Method for improving surface quality of cold-rolled high-strength steel based on cover annealing and leveling process

Abstract

The invention discloses a method for improving the surface quality of cold-rolled high-strength steel based on a cover annealing and leveling process, and belongs to the technical field of cold-rolled steel. According to the method, the existing bell-type annealing furnace and a finishing machine are utilized, and on the premise that equipment investment is not increased, dynamic hydrogen flow control and dynamic hydrogen purging time control in the bell-type annealing process are established, and steel coil tapping temperature control and final cooling table placement time control which dynamically change along with changes of environment temperature and humidity are established; and the convexity and roughness of the leveling working roll, the leveling speed and the leveling elongation are controlled, so that the surface quality of the cover annealing product is improved while the performance of the cover annealing product is stably controlled, and the cover annealing unit is ensured to operate stably and the product quality meets the requirements of the market and users.

Description

Technical Field

[0001] The invention belongs to the technical field of cold-rolled steel, and in particular relates to a method for improving the surface quality of cold-rolled high-strength steel based on a hood annealing and leveling process. Background Art

[0002] At present, major steel enterprises generally use continuous annealing furnaces to produce cold-rolled high-strength steel and mild steel products. However, for some special steels or enterprises that do not have continuous annealing furnaces to produce high-strength steel and mild steel products, hood annealing furnaces must be used to perform post-rolling heat treatment on cold-rolled strip. Hood annealing furnaces are better than continuous annealing in producing special performance steel plates, especially for high-strength steel and mild steel products, hood annealing has better performance control capabilities. However, for high-surface-level products, due to the limitations of hood annealing and subsequent leveling unit equipment and processes, the physical quality of its products is lower than that of products produced by continuous annealing units. Therefore, for some products with special performance requirements, or enterprises that do not have continuous annealing production lines, it is impossible to switch to continuous annealing production. However, since such products are generally used as panels for automobiles or home appliances, they will be stamped, painted, and other processes during subsequent user use. Therefore, the requirements for product surface quality are gradually increasing, especially for surface roughness uniformity, surface color difference, surface dark prints and other defects. The requirements are becoming more and more stringent. Therefore, special performance requirements and higher-level surface requirements have become the main contradictions and technical bottlenecks restricting the stable production of hood annealing products.

[0003] The Chinese invention patent application number 201410104188.4 discloses a low-cost manufacturing method for 700MPa grade cold-rolled high-strength steel and thin steel strip based on hood annealing treatment. The chemical composition and weight percentage of the cold-rolled high-strength steel are: C: 0.15-0.20; Si: 0.20-0.50; Mn: 0.7-1.2; P≤0.023; S≤0.015; V: 0.05-0.10; N: ≤0.015; O: ≤0.004; The rest is iron Fe and unavoidable impurities; the manufacturing method comprises hot rolling, primary cold rolling, hood annealing and secondary cold rolling, and the steps are as follows: (1) the hot rolling process conditions are as follows: the continuous casting billet thickness is 175 mm, the heating temperature in the heating furnace is 1150-1280°C, and the heating time is 100-160 minutes; the rough rolling process is carried out for 5 passes, the intermediate billet thickness is 28-32 mm, the hot rolling final rolling temperature is 890-930°C, the laminar cooling is performed, the cooling rate is 5-20°C / s, and the coiling temperature is 5 70℃~630℃; the thickness of the hot-rolled finished product is ≤4mm; (2) cold rolling: the hot-rolled finished product is pickled to remove the surface iron oxide scale and re-rolled; then cold rolling is carried out on a reversible cold rolling mill, rolling is carried out in 8 to 12 passes, and a rolling process is completed, with a total reduction rate of 75% to 92%; (3) hood annealing, the process conditions are as follows: the cold-rolled finished product is hood annealed, the annealing temperature is 630 to 730℃, the holding time is controlled in the range of 10-16h, and then slow cooling is carried out; V(C,N ) The particle size of the precipitated phase is 5-30nm, and the crystal grain part grows appropriately, so that the grain size is 6-10μm, and fine grain strengthening is achieved; the tensile strength of the steel strip after annealing is not less than 650MPa, and the elongation is not less than 20%; (4) The secondary cold rolling process is to carry out secondary cold rolling of the annealed steel strip on a reversible cold rolling mill, 1-2 times; the reduction rate is 5%-15%, and the strength of the annealed steel is increased to 700MPa level through dislocation strengthening and substructure strengthening, and the elongation is not less than 8%. The main design content of this patent is basically a method for controlling the metal microstructure and performance of the metal during the process from hot rolling to primary cold rolling, hood annealing, and secondary cold rolling. Its purpose is to ensure that the mechanical properties of the finished product meet the requirements of more than 700Mpa, but it lacks a technical solution for high-level quality control of the finished product surface during hood annealing.The Chinese invention patent with application number 201710957654.7 discloses a method and device for manufacturing cold-rolled high-strength steel, the method comprising: heating a steel strip, controlling the heating furnace temperature to be 1180-1200°C, and controlling the heating time to be 180-200min; performing rough rolling on the heated steel strip, controlling the rough rolling temperature to be 980-1000°C; performing finish rolling on the steel strip after rough rolling, controlling the finish rolling final rolling temperature to be 860-880°C; performing laminar cooling on the steel strip after finish rolling, during the laminar cooling process, controlling the cooling manifold in the main cooling area to be in an open state, and controlling the cooling manifold in the feedback area to be in a closed state; in this way, during the laminar cooling process, controlling the cooling manifold in the main cooling area to be in an open state, and controlling the cooling manifold in the feedback area to be in a closed state, can avoid abnormal feedback adjustment caused by temperature fluctuations, thereby improving the control accuracy of the strip coiling temperature, avoiding drastic fluctuations in the coiling temperature, and ensuring the stability of cold rolling in subsequent processes. The patent mainly involves the adjustment and control of the controlled rolling and cooling of high-strength steel products in the hot rolling process, but does not involve the technical solution for controlling the surface quality of high-level products in the cold rolling process, especially in the annealing and leveling processes. In order to ensure the stable production of high-level surface quality cold-rolled high-strength steel using the existing hood annealing + single-frame leveling unit, it is urgently needed to conduct in-depth research on the key processes and parameters in the process of producing high-level surface quality cold-rolled high-strength steel using the hood annealing + single-frame leveling unit. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a method for improving the surface quality of cold-rolled high-strength steel based on hood annealing and skin-passing process. The present invention utilizes the existing hood annealing furnace and skin-passing machine. Under the premise of not increasing the equipment investment, by optimizing the annealing process, optimizing the skin-passing process, optimizing the skin-passing roller requirements, etc., the performance of the hood annealing product is stably controlled while improving the surface quality of the hood annealing product, thereby ensuring that the hood annealing unit operates stably and the product quality meets the requirements of the market and users.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for improving the surface quality of cold-rolled high-strength steel based on a hood annealing and flattening process, comprising the following steps:

[0007] (1) Establish dynamic hydrogen flow control and dynamic hydrogen purge time control that change with the annealing heating temperature during the hood annealing process to ensure that the cleaning and reduction effects of hydrogen on the steel plate surface are fully exerted, while avoiding decarburization color difference defects caused by excessive reaction of hydrogen with carbon elements in the steel plate during the high temperature stage;

[0008] (2) Establish a temperature control system for steel coils that changes dynamically with the ambient temperature and humidity to avoid oxidation color defects caused by excessive differences between the temperature and humidity of the steel coils and the ambient temperature when they are out of the furnace; in order to avoid secondary oxidation of the steel coils in the storage area after they are out of the furnace due to the influence of the temperature of the surrounding steel coils, control the placement time of the steel coils in the final cooling station after they are out of the furnace;

[0009] (3) To avoid the defects of strangulation and rolling caused by the mismatch of the convexity of the flat work roll, the convexity of the flat work roll is controlled; to avoid the defects of scratches and rolling caused by the mismatch of the roughness of the flat work roll, the roughness of the flat work roll is controlled;

[0010] (4) To avoid defects such as leveling liquid residue and color difference caused by mismatching leveling speed, the leveling speed is controlled; to avoid leveling scratches, ripples and other defects caused by mismatching leveling elongation, the leveling elongation is controlled.

[0011] Based on the above technical solution, further, the cold-rolled high-strength steel includes BH440, 45# steel, and strip steel with a tensile strength of more than 800 MPa.

[0012] Based on the above technical solution, further, the charging capacity of the bell annealing is 10 to 200 tons.

[0013] Based on the above technical solution, further, the dynamic hydrogen flow control and dynamic hydrogen purge time control described in step (1) are as follows: when the annealing heating temperature is 30°C≤300°C, 12m 3 / h≤Hydrogen flow rate<15m 3 / h, 5h≤Hydrogen purge time<7h; 300℃≤Annealing heating temperature<450℃, 10m 3 / h≤Hydrogen flow rate<12m 3 / h, 3h≤Hydrogen purge time<5h; 450℃≤Annealing heating temperature<600℃, 8m 3 / h≤Hydrogen flow rate<10m 3 / h, 2h≤Hydrogen purge time<3h; 600℃≤Annealing heating temperature≤820℃, 5m 3 / h≤Hydrogen flow rate<6m 3 / h, 1h≤hydrogen purge time<2h.

[0014] Based on the above technical solution, further, the temperature of the steel coil out of the furnace described in step (2) is controlled as follows: when 5°C≤ambient temperature<15°C and 10%≤ambient humidity<40%, 30°C≤steel coil out of the furnace temperature<50°C and 8s≤steel coil final cooling table placement time<20s; when 15°C≤ambient temperature<25°C and 15%≤ambient humidity<45%, 35°C≤steel coil out of the furnace temperature<55°C and 12s≤steel coil final cooling table placement time<24s; when 25°C≤ambient temperature<45°C and 25%≤ambient humidity<60%, 40°C≤steel coil out of the furnace temperature<60°C and 20s≤steel coil final cooling table placement time<40s; when 45°C≤ambient temperature<60°C and 30%≤ambient humidity<70%, 55°C≤steel coil out of the furnace temperature<85°C and 40s≤steel coil final cooling table placement time<60s.

[0015] Based on the above technical solution, further, in step (2), when 5°C≤ambient temperature<15°C, 10%≤ambient humidity<25%, 40°C≤steel coil out-of-furnace temperature<50°C, 8s≤steel coil final cooling table placement time<12s; when 5°C≤ambient temperature<15°C, 25%≤ambient humidity<40%, 30°C≤steel coil out-of-furnace temperature<40°C, 12s≤steel coil final cooling table placement time<20s; when 15°C≤ambient temperature<25°C, 15%≤ambient humidity<30%, 45°C≤steel coil out-of-furnace temperature<55°C, 12s≤steel coil final cooling table placement time<18s; when 15°C≤ambient temperature<25°C, 30%≤ambient humidity<45%, 35°C≤steel coil out-of-furnace temperature<45°C, 18s≤steel coil final cooling table placement time Placement time <24s; ​​25℃≤ambient temperature <45℃, 25%≤ambient humidity <40%, 50℃≤steel coil out-of-furnace temperature <60℃, 20s≤steel coil final cooling table placement time <30s; 25℃≤ambient temperature <45℃, 40%≤ambient humidity <60%, 40℃≤steel coil out-of-furnace temperature <50℃, 30s≤steel coil final cooling table placement time <40s; 45℃≤ambient temperature <60℃, 30%≤ambient humidity <50%, 55℃≤steel coil out-of-furnace temperature <70℃, 40s≤steel coil final cooling table placement time <50s; 45℃≤ambient temperature <60℃, 50%≤ambient humidity <70%, 70℃≤steel coil out-of-furnace temperature <85℃, 50s≤steel coil final cooling table placement time <60s.

