High-corrosion-resistance enameled steel plate and production method thereof

Abstract

The invention discloses a high-corrosion-resistance enameled steel plate which comprises the following main chemical components in percentage by mass: 0.030-0.070% of C, less than or equal to 0.05% of Si, 0.2-0.9% of Mn, 0.05-0.15% of P, less than or equal to 0.006% of S, 0.03-0.1% of Ti, 0.3-0.5% of Cr, 0.05-0.2% of Ni, 0.2-0.3% of Cu, less than or equal to 0.006% of N and the balance of Fe. And the balance of Fe and inevitable residual elements. According to the invention, a component system of low Si + precise P (high P)-Cr-Cu-Ni + Ti microalloying is adopted, and an improved preparation process is combined, so that the obtained steel plate has excellent corrosion resistance, fish scaling resistance, adherence and good strong plasticity matching; and the service life of enamel equipment can be effectively prolonged, and the industrial pain point of corrosion resistance damage fish scaling / adherence of the enamel steel plate is solved.

Description

Technical Field

[0001] This invention belongs to the field of strip steel production technology, specifically relating to a high corrosion-resistant enamel steel plate and its production method. Background Technology

[0002] Enameled steel sheet is a composite material formed by coating steel sheet with inorganic non-metallic materials and firing at high temperatures. This process creates strong chemical bonds between the steel sheet and the inorganic coating, preventing the metal surface from oxidizing and rusting. It exhibits excellent corrosion resistance and significantly extends the service life of the metal. Enameled steel sheet is not only resistant to acids and alkalis but also to high temperatures, making it widely used in industries such as home appliances, chemicals, pharmaceuticals, and food processing. It is used to manufacture equipment such as water heater inner tanks, reaction vessels, and piping.

[0003] However, enamel-lined steel plates have a limited service life. After prolonged use, the enamel layer may peel off, and severe impacts or harsh reactions can also damage it. Because existing enamel-lined steel plates have poor corrosion resistance, once the enamel layer is damaged and the internal metal is exposed, the steel substrate will corrode rapidly, rendering it unusable and severely impacting the equipment's lifespan. Summary of the Invention

[0004] The main objective of this invention is to provide a high corrosion-resistant enamel steel plate. After the enamel layer is damaged, a dense and highly adhesive rust protective film is formed on the surface of the steel plate. This protective film has fine rust grains and low porosity, which can effectively prevent rust from developing and spreading into the interior of the steel, thereby slowing down the corrosion rate and extending the service life of enamel equipment. At the same time, the steel plate has excellent adhesion and anti-scaling properties, which can effectively solve the industry pain point of "corrosion resistance inevitably leads to scaling / adhesion" in enamel steel plates.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high corrosion-resistant enamel steel plate, the main chemical components of which include C, Si, Mn, P, S, Ti, Cr, Cu, Ni, and N elements, with the remainder being Fe and unavoidable residual elements. The components and their mass percentages are as follows: C 0.030~0.070%, Si≤0.05%, Mn 0.2~0.9%, P 0.05~0.15%, S≤0.006%, Ti 0.03~0.1%, Cr 0.3~0.5%, Ni 0.05~0.2%, Cu 0.2~0.3%, N≤0.006%.

[0006] Preferably, the P content in the high corrosion-resistant enamel steel plate is 0.08~0.12%.

[0007] Preferably, in the high corrosion-resistant enamel steel plate, the Ti content is ≥ C content + N content.

[0008] Preferably, in the high corrosion-resistant enamel steel plate, the Ni content + 3P content is ≥0.3%, and the Cr content + P content is ≥0.4%.

