Cold rolling method for producing nickel-chromium austenitic stainless steel
By optimizing cold rolling process parameters and adjusting equipment, the problem of friction mark defects in stainless steel cold rolling was solved, product quality was improved and waste was reduced, achieving efficient production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHANGJIAGANG POHANG STAINLESS STEEL
- Filing Date
- 2024-12-11
- Publication Date
- 2026-06-26
Smart Images
Figure CN119702709B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of stainless steel manufacturing technology, and in particular to a cold rolling method for producing nickel-chromium austenitic stainless steel. Background Technology
[0002] Stainless steel is classified into five categories according to its metallic structure: austenitic stainless steel, ferritic stainless steel, austenitic-ferritic (duplex) stainless steel, martensitic stainless steel, and precipitation hardening stainless steel. Austenitic stainless steel is the most commonly used type on the market, accounting for approximately 80% of the market share. Austenitic stainless steel is further divided into two series based on its chemical composition: chromium-nickel series (300 series in the US) austenitic stainless steel and chromium-manganese series (200 series in the US) austenitic stainless steel. The 300 series stainless steel (such as 304 stainless steel) is more widely used.
[0003] In stainless steel, two opposing forces operate simultaneously: ferrite-forming elements continuously form ferrite, and austenite-forming elements continuously form austenite. The final crystal structure depends on the relative amounts of these two types of additive elements. Chromium is a ferrite-forming element, so it competes with austenite-forming elements in the formation of the stainless steel crystal structure. Because both iron and chromium are ferrite-forming elements, 400 series stainless steel is a fully ferritic stainless steel and is magnetic. In the process of adding the austenite-forming element nickel to iron-chromium stainless steel, as the nickel content increases, the amount of austenite formed gradually increases until all the ferrite structure is transformed into an austenitic structure, thus forming 300 series stainless steel.
[0004] Stainless steel produced using existing rolling mills is prone to developing grayish-white dotted friction marks. These defects are persistent and severely impact the usability of stainless steel products, affecting not only surface aesthetics but also causing problems for downstream customers. Grinding is difficult to eliminate these friction marks on the steel plate surface, and they can easily lead to cracking during stamping processes. Furthermore, these friction mark defects account for a large proportion of defects in cold rolling mills. Once they appear, the only options are re-rolling or downgrading, resulting in waste of materials, processing costs, and energy, and severely impacting the profitability of stainless steel manufacturers. Summary of the Invention
[0005] To address the aforementioned problems, the present invention aims to provide a cold rolling method for producing nickel-chromium austenitic stainless steel. This method can effectively improve the friction mark defects generated on the surface of stainless steel during the production process, thereby enhancing the quality of austenitic stainless steel products.
[0006] To achieve the above objectives, the present invention provides a cold rolling method for producing nickel-chromium austenitic stainless steel, the method comprising sequentially performing raw material uncoiling, cold rolling, cold annealing followed by pickling, and finishing followed by edge trimming or coil splitting.
[0007] In the cold rolling process, the service life of the first intermediate roll is controlled to be 450 tons / cycle to 650 tons / cycle.
[0008] The surface roughness Ra of the work roll in the second pass is controlled to be 0.6μm-0.8μm;
[0009] The thrust bearing for the control mill is a single bearing type.
[0010] In the above-mentioned cold rolling method, the nickel-chromium austenitic stainless steel includes 304 stainless steel and / or 316 stainless steel.
[0011] The cold rolling method of this invention includes: uncoiling the raw material, cold rolling to the target thickness, cold annealing followed by pickling to remove stress and surface oxide scale, and finishing by trimming or slitting. This invention primarily improves the surface defects of stainless steel by controlling the process parameters during cold rolling (and further by controlling the uncoiling process), thereby enhancing the quality of austenitic stainless steel products.
[0012] In the above cold rolling method, the raw material uncoiling refers to the process of threading the raw material coil (material) into the uncoiling machine. During the raw material uncoiling process, the uncoiling method can be controlled to be left-hand winding.
[0013] In some specific embodiments, the taper of the first intermediate roll can be 1‰-1.5‰. The convexity of the second intermediate roll can be 260-300μm. By controlling the taper of the first intermediate roll and the convexity of the second intermediate roll, it is beneficial to achieve a good strip shape. Apart from this, the present invention does not have special requirements for the distance, angle, etc. between the rolls.
[0014] In some specific embodiments, the number of cold rolling passes can be adjusted according to the thickness of the strip. For example, rolling a 3.2mm thick strip to a 0.6mm thickness can be done in 9 passes, and rolling a 3.2mm thick strip to a 1.0mm thickness can be done in 7 passes. In some specific embodiments, the number of cold rolling passes can be 5-9.
[0015] In the aforementioned cold rolling method, the service life of the first intermediate roll is controlled to be between 450 tons / cycle and 650 tons / cycle throughout the entire cold rolling process. Specific values include 450 tons / cycle, 500 tons / cycle, 550 tons / cycle, 600 tons / cycle, and 650 tons / cycle, as well as a range with any two of these values as endpoints. In some specific implementations, the service life can be adjusted accordingly for cold-rolled raw materials of different sizes. Specifically, for cold-rolled raw materials with a width of 1 meter, the service life of the first intermediate roll can be 450-550 tons / cycle. For raw materials with a width of 4 feet, the service life of the first intermediate roll can be 550-650 tons / cycle.
