A method for preparing a continuously cast large round billet for forging cold rolling roll sleeves

Abstract

This invention discloses a method for preparing a large round billet for continuous casting of forged cold-rolled roll sleeves, comprising: controlling the composition system, wherein the chemical composition of the raw material steel is: C: 0.65-0.75%, Si: 0.25-0.40%, Mn: 0.35-0.50%, P≤0.020%, S≤0.020%, Cr: 1.90-2.10%, Ni: 0.30-0.45%, Mo: 0.20-0.40%, V: 0.05-0.10%; and controlling the continuous casting process parameters, wherein the superheat is controlled within a certain range. The casting temperature is maintained between 15 and 35°C, the casting speed is kept stable at 0.24 ± 0.01 m / min, the crystallizer water flow is controlled at 3700 L / min, and the secondary cooling water flow in the crystallizer is controlled at 0.12 L / Kg. During continuous casting, a 200 A / 2.5 HZ electromagnetic stirring of the casting flow and a 500 A / 1.2 HZ strong end electromagnetic stirring are used. The heat treatment process parameters for the continuously cast round billets are controlled as follows: red-charging annealing of the continuously cast round billets, furnace charging temperature ≥ 400°C, heating rate ≤ 100°C / h, holding at 730°C for ≥ 15 h, furnace cooling to 400°C, and air cooling upon exiting the furnace. This invention ensures the hardness and wear resistance of the cold-rolled roll sleeves while improving toughness and machinability, avoiding surface cracking and internal cracking of the roll sleeves during the casting and forging processes, ultimately achieving high-efficiency production and long service life of the roll sleeves.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting and continuous casting technology, specifically relating to a method for preparing a large round billet for continuous casting of forged cold rolling roll sleeves. Background Technology

[0002] As a key component in steel rolling production, the performance and quality of rolling rolls directly determine the output of the rolling mill and the quality of the finished product. Cold rolling rolls typically operate at low rolling temperatures, and their surfaces are subjected to significant stress during the rolling process, thus requiring materials with high hardness and wear resistance. To significantly reduce the production and operating costs of cold rolling rolls, the use of roll sleeves has gradually increased in recent years. The roll sleeve is embedded outside the cold rolling roll, bearing most of the stress during the rolling process. When the roll sleeve develops cracks or other defects and cannot continue to be used, it can be replaced and the roll can be put back into service.

[0003] Cold-rolled roll sleeves are typically made of high-carbon steel and are produced by forging from unrolled billets. This requires minimal center cracks or shrinkage cavities to prevent cracking after forging and the appearance of cracks on the inner surface of the roll sleeve. Cracks in these areas would increase the amount of machining required on the inner surface or even render the roll sleeve unusable, impacting production efficiency. Furthermore, the high carbon content of the high-carbon steel used as raw material for cold-rolled roll sleeves reduces the machining efficiency of the roll sleeves.

[0004] Therefore, developing a method for preparing a continuously cast large round billet for forging cold rolling roll sleeves, while ensuring the material's hardness and wear resistance, reducing the risk of cracking during forging and use, and improving the production efficiency and service life of the roll sleeves, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a method for preparing a continuously cast large round billet for forging cold-rolled roll sleeves, comprising:

[0006] Composition system control: The chemical composition of the raw steel is controlled by weight percentage as follows: C: 0.65-0.75%, Si: 0.25-0.40%, Mn: 0.35-0.50%, P≤0.020%, S≤0.020%, Cr: 1.90-2.10%, Ni: 0.30-0.45%, Mo: 0.20-0.40%, V: 0.05-0.10%, with the balance being Fe and unavoidable impurities;

[0007] Continuous casting process parameter control: The superheat during continuous casting is controlled at 15~35℃, the casting speed is stably controlled at 0.24±0.01m / min, the water flow rate in the crystallizer is controlled at 3700L / min, the water flow rate in the secondary cooling tank of the crystallizer is controlled at 0.12L / Kg, and electromagnetic stirring of the casting stream and strong end electromagnetic stirring are set during continuous casting. The reversal time is controlled at 20s. Among them, the stirring current of the casting stream electromagnetic stirring is 200A and the stirring frequency is 2.5HZ, and the stirring current of the strong end electromagnetic stirring is 500A and the stirring frequency is 1.2HZ.

[0008] Parameter control of heat treatment process for continuously cast round billets: red charging annealing of continuously cast round billets, charging temperature ≥400℃, heating rate ≤100℃ / h, holding at 730℃ for ≥15h, furnace cooling to 400℃ and air cooling after exiting the furnace.

