Thick gauge shear blade steel 75Cr1 open flat and method of production thereof

Abstract

The application provides a thick-gauge cutting blade steel 75Cr1 open flat and a production method thereof, compared with the prior art, the application optimizes a conventional transverse cutting plate production process, especially for thick-gauge 12-20mm, high-strength 75Cr1, by means of a hot coil direct sheath annealing intermediate process, plasticity is improved, and cutting property is improved; in the transverse cutting process, by means of ''small deformation straightening'' and a non-edge cutting process, excellent thick-gauge cutting blade steel 75Cr1 open flat is generated. The application judges whether the hot-rolled strip steel is subjected to sheath annealing before transverse cutting according to the size of the critical value Agt of the hot-rolled strip steel and the size of the critical value A 临 of fracture occurring in the straightening process, selects the sheath annealing process according to the need, and saves the cost. In addition, the annealing process designed in the application can improve the microstructure and performance of the product, so that the product performance of the thick steel plate meets the requirements.

Description

Technical Field

[0001] This invention belongs to the technical field of steel production process for shear blades, and relates to a thick-gauge 75Cr1 shear blade steel plate and its production method. Background Technology

[0002] 75Cr1 possesses high strength and hardness, and is commonly used in the manufacture of diamond and carbide saw blade substrates. Hot-rolled 75Cr1 coils are typically 3-8mm thick and are mainly delivered in flat sheets. For the production of thinner 75Cr1 sheets, the industry has developed relatively mature manufacturing technologies, capable of achieving uniform microstructure, good surface quality, and dimensional accuracy to meet the requirements of tool machining.

[0003] One application of thick-gauge 75Cr1 steel is in manufacturing shear blades for slitting equipment, typically ranging from 12-20mm in thickness. Thick-gauge 75Cr1 contains approximately 0.75% carbon, resulting in a high proportion of hard cementite in its rolled microstructure. Since plastic deformation in metals relies on the movement of internal dislocations, the cementite significantly hinders this movement, preventing stress release through plastic deformation and leading to brittle fracture. Therefore, 75Cr1 steel for shear blades, while possessing high strength, has low elongation. Using conventional hot rolling and cross-cutting processes to produce cross-cut plates easily results in brittle fracture, impacting production efficiency and costs.

[0004] In summary, providing a thick-gauge 75Cr1 steel cutting plate to improve the problem of brittle fracture is an urgent issue to be addressed. Summary of the Invention

[0005] This invention provides a thick-gauge slitting plate made of 75Cr1 steel for shear blades and its production method. Through a reasonable production process, a cross-cutting and straightening scheme is provided to produce a thick-gauge slitting plate made of 75Cr1 steel for shear blades. The product thickness is 12-20mm. The slitting plate has a good shape and a good shear blade surface, and no brittle fracture occurs during the slitting process.

[0006] The specific technical solution of this invention is as follows:

[0007] This invention provides a method for producing thick-gauge 75Cr1 steel slitting plates, including cross-cutting, employing a small straightening scheme, and using one and two straightening processes; wherein, on straightening machine #1: the 1st roll is lifted by 5.00-9.50mm, the 3rd roll by 0.01-0.15mm, the 5th roll by 0.01mm, and the 7th roll is not lifted; on straightening machine #2: the 1st roll is lifted by 0.30-0.50mm, the 3rd roll by 2.85-3.85mm, and the 5th, 7th, 9th, and 11th rolls are lifted by 0.30-0.45mm.

