UNS S32615 high-silicon stainless steel and medium-frequency smelting preparation method thereof

Abstract

The invention relates to the field of high-silicon stainless steel materials, and particularly discloses UNS S32615 high-silicon stainless steel and a medium-frequency smelting preparation method thereof. The UNS S32615 high-silicon stainless steel comprises the following chemical components in percentage by mass: 0.02%-0.03% of C, 5.6%-5.8% of Si, 1.5%-1.8% of Mn, less than or equal to 0.02% of P, less than or equal to 0.005% of S, 17.0%-17.5% of Cr, 20.8%-21.8% of Ni, 0.4%-0.6% of Mo, 1.6%-1.8% of Cu and the balance of Fe and inevitable impurities, and the content of ferrite is controlled to be below 2%. The high-frequency smelting preparation method comprises the following six steps: proportioning according to a formula, charging and melting, melting down, precipitating and deoxidizing, slagging off and making new slag, alloying and diffusing and deoxidizing, and casting molten steel. By optimizing the alloy component design and reasonably controlling the smelting process, ferrite precipitation and the content of non-metallic inclusions are reduced, the purity and the corrosion resistance of the steel are remarkably improved, meanwhile, the hot working performance and the yield of the UNS S32615 high-silicon stainless steel are improved, and the UNS S32615 high-silicon stainless steel has wide application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of high-silicon stainless steel ingot preparation, and in particular to UNS S32615 high-silicon stainless steel and a medium-frequency smelting preparation method thereof. Background Art

[0002] UNS S32615 high silicon stainless steel is widely used in chemical equipment, energy field and other applications requiring corrosion resistance due to its excellent corrosion resistance to high temperature concentrated sulfuric acid and nitric acid, low alloy cost and good mechanical properties. The alloy contains a high content of silicon, which forms a composite passivation film mainly composed of SiO2 and Cr2O3 on its surface. This passivation film can effectively inhibit the cathode reaction, thereby improving the substrate's ability to resist uniform corrosion and intergranular corrosion. However, although the high silicon content significantly improves its corrosion resistance, it still faces many technical challenges in the actual production process.

[0003] First, high silicon content will bring some unfavorable production problems. High silicon content may lead to casting defects and increased component segregation during steel production, poor fluidity of molten steel, and easily lead to uneven ingot structure. This unevenness not only affects the performance of the alloy, but also increases the difficulty of subsequent processing. Especially in the smelting process, the presence of oxide inclusions will further increase the defective rate of the product.

[0004] Secondly, higher silicon content will lead to an increase in ferrite precipitation, which directly affects the hot working properties of the alloy. High silicon content reduces the size of the austenite unit cell, thereby reducing the solubility of carbon and promoting the precipitation of intermediate phases. The precipitated intermediate phases such as Cr3Si and Cr2C6 not only reduce the plasticity of the alloy, but may also cause hot cracks in the subsequent processing process, seriously affecting the mechanical properties and yield rate of the product.

[0005] In the prior art, the non-metallic inclusion content of conventional UNS S32615 stainless steel is shown in Table 1 below:

[0006] Table 1: Non-metallic inclusion content of conventional UNS S32615 stainless steel:

[0007]

[0008] In addition, although the existing medium frequency smelting technology has advantages in energy efficiency and melting time, the deoxidation effect during the smelting process is not ideal and the inclusion content is high. These inclusions will not only affect the strength and toughness of the alloy, but may also cause cracking of the product during hot working. For high-silicon stainless steel, the presence of inclusions will also increase the probability of ferrite precipitation, further reducing the overall performance of the alloy.

[0009] Therefore, although UNS S32615 high silicon stainless steel has good corrosion resistance, its production efficiency and yield rate are restricted due to these defects in the existing production process, and the quality and stability of the product are difficult to meet the needs of high-end applications. Therefore, it is necessary to improve the existing smelting and hot working methods, reduce the inclusion content, control the precipitation of ferrite, and further optimize the composition and structure of the alloy to improve its overall performance and meet higher requirements for industrial applications. Summary of the invention

[0010] The technical problem to be solved by the present invention is to provide a UNS S32615 high-silicon stainless steel to solve the problems of excessively high ferrite content, poor hot working performance and insufficient corrosion resistance of conventional UNS S32615 stainless steel in the prior art.

