Low-nickel high-nitrogen super austenitic stainless steel, pipe blank, pipe blank preparation method and application thereof

Abstract

This invention discloses a low-nickel, high-nitrogen super austenitic stainless steel, its billet, a billet preparation method, and its applications. The chemical composition of the stainless steel is: C≤0.020%, Si≤0.60%, Mn≤0.80%, P≤0.025%, S≤0.020%, Cr: 19.50~20.50%, Ni: 16.50~17.50%, Mo: 6.0~6.3%, N: 0.45~0.55%, Cu: 0.5~1.0%, and ( w Ni + w Cu + w N )≥17.5, ( w Gr +3.3× w Mo +16× w N ≥45. This invention, through optimized control of chemical composition and a process design of initial rolling + homogenization treatment + radial forging + online solution treatment, enables the low-nickel, high-nitrogen super austenitic stainless steel to exhibit excellent corrosion resistance, significantly reducing alloy and manufacturing costs while meeting the basic performance requirements of super austenitic stainless steel.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel production technology, specifically relating to a low-nickel high-nitrogen super austenitic stainless steel, a low-nickel high-nitrogen super austenitic stainless steel tube blank, a method for preparing the low-nickel high-nitrogen super austenitic stainless steel tube blank, and their applications. Background Technology

[0002] Super austenitic stainless steel is a type of ultra-low carbon special stainless steel with a core alloy system of high chromium, high nickel, and high molybdenum, and the addition of elements such as nitrogen and copper. Its pitting corrosion resistance index (PREN) is generally ≥40. It has far superior resistance to pitting corrosion, crevice corrosion, and chloride stress corrosion compared to ordinary austenitic stainless steel, as well as excellent high and low temperature mechanical properties brought by nitrogen solid solution strengthening. It is widely used in highly corrosive industrial scenarios such as seawater desalination, flue gas desulfurization, and hydrometallurgy. Under medium and low temperature conditions, it can replace some nickel-based corrosion-resistant alloys, achieving a balance between performance and cost.

[0003] However, existing alloying systems for super austenitic stainless steel require the addition of large amounts of elements such as nickel, molybdenum, and nitrogen. The Ni content is typically around 18-25%, the N content between 0.18-0.25%, and the Mo content between 4-8%. Ni and Mo are precious metals, causing the cost of finished super austenitic stainless steel to fluctuate significantly due to their price variations. Furthermore, existing manufacturing processes suffer from a narrow range of possible specifications for super austenitic stainless steel billets, long production time, high energy consumption, low efficiency, and high production costs, severely hindering the widespread application of the product. Summary of the Invention

[0004] To address the aforementioned technical problems in the prior art, this invention provides a method for preparing low-nickel high-nitrogen super austenitic stainless steel, low-nickel high-nitrogen super austenitic stainless steel tube blanks, and their applications.

[0005] In a first aspect of the invention, the chemical composition of the provided low-nickel, high-nitrogen super austenitic stainless steel is controlled by mass percentage as follows: C≤0.020%, Si≤0.60%, Mn≤0.80%, P≤0.025%, S≤0.020%, Cr: 19.50~20.50%, Ni: 16.50~17.50%, Mo: 6.0~6.3%, N: 0.45~0.55%, Cu: 0.5~1.0%, with the balance being Fe and unavoidable impurities, and the mass percentage content of Ni, Cu, and N elements is controlled as follows ( w Ni + w Cu + w N The mass percentage content of Cr, Mo, and N elements is controlled to be ≥17.5%. wGr +3.3× w Mo +16× w N )≥45, of which, w Ni , w Cu , w N , w Gr , w Mo These represent the content values ​​of elements Ni, Cu, N, Cr, and Mo, expressed as a percentage by mass.

[0006] Furthermore, the chemical composition of the aforementioned low-nickel, high-nitrogen super austenitic stainless steel is controlled by mass percentage as follows: 0.010%≤C≤0.015%, 0.30%≤Si≤0.50%, 0.55%≤Mn≤0.75%, P≤0.020%, S≤0.002%, Cr: 19.55~20.30%, Ni: 16.55~17.20%, Mo: 6.05~6.25%, N: 0.46~0.52%, Cu: 0.55%~0.70%, with the balance being Fe and unavoidable impurities, and the mass percentage content of Ni, Cu, and N elements is controlled to be 17.56≤( w Ni + w Cu + w N The mass percentage content of Cr, Mo, and N elements is controlled to be ≤18.42, and the mass percentage content of these elements is controlled to be ≤46%. w Gr +3.3× w Mo +16× w N )≤49.

