Cold-rolled base material deformation resistance control method based on tissue homogenization and cold-rolled base material

Abstract

The application discloses a cold-rolled base material deformation resistance control method based on tissue homogenization and a cold-rolled base material, and belongs to the technical field of plate and strip rolling, and comprises the following steps: S1, rough rolling, adopting super large reduction rolling, single pass reduction is 40%-45%, and cumulative reduction is greater than or equal to 70%; S2, finish rolling, adopting small reduction rolling, single pass reduction is 10%-15%, and the interval time between finish rolling passes is 5-8 seconds; S3, multi-section variable rate laminar cooling is carried out, the cooling process comprises a fast cooling section, a medium cooling section and a slow cooling section, the cooling rate of the fast cooling section is 20-25 DEG C / s, the cooling rate of the medium cooling section is 10-15 DEG C / s, and the cooling rate of the slow cooling section is 5-8 DEG C / s; the standard deviation sigma of the ferrite grain size distribution of the hot-rolled plate coil is less than or equal to 1.5 mu m, the variation coefficient CV of the pearlite lamella spacing is less than or equal to 8%, so that the deformation resistance fluctuation range of the cold-rolled base material is controlled within ± 5%.

Description

Technical Field

[0001] This invention belongs to the field of strip rolling technology, and in particular relates to a method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization, and the cold-rolled base material itself. Background Technology

[0002] The deformation resistance of cold-rolled base material (hot-rolled coil) is a key parameter determining the rolling force, rolling stability, and final product quality (such as strip thickness accuracy, sheet shape quality, and uniformity of mechanical properties) during the cold rolling process. In actual production, due to the inhomogeneity of microstructure evolution during hot rolling (such as uneven ferrite-pearlite distribution, large differences in grain size, and inconsistent residual stress distribution), the deformation resistance fluctuates significantly at different locations within the same coil or even the same strip (currently at ±10% to ±15%). This results in a rolling force fluctuation coefficient as high as 8% to 12% during the cold rolling process, and strip thickness deviations of ±0.01 mm, severely restricting the high-quality production of high-end steel grades (such as high-strength steel, automotive steel, plain carbon steel, and low-alloy steel). Furthermore, in existing controlled rolling processes, the reduction in roughing passes is generally 25%–35%, and the reduction in finishing passes is 20%–30%, with a pass interval typically of 15–30 seconds. This results in a standard deviation of ferrite grain size distribution in hot-rolled base materials of approximately 3–5 μm and a pearlite lamellar spacing variation coefficient of approximately 15%–20%, leading to poor microstructure uniformity and failing to meet the quality requirements of high-end cold-rolled products. Summary of the Invention

[0003] To address the aforementioned technical deficiencies, this invention provides a method for controlling the deformation resistance of cold-rolled base material based on homogenized microstructure, as well as the cold-rolled base material itself. By synergistically optimizing the controlled rolling process of "large reduction in roughing rolling + small reduction in finishing rolling + ultra-short pass interval" and the controlled cooling process of "multi-stage variable rate laminar flow cooling," a high degree of homogenization of the microstructure of the hot-rolled base material is achieved, controlling the fluctuation range of deformation resistance within ±5%, and significantly improving the stability of the cold rolling process.

[0004] To achieve the above-mentioned technical objectives, the present invention is implemented through the following technical solution: The first objective of this invention is to provide a method for controlling the deformation resistance of cold-rolled base materials based on microstructure homogenization, comprising: S1. Rough rolling, using ultra-large reduction rolling, with a single-pass reduction of 40% to 45% and a cumulative reduction of ≥70%; S2, finishing rolling, uses small reduction rolling, with a single pass reduction of 10% to 15%, and the interval between finishing rolling passes is 5 to 8 seconds; S3. Perform multi-stage variable-rate laminar flow cooling. The cooling process includes a fast cooling section, a medium cooling section, and a slow cooling section. The cooling rate of the fast cooling section is 20℃ / s to 25℃ / s, the cooling rate of the medium cooling section is 10℃ / s to 15℃ / s, and the cooling rate of the slow cooling section is 5℃ / s to 8℃ / s. Through the synergy of the above processes, the standard deviation of ferrite grain size distribution σ in hot-rolled coils is ≤1.5μm, and the coefficient of variation of pearlite lamellar spacing CV is ≤8%, thereby controlling the deformation resistance fluctuation range of cold-rolled base material within ±5%.

