Process for producing marine stainless steel

Abstract

The present application belongs to the technical field of ship steel material, and relates to a production process of marine stainless steel. The present application aims to solve the problem that the marine stainless steel is difficult to inhibit local corrosion and has poor long-term hygiene performance. In the present application, iron ore, nickel-iron, chromium-iron, molybdenum-iron and smelting additives are smelted by an electric arc furnace, and then the steel liquid is obtained after decarburization treatment, chemical desulfurization and vacuum desulfurization, low-temperature dephosphorization and precise adjustment of impurity components in the steel liquid; subsequently, the refined steel liquid is subjected to ladle alloying to further adjust the element composition of the steel liquid, and the purity and uniformity of the stainless steel are deeply improved through vacuum degassing and electroslag remelting process; the preformed stainless steel after hot rolling is subjected to solid solution annealing and passivation polishing to further optimize the internal structure of the steel material and improve the surface performance, thereby obtaining the marine stainless steel. The marine stainless steel provided by the present application has strong corrosion resistance, can effectively inhibit local corrosion, and has long-lasting hygiene performance in the ship environment.

Description

Technical Field

[0001] This invention belongs to the field of marine steel technology and relates to a production process for marine stainless steel. Background Technology

[0002] Stainless steel, as a high-strength and corrosion-resistant material, has a wide range of applications in the shipbuilding industry. Initially, stainless steel was mainly used in marine valves, pumps, and a few internal components. With the large-scale production of newer stainless steels such as 316 and 316L, stainless steel gradually became a common material for marine piping systems. With the further development of the maritime and military industries, the application scope of marine stainless steel has continued to expand, gradually extending from special vessels such as warships, LNG carriers, and chemical tankers to various merchant ships and engineering vessels. At the same time, this increasingly wider range of applications has placed more stringent performance requirements on marine stainless steel.

[0003] In particular, marine stainless steel is widely used in various ship piping systems, including seawater pipelines, freshwater pipelines, and exhaust pipelines, due to its corrosion resistance and ease of maintenance. Currently, however, marine stainless steel for piping still faces several pressing issues, such as inhibiting localized corrosion, improving ease of maintenance, and enhancing hygienic properties. The biggest challenge facing marine stainless steel is how to solve these problems, enabling it to have good application value in various pipelines, fully leveraging its advantages, ensuring the long-term safe and reliable operation of ship systems, and reducing life-cycle costs.

[0004] Currently, the inability to suppress localized corrosion and poor long-term hygiene performance of marine stainless steel remain significant challenges for the industry.

[0005] Therefore, a production process for marine stainless steel is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a production process for marine-grade stainless steel. This invention uses an electric arc furnace to melt iron ore, ferronickel, ferrochrome, ferromolybdenum, and smelting additives. Through decarburization, chemical desulfurization, vacuum desulfurization, and low-temperature dephosphorization, the impurity composition in the molten steel is precisely adjusted to obtain refined molten steel. Subsequently, the refined molten steel is alloyed in a ladle to further adjust its elemental composition. Vacuum degassing and electroslag remelting processes further improve the purity and microstructure uniformity of the stainless steel. The pre-formed stainless steel after hot rolling undergoes solution annealing and passivation polishing to further optimize the internal structure and improve surface properties, resulting in marine-grade stainless steel.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A process for producing marine-grade stainless steel includes the following steps:

[0009] Unless otherwise specified, all parts in this invention are parts by weight, and percentages are percentages by weight.

[0010] Preheat 600 parts iron ore, 120 parts ferronickel, 280 parts ferrochrome, and 40 parts ferromolybdenum to 500℃ and then put them into an electric arc furnace. Set the electric arc furnace voltage to 550-600V and the current to 70-80kA. After forming a molten pool, add dolomite and lime to form initial slag and cover the molten pool. Pour the slag into the molten pool at a rate of 5-10m... 3 Oxygen is introduced at a flow rate of / min, fluorite is added, and after smelting for 30-40 minutes, oxidizing slag and initial molten steel are formed.

[0011] Stop introducing oxygen into the initial molten steel and remove oxidizing slag. Reduce the electric arc furnace voltage to 350-450V and the current to 50-60kA. Add scrap steel and ferromanganese into the initial molten steel and smelt for 20 minutes to obtain molten steel.

[0012] The purity of the raw materials is selected within the following ranges: nickel content of ferronickel is 20-30%; chromium content of ferrochrome is 60%; molybdenum content of ferromolybdenum is 30-40%; manganese content of ferromanganese is 65-80%; and the iron ore is magnetite with an iron content of 50-60%.

[0013] The scrap steel is composed of: 0.05% carbon, 0.3% manganese, 0.1% chromium, 0.2% nickel, 98% iron, and the rest being impurities.