[0016] Based on the above technical solution, further, the requirements for the crown and roughness of the smooth working roll in step (3) are as follows: when the tensile strength is 340MPa≤<590MPa and the strip thickness is 0.6mm≤<2.5mm, the crown value of the smooth working roll is 0.4~0.8mm, and the roughness of the working roll is 2.00~5.00μm; when the tensile strength is 590MPa≤<780MPa and the strip thickness is 0.6mm≤<2.5mm, the crown value of the smooth working roll is 0.4~0.8mm, and the roughness of the working roll is 2~6μm; when the tensile strength is 780MPa≤<1180MPa and the strip thickness is 0.6mm≤<2.5mm, the crown value of the smooth working roll is 0.4~0.8mm, and the roughness of the working roll is 2~6μm.

[0017] Based on the above technical solution, further, the requirements for the crown and roughness of the leveling work roll in step (3) are as follows: when the tensile strength is 340MPa≤<590MPa and the strip thickness is 0.6mm≤<0.9mm, the crown value of the leveling work roll is 0.70~0.8mm and the roughness of the work roll is 4.00~5.00μm; when the tensile strength is 340MPa≤<590MPa and the strip thickness is 0.9mm≤<1.2mm, the crown value of the leveling work roll is 0.60~0.69 mm, working roll roughness 3.00~3.99μm; 340MPa≤ tensile strength<590MPa, 1.2mm≤ strip thickness<1.8mm, flat working roll crown value 0.50~0.59mm, working roll roughness 2.50~2.99μm; 340MPa≤ tensile strength<590MPa, 1.8mm≤ strip thickness<2.5mm, flat working roll crown value 0.35~0.49mm, working roll roughness 2.00~2.49μm;

[0018] When the tensile strength is 590MPa≤<780MPa, the strip thickness is 0.6mm≤<0.9mm, the crown value of the flat work roll is 0.60~0.65mm, and the roughness of the work roll is 4.50~5.50μm; when the tensile strength is 590MPa≤<780MPa, the strip thickness is 0.9mm≤<1.2mm, the crown value of the flat work roll is 0.50~0.59mm, and the roughness of the work roll is 3.50~4.49μm; When the tensile strength is 590MPa≤<780MPa, the strip thickness is 1.2mm≤<1.8mm, the crown value of the flat work roll is 0.40~0.49mm, and the roughness of the work roll is 2.60~3.49μm; when the tensile strength is 590MPa≤<780MPa, the strip thickness is 1.8mm≤<2.5mm, the crown value of the flat work roll is 0.30~0.39mm, and the roughness of the work roll is 2.00~2.59μm;

[0019] When the tensile strength is 780MPa≤<1180MPa, the strip thickness is 0.6mm≤<0.9mm, the crown value of the flat work roll is 0.40~0.59mm, and the roughness of the work roll is 3.50~4.50μm; when the tensile strength is 780MPa≤<1180MPa, the strip thickness is 0.9mm≤<1.2mm, the crown value of the flat work roll is 0.30~0.39mm, and the roughness of the work roll is 2.50~3.49μm; When the tensile strength is 780MPa≤<1180MPa, the strip thickness is 1.2mm≤<1.8mm, the crown value of the smooth working roll is 0.20~0.29mm, and the roughness of the working roll is 2.00~2.49μm; when the tensile strength is 780MPa≤<1180MPa, the strip thickness is 1.8mm≤<2.5mm, the crown value of the smooth working roll is 0.05~0.19mm, and the roughness of the working roll is 1.50~1.99μm.

[0020] Based on the above technical scheme, further, the leveling speed and leveling elongation in step (4) are controlled as follows: when the tensile strength is 340MPa≤<590MPa and the strip thickness is 0.6mm≤<2.5mm, the leveling speed is 700~1150m / min and the leveling elongation is 0.3~1.5%; when the tensile strength is 590MPa≤<780MPa and the strip thickness is 0.6mm≤<2.5mm, the leveling speed is 550~1000m / min and the leveling elongation is 0.2~1.2%; when the tensile strength is 780MPa≤<1180MPa and the strip thickness is 0.6mm≤<2.5mm, the leveling speed is 500~900m / min and the leveling elongation is 0.2~1.1%.