[0009] This invention also provides a method for producing the above-mentioned high corrosion-resistant enamel steel plate, which mainly includes heating, precision rolling, laminar flow cooling, coiling, pretreatment, enamel coating, and firing steps. The key control conditions include the following: (1) Heating: The billet heating temperature is 1180~1220℃; (2) Finishing rolling: A 7-stand rolling mill is used. The starting temperature of finishing rolling is 1000~1050℃, the reduction of F1~F3 is ≥40%, the reduction of F6~F7 is ≤20%, and the finishing rolling temperature is 840~880℃. (3) Laminar flow cooling: Perform segmented cooling, using a decreasing cooling rate to cool to the winding temperature; (4) Winding: The winding temperature is 580~650℃; (5) Pretreatment: Remove iron oxide scale and oil stains from the surface of the steel plate and control the surface roughness of the steel plate; (6) Enameling: The enamel coating process adopts wet enamel coating or electrostatic dry enamel coating, and enamel powder or enamel slurry is evenly coated on the surface of the steel plate. (7) Enameling: The enamelting temperature is 840~900℃ and the enamelting time is 20~40min.

[0010] In the above scheme, the billet needs to undergo deep desulfurization treatment and LF refining.

[0011] In the above scheme, the billet heating time is 20~150min.

[0012] In the above scheme, the segmented cooling step includes: first cooling to 680~750℃ at a rate of 25~50℃ / s (first segment), and then cooling to the winding temperature at a rate of 10~20℃ / s (second segment).

[0013] Preferably, the cooling rate of the first stage is 37~50℃ / s.

[0014] In the above scheme, the enamel materials involved in the enamel powder and enamel slurry include a matrix agent and an adhesive agent; wherein the matrix agent includes silicon dioxide, zirconium oxide, etc.; and the adhesive agent includes one or more of cobalt oxide, nickel oxide, etc.

[0015] Furthermore, the components in the matrix agent and their mass percentage in the enamel material include: 70-80% silicon dioxide, 5-8% zirconium oxide, and 3-5% boron oxide; the components in the adhesive agent and their mass percentage in the enamel material include: 1.5-2.5% nickel oxide and 0.5-1.5% cobalt oxide.

[0016] Furthermore, the enamel material contains one or more additives such as flux and opacifier.

[0017] Furthermore, the matrix agent accounts for more than 80% of the mass of the enamel material.

[0018] The principles of this invention include: I. Ingredient Design; C: Solid solution carbon increases the yield strength and tensile strength of steel, and combines with Ti to form TiC, which acts as an effective hydrogen trap, improving the anti-scaling performance of enamel steel. However, increased carbon content decreases plasticity, and solid solution carbon is detrimental to the enameling performance of enamel steel. On the one hand, higher carbon content leads to higher pearlite content. Pearlite is a two-phase structure of ferrite and lamellar cementite. Cementite does not react with the enamel layer, reducing the bonding force between the matrix and the enamel layer. On the other hand, higher solid solution carbon content results in more CO and CO2 gases being generated during the enameling process. These gases damage the density of the enamel layer, and in severe cases, pinhole defects will occur. To balance mechanical properties, anti-scaling performance, and enameling performance, this invention controls the C content in the steel to be 0.030~0.070%.

[0019] Si: The main component of enamel powder is SiO2. During the enamel firing process, FeO formed by the oxidation of the matrix combines with SiO2 in the enamel layer to form Fe2SiO4, forming chemical bonds. This chemical bond is one of the main mechanisms for the adhesion between the matrix and the enamel layer. Si in steel will form SiO2, which slows down the chemical reaction between the matrix and the enamel layer, which is detrimental to the adhesion between the matrix and the enamel layer. Therefore, the weight percentage of Si is controlled to ≤0.05%.

[0020] Mn: Mn is dissolved in ferrite and austenite, which can improve strength and reduce plasticity. Too low a manganese content will cause FeS to precipitate, reducing the hot plasticity of steel. Too high a manganese content will result in excessive strength and poor formability. Taking all factors into consideration, the weight percentage of Mn should be controlled at 0.2~0.9%.

[0021] P: P can form a stable oxide, iron phosphate, with iron in steel. This oxide can adhere to the steel surface to form a dense oxide film, which hinders further corrosion by the corrosive medium. However, P is prone to segregation in steel, which reduces the toughness and weldability of steel. This invention further combines the Cu-Ni-Cr strengthening system to control the weight percentage of P to 0.05~0.15%.

