Preparation method of corrosion-resistant oxide layer on surface of 2000MPa-grade hot-formed steel
By calculating the phase change curve and electron back dispersion diffraction technology, a dense Fe3O4 oxide layer was prepared, which solved the problem of rust on the surface of hot-rolled steel plates and improved corrosion resistance and uniformity.
Patent Information
- Application Number
- CN202510183312.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-19
- Publication Date
- 2025-06-17
AI Technical Summary
During the hot rolling process, the surface of the hot rolling steel plate is rusted due to the formation of iron oxide sheet, making it difficult to enter the high-end market, and the existing technology is difficult to achieve a dense and uniform structure of the oxide layer, affecting corrosion resistance.
By calculating the phase change curves at different cooling rates and temperatures, combined with electron back dispersion diffraction technology, the structure of the micro-domain oxide layer was judged, and a corrosion-resistant oxide layer with a thickness of less than 6 μm and a porosity of less than 13% was prepared.
The preparation of extremely thin and dense oxide layers is achieved, which improves the corrosion resistance and uniformity of the steel plate, and provides a theoretical basis for product quality upgrades.
Smart Images
Figure CN120160869A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of hot-rolled steel plate manufacturing, and particularly relates to a method for preparing a corrosion-resistant oxide layer on the surface of a 2000MPa grade hot-formed steel. Background Art
[0002] At present, due to rust on the surface of some hot-rolled steel plates, it is difficult to enter the high-end market. The hot-rolled steel plate is always at a high temperature during the hot-rolling process. Even when it enters the coiling and cooling stage, the temperature is still as high as about 700°C, and scale is continuously generated. By regulating the microstructure of the oxide layer micro-region, it plays an important role in achieving a dense and uniform corrosion-resistant oxide layer structure.
[0003] After hot-formed steel is rolled and enters the cooling and coiling stage, although the scale has been removed by descaling water during the rolling process, since the temperature is still very high at this time, scale will be generated again. Different coiling systems have an important impact on the oxide layer structure type. The properties of oxide layers with different structure types vary greatly. When the cooling rate is relatively fast and the coiling temperature is relatively high, the oxide layer is mostly pearlite prior to eutectoid, and the interface is mostly residual FeO phase. Since the FeO phase has a low elastic modulus and belongs to a loose and porous structure, the bonding and denseness of this structure type of oxide layer with the steel matrix are poor, which is not conducive to the improvement of corrosion resistance. Therefore, it is an urgent problem to achieve precise control of the oxide layer tissue type to obtain an oxide layer with better corrosion resistance. Summary of the Invention
[0004] The purpose of the present invention is to provide a method for preparing a corrosion-resistant oxide layer on the surface of a 2000MPa grade hot-formed steel. Based on the secondary basic data of the industrial site, the phase transformation curves of the scale on the surface of the experimental steel at different cooling rates and temperatures are calculated, the microstructure of the oxide layer is preliminarily predicted, the phase transformation curves of the FeO phase at different temperatures and different cooling rates are plotted, and at the same time, the micro-region oxide layer structure is determined to obtain an extremely thin and dense oxide layer; this oxide layer has outstanding characteristics such as a dense structure of the Fe3O4 layer with a thickness less than 6μm and a porosity less than 13%, as well as excellent uniformity.
[0005] To achieve the above purpose, the present invention is realized through the following technical solutions:
[0006] A method for preparing a corrosion-resistant oxide layer on the surface of a 2000MPa grade hot-formed steel, comprising the following steps:
[0007] 1) Prepare a specimen from 2000MPa hot-formed steel, and polish the surface of the specimen;
[0008] 2) Place the specimen in a heating furnace for pre-oxidation heating, with a heating rate less than 10°C / min, and hold for 6 - 10 minutes after heating to the target temperature;
[0009] 3) Extract the rolling process parameters of the current steel plate from the secondary computer database in the industrial field, and use them as basic data for the input variables of the phase transformation model under continuous cooling conditions;
[0010] 4) Calculate the structure transformation points of the oxide layer on the surface of the hot-formed steel under the corresponding cooling regime under different rolling process parameters, and establish a temperature curve;
[0011] 5) According to the established temperature curve, combine microscopic characterization and EDS elemental analysis to continuously track and observe the dynamic transformation of the FeO phase, obtain the phase transformation curves under different cooling regimes, and at the same time combine electron backscatter diffraction technology to identify and determine the fine-grained Fe3O4 phase oxide layer at the interface, and obtain the structure transformation interval of the Fe3O4 phase at different moments of phase transformation;
[0012] 6) Based on the obtained structure transformation interval of the Fe3O4 phase, determine the process parameters for the formation of the corrosion-resistant oxide layer on the surface of the hot-formed steel, and prepare the corrosion-resistant oxide layer on the surface of the 2000MPa grade hot-formed steel plate.
