High-strength hot-dip coating steel strip production method and continuous horizontal annealing furnace used by same

Abstract

The invention relates to the field of continuous hot dipping of strip steel, in particular to a production method of a high-strength hot-dip coating steel strip and a continuous horizontal annealing furnace used by the method. The pre-oxidation zone is arranged in the horizontal annealing furnace, the strip steel is subjected to pre-oxidation treatment after entering the front open fire heating zone, an iron oxide film which is sufficient in thickness and uniform is formed on the surface of the strip steel, and the iron oxide film is completely reduced in the reducing furnace zone to form a sponge iron layer to cover the surface of the strip steel; the sponge iron layer isolates liquid metal from alloy elements such as silicon and manganese in the base plate during hot dipping, and under the condition that it is ensured that the strength of the strip steel is larger than 590 MPa, a plating layer of the strip steel has good adhesive force.

Description

Technical Field

[0001] The present application relates to the field of continuous hot-dip coating of steel strips, and in particular to a method for producing high-strength hot-dip coated steel strips and a continuous horizontal annealing furnace used in the method. Background Art

[0002] With the implementation of the global carbon reduction strategy, the sales of high-strength steel continuous hot-dip coating products with a strength greater than 590MPa have achieved rapid growth, but they have become a production problem because they contain elements such as Si and Mn that affect the plating performance.

[0003] In the well-known high-strength steel continuous hot-dip plating technology, a vertical American Steel Union continuous hot-dip plating production line with radiation tube heating is used for production. In order to solve the problem of plating suitability of substrates with high alloy components, a pre-oxidation zone is set in the heating section of the continuous annealing furnace. In the pre-oxidation zone, the iron in the strip is preferentially oxidized to form an iron oxide film on the surface of the substrate. In the subsequent reducing furnace zone, the iron oxide film is reduced to sponge iron covering the surface of the substrate, thereby ensuring that the coating has good adhesion. However, this technology cannot be used in horizontal annealing furnaces.

[0004] In the well-known horizontal continuous hot-dip production line of the modified Sendzimir process with open flame heating, the open flame heating speed is fast, which can heat the steel plate to the temperature required by the process in a relatively short time; although the open flame heating zone can also adjust the furnace gas composition to cause a certain pre-oxidation of the strip, the pre-oxidation effect fluctuates greatly, the adhesion of the coated product is difficult to control, the yield rate is low, and the achievable strength is also low, and it is impossible to stably produce products with a strength greater than 590MPa.

[0005] The patent application of the present invention is to enable the horizontal improved Sendzimir process continuous hot dip galvanizing production line with open flame heating to stably produce products with a strength greater than 590 MPa. Summary of the invention

[0006] In order to enable a horizontal annealing furnace to achieve high-strength production quality, the present application provides a method for producing a high-strength hot-dip coated steel strip and a continuous horizontal annealing furnace used in the method.

[0007] In the first aspect, the method for producing a high-strength hot-dip coated steel strip provided in the present application adopts the following technical solution: The method for producing high-strength hot-dip coated steel strip adopts a continuous horizontal annealing furnace for annealing, comprising the following steps: Step S1: preheating the steel strip using waste gas with residual heat to obtain preheated steel strip, thereby reducing energy consumption; Step S2: heating and soaking the steel strip so that the steel strip reaches the temperature required for pre-oxidation accurately; Step S3: Pre-oxidize the strip after heat treatment to obtain a pre-oxidized strip with an iron oxide film on its surface; Step S4: Re-heat the strip after pre-oxidation treatment to further increase the temperature of the pre-oxidized strip to reach the temperature required by the annealing process; Step S5: Cool the strip with a sponge iron layer to reach the temperature required for hot-dip plating, and transfer the strip from the continuous horizontal annealing furnace to the device for hot-dip plating; During the re-heat treatment process in Step S4 and the cooling treatment process in Step S5, introduce H2 into the continuous horizontal annealing furnace to make the furnace gas highly reducing, so that the iron oxide on the surface of the pre-oxidized strip is reduced to sponge iron, and a strip with a sponge iron layer on its surface is obtained.