[0009] Furthermore, in the above-mentioned method for preparing continuously cast large round billets for forging cold-rolled roll sleeves, the smelting of raw steel is carried out through a process route of electric furnace smelting + LF refining + VD vacuum treatment.

[0010] As one embodiment, the above-mentioned method for preparing a continuously cast large round billet for forging cold rolling roll sleeves is used to prepare a φ690mm continuously cast large round billet for cold rolling roll sleeves, comprising:

[0011] In the composition system control, the steelmaking process follows the route of "electric furnace smelting → LF refining → VD vacuum degassing". During LF refining, the composition is adjusted, and the LF outlet temperature is controlled at 1625℃. The LF outlet composition by weight percentage is controlled as follows: C: 0.70%, Si: 0.37%, Mn: 0.47%, P: 0.017%, S: 0.0012%, Cr: 2.00%, Ni: 0.38%, Mo: 0.35%, V: 0.07%. During VD vacuum degassing, the VD vacuum degree is controlled at ≤67pa, the holding time is controlled at 17min, and the VD outlet temperature is controlled at 1545℃.

[0012] In the continuous casting process parameter control, the tundish superheat is controlled at 16-30℃, the casting speed is stabilized at 0.24m / min, the crystallizer water flow is controlled at 3700L / min, the secondary cooling water flow is controlled at 0.12L / Kg, the stirring current of the electromagnetic stirring of the casting stream is 200A, the stirring frequency is 2.5HZ, and the reversing time is 20s, and the stirring current of the strong end electromagnetic stirring is 500A, the stirring frequency is 1.2HZ, and the reversing time is 20s;

[0013] In the process parameter control of heat treatment of continuously cast round billets, the charging temperature of the continuously cast round billets is controlled at 480℃, and the temperature is increased to 730℃ at a rate of ≤100℃ / h and held for 15h. The billets are then cooled in the furnace to 400℃ and air-cooled.

[0014] The method for preparing continuously cast large round billets for forging cold-rolled roll sleeves of the present invention has the following advantages and beneficial effects:

[0015] This invention addresses the issues of composition design, continuous casting process, and billet heat treatment. By reducing carbon (C), adding nickel (Ni), and adding v (V) to the steel composition, it ensures the hardness and wear resistance of cold-rolled roll sleeves while improving toughness and machinability. High-quality control of continuously cast round billets is achieved through low superheat, constant casting speed, and strong end-efficiency electromagnetic stirring. By controlling the furnace loading temperature and heating rate of the continuously cast billet, the stress in the billet is reduced, preventing surface cracking and internal cracking of the roll sleeves during the forging process. Ultimately, this invention achieves high-efficiency production and long service life of the roll sleeves. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0017] Overall, the method for preparing continuously cast large round billets for forged cold rolling roll sleeves of the present invention ensures the production efficiency and service life of cold rolling roll sleeves through the adjustment of alloy composition and process control. The main technical means include composition design and continuous casting large round billet production process control.

[0018] In terms of composition design, this invention improves the machinability of steel by reducing the carbon (C) content and adding appropriate amounts of nickel (Ni) and vanadium (V), while ensuring its strength and toughness, thus reducing the risk of cracking during the use of cold-rolled roll sleeves. Carbon (C) in steel increases its strength and hardness, but reduces its plasticity and impact resistance, significantly decreasing its machinability. Nickel (Ni) in steel increases its strength and hardness while maintaining good plasticity and toughness, and also improves its hardenability. Adding appropriate amounts of Ni can effectively ensure the hardness and toughness of the steel, guaranteeing its service life while reducing the risk of cracking. Vanadium (V) significantly improves the hardenability of steel. Adding appropriate amounts of vanadium can increase strength, reduce overheating tendency, improve tempering stability, and significantly refine grains, thereby increasing strength and toughness.

[0019] In terms of process control for continuously cast large round billets, due to their large cross-section, and based on the characteristics of metal solidification, large round billets inevitably suffer from defects such as central porosity, central shrinkage cavities, and central segregation after cooling. After being forged into roll sleeves, these billets are prone to developing cracks on the inner wall, affecting yield and even leading to scrap, thus impacting product lifespan. This invention develops a large-section continuous casting process and heat treatment process, effectively reducing various central defects, avoiding surface cracks during continuous casting and cooling, significantly improving the pass rate in the forging process of cold rolling roll sleeves, and ensuring the stability of performance during subsequent cold rolling roll use.

