High toughness and high wear resistance saw blade steel plate for engineering machinery equipment and manufacturing method thereof

Abstract

The application discloses a high-toughness and high-wear-resistance saw blade steel plate for engineering machinery equipment and a manufacturing method thereof, and belongs to the technical field of metallurgical saw blade steel production. The chemical composition of the steel plate is as follows in terms of percentage by weight: C: 0.53-0.60%, Si: 0.25-0.39%, Mn: 1.05-1.25%, Nb: 0.04-0.06%, Ni: 0.06-0.10%, Cr: 0.15-0.25%, B: 0.0015-0.0025%, Ca: 0.012-0.020%, H: ≤0.0002%, P: ≤0.020%, S: ≤0.020%, and the balance of Fe and inevitable impurities. The steel plate is produced by adopting optimized steelmaking, heating, rolling, controlled cooling and tempering processes, and has the hardness of 58-65 HRC, the impact energy Akv of-15 DEG C of ≥29J and the plate shape unevenness of ≤5mm / 2m.

Description

Technical Field

[0001] This invention relates to the field of metallurgical saw blade steel production technology, and in particular to a high-toughness, high-wear-resistant saw blade steel plate for engineering machinery equipment and its manufacturing method. Background Technology

[0002] Saw blade steel for engineering equipment is mainly used for cutting granite, marble, and other stone materials in engineering equipment. During the cutting process, the saw blade vibrates, therefore, the steel used for saw blades must possess high wear resistance while also having excellent toughness to resist impact loads, preventing brittle fractures such as tooth chipping. With the continuous increase in cutting speed, the diversification of processed materials, and the improvement of equipment automation, the performance provided by traditional general-purpose saw blade steel (such as 50MnCr2V, 65Mn, 75Cr1, etc.) is no longer sufficient to meet the requirements of saw blade steel for engineering equipment. Currently, saw blade steel for engineering equipment has gradually formed a series of products ranging from high carbon to low carbon. Low carbon steel (C≤0.25%) can be water-quenched, has good toughness, but insufficient wear resistance. Medium and high carbon steel (C>0.25%) has high hardness and good wear resistance, but suffers from poor toughness and is prone to cracking. Furthermore, to avoid quenching cracking, medium and high carbon saw blade steel requires salt bath heating and oil quenching, which are complex heat treatment processes, costly, and produce oil fumes during oil quenching, which is environmentally unfriendly. Therefore, the key technological direction for the development of a new generation of saw blade steel plates for engineering machinery equipment is to develop saw blade steel plates with excellent high toughness and high wear resistance to meet the requirements of downstream users.

[0003] Compared with existing technologies: To date, there are very few reports, both domestically and internationally, on the development of saw blade steel plates for engineering machinery equipment with high toughness and high wear resistance. Prior to this invention, patent application number 201910576051.1 disclosed "A High-Temperature Deformation Resistant 75Cr1 Saw Blade Steel and Its Production Process," which has a high carbon content (0.72-0.80%), easily producing acicular martensite after quenching. Although it has high strength and good wear resistance, its toughness is insufficient (the service temperature is only room temperature), and the high carbon content poses a risk of billet fracture. Although the saw blade steel production methods disclosed in the above patent documents have high wear resistance, they do not consider the control of toughness indicators. Using the technical solution provided by this invention, the above shortcomings can be effectively overcome, and saw blade steel plates for engineering machinery equipment with high toughness and high wear resistance can be developed using 135-200mm thick saw blade steel continuous casting billets to meet the technical requirements of downstream users. Summary of the Invention

[0004] The purpose of this invention is to overcome the aforementioned technical problems and deficiencies, and to provide a high-toughness, high-wear-resistant saw blade steel plate for engineering machinery and its manufacturing method. This method employs optimized steelmaking, heating, rolling, controlled cooling, and tempering processes to produce high-toughness and high-wear-resistant saw blade steel plates for engineering machinery with thicknesses of 10–30 mm and widths of 3200–4000 mm. The hardness is 58–65 HRC, the impact energy Akv at -15℃ is ≥29 J, and the plate shape unevenness is ≤5 mm / 2 m, thus solving the problem that saw blade steel plates for engineering machinery cannot simultaneously achieve high toughness and high wear resistance.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] This invention provides a high-toughness, high-wear-resistant saw blade steel plate for engineering machinery equipment. The chemical composition of the steel plate, by weight percentage, is as follows: C: 0.53%–0.60%, Si: 0.25%–0.39%, Mn: 1.05%–1.25%, Nb: 0.04%–0.06%, Ni: 0.06%–0.10%, Cr: 0.15%–0.25%, B: 0.0015%–0.0025%, Ca: 0.012%–0.020%, H≤0.0002%, P≤0.020%, S≤0.020%, with the balance being Fe and unavoidable impurities.

[0007] The roles of the main elements in the chemical composition of the steel plate of this invention are as follows: C: Carbon is one of the basic elements in steel. A lower carbon content is beneficial to improving the plasticity of the product, but too low a carbon content is not conducive to improving strength and hardness and subsequent heat treatment. Therefore, a carbon content of 0.53% to 0.60% is selected.