[0008] By adopting the above technical solution, the waste gas pre-heat treatment process in the annealing furnace is used to heat the strip first, saving energy; the first heat treatment process ensures that the strip quickly reaches the required temperature, shortening the overall heating time, reducing energy consumption, and improving production efficiency; and the temperature of the strip is evenly distributed, making it more uniform and avoiding local overheating or underheating, which may affect the subsequent pre-oxidation effect; the pre-oxidation treatment process forms a uniform iron oxide film on the surface of the strip by precisely controlling the furnace gas composition and temperature, laying a foundation for the subsequent reduction to a sponge iron layer; the re-heat treatment process quickly raises the temperature of the strip again, keeps the temperature of the strip with an iron oxide thin film uniform and makes the strip reach the temperature required by the annealing process; at the same time, when the strip is in the pre-heat treatment process, the first heat treatment process, the pre-oxidation treatment process, and the second heat treatment process, the furnace gas is in an oxidizing atmosphere, and a uniform iron oxide thin film can be obtained on the surface; through this series of processes, the temperature of the strip can completely and uniformly reach the temperature required by the annealing process, ensuring the mechanical properties of the product. When the strip is in the cooling treatment process, the temperature of the strip is quickly reduced to reach the hot-dip plating temperature, ensuring the process requirements of hot-dip plating and also ensuring the material properties; overall, the quality and stability of the continuous hot-dip plating of high-strength steel are improved; at the same time, during the second heat treatment process and the cooling treatment process, hydrogen is introduced into the furnace to control the furnace gas to be highly reducing, ensuring that the iron oxide thin film on the surface of the strip is completely reduced to a sponge iron layer and covering the surface of the strip, so as to isolate the liquid metal from alloy elements such as silicon and manganese in the substrate during hot-dip plating, ensuring good coating adhesion.

[0009] Optionally, in the pre-oxidation treatment process of Step S3, the furnace gas composition is CO < 0.5%, CO2 = 30% - 50%, O2 = 2.0% - 4.0%, and the balance is nitrogen and water vapor.

[0010] Optionally, in the pre-oxidation treatment process of step S3, the temperature of the strip is controlled at 650°C - 670°C, and the temperature difference along the width direction of the strip < 2.0°C.

[0011] Optionally, in the preheating treatment process of step S1, the furnace gas composition is CO < 0.2%, CO2 = 30% - 80%, O2 = 2.0% - 5.0%, and the balance is nitrogen and water vapor. In the heating treatment process of step S2, the furnace gas composition is CO < 20%, CO2 = 20% - 60%, O2 = 0.5% - 1.5%, and the balance is nitrogen and water vapor. In the reheating treatment process of step S4, the furnace gas composition is CO = 20% - 30%, CO2 = 40% - 50%, O2 < 0.2%, and the balance is nitrogen and water vapor.

[0012] Optionally, in the cooling treatment process of step S5, H2 + N2 gas with a dew point ≤ -60°C is introduced into the continuous horizontal annealing furnace. In the reheating treatment process of step S4 and the cooling treatment process of step S5, the furnace gas composition is H2 = 10% - 35%, the balance is nitrogen, O2 < 40 ppm, and the dew point temperature < -35°C.

[0013] In a second aspect, the present application provides a continuous horizontal annealing furnace for strip steel, which processes the strip steel by the above processing method and adopts the following technical solutions: Optionally, it includes a furnace body, and the furnace body includes an oxidizing furnace zone where the furnace gas contains oxidizing gases O2, CO2, and H2O, and a reducing furnace zone where the furnace gas contains reducing gas H2.

[0014] By adopting the above technical solutions, the oxidizing furnace zone is used to form a uniformly thick iron oxide film on the surface of the strip steel. The reducing furnace zone is used to completely reduce the iron oxide thin film on the surface of the strip steel into a sponge iron layer, covering the surface of the strip steel, so as to isolate liquid metal from alloy elements such as silicon and manganese in the substrate during subsequent hot-dip plating operations, ensuring good coating adhesion.

[0015] Optionally, the oxidizing furnace zone includes a preheating zone, a front open-flame heating zone, a first soaking zone, a pre-oxidation zone, and a rear open-flame heating zone. The reducing furnace zone includes a second soaking zone, a radiant tube heating zone, a third soaking zone, a cooling zone, a fourth soaking zone, a hot tension roll zone, and a furnace nose zone.