[0011] In order to overcome the defects of the above prior art, the present invention provides a UNS S32615 high-silicon stainless steel, whose chemical composition includes, by mass fraction, C: 0.02-0.03%, Si: 5.6-5.8%, Mn: 1.5-1.8%, P: ≤0.02%, S: ≤0.005%, Cr: 17.0-17.5%, Ni: 20.8-21.8%, Mo: 0.4-0.6%, Cu: 1.6-1.8%, and the balance is Fe and inevitable impurities.

[0012] Compared with the prior art, the UNS S32615 high-silicon stainless steel of the present application has the following advantages: through the above-mentioned composition design, the stainless steel of the present invention not only has excellent high-temperature concentrated sulfuric acid and nitric acid corrosion resistance, but also improves the hot processing performance while maintaining good corrosion resistance. The ferrite content is controlled to be less than 2%, making the grain size of the material more uniform, avoiding the tendency of thermal cracking caused by excessive ferrite precipitation. The final UNS S32615 high-silicon stainless steel has high purity, high corrosion resistance and high mechanical stability, which meets the strict requirements of chemical equipment production and complex working conditions, and significantly improves the market competitiveness and application breadth of the material. The principles of the specific composition design are as follows:

[0013] C content (0.02%-0.03%): Accurately control the carbon content within a low range, effectively reduce the equilibrium concentration of free oxygen in the molten steel, reduce the formation of oxide inclusions, and avoid the precipitation of excessive carbides, thereby improving the corrosion resistance and mechanical properties of the steel;

[0014] Si content (5.6%-5.8%): High silicon content improves the ability to form SiO2 and Cr2O3 composite passivation films on the surface of the material, significantly enhancing the performance against high-temperature concentrated sulfuric acid and nitric acid corrosion;

[0015] Mn content (1.5%-1.8%): Manganese not only acts as a deoxidizer, forming a low-melting-point composite oxide with oxidation products to facilitate the removal of inclusions, but also acts as an austenite-forming element to inhibit ferrite precipitation and further improve the hot working properties of the material;

[0016] Ni content (20.8%-21.8%): High nickel content, as an austenite stabilizing element, reduces the precipitation of ferrite, improves the stability of the matrix, and gives the material excellent mechanical properties and corrosion resistance. High Ni and high Si content also have a synergistic effect: Ni content between 20.8%-21.8% helps to stabilize the austenite matrix and inhibit the precipitation of ferrite, while the Si content helps to enhance the formation of the passivation film, further improving the corrosion resistance of the material.

[0017] Cr (17.0%-17.5%) and Mo (0.4%-0.6%): synergistic effect further enhances corrosion resistance, especially corrosion resistance in high temperature and highly corrosive environment. At the same time, the appropriate amount of Mo also avoids the negative impact of excessive ferrite content on hot working performance;

[0018] P and S content (P≤0.02%, S≤0.005%): Strictly limit the content of harmful elements, effectively improve the hot working properties of the material, and reduce the crack tendency and segregation phenomenon.

[0019] In a possible implementation manner, the content of ferrite in the UNS S32615 high-silicon stainless steel is less than 2%.

[0020] Compared with the prior art, the above technical solution limits the ferrite content to less than 2% through precise composition design and smelting process. Ferrite is a brittle phase in stainless steel at high temperature. Excessive ferrite will cause cracks or reduce the toughness of the material during hot working. By controlling its content, the tendency of hot cracks caused by ferrite precipitation to the material can be avoided, thereby improving the processing performance of steel.

[0021] Another technical problem to be solved by the present invention is to provide a UNS S32615 high-silicon stainless steel to solve the problems of difficult deoxidation, high inclusion content and ferrite precipitation in the production process in the conventional preparation method of UNS S32615 stainless steel in the prior art.

