High-performance blade steel large roll annealing process

Abstract

The invention relates to a high-performance blade steel large coil annealing process, which belongs to the technical field of blade steel large coil processing, and comprises the following steps: S1, providing a steel coil and charging the steel coil into a furnace; s2, performing heat treatment in a protective atmosphere: S2-1, performing first-stage heating and protection; s2-2, carrying out second-stage temperature rise and protection; s3, segmented cooling: S3-1, first-stage cooling and isothermal treatment; s3-2, performing second-stage cooling to room temperature; s4, acid pickling treatment; and S5, discharging and air cooling. According to the high-performance blade steel large roll annealing process, slow cooling is conducted by controlling the key second cooling rate C2, heat preservation is conducted at the specific temperature T3, and thermal stress and structural stress are effectively eliminated; the longitudinal curvature of the finally obtained blade steel large roll is smaller than or equal to 1.5 mm / m, the pressure and the rejection rate of the follow-up straightening procedure are greatly reduced, the yield is increased, the dimensional stability and the straightness of a product are remarkably improved, excellent structure and performance uniformity are achieved, and a solid foundation is laid for the extreme sharpness and durability of a cutter.

Description

Technical Field

[0001] This invention relates to the field of blade steel coil processing technology, specifically to a high-performance blade steel coil annealing process. Background Technology

[0002] High-performance blade steels (such as martensitic stainless steel and high-carbon high-chromium steel) are widely used in high-end cutting tools, cutting tools, and precision components due to their high hardness, high wear resistance, and good corrosion resistance. These steels are usually produced in large coils (each coil weighing more than 10 tons) to facilitate subsequent continuous and large-scale processing.

[0003] However, existing technologies face a series of challenging problems when annealing large coils of high-performance blade steel:

[0004] 1. Challenges in achieving uniform microstructure and controlling hardness: Due to their enormous heat capacity and tight winding structure, large coils experience slow and uneven heat transfer during traditional annealing processes. This easily leads to excessive temperature differences between the surface and core of the coil, and between the beginning and end and the middle of the coil. This uneven temperature field results in inconsistent austenitization, carbide dissolution, and precipitation behavior, ultimately causing large fluctuations in the overall hardness of the coil after annealing (e.g., fluctuations exceeding ±3 HRC), and uneven microstructure, severely affecting subsequent processing performance and service life.

[0005] 2. Challenges in controlling internal stress and deformation: During heating and cooling, the huge temperature difference will generate significant thermal stress, which, combined with the original rolling stress, can easily cause large coils to undergo plastic deformation after annealing. This manifests as excessive longitudinal curvature (sickle bend) (e.g., >2.5mm / m), which makes subsequent straightening and slitting processes difficult and may even cause product scrap.

[0006] 3. Surface quality issues: Despite the use of a protective atmosphere, oxidation and decarburization can still occur on the surface of the steel coil during prolonged high-temperature annealing if the local oxygen partial pressure control within the furnace is imprecise or the atmosphere has poor fluidity. For high-performance blade steels, even a micron-sized decarburized layer (e.g., >0.05 mm) can significantly reduce the edge strength and sharpness retention of the final cutting tool.

[0007] 4. Process efficiency and energy consumption issues: To ensure that the core of the large coil reaches the process temperature, traditional annealing processes often require excessively long holding times, resulting in low production efficiency and huge energy consumption. At the same time, if the cooling process is not properly controlled, excessively slow cooling to avoid the brittle temperature range further slows down the overall production pace.

[0008] Currently, while some technologies attempt to address these issues by optimizing temperature profiles or improving furnace design, these approaches often fall short of achieving the same level of microstructure uniformity, dimensional stability, and surface quality in large coils of blade steel while maintaining high efficiency. Therefore, there is an urgent need in this field to develop a dedicated annealing process for large coils of high-performance blade steel that can systematically solve these problems and stably produce high-performance, highly consistent products. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a high-performance blade steel large-coil annealing process, which has advantages such as good heat treatment uniformity, strong stability, high flatness, high production quality, and high production efficiency, thus solving the problems mentioned in the background technology.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] An annealing process for large coils of high-performance blade steel includes the following steps:

[0012] S1. Provide steel coils and load them into the furnace: Provide large coils of high-performance blade steel to be processed and place them in a continuous annealing furnace.