[0005] Preferably, the initial rolling temperature in the roughing stage is 1150℃~1200℃, and the final rolling temperature is 950℃~1000℃.

[0006] Preferably, the final rolling temperature in the finishing rolling stage is 820℃~880℃.

[0007] Preferably, the specific path of the multi-stage variable-rate laminar flow cooling is as follows: cooling from the final rolling temperature to 750°C at a rate of 20°C / s to 25°C / s, then cooling to 650°C at a rate of 10°C / s to 15°C / s, and finally cooling to the coiling temperature of 580°C at a rate of 5°C / s to 8°C / s.

[0008] Preferably, the ultra-large reduction rolling breaks the initial as-cast structure into recrystallized austenite grains of 15μm to 25μm.

[0009] Preferably, the range of deformation resistance fluctuation is ≤±2%.

[0010] Preferably, the EBSD statistical grain size distribution is used to calculate the standard deviation σ.

[0011] Preferably, TEM is used to measure the interlamellar spacing λ, and the coefficient of variation CV is calculated as (standard deviation / mean) × 100%.

[0012] Preferably, a quantitative relationship model is established between the organized uniformity parameter and the deformation resistance fluctuation rate: ΔK / K=a·σ+b·CV+c, where a, b, and c are fitting coefficients related to the steel composition, σ is the standard deviation of the grain size distribution, ΔK / K is the cold rolling deformation resistance fluctuation rate, and CV is the coefficient of variation.

[0013] The second objective of this invention is to provide a cold-rolled base material prepared using the above-mentioned method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization.

[0014] The advantages and technical effects of this invention are: This invention reduces the range of deformation resistance fluctuation of cold-rolled base material from ±10% to ±15% in the prior art to ≤±5% through process synergy, and in preferred embodiments it can reach ≤±2%.

[0015] This invention reduces the standard deviation σ of ferrite grain size distribution from the existing 3-5 μm to ≤0.8 μm, and the coefficient of variation CV of pearlite interlamellar spacing from the existing 15%-20% to ≤4%.

[0016] This invention enhances the stability of the cold rolling process: the rolling force fluctuation coefficient during the cold rolling process is reduced to ≤3%, and the strip thickness deviation is reduced to ≤±0.005mm.

[0017] This invention is applicable to various steel types, including plain carbon steel, low alloy steel, and automotive steel. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A flowchart of a preferred embodiment of the present invention is shown. Detailed Implementation

[0020] To make the above-mentioned objectives, control system design, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] Please see Figure 1 A method for controlling the deformation resistance of cold-rolled base materials based on microstructure homogenization, comprising: S1. Treatment of excessive reduction during the roughing stage.

[0022] The rolling process employs ultra-large reduction, with single-pass reduction controlled at 40%–45% and cumulative reduction ≥70%. The initial rolling temperature is controlled at 1150℃–1200℃, and the final rolling temperature is controlled at 950℃–1000℃. Through large deformation during rough rolling, the as-cast columnar crystal structure is fully broken down, and the initial coarse as-cast structure is broken into fine recrystallized austenite grains.

[0023] S2, coordinated control of small reduction and ultra-short pass interval in the finishing rolling stage.

[0024] Small reduction rolling is adopted, with the single-pass reduction controlled at 10% to 15% and the cumulative reduction controlled at 15% to 25%; the finishing rolling interval is shortened to 5 to 8 seconds; the final rolling temperature is controlled at 820℃ to 880℃; by using short pass intervals, the static recrystallization and growth of austenite grains between passes is suppressed, thus maintaining the fine size of austenite grains.

