Industrial production method for extreme specification products of cold-rolled low-carbon steel strip for household appliances with low-pass mill elongation control

Abstract

The present invention discloses a method for industrializing the production of cold-rolled low-carbon steel strip for household appliances with limited specifications and controlled by low-pass mill elongation. During the pass mill process, when industrially producing cold-rolled low-carbon steel strip for household appliances with a thickness of 0.5 to 0.6 mm and a width greater than 1500 mm, the elongation control mode is no longer used. Instead, a rolling force and tension control mode is adopted. The rolling force control mode is to control the elongation by varying only the rolling force, while the rolling force and tension control mode is to control the elongation by varying both the rolling force and tension simultaneously. The purpose of the invention is to provide a method for industrializing the production of cold-rolled low-carbon steel strip for household appliances with limited specifications and controlled by low-pass mill elongation. The cold-rolled low-carbon steel strip produced by this method not only effectively eliminates the product yield plateau but also effectively reduces the pass mill elongation, reducing the previously high pass mill elongation to a pass mill elongation that can be achieved on-site, making it suitable for industrial mass production of limited specifications.

Description

Technical Field

[0001] The present invention relates to the technical field of low-carbon household appliances and steel furniture manufacturing, and in particular to an industrialized production method for a low-carbon steel strip with extreme specifications for household appliances that is cold-rolled and controlled by a low-pass mill elongation rate. Background Art

[0002] Cold-rolled low-carbon appliance steel boasts higher strength and hardness, as well as better plasticity and toughness than conventional low-carbon steel. It also exhibits excellent cold formability and can be formed using methods such as hemming, bending, and stamping. It is widely used in the manufacture of various products, including television back panels, air conditioner back panels, laptop and desktop computer back panels, containers, housings, and automotive parts. Cold-rolled low-carbon steel strip for home appliances utilizes a state-of-the-art continuous annealing process based on traditional low-carbon steel design. Without the addition of any expensive alloying elements, the chemical composition, hot rolling process, and continuous annealing process are optimized to produce cold-rolled low-carbon steel suitable for use in home appliances and steel furniture.

[0003] Cold-rolled low-carbon appliance steel sheets produced using continuous annealing have equiaxed, polygonal grains, small and uniform grains, a high content of interstitial atoms, and high strength and hardness. Due to the high strength and hardness of cold-rolled low-carbon appliance steel, the elongation of the skin-pass mill cannot meet design requirements when producing some extreme specifications in industrial production. Inadequate elongation control results in the inability to eliminate the yield plateau in low-carbon appliance steel products. This inability to eliminate the yield plateau significantly impacts the product's stamping performance during die stamping, inducing stamping cracking and resulting in economic losses.

[0004] Through repeated industrial production and practice, the present invention strictly controls the contents of C, Mn, N and harmful elements P, O, and S, so that the interstitial atoms of carbon and nitrogen in the steel combine to form carbonitrides, ensuring that the steel strip has a certain strength. In terms of hot rolling process control, a low-temperature coiling mode of 630-660°C is adopted, while a rapid cooling mode of pre-dispersion separation is used to obtain a fine and uniform ferrite structure, further improving the strength of the steel strip. In terms of annealing process control, an annealing temperature of 680-720°C is adopted, combined with a high-speed rolling of 150-180m / min, to alleviate the uneven performance of the steel strip caused by fine grain strengthening. The overall design of cold-rolled low-carbon household appliance steel emphasizes that the product has higher strength than ordinary low-carbon steel, and is suitable for household appliances and steel furniture fields where ordinary low-carbon steel cannot meet the requirements. For industrial production of some extreme specification products of cold-rolled low-carbon household appliance steel with a thickness of 0.5-0.6mm and a width greater than 1500mm. Due to the increased strength, the elongation achieved at the on-site leveler mill cannot meet design requirements in industrial production. The low leveler elongation makes it difficult to eliminate the yield plateau, significantly impacting the stamping performance of the product during die stamping. This invention focuses on achieving stable elongation control and eliminating the yield plateau in the industrial production of cold-rolled low-carbon steel strip for household appliances, using a low leveler mill elongation mode. Summary of the Invention