[0016] In this invention, the wedge value is a common definition in the art, specifically the difference between the thickness from the drive side edge of the strip to 25mm from the strip and the thickness from the working side edge to 25mm from the strip, i.e., Δhd = Δh 25-DS -△h 25-WS In the formula, △h d For wedge deviation, mm; △h 25-DS The thickness of the strip steel is 25 mm from the drive side edge; △h 25-WS The thickness of the strip is 25mm from the working edge, in mm.
[0017] In this invention, the head of the raw material refers to a 100m length range from the beginning of the raw material (towards the end), and the tail of the raw material refers to a 100m length range from the end of the raw material (towards the beginning).
[0018] This invention has found that friction mark defects in stainless steel during cold rolling mainly occur in the second pass. By controlling the roughness of the work rolls in the second pass, it is beneficial to reduce or eliminate the occurrence of defects. The roughness of the work rolls in the second pass is generally controlled to be 0.6μm-0.8μm, for example, specific values such as 0.6μm, 0.65μm, 0.7μm, 0.75μm, 0.8μm, etc., or a range with any two of the above specific values as endpoints.
[0019] In this invention, when the absolute value of the wedge value of the cold-rolled raw material is ≥25, or the misalignment of the head of the cold-rolled raw material is >10mm or more, or the misalignment of the tail of the cold-rolled raw material is 10mm or more (i.e., at least one of the above conditions is met), the cold-rolled raw material is an abnormal material; cold-rolled raw materials other than abnormal materials are normal materials.
[0020] In the above cold rolling method, when the cold-rolled raw material is an abnormal material, the rolling speed of the first pass is controlled to be 120-180 mpm, for example, specific values such as 120 mpm, 130 mpm, 140 mpm, 150 mpm, 160 mpm, 170 mpm, 180 mpm, and any two of the above specific values as endpoints; when the cold-rolled raw material is a normal material, the rolling speed of the first pass is controlled to be 170-230 mpm, for example, specific values such as 170 mpm, 180 mpm, 190 mpm, 200 mpm, 210 mpm, 220 mpm, 230 mpm, and any two of the above specific values as endpoints.
[0021] In the above-described cold rolling method, when the raw material is an abnormal material, the speed of the intermediate work rolls during the cold rolling process can be controlled to be 300-600 mpm, for example, specific values such as 300 mpm, 350 mpm, 400 mpm, 450 mpm, 500 mpm, 550 mpm, and 600 mpm, as well as a range with any two of the above specific values as endpoints. In this invention, intermediate passes refer to all passes other than the first and last passes, that is, the passes between the first and last passes.
[0022] Furthermore, the speed of the intermediate work rolls can be adjusted accordingly based on the target rolling thickness of the abnormal material:
[0023] In the above cold rolling method, when the cold rolling raw material is an abnormal material and the target rolling thickness is less than 1.0 mm, the rolling speed of the intermediate passes can be controlled to be 400-600 mpm, for example, specific values such as 400 mpm, 450 mpm, 500 mpm, 550 mpm, 600 mpm, and any two of the above specific values as endpoints.
[0024] In the above cold rolling method, when the cold rolling raw material is an abnormal material and the target rolling thickness is 1.0mm-3.0mm, the rolling speed of the intermediate passes can be controlled to be 350-550mpm, for example, specific values such as 350mpm, 400mpm, 450mpm, 500mpm, 550mpm, etc., and a range with any two of the above specific values as endpoints.
[0025] In the above cold rolling method, when the cold rolling raw material is an abnormal material and the target rolling thickness is 3.0 mm or more, the rolling speed of the intermediate passes can be controlled to be 300-500 mpm, for example, specific values such as 300 mpm, 350 mpm, 400 mpm, 450 mpm, 500 mpm, etc., and a range with any two of the above specific values as endpoints.
[0026] In the above cold rolling method, when the cold-rolled raw material is an abnormal material, the rolling speed of the head and tail of the raw material is less than or equal to 50 mpm and the rolling time is greater than or equal to 60 s.
[0027] Furthermore, for the portion between the head and tail of the defective material, when it is necessary to increase the rolling speed, the rolling speed should be increased by 120-150 m / min, maintained at that speed for at least 10 seconds before further increasing the speed; when it is necessary to decrease the rolling speed, the rolling speed should be decreased by 120-180 m / min, maintained at that speed for at least 10 seconds before further decreasing the speed. This stepped speed change method can reduce the occurrence of defects.
[0028] In the above cold rolling method, by controlling the rolling speed and time of abnormal materials, it is possible to avoid damage to the work rolls and defects caused by raw materials with poor sheet shape.
[0029] In the above cold rolling method, when the raw material is a normal material, there are no special restrictions on the rolling speed at the head and tail of the material. To improve efficiency, the rolling speed can be adjusted to shorten the rolling time, thereby increasing production output. In some specific embodiments, the rolling speed at the head and tail of the raw material can be less than or equal to 50 mpm, and the rolling time can be greater than or equal to 30 s. There are no special restrictions on the way the rolling speed changes between the head and tail of the normal material; the above-mentioned stepped speed variation method can also be used.
