A production method for reducing performance fluctuations of hot-rolled strip steel

Abstract

The application relates to a production method for reducing performance fluctuation of hot-rolled strip steel, and belongs to the technical field of performance control of hot-rolled strip steel. c_set and the target cooling rate V c‑obj satisfies |V c_set‑ V c‑obj | / V c‑obj <=13%, the cooling mode executes the preceding normal cooling mode; when 13%<|V c_set‑ V c‑obj | / V c‑obj and V c_set‑ V c‑obj >0, the cooling mode executes the preceding sparse cooling mode; when 13%<|V c_set‑ V c‑obj | / V c‑obj <=19% and V c_set‑ V c‑obj <0, the cooling mode executes the preceding concentrated cooling mode; when 19%<|V c_set‑ V c‑obj | / V c‑obj and V c_set‑ V c‑obj <0, the cooling mode executes the preceding intensive cooling mode. The application has the beneficial effect of reducing the performance fluctuation of the hot-rolled strip steel caused by the change of the cooling rate.

Description

Technical Field

[0001] This invention relates to a production method for reducing performance fluctuations in hot-rolled strip steel, belonging to the field of hot-rolled strip steel performance control technology. Background Technology

[0002] In the field of hot-rolled strip steel, for low-carbon alloy steel with a phase transformation structure of ferrite and pearlite, the cooling rate affects the ferrite nucleation rate, the size and morphology of micrograins, and consequently the mechanical properties of the strip steel, including strength, hardness, and elongation. A suitable cooling rate can give the strip steel good strength, ductility, toughness, and formability, improving the overall mechanical properties of the steel. However, in product design, the control of the cooling rate is mainly achieved through the design of the cooling mode. Common practice is to use one cooling mode for one steel grade, or to use different cooling modes for a certain steel grade based on thickness range. In actual production, technicians focus more on whether the temperature parameters are met and whether the cooling mode is used as designed, often neglecting the variation in the actual cooling rate. In fact, for the same batch of cast billets with the same composition, rolled into finished products of the same thickness, even using the same hot rolling process and meeting the target process parameters, changes in rolling conditions, such as workpiece temperature and rolling speed, will cause drastic changes in the cooling rate of the strip steel during the cooling process, inevitably leading to significant fluctuations in its mechanical properties. Summary of the Invention

[0003] The purpose of this invention is to provide a production method for reducing performance fluctuations in hot-rolled strip steel, thereby reducing performance fluctuations caused by changes in cooling rate and solving the problems existing in the background art.

[0004] The technical solution of this invention is:

[0005] A production method for reducing performance fluctuations in hot-rolled strip steel includes a heating process, a roughing process, a finishing process, a cooling process, and a coiling process, and is controlled according to the following requirements:

[0006] (1) Calculate the preset cooling rate V of the cooling process in the finishing rolling process. c set ;

[0007] V c_set =-C+0.949*V FM -1.991*H-0.039*FDT+0.1492*CT (1)

[0008] In the formula, 10.8 ≤ C ≤ 11, V FM The setting speed for the final stand of the finishing mill is (m / s), H is the target thickness of the finished product (mm), FDT is the setting temperature for the final rolling (°C), and CT is the setting temperature for the coiling (°C).

[0009] (2) The cooling mode of the cooling process is executed according to the following logic:

[0010] When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfy | V c_set- V c-obj | / V c-obj When the concentration is ≤13%, the cooling mode will switch to the normal front-end cooling mode.

[0011] When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfying 13% < |V c_set- V c-obj | / V c-obj And V c_set- V c-obj When the value is greater than 0, the cooling mode will be the front-end sparse cooling mode.

[0012] When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfying 13% < |V c_set- V c-obj | / V c-obj ≤19% and V c_set- V c-obj When <0, the cooling mode is the front-end centralized cooling mode;

[0013] When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfying 19% < |V c_set- V c-obj | / V c-obj And V c_set- V c-obj When <0, the cooling mode executes the front-end encrypted cooling mode.

[0014] The cooling rates of the front-end sparse cooling mode, front-end normal cooling mode, front-end centralized cooling mode, and front-end dense cooling mode are different. The cooling rate of the front-end sparse cooling mode is less than that of the front-end normal cooling mode, the cooling rate of the front-end normal cooling mode is less than that of the front-end centralized cooling mode, and the cooling rate of the front-end centralized cooling mode is less than that of the front-end dense cooling mode.

[0015] The aforementioned normal cooling mode is the default cooling mode at the beginning of the cooling process.

[0016] The cooling rate of the front-end sparse cooling mode is 25-35℃ / s, the cooling rate of the front-end ordinary cooling mode is 35-45℃ / s, the cooling rate of the front-end concentrated cooling mode is 70-80℃ / s, and the cooling rate of the front-end dense cooling mode is 110-120℃ / s.

[0017] In Equation 1, C = 10.9.

