Cover stripping method for controlling edge oxidation color of fine blanking strip steel

Abstract

The invention discloses a cover annealing method for controlling edge oxidation color of fine blanking strip steel, which comprises the following steps of: S1, loading a rolled fine blanking strip steel coil into an all-hydrogen cover type furnace, starting heating after preparation work is finished, synchronously starting all-hydrogen purging, and controlling the hydrogen flow to be less than or equal to 11m < 3 > / h; s2, the full-hydrogen bell-type furnace is heated to 100-120 DEG C for low-temperature heat preservation; and S3, after low-temperature heat preservation is finished, heating continues to reach the process heat preservation temperature for heat preservation, after heat preservation is finished, heating cover cooling is conducted, cooling is conducted through a cooling cover, and discharging is conducted after the temperature is reduced to the discharging temperature. The problems that the cost of large-flow hydrogen is greatly increased and oxidation color on the edge of strip steel cannot be effectively removed can be solved.

Description

Technical Field

[0001] The invention relates to a manufacturing process of automobile fine blanking strip steel, in particular to a method for controlling the oxidized color of the edge of the fine blanking strip steel. Background Art

[0002] Annealing fine-blanked strip is a metal heat treatment process that involves slowly heating the metal to a specific temperature, holding it for a sufficient time, and then cooling it at an appropriate rate to achieve spheroidization or recrystallization of the structure, reduce hardness, and improve machinability. Because fine-blanked strip is typically produced using narrow strip rolling and bell-type annealing furnaces, residual emulsion moisture on the strip surface during rolling is inevitably carried into the hydrogen bell-type furnace. At high temperatures, this water vapor accumulates at the edge of the coil, where it oxidizes Fe and forms iron oxide, which then undergoes a reduction reaction with H₂. This results in a wavy surface color difference due to over-reduction, commonly known as oxidation color.

[0003] In the existing technology, the improvement is mainly achieved by controlling the surface moisture content of the rolled strip, reducing the dew point in the bell furnace, and increasing the hydrogen flow in the bell furnace. However, the water content of the emulsion in the strip rolling accounts for the majority, and no matter whether the squeeze roller or air purge is used, it is impossible to completely avoid the residual moisture on the surface of the strip, and the dew point in the furnace cannot be ideally controlled; the bell furnace is heated with a large flow of hydrogen (for example, more than 15m 3 / h) purging to remove most of the water vapor can improve the oxidation color to a certain extent, but it will increase the hydrogen consumption and significantly increase the annealing cost, and the oxidation color cannot be effectively removed. Summary of the Invention

[0004] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method for controlling the oxidation color of the edges of fine-blanked strip steel by covering and evaporating the strip steel. The method performs low-temperature insulation at 100-120°C and adopts a small flow rate of hydrogen purge, which can solve the problem that the cost of large flow rate of hydrogen increases significantly and cannot effectively remove the oxidation color of the strip steel edges.

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

[0006] A method for controlling the oxidation color of the edge of fine blanking strip steel comprises the following steps:

[0007] S1: Load the rolled fine blanking strip steel coil into the full hydrogen bell furnace. After the preparation is completed, start heating and simultaneously start full hydrogen purge. Control the hydrogen flow rate to ≤11m 3 / h;

[0008] S2, heating the full hydrogen bell furnace to 100-120°C for low temperature insulation;

[0009] S3, after the low-temperature insulation is completed, continue heating to the process insulation temperature for insulation. After the insulation is completed, cool the heating cover and change to the cooling cover for cooling. After the temperature drops to the furnace outlet temperature, take the furnace out.

[0010] Preferably, in step S1, the hydrogen flow rate is controlled at 5 to 11 m 3 / h.

[0011] Preferably, in step S1, the calculation formula of the hydrogen flow rate is as follows:

[0012] Q=6.05×D 2 ×W×K

[0013] Where Q is the hydrogen flow rate, unit is m 3 / h;

[0014] D is the outer diameter of the fine blanking strip steel coil, in m;

[0015] W is the width of the fine blanking strip steel coil, in m;

[0016] K is the furnace loading coefficient, and its value range is 0.7<K<1.0.

[0017] Preferably, in step S2, the low-temperature insulation time is 2 to 5 hours.