[0014] Argon-oxygen decarburization furnace is used to blow a mixture of argon and oxygen into molten steel for decarburization treatment, wherein the flow rate of argon is 10-30 m³ / h. 3 / min, oxygen flow rate is 10-15m 3 The furnace temperature was 1600-1700℃, and the slag basicity was adjusted to 2.5-3.5. After smelting for 100 minutes, the slag was removed to obtain decarburized steel liquid.

[0015] Dolomite and lime were added to the decarburized steel liquid to adjust the slag basicity to 3.0, and the solution was heated to 20m³. 3 Argon gas was blown in at a flow rate of / min and stirred at a speed of 100 rpm, maintaining the temperature of the decarburized steel liquid at 1600-1650℃. After treatment for 20 min, chemically desulfurized steel liquid was obtained; furthermore, under an operating pressure of 30 Pa, argon gas was blown in at a speed of 10 m 3 Argon gas was blown in at a flow rate of / min, and the desulfurized steel liquid was obtained after holding at 1600℃ for 30min.

[0016] Unless otherwise specified, alkalinity in this invention refers to the mass ratio of CaO to SiO2.

[0017] Add 5m to the desulfurized steel liquid 3Oxygen was blown in at a flow rate of / min, and ferrous oxide, sodium oxide and manganese oxide were added. The temperature of the desulfurized steel liquid was adjusted to 1400-1450℃, and the slag basicity was adjusted to 3.5. After treatment for 60 minutes, the phosphorus-rich slag was removed to obtain refined steel liquid.

[0018] The refined molten steel is transferred into a preheated ladle, and the nickel mass fraction of the refined molten steel is adjusted to 8.4-9.0 wt% at 1100℃, while ensuring that the sulfur content is less than 0.01 wt% and the phosphorus content is less than 0.02 wt%. After processing for 30 minutes, alloy molten steel is obtained.

[0019] The alloy steel molten material was heated to 1500℃ under an operating pressure of 50 Pa, using a flow rate of 10 m³ / s. 3 Argon gas is used to bottom-blow the alloy steel liquid at a rate of / min, and after holding for 30 minutes, it is cast into an alloy electrode for electroslag remelting.

[0020] Under a melting current of 5kA and an argon atmosphere, pre-melted electroslag material is added to the bottom of the crystallizer. After preheating for 20 minutes, a slag pool is formed. The alloy electrode is slowly fed into the slag pool at a rate of 20mm / min. The remelting cycle is 5 hours. After treatment, the steel ingot is cooled to obtain a remelted steel ingot. The remelted steel ingot is heated to 1200℃ and held at that temperature. It is then hot-rolled under operating conditions of 10MPa front tension and 5MPa back tension. The rolling speed is maintained at 2.5m / s. After cooling, the rolled product becomes precast stainless steel.

[0021] Precast stainless steel was heated to 1050℃, held for 60 min, and then cooled to 700℃ at a rate of 10℃ / min. It was then quenched with deionized water at 25℃ and cooled to 25℃ before passivation and polishing. The precast stainless steel that had undergone solution annealing was then cleaned with acetone and 0.5wt% sulfuric acid aqueous solution. The cleaned precast stainless steel was then immersed in 20wt% citric acid aqueous solution, heated to 80℃ and treated for 2 hours. After cleaning and drying, marine stainless steel was obtained.

[0022] Preferably, the amount of dolomite added is 0.5 parts; the amount of lime added is 2 parts; in subsequent steps, the ratio of the two added is 1:4.

[0023] Preferably, nickel-iron is used to adjust the nickel mass fraction of the refined molten steel.

[0024] Preferably, for every 1000 parts by weight of the desulfurized molten steel, the amount of ferrous oxide added is 0.5 parts, the amount of sodium oxide added is 0.1 parts, and the amount of manganese oxide added is 0.2 parts.

[0025] Preferably, the electroslag material includes: lime, silica, alumina, and fluorite; wherein the amount of lime added is 50 parts, the amount of silica added is 30 parts, the amount of alumina added is 10 parts, and the amount of fluorite added is 10 parts.

[0026] Preferably, the pre-formed stainless steel obtained by hot rolling is a stainless steel pipe.

[0027] The marine stainless steel produced by this invention, when made into seamless steel pipes, has a maximum working pressure greater than 250 Bar and a maximum pressure resistance greater than 375 Bar.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. The smelting process employs a combination of oxidation and reduction smelting, and optimizes the elemental composition of stainless steel in the early stages of smelting through decarburization treatment. This enhances the strength after forming and ensures its excellent corrosion resistance. Oxidation smelting introduces both impurity oxides and alloy oxides into the slag. Subsequent reduction smelting, by selecting scrap steel and ferromanganese as reducing agents and controlling reduction conditions, selectively reduces the alloy oxides in the slag to metallic chromium and manganese, allowing them to return to the molten steel. Impurity oxides remain in the slag, achieving efficient recovery of alloying elements and effective separation of impurities. Furthermore, decarburization treatment optimizes the elemental composition of the stainless steel, resulting in a dual improvement in both strength and corrosion resistance.