[0018] The hot-rolled strip steel has the following composition by mass percentage: C: ≤0.10%, Mn: ≤1.25%, S: ≤0.005%, P: ≤0.012%, Si: ≤0.13%, Als: 0.02~0.08%, N≤0.006%, Nb+Ti≤0.040%, with the remainder being Fe and unavoidable impurities.

[0019] The beneficial effects of this invention are as follows: This invention uses controlled rolling and cooling of the billet. By pre-calculating and logically judging the pre-set cooling rate, the cooling rate of the cooling process is dynamically adjusted, effectively solving the problem of large performance fluctuations caused by changes in on-site rolling conditions. This ensures that the performance of different batches of products converges within a narrow range (strength fluctuation within 23 MPa and elongation fluctuation within 5% for thicknesses below 6 mm; strength fluctuation within 29 MPa and elongation fluctuation within 6% for thicknesses above 6 mm), providing more stable and reliable products for subsequent processes or downstream users. This invention mainly applies the principle of precisely controlling the proportion of phase transformation structures, which reduces production control difficulty, benefits downstream users' production and use, helps increase market share, and can generate significant economic benefits. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0021] A production method for reducing performance fluctuations in hot-rolled strip steel includes a heating process, a roughing process, a finishing process, a cooling process, and a coiling process, and is controlled according to the following requirements:

[0022] (1) Calculate the preset cooling rate V of the cooling process in the finishing rolling process. c_set ;

[0023] V c_set =-C+0.949*V FM -1.991*H-0.039*FDT+0.1492*CT (1)

[0024] In the formula, 10.8 ≤ C ≤ 11, V FM The setting speed for the final stand of the finishing mill is (m / s), H is the target thickness of the finished product (mm), FDT is the setting temperature for the final rolling (°C), and CT is the setting temperature for the coiling (°C).

[0025] (2) The cooling mode of the cooling process is executed according to the following logic:

[0026] When the preset cooling rate V c_setWith the target cooling rate V c-obj Satisfy | V c_set- V c-obj | / V c-obj When the concentration is ≤13%, the cooling mode will switch to the normal front-end cooling mode.

[0027] When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfying 13% < |V c_set -V c-obj | / V c-obj And V c_set -V c-obj When the value is greater than 0, the cooling mode will be the front-end sparse cooling mode.

[0028] When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfying 13% < |V c_set -V c-obj | / V c-obj ≤19% and V c_set -V c-obj When <0, the cooling mode is the front-end centralized cooling mode;

[0029] When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfying 19% < |V c_set -V c-obj | / V c-obj And V c_set- V c-obj When <0, the cooling mode executes the front-end encrypted cooling mode.

[0030] The cooling rates of the front-end sparse cooling mode, front-end normal cooling mode, front-end centralized cooling mode, and front-end dense cooling mode are different. The cooling rate of the front-end sparse cooling mode is less than that of the front-end normal cooling mode, the cooling rate of the front-end normal cooling mode is less than that of the front-end centralized cooling mode, and the cooling rate of the front-end centralized cooling mode is less than that of the front-end dense cooling mode.

[0031] The aforementioned normal cooling mode is the default cooling mode at the beginning of the cooling process.

[0032] The cooling rate of the front-end sparse cooling mode is 25-35℃ / s, the cooling rate of the front-end ordinary cooling mode is 35-45℃ / s, the cooling rate of the front-end concentrated cooling mode is 70-80℃ / s, and the cooling rate of the front-end dense cooling mode is 110-120℃ / s.

[0033] In Equation 1, C = 10.9.

[0034] The hot-rolled strip steel has the following composition by mass percentage: C: ≤0.10%, Mn: ≤1.25%, S: ≤0.005%, P: ≤0.012%, Si: ≤0.13%, Als: 0.02~0.08%, N≤0.006%, Nb+Ti≤0.040%, with the remainder being Fe and unavoidable impurities.

[0035] In this embodiment, the hot-rolled strip steel production process includes heating, roughing, finishing, cooling and coiling processes; the main process equipment includes: a regenerative heating furnace, two roughing mills, seven finishing mills, laminar flow cooling equipment and an underground coiler.

[0036] Billet: Thickness 230mm, width 1550mm. Billet composition by mass percentage: C: 0.09%, Mn: 0.70%, S: 0.005%, P: 0.012%, Si: 0.05%, Als: 0.025%, N: 0.004%, Nb: 0.018%, Ti: 0.015%, the remainder being Fe and unavoidable impurities.

[0037] The processes for each step are described below:

[0038] (1) Heating process: The billet heating and tapping temperature is shown in Table 1.

[0039] (2) Rough rolling process: After heating, the billet is rolled in three passes of the R1 two-roll reversible rolling mill to reduce its thickness to 125-130mm; finally, it is rolled in five passes of the R2 four-roll reversible rolling mill to produce an intermediate billet with a thickness of 40-56mm.