[0018] Preferably, in step S2, the calculation formula for the low-temperature holding time is as follows:

[0019] T=1.3×D 2 ×K

[0020] Where, T is the low temperature holding time, unit is h;

[0021] D is the outer diameter of the fine blanking strip steel coil, in m;

[0022] K is the furnace loading coefficient, and its value range is 0.7<K<1.0.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention heats the fine blanking steel strip to 100-120°C for low-temperature insulation, so that the moisture in the steel coil material in the furnace can be fully volatilized, thereby avoiding the formation of iron oxide, and further preventing the iron oxide from being reduced by H2 to form oxidation color in the high-temperature stage;

[0025] 2. The present invention adopts a small flow rate of hydrogen purge, which is much lower than the hydrogen flow rate of more than 15m in the heating stage of the conventional annealing process. 3 / h, which not only ensures the uniform temperature of the steel coil in the furnace chamber, but also avoids the edge wave marks left by the large flow of hydrogen blowing inside the steel coil, while reducing costs;

[0026] 3. The present invention can fundamentally control the oxidation color of the surface of the fine blanking strip. After annealing, the surface gloss of the fine blanking strip is uniform, the quality is greatly improved, and there is no need to cut off the oxidation color edge, thereby improving the yield rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0028] Figure 1 This is a flow chart of the method for controlling the oxidation color of the edge of fine-blanked strip steel of the present invention;

[0029] Figure 2 This is a schematic diagram of the surface of the fine-blanked steel strip after the cover is withdrawn in Example 1 of the present invention;

[0030] Figure 3 Schematic diagram of the surface of the fine-blanked strip after the hood is withdrawn using conventional technology. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below with reference to specific examples. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form.

[0032] like Figure 1 As shown, the present invention provides a method for controlling the oxidation color of the edge of fine blanking strip, comprising the following steps:

[0033] S1: Load the rolled fine blanking strip steel coil into the full hydrogen bell furnace. After the preparation is completed, start heating and simultaneously start full hydrogen purge. Control the hydrogen flow rate to ≤11m 3 / h;

[0034] In this step, the fine blanking strip steel coil can be a fine blanking cold rolled steel coil. The preparation work of the full hydrogen bell furnace includes vacuuming, checking for cold leaks, and introducing protective gas. The hydrogen flow rate is controlled at 5 to 11 m 3 / h, using a small flow rate for circulating purge, with a hydrogen flow rate much lower than the conventional hood-recessing process heating stage (greater than 15m 3 / h), which not only ensures uniform temperature of the steel coil in the furnace chamber, but also avoids the edge ripple marks left by the large flow of hydrogen purge inside the steel coil. The hydrogen flow rate is calculated and set according to the different outer diameters, widths, and furnace load coefficients. Therefore, in a specific embodiment, the calculation formula for hydrogen flow rate is as follows:

[0035] Q=6.05×D 2 ×W×K

[0036] Where Q is the hydrogen flow rate, unit is m 3 / h;

[0037] D is the outer diameter of the fine blanking strip steel coil, in m;

[0038] W is the width of the fine blanking strip steel coil, in m;

[0039] K is the furnace loading coefficient, and its value range is 0.7<K<1.0. Where K=Π×(D / 2) 2 ×h / N, Π is taken as 3.14, D is the outer diameter of the fine blanking strip steel coil, h is the charging height, N is the capacity of the bell-type furnace chamber. When designing the charging, the charging coefficient should be ensured to be between 0.7<K<1.0.

[0040] S2, heating the full hydrogen bell furnace to 100-120°C for low temperature insulation;

[0041] In this step, the low-temperature insulation temperature is controlled at 100-120°C, which can ensure that the temperature of each area in the furnace cavity of the full hydrogen bell-type furnace is greater than 100°C. At this temperature, the water evaporates quickly, and at the same time is lower than the oxidation reaction temperature of water vapor and Fe, avoiding the formation of iron oxide, and further avoiding the iron oxide being reduced by H2 to form oxidation color in the high-temperature stage.

[0042] At the above temperature, the low-temperature holding time is 2 to 5 hours, which can ensure that the moisture of the steel coil in the furnace is fully volatilized. The low-temperature holding time can be calculated and set according to different outer diameters, widths and furnace loading coefficients. Therefore, in a specific embodiment, the calculation formula for the low-temperature holding time is as follows:

[0043] T=1.3×D 2 ×K

[0044] Where, T is the low temperature holding time, unit is h;

[0045] D is the outer diameter of the fine blanking strip steel coil, in m;

[0046] K is the furnace loading coefficient, and its value range is 0.7<K<1.0; where K=Π×(D / 2) 2 ×h / N, Π is taken as 3.14, D is the outer diameter of the fine blanking strip steel coil, h is the charging height, N is the capacity of the bell-type furnace chamber. When designing the charging, the charging coefficient should be ensured to be between 0.7<K<1.0.

