Cold rolling method for producing nickel-chromium austenitic stainless steel

Abstract

The invention provides a cold rolling method for producing nickel-chromium austenitic stainless steel. The method comprises the steps of uncoiling, cold rolling, cold annealing for annealing and pickling, and finishing for trimming or coil dividing which are carried out in sequence. Wherein the service cycle of the first intermediate roller is controlled to be 450 tons / time to 650 tons / time; the roughness of a second-pass working roller is controlled to be 0.6-0.8 [mu] m; and the type of the thrust bearing of the rolling mill is controlled to be a single-bearing type. The method can effectively improve the gray dotted friction mark defect generated on the stainless steel surface in the production process and improve the quality of the austenitic stainless steel product.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel manufacturing, and in particular to a cold rolling method for producing nickel-chromium austenitic stainless steel. Background Art

[0002] Stainless steel is divided into five categories according to its metal structure: austenitic stainless steel, ferritic stainless steel, austenitic-ferritic (duplex) stainless steel, martensitic stainless steel and precipitation hardening stainless steel. The commonly used stainless steel in the market is mainly austenitic stainless steel, accounting for about 80% of the market share. Austenitic stainless steel is divided into two series according to its chemical composition: chromium-nickel series (300 series in the United States) austenitic stainless steel and chromium-manganese series (200 series in the United States) austenitic stainless steel. Among them, 300 series stainless steel (such as 304 stainless steel) is more popular.

[0003] In stainless steel, there are two opposing forces at work: ferrite formers continue to form ferrite, and austenite formers continue to form austenite. The final crystal structure depends on the relative amounts of the two added elements. Chromium is a ferrite former, so chromium competes with austenite formers in the formation of the stainless steel crystal structure. Because both iron and chromium are ferrite formers, 400 series stainless steels are completely ferritic and magnetic. When the austenite former nickel is added to the iron-chromium stainless steel, more austenite is formed as the nickel content increases, until all the ferrite structure is converted to austenite structure, thus forming 300 series stainless steel.

[0004] In the existing production method, stainless steel rolled by a rolling mill is prone to gray-white dot-shaped friction mark defects. This defect persists for a long time, seriously affecting the use of stainless steel products, not only affecting the surface aesthetics, but also causing trouble for downstream customers. The friction mark defects on the surface of the steel plate are difficult to eliminate by grinding, and cracking is prone to occur in the stamping process. In addition, this type of friction mark defect accounts for a large proportion of the defect classification of cold rolling mills. Once it occurs, it can only be determined to be re-rolled or downgraded, which not only causes waste of materials, processing fees, energy, etc., but also seriously affects the profitability of stainless steel manufacturers. Summary of the invention

[0005] In order to solve the above problems, the present invention aims to provide a cold rolling method for producing nickel-chromium austenitic stainless steel, which can effectively improve the friction mark defects generated on the stainless steel surface during the production process and improve the quality of austenitic stainless steel products.

[0006] In order to achieve the above object, the present invention provides a cold rolling method for producing nickel-chromium austenitic stainless steel, which comprises the following steps: uncoiling raw materials, cold rolling, cold annealing, annealing and pickling, and finishing, trimming or coiling;

[0007] Wherein, in the cold rolling process, the use cycle of the first intermediate roll is controlled to be 450 tons / time-650 tons / time;

[0008] The roughness Ra of the working roll in the second pass is controlled to be 0.6μm-0.8μm;

[0009] The type of control rolling mill thrust bearing is single bearing type.

[0010] In the above cold rolling method, the nickel-chromium austenitic stainless steel includes 304 stainless steel and / or 316 stainless steel.

[0011] The cold rolling method of the present invention comprises: uncoiling the raw material, cold rolling to a target thickness, cold annealing and pickling to remove stress and remove surface oxide scale, and finishing to trim or split the coil. The present invention mainly controls the process parameters in cold rolling (and can further control the uncoiling process) to improve the friction mark defects generated on the surface of stainless steel and improve the quality of austenitic stainless steel products.

[0012] In the above cold rolling method, the raw material unwinding refers to the process of threading the raw material coil (material) in the unwinding machine. During the raw material unwinding process, the unwinding mode can be controlled to be left-winding.

[0013] In some specific embodiments, the taper of the first intermediate roller may be 1‰-1.5‰. The convexity of the second intermediate roller may be 260-300 μm. By controlling the taper of the first intermediate roller and the convexity of the second intermediate roller, it is beneficial to make the strip steel have a good plate shape. In addition, the present invention has no special requirements for the distance and angle between the rollers.

[0014] In some specific embodiments, the number of cold rolling passes can be adjusted according to the thickness of the strip. For example, 9 passes can be used to roll a material with a thickness of 3.2 mm to a thickness of 0.6 mm, and 7 passes can be used to roll a material with a thickness of 3.2 mm to a thickness of 1.0 mm. In some specific embodiments, the number of cold rolling passes can be 5-9 passes.

