molten steel to transition smoothly and prepare for the next step. Each link is closely connected to synergistically improve the quality of the molten steel.

[0078] 5) Alloying and composite slag treatment (step 5)

[0079] After the converter molten steel is left to stand, it is quickly transferred to a medium frequency induction furnace, and chromium iron alloy, niobium iron alloy and nickel are added for alloying treatment to give the molten steel the required wear resistance, corrosion resistance and other performance characteristics. Chromium can improve the hardenability and wear resistance of steel, nickel enhances toughness and corrosion resistance, and niobium refines grains and strengthens the matrix. The composite slag treatment method is to add a slag-making agent to the molten steel after the alloying treatment is completed and perform a composite slag treatment. The slag-making agent has the functions of purifying the molten steel by adsorbing inclusions and desulfurizing. After weighing the raw materials in proportion, premix them at 520-490℃ for 1-1.5h to make the raw materials initially evenly mixed, and then heat them to 1900-2300℃ for smelting for 2-3h to ensure that the slag-making agent has stable composition and high activity. After cooling and crushing to a particle size of 5-10mm, add the molten steel to effectively remove impurities, complement each other with alloying, and jointly optimize the quality of molten steel. Sampling and analysis of qualified components ensures precise control of each element, avoids composition fluctuations affecting performance, and adjusts the molten steel temperature to 1500-1550℃ to provide a suitable process temperature window for subsequent processes.

[0080] The slag-forming agent used in the present invention comprises the following raw materials in parts by weight: 18-28 parts of lime, 11-20 parts of fluorite, 14-23 parts of bauxite, 8-13 parts of magnesium oxide, 12-19 parts of calcium oxide, 6-9 parts of silicon dioxide, 4-7 parts of borax, 2-5 parts of lithium carbonate, 1-2 parts of titanium dioxide and 0.6-1.8 parts of rare earth oxide.

[0081] In the production process of the niobium-containing hypereutectoid wear-resistant alloy steel of the present invention, the slag-forming agent plays a vital role. Through the coordinated cooperation of various raw materials, it can effectively reduce the oxygen content and hydrogen content in the alloy steel, thereby significantly improving mechanical properties such as impact toughness, bringing unexpected technical effects.

[0082] First, let's look at the specific synergistic mechanism of the raw materials. Lime and calcium oxide mainly play the role of slag desulfurization. They can not only react with sulfur in the molten steel to form sulfides that enter the slag phase and reduce the sulfur content, but also play a key role in the deoxidation process. When the molten steel is in a high-temperature melting state, the active ingredients in lime and calcium oxide will combine with the oxygen dissolved in the molten steel to form relatively stable oxides, which are then integrated into the slag phase and effectively removed, thereby reducing the oxygen content in the molten steel.

[0083] The addition of fluorite can reduce the melting point and viscosity of slag, greatly enhancing the fluidity of slag. This is not only conducive to the removal of inclusions, but also creates good conditions for the removal of harmful elements such as oxygen and hydrogen. The smoothly flowing slag can promptly carry away the oxidized substances and possible hydroxides on the surface of the molten steel, quickly discharge them from the system, prevent them from dissolving back into the molten steel, and indirectly reduce the oxygen and hydrogen content in the steel.

[0084] Bauxite contains more aluminum oxide and has a strong ability to absorb inclusions. It has a strong adsorption capacity for fine inclusions in molten steel, especially those particles carrying oxygen atoms on the surface. These adsorbed inclusions are separated from the molten steel system as the slag is discharged during the subsequent slag making process, which significantly reduces the oxygen content in the molten steel. At the same time, the presence of bauxite also inhibits the dissolution and enrichment of hydrogen in molten steel to a certain extent, because its adsorption reduces the microscopic sites available for hydrogen atoms to attach.

[0085] While adjusting the basicity of slag, magnesium oxide stabilizes the performance of slag, which is of great significance for reducing the oxygen and hydrogen content. The appropriate basicity environment can promote the positive desulfurization and deoxidation reactions, making it easier for sulfur and oxygen in the molten steel to combine with the active components in the slag-making agent. Moreover, the stable slag can effectively prevent oxygen and hydrogen in the external environment from penetrating into the molten steel, just like putting on a layer of protective clothing for the molten steel, reducing the introduction of new harmful elements during the high-temperature smelting stage.

[0086] As the basic component of slag, silicon dioxide participates in the construction of the physical and chemical structure of slag. It is intertwined with other raw materials to form an environment conducive to the removal of oxygen and hydrogen. On the one hand, its own chemical properties prompt it to react with certain oxides in the molten steel at high temperatures and transform into slag phase materials that are easier to discharge; on the other hand, it adjusts the viscosity, melting point and other properties of the slag, and cooperates with raw materials such as fluorite to ensure the smooth progress of the entire slag-making process and reduce harmful elements such as oxygen and hydrogen.

