A kind of high strength corrosion resistant steel and preparation method thereof

Abstract

The invention discloses a high-strength corrosion-resistant steel, comprising the following components in weight percentage: C: 0.005% to 0.015%, Si: 0.8% to 1.18%, P≤0.012%, S≤0.0015%, Ni: 0.6% to 0.9%, Cr: 1.6% to 1.9%, Cu: 0.6% to 0.9%, Al: 0.65% to 1.15%, Ce+Y: 0.05% to 0.5%, the balance being Fe and inevitable impurities. At the same time, the invention discloses a preparation method of the steel. The invention reduces chemical composition to facilitate production, reduces Cu content to improve quality, has excellent comprehensive mechanical properties and corrosion resistance, and meets the needs of marine engineering equipment such as large deep-sea drilling platforms and structural parts such as keels and reinforcements of large ocean-going ships.

Description

Technical Field

[0001] The invention relates to the field of steel production, and in particular to a high-strength corrosion-resistant steel and a preparation method thereof. Background Art

[0002] Corrosion is the main factor causing steel material failure. Large ocean-going transport ships are mostly subject to seawater corrosion, marine biological erosion, marine atmospheric corrosion, etc. and have to be periodically docked for maintenance, upkeep, and repair. Shipowners hope to operate them for a longer period of time to create more wealth. Marine engineering equipment such as giant offshore drilling platforms have outdated equipment and facilities due to complex corrosion factors. After a certain period of operation, equipment and structural parts must be replaced, resulting in huge losses.

[0003] At present, commonly used high-strength steels such as AH32, DH32, AH36, DH36, EH32, EH36, etc. do not have good corrosion resistance under various complex corrosion factors in the marine environment. L-shaped steels used for structural parts such as reinforcement ribs and keels also use the above-mentioned types of steel. The main disadvantage is that these steels do not take the anti-corrosion performance of the marine environment as the main factor in the composition design and preparation process, but rely on anti-corrosion coating. The surface anti-corrosion coating is peeled off during the production process due to anchor chains, docking and contact with other ships, exposing the steel substrate to the corrosive environment; on the other hand, the cargo loading and unloading process will also cause friction and impact on steel structural parts, causing the surface anti-corrosion layer to peel off, resulting in local corrosion of steel. These corrosion behaviors directly endanger the overall equipment operation safety and shorten the service life. Maintenance and repairs such as re-anti-corrosion coating lead to production suspension and production reduction, resulting in huge losses; after a certain period of service operation, equipment, structural parts or re-coating of anti-corrosion coatings and other maintenance and repairs are required, and serious ones may even lead to the scrapping of the entire equipment due to aging.

[0004] Therefore, giant offshore drilling platforms and other marine engineering equipment, ultra-large ocean-going ships have increasingly higher requirements on the resistance of steel used in construction to combined marine environment corrosion. Not only are high-strength steels required, but also higher requirements are placed on the steel's combined marine environment corrosion resistance, in order to ensure the safe operation of large ocean-going ships.

[0005] There are reports on corrosion-resistant steel in the prior art. For example, the invention patent (application number 202211225169.8) discloses "a corrosion-resistant steel, a preparation method and application thereof, and a crude oil storage tank". The chemical composition of the steel is as follows by weight: C: 0.03-0.07%, Si: 0.06-0.25%, Mn: 0.5-1.35%, P≤0.012%, S≤0.005%, Cu: 0.1-0.4%, Ni: 0.1-0.5%, Mo: 0.10-0.3 0%, V: 0.01-0.05%, Ti: 0.005-0.035%, Sn: 0.01-0.06%, Ce: 0.001-0.03%, La: 0.001-0.03%, Ca: 0.0002-0.005%, Mg: 0.0002-0.001%, Zr: 0.001-0.02%, Co: 0.005-0.3%, O≤0.0030%, N: 0.0045-0.0065%, the balance is Fe and unavoidable impurities. By optimizing the composition and proportion of the steel, the obtained steel has excellent corrosion resistance; and after high heat input welding, the obtained welding heat affected zone has excellent toughness, which can improve the production efficiency and service life of the crude oil storage tank made of steel. The patented technology has complex chemical composition, many types, and the production process is difficult to control.