[0021] Based on the above technical solution, further, the leveling speed and leveling elongation in step (4) are controlled as follows: when the tensile strength is 340MPa≤<590MPa and the strip thickness is 0.6mm≤<0.9mm, the leveling speed is 950~1150m / min and the leveling elongation is 0.3~0.5%; when the tensile strength is 340MPa≤<590MPa and the strip thickness is 0.9mm≤<1.2mm, the leveling speed is 880~949m / min. min, flattening elongation 0.5~0.8%; 340MPa≤ tensile strength<590MPa, 1.2mm≤ strip thickness<1.8mm, flattening speed 800~879m / min, flattening elongation 0.8~1.2%; 340MPa≤ tensile strength<590MPa, 1.8mm≤ strip thickness<2.5mm, flattening speed 700~799m / min, flattening elongation 1.2~1.5%;

[0022] When the tensile strength is 590MPa≤<780MPa, the strip thickness is 0.6mm≤<0.9mm, the leveling speed is 850~1000m / min, and the leveling elongation is 0.2~0.4%; when the tensile strength is 590MPa≤<780MPa, the strip thickness is 0.9mm≤<1.2mm, the leveling speed is 750~849m / min, and the leveling elongation is 0.4~0.6%; when the tensile strength is 590MPa≤<780MPa, the strip thickness is 1.2mm≤<1.8mm, the leveling speed is 650~749m / min, and the leveling elongation is 0.6~0.8%; when the tensile strength is 590MPa≤<780MPa, the strip thickness is 1.8mm≤<2.5mm, the leveling speed is 550~649m / min, and the leveling elongation is 0.8~1.2%;

[0023] When the tensile strength is 780MPa≤<1180MPa and the strip thickness is 0.6mm≤<0.9mm, the leveling speed is 800~900m / min and the leveling elongation is 0.2~0.3%; when the tensile strength is 780MPa≤<1180MPa and the strip thickness is 0.9mm≤<1.2mm, the leveling speed is 700~799m / min and the leveling elongation is 0.3~0.5%; when the tensile strength is 780MPa≤<1180MPa and the strip thickness is 1.2mm≤<1.8mm, the leveling speed is 600~699m / min and the leveling elongation is 0.5~0.8%; when the tensile strength is 780MPa≤<1180MPa and the strip thickness is 1.8mm≤<2.5mm, the leveling speed is 500~599m / min and the leveling elongation is 0.8~1.1%.

[0024] The beneficial effects of the present invention compared with the prior art are as follows:

[0025] The comprehensive scrap rate of defects caused by oxidation, color difference, flat roller mark, scratches, etc. before the implementation of the method of improving the surface quality of cold-rolled high-strength steel based on hood annealing and flattening process of the present invention is 2.35%, and the comprehensive scrap rate after implementation is 1.12%. The annual output of high-strength steel products with high surface level is 400,000 tons, and the price difference between genuine products and scrap products is 2,630 yuan / ton. The benefit calculation is: 400,000 tons*(2.35%-1.12%)*2630=12.94 million yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0027] Figure 1 This is the decarburization color difference defect image of the cold-rolled high-strength steel surface in Comparative Example 1.

[0028] Figure 2This is a picture of scratches and roller marks on the surface of the cold-rolled high-strength steel in Comparative Example 1.

[0029] Figure 3 This is a diagram of the imprint and rolling defects on the surface of the cold-rolled high-strength steel in Comparative Example 1.

[0030] Figure 4 This is a picture of the flat scratches and corrugated defects on the surface of the cold-rolled high-strength steel in Comparative Example 1.

[0031] Figure 5 This is a surface image of the cold-rolled high-strength steel in Example 1. DETAILED DESCRIPTION

[0032] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0033] Example 1

[0034] This embodiment provides a method for improving the surface quality of cold-rolled high-strength steel based on bell annealing and leveling process. The cold-rolled high-strength steel is BH440, and the furnace loading is 70-100t. The specific process is as follows:

[0035] (1) Optimizing the hood annealing process to improve the surface quality of cold-rolled high-strength steel:

[0036] 1) Hydrogen blowing process: establish dynamic hydrogen flow control and dynamic hydrogen purge time control that change with the annealing heating temperature during the annealing process to ensure that the cleaning and reduction effect of hydrogen on the steel plate surface is fully exerted, while avoiding the decarburization color difference defect caused by excessive reaction of hydrogen with carbon elements in the steel plate at the high temperature stage. The hydrogen flow control and hydrogen purge time control are shown in Table 1;

[0037] Table 1 Hydrogen flow rate and hydrogen purge time control

[0038] Furnace temperature T(℃) <![CDATA[Hydrogen flow rate V (m 3 / h)]]> Hydrogen purge time t(h) 30≤T＜300 14.2 6.5 300≤T＜450 11 4.4 450≤T＜600 9.5 2.7 600≤T≤820 5.4 1.8

[0039] 2) Steel coil out of furnace process control

[0040] I. Establish a temperature control system for the steel coils that changes dynamically with the ambient temperature and humidity to avoid oxidation color difference defects caused by large differences between the steel coils and the ambient temperature and humidity when they are out of the furnace. The temperature control system for the steel coils out of the furnace is shown in Table 2.

[0041] II. In order to avoid secondary oxidation caused by the temperature of surrounding steel coils in the storage area after the steel coils are taken out of the furnace, it is necessary to control the placement time of high surface level product steel coils in the final cooling table after they are taken out of the furnace. The specific placement time of steel coils in the final cooling table is shown in Table 2.

[0042] Table 2 Control of furnace temperature and steel coil placement time on the final cooling table

[0043]

[0044] (2) Optimize the flattening process to improve the surface quality of cold-rolled high-strength steel:

[0045] 1) Smooth working roll crown and roughness process

[0046] I. In order to avoid the defects of strangulation and rolling caused by the mismatch of the flat work roll crown, the crown of the flat work roll of high-strength steel products with high surface level is controlled. The crown range of the flat work roll is shown in Table 3.

[0047] II. In order to avoid scratches and roller mark defects caused by mismatch of the roughness of the flat work roll, the roughness of the flat work roll of high-strength steel products with high surface level is controlled. The roughness control of the flat work roll is shown in Table 3.

[0048] Table 3 Crown range of flat work roll and roughness control of flat work roll

[0049]

[0050] 2) Leveling speed and elongation control

[0051] I. In order to avoid defects such as leveling liquid residue and color difference caused by mismatch of leveling speed, the leveling speed of high-strength steel products with high surface level is controlled. The leveling speed control is shown in Table 4.