[0013] S2. Heat treatment under a protective atmosphere: Perform the following heat treatment procedure under a protective atmosphere:

[0014] S2-1, First stage of heating and protection: The furnace temperature is raised from room temperature to the first target temperature T1 at the first heating rate V1, and then held at T1 for a first duration t1.

[0015] S2-2, Second stage heating and protection: The furnace temperature is raised from T1 to the second target temperature T2 at the second heating rate V2, and then held at T2 for a second duration t2.

[0016] S3, Segmented Cooling:

[0017] S3-1, First stage cooling and isothermal: The furnace temperature is reduced from T2 to the third target temperature T3 at the first cooling rate C1, and held at T3 for a third duration t3.

[0018] S3-2, Second stage cooling to room temperature: The furnace temperature is reduced from T3 to room temperature at a second cooling rate C2 to complete the annealing process;

[0019] S4. Pickling treatment: After the annealing treatment, the blade steel coil is pickled. The pickling solution is a 10%-15% hydrochloric acid solution, and the pickling temperature is controlled at 40℃-60℃.

[0020] S5. Air cooling after pickling: After pickling, the steel is finally removed from the furnace and air cooled to room temperature to obtain high-performance blade steel.

[0021] Furthermore, the chemical composition of the high-performance blade steel, by mass percentage, includes:

[0022] C: 0.5%-1.2%, Cr: 12%-18%, Mo: 0.5%-3.0%, V: 0.1%-1.5%, balance being Fe and unavoidable impurities.

[0023] Furthermore, in S2-1, the first target temperature T1 is 650℃-750℃, the first heating rate V1 is 50℃ / h-150℃ / h, and the first duration t1 is 1h-4h.

[0024] Furthermore, in S2-2, the second target temperature T2 is 1000℃-1100℃, the second heating rate V2 is 80℃ / h-200℃ / h, and the second duration t2 is 2h-8h.

[0025] Furthermore, in S3-1, the third target temperature T3 is 450℃-550℃, the first cooling rate C1 is 50℃ / h-120℃ / h, and the third duration t3 is 3h-10h.

[0026] Furthermore, in S3-2, the second cooling rate C2 is 20℃ / h-60℃ / h.

[0027] Furthermore, the continuous annealing furnace is divided into a preheating zone, a heating zone, a soaking zone, and a cooling zone. Each zone is protected by a nitrogen-hydrogen mixed gas, with hydrogen accounting for 3%-8% of the volume.

[0028] Furthermore, the heat preservation stage employs a combination of electromagnetic induction heating and resistance heating to ensure that the temperature difference between the surface and core of the blade steel coil is ≤15℃. After the heat preservation stage is completed, ultrasonic vibration of 0.1MPa-0.5MPa is applied to the surface of the blade steel coil at a frequency of 20kHz-40kHz for a duration of 1-3 minutes.

[0029] Furthermore, the high-performance blade steel coils treated by the annealing process have a hardness of HRC 58-62, a longitudinal curvature of ≤1.5mm / m, and a surface decarburization layer depth of ≤0.03mm.

[0030] Another technical problem to be solved by the present invention is to provide an annealing furnace system for the annealing process of large coils of high-performance blade steel, comprising:

[0031] Furnace body;

[0032] Heating device, used to heat the inside of the furnace;

[0033] A cooling device for controlled cooling of the furnace interior;

[0034] An atmosphere control system is used to introduce and maintain a protective atmosphere into the furnace.

[0035] A temperature control unit, electrically connected to the heating and cooling devices, is configured to execute a heat treatment procedure.