[0008] Because thick-gauge 75Cr1 exhibits a "bowback" phenomenon in the width direction, and issues such as uncoiling, undercoiling, or upturning all require straightening equipment for improvement, it is necessary to utilize both primary and secondary straightening machines. In the straightening machine, the strip undergoes repeated bending under stress, causing elasto-plastic bending deformation, thus achieving the straightening effect. Too little deformation will not correct the shape, while too much deformation can lead to brittle fracture even in annealed coils. Although the plasticity of thick-gauge 75Cr1 is significantly improved after annealing, its thickness is still considerable, resulting in a much lower elongation compared to steels of ordinary thickness. Therefore, a small deformation straightening scheme is recommended, meaning both straightening machines #1 and #2 employ this scheme. Straightening machine #1 primarily functions to uncoil and initially improve the shape. Straightening machine #1: Roll 1 lifts 5.00-9.50mm, Roll 3 lifts 0.01-0.15mm, Roll 5 lifts 0.01mm, and Roll 7 has no lift. After the strip steel is sheared by the flying shear, it may buckle downwards or curl upwards, resulting in the flatness not meeting the requirements. Therefore, the No. 2 straightening machine also needs to be slightly deformed: the 1st roll is raised by 0.30-0.50mm, the 3rd roll is raised by 2.85-3.85mm, and the 5th, 7th, 9th and 11th rolls are raised by 0.30-0.45mm.

[0009] Furthermore, based on the Ag of hot-rolled strip and the critical value A for fracture during the straightening process... 临 The size of the strip determines whether it has been covered before transverse cutting;

[0010] During the straightening process, the strip is subjected to A 临 This can be determined through the following calculations:

[0011] ;

[0012] Where, if the Ag of hot-rolled strip steel is greater than A 临 In this case, hot-rolled strip steel does not need to be covered and can be directly cross-cut as described above, which saves process costs while ensuring that it does not break brittlely; of course, under this condition, it is also possible to cover and then cross-cut.

[0013] If At ≤ A 临 If the hot-rolled strip steel is not properly protected, it must be covered and unloaded before it can be cross-cut; otherwise, it will break brittlely, affecting normal production.

[0014] Among them, the critical value A for fracture during the straightening process 临The units are %; L0 is the original gauge length in mm; ΔL is the increment of the original gauge length when the steel plate is deformed by the pressure of the straightening roller in mm; h is the plate thickness in mm; and R is the radius of the straightening roller in mm (110 mm in this invention). If the elongation of the steel plate under the pressure of the straightening roller exceeds the maximum force total elongation (Agt value), it indicates that the steel plate of this thickness will experience brittle fracture during cross-cutting and straightening. Therefore, the deformation should be reduced as much as possible while improving the plate shape, as shown in the schematic diagram. Figure 2 As shown in the figure. This formula calculates the elongation rate based on the stress principle of the steel plate. By comparing this calculated elongation rate with the maximum force total elongation rate of the strip during the room temperature tensile test, it can be determined whether the strip will experience brittle fracture during the straightening process.

[0015] The specific heating temperature T = 730 + (d - 16) × 3, the holding time t = 6 + (d - 16) × 1 / 6, where the thickness d of the steel is in mm, the heating temperature T is in °C, and the holding time t is in h.

[0016] Annealing is a direct annealing treatment of hot-rolled strip steel, which transforms lamellar pearlite into spherical pearlite, which is dispersed in the matrix. This reduces the strip steel's strength but significantly improves its plasticity. The degree of spheroidization is closely related to the heating temperature and holding time. Higher temperatures and longer holding times, while ensuring the required spheroidization rate, also result in higher energy consumption, significantly increasing production costs and posing certain safety hazards. Furthermore, it can lead to decarburization and grain boundary oxidation in high-carbon steel, which is detrimental to surface quality control. If a lower heating temperature (below Ac1) is used, although some lamellar pearlite melts and a small amount of spherical pearlite appears on the surface microstructure of thick-gauge 75Cr1, the microstructure at the 1 / 4 thickness and center thickness positions remains in the hot-rolled state, and the plasticity is not improved. This is because the finishing reduction rate of thick-gauge 75Cr1 is small (50-68%), far lower than the conventional 90%, and the use of a sparse cooling method in the front section results in fewer nucleation points, leading to a coarse rolled microstructure and relatively large interlamellar spacing of pearlite, making it difficult to spheroidize. Furthermore, since the hot-rolled coil is directly annealed without cold rolling, the pearlite is not significantly elongated or broken, and crystal defects are not significantly increased, resulting in a poor annealing effect. Therefore, a higher annealing temperature process should be used for thick-gauge 75Cr1, and the annealing process should be adjusted according to different thicknesses. Based on the Ac1 temperature of this steel grade, the heating temperature for 16mm 75Cr1 is determined to be 730℃, and the holding time is 6h. Furthermore, the temperature T and time t should be adjusted accordingly based on the different steel thicknesses d. Specifically, the heating temperature T = 730 + (d - 16) × 3, and the holding time t = 6 + (d - 16) × 1 / 6, where the steel thickness d is in mm, the heating temperature T is in ℃, and the holding time t is in h.

