General corrosion resistant super duplex stainless steel and method for manufacturing the same

Abstract

The application discloses a kind of general corrosion resistant super duplex stainless steel and preparation method thereof, belong to stainless steel production technical field, the chemical composition of the general corrosion resistant super duplex stainless steel is controlled as follows by mass percent: 0.005%≤C≤0.020%, 0.48%≤Si≤0.64%, 0.74%≤Mn≤1.06%, 0.016%≤P≤0.028%, 0.002%≤S≤0.004%, 25.6%≤Cr≤26.4%, 6.7%≤Ni≤7.1%, 3.9%≤Mo≤4.2%, 0.26%≤N≤0.29%, 0.02%≤Al≤0.04%, O<0.003%, the balance is Fe and unavoidable impurities;The application has wide application in harsh environment high-end industrial field such as deep sea oil and gas, petrochemical industry, etc. by virtue of its metallurgical cleanliness, excellent general corrosion resistance and ultrahigh strength.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel production technology, specifically relating to a super duplex stainless steel resistant to overall corrosion and its preparation method. Background Technology

[0002] Super duplex stainless steel combines the performance advantages of both austenitic and ferritic stainless steels, making it a core structural material for equipment manufacturing in high-end industrial fields such as deep-sea oil and gas and petrochemicals. As operating conditions in these fields continue to evolve towards higher pressure, stronger corrosion, and longer service cycles, the industry's requirements for the comprehensive performance of steel are constantly increasing. High-quality super duplex stainless steel, possessing high metallurgical purity, excellent resistance to all-round corrosion, and ultra-high strength, has become a key research and development focus in the industry, as its performance level directly determines the service safety and service life of high-end equipment.

[0003] Existing ordinary super duplex stainless steel cannot simultaneously meet the above-mentioned multiple stringent requirements. Regarding metallurgical cleanliness, the inclusion levels (A, B, C, and D) are difficult to consistently control below 0.5, making inclusions vulnerable points for corrosion initiation and mechanical failure. In terms of overall corrosion resistance, the corrosion rate is high in high-chlorine, acidic, or alkaline cleaning agent environments, leading to surface rust or pitting after long-term use, compromising the long-term reliability of the equipment. In terms of strength, the yield strength generally does not reach 550 MPa, preventing the adoption of thinner-walled designs and limiting the potential for weight reduction and cost optimization. Summary of the Invention

[0004] To address the aforementioned technical problems in the existing technology, this invention provides a super duplex stainless steel resistant to overall corrosion and its preparation method.

[0005] In a first aspect of the invention, a super duplex stainless steel resistant to total corrosion is provided, the chemical composition of which is controlled by mass percentage as follows: 0.005%≤C≤0.020%, 0.48%≤Si≤0.64%, 0.74%≤Mn≤1.06%, 0.016%≤P≤0.028%, 0.002%≤S≤0.004%, 25.6%≤Cr≤26.4%, 6.7%≤Ni≤7.1%, 3.9%≤Mo≤4.2%, 0.26%≤N≤0.29%, 0.02%≤Al≤0.04%, O<0.003%, with the balance being Fe and unavoidable impurities.

[0006] Furthermore, the chemical composition of the aforementioned super duplex stainless steel resistant to total corrosion is controlled by mass percentage as follows: 0.014%≤C≤0.018%, 0.53%≤Si≤0.61%, 0.85%≤Mn≤1.02%, 0.022%≤P≤0.026%, 0.002%≤S≤0.003%, 25.69%≤Cr≤26.01%, 6.82%≤Ni≤7.05%, 3.93%≤Mo≤4.12%, 0.27%≤N≤0.28%, 0.02%≤Al≤0.03%, with the balance being Fe and unavoidable impurities.

[0007] Furthermore, the chemical composition of the above-mentioned super duplex stainless steel resistant to overall corrosion, by mass percentage, satisfies the following: Mn / Si≥1.6, 1.9≤(Si+Al) / (N+O)≤2.5.

[0008] Furthermore, based on the mass percentage content of each element, the pitting resistance equivalent PREN of the above-mentioned super duplex stainless steel resistant to general corrosion satisfies: PREN = Cr% + 3.3 × Mo% + 16 × N%, and PREN ≥ 43.

