Stainless precision strip steel with reduced surface contact resistance and method of production and use thereof

Abstract

The application discloses a production method of stainless precision strip steel with reduced surface contact resistance, which comprises the following steps: an austenitic cold-rolled stainless steel strip with a thickness of 0.3-0.35 mm is subjected to surface solid solution pickling to obtain a stainless steel raw material strip; a twenty-roller rolling mill is used to roll the stainless steel raw material strip to obtain a finished steel strip with a thickness of 0.1 mm; and the finished steel strip is subjected to cleaning, bright annealing and tension leveling. The application further discloses a stainless precision strip steel with reduced surface contact resistance manufactured by using the production method and a stack bipolar plate manufactured from the stainless precision strip steel. The application can realize that the surface contact resistance of the precision strip steel is less than or equal to 50 mΩ·cm 2 The cold-rolled steel plate with low contact resistance is provided for downstream stamping forming users, and subsequent production processes can avoid surface treatment or reduce the surface treatment process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of stainless precision strip steel production and manufacturing, in particular to a stainless precision strip steel with reduced surface contact resistance and a production method and application thereof. BACKGROUND

[0002] Hydrogen energy, as an environmentally friendly energy source, is recognized as one of the main energy sources in the future and is an ideal energy source for new energy vehicles. The bipolar plate of the electric pile is a key component of hydrogen energy vehicles and is the place where hydrogen and oxygen react. It plays a crucial role in the hydrogen energy conversion efficiency of the electric pile. The bipolar plate has high requirements for corrosion resistance, contact resistance and formability, etc. Currently, the main materials on the market are graphite, titanium and stainless steel. Stainless steel has the advantages of high corrosion resistance, high strength, good gas barrier property, easy forming and suitability for mass production, etc. It has become the first choice for hydrogen energy electric pile bipolar plates and has a broad market prospect in the future.

[0003] Currently, the research and manufacturing of hydrogen energy bipolar plates have become a hot topic in China, but no mass-produced standardized products and mature manufacturing processes have been formed. Related enterprises and research institutions have conducted more research on corrosion resistance, contact resistance and formability. Mainstream enterprises improve corrosion resistance and reduce surface contact resistance through surface modification treatment of austenitic stainless steel. Japan and South Korea are also researching and developing surface modification treatment technology of ferritic stainless steel. Contact resistance is a key indicator of hydrogen energy bipolar plates. The lower the contact resistance, the higher the efficiency of hydrogen energy conversion to electrical energy, and the higher the hydrogen energy utilization rate, which meets the direction of maximizing energy utilization. On the contrary, the higher the contact resistance, the more hydrogen energy is converted into heat energy, causing the electric pile to overheat, resulting in low efficiency of hydrogen energy conversion to electrical energy.

[0004] The stainless steel precision strip steel for bipolar plates is generally an austenitic stainless steel precision strip steel material with a thickness of 0.1mm or even thinner, which is required to be delivered in a solid solution state. After being formed into a bipolar plate by user micro-channel groove stamping, the stamped bipolar plate is combined into an electric pile in a stacked manner. The internal channel flow plays the role of air and water passage, and the part of the bipolar plate that contacts each other needs to reduce the contact resistance and improve the electrical conductivity to achieve the purpose of maximizing the conversion of hydrogen energy to electrical energy.

[0005] However, the current production method of stainless steel precision strip steel cannot meet the requirement of fully reducing the contact resistance. SUMMARY

[0006] In view of the above problems, the present application is proposed to provide a stainless precision strip steel with reduced surface contact resistance and a production method and application thereof. Thus, the contact resistance of the surface of the stainless precision strip steel can be reduced, the hydrogen energy conversion efficiency of the bipolar plate electric pile can be improved, and the design requirements of the hydrogen energy electric pile can be met.

[0007] Specifically, the present application is realized by the following technical solutions:

[0008] A production method of stainless precision strip steel with reduced surface contact resistance, comprising:

[0009] An austenitic cold-rolled stainless steel strip with a thickness of 0.3-0.35 mm is subjected to surface solid solution pickling to obtain a stainless steel raw material strip;

[0010] The stainless steel raw material strip is rolled by a twenty-roller rolling mill to obtain a finished steel strip with a thickness of 0.1 mm;

[0011] The finished steel strip is cleaned, bright annealed and tension leveled.