[0007] In a second aspect of the present invention, the method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blank includes the following steps: (1) Molten steel is produced by smelting using an electric furnace + AOD + LF process, and the molten steel is cast into steel ingots. The chemical composition of the steel ingots is controlled by mass percentage as follows: C≤0.020%, Si≤0.60%, Mn≤0.80%, P≤0.025%, S≤0.020%, Cr: 19.50~20.50%, Ni: 16.50~17.50%, Mo: 6.0~6.3%, N: 0.45~0.55%, Cu: 0.5~1.0%, with the balance being Fe and unavoidable impurities. The mass percentage content of Ni, Cu, and N elements is controlled as follows: ( w Ni+ w Cu + w N The mass percentage content of Cr, Mo, and N elements is controlled to be ≥17.5%. w Gr +3.3× w Mo +16× w N )≥45, of which, w Ni , w Cu , w N , w Gr , w Mo These represent the content values ​​of elements Ni, Cu, N, Cr, and Mo, respectively, expressed as a mass percentage. (2) The steel ingot is made into a tube blank by means of initial rolling, homogenization treatment and radial forging; (3) The tube blank is treated by online solution treatment and then water-cooled to obtain a low-nickel, high-nitrogen super austenitic stainless steel tube blank.

[0008] Furthermore, in the above-mentioned method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blanks, the chemical composition of the steel ingot is controlled by mass percentage as follows: 0.010%≤C≤0.015%, 0.30%≤Si≤0.50%, 0.55%≤Mn≤0.75%, P≤0.020%, S≤0.002%, Cr: 19.55~20.30%, Ni: 16.55~17.20%, Mo: 6.05~6.25%, N: 0.46~0.52%, Cu: 0.55%~0.70%, with the balance being Fe and unavoidable impurities, and the mass percentage content of Ni, Cu, and N elements is controlled to be 17.56≤( w Ni + w Cu + w N The mass percentage content of Cr, Mo, and N elements is controlled to be ≤18.42, and the mass percentage content of these elements is controlled to be ≤46%. w Gr +3.3× w Mo +16× w N )≤49.

[0009] Furthermore, in the above-mentioned method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blanks, the maximum single-pass deformation in the initial rolling is controlled to be ≤25%, the initial rolling temperature is controlled to be 1250~1270℃, and the final rolling temperature is controlled to be above 950℃.

[0010] Furthermore, in the above-mentioned method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blanks, the homogenization treatment temperature is controlled at 1220~1240℃, the holding time is controlled at 40h, and the furnace exit temperature is controlled at ≥1100℃.

[0011] Furthermore, in the above-mentioned method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blanks, the initial forging temperature of radial forging is controlled at 1230~1250℃, the final forging temperature is controlled at above 950℃, the number of radial forging passes is determined according to (initial rolled square billet specification - tube blank diameter) / (50~70), and the deformation of the first radial forging pass is controlled at ≤15%, where the units of the initial rolled square billet specification and the tube blank diameter are both mm.

[0012] Furthermore, in the above-mentioned method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blanks, the online solution treatment includes: after radial forging, the surface temperature of the tube blank is controlled above 950°C, and it is placed in a water tank for cooling. During the cooling process, the water temperature is controlled to not exceed 50°C. After the surface temperature of the tube blank is cooled to 200°C, it is taken out of the water tank for air cooling.

[0013] In a third aspect of the present invention, the provided low-nickel high-nitrogen super austenitic stainless steel tube blank is prepared by the above-described method for preparing low-nickel high-nitrogen super austenitic stainless steel tube blank.

[0014] In a fourth aspect of the invention, the application of the above-mentioned low-nickel, high-nitrogen super austenitic stainless steel tube blank in the production of seamless tubes for seawater desalination, marine engineering and other fields is also provided.

[0015] The low-nickel high-nitrogen super austenitic stainless steel, low-nickel high-nitrogen super austenitic stainless steel tube blank, and the preparation method of low-nickel high-nitrogen super austenitic stainless steel tube blank of the present invention, and their applications, have the following advantages and beneficial effects: This invention, through optimized control of chemical composition and innovative process design of initial rolling, homogenization treatment, radial forging, and online solution treatment, has developed a low-nickel, high-nitrogen super austenitic stainless steel and its tube blank, as well as a method for preparing the low-nickel, high-nitrogen super austenitic stainless steel tube blank. This low-nickel, high-nitrogen super austenitic stainless steel exhibits excellent corrosion resistance and can be used to produce seamless tubes for seawater desalination, marine engineering, and other fields. While meeting the basic performance requirements of super austenitic stainless steel, it significantly reduces alloy and manufacturing costs. 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 of the present invention, a low-nickel, high-nitrogen super austenitic stainless steel is provided. The low-nickel, high-nitrogen super austenitic stainless steel of the present invention is based on ordinary super austenitic stainless steel, with the content of the precious metal element Ni optimized to reduce the alloy cost of the material and the N content, which partially replaces Ni in terms of functionality, is significantly increased. At the same time, in order to ensure the performance and microstructure of the super austenitic stainless steel, other elements are adjusted simultaneously.