[0006] For example, the invention patent (application number 202210535812.0) discloses "a corrosion-resistant steel suitable for a high-humidity and hot marine environment and a method for preparing the same". The present invention relates to a corrosion-resistant steel suitable for a high-humidity and hot marine environment and a method for preparing the same, which belongs to the field of corrosion-resistant steel technology and solves the problems of high cost or limited corrosion resistance and poor long-term corrosion resistance of corrosion-resistant steel used in a high-humidity and hot marine environment in the prior art. The chemical composition weight percentage of the corrosion-resistant steel is: C≤0.06%, Si0.20-0.40%, Mn 0.4-0.8%, Ni 1.0-2.0%, Cr 0.4-0.6%, Cu 1.0-2.0%, Sb 0.2-0.6%, and the rest is Fe. The corrosion-resistant steel of the present invention has low cost and good corrosion resistance in a high-humidity and hot marine environment. The patented technology has a high Cu content, and Cu enrichment is easily generated during the production process, forming liquid Cu, and thermal cracking occurs, resulting in a reduced yield and an increase in the amount of waste.

[0007] Therefore, it is necessary to develop new high-strength corrosion-resistant steels and their preparation methods in a targeted manner, reduce the chemical composition to facilitate production, reduce the Cu content to improve quality, and provide high-strength corrosion-resistant steel products. Summary of the invention

[0008] Purpose of the invention: In view of the shortcomings and defects of the prior art, the present invention provides a high-strength corrosion-resistant steel and a preparation method thereof, which reduces the chemical composition to facilitate production, reduces the Cu content to improve quality, has excellent comprehensive mechanical properties and corrosion resistance, and meets the needs of marine engineering equipment such as large deep-sea drilling platforms and structural parts such as keels and stiffeners of large ocean-going ships.

[0009] Technical solution: A high-strength corrosion-resistant steel of the present invention is characterized in that it contains the following components in weight percentage: C: 0.005%~0.015%, Si: 0.8%~1.18%, P≤0.012%, S≤0.0015%, Ni: 0.6%~0.9%, Cr: 1.6%~1.9%, Cu: 0.6%~0.9%, Al: 0.65%~1.15%, Ce+Y: 0.05%~0.5%, and the balance is Fe and unavoidable impurities.

[0010] Preferably, the weight percentage of C is 0.005% to 0.012%.

[0011] Preferably, the weight percentage of Si is 0.85% to 1.0%.

[0012] Preferably, the weight percentage of Ni is 0.65% to 0.75%.

[0013] Preferably, the weight percentage of Cr is 1.65% to 1.75%.

[0014] Preferably, the weight percentage of Cu is 0.65% to 0.75%.

[0015] Preferably, the weight percentage of Al is 0.70% to 0.90%.

[0016] Preferably, the weight percentage of Ce+Y is 0.085% to 0.35%.

[0017] Principle analysis:

[0018] C (Carbon): This patent application adopts an ultra-low carbon component design, because C easily forms carbides such as Fe3C and Cr3C with Fe and Cr. These carbides form a potential difference with the Fe matrix to produce a battery that undergoes electrochemical corrosion, reducing the corrosion resistance of the material. The C content is added and controlled in the range of 0.005% to 0.015%, preferably 0.005% to 0.012%, in order to allow C to exist in the matrix in a solid solution state during the production process, thereby improving the strength of the L-shaped steel.