[0030] 2. After decarburization, the molten steel undergoes sequential chemical desulfurization and vacuum desulfurization, followed by low-temperature dephosphorization after cooling. Multiple slag removal processes eliminate sulfur and phosphorus elements from the molten steel, improving the strength and corrosion resistance of the formed stainless steel and enhancing its long-term hygienic performance in marine environments. In the initial refining stage, chemical desulfurization and vacuum desulfurization using slag significantly reduce the sulfur content in the molten steel, indirectly improving its plasticity and toughness, reducing sulfide inclusions, and improving the internal quality of the steel, laying the foundation for subsequent strength enhancement. Simultaneously, desulfurization precedes dephosphorization, optimizing the dephosphorization environment, enhancing the dephosphorization effect, and reducing the oxidation degree of alloying elements. The synergistic effect of these three processes significantly improves the purity, microstructure uniformity, and surface quality of the stainless steel, ultimately yielding high-quality marine stainless steel materials with enhanced strength, excellent corrosion resistance, and significantly improved long-term hygienic performance.

[0031] 3. By controlling the elemental composition of stainless steel through different raw materials in the smelting additives, and through the ladle alloying process after desulfurization and dephosphorization, the nickel, sulfur, and phosphorus contents in the stainless steel are precisely adjusted, ensuring the corrosion resistance of the formed stainless steel and effectively improving its strength. In the initial stage of smelting, smelting additives are used for significant compositional control, roughly adjusting the composition of the molten steel to near the target range. In the ladle alloying stage, micro-level and precise compositional fine-tuning is performed using alloy materials and refining agents to ensure that the content of all elements precisely meets the standards and to optimize performance. The final stainless steel material produced possesses both excellent corrosion resistance and good strength. The high chromium, high nickel, low carbon, low sulfur, and low phosphorus composition design ensures that the stainless steel has excellent corrosion resistance in marine environments such as seawater and sea air.

[0032] 4. By employing a pre-vacuum degassing process followed by electroslag remelting, gases and inclusions in the molten steel are removed to the greatest extent possible. This ensures the structural stability of the stainless steel after forming, significantly improving its purity, microstructure uniformity, and properties. It enhances the steel's strength and corrosion resistance while also improving its aging resistance in high-salt environments. Pre-vacuum degassing effectively removes dissolved gases from the molten steel, reduces bubble formation, and increases the density of the stainless steel, thereby improving its internal structural stability. Further electroslag remelting deeply removes non-metallic inclusions from the molten steel and allows for precise control of the solidification process, significantly improving the stainless steel's resistance to pitting corrosion, crevice corrosion, and intergranular corrosion.

[0033] 5. By sequentially performing solution annealing and passivation polishing processes, work hardening and residual stress are eliminated, while the corrosion resistance and appearance quality of stainless steel are synergistically improved. Solution annealing results in a uniform microstructure, eliminated internal stress, and increased plasticity in the stainless steel. While it doesn't directly enhance corrosion resistance, it indirectly improves corrosion resistance by improving the microstructure, providing more favorable conditions for the formation and stabilization of the subsequent passivation film. Passivation polishing, building upon solution annealing, further enhances the corrosion resistance of stainless steel and significantly improves its surface appearance. The synergistic effect of both processes optimizes the internal structure, eliminates inherent defects, and improves the surface condition, thus enhancing the external quality of the stainless steel. This results in optimal overall performance and a wider range of applications for the stainless steel. Attached Figure Description

[0034] Figure 1 This is a flowchart of the marine stainless steel production process in this invention. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below through some embodiments and experimental examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] Reference Figure 1 The flowchart shown illustrates that this invention provides a manufacturing process for marine-grade stainless steel, and the technical solution is as follows:

[0037] Example 1

[0038] 600 parts iron ore, 120 parts ferronickel, 280 parts ferrochrome, and 40 parts ferromolybdenum were preheated to 500°C and then fed into an electric arc furnace. The furnace voltage was set to 550V and the current to 70kA. After a molten pool was formed, 0.5 parts dolomite and 2 parts lime were added to form initial slag, which covered the molten pool. The slag was then poured into the molten pool at a rate of 5m... 3 Oxygen is introduced at a flow rate of / min, fluorite is added, and after smelting for 30 minutes, oxidizing slag and initial molten steel are formed.

[0039] Stop introducing oxygen into the initial molten steel and remove oxidizing slag. Reduce the electric arc furnace voltage to 350V and the current to 50kA. Add scrap steel and ferromanganese into the initial molten steel and smelt for 20 minutes to obtain molten steel.

[0040] An argon-oxygen decarburization furnace is used to blow a mixture of argon and oxygen into the molten steel for decarburization treatment, wherein the flow rate of argon is 10 m³ / s. 3 / min, oxygen flow rate is 10m 3 The furnace temperature was 1600℃, the slag basicity was adjusted to 2.5, and after smelting for 100 minutes, the slag was removed to obtain decarburized steel liquid.

