A method for producing low-carbon steel for room-temperature storage containers with high surface quality

Abstract

The present invention relates to a method for producing low-carbon steel for room-temperature storage containers with high surface quality. The method comprises the following steps: hot rolling: heating the ingot, rough rolling, finishing rolling, cold rolling, and coiling; cold rolling: pickling, cold rolling on a continuous rolling mill, and coiling; and annealing, leveling, oiling, and coiling. The method utilizes a continuous production process consisting of hot rolling, cold rolling, annealing, and leveling to produce a low-carbon cold-rolled steel strip with an easy-to-clean surface. By controlling the composition, hot rolling temperature, annealing, and surface roughness, the method achieves a good match between product performance and surface quality.

Description

Technical Field

[0001] The invention relates to a production method of low-carbon steel for room-temperature storage containers with high surface quality, belonging to the technical field of alloy materials. Background Art

[0002] Cold-rolled products are widely used in industries such as home appliances, office supplies, and container products because of their good surface quality, thin specifications, and good formability. However, the surface of the steel strip is easily corroded and scratches are easily generated during the coiling process, which affects the surface effect of the steel strip. Therefore, the surface of the steel strip needs to be oiled. Many products need to be coated during use, and the presence of surface anti-rust oil is not conducive to coating. They need to be cleaned before use. However, factors such as the surface quality of the steel strip and the oiling state affect subsequent cleaning. In order to control the cleaning of the steel strip surface, necessary process adjustments will damage the performance of the steel strip. The purpose of the present invention is to solve the problem of steel strip surface cleaning without affecting product quality and meeting the use requirements of cold-rolled steel strip.

[0003] Cold-rolled steel strip boasts excellent surface finish, flatness, dimensional accuracy, and mechanical properties. It is used in the manufacture of building panels, home appliances, office supplies, electronic machinery, and container products. Many products require surface treatment after processing and before painting. Typically, the production of canned steel involves coil uncoiling, stamping, surface treatment, assembly, and interior and exterior painting. Surface treatment is crucial, impacting subsequent painting processes. Common surface treatment processes include phosphating and silane treatment, with phosphating being gradually replaced by the more environmentally friendly silane treatment.

[0004] Silane treatment is the surface treatment of metal materials using organosilanes as the primary raw material. Compared to traditional phosphating, silane treatment offers advantages such as the absence of harmful heavy metal ions, phosphorus, shorter treatment time, no need for heating, no sediment generation, and simplified control. Silane treatment of cold-rolled strip is typically performed at the customer's end. The steel substrate undergoes flattening, cutting, forming, degreasing, cleaning, silane treatment, drying, and painting. However, silane treatment places higher demands on the strip, and is prone to problems such as wash spots and yellowing, which affect the washability. While this does not affect the final product, it can have a strong visual impact, adding significant pressure and inconvenience to subsequent processing and product development.

[0005] Patent application number CN 109943777A discloses a phosphated cold-rolled steel strip and manufacturing method. By adding phosphating equipment between the skin-leveler and oiler in a continuous annealing unit, the strip can be directly used for stamping and coating. However, this method targets phosphating treatment. With increasingly stringent environmental requirements, customers are increasingly adopting silane treatment, which has higher requirements and differs from the requirements of this patent. Furthermore, conventional products do not exhibit surface spotting after phosphating treatment, but silane treatment can easily leave residual water stains on the surface, resulting in surface spotting and affecting customer use. This patent application is designed specifically for products with different product requirements, such as those requiring silane treatment.

[0006] Patent application with publication number CN111218617A discloses a cold-rolled low-carbon steel strip SPCC with low yield strength and no yield platform and a production method thereof. The process is similar to that of the present patent application, but the emphasis is on eliminating the yield platform rather than on surface requirements, and the cold rolling process has a different emphasis.