[0013] The sample described is cylindrical.
[0014] The surface of the sample is polished with sandpaper not less than 1500#.
[0015] The target temperature described in step 2) is 900 - 950 °C.
[0016] The thickness of the corrosion-resistant oxide layer is below 6μm, and the porosity is less than 13%.
[0017] The rolling process parameters described in step 3) are the target coiling temperature and the cooling rate; the pre-oxidized sample is immediately cooled to the target coiling temperature.
[0018] The cooling rate of the cooling described is 15 - 18 °C / min.
[0019] The rolling process parameters in step 4) are the target coiling temperature; calculate the structure transformation points of the oxide layer on the surface of the hot-formed steel at the target coiling temperature and when the cooling rate is 2 - 17 °C / min, and establish a temperature curve.
[0020] Compared with the prior art, the beneficial effects of the present invention are:
[0021] 1) The corrosion-resistant oxide layer prepared by the present invention has a dense structure of Fe3O4 layer with a thickness less than 6 μm and a porosity less than 13%, as well as excellent uniformity characteristics. Based on the industrial field secondary computer database, the phase transformation curves of the scale on the surface of the experimental steel at different cooling rates and temperatures are calculated, the organizational structure of the oxide layer is preliminarily predicted, the phase transformation curves of the FeO phase at varying temperatures and different cooling rates are plotted, and at the same time, the structure of the micro-area oxide layer is determined by combining the analysis method of electron backscatter diffraction, realizing the preparation of an extremely thin and dense oxide layer, providing a practical theoretical basis for the quality upgrade of industrial field products.
[0022] 2) The corrosion-resistant oxide layer prepared by the present invention has a low porosity. The oxide layer covering the surface of the hot-formed steel plays a physical barrier role. If the oxide layer has a high density, the surface approaches an insulating state and the self-corrosion current is close to zero. However, the scale belongs to a porous structure type, and during the hot rolling process, defects such as breakage and cracks will occur in the scale, and corrosion behavior is inevitable. However, there are certain differences in the corrosion resistance of different types of oxide layer structures. The lower the self-corrosion current, the smaller the porosity. The ratio of the self-corrosion current of the specimen with the oxide layer to that of the specimen without the oxide layer is determined as the porosity, and the porosity of this type of oxide layer structure is < 13%.
[0023] 3) The area fraction of Fe3O4 + Fe phase in the corrosion-resistant oxide layer prepared by the present invention > 75%, ensuring the uniformity and density of the oxide layer. Through the on-site data tracking and collection and subsequent drawing calculations, combined with deep learning of microscopic characterization, the process window of the Fe3O4 + Fe phase is found. Description of the Drawings
[0024] Figure 1 It is the microstructure diagram of the corrosion-resistant and dense oxide layer of the fine-grained Fe3O4 phase in Example 1.
[0025] Figure 2 It is the microstructure diagram of the corrosion-resistant and dense oxide layer of the fine-grained Fe3O4 phase in Example 2.
[0026] Figure 3 It is the schematic diagram of the relationship between the coiling temperature - cooling rate - oxide layer structure type in Example 1.
[0027] Figure 4 It is the schematic diagram of the relationship between the coiling temperature - cooling rate - oxide layer structure type in Example 2. Detailed Description of the Invention
[0028] The present invention will be described in detail below in conjunction with the drawings of the specification, but it should be noted that the implementation of the present invention is not limited to the following embodiments.
