Production method of 0.4 mm-thick cold-rolled deep-drawing steel for household appliances

Abstract

The invention discloses a production method of cold-rolled deep drawing steel with the thickness of 0.4 mm for household appliances. The cold-rolled deep drawing steel 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 S i, less than or equal to 0.20% of Mn, less than or equal to 0.015% of P, 0.050-0.080% of T i, 0.020-0.070% of A, less than or equal to 0.010% of S, less than or equal to 0.0030% of O and less than or equal to 0.0030% of N. The production method comprises a steelmaking process; a hot rolling process; the parameters of the cold rolling process and the annealing process are as follows: the outlet temperature of a heating and soaking section is 760-830 DEG C, the outlet temperature of a slow cooling section is 600-700 DEG C, the outlet temperature of a rapid cooling section is less than or equal to 400 DEG C, the temperature of an overaging section is less than or equal to 400 DEG C, the outlet temperature of a final cooling section is less than or equal to 180 DEG C, and the ductility of a temper mill is 0.4-0.6% The cold-rolled deep-drawing steel disclosed by the invention has excellent processing forming performance and meets the use requirements of household appliances.

Description

Technical Field

[0001] The invention relates to a production method of cold-rolled deep-drawing steel with a thickness of 0.4 mm for household appliances. Background Art

[0002] Entering the 21st century, my country's home appliance manufacturing industry continues to develop rapidly and steadily, becoming the world's largest home appliance manufacturing base. The development of lightweight and high-efficiency home appliances will increase the demand for high-strength thin plates and develop thin-gauge home appliance plate products. The plate width demand is mainly to meet the needs of multiple-size cutting, so as to improve material utilization and reduce the production costs of home appliance companies. Since 2023, some customers have put forward the demand for cold-rolled deep-drawing steel products with a thickness of 0.4mm. This type of product adds an appropriate amount of Ti to ultra-low carbon steel, fixes the interstitial atoms C and N, so that the product has good plasticity while obtaining moderate strength, and requires ultra-low carbon, pure steel, and micro-alloying.

[0003] In order to ensure that the produced steel strip has low yield strength and good plasticity, the present invention strictly controls C, N elements and harmful elements O, S at a low level, and at the same time adds a proper amount of Ti alloy element to ultra-low carbon steel (the residual Ti calculation formula is: Ti residual=Ti-(3.4×N+1.5×S+4×C) to carry out composition design, and considering the influence of titanium yield and composition change, the excess titanium control range is 0.02%-0.04%), which is combined with carbon and nitrogen interstitial atoms in the steel to form carbonitride, so that the steel strip has obvious timelessness and achieves performance stability; at the same time, in order to ensure that the steel strip has suitable strength and is convenient for subsequent hole expansion, drawing, bending and other processing in the home appliance industry, the content of P and Mn strengthening elements is strictly controlled, and the hot rolling adopts a post-dispersion cooling mode to coarsen the metallographic structure of the product and reduce the tensile strength of the steel strip; at the same time, thin-gauge home appliance steel has strict requirements on inclusions and dimensional tolerances, and the steelmaking process strictly controls parameters such as oxygen blowing amount and oxygen blowing time, and the thickness tolerance control range of the cold rolling process is -0.03-0mm. The production process goes through smelting, 2250mm rolling mill, acid continuous rolling and continuous annealing processes, with a focus on designing the core processes of composition, hot rolling and cold rolling. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a production method of cold-rolled deep-drawing steel for household appliances with a thickness of 0.4 mm, which has excellent processing and forming performance and meets the use requirements of household appliances.

[0005] The thickness of the developed product is 0.4mm, which is an extremely thin product. The thickness of the patented product ranges from 0.7 to 1.6mm.

[0006] In terms of chemical composition design, the rare earth element Ce is not added, and it does not belong to rare earth steel. The control range of the chemical elements C, P, and N is more stringent;

[0007] In terms of production technology, in order to reduce the tensile strength, a dispersed cooling mode is used after hot rolling.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The present invention discloses a production method of cold-rolled deep-drawing steel for household appliances with a thickness of 0.4 mm, wherein the chemical composition by mass percentage is as follows: C≤0.0030%, Si≤0.030%, Mn≤0.20%, P≤0.015%, Ti0.050-0.080%, Al 0.020-0.070%, S≤0.010%, O≤0.0030%, N≤0.0030%, and the balance is Fe and unavoidable impurities; the production method comprises:

[0010] Steelmaking process: molten iron → converter steelmaking → RH refining → slab continuous casting; molten iron is pre-treated with desulfurization before converter smelting, and the sulfur content of the molten iron entering the converter is required to be less than 0.010%, and the slag removal area of ​​the molten iron is greater than 95%; converter smelting requires the tapping temperature to be ≥1660℃, and a turnover bag must be used for tapping, and the tapping temperature drop is required to be less than 70℃; the RH process requires deep decarburization treatment based on the composition and temperature of the molten steel supplied by the converter to RH. After decarburization, aluminum particles are added for deoxidation according to the oxygen setting situation. After circulating for more than 5 minutes, titanium iron and other alloys are added to adjust the composition; after the adjustment of the composition is completed, the vacuum cycle must be no less than 4 minutes before temperature measurement and sampling can be carried out. After the addition of titanium iron, the pure degassing time is guaranteed to be more than 6 minutes, and the superheat of the molten steel is 20-60℃;

[0011] Hot rolling process: slab heating → high-pressure water descaling → fixed width press → E1 R1 roughing mill rolling → E2R2 roughing mill rolling → flying shear → high-pressure water descaling → F1-F7 finishing mill rolling → encrypted laminar cooling → coiling → pallet transportation system → sampling and inspection; the slab heating temperature is 1160-1220℃; heating time is 150-250min; the rough rolling mode is 3+5; the finishing rolling temperature is 890-940℃, and the coiling temperature is 680-750℃;

[0012] Cold rolling process: pickling uncoiling → welding → straightening → pickling → rinsing → drying → trimming → continuous rolling mill cold rolling → slitting → coiling → offline inspection → weighing → marking → bundling → packaging → warehousing → continuous uncoiling → welding → cleaning → entrance looper → annealing furnace → exit looper → leveling → inspection looper → trimming → surface inspection → oiling → coiling → weighing → sampling and inspection; Annealing process parameters: outlet temperature of heating and soaking section 760-830℃, outlet temperature of slow cooling section 600-700℃, outlet temperature of rapid cooling section ≤400℃, temperature of over-aging section ≤400℃, outlet temperature of final cooling section ≤180℃, elongation of flat mill 0.4-0.6%.

[0013] Furthermore, the metallographic structure of the finished product is equiaxed ferrite with a grain size of 6.0-8.0.

[0014] Furthermore, a post-dispersed cooling mode is adopted.

[0015] Furthermore, the yield strength R p0.2 123-153MPa, tensile strength R m It is 275-310MPa.

[0016] Furthermore, the elongation of the finished product A 80 It is 40.0-50.5%.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are:

[0018] The steelmaking process adopts RH refining process plus vacuum degassing technology, the C and N element contents are no more than 0.0030%, and the steel is pure; Ti alloy elements are used to fix C and N interstitial atoms to form interstitial atom-free steel, which has no timeliness and good performance stability; the hot rolling process adopts low heating temperature to control the generation of iron oxide scale and save energy, and adopts post-dispersion cooling mode to coarsen the metallographic structure and reduce the yield / tensile strength of the steel strip; the continuous annealing process adopts high temperature annealing to achieve rapid recrystallization, in order to ensure smooth production and process stability control, match the appropriate elongation of the leveling machine.

[0019] A certain amount of Ti element is added to ultra-low carbon steel. Ti fixes the interstitial atoms of C and N to obtain interstitial atom-free IF steel, which makes the steel strip have significant non-aging characteristics; when the content of C and N elements is extremely low, the content of strengthening elements such as P and Mn is strictly controlled, and the hot rolling adopts a post-dispersion cooling mode, so that the steel strip has a lower yield / tensile strength and a higher elongation. The steelmaking process strictly controls the oxygen blowing amount to reduce the generation of inclusions; the hot rolling process adopts a low heating temperature and furnace temperature to reduce the formation of oxides on the surface of the steel strip and optimize the surface quality of the steel strip; the continuous annealing process adopts high temperature annealing, and at the same time, in order to ensure the smooth production and process stability control, the appropriate elongation of the leveler is matched. The finished product performance meets the following requirements: yield strength 120-160MPa, tensile strength ≤320MPa, elongation after fracture 40.0-50.5% (transverse, tensile test: L0=80mm, b=20mm), n value 0.22-0.24, r value 2.30-3.00, surface roughness 0.6-1.9μm. It ensures a low yield strength ratio ≤0.50 and high elongation after fracture, thus having excellent processing and forming performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Figure 1 The yield strength distribution of cold-rolled deep-drawn steel for home appliances with a thickness of 0.4 mm;

[0022] Figure 2 The tensile strength distribution of cold-rolled deep-drawn steel for home appliances with a thickness of 0.4 mm;

[0023] Figure 3 The elongation distribution of cold-rolled deep-drawn steel for home appliances with a thickness of 0.4 mm;

