Marine stainless steel production process

Abstract

The invention belongs to the technical field of ship steel, and relates to a production process of marine stainless steel. The invention aims to solve the problems that the marine stainless steel is difficult to restrain local corrosion and poor in long-term sanitary performance. According to the method, an electric arc furnace is used for smelting iron ore, ferronickel, ferrochrome, ferromolybdenum and smelting auxiliaries, and refined molten steel is obtained after impurity components in the molten steel are accurately adjusted through decarburization treatment, chemical desulfurization, vacuum desulfurization and low-temperature dephosphorization; then the refined molten steel is subjected to steel ladle alloying, the element composition of the molten steel is further adjusted, and the purity and the structure uniformity of the stainless steel are deeply improved through the vacuum degassing and electroslag remelting processes; and the prefabricated stainless steel subjected to hot rolling forming is subjected to solution annealing and passivation polishing, the internal structure of the steel is further optimized, the surface performance is improved, and the marine stainless steel is obtained. The marine stainless steel provided by the invention is high in corrosion resistance, can effectively inhibit local corrosion, and has lasting sanitation performance in a ship environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of ship steel, and relates to a production process of marine stainless steel. Background Art

[0002] As a material with high strength and corrosion resistance, stainless steel has a very wide range of applications in the ship field. In the early stage, stainless steel was mainly used in marine valves, pumps and a small number of interior components. With the large-scale production of new stainless steels such as 316 and 316L, stainless steel has gradually become a common material for ship piping systems. With the further development of the shipping industry and the military industry, the application scope of marine stainless steel has been continuously expanding, gradually extending from special ships such as warships, LNG ships, and chemical tankers to various merchant ships and engineering vessels. At the same time, the increasingly wide application scope has also put forward more stringent performance requirements for marine stainless steel.

[0003] In particular, in the piping system of ships, marine stainless steel is applied in various systems such as seawater pipelines, fresh water pipelines, and exhaust pipelines due to its corrosion resistance and maintenance convenience. At present, stainless steel for ship pipelines still faces some problems that need to be solved urgently, such as the inhibition of local corrosion, the improvement of easy maintenance performance, and the enhancement of hygienic performance. How to solve these problems, make marine stainless steel have good application value in various different pipelines, give full play to the advantages of marine stainless steel, ensure the long-term safe and reliable operation of the ship system, and reduce the life cycle cost is the biggest challenge faced by marine stainless steel.

[0004] At present, it is still an important problem faced by the industry that marine stainless steel is difficult to inhibit local corrosion and has poor long-term hygienic performance.

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

[0006] The purpose of the present invention is to provide a production process of marine stainless steel. The present invention uses an electric arc furnace to melt iron ore, ferronickel, ferrochrome, ferromolybdenum and smelting aids, and through decarburization treatment, chemical desulfurization and vacuum desulfurization, as well as low-temperature dephosphorization, the impurity components in the molten steel are precisely adjusted to obtain refined molten steel; then ladle alloying is carried out on the refined molten steel to further adjust the element composition of the molten steel, and the purity and tissue uniformity of the stainless steel are deeply improved through vacuum degassing and electroslag remelting processes; the prefabricated stainless steel after hot rolling forming is subjected to solution annealing and passivation polishing to further optimize the internal structure of the steel and improve the surface performance, and marine stainless steel is obtained.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A production process of marine stainless steel, comprising the following steps:

[0009] Unless otherwise specified, all parts in the present invention are by mass, and the percentages are by mass percentage.

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

[0011] Stop passing oxygen into the primary molten steel, remove the oxidizing slag, reduce the voltage of the electric arc furnace to 350 - 450 V and the current to 50 - 60 kA. Put scrap steel and ferromanganese into the primary molten steel and obtain molten steel after smelting for 20 min.

[0012] Among them, the selection range of the raw material purity is as follows: the nickel content of ferronickel is 20 - 30%; the chromium content of ferrochrome is 60%; the molybdenum content of ferromolybdenum is 30 - 40%; the manganese content of ferromanganese is 65 - 80%; the iron ore is magnetite, and the iron content is 50 - 60%.

[0013] Among them, the composition of the scrap steel is: 0.05% carbon, 0.3% manganese, 0.1% chromium, 0.2% nickel, 98% iron, and the rest are impurities.