[0008] Mn: Manganese is a solid solution strengthening element. Manganese can improve the stability of austenite and improve the strength and plasticity of steel. However, the manganese-sulfur ratio is low (<3), which brings quality risks to the continuous casting production of steel. Therefore, the manganese content can be controlled between 1.05% and 1.25%.

[0009] Si: Silicon is the main element in steel. The silicon content must reach a certain level to ensure the yield strength of steel. However, if the silicon content is too high, the iron oxide scale formed on the surface in the heating furnace is difficult to remove, thus affecting the surface quality of the steel. Therefore, the silicon content in steel is controlled between 0.25% and 0.39%.

[0010] P: Phosphorus in steel is a harmful element, and the lower the better. However, considering that the manufacturing cost will increase if the phosphorus content in steel is too low, it is required that P ≤ 0.020%.

[0011] S: Sulfur in steel is a harmful element, and the lower the better. However, considering that the manufacturing cost will increase if the sulfur content in steel is too low, it is required that S≤0.020%.

[0012] Ca: Trace amounts of calcium can be used as a deoxidizing and desulfurizing agent in steel, and can improve the morphology of non-metallic inclusions. It is widely used in calcium treatment to clean steel. By adding trace amounts of calcium to carbon steel, dispersed, thermally stable second-phase calcium oxide particles are formed in the steel. Considering cost, its reasonable range is controlled at 0.012 to 0.020%.

[0013] H: Hydrogen in steel is a harmful element that causes hydrogen embrittlement in steel plates, so the lower the better. However, considering that the manufacturing cost will increase if the hydrogen content in steel is too low, H is required to be ≤0.002%.

[0014] Niobium (Nb) inhibits the deformation and recrystallization of austenite during the high-temperature stage of billet heating and deformation in steel, refining the austenite grains. Simultaneously, the refined billet exhibits smaller pearlite cluster diameters and smaller interlamellar spacing during cooling, promoting the diffusion of alloying elements such as carbon and the spheroidization of carbides. This causes carbides in Nb-added saw blade steel to precipitate within the grains and rapidly spheroidize, reducing the risk of billet fracture under external vibration. Considering cost, the Nb content range of this invention is designed to be 0.04%–0.06%.

[0015] B: A relatively effective element for significantly improving the hardenability of steel. It readily segregates at grain boundaries, preventing carbon precipitation. Even trace amounts of boron can have a significant effect. However, excessive boron content can easily form boron carbonitrides, reducing toughness and causing hot brittleness. The reasonable range is 0.0015–0.0025%.

[0016] Cr: It is a major element that can effectively improve hardenability, inhibit ferrite formation, and promote the formation of martensite and bainite. It plays an important role in controlling phase transformation structure, promotes the formation of polygonal ferrite, pearlite and acicular ferrite with a large number of dislocations in the grain in the medium and low temperature range, and improves the strength, plasticity and toughness of steel plates. The Cr content range selected in this invention is 0.15% to 0.25%.

[0017] Ni: In steel, nickel can lower the phase transformation temperature, improve the microstructure, refine the grains, and increase the strength of the steel while maintaining good plasticity and toughness. However, excessively high Ni content will increase production costs. Therefore, this invention controls the Ni content to be between 0.06% and 0.10%.

[0018] Furthermore, the steel plate has a thickness of 10-30 mm and a width of 3200-4000 mm.

[0019] Furthermore, the steel plate is produced using a cast billet on a medium-thickness reciprocating rolling mill, with water as the cooling medium.

