A Cr2N corrosion-resistant coating on the inner wall of a carbon steel storage tank and its preparation method

Abstract

The present invention belongs to the technical field of corrosion-resistant coatings, and specifically relates to a Cr2N corrosion-resistant coating for the inner wall of a carbon steel storage tank and a preparation method thereof. The preparation method comprises the following steps: first, irradiating the steel with an argon ion radiation source, with the target chamber in a vacuum state during the irradiation process; then, subjecting the inner wall of the carbon steel storage tank to a double glow plasma chromium alloying treatment; and then subjecting the Cr alloy layer to an active screen ion nitriding treatment to prepare the Cr2N coating. The Cr2N coating prepared by this method exhibits a gradient distribution of internal microstructure components, with the Cr and N content gradually decreasing from the surface to the interior. The Cr2N coating is metallurgically bonded to the inner wall of the carbon steel storage tank, and interdiffusion occurs at the interface between the coating and the substrate, resulting in a dense coating structure that is resistant to corrosion from high and medium concentrations of sulfuric acid.

Description

Technical Field

[0001] The present invention belongs to the technical field of corrosion-resistant coatings, and in particular relates to a Cr2N corrosion-resistant coating for the inner wall of a carbon steel storage tank and a preparation method thereof. Background Art

[0002] Concentrated sulfuric acid storage tanks are typically composed primarily of steel, typically carbon steel. The inner walls of concentrated sulfuric acid storage tanks react directly with the sulfuric acid, causing chemical corrosion. This type of corrosion is a redox reaction between metals like iron and oxidants. Low and high concentrations of sulfuric acid are oxidizing acids, while medium concentrations are non-oxidizing. Oxidation can cause strong hydrogen depolarization corrosion of iron-carbon alloys. The corrosion rate increases with increasing sulfuric acid concentration. Literature indicates that the corrosion rate reaches its peak when the sulfuric acid concentration reaches 47% to 50%. As the concentration increases further, the oxidizing nature of the concentrated sulfuric acid causes the formation of a protective passivation film on the iron, gradually decreasing the corrosion rate. The corrosion rate is very low when the sulfuric acid concentration reaches 70% to 98%.

[0003] At present, more than 90% of the metal sulfuric acid storage tanks on the market are made of ordinary carbon steel. However, ordinary carbon steel cannot withstand sulfuric acid with a concentration below 80%. When ordinary carbon steel is used for sulfuric acid with a concentration below 80%, protective measures must be taken. The protective measures that are currently used more frequently on the market are: coatings, rubber linings, fiberglass linings or glass flake putty. The method of brushing anti-corrosion coatings on the inside of carbon steel shells is generally aimed at carbon steel storage tanks with low concentrations (below 45%) of dilute sulfuric acid at room temperature. The method of lining carbon steel shells with rubber is aimed at dilute sulfuric acid solutions at medium and low temperatures. It has special properties such as wear resistance, cavitation resistance, stress change resistance, and temperature fusion resistance, but it also has defects such as poor heat resistance, inability to withstand concentrated sulfuric acid with oxidizing properties, poor thermal conductivity, and a thin corrosion-resistant layer. Lining carbon steel shells with fiberglass linings or glass flake putty is a heavy resin anti-corrosion method, which is suitable for dilute sulfuric acid at a certain temperature. While the above methods can improve the corrosion resistance of carbon steel storage tanks against dilute sulfuric acid, they are not resistant to oxidizing concentrated sulfuric acid, such as sulfuric acid with a concentration of 80% or above at room temperature or a medium concentration of 65% to 80% above 65°C. Therefore, it is urgent to develop a material that can solve the corrosion problem of storing medium-concentration sulfuric acid. Summary of the Invention

[0004] The purpose of the present invention is to solve the deficiencies of the prior art and provide a Cr2N corrosion-resistant coating for the inner wall of a carbon steel storage tank and a preparation method thereof, specifically adopting the following technical solutions:

[0005] A method for preparing a Cr2N corrosion-resistant coating on the inner wall of a carbon steel storage tank comprises the following steps:

[0006] Step 1: Use an argon ion irradiation source to irradiate the steel. During the irradiation process, the target chamber is in a vacuum state, the temperature is 500℃~550℃, and the ion irradiation dose is 5×10 18 ~2×10 19 ions / cm 2 ;

[0007] Step 2: Performing a double glow plasma chromium alloying treatment on the inner wall of the carbon steel storage tank to form a Cr alloy layer after the double glow plasma chromium alloying treatment;

[0008] Step 3: Perform active screen ion nitriding treatment on the Cr alloy layer on the inner wall of the carbon steel storage tank to obtain a Cr2N coating.