[0017] Preferably, the production method of the thick-gauge 75Cr1 steel slitting plate includes molten iron pretreatment, converter smelting, LF+RH furnace refining, continuous casting, heating, rolling, cooling, shearing and cross-cutting.

[0018] The molten iron pretreatment requires both pre- and post-slag removal, and the [S] content after desulfurization should be ≤0.0030%.

[0019] The converter smelting process includes dephosphorization during the strengthening process, deoxidation and alloying during tapping, and strong stirring at the top and bottom of the argon station for a duration of ≥4 minutes.

[0020] The LF+RH furnace refining process involves white slag operation to ensure full reduction of the ladle top slag; adjusting the chemical composition to the target value; controlling the [Ca] content at 15-30ppm, with a target of 20ppm; and using a weak stirring time of 8-11min before and after feeding the calcium line.

[0021] The continuous casting process employs high-carbon steel protective slag to reduce adhesion during casting. The target temperature in the tundish is controlled 15-30°C above the liquidus temperature. The superheat of the molten steel is crucial to the microstructure of the billet; reducing superheat effectively increases the equiaxed crystal ratio, reduces the thickness of columnar crystals, and leads to the dispersion of central segregation. Higher superheat results in a large temperature gradient at the solidification front of the billet, maintaining a longer directional heat transfer time, which is conducive to the development of columnar crystals and inhibits the formation of equiaxed crystals, increasing central segregation. A constant casting speed of 1.1 m / min is maintained during the casting process. A constant casting speed is beneficial for the stability of the billet's internal quality, and the increased molten steel flow rate reduces the probability of large inclusions floating and being removed. Argon blowing flow rate is 8-10 N / min. This invention has a high carbon content and high crack sensitivity, especially in hot-charging production mode. Without manual cleaning, low casting speed is one of the important measures to reduce corner cracks. Furthermore, dynamic light reduction and electromagnetic stirring are used, with a reduction of 6.5-6.8 mm, which helps improve the internal quality of the billet.

[0022] The heating process involves heating the billet in a furnace, controlling the exit temperature at 1180-1200℃, and holding it in the furnace for 140-150 minutes. For medium and high carbon steel, the heating process directly affects the decarburized layer and thus the surface hardness of the strip. No alloying elements are added to the strip, and a heating temperature not exceeding 1200℃ ensures sufficient austenitization of the billet. By controlling the exit temperature and furnace time, the decarburized layer is kept as low as possible. Specifically, the preheating and first heating stage times are 60-75 minutes with a heating rate ≤5℃ / min; the second, third, and soaking stages times are 70-85 minutes with a heating rate ≥5.8℃ / min.

[0023] The rolling process is as follows: the roughing stage is rolled in the austenite recrystallization zone, the finishing rolling start temperature is controlled at 1010-1090℃, the finishing rolling stage increases the deformation band and dislocation density in the deformed austenite through cumulative large deformation, increases the phase deformation nuclei and refines the grains, and the final rolling temperature is controlled at 860-900℃.

[0024] The cooling process involves laminar flow cooling of the rolled steel sheet before coiling. The cooling method is sparse cooling at the front end, with a cooling rate controlled at 8-10℃ / s. The coiling temperature of the cooled steel sheet is controlled at 700-740℃, slightly higher than Ar1. After coiling, the phase transformation gradually shifts from the beginning and end of the hot coil towards the center. The support of the inner and outer layers eliminates the phenomenon of hot coil collapse. After the hot coil comes off the production line, it is concentrated in a high-temperature zone for slow cooling for 72 hours to reduce internal stress and prevent defects such as edge cracks.