[0018] Specifically, the chemical composition of the low-nickel, high-nitrogen super austenitic stainless steel of the present invention is controlled by mass percentage as follows: C≤0.020%, Si≤0.60%, Mn≤0.80%, P≤0.025%, S≤0.020%, Cr: 19.50~20.50%, Ni: 16.50~17.50%, Mo: 6.0~6.3%, N: 0.45~0.55%, Cu: 0.5~1.0%, with the balance being Fe and unavoidable impurities.

[0019] Preferably, the chemical composition of the low-nickel, high-nitrogen super austenitic stainless steel of the present invention is controlled by mass percentage as follows: 0.010%≤C≤0.015%, 0.30%≤Si≤0.50%, 0.55%≤Mn≤0.75%, P≤0.020%, S≤0.002%, Cr: 19.55~20.30%, Ni: 16.55~17.20%, Mo: 6.05~6.25%, N: 0.46~0.52%, Cu: 0.55%~0.70%, with the balance being Fe and unavoidable impurities.

[0020] The function of the required element and content control range for the low-nickel, high-nitrogen super austenitic stainless steel of this invention is described below: Carbon (C) is a double-edged sword in stainless steel. It can form carbides with elements like Mo and Cr, enhancing the hardness, strength, and wear resistance of stainless steel through solid solution strengthening and precipitation strengthening, and also promoting the stability of the austenitic structure. However, when stainless steel is heated in the range of 450–850°C, chromium carbides precipitate at the grain boundaries, inducing intergranular corrosion sensitization and reducing corrosion resistance. Simultaneously, excessively high carbon content increases material brittleness and deteriorates weldability. Therefore, while maintaining a relatively high Cr content, the C content should not be too high. In the super austenitic stainless steel of this invention, the C content is controlled below 0.020%, preferably 0.010%–0.015%.

[0021] Si mainly acts as a deoxidizer and alloying element in stainless steel. During steelmaking, it can deoxidize and purify molten steel. Appropriate addition can strengthen the matrix, improve high-temperature oxidation resistance and corrosion resistance, and enhance creep resistance. However, excessive addition will reduce the plasticity, toughness and weldability of stainless steel. Therefore, the Si content in the super austenitic stainless steel of this invention is controlled below 0.60%, preferably 0.30% to 0.50%.

[0022] Mn is an important alloying element in stainless steel, playing a key role in deoxidation and desulfurization, stabilizing the austenitic phase, and improving the strength and cold working properties of steel. In some high-nitrogen super austenitic stainless steels, Mn can synergistically increase the solubility of nitrogen and reduce porosity defects. However, for super austenitic stainless steels, even if the pitting resistance equivalent PREN value is ≥42, the large amount of MnS inclusions formed by excessive addition of Mn will reduce the steel's resistance to pitting corrosion and crevice corrosion. Therefore, the Mn content in the super austenitic stainless steel of this invention is controlled below 0.80%, preferably 0.55%~0.75%.

[0023] Both phosphorus (P) and sulfur (S) are harmful impurity elements in stainless steel and their content must be strictly controlled. S readily combines with manganese (Mn) to form MnS inclusions, reducing the steel's hot workability, toughness, and corrosion resistance, and can also cause hot brittleness. P readily segregates at grain boundaries, significantly reducing the steel's low-temperature toughness, exacerbating intergranular corrosion, and deteriorating weldability. Therefore, in the super austenitic stainless steel of this invention, the P content is controlled below 0.025%, and the S content is controlled below 0.020%, preferably P ≤ 0.020% and S ≤ 0.002%.

[0024] Cr is a key element for achieving the corrosion resistance of stainless steel. Cr readily forms a dense and stable Cr2O3 passivation film with oxygen, adhering to the steel surface and isolating it from corrosive media. This is the foundation for stainless steel's resistance to general corrosion and pitting corrosion. The higher the Cr content, the more stable the passivation film and the stronger the corrosion resistance. Simultaneously, as a strong ferrite-forming element, Cr's content directly affects the phase structure of stainless steel. Excessive Cr leads to the formation of ferrite phases within super austenitic stainless steel and promotes the precipitation of α´ and σ(χ) intermetallic compounds, increasing the steel's brittleness and reducing its ductility, toughness, and corrosion resistance. Therefore, the Cr content in the super austenitic stainless steel of this invention is controlled between 19.50% and 20.50%, preferably between 19.55% and 20.30%.

[0025] Ni is the core austenite-forming element in stainless steel, stabilizing the austenite phase structure. Combined with Cr, it regulates phase composition, forming the basis for good ductility and toughness. It enhances the stability of the passivation film, improves the corrosion resistance of stainless steel in reducing acids and seawater, and reduces the tendency for intergranular corrosion. Simultaneously, it improves low-temperature toughness, weldability, and cold-working formability, moderately increases strength through solid solution strengthening, and inhibits the precipitation of intermetallic compounds such as σ and χ. However, Ni is expensive, a key factor affecting the cost of super austenitic stainless steel products. This invention, while balancing excellent corrosion resistance and high-temperature oxidation resistance, controls the Ni content to 16.50%~17.50%, preferably 16.55%~17.20%.