[0052] II. In order to avoid defects such as flat scratches and corrugations caused by mismatch of flat elongation, the flat elongation of high-strength steel products with high surface level is controlled. The flat elongation control is shown in Table 4.

[0053] Table 4 Leveling speed and leveling elongation control

[0054]

[0055]

[0056] Example 2

[0057] This embodiment provides a method for improving the surface quality of cold-rolled high-strength steel based on bell annealing and leveling process. The cold-rolled high-strength steel is 45# steel with a furnace loading of 70-100t. The specific process is as follows:

[0058] (1) Optimizing the hood annealing process to improve the surface quality of cold-rolled high-strength steel:

[0059] 1) Hydrogen blowing process: establish dynamic hydrogen flow control and dynamic hydrogen purge time control that change with the annealing heating temperature during the annealing process to ensure that the cleaning and reduction effect of hydrogen on the steel plate surface is fully exerted, while avoiding the decarburization color difference defect caused by excessive reaction of hydrogen with carbon elements in the steel plate at the high temperature stage. The hydrogen flow control and hydrogen purge time control are shown in Table 5;

[0060] Table 5 Hydrogen flow rate and hydrogen purge time control

[0061] Furnace temperature T(℃) <![CDATA[Hydrogen flow rate V (m 3 / h)]]> Hydrogen purge time t(h) 30≤T＜300 13.8 6.1 300≤T＜450 11.4 3.8 450≤T＜600 9.9 2.2 600≤T≤820 5.7 1.6

[0062] 2) Steel coil out of furnace process control

[0063] I. Establish a temperature control system for the steel coils that changes dynamically with the ambient temperature and humidity to avoid oxidation color difference defects caused by large differences between the steel coils and the ambient temperature and humidity when they are out of the furnace. The temperature control system for the steel coils out of the furnace is shown in Table 6.

[0064] II. In order to avoid secondary oxidation caused by the temperature of surrounding steel coils in the storage area after the steel coils are taken out of the furnace, it is necessary to control the placement time of high surface level product steel coils in the final cooling table after they are taken out of the furnace. The specific placement time of steel coils in the final cooling table is shown in Table 6.

[0065] Table 6 Control of furnace temperature and coil placement time on the final cooling table

[0066]

[0067] (2) Optimize the flattening process to improve the surface quality of cold-rolled high-strength steel:

[0068] 1) Smooth working roll crown and roughness process

[0069] I. In order to avoid the defects of strangulation and rolling caused by the mismatch of the crown of the flat work roll, the crown of the flat work roll of high-strength steel products with high surface level is controlled. The crown range of the flat work roll is shown in Table 7.

[0070] II. In order to avoid scratches and roller mark defects caused by mismatch of the roughness of the flat work roll, the roughness of the flat work roll of high-strength steel products with high surface level is controlled. The roughness control of the flat work roll is shown in Table 7.

[0071] Table 7 Crown range of flat work roll and roughness control of flat work roll

[0072]

[0073] 2) Leveling speed and elongation control

[0074] I. To avoid defects such as leveling liquid residue and color difference caused by mismatch of leveling speed, the leveling speed of high-strength steel products with high surface level is controlled. See Table 8 for leveling speed control.

[0075] II. In order to avoid defects such as flat scratches and corrugations caused by mismatch of flat elongation, the flat elongation of high-strength steel products with high surface level is controlled. The flat elongation control is shown in Table 8.

[0076] Table 8 Leveling speed and leveling elongation control

[0077]

[0078] Example 3

[0079] This embodiment provides a method for improving the surface quality of cold-rolled high-strength steel based on bell annealing and leveling process. The cold-rolled high-strength steel is MP800, and the furnace loading is 70-100t. The specific process is as follows:

[0080] (1) Optimizing the hood annealing process to improve the surface quality of cold-rolled high-strength steel:

[0081] 1) Hydrogen blowing process: establish dynamic hydrogen flow control and dynamic hydrogen purge time control that change with the annealing heating temperature during the annealing process to ensure that the cleaning and reduction effect of hydrogen on the steel plate surface is fully exerted, while avoiding the decarburization color difference defect caused by excessive reaction of hydrogen with carbon elements in the steel plate at the high temperature stage. The hydrogen flow control and hydrogen purge time control are shown in Table 9;

[0082] Table 9 Hydrogen flow rate and hydrogen purge time control

[0083]

[0084]

[0085] 2) Steel coil out of furnace process control

[0086] I. Establish a temperature control system for the steel coils that changes dynamically with the ambient temperature and humidity to avoid oxidation color difference defects caused by large differences between the steel coils and the ambient temperature and humidity when they are out of the furnace. The temperature control system for the steel coils out of the furnace is shown in Table 10.

[0087] II. In order to avoid secondary oxidation caused by the temperature of surrounding steel coils in the storage area after the steel coils are taken out of the furnace, it is necessary to control the placement time of high surface level product steel coils in the final cooling table after they are taken out of the furnace. The specific placement time of steel coils in the final cooling table is shown in Table 10.

[0088] Table 10 Control of furnace temperature and steel coil placement time on the final cooling table

[0089]

[0090] (2) Optimize the flattening process to improve the surface quality of cold-rolled high-strength steel:

[0091] 1) Smooth working roll crown and roughness process

[0092] I. In order to avoid the defects of strangulation and rolling caused by the mismatch of the flat work roll crown, the crown of the flat work roll of high-strength steel products with high surface level is controlled. The crown range of the flat work roll is shown in Table 11.

