Method for preparing corrosion-resistant oxide layer on steel surface based on variable pressure oxidation process

Abstract

The application is to solve the problems of easy peeling and complex preparation process of the existing method for improving the corrosion resistance of steel. The method for preparing the corrosion-resistant oxide layer comprises the following steps: 1) placing a steel base material in a tube furnace, vacuumizing the tube furnace to 1kPa-50kPa, and pre-oxidizing the steel base material by heating to 500-1400 DEG C; 2) introducing air into the tube furnace, increasing the air pressure in the tube furnace to 80kPa-101.325kPa, and re-oxidizing the steel base material by heating to 500-1400 DEG C. The application uses carbon steel as the base body and adopts in-situ oxidation treatment, and has the advantages of simple and easy preparation method, controllable oxide layer thickness, convenient large-scale production, good combination of the obtained oxide layer and the base body, good corrosion resistance, insulation, low surface roughness and other characteristics.

Description

Technical Field

[0001] This invention belongs to the field of corrosion protection technology, specifically relating to a corrosion-resistant oxide layer for steel and its preparation method. Background Technology

[0002] Steel is primarily composed of iron, carbon, and other alloying elements, with a carbon content ranging from 0.02% to 2.1%. Due to its excellent mechanical properties and relatively low production cost, steel is widely used in construction, manufacturing, automotive, shipbuilding, and machinery industries. Overall, steel, with its unique cost-effectiveness and diverse applications, remains an indispensable material in modern industrial and infrastructure construction.

[0003] Currently, methods to improve the corrosion resistance of steel primarily involve post-production treatments such as coating protection, alloying, surface treatment, and cathodic protection. However, these methods have drawbacks: coatings are susceptible to peeling, wear, or aging; maintenance and recoating are costly; and exposed metal may corrode again. Surface treatments such as hot-dip galvanizing may require complex equipment and processes. Cathodic protection systems require regular inspection and maintenance, are complex to install, and may incur additional costs. Therefore, finding a simple, cost-effective, and rapid method to prepare steel with excellent corrosion resistance from the steel production or heat treatment process has become a pressing technical challenge for those skilled in the art. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of easy peeling of coatings and complicated preparation processes in existing methods for improving the corrosion resistance of steel, and to provide a method for preparing a corrosion-resistant oxide layer on the steel surface based on pressure swing oxidation process.

[0005] The present invention provides a method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation (PSO) technology, which is implemented according to the following steps:

[0006] 1. Place the steel substrate in a tube furnace, evacuate the furnace to a pressure of 1 kPa to 50 kPa, heat the steel substrate to 500 to 1400°C for pre-oxidation treatment, and then cool it with the furnace.

[0007] Second, air is then introduced into the tubular furnace to raise the gas pressure inside the furnace to 80 kPa to 101.325 kPa, and the steel substrate is heated to 500 to 1400°C for re-oxidation treatment, resulting in a corrosion-resistant oxide layer on the surface of the steel substrate.

[0008] The oxide layer obtained by atmospheric pressure oxidation on the steel surface is usually loose and porous, and easily detached. Liquids or vapors can easily penetrate the loose oxide layer to reach the substrate, providing minimal protection against steel corrosion. This invention, however, uses a pressure swing oxidation process to first perform pre-oxidation under low pressure conditions, resulting in a dense oxide layer. Then, by increasing the pressure and adjusting the growth rate of the oxide layer, it is made to grow more uniformly and with sufficient thickness. The resulting oxide layer has a strong barrier effect against corrosive liquids.

[0009] This invention utilizes steel with a carbon content of less than 2.11% as the target material for pressure swing oxidation treatment, resulting in lower costs. Furthermore, steel with a carbon content of less than 2.11% exhibits poor corrosion resistance. The preparation method is simple and easy to implement, and the oxide layer thickness can be controlled by adjusting temperature, holding time, gas pressure, and oxygen partial pressure, facilitating large-scale production. The resulting corrosion-resistant oxide layer on carbon steel has minimal impact on the original carbon steel's dimensions, making it suitable for precision structural processing. The surface is smooth and complete, and the process can be achieved during hot rolling or heat treatment. It has minimal impact on mechanical properties and utilizes the heat energy from other processing steps, saving resources and increasing economic efficiency. Attached Figure Description

[0010] Figure 1 This is a photograph of a carbon steel with a corrosion-resistant oxide layer prepared according to Example 1 of the present invention.