[0022] S: S consumes Ti elements, reducing the amount of TiC precipitation, which is detrimental to the scaling performance of steel plates. At the same time, S reacts with Cu to form CuS, consuming Cu in the steel and reducing the corrosion resistance of the steel plate. Therefore, S should be controlled to ≤0.006%.

[0023] Ti: Ti can combine with elements such as C, N, and S in steel to form second-phase particles, which act as excellent hydrogen storage traps and improve the anti-scaling performance of steel plates. However, excessive Ti content not only increases the strength of the material but also reduces its plasticity, worsening its forming and processing properties, and increasing the difficulty of smelting and casting. Taking all factors into consideration, the Ti weight percentage is controlled at 0.03~0.10%; and further controlled to Ti content ≥ C content + N content.

[0024] Cr: Under oxidizing conditions, Cr can form a dense and stable oxide film, which can hinder further erosion by corrosive media. However, if the Cr content is too high, it will cause enamel layer to crack. Taking all factors into consideration, the Cr weight percentage content should be controlled at 0.3-0.5%.

[0025] Cu: Cu promotes the formation of an amorphous internal rust layer rich in alloying elements between the steel matrix and the rust layer, thereby reducing the corrosion rate and preventing further corrosion of the steel. However, excessive Cu content will reduce the plasticity of the steel. Taking all factors into consideration, the Cu weight percentage should be controlled at 0.2-0.3%.

[0026] Ni: Ni can increase the self-corrosion potential of steel, thereby improving the stability and corrosion resistance of steel. At the same time, Ni can enhance the bonding force between enamel and steel plate. However, Ni alloys are expensive. Taking all factors into consideration, the Ni weight percentage is controlled at 0.05~0.2%.

[0027] Furthermore, this invention proposes for the first time to use P, Cu, Ni, and Cr as the main corrosion-resistant components. The introduced P compensates for the deficiencies of Cu / Cr / Ni in the control of rust layer structure. The introduction of Cu / Cr / Ni and the control of the content of Ni +3P and Cr +P are beneficial to suppressing the risk of P grain boundary segregation, and finally forming a dual corrosion-resistant barrier of "stable rust layer + uniform matrix".

[0028] Excessive nitrogen content will consume Ti elements, reducing the amount of TiC precipitation, which is detrimental to the scaling performance of steel plates. At the same time, excessive nitrogen content will lead to poor material plasticity. Therefore, the N content should be controlled at ≤0.006%.

[0029] II. Process Design; This invention controls the heating temperature to 1180~1220℃ to promote the full solid solution of Ti and P, resulting in a uniform composition and temperature distribution. This avoids low P levels and facilitates the formation of fine TiC and TiN particles after Ti solidification in subsequent processes. When the heating temperature is below 1180℃, P segregation in the continuously cast billet is not fully eliminated, and the billet has poor plasticity and high deformation resistance, leading to high rolling loads and difficulty in controlling the billet shape during rolling, potentially resulting in scrap steel. If the billet temperature is above 1220℃, Cu tends to segregate at grain boundaries, reducing grain boundary plasticity and increasing the likelihood of cracks. Furthermore, the austenite grains become too coarse, affecting corrosion resistance. Therefore, considering all factors, a heating temperature of 1180~1220℃ is optimal.

[0030] This invention controls the initial rolling temperature of the finishing mill to be 1000~1050℃, and the reduction of F1~F3 is ≥40%. The large reduction during the high-temperature stage of finishing milling promotes complete recrystallization of austenite grains, resulting in fine austenite grains. When the initial rolling temperature is below 1000℃, austenite cannot completely recrystallize; when the heating temperature is 1150~1250℃, it is difficult to reach an initial rolling temperature above 1050℃. Furthermore, controlling the reduction of F6~F7 to ≤20% effectively avoids problems such as cracking caused by excessive single-pass reduction exceeding the material's plasticity limit in the low-temperature finishing mill region.