[0093] II. In order to avoid scratches and roller mark defects caused by mismatch of the roughness of the flat work roll, the roughness of the flat work roll of high-strength steel products with high surface level is controlled. The roughness control of the flat work roll is shown in Table 11.

[0094] Table 11 Crown range of flat work roll and roughness control of flat work roll

[0095]

[0096] 2) Leveling speed and elongation control

[0097] I. To avoid defects such as residual leveling fluid and color difference caused by mismatch of leveling speed, the leveling speed of high-strength steel products with high surface level is controlled. See Table 12 for leveling speed control.

[0098] II. In order to avoid defects such as flat scratches and corrugations caused by mismatch of flat elongation, the flat elongation of high-strength steel products with high surface level is controlled. The flat elongation control is shown in Table 12.

[0099] Table 12 Leveling speed and leveling elongation control

[0100]

[0101] Example 4

[0102] This embodiment provides a method for improving the surface quality of cold-rolled high-strength steel based on bell annealing and leveling process. The cold-rolled high-strength steel is MP1200, and the furnace loading is 70-100t. The specific process is as follows:

[0103] (1) Optimizing the hood annealing process to improve the surface quality of cold-rolled high-strength steel:

[0104] 1) Hydrogen blowing process: establish dynamic hydrogen flow control and dynamic hydrogen purge time control that change with the annealing heating temperature during the annealing process to ensure that the cleaning and reduction effect of hydrogen on the steel plate surface is fully exerted, while avoiding the decarburization color difference defect caused by excessive reaction of hydrogen with carbon elements in the steel plate at the high temperature stage. See Table 13 for hydrogen flow control and hydrogen purge time control;

[0105] Table 13 Hydrogen flow rate and hydrogen purge time control

[0106] Furnace temperature T(℃) <![CDATA[Hydrogen flow rate V (m 3 / h)]]> Hydrogen purge time t(h) 30≤T＜300 14.6 5.2 300≤T＜450 11.3 4.0 450≤T＜600 9.1 2.4 600≤T≤820 5.6 1.4

[0107] 2) Steel coil out of furnace process control

[0108] I. Establish a temperature control system for the steel coils that changes dynamically with the ambient temperature and humidity to avoid oxidation color difference defects caused by large differences between the steel coils and the ambient temperature and humidity when they are out of the furnace. The temperature control system for the steel coils out of the furnace is shown in Table 14.

[0109] II. In order to avoid secondary oxidation caused by the temperature of surrounding steel coils in the storage area after the steel coils are taken out of the furnace, it is necessary to control the placement time of high surface level product steel coils in the final cooling table after they are taken out of the furnace. The specific placement time of steel coils in the final cooling table is shown in Table 14.

[0110] Table 14 Control of furnace temperature and steel coil placement time on the final cooling table

[0111]

[0112]

[0113] (2) Optimize the flattening process to improve the surface quality of cold-rolled high-strength steel:

[0114] 1) Smooth working roll crown and roughness process

[0115] I. In order to avoid the defects of strangulation and rolling caused by the mismatch of the flat work roll crown, the crown of the flat work roll of high-strength steel products with high surface level is controlled. The crown range of the flat work roll is shown in Table 15.

[0116] II. In order to avoid scratches and roller mark defects caused by mismatch of the roughness of the flat work roll, the roughness of the flat work roll of high-strength steel products with high surface level is controlled. The roughness control of the flat work roll is shown in Table 15.

[0117] Table 15 Crown range of flat work roll and roughness control of flat work roll

[0118]

[0119] 2) Leveling speed and elongation control

[0120] I. To avoid defects such as leveling liquid residue and color difference caused by mismatch of leveling speed, the leveling speed of high-strength steel products with high surface level is controlled. See Table 16 for leveling speed control.

[0121] II. In order to avoid defects such as flat scratches and corrugations caused by mismatch of flat elongation, the flat elongation of high-strength steel products with high surface level is controlled. The flat elongation control is shown in Table 16.

[0122] Table 16 Leveling speed and leveling elongation control

[0123]

[0124] Comparative Example 1

[0125] This comparative example provides a conventional process of bell annealing and leveling process in the production process of cold-rolled high-strength steel. The cold-rolled high-strength steel is BH440, and the furnace loading is 70-100t. The specific process is as follows:

[0126] 1) Hydrogen blowing process: hydrogen flow control and hydrogen purge time are shown in Table 17;

[0127] Table 17 Hydrogen flow rate and hydrogen purge time

[0128] Furnace temperature T(℃) <![CDATA[Hydrogen flow rate V (m 3 / h)]]> Hydrogen purge time t(h) 30≤T＜300 18.5 8.3 300≤T＜450 15.1 6.7 450≤T＜600 9.9 4.0 600≤T＜≤820 8.6 3.5

[0129] 2) The steel coil out-of-furnace temperature and the steel coil placement time on the final cooling table are shown in Table 18.

[0130] Table 18 Furnace temperature and coil placement time on the final cooling table

[0131]

[0132] 3) The convexity and roughness of the smooth working roll are shown in Table 19.

[0133] Table 19 Crown range and roughness of flat work roll

[0134]

[0135] 4) The leveling speed and leveling elongation control are shown in Table 20.