[0030] In the aforementioned cold rolling method, when the raw material is an abnormal material, the stress on the side guide plate is optimized to control the bilateral stress on the side guide plate in the first pass. When the raw material is a normal material, there are no special restrictions on the stress on the side guide plate.
[0031] The cold rolling method provided by the present invention can be implemented in a 20-roll Sendzimir mill.
[0032] The beneficial effects of this invention include:
[0033] 1. The cold rolling method provided by the present invention helps to eliminate the gray-white dotted friction marks on the surface of cold-rolled stainless steel and greatly improves the product quality of nickel-chromium stainless steel.
[0034] 2. The cold rolling method provided by this invention can effectively improve the friction mark defects on the surface of steel plates by changing the rolling process parameters, operating methods, and setting operating parameters according to the abnormal conditions of raw materials, thereby avoiding waste of materials, processing costs, energy, etc., improving product quality, meeting market demands, and generating higher economic value. Attached Figure Description
[0035] Figure 1 A photograph of a friction mark defect.
[0036] Figure 2aThis section describes the quantity and proportion of abnormal and normal cold-rolled raw material sheets from the third quarter of 2020 to May 2021.
[0037] Figure 2b The data represents the incidence of friction mark defects in normal and abnormal cold-rolled raw materials from the third quarter of 2020 to May 2021.
[0038] Figure 2c This is a trend analysis chart showing the incidence of friction marks as a function of wedge value.
[0039] Figure 3a This represents the percentage of wedge-shaped interval operations in the total operations from January to May 2021.
[0040] Figure 3b The correlation between wedge values and friction marks in cold-rolled raw materials from January to May 2021.
[0041] Figure 4a This data represents the off-gauge thickness of cold-rolled raw materials from the third quarter of 2020 to May 2021.
[0042] Figure 4b This is a photograph of friction marks defects on the surface of a steel strip.
[0043] Figure 5 This is a correlation diagram showing the relationship between the service life of the first intermediate roll of the rolling mill and the occurrence of friction mark defects.
[0044] Figure 6 This is a schematic diagram of the stepped acceleration process in Example 1.
[0045] Figure 7 The graph shows the results of the friction mark defect incidence rate in Application Example 1. Detailed Implementation
[0046] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.
[0047] This invention provides a cold rolling method for producing nickel-chromium austenitic stainless steel. The cold rolling method includes sequentially performing the following steps: raw material uncoiling, cold rolling, cold annealing followed by pickling, and finishing with edge trimming or slitting. During the raw material uncoiling process, the uncoiling method is controlled to be left-hand winding.
[0048] The following controls are implemented during the cold rolling process:
[0049] The service life of the first intermediate roller is controlled to be 450-650 tons / cycle;
[0050] The surface roughness of the work roll in the second pass is controlled to be 0.6-0.8 μm;
[0051] The thrust bearing for the control mill is a single bearing type.
[0052] Cold rolling is a process of rolling and deforming metal at a recrystallization temperature. It generally refers to the rolling of strip steel directly at room temperature without heating. During the rolling process, strip steel undergoes varying degrees of work hardening. Once the work hardening exceeds a certain level, the strip steel becomes too hard and brittle to continue rolling. Therefore, after a certain number of cold rolling passes, strip steel often undergoes softening heat treatment (such as recrystallization annealing) to restore its plasticity and reduce its resistance to deformation.
[0053] Existing cold-rolled stainless steel surfaces are prone to developing grayish-white dot-like friction marks. Through on-site verification of cold-rolled stainless steel sheet surfaces, the inventors discovered the following morphology and patterns of these grayish-white dot-like friction marks:
[0054] (1) Morphology of friction mark defects:
[0055] Figure 1 In the image, a, b, and c represent a photograph of the friction mark (to show its appearance to the naked eye), a photomicrograph (to show its microscopic appearance), and a photomicrograph (to show the details of the defect), respectively. From Figure 1 As can be seen from point a, the macroscopic manifestation of friction marks is a dot-like defect, generally without any tactile feel; from Figure 1 As can be seen from b, the surface of the grayish-white dotted friction marks shows obvious damage, consistent with the matrix composition; from Figure 1 As can be seen from c, the surface of the friction mark defect has multiple morphologies and has been rolled multiple times.
[0056] In summary, the surface defects of friction marks appear as small, dot-like breaks, which cannot be eliminated by grinding in severe cases. Under the microscopic morphology of friction marks, there are obvious rolling traces, indicating multi-pass rolling (traces that extend after multiple rolling passes).
[0057] (2) The relationship between the service life of the working roll and the occurrence of friction mark defects was studied, and the defect distribution and pattern were obtained as follows:
[0058] i) All of them are bifacial, with corresponding occurrences on the upper and lower surfaces, and multiple occurrences on the edges, distributed along one or more straight lines;
[0059] ii) Small positional deviations (off-center) of defects along the same straight line can be used to distinguish and confirm the occurrence of defects in a cycle;
[0060] iii) Based on the reduction amount, the occurrence cycle corresponds to the diameter of the rolling mill work roll, suggesting that it is affected by work roll damage.
[0061] According to the research, the surface defects of stainless steel sheets are friction marks, not roll marks.
[0062] Based on the above-mentioned distribution and occurrence patterns of friction mark defects, the inventors identified rolling deviation (Off-Center) as the key point of friction mark defects.