[0022] In order to overcome the above defects of the prior art, the present invention provides a medium frequency smelting preparation method of the UNS S32615 high silicon stainless steel, comprising the following steps:

[0023] S1: Ingredients

[0024] The ingredients are prepared according to the composition range of the UNS S32615 high silicon stainless steel;

[0025] S2: Adding and melting

[0026] In the medium frequency furnace, the bottom slag is first added to desulfurize, isolate the molten steel from air, reduce oxidation, and help melt lime; then the materials are added in the following order: iron block, nickel plate, iron plate, and recarburizer, electrolytic manganese and metallic silicon are added during the melting process;

[0027] S3: Melt-clear precipitation deoxidation

[0028] After the molten steel in the intermediate frequency furnace in step S2 is melted, precipitation deoxidation is performed;

[0029] S4: Slag removal and new slag making

[0030] A deoxidizer is added to the molten steel after the treatment in step S3 for deoxidation, and then the slag is removed and pre-molten slag is added for slag making. The pre-molten slag is a mixture of Al2O3 and CaO.

[0031] S5: Alloying and diffusion deoxidation

[0032] Adding metallic chromium, electrolytic Mn and metallic silicon for alloying, while adding diffusion deoxidizer in batches to diffuse deoxidize the molten steel;

[0033] S6: Casting

[0034] The slag amount is adjusted to maintain white slag, and the casting temperature of the molten steel is controlled before casting the molten steel to obtain UNS S32615 high silicon stainless steel.

[0035] Compared with the prior art, the medium frequency smelting preparation method of UNS S32615 high silicon stainless steel of the present application has the following advantages: the present invention realizes efficient deoxidation of molten steel by adopting a combination of precipitation deoxidation and diffusion deoxidation in the medium frequency smelting process, and uses Si-Ca blocks to quickly remove free oxygen through precipitation deoxidation, while diffusion deoxidation ensures the completeness of the deoxidation reaction and promotes the floating of inclusions by adding Al-CaO and Si-Ca mixtures in batches multiple times, which ultimately significantly reduces the oxygen content and non-metallic inclusion content in the molten steel. Through the above process, the inclusion content and distribution are significantly improved, the purity of the material is greatly improved, and the precise control of the Cr and Ni contents in the ingredient formula, as well as the adjustment of the casting temperature (1490±10°C), effectively inhibits the excessive precipitation of ferrite, ensuring that the ferrite content is less than 2%. This feature not only improves the corrosion resistance and mechanical properties of stainless steel, but also significantly improves the hot working performance, avoiding the crack problem caused by excessive precipitation of ferrite. Through the above method, the UNS S32615 high silicon stainless steel has remarkable excellent properties: high purity of molten steel, ferrite content less than 2%, low inclusion content and uniform distribution, and the final stainless steel product has better corrosion resistance, mechanical properties and hot working properties, which greatly improves the applicability of the material, especially in harsh chemical environments and high-temperature corrosion occasions. The synergistic optimization of the composition design and the medium frequency smelting method of the present invention realizes the preparation of high-performance UNS S32615 high silicon stainless steel from deoxidation, inclusion control to ferrite precipitation regulation, significantly improves the preparation efficiency and comprehensive material performance, and has broad industrial application prospects.

[0036] In a possible implementation, in step S2, the weight of the bottom ash is 1% of the molten steel, and the bottom ash is composed of CaO and CaF2 in a mass ratio of 5:5.

[0037] Compared with the prior art, the above technical scheme not only enhances the functional diversity of the slag (such as desulfurization, fluxing, and oxidation isolation) through the combination of CaO and CaF2, but also significantly improves the reaction efficiency of the slag and the stability of the furnace operation. Due to the precise match between the weight of the bottom slag and the mass of the molten steel (1%), it not only avoids the influence of excessive slag on the reaction efficiency, but also ensures the full contact between the bottom slag and the molten steel, thereby improving the ability to remove impurities. Combined with the above-mentioned desulfurization and anti-oxidation effects, it solves the problems of many sulfide inclusions and high oxide content in traditional smelting, and significantly improves the purity and performance stability of UNS S32615 high silicon stainless steel.

[0038] In a possible implementation manner, in step S3, the precipitation deoxidation is performed by adding Si-Ca blocks to the molten steel for deoxidation, and the weight of the Si-Ca blocks is 0.1% of the molten steel.