[0026] Nitrogen (N) is also a strong austenite-forming element and the only gaseous alloying element among the important elements of stainless steel. It is simple to prepare, abundant, and inexpensive. In this invention, the N content is increased to compensate for the performance loss caused by the reduced Ni content. Ni can significantly improve the room temperature and high temperature strength of austenitic stainless steel through solid solution strengthening, while reducing ductility and toughness. Simultaneously, the presence of Ni can further enhance the stability of the passivation film, improve the steel's resistance to pitting, crevice, and intergranular corrosion, and increase the PREN value. However, excessive Ni will reduce the cold and hot workability and cold forming properties of the steel, and also negatively impact intergranular corrosion resistance. Therefore, the N content in the super austenitic stainless steel of this invention is controlled between 0.45% and 0.55%, preferably 0.46% to 0.52%.

[0027] Mo is a core alloying element for improving the resistance of stainless steel to localized corrosion. As a ferrite-forming element, it can integrate into the passivation film to form a stable composite film, significantly improving resistance to pitting and crevice corrosion and increasing the PREN value. It also enhances corrosion resistance in chloride and acidic media. In synergy with Cr and N, it can achieve enhanced corrosion resistance. Furthermore, it can strengthen the steel through solidification, improving its strength and high-temperature performance. However, Mo is prone to segregation during solidification. Excessive Mo can lead to prolonged homogenization time, causing problems such as overheating, burning, and coarse grains. Severe Mo segregation can also lead to the precipitation of hard and brittle intermetallic phases, reducing the steel's ductility, toughness, cold formability, and weldability. Therefore, the Mo content in the super austenitic stainless steel of this invention is controlled between 6.0% and 6.3%, preferably between 6.05% and 6.25%.

[0028] Cu is an auxiliary alloying element in stainless steel. Adding a low amount can improve resistance to reducing acid corrosion, as well as cold workability and low-temperature toughness. A small amount of Cu can refine the grain size, moderately improve ductility and toughness, and can synergistically enhance corrosion resistance in media such as dilute sulfuric acid and phosphoric acid with Cr and Mo. However, excessive addition will reduce the high-temperature strength, hot workability, and weldability of the steel, and can easily induce grain boundary segregation. Therefore, the Cu content in the super austenitic stainless steel of this invention is controlled between 0.5% and 1.0%, preferably 0.55% to 0.70%.

[0029] Preferably, in the low-nickel, high-nitrogen super austenitic stainless steel of the present invention, the mass percentage content of Ni, Cu, and N elements is controlled as follows: w Ni + w Cu + w N The mass percentage content of Cr, Mo, and N elements is controlled to be ≥17.5%. w Gr +3.3× w Mo +16× w N )≥45, of which, w Ni , w Cu , w N 、w Gr , w Mo These represent the content values ​​of elements Ni, Cu, N, Cr, and Mo, expressed as a percentage by mass.

[0030] By ( w Ni + w Cu + w NThe value is controlled to ≥17.5, which ensures that the nickel equivalent is higher than the chromium equivalent, thereby ensuring the austenitic single-phase nature of the super austenitic stainless steel; w Gr +3.3× w Mo +16× w N ) is related to the corrosion resistance of materials, by ( w Gr +3.3× w Mo +16× w N The value is controlled at ≥45, which can meet the requirements of the service environment for corrosion resistance.

[0031] More preferably, in the low-nickel, high-nitrogen super austenitic stainless steel of the present invention, the mass percentage content of Ni, Cu, and N elements is controlled to be 17.56 ≤ ( w Ni + w Cu + w N The mass percentage content of Cr, Mo, and N elements is controlled to be ≤18.42, and the mass percentage content of these elements is controlled to be ≤46%. w Gr +3.3× w Mo +16× w N )≤49.

[0032] In a second aspect of the present invention, a method for preparing a low-nickel, high-nitrogen super austenitic stainless steel tube blank is provided, comprising the following steps: (1) Molten steel is produced by smelting using an electric furnace + AOD + LF process, and the molten steel is cast into steel ingots. The chemical composition of the steel ingots is controlled by mass percentage as follows: C≤0.020%, Si≤0.60%, Mn≤0.80%, P≤0.025%, S≤0.020%, Cr: 19.50~20.50%, Ni: 16.50~17.50%, Mo: 6.0~6.3%, N: 0.45~0.55%, Cu: 0.5~1.0%, with the balance being Fe and unavoidable impurities. The mass percentage content of Ni, Cu, and N elements meets the following requirements: w Ni + w Cu + w N )≥17.5, the mass percentage content of Cr, Mo, and N elements meets ( w Gr +3.3× w Mo +16×w N )≥45, of which, w Ni , w Cu , w N 、w Gr , w Mo These represent the content values ​​of elements Ni, Cu, N, Cr, and Mo, respectively, expressed as a mass percentage. (2) The steel ingot is made into a tube blank by means of initial rolling, homogenization treatment and radial forging; (3) The tube blank is treated by online solution treatment and then water-cooled to obtain a low-nickel, high-nitrogen super austenitic stainless steel tube blank.

