Method for batch production of thick DC03 cold-rolled steel strips on silicon steel production line

Abstract

The invention discloses a method for batch production of thick DC03 cold-rolled steel strips on a silicon steel production line. The method comprises the steps of converter smelting, vacuum treatment, continuous casting, hot rolling, acid rolling and continuous annealing. A unique annealing and stepped controlled cooling process is adopted; the DC03 comprises the following chemical components in percentage by mass: less than or equal to 0.0030% of C, less than or equal to 0.030% of Si, 0.15%-0.25% of Mn, 0.020%-0.055% of Alt, 0.050%-0.065% of Ti and the balance of Fe and inevitable impurities. On the premise of ensuring the mechanical properties (especially elongation and r value) of the product, the actual temperature of the strip steel at the outlet of the furnace area and in the subsequent process is greatly reduced, the problem of scalding of the rubber roller is fundamentally avoided, and stable and batch production of the thick DC03 (1.0-1.2 mm) on a silicon steel production line is realized.

Description

Technical Field

[0001] This invention belongs to the field of steel material rolling and heat treatment technology, and particularly relates to a method for mass production of thick DC03 cold-rolled steel strip on a silicon steel production line. Background Technology

[0002] IF steel (interstitial atomless steel) is widely used in the automotive and high-end home appliance fields due to its excellent deep drawing performance. DC03, as a typical IF steel, requires extremely low yield strength, high elongation and high plastic strain ratio (r value). Its core production process is continuous annealing, which aims to obtain a fully recrystallized equiaxed ferrite structure. In order to release capacity, Baogang East District silicon steel production line undertook the trial production and production of DC03 steel strip. However, the production line has inherent equipment limitations: (1) Insufficient furnace length: The annealing holding time is relatively short, and for thick products (≥1.0mm), there is a risk of insufficient recrystallization in the core. (2) Lack of complete cooling section: In particular, the lack of standard slow cooling and over-aging section results in an unsatisfactory cooling path for the strip after high-temperature annealing. (3) Problem of rubber roller burns: The non-oriented silicon steel produced on the silicon steel production line is all 0.4-0.6mm in size. Sizes above 1.0mm have exceeded the equipment limit. When producing thick DC03, the residual temperature of the strip at the furnace exit and after the controlled cooling section is too high, causing the rubber hanger roller at the exit to age and be damaged rapidly due to continuous high-temperature baking. The detached rubber impurities will adhere to the surface of the strip, causing serious surface quality defects (see Figure 1 Traditional solutions involve lowering the annealing temperature or speed, but this sacrifices the product's mechanical properties, particularly leading to insufficient recrystallization, increased strength, and deteriorated plasticity. Therefore, a synergistic process is urgently needed that can both guarantee the excellent deep-drawing performance of DC03 and fundamentally prevent roller burns. Summary of the Invention

[0003] To overcome the shortcomings of existing silicon steel production line equipment, the purpose of this invention is to provide a method for mass production of thick DC03 cold-rolled steel strip on a silicon steel production line. By significantly reducing the actual temperature of the strip at the furnace exit and in subsequent processes while ensuring the mechanical properties of the product (especially elongation and r-value), the problem of rubber roller burn is fundamentally eliminated, and the stable and mass production of thick DC03 (1.0~1.2mm) on the silicon steel production line is achieved.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for mass production of thick-gauge DC03 cold-rolled steel strip on a silicon steel production line. The method includes converter smelting, vacuum treatment, continuous casting, hot rolling, pickling, and continuous annealing. Its key feature is the use of a unique "annealing + stepped controlled cooling" process, as detailed below:

[0006] 1) Annealing temperature control: Set the outlet plate and strip temperature of the heating section and the soaking section to 815℃~830℃;

[0007] 2) Temperature control in the slow cooling section: After passing through the soaking section, the strip enters the slow cooling section, where the temperature of the strip at the exit of the section is controlled at 685℃~695℃;

[0008] 3) Temperature control of the controlled cooling section: The temperature of the strip at the outlet of the controlled cooling section is forcibly controlled within a low temperature range of 195℃ to 205℃;

[0009] The chemical composition of the DC03, by mass percentage, satisfies the following: C ≤ 0.0030%, Si ≤ 0.030%, Mn: 0.15%–0.25%, Alt: 0.020%–0.055%, Ti: 0.050%–0.065%, with the remainder being Fe and unavoidable impurities.

[0010] Furthermore, the continuous annealing process is for DC03 cold-rolled coils with a thickness of 1.0mm to 1.2mm.

[0011] Furthermore, the annealing speed is set to 65–85 m / min to ensure sufficient holding time at a relatively low annealing temperature.