[0041] Dolomite and lime were added to the decarburized steel liquid at a mass ratio of 1:4 to adjust the slag basicity to 3.0, and the solution was boiled at 20m³. 3 Argon gas was blown in at a flow rate of / min and stirred at a speed of 100 rpm, while maintaining the temperature of the decarburized steel liquid at 1600℃. After treatment for 20 min, chemically desulfurized steel liquid was obtained. Further, under an operating pressure of 30 Pa, argon gas was blown in at a speed of 10 m... 3 Argon gas was blown in at a flow rate of / min, and the desulfurized steel liquid was obtained after holding at 1600℃ for 30min.

[0042] Add 5m to 1000 parts of desulfurized molten steel 3Oxygen was blown in at a flow rate of / min, and 0.5 parts of ferrous oxide, 0.1 parts of sodium oxide and 0.2 parts of manganese oxide were added. The temperature of the desulfurized steel liquid was adjusted to 1400-1450℃, and the slag basicity was adjusted to 3.5. After treatment for 60 minutes, the phosphorus-rich slag was removed to obtain refined steel liquid.

[0043] The refined molten steel is transferred into a preheated ladle, and the nickel content of the refined molten steel is adjusted to 8.4 wt% at 1100℃, while ensuring that the sulfur content is less than 0.01 wt% and the phosphorus content is less than 0.02 wt%. After processing for 30 minutes, alloy molten steel is obtained.

[0044] The alloy steel molten material was heated to 1500℃ under an operating pressure of 50 Pa, using a flow rate of 10 m³ / s. 3 Argon gas is used to bottom-blow the alloy steel liquid at a rate of / min, and after holding for 30 minutes, it is cast into an alloy electrode for electroslag remelting.

[0045] Under a melting current of 5kA and an argon atmosphere, pre-melted electroslag material is added to the bottom of the crystallizer. After preheating for 20 minutes, a slag pool is formed. The alloy electrode is slowly fed into the slag pool at a rate of 20mm / min. The remelting cycle is 5 hours. After treatment, the steel ingot is cooled to obtain a remelted steel ingot. The remelted steel ingot is heated to 1200℃ and held at that temperature. It is then hot-rolled under operating conditions of 10MPa front tension and 5MPa back tension. The rolling speed is maintained at 2.5m / s. After cooling, the rolled product becomes precast stainless steel.

[0046] The electroslag material consists of: lime, silicon dioxide, alumina, and fluorite; the amount of lime added is 50 parts, the amount of silicon dioxide added is 30 parts, the amount of alumina added is 10 parts, and the amount of fluorite added is 10 parts.

[0047] Precast stainless steel was heated to 1050℃, held for 60 min, and then cooled to 700℃ at a rate of 10℃ / min. It was then quenched with deionized water at 25℃ and cooled to 25℃ before passivation and polishing. The precast stainless steel that had undergone solution annealing was then cleaned with acetone and 0.5wt% sulfuric acid aqueous solution. The cleaned precast stainless steel was then immersed in 20wt% citric acid aqueous solution, heated to 80℃ and treated for 2 hours. After cleaning and drying, marine stainless steel was obtained.

[0048] Examples 2-20 differ from Example 1 in operating parameters, but the process steps are the same. The parameter changes are summarized in Tables 1 and 2.

[0049] Table 1. Changes in operating parameters for Examples 1-20 (Part 1)

[0050]

[0051]

[0052] Table 2. Changes in operating parameters for Examples 1-20 (II)

[0053]

[0054]

[0055] Comparative Example 1

[0056] Unlike Example 1, the reduction smelting process was not performed, but all other process parameters remained the same.

[0057] Comparative Example 2

[0058] Unlike Example 1, the order of exchange reduction smelting and oxidation smelting is the same, but all other process parameters are the same.

[0059] Comparative Example 3

[0060] Unlike Example 1, no decarburization treatment was performed, but all other process parameters remained the same.

[0061] Comparative Example 4

[0062] Unlike Example 5, the order of chemical desulfurization and vacuum desulfurization is the same, but all other process parameters are the same.

[0063] Comparative Example 5

[0064] Unlike Example 5, the temperature for low-temperature dephosphorization was increased to 1600°C, while all other process parameters remained the same.

[0065] Comparative Example 6

[0066] Unlike Example 5, low-temperature dephosphorization was performed first, followed by chemical desulfurization and vacuum desulfurization in sequence, while other process parameters remained the same.

[0067] Comparative Example 7

[0068] Unlike Example 9, the nickel content was not fine-tuned during the ladle alloying process, while other process parameters remained the same.

[0069] Comparative Example 8

[0070] Unlike Example 9, pure nickel, cobalt, and molybdenum were used instead of ferronickel, ferrocobalt, and ferromolybdenum, while all other process parameters remained the same.

[0071] Comparative Example 9

[0072] Unlike Example 13, the vacuum degassing process was not performed; instead, electroslag remelting was carried out directly, while all other process parameters remained the same.