[0009] In a second aspect of the invention, the method for preparing the super duplex stainless steel resistant to general corrosion includes the following steps: (1) Composition control and composite deoxidation: The AOD-LF combined smelting process is adopted, and the alloying elements and nitrogen elements in the steel are controlled by combining AOD primary smelting and LF refining; the Al-Si composite deoxidation process is used for deoxidation during LF refining, so as to control the aluminum content in the steel while meeting the oxygen content requirements of the liquid steel. (2) Calcium treatment modification of inclusions: calcium treatment is performed on the deoxidized steel liquid to transform the high melting point solid Al2O3 inclusions in the steel into low melting point liquid calcium aluminate inclusions. The amount of calcium added during calcium treatment is controlled at 50~80ppm, and the mass ratio of calcium to aluminum in the steel is controlled at 0.20~0.40. (3) Soft stirring to enhance inclusion removal: After the calcium treatment is completed, a soft stirring process is implemented in the LF refining stage to promote the flotation and removal of inclusions. The argon blowing intensity of the soft stirring process is controlled at 1.5~2.0NL / min / t, and the argon blowing time is controlled at 25~30min.

[0010] Furthermore, in the above-mentioned method for preparing super duplex stainless steel resistant to total corrosion, after Al-Si composite deoxidation process in step (1), the total oxygen content of the finished steel is controlled to be <0.0030%.

[0011] Furthermore, in the above-mentioned method for preparing super duplex stainless steel resistant to overall corrosion, the amount of calcium added in step (2) is 54~70 ppm, and the mass ratio of calcium to aluminum in the steel, w(Ca) / w(Al), is 0.23~0.35.

[0012] Furthermore, in the above-mentioned method for preparing super duplex stainless steel resistant to overall corrosion, the low-melting-point liquid calcium aluminate in step (2) contains 12CaO·7Al2O3.

[0013] Furthermore, in the above-mentioned method for preparing super duplex stainless steel resistant to general corrosion, the non-metallic inclusions of type A and type B are both grade 0, and types C and D are both no higher than grade 0.5; the PREN value of the steel is not less than 43, and the room temperature yield strength Rp0.2 is not less than 580 MPa.

[0014] This invention, with its metallurgical purity, excellent resistance to all-round corrosion, and ultra-high strength, has wide applications in high-end industrial fields with harsh environments such as deep-sea oil and gas and petrochemicals. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for further understanding of the embodiments of this application and constitute a part of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 The image shows the effect of removing non-metallic inclusions from the super duplex stainless steel resistant to overall corrosion prepared according to the embodiments of this application. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0017] In a first aspect, a super duplex stainless steel resistant to total corrosion is provided, which has wide applications in high-end industrial fields with harsh environments such as deep-sea oil and gas and petrochemicals.

[0018] Specifically, the chemical composition of the super duplex stainless steel resistant to overall corrosion of the present invention is controlled by mass percentage as follows: 0.005%≤C≤0.020%, 0.48%≤Si≤0.64%, 0.74%≤Mn≤1.06%, 0.016%≤P≤0.028%, 0.002%≤S≤0.004%, 25.6%≤Cr≤26.4%, 6.7%≤Ni≤7.1%, 3.9%≤Mo≤4.2%, 0.26%≤N≤0.29%, 0.02%≤Al≤0.04%, O<0.003%, with the balance being Fe and unavoidable impurities.

[0019] Preferably, the chemical composition of the super duplex stainless steel resistant to overall corrosion of the present invention is controlled by mass percentage as follows: 0.014%≤C≤0.018%, 0.53%≤Si≤0.61%, 0.85%≤Mn≤1.02%, 0.022%≤P≤0.026%, 0.002%≤S≤0.003%, 25.69%≤Cr≤26.01%, 6.82%≤Ni≤7.05%, 3.93%≤Mo≤4.12%, 0.27%≤N≤0.28%, 0.02%≤Al≤0.03%, with the balance being Fe and unavoidable impurities.

[0020] Specifically, the chemical composition of the super duplex stainless steel resistant to overall corrosion of the present invention, by mass percentage, satisfies: Mn / Si≥1.6, 1.9≤(Si+Al) / (N+O)≤2.5. In the reaction process between elements during the smelting of high-purity super duplex stainless steel, Mn and Si compete for each other, so Mn / Si≥1.6 must be controlled. The main role of Al and Si elements in the smelting process of high-purity super duplex stainless steel is deoxidation, but they will also form nitrides and oxides with N and O, so 1.9≤(Si+Al) / (N+O)≤2.5 must be controlled.