[0019] Si (silicon): The alloy element Si is a non-carbide forming element. After the heat treatment process of this patent application, it forms SiO2, Cr2O3, Al2O3 on the surface of the steel with the added alloy elements Cr, Al, etc., and forms a passivation layer with a thickness of 1.5mm to 3.5mm together with the anti-corrosion factors such as Cr, Cu, Ni in the solid solution state. The Si atoms dissolved in the matrix can enhance the yield strength of the steel, but too high a Si content leads to a decrease in toughness. Therefore, the composition range of the alloy element Si is set in the range of 0.8% to 1.18%, preferably 0.85% to 1.0%.

[0020] P (Phosphorus): P in structural steel forms an enriched and dense layer with Cu, Ni, etc., which can effectively prevent oxygen and water in the air from entering the matrix, inhibit the corrosion rate, and improve the corrosion resistance of steel. However, if the P content is too high, the low-temperature toughness will be drastically reduced. Therefore, the P content in steel is controlled in the range of P≤0.012%.

[0021] S (sulfur): S in structural steel is a harmful element, which not only reduces the mechanical properties of steel, especially low-temperature toughness, but also reduces the corrosion resistance of steel. Therefore, the S content is controlled in a lower range: S≤0.0015%.

[0022] Ni (nickel): alloy element Ni is not a carbide-forming element, and forms an enriched dense layer with Cu, P, and Cr, which has excellent anti-oxidation and anti-corrosion properties; on the other hand, after passivation treatment by the heat treatment method of this patent application, a composite oxide passivation layer containing NiO and Ni2O3 (SiO2, Cr2O3, Al2O3, Fe x O y ), this composite oxide passivation layer is tightly bonded to the substrate and is not easy to peel off, so it can effectively prevent the further development of corrosion behavior and improve corrosion resistance. In addition, adding an appropriate amount of Ni to structural steel can improve the low-temperature toughness of steel, but Ni is an expensive alloy element. In order to control production costs, the composition range of the alloy element Ni is set in the range of 0.6% to 0.9%, preferably 0.65% to 0.75%.

[0023] Cr (chromium): Adding an appropriate amount of alloying element Cr can form an enriched dense layer with Cu, P, Ni, Al, etc. to protect the substrate from corrosion. Moreover, after the heat treatment process of this patent application, a composite oxide (NiO, Ni2O3, SiO2, Cr2O3, Al2O3, Fe x O y), to prevent the base steel from being corroded by the external environment. On the other hand, adding an appropriate amount of Cr can reduce the phase transition temperature of the steel, improve the hardenability, and obtain a martensitic structure after induction quenching treatment, so that the added alloy elements are evenly distributed in the matrix. After passivation heat treatment, a uniform composite oxide dense layer is obtained on the surface, which plays a role in resisting corrosion in harsh environments. In addition, after heat treatment, a supersaturated solid solution tempered martensitic structure can be obtained, and a steel section with a yield strength greater than 580MPa can be obtained. Although the more Cr is added, the better the corrosion resistance of the steel, but too much Cr content is prone to form a series of carbides Cr x C y , forming, growing and coarsening at the grain boundary, deteriorating the low temperature toughness. Therefore, the Cr content of the alloying element is set in the range of 1.6% to 1.9%, preferably 1.65% to 1.75%.

[0024] Al (aluminum): alloy element Al is an easily oxidizable element, but the Al2O3 produced by reacting with [O] has good corrosion resistance. Adding an appropriate amount of alloy element Al, on the one hand, Al is a highly efficient deoxidizing element, which can effectively remove harmful oxygen in steel and improve the comprehensive mechanical properties of steel. On the other hand, after passivation heat treatment, it forms dense NiO, Ni2O3, SiO2, Cr2O3, Al2O3, Fe x O y The passivation layer protects the steel and steel structures from corrosion. Although Al is a relatively cheap alloying element, too high Al content makes the continuous casting process difficult, so the Al content of the alloying element is set in the range of 0.65% to 1.15%, preferably 0.70% to 0.90%.