[0087] Borax plays a unique and critical role. After reducing the surface tension of steel, it becomes easier for bubbles in the molten steel to escape, which not only reduces the porosity defects, but also carries some oxygen and hydrogen atoms in the molten steel with it during the escape process. At the same time, the grain refinement effect of boron makes the microstructure of the steel more dense and uniform, reduces the possibility of the accumulation of impurity elements such as oxygen and hydrogen at the grain boundaries, and further improves the purity of the steel.

[0088] The gas produced by the decomposition of lithium carbonate at high temperature can play a role in stirring the molten steel. While making the composition of the molten steel uniform, the churning of the gas allows oxygen and hydrogen atoms in the deep part of the molten steel to have more opportunities to contact the surface of the slag-forming agent, accelerating their removal reaction. In addition, the lithium element reduces the hydrogen content of the steel, directly reducing the risk of hydrogen embrittlement from the root, laying the foundation for improving the impact toughness of the steel.

[0089] The titanium element in titanium dioxide is tightly combined with nitrogen and oxygen in steel to form fine nitrides and oxides. This process consumes the free oxygen in the molten steel. These fine particles can also play a role in heterogeneous nucleation in the molten steel, refine the grains, reduce the grain boundary area, and reduce the segregation of oxygen and hydrogen at the grain boundary, making the internal microstructure of the steel more stable when subjected to stress, and improving the impact toughness.

[0090] Rare earth oxides can help purify molten steel in all aspects with their multiple functions. Deoxidation and desulfurization are beyond words. Their ability to refine grains and improve the morphology of inclusions is effective in reducing oxygen and hydrogen content. Rare earth elements are adsorbed on the surface of inclusions, which promotes the spheroidization and refinement of inclusions. On the one hand, it reduces the negative effects of inclusions as oxygen and hydrogen adsorption carriers. On the other hand, it makes it easier for inclusions to float up and be discharged during the slag making process, making the molten steel purer.

[0091] In the process of preparing slag-making agent, it is extremely necessary and important to accurately control the amount of each raw material. If the amount of lime and calcium oxide deviates from the range of 18-28 parts and 12-19 parts, too little will not be enough to fully complete the slag desulfurization and deoxidation tasks, and the sulfur and oxygen content in the steel will not be reduced; too much may cause the slag basicity to be too high, causing the slag to be too viscous and poor fluidity, which will not only hinder the discharge of inclusions and harmful elements, but also may corrode the furnace lining and affect the stability of the entire steelmaking process.

[0092] The dosage of 11-20 parts of fluorite is the key to ensure good fluidity of slag. If the dosage is insufficient, the melting point and viscosity of the slag cannot be reduced, the slag making process is stuck, and the removal of oxygen, hydrogen and inclusions is hindered; if the dosage is too much, although the fluidity is good, the stability of the slag is reduced, and component segregation may occur, which is also not conducive to the precise control of the slag making effect.

[0093] The amount of bauxite, 14-23 parts, should be just right. If it is too little, the inclusions will not be adsorbed thoroughly, the molten steel will not be completely purified, and the oxygen content will be difficult to reduce; if it is too much, too many impurity elements may be introduced, or the chemical balance of the slag may be changed, interfering with the synergistic effect of other raw materials.

[0094] 8-13 parts of magnesium oxide are used to finely adjust the basicity of the slag. If it is too little, the slag performance cannot be stabilized, the removal of oxygen and hydrogen is affected, and the furnace lining is easily corroded; if it is too much, the slag basicity will be too high, causing a waste of resources and being unfavorable for the control of subsequent steelmaking process parameters.

[0095] 6-9 parts of silica are involved in constructing a suitable slag system. A small amount will result in an imperfect slag structure and will not be able to effectively assist in the removal of oxygen and hydrogen. A large amount will change the basic properties of the slag, causing abnormal slag viscosity, which is not conducive to the advancement of the slag making process.

[0096] The dosage of 4-7 parts of borax balances the surface tension control and grain refinement of steel. If it is too little, it will be difficult to fully play the role of reducing pore defects and refining grains, and the impact toughness of steel will be limited; if it is too much, too much boron may be introduced, changing other properties of steel and causing performance imbalance.

[0097] 2-5 parts of lithium carbonate have precise dosage requirements for high-temperature stirring and hydrogen content control. If it is too little, the stirring will be insufficient, the composition of the molten steel will be uneven, and the hydrogen removal effect will be poor; if it is too much, there will be too much decomposition gas, which will cause excessive churning of the molten steel, affect the smelting stability, and may also introduce too many lithium impurities.