[0011] Figure 2 This is a surface SEM image of carbon steel with a corrosion-resistant oxide layer prepared in Example 1 of the present invention;

[0012] Figure 3 This is a cross-sectional SEM image of the carbon steel with a corrosion-resistant oxide layer prepared in Example 1 of the present invention;

[0013] Figure 4 The polarization curve of carbon steel with a corrosion-resistant oxide layer prepared in Example 1 of the present invention in a 3.5 wt.% sodium chloride solution;

[0014] Figure 5 This is a surface roughness diagram of carbon steel with a corrosion-resistant oxide layer prepared in Example 1 of the present invention. Detailed Implementation

[0015] Specific Implementation Method 1: This implementation method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation process is carried out according to the following steps:

[0016] 1. Place the steel substrate in a tube furnace, evacuate the furnace to a pressure of 1 kPa to 50 kPa, heat the steel substrate to 500 to 1400°C for pre-oxidation treatment, and then cool it with the furnace.

[0017] Second, air is then introduced into the tubular furnace to raise the gas pressure inside the furnace to 80 kPa to 101.325 kPa, and the steel substrate is heated to 500 to 1400°C for re-oxidation treatment, resulting in a corrosion-resistant oxide layer on the surface of the steel substrate.

[0018] In step one of this embodiment, easily oxidizable (oxygen-consuming) powdered materials can be placed inside the tube furnace.

[0019] The method for preparing steel with a corrosion-resistant oxide layer and the method for preparing pressure-switched oxidation in this embodiment can be implemented during the hot rolling or heat treatment of steel.

[0020] In this embodiment, pressure swing oxidation is first carried out under low pressure or hypoxia conditions, and then oxidation is carried out again by increasing the gas pressure or to normal pressure. This process can be repeated. After low pressure oxidation or hypoxia oxidation, the gas pressure or oxygen partial pressure can be increased multiple times for oxidation.

[0021] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the carbon content of the steel substrate in step one is less than 2.11 wt%.

[0022] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that in step 1, a vacuum is drawn until the gas pressure inside the furnace is 1 kPa to 15 kPa.

[0023] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Three in that in step one, the steel substrate is heated to 700-900℃ for re-oxidation treatment for 10-60 minutes.

[0024] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that the steel substrate is suspended inside the tube furnace in step 1.

[0025] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the gas pressure inside the tubular furnace is increased to 101.325 kPa in step two.

[0026] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that in step two, the steel substrate is heated to 700-900℃ for re-oxidation treatment for 5-60 minutes.

[0027] Specific Implementation Method Eight: This implementation method differs from one of the specific implementation methods one to seven in that the heating rate of the steel substrate is controlled to be 5 to 50°C / min in step two.

[0028] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that step two involves repeating the pre-oxidation treatment of step one and the re-oxidation treatment of step two multiple times.

[0029] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that the thickness of the corrosion-resistant oxide layer in step 2 is 5 to 50 micrometers.

[0030] Example 1: This example describes a method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation (PSO) technology, implemented according to the following steps:

[0031] 1. In a tube furnace, suspend carbon steel Q235B in the middle of the crucible, put oxygen-consuming mixed powder into the crucible, evacuate the furnace until the gas pressure is 1±0.1kPa, close the gas valve of the tube furnace, and pre-oxidize the steel substrate to 700℃, 750℃, 800℃ and 850℃ respectively for 20min each, and then cool it with the furnace.

[0032] Second, air is then introduced into the tubular furnace to raise the gas pressure inside the furnace to atmospheric pressure. The steel substrate is then heated to 700℃, 750℃, 800℃ and 850℃ respectively for 20 minutes each time for re-oxidation treatment. The heating rate is 10℃ / min for each case. The substrate is then cooled with the furnace to obtain a corrosion-resistant oxide layer on the surface of the steel substrate.

[0033] In step one of this embodiment, the mixed powder consists of 0.2g carbon powder, 1.05g aluminum powder, and 1.7g alumina powder.

[0034] The microscopic image of the corrosion-resistant oxide layer on carbon steel obtained in this embodiment is shown below. Figure 1 The thickness of the oxide layer increases only slightly with increasing temperature, resulting in a denser oxide layer. Oxidation is diffusion-dominated, which weakens the oxidation rate and prevents the oxide layer from expanding.

[0035] Example 2: This example describes a method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation (PSO) technology, implemented according to the following steps:

[0036] 1. In a tube furnace, suspend carbon steel Q235B in the middle of the crucible, put oxygen-consuming mixed powder into the crucible, evacuate the furnace until the gas pressure is 40±0.1kPa, close the gas valve of the tube furnace, heat the steel substrate to 800℃ for pre-oxidation treatment for 20min, and then cool it with the furnace.

[0037] Second, air is then introduced into the tubular furnace to raise the gas pressure inside the furnace to 50 kPa. The steel substrates are then heated to 800°C and oxidized for 20 minutes. The heating rate is 10°C / min. The furnace is then cooled to obtain a corrosion-resistant oxide layer on the surface of the steel substrates.