[0063] The existing technology has the following drawbacks:
[0064] (1) Raw material plate shape difference (severe wedge shape, excessive thickness at the head and tail, etc.) Due to the limited ability of hot rolling mill to control plate shape, raw material plate shape difference is caused. However, at present, cold rolling mill has no clear prevention mechanism for defects induced by raw material plate shape difference, and relies entirely on experience for control.
[0065] (2) The lack of a protection mechanism for the replacement of the rolling mill work rolls leads to defects caused by the scratching of the work rolls.
[0066] (3) The inherent drawbacks of the rolling mill equipment itself result in poor ability to prevent defects such as damage to the work rolls.
[0067] Furthermore, the formation mechanism of gray-white dotted friction marks was investigated:
[0068] Figure 2a This data represents the quantity and proportion of abnormal and normal cold-rolled raw material strips from the third quarter of 2020 (3Q refers to the third quarter, 4Q refers to the fourth quarter, the same below) to May 2021. Abnormal strips refer to cold-rolled raw materials with an absolute wedge value greater than 25 or with a misalignment of more than 10mm at the head or tail. Cold-rolled raw materials other than abnormal strips are considered normal strips. Figure 2a The left vertical axis represents the incidence of friction marks, and the right vertical axis represents the proportion of abnormal material in all materials (normal material + abnormal material).
[0069] Figure 2b The slip retention rate represents the slip retention rate of normal and abnormal cold-rolled raw materials from the third quarter of 2020 to May 2021.
[0070] Combination Figure 2a and Figure 2b It can be seen that the ratio of abnormal material to normal material fluctuates little over time, but the incidence of friction mark defects in abnormal material is significantly higher than that in normal material.
[0071] Figure 2c for Figure 2a and Figure 2b A trend analysis chart of the incidence of friction marks as a function of wedge value after data merging. Figure 2c The intervals [0,10], (10,20], (20,30], and (30,+∞) represent the absolute value ranges of the wedge-shaped values. Figure 2c It can be seen that there is a significant correlation between the absolute value range of the raw material wedge and the incidence of friction mark defects; the larger the absolute value of the raw material wedge, the higher the incidence of friction mark defects.
[0072] Figure 3a This shows the percentage of work done in the wedge-shaped intervals in the total work done from January to May 2021. Figure 3b This illustrates the correlation between the wedge value and the incidence of friction marks in cold-rolled raw materials from January to May 2021. Figure 3a , Figure 3b It can also be seen that there is a significant correlation between the raw material wedge value and the friction mark occurrence rate; the larger the absolute value of the wedge value, the higher the friction mark occurrence rate.
[0073] Based on the above research, the inventors found that the absolute value of the wedge shape of cold-rolled raw materials is significantly correlated with the incidence of friction mark defects, and the wedge shape is the main influencing factor of friction mark defects.
[0074] The inventors also conducted the following research on the formation mechanism of friction mark defects:
[0075] (1) Off-Gauge excess thickness refers to the length of excess thickness at the head and tail, which can be used to characterize the adverse effects of the head / tail of cold-rolled raw materials. In this invention, excess thickness refers to exceeding 5% of the raw material thickness. Therefore, head and tail excess thickness refers to the situation where the thickness of the head or tail of the raw material exceeds 5% of the average thickness of the raw material.
[0076] Figure 4a This section describes the off-gauge thickness of cold-rolled raw materials from the third quarter of 2020 to May 2021. Since the MAX Roll Force (maximum tilting force) of the 20-roll Sendzimir mill is located at both the beginning and end, defects at the beginning and end can easily cause damage to the rolls; therefore, the impact of defects at the beginning and end is investigated. Figure 4a It can be seen that the Off-Gauge increases significantly with the increase of operation time, and the situation where the Off-Gauge is greater than 20m increases significantly with the increase of operation time.
[0077] Misalignment refers to the unevenness of the beginning and end of cold-rolled raw materials. This invention has found that when cold-rolled raw materials have misalignment, the cold-rolled strip still has misalignment, albeit to a lesser degree, but this results in friction mark defects. For example, the misalignment of the cold-rolled raw material is greater than 20mm, and the misalignment of the strip at the mill exit after cold rolling is greater than 10mm. In this case, friction mark defects will appear on the strip surface, such as… Figure 4b As shown.
[0078] Through research, the inventors discovered that excessive thickness at the beginning and end of the raw material, misalignment, and friction mark defects are significantly correlated and are the main factors contributing to friction mark defects.
[0079] (2) Figure 5This is a correlation diagram showing the service life of the first intermediate roll of a rolling mill and the occurrence of friction mark defects. From... Figure 5 It can be seen that the longer the service life of the first intermediate roll, the higher the incidence of friction mark defects. Therefore, the longer the rolling depth of the first intermediate roll, the higher the incidence of gray-white dot-like friction mark defects; the service life of the first intermediate roll is the main factor affecting the occurrence of friction mark defects.
[0080] In summary, poor shape of cold-rolled raw materials, absolute wedge value, and excessive thickness at the beginning and end leading to deviation are important factors causing friction mark defects. However, current hot rolling processes that supply raw materials to cold rolling mills utilize hot-roll mills, which are difficult to adjust in terms of shape, resulting in significant thickness differences on both sides (larger wedge, even larger at the beginning and end). Furthermore, the temperature at the beginning / end of the hot-roll mill is lower than in the middle (>100℃), leading to excessive thickness at the beginning and end, and a worse shape compared to the middle. Therefore, reducing or eliminating friction mark defects can be achieved by improving both the hot rolling process and the cold rolling process.