[0047] S3, after the low-temperature insulation is completed, continue heating to the process insulation temperature for insulation. After the insulation is completed, cool the heating cover and change to the cooling cover for cooling. After the temperature drops to the furnace outlet temperature, take the furnace out.

[0048] This step is the normal heating and insulation stage. The specific process insulation temperature, insulation time, furnace discharge temperature, etc. can be determined according to the type of fine blanking steel.

[0049] The bell-type furnace used in the present invention is a gas-heated or electric-heated full-hydrogen bell-type annealing furnace, the heating bell of which has a built-in temperature-controlled thermocouple, and the cooling bell is equipped with a spray device. The protective atmosphere during the annealing process is hydrogen; the temperature inside the heating bell of the full-hydrogen bell-type furnace can be adjusted in real time according to the data of the temperature-controlled thermocouple, which can further ensure that the temperature of each area in the full-hydrogen bell-type furnace reaches the low-temperature insulation temperature during the low-temperature insulation stage.

[0050] The following is a detailed description of the above-mentioned method for controlling the oxidation color of the edge of fine-blanked strip through a specific example.

[0051] Example 1

[0052] The method for controlling the oxidation color of the edge of fine-blanked strip steel in this embodiment specifically includes the following steps:

[0053] a) Use a fine-blanked cold-rolled steel coil with a thickness of 2.0 mm and a width of 500 mm, with an outer diameter of D = 1.5 m, and load it into a full hydrogen bell-type furnace to reach the heating condition. The furnace loading coefficient K is set to 0.75.

[0054] b) Temperature increase: Hydrogen flow rate Q = 6.05 × D 2 ×W×K=6.05×1.5 2 ×0.5×0.75=5.1m 3 / h, so the hydrogen flow rate is set to 5.1m 3 / h, start heating and raise the temperature to 120℃;

[0055] c) Low temperature insulation: insulation at 120℃, low temperature insulation time T = 1.3 × D 2 ×K=1.3×1.5 2 × 0.75 = 2.2 h, so the holding time is set to 2.2 hours;

[0056] d) Normal heating and heat preservation: After the low temperature heat preservation is completed, the process heat preservation is carried out, the temperature is raised to 680℃, and the heat preservation is carried out for 16 hours;

[0057] e) Cooling: After the process insulation is completed, the heating cover is cooled and the cooling cover is changed to cool. The furnace is taken out after the temperature drops to 70℃.

[0058] The surface of the fine blanking steel after the cover is withdrawn in this embodiment is as follows Figure 2 As shown, its surface gloss is uniform, and there is no wavy surface color difference (i.e. oxidation color) on the edge; Figure 3 For conventional annealing process (hydrogen flow rate greater than 15m 3 / h, without low-temperature insulation stage), the surface of the fine-blanked steel has a wavy surface color difference (i.e., oxidation color) on the surface edge; compared with the fine-blanked steel of the conventional annealing process, the fine-blanked steel of this embodiment is annealed by the above method, and the oxidation color of the strip surface is effectively controlled.

[0059] Example 2

[0060] The method for controlling the oxidation color of the edge of fine-blanked strip steel in this embodiment specifically includes the following steps:

[0061] a) Use a fine-blanked cold-rolled steel coil with a thickness of 1.6 and a width of 550 mm, with an outer diameter of D = 1.9 m, and load it into a full hydrogen bell-type furnace to reach the heating condition. The furnace loading coefficient K is 0.9.

[0062] b) Temperature increase: Hydrogen flow rate Q = 6.05 × D 2 ×W×K=6.05×1.9 2 ×0.55×0.9=10.8m 3 / h, so the hydrogen flow rate is set to 10.8m 3 / h, start heating and raise the temperature to 100℃;

[0063] c) Low temperature insulation: insulation at 100℃, low temperature insulation time T = 1.3 × D 2 ×K=1.3×1.9 2 × 0.9 = 4.2 h, so the holding time is set to 4.2 hours;

[0064] d) Normal heating and insulation: After the low-temperature insulation is completed, process insulation is carried out, heating to 720℃ and keeping warm for 21 hours;

[0065] e) Cooling: After the process insulation is completed, the heating cover is cooled and the cooling cover is changed to cool. The furnace is taken out after the temperature drops to 70℃.