[0005] The purpose of the present invention is to provide an industrial production method for extreme specification products of cold-rolled low-carbon steel strips for household appliances with low-pass mill elongation control. The cold-rolled low-carbon household appliance steel produced by this inventive method can not only effectively eliminate the product yield platform, but also effectively reduce the pass mill elongation, so that the original higher pass mill elongation is reduced to a pass mill elongation that can be achieved on site, which is suitable for industrial mass production of extreme specifications.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention discloses an industrialized production method for cold-rolled low-carbon steel strips for household appliances with extreme specifications and controlled by a low-pass mill elongation rate. In the pass mill process, when industrially producing cold-rolled low-carbon household appliance steel with a thickness of 0.5 to 0.6 mm and a width greater than 1500 mm, an elongation rate control mode is no longer used, but a rolling force and tension control mode is used instead. The rolling force control mode is: only the rolling force is changed to control the elongation rate; while the rolling force and tension mode is: both the rolling force and the tension are changed to control the elongation rate.

[0008] When cold-rolled low-carbon household appliance steel with a thickness of 0.5-0.6mm and a width greater than 1500mm passes through the leveler, the actual values ​​of the leveler inlet tension and outlet tension are adjusted according to the current rolling speed and rolling force of the strip, so that the rolling force of the leveler is maintained between the minimum rolling force (800KN) and 8 times the minimum rolling force; then the leveler inlet and outlet tension setting values ​​are fixed. The inlet and outlet tension setting values ​​are manually set by the operator through the control system, and then the setting command is sent by the second level. The set value adjusted by Trim (set value × (1+Trim%)) will be transmitted to the operator. The operator will set the upper and lower limits of the leveler inlet and outlet tension control according to the set value given by Trim. Specifically:

[0009] The upper limit of the tension setting value of the leveling mill entrance is 1.0554×10 6 N, lower limit 2.10×10 5 N; the upper limit of the tension setting value of the leveling mill outlet is 1.0215×10 6 N, lower limit 2.11×10 5 When the rolling force is controlled between 4850 and 6210 kN, the yield platform of the product can be effectively eliminated through the mechanical detection of the tensile curve.

[0010] Furthermore, the chemical composition of the cold-rolled low-carbon steel strip for household appliances is as follows by weight: C: 0.05-0.08%, Si: 0.020-0.035%, Mn: 0.20-0.35%, P: 0.010-0.020%, S: 0.008-0.015%, N: ≤50ppm, and the rest is Fe and unavoidable impurities.

[0011] Furthermore, using rolling force and tension to control the elongation can achieve a finished product thickness of 0.5mm and a width greater than 1500mm. The original elongation of the leveler is 0.7±0.05%, which is reduced to 0.6±0.05%; and a finished product thickness greater than 0.5~≤0.6mm and a width greater than 1500mm. The original elongation of the leveler is 0.9±0.05%, which is reduced to 0.7±0.05%.

[0012] Furthermore, the production process includes converter smelting, continuous casting, hot rolling, pickling, cold rolling, continuous annealing and tempering processes; in the hot rolling process, the billet heating temperature is 1210-1260°C, the hot rolling heating temperature is 1190-1220°C, the soaking temperature is 1200-1220°C, the furnace time is 150-220min, the soaking time is 20-50min, the final rolling temperature is 860-910°C, the coiling temperature is 630-660°C, the annealing temperature is 680-720°C, and the annealing speed is 150-180m / min.

[0013] Furthermore, the rolling force and tension are used to control the elongation. The finished product with a thickness of 0.5-0.6mm and a width of >1500mm meets the following requirements: yield strength ≥240MPa, tensile strength ≥310MPa, elongation ≥34.0%, and has excellent stamping forming performance.

