A control method for reducing the occurrence of pitting and craters on a 220 mm thick blank of a high-temperature rolled nickel-based steel

Abstract

The application discloses a control method for reducing the occurrence rate of pitting and pock of high-temperature rolling of a nickel-based steel blank with a thickness of 220 mm, and relates to the technical field of metallurgical processing. The method comprises the following steps: loading the nickel-based steel blank with a thickness of 220 mm into a furnace for heating, controlling the heating temperature to be 1220-1230 DEG C, controlling the total time in the furnace to be 320-400 min, and controlling the soaking time to be no less than 35 min; adopting a descaling box to perform two passes of descaling on the blank after heating; rolling the blank after descaling, and controlling the rough rolling end temperature and the second opening temperature to be both out of the temperature range of 900-960 DEG C during the rolling process, and continuously flushing the roll guard during the rolling process. The application optimizes the heating process, the descaling process and the rolling process, and solves the technical problem of high occurrence rate of pitting and pock of the nickel-based steel during high-temperature rolling in the prior art.

Description

Technical Field

[0001] This invention relates to the field of metallurgical processing technology, and in particular to a method for controlling the occurrence of pitting and crazing on the surface of nickel-based steel produced by high-temperature rolling of 220mm thick billets. Background Technology

[0002] Nickel-based steels (such as 9Ni steel) are special steels widely used in liquefied natural gas (LNG) storage tanks, cryogenic pressure vessels, and other fields, requiring extremely high low-temperature toughness. In the production process of nickel-based steels, thick billets (such as 220mm thick) are typically heated and rolled at high temperatures to obtain the required microstructure and dimensional accuracy.

[0003] However, during the high-temperature rolling of nickel-based steel from 220mm thick billets, defects such as pitting and roughness are prone to appear on the steel plate surface. These defects mainly stem from the following reasons: 1. During high-temperature heating, iron oxide scale forms rapidly on the surface of the steel billet. If descaling is incomplete, the iron oxide scale will be pressed into the surface of the steel plate during rolling, forming pits. 2. If the billet is kept in the furnace for too long or the heating time is insufficient, the billet temperature will be uneven, which will aggravate the formation and adhesion of iron oxide scale. 3. During the rolling process, if the steel plate stays in the high-temperature range for too long, secondary oxidation will be aggravated, further aggravating surface defects; 4. The slag removal effect of the roll guard plate is not good. The detached iron oxide scale adheres to the roller table and is pressed into the surface of the steel plate during subsequent rolling.

[0004] The aforementioned pitting and roughness defects not only affect the surface quality of steel plates but may also lead to product re-evaluation, salvage, or even scrapping, severely impacting production quality, cost control, and delivery cycle. Therefore, there is an urgent need to develop a method to effectively reduce the incidence of pitting in high-temperature rolled nickel-based steel from 220mm billets. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for controlling the occurrence of pitting on the surface of nickel-based steel with a thickness of 220mm at high temperature rolling.

[0006] To solve the above technical problems, the technical solution of the present invention is as follows: A method for controlling the occurrence of pitting and crazing in high-temperature rolled nickel-based steel with a billet thickness of 220mm includes: Heating process: Load 220mm thick nickel-based steel billets into the furnace and heat them. Control the heating temperature to 1220℃ to 1230℃, control the total time in the furnace to 320min to 400min, control the soaking time to not less than 35min, and control the furnace atmosphere to be a weakly oxidizing atmosphere with a residual oxygen content of 2% to 6%. Descaling process: The heated billet is descaled in two passes using a descaling box, and the sides of the billet are descaled simultaneously using side descaling nozzles. Rolling process: The descaled billet is rolled. During the rolling process, the finishing temperature of rough rolling and the second rolling temperature are controlled to not fall within the temperature range of 900°C to 960°C, and the roll guards are continuously washed during the rolling process.

[0007] As a preferred embodiment of the control method for reducing the occurrence rate of pitting and cratering in high-temperature rolled nickel-based steel with a thickness of 220mm billet according to the present invention, in the rolling process, the steel is tapped according to the upper limit of the heating temperature in the heating process, and the residence time of the steel plate in the high-temperature range is controlled to be less than or equal to a preset value.