[0009] The present invention adopts ion irradiation technology to irradiate the steel surface, which can significantly increase the internal defects of the steel metal, such as point defects, dislocation rings, vacancy clusters, line defects, etc., improve the ion penetration channels and positions, increase the diffusion distance of Cr ions, and enhance corrosion resistance; a Cr2N coating is prepared on the inner wall of the carbon steel storage tank by double glow plasma surface metallurgy technology, the surface structure of the Cr2N coating is a fine flaky structure, and the atomic ratio of Cr and N elements in the surface layer is 2:1; the internal structure components of the Cr2N coating are gradiently distributed, and the content of Cr and N elements gradually decreases from the surface to the inside; the Cr2N coating is metallurgically bonded to the inner wall of the carbon steel storage tank, there is interdiffusion at the interface between the coating and the substrate, the coating structure is dense, and the bonding strength is high, so that it can resist the corrosion of high and medium concentrations of sulfuric acid; the ion irradiation technology and double glow plasma surface alloying technology can greatly improve the permeability of Cr, the gradient distribution of the Cr component improves the relative continuity of the coating and interface structure and performance, and the internal stress is small under the action of external field thermal coupling. In addition, the Cr2N coating has high hardness, high melting point, excellent chemical stability and anti-friction and wear properties, and has good thermal stability at 700°C.

[0010] As a further preferred embodiment, after the double glow plasma chromium alloying treatment is performed on the inner wall of the carbon steel storage tank, the thickness of the Cr alloy layer on the inner wall of the carbon steel storage tank is 40μm to 60μm. If the Cr alloy layer is too thin, it is difficult to achieve corrosion resistance, while if the Cr alloy layer is too thick, there is a risk of spalling.

[0011] As a further preferred embodiment, the carbon steel selected is Q235 carbon steel, which is cheap, easily available on the market, and widely used in chemical companies and design units.

[0012] As a further preferred embodiment, the double glow plasma chromium alloying treatment in step 2 above employs source sputtering, and the selected target material is a pure chromium cylinder with a wall thickness of 5 mm. Cr targets are relatively brittle, and cylinders with walls that are too small are difficult to machine. However, cylinders that are too large require a more powerful sputtering power source during the chromium alloying process, increasing processing costs.

[0013] As a further preferred embodiment, the Cr cylinder wall is processed with through holes with an equidistant diameter of 3 mm and a hole spacing of 5 mm. The function of the through holes on the Cr cylinder wall is to improve the mobility of active Cr atoms in the plasma during the Cr infiltration process. The larger the pore size, the better the mobility of active Cr atoms in the plasma. However, an excessively large pore size will produce a hollow cathode discharge phenomenon, resulting in a high concentration of active Cr atoms in a local area of ​​the plasma, making the thickness of the Cr alloy layer uneven. In addition, the hollow cathode discharge phenomenon will also generate a large amount of heat, resulting in an excessively high local temperature of the target material, and even a risk of target melting.

[0014] The present invention also provides specific processing steps for the preparation method of the Cr2N corrosion-resistant coating on the inner wall of the carbon steel storage tank, which are as follows:

[0015] S1: Load the carbon steel tank into the double glow plasma surface treatment furnace and connect it to the workpiece electrode;

[0016] S2: Place the pure Cr cylinder inside the carbon steel tank, keep a distance of 20 mm between the outer wall of the Cr cylinder and the inner wall of the tank, and connect the Cr cylinder to the source electrode;

[0017] S3: Evacuate to a background vacuum of 10 -3 After Pa, argon gas was introduced;

[0018] S4: The steel was irradiated using an argon ion source. During the irradiation process, the target chamber was in a vacuum state, the temperature was 500℃~550℃, and the ion irradiation dose was 5×10 18 ~2×10 19 ions / cm 2 ;

[0019] S5: Turn on the workpiece electrode power supply and perform plasma bombardment pretreatment on the inner wall of the carbon steel storage tank. The process parameters set for the plasma bombardment pretreatment are: workpiece electrode voltage of 650V, argon gas pressure of 30Pa, treatment temperature of 600°C, and treatment time of 1h;

[0020] S6: Turn on the source electrode power supply and adjust the workpiece electrode power supply to perform double glow plasma chromium alloying treatment on the inner wall of the carbon steel storage tank. The process parameters set for the double glow plasma chromium alloying treatment are: source electrode voltage is 1100V-1200V, workpiece electrode voltage is 700V-800V, argon gas pressure is 50Pa, the distance between the source and workpiece electrodes is 20mm, the treatment temperature is 900℃-1000℃, and the treatment time is 3h-6h;

