High-strength corrosion-resistant steel and preparation method therefor

Abstract

Disclosed is a high-strength corrosion-resistant steel, comprising the following components in percentages by weight: 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 being Fe and inevitable impurities. Also disclosed is a preparation method for said steel. The present invention reduces chemical components for ease of production, lowers the Cu content to improve quality, and has excellent overall mechanical properties and corrosion resistance, meeting the requirements for structural components such as keels and stiffeners of large offshore engineering equipment such as deep-sea drilling platforms and large ocean-going vessels.

Description

High-strength corrosion-resistant steel and preparation method thereof Technical Field

[0001] The present invention relates to the field of steel production, and in particular to 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 vessels are mostly subject to seawater corrosion, marine biological erosion, marine atmospheric corrosion, etc., and have to be periodically docked for maintenance, upkeep, and repairs. Shipowners hope to have longer service life to create more wealth. Marine engineering equipment such as giant offshore drilling platforms are subject to compound corrosion factors, causing equipment and facilities to become obsolete. After a certain period of operation, equipment and structural parts must be replaced, resulting in huge losses.

[0003] Currently, commonly used high-strength steels such as AH32, DH32, AH36, DH36, EH32, and EH36 lack good corrosion resistance under the diverse and complex corrosion conditions of the marine environment. L-shaped steel used for structural components such as stiffeners and keels also utilize these types of steel. Their primary drawback is that these steel grades fail to prioritize marine corrosion resistance during their design and production, relying instead on corrosion protection coatings. During production, the surface coating can flake off due to anchor chains, docking, and contact with other vessels, exposing the steel substrate to the corrosive environment. Furthermore, cargo loading and unloading can also cause friction and impact on steel components, leading to flaking of the surface coating and localized corrosion. These corrosion behaviors directly endanger the operational safety of the entire equipment and shorten its service life. Maintenance and repairs such as re-coating lead to production stoppages and reductions, resulting in significant losses. After a certain period of service, maintenance and repairs such as replacement of equipment and structural components or re-coating of the anti-corrosion coating are required, which can even lead to the entire equipment becoming obsolete.

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

[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, its preparation method and application, 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 being Fe and unavoidable impurities. By optimizing the composition and proportions of the steel, the resulting steel has excellent corrosion resistance; and after high heat input welding, the resulting weld heat-affected zone has excellent toughness, thereby improving the production efficiency and service life of crude oil storage tanks made from the steel. This patented technology has a complex chemical composition, a large number of types, and a difficult production process to control.

[0006] For example, the invention patent (application number 202210535812.0) discloses "A corrosion-resistant steel suitable for high-humidity and hot marine environment and its preparation method". The present invention relates to a corrosion-resistant steel suitable for high-humidity and hot marine environment and its preparation method, which belongs to the field of corrosion-resistant steel technology and solves the problems of high cost, limited corrosion resistance, and poor long-term corrosion resistance of corrosion-resistant steel used in high-humidity and hot marine environment in the prior art. The chemical composition weight percentage of the corrosion-resistant steel is: C≤0.06%, Si 0.20-0.40%, Mn 0.4-0.8%, Ni 1.0-2.0%, Cr 0.4-0.6%, Cu 1.0-2.0%, Sb0.2-0.6%, and the rest is Fe. The corrosion-resistant steel of the present invention has low cost and good corrosion resistance in high-humidity and hot marine environment. The Cu content of this patented technology is relatively high, and Cu enrichment is easily generated during the production process, forming liquid Cu, which causes thermal cracking, resulting in a reduced yield and an increase in scrap.

[0007] Therefore, it is necessary to develop new high-strength corrosion-resistant steel and its preparation method 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.

[0008] Summary of the Invention

[0009] Purpose of the invention: In view of the shortcomings and defects of the existing technology, 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 reinforcements of large ocean-going ships.

[0010] 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% 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.

[0011] Preferably, the weight percentage of C is 0.005% to 0.012%.

[0012] Preferably, the weight percentage of Si is 0.85% to 1.0%.

[0013] Preferably, the weight percentage of Ni is 0.65% to 0.75%.

[0014] Preferably, the weight percentage of Cr is 1.65% to 1.75%.

[0015] Preferably, the weight percentage of Cu is 0.65% to 0.75%.

[0016] Preferably, the weight percentage of Al is 0.70% to 0.90%.

[0017] Preferably, the weight percentage of Ce+Y is 0.085% to 0.35%.

[0018] Principle analysis:

[0019] C (carbon): This patent application adopts an ultra-low carbon component design. Since 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 causes 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%. The purpose is 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.

[0020] 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 corrosion resistance 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%.

[0021] 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 the 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%.

[0022] S (sulfur): S in structural steel is a harmful element that 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 within a relatively low range: S≤0.0015%.

[0023] Ni (nickel): alloy element Ni is not a carbide-forming element, and forms a dense enriched 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 adheres tightly to the substrate and resists peeling, effectively preventing further corrosion and improving corrosion resistance. Furthermore, adding an appropriate amount of nickel to structural steel can improve its low-temperature toughness. However, nickel is an expensive alloying element. To control production costs, the nickel content is set within a range of 0.6% to 0.9%, preferably 0.65% to 0.75%.