[0098] Titanium dioxide is 1-2 parts. If the dosage is too little, the titanium element cannot combine fully with nitrogen and oxygen, resulting in poor grain refinement and fixation of harmful impurities. If the dosage is too much, on the one hand, the cost will increase, and on the other hand, it may lead to excessive enrichment of titanium in the steel, resulting in new performance problems.

[0099] Rare earth oxides are 0.6-1.8 parts. If the amount is small, the many advantages of deoxidation, desulfurization, grain refinement and improvement of inclusion morphology cannot be fully exerted, and the degree of steel liquid purification is limited; if the amount is large, the residual rare earth elements may affect certain special properties of the steel, such as work hardening characteristics, which is not conducive to meeting the diverse use needs of alloy steels.

[0100] Through reasonable raw material selection, precise proportioning and rigorous preparation process, the components of the slag-forming agent prepared in the present invention work synergistically to effectively reduce the oxygen and hydrogen content in the molten steel, improve the mechanical properties of the alloy steel such as impact toughness, and provide a solid guarantee for the production of high-quality alloy steel.

[0101] 6) Second heating and standing (step 6)

[0102] Then raise the temperature to 1580-1650℃ and let it stand for 5-10min. The purpose is similar to step 3. Let it stand at high temperature again to make the newly formed inclusions float up, further purify the molten steel, and allow the alloy elements to fully and evenly diffuse at high temperature to ensure the uniformity of the composition and performance of the molten steel, provide high-quality molten steel for subsequent casting, and continuously optimize the steel quality by advancing step by step with the previous steps.

[0103] 7) Calcification treatment (step 7)

[0104] Add calcium iron alloy to the ladle for calcification treatment for 5-10 minutes. Calcium can spheroidize the sulfides in the steel, reduce their harm to the steel performance, refine the grains, and improve the toughness and cutting performance of the steel. The tapping temperature is controlled at 1570-1600℃. The precise tapping temperature ensures good fluidity of the molten steel, facilitates casting operations, ensures the quality of the casting, and avoids defects such as insufficient pouring and cold shut caused by improper temperature, which affects the performance of the final product.

[0105] 8) Temperature adjustment before casting and casting (step 8)

[0106] Adjust the temperature of molten steel to 1520-1550℃ according to the size of the casting. The right casting temperature is the key to obtaining high-quality castings. If the temperature is too high, the casting is prone to defects such as shrinkage holes and cracks; if the temperature is too low, the molten steel has poor fluidity and cannot fill the cavity, causing problems such as lack of meat. After precise temperature control, the casting is cast, and the carefully prepared molten steel is formed into the required shape, providing qualified blanks for subsequent heat treatment, connecting the previous and the next to ensure process continuity.

[0107] 9) Cleaning and heat treatment (step 9)

[0108] The castings are cleaned to remove impurities such as sand and scale on the surface to ensure surface quality. Heat treatment is then carried out. During quenching, the quenching temperature is 920-1000℃, and the heat preservation time is 6-8h according to the thickness and size of the casting, so that the steel undergoes austenite transformation, and the subsequent cooling obtains martensitic structure, which greatly improves the hardness and wear resistance; during tempering, the tempering temperature is 220-550℃, and the heat preservation time is 6-8h to eliminate quenching stress, stabilize the structure, adjust the toughness and hardness matching, and finally obtain niobium-containing hypereutectoid wear-resistant alloy steel.

[0109] The steps of preparing niobium-containing hypereutectoid wear-resistant alloy steel cannot be interchanged, and each link is closely dependent on each other. The previous steps create conditions for the subsequent steps, and the subsequent steps are further optimized based on the previous results. Optimizing process parameters is of utmost importance, such as temperature, time, alloy addition, slag-making agent parameters, etc. in each link. Minor deviations will accumulate and amplify, affecting the organizational structure and performance of the steel. Only with precise control and coordinated efforts of each step can the potential of alloy elements be fully utilized, breaking through the limitations of traditional steel grades, and preparing high-performance niobium-containing hypereutectoid wear-resistant alloy steel to meet the needs of harsh working conditions.

[0110] In order to make the disclosure of the present invention more complete, it is described below through more specific embodiments.

[0111] Example 1

[0112] The chemical composition of the niobium-containing hypereutectoid wear-resistant alloy steel includes: 0.9% carbon, 0.6% silicon, 0.7% manganese, 0.8% chromium, 0.2% nickel, 0.05% niobium, 0.03% phosphorus, 0.03% sulfur, 12ppm oxygen, 3ppm hydrogen, and the balance is iron and unavoidable impurities.

[0113] Preparation process:

[0114] (1) Design the composition system according to the chemical composition in terms of mass percentage;

[0115] (2) adding raw materials including scrap steel (without adding ferrochrome, ferroniobium, and nickel) into a medium frequency induction furnace, melting and heating to 1506° C.;

[0116] (3) Then raise the temperature to 1580°C and let stand for 15 minutes;

[0117] (4) After standing still, the furnace was quickly transferred to the converter, which had an alkaline lining. Oxygen was blown quickly at the bottom of the converter for 3 minutes. After stopping the oxygen blowing, argon was blown for 7 minutes. The argon flow rate was controlled at 12 L / min, and then the furnace was allowed to stand still for 9 minutes.