[0073] Comparative Example 10

[0074] Unlike Example 13, in the electroslag remelting process, the electroslag material is not pre-melted, but the electroslag material and the alloy electrode are melted simultaneously, while other process parameters are the same.

[0075] Comparative Example 11

[0076] Unlike Example 17, the order of solution annealing and passivation polishing is changed, while other process parameters remain the same.

[0077] Comparative Example 12

[0078] Unlike Example 17, 20 wt% nitric acid aqueous solution was used instead of 20 wt% citric acid aqueous solution during the passivation and polishing process, while other process parameters remained the same.

[0079] Experimental Example 1

[0080] The compressive strength and corrosion resistance of the marine stainless steels prepared in Examples 1-4 and Comparative Examples 1-3 were tested. The results are summarized in Table 3.

[0081] The corrosion resistance test was conducted in accordance with the GB / T10125-2021 standard, using the neutral salt spray test (NSS) method to determine the mass change of marine stainless steel in different experimental groups. The salt spray treatment time was 96 hours. The greater the mass loss, the worse the corrosion resistance.

[0082] The compressive strength test was performed using a seamless steel pipe made of the corresponding stainless steel with an outer diameter D = 100 mm and a wall thickness t = 10 mm.

[0083] Table 3 shows the compressive strength and corrosion resistance of the marine stainless steel prepared in Examples 1-4 and Comparative Examples 1-3.

[0084] Compressive strength (Bar) <![CDATA[Mass loss (g / m 2 ) <!-- 7 -->]]> Example 1 386 0.8 Example 2 379 0.6 Example 3 387 0.8 Example 4 385 0.7 Comparative Example 1 302 5.1 Comparative Example 2 297 4.8 Comparative Example 3 204 11.9

[0085] As shown in Table 3, the compressive strength and corrosion resistance data of the stainless steels prepared in Examples 1-4 exhibit high compressive strength and low mass loss, indicating that the stainless steel prepared using the complete process has stable and excellent performance. Comparative Example 1, without reduction smelting, shows a significant decrease in strength and a sharp deterioration in corrosion resistance. This is because after oxidative smelting, both impurity oxides and alloy oxides enter the slag. Without subsequent reduction smelting, impurity oxides remain partially mixed in the final steel, further reducing the purity and performance of the steel. Comparative Example 2, by reversing the order of reduction smelting and oxidative smelting, also shows a significant decrease in stainless steel performance. This indicates that prior reduction smelting cannot effectively enrich impurity oxides in the slag, and subsequent oxidative smelting cannot compensate for the deficiencies of the earlier steps, resulting in poor impurity removal. Comparative Example 3, without decarburization treatment, shows the largest performance decline, attributed to excessively high carbon content, leading to the precipitation of grain boundary carbides, which damages the integrity and uniformity of the passivation film, thus severely reducing corrosion resistance. In summary, the specific sequence of oxidation smelting, reduction smelting, and decarburization, along with their respective process designs, exhibit a high degree of synergy. Oxidation smelting initially achieves the oxidative enrichment of impurities and alloying elements into the slag. Reduction smelting efficiently and selectively reduces and recovers alloying elements, maximizing their utilization rate and further refining the molten steel, removing some impurities. Decarburization further optimizes the elemental composition of stainless steel in the early stages of smelting, enhancing its post-forming strength and ensuring its excellent corrosion resistance.

[0086] Experimental Example 2

[0087] Referring to Experimental Example 1, the marine stainless steels prepared in Examples 5-8 and Comparative Examples 4-6 were tested for compressive strength and corrosion resistance. The results are summarized in Table 4.

[0088] The long-term sanitary properties of the marine stainless steels prepared in Examples 5-8 and Comparative Examples 4-6 were tested, and the results are summarized in Table 4.

[0089] Long-term hygiene performance was determined by biofilm formation and bacterial adhesion tests, as well as ease of cleaning tests.

[0090] The method for testing biofilm formation and bacterial adhesion was as follows: Stainless steel surfaces were ultrasonically cleaned and sterilized. A seawater culture of *Pseudomonas aeruginosa* was then incubated at 37°C on a shaker at 100 rpm for 72 hours. The experimental concentration of the *Pseudomonas aeruginosa* seawater culture was 100 CFU / mL. Polystyrene resin sheets were used as a positive control, and sterile culture medium alone was added as a negative control. The OD value (absorbance) of the crystal violet staining method was used to characterize biofilm formation; the lower the value, the less biofilm formed and the stronger the substrate's resistance to biofilm formation. The OD value of each experimental group was recorded with the negative control group having an OD value of 0% and the positive control group having an OD value of 100%.