[0015] In the above-mentioned cold rolling method, the service life of the first intermediate roller during the entire cold rolling process is controlled to be 450 tons / times to 650 tons / times, for example, specific values ​​such as 450 tons / times, 500 tons / times, 550 tons / times, 600 tons / times, 650 tons / times, and ranges with any two of the above-mentioned specific values ​​as endpoints. In some specific embodiments, 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 roller can be 450-550 tons / times. For raw materials with a width of 4 feet, the service life of the first intermediate roller can be 550-650 tons / times.

[0016] In the present invention, the wedge value is a common definition in the art, and specifically can be the difference between the thickness from the driving side edge of the strip to 25 mm of the strip and the thickness from the working side edge to 25 mm of the strip, that is, △hd = △h 25-DS -△h 25-WS , where △h d is the wedge deviation, mm; △h 25-DS is the thickness of the strip from the edge of the transmission side to 25mm, mm; △h 25-WS It is the thickness of the strip from the working side edge to 25mm, mm.

[0017] In the present invention, the head of the raw material refers to the range of 100 m in length from the head end of the raw material (towards the tail end), and the tail of the raw material refers to the range of 100 m in length from the tail end of the raw material (towards the head end).

[0018] The present invention has found that the friction mark defect of stainless steel during the cold rolling process mainly occurs in the second pass. By controlling the roughness of the working roll in the second pass, it is beneficial to reduce or eliminate the occurrence of defects. The roughness of the working roll in the second pass is generally controlled to be 0.6μm-0.8μm, for example, it can be 0.6μm, 0.65μm, 0.7μm, 0.75μm, 0.8μm and other specific values, and a range with any two of the above specific values ​​as endpoints.

[0019] In the present 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 greater than 10 mm, or the misalignment of the tail of the cold-rolled raw material is greater than 10 mm (that is, at least one of the above conditions is met), the cold-rolled raw material is an abnormal material; the cold-rolled raw materials other than the abnormal materials are normal materials.

[0020] In the above-mentioned 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 a range with any two of the above-mentioned 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 a range with any two of the above-mentioned specific values ​​as endpoints.

[0021] In the above cold rolling method, when the cold rolling raw material is an abnormal material, the speed of the intermediate pass working roll during the cold rolling process can be controlled to be 300-600 mpm, for example, 300 mpm, 350 mpm, 400 mpm, 450 mpm, 500 mpm, 550 mpm, 600 mpm and other specific values ​​and a range with any two of the above specific values ​​as endpoints. In the present invention, the intermediate pass refers to the other passes except the first pass and the last pass, that is, the pass between the first pass and the last pass.

[0022] Furthermore, the speed of the intermediate pass working rolls can be adjusted accordingly according to the rolling target thickness of the abnormal material:

[0023] In the above-mentioned cold rolling method, when the cold rolling raw material is an abnormal material and the rolling target thickness is below 1.0 mm, the rolling speed of the intermediate pass can be controlled to 400-600 mpm, for example, specific values ​​such as 400 mpm, 450 mpm, 500 mpm, 550 mpm, 600 mpm, and a range with any two of the above-mentioned specific values ​​as endpoints.

[0024] In the above-mentioned cold rolling method, when the cold rolling raw material is an abnormal material and the rolling target thickness is 1.0mm-3.0mm, the rolling speed of the intermediate pass can be controlled to be 350-550mpm, for example, specific values ​​such as 350mpm, 400mpm, 450mpm, 500mpm, 550mpm, and a range with any two of the above-mentioned specific values ​​as endpoints.

[0025] In the above-mentioned cold rolling method, when the cold-rolled raw material is an abnormal material and the target rolling thickness is above 3.0 mm, the rolling speed of the intermediate pass can be controlled to be 300-500 mpm, for example, specific values ​​such as 300 mpm, 350 mpm, 400 mpm, 450 mpm, 500 mpm, and a range with any two of the above-mentioned specific values ​​as endpoints.

[0026] In the above cold rolling method, when the cold rolling 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 seconds.

[0027] Furthermore, for the part between the head and tail of the abnormal material, when the rolling speed needs to be increased, the rolling speed is increased by 120-150m / min, maintained for more than 10s before continuing to increase the speed; when the rolling speed needs to be reduced, the rolling speed is reduced by 120-180m / min, maintained for more than 10s before continuing to reduce the speed. This step-by-step 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 that the raw materials with poor plate shape damage the working rolls and cause defects.

[0029] In the above cold rolling method, when the cold rolling raw material is a normal material, there is no special restriction on the rolling speed of the head and tail of the raw material; for the consideration of improving efficiency, the rolling speed can be adjusted to shorten the time, thereby increasing the production volume. In some specific embodiments, the rolling speed of 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 seconds. There is no special restriction on the rolling speed change method between the head and tail of the normal material, and the above-mentioned step speed change method can also be used.