[0118] (5) After the converter molten steel is left to stand, it is quickly transferred to a medium frequency induction furnace, and ferrochromium alloy, ferroniobium alloy and nickel are added to perform alloying treatment and composite slag treatment. After sampling and analysis are qualified, the temperature of the molten steel is adjusted to 1510° C. The composite slag treatment method is to add a slag-forming agent to the molten steel after the alloying treatment is completed and perform composite slag treatment, and the amount of the slag-forming agent added is 9.4 kg / t;

[0119] The preparation method of a slag-forming agent comprises the following steps: taking 20 parts of lime, 12 parts of fluorite, 14 parts of bauxite, 9 parts of magnesium oxide, 15 parts of calcium oxide, 6 parts of silicon dioxide, 5 parts of borax, 2 parts of lithium carbonate, 1.2 parts of titanium dioxide, and 0.6 parts of rare earth oxide by weight, premixing at 520° C. for 1.5 hours, heating to 1930° C. for smelting for 3 hours, and finally cooling and crushing to a particle size of 5-10 mm to obtain a slag-forming agent;

[0120] (6) Then raise the temperature to 1580°C and let stand for 10 min;

[0121] (7) Add calcium iron alloy into the ladle for calcification treatment for 9 minutes, and the tapping temperature is controlled at 1575°C;

[0122] (8) Then adjust the temperature of the molten steel to 1530°C to cast the casting;

[0123] (9) The casting is cleaned and heat treated to obtain niobium-containing hypereutectoid wear-resistant alloy steel. The heat treatment method is as follows: during quenching treatment, the quenching temperature is 930°C and the holding time is 7.5 h; during tempering treatment, the tempering temperature is 225°C and the holding time is 8 h.

[0124] Example 2

[0125] The chemical composition of the niobium-containing hypereutectoid wear-resistant alloy steel includes: 1.0% carbon, 0.8% silicon, 0.8% manganese, 2.0% chromium, 0.5% nickel, 0.1% niobium, 0.04% phosphorus, 0.035% sulfur, 10ppm oxygen, 4ppm hydrogen, and the balance is iron and unavoidable impurities.

[0126] Preparation process:

[0127] (1) Design the composition system according to the chemical composition in terms of mass percentage;

[0128] (2) adding raw materials including scrap steel (without adding ferrochrome, ferroniobium, and nickel) into a medium frequency induction furnace, melting and heating to 1530° C.;

[0129] (3) Then raise the temperature to 1620°C and let stand for 12 minutes;

[0130] (4) After standing still, the furnace was quickly transferred to the converter, which used an alkaline lining. Oxygen was blown quickly at the bottom of the converter for 7 minutes. After stopping the oxygen blowing, argon was blown for 8 minutes. The argon flow rate was controlled at 10 L / min, and then the furnace was allowed to stand for 9 minutes.

[0131] (5) After the converter molten steel is left to stand, it is quickly transferred to a medium frequency induction furnace, and ferrochromium alloy, ferroniobium alloy and nickel are added to perform alloying treatment and composite slag making treatment. After sampling and analysis are qualified, the temperature of the molten steel is adjusted to 1530° C. The composite slag making treatment method is to add a slag making agent to the molten steel after the alloying treatment is completed and perform composite slag making treatment, and the amount of the slag making agent added is 9 kg / t;

[0132] The preparation method of a slag-forming agent comprises the following steps: taking 22 parts of lime, 15 parts of fluorite, 18 parts of bauxite, 10 parts of magnesium oxide, 15 parts of calcium oxide, 7 parts of silicon dioxide, 5 parts of borax, 3 parts of lithium carbonate, 1.5 parts of titanium dioxide, and 1.2 parts of rare earth oxide by weight, premixing at 490° C. for 1.2 hours, heating to 2180° C. for smelting for 2.2 hours, and finally cooling and crushing to a particle size of 5-10 mm to obtain a slag-forming agent;

[0133] (6) Then raise the temperature to 1610°C and let stand for 8 minutes;

[0134] (7) Add calcium iron alloy into the ladle for calcification treatment for 7 minutes, and control the tapping temperature at 1580°C;

[0135] (8) Then adjust the temperature of the molten steel to 1540°C to cast the casting;

[0136] (9) The casting is cleaned and heat treated to obtain niobium-containing hypereutectoid wear-resistant alloy steel. The heat treatment method is as follows: during quenching treatment, the quenching temperature is 970°C and the holding time is 7 hours; during tempering treatment, the tempering temperature is 400°C and the holding time is 7 hours.