[0136] Table 20 Leveling speed and leveling elongation control

[0137]

[0138] Table 21 Summary of the failure rates and total failure rates of different defects in Examples 1-4 and Comparative Example 1

[0139]

[0140]

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the surface quality of cold-rolled high-strength steel based on hood annealing and leveling process, characterized in that: The steps include: (1) Establish dynamic hydrogen flow control and dynamic hydrogen purge time control that change with the annealing heating temperature during the hood annealing process to ensure that the cleaning and reduction effects of hydrogen on the steel plate surface are fully exerted, while avoiding decarburization color difference defects caused by excessive reaction of hydrogen with carbon elements in the steel plate during the high temperature stage; (2) Establish a temperature control system for steel coils that changes dynamically with the ambient temperature and humidity to avoid oxidation color defects caused by excessive differences between the temperature and humidity of the steel coils and the ambient temperature when they are out of the furnace; at the same time, avoid secondary oxidation of the steel coils in the storage area after they are out of the furnace due to the influence of the temperature of the surrounding steel coils, and control the placement time of the steel coils in the final cooling station after they are out of the furnace; (3) To avoid the defects of strangulation and rolling caused by the mismatch of the convexity of the flat work roll, the convexity of the flat work roll is controlled; to avoid the defects of scratches and rolling caused by the mismatch of the roughness of the flat work roll, the roughness of the flat work roll is controlled; (4) To avoid leveling liquid residue and color difference defects caused by mismatching leveling speed, the leveling speed is controlled; to avoid leveling scratches and corrugation defects caused by mismatching leveling elongation, the leveling elongation is controlled.

2. The method according to claim 1, characterized in that The cold-rolled high-strength steel includes BH440, 45# steel, and strip steel with a tensile strength of more than 800MPa.

3. The method according to claim 1, characterized in that The furnace capacity of bell annealing is 10 to 200 tons.

4. The method according to claim 1, characterized in that: The dynamic hydrogen flow control and dynamic hydrogen purge time control in step (1) are as follows: when the annealing heating temperature is 30°C ≤ 300°C, 12m 3 / h≤Hydrogen flow rate<15m 3 / h, 5h≤Hydrogen purge time<7h; 300℃≤Annealing heating temperature<450℃, 10m 3 / h≤Hydrogen flow rate<12m 3 / h, 3h≤Hydrogen purge time<5h; 450℃≤Annealing heating temperature<600℃, 8m 3 / h≤Hydrogen flow rate<10m 3 / h, 2h≤Hydrogen purge time<3h; 600℃≤Annealing heating temperature≤820℃, 5m 3 / h≤Hydrogen flow rate<6m 3 / h, 1h≤hydrogen purge time<2h.

5. The method according to claim 1, characterized in that The temperature of the steel coil out of the furnace described in step (2) is controlled as follows: when 5°C≤ambient temperature<15°C and 10%≤ambient humidity<40%, 30°C≤steel coil out of the furnace temperature<50°C and 8s≤steel coil final cooling table placement time<20s; when 15°C≤ambient temperature<25°C and 15%≤ambient humidity<45%, 35°C≤steel coil out of the furnace temperature<55°C and 12s≤steel coil final cooling table placement time<24s; when 25°C≤ambient temperature<45°C and 25%≤ambient humidity<60%, 40°C≤steel coil out of the furnace temperature<60°C and 20s≤steel coil final cooling table placement time<40s; when 45°C≤ambient temperature<60°C and 30%≤ambient humidity<70%, 55°C≤steel coil out of the furnace temperature<85°C and 40s≤steel coil final cooling table placement time<60s.

6. The method according to claim 5, characterized in that In step (2), when 5°C≤ambient temperature<15°C, 10%≤ambient humidity<25%, 40°C≤steel coil out-of-furnace temperature<50°C, 8s≤steel coil final cooling table placement time<12s; when 5°C≤ambient temperature<15°C, 25%≤ambient humidity<40%, 30°C≤steel coil out-of-furnace temperature<40°C, 12s≤steel coil final cooling table placement time<20s; when 15°C≤ambient temperature<25°C, 15%≤ambient humidity<30%, 45°C≤steel coil out-of-furnace temperature<55°C, 12s≤steel coil final cooling table placement time<18s; when 15°C≤ambient temperature<25°C, 30%≤ambient humidity<45%, 35°C≤steel coil out-of-furnace temperature<45°C, 18s≤steel coil final cooling table placement time<24s s; 25℃≤ambient temperature<45℃, 25%≤ambient humidity<40%, 50℃≤steel coil out-of-furnace temperature<60℃, 20s≤steel coil final cooling table placement time<30s; 25℃≤ambient temperature<45℃, 40%≤ambient humidity<60%, 40℃≤steel coil out-of-furnace temperature<50℃, 30s≤steel coil final cooling table placement time<40s; 45℃≤ambient temperature<60℃, 30%≤ambient humidity<50%, 55℃≤steel coil out-of-furnace temperature<70℃, 40s≤steel coil final cooling table placement time<50s; 45℃≤ambient temperature<60℃, 50%≤ambient humidity<70%, 70℃≤steel coil out-of-furnace temperature<85℃, 50s≤steel coil final cooling table placement time<60s.

7. The method according to claim 1, characterized in that The requirements for the crown and roughness of the leveling work roll in step (3) are as follows: when the tensile strength is 340MPa≤<590MPa and the strip thickness is 0.6mm≤<2.5mm, the crown value of the leveling work roll is 0.4~0.8mm and the roughness of the work roll is 2.00~5.00μm; when the tensile strength is 590MPa≤<780MPa and the strip thickness is 0.6mm≤<2.5mm, the crown value of the leveling work roll is 0.4~0.8mm and the roughness of the work roll is 2~6μm; when the tensile strength is 780MPa≤<1180MPa and the strip thickness is 0.6mm≤<2.5mm, the crown value of the leveling work roll is 0.4~0.8mm and the roughness of the work roll is 2~6μm.

