A method for smelting titanium-containing austenitic stainless steel

Abstract

This invention relates to the field of metallurgical technology, specifically disclosing a method for smelting titanium-containing austenitic stainless steel. Addressing the challenge of removing Ti inclusions due to their high stability, difficulty in flotation, lack of reaction with slag, and continuous precipitation during solidification, this invention significantly reduces the content of Ti-based inclusions and other harmful inclusions in molten steel through stepwise oxygen control and precise slag removal during AOD refining, and deep reduction under high-basicity slag conditions during LF refining. This substantially improves the purity of the molten steel, meeting the stringent quality requirements of high-end fields such as nuclear power and advanced petrochemicals. Furthermore, it enhances the stability of the smelting process, reduces ineffective alloy consumption and production scrap rates, saves overall production costs, and is suitable for large-scale industrial applications, providing a reliable technical solution for the high-quality preparation of titanium-containing austenitic stainless steel.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a method for smelting titanium-containing austenitic stainless steel. Background Technology

[0002] 0Cr18Ni10Ti stainless steel, a typical nickel-chromium-titanium alloyed austenitic stainless steel, is widely used in critical areas such as combustion pipelines in petrochemical equipment, boiler heat exchangers, and nuclear power plant pipelines due to its excellent high-temperature mechanical properties, corrosion resistance, and hot and cold working properties. By adding titanium to form titanium carbide, this steel significantly enhances its resistance to intergranular corrosion and high-temperature stability. It exhibits excellent creep resistance and stress fracture resistance in oxidizing media, and its overall performance surpasses that of similar 304 stainless steel.

[0003] However, titanium, as a highly reactive element, not only readily combines with carbon but also readily reacts with nitrogen and oxygen in steel to form TiN, TiC, or Ti(C,N) composite inclusions. These titanium-containing inclusions possess high hardness and high melting points, making them difficult to completely remove through conventional refining methods once formed during steelmaking. During subsequent solidification, due to the density difference between the inclusions and the molten steel, as well as interfacial energy interactions, they easily aggregate and grow, forming coarse inclusions ranging in size from a few micrometers to tens of micrometers. Furthermore, during subsequent hot working of the smelted steel ingot, the inclusions further deform and elongate along the deformation direction, forming linear or chain-like internal defects. This results in reflected wave defects during non-destructive testing of forged billets or rolled pipes, failing to meet the quality requirements of nuclear power and high-end petrochemical industries.

[0004] Therefore, how to optimize the smelting process and accurately control the quantity, size and distribution of titanium inclusions in 0Cr18Ni10Ti stainless steel has become a key technical requirement for breaking through the bottleneck of high-end stainless steel production and ensuring the product quality and production stability of my country's nuclear power and petrochemical industries. Summary of the Invention

[0005] In view of the problems of excessive titanium inclusions and high defect rate of non-destructive testing after hot working in the existing smelting process of 0Cr18Ni10Ti stainless steel, the present invention provides a smelting method for titanium-containing austenitic stainless steel.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the embodiments of the present invention is as follows:

[0007] This invention provides a method for smelting titanium-containing austenitic stainless steel, including electric furnace smelting, AOD refining, LF refining and casting processes;

[0008] The AOD refining process includes the following steps:

[0009] Slag-forming auxiliary materials are added to the molten steel obtained from electric furnace smelting for slag formation and decarburization. Then, a mixture of O2 and Ar gas is introduced for blowing. When the C mass content in the molten steel is 0.01%~0.03% and the temperature of the molten steel is 1680℃~1750℃, FeSi alloy is added for reduction and some of the reduction slag is removed. Then, the first group of aluminum particles is added. After the reduction is completed, the remaining reduction slag in the furnace is completely removed to obtain primary reduced molten steel.

[0010] Add reducing slag to the primary reduced molten steel, control the basicity R of the reducing slag to be 3~5, and then add a second group of aluminum particles for reduction to obtain secondary reduced molten steel;

[0011] Before the AOD refining process, Ti is added to the secondary reduction molten steel to obtain AOD refined molten steel.