[0030] In the above cold rolling method, when the cold rolling raw material is an abnormal material, the force of the side guide plate is optimized to control the double-sided force of the side guide plate in the first pass. When the cold rolling raw material is a normal material, there is no special restriction on the force of the side guide plate.

[0031] The cold rolling method provided by the present invention can be implemented in a twenty-roller Sendzimir rolling mill.

[0032] The beneficial effects of the present invention include:

[0033] 1. The cold rolling method provided by the present invention helps to eliminate the gray-white dot-shaped friction mark defects 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 the present invention can effectively improve the friction mark defects on the surface of the steel plate by changing the parameters and operating methods of the rolling process and setting the operating parameters according to the abnormal conditions of the raw materials, avoid waste of materials, processing fees, energy, etc., improve product quality, meet market demand, and generate higher economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a photo of the friction mark defect.

[0036] Figure 2aThe data shows the quantity and proportion of abnormal and normal materials in cold-rolled raw material plate shapes from the third quarter of 2020 to May 2021.

[0037] Figure 2b It is the incidence rate of friction mark defects for 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 occurrence rate of friction mark defects as the wedge value changes.

[0039] Figure 3a It is the proportion of wedge-shaped interval operations in the total operations from January to May 2021.

[0040] Figure 3b This is the correlation between the wedge value of cold-rolled raw materials and the occurrence of friction marks from January to May 2021.

[0041] Figure 4a This is the Off-Gauge over-thickness situation of cold-rolled raw materials from the third quarter of 2020 to May 2021.

[0042] Figure 4b This is a photo of the friction mark defects on the strip surface.

[0043] Figure 5 This is a correlation diagram between the service life of the first intermediate roll of the rolling mill and the occurrence of friction mark defects.

[0044] Figure 6 Schematic diagram of the step-by-step speed-up process in Example 1.

[0045] Figure 7 This is the result diagram of the friction mark defect incidence rate in Application Example 1. DETAILED DESCRIPTION

[0046] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0047] The present invention provides a cold rolling method for producing nickel-chromium austenitic stainless steel. The cold rolling method comprises the following steps: raw material uncoiling, cold rolling, cold annealing, annealing and pickling, and finishing, trimming or coiling. In the raw material uncoiling process, the uncoiling mode is controlled to be left coiling.

[0048] During the cold rolling process, the following controls are performed:

[0049] Control the service life of the first intermediate roller to 450-650 tons / time;

[0050] The roughness of the working roll in the second pass is controlled to be 0.6-0.8μm;

[0051] The type of control rolling mill thrust bearing is single bearing type.

[0052] Cold rolling is the process of rolling and deforming metal at the recrystallization temperature. It generally refers to the rolling process of steel strips at room temperature without heating. During the rolling process, the steel strips undergo different degrees of work hardening. When the work hardening exceeds a certain degree, the steel strips are too hard and brittle to continue rolling. Therefore, after a certain number of cold rolling passes, the steel strips are often subjected to softening heat treatment (recrystallization annealing, etc.) to restore the plasticity of the rolled piece and reduce the deformation resistance.

[0053] The existing cold-rolled stainless steel surface is prone to gray-white dot-shaped friction marks. After on-site confirmation of the surface of cold-rolled stainless steel plates, the inventors found that the gray-white dot-shaped friction marks have the following morphology and regularity:

[0054] (1) Morphology of friction mark defects:

[0055] Figure 1 a, b, and c in the figure are respectively the physical photo of the friction mark (used to show the state of the naked eye), the microscopic photo (used to show the microscopic state), and the microscopic photo (used to show the details of the defect). Figure 1 From a, it can be seen that the macroscopic manifestation of friction marks is point-like defects, which generally have no hand feeling. Figure 1 From b, we can see that the surface of the gray-white dot-shaped friction marks is obviously broken, which is consistent with the matrix composition; Figure 1 It can be seen from c that the friction mark defect surface has multiple morphologies and has been rolled multiple times.

[0056] To summarize the above research on the morphology, the surface defects of the friction marks appear as small point-shaped skin breaks, which cannot be eliminated by grinding in severe cases; there are obvious calendering marks in the microscopic morphology of the friction marks, and multiple pass calendering (traces of extension after multiple rolling passes).

[0057] (2) The relationship between the working roll service life and the occurrence of friction mark defects was studied, and the defect distribution and law were obtained as follows:

[0058] i) All occur on both sides of the entire length, with the upper and lower surfaces corresponding, and multiple occurrences on the edges, distributed in one or more straight lines;

[0059] ii) A small amount of position deviation (Off-Center) of defects on the same straight line can be used to distinguish and confirm the occurrence of defect cycles;

[0060] iii) According to the calculation of the reduction amount, the occurrence period corresponds to the diameter of the working roll of the rolling mill, which is presumed to be caused by the damage of the working roll.