[0025] The above-mentioned thick-gauge 75Cr1 steel cutting plate for shear blades comprises the following components by weight percentage:

[0026] C: 0.73%-0.77%, Si: 0.25%-0.35%, Mn: 0.75%-0.85%, P: ≤0.015%, S: ≤0.005%, Alt: 0.010-0.030%, Cr: 0.45%-0.55%, with the balance being Fe and unavoidable impurities.

[0027] The thickness of the 75Cr1 steel cutting plate used for the thick-gauge shear blade is 12-20mm.

[0028] The hot-rolled properties of the 75Cr1 steel sheet used for thick-gauge shear blades are: yield strength Rp 0.2 ≥420 MPa, tensile strength R m ≥870 MPa, elongation ≥7.5%, Att ≥6.0%, yield strength ratio: 0.48-0.55.

[0029] The microstructure of the 75Cr1 steel used for thick shear blades after annealing is as follows: the surface consists of spherical pearlite plus lamellar pearlite with a volume ratio not exceeding 5%, 1 / 4 of the thickness consists of spherical pearlite plus lamellar pearlite with a volume ratio of 5%-10%, and the center consists of spherical pearlite plus lamellar pearlite with a volume ratio of 10%-15%.

[0030] Mechanical properties of the 75Cr1 steel used for thick shear blades after annealing: Yield strength Rp 0.2 320-410MPa, tensile strength R m Strength: 720-790 MPa, yield strength ratio: 0.44-0.52, Ag ≥ 12.0%, elongation: 14.0-16.5%. The flat plate has good shape and shearing surface, and no brittle fracture occurred during the leveling process.

[0031] The 75Cr1 steel used for thick shear blades, after annealing, has a spheroidization rate of 95-100% on the surface of the thickness direction, 90-95% on 1 / 4 of the thickness, and 85-90% in the center. The spheroidization rate of the entire thickness meets the requirements, and the plasticity is sufficiently improved.

[0032] Compared with existing technologies, this invention optimizes the conventional cross-cutting plate production process, especially for thick-gauge, high-strength 75Cr1, by improving plasticity and enhancing machinability through the intermediate process of direct annealing of hot-rolled plates. Furthermore, this invention quantitatively determines the critical value A for fracture during the straightening process of thick-gauge 75Cr1. 临 The key parameter Agt (total elongation at maximum force) in the room temperature tensile test of rolled 75Cr1 is compared with it as the criterion. If Agt > A 临 It possesses the conditions for cross-cutting. During the cross-cutting process, a high-quality 75Cr1 steel sheet for thick shear blades is generated through a combination of "small deformation straightening" and a no-edge-cutting process. This invention is based on the Att of hot-rolled strip steel and the critical value A for fracture during the straightening process. 临 The size of the strip determines whether it needs to be annealed before cross-cutting, allowing for the selection of the annealing process as needed, thus saving costs. Furthermore, the annealing process designed in this invention can improve the microstructure and properties of the product, ensuring that the performance of thick steel plates meets requirements. Attached Figure Description

[0033] Figure 1 The microstructure of Embodiment 3 of the present invention is shown under an optical microscope.

[0034] Figure 2 The critical value A for fracture during the straightening process. 临 Calculation diagram. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Examples 1-5

[0037] A thick-gauge scissor blade made of 75Cr1 steel comprises the following components by weight percentage:

[0038] As shown in Table 1, the balance not shown in Table 1 is for Fe and unavoidable impurities.

[0039] Comparative Example 1-1-Comparative Example 3

[0040] A thick-gauge scissor blade made of 75Cr1 steel comprises the following components by weight percentage:

[0041] As shown in Table 1, the balance not shown in Table 1 is for Fe and unavoidable impurities.

[0042] The component analysis in Table 1 was performed according to GB / T 4336 "Spark Source Atomic Emission Spectrometry Analysis Method (Conventional Method) for Carbon Steel and Medium-Low Alloy Steel".