[0021] Specifically, calculated based on the mass percentage content of each element, the pitting resistance equivalent PREN of the super duplex stainless steel resistant to general corrosion of the present invention satisfies: PREN = Cr% + 3.3 × Mo% + 16 × N%, and PREN ≥ 43. PREN (pitting resistance equivalent) is a value obtained by weighted summation of the key corrosion-resistant elements (Cr, Mo, N) in the material (PREN = Cr% + 3.3 × Mo% + 16 × N%). The higher this value, the stronger the material's "survival ability," i.e., its corrosion resistance, in harsh environments (such as seawater and chemical media). In the steel involved in this invention, PREN is required to be above 43.

[0022] The function of the required elemental and content control ranges for the all-corrosion resistant super duplex stainless steel of this invention is described below: Carbon (C) is the primary controlled element in super duplex stainless steel and is an essential strength element (solid solution strengthening). However, its combination with chromium (Cr) to form carbides leads to "chromium-depleted zones," initiating intergranular corrosion. Strictly low carbon content is essential. In the steel involved in this invention, the C content is controlled at 0.005~0.020%.

[0023] Silicon (Si) is a deoxidizer used in the smelting process of super duplex stainless steel, which can improve the high-temperature strength of the material. However, excessive Si can promote ferrite formation, increase intermetallic brittleness, and reduce impact toughness. In the steel involved in this invention, the Si content is controlled at 0.48~0.64%.

[0024] In super duplex stainless steel, manganese (Mn) acts as an auxiliary austenite-forming element (replacing part of Ni) and can improve hot workability. However, excessive Mn content can lead to the formation of MnS inclusions with sulfur, which become the initiation source of pitting corrosion and severely impair corrosion resistance. In the steel involved in this invention, the Mn content is controlled at 0.74~1.06%.

[0025] Phosphorus (P) is a harmful impurity in super duplex stainless steel. It segregates at grain boundaries, leading to increased temper brittleness and susceptibility to intergranular corrosion. P is considered an impurity and residual element, and a lower content is better. However, since P originates from raw materials used in smelting, low-phosphorus raw materials are more expensive, which is detrimental to cost control. Therefore, the P content in the steel involved in this invention is controlled at 0.016~0.028%.

[0026] Sulfur (S) readily forms sulfide inclusions in super duplex stainless steel, severely impairing its corrosion resistance (a site for pitting corrosion initiation) and hot workability. However, as a free-machining element, a certain amount of S can improve the material's machinability, making it more suitable for the machining and manufacturing of intricate and complex parts. In the steel involved in this invention, the S content is controlled at 0.002-0.004%.

[0027] Chromium (Cr) is fundamental to the corrosion resistance of super duplex stainless steel. The dense passivation film it forms provides resistance to oxidation and pitting corrosion, and is a key contributor to the PREN value. However, excessive Cr can promote excessive ferrite phase and precipitation of the σ phase (brittle phase), impairing toughness. In the steel involved in this invention, the Cr content is controlled at 25.6% to 26.4%.

[0028] In super duplex stainless steel, nickel (Ni) acts as an austenite stabilizer, balancing the duplex phase ratio (approximately 50 / 50) and improving toughness and resistance to stress corrosion cracking (SCC). However, Ni is a precious metal element, resulting in high cost. Furthermore, excessive Ni can suppress ferrite, disrupt the duplex phase balance, and increase the tendency for σ-phase precipitation. In the steel involved in this invention, the Ni content is controlled at 6.7–7.1%.

[0029] Mo (Mo) is a key element in super duplex stainless steel, playing a role in resisting chloride ion pitting and crevice corrosion, and significantly improving stability in seawater / acidic environments. However, excessive Mo easily forms intermetallic compounds (such as the χ phase), deteriorating hot workability and toughness. In the steel involved in this invention, the Mo content is controlled at 3.9~4.2%.

[0030] Nitrogen (N) is the soul of super duplex stainless steel, contributing the most to the PREN value. N is an inexpensive austenite stabilizer that can significantly improve strength, inhibit σ-phase precipitation, and improve weldability. However, uncontrolled N content can lead to microstructure instability, and supersaturation may result in porosity or nitride formation. In the steel involved in this invention, the N content is controlled at 0.26~0.29%.

[0031] Al (aluminum) is an important deoxidizer in high-purity super duplex stainless steel to control oxygen content. However, Al is also a source of Al₂O₃ inclusions. Oxide inclusions can fracture the matrix, becoming fatigue crack initiation points and corrosion weak points. Therefore, it is usually strictly limited as a residual element. In the steel involved in this invention, the Al content is controlled at 0.02~0.04%.