[0039] Compared with the prior art, the above technical solution combines the strong deoxidation ability of Si and the modified inclusion effect of Ca through the use of Si-Ca blocks, and achieves the dual effects of deoxidation and inclusion morphology optimization through the synergistic effect of the two. And by accurately controlling the amount of Si-Ca blocks (0.1% of the weight of molten steel), the high efficiency of the deoxidation reaction and the thoroughness of inclusion removal are ensured, avoiding the side effects caused by improper dosage of deoxidizers in traditional technologies (such as increased number of inclusions or composition disturbances), effectively overcoming the problems of high content and difficult separation of oxide inclusions in the prior art, and providing a guarantee for the high-quality preparation of UNS S32615 high-silicon stainless steel.

[0040] In a possible implementation, in step S4, the deoxidizer is Si-Ca wire, the mass of the pre-molten slag is 8-12 kg, and the mass ratio of Al2O3 to CaO is 40:60.

[0041] Compared with the prior art, the above technical scheme is adopted, through the combination of Si-Ca wire and pre-melted slag, which not only removes oxygen and inclusions synergistically through physical and chemical effects during the deoxidation process, but also forms a slag layer to protect the molten steel, avoiding the problem of secondary oxidation in the traditional process. The deoxidation and inclusion modification effect of the Si-Ca wire cooperates with the adsorption and isolation effect of the pre-melted slag, successfully solving the problems of many oxidized inclusions and insufficient purity of the molten steel in the prior art. Through the dual optimization of deoxidation and inclusion removal, the quality and processing adaptability of UNS S32615 high-silicon stainless steel are improved.

[0042] In a possible implementation, in step S5, the diffusion deoxidizer is added in batches 5 times with an interval of 5-7 minutes, and the total diffusion deoxidation time is 30-70 minutes.

[0043] Compared with the prior art, the above technology combines adding diffusion deoxidizer in batches with a reasonable time interval, which not only optimizes the efficiency of the deoxidation reaction, but also provides time for inclusions to fully float up, making the deoxidation and inclusion removal process of the molten steel more scientific and reasonable. At the same time, the control of the total deoxidation time (30-70 minutes) and the batch operation work together to ensure the stability and purity of the molten steel composition, solve the problems of insufficient deoxidation efficiency, many residual inclusions, and large fluctuations in molten steel quality in the prior art, and finally achieve efficient preparation and performance improvement of UNS S32615 high-silicon stainless steel.

[0044] In a possible implementation manner, in step S5, the diffusion deoxidizer is a mixture of Al-CaO and Si-Ca, and the total mass of the diffusion deoxidizer is 0.1-0.2% of the molten steel.

[0045] Compared with the prior art, the above technical solution uses a mixture of Al-CaO and Si-Ca as a diffusion deoxidizer, which exerts a synergistic deoxidation effect through its unique physical and chemical properties, effectively reducing the oxygen content of the molten steel and the number of non-metallic inclusions. At the same time, the total mass range of the deoxidizer (0.1-0.2%) is reasonably controlled to achieve an optimal balance between the deoxidation efficiency and the inclusion separation effect, thereby avoiding the problem of residual inclusions caused by excessive use.

[0046] In a possible implementation, in step S6, the temperature of casting the molten steel is 1490±10°C.

[0047] Compared with the prior art, the above technical scheme is adopted to accurately control the casting temperature within the range of 1490±10°C, which can not only ensure that the molten steel has good fluidity and uniformity, but also reduce the precipitation of ferrite and the residue of non-metallic inclusions, thereby solving the problem of unstable billet quality caused by improper casting temperature in the prior art, and significantly improving the yield and comprehensive performance of UNSS32615 high silicon stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a flow chart of a medium frequency smelting preparation method of UNS S32615 high silicon stainless steel according to the present invention;

[0049] Figure 2 This is the ferrite metallographic diagram of the stainless steel obtained in Example 3;

[0050] Figure 3 The ferrite metallographic diagram of the stainless steel obtained in Example 1;

[0051] Figure 4 This is the ferrite metallographic diagram of the stainless steel obtained in Example 2. DETAILED DESCRIPTION

[0052] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0053] The invention provides a UNS S32615 high-silicon stainless steel, the chemical components of which include, by mass fraction, C: 0.02-0.03%, Si: 5.6-5.8%, Mn: 1.5-1.8%, P: ≤0.02%, S: ≤0.005%, Cr: 17.0-17.5%, Ni: 20.8-21.8%, Mo: 0.4-0.6%, Cu: 1.6-1.8%, and the balance is Fe and inevitable impurities.