[0016] By adopting the above technical solution, the preheating zone is used for the preheating treatment in step S1. The setting of the preheating zone can maximize the utilization of the heat that is not fully utilized in the front open-flame heating zone, slow down the oxidation corrosion on the strip surface, and protect the surface quality of the strip; the front open-flame heating zone and the first soaking zone are used for the first heating treatment in step S2. The front open-flame heating zone utilizes the characteristic of rapid temperature rise to ensure that the strip quickly reaches the required temperature, shortens the overall heating time, reduces energy consumption, and improves production efficiency; the function of the first soaking zone is to balance the temperature distribution of the strip, make it more uniform, and avoid local overheating or underheating phenomena that affect the subsequent pre-oxidation effect in the pre-oxidation zone; the pre-oxidation zone and the rear open-flame heating zone are used for the pre-oxidation treatment in step S3. The pre-oxidation zone forms a uniform iron oxide film with sufficient thickness on the strip surface through precise control of the furnace gas composition and temperature, laying a foundation for the subsequent reduction to a sponge iron layer in the oxidizing furnace zone; the rear open-flame heating zone rapidly raises the strip temperature again to ensure a temperature close to that required by the annealing process, thus saving energy; meanwhile, the furnace gas composition in the preheating zone is oxidative to ensure complete combustion of CO in the furnace gas coming from the front open-flame heating zone and maximize energy utilization; the furnace gas compositions in the front open-flame heating zone, the first soaking zone, and the rear open-flame heating zone are slightly oxidative to ensure that the heat in the vast majority of the fuel gas is released; the furnace gas composition in the pre-oxidation zone is precisely controlled and oxidative to ensure uniform, adjustable, and controllable pre-oxidation effects, enabling more precise temperature and surface state control of the strip in the oxidizing furnace zone; the second soaking zone, the radiant tube heating zone, and the third soaking zone are used for the re-heating treatment in step S4. The second soaking zone equalizes the temperature of the strip coming out of the front open-flame heating zone; the radiant tube heating zone can further increase the strip temperature to reach the temperature required by the annealing process; the third soaking zone equalizes the temperature of the strip coming out of the radiant tube heating zone; through this series of processes, the strip temperature can reach the temperature required by the annealing industry completely and uniformly, ensuring the mechanical properties of the product and creating good conditions for the reduction of the surface iron oxide film; meanwhile, starting from the second soaking zone, hydrogen is introduced into the furnace to control the furnace gas to be highly reducing, ensuring complete reduction of the iron oxide film on the strip surface coming from the rear open-flame heating zone to a sponge iron layer, covering the strip surface, and isolating the liquid metal from alloying elements such as silicon and manganese in the substrate during hot-dip plating to ensure good coating adhesion; the cooling zone, the fourth soaking zone, the hot tension roll zone, and the furnace nose zone are used for the cooling treatment in step S5. The cooling zone is used to quickly reduce the strip temperature to reach the hot-dip plating temperature, meeting the process requirements of hot-dip plating and ensuring material properties; the fourth soaking zone and the hot tension roll zone help eliminate internal stress and improve the flatness of the strip; the furnace nose zone serves as the final treatment link to ensure the smooth entry of the strip into the subsequent hot-dip plating device, overall improving the quality and stability of continuous hot-dip plating of high-strength steel.

[0017] Optionally, isolation furnace walls are provided between the preheating zone, the front open-flame heating zone, the first soaking zone, the pre-oxidation zone, the rear open-flame heating zone, and the second soaking zone. Furnace rolls for transporting the strip steel are provided inside the isolation furnace walls; above the furnace rolls inside the furnace body, there are plate thermometers for detecting the temperature of the strip steel.

[0018] By adopting the above technical solution, the isolation furnace walls between the preheating zone, the front open-flame heating zone, the first soaking zone, the pre-oxidation zone, and the rear open-flame heating zone effectively prevent the heat and gas between each zone from interfering with each other, ensuring that the temperature and atmosphere conditions within each zone are more stable and controllable; the furnace rolls provided inside these isolation furnace walls ensure the smooth transmission of the strip steel and also avoid the phenomenon of surface scratches on the strip steel caused by mechanical contact with the isolation walls; at the same time, the plate thermometers provided inside the furnace body can monitor in real time whether the temperature of the strip steel when it leaves this zone meets the process requirements, and timely adjust the heating parameters to ensure uniform temperature distribution of the strip steel during the entire annealing process, improving the quality and stability of the final product.

[0019] Optionally, a flue gas channel is provided on the furnace body. One end of the flue gas channel communicates with the preheating zone, and the other end communicates with the rear open-flame heating zone. The flue gas channel is provided with an air induction system for guiding the combustion flue gas in the rear open-flame heating zone into the preheating zone without affecting the composition of the furnace gas in the pre-oxidation zone 24.