[0024] 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, and a uniform composite oxide dense layer is obtained on the surface after passivation heat treatment, 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, excessive Cr content is prone to form a series of carbides Cr x C y Cr forms, grows, and coarsens at grain boundaries, deteriorating low-temperature toughness. Therefore, the Cr content of the alloying element is set within the range of 1.6% to 1.9%, preferably 1.65% to 1.75%.

[0025] Al (aluminum): alloy element Al is an easily oxidized 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 steel and steel structures from corrosion. Although Al is a relatively cheap alloying element, too high an Al content makes the continuous casting process difficult. Therefore, the Al content of the alloying element is set within the range of 0.65% to 1.15%, preferably 0.70% to 0.90%.

[0026] Cu (copper): A certain amount of Cu, an alloying element, is added to steel. On the one hand, it can form an enriched and 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 cause thermal cracking during the production process. Therefore, the Cu content range is set to 0.6% to 0.9%, preferably 0.65% to 0.75%.

[0027] Ce+Y (Cerium + Yttrium): Adding rare earth elements Ce+Y has the functions of (1) further removing residual oxygen [O] in steel; (2) removing carbides in steel; and (3) improving the fluidity of 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%.

[0028] The method for preparing high-strength corrosion-resistant steel of the present invention is characterized by comprising the following steps:

[0029] 1) Converter, electric furnace smelting, and 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, and sampling is performed for analysis of alloy element content and target value adjustment. LF ladle furnace desulfurization is performed. Al blocks are added for deoxidation, and Al wire is fed for Al alloying. A vacuum degassing cycle is adopted with a vacuum degree of ≤ 2 mbar. Ce+Y composite rare earth wire is fed, and argon is blown for stirring. After removing harmful inclusions from the steel, the steel is continuously cast into a 260 mm × 360 mm rectangular billet.

[0030] 2) Rolling: The heating temperature of the billet is 1120℃~1220℃, the holding time is 3.5h~4.5h, and the billet is rolled after being taken out of the furnace. The starting rolling temperature is 1000℃~1040℃, and the finishing rolling temperature is 815℃~850℃;

[0031] 3) Cooling after rolling: After rolling, the steel is cooled by a blower, and the red-return temperature is 460℃~660℃;

[0032] 4) Heat treatment:

[0033] Induction quenching: Roller-hearth continuous medium-frequency induction quenching equipment is used to quench the rolled L-shaped steel in the temperature range of 896℃ to 910℃, and the roller speed is set at 300mm / min to 1000mm / min;

[0034] Principle Analysis: Using induction heat treatment for long L-shaped steel can, on the one hand, prevent distortion during the quenching process and achieve good surface quality. On the other hand, after quenching, a solid solution martensite is obtained, and the alloying elements are evenly distributed in the matrix, thus achieving excellent comprehensive mechanical properties and a yield strength exceeding 580 MPa.

[0035] Surface composite oxide passivation treatment: The induction-hardened L-shaped steel is subjected to passivation heat treatment in the temperature range of 416°C to 618°C. The ambient atmosphere during the heat treatment is air, and no N3 or Ar inert gas is introduced. The heat treatment is carried out for 90min to 150min, and the steel is taken out of the furnace and air-cooled to room temperature to obtain a composite oxide passivation layer of 1.5mm to 3.5mm, thus completing the preparation.

[0036] Principle analysis: During heat treatment in an air environment, [O] in the air reacts with alloying elements such as Ni, Si, Cr, and Al on the steel surface to form a dense, corrosion-resistant composite oxide to protect the substrate from further corrosion from the environment. Heat treatment of L-shaped steel in this temperature range can also eliminate residual internal stress generated 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 will be difficult to obtain a composite oxide passivation layer with a thickness of 1.5mm to 3.5mm.

[0037] Wherein, the alloy material and auxiliary materials in step 1) include CaO, blast furnace iron, scrap steel, low carbon CrFe, SiFe, NiFe, Cu; the composite oxides in step 4) include NiO, Ni2O3, SiO2, Cr2O3, Al2O3, Fe x O y .