[0054] The design principle of the percentage of the above-mentioned components of the present invention is as follows:

[0055] The upper limit of C content is designed to be 0.02-0.03, which reduces the equilibrium concentration of free oxygen in molten steel during medium frequency smelting;

[0056] The silicon content is designed to be 5.6-5.8, which improves the corrosion resistance of UNS S32615 high silicon steel;

[0057] The Mn content is designed to be 1.5-1.8, which plays a deoxidizing role in medium frequency smelting and can form low-melting-point composite oxides with other oxidation products, which is conducive to the separation of oxides and molten steel. At the same time, Mn is also an austenite-forming element, which can slow down the precipitation of ferrite;

[0058] The P content is designed to be less than 0.02, and the S content is less than 0.005. S and P are harmful elements in steel;

[0059] The Cr content is designed to be: 17.0-17.5, which can improve the corrosion resistance and increase the precipitation of ferrite;

[0060] The Ni content is designed to be 20.8-21.8. Ni is an austenite-forming element that can reduce ferrite precipitation and stabilize the matrix.

[0061] The Mo content is designed to be 0.4-0.6. On the one hand, Mo can improve the corrosion resistance, and at the same time increase the precipitation of ferrite;

[0062] As a preferred solution, the ferrite content in the UNS S32615 high silicon stainless steel is less than 2%.

[0063] Specifically, ferrite F = 3.1373×[Cr]+[Mo]+1.5686*[Nb]+4.7059*[Si]-2.3529*[Ni]-1.1765*[Mn]-25.88-0.5*[Cu]-70.5892*[C]+[N], so according to the above formula, the ferrite F in the present invention is about 1.3%.

[0064] The present invention also provides a medium frequency smelting method for preparing the UNS S32615 high silicon stainless steel, the flow chart of which is as follows: Figure 1 As shown, the following steps are included:

[0065] S1: Ingredients

[0066] The ingredients are prepared according to the composition range of the UNS S32615 high silicon stainless steel;

[0067] S2: Adding and melting

[0068] In the medium frequency furnace, the bottom slag is first added to desulfurize, isolate the molten steel from air, reduce oxidation, and help melt lime; then the materials are added in the following order: iron block, nickel plate, iron plate, and recarburizer, electrolytic manganese and metallic silicon are added during the melting process;

[0069] S3: Melt-clear precipitation deoxidation

[0070] After the molten steel in the intermediate frequency furnace in step S2 is melted, precipitation deoxidation is performed;

[0071] S4: Slag removal and new slag making

[0072] A deoxidizer is added to the molten steel after the treatment in step S3 for deoxidation, and then the slag is removed and pre-molten slag is added for slag making. The pre-molten slag is a mixture of Al2O3 and CaO.

[0073] S5: Alloying and diffusion deoxidation

[0074] Adding metallic chromium, electrolytic Mn and metallic silicon for alloying, while adding diffusion deoxidizer in batches to diffuse deoxidize the molten steel;

[0075] S6: Casting

[0076] The slag amount is adjusted to maintain white slag, and the casting temperature of the molten steel is controlled before casting the molten steel to obtain UNS S32615 high silicon stainless steel.

[0077] As a preferred solution, in step S2, the weight of the bottom ash is 1% of the molten steel, and the composition of the bottom ash is CaO and CaF2 in a mass ratio of 5:5.

[0078] As a preferred solution, in step S3, the precipitation deoxidation is carried out by adding Si-Ca blocks to the molten steel for deoxidation, and the weight of the Si-Ca blocks is 0.1% of the molten steel.

[0079] As a preferred solution, in step S4, the deoxidizer is Si-Ca wire, the mass of the pre-molten slag is 8-12 kg, and the mass ratio of Al2O3 to CaO is 40:60.

[0080] As a preferred solution, in step S5, the diffusion deoxidizer is added in batches 5 times with an interval of 5-7 minutes, and the total diffusion deoxidation time is 30-70 minutes.

[0081] As a preferred solution, in step S5, the diffusion deoxidizer is a mixture of Al-CaO and Si-Ca, and the total mass of the diffusion deoxidizer is 0.1-0.2% of the molten steel.