[0061] According to research, the surface defects of stainless steel plates are friction mark defects, not roller mark defects.

[0062] According to the above-mentioned distribution and occurrence law of friction mark defects, the inventors confirmed that rolling deviation (Off-Center) is the key point of friction mark defects.

[0063] The prior art has the following disadvantages:

[0064] (1) Poor raw material shape (severe wedge shape, excessive thickness at the head and tail, etc.). This is due to the limited ability of the hot rolling furnace coil mill to control the plate shape, resulting in poor raw material shape. However, at present, cold rolling mills have no clear prevention mechanism for defects induced by poor raw material shape, and control is entirely based on experience.

[0065] (2) There is no protection mechanism when replacing the working rolls of the rolling mill, which causes defects after the working rolls are scratched.

[0066] (3) The shortcomings of the rolling mill equipment itself lead to its poor ability to prevent defects such as work roll damage.

[0067] Furthermore, the generation mechanism of gray-white dot-shaped friction mark defects is studied:

[0068] Figure 2a It is the number and proportion of abnormal and normal materials in the cold-rolled raw material plate shape from the third quarter of 2020 (3Q is the third quarter, 4Q is the fourth quarter, the same below) to May 2021. Abnormal materials refer to cold-rolled raw materials with an absolute value of wedge greater than 25 or cold-rolled raw materials with a head misalignment or tail misalignment of more than 10mm. Cold-rolled raw materials other than abnormal materials are normal materials. Figure 2a The left vertical axis in the middle is the friction mark occurrence rate, and the right vertical axis is the proportion of abnormal materials in all materials (normal materials + abnormal materials).

[0069] Figure 2b It is the friction mark defect incidence rate (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 raw materials to normal raw materials fluctuates slightly over time, but the incidence of friction mark defects in abnormal materials is significantly greater than that in normal materials.

[0071] Figure 2c for Figure 2a and Figure 2b Trend analysis chart of the friction mark defect incidence rate changing with the wedge value after data merging. Figure 2c [0,10], (10,20], (20,30], (30,+∞) are the absolute value intervals of the wedge value. Figure 2c It can be seen that there is a significant correlation between the absolute value range of the raw material wedge value and the occurrence rate of friction mark defects. The larger the absolute value of the raw material wedge value, the higher the occurrence rate of friction mark defects.

[0072] Figure 3a It shows the proportion of wedge-shaped interval workload in the total workload from January to May 2021. Figure 3b The figure shows the correlation between the wedge value of cold-rolled raw materials and the incidence of friction marks from January to May 2021. Figure 3a , Figure 3b It can also be seen that there is an obvious correlation between the raw material wedge value and the occurrence rate of friction marks. The larger the absolute value of the wedge value, the higher the occurrence rate of friction marks.

[0073] Based on the above research, the inventors found that the absolute value of the wedge value of the cold-rolled raw material has a significant correlation with the occurrence rate of friction mark defects, and the wedge value is the main influencing factor of the friction mark defect.

[0074] The inventors also conducted the following research on the generation mechanism of friction mark defects:

[0075] (1) Off-Gauge over-thickness refers to the over-thickness length of the head and tail, which can be used to characterize the adverse effects of the head / tail of the cold-rolled raw material. In the present invention, over-thickness refers to more than 5% of the raw material thickness. Head and tail over-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 is the off-gauge over-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 twenty-roll Sendzimir mill is both at the head / tail, poor head and tail conditions can also easily cause damage to the rolls, so the impact of the head and tail is confirmed. Figure 4a It can be seen that the Off-Gauge increases significantly with the increase of operation time, and the Off-Gauge increases significantly with the increase of operation time when it is greater than 20m.

[0077] Misalignment refers to the situation where the head and tail of the cold-rolled raw material are not aligned. The present invention has found that when the cold-rolled raw material has misalignment, the strip steel after cold rolling still has misalignment, the misalignment degree is reduced, but friction mark defects are generated. For example, the misalignment of the cold-rolled raw material is greater than 20mm, and the misalignment of the strip steel at the exit of the rolling mill after cold rolling is greater than 10mm. At this time, friction mark defects will occur on the surface of the strip steel, such as Figure 4b shown.

[0078] After research, the inventors found that excessive thickness at the head and tail of the raw material and misalignment are significantly correlated with the occurrence of friction mark defects, and are the main factors causing friction mark defects.

