Method for improving surface quality of 590DP steel cold-rolled sheet in continuous annealing process
By controlling the dew point temperature during the continuous annealing process and using a humidifier to oxidize elements such as Mn, the problem of pitting defects on the surface of the 590DP steel cold-rolled plate is solved, and product quality and economic benefits are improved.
Patent Information
- Application Number
- CN202310748776.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-25
- Publication Date
- 2024-12-27
AI Technical Summary
The prior art cannot effectively control the pitting defects on the surface of 590DP steel cold rolled plates, resulting in poor surface quality and affecting the quality and economic benefits of galvanized plates.
During the continuous annealing process, by adding a humidifier on the insulating furnace, the dew point temperature is controlled between -40℃ or -5℃ and 0℃, and the humidification nitrogen is used to convert elements such as Mn from external oxidation to internal oxidation, reducing the need for reducing the temperature of dew point between -40℃ or -5℃ and -0℃. Generation and drop of oxide particles.
The depth and frequency of the surface of cold-rolled steel are effectively controlled, and the surface quality and economic benefits of 590DP steel products are improved.
Smart Images
Figure CN119193997A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to metal material processing technology, and more specifically to a method for improving the surface quality of a 590DP steel cold-rolled sheet during a continuous annealing process. Background Art
[0002] In the production process of cold-rolled steel strip, water vapor in the continuous annealing furnace will decompose into hydrogen and oxygen at high temperature. When the steel strip passes through the continuous annealing furnace, the alloy elements such as Mn, Si, and Al on the surface of the steel strip will react with the decomposed oxygen to produce oxide particles attached to the surface of the steel strip. During the water cooling process of the steel strip, the precipitates produced on its surface will peel off and enter the cooling water solution in the quenching tank to form suspended particles. In the long-term production process, these particles will aggregate and grow, and cause defects such as small black spots on the surface when the steel strip is squeezed and contacted with the sinking roller.
[0003] In recent years, as users' requirements for the surface quality of cold-rolled galvanized products have gradually increased, the pitting defects on the surface of cold-rolled DQ steel, as a typical surface defect, have seriously affected the quality of subsequent galvanized sheets, reduced product grades, and caused great losses to the company's economic benefits. Most of the current solutions are limited to online drainage of the quench tank, shutdown cleaning, replacement of sinking rollers, etc., which are all symptomatic measures and cannot fundamentally solve the problem of quench tank scaling. At present, a humidification system has been introduced in the annealing furnace, which can control the depth and frequency of pitting defects on the surface of the cold-rolled sheet by adjusting the dew point, but the influence of the dew point on the pitting defects on the surface of the cold-rolled sheet does not show a simple monotonic trend, which has caused certain troubles in actual control. 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 improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing, which can effectively control the surface pitting problem of cold-rolled DQ steel.
[0005] To achieve the above object, the present invention adopts the following technical solution:
[0006] A method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing, comprising three stages of continuous annealing, heat preservation and cooling;
[0007] A humidifier is added to the heat preservation furnace in the heat preservation stage, and the dew point temperature of the heat preservation and soaking section in the heat preservation furnace is controlled by the humidifier.
[0008] Preferably, the temperature of the continuous annealing stage is controlled between 750°C and 900°C.
[0009] Preferably, humidified nitrogen is introduced into the humidifier.
[0010] Preferably, the dew point temperature is not higher than -40°C or between -5°C and 0°C.
[0011] Preferably, the dew point temperature is -40°C.
[0012] Preferably, the dew point temperature is 0°C.
[0013] The present invention provides a method for improving the surface quality of a 590DP steel cold-rolled sheet during a continuous annealing process. After on-site tracking, a large amount of data collection and analysis, the optimal dew point control temperature is recommended. Within this dew point temperature range, elements such as Mn can be transformed from external oxidation to internal oxidation to the greatest extent, and the depth and frequency of pitting defects of the cold-rolled steel during the continuous annealing process can be effectively controlled, thereby improving the surface quality of the 590DP steel product, thereby improving the product grade, bringing considerable economic benefits, and having good practical application prospects. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 This is a SEM surface morphology of the 590DP steel after continuous annealing obtained in Example 1 of the method for improving the surface quality of the 590DP steel cold-rolled sheet during the continuous annealing process of the present invention;
[0015] Figure 2 This is a SEM surface morphology of 590DP steel after continuous annealing obtained by the method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing in the comparative example;
[0016] Figure 3 This is a SEM surface morphology of the 590DP steel after continuous annealing obtained in Example 2 of the method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing of the present invention. DETAILED DESCRIPTION
[0017] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.
[0018] The present invention provides a method for improving the surface quality of a 590DP steel cold-rolled sheet during a continuous annealing process, comprising three stages: continuous annealing, heat preservation and cooling;
[0019] A humidifier is added to the insulation furnace during the insulation stage, and the dew point temperature of the insulation and soaking section in the insulation furnace is controlled by the humidifier.
[0020] The temperature in the continuous annealing stage is controlled between 750°C and 900°C.
[0021] Humidified nitrogen is introduced into the humidifier.
[0022] The dew point temperature of the insulation and soaking section in the insulation furnace is controlled by a humidifier to be no higher than -40°C or between -5°C and 0°C.
[0023] The dew point temperature of the insulation and soaking section in the insulation furnace is controlled at -40℃ by a humidifier.
[0024] The dew point temperature of the insulation and soaking section in the insulation furnace is controlled to 0℃ by a humidifier.