[0031] This invention controls the final rolling temperature to 840~880℃ to obtain fine austenite grains, providing more nucleation sites for the austenite-to-ferrite phase transformation, thus improving the strength and toughness of the steel plate. When the final rolling temperature is higher than 880℃, the austenite grains are too coarse; when the final rolling temperature is lower than 840℃, the material has poor plasticity, high deformation resistance, and is prone to cracking, which is also not conducive to plate shape control.

[0032] This invention employs a segmented cooling process. First, the temperature is cooled to 680-750°C at a rate of 25-50°C / s, and then further cooled to the coiling temperature at a rate of 10-20°C / s. The first segment uses a relatively high cooling rate (25-50°C / s) to cool to 680-750°C, causing austenite to rapidly transform into ferrite, thus preventing the segregation of phosphorus (P) at grain boundaries in the "high-P" steel system described in this invention. The second segment cools slowly (10-20°C / s) to the coiling temperature, releasing the thermal stress inside the steel plate, reducing midpoint defects, lowering distortion energy, and improving the steel's plasticity and toughness.

[0033] This invention controls the coiling temperature to 580~650℃, which promotes the dispersed precipitation of fine TiC. If the coiling temperature is too low, the TiC precipitation kinetics are insufficient, resulting in a small amount of precipitated TiC. If the coiling temperature is too high, TiC tends to aggregate and grow, further reducing the amount of TiC. TiC is an excellent hydrogen storage trap in steel, improving the steel plate's resistance to scaling and explosion, while also reducing the amount of carbon in the steel that escapes as bubbles during the enameling process.

[0034] The pretreatment process described in step (5) of this invention uses shot peening to control the surface roughness Ra of the steel plate to 1.5~3.0μm. This further utilizes the surface roughness of the steel plate to increase the mechanical interlocking force between the steel plate and the enamel layer, thereby improving the adhesion performance. If the surface roughness is too coarse (Ra>3.0μm), the enamel layer will be too thin in some areas, and if it is too fine (Ra<1.5μm), the mechanical interlocking will be insufficient.

[0035] This invention employs a firing temperature of 840-900℃ and a firing time of 20-40 minutes to ensure a tight bond between the steel plate and the enamel layer through a high-temperature chemical reaction, guaranteeing excellent adhesion of the enamel-lined steel plate. If the firing temperature is too low or the firing time is too short, the reaction between the steel plate and the enamel layer will be insufficient, resulting in poor adhesion. Conversely, if the firing temperature is too high or the firing time is too long, the strength of the steel plate will be significantly reduced, thus shortening the service life of the enamel-lined steel plate.

[0036] Compared with the prior art, the beneficial effects of the present invention include: 1) This patent provides a high corrosion-resistant enamel steel plate and its production method. In response to the problem of balancing corrosion resistance with other properties, it proposes for the first time to adopt a synergistic composition system based on low Si + precise P (high P) - Cr - Cu - Ni + Ti microalloying. This system can effectively take into account the correlation between "corrosion-resistant elements - enamel reaction - hydrogen trap", thus solving the industry pain point of "corrosion resistance inevitably leads to damage and scaling / adhesion" in enamel steel plates.

[0037] 2) This invention further incorporates improved processes such as a two-stage cooling scheme with decreasing deceleration rate to avoid the segregation of P elements at grain boundaries in the "high P" steel system, release the thermal stress inside the steel plate, reduce defects at the steel center, reduce the distortion energy in the steel, promote the precise control of uniform composition, fine structure and dispersed precipitates, and ensure high plasticity and toughness of the steel.