[0043] Table 1 Chemical composition of various embodiments and comparative examples of the present invention

[0044]

[0045] The production method of 75Cr1 steel sheet for thick shear blades described in the various embodiments and comparative examples includes molten iron pretreatment, converter smelting, LF+RH furnace refining, continuous casting, heating, rolling, cooling, shearing and cross-cutting.

[0046] The molten iron pretreatment requires both pre- and post-slag removal, and the [S] content after desulfurization should be ≤0.0030%.

[0047] The converter smelting process includes dephosphorization during the strengthening process, deoxidation and alloying during tapping, and strong stirring at the top and bottom of the argon station for a duration of ≥4 minutes.

[0048] The LF+RH furnace refining process involves white slag operation to ensure full reduction of the ladle top slag; adjusting the chemical composition to the target value; controlling the [Ca] content at 15-30ppm, with a target of 20ppm; and using a weak stirring time of 8-11min before and after feeding the calcium line.

[0049] The continuous casting process employs high-carbon steel protective slag to reduce adhesion during casting. The target temperature in the tundish is controlled at 15-30°C above the liquidus temperature. A constant casting speed of 1.1 m / min is maintained during the casting process, and the argon flow rate of the stopper rod is 8-10 N / min. Dynamic light reduction and electromagnetic stirring are used, with a reduction of 6.5-6.8 mm, which helps improve the internal quality of the billet.

[0050] The heating process involves the billet entering a heating furnace for heating, with the exit temperature controlled at 1180-1200℃ and the time spent in the furnace at 140-150 minutes. Specifically, the preheating and first heating stage takes 60-75 minutes with a heating rate ≤5℃ / min; the second, third, and soaking stages take 70-85 minutes with a heating rate ≥5.8℃ / min.

[0051] The rolling process is as follows: the roughing stage is rolled in the austenite recrystallization zone, the finishing rolling start temperature is controlled at 1010-1090℃, and the finishing rolling temperature is controlled at 860-900℃.

[0052] The cooling process involves laminar cooling of the rolled steel plate before coiling. The cooling method is sparse cooling at the front end, with the cooling rate controlled at 8-10℃ / s. The coiling temperature of the cooled steel plate is controlled at 700-740℃. After the hot coil comes off the production line, it is piled up in a high-temperature zone for slow cooling for 72 hours.

[0053] Covering and unloading: The heating temperature for 16mm 75Cr1 is set at 730℃, and the holding time is 6h. The temperature T and time t should be adjusted accordingly based on the thickness d of the steel. Specifically, the heating temperature T = 730 + (d - 16) × 3, and the holding time t = 6 + (d - 16) × 1 / 6, where the thickness d of the steel is in mm, the heating temperature T is in ℃, and the holding time t is in h.

[0054] The cross-cutting process involves using both primary and secondary straightening machines, employing a small deformation straightening scheme. This means both straightening machines #1 and #2 utilize this scheme. Straightening machine #1 primarily functions to uncoil and initially improve the strip shape. For #1 straightening machine: roll 1 is raised by 5.00-9.50mm, roll 3 by 0.01-0.15mm, roll 5 by 0.01mm, and roll 7 by no raising. After the strip is sheared by the flying shear, it may buckle or warp, resulting in insufficient straightness. Therefore, straightening machine #2 also requires small deformation: roll 1 is raised by 0.30-0.50mm, roll 3 by 2.85-3.85mm, and rolls 5, 7, 9, and 11 by 0.30-0.45mm.

[0055] During the straightening process, the strip is subjected to A 临 This can be determined through the following calculations:

[0056] ;

[0057] If the elongation of the steel plate under the pressure of the straightening rollers exceeds the total elongation under maximum force, it indicates that the steel plate of this thickness is at risk of fracture during cross-cutting and straightening. Therefore, the deformation should be reduced as much as possible while improving the plate shape.

[0058] The main process parameters of the steelmaking process in each embodiment and comparative example are shown in Table 2, and the main heating process parameters are shown in Table 3.

[0059] Table 2. Main process parameters of steelmaking procedures in various embodiments and comparative examples of the present invention.