[0038] Beneficial Effects: Compared with existing technologies, this invention offers the following significant advantages: The resulting L-shaped steel exhibits a room-temperature yield strength exceeding 580 MPa; a V-notch impact energy of ≥90 J at -75°C; and corrosion resistance: Corrosion rate in an artificial corrosive environment of 10% HCl + 20% NaCl + 10% HS + 60% H₂O (water) solution is ≤0.03 mm / year. Reducing the chemical composition facilitates production, while lowering the Cu content improves quality. The steel exhibits excellent comprehensive mechanical properties and corrosion resistance, meeting the requirements of marine engineering equipment such as large deep-sea drilling platforms, as well as structural components such as keels and stiffeners on large ocean-going vessels. Calculations indicate that the steel produced by this invention is approximately 1,200 yuan more profitable per ton than conventional steel. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0040] Five examples were prepared according to the chemical element composition, mass percentage, and production method requirements of the present invention, namely Example 1, Example 2, Example 3, Example 4, and Example 5. To verify the effects of the chemical element composition and mass percentage, as well as the finishing rolling temperature, induction quenching temperature, and passivation heat treatment process parameters during the production process, on performance parameters, three comparative examples were prepared, namely Comparative Example 1, Comparative Example 2, and Comparative Example 3. Eight batches of steel were smelted and produced. The mass percentages of the chemical elements in Comparative Example 1 were outside the scope of the present invention, while the process parameters of the production process were within the scope of the present invention. The mass percentages of the chemical elements in Comparative Example 2 were within the scope of the present invention, while the process parameters of the production process were outside the scope of the present invention. Both the mass percentages of the chemical elements and the process parameters of the production process in Comparative Example 3 were outside the scope of the present invention. The weight percentages of the chemical element compositions of the five examples and the three comparative examples are shown in Table 1, with the remainder being Fe and unavoidable impurities. The production process control parameters and the performance and quality of the L-shaped steel are shown in Table 2.

[0041] Artificial simulation corrosion test method: 1. The embodiment samples and comparative samples of the present invention are processed into block corrosion samples with a size of 50mm×50mm×5mm, polished on 6 sides with No. 800 metallographic sandpaper, cleaned the surface with pure alcohol and blown dry; 2. Corrosion liquid preparation: 10% HCl+20% NaCl+10% HS+60% H2O mixed solution is placed in a 1 cubic meter glass container; 3. The samples are placed in the glass container with a distance of about 100mm between each sample, the sample process temperature is about 25°C, and the solution is stirred after the sample is placed in the corrosion liquid container; 4. The samples are taken out at the corrosion time of 24 hours, 168 hours, 240 hours, and 720 hours, respectively, and the surface is blown dry after cleaning with alcohol. The depth of the corrosion pits is tested with a thickness gauge, and the number of pits is detected to be ≥50. The arithmetic mean of the detected corrosion depths is calculated and extrapolated to the annual (365-day) corrosion rate.

[0042] Table 1 Comparison of chemical compositions of the present invention and comparative examples (wt%)

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

[0044] As can be seen from Tables 1 and 2, the L-shaped steels produced according to the chemical compositions and mass percentages and the parameters for production process control of Examples 1-5 of the present invention 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. However, the comparative steels produced according to Comparative Examples 1, 2, and 3, whose steel composition ranges and / or production processes are outside 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 591 MPa, the impact energy at -75°C reaches 298 J, and the average annual corrosion rate is 0.015 mm / year. It has excellent comprehensive performance and is safe and reliable for manufacturing large deep-sea drilling platforms, marine tidal power generation and other marine engineering, as well as keels, reinforcements and other structural parts of large ocean-going ships. It has excellent corrosion resistance and can significantly improve the operational safety of steel structure projects and greatly increase the service life. It has huge economic and social benefits and is the best embodiment.

Claims

1. A high-strength corrosion-resistant steel, characterized by: The invention comprises the following components in the following weight percentages: 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.

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

9. The method for preparing high-strength corrosion-resistant steel according to any one of claims 1 to 8, characterized in that: The steps include: 1) Converter, electric furnace smelting, and 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, and sampling is performed for analysis of alloy element content and target value adjustment. LF ladle furnace desulfurization is performed. Al blocks are added for deoxidation, and Al wire is fed for Al alloying. A vacuum degassing cycle is adopted with a vacuum degree of ≤ 2 mbar. Ce+Y composite rare earth wire is fed, and argon is blown for stirring. After removing harmful inclusions from the steel, the steel is continuously cast into a 260 mm × 360 mm rectangular billet. 2) Rolling: The heating temperature of the billet is 1120℃~1220℃, the holding time is 3.5h~4.5h, and the billet is rolled after being taken out of the furnace. The starting rolling temperature is 1000℃~1040℃, and the finishing rolling temperature is 815℃~850℃; 3) Cooling after rolling: After rolling, the steel is cooled by a blower, and the red-return temperature is 460℃~660℃; 4) Heat treatment: Induction quenching: Roller bottom continuous medium frequency induction quenching equipment is used to quench the rolled L-shaped steel at a temperature of 896℃~910℃. The quenching treatment is carried out in the range of degrees, and the roller speed is set to 300mm / min~1000mm / min; Surface composite oxide passivation treatment: The induction-hardened L-shaped steel is subjected to passivation heat treatment in the temperature range of 416°C to 618°C. The ambient atmosphere during the heat treatment is air, and no N3 or Ar inert gas is introduced. The heat treatment is carried out for 90min to 150min, and the steel is taken out of the furnace and air-cooled to room temperature to obtain a composite oxide passivation layer of 1.5mm to 3.5mm, thus completing the preparation.

10. The method for preparing high-strength corrosion-resistant steel according to claim 9, characterized in that: In the step 1), the alloy material and auxiliary materials include CaO, blast furnace iron, scrap steel, low carbon CrFe, SiFe, NiFe, and Cu; in the step 4), the composite oxide includes NiO, Ni2O3, SiO2, Cr2O3, Al2O3, Fe x O y .

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