[0020] The objective of this invention is achieved through the following technical solution: This invention provides a method for manufacturing high-toughness, high-wear-resistant saw blade steel plates for engineering machinery, comprising: steel smelting → ladle refining (LF refining) + RH vacuum degassing → B alloying → continuous casting → billet heating → controlled rolling → cooling and tempering; specifically including the following steps: 1) Steel smelting to continuous casting: Smelting according to the following composition, with the following chemical composition by weight percentage: C: 0.53%~0.60%, Si: 0.25%~0.39%, Mn: 1.05%~1.25%, Nb: 0.04%~0.06%, Ni: 0.06%~0.10%, Cr: 0.15%~0.25%, B: 0.0015%~0.0025%, Ca: 0.012%~0.020%, H≤0.0002%, P≤0.020%, S≤0.020%, with the balance being Fe and unavoidable impurities. Molten iron undergoes pretreatment, converter smelting, LF refining, RH vacuum degassing, and continuous casting. After RH vacuum degassing, B-Fe alloy is added for B alloying to ensure it doesn't float on the slag layer. Slab continuous casting is then performed with a superheat of 9–12°C and a casting speed of 0.8–1.1 m / min (reducing superheat and casting speed improves macroscopic segregation in the slab, decreases the spacing of secondary dendrite arms in the solidification structure, and helps reduce slab segregation and internal structural defects). Electromagnetic stirring is used in the secondary cooling zone during the continuous casting stage. The stirring method involves alternating forward and reverse rotation, with forward stirring lasting 20–30 seconds and reverse stirring lasting 40–50 seconds. The current is 600–1000 A, and the frequency is 25–40 Hz. This process ensures that the molten steel is continuously cast into a billet with an isometric crystal ratio of no less than 85%. Simultaneously, a strong cooling process is employed in the fan-shaped section of the continuous casting process. The total cooling water flow rate in the first half is 500–700 L / min to maintain a large temperature gradient between the surface and core at the end of the solidification process (>200℃). Light reduction of 5–10 mm is then applied. The total cooling water flow rate in the second half is 900–1300 L / min. / min, to ensure a large temperature gradient temperature field with a temperature difference of >400℃ between the surface and core at the end of continuous casting solidification, and then implement heavy pressure with a reduction of 15-20mm (by optimizing the electromagnetic stirring process in the continuous casting stage, the equiaxed crystal ratio of the continuously cast billet is significantly improved; strong cooling is used in the fan-shaped section and the cooling water volume of different sections is controlled to ensure the temperature gradient in the thickness direction of the billet; at the same time, light and heavy pressure are applied in different sections, which can help reduce billet segregation and ensure that strain penetrates to 1 / 4 of the billet (the location improved under light pressure) and 1 / 2 of the core (the location improved under heavy pressure), which can significantly improve defects in different locations of the billet cross-section, and prepare for subsequent steel plate processing. (To ensure high toughness), after the billet comes off the production line, it is placed in a pit for heat preservation, homogenization, and dehydrogenation treatment. The temperature in the pit is between 750 and 850°C, and the holding time is not less than 72 hours. Then it is slowly cooled to room temperature at a cooling rate of 10 to 20°C / hour. (The continuous casting billet is subjected to heat preservation, homogenization, and dehydrogenation treatment, and the homogenization temperature, time, and cooling rate are controlled to promote the diffusion of elements such as Mn, C, and H, reduce the impact of their component segregation on the microstructure and corner cracks of the billet, and at the same time ensure that the H content is not greater than 2 ppm, while also avoiding the third type of brittle zone of internal stress release during the slow cooling process). 2) Billet Heating: The billet is fed into a walking beam furnace for heating, passing through a preheating section, a heating section, and a soaking section before exiting the furnace. The preheating section temperature range is 400–600℃ (limiting the preheating temperature avoids direct contact with the heating and soaking sections, preventing excessive temperature differences that could cause billet fracture; it also promotes the dissolution and diffusion of Nb carbides into the matrix, reducing central segregation and effectively lowering the concentration and diffusion of H, C, Mn, and B within the billet). The heating section temperature range is 1230–1250℃, and the soaking section temperature range is 1210–1220℃. The total time spent in the furnace during the preheating, heating, and soaking sections is controlled to be 4.0–5.0 hours, with the heating and soaking sections taking 3.5–4.0 hours. The furnace temperature is adjusted accordingly. The opening of the upper and lower burners is controlled to maintain an air-fuel ratio of 1:1.7 to 1:2.1. A portion of the furnace head is reserved to ensure that the temperature difference between the upper and lower surfaces of the billet is within 10℃. (The heating section provides high-temperature heating to ensure temperature uniformity across the billet and partial dissolution of Nb carbides in the matrix. It also further promotes the diffusion of elements such as Mn, Cr, C, B, and Nb, mitigating their impact on microstructure and properties due to component segregation. Controlling the air-fuel ratio and the reserved space at the furnace head improves billet temperature uniformity, ensuring uniform transverse and longitudinal metal flow on the steel plate surface. Combined with the billet composition, reducing the heating temperature of the soaking zone decreases energy consumption, and controlling the furnace time effectively promotes the full diffusion of elements such as C, Mn, Cr, and B, while also suppressing the impact of coarsening of the original austenite grains on performance.) 3) Controlled rolling: The billet is rolled in two stages: the first stage is recrystallization rolling (rough rolling), with an initial rolling temperature ≥1150℃ and a final rolling temperature range of 980~1010℃. The reduction rate in the last three passes of the rough rolling stage is not less than 15% per pass (the last three passes of the rough rolling stage use a large reduction rate to promote dynamic recrystallization of austenite grains, refine the grains, and improve the core structure of thick steel plates). The thickness of the intermediate billet is 1.5~2.5 times the thickness of the finished product. During the intermediate billet's warming process, 1~2 passes of descaling water are sprayed onto it. The first stage (finish rolling) involves a 1-1.5 min interval, with a descaling machine pressure of 20-25 MPa to ensure a temperature difference of over 50℃ between the surface and core (this inhibits austenite grain growth, creates a temperature gradient on the inner and outer surfaces of the billet, promotes the penetration of rolling deformation into the thickness center, refines grains at half the thickness, improves the core microstructure of thick steel plates, reduces microstructural inhomogeneity-induced stress, and accelerates the temperature drop of the intermediate billet, reducing waiting time). The second stage (finish rolling) has an initial rolling temperature range of 930-950℃ and a finishing rolling speed of 5.6-6.8. The rolling speed is m / s, and the final rolling temperature range is 850–870℃. The first two passes in the finishing rolling stage ensure a reduction rate of over 20%, with no more than five finishing rolling passes. The final finishing rolling pass serves as a leveling pass, using a small reduction rate of 0.2%–0.5%. (By controlling the reduction speed and the reduction rate in the finishing rolling stage, the dislocation density, vacancies, and deformation bands within the austenite body are ensured, promoting NbC phase precipitation, providing more nucleation sites, refining the microstructure, and simultaneously expanding the austenite transformation zone by adding Nb, inhibiting austenite deformation recrystallization during the high-temperature deformation stage, and refining the austenite grains.) During the cooling process, there are more pearlite nucleation sites, resulting in smaller pearlite cluster diameters (5-10 μm) and pearlite lamellar spacing (4-8 μm) in the hot-rolled steel sheet. This ensures that martensite acicularis nucleates and grows within the austenite grains after online cooling. Grain boundaries hinder its growth, resulting in finer martensite acicularis, ultimately ensuring the strength and toughness of the steel sheet. The final pass uses a small reduction rate as a leveling pass to flatten the steel sheet shape, reduce internal stress, and prevent water retention in the steel sheet due to breakage and curling after controlled cooling, which would affect the uniformity of microstructure and properties. 4) Cooling + Tempering: The rolled steel plate is cooled using a UFC (Ultra-Fast Cooling System). The UFC cooling process employs fully automatic controlled cooling. The initial cooling temperature is 730–770℃, and the final cooling temperature is 150–200℃. The steel plate is fed in with the head and tail shielded. The upper manifold opening correction value is -300–-500mm, and the lower manifold opening correction value is -600–-800mm. The manifolds open from back to front (opposite to the steel plate's running direction). The water ratio between the upper and lower manifolds is 1:2.1–2.5. The roller speed of the steel plate conveyor is 0.3–0.6 m / s, and the acceleration is 0.002–0.005 m / s². 2After the steel plate exits controlled cooling, the side spray and air purging are activated, with the side spray pressure and water flow rate being 2-5 MPa and 120-150 m³ / h, respectively. 3 / h, the air purging pressure is 10-15MPa (after the steel plate enters the water, the manifold is opened from back to front to ensure that the proportion of polygonal ferrite in the microstructure of the steel plate before cooling is 10%-15%). During UFC cooling, the final cooling temperature and the head and tail shielding parameters of the controlled-cooling steel plate are controlled to effectively regulate the temperature uniformity of different positions of the head, middle and tail of the steel plate to ensure the strength, toughness and shape of the steel plate. The side spray and air purging are used to control the shape of the steel plate, reduce the probability of head and tail shape problems, and ensure the hardness of the steel plate. After cooling, the microstructure of the steel plate is ferrite + The steel plate is composed of martensite, with ferrite accounting for 10%–15% and martensite accounting for 85%–90%. After cooling, the steel plate is subjected to medium-temperature tempering in a heat treatment furnace at a tempering temperature of 450–500°C and a tempering time of 2.0–3.0 mm / min. (Medium-temperature tempering, combined with the addition of Nb, can promote carbon diffusion and has a strong carbide spheroidizing effect. At the same time, as the tempering temperature increases, although the martensitic twins gradually decrease, the toughness is improved. Meanwhile, the NbC and other microparticles precipitated in the Nb-added saw blade steel also ensure hardness and reduce internal stress.)