[0038] 3) The steel plate obtained by this invention has excellent corrosion resistance, anti-scaling performance, adhesion performance and good strength-plasticity matching. After the surface enamel layer is damaged, a dense and highly adhesive oxide protective film can be generated on the steel surface, which can prevent rust from developing and spreading inward, thereby slowing down the corrosion rate and extending the service life of enamel equipment. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0040] Examples 1-10 The production method of the high corrosion-resistant enamel steel plate described in Examples 1-10 mainly includes the steps of heating, precision rolling, laminar flow cooling, coiling, pretreatment, enameling, and firing. The key control conditions include the following: (1) Heating: The billet heating temperature is 1180~1220℃ and the heating time is 20~150min; the billet smelting process used requires deep desulfurization treatment and LF refining. (2) Finishing rolling: A 7-stand rolling mill is used. The starting temperature of finishing rolling is 1000~1050℃, the reduction of F1~F3 is ≥40%, the reduction of F6~F7 is ≤20%, and the finishing rolling temperature is 840~880℃. (3) Laminar flow cooling: Perform segmented cooling and cool to the winding temperature at a decreasing cooling rate; the specific steps include: first cooling to 680~750℃ at a rate of 25~50℃ / s, and then cooling to the winding temperature at a rate of 10~20℃ / s. (4) Winding: The winding temperature is 580~650℃; (5) Pretreatment: The pretreatment process adopts shot peening to remove iron oxide scale and oil stains on the surface of the steel plate, and controls the surface roughness Ra of the steel plate to be controlled at 1.5~3.0μm; (6) Enameling: The enamel coating process can be carried out by wet enamel coating or electrostatic dry enamel coating, so as to uniformly coat the enamel material on the surface of the steel plate. The main components and their mass percentages in the enamel material (the enamel material formula used in different embodiments and comparative examples are the same) include: silicon oxide 70~80%, zirconium oxide 5~8%, boron oxide 3~5%, nickel oxide 1.5~2.5%, and cobalt oxide 0.5~1.5%; (7) Enameling: The enamelting temperature is 840~900℃ and the enamelting time is 20~40min.

[0041] Comparative Example 1 An enamel-lined steel plate, the production method of which is largely the same as that in Example 1, differs in that: 1) The chemical composition of the steel includes: carbon (C) 0.050%, silicon (Si) 0.035%, manganese (Mn) 0.58%, phosphorus (P) 0.013%, sulfur (S) 0.004%, titanium (Ti) 0.085%, chromium (Cr) 0.42%, nickel (Ni) 0.12%, copper (Cu) 0.26%, nitrogen (N) 0.005%, with the remainder being Fe and unavoidable residual elements; 2) The heating temperature is 1200℃, the initial rolling temperature is 1039℃; during the finishing rolling process, the reduction rate of F1 is 55%, the reduction rate of F2 is 52%, the reduction rate of F3 is 49%, the reduction rate of F6 is 17%, and the reduction rate of F7 is 14%; the final rolling temperature is 860℃, the first stage cooling rate is 35℃ / s, the intermediate temperature is 730℃, the second stage cooling rate is 19℃ / s, the coiling temperature is 610℃; the enameling temperature is 870℃, and the enameling time is 31min.

[0042] Comparative Example 2 An enamel-lined steel plate, the production method of which is largely the same as that in Example 1, differs in that: 1) The chemical composition of the steel includes: carbon (C) 0.048%, silicon (Si) 0.042%, manganese (Mn) 0.65%, phosphorus (P) 0.128%, sulfur (S) 0.003%, titanium (Ti) 0.059%, chromium (Cr) 0.48%, nickel (Ni) 0.18%, copper (Cu) 0.28%, nitrogen (N) 0.004%, with the remainder being Fe and unavoidable residual elements; 2) The heating temperature is 1196℃, the initial rolling temperature is 1020℃; during finishing rolling, the reduction rate of F1 is 51%, the reduction rate of F2 is 48%, the reduction rate of F3 is 45%, the reduction rate of F6 is 15%, and the reduction rate of F7 is 12%; the final rolling temperature is 850℃, the first stage cooling rate is 16℃ / s, the intermediate temperature is 780℃, the second stage cooling rate is 30℃ / s, and the coiling temperature is 630℃; the enameling temperature is 866℃, and the enameling time is 35min.