[0014] Use an argon-oxygen decarburization furnace to blow an argon-oxygen mixture into the molten steel for decarburization treatment. Among them, the flow rate of argon is 10 - 30 m 3 / min, and the flow rate of oxygen is 10 - 15 m 3 / min, the temperature in the furnace is 1600 - 1700 °C, adjust the slag basicity to 2.5 - 3.5, and after smelting for 100 min, remove the slag to obtain decarburized molten steel.

[0015] Add dolomite and lime to the decarburized molten steel, adjust the slag basicity to 3.0, blow argon at a flow rate of 20 m 3 / min and stir at a speed of 100 rpm, keep the temperature of the decarburized molten steel at 1600 - 1650 °C, and obtain chemically desulfurized molten steel after treatment for 20 min; further, under an operating pressure of 30 Pa, blow argon at a flow rate of 10 m 3 / min and keep it at 1600 °C for 30 min to obtain desulfurized molten steel.

[0016] Unless otherwise specified, the basicity in the present invention refers to the mass ratio of CaO / SiO2.

[0017] Blow argon into the desulfurized molten steel at a flow rate of 5 m 3Oxygen is blown in at a flow rate of / min, and ferrous oxide, sodium oxide, and manganese oxide are added. The temperature of the desulfurized molten steel is adjusted to 1400 - 1450 °C, and the basicity of the slag is adjusted to 3.5. After 60 minutes of treatment, the phosphorus-rich slag is removed to obtain refined molten steel.

[0018] The refined molten steel is transferred into a preheated ladle. At 1100 °C, the nickel mass fraction of the refined molten steel is adjusted to 8.4 - 9.0 wt%, and the sulfur content is ensured to be less than 0.01 wt% and the phosphorus content is less than 0.02 wt%. After 30 minutes of treatment, alloy steel liquid is obtained.

[0019] Under an operating pressure of 50 Pa, the alloy steel liquid is heated to 1500 °C, and argon with a flow rate of 10 m 3 / min is used for bottom blowing the alloy steel liquid. After maintaining for 30 minutes, it is cast into an alloy electrode for electroslag remelting.

[0020] Under a melting current of 5 kA and an argon atmosphere, the pre-melted electroslag material is added to the bottom of the mold. After preheating for 20 minutes, a slag pool is formed. The alloy electrode is slowly fed into the slag pool at a rate of 20 mm / min. The remelting cycle is 5 hours. After treatment and cooling, a remelted steel ingot is obtained; the remelted steel ingot is heated to 1200 °C and held for heat preservation. Under the operating conditions of a front tension of 10 MPa and a back tension of 5 MPa, hot rolling forming is carried out, and the rolling speed is maintained at 2.5 m / s. After the rolling product is cooled, it is the prefabricated stainless steel.

[0021] The prefabricated stainless steel is heated to 1050 °C, held for 60 minutes, cooled to 700 °C at a cooling rate of 10 °C / min, quenched with deionized water at 25 °C, and cooled to 25 °C for passivation polishing; the prefabricated stainless steel after solution annealing treatment is successively cleaned with acetone and a 0.5 wt% sulfuric acid aqueous solution. The cleaned prefabricated stainless steel is immersed in a 20 wt% citric acid aqueous solution, heated to 80 °C and treated for 2 hours. After cleaning and drying, marine stainless steel is obtained.

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

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

[0024] Preferably, based on the mass of the desulfurized molten steel being 1000 parts, the addition amount of ferrous oxide is 0.5 parts; the addition amount of sodium oxide is 0.1 parts; the addition amount of manganese oxide is 0.2 parts.

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

[0026] Preferably, the prefabricated stainless steel obtained by hot rolling forming is a stainless steel pipe.

[0027] The marine stainless steel produced by the present invention, after being made into a seamless steel pipe, 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. In the smelting process, oxidation smelting and reduction smelting are combined, and the element composition of stainless steel is optimized in the early stage of smelting through decarburization treatment, enhancing the strength after forming and ensuring its excellent corrosion resistance. Oxidation smelting enables impurity oxides and alloy oxides to enter the slag together. In the subsequent reduction smelting, by selecting scrap steel and ferromanganese as reducing agents and controlling the reduction conditions, the alloy oxides in the slag are selectively reduced to metallic chromium and manganese, which are returned to the molten steel, while the impurity oxides are left in the slag, realizing the efficient recovery of alloy elements and the effective separation of impurities. Further, the element composition of stainless steel is optimized through decarburization treatment, achieving a double improvement in the strength and corrosion resistance of stainless steel.