[0079] (2) Figure 5This is the correlation diagram between the use period of the first intermediate roll of the rolling mill and the occurrence of friction mark defects. Figure 5 It can be seen that the longer the service life of the first intermediate roll is, the higher the occurrence rate of friction mark defects. It can be seen that the longer the rolling volume of the first intermediate roll of the rolling mill is, the higher the occurrence rate of gray-white dot-shaped 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, the poor shape of cold-rolled raw materials, the absolute value of the wedge value, and the deviation induced by the excessive thickness of the head and tail are important factors leading to the occurrence of friction mark defects. In the prior art, the hot rolling project that provides raw materials for cold rolling uses a furnace coil mill, which is difficult to adjust the plate shape, resulting in a large difference in thickness on both sides (large Wedge, larger head and tail). In addition, the temperature of the head / tail during the rolling process of the furnace coil mill is lower than that in the middle (>100℃), resulting in excessive thickness of the head and tail and a worse plate shape than in the middle. Therefore, the occurrence of friction mark defects can be reduced or eliminated by improving the hot rolling process on the one hand; on the other hand, it can be achieved by improving the cold rolling process.

[0081] The cold rolling method for producing nickel-chromium austenitic stainless steel provided by the present invention can alleviate the problem of friction mark defects caused by axial force generated by the working roll due to poor cold-rolled plate shape deviation (large absolute value of wedge value, excessive thickness at the head and tail), and alleviate the damage of poor raw materials to the working roll of the cold rolling mill.

[0082] The cold rolling method for producing nickel-chromium austenitic stainless steel provided by the present invention comprises uncoiling, cold rolling, cold annealing, annealing and pickling, and finishing, trimming or coiling in sequence;

[0083] Among them, the service life of the first intermediate roll is controlled to be 450-650 ton / time; the roughness of the working roll of the second pass is controlled to be 0.6-0.8 μm; the type of the thrust bearing of the rolling mill is controlled to be a single bearing type; and the uncoiling mode is controlled to be left coiling.

[0084] According to a specific embodiment of the present invention, the cold rolling method can be carried out in a twenty-roll Sendzimir mill. The Sendzimir mill was invented by Dr. Sendzimir in 1933. At that time, it was mainly used to produce low-carbon strip steel with a width of 800 mm and a thickness of 0.13 mm. At present, more than 90% of cold-rolled stainless steel strips are produced by the Sendzimir mill. The mill has the following main characteristics in terms of structural performance: (a) It has an integrally cast (or forged) frame with high rigidity, and the rolling force acts radially on each section of the frame. (b) The working roll diameter is small and the pass reduction rate is large, up to 60%. Some materials can be rolled into very thin strips without intermediate annealing. (c) It has axial and radial roll shape adjustment, roll diameter size compensation, rolling line adjustment and other mechanisms, and adopts hydraulic reduction and AGC system, so the product plate shape is good and the dimensional accuracy is high. (d) The equipment is light in weight, and the mass of the rolling mill is only one-third of that of a four-roll mill of the same specification. The rolling mill has small overall dimensions and requires less infrastructure investment.

[0085] The roll system of the twenty-roll Sendzimir rolling mill applicable to the present invention is arranged in a tower shape according to 1-2-3-4, and is symmetrically arranged in 8 plum blossom holes of the frame. The roll system of the rolling mill is distributed from the inside to the outside as follows: the upper and lower working rolls are respectively supported on the two first intermediate rolls; the upper and lower pairs of first intermediate rolls are supported on the three second intermediate rolls; and the six second intermediate rolls are supported on the eight support roll groups fixed in the plum blossom holes on the outer layer.

[0086] According to a specific embodiment of the present invention, by increasing the roughness of the second pass working roll, the deviation of the steel strip can be slowed down and the friction mark defect can be avoided. In the existing method, the roughness Ra of the working roll is generally 0.5-0.6μm. In the present invention, the roughness Ra of the second pass working roll is increased to 0.6-0.8μm; the roughness of the working rolls of other passes except the second pass can be controlled to 0.5-0.6μm.

[0087] According to a specific embodiment of the present invention, when replacing the working roll, a pad can be used as a working roll protection plate to prevent the working roll from being scratched, thereby avoiding scratches on the surface of the strip steel and causing friction mark defects.

[0088] In the above-mentioned cold rolling method, increasing the roughness of the work rolls and using backing plates when replacing the work rolls can prevent the friction mark defect by preventing the mill work rolls from scratching.

[0089] According to the research of the present invention, the use of the first intermediate roller for too long will cause friction mark defects. Specifically, the first intermediate roller has a taper. If the first intermediate roller is used for a long time, the taper of the first intermediate roller will wear out, and the plate shape cannot be accurately controlled, resulting in the strip deviation and friction mark defects. In addition, the longer the first intermediate roller is used, the longer the strip shape is, and the poor plate shape damages the working roller and causes friction mark defects. The above method provided by the present invention adjusts the use cycle of the first intermediate roller, which can avoid the first intermediate roller from inducing strip deviation due to taper wear, thereby avoiding the occurrence of friction mark defects. In some specific embodiments, the use cycle of the first intermediate roller can be controlled to 450 tons / time-650 tons / time.