[0137] Example 3

[0138] The chemical composition of the niobium-containing hypereutectoid wear-resistant alloy steel includes: 1.2% carbon, 1.0% silicon, 1.0% manganese, 3.5% chromium, 0.8% nickel, 0.15% niobium, 0.045% phosphorus, 0.036% sulfur, 14.8ppm oxygen, 4.6ppm hydrogen, and the balance is iron and unavoidable impurities.

[0139] Preparation process:

[0140] (1) Design the composition system according to the chemical composition in terms of mass percentage;

[0141] (2) adding raw materials including scrap steel (without adding ferrochrome, ferroniobium, and nickel) into a medium frequency induction furnace, melting and heating to 1545° C.;

[0142] (3) Then raise the temperature to 1650°C and let stand for 10 min;

[0143] (4) After standing still, the furnace was quickly transferred to the converter, which had an alkaline lining. Oxygen was blown quickly at the bottom of the converter for 9 minutes. After the oxygen was stopped, argon was blown for 7 minutes. The argon flow rate was controlled at 7L / min, and then the furnace was allowed to stand for 6 minutes.

[0144] (5) After the converter molten steel is left to stand, it is quickly transferred to a medium frequency induction furnace, and ferrochromium alloy, ferroniobium alloy and nickel are added to perform alloying treatment and composite slag making treatment. After sampling and analysis are qualified, the temperature of the molten steel is adjusted to 1550° C. The composite slag making treatment method is to add a slag making agent to the molten steel after the alloying treatment is completed and perform composite slag making treatment, and the amount of the slag making agent added is 8.3 kg / t;

[0145] The preparation method of a slag-forming agent comprises the following steps: taking 27 parts of lime, 19 parts of fluorite, 23 parts of bauxite, 12 parts of magnesium oxide, 18 parts of calcium oxide, 9 parts of silicon dioxide, 7 parts of borax, 5 parts of lithium carbonate, 2 parts of titanium dioxide, and 1.5 parts of rare earth oxide by weight, premixing at 490° C. for 1 hour, heating to 2300° C. for smelting for 2 hours, and finally cooling and crushing to a particle size of 5-10 mm to obtain a slag-forming agent;

[0146] (6) Then raise the temperature to 1640°C and let stand for 6 minutes;

[0147] (7) Add calcium iron alloy into the ladle for calcification treatment for 9 minutes, and the tapping temperature is controlled at 1580°C;

[0148] (8) Then, the temperature of the molten steel is adjusted to 1542°C for casting;

[0149] (9) The casting is cleaned and heat treated to obtain niobium-containing hypereutectoid wear-resistant alloy steel. The heat treatment method is as follows: during quenching treatment, the quenching temperature is 1000°C and the holding time is 6 h; during tempering treatment, the tempering temperature is 540°C and the holding time is 6 h.

[0150] Example 4

[0151] The chemical composition of the niobium-containing hypereutectoid wear-resistant alloy steel includes: 0.9% carbon, 0.7% silicon, 0.7% manganese, 1.5% chromium, 0.3% nickel, 0.08% niobium, 0.035% phosphorus, 0.032% sulfur, 11ppm oxygen, 3.5ppm hydrogen, and the balance is iron and unavoidable impurities.

[0152] Preparation process:

[0153] (1) Design the composition system according to the chemical composition in terms of mass percentage;

[0154] (2) adding raw materials including scrap steel (without adding ferrochrome, ferroniobium, and nickel) into a medium frequency induction furnace, melting and heating to 1512° C.;

[0155] (3) Then raise the temperature to 1586°C and let stand for 14 minutes;

[0156] (4) After standing still, the furnace was quickly transferred to the converter, which had an alkaline lining. Oxygen was blown quickly at the bottom of the converter for 4 minutes. After the oxygen was stopped, argon was blown for 6 minutes. The argon flow rate was controlled at 9 L / min, and then the furnace was allowed to stand still for 9 minutes.

[0157] (5) After the converter molten steel is left to stand, it is quickly transferred to a medium frequency induction furnace, and ferrochromium alloy, ferroniobium alloy and nickel are added to perform alloying treatment and composite slag making treatment. After sampling and analysis are qualified, the temperature of the molten steel is adjusted to 1520° C. The composite slag making treatment method is to add a slag making agent to the molten steel after the alloying treatment is completed and perform composite slag making treatment, and the amount of the slag making agent added is 8.8 kg / t;

[0158] The preparation method of a slag-forming agent comprises the following steps: taking 20 parts of lime, 13 parts of fluorite, 16 parts of bauxite, 9 parts of magnesium oxide, 14 parts of calcium oxide, 7 parts of silicon dioxide, 5 parts of borax, 3 parts of lithium carbonate, 1.2 parts of titanium dioxide, and 0.9 parts of rare earth oxide by weight, premixing at 500° C. for 1.1 hours, heating to 2100° C. for smelting for 2.5 hours, and finally cooling and crushing to a particle size of 5-10 mm to obtain a slag-forming agent;