[0060]

[0061] Table 3. Main heating process parameters of each embodiment and comparative example of the present invention

[0062]

[0063] The hot-rolled mechanical properties of the various embodiments and comparative examples of the present invention are shown in Table 4. All tensile tests were conducted in accordance with GB / T 228.1.

[0064] Table 4. Hot-rolled mechanical properties of various embodiments and comparative examples of the present invention

[0065]

[0066] The above Examples 1 and Comparative Examples 1-1 and 1-2 are the same hot-rolled steel produced with the same composition and using the same method. Examples 3 and 2 are the same hot-rolled steel produced with the same composition and using the same method. Examples 5 and 3 are the same hot-rolled steel produced with the same composition and using the same method.

[0067] The main parameters and performance of the annealing process in each embodiment of the present invention are shown in Table 5. The lifting amount of each straightening roller and the cross-cutting result during the cross-cutting process of each embodiment and comparative example are shown in Table 6. Comparative examples 1-2 and 2-2 were not annealed; comparative example 1-1 was annealed according to example 1; comparative example 3 was annealed, but the annealing parameters did not meet the requirements of the present invention.

[0068] Table 5 Annealing parameters and mechanical properties after annealing for each embodiment and comparative example of the present invention.

[0069]

[0070] Table 6. The lifting amount of each straightening roller and the cross-cutting process in various embodiments of the present invention.

[0071]

[0072] Comparative Example 1-1 shows that 12mm hot-rolled 75Cr1 undergoes unnecessary annealing (Agt > A). 临 After that, without using the small straightening scheme, the brittle fracture of straightening step #1 still occurred; in comparative examples 1-2, 12mm hot-rolled 75Cr1 without annealing could be successfully leveled directly using the small straightening scheme of this invention, indicating that when Agt > A 临 It can be directly leveled without annealing. This verifies the "Agt of hot-rolled strip and the critical value A for fracture during straightening". 临 The size of the strip can be used to determine the effectiveness of "covering and retracting" before transverse cutting. Moreover, through Comparative Examples 1-1 and 1-2, it can be seen that a small straightening scheme is a necessary condition for the successful leveling of 75Cr1.

[0073] Comparative Example 2 and Example 3 show that for 16mm hot-rolled 75Cr1, when Att < A 临 Under these conditions, even with a small straightening scheme during leveling production, brittle fracture of straightening step #1 still occurs, indicating that when Agt < A 临，Forced annealing is required. By combining Comparative Example 2 and Example 3, it can be verified that "Agt of hot-rolled strip and the critical value A for fracture during straightening process" are required. 临 The size of the strip can be used to determine the effectiveness of "whether the hot-rolled strip is covered before transverse cutting".

[0074] Comparative Example 3 shows that although the 20mm hot-rolled 75Cr1 strip was annealed, it was not annealed according to the specified annealing process parameters. This resulted in a lower spheroidization rate in the thickness direction (surface, 1 / 4 position, and center position) of the strip after annealing. The strip strength was high, but the plasticity was still low, and Ag < A after annealing. 临 When leveling production using a small straightening scheme, brittle fracture occurred in step #1. Combined with Comparative Example 3 and Example 5, it can be illustrated that annealing must be performed within a specified range to achieve a certain spheroidization rate in the thickness direction (95-100% spheroidization rate on the surface of the thickness direction, 90-95% on the 1 / 4 thickness, and 85-90% spheroidization rate at the center), thereby improving strength and toughness. It is essential that the strip's Ag > A after annealing. 临 Only then can leveling production proceed smoothly, and the "Agt of hot-rolled strip and the critical value A for fracture during straightening" can be verified. 临 The size of the strip can be used to determine the effectiveness of "whether the hot-rolled strip is covered before transverse cutting".

[0075] In summary, the 75Cr1 steel sheet for thick-gauge saw blades, designed and produced according to the chemical composition, steelmaking, heating, rolling, annealing, and cross-cutting processes provided by this invention, exhibits the following mechanical properties: yield strength Rp 0.2 320-410MPa, tensile strength R m Strength: 720-790 MPa, yield strength ratio: 0.44-0.52, Ag ≥ 12.0%, elongation: 14.0-16.5%. The flat plate has good shape and shearing surface, and no brittle fracture occurred during the leveling process.