[0025] S3, multi-stage variable rate laminar flow cooling.

[0026] The laminar cooling process after finishing rolling is divided into three stages: Rapid cooling section: Cooling from the final rolling temperature to 750℃ at a cooling rate of 20℃ / s to 25℃ / s; Intermediate cooling section: Cools from 750℃ to 650℃ at a cooling rate of 10℃ / s to 15℃ / s; Slow cooling section: Cooling from 650°C to 580°C winding temperature at a cooling rate of 5°C / s to 8°C / s.

[0027] S4. Quantitative control of tissue uniformity and deformation resistance.

[0028] Through the synergistic process of S1 to S3, the standard deviation of ferrite grain size distribution in hot-rolled coils is controlled to be σ≤1.5μm, and the coefficient of variation of pearlite lamellar spacing is CV≤8%; a quantitative relationship model between microstructure uniformity parameters and deformation resistance fluctuation rate is established to achieve a deformation resistance fluctuation range of ≤±5% for cold-rolled base materials.

[0029] To better understand the technical solution of the present invention, the following non-limiting explanation is provided: This invention achieves high homogenization of the microstructure (ferrite grain size, pearlite lamellar spacing) of hot-rolled base material through an innovative controlled rolling and controlled cooling synergistic process, establishes a quantitative relationship between microstructure homogenization and deformation resistance, controls the deformation resistance fluctuation range of cold-rolled base material to ≤±5% (currently ±10%~±15%), the rolling force fluctuation coefficient during cold rolling process to ≤3% (currently 8%~12%), and the strip thickness deviation to ≤±0.005mm (currently ±0.01mm).

[0030] This invention employs a three-stage differentiated reduction strategy: In the roughing stage, ultra-large reduction rolling is used, with the single-pass reduction increasing to 40%–45%, the maximum single-pass reduction reaching 50%, and the cumulative reduction ≥70%. The initial rolling temperature is 1150–1200℃, and the final rolling temperature is 950–1000℃. Through the large deformation of roughing rolling, the cast columnar crystal structure is fully broken, and the initial coarse cast structure (grain size >100μm) is broken into fine recrystallized austenite grains (size 15–25μm).

[0031] In the finishing rolling stage: small reduction rolling is adopted, with the single-pass reduction reduced to 10% to 15%, the cumulative reduction to 15% to 25%, and the final rolling temperature to 820 to 880℃; by rolling with small reduction in the finishing rolling in the non-recrystallized austenite region, strain-induced precipitation and deformation bands are used to promote ferrite nucleation and achieve further refinement of ferrite grains.

[0032] Pass interval control: The fine rolling pass interval is shortened to 5-8 seconds, with a minimum interval of 5 seconds; by reducing the static recrystallization and grain growth time of austenite between passes through the ultra-short pass interval, the fine size of austenite grains (8-15μm) is maintained, laying the foundation for the uniformity of subsequent phase transformation structure.

[0033] The laminar cooling process after finishing rolling is divided into three stages: rapid cooling stage: the cooling rate is 20-25℃ / s, cooling from the final rolling temperature to 750℃; this stage rapidly passes through the pearlite transformation nose temperature range (about 700-650℃), suppressing the coarsening of pearlite lamellars, while using the large undercooling generated by rapid cooling to promote the refinement of the pearlite lamellar spacing.

[0034] Intermediate cooling section: The cooling rate is 10-15℃ / s, cooling from 750℃ to 650℃; This section cools at a moderate rate in the ferrite transformation region (approximately 750-650℃), ensuring sufficient nucleation of ferrite (fine proeutectoid ferrite grains) while avoiding non-uniform transformation caused by excessively rapid cooling.

[0035] Slow cooling section: The cooling rate is 5-8℃ / s, cooling from 650℃ to 580℃ (coiling temperature); this section uses slow cooling to reduce the temperature gradient inside the strip, reduce residual stress, and at the same time avoid abnormal growth of ferrite grains caused by slow cooling.

