Production method of 304 cold-rolled stainless precision strip steel for lithium battery shell

Abstract

The novel lithium battery shell has strict requirements on the performance, the surface, the plate shape and the like of stainless steel precision strip steel. The invention relates to a production process of 304 cold-rolled stainless precision strip steel for a lithium battery shell. Compared with a conventional process, a roller heat treatment process is added. By controlling the components of the raw materials and adding special rolling, annealing and straightening processes, the problems of poor plate shape, non-uniform performance, poor surface and the like in the production process of the stainless steel band are effectively solved, and the high-quality requirement of the lithium battery shell industry is met.

Description

Technical Field

[0001] The invention relates to a production method of stainless steel precision strip, and in particular to a production method of 304 cold-rolled stainless steel precision strip for lithium battery shells. Background Art

[0002] With the development of the industry, it has become a trend for battery shells to be replaced by stainless steel instead of aluminum alloy. Stainless steel has excellent corrosion resistance and high strength, which can meet the requirements of large capacity and long battery life of the battery. The new lithium battery shell has strict requirements on the performance, surface, plate type, etc. of stainless steel precision strip. A lithium battery shell uses 304 stainless steel, which requires hardness HV150±5 and roughness controlled below Ra0.2um. The surface needs to be electroplated later, so there must not be any defects. The plate type requires the flatness to be controlled below 0.5mm / m. Conventional 304 is hard at around HV160 after annealing, and with later straightening, the hardness basically reaches around HV170. In addition, the roughness below Ra0.2um increases the difficulty of surface control, and various defects are very obvious, which is not conducive to subsequent electroplating. By controlling the raw material composition, subjecting the rollers to special heat treatment, and adding special rolling, annealing and straightening processes, the special needs of lithium battery shells can be met.

[0003] The purpose of the present invention is to provide a production process for 304 cold-rolled stainless steel strip for lithium battery shells, with a target thickness of 0.1-0.4 mm. Through a series of precise controls, the surface defects that occur during the production process are effectively solved, and high-precision plate shape and performance control are achieved, reaching the forefront of the production of such products in China. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems and provide a method for producing 304 cold-rolled stainless precision strip steel for lithium battery shells.

[0005] The object of the present invention is achieved as follows: A production method for 304 cold-rolled stainless precision strip steel for lithium battery shells, comprising the following steps: Step 1: Material selection: Select 304 series stainless steel; Step 2: Roller preparation: Select a D2 roller with a diameter of 30-32 mm for aging treatment in a bell-type furnace, the heating temperature is 230±5°C, the insulation time is 1.1-1.3h, and the furnace is cooled, and then coarse grinding + fine grinding are performed on a grinder, and the final roller roughness is controlled at Ra0.13-0.18um; Step 3: Rolling: The total rolling deformation from raw materials to finished products is controlled at 56%-70%, and the rolling passes are divided into 4-5 passes, and the deformation of the first pass is set to 23-25%, The roughness of the roller is Ra0.35-0.5um. The heat-treated D2 roller is used for the finished product, and the roughness is selected to be Ra0.13~0.18um. The thickness accuracy is controlled at ±0.005mm. The rolling speed of the finished product does not exceed 100m / min, and the rolling speed of the remaining passes is 300m / min~500m / min; Step 4: Annealing: The rolled stainless steel strip is annealed at an annealing temperature of 1150±10℃, the TV value, i.e., thickness*speed, is 6.8~7.0, and the speed of the cooling fan is 1800~2000rpm; Step 5: Straightening: The annealed stainless steel strip is straightened, and the straightening tension is set to 85N / mm 2 -125N / mm 2 , entrance gap -1.5~-3mm, straightening speed 80~180m / min.

[0006] In step 1, the composition of 304 series stainless steel is controlled as follows: C: 0.03-0.05%, Si: 0.4-0.6%, Mn: 1.0-1.2%, P≤0.04%, S≤0.01%, Cr: 18-18.5%, Ni: 8.3-8.5%, Mo≤0.2%.

[0007] The beneficial effects of the present invention are as follows: the present invention relates to a production process of 304 cold-rolled stainless precision strip steel for lithium battery shells, the process comprising material selection, roll preparation, rolling, annealing, and straightening. Compared with conventional processes, a roll heat treatment process is added, which effectively solves the problems of poor plate shape, unstable performance, and poor surface of stainless steel strips in the production process, so that the product size tolerance fluctuation is small, the performance is stable, the plate shape is good, the quality is significantly improved, and it is suitable for large-scale industrial production, meeting the high quality requirements of the lithium battery shell industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will be further described below in conjunction with the accompanying drawings.