[0020] Specifically, the method for preparing the continuously cast large round billet for forging cold-rolled roll sleeves of the present invention includes:

[0021] Composition system control: The chemical composition of the raw steel is controlled by weight percentage as follows: C: 0.65-0.75%, Si: 0.25-0.40%, Mn: 0.35-0.50%, P≤0.020%, S≤0.020%, Cr: 1.90-2.10%, Ni: 0.30-0.45%, Mo: 0.20-0.40%, V: 0.05-0.10%, with the balance being Fe and unavoidable impurities.

[0022] Continuous casting process parameter control: The continuous casting process adopts low superheat, constant casting speed, and strong end electromagnetic stirring and other process control methods to achieve high-quality production. The superheat of the continuous casting process is controlled at 15~35℃, the casting speed is stably controlled at 0.24±0.01m / min, the water flow rate of the crystallizer is controlled at 3700L / min, and the secondary cooling water flow rate of the crystallizer is controlled at 0.12L / Kg. During the continuous casting process, electromagnetic stirring of the casting stream and strong end electromagnetic stirring are set, and the reversal time is controlled at 20s. Among them, the stirring current of the casting stream electromagnetic stirring is 200A and the stirring frequency is 2.5HZ, and the stirring current of the strong end electromagnetic stirring is 500A and the stirring frequency is 1.2HZ.

[0023] Control of heat treatment process parameters for continuously cast round billets: Red charging annealing of continuously cast round billets, furnace charging temperature ≥400℃, heating rate ≤100℃ / h, holding at 730℃ for ≥15h, furnace cooling to 400℃ and air cooling after removal from the furnace, to ensure that stress cracking does not occur in continuously cast round billets.

[0024] Furthermore, in the preparation method of the continuously cast large round billet for forging cold rolling roll sleeve of the present invention, the smelting of raw steel is carried out through the process route of electric furnace smelting + LF refining + VD vacuum treatment. Through LF refining and VD vacuum degassing, the gas content, S content and inclusion level in the steel can be guaranteed, reducing the cracking risk in the subsequent forging and product use process.

[0025] The following detailed description, with reference to specific embodiments, illustrates the preparation method of the continuously cast large round billet for forged cold rolling roll sleeves according to the present invention. The embodiments of the present invention are used to prepare φ690mm continuously cast large round billets for cold rolling roll sleeves, and the process route is as follows: 80t electric furnace → 80t LF refining → 80t VD vacuum degassing → continuous casting of φ690mm large round billet → annealing, specifically including:

[0026] (1) The process route of “electric furnace smelting → LF refining → VD vacuum degassing” is adopted for steel smelting. During LF refining, the composition is adjusted. The LF outlet temperature is controlled at 1625℃. The LF outlet composition is controlled by weight percentage as follows: C: 0.70%, Si: 0.37%, Mn: 0.47%, P: 0.017%, S: 0.0012%, Cr: 2.00%, Ni: 0.38%, Mo: 0.35%, V: 0.07%. During VD vacuum degassing, the VD vacuum degree is controlled at ≤67pa, the holding time is controlled at 17min, and the VD outlet temperature is controlled at 1545℃.

[0027] (2) The continuous casting process parameters for φ690mm large round billets are controlled as follows: the superheat of the tundish is controlled at 16~30℃, the casting speed is stabilized at 0.24m / min, the water flow rate of the crystallizer is controlled at 3700L / min, the water flow rate of the secondary cooling is controlled at 0.12L / Kg, the stirring current of the electromagnetic stirring of the casting stream is 200A, the stirring frequency is 2.5HZ, the reversing time is 20s, and the stirring current of the strong end electromagnetic stirring is 500A, the stirring frequency is 1.2HZ, and the reversing time is 20s.

[0028] (3) The process parameters for annealing of continuously cast round billets are controlled as follows: the continuously cast round billets are sent for annealing in red heat, the furnace temperature is controlled at 480℃, the temperature is increased to 730℃ at a rate of ≤100℃ / h and held for 15h, and then the furnace is cooled to 400℃ and then air-cooled.

[0029] The φ690mm forged cold-rolled roll sleeve prepared using this invention exhibits no surface transverse cracks or total cracks in the continuously cast large round billet. The core quality of the billet is excellent. Low-magnification microstructure inspection shows that, according to YB / T 4149, the low-magnification quality is rated as follows: center porosity ≤ 1.0 grade, center crack ≤ 0.5 grade, center shrinkage cavity 0 grade, and intermediate crack 0 grade, achieving a good quality level. Furthermore, the φ690mm continuously cast large round billet prepared using this invention shows no cracking during the forging process of the cold-rolled roll sleeve, and the inner surface of the roll sleeve is free of cracks. Compared with conventional steel grades in the prior art, the machining efficiency is increased by 20%, machining loss is reduced by 10%, and the roll sleeve flaw detection pass rate reaches 100%. After the prepared cold-rolled roll sleeve is embedded in the roll surface and put into use, its service life is increased by 5-8% compared with the roll sleeve of the prior art.