[0036] Compared with the prior art, the present invention provides a high-performance blade steel large coil annealing process, which has the following beneficial effects:

[0037] 1. The high-performance blade steel coil annealing process, by controlling the key second cooling rate C2 for slow cooling and holding at a specific temperature T3, effectively eliminates thermal stress and structural stress; the final blade steel coil has a longitudinal curvature of ≤1.5mm / m, which greatly reduces the pressure and scrap rate of the subsequent straightening process, improves the yield, and significantly enhances the dimensional stability and straightness of the product.

[0038] 2. The annealing process for this high-performance blade steel coil employs a precise heat treatment procedure of "stepped heating + segmented controlled cooling," and optimizes specific temperature, rate, and time parameters to ensure uniform heating and complete and consistent phase transformation throughout the heat treatment process. In particular, by combining electromagnetic induction and resistance heating technologies, the temperature difference between the surface and core of the coil is effectively controlled to ≤15℃, fundamentally guaranteeing the uniformity of austenitization and carbide transformation throughout the coil. Ultimately, this results in minimal fluctuations in product hardness and achieves excellent microstructure and property uniformity.

[0039] 3. This high-performance blade steel large-coil annealing process creates a highly reducing environment by introducing a specific ratio of nitrogen-hydrogen mixed protective gas into each section of the continuous annealing furnace and precisely controlling the furnace atmosphere. This minimizes the decarburization reaction. Ultimately, it ensures that the decarburized layer depth on the product surface is ≤0.03mm, perfectly preserving the alloying elements and carbon content on the steel surface. This lays a solid foundation for the extreme sharpness and durability of the blades and effectively inhibits surface oxidation and decarburization.

[0040] 4. This high-performance blade steel large-coil annealing process, through the use of a carefully designed balance point, avoids unnecessary excessive heat preservation while ensuring optimal performance, thus improving production efficiency. Simultaneously, the integrated temperature and atmosphere control unit can automatically, accurately, and reliably reproduce this process, ensuring the stability of large-scale production and product consistency. It also enables automatic calibration of process parameters, reducing human intervention errors and effectively improving production efficiency and process reliability. Attached Figure Description

[0041] Figure 1 This is a process flow diagram of a high-performance blade steel large coil annealing process according to the present invention.

[0042] Figure 2 This is a system block diagram of a continuous annealing furnace system for a high-performance blade steel large coil annealing process according to the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Example 1:

[0045] Please see Figures 1 to 2 The high-performance blade steel large coil annealing process in this embodiment includes the following steps:

[0046] S1. Provide steel coils and load them into the furnace:

[0047] A large coil of high-performance blade steel is provided for processing, with the following chemical composition by mass percentage: C: 0.8%, Cr: 14.5%, Mo: 1.2%, V: 0.8%, with the balance being Fe and unavoidable impurities. The coil has a unit weight of 15 tons and a strip thickness of 0.5 mm. It is loaded onto the furnace rolls of a continuous annealing furnace.

[0048] S2. Heat treatment under a protective atmosphere:

[0049] A nitrogen-hydrogen mixture, with hydrogen comprising 5% by volume, is introduced into the continuous annealing furnace as a protective atmosphere. This atmosphere is maintained in all sections of the furnace to ensure that the oxygen content is below 10 ppm. A precise heat treatment procedure is then performed.

[0050] S2-1, First Stage Heating and Protection: The furnace temperature is raised from room temperature (approximately 25°C) to the first target temperature T1 = 700°C at a first heating rate V1 of 100°C / h. After reaching T1, the temperature is held for a first duration t1 = 2 hours. This stage aims to uniformly preheat the steel coil and partially recover work hardening energy, preparing for subsequent high-temperature austenitization.

[0051] S2-2, Second Stage Heating and Protection: The furnace temperature is raised from 700℃ to the second target temperature T2 = 1050℃ at a second heating rate V2 of 150℃ / h. After reaching T2, the temperature is held for a second duration t2 = 5 hours. During this high-temperature austenitizing stage, a combination of electromagnetic induction heating and resistance heating is used. By combining the rapid penetration of induction heating with the uniform temperature of resistance heating, the temperature difference between the surface and core of the large coil is ensured to be controlled within 12℃. After the holding period, ultrasonic vibration is immediately applied to the surface of the large coil at a pressure of 0.3MPa, a frequency of 30kHz, and a duration of 2 minutes. This operation effectively breaks up coarse carbides at grain boundaries, promotes the diffusion of alloying elements, and refines the grains.