[0159] (6) Then raise the temperature to 1580°C and let stand for 10 min;

[0160] (7) Add calcium iron alloy into the ladle for calcification treatment for 6 minutes, and the tapping temperature is controlled at 1582°C;

[0161] (8) Then adjust the temperature of the molten steel to 1530°C to cast the casting;

[0162] (9) The casting is cleaned and heat treated to obtain niobium-containing hypereutectoid wear-resistant alloy steel. The heat treatment method is as follows: during quenching treatment, the quenching temperature is 950°C and the holding time is 7 hours; during tempering treatment, the tempering temperature is 300°C and the holding time is 8 hours.

[0163] Example 5

[0164] The chemical composition of the niobium-containing hypereutectoid wear-resistant alloy steel includes: 1.1% carbon, 0.9% silicon, 0.9% manganese, 2.5% chromium, 0.6% nickel, 0.12% niobium, 0.04% phosphorus, 0.038% sulfur, 13ppm oxygen, 4.5ppm hydrogen, and the balance is iron and unavoidable impurities.

[0165] Preparation process:

[0166] (1) Design the composition system according to the chemical composition in terms of mass percentage;

[0167] (2) adding raw materials including scrap steel (without adding ferrochrome, ferroniobium, and nickel) into a medium frequency induction furnace, melting and heating to 1525° C.;

[0168] (3) Then raise the temperature to 1590°C and let stand for 13 minutes;

[0169] (4) After standing still, the furnace was quickly transferred to the converter, and the converter used an alkaline lining. Oxygen was blown quickly at the bottom of the converter for 5 minutes. After stopping the oxygen blowing, argon was blown for 7 minutes. The argon flow rate was controlled at 12L / min, and then the furnace was allowed to stand for 8 minutes.

[0170] (5) After the converter molten steel is left to stand, it is quickly transferred to a medium frequency induction furnace, and ferrochromium alloy, ferroniobium alloy and nickel are added to perform alloying treatment and composite slag making treatment. After sampling and analysis are qualified, the temperature of the molten steel is adjusted to 1550° C. The composite slag making treatment method is to add a slag making agent to the molten steel after the alloying treatment is completed and perform composite slag making treatment, and the amount of the slag making agent added is 9.2 kg / t;

[0171] The preparation method of a slag-forming agent comprises the following steps: taking 25 parts of lime, 17 parts of fluorite, 20 parts of bauxite, 11 parts of magnesium oxide, 17 parts of calcium oxide, 8 parts of silicon dioxide, 6 parts of borax, 4 parts of lithium carbonate, 1.8 parts of titanium dioxide, and 1.5 parts of rare earth oxide by weight, premixing at 495° C. for 1.3 hours, heating to 2070° C. for smelting for 2.3 hours, and finally cooling and crushing to a particle size of 5-10 mm to obtain a slag-forming agent;

[0172] (6) Then raise the temperature to 1650°C and let stand for 5 minutes;

[0173] (7) Adding calcium iron alloy into the ladle for calcification treatment for 7 minutes, the tapping temperature is controlled at 1600°C;

[0174] (8) Then the temperature of the molten steel is adjusted to 1550°C for casting;

[0175] (9) The casting is cleaned and heat treated to obtain niobium-containing hypereutectoid wear-resistant alloy steel. The heat treatment method is as follows: during quenching treatment, the quenching temperature is 980°C and the holding time is 6 h; during tempering treatment, the tempering temperature is 450°C and the holding time is 6.5 h.

[0176] Comparative Example 1

[0177] Chemical composition of alloy steel: It adopts the conventional composition of high manganese steel, namely 1.2% carbon, 12% manganese, the remainder is iron and unavoidable impurities, and no alloy elements such as niobium, chromium and nickel are added.

[0178] Preparation process: The traditional high manganese steel smelting and casting process is adopted. No complicated slag making, refining and precise temperature control operations are performed. The steel ingot is directly cast after smelting in an ordinary electric furnace, and then a simple water toughening treatment is performed. The quenching temperature is 1080℃, the holding time is 9h, and the tempering temperature is 300℃, and the holding time is 5h.

[0179] Comparative Example 2

[0180] The chemical composition of the alloy steel includes: 0.6% carbon, 0.4% silicon, 0.5% manganese, 0.5% chromium, no addition of key alloying elements such as niobium and nickel, 0.05% phosphorus, 0.045% sulfur, 20ppm oxygen content, 8ppm hydrogen content, and the balance is iron and unavoidable impurities.