[0030] 2. After decarburization treatment, the molten steel is subjected to chemical desulfurization and vacuum desulfurization in sequence, and low-temperature dephosphorization is carried out after cooling. Through multiple slag removals, sulfur and phosphorus elements in the molten steel are removed, improving the strength and corrosion resistance of the formed stainless steel and enhancing its long-term hygienic performance in the marine environment. In the initial stage of refining, chemical desulfurization and vacuum desulfurization are carried out using slag, significantly reducing the sulfur content in the molten steel, indirectly improving the plasticity and toughness of the steel, reducing sulfide inclusions, and improving the internal quality of the steel, laying a foundation for subsequent strength improvement. At the same time, desulfurization prior to dephosphorization can optimize the dephosphorization environment, strengthen the dephosphorization effect, and reduce the oxidation degree of alloy elements. The sequential cooperation of the three processes greatly improves the purity, tissue uniformity, and surface quality of stainless steel, ultimately obtaining high-quality marine stainless steel materials with enhanced strength, excellent corrosion resistance, and significantly improved long-term hygienic performance.

[0031] 3. The elemental composition of stainless steel is regulated by different raw materials in the smelting aids, 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, a large - scale composition control is carried out using smelting aids to roughly adjust the liquid steel composition to near the target range. In the ladle alloying stage, alloy materials and refining agents are used for microscopic and precise composition fine - tuning to ensure that all element contents precisely meet the standards and achieve performance optimization. The finally produced stainless steel material has both excellent corrosion resistance and good strength. The composition design of high chromium, high nickel, low carbon, low sulfur, and low phosphorus ensures that the stainless steel has excellent corrosion resistance in marine environments such as seawater and sea atmosphere.

[0032] 4. By performing electroslag remelting after pre - vacuum degassing, the gases and inclusions in the liquid steel are removed to the greatest extent, ensuring the structural stability of the formed stainless steel, significantly improving the purity, tissue uniformity, and performance of the steel, enhancing its strength and corrosion resistance, and at the same time improving its aging resistance in high - salt environments. Pre - vacuum degassing effectively removes the dissolved gases in the liquid steel, reduces the formation of bubbles, improves the density of the stainless steel, thereby improving the internal structural stability of the stainless steel. Further electroslag remelting deeply removes the non - metallic inclusions in the liquid steel and realizes precise control of the solidification process, thus significantly improving the pitting corrosion resistance, crevice corrosion resistance, and intergranular corrosion resistance of the stainless steel.

[0033] 5. By performing solution annealing and passivation polishing processes successively, while eliminating work - hardening and residual stress, the corrosion resistance and appearance quality of the stainless steel are synergistically improved. After solution annealing, the stainless steel has a uniform structure, the internal stress is eliminated, and the plasticity is improved. It does not directly enhance the corrosion resistance, but by improving the tissue state, it provides more favorable conditions for the formation and stability of the subsequent passivation film, thereby indirectly enhancing the corrosion resistance. Passivation polishing further enhances the corrosion resistance of the stainless steel and significantly improves the surface appearance quality on the basis of solution annealing. The synergistic effect of the two realizes the optimization of the internal structure, elimination of internal defects, improvement of the surface state by passivation polishing, and improvement of the external quality of the stainless steel, making the comprehensive performance of the stainless steel reach the optimal level and having a wider application range. Brief Description of the Drawings

[0034] Figure 1 It is a flow chart of the production process of marine stainless steel in the present invention. Detailed Embodiments

[0035] The technical solutions of the present invention will be clearly and completely described below through some embodiments and experimental examples. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0036] Referring to Figure 1 the flowchart shown, the present invention provides a marine stainless steel production process, and the technical solution is as follows:

[0037] Example 1

[0038] Preheat 600 parts of iron ore, 120 parts of ferronickel, 280 parts of ferrochrome, and 40 parts of ferromolybdenum to 500 °C and then put them into an electric arc furnace. Set the voltage of the electric arc furnace to 550 V and the current to 70 kA. After forming a molten pool, put 0.5 part of dolomite and 2 parts of lime into it to form an initial slag and cover the molten pool. Pass oxygen into the molten pool at a flow rate of 5 m 3 / min, add fluorite, and after smelting for 30 min, an oxidizing slag and primary molten steel are formed.