[0008] As a preferred embodiment of the method for controlling the occurrence rate of pitting and crazing in high-temperature rolled nickel-based steel with a thickness of 220mm as described in this invention, the rolling process includes: continuously rinsing the roll guards during the rolling process. The roll guard plate is rinsed with flushing water with a pressure of not less than 0.8 MPa and a flow rate of not less than 200 L / min.

[0009] As a preferred embodiment of the control method for reducing the occurrence rate of pitting and crazing in high-temperature rolled nickel-based steel with a thickness of 220mm billet according to the present invention, in the heating process, the actual furnace exit temperature is controlled to be 1222℃~1240℃.

[0010] As a preferred embodiment of the control method for reducing the occurrence rate of pitting on the surface of nickel-based steel rolled at high temperature with a thickness of 220mm billet according to the present invention, wherein: in the heating process, the homogenization time is controlled to be 36min~123min.

[0011] As a preferred embodiment of the method for controlling the occurrence rate of pitting and crazing in high-temperature rolled nickel-based steel with a thickness of 220mm as described in this invention, the method further includes, after the rolling process: The surface quality of the rolled steel plate is inspected to obtain data on the occurrence of surface pitting and crazing. The data is then compared with a preset quality threshold. When the data exceeds the preset quality threshold, a process parameter adjustment command is output.

[0012] The beneficial effects of this invention are: (1) By optimizing the heating process, controlling the heating temperature to 1220-1230℃, the total time in the furnace to 320-400min, and the soaking time to ≥35min, and controlling the weak oxidizing atmosphere in the furnace (2%-6% residual oxygen), the present invention effectively reduces the amount of iron oxide scale generated during high-temperature heating, creating favorable conditions for subsequent descaling.

[0013] (2) The present invention employs two-stage descaling combined with side descaling nozzles to comprehensively descale the surface and sides of the billet, which significantly improves the descaling effect and avoids pressing defects caused by residual iron oxide scale.

[0014] (3) In the rolling process, the present invention controls the finishing temperature of rough rolling and the second rolling temperature to avoid the easily oxidized temperature range of 900-960℃, which effectively inhibits secondary oxidation during the rolling process and reduces the formation of iron oxide scale.

[0015] (4) By modifying the slag flushing water system of the roll guard plate, the present invention improves the water pressure and flow rate, enhances the flushing effect of iron oxide scale, and avoids the detached iron oxide scale from sticking and adsorbing on the roller table and being pressed into the steel plate surface. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart illustrating the method for controlling the occurrence of pitting and crazing in high-temperature rolled nickel-based steel with a thickness of 220mm, as provided by the present invention. Detailed Implementation

[0018] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0019] Figure 1 This is a flowchart illustrating a method for controlling the incidence of pitting and crazing in high-temperature rolled nickel-based steel with a billet thickness of 220mm, as provided in an embodiment of this application. The method specifically includes the following steps: Step S1: Heating process: Load the 220mm thick nickel-based steel billet into the furnace and heat it. Control the heating temperature to 1220℃ to 1230℃, control the total time in the furnace to 320min to 400min, control the soaking time to not less than 35min, and control the atmosphere in the furnace to be a weak oxidizing atmosphere with a residual oxygen content of 2% to 6%.

[0020] Specifically, in this embodiment, the actual furnace exit temperature is controlled at 1222℃~1240℃, and the soaking time is controlled at 36min~123min. Through the above heating process control, the amount of iron oxide scale generated in the billet during the heating process is effectively reduced.

[0021] Step S2: Descaling process: The heated billet is descaled in two passes using a descaling box, and the sides of the billet are descaled simultaneously using side descaling nozzles.

[0022] Specifically, through multi-directional and multi-pass descaling operations, the iron oxide scale on the surface and sides of the billet is completely removed, providing good surface conditions for subsequent rolling.

[0023] Step S3: Rolling process: Roll the descaled billet. During the rolling process, control the finishing temperature of rough rolling and the second rolling temperature to not fall within the temperature range of 900℃ to 960℃, and continuously rinse the roll guards during the rolling process.