[0014] Compared with the prior art, the present invention has the following beneficial technical effects:

[0015] The present invention introduces an industrial production method for extreme specification products of cold-rolled low-carbon steel strips for household appliances with low leveling mill elongation. The rolling force and tension are used to control the elongation in the continuous leveling mill process. Through repeated industrial production practices, when industrially producing cold-rolled low-carbon household appliance steel with a thickness of 0.5 to 0.6 mm and a width greater than 1500 mm, a rolling force and tension control mode is adopted. Producing extreme specification products under this mode can effectively reduce the initial elongation design requirements, and the lower elongation design can still eliminate the product yield platform. The finished product performance meets the customer's stamping requirements and is suitable for the field of household appliances and steel furniture manufacturing. In terms of industrial production, the industrial batch production capacity of extreme specifications and the unit hourly output have been greatly improved. The company's production capacity has been improved, which directly improves economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below with reference to the accompanying drawings.

[0017] Figure 1 This is the metallographic structure of the finished product. DETAILED DESCRIPTION

[0018] A method for industrializing the production of cold-rolled low-carbon steel strips for household appliances with controlled elongation at a low level, comprising:

[0019] 1. Smelting process

[0020] The steelmaking process includes: molten iron pretreatment - top-bottom combined blowing in a converter (BOF) - LF refining - slab continuous casting - and slow cooling. During the BOF process, oxygen is blown for decarburization and temperature increase. Later in the process, ferroaluminum and ferromanganese are added for deoxidation and alloying. The phosphorus and sulfur (P) content is controlled to prevent overoxidation of the molten steel. The tapping temperature is ≥1600°C, and the P content of the BOF tapping steel is ≤0.020% and the S content is ≤0.015%. The LF refining process utilizes argon blowing throughout the LF process, maintaining a good reducing atmosphere. Aluminum pellets are used for slag deoxidation. Later in the LF process, ferromanganese alloy is added to adjust the molten steel composition to the target. During the slab continuous casting process, the molten steel inlet temperature is controlled between 1529°C and 1567°C, the superheat between 25°C and 40°C, and the casting speed is controlled between 1.00 and 1.80 m / min. The ingot shall be inspected at low magnification. There shall be no shrinkage cavities, bubbles, cracks, inclusions or white spots that may affect the product performance on the low magnification microstructure test piece. The segregation of the continuous casting ingot shall not be greater than Class B 1.0, and the central porosity shall not be greater than Level 1.0.

[0021] 2 Hot rolling process

[0022] The hot rolling process includes: billet heating - high-pressure water dephosphorization - width-fixing press - E1R1 roughing mill rolling - E2R2 roughing mill rolling - flying shear - high-pressure water dephosphorization - F1~F7 finishing mill rolling - dense laminar cooling 11 mode pre-dispersion - coiling; this process uses a walking beam heating furnace to heat the billet (heating process see Table 1), rough rolling adopts double-stand R1 and R2 reciprocating rolling, the rough rolling mode adopted is 3+3, and finishing rolling adopts F1~F7 continuous rolling process. The specific hot rolling process is shown in Table 2.

[0023] Table 1 Billet heating process

[0024]

[0025] Table 2 Rolling process

[0026]

[0027] 3 Annealing process

[0028] The cold rolling process includes: pickling uncoiling, welding, straightening, pickling, rinsing, drying, trimming, cold rolling on a continuous rolling mill, slitting, and coiling. The annealing process includes: annealing uncoiling, welding, cleaning, entry looper, annealing furnace, exit looper, leveling, looper inspection, trimming, surface inspection, oiling, coiling, weighing, sampling and inspection, and packaging. See Table 3 for the annealing process and Table 4 for the leveler process.

[0029] Table 3 Annealing process

[0030]

[0031]

[0032] Table 4 Leveling machine process

[0033]

[0034] 4 Example Analysis

[0035] 4.1 Steelmaking ingredients

[0036] According to the above steelmaking process requirements, the actual slab chemical composition (mass percentage) is shown in Table 5 below.

[0037] Table 5 Chemical composition of examples wt.%

[0038]

[0039] 4.2 Hot rolling process

[0040] According to the above hot rolling process requirements, the hot rolling thickness is 2.7mm and 3.0mm, and the actual process is shown in Table 6.

[0041] Table 6 Hot rolling process

[0042]

[0043] 4.3 Continuous Annealing Process

[0044] According to the above continuous annealing process requirements, the cold rolling thickness is 0.5mm and 0.6mm, and the actual process is shown in Tables 7 and 8.