[0039] Stop passing oxygen into the primary molten steel, remove the oxidizing slag, reduce the voltage of the electric arc furnace to 350 V and the current to 50 kA. Put scrap steel and ferromanganese into the primary molten steel and smelt for 20 min to obtain molten steel.

[0040] Use an argon-oxygen decarburization furnace to blow an argon-oxygen mixture into the molten steel for decarburization treatment. The flow rate of argon is 10 m 3 / min, and the flow rate of oxygen is 10 m 3 / min. The temperature in the furnace is 1600 °C. Adjust the slag basicity to 2.5. After smelting for 100 min, remove the slag to obtain decarburized molten steel.

[0041] Add dolomite and lime to the decarburized molten steel according to a mass ratio of 1:4, adjust the slag basicity to 3.0, blow argon at a flow rate of 20 m 3 / min and stir at a speed of 100 rpm. Keep the temperature of the decarburized molten steel at 1600 °C. After treatment for 20 min, chemically desulfurized molten steel is obtained; further, under an operating pressure of 30 Pa, blow argon at a flow rate of 10 m 3 / min and keep it at 1600 °C for 30 min to obtain desulfurized molten steel.

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

[0043] The refined molten steel is transferred into a preheated ladle. At 1100 °C, the nickel mass fraction of the refined molten steel is adjusted to 8.4 wt%, and it is ensured that the sulfur content is less than 0.01 wt% and the phosphorus content is less than 0.02 wt%. After 30 minutes of treatment, alloy steel liquid is obtained.

[0044] Under an operating pressure of 50 Pa, the alloy steel liquid is heated to 1500 °C, and argon with a flow rate of 10 m 3 / min is used for bottom blowing of the alloy steel liquid. After maintaining for 30 minutes, it is cast into an alloy electrode for electroslag remelting.

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

[0046] Among them, the composition of the electroslag material is: lime, silica, alumina, fluorite; the addition amount of lime is 50 parts, the addition amount of silica is 30 parts, the addition amount of alumina is 10 parts, and the addition amount of fluorite is 10 parts.

[0047] The prefabricated stainless steel is heated to 1050 °C, held for 60 minutes, cooled to 700 °C at a cooling rate of 10 °C / min, quenched with deionized water at 25 °C, and after cooling to 25 °C, passivation polishing is carried out; the prefabricated stainless steel after solution annealing treatment is successively cleaned with acetone and a 0.5 wt% sulfuric acid aqueous solution, and the cleaned prefabricated stainless steel is immersed in a 20 wt% citric acid aqueous solution, heated to 80 °C and treated for 2 hours, and after cleaning and drying, marine stainless steel is obtained.

[0048] Example 2 - 20 is different from Example 1 in terms of operating parameters, and the process steps are the same. The parameter changes are summarized in Tables 1 and 2.

[0049] Table 1 Changes in operating parameters of Examples 1 - 20 (I)

[0050]

[0051]

[0052] Table 2 Variation of operating parameters in Examples 1 - 20 (Part 2)

[0053]

[0054]

[0055] Comparative Example 1

[0056] Differing from Example 1, the reduction smelting process is not carried out, and other process parameters are the same.

[0057] Comparative Example 2

[0058] Differing from Example 1, the sequence of reduction smelting and oxidation smelting is exchanged, and other process parameters are the same.

[0059] Comparative Example 3

[0060] Differing from Example 1, the decarbonization treatment is not carried out, and other process parameters are the same.

[0061] Comparative Example 4

[0062] Differing from Example 5, the sequence of chemical desulfurization and vacuum desulfurization is exchanged, and other process parameters are the same.

[0063] Comparative Example 5

[0064] Differing from Example 5, the temperature of low - temperature dephosphorization is increased to 1600 °C, and other process parameters are the same.

[0065] Comparative Example 6

[0066] Differing from Example 5, low - temperature dephosphorization is carried out first, followed by chemical desulfurization and vacuum desulfurization in sequence, and other process parameters are the same.

[0067] Comparative Example 7

[0068] Differing from Example 9, during the ladle alloying process, the content of nickel is not fine - tuned, and other process parameters are the same.