[0081] The cold rolling method for producing nickel-chromium austenitic stainless steel provided by this invention can alleviate the problem of friction marks caused by axial force generated on the work rolls due to poor cold rolling sheet shape deviation (large absolute value of wedge and excessive thickness at the head and tail), and reduce the damage of poor raw materials to the work rolls of the cold rolling mill.
[0082] The cold rolling method for producing nickel-chromium austenitic stainless steel provided by the present invention includes sequential uncoiling, cold rolling, cold annealing followed by pickling, finishing followed by edge trimming or coil splitting.
[0083] Specifically, the service life of the first intermediate roll is controlled to be 450-650 tons / cycle; the roughness of the work roll of the second pass is controlled to be 0.6-0.8μm; the type of the mill thrust bearing is controlled to be a single bearing type; and the uncoiling method is controlled to be left-hand winding.
[0084] According to a specific embodiment of the present invention, the above-mentioned cold rolling method can be carried out in a 20-roll Sendzimir mill. The Sendzimir mill was invented by Dr. Sendzimir in 1933, initially mainly used for producing low-carbon strip steel with a width of 800 mm and a thickness of 0.13 mm. Currently, over 90% of cold-rolled stainless steel strip steel is produced by Sendzimir mills, which have the following main structural characteristics: (a) They have an integrally cast (or forged) frame with high rigidity, and the rolling force acts radially on each section of the frame. (b) The work roll diameter is small, and the pass reduction rate is large, reaching up to 60%. Some materials can be rolled into very thin strips without intermediate annealing. (c) They have axial and radial roll shape adjustment, roll diameter compensation, and rolling line adjustment mechanisms, and adopt hydraulic reduction and AGC systems, resulting in good product shape and high dimensional accuracy. (d) The equipment is lightweight; the mill weight is only one-third that of a four-roll mill of the same specifications. The rolling mill has a small external size and requires less infrastructure investment.
[0085] The roll system of the 20-roll Sendzimir mill to which this invention is applicable is arranged in a 1-2-3-4 tower shape, symmetrically set in the eight quincunx holes of the stand. The roll system distribution from the inside out of the mill is as follows: the upper and lower work rolls rest on the two first intermediate rolls respectively; the upper and lower pairs of first intermediate rolls are supported on three second intermediate rolls; and the six second intermediate rolls are supported on eight support roll groups fixed in the quincunx holes on the outer layer.
[0086] According to a specific embodiment of the present invention, by increasing the roughness of the second-pass work roll, steel strip misalignment can be slowed down, and friction mark defects can be avoided. In existing methods, the roughness Ra of the work roll is generally 0.5-0.6 μm, while the present invention increases the roughness Ra of the second-pass work roll to 0.6-0.8 μm; the roughness of the work rolls in other passes besides the second pass can be controlled to be 0.5-0.6 μm.
[0087] According to a specific embodiment of the present invention, when replacing the work roll, a pad can be used as a protective plate for the work roll to prevent scratches on the work roll and thus avoid scratches from being imprinted on the surface of the strip steel, resulting in friction mark defects.
[0088] In the above cold rolling method, increasing the roughness of the work rolls and using a backing plate when changing work rolls can prevent friction mark defects by preventing work roll abrasions.
[0089] According to the research of this invention, prolonged use of the first intermediate roll can lead to friction mark defects. Specifically, the first intermediate roll has a taper; if it is used for a long time, the taper of the first intermediate roll will wear down, making it impossible to accurately control the strip shape, resulting in strip misalignment and friction mark defects. Furthermore, the longer the first intermediate roll is used, the longer the strip shape becomes, and the shape difference damages the work roll, further leading to friction mark defects. The method provided by this invention adjusts the service life of the first intermediate roll, which can prevent strip misalignment induced by taper wear, thereby avoiding friction mark defects. In some specific embodiments, the service life of the first intermediate roll can be controlled to be 450 tons / cycle to 650 tons / cycle.
[0090] According to a specific embodiment of the present invention, the service life of the first intermediate roll can be adjusted according to the cold-rolled raw material. For example, when the cold-rolled raw material is 1 meter wide, the service life of the intermediate roll can be 450-550 tons / cycle; when the cold-rolled raw material is 4 feet wide, the service life of the intermediate roll can be 550-650 tons / cycle. Compared to methods where the service life of the first intermediate roll is typically 600 tons / cycle for 1-meter wide cold-rolled raw material and 700 tons / cycle for 4-foot wide cold-rolled raw material, the method provided by the present invention can reduce the service time of the first intermediate roll, reduce the damage to the work roll caused by sheet shape differences, and thus avoid friction mark defects.
[0091] According to a specific embodiment of the present invention, the above method may further include optimizing the avoidance of scratching the work rolls by using side guide plates, which is beneficial to the smooth rolling of steel plates.