[0012] Optionally, the surface defect rate of the stainless steel raw material strip is ≤0.5%, and the same plate difference is ≤1.0%.

[0013] Optionally, the convexity of the transmission roller of the twenty-roller rolling mill is 0.25-0.35, the taper of the first intermediate roller is 0.23%-0.27%, and the diameter of the work roller is 28-30 mm.

[0014] Optionally, the rolling comprises in sequence:

[0015] First-pass rolling, with a deformation rate of not more than 30% and a tension of not more than 200 N / mm 2 , using a work roller with a roller surface roughness of 0.2-0.3 μm and a rolling speed of not more than 200 m / min;

[0016] Intermediate-pass rolling, with a deformation rate of not more than 25% and a tension of not more than 400 N / mm 2 , using a work roller with a roller surface roughness of 0.1-0.15 μm and a rolling speed of 300-400 m / min;

[0017] Final-pass rolling, with a deformation rate of not more than 25% and a tension of not more than 400 N / mm 2 , using a work roller with a roller surface roughness of 0.04-0.08 μm and a rolling speed of not more than 200 m / min.

[0018] Optionally, the cleaning uses a cleaning aqueous solution with a pH value of 7-8.5 and a temperature of 70-80 °C, at a cleaning speed of 25-35 m / min.

[0019] Optionally, the bright annealing is performed by a vertical bright annealing furnace, with a furnace temperature of 1120-1150 °C and an annealing speed of 20-40 m / min.

[0020] Optionally, the tension leveling has an elongation of 1.0-1.5% and a tension leveling speed of 120-150 m / min.

[0021] A stainless precision strip steel is manufactured by the above production method.

[0022] Optionally, the plate shape unevenness of the stainless precision strip steel is ≤0.15 mm / m, the surface roughness is ≤0.1 μm, the water contact angle is ≤30°, and the surface contact resistance is ≤50 mΩ·cm. 2 .

[0023] A stack bipolar plate is manufactured by the above stainless precision strip steel.

[0024] As can be seen from the above technical solutions, the stainless precision strip steel with reduced surface contact resistance and the production method and application thereof have at least the following beneficial effects:

[0025] The stainless precision strip steel manufactured by the production method has good plate shape quality, smooth and clean surface, and the surface contact resistance of the stainless precision strip steel is significantly reduced, which can well meet the manufacturing requirements of the stack bipolar plate for hydrogen energy automobile.

[0026] The present application is a practical rolling, heat treatment and other production scheme for the surface contact resistance of the stainless steel precision strip steel for bipolar plate, and the surface contact resistance of the precision strip steel is ≤50 mΩ·cm 2 in the steel strip production stage, to provide a low contact resistance cold-rolled steel plate for the downstream stamping forming user, and the subsequent production process can avoid surface treatment or reduce the surface treatment process. DETAILED DESCRIPTION

[0027] In order to fully understand the purpose, features and effects of the present application, the present application will be described in detail through the following specific embodiments. The process method of the present application adopts conventional methods or devices in the art except the following contents. Unless otherwise stated, the following terms have the meanings commonly understood by those skilled in the art.

[0028] For the surface contact resistance problem of the stainless steel precision strip steel for the stack bipolar plate of hydrogen energy automobile, the inventors of the present application believe that the stainless steel itself is a conductor, and the gap between the stacked steel plates leads to poor conductivity, so the surface contact resistance is reduced from the perspective of increasing the contact area between the steel plates.

[0029] In order to increase the contact area between the steel plates, the inventors further analyzed and proposed to increase the contact area between the steel plates from the control of the plate shape unevenness, surface roughness and cleanliness of the strip steel.

[0030] From a macroscopic point of view, if the strip shape of the steel strip is good, the contact area of the steel strip as a whole is large, if the strip shape of the steel strip is not good, the warped part of the steel strip does not contact each other, the overall conductivity of the steel strip is poor, and the contact resistance is high. After a large number of experimental researches, the inventors propose that the strip shape unevenness of the steel strip should be controlled to be less than 0.15 mm / m.