[0033] Preferably, in the method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube billets of the present invention, the chemical composition of the steel ingot is controlled by mass percentage as follows: 0.010%≤C≤0.015%, 0.30%≤Si≤0.50%, 0.55%≤Mn≤0.75%, P≤0.020%, S≤0.002%, Cr: 19.55~20.30%, Ni: 16.55~17.20%, Mo: 6.05~6.25%, N: 0.46~0.52%, Cu: 0.55%~0.70%, with the balance being Fe and unavoidable impurities, and the mass percentage content of Ni, Cu, and N elements satisfies 17.56≤( w Ni + w Cu + w N The mass percentage content of Cr, Mo, and N elements is ≤18.42, and the mass percentage content of these elements satisfies 46≤( w Gr +3.3× w Mo +16× w N )≤49, where, w Ni , w Cu , w N 、w Gr , w Mo These represent the content values ​​of elements Ni, Cu, N, Cr, and Mo, expressed as a percentage by mass.

[0034] In the method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blanks of the present invention, the electric furnace + AOD + LF process includes raw material smelting, steel purification, ladle refining, etc. The technical parameters involved can be carried out in accordance with the existing technology, and the present invention does not make specific limitations on them.

[0035] Preferably, in the method for preparing low-nickel, high-nitrogen super austenitic stainless steel billets of the present invention, a square billet with a specification of (450~500) mm × (450~500) mm is obtained by initial rolling. The maximum single-pass deformation of the initial rolling is controlled to be ≤25%, the initial rolling temperature is controlled to be 1250~1270℃, and the final rolling temperature is controlled to be above 950℃. After rolling, the billet is air-cooled. Through initial rolling, the microstructure of the steel ingot is transformed into a rolled microstructure, improving the hot working properties of the material and making its specifications suitable for the machining range of radial forging mills.

[0036] In some preferred embodiments, in order to ensure that the billet surface is smooth and free of defects after homogenization, the initial rolled square billet needs to be surface-ground before homogenization.

[0037] In some preferred embodiments, in order to prevent the iron oxide scale from being too thick after homogenization treatment, a high-temperature anti-oxidation coating is sprayed onto the initial rolled billet before homogenization treatment.

[0038] Preferably, in the method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blanks of the present invention, the homogenization treatment temperature is controlled at 1220~1240℃, the holding time is controlled at 40h, the furnace exit temperature is controlled at ≥1100℃, and the blanks are cooled separately to bring the temperature of the blanks down to room temperature in the shortest possible time.

[0039] Preferably, in the method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blanks of the present invention, the initial forging temperature of radial forging is controlled at 1230~1250℃, the final forging temperature is controlled at above 950℃, the number of radial forging passes is determined according to (initial rolled square billet specification - tube blank diameter) / (50~70), and the deformation of the first radial forging pass is controlled at ≤15%, wherein the units of the initial rolled square billet specification and the tube blank diameter are both mm. By controlling the radial forging process parameters as described above, the produced tube blank has good surface quality, no crack defects, uniform internal structure, and no harmful phase precipitation.

[0040] Preferably, in the method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blanks of the present invention, the online solution treatment includes: after radial forging, the surface temperature of the tube blank is controlled above 950°C, and it is placed in a water tank for cooling. During the cooling process, the water temperature is controlled to not exceed 50°C. After the surface temperature of the tube blank is cooled to 200°C, it is taken out of the water tank and air-cooled. The tube blank treated by the "online solution treatment" method has comparable corrosion resistance to the tube blank treated by the existing "offline solution treatment" method, and reduces the time and energy consumption of repeated heating and holding, thus greatly saving production costs.

[0041] In a third aspect, the present invention provides a low-nickel, high-nitrogen super austenitic stainless steel tube blank prepared by the above-described method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blanks. Depending on practical application requirements, the diameter of the low-nickel, high-nitrogen super austenitic stainless steel tube blank can be 140~320mm, offering a wide range of specifications and strong applicability.

[0042] In a fourth aspect of the invention, the application of the aforementioned low-nickel, high-nitrogen super austenitic stainless steel tube blank in the production of seamless tubes for seawater desalination, marine engineering, and other fields is provided. The low-nickel, high-nitrogen super austenitic stainless steel tube blank, while meeting the basic properties of super austenitic stainless steel, greatly reduces alloy and manufacturing costs.

[0043] The following detailed description of the low-nickel high-nitrogen super austenitic stainless steel, low-nickel high-nitrogen super austenitic stainless steel tube blank, and their preparation method are provided in conjunction with embodiments and comparative examples.