[0024] Figure 4 This is the metallographic structure of the finished product. DETAILED DESCRIPTION

[0025] A method for producing cold-rolled deep-drawn steel for household appliances with a thickness of 0.4 mm, comprising:

[0026] Smelting process:

[0027] Desulfurization pretreatment: KR hot metal desulfurization technology is used, and the final sulfur content after deep desulfurization is required to be within 0.010%. KR desulfurization is desulfurized by mechanical stirring. The stirring head is inserted into the molten iron and rotated to create a vortex in the molten iron. Then desulfurizer is added into the molten iron vortex to make the desulfurization reaction between the desulfurizer and the sulfur in the molten iron occur during continuous stirring. After desulfurization is completed, the desulfurization slag is thoroughly scraped off. The scraping area of ​​the molten iron slag is required to be greater than 95% to prevent high-sulfur slag from being added to the converter and causing backsulfurization.

[0028] Converter smelting: The molten iron is pre-treated for desulfurization before converter smelting. The converter dephosphorization process mainly relies on slag with high basicity, high oxidation and large slag volume for dephosphorization. However, in order to achieve deep dephosphorization, it is necessary to create conditions so that the phosphorus in the molten iron can be oxidized into the slag in large quantities to achieve the goal of deep dephosphorization. The phosphorus content of the molten iron entering the converter is ≤0.015%. Oxygen is blown to decarburize and heat up, and the P and S components are controlled to prevent the molten steel from overoxidation. The converter terminal temperature is controlled above 1660℃, and a turnover bag must be used for steel tapping. The temperature drop of steel tapping is required to be less than 70℃. Ferromanganese is added for alloying during the converter tapping process, and lime and modifiers are added for top slag modification.

[0029] Refining: RH refining furnace carries out decarburization treatment according to the composition and temperature of molten steel in place. RH decarburization is the most important decarburization link in the production of ultra-low carbon steel. Due to the high temperature and strong stirring during vacuum treatment, all factors that are conducive to increasing the decarburization rate can accelerate the decarburization reaction. In the process of rapid pressure reduction in the vacuum chamber, as the lifting gas flow rate increases, the circulation flow rate and volume coefficient increase, the decarburization rate is increased, and the decarburization reaction is accelerated. After decarburization, deoxidizer and component aluminum are added according to the oxygen determination situation. After circulating for more than 5 minutes, titanium iron, niobium iron, metal manganese, micro-carbon silicon iron, phosphorus and other alloys are added to adjust the composition. After the adjustment of the composition, ensure that the vacuum cycle is 4 minutes before measuring the temperature and sampling. After the addition of titanium iron, the pure degassing time is guaranteed to be more than 6 minutes to ensure the uniformity of the temperature and composition of the molten steel. At the same time, it is conducive to the floating of molten steel inclusions and improve the cleanliness of the molten steel.

[0030] Continuous casting: Continuous casting protects pouring to prevent secondary oxidation of molten steel and avoid secondary oxidation of steel. Constant pulling speed is adopted, and the pulling speed is controlled at 0.8-2.0m / min. The appropriate superheat degree of pouring is controlled, and the superheat degree during pouring is controlled at about 20-60℃, which promotes the floating of inclusions and realizes multi-furnace pouring.

[0031] Hot rolling process:

[0032] The ingot is heated by a walking-beam heating furnace (the heating process is shown in Table 1). The rough rolling adopts double-stand R1 and R2 reciprocating rolling. The rough rolling mode is 3+5, and the descaling water pressure is not less than 250 bar. The finishing rolling adopts the F1-F7 continuous rolling process. The finishing rolling temperature is 890-940°C to ensure rolling in the austenite single-phase zone. The coiling temperature is 680-750°C to ensure the normal precipitation of carbonitrides and improve the processing and forming performance. The specific hot rolling process is shown in Table 2.

[0033] Table 1 Billet heating system

[0034]

[0035] Table 2 Rolling process

[0036]

[0037] Annealing process:

[0038] Annealing uses a vertical continuous annealing furnace, which is cooled by a reducing atmosphere and a nitrogen-hydrogen mixed protective atmosphere. The temperature range of the heating section and the soaking section is 760-820°C to ensure complete recrystallization of the grains. The temperature control of each section of the heating furnace is shown in Table 3, and the elongation control of the leveler is shown in Table 4.

[0039] Table 3 Annealing process

[0040]

[0041] Table 4 Elongation of the flat-pass mill

[0042]

[0043] Example Analysis

[0044] Steelmaking ingredients:

[0045] According to the above steelmaking process requirements, the actual slab chemical composition (mass percentage) is shown in Table 5 below.

