Oriented silicon steel high-temperature annealing method for improving temperature fluctuation of steel coil

Abstract

The invention belongs to the technical field of oriented silicon steel preparation, and particularly relates to an oriented silicon steel high-temperature annealing method for improving temperature fluctuation of a steel coil. According to the method, the atmosphere switching rate in the high-temperature annealing process is controlled to be not larger than 5 Nm < 3 >. H <-2 >, that is, in the atmosphere switching process, the variable quantity of the atmosphere flow is controlled to be not larger than 5 Nm < 3 > / h. According to the method, the temperature fluctuation of the steel coil is reduced by slowing down the atmosphere switching speed, so that the plate shape reject ratio is reduced, the furnace body structure does not need to be additionally modified, the operation is simple, and the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of oriented silicon steel preparation, and in particular relates to a high-temperature annealing method for oriented silicon steel for improving temperature fluctuation of steel coils. Background Art

[0002] Existing oriented silicon steel production mostly uses bell-type furnaces or ring furnaces for high-temperature annealing. During the high-temperature annealing process, oriented silicon steel is coiled and placed on the furnace table. The inner and outer rings of the steel coil are most affected by temperature fluctuations. In the high-temperature section, the strength of the steel coil is low. If there is a local temperature fluctuation, it is easy to cause stress fluctuations in the outer ring, and plate quality problems such as buckling and poor edges will occur. Summary of the invention

[0003] The present invention aims to solve the above-mentioned problem and provides a high-temperature annealing method for oriented silicon steel for improving the temperature fluctuation of steel coils. By slowing down the atmosphere switching speed between the high-temperature annealing process sections of oriented silicon steel, the temperature fluctuation of the steel coils and the resulting thermal stress impact amplitude of the steel coils are reduced, thereby reducing the poor plate shape.

[0004] According to the technical solution of the present invention, the high temperature annealing method for oriented silicon steel for improving the temperature fluctuation of steel coil is to control the rate of atmosphere switching during high temperature annealing to not more than 5 Nm 3 ·h -2 , that is, the change in atmosphere flow during the atmosphere switching process should not exceed 5 Nm per hour 3 / h.

[0005] Furthermore, the speed of atmosphere switching during high temperature annealing is controlled to be 1-5 Nm 3 ·h -2 .

[0006] Further, the atmosphere switching includes: switching the nitrogen atmosphere to a mixed atmosphere of hydrogen and nitrogen, switching the mixed atmosphere of hydrogen and nitrogen to pure hydrogen, switching pure hydrogen to a mixed atmosphere of hydrogen and nitrogen, and switching the mixed atmosphere of hydrogen and nitrogen to atmosphere.

[0007] Furthermore, in the mixed atmosphere of hydrogen and nitrogen, the volume percentage of hydrogen is 70-80%.

[0008] Further, the following steps are included: S1: In a nitrogen atmosphere, the temperature in the annealing furnace is raised to 650-750°C; S2: Switch the nitrogen atmosphere to a mixed atmosphere of hydrogen and nitrogen, and perform a heat preservation operation; S3: After one heat preservation, the temperature in the annealing furnace is increased to 1150-1200°C; S4: Switch the mixed atmosphere to pure hydrogen for secondary heat preservation; S5: After the second heat preservation, the pure hydrogen is switched to a mixed atmosphere of hydrogen and nitrogen, and the temperature in the annealing furnace is lowered to 650-700°C; S6: Switch the mixed atmosphere of hydrogen and nitrogen to a nitrogen atmosphere, and continue to lower the temperature in the annealing furnace.

[0009] Furthermore, in step S1, the flow rate of the nitrogen atmosphere is 10-16 Nm 3 / h; In step S2, the flow rate of the mixed atmosphere of hydrogen and nitrogen is 12-18 Nm 3 / h; In step S4, the flow rate of pure hydrogen is 5-10 Nm 3 / h; In step S5, the flow rate of the mixed atmosphere of hydrogen and nitrogen is 10-16 Nm 3 / h; In step S6, the flow rate of the nitrogen atmosphere is 8-16 Nm 3 / h.

[0010] Furthermore, in step S1, the heating rate is 150-300°C / h; In step S3, the heating rate is 15-20°C / h.

[0011] Furthermore, in step S2, the insulation time is 15-25 h; In step S4, the secondary insulation time is 15-30 h.