[0092] Specifically, the side guide optimization methods include: (1) changing the side guide plate of the first pass from being stressed on one side to being stressed on both sides. By improving the side guide stress, both sides can be stressed at the same time, preventing deviation caused by poor material; (2) optimizing the side guide centering to unify the side guide position sensor.
[0093] According to a specific embodiment of the present invention, the above method may further include changing the type of the mill thrust bearing by changing the double-layer bearing type to a single bearing type to prevent damage to the work roll caused by bearing damage. The single bearing used in the present invention is beneficial to the smooth operation of the work roll and can avoid friction marks caused by uneven force distribution.
[0094] According to a specific embodiment of the present invention, the above method may further include controlling the uncoiling method to be left-hand winding. Left-hand winding can reduce the strip running length, ensure tension stability, and prevent deviation. By changing the uncoiling method, it is beneficial to position the thicker side of the raw material on the drive side, thus mitigating raw material deviation.
[0095] According to a specific embodiment of the present invention, the above method may further include increased manual plate shape control intervention and manual adjustment of the defective positions of the head and tail plates.
[0096] According to a specific embodiment of the present invention, the above method may further include adjusting the AFC shape control target of the rolling mill. Existing methods do not provide specific control in this regard, while the present invention, by controlling the pressure (I-unit) at the contact surface between the strip and the shape roll, can adjust the shape control target, which is beneficial for achieving a better shape and avoids severe damage to the work rolls caused by shape defects (edge waviness, center waviness, etc.) leading to friction marks. Specifically, the pressure at the contact surface between the edge of the strip (the portion within 10cm of the edge, and the remaining portion as the center) and the shape roll can be controlled to -15N / mm. 2 Up to -5N / mm 2 To reduce edge waviness; the pressure at the contact surface between the middle of the strip and the plate roll is controlled at 5 N / mm. 2 Up to 15 N / mm 2 To reduce the mid-wave.
[0097] According to a specific embodiment of the present invention, the head and tail of cold-rolled raw materials can be strengthened by slow operation. By increasing the slow operation time at the head and tail, the occurrence of friction marks caused by the work rolls when the defective parts of the raw materials at the head and tail pass through can be reduced.
[0098] According to a specific embodiment of the present invention, the above method may further include formulating corresponding operating standards based on the material type (abnormal material, normal material), and by controlling the maximum speed, increasing the plate shape control time, refining the operation, and establishing operating standards for abnormal materials, damage to the work rolls can be minimized.
[0099] According to a specific embodiment of the present invention, the above method may specifically include establishing the following operational standards for defective raw material coils with poor sheet shape:
[0100] In the above cold rolling method, when the raw material is abnormal (|wedge value|≥25, poor plate shape, or head and / or tail misalignment>10m, etc.), the rolling speed of the first pass can be controlled to be 120-180mpm.
[0101] In the above cold rolling method, when the raw material is an abnormal material, the rolling speed of the intermediate passes can be controlled according to the thickness of the raw material. Specifically, for abnormal materials with a target rolling thickness ≤ 1.0 mm, the rolling speed of the intermediate passes can be controlled at 400-600 mpm; for abnormal materials with a target rolling thickness greater than 1.0 mm and less than 3.0 mm, the rolling speed of the intermediate passes can be controlled at 350-550 mpm; for abnormal materials with a target rolling thickness ≥ 3.0 mm, the rolling speed of the intermediate passes can be controlled at 300-500 mpm. The total number of cold rolling passes can be selected according to the thickness of the raw material and the target rolling thickness, generally 5-9 passes.
[0102] In the aforementioned cold rolling method, when the raw material is an abnormal material, the head and tail sections can be rolled at slow speeds. Specifically, the rolling speed of the head and tail sections of the abnormal material can be controlled to be less than or equal to 50 mpm, and the running time can be controlled to be greater than or equal to 60 s.
[0103] In the above cold rolling method, when the raw material is an abnormal material, the side guide plate of the first pass is controlled to be subjected to force on both sides to avoid unilateral force.
[0104] The above method can also be used to develop operating standards for normal materials. Normal materials refer to raw materials other than abnormal materials.
[0105] In the above cold rolling method, when the raw material is normal material, the rolling speed of the first pass can be controlled to be 170-230 mpm.
[0106] In the above cold rolling method, when the raw material is normal material, there are no special restrictions on the rolling speed of intermediate passes.
[0107] In the aforementioned cold rolling method, when the raw material is a normal material, there are no special restrictions on the rolling speed at the head and tail. In some specific implementations, the rolling speed at the head and tail of the normal material can be controlled to be less than or equal to 50 mpm, and the running time can be controlled to be greater than or equal to 30 s. Based on this, the higher the rolling speed and the shorter the rolling time, the greater the production volume.
[0108] According to a specific embodiment of the present invention, the above method can also prevent damage to the work rolls due to excessive speed by changing the speed-up mode of each pass during rolling.