[0012] The LF refining process includes the following steps:

[0013] Argon gas is introduced into the AOD refined steel liquid to stir and break the slag shell. Then aluminum wire is fed in, and then electricity is supplied to raise the temperature. During the heating process, slag-forming auxiliary materials are added, and the slag basicity R is controlled to be 3~5. When the slag turns white and the temperature is ≥1600℃, alloy is added to fine-tune the composition, and then silicon-calcium powder is added for deoxidation. The white slag is maintained for ≥20min.

[0014] Ti inclusions (mainly TiN, TiC, Ti2O3, Ti(C,N) etc.) are more difficult to remove than ordinary deoxidizing inclusions (such as Al2O3, SiO2, MnO etc.). This is mainly because: (1) Ti has a much stronger affinity for O, N, and C than ordinary deoxidizing elements (Al, Si, Mn), resulting in a significantly lower free energy of formation and significantly higher stability than ordinary deoxidizing inclusions; (2) The density difference between TiN, TiC and molten steel is only 1 / 2 that of Al2O3, and the floating speed is only 1 / 4 that of Al2O3 of the same size (because speed is proportional to density difference), further exacerbating the difficulty of floating; (3) The removal of ordinary deoxidizing inclusions largely depends on the reaction and dissolution with slag, while the chemical inertness of Ti inclusions makes them completely impossible to remove by this method. O3 can react with CaO in the slag to form low-melting-point calcium aluminate (such as CaO·Al2O3, melting point 1605℃), which dissolves in the slag; while Ti inclusions (such as TiN, TiC) hardly react with CaO, SiO2 and other components in the slag, and the slag has no absorption capacity for them, so they can only rely on the only way of floating to remove them. As mentioned above, their density is relatively high and it is difficult to float; (4) Ordinary deoxidation inclusions are mainly generated in the deoxidation stage and float for a long time afterward; while Ti inclusions are not only generated during the refining period, but also continue to precipitate during the cooling and solidification of the molten steel (the unreacted Ti in the molten steel will decrease with the temperature and solubility, and precipitate Ti(C,N) at the grain boundary or within the grain). At this time, the molten steel is semi-solid, the viscosity increases sharply, the fluidity becomes worse, and the newly precipitated inclusions are difficult to remove.

[0015] Compared to existing technologies, the smelting method for titanium-containing austenitic stainless steel provided by this invention involves first adding FeSi alloy for pre-deoxidation, removing part of the slag, and then adding the first group of aluminum particles for reduction. This avoids Al preferentially reacting with the large amounts of FeO, MnO, and SiO2 in the slag, allowing Al to directly act on the dissolved oxygen in the molten steel and rapidly reduce the oxygen content. Secondly, the Al2O3 generated by Al deoxidation reacts with CaO and SiO2 in the residual slag to form a low-melting-point CaO-Al2O3-SiO2 ternary slag phase, significantly improving the slag fluidity. Simultaneously, the aluminum reduction process deeply reduces the Cr element in the slag (reducing the Cr2O3 content in the slag), and the heat released by the aluminum-oxygen reaction further enhances the fluidity of the steel slag. This dual effect creates favorable conditions for thorough slag removal after the first reduction, significantly reducing the slag residue rate and preventing oxidizing substances such as FeO and MnO in the residual slag from entering the secondary reduction stage with the molten steel. This creates a clean environment with low oxygen and low slag volume for subsequent high-basicity slag-under-slag secondary reduction and titanium alloying. Furthermore, if the Cr2O3 content in the slag is too high, Cr 3+It will change the surface tension of the molten steel, hindering the diffusion of N into the bubbles and affecting the denitrification effect; while the reduction of Cr2O3 in the slag by aluminum reduction can alleviate this problem, indirectly promote the removal of N from the molten steel, and reduce the risk of TiN inclusion formation during subsequent titanium alloying.

[0016] The second group of aluminum particles is added under the protection of high-basicity (R=3~5) reducing slag, which can deeply remove dissolved oxygen from the molten steel. The reduction of O content can weaken its promoting effect on N dissolution. At the same time, the high-basicity slag can adsorb non-metallic inclusions in the molten steel, avoid nitrogen adsorption on the surface of the inclusions and re-dissolution, create a low-oxygen environment for subsequent titanium alloying, and avoid the formation of coarse TiO2 or Ti(C,O) inclusions due to excessive oxidation of titanium.