[0021] S7: Nitrogen is introduced, and the power supply to the source electrode and workpiece electrode is adjusted to perform active screen ion nitriding treatment on the inner wall of the carbon steel storage tank. The treatment process parameters are: active screen voltage of 700V-800V, workpiece electrode voltage of 500V-600V, nitrogen to argon ratio (nitrogen-argon ratio) of 2:1, nitrogen-argon mixed gas pressure of 100Pa, source and workpiece electrode spacing of 20mm, treatment temperature of 750°C, and treatment time of 12h-18h. Among the above process parameters, the nitrogen-argon ratio, treatment temperature, and treatment time are critical. The nitrogen-argon ratio is a key factor in obtaining a Cr2N coating. If the nitrogen-argon ratio is too low, it is difficult to obtain a Cr2N coating, and the Cr2N coating is thin. If the nitrogen-argon ratio is too high, the Cr2N coating will be transformed into a CrN coating, which is more brittle than the Cr2N coating and easily peels off. If the treatment temperature is too low, atomic diffusion is more difficult, and the Cr2N coating is relatively thin. If the treatment temperature is too high, it will affect the matrix structure. The longer the treatment time, the more complete the atomic diffusion and the thicker the coating. However, the later the treatment, the longer it takes to increase the coating thickness. It is difficult to obtain a sufficient coating thickness if the treatment time is less than 12 hours. Therefore, a treatment time of less than 18 hours is a more reasonable treatment time.

[0022] As a further preferred embodiment, in the above S5 , the source electrode voltage is 1200 V, the workpiece electrode voltage is 700 V, the processing temperature is 900° C., and the processing time is 6 h.

[0023] As a further preferred embodiment, in the above S6, the active screen voltage is 700V, the workpiece pole voltage is 600V, and the processing time is 18 hours.

[0024] The beneficial effects of the present invention are as follows: the present invention adopts double glow plasma surface metallurgy technology to prepare a Cr2N coating on the inner wall of a carbon steel storage tank, the internal structure composition of the Cr2N coating is gradiently distributed, and the content of Cr and N elements gradually decreases from the surface to the inside; the Cr2N coating is metallurgically bonded to the inner wall of the carbon steel storage tank, there is interdiffusion at the interface between the coating and the substrate, the coating structure is dense, and the coating thickness is 250μm to 300μm, so that it can resist the corrosion of high-concentration and medium-concentration sulfuric acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 Shown is the XRD pattern of the prepared Cr2N coating;

[0027] Figure 2 Shown are the surface morphology of the prepared Cr2N coating and its EDS spectrum analysis results; (a) is the surface morphology of the Cr2N coating; (b) is the EDS spectrum analysis result;

[0028] Figure 3 Shown are the cross-sectional morphology of the prepared Cr2N coating and its EDS energy spectrum analysis results; (a) is the cross-sectional morphology of the Cr2N coating; (b) is the EDS energy spectrum analysis result diagram. DETAILED DESCRIPTION

[0029] The following will provide a clear and complete description of the concept, specific structure and technical effects of the present invention in conjunction with the embodiments and drawings to fully understand the purpose, scheme and effects of the present invention.

[0030] Example 1

[0031] A Cr2N corrosion-resistant coating on the inner wall of a carbon steel storage tank, the preparation method of which comprises the following steps:

[0032] S1: A pure Cr cylinder is used as the Cr infiltration target material. The wall thickness of the Cr cylinder is 5 mm. Through holes with a diameter of 3 mm and a hole spacing of 5 mm are machined on the wall of the Cr cylinder.

[0033] S2: The steel was irradiated using an argon ion source. During the irradiation process, the target chamber was in a vacuum state, the temperature was 500℃~550℃, and the ion irradiation dose was 2×10 19 ions / cm 2 ;

[0034] S3: The Q235 carbon steel sulfuric acid storage tank is a cylindrical part with a height of 15,500 mm and a diameter of 16,000 mm. After the inner wall of the Q235 carbon steel sulfuric acid storage tank is degreased, derusted, and degreased, it is placed in a double glow plasma chromium alloying furnace;

[0035] S4: plasma bombardment pretreatment is used, and the process parameters are: workpiece electrode voltage is 650V, argon gas pressure is 30Pa, treatment temperature is 600℃, and treatment time is 1h;

[0036] S5: Using double glow plasma surface metallurgy technology, pure Cr cylinder is used as the source sputtering target material, and Q235 carbon steel sulfuric acid storage tank is used as the workpiece electrode to perform Cr alloying treatment on the Q235 carbon steel sulfuric acid storage tank. The process parameters are: source electrode voltage is 1200V, workpiece electrode voltage is 700V, argon gas pressure is 50Pa, the distance between the source and workpiece electrodes is 20mm, the treatment temperature is 900℃, and the treatment time is 6h.