[0012] The technical solution of the present invention has the following advantages over the prior art: The present invention proposes that when the high-temperature annealing atmosphere of oriented silicon steel is switched, the radial thermal conductivity of the steel coil will change due to the change of the gas medium, causing rapid heat absorption inside the coil, thereby causing the temperature fluctuation of the outer surface of the steel coil. The detection theory is reliable; based on this, the method of the present invention reduces the temperature fluctuation of the steel coil by slowing down the atmosphere switching speed, thereby reducing the plate shape defect rate, and does not require additional modification of the furnace structure, and the operation is simple and low-cost. DETAILED DESCRIPTION

[0013] The present invention designs a method for improving the temperature fluctuation of steel coils during high-temperature annealing of oriented silicon steel, slowing down the switching speed when the atmosphere is switched, improving and eventually eliminating the temperature fluctuation, and reducing the edge loss rate of the steel coils.

[0014] Specifically, slow down the atmosphere switching during high temperature annealing by no more than 5 Nm 3 ·h -2Preferably, due to the limited adjustment accuracy of the solenoid valve, setting a too low adjustment rate will cause the solenoid valve to have a long non-reactive zone. At the same time, the atmosphere switching time is too long, which will affect the specific execution of the process section. The speed of atmosphere switching during high temperature annealing is controlled to be 1-5 Nm 3 ·h -2 , for example, it can be 1 Nm 3 ·h -2 , 2 Nm 3 ·h -2 , 3 Nm 3 ·h -2 , 4 Nm 3 ·h -2 , 5 Nm 3 ·h -2 wait.

[0015] Among them, the atmosphere switching includes: switching the nitrogen atmosphere to a mixed atmosphere of hydrogen and nitrogen, switching the mixed atmosphere of hydrogen and nitrogen to pure hydrogen, switching pure hydrogen to a mixed atmosphere of hydrogen and nitrogen, and switching the mixed atmosphere of hydrogen and nitrogen to atmosphere.

[0016] It is conceivable that based on the annealing process requirements, when the flow rate of the mixed atmosphere of hydrogen and nitrogen needs to be adjusted during the annealing process, the above-mentioned atmosphere switching speed should also be referred to, that is, the flow rate adjustment speed should be controlled not to exceed 5 Nm 3 ·h -2 , preferably 1-5 Nm 3 ·h -2 .

[0017] Preferably, in the mixed atmosphere of hydrogen and nitrogen, the volume percentage of hydrogen is 70-80%, for example, 70%, 80%, etc. In one embodiment, the volume ratio of hydrogen to nitrogen in the mixed atmosphere is 3:1.

[0018] The nitrogen atmosphere was switched to a mixed atmosphere of hydrogen and nitrogen at a switching speed of 5 Nm 3 ·h -2 "For example, the flow rate of nitrogen atmosphere before switching is set to 12 Nm 3 / h, the mixed atmosphere flow rate after switching is 12 Nm 3 / h, of which the hydrogen flow rate is 9 Nm 3 / h, the nitrogen flow rate is 3 Nm 3 / h, the atmosphere switching process is: the nitrogen flow rate is 12 Nm 3 / h, decreasing by 5 Nm per hour 3 / h until the final flow rate is 3 Nm 3 / h; the hydrogen flow rate increases from 0 to 5 Nm per hour 3 / h until the final flow rate is 9 Nm 3 / h.

[0019] The high temperature annealing method for oriented silicon steel provided by the above method may include the following steps: S1: In a nitrogen atmosphere, the temperature in the annealing furnace is raised to 650-750°C; S2: Switch the nitrogen atmosphere to a mixed atmosphere of hydrogen and nitrogen, and perform a heat preservation operation; S3: After one heat preservation, the temperature in the annealing furnace is increased to 1150-1200°C; S4: Switch the mixed atmosphere to pure hydrogen for secondary heat preservation; S5: After the second heat preservation, the pure hydrogen is switched to a mixed atmosphere of hydrogen and nitrogen, and the temperature in the annealing furnace is lowered to 650-700°C; S6: Switch the mixed atmosphere of hydrogen and nitrogen to a nitrogen atmosphere, and continue to lower the temperature in the annealing furnace.

[0020] Preferably, in step S1, the flow rate of the nitrogen atmosphere is 10-16 Nm 3 / h, for example, 10 Nm 3 ·h -2 , 12Nm 3 ·h -2 , 14 Nm 3 ·h -2 , 16 Nm 3 ·h -2 wait.