[0044] Example 1 The chemical composition of the low-nickel, high-nitrogen super austenitic stainless steel in Example 1, by mass percentage, is: C: 0.015%, Si: 0.27%, Mn: 0.67%, P: 0.019%, S: 0.002%, Cr: 19.68%, Ni: 16.73%, Mo: 6.22%, N: 0.49%, Cu: 0.58%, with the balance being Fe and unavoidable impurities. w Ni + w Cu + w N ) = 17.8, ( w Gr +3.3× w Mo +16× w N =48.046.

[0045] The specific process of preparing the low-nickel, high-nitrogen super austenitic stainless steel tube blank in Example 1 includes: (1) Steel that meets the above composition requirements is smelted by electric furnace + AOD + LF process and cast into 8-ton ingots. (2) The die casting ingot is made into a tube blank by means of initial rolling, homogenization treatment and radial forging. The initial rolling temperature is 1270℃, the final rolling temperature is 980℃, and the initial rolling square billet is 480mm×480mm. The homogenization treatment temperature is 1230℃, the holding temperature is 40h, and the furnace exit temperature is 1190℃. The radial forging temperature is 1240℃, the final forging temperature is 970℃, the first forging deformation is 15%, and a radial forged tube blank with a specification of φ280mm is obtained by four forging passes. (3) The tube blank is treated by online solution treatment and then water-cooled to obtain a low-nickel, high-nitrogen super austenitic stainless steel tube blank.

[0046] The low-nickel, high-nitrogen super austenitic stainless steel produced in Example 1 was subjected to pitting corrosion testing according to ASTM G48 A method. The test conditions were 50°C and 72 hours. After the test, no obvious corrosion pits were observed on the product surface. Based on the actual test data, the weight loss per unit area was 0.24 g / m². 2 It has excellent corrosion resistance and is well-suited for highly corrosive industrial applications.

[0047] Furthermore, by optimizing the content of the precious metal element Ni, this invention significantly reduces the alloy cost of the material. According to actual production tests, the low-nickel, high-nitrogen super austenitic stainless steel produced in Example 1 has a manufacturing cost reduction of 1,900 yuan / ton compared to existing conventional super austenitic stainless steel.

[0048] Example 2 The chemical composition of the low-nickel, high-nitrogen super austenitic stainless steel in Example 2, by mass percentage, is: C: 0.015%, Si: 0.31%, Mn: 0.65%, P: 0.018%, S: 0.002%, Cr: 19.65%, Ni: 16.61%, Mo: 6.25%, N: 0.51%, Cu: 0.59%, with the balance being Fe and unavoidable impurities. w Ni + w Cu + w N ) = 17.71, ( w Gr +3.3× w Mo +16× w N =48.453.

[0049] The specific process of preparing the low-nickel, high-nitrogen super austenitic stainless steel tube blank in Example 2 includes: (1) Steel that meets the above composition requirements is smelted by electric furnace + AOD + LF process and cast into 8-ton ingots. (2) The die casting ingot is made into a tube blank by means of initial rolling, homogenization treatment and radial forging. The initial rolling temperature is 1270℃, the final rolling temperature is 990℃, and the initial rolling square billet is 490mm×490mm. The homogenization treatment temperature is 1230℃, the holding temperature is 40h, and the furnace exit temperature is 1170℃. The radial forging temperature is 1250℃, the final forging temperature is 950℃, the first forging deformation is 15%, and a radial forged tube blank with a specification of φ220mm is obtained by five forging passes. (3) The tube blank is treated by online solution treatment and then water-cooled to obtain a low-nickel, high-nitrogen super austenitic stainless steel tube blank.

[0050] The low-nickel, high-nitrogen super austenitic stainless steel produced in Example 2 was subjected to pitting corrosion testing according to ASTM G48 A method. The test conditions were 50°C and 72 hours. After the test, no obvious corrosion pits were observed on the product surface. Based on the actual test data, the weight loss per unit area was 0.22 g / m². 2 It has excellent corrosion resistance and is well-suited for highly corrosive industrial applications.

[0051] Furthermore, by optimizing the content of the precious metal element Ni, this invention significantly reduces the alloy cost of the material. According to actual production tests, the low-nickel, high-nitrogen super austenitic stainless steel produced in Example 2 has a manufacturing cost reduction of 2070 yuan / ton compared with existing conventional super austenitic stainless steel.

[0052] Example 3 The chemical composition of the low-nickel, high-nitrogen super austenitic stainless steel in Example 3, by mass percentage, is: C: 0.014%, Si: 0.30%, Mn: 0.70%, P: 0.020%, S: 0.002%, Cr: 19.60%, Ni: 16.76%, Mo: 6.15%, N: 0.50%, Cu: 0.57%, with the balance being Fe and unavoidable impurities. w Ni + w Cu + w N ) = 17.83, ( w Gr +3.3× w Mo +16× w N =48.895.