[0021] Furthermore, the thickness of the cast billet is 135–200 mm.

[0022] Furthermore, in step 1), the raw material is pretreated with KR molten iron to control the S content to be below 0.020%, and then enters the converter after slag removal; during converter smelting, the P content is controlled to be ≤0.020%, and the C content is controlled to be between 0.53% and 0.60% at the end of converter smelting. Argon gas is blown for more than 30 minutes when tapping the steel (argon blowing and calming before continuous casting can promote the removal of inclusions in the molten steel and improve the uniformity of the steel composition); then LF refining and RH vacuum degassing are carried out, and the RH vacuum is maintained for more than 35 minutes.

[0023] Furthermore, during the converter smelting process, a double-slag method is used for phosphorus removal.

[0024] Furthermore, in step 1), the first half of the forced cooling process consists of sections 1 to 4, and the second half consists of sections 5 to 8.

[0025] Furthermore, in step 2), the number of reserved empty spaces in the furnace head is 2 to 4.

[0026] Furthermore, in step 3), before rolling, the billet after exiting the furnace is descaled with high-pressure water for 0.3 to 0.5 minutes, and the descaling machine pressure is 15 to 20 MPa.

[0027] Furthermore, in step 4), 8-12 sets of water are turned on in both the upper and lower manifolds, with the water flow in the upper manifold being 250-280 m³. 3 / h.

[0028] Using the above-mentioned composition and process scheme, a saw blade steel plate with a thickness of 135-200mm and high toughness and wear resistance was developed for engineering machinery equipment. This was achieved by using a continuous casting billet of 135-200mm thick saw blade steel and employing a heating, rolling, controlled cooling, and tempering process. The plate has the following technical specifications: hardness 58-65HRC, impact energy Akv ≥ 29J at -15℃, and flatness ≤ 5mm / 2m.