8. The method according to claim 7, characterized in that The requirements for the crown and roughness of the leveling work roll in step (3) are as follows: when the tensile strength is 340MPa≤<590MPa and the strip thickness is 0.6mm≤<0.9mm, the crown value of the leveling work roll is 0.70~0.8mm and the roughness of the work roll is 4.00~5.00μm; when the tensile strength is 340MPa≤<590MPa and the strip thickness is 0.9mm≤<1.2mm, the crown value of the leveling work roll is 0.60~0.69mm and the roughness of the work roll is 0. Roughness 3.00~3.99μm; 340MPa≤tensile strength<590MPa, 1.2mm≤strip thickness<1.8mm, flat work roll crown value 0.50~0.59mm, work roll roughness 2.50~2.99μm; 340MPa≤tensile strength<590MPa, 1.8mm≤strip thickness<2.5mm, flat work roll crown value 0.35~0.49mm, work roll roughness 2.00~2.49μm; When the tensile strength is 590MPa≤<780MPa, the strip thickness is 0.6mm≤<0.9mm, the crown value of the flat work roll is 0.60~0.65mm, and the roughness of the work roll is 4.50~5.50μm; when the tensile strength is 590MPa≤<780MPa, the strip thickness is 0.9mm≤<1.2mm, the crown value of the flat work roll is 0.50~0.59mm, and the roughness of the work roll is 3.50~4.49μm; When the tensile strength is 590MPa≤<780MPa, the strip thickness is 1.2mm≤<1.8mm, the crown value of the flat work roll is 0.40~0.49mm, and the roughness of the work roll is 2.60~3.49μm; when the tensile strength is 590MPa≤<780MPa, the strip thickness is 1.8mm≤<2.5mm, the crown value of the flat work roll is 0.30~0.39mm, and the roughness of the work roll is 2.00~2.59μm; When the tensile strength is 780MPa≤<1180MPa, the strip thickness is 0.6mm≤<0.9mm, the crown value of the flat work roll is 0.40~0.59mm, and the roughness of the work roll is 3.50~4.50μm; when the tensile strength is 780MPa≤<1180MPa, the strip thickness is 0.9mm≤<1.2mm, the crown value of the flat work roll is 0.30~0.39mm, and the roughness of the work roll is 2.50~3.49μm; When the tensile strength is 780MPa≤<1180MPa, the strip thickness is 1.2mm≤<1.8mm, the crown value of the smooth working roll is 0.20~0.29mm, and the roughness of the working roll is 2.00~2.49μm; when the tensile strength is 780MPa≤<1180MPa, the strip thickness is 1.8mm≤<2.5mm, the crown value of the smooth working roll is 0.05~0.19mm, and the roughness of the working roll is 1.50~1.99μm.

9. The method according to claim 1, characterized in that: In step (4), the leveling speed and leveling elongation are controlled as follows: when the tensile strength is 340MPa≤<590MPa and the strip thickness is 0.6mm≤<2.5mm, the leveling speed is 700~1150m / min and the leveling elongation is 0.3~1.5%; when the tensile strength is 590MPa≤<780MPa and the strip thickness is 0.6mm≤<2.5mm, the leveling speed is 550~1000m / min and the leveling elongation is 0.2~1.2%; when the tensile strength is 780MPa≤<1180MPa and the strip thickness is 0.6mm≤<2.5mm, the leveling speed is 500~900m / min and the leveling elongation is 0.2~1.1%.

10. The method according to claim 9, characterized in that In step (4), the leveling speed and leveling elongation are controlled as follows: when the tensile strength is 340MPa≤<590MPa, and the strip thickness is 0.6mm≤<0.9mm, the leveling speed is 950~1150m / min, and the leveling elongation is 0.3~0.5%; when the tensile strength is 340MPa≤<590MPa, and the strip thickness is 0.9mm≤<1.2mm, the leveling speed is 880~949m / min, and the leveling elongation is 0.3~0.5%; Elongation 0.5~0.8%; 340MPa≤tensile strength<590MPa, 1.2mm≤strip thickness<1.8mm, flattening speed 800~879m / min, flattening elongation 0.8~1.2%; 340MPa≤tensile strength<590MPa, 1.8mm≤strip thickness<2.5mm, flattening speed 700~799m / min, flattening elongation 1.2~1.5%; When the tensile strength is 590MPa≤<780MPa, the strip thickness is 0.6mm≤<0.9mm, the leveling speed is 850~1000m / min, and the leveling elongation is 0.2~0.4%; when the tensile strength is 590MPa≤<780MPa, the strip thickness is 0.9mm≤<1.2mm, the leveling speed is 750~849m / min, and the leveling elongation is 0.4~0.6%; when the tensile strength is 590MPa≤<780MPa, the strip thickness is 1.2mm≤<1.8mm, the leveling speed is 650~749m / min, and the leveling elongation is 0.6~0.8%; when the tensile strength is 590MPa≤<780MPa, the strip thickness is 1.8mm≤<2.5mm, the leveling speed is 550~649m / min, and the leveling elongation is 0.8~1.2%; When the tensile strength is 780MPa≤<1180MPa and the strip thickness is 0.6mm≤<0.9mm, the leveling speed is 800~900m / min and the leveling elongation is 0.2~0.3%; when the tensile strength is 780MPa≤<1180MPa and the strip thickness is 0.9mm≤<1.2mm, the leveling speed is 700~799m / min and the leveling elongation is 0.3~0.5%; when the tensile strength is 780MPa≤<1180MPa and the strip thickness is 1.2mm≤<1.8mm, the leveling speed is 600~699m / min and the leveling elongation is 0.5~0.8%; when the tensile strength is 780MPa≤<1180MPa and the strip thickness is 1.8mm≤<2.5mm, the leveling speed is 500~599m / min and the leveling elongation is 0.8~1.1%.

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