[0090] According to a specific embodiment of the present invention, the service life of the first intermediate roller can be adjusted accordingly 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 roller can be 450-550 tons / time; when the cold-rolled raw material is 4 feet wide, the service life of the intermediate roller can be 550-650 tons / time. Compared with the method in which the service life of the first intermediate roller is usually 600 tons / time for the cold-rolled raw material with a width of 1 meter, and the service life of the first intermediate roller is 700 tons / time for the cold-rolled raw material with a width of 4 feet, the above method provided by the present invention can reduce the service life of the first intermediate roller, reduce the damage to the working roller caused by the plate shape difference, and thus avoid friction mark defects.

[0091] According to a specific embodiment of the present invention, the method may further include optimizing the side guide plates to avoid scratching the working rolls, thereby facilitating smooth rolling of the steel plates.

[0092] Specifically, the side guide optimization method includes: (1) changing the side guide plate of the first pass from being subjected to single-sided force to being subjected to double-sided force. By improving the side guide force, both sides can be subjected to force at the same time to prevent deviation caused by defective materials; (2) optimizing the side guide alignment to unify the side guide position sensors.

[0093] According to a specific embodiment of the present invention, the method may further include changing the type of the rolling mill thrust bearing, by changing the double-layer bearing type to a single bearing type, to prevent the working roll from being damaged after the bearing is damaged. The single bearing used in the present invention is conducive to the stability of the working roll and can avoid friction marks caused by uneven force.

[0094] According to a specific embodiment of the present invention, the method may further include controlling the unwinding mode to be left-winding. The left-winding mode can reduce the running length of the strip, ensure the tension stability, and prevent deviation. By changing the unwinding mode, it is beneficial to place the thicker side of the raw material on the driving side, thereby slowing down the deviation of the raw material.

[0095] According to a specific embodiment of the present invention, the method may further include increasing manual plate shape control intervention and manually adjusting the head and tail plate shape improper positions.

[0096] According to a specific embodiment of the present invention, the above method may also include adjusting the AFC flatness control target of the rolling mill. The existing method does not perform special control in this regard, while the present invention can adjust the flatness control target by controlling the pressure (I-unit) of the contact surface between the strip and the flatness roller, which is conducive to good adjustment of the flatness trend and avoids the flatness difference (edge ​​waves, middle waves, etc.) seriously damaging the working roll and causing friction mark defects. Specifically, the pressure of the edge of the strip (the part within 10 cm from the edge, and the rest is the middle part) and the contact surface of the flatness roller can be controlled to -15N / mm 2 To -5N / mm 2 To reduce the edge waves; the pressure of the middle of the strip and the contact surface of the plate roller is controlled to 5N / mm 2 Up to 15N / mm 2 , to reduce mid-waves.

[0097] According to a specific embodiment of the present invention, the head and tail of the cold-rolled raw material can be strengthened by slow operation. By increasing the slow speed time of the head and tail, the occurrence of friction marks caused by the working rolls when the defective parts of the head and tail raw materials pass through can be slowed down.

[0098] According to a specific implementation plan of the present invention, the above method may also include formulating corresponding operating standards according to the material type (abnormal material, normal material). By controlling the maximum speed, increasing the plate shape control time, refining the operation, and formulating abnormal material operation benchmarks, the damage to the working rolls can be minimized.

[0099] According to a specific embodiment of the present invention, the above method may specifically include formulating the following abnormal material operation benchmarks for raw material rolls with bad plate shapes:

[0100] In the above cold rolling method, when the raw material is abnormal (|wedge value|≥25, poor plate shape, or head and tail and / or tail misalignment>10m, etc.), the rolling speed of the first pass can be controlled to 120-180mpm.

[0101] In the above cold rolling method, when the raw material is an abnormal material, the rolling speed of the intermediate pass can be controlled according to the raw material thickness, specifically: for abnormal materials with a rolling target thickness of ≤1.0mm, the rolling speed of the intermediate pass can be controlled to 400-600mpm; for abnormal materials with a rolling target thickness of greater than 1.0mm and less than 3.0mm, the rolling speed of the intermediate pass can be controlled to 350-550mpm; for abnormal materials with a rolling target thickness of ≥3.0mm, the rolling speed of the intermediate pass can be controlled to 300-500mpm. The total number of cold rolling passes can be selected according to the thickness of the material and the rolling target thickness, generally 5-9 passes.

[0102] In the above cold rolling method, when the raw material is an abnormal material, the head and tail can be operated at a slow speed. Specifically, the rolling speed of the head and tail 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 seconds.

[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 double-sided force to avoid single-sided force.

[0104] The above method can also formulate operating standards for normal materials. The 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 a normal material, the rolling speed of the intermediate pass is not particularly limited.