[0009] Figure 1This is a heat treatment process diagram of the roll of the present invention. The roll is placed in a bell-type furnace for aging treatment, heated to 230±5°C at a rate of 65°C / h, and then kept warm. The holding time is set to 1.1~1.3h, and finally the roll is taken out after cooling to room temperature with the furnace. DETAILED DESCRIPTION

[0010] A type of 304 stainless steel used for lithium battery shells requires a hardness of HV150±5 and a roughness controlled below Ra0.2um. The surface needs to be electroplated later, so there cannot be any defects. The plate type is required to have a flatness of less than 0.5mm / m. Conventional 304 has a hardness of about HV160 after annealing, and with subsequent straightening, the hardness basically reaches about HV170. In addition, the roughness below Ra0.2um makes it more difficult to control the surface, and various defects are very obvious, which is not conducive to subsequent electroplating. By controlling the raw material composition, subjecting the rollers to special heat treatment, and adding special rolling, annealing and straightening processes, the special needs of lithium battery shells can be met.

[0011] The technical solution of the present invention is: material selection - roll preparation - rolling - annealing - straightening. The specific implementation method is as follows: 1. Material selection: The present invention uses 304 series stainless steel, and the main components are controlled as shown in the following table (unit %).

[0012]

[0013] 2. Roller preparation: Select a D2 roll with a diameter of 30~32mm (D2 roll is a roll made of high-carbon, high-chromium, high-molybdenum tool steel with excellent wear resistance, impact resistance and heat resistance) for aging treatment in a bell-type furnace, heating temperature 230±5℃, insulation time 1.1~1.3h, cooling with the furnace (see the attached figure for the process), and then rough grinding + fine grinding on the grinder, and the final roll roughness is controlled at Ra0.13-0.18um.

[0014] 3. Rolling: In order to obtain good plate shape and performance, the total rolling deformation from raw materials to finished products is controlled at 56%~70%, and the rolling passes are divided into 4~5 passes. The deformation of the first pass is set at 23%, and the roller roughness is Ra0.35-0.5um. The finished product pass uses a heat-treated D2 roller with a roughness of Ra0.13~0.18um. The roller must not have defects such as spiral lines, sand marks, meat loss, color difference, scratches, etc. The thickness accuracy of the finished product is controlled at ±0.005mm. In order to ensure the accuracy of the finished product, the rolling speed of the finished product does not exceed 100m / min.

[0015] 4. Annealing: Anneal the stainless steel strip after fine rolling at 1150±10℃, TV (thickness*speed) value 6.8~7.0, cooling fan 1800~2000rpm. In order to ensure that the steel strip does not produce folds after annealing, the position of the graphite roller in the annealing furnace is adjusted to 50%-70%, the position of the 1#, 3#, 4#, 6# cooling baffles is adjusted to 20-40% or 70%-85%, and the position of the 2# and 5# cooling baffles is fixed at 50%.

[0016] 5. Straightening: The annealed stainless steel strip is straightened with constant tension, and the straightening tension is set to 85N / mm 2 -125N / mm 2 , entrance gap -1.5~-3mm, straightening speed 80~180m / min.

[0017] The technical parameters of the stainless steel strip obtained using this process are as follows: 1) Thickness tolerance: ±0.005mm; 2) Vickers hardness (HV): (150~160)HV1000g; 3) Yield strength (Rm): (260~300)MPa; 4) Tensile strength (Rm): (600~700)MPa; 5) Roughness Ra: 0.13~0.2um; 6) Flatness: ≤0.5 (mm / m). Example 1

[0018] 1. Material selection: 304 series stainless steel is selected, and the main components are controlled as shown in the following table (unit %).

[0019]

[0020] 2. Roller preparation: Select a D2 roll with a diameter of 32 mm for aging treatment in a bell-type furnace with a heating temperature of 235°C and a holding time of 1.1 h. Cool it with the furnace, and then perform coarse grinding and fine grinding on a grinder. The final roll roughness is controlled at Ra0.15um.

[0021] 3. Rolling: The raw material thickness is 1.0mm, and the rolled product thickness is 0.33mm. The rolling passes are divided into 5 passes. The deformation of the first pass is set to 23%, and the roller roughness is Ra0.36um. The finished product pass uses the heat-treated D2 roller with a roughness of Ra0.158um. Before the roller is put on the machine, defects such as spiral pattern, sand mark, meat loss, color difference, and scratches are checked. The thickness accuracy of the finished product is controlled at ±0.005mm, and the rolling speed of the finished product is 90m / min.

[0022] 4. Annealing: The rolled stainless steel strip is annealed at 1150°C, TV (thickness*speed) value 7.0, and cooling fan 2000rpm. In order to ensure that the steel strip does not produce folds after annealing, the position of the graphite roller in the annealing furnace is adjusted to 60%, the position of the 1#, 3#, 4#, and 6# cooling baffles is adjusted to 30%, and the position of the 2# and 5# cooling baffles is fixed at 50%.