[0046] Table 5 Chemical composition of examples wt.%

[0047]

[0048]

[0049] Hot rolling performance:

[0050] According to the above designed chemical composition and hot rolling process, the room temperature tensile properties of the hot rolled plate are shown in Table 6, the tensile specimen L0 = 80 mm, b = 20 mm (transverse), and the test method refers to GB / T 228.1.

[0051] Table 6 Hot rolling tensile properties

[0052]

[0053] Finished product performance:

[0054] Cold rolling and annealing are performed on the basis of the above hot rolling properties. The range of room temperature tensile mechanical properties of the finished product is shown in Table 7. The distribution of the yield strength, tensile strength and elongation performance indicators of the steel strip is as follows: Figures 1 to 3 As shown, the metallographic structure is equiaxed ferrite, the grain size is 6.0-8.0, and the organizational morphology is shown in Figure 4 .

[0055] Table 7 Finished product tensile properties

[0056]

[0057] In summary, this product has passed performance tests and all performance requirements are met. It has also met processing and forming requirements after user trials. It has achieved stable batch supply with a supply volume of ≥5,000 tons.

[0058] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing cold-rolled deep-drawn steel for household appliances with a thickness of 0.4 mm, characterized in that: Its chemical composition by mass percentage: C≤0.0030%, Si≤0.030%, Mn≤0.20%, P≤0.015%, Ti 0.050-0.080%, Al 0.020-0.070%, S≤0.010%, O≤0.0030%, N≤0.0030%, the balance being Fe and unavoidable impurities; The production method includes: Steelmaking process: molten iron → converter steelmaking → RH refining → slab continuous casting; molten iron is pre-treated with desulfurization before converter smelting, and the sulfur content of the molten iron entering the converter is required to be less than 0.010%, and the slag removal area of ​​the molten iron is greater than 95%; converter smelting requires the tapping temperature to be ≥1660℃, and a turnover bag must be used for tapping, and the tapping temperature drop is required to be less than 70℃; the RH process requires deep decarburization treatment based on the composition and temperature of the molten steel supplied by the converter to RH. After decarburization, aluminum particles are added for deoxidation according to the oxygen setting situation. After circulating for more than 5 minutes, titanium iron and other alloys are added to adjust the composition; after the adjustment of the composition is completed, the vacuum cycle must be no less than 4 minutes before temperature measurement and sampling can be carried out. After the addition of titanium iron, the pure degassing time is guaranteed to be more than 6 minutes, and the superheat of the molten steel is 20-60℃; Hot rolling process: slab heating → high-pressure water descaling → fixed width press → E1R1 roughing mill rolling → E2R2 roughing mill rolling → flying shear → high-pressure water descaling → F1-F7 finishing mill rolling → encrypted laminar cooling → coiling → pallet transportation system → sampling and inspection; the slab heating temperature is 1160-1220℃; heating time is 150-250min; the rough rolling mode is 3+5; the finishing rolling temperature is 890-940℃, and the coiling temperature is 680-750℃; Cold rolling process: pickling uncoiling → welding → straightening → pickling → rinsing → drying → trimming → continuous rolling mill cold rolling → slitting → coiling → offline inspection → weighing → marking → bundling → packaging → warehousing → continuous uncoiling → welding → cleaning → entrance looper → annealing furnace → exit looper → leveling → inspection looper → trimming → surface inspection → oiling → coiling → weighing → sampling and inspection; Annealing process parameters: outlet temperature of heating and soaking section 760-830℃, outlet temperature of slow cooling section 600-700℃, outlet temperature of rapid cooling section ≤400℃, temperature of over-aging section ≤400℃, outlet temperature of final cooling section ≤180℃, elongation of flat mill 0.4-0.6%.

2. The method for producing cold-rolled deep-drawn steel for household appliances with a thickness of 0.4 mm according to claim 1, characterized in that: The metallographic structure of the finished product is equiaxed ferrite with a grain size of 6.0-8.

0.

3. The method for producing cold-rolled deep-drawn steel for household appliances with a thickness of 0.4 mm according to claim 1, characterized in that: Adopt post-dispersed cooling mode.

4. The method for producing cold-rolled deep-drawn steel for household appliances with a thickness of 0.4 mm according to claim 1, characterized in that: Finished product quality meets the following requirements: Yield strength R p0.2 123-153MPa, tensile strength R m It is 275-310MPa.

5. The method for producing cold-rolled deep-drawn steel for household appliances with a thickness of 0.4 mm according to claim 1, characterized in that: Finished product elongation A 80 It is 40.0-50.5%.

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