[0036] The overall effect of the above-mentioned controlled cooling process is that the residual stress of the strip is reduced to 40-60 MPa (compared to the conventional level of about 80-120 MPa), the cold rolling deformation resistance is reduced from the conventional 200-250 MPa to 160-190 MPa, and the deformation resistance fluctuation range is ≤±2% (currently ±10% to ±15%).

[0037] Ferrite grain size distribution: The grain size distribution was statistically analyzed using EBSD (electron backscatter diffraction), and the standard deviation σ was calculated. σ was required to be ≤1.5μm.

[0038] Pearlite interlamellar spacing: The interlamellar spacing λ was measured using TEM (transmission electron microscopy), and the coefficient of variation CV was calculated as standard deviation / mean value × 100%. The requirement was that CV ≤ 8%.

[0039] This invention establishes a quantitative relationship between the microstructure uniformity parameters (σ, CV) and the cold rolling deformation resistance fluctuation rate ΔK / K: ΔK / K = a·σ + b·CV + c, where a, b, and c are fitting coefficients related to the steel composition and are determined by regression analysis; when σ≤1.5μm and CV≤8%, ΔK / K≤±5%.

[0040] This invention establishes a quantitative relationship between microstructure uniformity (standard deviation of ferrite grain size distribution and coefficient of variation of pearlite lamellar spacing) and deformation resistance fluctuation, breaking through the limitations of traditional empirical adjustment and achieving precise control of deformation resistance at its source. This invention employs a controlled rolling process with ultra-large reduction in roughing, small reduction in finishing, and ultra-short pass intervals. Through the synergistic effect of large deformation in roughing to break the as-cast microstructure, small reduction in finishing to refine the grains, and short intervals to suppress grain growth, the standard deviation of ferrite grain size distribution is reduced from the existing 3-5 μm to ≤0.8 μm, and the microstructure uniformity is improved by 3-6 times. This invention employs a multi-stage variable-rate laminar flow cooling controlled cooling process. Through segmented and precise control of rapid cooling to suppress pearlite coarsening, intermediate cooling to refine ferrite, and slow cooling to reduce residual stress, the variation coefficient of pearlite lamellar spacing is reduced from the existing 15% to 20% to ≤4%, and the residual stress is reduced to 40 to 60 MPa. This invention can reduce the deformation resistance fluctuation range of cold-rolled base material from the existing ±10% to ±15% to ≤±5% (≤±2% in the preferred embodiment), reduce the rolling force fluctuation coefficient of the cold rolling process from the existing 8% to 12% to ≤3%, and reduce the strip thickness deviation from the existing ±0.01mm to ≤±0.005mm, thus significantly improving product quality. This invention has a wide range of applications, covering the production and subsequent cold rolling processes of hot-rolled steel coils such as plain carbon steel (e.g., Q195, Q235), low alloy steel (e.g., Q345, Q390), and automotive steel (e.g., IF steel, BH steel, DP steel), and has good industrial promotion value.

[0041] Example 1: Rough rolling: The slab is heated to 1150℃~1200℃ and rolled with a large reduction on a roughing mill. The reduction per pass is set to 40%~45% (maximum up to 50%), ensuring a cumulative reduction of over 70%. The final rolling temperature is controlled at 950℃~1000℃. This step fully breaks down the original coarse as-cast structure (>100μm) into fine recrystallized austenite grains of 15μm~25μm.

[0042] Finishing rolling: Rolling with a small reduction is performed on the finishing mill. The reduction per pass is reduced to 10%–15%, and the cumulative reduction is controlled at 15%–25%. The pass interval is strictly controlled at 5–8 seconds (minimum 5 seconds) to prevent austenite grain growth. The final rolling temperature is set in the non-recrystallized austenite region, utilizing strain-induced precipitation and deformation bands to promote ferrite nucleation.

[0043] Laminar flow cooling: Rapid cooling: Quickly transforms the nasal tip area through pearlite, inhibiting pearlite coarsening and refining the interlamellar spacing.