[0066] The surface gloss of the fine blanking steel after annealing in this embodiment is uniform, and there is no wavy surface color difference (i.e., oxidation color) on the edge; it can be seen that after the fine blanking steel in this embodiment is annealed using the above method, the oxidation color of the strip surface is effectively controlled.

[0067] Example 3

[0068] The method for controlling the oxidation color of the edge of fine-blanked strip steel in this embodiment specifically includes the following steps:

[0069] a) Use a fine-blanked cold-rolled steel coil with a thickness of 3.0 and a width of 450 mm, with an outer diameter of D = 1.7 m, and load it into a full hydrogen bell-type furnace to reach the heating condition. The furnace loading coefficient K is set to 0.8.

[0070] b) Temperature increase: Hydrogen flow rate Q = 6.05 × D 2 ×W×K=6.05×1.7 2 ×0.45×0.8=6.3m 3 / h, so the hydrogen flow rate is set to 6.3m3 / h, start heating and raise the temperature to 110℃;

[0071] c) Low temperature insulation: insulation at 110℃, low temperature insulation time T = 1.3 × D 2 ×K=1.3×1.7 2 × 0.8 = 3h, so the holding time is set to 3 hours;

[0072] d) Normal heating and insulation: After the low-temperature insulation is completed, heat to 730°C and keep warm for 24 hours;

[0073] e) Cooling: After the process insulation is completed, the heating cover is cooled and the cooling cover is changed to cool. The furnace is taken out after the temperature drops to 70℃.

[0074] The surface gloss of the fine blanking steel after annealing in this embodiment is uniform, and there is no wavy surface color difference (i.e., oxidation color) on the edge; it can be seen that after the fine blanking steel in this embodiment is annealed using the above method, the oxidation color of the strip surface is effectively controlled.

[0075] In summary, the hooding method of the present invention for controlling the oxidation color of the edges of fine-blanked strip steel is to heat to 100-120°C for low-temperature insulation, so that the residual moisture in the steel coil in the furnace can be fully volatilized, thereby avoiding the formation of iron oxide, and further avoiding the iron oxide being reduced by H2 to form oxidation color in the high-temperature stage. The present invention adopts a small flow of hydrogen purge to avoid the edge wave marks left by large flow of hydrogen purge in the steel coil, while reducing costs. After hooding, the surface oxidation color of the fine-blanked steel of the present invention is fundamentally controlled, the surface gloss of the strip is uniform, the quality is greatly improved, and the yield rate is increased.

[0076] In summary, the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, and all of these should be included in the scope of the claims of the present invention.

Claims

1. A method for controlling the oxidation color of the edge of fine blanking strip, characterized in that: The following steps are involved: S1: Load the rolled fine blanking strip steel coil into the full hydrogen bell furnace. After the preparation is completed, start heating and simultaneously start full hydrogen purge. Control the hydrogen flow rate to ≤11m 3 / h; S2, heating the full hydrogen bell furnace to 100-120°C for low temperature insulation; S3, after the low-temperature insulation is completed, continue heating to the process insulation temperature for insulation. After the insulation is completed, cool the heating cover and change to the cooling cover for cooling. After the temperature drops to the furnace outlet temperature, take the furnace out.

2. The method for controlling the oxidation color of the edge of fine blanking strip according to claim 1, characterized in that: In step S1, the hydrogen flow rate is controlled at 5-11m 3 / h.

3. The method for controlling the oxidation color of the edge of fine blanking strip according to claim 1 or 2, characterized in that: In step S1, the calculation formula of the hydrogen flow rate is as follows: Q=6.05×D 2 ×W×K Where Q is the hydrogen flow rate, unit is m 3 / h; D is the outer diameter of the fine blanking strip steel coil, in m; W is the width of the fine blanking strip steel coil, in m; K is the furnace loading coefficient, and its value range is 0.7<K<1.

0.

4. The method for controlling the oxidation color of the edge of fine blanking strip according to claim 1, characterized in that: In step S2, the low-temperature insulation time is 2 to 5 hours.

5. The method for controlling the oxidation color of the edge of fine blanking strip according to claim 1 or 4, characterized in that: In step S2, the calculation formula of the low-temperature holding time is as follows: T=1.3×D 2 ×K Where, T is the low temperature holding time, unit is h; D is the outer diameter of the fine blanking strip steel coil, in m; K is the furnace loading coefficient, and its value range is 0.7<K<1.0.

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