[0020] By adopting the above technical solution, the design of the flue gas channel enables the flue gas with a large fluctuation range of components generated by combustion in the rear open-flame heating zone to be directly introduced into the preheating zone for further combustion, without flowing into the pre-oxidation zone where the furnace gas composition is strictly controlled, interfering with the furnace gas composition in the pre-oxidation zone and affecting the pre-oxidation effect.

[0021] Optionally, a furnace gas composition detection system is provided in each zone. Among them, the furnace gas composition detection systems in the preheating zone, the front open-flame heating zone, the first soaking zone, the pre-oxidation zone, and the rear open-flame heating zone are used to detect the contents of CO, CO2, and O2; the furnace gas composition detection systems in the second soaking zone, the radiant tube heating zone, the third soaking zone, the cooling zone, the fourth soaking zone, the hot tension roll zone, and the furnace nose zone are used to detect the contents of H2, O2ppm, and the dew point temperature.

[0022] By adopting the above technical solutions, the flue gas composition detection systems in the preheating zone, the front open-flame heating zone, the first soaking zone, the pre-oxidation zone, and the rear open-flame heating zone can monitor the contents of CO, CO2, and O2 in real time, ensuring that these key parameters are always within the specified ranges, thereby effectively controlling the combustion state, and then controlling the preheating and heating processes of the strip steel, improving the heating efficiency and uniformity; while in the second soaking zone, the radiant tube heating zone, the third soaking zone, the cooling zone, the fourth soaking zone, the hot tension roll zone, and the furnace nose zone, the flue gas composition detection system is used to detect the contents of H2 and O2ppm and the dew point temperature, ensuring that the gas content and temperature in these zones are maintained in an ideal reduction state, ensuring the coating adhesion, and at the same time reducing the occurrence probability of defects; in this way, the entire production process is more stable and reliable, and high-strength steel products with a strength exceeding 590 MPa can be efficiently produced.

[0023] In summary, the present application includes at least one of the following beneficial technical effects: 1. The preheating zone is used to maximize the utilization of the heat that is not fully utilized in the front open-flame heating zone. The front open-flame heating zone is used to shorten the time for the strip steel to reach the required temperature. The first soaking zone is used to balance the temperature distribution of the strip steel. The pre-oxidation zone is used to form an iron oxide film on the surface of the strip steel. The rear open-flame heating zone is used to raise the temperature of the strip steel again. 2. The flue gas in the furnace is in an oxidative nature from the preheating zone to the rear open-flame soaking zone. While heating the strip steel, a uniform iron oxide film is generated on the surface, laying a foundation for the subsequent reduction into a sponge iron layer. 3. The second soaking zone is used to keep the strip steel in a state of balanced temperature after being treated by the rear open-flame. The radiant tube heating zone is used to make the strip steel reach the annealing required temperature. The third soaking zone is used to homogenize the temperature of the strip steel again. The cooling zone is used to quickly reduce the temperature of the strip steel. The fourth soaking zone is used to eliminate the internal stress of the strip steel. The hot tension roll zone and the furnace nose zone are used to ensure the smooth entry of the strip steel into the hot-dip plating process. 4. Hydrogen is introduced starting from the second soaking zone, making the flue gas in a highly reducing nature. The iron oxide film on the surface of the strip steel is completely reduced into a sponge iron layer in the oxidative furnace zone to ensure the adhesion of the hot-dip coating. 5. The isolation furnace wall can effectively ensure the heat and gas interference of each component. The furnace rolls are used for the smooth transportation of the strip steel and reduce the scratching phenomenon of the strip steel. The strip temperature gauge is used to detect the temperature of the strip steel in real time, facilitating the staff to adjust the temperature parameters of each zone in a timely manner. 6. The flue gas passage is used to introduce the flue gas burned in the rear open-flame heating zone into the preheating zone for re-combustion, reducing the entry of flue gas into the pre-oxidation zone, thereby reducing the impact on the pre-oxidation effect of the strip steel. 7. The furnace gas composition detection system can be used to detect the contents of CO, CO2, and O2 in the preheating zone, the front open flame heating zone, the first soaking zone, the pre-oxidation zone, and the rear open flame heating zone in real time. In the second soaking zone, the radiant tube heating zone, the third soaking zone, the cooling zone, the fourth soaking zone, the hot tension roll zone, and the furnace nose zone, the furnace gas composition detection system is used to detect the contents of H2, O2 ppm, and the dew point temperature. By monitoring the atmosphere and temperature in each zone, the annealing furnace can produce high-strength steel products with a strength exceeding 590 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic structural diagram of a strip continuous horizontal annealing furnace including a furnace body.