[0031] From a microscopic point of view, if the surface roughness of the steel strip is low, the contact area of the steel strip on the micro area is large, if the surface roughness of the steel strip is high, the contact area between the steel strips on the micro area is small, the overall conductivity of the steel strip is poor, and the contact resistance is high. After a large number of experimental researches, the inventors propose that the surface roughness Ra of the steel strip is ≤0.1 μm.

[0032] In addition, the cleanliness of the surface of the steel strip also has an influence on the contact resistance. In the production process of rolling, pickling in the front process, slitting, etc., part of the acid mark, the dirty mark, the organic matter, etc. will be left on the surface, the existence of these substances will block the direct contact between the steel strips, reduce the contact area of the steel strips, cause the contact resistance to increase, and the conductivity to decrease. Therefore, it is necessary to ensure the cleanliness of the surface of the steel strip. After a large number of experimental researches, the inventors propose that the cleanliness index of the surface of the steel strip is that the water contact angle is ≤30°.

[0033] On the basis of the above inventive concept and research results, the inventors of the present application creatively propose a production method for reducing the surface contact resistance of the stainless steel precision strip, which comprises the following steps: austenitic cold-rolled stainless steel strips with a thickness of 0.3-0.35 mm are subjected to surface solid solution pickling to obtain stainless steel raw strip; a twenty-roll rolling mill is used to roll the stainless steel raw strip to obtain finished steel strips with a thickness of 0.1 mm; the finished steel strips are cleaned, bright annealed and tension-straightened.

[0034] As a preferred embodiment, the production method of the present application comprises the following steps:

[0035] Step one, material selection

[0036] The raw steel strip requires good surface quality, therefore, the austenitic cold-rolled stainless steel strips with a thickness of 0.3-0.35 mm are selected and subjected to surface solid solution pickling treatment to obtain the stainless steel raw strip with a surface defect rate of ≤0.5% and a same plate difference of ≤1.0%. The specific operation process of the solid solution pickling can refer to the related schemes in the prior art, which will not be described here.

[0037] Step two, rolling

[0038] Firstly, the roll system is configured, and a 650mm wide twenty-roll mill is used for production, and the crown of the driving roll, the taper of the first intermediate roll and the diameter of the working roll need to be determined. In order to ensure the plate shape quality, the inventors determine that the crown of the driving roll is selected to be 0.25-0.35, the taper of the first intermediate roll is selected to be 0.23%-0.27%, and the diameter of the working roll is selected to be 28-30mm after research.

[0039] In the present application, three working rolls (each working roll is two) should be prepared according to the rolling pass, and the working rolls are ground to control the roughness of the roll surface. The roughness of the three working rolls is 0.2-0.3μm, 0.1-0.15μm and 0.04-0.08μm respectively. As a preferred example, the 1# roll (i.e. the first working roll) is ground by using a diamond grinding wheel, the grit size of the grinding wheel is controlled to be 100-120 mesh, and the roughness of the roll surface is controlled to be 0.2-0.3μm. The 2# roll (i.e. the second working roll) is further ground by using a 400-500 mesh diamond grinding wheel on the basis of the 1# grinding, and the roughness of the roll surface is controlled to be 0.1-0.15μm. The 3# roll (i.e. the third working roll) is further polished by using the electroplating method on the basis of the 2# grinding, and the roughness of the roll surface is controlled to be 0.04-0.08μm.

[0040] Any twenty-roll mill meeting the above settings can be used in the production method of the present application.

[0041] After the roll system is configured, the stainless steel raw material strip is rolled into a finished product strip with a thickness of 0.1mm by multi-pass rolling. In order to ensure low surface roughness and good plate shape quality, the deformation rate, tension, rolling speed and temperature of each pass need to be strictly controlled.

[0042] As a preferred example, the rolling process specifically includes:

[0043] The first pass rolling uses the 1# roll, the deformation rate is controlled to be below 30%, the tension is controlled to be 200N / mm 2 The rolling speed is controlled to be below 200m / min.