[0107] In the above cold rolling method, when the raw material is a normal material, there is no special restriction on the rolling speed of the head and tail. In some specific embodiments, the rolling speed of 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 seconds. On this basis, 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 the working rolls from being damaged due to excessive speed increase by changing the speed increase mode of each pass during rolling of the rolling mill.

[0109] In the existing method, each time the rolling mill speeds up, the working rolls are subjected to a large force during the rapid speed increase (only once), which can easily cause damage to the working rolls. When the damaged working rolls roll steel plates, periodic friction marks will be generated. Figure 6As shown, the present invention adjusts the speed-up mode of each pass from rapid speed-up to step speed-up (speed is a step-like slow increase), which can reduce the situation where the working roll is subjected to a large instantaneous force and avoid damage to the working roll during the speed-up process. In some specific embodiments, the specific process of step speed-up can be: at the head of the strip (within a length range of less than or equal to 100m from the head 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. Within a length range of more than 100m from the head end of the material, the rolling speed is increased by 120-150m / min, maintained at the speed for more than 10s and then continued to increase the speed, and maintained at a constant speed after reaching the maximum speed; within a length range of more than 100m from the tail end of the material, the rolling speed is reduced by 120-180m / min, maintained at the speed for more than 10s and then continued to decelerate. Within a length range of less than or equal to 100m from the tail 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 step-by-step speed increase method is usually adopted to reduce the occurrence of defects; for normal materials, the above-mentioned step-by-step speed increase method can be optionally adopted.

[0110] In the above cold rolling method, the nickel-chromium series 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 twenty-roll Sendzimir mill. The roll system of the twenty-roll Sendzimir mill is arranged in a tower shape according to 1-2-3-4, and is symmetrically arranged in 8 plum blossom holes of the frame. The roll system of the mill is distributed from the inside to the outside as follows: the upper and lower working rolls are respectively supported on the two first intermediate rolls; the upper and lower pairs of first intermediate rolls are supported on the three second intermediate rolls; and the six second intermediate rolls are supported on the eight support roll groups fixed in the plum blossom holes on the outer layer.

[0113] The cold rolling method includes the following steps: uncoiling the raw material, cold rolling, cold annealing, annealing and pickling, and finishing, trimming or coiling.

[0114] Among them, during the unwinding process, the unwinding mode is controlled to be left-winding;

[0115] During the rolling process, the following controls are performed:

[0116] (1) The roughness Ra of the working roll in the second pass is 0.6-0.8 μm, and the roughness Ra of the working roll in other passes is 0.5-0.6 μm; when replacing the working roll, use the pad as the working roll protection plate to prevent the working roll from being scratched and causing friction marks;

[0117] (2) Control the use cycle of the first intermediate roll during the entire rolling process, specifically:

[0118] For a material with a width of 1 meter, the service life of the first intermediate roller is 500 tons / time;

[0119] For a 4-foot-wide material, the first intermediate roller has a service life of 600 tons / time;

[0120] (3) For abnormal materials, optimize the side guide and control the side guide plate of the first pass to bear force on both sides; optimize the side guide centering and unify the side guide position sensors;

[0121] (4) The thrust bearing of the control rolling mill is a single bearing;

[0122] (5) Perform plate shape control, including:

[0123] Strengthen the slow operation of the head and tail, and increase the slow time of the head and tail;

[0124] The manual plate shape control intervention is increased, and the head and tail plate shape positions with bad shapes are adjusted manually;

[0125] Adjust the AFC profile control target of the rolling mill to control the pressure of the contact surface between the strip and the profile roller; specifically, control the pressure of the contact surface between the edge of the strip and the profile roller to -10N / mm 2 , the pressure between the middle of the strip and the contact surface of the plate roller is controlled to 10N / mm 2 ;

[0126] (6) For normal materials and abnormal materials, the rolling speed and the side guide plate force are controlled respectively:

[0127] For abnormal materials, the rolling speed of the first pass is 150 mpm; for abnormal materials with rolling target thickness ≤ 1.0 mm, the rolling speed of the intermediate pass is 500 mpm; for abnormal materials with rolling target thickness greater than 1.0 mm and less than 3.0 mm, the rolling speed of the intermediate pass is 450 mpm; for abnormal materials with rolling target thickness ≥ 3.0 mm, the rolling speed of the intermediate pass is 400 mpm;

[0128] Slow speed control of abnormal materials at the head and tail, control speed is less than or equal to 50mpm, and the running time is greater than or equal to 60s;

[0129] For abnormal materials, control the force on both sides of the side guide plate in the first pass to avoid unilateral force;

[0130] For normal materials, there is no special restriction on the rolling speed of each pass;

[0131] There is no special restriction 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 seconds;

[0132] For normal materials, there are no special restrictions on the stress conditions of the side guides.