[0076] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for producing a thick-gauge 75Cr1 steel slitting plate, characterized in that, The production method includes cross-cutting, employing a small straightening scheme, and utilizing one and two straightening processes; wherein, for straightening machine #1: the 1st roll is lifted by 5.00-9.50mm, the 3rd roll by 0.01-0.15mm, the 5th roll by 0.01mm, and the 7th roll is not lifted; for straightening machine #2: the 1st roll is lifted by 0.30-0.50mm, the 3rd roll by 2.85-3.85mm, and the 5th, 7th, 9th, and 11th rolls are lifted by 0.30-0.45mm. Based on the Att of hot-rolled strip and the critical value A for fracture during straightening. 临 The size of the strip determines whether it has been covered before transverse cutting; If the Ag of hot-rolled strip steel is greater than A 临 Then the hot-rolled strip steel can be directly subjected to the above-mentioned cross-cutting. If At ≤ A 临 Therefore, hot-rolled strip steel must be covered and unwound before it can be cross-cut. ； Among them, the critical value A for fracture during the straightening process 临 The units are %; L0 is the original gauge length in mm; ΔL is the increment of the original gauge length when the steel plate is deformed by the pressure of the straightening roller in mm; h is the plate thickness in mm; and R is the radius of the straightening roller in mm.

2. The production method according to claim 1, characterized in that, The hood has the following characteristics: heating temperature T = 730 + (d - 16) × 3, holding time t = 6 + (d - 16) × 1 / 6, where the thickness d of the steel is in mm, the heating temperature T is in °C, and the holding time t is in h.

3. The production method according to claim 1 or 2, characterized in that, The production method includes the following process flow: molten iron pretreatment, converter smelting, LF+RH furnace refining, continuous casting, heating, rolling, cooling, annealing and cross-cutting.

4. A thick-gauge 75Cr1 steel slitting plate for shear blades produced by the production method according to any one of claims 1-3, characterized in that, The 75Cr1 steel cutting plate for thick shear blades comprises the following components by weight percentage: C: 0.73%-0.77%, Si: 0.25%-0.35%, Mn: 0.75%-0.85%, P: ≤0.015%, S: ≤0.005%, Alt: 0.010-0.030%, Cr: 0.45%-0.55%, with the balance being Fe and unavoidable impurities.

5. The 75Cr1 steel cutting plate for thick-gauge shear blades according to claim 4, characterized in that, The thickness of the 75Cr1 steel cutting plate used for the thick-gauge shear blade is 12-20mm.

6. The 75Cr1 steel cutting plate for thick-gauge shear blades according to claim 4, characterized in that, The hot-rolled properties of the 75Cr1 steel sheet used for thick-gauge shear blades are: yield strength Rp 0.2 ≥420 MPa, tensile strength R m ≥870 MPa, elongation ≥7.5%, Att ≥6.0%, yield strength ratio: 0.48-0.

55.

7. The 75Cr1 steel cutting plate for thick-gauge shear blades according to claim 4, characterized in that, The microstructure of the 75Cr1 steel used for thick shear blades after annealing is as follows: the surface is spherical pearlite + no more than 5% lamellar pearlite, 1 / 4 of the thickness is spherical pearlite + 5%-10% lamellar pearlite, and the center position is spherical pearlite + 10%-15% lamellar pearlite. The spheroidization rate of the 75Cr1 steel used for thick shear blades after annealing is 95-100% on the surface of the thickness direction, 90-95% on the 1 / 4 thickness, and 85-90% in the center.

8. The 75Cr1 steel cutting plate for thick-gauge shear blades according to claim 4, characterized in that, Mechanical properties of the 75Cr1 steel used for thick shear blades after annealing: Yield strength Rp 0.2 320-410MPa, tensile strength R m 720-790MPa, yield strength ratio: 0.44-0.52, Agt≥12.0%, elongation: 14.0-16.5%, no brittle fracture occurred during the leveling process.

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