[0025] There are two ranges of dew point temperature in the holding furnace through the humidifier, that is, to avoid the middle range of dew point, because the external oxidation in the middle will be relatively significant, affecting the surface quality of the strip. The dew point temperature is ≤-40℃ to reduce the oxygen partial pressure, so even if the external oxidation produces fine oxide particles, it will not affect the surface quality of the strip; while the dew point temperature is -5℃~0℃ to make the strip produce internal oxidation, forming a uniform internal oxide layer, which is not easy to fall off, and can improve the surface quality of the strip.
[0026] Example 1
[0027] This embodiment 1 provides a method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing, the steps comprising:
[0028] The cold rolled 590DP steel strip was continuously annealed at a heating temperature of 800° C. The composition of the strip steel used is shown in Table 1.
[0029] Then keep warm, and introduce humidified nitrogen through a humidifier in this heat-keeping and equalizing section to control the dew point temperature at -40°C.
[0030] Then slowly cool in air.
[0031] After continuous annealing, the SEM surface morphology of the obtained 590DP steel is as follows: Figure 1 As shown, from Figure 1 It can be seen that the product surface quality is excellent and the oxide coverage is extremely low.
[0032] Table 1 Composition of cold rolled 590DP steel (wt.%)
[0033] Element C Mn Si Al content 0.0653 1.69 0.385 0.0446
[0034] Comparative Example
[0035] This comparative example provides a method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing, the steps comprising:
[0036] The cold-rolled 590DP steel strip was continuously annealed at a heating temperature of 800° C. The composition of the steel strip used was consistent with that of Example 1, as shown in Table 1.
[0037] Then keep warm, and introduce humidified nitrogen through a humidifier in the heat-averaging section to control the dew point temperature at -15°C.
[0038] Then slowly cool in air.
[0039] After continuous annealing, the SEM surface morphology of the obtained 590DP steel is as follows: Figure 2 As shown, from Figure 2 It can be seen that the surface morphology of the product is poor and the oxide coverage is significantly higher.
[0040] Example 2
[0041] This embodiment 2 provides a method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing, the steps comprising:
[0042] The cold-rolled 590DP steel strip was continuously annealed at a heating temperature of 800° C. The composition of the steel strip used was consistent with that of Example 1, as shown in Table 1.
[0043] Then keep warm, and introduce humidified nitrogen through a humidifier in this heat-averaging section to control the dew point temperature to 0°C.
[0044] Then slowly cool in air.
[0045] After continuous annealing, the SEM surface morphology of the obtained 590DP steel is as follows: Figure 3 As shown, from Figure 3 It can be seen that the product surface quality is excellent and the oxide coverage is extremely low.
[0046] Example 3
[0047] This embodiment 3 provides a method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing, the steps comprising:
[0048] The cold-rolled 590DP steel strip was continuously annealed at a heating temperature of 800° C. The composition of the steel strip used was consistent with that of Example 1, as shown in Table 1.
[0049] Then keep warm, and introduce humidified nitrogen through a humidifier in this heat-averaging section to control the dew point temperature to -5°C.
[0050] Then slowly cool in air.
[0051] After continuous annealing, the SEM surface morphology of the obtained 590DP steel is as follows: Figure 3 As shown, from Figure 3 It can be seen that the product surface quality is excellent and the oxide coverage is extremely low.
[0052] Example 4
[0053] This embodiment 4 provides a method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing, the steps comprising:
[0054] The cold-rolled 590DP steel strip was continuously annealed at a heating temperature of 800° C. The composition of the steel strip used was consistent with that of Example 1, as shown in Table 1.
[0055] Then keep warm, and introduce humidified nitrogen through a humidifier in the heat-averaging section to control the dew point temperature to -50°C.
[0056] Then slowly cool in air.
[0057] After continuous annealing, the SEM surface morphology of the obtained 590DP steel is as follows: Figure 3 As shown, from Figure 3 It can be seen that the product surface quality is excellent and the oxide coverage is extremely low.
[0058] Example 5
[0059] This embodiment 5 provides a method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing, the steps comprising:
[0060] The cold-rolled 590DP steel strip was continuously annealed at a heating temperature of 800° C. The composition of the steel strip used was consistent with that of Example 1, as shown in Table 1.
[0061] Then keep warm, and introduce humidified nitrogen through a humidifier in the heat-averaging section to control the dew point temperature at -60°C.
[0062] Then slowly cool in air.
[0063] After continuous annealing, the SEM surface morphology of the obtained 590DP steel is as follows: Figure 3 As shown, from Figure 3 It can be seen that the product surface quality is excellent and the oxide coverage is extremely low.
[0064] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.
Claims
1. A method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing, comprising three stages of continuous annealing, heat preservation and cooling, characterized in that: A humidifier is added to the heat preservation furnace in the heat preservation stage, and the dew point temperature of the heat preservation and soaking section in the heat preservation furnace is controlled by the humidifier.
2. The method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing according to claim 1, characterized in that: The temperature of the continuous annealing stage is controlled between 750°C and 900°C.
3. The method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing according to claim 1, characterized in that: Humidified nitrogen is introduced into the humidifier.
4. The method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing according to claim 3, characterized in that: The dew point temperature is not higher than -40°C or between -5°C and 0°C.
5. The method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing according to claim 3, characterized in that: The dew point temperature is -40°C.
6. The method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing according to claim 3, characterized in that: The dew point temperature is 0°C.
7. The method for improving the surface quality of 590DP steel cold-rolled sheet during continuous annealing according to claim 1, characterized in that: The 590DP steel cold rolled sheet comprises the following components by weight percentage: C：0.0653％； Mn: 1.69% Si: 0.385% Al：0.0446。