[0030] In summary, the method for preparing the continuously cast large round billet for forging cold rolling roll sleeves of the present invention has the following advantages and beneficial effects:

[0031] This invention addresses the issues of composition design, continuous casting process, and billet heat treatment. By reducing carbon (C), adding nickel (Ni), and adding v (V) to the steel composition, it ensures the hardness and wear resistance of cold-rolled roll sleeves while improving toughness and machinability. High-quality control of continuously cast round billets is achieved through low superheat, constant casting speed, and strong end-efficiency electromagnetic stirring. By controlling the furnace loading temperature and heating rate of the continuously cast billet, the stress in the billet is reduced, preventing surface cracking and internal cracking of the roll sleeves during the forging process. Ultimately, this invention achieves high-efficiency production and long service life of the roll sleeves.

[0032] It should be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device.

[0033] It should also be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A method for preparing a continuously cast large round billet for forging cold-rolled roll sleeves, characterized in that, include: Composition system control: The chemical composition of the raw steel is controlled by weight percentage as follows: C: 0.65~0.75%, Si: 0.25~0.40%, Mn: 0.35~0.50%, P≤0.020%, S≤0.020%, Cr: 1.90~2.10%, Ni: 0.30~0.45%, Mo: 0.20~0.40%, V: 0.05~0.07%, with the balance being Fe and unavoidable impurities. The smelting of the raw steel is carried out through the process route of electric furnace smelting + LF refining + VD vacuum treatment. Continuous casting process parameter control: The superheat during continuous casting is controlled at 15~35℃, the casting speed is stably controlled at 0.24±0.01m / min, the water flow rate in the crystallizer is controlled at 3700L / min, the secondary cooling water flow rate in the crystallizer is controlled at 0.12L / Kg, and electromagnetic stirring of the casting stream and strong end electromagnetic stirring are set during continuous casting. The reversal time is controlled at 20s. Among them, the stirring current of the electromagnetic stirring of the casting stream is 200A and the stirring frequency is 2.5HZ, and the stirring current of the strong end electromagnetic stirring is 500A and the stirring frequency is 1.2HZ. Parameter control of heat treatment process for continuously cast round billets: red charging annealing of continuously cast round billets, charging temperature ≥400℃, heating rate ≤100℃ / h, holding at 730℃ for ≥15h, furnace cooling to 400℃ and air cooling after exiting the furnace. The low-magnification quality of the continuously cast round billet is rated according to YB / T 4149 as follows: central porosity ≤ 1.0 grade, central crack ≤ 0.5 grade, central shrinkage cavity 0 grade, and intermediate crack 0 grade.

2. The method for preparing a continuously cast large round billet for forging cold rolling roll sleeves as described in claim 1, used for preparing a φ690mm continuously cast large round billet for cold rolling roll sleeves, comprising: In the composition system control, the steelmaking process adopts the route of "electric furnace smelting → LF refining → VD vacuum degassing". During LF refining, the composition is adjusted. The LF outlet temperature is controlled at 1625℃, and the LF outlet composition by weight percentage is controlled as follows: C: 0.70%, Si: 0.37%, Mn: 0.47%, P: 0.017%, S: 0.0012%, Cr: 2.00%, Ni: 0.38%, Mo: 0.35%, V: 0.07%. During VD vacuum degassing, the VD vacuum degree is controlled at ≤67pa, the holding time is controlled at 17min, and the VD outlet temperature is controlled at 1545℃. In the continuous casting process parameter control, the tundish superheat is controlled at 16~30℃, the casting speed is stabilized at 0.24m / min, the crystallizer water flow is controlled at 3700L / min, the secondary cooling water flow is controlled at 0.12L / Kg, the stirring current of the electromagnetic stirring of the casting stream is 200A, the stirring frequency is 2.5HZ, and the reversing time is 20s, and the stirring current of the strong end electromagnetic stirring is 500A, the stirring frequency is 1.2HZ, and the reversing time is 20s; In the process parameter control of heat treatment of continuously cast round billets, the charging temperature of the continuously cast round billets is controlled at 480℃, and the temperature is increased to 730℃ at a rate of ≤100℃ / h and held for 15h. The billets are then cooled in the furnace to 400℃ and air-cooled.