[0007] Problems with existing technologies: Cold-rolled products are generally cleaned on the surface after forming. If the surface is not good, it is easy for the surface cleaning to be unclean. However, when processing the surface, the forming performance is often affected by process adjustments. Both will cause the product performance to fail to meet the performance requirements. In order to ensure surface smoothness, the leveling amount of the leveling machine will be increased. If the leveling amount is too large, the elongation of the product will be reduced, which is not conducive to subsequent stamping and forming.

[0008] To solve the above problems, the purpose of the present invention is to provide a method for producing low-carbon steel for room-temperature storage containers with high surface quality, which solves the matching of surface color difference, cleaning spots and forming performance without increasing production costs. Summary of the Invention

[0009] To address the above-mentioned problems, the present invention discloses a method for producing low-carbon steel for room-temperature storage containers with high surface quality. This method can meet the requirements of good formability without cracking, no surface spots or color differences such as yellowing, and a clean surface. The matching of the production components and processes of the present invention can effectively solve the problem of matching surface cleaning and formability, which is conducive to large-scale industrial production. The specific technical solution is as follows:

[0010] A method for producing low-carbon steel for room-temperature storage containers with high surface quality, comprising:

[0011] Step 1: Hot rolling process: billet heating - rough rolling - finishing rolling - layer cooling - coiling;

[0012] Step 2: Cold rolling process: pickling uncoiling - pickling - continuous rolling mill cold rolling - coiling;

[0013] Step 3: Continuous unwinding process: continuous unwinding, annealing, leveling, oiling, and coiling.

[0014] Furthermore, the chemical composition and mass content of the ingot are: C: 0.015% to 0.035%, Si≤0.02%, Mn: 0.03% to 0.12%, P≤0.015%, S≤0.015%, and the rest are iron elements and unavoidable impurity elements, and its composition follows the following rule: C≥0.2Mn+0.009.

[0015] Furthermore, the slab is heated in a heating furnace in the hot rolling process of step 1, and is taken out of the furnace after heating for 2 to 3 hours at a temperature of 1140 to 1180° C. for rough rolling.

[0016] Furthermore, the hot rolling process in step 1 includes finishing rolling and rough rolling. After being taken out of the furnace, the steel is first subjected to rough rolling, and then rough rolling is performed on the first stand and the second stand. The first stand is used for one pass, and then the second stand is used for rough rolling. The second stand is used for a total of five passes.

[0017] After the rough rolling is completed, it enters the finishing rolling, which uses 7 stands. The finishing rolling process is completed through 7 stands in sequence. After finishing rolling, it enters the layer cooling process. The finishing rolling outlet temperature is 800-830℃.

[0018] During the rough rolling and finish rolling, descaling water is sprayed on the surface of the strip to ensure that the surface iron oxide scale falls off;

[0019] The inlet thickness of the hot-rolled strip steel is 38-48 mm, and the outlet thickness is 3.0-6.0 mm.

[0020] Furthermore, after the finish rolling, the strip enters layer cooling, which uses multiple water pipes to cool the strip. By switching different water pipes, the layer cooling outlet temperature and the coiling temperature are controlled, and then the strip enters the coiler for coiling, with a coiling temperature of 680-720°C.

[0021] Furthermore, in the step 2 cold rolling process, the strip is first pickled. The pickling process is that after the strip exits the scale breaker, it enters the pickling tank. The length of each pickling tank is 20 to 25 meters, and there are 3 to 5 acid tanks in total, with a total length of 60 to 120 meters. Within the design speed of the production line, the pickling speed is ≤200m / min to ensure that the iron oxide scale on the surface of the product is cleaned. After the speed is reduced, it is in the over-pickling state. After pickling, it enters the rinsing section and sprays desalted water to remove hydrochloric acid on the surface.

[0022] Furthermore, in step 2, after pickling in the cold rolling process, the cold rolling process is entered, and the thickness is cold rolled to 0.5-1.5 mm, and the cold rolling reduction rate is ensured to be 75%-85%. The cold rolling process uses multiple stands for sequential cold rolling, and emulsion is used for lubrication between the stands, and the saponification value of the emulsion is 180-190 mgKOH / g.