[0029] The beneficial effects of this invention are: 1) After deep desulfurization pretreatment of KR hot metal, the slag is thoroughly removed. The converter employs a double-slag method for P removal, resulting in lower P and S content in the billet. By controlling the argon blowing time and maintaining the RH vacuum degassing time, defects such as center segregation and excessive inclusions in the billet caused by high Mn, Cr, and C content are overcome, thus improving the plasticity and toughness of the steel plate. Reducing superheat and continuous casting speed can improve macroscopic segregation in the continuously cast billet, decrease the spacing of secondary dendrite arms in the solidification structure of the billet, and help reduce billet segregation and internal structural defects. By optimizing the electromagnetic stirring process in the continuous casting stage, the equiaxed crystal ratio of the continuously cast billet is significantly improved. Strong cooling is used in the fan-shaped section, and the cooling water volume of different sections is controlled to ensure the temperature gradient in the thickness direction of the billet. At the same time, light and heavy pressure are applied in different sections, which helps to reduce billet segregation and ensure that strain penetrates to 1 / 4 of the billet (the improved position under light pressure) and 1 / 2 of the core (the improved position under heavy pressure). This can significantly improve defects in different positions of the billet cross section and provide a guarantee for the strength and toughness of the subsequent steel plate. Meanwhile, the billet after leaving the line is subjected to heat preservation homogenization and dehydrogenation treatment, and the homogenization temperature, time and cooling rate are controlled to promote the diffusion of elements such as Mn, C, B and H, reduce their impact on the microstructure and properties due to component segregation, ensure that the H content is not greater than 2ppm, and also avoid the third type of brittle zone of internal stress release during slow cooling. 2) The preheating temperature of the billet is limited to avoid direct contact with the heating and soaking zones, which could lead to excessive temperature differences and the risk of billet fracture. This also promotes the partial dissolution of Nb carbides in the matrix and facilitates their full diffusion, reducing central segregation and effectively lowering the concentration and diffusion of H, C, Mn, and B within the billet. The heating zone provides high-temperature heating to ensure temperature uniformity across the billet and the partial dissolution of Nb carbides in the matrix. It further promotes the diffusion of elements such as Mn, Cr, C, B, and Nb, mitigating their impact on microstructure and properties due to component segregation. Simultaneously, the air-fuel ratio and furnace head clearance are controlled to improve billet temperature uniformity, ensuring uniform transverse and longitudinal metal flow on the steel plate surface. Combined with the billet composition, reducing the heating temperature in the soaking zone decreases energy consumption, and controlling the time spent in the furnace effectively promotes the full diffusion of elements such as C, Mn, Cr, and B, while also suppressing the impact of coarsening of the original austenite grains on performance. 3) The last three passes of the roughing stage employ a high reduction rate to promote dynamic recrystallization of austenite grains, refining the grains and improving the core microstructure of thick steel plates. During the intermediate temperature cooling process, descaling water sprayed into the mill inhibits austenite grain growth and simultaneously creates a temperature gradient on the inner and outer surfaces of the billet, promoting the penetration of rolling deformation towards the thickness center, refining the grains at half the thickness, thus improving the core microstructure of thick steel plates, reducing microstructural inhomogeneity and stress, and accelerating the temperature drop of the intermediate billet, reducing the cooling time. By controlling the reduction rate and the reduction rate in the finishing stage, the dislocation density, vacancies, and deformation bands within the austenite are ensured, promoting NbC phase precipitation, providing more nucleation sites, and refining the grains. The addition of Nb expands the austenite transformation zone, inhibits the deformation and recrystallization of austenite during the high-temperature deformation stage, refines the austenite grains, and increases the number of pearlite nucleation points during cooling. As a result, the diameter of pearlite clusters (5-10 μm) and the spacing between pearlite lamellars (4-8 μm) in the hot-rolled steel sheet are smaller. This ensures that martensite aciculars nucleate and grow within the austenite grains during quenching, while grain boundaries hinder their growth. Therefore, the martensite aciculars are finer, ultimately ensuring the strength and toughness of the steel sheet. The final pass uses a small reduction rate as a leveling pass to flatten the shape of the steel sheet, reduce the internal stress of the steel sheet, and avoid water retention in the steel sheet due to broken waves and curling heads after controlled cooling, which would affect the uniformity of the microstructure and properties. 4) During UFC cooling, the manifold is opened from back to front after the steel plate is immersed in water to ensure that the proportion of polygonal ferrite in the microstructure of the steel plate is 10% to 15% before cooling. During UFC cooling, the final cooling temperature and the shielding parameters of the head and tail of the steel plate are controlled to effectively regulate the temperature uniformity of different positions of the head, middle and tail of the steel plate, so as to ensure the strength, toughness and shape of the steel plate. The side spray and air blowing are used to help control the shape of the steel plate, reduce the probability of the shape problems of the head and tail, and ensure the hardness of the steel plate. After cooling, the microstructure of the steel plate is ferrite + martensite, with the proportion of ferrite being 10% to 15% and the proportion of martensite being 85% to 90%. Medium-temperature tempering is used. Combined with the addition of Nb, it can promote carbon diffusion and has a strong carbide spheroidizing effect. At the same time, as the tempering temperature increases, although the martensite twins gradually decrease, the toughness is improved. At the same time, the NbC and other small particles precipitated in the Nb-added saw blade steel also ensure hardness and reduce internal stress. 5) Using the above-mentioned composition and process scheme, a saw blade steel plate with a thickness of 10-30 mm and a width of 3200-4000 mm was developed for engineering machinery equipment. This plate, made from a 135-200 mm thick continuously cast billet of saw blade steel, employs heating, rolling, controlled cooling, and tempering processes, and features high toughness and high wear resistance. The technical specifications of the produced plate are: hardness 58-65 HRC, impact energy Akv ≥ 29 J at -15℃, and flatness ≤ 5 mm / 2 m. Detailed Implementation