[0109] In existing methods, the rapid acceleration of the rolling mill coil during each pass, especially the single acceleration, causes significant instantaneous stress on the work rolls, easily leading to work roll damage. Damaged work rolls result in periodic friction marks when rolling steel sheets. To address this, [further measures are needed]. Figure 6As shown, this invention adjusts the speed-up mode for each pass from rapid speed-up to stepped speed-up (the speed increases slowly in steps), which can reduce the instantaneous large force on the work roll and avoid damage to the work roll during the speed-up process. In some specific embodiments, the specific process of stepped speed-up can be as follows: at the head of the strip (within a length range of less than or equal to 100m from the beginning of the material), the rolling speed is controlled to be less than or equal to 50mpm and the rolling time is greater than 60s. Within a length range of more than 100m from the beginning of the material, the rolling speed is increased by 120-150m / min, maintained at that speed for more than 10s, and then the speed is increased again until the maximum speed is reached and then maintained at a constant speed. Within a length range of more than 100m from the end of the material, the rolling speed is decreased by 120-180m / min, maintained at that speed for more than 10s, and then the speed is decreased again. Within a length range of less than or equal to 100m from the end of the material, the rolling speed is controlled to be less than or equal to 50mpm and the rolling time is greater than 60s. For abnormal materials, the above-mentioned stepped speed increase method is usually used to reduce the occurrence of defects; for normal materials, the above-mentioned stepped speed increase method can be used optionally.
[0110] In the above cold rolling method, the nickel-chromium austenitic stainless steel may specifically include 304 stainless steel and / or 316 stainless steel.
[0111] Example 1
[0112] This embodiment provides a cold rolling method for producing nickel-chromium austenitic stainless steel, which is carried out in a 20-roll Sendzimir mill. The roll system of the 20-roll Sendzimir mill is arranged in a 1-2-3-4 tower shape, symmetrically set in eight quincunx holes of the stand. The roll system distribution from the inside out is as follows: the upper and lower work rolls rest on two first intermediate rolls respectively; the upper and lower pairs of first intermediate rolls are supported on three second intermediate rolls; and the six second intermediate rolls are supported on eight support roll groups fixed in the quincunx holes on the outer layer.
[0113] The cold rolling method includes the following steps in sequence: uncoiling the raw material, cold rolling, cold annealing followed by pickling, and finishing followed by trimming or slitting.
[0114] During the unwinding process, the unwinding method is controlled to be left-hand winding;
[0115] The following controls are implemented during the rolling process:
[0116] (1) The surface roughness Ra of the work roll in the second pass is 0.6-0.8μm, and the surface roughness Ra of the work roll in other passes is 0.5-0.6μm. When changing the work roll, use a pad as a protective plate for the work roll to prevent the work roll from being scratched and causing friction marks.
[0117] (2) Control the usage cycle of the first intermediate roll throughout the entire rolling process, specifically:
[0118] For raw materials with a width of 1 meter, the first intermediate roller has a service life of 500 tons / cycle;
[0119] For raw materials with a width of 4 feet, the first intermediate roller has a service life of 600 tons per cycle;
[0120] (3) For abnormal materials, optimize the side guide and control the side guide plate of the first pass to be subjected to double-sided force; and optimize the centering of the side guide and unify the side guide position sensor;
[0121] (4) Control the mill thrust bearing to be a single bearing;
[0122] (5) Perform panel shape control, including:
[0123] Strengthen slow-speed operations at the head and tail, and increase the slow-speed time at the head and tail;
[0124] Manual intervention in pattern control has been increased, and the positions of defective patterns at the beginning and end of the pattern are manually adjusted.
[0125] Adjust the AFC (Adjustment Factor Control) target of the rolling mill to control the pressure at the contact surface between the strip and the rolls; specifically, control the pressure at the contact surface between the edge of the strip and the rolls to -10 N / mm. 2 The pressure at the contact surface between the middle of the strip and the plate roll is controlled to 10 N / mm. 2 ;
[0126] (6) Control the rolling speed and the force on the side guide plate for normal and abnormal materials respectively:
[0127] For abnormal materials, the rolling speed of the first pass is 150 mpm; for abnormal materials with a rolling target thickness ≤ 1.0 mm, the rolling speed of the intermediate passes is 500 mpm; for abnormal materials with a rolling target thickness greater than 1.0 mm and less than 3.0 mm, the rolling speed of the intermediate passes is 450 mpm; for abnormal materials with a rolling target thickness ≥ 3.0 mm, the rolling speed of the intermediate passes is 400 mpm.
[0128] Slow speed control at the beginning and end of abnormal materials, with a control speed of less than or equal to 50 mpm and a running time of greater than or equal to 60 s;
[0129] For materials with abnormal characteristics, control the force on both sides of the side guide plate in the first pass to avoid force on one side;
[0130] For normal materials, there are no special restrictions on the rolling speed of each pass;
[0131] There are no special restrictions on the rolling speed and time of the head and tail of the normal material. In this embodiment, the rolling speed of the head and tail of the normal material is controlled to be less than or equal to 50 mpm and the running time is greater than or equal to 30 s.
[0132] For normal materials, there are no special restrictions on the stress on the side guide plate.
[0133] (7) For abnormal materials, the speed increase of the rolling mill in each pass is controlled as a step speed increase. The specific process is as follows: at the head and tail of the abnormal material, the rolling speed is controlled to be less than or equal to 50 m / min and the rolling time is greater than or equal to 60 s; in the part between the head and tail of the abnormal material, the speed is increased by 120-150 m / min each time, and the speed is maintained for more than 10 s before the speed is increased again. After reaching the maximum speed, the speed is maintained at a constant speed; when the speed needs to be reduced, the speed is reduced by 120-180 m / min each time, and the speed is maintained for more than 10 s before the speed is reduced again until the rolling speed required at the tail is reached.