[0023] Furthermore, in the continuous annealing process of step 3, the annealing soaking temperature is: 820-850°C, the annealing time is 2-6 minutes, the steel is slowly cooled to 680-700°C, and then rapidly cooled to 380-420°C. After the aging treatment, a cooling treatment is also included, and water quenching is performed after cooling to 100-120°C; then, the leveling reduction is 1.2%-1.8%, and the hydrogen content in the furnace is ≥2%.

[0024] Furthermore, the roughness of the leveling roller in step 3 is as follows: the roughness Ra is 3.0-4.0 μm, and the roughness peak value RPc is 75-100 cm -1 After cleaning, the amount of oil applied on one side of the strip surface is 300-800 mg / ㎡. Within the roughness range, the roughness is proportional to the amount of oil applied. The roughness will decrease with the number of rolled coils during the rolling process, and the amount of oil applied will decrease accordingly. The roughness of the first two rolls of strip steel has a large attenuation. The amount of oil applied to the first two rolls of strip steel is 700-800 mg / ㎡, and the amount of oil applied to rolls 3-6 is 500-700 mg / ㎡. The amount of oil applied to the 6th roll of strip steel and beyond is 300-500 mg / ㎡.

[0025] Furthermore, the oil coating is anti-rust oil, the components of which include mineral oil refined from petroleum, synthetic oil made from synthetic materials and a rust inhibitor mixture.

[0026] The beneficial effects of the present invention are:

[0027] The invention can stably produce easy-to-clean strip steel with a specification of ≤1.5 mm, and the surface quality after cleaning is good.

[0028] The present invention relies on the entire process from steelmaking to cold rolling, from the initial composition design to the final oiling, and the whole process is combined to achieve a clever combination of performance and surface quality, ensuring that the product quality meets the use requirements of the downstream product manufacturing end. The strip steel of the present invention is usually processed into oil drums, small tanks, square boxes, etc.

[0029] The present invention improves the cleanability of the strip surface by designing ingredients, matching ingredients and controlling post-process technology, while meeting the forming performance requirements and coordinating the subsequent oiling amount, thereby ensuring the surface quality of the product and meeting customer needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a surface diagram of the product obtained by the process of the present invention,

[0031] Wherein: (a) is the surface image of the product of Example 1, (b) is the surface image of the product of Example 2;

[0032] Figure 2 This is the product surface diagram obtained by conventional process. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0034] Hot rolling process: billet heating - rough rolling - finishing rolling - layer cooling - coiling;

[0035] The composition of the ingot is: C: 0.015%~0.035%, Si: ≤0.02%, Mn: 0.03%~0.12%, P: ≤0.015%, S≤0.015%, and the rest are iron elements and unavoidable impurity elements. The composition control of this patent is mainly based on controlling Mn, and its composition follows the following rule: C≥0.2Mn+0.009. If it is not achieved, carbon needs to be supplemented in the subsequent refining process to meet the composition control requirements.

[0036] Hot rolling is divided into finishing rolling and rough rolling. Descaling water is added in the middle to ensure that the surface iron oxide scale falls off, otherwise the surface is full of pits caused by the iron oxide scale. After leaving the furnace, it is first rough rolled, which is divided into the first and second stands for rough rolling. The first stand is rolled for 1 pass, and the second stand is used for subsequent rough rolling. The second stand is rolled back and forth for a total of 5 passes. The hot rolling process is specifically as follows: heating in a heating furnace, heating for 2 to 3 hours before leaving the furnace, the hot rolling furnace temperature is 1140 to 1180 ° C, and then entering rough rolling. The furnace temperature of 1140 to 1180 ° C and the finishing outlet temperature of 800 to 830 ° C are controlled to reduce the thickness of the decarburized layer and inhibit the precipitation of Mn elements on the surface, while not excessively reducing the strength of the product. The rough rolling process is completed in one pass on the first stand, followed by five reciprocating passes on the second stand, before entering the subsequent seven-stand finishing process. After finishing in seven stands, the product enters the layer cooling process, with the finishing exit temperature at 800-830°C. Conventional products cool to 860-890°C, which is higher than the finishing exit temperature of this patented product. The product then enters the coiler for coiling. The coiling temperature is 680-720°C; the hot-rolled thickness is 3.0-6.0mm. The thickness is the thickness after rolling from the first to the seventh stand, and the entrance thickness is generally between 38-48mm. There is no thickness gauge between stands, only at the exit. Therefore, the thickness between stands is a theoretical value. The main purpose is to ensure the relative stability of the rolling force between stands by balancing the rolling force between stands.