[0053] The specific process of preparing the low-nickel, high-nitrogen super austenitic stainless steel tube blank in Example 3 includes: (1) Steel that meets the above composition requirements is smelted by electric furnace + AOD + LF process and cast into 8-ton ingots. (2) The die casting ingot is made into a tube blank by means of initial rolling, homogenization treatment and radial forging. The initial rolling temperature is 1270℃, the final rolling temperature is 970℃, and the initial rolling square billet is 470mm×470mm. The homogenization treatment temperature is 1230℃, the holding temperature is 40h, and the furnace exit temperature is 1180℃. The radial forging temperature is 1250℃, the final forging temperature is 960℃, the first forging deformation is 15%, and a radial forged tube blank with a specification of φ160mm is obtained by five forging passes. (3) The tube blank is treated by online solution treatment and then water-cooled to obtain a low-nickel, high-nitrogen super austenitic stainless steel tube blank.

[0054] The low-nickel, high-nitrogen super austenitic stainless steel produced in Example 3 was subjected to pitting corrosion testing according to ASTM G48 A method. The test conditions were 50°C and 72 hours. After the test, no obvious corrosion pits were observed on the product surface. Based on the actual test data, the weight loss per unit area was 0.31 g / m². 2 It has excellent corrosion resistance and is well-suited for highly corrosive industrial applications.

[0055] Furthermore, by optimizing the content of the precious metal element Ni, this invention significantly reduces the alloy cost of the material. According to actual production tests, the low-nickel, high-nitrogen super austenitic stainless steel produced in Example 3 has a manufacturing cost reduction of 1,890 yuan / ton compared with existing conventional super austenitic stainless steel.

[0056] Comparative Example The chemical composition of the comparative super austenitic stainless steel, by mass percentage, is: C: 0.015%, Si: 0.38%, Mn: 0.76%, P: 0.020%, S: 0.003%, Cr: 19.72%, Ni: 17.92%, Mo: 6.18%, N: 0.20%, Cu: 0.68%, with the balance being Fe and unavoidable impurities. w Ni + w Cu + w N ) = 18.8, ( w Gr +3.3× w Mo +16× w N =43.314.

[0057] The specific process of preparing the comparative super austenitic stainless steel tube billet includes: producing a 3-ton die casting ingot through "electric furnace + AOD + LF", and producing a φ148mm tube billet using "homogenization + radial forging + offline solution treatment". The homogenization treatment temperature is 1230℃, held for 40h, and the furnace exit temperature is 1190℃; the radial forging stage heating temperature is 1250℃, the first forging deformation is 15%, and after five forgings, the final forging temperature is 960℃; after radial forging, the tube billet is placed in a solution furnace for offline solution treatment at a solution temperature of 1120℃, held for 4h, and then water-cooled.

[0058] The super austenitic stainless steel produced in the comparative example was subjected to pitting corrosion testing according to ASTM G48 A method. The test conditions were 50℃ and 72h. After the test, obvious corrosion pits were observed on the product surface. According to the actual test data, the weight loss per unit area was 1.27g / m². 2 It has poor corrosion resistance.

[0059] Furthermore, since the comparative example did not optimize the content of the precious metal element Ni, its alloy cost is relatively high. According to actual production tests, the manufacturing cost of the super austenitic stainless steel produced by the comparative example is more than RMB 1,500 per ton higher than that of the low-nickel, high-nitrogen super austenitic stainless steel of the present invention.

[0060] In summary, this invention, through optimized control of chemical composition and innovative process design involving initial rolling, homogenization treatment, radial forging, and online solution treatment, has developed a low-nickel, high-nitrogen super austenitic stainless steel and its tube blank, as well as a method for preparing the low-nickel, high-nitrogen super austenitic stainless steel tube blank. This low-nickel, high-nitrogen super austenitic stainless steel exhibits excellent corrosion resistance and can be used to produce seamless tubes for seawater desalination, marine engineering, and other fields. While meeting the basic performance requirements of super austenitic stainless steel, it significantly reduces alloy and manufacturing costs.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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 low-nickel, high-nitrogen super austenitic stainless steel, characterized in that, The chemical composition of the low-nickel, high-nitrogen super austenitic stainless steel is controlled by mass percentage as follows: C≤0.020%, Si≤0.60%, Mn≤0.80%, P≤0.025%, S≤0.020%, Cr: 19.50~20.50%, Ni: 16.50~17.50%, Mo: 6.0~6.3%, N: 0.45~0.55%, Cu: 0.5~1.0%, with the balance being Fe and unavoidable impurities. Furthermore, the mass percentage content of Ni, Cu, and N elements is controlled as follows: (…). w Ni +w Cu + w N The mass percentage content of Cr, Mo, and N elements is controlled to be ≥17.5%. w Gr +3.3× w Mo +16× w N )≥45, of which, w Ni , w Cu , w N , w Gr , w Mo These represent the content values ​​of elements Ni, Cu, N, Cr, and Mo, respectively, expressed as a mass percentage.