[0133] (7) For abnormal materials, the speed increase of the rolling mill is controlled to be a step-by-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 mpm and the rolling time is greater than or equal to 60 seconds; 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 seconds before continuing to increase the speed, and the speed is maintained at a constant level after reaching the maximum 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 seconds before continuing to reduce the speed until it is reduced to the rolling speed required at the tail.

[0134] Application Example 1

[0135] The cold rolling method for producing nickel-chromium austenitic stainless steel of the present invention is applied to the cold rolling production of 304 stainless steel and 316 stainless steel, and the production method in each time period is as follows:

[0136] The cold rolling process from 2019 to 2021 is:

[0137] For a cold-rolled material with a width of 1 meter, the service life of the first intermediate roller is 600 tons / time; for a cold-rolled material with a width of 4 feet, the service life of the first intermediate roller is 700 tons / time;

[0138] The roughness Ra of the working roll in the second pass is 0.5-0.6μm;

[0139] When the working roll is replaced, the work roll scratches cannot be avoided without using the pad;

[0140] The side guide is subjected to unilateral force, and the side guide alignment optimization is not performed;

[0141] The thrust bearing type of the rolling mill is a double-layer bearing type;

[0142] The unwinding method adopts an unwinding machine;

[0143] No special control is performed on the AFC plate shape control of the rolling mill;

[0144] When the rolling mill is rolling, the speed increase mode of each pass is rapid speed increase, with only one speed increase and one speed reduction (refer to Figure 6 The “sharp increase” in

[0145] The cold rolling process after 2022 is carried out according to the cold rolling process of Example 1.

[0146] like Figure 7 As shown, the incidence rate of gray-white dot-shaped friction marks ( Figure 7The gray-white dot-shaped friction mark degradation rate in the process has decreased significantly year by year. The gray-white dot-shaped friction mark occurrence rate was 0.58% before the process improvement. After the improvement, the gray-white dot-shaped friction mark occurrence rate continued to decrease and can be stabilized at about 0.02%, and the lowest can reach 0.01%. The gray-white dot-shaped friction mark defect has been significantly improved. The above results show that the cold rolling method provided by the present invention can effectively prevent the occurrence of gray-white dot-shaped 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 uncoiling, cold rolling, cold annealing, annealing and pickling, finishing, trimming or coiling in sequence; in, In the cold rolling process, the use cycle of the first intermediate roll is controlled to be 450 tons / time-650 tons / time; The roughness of the working roll in the second pass is controlled to be 0.6μm-0.8μm; The type of control rolling mill thrust bearing is single bearing type.

2. The cold rolling method according to claim 1, wherein: During the unwinding process of the raw material, the unwinding mode is controlled to be left-winding.

3. The cold rolling method according to claim 1, wherein: For a cold-rolled material with a width of 1 meter, the service life of the first intermediate roller is 450-550 tons / time; For a material with a width of 4 feet, the service life of the first intermediate roller is 550-650 tons / time.

4. The cold rolling method according to claim 1, wherein: When the absolute value of the wedge value of the cold-rolled raw material is ≥25, or the misalignment of the head is more than 10mm, or the misalignment of the tail is more than 10mm, the cold-rolled raw material is an abnormal material; cold-rolled raw materials other than abnormal materials are normal materials.

5. The cold rolling method according to claim 4, wherein: When the cold-rolled raw material is an abnormal material, the rolling speed of the first pass is controlled to be 120-180 mpm; when the cold-rolled raw material is a normal material, the rolling speed of the first pass is controlled to be 170-230 mpm.

6. The cold rolling method according to claim 4, wherein: When the cold-rolled raw material is an abnormal material, the speed of the intermediate pass working roll is controlled to 300-600mpm.

7. The cold rolling method according to claim 4, wherein: When the cold-rolled raw material is an abnormal material and the rolling target thickness is less than 1.0 mm, the rolling speed of the intermediate pass is controlled to be 400-600 mpm; When the cold-rolled raw material is an abnormal material and the rolling target thickness is 1.0-3.0 mm, the rolling speed of the intermediate pass is controlled to be 350-550 mpm; When the cold-rolled raw material is an abnormal material and the rolling target thickness is above 3.0 mm, the rolling speed of the intermediate pass is controlled to be 300-500 mpm.

8. The cold rolling method according to claim 4, wherein: 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 seconds; Preferably, for the part between the head and tail of the abnormal material, when it is necessary to increase the rolling speed, the rolling speed is increased by 120-150m / min, and the speed is maintained for more than 10s before continuing to increase the speed; when it is necessary to reduce the rolling speed, the rolling speed is reduced by 120-180m / min, and the speed is maintained for more than 10s before continuing to reduce the speed.

9. The cold rolling method according to claim 4, wherein: When the cold-rolled raw material is an abnormal material, the double-sided force of the side guide plate is controlled.

10. The cold rolling method according to claim 1, wherein: The nickel-chromium series austenitic stainless steel includes 304 stainless steel and / or 316 stainless steel.

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