[0040] (3) Finishing rolling process: The starting and ending temperatures of the finishing rolling are shown in Table 1. When the high temperature gauge at the entry point of the finishing rolling mill detects the head of the strip, the preset cooling rate V of the cooling process is calculated according to Equation 1. c_set ;

[0041] When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfy | V c_set- V c-obj | / V c-obj When ≤13%, the initial default cooling mode C will be used. mode2 Issued to the secondary control system of the cooling process;

[0042] When V c_set With V c-obj Satisfying 13% < |V c_set- V c-obj | / V c-obj And V c_set- V c-obj When >0, the front-end sparse cooling mode C is activated. mode1 Issued to the secondary control system of the cooling process;

[0043] When V c_set With V c-obj Satisfying 13% < |V c_set- V c-obj | / V c-obj ≤19% and V c_set- V c-obj When <0, switch to front-end centralized cooling mode C. mode3 Issued to the secondary control system of the cooling process;

[0044] When V c_set With V c-obj Satisfying 19% < |V c_set -V c-obj | / V c-obj And V c_set- V c-obj When <0, the front-end encryption cooling mode C will be activated. mode4 The data is sent to the secondary control system of the cooling process.

[0045] (4) Cooling and coiling process: The coiling temperature is shown in Table 1. The initial default cooling mode is the front-end normal cooling mode. When the strip enters the cooling area, the cooling strategy is executed according to the cooling mode received by the secondary control system.

[0046] Table 1

[0047]

[0048] Table 2 Hot rolling process parameters and cooling modes for each embodiment

[0049]

[0050] Table 3 Results of Performance Testing of Hot-Rolled Steel Strip Products

[0051]

[0052]

Claims

1. A production method for reducing performance fluctuations in hot-rolled strip steel, comprising a heating process, a roughing process, a finishing process, a cooling process, and a coiling process, characterized in that: Control should be implemented according to the following requirements: (1) Calculate the preset cooling rate V of the cooling process in the finishing rolling process. c_set ; V c_set = -C +0.949*V FM -1.991*H -0.039*FDT +0.1492*CT (1) In the formula, 10.8 ≤ C ≤ 11, V FM The setting speed for the final stand of the finishing mill is (m / s), H is the target thickness of the finished product (mm), FDT is the final rolling setting temperature (°C), and CT is the coiling setting temperature (°C). (2) The cooling mode of the cooling process shall be executed according to the following logical judgment: When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfy | V c_set- V c-obj | / V c-obj When the temperature is ≤13%, the cooling mode will be the normal front-end cooling mode. When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfying 13% < |V c_set- V c-obj | / V c-obj And V c_set- V c-obj When the value is greater than 0, the cooling mode will be the front-end sparse cooling mode. When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfying 13% < |V c_set- V c-obj | / V c-obj ≤19% and V c_set- V c-obj When <0, the cooling mode is the front-end centralized cooling mode; When the preset cooling rate V c_set With the target cooling rate V c-obj Satisfying 19% < |V c_set- V c-obj | / V c-obj And V c_set- V c-obj When <0, the cooling mode executes the front-end encrypted cooling mode.

2. The production method for reducing performance fluctuations of hot-rolled strip steel according to claim 1, characterized in that: The cooling rates of the front-end sparse cooling mode, front-end normal cooling mode, front-end centralized cooling mode, and front-end dense cooling mode are different. The cooling rate of the front-end sparse cooling mode is less than that of the front-end normal cooling mode, the cooling rate of the front-end normal cooling mode is less than that of the front-end centralized cooling mode, and the cooling rate of the front-end centralized cooling mode is less than that of the front-end dense cooling mode.

3. The production method for reducing performance fluctuations of hot-rolled strip steel according to claim 2, characterized in that: The aforementioned normal cooling mode is the default cooling mode at the beginning of the cooling process.

4. The production method for reducing performance fluctuations of hot-rolled strip steel according to claim 3, characterized in that: The cooling rate of the front-end sparse cooling mode is 25-35℃ / s, the cooling rate of the front-end ordinary cooling mode is 35-45℃ / s, the cooling rate of the front-end concentrated cooling mode is 70-80℃ / s, and the cooling rate of the front-end dense cooling mode is 110-120℃ / s.

5. A production method for reducing performance fluctuations of hot-rolled strip steel according to claim 1, characterized in that: In the above formula (1), C = 10.

9.

6. The production method for reducing performance fluctuations of hot-rolled strip steel according to claim 1, characterized in that: The hot-rolled strip steel has the following composition by mass percentage: C: ≤0.10%, Mn: ≤1.25%, S: ≤0.005%, P: ≤0.012%, Si: ≤0.13%, Als: 0.02~0.08%, N≤0.006%, Nb+Ti≤0.040%, with the remainder being Fe and unavoidable impurities.

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