2. The low-nickel, high-nitrogen super austenitic stainless steel according to claim 1, characterized in that, The chemical composition of the low-nickel, high-nitrogen super austenitic stainless steel is controlled by mass percentage as follows: 0.010%≤C≤0.015%, 0.30%≤Si≤0.50%, 0.55%≤Mn≤0.75%, P≤0.020%, S≤0.002%, Cr: 19.55~20.30%, Ni: 16.55~17.20%, Mo: 6.05~6.25%, N: 0.46~0.52%, Cu: 0.55%~0.70%, with the balance being Fe and unavoidable impurities. Furthermore, the mass percentage content of Ni, Cu, and N elements is controlled to be 17.56 ≤ (…). w Ni +w Cu + w N The mass percentage content of Cr, Mo, and N elements is controlled to be ≤18.42, and the mass percentage content of these elements is controlled to be ≤46%. w Gr +3.3× w Mo +16× w N )≤49.

3. A method for preparing a low-nickel, high-nitrogen super austenitic stainless steel tube blank, characterized in that, Includes the following steps: (1) Molten steel is produced by smelting using an electric furnace + AOD + LF process, and the molten steel is cast into steel ingots. The chemical composition of the steel ingots is controlled by mass percentage as follows: C≤0.020%, Si≤0.60%, Mn≤0.80%, P≤0.025%, S≤0.020%, Cr: 19.50~20.50%, Ni: 16.50~17.50%, Mo: 6.0~6.3%, N: 0.45~0.55%, Cu: 0.5~1.0%, with the balance being Fe and unavoidable impurities. The mass percentage content of Ni, Cu, and N elements meets the following requirements: w Ni +w Cu + w N )≥17.5, the mass percentage content of Cr, Mo, and N elements meets ( w Gr +3.3× w Mo +16× w N )≥45, of which, w Ni , w Cu , w N , w Gr , w Mo These represent the content values ​​of elements Ni, Cu, N, Cr, and Mo, respectively, expressed as a mass percentage. (2) The steel ingot is made into a tube blank by means of initial rolling, homogenization treatment and radial forging; (3) The tube blank is treated by online solution treatment and then water-cooled to obtain a low-nickel, high-nitrogen super austenitic stainless steel tube blank.

4. The method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blank according to claim 3, characterized in that, The chemical composition of the steel ingot is controlled by mass percentage as follows: 0.010%≤C≤0.015%, 0.30%≤Si≤0.50%, 0.55%≤Mn≤0.75%, P≤0.020%, S≤0.002%, Cr: 19.55~20.30%, Ni: 16.55~17.20%, Mo: 6.05~6.25%, N: 0.46~0.52%, Cu: 0.55%~0.70%, with the balance being Fe and unavoidable impurities, and the mass percentage content of Ni, Cu, and N elements satisfies 17.56 ≤ ( w Ni +w Cu + w N The mass percentage content of Cr, Mo, and N elements is ≤18.42, and the mass percentage content of these elements satisfies 46≤( w Gr +3.3× w Mo +16× w N )≤49.

5. The method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blank according to claim 3 or 4, characterized in that, The maximum single-pass deformation in the initial rolling is controlled to be ≤25%, the initial rolling temperature is controlled to be 1250~1270℃, and the final rolling temperature is controlled to be above 950℃.

6. The method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blank according to claim 3 or 4, characterized in that, The homogenization treatment temperature is controlled at 1220~1240℃, the holding time is controlled at 40h, and the furnace exit temperature is controlled at ≥1100℃.

7. The method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blank according to claim 3 or 4, characterized in that, The initial forging temperature of radial forging is controlled at 1230~1250℃, and the final forging temperature is controlled at above 950℃. The number of passes for radial forging is determined according to (initial rolled square billet specification - tube billet diameter) / (50~70). The deformation of the first pass of radial forging is controlled at ≤15%. The units of the initial rolled square billet specification and the tube billet diameter are both mm.

8. The method for preparing low-nickel, high-nitrogen super austenitic stainless steel tube blank according to claim 3 or 4, characterized in that, Online solution treatment includes: after radial forging, the surface temperature of the tube blank is controlled above 950℃, and it is placed in a water tank for cooling. During the cooling process, the water temperature is controlled not to exceed 50℃. After the surface temperature of the tube blank is cooled to 200℃, it is taken out of the water tank for air cooling.

9. A low-nickel, high-nitrogen super austenitic stainless steel tube blank, characterized in that, The low-nickel, high-nitrogen super austenitic stainless steel tube blank is prepared using the method described in any one of claims 3 to 8.

10. The application of the low-nickel, high-nitrogen super austenitic stainless steel tube blank as described in claim 9 in the production of seamless tubes for seawater desalination, marine engineering and other fields.