[0030] The following examples are used to illustrate the content of the present invention. These examples are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0031] A high-toughness, high-wear-resistant saw blade steel plate for engineering machinery equipment, wherein the chemical composition of the steel plate, by weight percentage, is: C: 0.53%–0.60%, Si: 0.25%–0.39%, Mn: 1.05%–1.25%, Nb: 0.04%–0.06%, Ni: 0.06%–0.10%, Cr: 0.15%–0.25%, B: 0.0015%–0.0025%, Ca: 0.012%–0.020%, H≤0.0002%, P≤0.020%, S≤0.020%, with the balance being Fe and unavoidable impurities. The steel plate has a thickness of 10–30 mm and a width of 3200–4000 mm, and is produced using 135–200 mm cast billets on a medium-thickness reciprocating rolling mill, with water as the cooling medium.

[0032] The manufacturing method of the aforementioned high-toughness, high-wear-resistant saw blade steel plate for engineering machinery includes steel smelting → ladle refining (LF refining) + RH vacuum degassing → B alloying → continuous casting → billet heating → controlled rolling → cooling and tempering; specifically, it includes the following steps: 1) Steelmaking to continuous casting: Smelting according to the above composition. Raw materials undergo KR hot metal pretreatment to control the S content below 0.020%, and after slag removal, they enter the converter. In the converter smelting, a double-slag method is used to remove P, controlling the P content ≤0.020%. At the end of the converter smelting, the C content is controlled at 0.53%–0.60%, and argon gas is blown for at least 30 minutes during tapping. Next, LF refining and RH vacuum degassing are performed, with the RH vacuum maintained for at least 35 minutes. After RH vacuum degassing, B-Fe alloy is added for B alloying, ensuring it is added to the molten steel and avoids floating on the slag layer. Slab continuous casting is then performed, with a superheat of 9–12℃ and a casting speed of 0.8–1.1 m / min. During the continuous casting stage, electromagnetic stirring is used in the secondary cooling zone, with alternating forward and reverse stirring. The forward stirring time is 20–30 s, and the reverse stirring time is 40–50 s, with a current of 600–1000 A and a frequency of… The ferroalloy temperature is 25–40 Hz, allowing the molten steel to be continuously cast into a billet with an isometric crystal ratio of no less than 85%. In the fan-shaped section of the continuous casting process, a strong cooling process is employed. The total cooling water flow rate for sections 1–4 is 500–700 L / min to ensure a large temperature gradient with a surface-to-core temperature difference >200°C at the end of the solidification process. Light cooling is then applied with a reduction of 5–10 mm. For sections 5–8, the total cooling water flow rate is 900–1300 L / min to ensure a surface-to-core temperature gradient with a surface-to-core temperature difference >400°C at the end of the solidification process. Then, heavy cooling is applied with a reduction of 15–20 mm. After casting, the billet is placed in a pit for heat preservation, homogenization, and hydrogen removal treatment. The pit holding temperature is between 750–850°C for at least 72 hours, followed by slow cooling to room temperature at a rate of 10–20°C / hour, while ensuring the hydrogen content is no more than 2 ppm. 2) Billet Heating: The billet is fed into a walking beam furnace for heating. The billet passes through the preheating section, heating section, and soaking section in sequence before exiting the furnace. The temperature range of the preheating section is 400-600℃, the temperature range of the heating section is 1230-1250℃, and the temperature range of the soaking section is 1210-1220℃. The total time in the furnace for the preheating, heating, and soaking sections is controlled at 4.0-5.0 hours, of which the time in the heating and soaking sections is 3.5-4.0 hours. The opening degree of the upper and lower burners in the furnace is adjusted to control the air-fuel ratio at 1:1.7-1:2.1. 2-4 empty spaces are reserved at the furnace head to ensure that the temperature difference between the upper and lower surfaces of the billet is within 10℃. 3) Controlled Rolling: Before rolling, the cast billet is descaled with high-pressure water for 0.3–0.5 minutes. The descaling machine pressure is 15–20 MPa. Rolling is performed in two stages: The first stage is recrystallization rolling (rough rolling), with an initial rolling temperature ≥1150℃ and a final rolling temperature range of 980–1010℃. The reduction rate in the last three passes of the rough rolling stage is not less than 15% per pass, and the thickness of the intermediate billet is 1.5–2.5 times the thickness of the finished product. During the intermediate billet's warming process, 1–2 passes of descaling water are sprayed for 1–1.5 minutes, with a descaling machine pressure of 20–25 MPa, ensuring a temperature difference of over 50℃ between the surface and core. The second stage (finish rolling) has an initial rolling temperature range of 930–950℃, and a rolling speed of 5.6–6.8. The rolling speed is m / s, the final rolling temperature range is 850~870℃, the first two passes of the finishing rolling stage ensure a reduction rate of more than 20%, the finishing rolling is no more than five passes, and the last pass of finishing rolling is used as a leveling pass with a small reduction rate of 0.2%~0.5%. Therefore, the diameter of pearlite clusters (5~10μm) and the spacing between pearlite lamellars in the hot-rolled steel plate are smaller (4~8μm). 4) Cooling + Tempering: The rolled steel plate is cooled using a UFC (Ultra-Fast Cooling System). The UFC cooling process employs fully automatic controlled cooling. The initial cooling temperature is 730–770℃, and the final cooling temperature is 150–200℃. The steel plate is shielded at both ends before insertion. The upper manifold opening correction value is -300–-500mm, and the lower manifold opening correction value is -600–-800mm. The manifolds open from back to front (opposite to the steel plate's running direction). 8–12 sets of water are opened in both the upper and lower manifolds, with the upper manifold having a water flow rate of 250–280m³. 3 / h; the water ratio (water volume ratio) between the upper and lower manifolds is 1:2.1~2.5; the roller speed of the steel plate conveyor is 0.3~0.6m / s, and the acceleration is 0.002~0.005m / s². 2 After the steel plate exits controlled cooling, the side spray and air purging are activated, with the side spray pressure and water flow rate being 2-5 MPa and 120-150 m³ / h, respectively. 3 / h, the air purging pressure is 10~15MPa (after the steel plate is put into the water, the manifold is opened from back to front to ensure that the proportion of polygonal ferrite in the microstructure of the steel plate before cooling is 10%~15%, and the microstructure of the steel plate after cooling is ferrite + martensite, of which the proportion of ferrite is 10%~15% and the proportion of martensite is 85%~90%); the cooled steel plate is tempered at medium temperature in a heat treatment furnace, the tempering temperature is 450~500°C, and the tempering time is 2.0~3.0mm / min.