[0037] After finishing rolling, several water pipes are used to cool the strip. By switching different water pipes, the outlet temperature of the layer cooling and the coiling temperature are controlled to cool to 800-830℃. The strip then enters the coiler for coiling at a temperature of 680-720℃.

[0038] Cold rolling process: pickling uncoiling - pickling - continuous rolling mill cold rolling - coiling;

[0039] The pickling process is that after the strip steel leaves the scale breakers, it enters the pickling tank. Each pickling tank is about 20 to 25 meters long, with a total of 3 to 5 pickling tanks, and the total length is generally between 60 and 120 meters. Within the design speed of the production line, the pickling speed ≤ 200m / min can ensure that the iron oxide scale on the surface of the product is completely washed away. After the speed is reduced, it is in the over-pickling state. After pickling, there is a rinsing section to spray desalted water to remove hydrochloric acid on the surface.

[0040] After pickling, the strip is cold-rolled to a thickness of 0.5-1.5mm, maintaining a cold rolling reduction ratio between 75% and 85%. An emulsion lubricant with a saponification value of 180-190 mgKOH / g is used between the cold rolling stands. The cold rolling mill consists of five stands, with thickness gauges at the inlet and outlet. The intermediate reduction ratio is calculated, and the ratio distribution varies between production lines and manufacturers. For the five stands of the Shagang production line, rolling 2.0mm and 0.19mm gauges, the calculated reduction ratios for stands 1 to 5 are 38.65%, 41.9%, 36.0%, 35.5%, and 31.4%, respectively. This reduction ratio is adjustable, and the purpose of this distribution is to ensure even distribution of rolling force between stands and ensure rolling stability.

[0041] Continuous unwinding process: continuous unwinding uncoiling - annealing - leveling - oiling - coiling.

[0042] Annealing: Soaking temperature: 820-850°C, annealing time: 2-6 minutes, slow cooling to 680-700°C, followed by rapid cooling to 380-420°C. After aging, cooling to 100-120°C is followed by water quenching. Then, leveling reduction is applied by 1.2%-1.8%. Furnace hydrogen content is ≥2%.

[0043] The roughness of the leveling roller is as follows: roughness (Ra) 3.0 ~ 4.0 μm, roughness peak value (RPc) 75 ~ 100 cm -1 Values ​​below or above these values ​​are outside the scope of the patent. To ensure surface roughness, the flattening reduction rate is between 1.2% and 1.8%. Accordingly, the amount of oil applied to a single side of the cleaned strip surface is between 300 and 800 mg / m2. Values ​​above or below this range are outside this scope. Within the roughness range, there is a corresponding relationship between the amount of oil applied and values ​​outside this range are not within the scope of this patent. Furthermore, test results have shown that surface quality in the excess area will not meet product quality requirements. Roughness is directly proportional to the amount of oil applied. During the rolling process, roughness decreases with the number of coils produced, and the amount of oil applied decreases accordingly. In principle, the roughness of the first two coils decreases significantly. The amount of oil applied to the first two coils is 700 to 800 mg / m2, to coils 3 to 6, between 500 and 700 mg / m2, and to coils 6 and beyond, between 300 and 500 mg / m2. Rust-preventive oils are primarily composed of petroleum-derived mineral oils, synthetic oils made from synthetic materials, and rust inhibitors.

