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

Abstract

The invention discloses a method for preparing a corrosion-resistant oxide layer on a steel surface based on a variable-pressure oxidation process, and aims to solve the problems that a coating is easy to peel off and the preparation process is relatively complicated in the conventional method for improving the corrosion resistance of steel. The method for preparing the corrosion-resistant oxidation layer comprises the following steps: 1, placing the steel base material in a tubular furnace, vacuumizing until the air pressure in the furnace is 1-50kPa, and heating the steel base material to 500-1400 DEG C for pre-oxidation treatment; and 2, air is introduced into the tubular furnace, the air pressure in the tubular furnace is increased to 80 kPa to 101.325 kPa, and the temperature of the steel base material is increased to 500 DEG C to 1400 DEG C for reoxidation treatment. According to the invention, the carbon steel is used as the matrix, an in-situ oxidation treatment mode is adopted, the preparation method is simple and easy to implement, the thickness of the oxide layer can be regulated and controlled, large-scale production is facilitated, and the obtained oxide layer is well combined with the matrix and has the characteristics of good corrosion resistance, insulativity, low surface roughness and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of corrosion protection, and in particular relates to a corrosion-resistant oxide layer of steel and a preparation method thereof. Background Art

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

[0003] The current methods for improving the corrosion resistance of steel basically adopt post-production treatment, such as coating protection, alloying, surface treatment and cathodic protection. However, the disadvantages of the above methods are that the coating is at risk of peeling, wear or aging, and the maintenance and re-coating costs are high, which causes the exposed metal to 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. How to simply, cost-effectively and quickly prepare steel with excellent corrosion resistance from the steel production process or heat treatment process has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that the coating of the existing method for improving the corrosion resistance of steel is easy to peel off and the preparation process is relatively complicated, and to provide a method for preparing a corrosion-resistant oxide layer on the steel surface based on a pressure swing oxidation process.

[0005] The method of preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process of the present invention is implemented by the following steps:

[0006] 1. Place the steel substrate in a tube furnace, evacuate the air pressure in the tube furnace to 1kPa~50kPa, heat the steel substrate to 500~1400℃ for pre-oxidation treatment, and cool it down with the furnace;

[0007] Second, air is introduced into the tube furnace to increase the gas pressure in the tube furnace to 80kPa to 101.325kPa, and the steel substrate is heated to 500 to 1400°C for reoxidation to obtain a corrosion-resistant oxide layer on the surface of the steel substrate.

[0008] The oxide layer formed on the steel surface by atmospheric pressure oxidation is usually loose and porous and easily falls off. Liquids or vapors can easily pass through the loose oxide layer and reach the substrate, which has little effect on corrosion protection of the steel. However, the present invention uses a pressure swing oxidation process to first perform a pre-oxidation treatment under low pressure conditions to obtain a dense oxide layer. Then, by increasing the pressure, the growth rate of the oxide layer is adjusted to make the oxide layer grow more uniformly and have sufficient thickness. The resulting oxide layer has a strong barrier effect against corrosive liquids.

[0009] The present invention utilizes steel with a carbon content of less than 2.11% as the object of pressure-switch oxidation treatment, which has low cost. Steel with a carbon content of less than 2.11% has poor corrosion resistance. The preparation method is simple and easy, and the thickness of the oxide layer can be regulated by temperature, holding time, air pressure and oxygen partial pressure, which is convenient for large-scale production. The obtained carbon steel corrosion-resistant oxide layer has little effect on the size of the original carbon steel and is suitable for precision structural processing. The surface is flat and complete, which can be achieved during hot rolling or heat treatment, has little effect on mechanical properties, and utilizes heat energy in other treatment processes to save economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a photo of the carbon steel with a corrosion-resistant oxide layer prepared in Example 1 of the present invention;

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

[0015] Specific embodiment 1: The method for preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process in this embodiment is implemented according to the following steps:

[0016] 1. Place the steel substrate in a tube furnace, evacuate the air pressure in the tube furnace to 1kPa~50kPa, heat the steel substrate to 500~1400℃ for pre-oxidation treatment, and cool it down with the furnace;

[0017] Second, air is introduced into the tube furnace to increase the gas pressure in the tube furnace to 80kPa to 101.325kPa, and the steel substrate is heated to 500 to 1400°C for reoxidation to obtain a corrosion-resistant oxide layer on the surface of the steel substrate.

[0018] In step 1 of this embodiment, powdered material that is easily oxidizable (consuming oxygen) may be placed in a tube furnace.

[0019] The steel with the corrosion-resistant oxide layer and the pressure-switch oxidation preparation method of this embodiment can be implemented during the hot rolling or heat treatment process of the steel.

[0020] In this embodiment, the pressure swing oxidation is first carried out under low pressure or anoxic conditions, and then the oxidation is carried out again at increased pressure or normal pressure. This process can be cyclical; and after low-pressure oxidation or anoxic oxidation, the pressure or oxygen partial pressure can be increased multiple times for oxidation.

[0021] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the carbon content of the steel substrate in step 1 is lower than 2.11 wt%.

[0022] Specific embodiment three: This embodiment differs from specific embodiment one or two in that in step one, the vacuum is evacuated until the pressure in the furnace reaches 1 kPa to 15 kPa.

[0023] Specific embodiment 4: This embodiment differs from specific embodiment 3 in that in step 1, the steel substrate is heated to 700-900° C. and reoxidized for 10-60 minutes.

[0024] Specific embodiment 5: This embodiment differs from any one of specific embodiments 1 to 4 in that in step 1, the steel substrate is suspended in a tube furnace.