[0082] As a preferred solution, in step S6, the temperature of casting the molten steel is 1490±10°C.

[0083] In combination with the above technical solution, an embodiment specifically combined with actual data is given below to further expand the content of the invention of the present invention:

[0084] Example 1

[0085] This embodiment provides a UNS S32615 high silicon stainless steel and a medium frequency smelting preparation method thereof, specifically, smelting UNS S32615 high silicon stainless steel by 1 ton of medium frequency, and the preparation method comprises the following steps:

[0086] S1: Ingredients

[0087] Weigh the following raw materials by mass fraction: C: 0.02%, Si: 5.65%, Mn: 1.6%, Cr: 17.3%, Ni: 21.2%, Mo: 0.45%, Cu: 1.9%, and the rest is Fe and unavoidable impurities. Mix the ingredients according to the above composition range.

[0088] S2: Adding and melting

[0089] In the medium frequency furnace, the bottom slag is first added. The mass of the bottom slag is 1% of the weight of the molten steel. The composition is CaO and CaF2 in a ratio of 5:5. The purpose is to desulfurize, isolate the molten steel from contact with air, reduce oxidation, and help melt lime. Then add the following order: iron block, nickel plate and iron plate to the bottom of the furnace. Carbonizer, electrolytic manganese and metallic silicon are added during the melting process to control the carbon content and deoxidize.

[0090] S3: Melt-clear precipitation deoxidation

[0091] After the molten steel is completely melted, add Si-Ca blocks at a rate of 0.1% of the weight of the molten steel for precipitation deoxidation to reduce the oxygen content in the molten steel and improve its purity.

[0092] S4: Slag removal and new slag making

[0093] Si-Ca wire (mass about 1kg) is added for further deoxidation, and slag is removed after deoxidation is completed. 5kg of pre-melted slag is added for slag making, and the pre-melted slag ratio is Al2O3 and CaO mass ratio of 40:60, which is prepared by electric melting method.

[0094] S5: Alloying and diffusion deoxidation

[0095] After the new slag is made, metal chromium, electrolytic manganese and metal silicon are added for alloying, and diffusion deoxidation treatment is carried out at the same time. The diffusion deoxidizer is a mixture of Al-CaO and Si-Ca, which is added in 5 batches, with an interval of 6 minutes between each batch, and a total diffusion deoxidation time of 35 minutes.

[0096] S6: Casting

[0097] After adjusting the slag amount to keep the white slag and adjusting the molten steel casting temperature to 1487℃, the molten steel casting is completed to obtain the UNS S32615 high silicon stainless steel ingot that meets the requirements. The ferrite metallographic diagram is as follows: Figure 3 The non-metallic inclusion content is shown in Table 2:

[0098] Table 2: Non-metallic inclusion content in Example 1

[0099]

[0100] Example 2

[0101] This embodiment provides a UNS S32615 high silicon stainless steel and a medium frequency smelting preparation method thereof, specifically, smelting UNS S32615 high silicon stainless steel by 2 tons of medium frequency, and the preparation method comprises the following steps:

[0102] S1: Ingredients

[0103] Weigh the following raw materials by mass fraction: C: 0.025%, Si: 5.75%, Mn: 1.7%, Cr: 17.4%, Ni: 21.5%, Mo: 0.55%, Cu: 1.7%, and the rest is Fe and unavoidable impurities. Mix the ingredients according to the above composition range.

[0104] S2: Adding and melting

[0105] In the medium frequency furnace, the bottom slag is first added. The mass of the bottom slag is 1% of the weight of the molten steel. The composition is CaO and CaF2 in a ratio of 5:5. The purpose is to desulfurize, isolate the molten steel from contact with air, reduce oxidation, and help melt lime. Then add the following order: iron block, nickel plate and iron plate to the bottom of the furnace. Carbonizer, electrolytic manganese and metallic silicon are added during the melting process to control the carbon content and deoxidize.

[0106] S3: Melt-clear precipitation deoxidation

[0107] After the molten steel is completely melted, add Si-Ca blocks at a rate of 0.1% of the weight of the molten steel for precipitation deoxidation to reduce the oxygen content in the molten steel and improve its purity.