[0181] Preparation process: Iron is added into a medium frequency induction furnace, and the temperature is raised to 1400°C after simple deoxidation. No fine slag-forming agent is prepared and added. Only conventional argon blowing for impurity removal is performed for 4 minutes. The argon flow rate is unstable at 4-8L / min. Afterwards, no calcification treatment is performed in the ladle, and the steel ingot is directly cast. The heat treatment process is quenching temperature at 880°C, holding time for 5h, tempering temperature at 180°C, and holding time for 4h.

[0182] Comparative Example 3

[0183] The chemical composition of the alloy steel includes: 1.5% carbon, 1.2% silicon, 1.2% manganese, 4.0% chromium, 1.0% nickel, but no niobium is added, 0.06% phosphorus, 0.05% sulfur, 25ppm oxygen content, 10ppm hydrogen content, and the balance is iron and unavoidable impurities.

[0184] Preparation process: Some processes similar to Example 2 of the present invention are adopted, such as medium frequency induction furnace smelting, heating to 1620°C, standing time as short as 10min, followed by alloying treatment and composite slag making treatment, but the slag making agent raw materials are simple, only lime, fluorite, and silica are mixed in proportion (22:15:7), and no fine premixing, smelting and particle size control are performed, the argon blowing treatment after the converter is not standardized, the calcification treatment time in the ladle is too short to 5min, the steel tapping temperature is controlled at 1550°C, and the heat treatment process is quenching temperature at 1050°C, holding time 9h, tempering temperature at 550°C, and holding time 10h.

[0185] Testing of performance indicators of hypereutectoid wear-resistant alloy steel containing niobium:

[0186] 1. Wear resistance test

[0187] The alloy steel samples prepared in Examples 1-5 and Comparative Examples 1-3 were respectively subjected to wear resistance tests using an MLS-225 wet material wear tester to simulate the actual working conditions of a rod mill, with quartz sand as the abrasive, the speed set at 200 r / min, and the wear time set at 10 h. The test results are shown in the following table:

[0188] Sample No. Wear amount (g) Wear rate (%) Example 1 0.81 0.164 Example 2 0.75 0.151 Example 3 0.89 0.175 Example 4 0.77 0.156 Example 5 0.85 0.170 Comparative Example 1 2.60 0.522 Comparative Example 2 1.82 0.361 Comparative Example 3 1.64 0.325

[0189] It can be seen from the data in the table that the wear amount and wear rate of Examples 1-5 are significantly lower than those of Comparative Examples 1-3. The alloy steel of the present invention has a wear resistance far exceeding that of the comparative samples due to the reasonable chemical composition design, especially the addition of niobium elements to refine the grains and form a dispersion strengthening phase, as well as a strict preparation process to ensure the purity of the steel. For example, the high manganese steel in Comparative Example 1 has severe wear due to the lack of addition of key alloying elements to improve the organizational structure and the extensive process; Comparative Example 2 has an unreasonable component design and a simple process, and also exhibits poor wear resistance; Comparative Example 3 partially borrows from the process but lacks niobium and the process details are not well controlled, so the wear resistance is not as good as that of the embodiments of the present invention.

[0190] 2. Toughness test

[0191] The impact toughness test was carried out on each sample using a JB-30B impact testing machine, processed according to the standard sample size, and the test temperature was room temperature. The test results are shown in the following table:

[0192]

[0193] As can be seen from the table, the impact toughness values ​​of Examples 1-5 are much higher than those of Comparative Examples 1-3. The present invention achieves good strength-toughness matching of steel by synergistic action of elements such as manganese, nickel, and niobium to refine grains and optimize organizational structure, and then combines reasonable heat treatment process. The high manganese steel of Comparative Example 1 is not tough enough and is prone to cracking under impact; the toughness of Comparative Example 2 is extremely low due to defects in composition and process; although Comparative Example 3 has some improvements, the toughness is still not ideal due to factors such as lack of niobium.

[0194] 3. Corrosion resistance test

[0195] Each sample was immersed in 5% sodium chloride solution for 30 days, the surface rust was observed and the corrosion rate was calculated using the weight loss method. The test results are shown in the following table:

[0196] Sample No. Corrosion rate (mm / year) Example 1 0.082 Example 2 0.075 Example 3 0.088 Example 4 0.078 Example 5 0.085 Comparative Example 1 0.551 Comparative Example 2 0.453 Comparative Example 3 0.402

[0197] As can be seen from the above table, the corrosion rates of Examples 1-5 are much lower than those of Comparative Examples 1-3. The alloy steel of the present invention has excellent corrosion resistance by virtue of measures such as the formation of a protective film by chromium elements and the improvement of the morphology of inclusions by rare earth elements. The high manganese steel of Comparative Example 1 has poor corrosion resistance, Comparative Example 2 has serious corrosion due to poor composition and rough process, and Comparative Example 3 has poor corrosion resistance despite the adjustment of composition but insufficient process.