[0012] Furthermore, the chemical composition of the DC03 by mass percentage is as follows: C 0.0021%, Si 0.004%, Mn 0.18%, Alt 0.038%, Ti 0.062%, with the remainder being Fe and unavoidable impurities.

[0013] Furthermore, the 3.2mm thick hot-rolled raw material is rolled to a finished thickness of 1.0mm using a pickling and rolling mill.

[0014] Furthermore, continuous annealing: The following core process parameters are executed on the silicon steel continuous annealing line:

[0015] Annealing temperature: 822~829℃, annealing speed: 70~83m / min;

[0016] Slow cooling section outlet temperature: 687~693℃;

[0017] Cooling section outlet temperature: 195~202℃.

[0018] Furthermore, the produced thick-gauge DC03 cold-rolled steel strip meets the following performance requirements: yield strength 125-146 MPa, tensile strength 281-291 MPa, elongation 42.0-46.0%, n value 0.24-0.26, and r value 2.8-3.9.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] 1. Completely solve the problem of rubber roller burns: By significantly reducing the outlet temperature of the controlled cooling section from about 400℃ to about 200℃, the temperature of the strip body is lower than the tolerance limit of the rubber roller, fundamentally eliminating potential surface quality problems and ensuring smooth mass production.

[0021] 2. Balancing performance and quality: While reducing the annealing temperature (815~830℃, original temperature 860℃) and furnace speed, the precise process window design ensures that the mechanical properties of thick DC03 products (taking 1.0mm as an example) fully meet the standard requirements: yield strength 120~150MPa, tensile strength 280~300MPa, elongation ≥40%, and r-value ≥2.8.

[0022] 3. High adaptability and significant benefits: This invention makes full use of existing silicon steel production line equipment and makes up for hardware shortcomings through process innovation, realizing stable batch production of high value-added products on production lines without ideal cooling conditions, thereby improving equipment utilization and market competitiveness. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings.

[0024] Figure 1 Quality issues with rubber rollers and steel strips (left image shows rubber rollers, right image shows steel strips); Detailed Implementation

[0026] The present invention will be further illustrated by specific embodiments below.

[0027] Example 1: Mass production of 1.0mm thick DC03-L cold-rolled steel strip raw material: hot-rolled coils supplied by a plate mill were used, and their chemical composition met the following requirements: C 0.0021%, Si 0.004%, Mn 0.18%, Alt 0.038%, Ti 0.062%.

[0028] Cold rolling: The 3.2mm thick hot-rolled raw material is rolled to a finished thickness of 1.0mm using a pickling and rolling mill.

[0029] Continuous annealing: The following core process parameters are executed on the silicon steel continuous annealing line:

[0030] Annealing temperature: 822~829℃ (exit temperature of RTF and SF section strip), annealing speed: 70~83m / min;

[0031] Slow cooling section outlet temperature: 687~693℃;

[0032] Cooling section outlet temperature: 195~202℃

[0033] Final performance: The steel coils produced under this process were tested, and the results were as follows: yield strength 125–146 MPa, tensile strength 281–291 MPa, elongation 42.0–46.0%, n-value 0.24–0.26, and r-value 2.8–3.9. All mechanical properties were excellent, and no signs of scorching were observed on the exit rollers throughout the entire production process, and the surface quality of the strip remained intact. See Table 1 for details.

[0034] Table 1 Mechanical Properties of Products

[0035]

[0036]

[0037] Comparative Example 1: Cooling section temperature 380℃ (outside the scope of this invention)

[0038] Raw materials: The same 1.0mm thick DC03 cold-rolled coil as in the example.

[0039] Continuous annealing: Except for the temperature of the controlled cooling section, the rest of the process was similar to that in the example: annealing temperature: 840℃, annealing speed: 100m / min.

[0040] Cooling section outlet temperature: 380℃.

[0041] Problems and Results: After exiting the controlled cooling section, the strip still carries extremely high heat. When passing the exit rubber roller (hanger roller), the high temperature causes severe thermal degradation and burns on the roller surface within a short time (approximately after 2-3 rolls of continuous production). The roller surface becomes sticky, blistering and flaking off. The flaked rubber particles adhere to the strip surface, forming indentation defects, resulting in substandard strip surface quality. Machine shutdown and roller replacement are necessary, making continuous mass production impossible. Although the strip's mechanical properties are acceptable at this point (yield strength 145MPa, tensile strength 290MPa, elongation 41%, n-value 0.25, r-value 2.95), the significantly increased scrap rate due to surface defects proves this process is unfeasible.