[0043] Comparative Example 3 An enamel-lined steel plate, the production method of which is largely the same as that in Example 1, differs in that: 1) The chemical composition of the steel includes: carbon (C) 0.049%, silicon (Si) 0.033%, manganese (Mn) 0.69%, phosphorus (P) 0.058%, sulfur (S) 0.0039%, titanium (Ti) 0.06%, chromium (Cr) 0.3%, nickel (Ni) 0.06%, copper (Cu) 0.28%, nitrogen (N) 0.0048%, with the remainder being Fe and unavoidable residual elements; 2) The heating temperature is 1183℃, the initial rolling temperature is 1040℃; during finishing rolling, the reduction rate of F1 is 60%, the reduction rate of F2 is 58%, the reduction rate of F3 is 49%, the reduction rate of F6 is 16%, and the reduction rate of F7 is 9%; the final rolling temperature is 867℃, the first stage cooling rate is 37℃ / s, the intermediate temperature is 736℃, the second stage cooling rate is 13℃ / s, the coiling temperature is 643℃; the enameling temperature is 886℃, and the enameling time is 35min.

[0044] The chemical composition, process parameters, and application performance of each embodiment and comparative example are shown in Tables 1-3. Anti-scaling performance was evaluated according to GB / T 29515, adhesion performance according to EN 10209, and corrosion resistance was evaluated by testing the corrosion rate of the steel in fresh water.

[0045] Table 1 Chemical composition (wt%) of each embodiment

[0046] Table 2 Production process parameters for each embodiment Table 2-1

[0047] Table 2-2

[0048] Table 3 Performance test results for each embodiment

[0049] The embodiments of the present invention have been described above, but the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and these forms are all within the protection scope of the present invention.

Claims

1. A high corrosion-resistant enamel steel plate, characterized in that, The main chemical components and their mass percentages include: C 0.030~0.070%, Si≤0.05%, Mn 0.2~0.9%, P 0.05~0.15%, S≤0.006%, Ti 0.03~0.1%, Cr 0.3~0.5%, Ni 0.05~0.2%, Cu 0.2~0.3%, N≤0.006%; the remainder is Fe and unavoidable residual elements.

2. The high corrosion-resistant enamel steel plate according to claim 1, characterized in that, The P content in the high corrosion-resistant enamel steel plate is 0.08~0.12%.

3. The high corrosion-resistant enamel steel plate according to claim 1, characterized in that, Ni content + 3P content ≥ 0.3%, Cr content + P content ≥ 0.4%.

4. The high corrosion-resistant enamel steel plate according to claim 1, characterized in that, The Ti content is greater than or equal to the C content plus the N content.

5. The method for producing the high corrosion-resistant enamel steel plate according to any one of claims 1 to 4, characterized in that, The processes include heating, finishing rolling, laminar flow cooling, coiling, pretreatment, enameling, and firing. The key control conditions include the following: (1) Heating: The billet heating temperature is 1180~1220℃; (2) Finishing rolling: A 7-stand rolling mill is used. The starting temperature of finishing rolling is 1000~1050℃, the reduction of F1~F3 is ≥40%, the reduction of F6~F7 is ≤20%, and the finishing rolling temperature is 840~880℃. (3) Laminar flow cooling: Perform segmented cooling, using a decreasing cooling rate to cool to the winding temperature; (4) Winding: The winding temperature is 580~650℃; (5) Pretreatment: Remove iron oxide scale and oil stains from the surface of the steel plate and control the surface roughness of the steel plate; (6) Enameling: Applying enamel powder or enamel slurry evenly to the surface of the steel plate; (7) Enameling: Enameling temperature 840~900℃.

6. The production method according to claim 5, characterized in that, The heating time for the billet is 20~150 minutes.

7. The production method according to claim 5, characterized in that, The segmented cooling step includes: first cooling to 680-750°C at a rate of 25-50°C / s, and then cooling to the winding temperature at a rate of 10-20°C / s.

8. The production method according to claim 7, characterized in that, The cooling rate of the first stage is 37~50℃ / s.

9. The production method according to claim 5, characterized in that, In the pretreatment process, the surface roughness of the steel plate is controlled at 1.5~3.0μm.

10. The production method according to claim 5, characterized in that, The firing time is 20-40 minutes.

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