[0134] Application Example 1
[0135] The cold rolling method of the present invention for producing nickel-chromium austenitic stainless steel is applied to the cold rolling production of 304 stainless steel and 316 stainless steel. The production methods for each time period are as follows:
[0136] The cold rolling process from 2019 to 2021 was as follows:
[0137] For cold-rolled raw materials with a width of 1 meter, the service life of the first intermediate roll is 600 tons / cycle; for cold-rolled raw materials with a width of 4 feet, the service life of the first intermediate roll is 700 tons / cycle.
[0138] The surface roughness Ra of the work roll in the second pass is 0.5-0.6 μm;
[0139] If a shim is not used when changing the work roll, scratches on the work roll cannot be avoided.
[0140] The side guide is subjected to force on one side only, and no side guide centering optimization has been performed;
[0141] The thrust bearing of the rolling mill is a double-layer bearing type;
[0142] Unwinding is performed using an uncoiler;
[0143] No special control is applied to the AFC strip shape control of the rolling mill;
[0144] During rolling, the speed-up mode for each pass is rapid acceleration, with only one acceleration and one deceleration (see reference). Figure 6 (The "rapid acceleration" in the text).
[0145] Cold rolling processes after 2022 shall be carried out in accordance with the cold rolling process of Example 1.
[0146] like Figure 7 As shown, the incidence of gray-white dotted friction marks ( Figure 7The degradation rate of gray-white dotted friction marks in the stainless steel has decreased significantly year by year. Before the process improvement, the incidence of gray-white dotted friction marks was 0.58%. After the improvement, the incidence rate continued to decrease, stabilizing at around 0.02%, and reaching a minimum of 0.01%, indicating a significant improvement in the quality of gray-white dotted friction mark defects. The above results demonstrate that the cold rolling method provided by this invention can effectively prevent the occurrence of gray-white dotted friction mark defects and significantly improve the quality of cold-rolled stainless steel.
Claims
1. A cold rolling method for producing nickel-chromium austenitic stainless steel, the method comprising sequentially performing uncoiling, cold rolling, cold annealing followed by pickling, finishing followed by edge trimming or slitting; in, In the cold rolling process, the service life of the first intermediate roll is controlled to be 450 tons / cycle to 650 tons / cycle; The surface roughness of the work roll in the second pass is controlled to be 0.6μm-0.8μm; The type of thrust bearing for the control mill is a single bearing type; When the absolute value of the wedge shape of the cold-rolled raw material is ≥25, or the misalignment at the head is ≥10mm, or the misalignment at the tail is ≥10mm, the cold-rolled raw material is considered abnormal; cold-rolled raw materials other than abnormal materials are considered normal materials; wherein, the wedge shape value is the difference between the thickness from the edge of the strip on the drive side to 25mm of the strip and the thickness from the edge of the working side to 25mm of the strip; the head of the raw material refers to a length of 100m from the beginning to the end of the raw material, and the tail of the raw material refers to a length of 100m from the end to the beginning of the raw material; When the cold-rolled raw material is an abnormal material, the rolling speed of the first pass should be controlled at 120-180 mpm; when the cold-rolled raw material is a normal material, the rolling speed of the first pass should be controlled at 170-230 mpm. When the cold-rolled raw material is an abnormal material, the rolling speed of the head and tail of the cold-rolled raw material is less than or equal to 50 mpm and the rolling time is greater than or equal to 60 s. For the section between the head and tail of the abnormal material, when it is necessary to increase the rolling speed, the rolling speed should be increased by 120-150 m / min, and the speed should be maintained for more than 10 seconds before continuing to increase the speed; when it is necessary to decrease the rolling speed, the rolling speed should be decreased by 120-180 m / min, and the speed should be maintained for more than 10 seconds before continuing to decrease the speed.
2. The cold rolling method according to claim 1, wherein, During the unwinding process of the raw materials, the unwinding method is to roll from the left.
3. The cold rolling method according to claim 1, wherein, For cold-rolled raw materials with a width of 1 meter, the service life of the first intermediate roll is 450-550 tons / cycle; For raw materials with a width of 4 feet, the first intermediate roller has a service life of 550-650 tons per cycle.
4. The cold rolling method according to claim 1, wherein, When the cold-rolled raw material is an abnormal material, the speed of the intermediate work rolls should be controlled at 300-600 mpm.
5. The cold rolling method according to claim 1, wherein, When the cold-rolled raw material is an abnormal material and the target rolling thickness is less than 1.0 mm, the rolling speed of the intermediate passes should be controlled at 400-600 mpm. When the cold-rolled raw material is an abnormal material and the target rolling thickness is greater than 1.0 mm and less than 3.0 mm, the rolling speed of the intermediate passes should be controlled at 350-550 mpm. When the cold-rolled raw material is an abnormal material and the target rolling thickness is 3.0 mm or more, the rolling speed of the intermediate passes should be controlled at 300-500 mpm.
6. The cold rolling method according to claim 1, wherein, When the cold-rolled raw material is an abnormal material, control the bilateral stress of the side guide plate.
7. The cold rolling method according to claim 1, wherein, The nickel-chromium austenitic stainless steel includes 304 stainless steel or 316 stainless steel.