[0069] Comparative Example 8

[0070] Differing from Example 9, pure nickel, cobalt, and molybdenum are used instead of ferronickel, ferro - cobalt, and ferromolybdenum, and other process parameters are the same.

[0071] Comparative Example 9

[0072] Differing from Example 13, the vacuum degassing process is not carried out, and electroslag remelting is directly carried out, and other process parameters are the same.

[0073] Comparative Example 10

[0074] Different from 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, and other process parameters are the same.

[0075] Comparative Example 11

[0076] Different from Example 17, the sequence of solution annealing and passivation polishing is exchanged, and other process parameters are the same.

[0077] Comparative Example 12

[0078] Different from Example 17, during the passivation polishing process, 20wt% nitric acid aqueous solution is used to replace 20wt% citric acid aqueous solution, and other process parameters are 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 obtained results are summarized in Table 3.

[0081] For the corrosion resistance test, referring to the GB / T 10125-2021 standard, the neutral salt spray test (NSS) method was used to measure the mass change of the 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 carried out after using the corresponding stainless steel to prepare seamless steel pipes with an outer diameter D = 100mm and a wall thickness t = 10mm.

[0083] Table 3 Compressive strength and corrosion resistance of marine stainless steels 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 the compressive strength and corrosion resistance data in Table 3, the stainless steels prepared in Examples 1-4 have relatively high compressive strength values and relatively low mass loss values, indicating that the stainless steels prepared by the complete process have stable and excellent properties. In Comparative Example 1, reduction smelting was not carried out, and the strength was significantly reduced and the corrosion resistance deteriorated sharply. This is because after oxidation smelting, both impurity oxides and alloy oxides enter the slag. Without subsequent reduction smelting, the impurity oxides are still partially mixed in the final steel, further reducing the purity and properties of the steel. In Comparative Example 2, the order of reduction smelting and oxidation smelting was exchanged, and the properties of the stainless steel also decreased significantly. This shows that if reduction smelting is carried out first, the impurity oxides cannot be effectively enriched into the slag, and the subsequent oxidation smelting cannot make up for the deficiencies in the previous steps, resulting in poor impurity removal effect. In Comparative Example 3, decarburization treatment was not carried out, and the performance decreased the most. This is attributed to the too high carbon content, which leads to the precipitation of carbide at the grain boundary, damaging the integrity and uniformity of the passivation film, thus severely reducing the corrosion resistance. In summary, the specific order of oxidation smelting, reduction smelting, and decarburization treatment and their respective process designs have a high degree of synergy. Oxidation smelting initially realizes the oxidation and enrichment of impurities and alloy elements into the slag. Reduction smelting efficiently and selectively reduces and recovers alloy elements, maximizing the utilization rate of alloy elements, and further realizing the refining of molten steel to remove some impurities. Further decarburization treatment deeply optimizes the elemental composition of stainless steel at the early stage of smelting, enhancing the strength after forming and ensuring its excellent corrosion resistance.

[0086] Experimental Example 2

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

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

[0089] The long-term hygienic properties were determined by biofilm formation and bacterial adhesion tests and easy cleanability tests.

[0090] The method for biofilm formation and bacterial attachment test is as follows: After ultrasonic cleaning the stainless-steel surface, it is sterilized. The seawater culture solution of Pseudomonas aeruginosa is used for constant-temperature culture at 37 °C with a shaker at 100 rpm for 72 hours. Among them, the experimental concentration of the seawater culture solution of Pseudomonas aeruginosa is 100 CFU / mL. Polystyrene resin sheets are used as the positive control group, and only sterile culture solution is added as the negative control group. The OD value (absorbance) of the crystal violet staining method is used to characterize the biofilm formation situation. The lower the value, the less biofilm is formed, and the stronger the ability of the substrate to resist biofilm formation. Taking the OD value of the negative control group as 0% and the OD value of the positive control group as 100%, the OD values of each experimental group are recorded.

[0091] The method for easy cleanability test is as follows: 20 parts of marine heavy oil, 2 parts of calcium carbonate powder, 1 part of magnesium hydroxide powder and 10 parts of soybean oil are mixed as the simulated dirt. The simulated dirt is evenly smeared on the stainless-steel surface, dried at 60 °C for 2 hours, then washed at a 20 kHz ultrasonic frequency with a 2 wt% concentration of neutral cleaner for 10 min, and after natural drying, the attachment situation of the dirt on the stainless-steel surface is observed.