[0091] The method for easy-to-clean test is as follows: 20 parts marine heavy oil, 2 parts calcium carbonate powder, 1 part magnesium hydroxide powder, and 10 parts soybean oil are mixed to form a simulated dirt. The simulated dirt is evenly applied to the stainless steel surface, dried at 60°C for 2 hours, and then washed for 10 minutes with a 2wt% neutral detergent at an ultrasonic frequency of 20kHz. After air drying, the adhesion of dirt on the stainless steel surface is observed.

[0092] Table 4 shows the compressive strength, corrosion resistance, and long-term sanitary properties of the marine stainless steel prepared in Examples 5-8 and Comparative Examples 4-6.

[0093]

[0094]

[0095] As shown in Table 4, the compressive strength, corrosion resistance, and long-term hygienic performance data remain at a high and stable level, and the corrosion resistance is also strong. Comparative Example 4, which swapped the order of chemical desulfurization and vacuum desulfurization, showed a significant decrease in both compressive strength and corrosion resistance. This demonstrates that vacuum desulfurization, performed first, has limited efficiency due to the high initial sulfur content in the molten steel, and its desulfurization effect is not as good as the combined process of chemical desulfurization followed by vacuum desulfurization. Comparative Example 5, by increasing the low-temperature dephosphorization temperature to 1600℃, further decreased the compressive strength and corrosion resistance, while the OD value increased significantly. This indicates that low-temperature dephosphorization is more conducive to the transfer of phosphorus to the slag, thus enhancing the dephosphorization effect. High temperatures, on the other hand, reduce dephosphorization efficiency and may even lead to phosphorus reversion. Comparative Example 6, which performed low-temperature dephosphorization first, followed by chemical desulfurization and then vacuum desulfurization, exhibited the worst compressive strength, corrosion resistance, and long-term hygienic performance. This shows that the presence of sulfur has an adverse effect on the dephosphorization process. In summary, the sequence of desulfurization followed by dephosphorization better utilizes the different metallurgical properties of sulfur and phosphorus, achieving a more efficient and thorough desulfurization and dephosphorization effect. Ultimately, this has a crucial impact on the various properties of stainless steel, especially its corrosion resistance and long-term hygienic performance. Chemical desulfurization, as the first step in the desulfurization process, primarily aims to rapidly reduce the sulfur content in the molten steel, creating favorable conditions for subsequent deeper vacuum desulfurization, reducing the burden on vacuum desulfurization, and improving overall desulfurization efficiency. Vacuum desulfurization is the core of deep desulfurization, capable of reducing sulfur content to extremely low levels and simultaneously removing gases and inclusions from the molten steel, achieving deeper refining and improving the purity of the steel. Low-temperature dephosphorization is not a simple cooling operation, but a critical step with extremely stringent temperature control requirements. The low-temperature environment may be more conducive to the transfer of phosphorus to the slag, enhancing the dephosphorization effect, while reducing the oxidation loss of alloying elements and positively impacting the microstructure of the steel. The specific process sequence of chemical desulfurization, followed by vacuum desulfurization and low-temperature dephosphorization achieves maximum desulfurization and dephosphorization efficiency through a high degree of synergy, and comprehensively improves the performance of stainless steel, especially enhancing the surface's stain resistance and antibacterial properties, and significantly improving its long-term hygiene performance.

[0096] Experimental Example 3

[0097] Referring to Experimental Example 1, the compressive strength and corrosion resistance of the marine stainless steels prepared in Examples 9-12 and Comparative Examples 7-8 were tested. The results are summarized in Table 5.

[0098] Table 5 shows the compressive strength and corrosion resistance of the marine stainless steels prepared in Examples 9-12 and Comparative Examples 7-8.

[0099] Compressive strength (Bar) <![CDATA[Mass loss (g / m 2 )]]> Example 9 389 0.7 Example 10 379 0.9 Example 11 392 1.0 Example 12 397 1.1 Comparative Example 7 328 13.4 Comparative Example 8 376 5.9

[0100] As shown in Table 5, the compressive strength and corrosion resistance data of Examples 9-12 remained at a high and relatively stable level, and the corrosion resistance was also relatively high. In Comparative Example 7, due to the lack of fine-tuning of the nickel content during the ladle alloying process, the compressive strength decreased significantly, and the corrosion resistance also dropped sharply. This indicates that fine-tuning the nickel content during ladle alloying plays a crucial role in the performance of the final product, especially its corrosion resistance. Comparative Example 8 used pure nickel, cobalt, and molybdenum instead of ferronickel, ferrocobalt, and ferromolybdenum in the process. The compressive strength remained almost unchanged, but the corrosion resistance decreased significantly. This shows that even with the same alloying element composition, the choice of alloying raw materials can affect the performance of stainless steel, and using ferroalloys is superior to using pure metal alloys. In summary, using ferroalloys as alloying raw materials better meets the specific smelting process and composition control requirements, and can better synergize with smelting aids, ultimately resulting in stainless steel products with superior overall performance. Smelting additives play a crucial role in the initial stages of smelting, primarily by roughly adjusting the composition of the molten steel to near the target range. Then, through ladle alloying, building upon the initial control provided by the smelting additives, alloying materials and refining agents are used to precisely fine-tune the content of key elements in stainless steel, ensuring that all element contents accurately meet standards and further optimizing performance. Together, these two processes construct a highly efficient and precise composition control system that combines coarse and fine adjustments, guaranteeing both smelting efficiency and achieving accurate composition control and performance optimization.