[0025] Cu (copper): A certain amount of alloy element Cu is added to the steel. On the one hand, it can form an enriched dense layer with Cr, P, Ni, Al, etc., which can significantly enhance the corrosion resistance of the steel. On the other hand, after the heat treatment process of this patent application, the copper oxides CuO, Cu2O, etc. formed on the surface have good resistance to erosion by marine microorganisms. In addition, after heat treatment, a strengthening phase is formed in the matrix, which can improve the yield strength of the steel. However, excessive Cu content is prone to thermal cracking during the production process, so the Cu component range is set in the range of 0.6% to 0.9%, preferably 0.65% to 0.75%.

[0026] Ce+Y (Cerium + Yttrium): Adding rare earth elements Ce+Y has the functions of (1) further removing residual oxygen [O] in the steel; (2) removing carbides in the steel; and (3) improving the fluidity of the steel, making the continuous casting process smoother. Rare earth elements are easily oxidized elements, and adding excessive rare earth elements can easily clog the continuous casting nozzle. Therefore, the rare earth (Ce+Y) composition range is set in the range of 0.05% to 0.5%, preferably 0.085% to 0.35%.

[0027] The method for preparing high-strength corrosion-resistant steel of the present invention is characterized by comprising the following steps:

[0028] 1) Converter, electric furnace smelting, continuous casting: alloy materials and auxiliary materials are loaded into the converter or electric furnace for melting, FeO is added for P removal, oxygen is blown for decarburization, sampling is analyzed for alloy element content and the target value is adjusted, LF ladle furnace is used for S removal, Al blocks are added for deoxidation, Al wire is fed for Al alloying, vacuum degassing cycle is adopted, vacuum degree ≤ 2 mbar, Ce+Y composite rare earth wire is fed, argon is blown for stirring, harmful inclusions in the steel are removed and then continuously cast into 260mm×360mm rectangular billets;

[0029] 2) Rolling: The heating temperature of the ingot is 1120℃~1220℃, the holding time is 3.5h~4.5h, and the ingot is rolled after it comes out of the furnace. The starting rolling temperature is 1000℃~1040℃, and the final rolling temperature is 815℃~850℃;

[0030] 3) Cooling after rolling: After rolling, the steel is cooled by air blower, and the red-returning temperature is 460℃~660℃;

[0031] 4) Heat treatment:

[0032] Induction quenching: The rolled L-shaped steel is quenched in the temperature range of 896℃~910℃ by using roller bottom continuous medium frequency induction quenching facilities, and the roller speed is set at 300mm / min~1000mm / min;

[0033] Principle analysis: For long L-shaped steel, the induction heat treatment method can prevent distortion during quenching and obtain good surface quality. On the other hand, after quenching, solid solution martensite is obtained, and the alloy elements are evenly distributed in the matrix, thereby obtaining good comprehensive mechanical properties, and the yield strength is higher than 580Mpa.

[0034] Surface composite oxide passivation treatment: The L-shaped steel after induction quenching is passivated heat treated in the temperature range of 416℃~618℃. The ambient atmosphere during the heat treatment process is air, and no N2 or inert gas Ar is introduced. The heat is kept for 90min~150min, and then air-cooled to room temperature after being taken out of the furnace to obtain a composite oxide passivation layer of 1.5mm~3.5mm, completing the preparation.

[0035] Principle analysis: Heat treatment in air environment, using [O] in the air to react with alloy elements Ni, Si, Cr, Al, etc. on the steel surface to form a dense corrosion-resistant composite oxide to protect the matrix from further corrosion from the environment. Heat treatment of L-shaped steel in this temperature range can also eliminate the residual internal stress caused by induction quenching and avoid stress corrosion. If the passivation temperature is too high, the strength of the steel will be significantly reduced. If the treatment temperature is too low, it is difficult to obtain a composite oxide passivation layer with a thickness of 1.5mm to 3.5mm.

[0036] The alloy material and auxiliary materials in step 1) include CaO, blast furnace iron, scrap steel, low carbon CrFe, SiFe, NiFe, and Cu; the composite oxides in step 4) include NiO, Ni2O3, SiO2, Cr2O3, Al2O3, Fe x O y .