[0108] S4: Slag removal and new slag making

[0109] Si-Ca wire (mass about 2kg) is added for further deoxidation, and slag is removed after deoxidation is completed. 10kg of pre-melted slag is added for slag making, and the pre-melted slag ratio is Al2O3 and CaO mass ratio of 40:60, which is prepared by electric melting method.

[0110] S5: Alloying and diffusion deoxidation

[0111] After the new slag is made, metal chromium, electrolytic manganese and metal silicon are added for alloying, and diffusion deoxidation treatment is carried out at the same time. The diffusion deoxidizer is a mixture of Al-CaO and Si-Ca, which is added in 5 batches, with an interval of 7 minutes between each batch, and a total diffusion deoxidation time of 70 minutes.

[0112] S6: Casting

[0113] After adjusting the slag amount to keep the white slag and adjusting the molten steel casting temperature to 1492℃, the molten steel casting is completed to obtain the UNS S32615 high silicon stainless steel ingot that meets the requirements. The ferrite metallographic diagram is as follows: Figure 4 The non-metallic inclusion content is shown in Table 3 below:

[0114] Table 3: Non-metallic inclusion content in Example 2

[0115]

[0116] Example 3

[0117] This embodiment provides a UNS S32615 high silicon stainless steel and a medium frequency smelting preparation method thereof, specifically, smelting the UNS S32615 high silicon stainless steel by 3 tons of medium frequency, and the preparation method comprises the following steps:

[0118] S1: Ingredients

[0119] Weigh the following raw materials by mass fraction: C 0.03%, Si 5.8%, Mn 1.8%, Cr 17.5%, Ni 21.8%, Mo 0.6%, Cu 1.8%, and the rest is Fe and unavoidable impurities. Mix the ingredients according to the above composition range.

[0120] S2: Adding and melting

[0121] In the medium frequency furnace, the bottom slag is first added. The mass of the bottom slag is 1% of the weight of the molten steel. The composition is CaO and CaF2 in a ratio of 5:5. It is used for desulfurization, isolating the molten steel from contact with air, reducing oxidation, and melting lime. Then add the following order: iron block, nickel plate and iron plate to the bottom of the furnace. Carbonizer, electrolytic manganese and metallic silicon are added during the melting process to control the carbon content and deoxidize.

[0122] S3: Melt-clear precipitation deoxidation

[0123] After the molten steel is completely melted, add Si-Ca blocks at a rate of 0.1% of the weight of the molten steel for precipitation deoxidation to reduce the oxygen content in the molten steel and improve its purity.

[0124] S4: Slag removal and new slag making

[0125] Si-Ca wire (mass about 3kg) is added for further deoxidation, and slag is removed after deoxidation is completed. 15kg of pre-melted slag is added for slag making, and the pre-melted slag ratio is Al2O3 and CaO mass ratio of 40:60, which is prepared by electric melting method.

[0126] S5: Alloying and diffusion deoxidation

[0127] After the new slag is made, metal chromium, electrolytic manganese and metal silicon are added for alloying, and diffusion deoxidation is carried out at the same time. The diffusion deoxidizer is a mixture of Al-CaO and Si-Ca, which is added in 5 batches, with an interval of 7 minutes between each batch. The total diffusion deoxidation time is 70 minutes, and the total mass of diffusion deoxidation is 0.2% of the molten steel.

[0128] S6: Casting

[0129] Adjust the slag amount to keep the white slag, adjust the molten steel casting temperature to 1500℃, complete the casting of the molten steel, and obtain the UNS S32615 high silicon stainless steel ingot that meets the requirements. Its ferrite metallographic diagram is as follows: Figure 2 shown.