[0029] Example 1
[0030] Process more than 4 pieces of 2000MPa grade hot-formed steel Cylindrical specimens were polished with 1500# sandpaper to remove the surface oxide layer and dirt, ensuring a smooth surface. Subsequently, the specimens were placed in a heating furnace for pre-oxidation heating at a temperature of 890 °C in an air atmosphere + 6% water vapor atmosphere with a heating rate of 7 °C / min. After heating to the target temperature of 890 °C, they were soaked for 6 min to ensure uniform preheating of the specimens and ensure that the oxide layer uniformly covered the specimen surface.
[0031] After pre-oxidation of the hot-formed steel specimens, they were cooled to the target coiling temperature of 690 °C at a cooling rate of 18 °C / s. Subsequently, 4 specimens (or more specimens) were cooled to room temperature at cooling rates of 2 °C / min, 6 °C / min, 11 °C / min, and 17 °C / min respectively. Based on the cooling parameters, the phase transformation points of the oxide layer were established. Through the observation of a scanning electron microscope, the microstructures at different cooling rates and coiling temperatures were obtained. Using ☆ to represent the structural transformation point of the Fe3O4 phase, in combination with the deep learning graph of the microstructures (see Figure 1 ), a structural transformation curve (phase transformation model) with a fine-grained Fe3O4 phase at the interface was established, as shown in Figure 3 .
[0032] From Figure 1 and Figure 3 , it can be seen that Figure 3 in the upper half of the dotted line in ☆ area is the generation area of the fine-grained Fe3O4 phase. According to the image and the structural characteristics of the Fe3O4 phase, it can be known that the oxide layer densely covers the surface of the steel matrix, and the grain size of the Fe3O4 phase is less than 500 nm, and the thickness of the oxide layer is about 5 μm (obtained by measuring the scale in Figure 1 ). The porosity is the ratio of the self-corrosion current density of the specimen with mill scale to that of the specimen without mill scale. By calculating, the porosity of the oxide layer is about 12%.
[0033] In summary, through the microscopic regulation of the cooling rate and microstructure, the oxide layer is more uniform, which effectively guarantees the corrosion resistance of the steel plate.
[0034] As can be seen from Example 1, through process regulation and model establishment, the corrosion resistance of the steel plate is effectively guaranteed.
[0035] Example 2
[0036] The 2000 MPa grade hot-formed steel was processed into more than 4 Cylindrical specimens were used. At the same time, the surface of the specimens was polished with 1500# sandpaper to remove the surface oxide layer and dirt, ensuring a smooth surface. Subsequently, the specimens were placed in a heating furnace for pre-oxidation heating. The heating temperature was 890 °C, the ambient atmosphere was an air atmosphere + 10% steam atmosphere, the heating rate was 8 °C / min, and after heating to the target temperature of 910 °C, it was soaked for 8 min to ensure the uniform preheating of the specimens and ensure that the oxide layer uniformly covered the surface of the specimens.
[0037] After the pre-oxidation of the hot-formed steel specimens, they were cooled to the target coiling temperature of 600 °C at a cooling rate of 16 °C / s in the industrial field secondary computer database. Subsequently, multiple specimens were further cooled to room temperature at cooling rates of 2 °C / min, 6 °C / min, 11 °C / min, and 17 °C / min respectively. According to the cooling parameters, the phase transformation points of the oxide layer were established. The structure transformation point of the Fe3O4 phase was represented by ☆. In combination with the deep learning graph of the microstructural organization (see Figure 2 ), the structure transformation curve with fine-grained Fe3O4 phase at the interface was established, as shown in Figure 4 .
[0038] From Figure 2 and Figure 4 , it can be seen that Figure 4 In the upper half part ☆ area of the dotted line in, it is the generation area of the fine-grained Fe3O4 phase. According to the image and the structural characteristics of the Fe3O4 phase, it can be known that the oxide layer densely covers the surface of the steel matrix, and the grain size of the Fe3O4 phase is less than 400 nm, and the thickness of the oxide layer is about 5.6 μm (obtained by measuring the scale in Figure 3 ). By calculating, the porosity of the oxide layer is about 14%. In summary, through the microscopic regulation of the cooling rate and microstructure, the oxide layer is more uniform, which well ensures the corrosion resistance of the steel plate.