[0037] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the room temperature yield strength of the L-shaped steel obtained by the present invention is greater than 580MPa; the impact energy of the V-notch at -75℃ is ≥90J, and the corrosion resistance is: artificial corrosion environment: the corrosion rate of 10%HCl+20NaCl+10%HS+60%H2O (water) solution is ≤0.03mm / year. Reducing the chemical composition facilitates production, reducing the Cu content improves the quality, and has excellent comprehensive mechanical properties and corrosion resistance, meeting the needs of marine engineering equipment such as large deep-sea drilling platforms and large ocean-going ship keels, reinforcements and other structural parts. According to calculations, the steel of the present invention is about 1,200 yuan more efficient per ton than ordinary steel. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0039] According to the chemical element composition, mass percentage and production method requirements of the present invention, 5 embodiments were prepared, namely, embodiment 1, embodiment 2, embodiment 3, embodiment 4 and embodiment 5. In order to verify the influence of each chemical element component and mass percentage content as well as the finishing rolling temperature, induction quenching temperature and passivation heat treatment process parameters on the performance parameters during the preparation process, three comparative embodiments were prepared, namely comparative embodiment 1, comparative embodiment 2 and comparative embodiment 3, that is, 8 batches of steel were smelted and prepared. Among them, the mass percentage content of the chemical components of comparative embodiment 1 is not within the scope of the present invention, while the process parameters of the preparation process are within the scope of the present invention, the mass percentage content of the chemical components of comparative embodiment 2 is within the scope of the present invention, while the process parameters of the preparation process are not within the scope of the present invention, and the mass percentage content of the chemical components of comparative embodiment 3 and the process parameters of the preparation process are not within the scope of the present invention. The weight percentage of the chemical element components of the five embodiments and the three comparative embodiments is shown in Table 1, wherein the remainder is Fe and unavoidable impurities. The control parameters of the preparation process and the performance and quality of L-shaped steel are shown in Table 2.

[0040] Artificial simulation corrosion test method: 1. Process the embodiment sample and the comparative sample of the present invention into a block corrosion sample with a size of 50mm×50mm×5mm, polish 6 sides with 800 metallographic sandpaper, clean the surface with pure alcohol and blow dry; 2. Preparation of corrosion liquid: a mixed solution of 10% HCl+20% NaCl+10% HS+60% H2O is placed in a 1 cubic meter glass container; 3. Place the sample in the glass container, the distance between each sample is about 100mm, the sample process temperature is about 25°C, and the solution is stirred after the sample is placed in the corrosion liquid container; 4. Take out the sample at the corrosion time of 24 hours, 168 hours, 240 hours, and 720 hours, clean it with alcohol and blow dry the surface, use a thickness gauge to test the depth of corrosion pits, detect the number of pits ≥50, calculate the arithmetic mean of the detected corrosion depth, and extrapolate it to the annual (365 days) corrosion rate.

[0041] Table 1 Comparison of chemical compositions of the embodiments of the present invention and the comparative embodiments (wt%)

[0042]

[0043] Table 2 Effect of production process control on steel performance of the embodiments of the present invention and the comparative embodiments

[0044]

[0045] It can be seen from Table 1 and Table 2 that the L-shaped steels produced by the chemical composition and mass percentage of Examples 1-5 of the present invention and the parameters of the production process control have a room temperature yield strength higher than 580 MPa, a -75°C impact energy higher than 90 J, and an average annual corrosion rate lower than 0.03 mm / year, while the comparative steels produced by Comparative Example 1, Comparative Example 2 and Comparative Example 3 whose steel composition ranges or / and production processes are not within the scope of the present invention have a room temperature yield strength lower than 528 MPa, a -75°C impact energy lower than 67 J, and an average annual corrosion rate higher than 0.03 mm / year. Among them, the room temperature yield strength of the L-shaped steel prepared in Example 2 of the present invention is 591MPa, the impact energy at -75°C reaches 298J, the average annual corrosion rate is 0.015mm / year, and the comprehensive performance is excellent. It is safe and reliable for manufacturing large deep-sea drilling platforms, marine tidal power generation and other marine projects, as well as keels, reinforcements and other structural parts of large ocean-going ships. It has excellent corrosion resistance, can significantly improve the operational safety of steel structure projects, greatly increase the service life, and has huge economic and social benefits. It is the best embodiment.