[0023] 5. Tension straightening: The annealed stainless steel strip is straightened, and the straightening tension is set to 120N / mm 2 , entrance gap -1.8mm, straightening speed 150m / min.

[0024] The main technical indicators of the products produced by the above process can reach: 1) Thickness: 0.299 / 0.334mm; 2) Vickers hardness (HV): (156 / 158) HV1000g; 3) Yield strength (Rm): 278MPa; 4) Tensile strength (Rm): 685MPa; 5) Roughness Ra: 0.145um; 6) Flatness: ≤0.3 (mm / m). Example 2

[0025] 1. Material selection: 304 series stainless steel is selected, and the main components are controlled as shown in the following table (unit %).

[0026]

[0027] 2. Roller preparation: Select a D2 roll with a diameter of 30 mm for aging treatment in a bell-type furnace with a heating temperature of 230°C and a holding time of 1.2 h. Cool it with the furnace, and then perform coarse grinding and fine grinding on a grinder. The final roll roughness is controlled at Ra0.17um.

[0028] 3. Rolling: The raw material thickness is 0.6mm, and the rolled product thickness is 0.2mm. The rolling passes are divided into 5 passes. The deformation of the first pass is set to 23%, and the roller roughness is Ra0.35um. The finished product pass uses the heat-treated D2 roller with a roughness of Ra0.178um. Before the roller is put on the machine, defects such as spiral pattern, sand mark, meat loss, color difference, and scratches are checked. The thickness accuracy of the finished product is controlled at ±0.005mm, and the rolling speed of the finished product is 95m / min.

[0029] 4. Annealing: The rolled stainless steel strip is annealed at 1140°C, TV (thickness*speed) value 6.8, and cooling fan 1800rpm. In order to ensure that the steel strip does not produce folds after annealing, the position of the graphite roller in the annealing furnace is adjusted to 70%, the position of the 1#, 3#, 4#, and 6# cooling baffles is adjusted to 75%, and the position of the 2# and 5# cooling baffles is fixed at 50%.

[0030] 5. Tension straightening: The annealed stainless steel strip is straightened, and the straightening tension is set to 112N / mm 2 , entrance gap -2mm, straightening speed 135m / min.

[0031] The main technical indicators of the products produced by the above process can reach: 1) Thickness tolerance: 0.197 / 0.204mm; 2) Vickers hardness (HV): (153 / 155) HV1000g; 3) Yield strength (Rm): 265MPa; 4) Tensile strength (Rm): 675MPa; 5) Roughness Ra: 0.155um; 6) Flatness: ≤0.2 (mm / m).

[0032] It should be emphasized that the above production method is only used to illustrate the present invention, and does not limit the scope of use of the present invention. In addition, after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, but these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for producing 304 cold-rolled stainless precision steel strip for lithium battery shells, characterized in that: The following steps are involved: Step 1: Material selection: Choose 304 series stainless steel; Step 2: Roller preparation: Select D2 rolls with a diameter of 30-32 mm for aging treatment in a bell-type furnace, heating temperature 230±5℃, holding time 1.1-1.3h, cooling with the furnace, and then rough grinding + fine grinding on a grinder, and the final roll roughness is controlled at Ra0.13-0.18um; Step 3: Rolling: The total rolling deformation from raw material to finished product is controlled at 56%~70%. The rolling passes are divided into 4~5 passes. The deformation of the first pass is set at 23-25%, and the roller roughness is Ra0.35-0.5um. The finished product pass uses a heat-treated D2 roller with a roughness of Ra0.13~0.18um. The thickness accuracy is controlled at ±0.005mm. The finished product rolling speed does not exceed 100m / min, and the rolling speed of the remaining passes is 300m / min~500m / min. Step 4: Annealing: Anneal the rolled stainless steel strip at a temperature of 1150±10°C, a TV value (thickness*speed) of 6.8~7.0, and a cooling fan speed of 1800~2000rpm; Step 5: Straightening: Straighten the annealed stainless steel strip, and set the straightening tension to 85N / mm 2 -125N / mm 2 , entrance gap -1.5~-3mm, straightening speed 80~180m / min.

2. The method for producing 304 cold-rolled stainless precision steel strip for lithium battery shell according to claim 1, characterized in that: In step 1, the composition of 304 series stainless steel is controlled as follows: C: 0.03-0.05%, Si: 0.4-0.6%, Mn: 1.0-1.2%, P≤0.04%, S≤0.01%, Cr: 18-18.5%, Ni: 8.3-8.5%, Mo≤0.2%.

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