[0101] Experiment Example 4

[0102] The pitting corrosion resistance of the marine stainless steels prepared in Examples 13-16 and Comparative Examples 9-10 was tested, and the results are summarized in Table 6.

[0103] The test method for pitting corrosion resistance refers to GB / T 13671 standard. The corrosion potential E1 and pitting potential E of different samples are tested. b100 and the most positive potential E for repassivation rp The reference electrode is a calomel electrode.

[0104] The stronger the resistance to pitting corrosion, the stronger the stainless steel's resistance to localized corrosion.

[0105] Table 6 shows the pitting corrosion resistance of the marine stainless steels prepared in Examples 13-16 and Comparative Examples 9-10.

[0106]

[0107]

[0108] As shown in Table 6, the compressive strength and corrosion resistance data indicate that the steels prepared in Examples 13-16 all exhibited good pitting corrosion resistance. In Comparative Example 9, due to the absence of vacuum degassing, all electrochemical indicators showed a precipitous deterioration, especially the pitting potential and repassivation potential, indicating that the lack of vacuum degassing had a severely negative impact on the pitting corrosion resistance of stainless steel. In Comparative Example 10, due to the absence of pre-melting electroslag material in the electroslag remelting process, all electrochemical indicators also showed a significant performance decline. In summary, vacuum degassing effectively removes impurity gases, reduces porosity formation, improves the internal density of the steel, helps improve the fluidity of molten steel, promotes uniform solidification, and yields stainless steel with a more uniform microstructure. Pre-melting electroslag material can quickly form a liquid electroslag layer, establishing a stable molten pool, creating favorable conditions for stable electrode melting and uniform solidification of the molten steel. The synergistic effect of vacuum degassing and electroslag remelting significantly improves the purity, microstructure uniformity, and properties of the steel, and has a significant optimizing effect on the pitting corrosion resistance of steel in marine environments.

[0109] Experimental Example 5

[0110] Referring to Experimental Example 1, the corrosion resistance of the marine stainless steels prepared in Examples 17-20 and Comparative Examples 11-12 was tested. The results are summarized in Table 7.

[0111] The gloss of the marine stainless steel prepared in Examples 17-20 and Comparative Examples 11-12 was tested at 20°, and the results are summarized in Table 7.

[0112] Table 7. Corrosion resistance and gloss of the marine stainless steels prepared in Examples 17-20 and Comparative Examples 11-12

[0113] <![CDATA[Mass loss (g / m 2 )]]> 20° Gloss (GU) Example 17 0.8 189 Example 18 0.6 204 Example 19 0.8 211 Example 20 0.7 197 Comparative Example 11 2.4 102 Comparative Example 12 15.9 175

[0114] As shown in Table 7, the corrosion resistance and gloss data of the steels prepared in Examples 17-20 exhibited good corrosion resistance and gloss. In Comparative Example 11, the corrosion resistance decreased to some extent and gloss was also reduced due to the interchange of the solution annealing and passivation polishing order. In Comparative Example 12, the corrosion resistance was significantly reduced and gloss was also somewhat lost due to the use of nitric acid instead of citric acid during the passivation polishing process. In summary, the core function of solution annealing is to eliminate work hardening and residual stress, obtain a uniform microstructure, and improve plasticity. Although solution annealing itself may not directly enhance corrosion resistance, it improves the internal state of stainless steel, laying a solid foundation for the formation and stabilization of the subsequent passivation film. Passivation polishing, based on the internal optimization achieved by solution annealing, further enhances the corrosion resistance of stainless steel and significantly improves the surface appearance quality. If passivation polishing is performed first, followed by solution annealing, the heating and cooling during the solution annealing process will damage the already formed passivation film and polished surface, leading to instability of the passivation film and a decrease in surface gloss. Meanwhile, prior passivation polishing cannot fully eliminate work hardening and residual stress within stainless steel, resulting in a poor internal microstructure that, in turn, affects the long-term stability and corrosion resistance of the passivation film. Furthermore, high-concentration nitric acid may over-oxidize the stainless steel surface, leading to a loose and uneven passivation film, which actually reduces corrosion resistance. This means that citric acid can gently promote the formation of the passivation film during polishing, resulting in a bright and corrosion-resistant surface.