[0052] S3, Segmented Cooling:

[0053] S3-1, First Stage Cooling and Isothermal Treatment: After the initial holding period, the furnace temperature is rapidly reduced from 1050℃ to the third target temperature T3=500℃ at a first cooling rate C1 of 80℃ / h. Upon reaching T3, the holding period is t3=6 hours. This stage is the critical range for the transformation of sorbite or bainite; isothermal treatment yields a uniform and fine microstructure.

[0054] S3-2, Second stage cooling to room temperature: After the isothermal transformation is completed, the furnace temperature is slowly reduced from 500°C to room temperature (approximately 25°C) at a second cooling rate C2 of 40°C / h. This slow cooling process aims to eliminate residual internal stress to the greatest extent possible.

[0055] S4. Pickling treatment:

[0056] After annealing, the steel coil is fed into the pickling unit. A 12% hydrochloric acid solution is used as the pickling solution, and the pickling temperature is controlled at 50℃ to remove the extremely thin oxide film that may form during the annealing process.

[0057] S5. Air cool after baking:

[0058] After pickling, the large coil of blade steel is finally removed from the furnace and allowed to cool naturally to room temperature in the air to obtain the high-performance blade steel product.

[0059] Comparative Example 1:

[0060] Large coils of blade steel of the same batch and specification were processed using parameters similar to those used in traditional annealing processes: a single resistance heating method was employed, heating to 1050℃ and holding for 6 hours, followed by direct furnace cooling to room temperature at a rate of 50℃ / h. No stepped heating or segmented isothermal cooling was performed, and no ultrasonic vibration was applied.

[0061] Performance testing and results analysis:

[0062] The blade steel products obtained in Example 1 and Comparative Example 1 of this invention were subjected to performance testing, and the results are recorded in Table 1.

[0063] Table 1

[0064]

[0065] Results analysis:

[0066] As can be seen from the above test results, the blade steel coils processed by the process of the present invention (Example 1) are significantly better than Comparative Example 1 in all key performance indicators.

[0067] Hardness and uniformity: The product of this invention not only has a higher average hardness, but more importantly, the hardness fluctuation range of the whole roll (±1.0 HRC) is much smaller than that of the comparative example (±3.5 HRC). This is due to the extreme temperature uniformity brought about by composite heating and stepped process.

[0068] Dimensional stability: The longitudinal curvature of the present invention (1.0 mm / m) is better than that of the comparative example (3.0 mm / m), proving that the segmented cooling process effectively releases internal stress.

[0069] Surface quality: By precisely controlling the protective atmosphere with low hydrogen content, this invention successfully controls the decarburized layer depth to 0.02mm, meeting the stringent surface quality requirements of high-end cutting tools.

[0070] Microstructure: This invention achieves a more uniform and refined microstructure through the assistance of ultrasonic vibration, which is the fundamental reason for its superior overall performance.

[0071] Example 2:

[0072] As another embodiment of the present invention, a blade steel coil with a higher carbon and vanadium content is processed, the composition of which is: C: 1.1%, Cr: 16%, Mo: 2.5%, V: 1.3%.

[0073] The process parameters were adjusted as follows: T2=1080℃, t2=6 hours; T3=480℃, t3=8 hours; ultrasonic vibration pressure 0.4MPa. The final product achieved a hardness of HRC 61-62, while also achieving excellent uniformity and flatness.

[0074] In summary, this invention has successfully solved many industry problems in the annealing of large coils of high-performance blade steel through a systematic process that integrates specific temperature curves, composite heating, ultrasonic assistance, and precise atmosphere control, and has enabled the stable production of high-performance, highly consistent products.