[0032] Oxygen (O) readily forms oxide inclusions in super duplex stainless steel, and is considered a "pure impurity," so the lower the content, the better. During high-temperature rolling or forging, these hard and brittle inclusions become stress concentration points, leading to edge cracks and surface cracks in the sheet. In the steel involved in this invention, the O content is controlled below 0.003%.

[0033] In a second aspect of the present invention, a method for preparing a super duplex stainless steel resistant to general corrosion is provided, comprising the following steps: (1) Composition control and composite deoxidation: The AOD-LF combined smelting process is adopted, and the alloying elements and nitrogen elements in the steel are controlled by combining AOD primary smelting and LF refining; the Al-Si composite deoxidation process is used for deoxidation during LF refining, so as to control the aluminum content in the steel while meeting the oxygen content requirements of the liquid steel. (2) Calcium treatment modification of inclusions: calcium treatment is performed on the deoxidized steel liquid to transform the high melting point solid Al2O3 inclusions in the steel into low melting point liquid calcium aluminate inclusions. The amount of calcium added during calcium treatment is controlled at 50~80ppm, and the mass ratio of calcium to aluminum in the steel is controlled at 0.20~0.40. (3) Soft stirring to enhance inclusion removal: After the calcium treatment is completed, a soft stirring process is implemented in the LF refining stage to promote the flotation and removal of inclusions. The argon blowing intensity of the soft stirring process is controlled at 1.5~2.0NL / min / t, and the argon blowing time is controlled at 25~30min.

[0034] Preferably, in the preparation method of the super duplex stainless steel resistant to total corrosion of the present invention, after Al-Si composite deoxidation process in step (1), the total oxygen content of the finished steel is controlled to be <0.0030%.

[0035] Preferably, in the preparation method of the super duplex stainless steel resistant to overall corrosion of the present invention, the amount of calcium added in the calcium treatment in step (2) is 54~70ppm, and the mass ratio of calcium to aluminum in the steel w(Ca) / w(Al) is 0.23~0.35.

[0036] Preferably, in the preparation method of the super duplex stainless steel resistant to overall corrosion of the present invention, the low melting point liquid calcium aluminate in step (2) contains 12CaO·7Al2O3.

[0037] Preferably, in the preparation method of the super duplex stainless steel resistant to general corrosion of the present invention, the super duplex stainless steel prepared has non-metallic inclusions of type A and type B both at grade 0, and type C and type D both at grade 0.5; the PREN value of the steel is not less than 43, and the room temperature yield strength Rp0.2 is not less than 580 MPa.

[0038] The following detailed description of the present invention, including its preparation method, is based on specific embodiments.

[0039] Table 1: Composition (wt.%) of the super duplex stainless steel resistant to overall corrosion in Examples 1-3

[0040] Example 1 The chemical composition of the super duplex stainless steel resistant to overall corrosion in Example 1, by mass percentage, is as follows: C: 0.018, Si: 0.53, Mn: 0.85, P: 0.025, S: 0.003, Cr: 25.69, Ni: 6.82, Mo: 3.93, N: 0.28, Al: 0.03, O: 0.0028, with the balance being Fe and unavoidable impurities.

[0041] The specific process of preparing the super duplex stainless steel resistant to overall corrosion in Example 1 includes: (1) Composition control and composite deoxidation: The AOD-LF combined smelting process is adopted. The alloying elements and nitrogen elements in the steel are precisely controlled by combining AOD primary smelting and LF refining. During the LF refining process, the Al-Si composite deoxidation process is used to deoxidize the steel while meeting the oxygen content requirements of the liquid steel and controlling the aluminum content in the steel.

[0042] (2) Calcium treatment modification of inclusions: Calcium treatment is performed on the deoxidized molten steel to transform the high melting point solid Al2O3 inclusions in the steel into low melting point liquid calcium aluminate inclusions; in this embodiment, the amount of calcium added is controlled at 69 ppm, and the mass ratio of calcium to aluminum in the steel is controlled at 0.23.

[0043] (3) Soft stirring to enhance inclusion removal: After the calcium treatment is completed, a soft stirring process is implemented in the LF refining stage to promote the flotation and removal of inclusions; in this embodiment, the argon blowing intensity is controlled at 1.8NL / min / t and the argon blowing time is controlled at 30min.