[0092] Table 4 Compressive strength, corrosion resistance and long-term hygiene performance of the marine stainless steel prepared in Examples 5-8 and Comparative Examples 4-6

[0093]

[0094]

[0095] As shown in the data of compressive strength, corrosion resistance and long-term hygienic performance in Table 4, the values of compressive strength still remain at a relatively high level and are relatively stable, and the corrosion resistance is also relatively strong. In Comparative Example 4, the order of chemical desulfurization and vacuum desulfurization was exchanged, and both the compressive strength and corrosion resistance showed obvious performance degradation, which proved that when vacuum desulfurization was carried out first, due to the relatively high initial sulfur content in the molten steel, the efficiency of vacuum desulfurization was limited, and the desulfurization effect was not as good as the combined process of chemical desulfurization first and then vacuum desulfurization. In Comparative Example 5, the low-temperature dephosphorization temperature was increased to 1600 °C, and the compressive strength and corrosion resistance performance further decreased, and the OD value also increased significantly, which indicated that low-temperature dephosphorization was more conducive to the transfer of phosphorus elements to the slag, thereby strengthening the dephosphorization effect, while high temperature would instead reduce the dephosphorization efficiency and even cause the rephosphorization of phosphorus elements. In Comparative Example 6, low-temperature dephosphorization was carried out first, followed by chemical desulfurization and vacuum desulfurization in sequence, resulting in the worst compressive strength, corrosion resistance and long-term hygienic performance, which showed that the presence of sulfur elements would have an adverse effect on the dephosphorization process. In summary, the sequence of desulfurization first and then dephosphorization makes better use of the different metallurgical characteristics of sulfur and phosphorus elements, achieving a more efficient and thorough desulfurization and dephosphorization effect, and ultimately having a crucial impact on the various properties of stainless steel, especially corrosion resistance and long-term hygienic performance. As the first step of the desulfurization process, chemical desulfurization mainly serves 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 the overall desulfurization efficiency; vacuum desulfurization is the core link of deep desulfurization, which can reduce the sulfur content to an extremely low level, and synergistically remove gases and inclusions in the molten steel, achieving deeper refining and improving the purity of steel; low-temperature dephosphorization is not simply a temperature reduction operation, but a key step with extremely strict temperature control requirements. A low-temperature environment may be more conducive to the transfer of phosphorus elements to the slag, strengthening the dephosphorization effect, while reducing the oxidation loss of alloying elements and having a positive impact on the microstructure of steel. The specific process sequence of chemical desulfurization first, then vacuum desulfurization, and then low-temperature dephosphorization achieves the maximization of desulfurization and dephosphorization efficiency and the comprehensive improvement of the performance of stainless steel through a high degree of synergy, especially improving the stain resistance and antibacterial properties on the surface of stainless steel and significantly enhancing its long-term hygienic performance.

[0096] Experimental Example 3

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

[0098] Table 5 Compressive Strength and Corrosion Resistance of Marine Stainless Steel 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 the compressive strength and corrosion resistance data in Table 5, the compressive strength values of Examples 9-12 still remained at a relatively high and stable level, and the corrosion resistance was also relatively high. In Comparative Example 7, since the nickel content was not fine-tuned during the ladle alloying process, the compressive strength decreased significantly and the corrosion resistance also decreased sharply. This indicates that the fine-tuning of the nickel content during the ladle alloying process plays a crucial role in the performance of the final product, especially the corrosion resistance. In Comparative Example 8, pure nickel, cobalt, and molybdenum were used instead of ferronickel, ferro-cobalt, and ferromolybdenum in the process. The compressive strength remained almost unchanged, but the corrosion resistance decreased significantly, indicating that in the selection of alloy raw materials, even if the alloy element compositions are the same, it may still affect the performance of stainless steel, and using ferroalloys is better than using pure metal alloy materials. In summary, using ferroalloys as alloy raw materials is more in line with the specific smelting process and composition control requirements, can better synergize with smelting aids, and ultimately obtain stainless steel products with better comprehensive performance. The smelting aids play a role in the initial stage of smelting, mainly responsible for roughly adjusting the steel liquid composition to near the target range, and through ladle alloying, on the basis of the preliminary control of the smelting aids, using alloy materials and refining agents to precisely fine-tune the key element contents of stainless steel, ensuring that all element contents meet the standards precisely and further optimizing the performance. The two cooperate with each other to jointly build a composition control system that combines coarseness and fineness and is efficient and precise, which not only ensures the smelting efficiency but also achieves the accuracy of composition control and the optimization of performance.