[0033] 5) Air cool to room temperature.

[0034] Examples 1-6 Table 1 shows the chemical composition of the steel in the examples; Table 2 shows the smelting process of the steel in the examples; Table 3 shows the heating and descaling of the billets of the steel in the examples; Table 4 shows the rolling process of the steel in the examples; Table 5 shows the cooling and tempering process of the steel in the examples; Table 6 shows the dimensions, properties and flatness of the steel in the examples.

[0035] Table 1. Chemical composition (wt, %) of the steel in the embodiments of the present invention

[0036] Note: Impurity elements in steel: P≤0.02%, S≤0.020%.

[0037] Table 2. Smelting process of steel in the examples

[0038] Table 3 Heating and descaling processes for steel billets in the examples

[0039] Table 4 Rolling process of steel in the examples

[0040] Table 5 Cooling and tempering processes for the steel in the examples

[0041] Table 6. Dimensions, properties, and flatness of the steel in the examples.

[0042] This invention provides a saw blade steel plate for engineering machinery with a thickness of 10-30mm and a width of 3200-4000mm, exhibiting high toughness and high wear resistance, developed using 135-200mm thick continuously cast saw blade steel billets and employing heating, rolling, controlled cooling, and tempering processes. The technical specifications of the produced plate are: hardness 58-65HRC, impact energy Akv ≥29J at -15℃, and plate unevenness ≤5mm / 2m.

[0043] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-toughness, high-wear-resistant saw blade steel plate for engineering machinery equipment, characterized in that, Its chemical composition by weight percentage is as follows: C: 0.53%–0.60%, Si: 0.25%–0.39%, Mn: 1.05%–1.25%, Nb: 0.04%–0.06%, Ni: 0.06%–0.10%, Cr: 0.15%–0.25%, B: 0.0015%–0.0025%, Ca: 0.012%–0.020%, H≤0.0002%, P≤0.020%, S≤0.020%, with the balance being Fe and unavoidable impurities.

2. The high-toughness, high-wear-resistant saw blade steel plate for engineering machinery equipment according to claim 1, characterized in that, The steel plate has a thickness of 10-30 mm and a width of 3200-4000 mm.

3. The high-toughness, high-wear-resistant saw blade steel plate for engineering machinery equipment according to claim 1, characterized in that, The steel plate has a hardness of 58-65 HRC, an impact energy Akv ≥ 29 J at -15℃, and a plate shape unevenness ≤ 5 mm / 2 m.