[0044] Several specific embodiments of the present invention in specific applications are given below.

[0045] Example 1

[0046] 1. Melting composition: C: 0.032%, Si: 0.02%, Mn: 0.11%, P: 0.014%, S: 0.0030%, continuous casting speed 1.2m / min, billet thickness 200mm;

[0047] 2. Hot rolling furnace temperature 1150℃, finishing rolling outlet temperature 828℃, coiling temperature 701℃; hot rolling thickness 4.0mm;

[0048] 3. After pickling, the strip is cold rolled to a thickness of 1.0 mm, with a reduction rate of 75% and an emulsion saponification value of 182 KOH / g;

[0049] 4. Annealing temperature: 825℃, leveling reduction: 1.4%;

[0050] 5. Correspondingly, the roughness of the leveling roller is as follows: roughness (Ra) 3.5μm, roughness peak number (RPc) 82cm -1 The initial roll oil coating amount is 750mg / ㎡ per side.

[0051] Product surface corresponds to Figure 1 In Figure (a), the surface is clean.

[0052] Example 2

[0053] 1. Melting composition: C: 0.024%, Si: 0.01%, Mn: 0.09%, P: 0.010%, S: 0.0028%, continuous casting speed 1.05m / min, billet thickness 220mm;

[0054] 2. Hot rolling furnace temperature 1180℃, finishing rolling outlet temperature 806℃, coiling temperature 694℃; hot rolling thickness 4.5mm;

[0055] 3. After pickling, the strip is cold rolled to a thickness of 1.2 mm, with a cold rolling reduction of 73% and an emulsion saponification value of 186 KOH / g;

[0056] 4. Annealing temperature 823℃, leveling reduction 1.5%;

[0057] 5. Correspondingly, the roughness of the leveling roller is as follows: roughness (Ra) 4.0μm, roughness peak number (RPc) 76cm -1 The initial roll oil coating amount is 800mg / ㎡ per side.

[0058] Product surface corresponds to Figure 1 In (b), the surface is clean.

[0059] Example 3

[0060] 1. Melting composition: C: 0.018%, Si: 0.03%, Mn: 0.17%, P: 0.012%, S: 0.0030%, continuous casting speed 1.2m / min, billet thickness 220mm;

[0061] 2. Hot rolling furnace temperature 1200℃, finishing rolling outlet temperature 868℃, coiling temperature 660℃; hot rolling thickness 4.0mm;

[0062] 3. After pickling, the strip is cold rolled to a thickness of 1.0 mm, with a reduction rate of 75% and an emulsion saponification value of 190 KOH / g;

[0063] 4. Annealing temperature 830℃, flattening reduction 1.2%;

[0064] 5. Correspondingly, the roughness of the leveling roller is as follows: roughness (Ra) 2.5μm, roughness peak number (RPc) 102cm -1 The initial roll has a single side of 500mg / ㎡.

[0065] The surface quality of the product is difficult to guarantee, and the surface quality of the product Figure 2 .

[0066] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for producing low-carbon steel for room-temperature storage containers with high surface quality, characterized in that: include: Step 1: Hot rolling process: billet heating - rough rolling - finishing rolling - layer cooling - coiling; The chemical composition and mass content of the ingot are: C: 0.015% to 0.035%, Si≤0.02%, Mn: 0.03% to 0.12%, P≤0.015%, S≤0.015%, and the rest are iron and unavoidable impurity elements, and the composition follows the following rule: C≥0.2Mn+0.009; The billet is heated to a furnace temperature of 1140-1180°C and then subjected to rough rolling; Finishing rolling outlet temperature 800~830℃; The strip steel inlet thickness of the hot rolling process is 38-48 mm, and the outlet thickness is 3.0-6.0 mm; The coiling temperature after layer cooling is 680~720℃; Step 2: Cold rolling process: pickling uncoiling - pickling - continuous rolling mill cold rolling - coiling; Cold rolled to a thickness of 0.5-1.5 mm, ensuring a cold rolling reduction of 75%-85%; Step 3: Continuous unwinding process: continuous unwinding, annealing, leveling, oiling, and coiling; Annealing soaking temperature: 820-850℃, annealing time 2-6min, slow cooling to 680-700℃, then rapid cooling to 380-420℃; after aging treatment, cooling treatment is also included, cooling to 100-120℃ and then water quenching treatment; hydrogen content in the furnace ≥2%; The leveling reduction is 1.2% to 1.8%.