[0037] S6: The Cr2N coating was prepared by nitrogen infiltration on the Cr alloy layer using active screen ion nitriding technology. The process parameters were as follows: active screen voltage was 700 V, workpiece pole voltage was 600 V, nitrogen to argon ratio was 2:1, nitrogen-argon mixed gas pressure was 100 Pa, source pole to workpiece pole spacing was 20 mm, treatment temperature was 750 ° C, and treatment time was 18 h.

[0038] from Figure 1 It can be seen that the main phase of the prepared Cr2N coating is Cr2N phase; Figure 2 It can be seen that the surface structure of the Cr2N coating is a fine scaly structure, and the atomic ratio of Cr and N elements in the surface layer is 2:1; Figure 3 It can be seen that the Cr2N coating has a dense structure without obvious defects such as holes and microcracks. The Cr and N elements in the coating are distributed in a gradient, and their content gradually decreases from the surface to the inside, indicating that the Cr2N coating is metallurgically bonded to the Q235 carbon steel sulfuric acid storage tank substrate. The following table shows the EDS spectrum chemical element analysis results of the prepared Cr2N coating:

[0039]

[0040] The Cr2N coating prepared in Example 1 was subjected to corrosion resistance tests, and the results are shown in Table 1:

[0041] Table 1 shows the electrochemical corrosion data of Q235 steel and Cr2N coating. E is the self-corrosion potential, which reflects the corrosion resistance of the sample. The more positive the self-corrosion potential, the more difficult the sample is to corrode. I is the corrosion current density, which reflects the corrosion rate of the sample. The smaller the corrosion current density, the slower the corrosion rate of the sample. Etchrate is the corrosion rate v, and its technical formula is as follows:

[0042]

[0043] Where: v——corrosion rate, mm / a;

[0044] m1——mass of sample before the experiment, g;

[0045] m2——mass of the sample after the experiment, g;

[0046] s——total area of ​​the sample, cm 2;

[0047] t——test time, h;

[0048] d——density of the material, kg / m 3 .

[0049] Table 1 Electrochemical corrosion data of Q235 steel and Cr2N coating

[0050]

[0051] Example 2

[0052] A Cr2N corrosion-resistant coating on the inner wall of a carbon steel storage tank, the preparation method of which comprises the following steps:

[0053] S1: A pure Cr cylinder is used as the Cr infiltration target material. The wall thickness of the Cr cylinder is 5 mm. Through holes with a diameter of 3 mm and a hole spacing of 5 mm are machined on the wall of the Cr cylinder.

[0054] S2: The steel was irradiated using an argon ion source. During the irradiation process, the target chamber was in a vacuum state, the temperature was 500℃~550℃, and the ion irradiation dose was 5×10 18 ions / cm 2 ;

[0055] S3: The Q235 carbon steel sulfuric acid storage tank is a cylindrical part with a height of 15,500 mm and a diameter of 16,000 mm. After the inner wall of the Q235 carbon steel sulfuric acid storage tank is degreased, derusted, and degreased, it is placed in a double glow plasma chromium alloying furnace;

[0056] S4: plasma bombardment pretreatment is used, and the process parameters are: workpiece electrode voltage is 650V, argon gas pressure is 30Pa, treatment temperature is 600℃, and treatment time is 1h;

[0057] S5: Using double glow plasma surface metallurgy technology, pure Cr cylinder is used as the source sputtering target material, and Q235 carbon steel sulfuric acid storage tank is used as the workpiece electrode to perform Cr alloying treatment on the Q235 carbon steel sulfuric acid storage tank. The process parameters are: source electrode voltage is 1100V, workpiece electrode voltage is 800V, argon gas pressure is 50Pa, the distance between the source and workpiece electrodes is 20mm, the treatment temperature is 1000℃, and the treatment time is 3h.

[0058] S6: The Cr2N coating is prepared by nitrogen infiltration on the Cr-infiltrated alloy layer using active screen ion nitriding technology. The process parameters are: active screen voltage is 800V, workpiece pole voltage is 500V, nitrogen and argon ratio is 2:1, nitrogen and argon mixed gas pressure is 100Pa, the distance between the source and the workpiece pole is 20mm, the processing temperature is 750℃, and the processing time is 12h.