[0044] The intermediate pass rolling uses the 2# roll, and the intermediate pass rolling at least includes two passes of rolling, the deformation rate of each pass is controlled to be below 25%, and the tension is controlled to be 400N / mm 2 The rolling speed is 300-400m / min.

[0045] The final pass rolling uses the 3# roll, the deformation rate is controlled to be below 25%, and the tension is controlled to be 400N / mm 2 The rolling speed is controlled to be below 200m / min.

[0046] During the rolling process described above, rolling oil is used for lubrication and cooling, and the temperature is controlled between 39°C and 42°C.

[0047] In this invention, the crown of the drive roller is selected as 0.25 to 0.35, the taper of the first intermediate roller is selected as 0.23% to 0.27%, and the diameter of the work roller is selected as 28 to 30 mm. The main purpose is to lay the foundation for controlling a good plate shape, and at the same time, to control the deformation rate, tension and rolling speed of each pass during the rolling process to achieve a good plate shape.

[0048] In addition, the surface roughness of the strip is reduced by lowering the roughness of the work rolls.

[0049] Step 3: Cleaning, bright annealing, and tensile straightening

[0050] After rolling, the finished steel strip is first cleaned. Normal steel strip does not undergo a cleaning process; however, to improve the cleanliness of the stainless steel strip surface, an additional surface cleaning process is added. The pH value of the cleaning solution is controlled at 7–8.5, and the water temperature is controlled at 70–80℃. After cleaning, the strip is dried, with the drying oven temperature controlled at 100–120℃ and the steel strip speed at 25–35 m / min. It should be noted that the cleaning solution used in this process is obtained by diluting a cleaning agent with water. The cleaning agent can be any cleaning agent conventionally used in the art for cleaning steel strip surfaces and can be purchased commercially. In actual production, those skilled in the art can select appropriate cleaning agents and cleaning solution concentrations as needed, as long as they meet the pH value and temperature specified in this invention.

[0051] The finished steel strip is then fed into a vertical bright annealing furnace for annealing, with the furnace temperature controlled at 1120-1150℃ and the steel strip speed at 20-40m / min.

[0052] The finished steel strip was then straightened using a tension straightening machine to determine the plate shape quality. The tension straightening elongation was 1.0% to 1.5%, and the tension straightening speed was controlled at 120 to 150 m / min.

[0053] By utilizing the pH value, water temperature, and strip cleaning speed of the aqueous solution employed in this invention, rolling oil, organic matter, and other contaminants on the strip surface can be thoroughly removed, resulting in a clean and dirt-free surface. Specifically, the water contact angle is used to represent the degree of surface cleanliness; the smaller the water contact angle, the cleaner the strip surface. Straightening is performed to further improve the flatness of the strip.

[0054] The present application adopts 0.3-0.35mm thickness, plate type and good 2B surface austenitic stainless steel, through the optimization of rolling process parameters, roll configuration and roll surface roughness control and the increase of cleaning process, the plate shape quality of the steel plate is improved, the roughness is reduced and the cleanliness of the surface is increased, etc., the surface contact resistance of the steel strip is reduced, and the conductivity is improved. Specifically, the plate shape unevenness of the stainless precision strip steel obtained by the above production method is ≤0.15mm / m, the surface roughness is ≤0.1μm and the water contact angle is ≤30°, and the surface contact resistance is ≤50mΩ·cm 2 , so as to meet the requirements of the hydrogen energy automobile electric pile bipolar plate very well.

[0055] Embodiment

[0056] The present application will be further described by way of examples below, but the present application is not limited to the scope of the examples. The experimental methods in the following examples without specific conditions are selected according to conventional methods and conditions, or according to the instructions of the commodity.

[0057] In the following examples, the plate shape unevenness, surface roughness and water contact angle can be detected according to the relevant methods in stainless steel precision foil (GB / T 41608).

[0058] Example 1

[0059] (1) Selection of materials: select 0.30mm thick austenitic cold-rolled stainless steel strip 304L, solid solution pickling surface. Surface defect rate 0.35, same plate difference 0.5%.

[0060] (2) Roll configuration: the crown of the transmission roll is selected as 0.3, the taper of the first intermediate roll is selected as 0.25%, and the diameter of the work roll is selected as 30mm.