[0101] Experimental 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 obtained results are summarized in Table 6.

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

[0104] The stronger the pitting corrosion resistance, the stronger the resistance of the stainless steel to local corrosion.

[0105] Table 6 Pitting Corrosion Resistance of Marine Stainless Steels Prepared in Examples 13-16 and Comparative Examples 9-10

[0106]

[0107]

[0108] As shown in the compressive strength and corrosion resistance data in Table 6, the pitting resistance of the steel prepared in Examples 13 - 16 is relatively good. In Comparative Example 9, since the vacuum degassing process is not carried out, all electrochemical indexes show a cliff-like deterioration, especially the pitting potential and the repassivation potential, indicating that not carrying out the vacuum degassing process has an extremely serious negative impact on the pitting resistance of stainless steel. In Comparative Example 10, since the electroslag remelting process does not pre-melt the electroslag material, all electrochemical indexes also show an obvious performance decline. In summary, vacuum degassing can effectively remove impurity gases, reduce the formation of pores, improve the internal structure density of the steel, help to improve the fluidity of the molten steel, promote uniform solidification, and obtain stainless steel with a more uniform organizational structure; pre-melting the electroslag material can quickly form a liquid electroslag layer, establish a stable molten pool, and create favorable conditions for the smooth melting of the electrode and the uniform solidification of the molten steel. The synergistic effect of vacuum degassing and electroslag remelting significantly improves the purity, tissue uniformity and performance of the steel, and has an obvious optimization effect on the pitting resistance of the steel in the marine environment.

[0109] Experimental Example 5

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

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

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

[0113] <![CDATA[Mass loss (g / m 2 )]]> 20° Glossiness (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 the corrosion resistance and glossiness data in Table 7, the corrosion resistance and glossiness of the steel prepared in Examples 17 - 20 are both good. In Comparative Example 11, due to the exchange of the order of solution annealing and passivation polishing, the corrosion resistance decreased to a certain extent and the glossiness also decreased. In Comparative Example 12, due to the use of nitric acid instead of citric acid during passivation polishing, the corrosion resistance decreased significantly and there was also a certain loss of glossiness. In summary, the core role 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 the stainless steel and lays a solid foundation for the formation and stability of the subsequent passivation film. Passivation polishing, on the other hand, further enhances the corrosion resistance of the stainless steel and significantly improves the surface appearance quality on the basis of optimizing the interior by solution annealing. If passivation polishing is carried out first and then solution annealing, the heating and cooling during the solution annealing process will damage the formed passivation film and polished surface, resulting in an unstable passivation film and a decrease in surface glossiness. At the same time, performing passivation polishing first cannot fully eliminate the work hardening and residual stress inside the stainless steel, and the poor internal tissue state will in turn affect the long-term stability and corrosion resistance of the passivation film. In addition, high-concentration nitric acid may over-oxidize the surface of the stainless steel, resulting in a loose and uneven passivation film, which instead reduces the corrosion resistance. It is represented that citric acid can gently promote the formation of the passivation film while polishing, obtaining a surface that is both bright and corrosion-resistant.

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

Claims

1. A marine stainless steel production process, characterized in that: The production process is as follows: Put iron ore, ferronickel, ferrochrome, ferromolybdenum and smelting additives into an electric arc furnace for smelting to obtain molten steel liquid; During the smelting process, an argon-oxygen decarburization furnace is used to blow an argon-oxygen mixture into the molten steel for decarburization treatment, where the flow rate of argon is 10 - 30 m 3 / min, the flow rate of oxygen is 10 - 15 m 3 / min, the temperature in the furnace is 1600 - 1700 °C, the basicity of the slag is adjusted to 2.5 - 3.5, and after 100 minutes of smelting, the slag is removed to obtain decarburized molten steel; Carry out chemical desulfurization and vacuum desulfurization on the decarbonized steel liquid in sequence to obtain desulfurized steel liquid; After cooling the desulfurized steel liquid, carry out low-temperature dephosphorization to obtain refined steel liquid; Carry out ladle alloying on the refined steel liquid in a ladle refining furnace to obtain alloy steel liquid; After carrying out vacuum degassing and electroslag remelting on the alloy steel liquid, hot rolling is carried out to form prefabricated stainless steel; Carry out solution annealing on the prefabricated stainless steel, and carry out passivation polishing after cooling to obtain the marine stainless steel.