[0044] The non-metallic inclusions of the super duplex stainless steel obtained in this embodiment were rated as follows: Class A 0, Class B 0, Class C 0.5, and Class D 0.5; the pitting resistance equivalent PREN value was 43.14; and the yield strength Rp0.2 was 580 MPa, demonstrating both excellent resistance to general corrosion and mechanical properties.

[0045] Example 2 The chemical composition of the super duplex stainless steel resistant to overall corrosion in Example 2, by mass percentage, is as follows: C: 0.014, Si: 0.61, Mn: 1.02, P: 0.022, S: 0.002, Cr: 26.01, Ni: 7.05, Mo: 4.12, N: 0.27, Al: 0.02, O: 0.0029, with the balance being Fe and unavoidable impurities.

[0046] The specific process of preparing the super duplex stainless steel resistant to overall corrosion in Example 2 includes: (1) Composition control and composite deoxidation: The AOD-LF combined smelting process is adopted. The alloying elements and nitrogen elements in the steel are precisely controlled by combining AOD primary smelting and LF refining. During the LF refining process, the Al-Si composite deoxidation process is used to deoxidize the steel while meeting the oxygen content requirements of the liquid steel and controlling the aluminum content in the steel.

[0047] (2) Calcium treatment modification of inclusions: Calcium treatment is performed on the deoxidized molten steel to transform the high melting point solid Al2O3 inclusions in the steel into low melting point liquid calcium aluminate inclusions; in this embodiment, the amount of calcium added is controlled at 54 ppm, and the mass ratio of calcium to aluminum in the steel is controlled at 0.27.

[0048] (3) Soft stirring to enhance inclusion removal: After the calcium treatment is completed, a soft stirring process is implemented in the LF refining stage to promote the flotation and removal of inclusions; in this embodiment, the argon blowing intensity is controlled at 2.0 NL / min / t and the argon blowing time is controlled at 25 min.

[0049] The non-metallic inclusions of the super duplex stainless steel obtained in this embodiment were rated as follows: Class A 0, Class B 0, Class C 0, and Class D 0.5; the pitting resistance equivalent PREN value was 43.93; and the yield strength Rp0.2 was 594 MPa, demonstrating both excellent resistance to general corrosion and mechanical properties.

[0050] Example 3 The chemical composition of the super duplex stainless steel resistant to overall corrosion in Example 3, by mass percentage, is as follows: C: 0.016, Si: 0.56, Mn: 0.91, P: 0.026, S: 0.003, Cr: 25.87, Ni: 6.93, Mo: 4.06, N: 0.28, Al: 0.02, O: 0.0027, with the balance being Fe and unavoidable impurities.

[0051] The specific process of preparing the super duplex stainless steel resistant to overall corrosion in Example 3 includes: (1) Composition control and composite deoxidation: The AOD-LF combined smelting process is adopted. The alloying elements and nitrogen elements in the steel are precisely controlled by combining AOD primary smelting and LF refining. During the LF refining process, the Al-Si composite deoxidation process is used to deoxidize the steel while meeting the oxygen content requirements of the liquid steel and controlling the aluminum content in the steel.

[0052] (2) Calcium treatment modification of inclusions: Calcium treatment is performed on the deoxidized molten steel to transform the high melting point solid Al2O3 inclusions in the steel into low melting point liquid calcium aluminate inclusions; in this embodiment, the amount of calcium added is controlled at 70 ppm, and the mass ratio of calcium to aluminum in the steel is controlled at 0.35.

[0053] (3) Soft stirring to enhance inclusion removal: After the calcium treatment is completed, a soft stirring process is implemented in the LF refining stage to promote the flotation and removal of inclusions; in this embodiment, the argon blowing intensity is controlled at 1.6NL / min / t and the argon blowing time is controlled at 28min.

[0054] The non-metallic inclusions of the super duplex stainless steel obtained in this embodiment were rated as follows: Class A 0, Class B 0, Class C 0.5, and Class D 0; the pitting resistance equivalent PREN value was 43.75; and the yield strength Rp0.2 was 591 MPa, demonstrating both excellent resistance to general corrosion and mechanical properties.

[0055] In summary, this invention, with its metallurgical cleanliness, excellent resistance to all-round corrosion and ultra-high strength, has wide applications in high-end industrial fields with harsh environments such as deep-sea oil and gas and petrochemicals.