Claims

1. A method for preparing high-strength corrosion-resistant steel, characterized in that: The high-strength corrosion-resistant steel comprises the following components in weight percentage: C: 0.005% to 0.015%, Si: 0.8% to 1.18%, P≤0.012%, S≤0.0015%, Ni: 0.6% to 0.9%, Cr: 1.6% to 1.9%, Cu: 0.6% to 0.9%, Al: 0.65% to 1.15%, Ce+Y: 0.05% to 0.5%, and the balance is Fe and unavoidable impurities; The method for preparing the high-strength corrosion-resistant steel comprises the following steps: 1) Converter, electric furnace smelting, continuous casting: alloy materials and auxiliary materials are charged into a converter or electric furnace for melting, FeO is added for P removal, oxygen is blown for decarburization, sampling and analysis of alloy element content are performed and target value is adjusted, LF ladle furnace is used for S removal, Al block is added for deoxidation, Al wire is fed for Al alloying, vacuum degassing cycle is adopted, vacuum degree is ≤2 mbar, Ce+Y composite rare earth wire is fed, argon is blown for stirring, harmful inclusions in the steel are removed, and then continuous casting is performed into a 260mm×360mm rectangular billet; the alloy materials and auxiliary materials include CaO, blast furnace iron, scrap steel, low carbon CrFe, SiFe, NiFe and Cu; 2) Rolling: The heating temperature of the ingot is 1120℃~1220℃, the holding time is 3.5h~4.5h, and the ingot is rolled after it comes out of the furnace. The starting rolling temperature is 1000℃~1040℃, and the final rolling temperature is 815℃~850℃; 3) Cooling after rolling: After rolling, the steel is cooled by air blower, and the red-returning temperature is 460℃~660℃; 4) Heat treatment: Induction quenching: The rolled L-shaped steel is quenched in the temperature range of 896℃~910℃ by using roller bottom continuous medium frequency induction quenching facilities, and the roller speed is set at 300mm / min~1000mm / min; Surface composite oxide passivation treatment: The L-shaped steel after induction quenching is passivated heat treated in the temperature range of 416℃~618℃. The ambient atmosphere during the heat treatment process is air, and no N2 or inert gas Ar is introduced. The heat is kept for 90min~150min, and then air-cooled to room temperature after being taken out of the furnace to obtain a composite oxide passivation layer of 1.5mm~3.5mm, completing the preparation.

2. The method for preparing high-strength corrosion-resistant steel according to claim 1, characterized in that: The weight percentage of C is 0.005% to 0.012%.

3. The method for preparing high-strength corrosion-resistant steel according to claim 1, characterized in that: The weight percentage of Si is 0.85% to 1.0%.

4. The method for preparing high-strength corrosion-resistant steel according to claim 1, characterized in that: The weight percentage of Ni is 0.65% to 0.75%.

5. The method for preparing high-strength corrosion-resistant steel according to claim 1, characterized in that: The weight percentage of Cr is 1.65% to 1.75%.

6. The method for preparing high-strength corrosion-resistant steel according to claim 1, characterized in that: The weight percentage of Cu is 0.65% to 0.75%.

7. The method for preparing high-strength corrosion-resistant steel according to claim 1, characterized in that: The weight percentage of Al is 0.70% to 0.90%.

8. The method for preparing high-strength corrosion-resistant steel according to claim 1, characterized in that: The weight percentage of Ce+Y is 0.085% to 0.35%.

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