[0039] The corrosion-resistant oxide layer prepared by the present invention has a dense structure of the Fe3O4 layer with a thickness less than 6 μm and a porosity less than 13% and excellent uniformity characteristics. Based on the industrial field secondary computer database, the phase transformation curves of the mill scale on the surface of the experimental steel at different cooling rates and temperatures were calculated, the microstructure of the oxide layer was preliminarily predicted, the variable temperature and phase transformation curves of the FeO phase at different cooling rates were drawn, and at the same time, the micro-region oxide layer structure was determined by combining the analysis method of electron backscatter diffraction, realizing the preparation of an extremely thin and dense oxide layer, providing a realistic theoretical basis for the quality upgrade of industrial field products.
Claims
1. A method for preparing a corrosion-resistant oxide layer on the surface of a 2000MPa grade hot-formed steel, characterized in that: The following steps are involved: 1) The specimen is made of 2000MPa hot-formed steel, and the surface of the specimen is polished; 2) The sample is placed in a heating furnace for pre-oxidation heating at a heating rate of less than 10°C / min. After heating to the target temperature, it is heated for 6 to 10 minutes; 3) Extract the current steel plate rolling process parameters from the secondary computer database of the industrial site, and use them as basic data as input variables of the phase change model under continuous cooling conditions; 4) Calculate the structural transition point of the oxide layer on the surface of hot-formed steel under different rolling process parameters and corresponding cooling system, and establish the temperature curve; 5) Based on the established temperature curve, the dynamic transformation of the FeO phase is continuously tracked and observed in combination with microscopic characterization and EDS elemental analysis to obtain the phase change curves under different cooling regimes. At the same time, the fine-grained Fe3O4 phase oxide layer at the interface is identified and determined in combination with electron backscatter diffraction technology to obtain the structural transformation range of the Fe3O4 phase at different phase transition times; 6) Based on the obtained structural transformation range of the Fe3O4 phase, the process parameters for forming the corrosion-resistant oxide layer on the surface of the hot-formed steel are determined, and the corrosion-resistant oxide layer on the surface of a 2000MPa grade hot-formed steel plate is prepared.
2. The method for preparing a 2000MPa grade hot-formed steel surface corrosion-resistant oxide layer according to claim 1, characterized in that: The sample is cylindrical.
3. The method for preparing a 2000MPa grade hot-formed steel surface corrosion-resistant oxide layer according to claim 1, characterized in that: The surface of the sample is polished with sandpaper of no less than 1500#.
4. The method for preparing a 2000MPa grade hot-formed steel surface corrosion-resistant oxide layer according to claim 1, characterized in that: The target temperature described in step 2) is 900-950°C.
5. The method for preparing a 2000MPa grade hot-formed steel surface corrosion-resistant oxide layer according to claim 1, characterized in that: The thickness of the corrosion-resistant oxide layer is less than 6 μm, and the porosity is less than 13%.
6. The method for preparing a 2000MPa grade hot-formed steel surface corrosion-resistant oxide layer according to claim 1, characterized in that: The rolling process parameters described in step 3) are the target coiling temperature and the cooling rate; the pre-oxidized sample is immediately cooled to the target coiling temperature.
7. The method for preparing a corrosion-resistant oxide layer on the surface of a 2000MPa grade hot-formed steel according to claim 6, characterized in that: The cooling rate of the cooling is 15-18°C / min.
8. The method for preparing a 2000MPa grade hot-formed steel surface corrosion-resistant oxide layer according to claim 1, characterized in that: In step 4), the rolling process parameter is the target coiling temperature; the structural transition point of the oxide layer on the surface of the hot-formed steel is calculated at the target coiling temperature and at a cooling rate of 2 to 17°C / min, and a temperature curve is established.