[0021] In step S2, the flow rate of the mixed atmosphere of hydrogen and nitrogen is 12-18 Nm 3 / h, for example, 12 Nm 3 ·h -2 , 14 Nm 3 ·h -2 , 16 Nm 3 ·h -2 , 18 Nm 3 ·h -2 wait.

[0022] In step S4, the flow rate of pure hydrogen is 5-10 Nm 3 / h, for example, 5 Nm 3 ·h -2 , 6 Nm 3 ·h -2 , 8Nm 3 ·h -2 , 10 Nm 3 ·h -2 wait.

[0023] In step S5, the flow rate of the mixed atmosphere of hydrogen and nitrogen is 10-16 Nm 3 / h, for example, 10 Nm 3 ·h -2 , 12 Nm 3 ·h -2 , 14 Nm 3 ·h -2 , 16 Nm 3 ·h -2 wait.

[0024] In step S6, the flow rate of nitrogen atmosphere is 8-16 Nm 3 / h, for example, 8 Nm 3 ·h -2 , 10 Nm 3 ·h -2 , 12Nm 3 ·h -2 , 14 Nm 3 ·h -2 , 16 Nm 3 ·h -2 wait.

[0025] The steps and parameters of the above-mentioned high temperature annealing method for oriented silicon steel are specifically shown in Table 1.

[0026] Table 1

[0027] Preferably, step S1 is a rapid heating stage, the heating rate is 150-300°C / h, in some embodiments, the heating rate is 200°C / h, and the duration of step S1 can be 3.15-3.65 hours according to the heating rate and temperature change. After the heating is completed, the insulation time in step S2 is 15-25 hours.

[0028] In step S3, the heating rate is 15-20°C / h. In some embodiments, the heating process is divided into two stages, first heating to 850-920°C, and then heating to 1150-1200°C. For example, first heating to 850-920°C at a heating rate of 20°C / h for 5-13.5 h; then heating to 1150-1200°C at a heating rate of 18°C / h for 12.8-19.4 h. The mixed atmosphere can use different flow rates in these two heating processes. The process of flow change can be analogous to atmosphere switching, and the switching speed is controlled not to exceed 5 Nm 3 ·h -2 After the temperature is raised, the second heat preservation time in step S4 is 15-20 h.

[0029] The heating rate of step S6 can be -20°C / h, and the duration can be 24-26.5 h.

[0030] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention. Example 1

[0031] This embodiment provides a high temperature annealing method for oriented silicon steel, comprising the following steps: S1: At flow rate of 12 Nm 3 / h nitrogen atmosphere, raise the temperature in the annealing furnace to 700°C at a heating rate of 200°C / h; S2: 1 Nm 3 ·h -2 The atmosphere switching speed was set to switch the nitrogen atmosphere to a mixed atmosphere of hydrogen and nitrogen for a heat preservation. In the mixed atmosphere, the hydrogen flow rate was 9 Nm 3 / h, nitrogen flow rate is 3 Nm 3 / h, the holding time is 20 h; S3: After the first heat preservation, the mixed atmosphere of hydrogen and nitrogen is maintained, and the temperature in the annealing furnace is increased to 900°C at a heating rate of 20°C / h; and then the temperature in the annealing furnace is increased to 1200°C at a heating rate of 18°C / h; S4: Switch the mixed atmosphere to a flow rate of 9 Nm 3 / h of pure hydrogen, and then conduct secondary heat preservation for 20 h; S5: After the second heat preservation, the pure hydrogen is switched to a mixed atmosphere of hydrogen and nitrogen. In the mixed atmosphere, the hydrogen flow rate is 12 Nm 3 / h, nitrogen flow rate is 4 Nm 3 / h; at the same time, stop heating and lower the temperature in the annealing furnace to 670℃; S6: Switch the mixed atmosphere of hydrogen and nitrogen to a flow rate of 9 Nm 3 / h of nitrogen atmosphere and continue to lower the temperature in the annealing furnace. Example 2

[0032] This embodiment provides a high temperature annealing method for oriented silicon steel, and its steps are basically the same as those in the embodiment, except that the speed of atmosphere switching (including steps S2, S4-S6) is 5 Nm 3 ·h -2 . Comparative Example 1

[0033] This comparative example provides a high temperature annealing method for oriented silicon steel, the steps of which are basically the same as those of the embodiment, except that during the atmosphere switching process, an instantaneous switching method is adopted, that is, the corresponding atmosphere is directly switched to the required flow rate. Comparative Example 2

[0034] This comparative example provides a method for high temperature annealing of oriented silicon steel, and its steps are basically the same as those in the embodiment, except that the speed of atmosphere switching is 10 Nm 3 ·h -2 . Results Analysis

[0035] The temperature fluctuations during the methods of Example 1-2 and Comparative Example 1-2 and the proportion of defective lengths of finished plate shapes such as horseshoe prints and bowl bends were detected, and the results are shown in Table 2. Specifically, thermocouples were arranged on the surface of the oriented silicon steel coil to measure the temperature, so as to obtain the maximum temperature fluctuation on the surface of the coil before and after the atmosphere switching.