[0025] Reference numerals: 1, furnace body; 2, oxidizing furnace zone; 21, preheating zone; 22, front open flame heating zone; 23, first soaking zone; 24, pre-oxidation zone; 25, rear open flame heating zone; 3, reducing furnace zone; 31, second soaking zone; 32, radiant tube heating zone; 33, third soaking zone; 34, cooling zone; 35, fourth soaking zone; 36, hot tension roll zone; 37, furnace nose zone; 4, isolation furnace wall; 5, furnace roll; 6, strip temperature gauge; 7, flue gas passage; 8, hot tension roll. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following will Figure 1 further describe the present application in detail.

[0027] Referring to Figure 1 , the strip continuous horizontal annealing furnace includes a furnace body 1. The furnace body 1 includes an oxidizing furnace zone 2 and a reducing furnace zone 3. The oxidizing furnace zone 2 includes a preheating zone 21, a front open flame heating zone 22, a first soaking zone 23, a pre-oxidation zone 24, and a rear open flame heating zone 25 arranged in sequence. The reducing furnace zone 3 includes a second soaking zone 31, a radiant tube heating zone 32, a third soaking zone 33, a cooling zone 34, a fourth soaking zone 35, a hot tension roll zone 36, and a furnace nose zone 37 arranged in sequence.

[0028] Referring to Figure 1 , an isolation furnace wall 4 is provided between each zone. A furnace roll 5 is arranged inside the isolation furnace wall 4. The furnace roll 5 is rotatably connected inside the furnace body 1, and the furnace roll 5 abuts against the lower end surface of the strip. Directly above the furnace roll 5, a strip temperature gauge 6 for measuring the temperature of the strip is arranged inside the isolation furnace wall 4. Two hot tension rolls 8 are arranged in the hot tension roll zone 36. The hot tension rolls 8 are rotatably connected in the hot tension roll zone 36. The hot tension rolls 8 tighten the abutting strip and guide it to the furnace nose zone 37. The furnace nose zone 37 is used to guide the strip into the hot-dip plating equipment.

[0029] Referring to Figure 1, a flue gas passage 7 is provided on the furnace body 1. One end of the flue gas passage 7 is connected to the preheating zone 21, and the other end of the flue gas passage 7 is connected to the post-flame heating zone 25. The flue gas passage 7 is provided with an air induction system for guiding the flue gas burned in the post-flame heating zone 25 into the preheating zone 21. The air induction system is a fan with a water-cooled jacket.

[0030] Refer to Figure 1 , a flue gas component detection system is provided in each zone. Among them, the flue gas component detection systems located in the preheating zone 21, the pre-flame heating zone 22, the first soaking zone 23, the pre-oxidation zone 24, and the post-flame heating zone 25 are used to detect the contents of CO%, CO2%, and O2%; the flue gas component detection systems located in the radiant tube heating zone 32, the second soaking zone 31, the cooling zone 34, the fourth soaking zone 35, the hot tension roll zone 36, and the furnace nose zone 37 are used to detect the contents of H2% and O2ppm and the dew point temperature. The flue gas component detection system is a gas detector.

[0031] The strip passes through each zone in the oxidizing furnace zone 2 and the reducing furnace zone 3 in sequence. The preheating zone 21 is used to preliminarily heat the strip to ensure that the temperature of the strip is uniform when it enters the subsequent high-temperature zone and reduce the influence brought by the temperature difference. The pre-flame heating zone 22 quickly raises the temperature of the strip to shorten the overall heating time. The first soaking zone 23 is used to balance the temperature of the strip. The pre-oxidation zone 24 is used to form an iron oxide film on the surface of the strip. When the strip is in the pre-oxidation zone, the temperature is controlled at 650°C - 670°C, and the temperature difference along the width of the strip < 2.0°C. The post-flame heating zone 25 is used to raise the temperature of the strip again.

[0032] The second soaking zone 31 is used to raise the temperature of the strip again. The radiant tube heating zone 32 is used to improve the adhesion of the coating on the surface of the strip and reduce the occurrence of oxidation reaction. The third soaking zone 33 further raises the temperature of the strip. The cooling zone 34 is used to quickly reduce the temperature of the strip to ensure the material properties. The fourth soaking zone 35 and the hot tension roll zone 36 are used to eliminate internal stress and improve the flatness of the strip. The furnace nose zone 37 is used for the strip to smoothly exit the furnace.