[0038] In this embodiment, the gas pressure inside the furnace in the second step is reduced to decrease the overall oxide layer thickness, under the condition of a relatively dense and thick pre-oxidized film.

[0039] Example 3: This example describes a method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation (PSO) technology, implemented according to the following steps:

[0040] 1. In a tube furnace, suspend carbon steel Q235B in the middle of the crucible, put oxygen-consuming mixed powder into the crucible, evacuate the furnace until the gas pressure is 1±0.1kPa, close the gas valve of the tube furnace, heat the steel substrate to 800℃ for pre-oxidation treatment for 10min, and then cool it with the furnace.

[0041] Second, air is then introduced into the tubular furnace to raise the gas pressure inside to atmospheric pressure. The steel substrate is then heated to 800℃ and oxidized for 10 minutes, with a heating rate of 10℃ / min. The furnace is then cooled.

[0042] Third, the pre-oxidation treatment in step one and the re-oxidation treatment in step two are repeated multiple times to obtain a corrosion-resistant oxide layer on the surface of the steel substrate.

[0043] This embodiment can adjust the oxide layer thickness by adjusting the temperature of each stage of pressure swing oxidation, as well as by adjusting the vacuum degree (air atmosphere) or oxygen partial pressure; the oxide layer thickness can also be adjusted by adjusting the oxidation time.

[0044] Comparative Example 1

[0045] Same as Example 1, except that low-pressure pre-oxidation is not performed.

[0046] In this embodiment, the carbon steel will form a loose, porous oxide layer that is easy to peel off, resulting in a very poor surface condition.

[0047] Comparative Example 2

[0048] Same as Example 1, except that step two, atmospheric pressure re-oxidation treatment, is not performed.

[0049] The oxide layer obtained in this embodiment is extremely thin and has poor corrosion resistance.

[0050] Example 1

[0051] Example 1 was measured, and the thickness of the oxide layer at 700-850℃ was compared. The results are shown in Table 1.

[0052] Table 1

[0053] 700 6.40 750 16.87 800 19.88 850 20.09

[0054] Example 2

[0055] The corrosion resistance of the oxide layer prepared in Example 1 was determined using a standard three-electrode system. A standard calomel electrode, a graphite rod, and the sample were used as the reference electrode, counter electrode, and working electrode, respectively. The scan rate was 1 mV / s. All tests were performed in a 3.5 wt% NaCl solution at room temperature. Before testing, an open-circuit potential test was conducted for 30 min to stabilize the sample; the results are shown in Table 2.

[0056] Table 2

[0057] 0 <![CDATA[1.15×10 -6 ]]> -0.80 700 <![CDATA[3.00×10 -6 ]]> -0.59 750 <![CDATA[3.55×10 -7 ]]> -0.35 800 <![CDATA[3.31×10 -7 ]]> -0.41 850 <![CDATA[1.50×10 -7 ]]> -0.34

[0058] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation process, characterized in that... The method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation is implemented according to the following steps:

1. Place the steel substrate in a tube furnace, evacuate the furnace to a pressure of 1 kPa to 50 kPa, heat the steel substrate to 700 to 900°C for pre-oxidation treatment for 10 to 60 minutes, and then cool it with the furnace. Second, air is then introduced into the tubular furnace to raise the gas pressure inside the tubular furnace to 80 kPa~101.325 kPa, and the steel substrate is heated to 700~900℃ for re-oxidation treatment for 5~60 minutes to obtain a corrosion-resistant oxide layer on the surface of the steel substrate. The steel substrate mentioned above is carbon steel Q235B.

2. The method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation process according to claim 1, characterized in that... In step one, the carbon content of the steel substrate is less than 2.11 wt%.

3. The method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation process according to claim 1, characterized in that... In step one, a vacuum is drawn until the gas pressure inside the tube furnace reaches 1 kPa to 15 kPa.

4. The method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation process according to claim 1, characterized in that... In step one, the steel substrate is suspended inside the tube furnace.

5. The method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation process according to claim 1, characterized in that... In step two, the gas pressure inside the tubular furnace is increased to 101.325 kPa.

6. The method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation process according to claim 1, characterized in that... In step two, the heating rate of the steel substrate is controlled to be 5~50℃ / min.

7. The method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation process according to claim 1, characterized in that... In step two, the pre-oxidation treatment from step one and the re-oxidation treatment from step two are repeated multiple times.

8. The method for preparing a corrosion-resistant oxide layer on a steel surface based on pressure swing oxidation process according to claim 1, characterized in that... In step two, the thickness of the corrosion-resistant oxide layer is 5 to 50 micrometers.

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