[0075] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0076] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An annealing process for large coils of high-performance blade steel, characterized in that, Includes the following steps: S1. Provide steel coils and load them into the furnace: Provide large coils of high-performance blade steel to be processed and place them in a continuous annealing furnace. S2. Heat treatment under a protective atmosphere: Perform the following heat treatment procedure under a protective atmosphere: S2-1, First stage of heating and protection: The furnace temperature is raised from room temperature to the first target temperature T1 at the first heating rate V1, and then held at T1 for a first duration t1. S2-2, Second stage heating and protection: The furnace temperature is raised from T1 to the second target temperature T2 at the second heating rate V2, and then held at T2 for a second duration t2. S3, Segmented Cooling: S3-1, First stage cooling and isothermal: The furnace temperature is reduced from T2 to the third target temperature T3 at the first cooling rate C1, and held at T3 for a third duration t3. S3-2, Second stage cooling to room temperature: The furnace temperature is reduced from T3 to room temperature at a second cooling rate C2 to complete the annealing process; S4. Pickling treatment: After the annealing treatment, the blade steel coil is pickled. The pickling solution is a 10%-15% hydrochloric acid solution, and the pickling temperature is controlled at 40℃-60℃. S5. Air cooling after pickling: After pickling, the steel is finally removed from the furnace and air cooled to room temperature to obtain high-performance blade steel.

2. The annealing process for large coils of high-performance blade steel according to claim 1, characterized in that, The chemical composition of the high-performance blade steel, by mass percentage, includes: C: 0.5%-1.2%, Cr: 12%-18%, Mo: 0.5%-3.0%, V: 0.1%-1.5%, balance Fe and unavoidable impurities.

3. The annealing process for large coils of high-performance blade steel according to claim 1, characterized in that: In S2-1, the first target temperature T1 is 650℃-750℃, the first heating rate V1 is 50℃ / h-150℃ / h, and the first duration t1 is 1h-4h.

4. The annealing process for large coils of high-performance blade steel according to claim 1, characterized in that: In S2-2, the second target temperature T2 is 1000℃-1100℃, the second heating rate V2 is 80℃ / h-200℃ / h, and the second duration t2 is 2h-8h.

5. The annealing process for large coils of high-performance blade steel according to claim 1, characterized in that: In S3-1, the third target temperature T3 is 450℃-550℃, the first cooling rate C1 is 50℃ / h-120℃ / h, and the third duration t3 is 3h-10h.

6. The annealing process for large coils of high-performance blade steel according to claim 1, characterized in that: In S3-2, the second cooling rate C2 is 20℃ / h-60℃ / h.

7. The annealing process for large coils of high-performance blade steel according to claim 1, characterized in that: The continuous annealing furnace is divided into a preheating zone, a heating zone, a soaking zone, and a cooling zone. Each zone is protected by a nitrogen-hydrogen mixed gas, with hydrogen accounting for 3%-8% of the volume.

8. The annealing process for large coils of high-performance blade steel according to claim 1, characterized in that: The heat preservation stage employs a combination of electromagnetic induction heating and resistance heating to ensure that the temperature difference between the surface and core of the blade steel coil is ≤15℃. After the heat preservation stage is completed, ultrasonic vibration of 0.1MPa-0.5MPa is applied to the surface of the blade steel coil at a frequency of 20kHz-40kHz for a duration of 1-3 minutes.

9. The annealing process for large coils of high-performance blade steel according to claim 1, characterized in that: The high-performance blade steel coils treated by the annealing process have a hardness of HRC 58-62, a longitudinal curvature of ≤1.5mm / m, and a surface decarburization layer depth of ≤0.03mm.

10. An annealing furnace system for implementing the high-performance blade steel large coil annealing process according to any one of claims 1-8, characterized in that, include: Furnace body; Heating device, used to heat the inside of the furnace; A cooling device for controlled cooling of the furnace interior; An atmosphere control system is used to introduce and maintain a protective atmosphere into the furnace. A temperature control unit, electrically connected to the heating and cooling devices, is configured to perform the heat treatment procedure as described in any one of claims 1-8.

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