2. The method for producing low-carbon steel for room-temperature storage containers with high surface quality according to claim 1, characterized in that: The casting in the hot rolling process of step 1 is heated in a heating furnace and is taken out of the furnace after being heated for 2 to 3 hours.

3. The method for producing low-carbon steel for room-temperature storage containers with high surface quality according to claim 1, characterized in that: The hot rolling process in step 1 includes finishing rolling and rough rolling. After being taken out of the furnace, it is first subjected to rough rolling, and then rough rolling is performed on the first stand and the second stand. The first stand is rolled once, and then the second stand is used for rough rolling. The second stand is rolled back and forth for a total of five passes. After the rough rolling is completed, it enters the finishing rolling process. The finishing rolling adopts 7 stands and the finishing rolling process is completed in sequence through 7 stands. After the finishing rolling, it enters the layer cooling process. During the rough rolling and finish rolling, descaling water is sprayed toward the surface of the strip to ensure that the surface iron oxide scale falls off.

4. The method for producing low-carbon steel for room-temperature storage containers with high surface quality according to claim 1, characterized in that: After the finishing rolling, the strip enters the layer cooling stage, which uses multiple water pipes to cool the strip. By switching different water pipes, the layer cooling outlet temperature and the coiling temperature are controlled, and then the strip enters the coiler for coiling.

5. The method for producing low-carbon steel for room-temperature storage containers with high surface quality according to claim 1, characterized in that: In the step 2 cold rolling process, the strip is first pickled. The pickling process is that after the strip leaves the scale breaker, it enters the pickling tank. The length of each pickling tank is 20 to 25 meters. There are 3 to 5 pickling tanks in total, with a total length of 60 to 120 meters. Within the design speed of the production line, the pickling speed is ≤ 200 m / min to ensure that the iron oxide scale on the surface of the product is cleaned. After the speed is reduced, it is in the over-pickling state. After pickling, it enters the rinsing section and sprays desalted water to remove hydrochloric acid on the surface.

6. The method for producing low-carbon steel for room-temperature storage containers with high surface quality according to claim 1, characterized in that: In step 2, after pickling in the cold rolling process, the steel enters the cold rolling process. The cold rolling process uses multiple stands for sequential cold rolling, and emulsion is used for lubrication between the stands. The saponification value of the emulsion is 180-190 mgKOH / g.

7. The method for producing low-carbon steel for room-temperature storage containers with high surface quality according to claim 1, characterized in that: The roughness of the leveling roller in step 3 is as follows: the roughness Ra is 3.0-4.0 μm, and the roughness peak number RPc is 75-100 cm -1 After cleaning, the amount of oil applied on one side of the strip surface is 300-800 mg / ㎡. Within the roughness range, the roughness is proportional to the amount of oil applied. The roughness will decrease with the number of rolled coils during the rolling process, and the amount of oil applied will decrease accordingly. The roughness of the first two rolls of strip steel has a large attenuation. The amount of oil applied to the first two rolls of strip steel is 700-800 mg / ㎡, and the amount of oil applied to rolls 3-6 is 500-700 mg / ㎡. The amount of oil applied to the 6th roll of strip steel and beyond is 300-500 mg / ㎡.

8. The method for producing low-carbon steel for room-temperature storage containers with high surface quality according to claim 1, characterized in that: The oiling is rust-proof oil, and its components include mineral oil refined from petroleum, synthetic oil made from synthetic materials and rust-proof agent mixture.

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