4. The method for manufacturing the high-toughness, high-wear-resistant saw blade steel plate for engineering machinery equipment as described in any one of claims 1-3, characterized in that, Includes the following steps: 1) Steelmaking to Continuous Casting: Molten iron undergoes pretreatment, converter smelting, LF refining, RH vacuum degassing, and continuous casting. After RH vacuum degassing, B-Fe alloy is added for B alloying. Slab continuous casting is then performed with a superheat of 9–12°C and a casting speed of 0.8–1.1 m / min. Electromagnetic stirring is used in the secondary cooling zone during the continuous casting stage, with alternating forward and reverse stirring. Forward stirring time is 20–30 s, reverse stirring time is 40–50 s, current is 600–1000 A, and frequency is 25–40 Hz. This ensures that the molten steel yields a continuously cast billet with an isometric crystal ratio of no less than 85%. Simultaneously, in the fan-shaped section of the continuous casting process, electromagnetic stirring is employed. The forced cooling process involves a total cooling water flow of 500–700 L / min in the first half to ensure a large temperature gradient with a temperature difference of >200℃ between the surface and core at the end of the continuous casting solidification, followed by light reduction of 5–10 mm. In the second half, the total cooling water flow is 900–1300 L / min to ensure a large temperature gradient with a temperature difference of >400℃ between the surface and core at the end of the continuous casting solidification, followed by heavy reduction of 15–20 mm. After casting, the billet is placed in a heat preservation pit for homogenization and dehydrogenation treatment. The pit temperature is maintained between 750–850℃ for at least 72 hours, followed by slow cooling to room temperature at a rate of 10–20℃ / hour, ensuring that the hydrogen content is no more than 2 ppm. 2) Billet Heating: The billet is fed into the heating furnace for heating. The billet passes through the preheating section, heating section and soaking section in sequence before exiting the furnace. The temperature of the preheating section is 400-600℃, the temperature of the heating section is 1230-1250℃, and the temperature of the soaking section is 1210-1220℃. The total time in the furnace for the preheating section, heating section and soaking section is controlled at 4.0-5.0 hours, of which the time in the heating section and soaking section is 3.5-4.0 hours. The opening degree of the upper and lower burners of the heating furnace is adjusted to control the air-fuel ratio at 1:1.7-1:2.

1. Some space is reserved at the furnace head to ensure that the temperature difference between the upper and lower surfaces of the billet is within 10℃. 3) Controlled Rolling: The billet is rolled in two stages: The first stage is rough rolling, with an initial rolling temperature ≥1150℃ and a final rolling temperature of 980~1010℃. The reduction rate in the last three passes of the rough rolling stage is no less than 15% per pass, and the thickness of the intermediate billet is 1.5~2.5 times the thickness of the finished steel plate. During the intermediate billet's warming process, 1~2 passes of descaling water are sprayed, with a descaling time of 1~1.5 min and a descaling machine pressure of 20~25 MPa, ensuring a temperature difference of over 50℃ between the surface and core. The second stage is finish rolling, with an initial rolling temperature of 930~950℃ and a rolling speed of 5.6~6.

8. m / s, finishing rolling temperature is 850~870℃, the first two passes of finishing rolling ensure a reduction rate of more than 20%, the finishing rolling is no more than five passes, the last pass of finishing rolling is used as a leveling pass, with a small reduction rate of 0.2%~0.5%, to obtain the rolled steel plate. 4) Cooling + Tempering: The rolled steel plate adopts ultra-fast cooling, with an initial cooling temperature of 730-770℃ and a final cooling temperature of 150-200℃. The steel plate is fed in with the head and tail shielded. The upper manifold opening correction value is -300 to -500mm, and the lower manifold opening correction value is -600 to -800mm. The manifolds open from back to front, opposite to the steel plate's running direction. The water ratio between the upper and lower manifolds is 1:2.1-2.

5. The roller speed of the steel plate conveyor is 0.3-0.6m / s, and the acceleration is 0.002-0.005m / s². 2 After the steel plate exits controlled cooling, the side spray and air purging are activated, with the side spray pressure and water flow rate being 2–5 MPa and 120–150 m³ / h, respectively. 3 / h, the air purging pressure is 10~15MPa; the cooled steel plate is tempered at a medium temperature of 450~500°C and the tempering time is 2.0~3.0mm / min.

5. The manufacturing method according to claim 4, characterized in that, In step 1), the raw materials are pretreated with KR molten iron to control the S content to be below 0.020%, and then enter the converter after slag removal. During converter smelting, the P content is controlled to be ≤0.020%, and the C content is controlled to be between 0.53% and 0.60% at the end of converter smelting. Argon gas is blown for more than 30 minutes when tapping the steel. Then, LF refining and RH vacuum degassing are carried out, and the RH vacuum is maintained for more than 35 minutes. In the forced cooling process, the first half consists of sections 1 to 4, and the second half consists of sections 5 to 8.

6. The manufacturing method according to claim 5, characterized in that, During the converter smelting process, the double slag method is used for phosphorus removal.

7. The manufacturing method according to claim 4, characterized in that, The thickness of the billet is 135-200mm; the steel plate is produced using the billet on a medium-thickness reciprocating rolling mill, with water as the cooling medium.

8. The manufacturing method according to claim 4, characterized in that, In step 2), the number of empty spaces reserved at the furnace head is 2 to 4; In step 3), before rolling, the billet after exiting the furnace is descaled with high-pressure water for 0.3 to 0.5 minutes, and the descaling machine pressure is 15 to 20 MPa.

9. The manufacturing method according to claim 4, characterized in that, In step 3), the diameter of the pearlite clusters in the rolled steel plate is 5-10 μm, and the spacing between the pearlite lamellars is 4-8 μm.

10. The manufacturing method according to claim 4, characterized in that, In step 4), the proportion of polygonal ferrite in the microstructure of the steel plate before cooling is 10% to 15%; During the cooling process, 8-12 sets of water are opened in both the upper and lower manifolds, with the water flow rate in the upper manifold being 250-280m³. 3 / h; After cooling, the microstructure of the steel plate is ferrite + martensite, with ferrite accounting for 10% to 15% and martensite accounting for 85% to 90%.

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