[0024] Specifically, the rolling process avoids the easily oxidized temperature range of 900-960℃, effectively suppressing secondary oxidation during rolling. Simultaneously, a high-temperature fast rolling process is adopted, with steel tapped at the upper limit of the heating temperature, reducing the number of rolling passes, increasing rolling speed, and shortening the residence time of the steel plate in the high-temperature range. During rolling, slag-flushing water with a pressure of not less than 0.8MPa and a flow rate of not less than 200L / min is used to continuously flush the roll guards, preventing detached iron oxide scale from adhering to the roll table and being pressed into the steel plate surface.

[0025] Step S4: Tracking and Feedback Process: Perform surface quality inspection on the rolled steel plate, obtain data on the occurrence of surface pitting and crazing, and compare the data with a preset quality threshold. When the data exceeds the preset quality threshold, output a process parameter adjustment command.

[0026] Specifically, the surface quality of the rolled steel plate is tracked and recorded, and the process parameters of the heating, descaling or rolling steps are fed back and adjusted based on the actual occurrence of surface pitting and crazing, forming a closed-loop control.

[0027] After adopting the above method, the incidence of pitting and crazing in high-temperature rolled nickel-based steel with a billet thickness of 220mm was significantly reduced. Since its implementation in January 2025, continuous tracking statistics show that the incidence of pitting and crazing has decreased by more than 10%. Based on a monthly output of 1000 tons, this translates to a reduction of 100 tons of unplanned production per month, and 1200 tons per year. This represents a cost reduction of 100 yuan per ton, resulting in an annual cost reduction of 120,000 yuan, demonstrating significant economic benefits.

[0028] Therefore, the technical solution of this application solves the technical problem of high incidence of pitting and crazing in nickel-based steel during high-temperature rolling by optimizing the heating process, descaling process and rolling process, thereby improving the surface quality of steel plates, reducing quality loss and increasing product qualification rate.

[0029] In addition to the above embodiments, the present invention may have other implementation methods; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for controlling the occurrence of pitting and crazing in high-temperature rolled nickel-based steel with a billet thickness of 220mm, characterized in that: include: Heating process: Load 220mm thick nickel-based steel billets into the furnace and heat them. Control the heating temperature to 1220℃ to 1230℃, control the total time in the furnace to 320min to 400min, control the soaking time to not less than 35min, and control the furnace atmosphere to be a weakly oxidizing atmosphere with a residual oxygen content of 2% to 6%. Descaling process: The heated billet is descaled in two passes using a descaling box, and the sides of the billet are descaled simultaneously using side descaling nozzles. Rolling process: The descaled billet is rolled. During the rolling process, the finishing temperature of rough rolling and the second rolling temperature are controlled to not fall within the temperature range of 900°C to 960°C, and the roll guards are continuously washed during the rolling process.

2. The method for controlling the occurrence rate of pitting and crazing in high-temperature rolled nickel-based steel with a thickness of 220mm billet according to claim 1, characterized in that: In the rolling process, steel is tapped at the upper limit of the heating temperature in the heating process, and the dwell time of the steel plate in the high-temperature range is controlled to be less than or equal to a preset value.

3. The method for controlling the occurrence rate of pitting and crazing in high-temperature rolled nickel-based steel with a thickness of 220mm billet according to claim 1, characterized in that: In the rolling process, the continuous rinsing of the roll guards includes: The roll guard plate is rinsed with flushing water with a pressure of not less than 0.8 MPa and a flow rate of not less than 200 L / min.

4. The method for controlling the occurrence rate of pitting and crazing in high-temperature rolled nickel-based steel with a thickness of 220mm billet according to claim 1, characterized in that: In the heating process, the actual furnace exit temperature is controlled to be 1222℃~1240℃.

5. The method for controlling the occurrence rate of pitting and crazing in high-temperature rolled nickel-based steel with a billet thickness of 220mm, as described in claim 1, is characterized in that: In the heating process, the heat equalization time is controlled to be 36 min to 123 min.

6. The method for controlling the occurrence rate of pitting and crazing in high-temperature rolled nickel-based steel with a thickness of 220mm billet according to claim 1, characterized in that: Following the rolling process, the process further includes: The surface quality of the rolled steel plate is inspected to obtain data on the occurrence of surface pitting and crazing. The data is then compared with a preset quality threshold. When the data exceeds the preset quality threshold, a process parameter adjustment command is output.

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