[0036] Table 2

[0037] The results show that, using the method of the present invention (Examples 1 and 2), the maximum temperature fluctuation level at each atmosphere switching node is at a low level, and the proportion of poor finished plate length is low. At the same time, when the atmosphere switching speed is slower, the maximum temperature fluctuation and the proportion of poor finished plate length are slightly lower. However, considering that the long atmosphere switching time will affect the specific execution of the process section, the atmosphere switching speed should not be further reduced. In Comparative Example 1, the instantaneous switching method is adopted, and the maximum temperature fluctuation level and the proportion of poor finished plate length are much higher than those of Examples 1 and 2; in Comparative Example 2, the atmosphere switching speed is faster, and the maximum temperature fluctuation level and the proportion of poor finished plate length are higher than those of Examples 1 and 2, and are between the example and Comparative Example 1.

[0038] Obviously, the above embodiments are only examples for clear explanation and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the invention.

Claims

1. A high temperature annealing method for oriented silicon steel for improving temperature fluctuation of steel coils, characterized in that: Control the speed of atmosphere switching during high temperature annealing to no more than 5 Nm 3 ·h -2 .

2. The high temperature annealing method for oriented silicon steel according to claim 1, characterized in that: Control the speed of atmosphere switching during high temperature annealing to 1-5 Nm 3 ·h -2 .

3. The high temperature annealing method for oriented silicon steel according to claim 1 or 2, characterized in that: The atmosphere switching includes: switching the nitrogen atmosphere to a mixed atmosphere of hydrogen and nitrogen, switching the mixed atmosphere of hydrogen and nitrogen to pure hydrogen, switching pure hydrogen to a mixed atmosphere of hydrogen and nitrogen, and switching the mixed atmosphere of hydrogen and nitrogen to atmosphere.

4. The high temperature annealing method for oriented silicon steel according to claim 3, characterized in that: In the mixed atmosphere of hydrogen and nitrogen, the volume percentage of hydrogen is 70-80%.

5. The high temperature annealing method for oriented silicon steel according to claim 3, characterized in that: The following steps are included: S1: In a nitrogen atmosphere, the temperature in the annealing furnace is raised to 650-750°C; S2: Switch the nitrogen atmosphere to a mixed atmosphere of hydrogen and nitrogen, and perform a heat preservation operation; S3: After one heat preservation, the temperature in the annealing furnace is increased to 1150-1200°C; S4: Switch the mixed atmosphere to pure hydrogen for secondary heat preservation; S5: After the second heat preservation, the pure hydrogen is switched to a mixed atmosphere of hydrogen and nitrogen, and the temperature in the annealing furnace is lowered to 650-700°C; S6: Switch the mixed atmosphere of hydrogen and nitrogen to a nitrogen atmosphere, and continue to lower the temperature in the annealing furnace.

6. The high temperature annealing method for oriented silicon steel according to claim 5, characterized in that: In step S1, the flow rate of the nitrogen atmosphere is 10-16 Nm 3 / h; In step S2, the flow rate of the mixed atmosphere of hydrogen and nitrogen is 12-18 Nm 3 / h; In step S4, the flow rate of pure hydrogen is 5-10 Nm 3 / h; In step S5, the flow rate of the mixed atmosphere of hydrogen and nitrogen is 10-16 Nm 3 / h; In step S6, the flow rate of the nitrogen atmosphere is 8-16 Nm 3 / h.

7. The high temperature annealing method for oriented silicon steel according to claim 5, characterized in that: In step S1, the heating rate is 150-300°C / h; In step S3, the heating rate is 15-20°C / h.

8. The high temperature annealing method for oriented silicon steel according to claim 5, characterized in that: In step S2, the insulation time is 15-25 h; In step S4, the secondary insulation time is 15-20 h.

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