[0198] Through the detection tests of the above performance indicators, it is fully proved that the niobium-containing hypereutectoid wear-resistant alloy steel of the present invention has significant progress in wear resistance, toughness, corrosion resistance, etc. compared with the existing technology, can meet the high performance requirements of large rod mill liners and the like under complex working conditions, and has broad application prospects.

[0199] In summary, the niobium-containing hypereutectoid wear-resistant alloy steel and its preparation method of the present invention overcome many defects of the prior art, achieve excellent comprehensive performance through unique composition design and sophisticated preparation process, and provide a valuable new material and new technology solution for the industrial wear-resistant field.

[0200] The above contents are further detailed descriptions of the present invention in combination with specific / preferred implementations, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, they can also make several substitutions or modifications to these described embodiments without departing from the concept of the present invention, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for preparing a hypereutectoid wear-resistant alloy steel containing niobium, characterized in that: The following steps are involved: (1) Design the composition system according to the chemical composition in terms of mass percentage; (2) adding raw materials including scrap steel into a medium frequency induction furnace and melting and heating to 1500-1550°C; (3) Then raise the temperature to 1580-1650°C and let stand for 10-15 minutes; (4) After standing still, the converter is quickly transferred to the converter, which uses an alkaline lining. Oxygen is blown quickly at the bottom of the converter for 3-10 minutes. After stopping the oxygen blowing, argon is blown for 5-10 minutes, and then the converter is allowed to stand still for 5-10 minutes. (5) After the converter molten steel is left to stand, it is quickly transferred to a medium frequency induction furnace, and ferrochromium alloy, ferroniobium alloy, and nickel are added for alloying treatment and composite slag treatment. After sampling and analysis are qualified, the molten steel temperature is adjusted to 1500-1550° C. The composite slag treatment method is to add a slag-forming agent to the molten steel after the alloying treatment is completed and then perform composite slag treatment; (6) Then raise the temperature to 1580-1650°C and let stand for 5-10 minutes; (7) Add calcium iron alloy into the ladle for calcification treatment for 5-10 minutes, and control the tapping temperature at 1570-1600°C; (8) Adjust the temperature of the molten steel to 1520-1550°C according to the size of the casting, and then cast the casting; (9) Cleaning the casting and producing niobium-containing hypereutectoid wear-resistant alloy steel after heat treatment.

2. The method for preparing niobium-containing hypereutectoid wear-resistant alloy steel according to claim 1, characterized in that: In step (2), ferrochromium alloy, ferroniobium alloy and nickel are not added to the raw materials including scrap steel.

3. The method for preparing niobium-containing hypereutectoid wear-resistant alloy steel according to claim 1, characterized in that: In step (4), the argon flow rate is controlled at 6-14 L / min.

4. The method for preparing niobium-containing hypereutectoid wear-resistant alloy steel according to claim 1, characterized in that: The preparation method of the slag-forming agent described in step (5) comprises the following steps: weighing the raw materials in proportion, premixing them at 520-490° C. for 1-1.5 h, heating them to 1900-2300° C. for smelting for 2-3 h, and finally cooling and crushing them to obtain the slag-forming agent.

5. The method for preparing niobium-containing hypereutectoid wear-resistant alloy steel according to claim 4, characterized in that: The particle size of the slag-forming agent is 5-10 mm.

6. The method for preparing niobium-containing hypereutectoid wear-resistant alloy steel according to claim 5, characterized in that: The amount of slag-forming agent added in step (6) ranges from 8.2 to 9.5 kg / t.

7. The method for preparing a niobium-containing hypereutectoid wear-resistant alloy steel according to claim 1, characterized in that: The qualified components of the sample analyzed in step (5) are as follows: carbon: 0.8-1.2%, silicon: 0.6-1.0%, manganese: 0.6-1.0%, chromium: 0.8-3.5%, nickel: 0.1-0.8%, niobium: 0.05-0.15%, phosphorus less than 0.05%, sulfur <0.04%, and the balance is iron and unavoidable impurities.

8. The method for preparing a niobium-containing hypereutectoid wear-resistant alloy steel according to claim 1, characterized in that: The heat treatment method after cleaning the casting in step (9) is as follows: during quenching treatment, the quenching temperature is 920-1000°C, and the insulation time is 6-8h according to the thickness and size of the casting; during tempering treatment, the tempering temperature is 220-550°C, and the insulation time is 6-8h.

9. A niobium-containing hypereutectoid wear-resistant alloy steel prepared according to the method according to any one of claims 1 to 8.

10. Application of the niobium-containing hypereutectoid wear-resistant alloy steel according to claim 9 in a large rod mill liner, characterized in that: The thickness of the lining plate is 50-150 mm.

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