[0061] (3) Roll grinding: according to the rolling pass, three work rolls are prepared, and the work roll is ground to control the roughness of the roll surface. The 1# roll is ground by diamond grinding wheel, the grit size is 100 mesh, and the roughness of the roll surface is controlled at 0.28μm. The 2# roll is ground by diamond grinding wheel with a grit size of 400 mesh based on the grinding of the 1#, and the roughness of the roll surface is controlled at 0.15μm. The 3# roll is polished by electroplating based on the grinding of the 2#, and the roughness of the roll surface is controlled at 0.08μm.

[0062] (4) Rolling: the stainless steel raw material coil is rolled into a finished product with a thickness of 0.1mm in five passes, while ensuring low surface roughness and good plate shape quality. The specific control is as follows: the first pass deformation rate is controlled at 25%, the tension is controlled at 180N / mm 2 The second, third and fourth pass deformation rates are controlled at 20%, and the tension is controlled at 350N / mm2 The deformation rate of the final pass is controlled at 13%, and the tension is controlled at 300 N / mm 2 The rolling speed of the first pass is controlled at 180 m / min, and the rolling speeds of the second, third and fourth passes are 400 m / min. The rolling speed of the final pass is controlled at 180 m / min, and the rolling oil temperature is 42℃. The first pass adopts a 1# roller, the second, third and fourth passes adopt a 2# roller, and the final pass adopts a 3# roller.

[0063] (5) Cleaning: The normal steel strip does not pass through the cleaning process. In order to improve the cleanliness of the surface of the stainless steel strip, a steel strip surface cleaning process is added. The pH value of the cleaning aqueous solution is 7.4, the water temperature is controlled at 75℃, the drying box temperature is controlled at 120℃, and the steel strip speed is 25 m / min.

[0064] (6) Bright annealing: The vertical bright furnace is used for annealing, the furnace temperature is controlled at 1120℃, and the steel strip speed is 25 m / min.

[0065] (7) Tension leveling: The steel strip is straightened by a tension bending straightening machine to determine the plate shape quality. The tension leveling elongation is 1.2%, and the tension leveling speed is controlled at 120 m / min.

[0066] The plate shape quality of the steel strip obtained in this embodiment is good, and the unevenness is 0.10 mm / m. The surface of the steel strip is smooth and flat, and the roughness Ra is less than or equal to 0.09 μm. The surface of the steel strip is clean and tidy, and the cleanliness index is the water contact angle of 28°. The surface contact resistance of the precision steel strip is 43 mΩ·cm 2 , which reduces the subsequent surface treatment process and provides convenience for the user's production.

[0067] Example 2

[0068] (1) Material selection: Select 0.35 mm thick austenitic cold-rolled stainless steel strip 316L, and solid solution acid washing surface. The surface quality is required to be good, and the surface defect rate is 0.4%, and the same plate difference is 0.5%.

[0069] (2) Roll configuration: A twenty-roll mill with a width of 650 mm is used for production, and the crown of the drive roll, the taper of the first intermediate roll and the diameter of the work roll need to be determined. In order to ensure the plate shape quality, the crown of the drive roll is selected to be 0.30, the taper of the first intermediate roll is selected to be 0.25%, and the diameter of the work roll is selected to be 30 mm.

[0070] (3) Grinding roller: three pairs of work rolls are prepared according to the rolling pass, and the work rolls are ground to control the roughness of the roll surface. The 1# roll is ground by diamond grinding wheel, the grit size is controlled to 120 mesh, and the roughness of the roll surface is 0.2 μm. The 2# roll is ground by diamond grinding wheel with a grit size of 500 mesh based on the 1# grinding, and the roughness of the roll surface is 0.1 μm. The 3# roll is polished by electroplating based on the 2# grinding, and the roughness of the roll surface is controlled to 0.04 μm.