[0033] This embodiment also provides a production method for high-strength hot-dip coated steel strip; The following further elaborates on this application in combination with examples and comparative examples; The following takes Example 1 as an example for illustration: Example 1 This embodiment provides a method for producing high-strength hot-dip coated steel strip: The strip is transported into a continuous horizontal strip annealing furnace, and the CO content, CO2 content, and O2 content in the preheating zone 21, the front open-flame heating zone 22, the first soaking zone 23, the pre-oxidation zone 24, and the rear open-flame heating zone 25 are adjusted. The CO content in the preheating zone 21 is 0.1%, the CO2 content is 50%, the O2 content is 30%, and the remaining gases are N2 and water vapor; the CO content in the front open-flame heating zone 22 is 10%, the CO2 content is 40%, the O2 content is 1%, and the remaining gases are N2 and water vapor; the CO content in the first soaking zone 23 is 10%, the CO2 content is 40%, the O2 content is 1%, and the remaining gases are N2 and water vapor; the CO content in the pre-oxidation zone 24 is 0.2%, the CO2 content is 40%, the O2 content is 3%, and the remaining gases are N2 and water vapor, where the temperature in the pre-oxidation zone 24 is controlled at 660 °C; the CO content in the rear open-flame heating zone 25 is 0.3%, the CO2 content is 35%, the O2 content is 3%. Secondly, monitor the H2 content, O2 concentration, and dew point temperature in the second soaking zone 31, the radiant tube heating zone 32, the cooling zone 34, the fourth soaking zone 35, the hot tension roll zone 36, and the furnace nose zone 37. The H2 content in the second soaking zone 31 is controlled at 17%, the O2 concentration is controlled at 20 ppm, and the dew point temperature is controlled at -37 °C; the H2 content in the radiant tube heating zone 32 is controlled at 18%, the O2 concentration is controlled at 19 ppm, and the dew point temperature is controlled at -36 °C; the H2 content in the third soaking zone 33 is controlled at 16%, the O2 concentration is controlled at 25 ppm, and the dew point temperature is controlled at -39 °C; the H2 content in the cooling zone 34 is controlled at 17%, the O2 concentration is controlled at 20 ppm, and the dew point temperature is controlled at -37 °C; the H2 content in the fourth soaking zone 35 is controlled at 17%, the O2 concentration is controlled at 21 ppm, and the dew point temperature is controlled at -38 °C; the H2 content in the hot tension roll zone 36 is controlled at 16%, the O2 concentration is controlled at 20 ppm, and the dew point temperature is controlled at -37 °C; the H2 content in the furnace nose zone 37 is controlled at 18%, the O2 concentration is controlled at 22 ppm, and the dew point temperature is controlled at -36 °C.

[0034] In the above method, the surface of the strip is oxidized in the pre-oxidation zone 24 to form an iron oxide film, and the iron oxide film is reduced to a sponge iron layer in the subsequent reducing furnace zone and covers the surface of the substrate.

[0035] As shown in Table 1, the difference between Examples 1-5 lies in that the temperatures and atmosphere ratios in each zone of the horizontal annealing furnace are different.

[0036] Example 6 The difference between this embodiment and Embodiment 1 is that in the preheating zone 21, the furnace gas composition is 1% CO, 85% CO2, and 1% O2.

[0037] Embodiment 7 The difference between this embodiment and Embodiment 1 is that in the front open-flame heating zone 22, the furnace gas composition is 25% CO, 70% CO2, and 0.3% O2.

[0038] Embodiment 8 The difference between this embodiment and Embodiment 1 is that in the first soaking zone 23, the furnace gas composition is 25% CO, 72% CO2, and 3% O2.

[0039] Embodiment 9 The difference between this embodiment and Embodiment 1 is that in the pre-oxidation zone 24, the furnace gas composition is 0.7% CO, 70% CO2, and 1% O2, and the temperature is controlled to 700 °C. Embodiment 10 The difference between this embodiment and Embodiment 1 is that in the rear open-flame heating zone 25, the furnace gas composition is 3% CO, 55% CO2, and 5% O2.

[0040] Embodiment 11 The difference between this embodiment and Embodiment 1 is that in the second soaking zone 31, the furnace gas composition is 30% H2, 45 ppm O2, and the dew point temperature is -30 °C.