[0025] Specific embodiment 6: This embodiment differs from any one of specific embodiments 1 to 5 in that the gas pressure in the tube furnace is increased to 101.325 kPa in step 2.

[0026] Specific embodiment seven: The difference between this embodiment and any one of specific embodiments one to six is ​​that in step two, the steel substrate is heated to 700-900° C. and subjected to reoxidation treatment for 5-60 minutes.

[0027] Specific embodiment eight: This embodiment differs from any one of specific embodiments one to seven in that the heating rate of the steel substrate in step two is controlled to be 5-50° C. / min.

[0028] Specific embodiment 9: This embodiment differs from any one of specific embodiments 1 to 8 in that in step 2, the pre-oxidation treatment in step 1 and the re-oxidation treatment in step 2 are cycled multiple times in sequence.

[0029] Specific embodiment ten: The difference between this embodiment and any one of specific embodiments one to nine is that the thickness of the corrosion-resistant oxide layer in step two is 5 to 50 microns.

[0030] Example 1: The method of preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process in this embodiment is implemented according to the following steps:

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

[0032] 2. Then, air is introduced into the tube furnace, the gas pressure in the tube furnace is increased to normal pressure, and the steel substrate is heated to 700°C, 750°C, 800°C and 850°C respectively, and then oxidized for 20 minutes each. The heating rate is 10°C / min, and the furnace is cooled to obtain a corrosion-resistant oxide layer on the surface of the steel substrate.

[0033] In step 1 of this embodiment, the mixed powder consists of 0.2 g of carbon powder, 1.05 g of aluminum powder and 1.7 g of aluminum oxide powder.

[0034] The microscopic image of the corrosion-resistant oxide layer of carbon steel obtained in this embodiment is shown in FIG. Figure 1 The thickness of the oxide layer increases slightly with increasing temperature, and the resulting oxide layer is denser. Oxidation is dominated by diffusion, which will weaken the oxidation rate and prevent the expansion of the oxide layer.

[0035] Example 2: The method of preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process in this example is implemented according to the following steps:

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

[0037] 2. Then, air is introduced into the tube furnace, and the air pressure in the tube furnace is increased to 50 kPa. The steel substrates are heated to 800 ° C and oxidized for 20 minutes at a heating rate of 10 ° C / min. The steel substrates are cooled in the furnace to obtain a corrosion-resistant oxide layer on the surface of the steel substrates.

[0038] In this embodiment, the gas pressure in the second step furnace is lowered to reduce the overall oxide layer thickness while having a denser and thicker pre-oxidation film.

[0039] Example 3: The method of preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process in this embodiment is implemented according to the following steps:

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

[0041] Second, air was introduced into the tube furnace to increase the pressure inside the tube furnace to normal pressure, and the steel substrate was heated to 800℃ and then oxidized for 10 minutes at a heating rate of 10℃ / min. The steel substrate was cooled with the furnace.

[0042] 3. The pre-oxidation treatment in step 1 and the re-oxidation treatment in step 2 are cycled for multiple times to obtain a corrosion-resistant oxide layer on the surface of the steel substrate.

[0043] In this embodiment, the thickness of the oxide layer can be adjusted by adjusting the temperature of each stage of the variable pressure oxidation, and adjusting the vacuum degree (air atmosphere) or oxygen partial pressure conditions; the thickness of the oxide layer 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] The carbon steel in this embodiment will generate a loose and expanded oxide layer that is easy to fall off and has an extremely poor surface condition.

[0047] Comparative Example 2

[0048] The same as Example 1, except that the second step of normal pressure reoxidation treatment is not performed.

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

[0050] Effect Example 1

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

[0052] Table 1

[0053] Temperature Thickness μm 700 6.40 750 16.87 800 19.88 850 20.09

[0054] Effect Example 2

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

[0056] Table 2

[0057] Sample pressure swing oxidation temperature / ℃ <![CDATA[i corr (Acm -2 )]]> <![CDATA[E corr (Plumbing SCE)]]> 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 descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection 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 a pressure swing oxidation process, characterized in that The method for preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process is implemented according to the following steps:

1. Place the steel substrate in a tube furnace, evacuate the tube furnace until the pressure is 1kPa to 50kPa, heat the steel substrate to 500 to 1400°C for pre-oxidation treatment, and cool it with the furnace; Second, air is introduced into the tubular furnace to increase the gas pressure in the tubular furnace to 80 kPa to 101.325 kPa, and the steel substrate is heated to 500 to 1400° C. for reoxidation treatment to obtain a corrosion-resistant oxide layer on the surface of the steel substrate.

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

3. The method for preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process according to claim 1, characterized in that In step 1, the vacuum is evacuated until the pressure in 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 a pressure swing oxidation process according to claim 1, characterized in that In step 1, the steel substrate is heated to 700-900° C. and subjected to reoxidation treatment for 10-60 minutes.

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

6. The method for preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process according to claim 1, characterized in that In step 2, the gas pressure in the tube furnace is increased to 101.325 kPa.

7. The method for preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process according to claim 1, characterized in that In step 2, the steel substrate is heated to 700-900° C. and subjected to reoxidation treatment for 5-60 minutes.

8. The method for preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process according to claim 1, characterized in that In step 2, the heating rate of the steel substrate is controlled to be 5 to 50° C. / min.

9. The method for preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process according to claim 1, characterized in that In step 2, the pre-oxidation treatment in step 1 and the re-oxidation treatment in step 2 are cycled for multiple times.

10. The method for preparing a corrosion-resistant oxide layer on a steel surface based on a pressure swing oxidation process according to claim 1, characterized in that The thickness of the corrosion-resistant oxide layer in step 2 is 5 to 50 microns.

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