[0056] In the description of this specification, the term "embodiment" means a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. The illustrative expressions of the above terms in this specification do not necessarily refer to the same embodiment. Furthermore, those skilled in the art can combine or combine the different embodiments and features described in this specification without creating contradiction.

[0057] It should be noted that, unless otherwise specified, the terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, when a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum. Further, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Moreover, when multiple ranges are provided to describe features, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0058] It should also be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A super duplex stainless steel resistant to total corrosion, characterized in that, The chemical composition of the super duplex stainless steel resistant to total corrosion is controlled by mass percentage as follows: 0.005%≤C≤0.020%, 0.48%≤Si≤0.64%, 0.74%≤Mn≤1.06%, 0.016%≤P≤0.028%, 0.002%≤S≤0.004%, 25.6%≤Cr≤26.4%, 6.7%≤Ni≤7.1%, 3.9%≤Mo≤4.2%, 0.26%≤N≤0.29%, 0.02%≤Al≤0.04%, O<0.003%, with the balance being Fe and unavoidable impurities.

2. The super duplex stainless steel resistant to total corrosion according to claim 1, characterized in that, The chemical composition of the super duplex stainless steel resistant to total corrosion is controlled by mass percentage as follows: 0.014%≤C≤0.018%, 0.53%≤Si≤0.61%, 0.85%≤Mn≤1.02%, 0.022%≤P≤0.026%, 0.002%≤S≤0.003%, 25.69%≤Cr≤26.01%, 6.82%≤Ni≤7.05%, 3.93%≤Mo≤4.12%, 0.27%≤N≤0.28%, 0.02%≤Al≤0.03%, with the balance being Fe and unavoidable impurities.

3. The super duplex stainless steel resistant to overall corrosion according to claim 1, characterized in that, The chemical composition of the super duplex stainless steel resistant to total corrosion, by mass percentage, satisfies: Mn / Si≥1.6, 1.9≤(Si+Al) / (N+O)≤2.

5.

4. The super duplex stainless steel resistant to total corrosion according to claim 1, characterized in that, Based on the mass percentage content of each element, the pitting resistance equivalent PREN of the super duplex stainless steel resistant to general corrosion satisfies: PREN = Cr% + 3.3 × Mo% + 16 × N%, and PREN ≥ 43.

5. A method for preparing a super duplex stainless steel resistant to overall corrosion, characterized in that, Includes the following steps: (1) Composition control and composite deoxidation: The AOD-LF combined smelting process is adopted, and the alloying elements and nitrogen elements in the steel are controlled by combining AOD primary smelting and LF refining; the Al-Si composite deoxidation process is used for deoxidation during LF refining, so as to control the aluminum content in the steel while meeting the oxygen content requirements of the liquid steel. (2) Calcium treatment modification of inclusions: calcium treatment is performed on the deoxidized steel liquid to transform the high melting point solid Al2O3 inclusions in the steel into low melting point liquid calcium aluminate inclusions. The amount of calcium added during calcium treatment is controlled at 50~80ppm, and the mass ratio of calcium to aluminum in the steel is controlled at 0.20~0.

40. (3) Soft stirring to enhance inclusion removal: After the calcium treatment is completed, a soft stirring process is implemented in the LF refining stage to promote the flotation and removal of inclusions. The argon blowing intensity of the soft stirring process is controlled at 1.5~2.0NL / min / t, and the argon blowing time is controlled at 25~30min.

6. The method for preparing the super duplex stainless steel resistant to overall corrosion according to claim 5, characterized in that, In step (1), after Al-Si composite deoxidation process, the total oxygen content of the finished steel is controlled to be <0.0030%.

7. The method for preparing the super duplex stainless steel resistant to overall corrosion according to claim 5, characterized in that, In step (2), the amount of calcium added during calcium treatment is 54~70 ppm, and the mass ratio of calcium to aluminum in the steel, w(Ca) / w(Al), is 0.23~0.

35.

8. The method for preparing the super duplex stainless steel resistant to overall corrosion according to claim 5, characterized in that, The low-melting-point liquid calcium aluminate in step (2) contains 12CaO·7Al2O3.

9. The method for preparing the super duplex stainless steel resistant to overall corrosion according to claim 5, characterized in that, In the prepared super duplex stainless steel, the non-metallic inclusions of type A and type B are both grade 0, and the inclusions of type C and type D are both no higher than grade 0.5; the PREN value of the steel is not less than 43, and the room temperature yield strength Rp0.2 is not less than 580 MPa.

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