[0041] Embodiment 12 The difference between this embodiment and Embodiment 1 is that in the radiant tube heating zone 32, the furnace gas composition is 9% H2, 42 ppm O2, and the dew point temperature is -27 °C.

[0042] Embodiment 13 The difference between this embodiment and Embodiment 1 is that in the third soaking zone 33, the furnace gas composition is 5% H2, 50 ppm O2, and the dew point temperature is -25 °C.

[0043] Embodiment 14 The difference between this embodiment and Embodiment 1 is that in the cooling zone 34, the furnace gas composition is 28% H2, 47 ppm O2, and the dew point temperature is -32 °C.

[0044] Embodiment 15 The difference between this embodiment and Embodiment 1 is that in the fourth soaking zone 35, the furnace gas composition is 6% H2, 42 ppm O2, and the dew point temperature is -33 °C.

[0045] Example 16 The difference between this example and Example 1 is that the furnace gas composition in the hot tension roll zone 36 has a hydrogen (H2) content of 8% and an oxygen (O2) content of 48 ppm, and the dew point temperature is -28°C.

[0046] Example 17 The difference between this example and Example 1 is that the furnace gas composition in the furnace nose zone 37 has a hydrogen (H2) content of 7% and an oxygen (O2) content of 43 ppm, and the dew point temperature is -31°C.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that the pre-oxidation zone 24 is not provided.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that the flue gas passage 7 is not provided.

[0049] Detection of Coating Adhesion Performance The detection was carried out with reference to the industry standard method of YB / T 4457-2022 "Continuous Hot-Dip Coated Steel Sheets and Strips for Building Use": When the thickness of the steel sheet or strip is 0.6 mm < t ≤ 5.0 mm, a 180° bending test method is adopted; the coating is subjected to a transverse 180° bending test according to the specified diameter, and no zinc layer peeling is allowed after tearing off the adhesive tape 5 mm or more away from the edge of the bending area.

[0050] The results are shown in Table 2.

[0051] Combining Examples 1-17 and Comparative Examples 1-2 and referring to Table 2, it can be seen that when the coating adhesion amounts are close, there are significant differences in the zinc layer states after bending for each example and comparative example.

[0052] Combining Examples 1-5 and Comparative Examples 1-2 and referring to Table 2, it can be seen that the zinc layer adhesion of the strip steel in Examples 1-5 is qualified and the zinc layer is intact, indicating that the oxidizing furnace zone can form an iron oxide film with sufficient thickness and uniformity on the surface of the strip steel, and the reducing furnace zone facilitates the complete reduction of the iron oxide film on the surface of the strip steel into a sponge iron layer, and the coating has good adhesion; and the flue gas passage can allow the flue gas generated in the post-flame heating zone to enter the preheating zone, enabling the temperature of the strip steel in the preheating zone to reach the predetermined temperature quickly and also reducing the entry of flue gas into the subsequent reducing furnace zone, reducing the influence on the reduction process of the strip steel coating.

[0053] It can be seen from combining Examples 1-5 and Examples 6-17 and in conjunction with Table 2 that the atmosphere and temperature parameters in the preheating zone, front open-flame heating zone, first soaking zone, pre-oxidation zone, rear open-flame heating zone, second soaking zone, radiant tube heating zone, third soaking zone, cooling zone, fourth soaking zone, hot tension roll zone, furnace nose zone, etc. in the annealing furnace exceed the scope defined in this application. The adhesion of some strip steel surfaces is unqualified, and even qualified strip steel has coating cracks. However, Examples 6-17 are still superior to Comparative Examples 1-2.

[0054] The above are all the preferred embodiments of this application. The protection scope of this application is not limited by this. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A method for producing a high-strength hot-dip coated steel strip, characterized in that: Annealing is carried out in a continuous horizontal annealing furnace, comprising the following steps: Step S1: preheating the steel strip using waste gas with residual heat to obtain preheated steel strip, thereby reducing energy consumption; Step S2: heating and soaking the steel strip so that the steel strip reaches the temperature required for pre-oxidation accurately; Step S3: pre-oxidizing the heated steel strip to obtain a pre-oxidized steel strip with an iron oxide film on the surface; Step S4: heating the pre-oxidized steel strip again, so that the temperature of the pre-oxidized steel strip is increased again to reach the temperature required by the annealing process; Step S5: cooling the steel strip with the sponge iron layer to reach the temperature required for hot dip coating, and sending the steel strip from the continuous horizontal annealing furnace to a device for hot dip coating; During the reheating process in step S4 and the cooling process in step S5, H2 is introduced into the continuous horizontal annealing furnace to make the furnace gas highly reducing, thereby reducing the iron oxide on the surface of the pre-oxidized strip into sponge iron, thereby obtaining a strip with a sponge iron layer on the surface.