[0017] In the LF refining process, the slag basicity R (CaO / SiO2) is controlled at 3-5 by adding slag-forming additives. In a high-basicity slag system, the activity of CaO is significantly increased. High-activity CaO can react efficiently with sulfur in the molten steel, making the desulfurization reaction more thorough. Low sulfur content can prevent the formation of low-melting-point harmful phases such as FeS and TiS in the steel, preventing hot brittleness defects during hot working. In titanium-containing austenitic stainless steel, Ti easily reacts with SiO2 in the slag to form high-melting-point TiSiO4 inclusions. When the slag basicity R = 3-5, excess CaO will preferentially combine with SiO2 to form a low-melting-point CaO-SiO2 slag phase, occupying SiO2 reaction sites and reducing its contact reaction with Ti from the source. At the same time, high-basicity slag can adsorb fine TiN and TiC inclusions already formed in the molten steel, preventing their aggregation and growth, and reducing the inclusion content in the molten steel.

[0018] Furthermore, the C content of the molten steel obtained from the electric furnace smelting is 1.5%~2.0% and the Si content is ≤0.5%.

[0019] Specifically, the tapping temperature after electric furnace smelting is ≥1650℃.

[0020] Furthermore, in the AOD refining process, the blowing process specifically includes the following steps:

[0021] A mixture of O2 and Ar was introduced into the molten steel in the following order: O2 to Ar volume ratios of (4~6):1, (2~4):1, (0.5~1.5):1, 1:(2~4), and 1:(4~6). The blowing time for each stage was 8 to 15 minutes. The total flow rate of O2 and Ar was 800 Nm³. 3 / h~1200Nm 3 / h.

[0022] It should be noted that initially, a mixed gas with a volume ratio of O2 to Ar of (4~6):1 was used for blowing. When the temperature of the molten steel was raised to 1700℃~1720℃, the oxygen-argon ratio was adjusted.

[0023] The preferred staged blowing method can control the C content in the molten steel at 0.01%~0.03%, reducing the content of TiC inclusions generated by the subsequent addition of Ti elements. At the same time, the use of high-flow-rate stirring can also promote the homogenization of the composition and temperature of the molten steel, help the early inclusions to collide, grow and float, and reduce the N and H content in the molten steel by high argon ratio degassing in the later stage, thereby reducing the precipitation of Ti inclusions during solidification.

[0024] Furthermore, in the AOD refining process, the reduction time after adding FeSi alloy is 5 min to 10 min.

[0025] Furthermore, in the AOD refining process, after adding FeSi alloy, 50% to 60% of the reducing slag is removed.

[0026] The slag after FeSi pre-reduction is viscous due to its high SiO2 content and abundant FeO residue. Direct, thorough slag removal can cause it to adhere to the furnace wall or entrain molten steel, resulting in incomplete removal. Furthermore, the large amount of SiO2 in the FeSi pre-reduction slag means that if aluminum particles are added directly without slag removal, Al will preferentially react with the abundant SiO2 in the slag to form Al2O3-SiO2 composite inclusions. If these inclusions remain in the molten steel, they are not only difficult to remove through subsequent processes but can also scratch the surface of the billet during hot working, leading to cracking defects. Removing most of the slag significantly reduces the total amount of SiO2 in the slag. After adding aluminum particles, they preferentially react directly with dissolved oxygen in the molten steel. The Al2O3 generated from this reaction reacts with a small amount of residual CaO and SiO2 in the slag to form a low-melting-point CaO-Al2O3-SiO2 ternary slag phase. This significantly improves the slag's fluidity, facilitating thorough slag removal, significantly reducing slag residue, and consequently significantly reducing the content of harmful inclusions in the steel.

[0027] Furthermore, in the AOD refining process, the reduction time after adding the first group of aluminum granules is 5 min to 10 min.

[0028] The optimal reduction time allows Al to fully react with dissolved oxygen in the molten steel. At the same time, it also allows the Al2O3 generated from the reaction of the first group of aluminum particles to react with the CaO in the small amount of residual slag to form low-melting-point calcium aluminate.

[0029] Furthermore, in the AOD refining process, FeSi alloy is added according to the control of Si mass content in molten steel at 0.3%~0.4%; the amount of the first group of aluminum particles added is 1.5kg / t~2.5kg / t.

[0030] It should be noted that in the AOD refining process, Ar is introduced to protect the surface of the molten steel after the slag is thoroughly removed.