[0115] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A manufacturing process for marine stainless steel, characterized in that: The production process is as follows: Iron ore, ferronickel, ferrochrome, and ferromolybdenum are preheated to 500°C and then fed into an electric arc furnace for smelting. The furnace voltage is set to 580V and the current to 77kA. After a molten pool is formed, dolomite and lime are added to form initial slag, which covers the molten pool. The slag is then poured into the molten pool at a rate of 7.8m... 3 Oxygen is introduced at a flow rate of / min, fluorite is added, and after smelting for 38 minutes, oxidizing slag and initial molten steel are formed; the reduction smelting process is as follows: stop the introduction of oxygen into the initial molten steel, remove the oxidizing slag, reduce the electric arc furnace voltage to 410V and the current to 59kA, add scrap steel and ferromanganese into the initial molten steel, and obtain molten steel after smelting for 20 minutes. During the smelting process, an argon-oxygen decarburization furnace is used to blow a mixture of argon and oxygen into the molten steel for decarburization treatment, wherein the flow rate of argon is 25 m³ / s. 3 / min, oxygen flow rate is 14.5m 3 The furnace temperature was 1680℃, the slag basicity was adjusted to 3.1, and after smelting for 100 minutes, the slag was removed to obtain decarburized steel liquid. The decarburized steel liquid was subjected to chemical desulfurization and vacuum desulfurization sequentially to obtain desulfurized steel liquid. The chemical desulfurization process was as follows: dolomite and lime were added to the decarburized steel liquid to adjust the slag basicity to 3.0, and the solution was heated at a rate of 20m... 3 Argon gas was blown in at a flow rate of / min and stirred at a speed of 100 rpm, maintaining the temperature of the decarburized steel liquid at 1645℃. After treatment for 20 min, chemically desulfurized steel liquid was obtained. The vacuum desulfurization process was as follows: under an operating pressure of 30 Pa, argon gas was blown in at a flow rate of 10 m³ / min and stirred at a speed of 100 rpm. 3 Argon gas was blown in at a flow rate of / min, and the desulfurized steel liquid was obtained after holding at 1600℃ for 30min. After cooling the desulfurized molten steel, low-temperature dephosphorization is carried out to obtain refined molten steel; the refined molten steel is then alloyed in a ladle refining furnace to obtain alloy molten steel. After vacuum degassing and electroslag remelting of molten alloy steel, it is hot-rolled to obtain precast stainless steel; the precast stainless steel is then solution annealed, cooled, and passivated and polished to obtain marine stainless steel.

2. The marine stainless steel production process according to claim 1, characterized in that: By mass fraction, the amount of iron ore added is 600 parts, the amount of ferronickel added is 120 parts, the amount of ferrochrome added is 280 parts, and the amount of ferromolybdenum added is 40 parts; the iron ore is magnetite; the smelting aids include: ferromanganese, dolomite, lime, scrap steel and fluorite; the smelting process includes oxidation smelting and reduction smelting.

3. The marine stainless steel production process according to claim 1, characterized in that: The low-temperature dephosphorization process is as follows: 5m... 3 Oxygen was blown in at a flow rate of / min, and ferrous oxide, sodium oxide and manganese oxide were added. The temperature of the desulfurized steel liquid was adjusted to 1400-1450℃, and the slag basicity was adjusted to 3.

5. After treatment for 60 minutes, the phosphorus-rich slag was removed to obtain refined steel liquid.

4. The marine stainless steel production process according to claim 1, characterized in that: The ladle alloying process is as follows: the refined molten steel is transferred into a preheated ladle, the nickel mass fraction of the refined molten steel is adjusted to 8.9 wt% at 1100℃, and the alloy molten steel is obtained after 30 minutes of treatment.

5. The marine stainless steel production process according to claim 1, characterized in that: The vacuum degassing process is as follows: The alloy steel molten material is heated to 1500℃ under an operating pressure of 50Pa, using a flow rate of 10m³ / h. 3 Argon gas is used to bottom-blow the alloy steel liquid at a rate of / min, and after holding for 30 minutes, it is cast into an alloy electrode for electroslag remelting.

6. The marine stainless steel production process according to claim 5, characterized in that: The electroslag remelting process is as follows: under a melting current of 5kA and an argon atmosphere, the pre-melted electroslag material is added to the bottom of the crystallizer. After preheating for 20 minutes, a slag pool is formed. The alloy electrode is slowly fed into the slag pool at a rate of 20mm / min. The remelting cycle is 5 hours. After processing and cooling, a remelted steel ingot is obtained. The remelted steel ingot is hot-rolled to obtain precast stainless steel.

7. The marine stainless steel production process according to claim 1, characterized in that: The solution annealing process is as follows: the precast stainless steel is heated to 1050℃, held for 60 min, and then cooled to 700℃ at a cooling rate of 10℃ / min. After quenching with deionized water at 25℃, it is cooled to 25℃ and then passivated and polished. The passivation and polishing process is as follows: the precast stainless steel that has undergone solution annealing is cleaned with acetone and 0.5wt% sulfuric acid aqueous solution. The cleaned precast stainless steel is then immersed in 20wt% citric acid aqueous solution, heated to 80℃ and treated for 2 hours. After cleaning and drying, marine stainless steel is obtained.

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