[0071] (4) Rolling: the stainless steel raw material coil is rolled to the finished product of 0.1 mm thickness in five passes, while ensuring low surface roughness and good plate shape quality. The specific control is as follows: the first pass deformation rate is controlled to 28%, the tension is controlled to 180 N / mm 2 , the second, third and fourth pass deformation rate is controlled to 22%, the tension is controlled to 350 N / mm 2 , the final pass deformation rate is controlled to 20%, and the tension is controlled to 200 N / mm 2 . The rolling speed of the first pass and the final pass is controlled to 180 m / min, and the rolling speed of the intermediate pass is 350 m / min. Rolling oil is used for lubrication and cooling during rolling, and the temperature is controlled to 42℃. The 1# roll is used for the first pass, the 2# roll is used for the second pass, and the 3# roll is used for the third pass.

[0072] (5) Cleaning: the normal steel strip does not go through the cleaning process, in order to improve the cleanliness of the surface of the stainless steel strip, a steel strip surface cleaning process is added. The PH value of the cleaning water solution is controlled to 8.2, the water temperature is controlled to 75℃, the drying box temperature is controlled to 110℃, and the steel strip speed is 35 m / min.

[0073] (6) Bright annealing: vertical bright annealing furnace is used for annealing, the furnace temperature is controlled to 1150℃, and the steel strip speed is 30 m / min.

[0074] (7) Straightening: the steel strip is straightened by the stretch bending straightening machine to determine the plate shape quality, the stretch straightening elongation is 1.3%, and the stretch straightening speed is controlled to 140 m / min.

[0075] The plate shape quality of the steel strip obtained in this embodiment is good, the unevenness is 0.10 mm / m; the surface of the steel strip is smooth and smooth, the roughness Ra is ≤0.07 μm; the surface of the steel strip is clean and tidy, the cleanliness index water contact angle is 26°. The surface contact resistance of the precision steel strip is 45 mΩ·cm 2 , which reduces the subsequent surface treatment process and provides convenience for the user's production.

[0076] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any substitutions, modifications, combinations, changes, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and are included in the protection scope of the present application.

Claims

1. A method for producing stainless precision strip with reduced surface contact resistance, characterized in that, include: Austenitic cold-rolled stainless steel strip with a thickness of 0.3 to 0.35 mm is subjected to surface solution pickling to obtain stainless steel raw material strip; The stainless steel raw material strip is rolled using a 20-roll mill to obtain a finished steel strip with a thickness of 0.1 mm; the finished steel strip is then cleaned, bright annealed, and tension leveled. The drive roll of the 20-roll mill has a crown of 0.25–0.35, the taper of the first intermediate roll is 0.23%–0.27%, and the diameter of the work roll is 28–30 mm. The rolling process includes: a first pass rolling with a deformation rate not exceeding 30% and a tension not exceeding 200 N / mm. 2 The rolling process uses work rolls with a surface roughness of 0.2–0.3 μm, and the rolling speed does not exceed 200 m / min; for intermediate passes, the deformation rate does not exceed 25%, and the tension does not exceed 400 N / mm. 2 The rolling mill uses work rolls with a surface roughness of 0.1–0.15 μm and a rolling speed of 300–400 m / min; in the final pass, the deformation rate does not exceed 25% and the tension does not exceed 400 N / mm. 2 The rolling mill uses work rolls with a surface roughness of 0.04 to 0.08 μm and a rolling speed not exceeding 200 m / min; the elongation of the tension leveling is 1.0 to 1.5% and the tension leveling speed is 120 to 150 m / min. The cleaning process uses a cleaning aqueous solution with a pH value of 7-8.5 and a temperature of 70-80℃, and the cleaning speed is 25-35 m / min. The bright annealing is carried out in a vertical bright annealing furnace with a furnace temperature of 1120-1150℃ and an annealing speed of 20-40 m / min. The stainless precision strip has the following characteristics: flatness ≤ 0.15 mm / m, surface roughness ≤ 0.1 μm, water contact angle ≤ 30°, and surface contact resistance ≤ 50 mΩ·cm. 2 .

2. The production method according to claim 1, characterized in that, The surface defect rate of the stainless steel raw material strip is ≤0.5%, and the difference between the same plate is ≤1.0%.

3. A stainless precision strip steel, manufactured using the production method described in any one of claims 1 to 2.

4. A bipolar plate for an electric stack, manufactured using the stainless precision strip steel described in claim 3.