[0042] Comparative Example 2: Cooling section temperature 220℃ (close to but still higher than the upper limit of the present invention) Raw material: 1.0mm thick DC03 cold-rolled coil, the same as in the example.

[0043] Continuous annealing: Annealing temperature: 820℃, annealing speed: 85m / min.

[0044] The outlet temperature of the controlled cooling section is 220℃ (still higher than the 205℃ upper limit specified in this invention). Problems and Results: Under this condition, although the strip temperature decreases, it is still too high for continuously running rubber rollers. After producing approximately several dozen rolls, the rubber rollers begin to show obvious burn marks and premature wear. Although this does not immediately cause mass surface defects, the lifespan of the rubber rollers is significantly shortened, requiring frequent maintenance and replacement, severely impacting the continuous operation efficiency and stability of the production line, and increasing maintenance costs and production risks. This process also cannot meet the requirements for long-term, stable, and mass production.

[0045] A comparison between the examples and the comparative examples clearly shows that:

[0046] 1. The outlet temperature of the controlled cooling section is the decisive factor in whether the problem of rubber roller burn can be solved. It must be strictly controlled below 205℃ to fundamentally ensure the long-term safe operation of the rubber roller.

[0047] 2. Comparative Examples 1 and 2 show that even if other process parameters (such as annealing temperature) are optimized, the problem of rubber roller burn cannot be avoided as long as the temperature of the controlled cooling section fails to drop below the critical value of the present invention, thus proving the necessity and criticality of the temperature window set in the present invention.

[0048] 3. This invention achieves the best balance between ensuring product performance and resolving potential equipment operation hazards through the synergistic design of "annealing + stepped controlled cooling". It is the only feasible and stable method to realize the mass production of thick DC03 on silicon steel production lines.

[0049] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for mass production of thick-gauge DC03 cold-rolled steel strip on a silicon steel production line, comprising converter smelting, vacuum treatment, continuous casting, hot rolling, pickling, and continuous annealing; characterized in that, It employs a unique "annealing + stepped controlled cooling" process, as detailed below: 1) Annealing temperature control: Set the outlet plate and strip temperature of the heating section and the soaking section to 815℃~830℃; 2) Temperature control in the slow cooling section: After passing through the soaking section, the strip enters the slow cooling section, where the temperature of the strip at the exit of the section is controlled at 685℃~695℃; 3) Temperature control of the controlled cooling section: The temperature of the strip at the outlet of the controlled cooling section is forcibly controlled within a low temperature range of 195℃ to 205℃; The chemical composition of the DC03, by mass percentage, satisfies the following: C ≤ 0.0030%, Si ≤ 0.030%, Mn: 0.15%–0.25%, Alt: 0.020%–0.055%, Ti: 0.050%–0.065%, with the remainder being Fe and unavoidable impurities.

2. The method for mass production of thick-gauge DC03 cold-rolled steel strip on a silicon steel production line according to claim 1, characterized in that, The continuous annealing process is for DC03 cold-rolled coils with a thickness of 1.0mm to 1.2mm.

3. The method for mass production of thick-gauge DC03 cold-rolled steel strip on a silicon steel production line according to claim 1 or 2, characterized in that, The annealing rate is set to 65–85 m / min to ensure sufficient holding time at a relatively low annealing temperature.

4. The method for mass production of thick-gauge DC03 cold-rolled steel strip on a silicon steel production line according to claim 1, characterized in that, The chemical composition of the DC03, by mass percentage, satisfies the following: C 0.0021%, Si 0.004%, Mn 0.18%, Alt 0.038%, Ti 0.062%, with the remainder being Fe and unavoidable impurities.

5. The method for mass production of thick-gauge DC03 cold-rolled steel strip on a silicon steel production line according to claim 1 or 4, characterized in that, The 3.2mm thick hot-rolled raw material is rolled to a finished thickness of 1.0mm using an acid rolling mill.

6. The method for mass production of thick-gauge DC03 cold-rolled steel strip on a silicon steel production line according to claim 5, characterized in that, Continuous annealing: The following core process parameters are executed on the silicon steel continuous annealing line: Annealing temperature: 822~829℃, annealing speed: 70~83m / min; Slow cooling section outlet temperature: 687~693℃; Cooling section outlet temperature: 195~202℃.

7. The method for mass production of thick-gauge DC03 cold-rolled steel strip on a silicon steel production line according to claim 1, characterized in that, The produced thick-gauge DC03 cold-rolled steel strip meets the following performance requirements: yield strength 125~146MPa, tensile strength 281~291MPa, elongation 42.0~46.0%, n value 0.24~0.26, and r value 2.8~3.9.

Images