[0045] Table 7 Continuous Annealing Process

[0046]

[0047] Table 8 Leveling machine process

[0048]

[0049] The mechanical properties of the steel strip products obtained through the above process are shown in Table 9. The test method refers to GB / T228.1.

[0050] Table 9 Tensile properties of finished products

[0051]

[0052]

[0053] The metallographic structure of the finished product is equiaxed polygonal ferrite with a grain size of 8.0 to 8.5. Figure 1 .

[0054] In summary, this product has passed performance testing and has met user requirements in various aspects, and is now available in batches.

[0055] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for industrial production of cold-rolled low-carbon steel strip for household appliances with controlled elongation at a low level, characterized by: In the skin-pass mill process, when industrially producing cold-rolled low-carbon household appliance steel with a thickness of 0.5-0.6 mm and a width greater than 1500 mm, the elongation control mode is no longer used. Instead, the rolling force and tension control mode is adopted. The rolling force control mode is to control the elongation by changing only the rolling force; while the rolling force and tension mode is to control the elongation by changing both the rolling force and the tension. When cold-rolled low-carbon household appliance steel with a thickness of 0.5-0.6mm and a width greater than 1500mm passes through the leveler, the actual values ​​of the leveler inlet and outlet tensions are adjusted according to the current rolling speed and rolling force of the strip, so that the rolling force of the leveler is maintained between the minimum rolling force and 8 times the minimum rolling force; then the leveler inlet and outlet tension setting values ​​are fixed. The inlet and outlet tension setting values ​​are manually set by the operator through the control system, and then the setting instructions are sent by the second level. The setting values ​​adjusted by Trim are transmitted to the operator, and the operator sets the upper and lower limits of the leveler inlet and outlet tension control according to the setting values ​​given by Trim. Specifically: The upper limit of the tension setting value of the leveling mill entrance is 1.0554×10 6 N, lower limit 2.10×10 5 N; the upper limit of the tension setting value of the leveling mill outlet is 1.0215×10 6 N, lower limit 2.11×10 5 When the rolling force is controlled between 4850 and 6210 kN, the yield platform of the product can be effectively eliminated through the mechanical detection of the tensile curve.

2. The industrialized production method of cold-rolled low-carbon steel strip for household appliances with controlled elongation at a low level according to claim 1, characterized in that: The chemical composition weight percentage of the cold-rolled low-carbon steel strip for household appliances is: C: 0.05-0.08%, Si: 0.020-0.035%, Mn: 0.20-0.35%, P: 0.010-0.020%, S: 0.008-0.015%, N: ≤50ppm, and the rest is Fe and unavoidable impurities.

3. The industrialized production method of cold-rolled low-carbon steel strip for household appliances with controlled elongation at a low level according to claim 2, characterized in that: Using rolling force and tension to control the elongation can achieve a finished product thickness of 0.5mm and a width greater than 1500mm. The original elongation of the leveler is 0.7±0.05%, which is reduced to 0.6±0.05%; and a finished product thickness greater than 0.5~≤0.6mm and a width greater than 1500mm. The original elongation of the leveler is 0.9±0.05%, which is reduced to 0.7±0.05%.

4. The industrialized production method of cold-rolled low-carbon steel strip for household appliances with controlled elongation at a low level according to claim 2, characterized in that: The production process includes converter smelting, continuous casting, hot rolling, pickling, cold rolling, continuous annealing and tempering processes; in the hot rolling process, the billet heating temperature is 1210-1260°C, the hot rolling heating temperature is 1190-1220°C, the soaking temperature is 1200-1220°C, the furnace time is 150-220 minutes, the soaking time is 20-50 minutes, the final rolling temperature is 860-910°C, the coiling temperature is 630-660°C, the annealing temperature is 680-720°C, and the annealing speed is 150-180 m / min.

5. The industrialized production method of cold-rolled low-carbon steel strip for household appliances with controlled elongation at a low level mill according to claim 4, characterized in that: The rolling force and tension are used to control the elongation. The finished product with a thickness of 0.5-0.6mm and a width of >1500mm meets the following requirements: yield strength ≥240MPa, tensile strength ≥310MPa, elongation ≥34.0%, and has excellent stamping forming performance.

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