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

3. A production process of marine stainless steel according to claim 2, characterized in that: The process of oxidative smelting is as follows: preheat the iron ore, nickel iron, ferrochrome and ferromolybdenum to 500 °C and then put them into an electric arc furnace. Set the voltage of the electric arc furnace to 550 - 600 V and the current to 70 - 80 kA. After forming a molten pool, put in the dolomite and lime to form an initial slag and cover the molten pool. Then, introduce oxygen into the molten pool at a flow rate of 5 - 10 m 3 / min, add the fluorite, and after smelting for 30 - 40 min, an oxidizing slag and an initially molten steel liquid are formed. The process of reduction smelting is as follows: stop introducing oxygen into the initially molten steel liquid, remove the oxidizing slag, reduce the voltage of the electric arc furnace to 350 - 450 V and the current to 50 - 60 kA. Put in the scrap steel and ferromanganese into the initially molten steel liquid and obtain the molten steel liquid after smelting for 20 min.

4. A marine stainless steel production process according to claim 1, characterized in that: The process of chemical desulfurization is as follows: Add dolomite and lime to the decarburized molten steel, adjust the basicity of the slag to 3.0, blow argon at a flow rate of 20 m 3 / min and stir at a rotational speed of 100 rpm, keep the temperature of the decarburized molten steel at 1600 - 1650 °C, and obtain chemically desulfurized molten steel after treatment for 20 min; The process of vacuum desulfurization is as follows: Under an operating pressure of 30 Pa, blow argon into the chemically desulfurized molten steel at a flow rate of 10 m 3 / min, and obtain the desulfurized molten steel after heat preservation at 1600 °C for 30 min.

5. A marine stainless steel production process according to claim 1, characterized in that: The process of low-temperature dephosphorization is as follows: blowing oxygen into the desulfurized molten steel at a flow rate of 5 m 3 / min, adding ferrous oxide, sodium oxide and manganese oxide, adjusting the temperature of the desulfurized molten steel to 1400 - 1450 °C, adjusting the slag basicity to 3.5, after treating for 60 min, skimming off the phosphorus-rich slag to obtain the refined molten steel.

6. A marine stainless steel production process according to claim 1, characterized in that: The process of ladle alloying is: transfer the refined steel liquid into a preheated ladle, adjust the nickel mass fraction of the refined steel liquid to 8.4-9.0 wt% at 1100 °C, and obtain the alloy steel liquid after treatment for 30 min.

7. A marine stainless steel production process according to claim 1, characterized in that: The process of the vacuum degassing is as follows: the alloy steel liquid is heated to 1500 °C under an operating pressure of 50 Pa, and argon gas with a flow rate of 10 m 3 / min is used for bottom blowing of the alloy steel liquid, and after maintaining for 30 min, it is cast into an alloy electrode for the electroslag remelting.

8. A marine stainless steel production process according to claim 7, characterized in that: The process of electroslag remelting is: under a melting current of 5 kA and an argon atmosphere, add pre-melted electroslag materials to the bottom of the mold, form a slag pool after preheating for 20 min, slowly feed the alloy electrode into the slag pool at a rate of 20 mm / min, the remelting cycle is 5 hours, and after treatment, it is cooled to obtain a remelted ingot; the remelted ingot is hot rolled to form the prefabricated stainless steel.

9. A marine stainless steel production process according to claim 1, characterized in that: The process of solution annealing is: heat the prefabricated stainless steel to 1050 °C, keep it warm for 60 min, cool it to 700 °C at a cooling rate of 10 °C / min, then quench it with deionized water at 25 °C, and carry out the passivation polishing after cooling to 25 °C; the process of passivation polishing is: successively clean the prefabricated stainless steel treated by the solution annealing with acetone and a 0.5 wt% sulfuric acid aqueous solution, immerse the cleaned prefabricated stainless steel in a 20 wt% citric acid aqueous solution, heat it to 80 °C and treat it for 2 hours, and obtain the marine stainless steel after cleaning and drying.

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