[0044] Intermediate cooling: Ensures sufficient nucleation in the ferrite transformation region to obtain fine proeutectoid ferrite.

[0045] Slow cooling: Reduces the temperature gradient, decreases residual stress, and prevents abnormal ferrite growth.

[0046] Results verification: Testing showed that the standard deviation of ferrite grain size distribution σ in the hot-rolled coils obtained in the examples was ≤0.8μm, and the coefficient of variation (CV) of pearlite lamellar spacing was ≤4%. The established quantitative relationship model showed that when σ≤1.5μm and CV≤8%, the deformation resistance fluctuation rate ΔK / K≤±5%.

[0047] Comparative Example 1 (Conventional Process): The roughing reduction was 30%, the finishing reduction was 25%, the pass interval was 20 seconds, and the cooling rate was constant at 15℃ / s. Test results showed σ≈4.5μm, CV≈18%, and deformation resistance fluctuation rate≈±12%.

[0048] Conclusion: Compared with the comparative example, the embodiments of the present invention show that the tissue uniformity is improved by 3 to 6 times and the fluctuation of deformation resistance is significantly reduced.

[0049] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization, characterized in that, include: S1. Rough rolling, using ultra-large reduction rolling, with a single pass reduction of 40% to 45% and a cumulative reduction of ≥70%; S2, finishing rolling, uses small reduction rolling, with a single pass reduction of 10% to 15%, and the interval between finishing rolling passes is 5 to 8 seconds; S3. Perform multi-stage variable-rate laminar flow cooling. The cooling process includes a fast cooling section, a medium cooling section, and a slow cooling section. The cooling rate of the fast cooling section is 20℃ / s to 25℃ / s, the cooling rate of the medium cooling section is 10℃ / s to 15℃ / s, and the cooling rate of the slow cooling section is 5℃ / s to 8℃ / s. Through the synergy of the above processes, the standard deviation of ferrite grain size distribution σ in hot-rolled coils is ≤1.5μm, and the coefficient of variation of pearlite lamellar spacing CV is ≤8%, thereby controlling the deformation resistance fluctuation range of cold-rolled base material within ±5%.

2. The method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization according to claim 1, characterized in that, The initial rolling temperature during the roughing stage is 1150℃~1200℃, and the final rolling temperature is 950℃~1000℃.

3. The method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization according to claim 1, characterized in that, The final rolling temperature in the finishing rolling stage is 820℃~880℃.

4. The method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization according to claim 1, characterized in that, The specific path of the multi-stage variable rate laminar flow cooling is as follows: cooling from the final rolling temperature to 750°C at a rate of 20°C / s to 25°C / s, then cooling to 650°C at a rate of 10°C / s to 15°C / s, and finally cooling to the coiling temperature of 580°C at a rate of 5°C / s to 8°C / s.

5. The method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization according to claim 1, characterized in that, The ultra-large reduction rolling process breaks the initial as-cast microstructure into recrystallized austenite grains of 15μm to 25μm.

6. The method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization according to claim 1, characterized in that, The range of deformation resistance fluctuation is ≤±2%.

7. The method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization according to claim 1, characterized in that, The standard deviation σ was calculated using the EBSD statistical method to analyze the grain size distribution.

8. The method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization according to claim 7, characterized in that, The interlamellar spacing λ was measured using TEM, and the coefficient of variation CV was calculated as (standard deviation / mean) × 100%.

9. The method for controlling the deformation resistance of cold-rolled base material based on microstructure homogenization according to claim 8, characterized in that, A quantitative relationship model is established between the organized uniformity parameter and the deformation resistance fluctuation rate: ΔK / K=a·σ+b·CV+c, where a, b, and c are fitting coefficients related to the steel composition, σ is the standard deviation of the grain size distribution, ΔK / K is the cold rolling deformation resistance fluctuation rate, and CV is the coefficient of variation.

10. A cold-rolled base material, characterized in that: It is prepared using the cold-rolled base material deformation resistance control method based on microstructure homogenization as described in any one of claims 1-9.

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