[0059] Obviously, the described embodiments are only some of the embodiments of the present application, rather than all of the embodiments. Mentioning "embodiments" in this article means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present embodiment application. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It can be understood explicitly and implicitly by those skilled in the art that the embodiments described herein can be combined with other embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application. Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and purpose of the present invention, and the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a Cr2N corrosion-resistant coating on the inner wall of a carbon steel storage tank, characterized in that: The preparation method comprises the following steps: Step 1: The steel was irradiated with an argon ion source. During the irradiation process, the target chamber was in a vacuum state, the temperature was 500°C~550°C, and the ion irradiation dose was 5×10 18 ~2×10 19 ions / cm 2 ; Step 2: performing a double glow plasma chromium alloying treatment on the inner wall of the carbon steel storage tank, wherein a Cr alloy layer is formed after the double glow plasma chromium alloying treatment; Step 3: Perform active screen ion nitriding treatment on the Cr alloy layer on the inner wall of the steel storage tank to obtain a Cr2N coating; During the ion nitriding treatment of the active screen, the ratio of nitrogen to argon is 2:1; The atomic ratio of Cr and N in the Cr2N coating is 2:

1. The internal structure of the Cr2N coating is distributed in a gradient manner, and the content of Cr and N decreases gradually from the surface to the inside.

2. The preparation method according to claim 1, characterized in that Before step 1, the inner wall of the carbon steel storage tank is also pre-treated by plasma bombardment.

3. The preparation method according to claim 1, characterized in that After the inner wall of the carbon steel storage tank is subjected to the double glow plasma chromium alloying treatment, the thickness of the Cr alloy layer on the inner wall of the carbon steel storage tank is 40 μm to 60 μm.

4. The preparation method according to claim 3, characterized in that The carbon steel selected is Q235 carbon steel.

5. The preparation method according to claim 1, characterized in that In the step 1, the double glow plasma Cr alloying treatment adopts source sputtering, and the selected target material is a pure Cr tube with a wall thickness of 5 mm.

6. The preparation method according to claim 5, characterized in that Cr alloy processing is performed on the Cr cylinder wall to form through holes with a diameter of 3 mm and a hole spacing of 5 mm that are evenly arranged.

7. The preparation method according to claim 1, characterized in that The specific process of the preparation method is as follows: S1: Load the carbon steel tank into the double glow plasma surface treatment furnace and connect it to the workpiece electrode; S2: Place the pure Cr cylinder inside the carbon steel tank, keeping a distance of 20 mm from the inner wall of the tank, and connect the Cr cylinder to the source electrode; S3: Evacuate to a background vacuum of 10 -3 After Pa, argon gas was introduced; S4: Steel was irradiated using an argon ion source. During the irradiation process, the target chamber was in a vacuum state, the temperature was 500°C~550°C, and the ion irradiation dose was 5×10 18 ~2×10 19 ions / cm 2 ; S5: Turn on the workpiece electrode power supply and perform plasma bombardment pretreatment on the inner wall of the carbon steel storage tank. The process parameters set for the plasma bombardment pretreatment are: workpiece electrode voltage of 650 V, argon gas pressure of 30 Pa, treatment temperature of 600 °C, and treatment time of 1 h. S6: Turn on the source electrode power supply and adjust the workpiece electrode power supply to perform double glow plasma chromium alloying treatment on the inner wall of the carbon steel storage tank. The process parameters set for the double glow plasma chromium alloying treatment are: source electrode voltage of 1100 V-1200 V, workpiece electrode voltage of 700 V-800 V, argon gas pressure of 50 Pa, source and workpiece electrode spacing of 20 mm, treatment temperature of 900 ° C-1000 ° C, and treatment time of 3 h-6 h; S7: nitrogen is introduced, the power supply of the source electrode and the workpiece electrode is adjusted, and the inner wall of the carbon steel storage tank is subjected to active screen ion nitriding treatment. The process parameters set for the active screen ion nitriding treatment are: active screen voltage is 700 V-800 V, workpiece electrode voltage is 500 V-600 V, nitrogen and argon ratio is 2:1, nitrogen-argon mixed gas pressure is 100 Pa, the distance between the source electrode and the workpiece electrode is 20 mm, the treatment temperature is 750 ° C, and the treatment time is 12 h-18 h.

8. The preparation method according to claim 7, characterized in that In the S5, the source electrode voltage is 1200 V, the workpiece electrode voltage is 700 V, the processing temperature is 900° C., and the processing time is 6 h.

9. The preparation method according to claim 7, characterized in that In the S6, the active screen voltage is 700 V, the workpiece electrode voltage is 600 V, and the processing time is 18 h.

10. A Cr2N corrosion-resistant coating on the inner wall of a carbon steel storage tank, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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