2. The method for producing a high-strength hot-dip coated steel strip according to claim 1, characterized in that: In the pre-oxidation process of step S3, the furnace gas composition is CO<0.5%, CO2=30%-50%, O2=2.0%-4.0%, and the remainder is nitrogen and water vapor.

3. The method for producing a high-strength hot-dip coated steel strip according to claim 1, characterized in that: In the pre-oxidation treatment process of step S3, the temperature of the steel strip is controlled at 650°C-670°C, and the temperature difference along the width direction of the steel strip is less than 2.0°C.

4. The method for producing a high-strength hot-dip coated steel strip according to claim 1, characterized in that: In the preheating process of step S1, the furnace gas composition is CO <0.2%, CO2 = 30%-80%, O2 = 2.0%-5.0%, and the balance is nitrogen and water vapor. In the heating process of step S2, the furnace gas composition is CO <20%, CO2 = 20%-60%, O2 = 0.5%-1.5%, and the balance is nitrogen and water vapor. In the re-heating process of step S4, the furnace gas composition is CO = 20%-30%, CO2 = 40%-50%, O2 <0.2%, and the balance is nitrogen and water vapor.

5. The method for producing a high-strength hot-dip coated steel strip according to claim 1, characterized in that: In the cooling treatment process of step S5, H2+N2 gas with a dew point ≤-60°C is introduced into the continuous horizontal annealing furnace. In the reheating treatment process of step S4 and the cooling treatment process of step S5, the furnace gas composition is H2=10%-35%, the balance is nitrogen, O2<40ppm, and the dew point temperature is<-35°C.

6. Continuous horizontal annealing furnace for strip steel, characterized by: The strip steel is processed by the production method according to any one of claims 1 to 5, comprising a furnace body (1), wherein the furnace body (1) comprises an oxidizing furnace zone (2) in which the furnace gas contains oxidizing gases O2, CO2 and H2O, and a reducing furnace zone (3) in which the furnace gas contains reducing gas H2.

7. The continuous horizontal annealing furnace for strip steel according to claim 6, characterized in that: The oxidizing furnace zone (2) includes a preheating zone (21), a front open flame heating zone (22), a first soaking zone (23), a pre-oxidation zone (24) and a rear open flame heating zone (25); the reducing furnace zone (3) includes a second soaking zone (31), a radiant tube heating zone (32), a third soaking zone (33), a cooling zone (34), a fourth soaking zone (35), a hot roller zone (36) and a furnace nose zone (37).

8. The continuous horizontal annealing furnace for strip steel according to claim 7, characterized in that: An isolation furnace wall (4) is provided between the preheating zone (21), the front open flame heating zone (22), the first soaking zone (23), the pre-oxidation zone (24), the rear open flame heating zone (25), and the second soaking zone (31); a furnace roller (5) for transporting the steel strip is provided in the isolation furnace wall (4); and a plate temperature meter (6) for detecting the temperature of the steel strip is provided in the furnace body (1) and above the furnace roller (5).

9. The continuous horizontal annealing furnace for strip steel according to claim 7, characterized in that: The furnace body (1) is provided with a flue gas passage (7), one end of the flue gas passage (7) being in communication with the preheating zone (21), and the other end of the flue gas passage (7) being in communication with the post-open flame heating zone (25), and the flue gas passage (7) being provided with an air induction system for guiding the flue gas burning in the post-open flame heating zone (25) into the preheating zone (21) without affecting the composition of the furnace gas in the pre-oxidation zone (24).

10. The continuous horizontal annealing furnace for strip steel according to claim 7, characterized in that: A furnace gas composition detection system is provided in each zone. The furnace gas composition detection systems in the preheating zone (21), the front open flame heating zone (22), the first soaking zone (23), the pre-oxidation zone (24), and the rear open flame heating zone (25) are used to detect the contents of CO, CO2, and O2; the furnace gas composition detection systems in the second soaking zone (31), the radiant tube heating zone (32), the third soaking zone (33), the cooling zone (34), the fourth soaking zone (35), the hot sheeting roller zone (36), and the furnace nose zone (37) are used to detect the contents of H2 and O2 ppm and the dew point temperature.

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