[0130] The UNS S32615 high silicon stainless steel ingot prepared in the above Example 3 is compared with the general UNSS32615 stainless steel ingot prepared in the prior art. The comparison of non-metallic inclusion content is shown in Table 4 below:

[0131] Table 4: Comparison of non-metallic inclusion content in Example 3 with that in prior art steel ingots:

[0132]

[0133] In summary, the present invention provides a UNS S32615 high silicon stainless steel and a medium frequency smelting preparation method thereof, which optimizes the composition ratio of high silicon stainless steel and the medium frequency smelting process, reasonably controls the content of alloying elements such as C, Si, Mn, Cr, Ni, Mo, Cu, designs a suitable ferrite content, combines precipitation deoxidation, diffusion deoxidation, slag making and precise control of casting temperature and other steps, significantly reduces the content of non-metallic inclusions in molten steel, inhibits excessive precipitation of ferrite, thereby improving the purity, corrosion resistance and hot working properties of the material. The present invention effectively solves the problems of poor hot working properties of high silicon stainless steel, difficult to control ferrite precipitation and high inclusion content in the prior art, and provides efficient and reliable technical guarantees for the promotion and application of UNS S32615 high silicon stainless steel in chemical equipment and other fields, and has important industrial value and market prospects.

[0134] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0135] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A UNS S32615 high silicon stainless steel, characterized in that: Its chemical composition by mass fraction includes: C: 0.02-0.03%, Si: 5.6-5.8%, Mn: 1.5-1.8%, P: ≤0.02%, S: ≤0.005%, Cr: 17.0-17.5%, Ni: 20.8-21.8%, Mo: 0.4-0.6%, Cu: 1.6-1.8%, and the balance is Fe and unavoidable impurities.

2. The UNS S32615 high silicon stainless steel according to claim 1, characterized in that: The content of ferrite in the UNS S32615 high silicon stainless steel is less than 2%.

3. A medium frequency smelting method for preparing UNS S32615 high silicon stainless steel as claimed in any one of claims 1 to 2, characterized in that: The following steps are involved: S1: Ingredients The ingredients are prepared according to the composition range of the UNS S32615 high silicon stainless steel; S2: Adding and melting In the medium frequency furnace, the bottom slag is first added to desulfurize, isolate the molten steel from air, reduce oxidation, and help melt lime; then the materials are added in the following order: iron block, nickel plate, iron plate, and recarburizer, electrolytic manganese and metallic silicon are added during the melting process; S3: Melt-clear precipitation deoxidation After the molten steel in the intermediate frequency furnace in step S2 is melted, precipitation deoxidation is performed; S4: Slag removal and new slag making Adding a deoxidizer to the molten steel after the treatment in step S3 to deoxidize, then slagging, adding pre-melted slag to slag, wherein the pre-melted slag is a mixture of Al2O3 and CaO; S5: Alloying and diffusion deoxidation Adding metallic chromium, electrolytic Mn and metallic silicon for alloying, while adding diffusion deoxidizer in batches to diffuse deoxidize the molten steel; S6: Casting The slag amount is adjusted to maintain white slag, and the casting temperature of the molten steel is controlled before casting the molten steel to obtain UNS S32615 high silicon stainless steel.

4. The medium frequency smelting method for preparing UNS S32615 high silicon stainless steel according to claim 3 is characterized in that: In step S2, the weight of the bottom ash is 1% of the molten steel, and the composition of the bottom ash is CaO and CaF2 in a mass ratio of 5:

5.

5. The medium frequency smelting method for preparing UNS S32615 high silicon stainless steel according to claim 3 is characterized in that: In step S3, the precipitation deoxidation method is: adding Si-Ca blocks to the molten steel for deoxidation, and the weight of the Si-Ca blocks is 0.1% of the molten steel.

6. The medium frequency smelting method for preparing UNS S32615 high silicon stainless steel according to claim 3 is characterized in that: In the step S4, the deoxidizer is Si-Ca wire, the mass of the pre-molten slag is 8-12 kg, and the mass ratio of Al2O3 to CaO is 40:

60.

7. The medium frequency smelting method for preparing UNS S32615 high silicon stainless steel according to claim 3 is characterized in that: In the step S5, the diffusion deoxidizer is added in batches for 5 times with an interval of 5-7 minutes, and the total diffusion deoxidation time is 30-70 minutes.

8. The medium frequency smelting method for preparing UNS S32615 high silicon stainless steel according to claim 7, characterized in that: In the step S5, the diffusion deoxidizer is a mixture of Al-CaO and Si-Ca, and the total mass of the diffusion deoxidizer is 0.1-0.2% of the molten steel.

9. The medium frequency smelting method for preparing UNS S32615 high silicon stainless steel according to claim 3, characterized in that: In step S6, the temperature of the molten steel casting is 1490±10°C.

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