[0031] Furthermore, in the AOD refining process, the reducing slag includes quicklime and fluorite, and the amount of reducing slag added is 50 kg / t to 65 kg / t.

[0032] Specifically, the amount of quicklime added is 35 kg / t to 40 kg / t, and the amount of fluorite added is 15 kg / t to 25 kg / t.

[0033] Furthermore, in the AOD refining process, the amount of the second group of aluminum granules added is 1.5 kg / t to 2.0 kg / t.

[0034] Furthermore, in the AOD refining process, the reduction time after adding the second group of aluminum granules is 7 min to 10 min.

[0035] The optimal amount of aluminum granules added and the optimal reduction time can effectively remove the trace dissolved oxygen remaining after the first reduction. Furthermore, the high alkalinity slag (R=3~5) has a strong adsorption capacity for Al2O3, and the optimal reduction time allows the fine Al2O3 particles to collide, grow, and float to the surface, where they are ultimately adsorbed by the slag.

[0036] Furthermore, in the AOD refining process, after adding the Ti, the steel is tapped after maintaining the process for 3 to 6 minutes.

[0037] Specifically, Ti is added to make the Ti content in the molten steel 0.42% to 0.52% by mass.

[0038] The difference between this invention and existing processes lies in the addition of Ti before tapping from the AOD furnace, rather than during the LF refining stage as in existing processes. In this invention, after smelting in the AOD furnace, the steel and slag are directly mixed, and then the molten steel and slag are transferred together into the refining ladle of the ladle refining furnace (LF).

[0039] The advantages of this design are twofold: Firstly, the steel-slag mixing operation significantly increases the contact area between the molten steel and the slag. Especially during the process of transferring the molten steel from the AOD furnace to the LF refining ladle, the slag can more fully adsorb inclusions generated by the addition of Ti (such as TiN, Ti(C,O) etc.), greatly reducing the initial residual amount of Ti-based inclusions in the molten steel. Secondly, the pre-addition of metallic titanium allows sufficient time for subsequent LF refining, enabling the original inclusions in the metallic titanium raw material to float to the slag sufficiently, and also allowing the newly generated Ti-based inclusions in the molten steel during LF refining to fully react with the slag and be adsorbed, ultimately achieving further deep purification of the molten steel and providing a foundation of higher purity molten steel for subsequent casting processes.

[0040] It should be noted that argon gas is used to protect the surface of the molten steel during the tapping process of AOD-refined molten steel.

[0041] Specifically, in the LF refining process, argon gas is introduced into the AOD refined molten steel and stirred for 5 to 8 minutes, with an argon gas flow rate of 20 L / min to 30 minutes.

[0042] Furthermore, in the LF refining process, the aluminum wire is added according to the control of the Al mass content in the molten steel being 0.08%~0.15%.

[0043] Furthermore, in the LF refining process, the slag-forming auxiliary materials include lime and fluorite.

[0044] Furthermore, in the LF refining process, the amount of silicon-calcium powder added is 0.15 kg / t to 0.25 kg / t.

[0045] Furthermore, the tapping temperature of the LF refining process is 1560℃~1580℃.

[0046] Specifically, the composition of the molten steel after LF refining meets the following requirements: C 0.04%~0.05%, Mn 1.00%~1.50%, Si 0.30%~0.50%, S≤0.002%, P≤0.03%, Cr 18.00%~18.50%, Ti 0.40%~0.52%, Ni 10.00%~12.00%, Al 0.08%~0.15%, N≤0.02%, O≤25ppm, with the balance being Fe and unavoidable impurities.

[0047] Furthermore, the casting process specifically includes the following steps:

[0048] During the casting process, when the volume of molten steel entering the riser accounts for 1 / 3 to 1 / 2 of the total volume of the riser, the molten steel is subjected to flow reduction and feeding; when the volume of molten steel entering the riser accounts for 2 / 3 to 3 / 4 of the total volume of the riser, an exothermic agent is added into the riser. After casting is completed, carbonized rice husks are added, cooled, and demolded to obtain the ingot.

[0049] When the volume of molten steel entering the riser accounts for 1 / 3 to 1 / 2 of the total volume of the riser, the flow reduction and feeding of the molten steel can ensure that there is sufficient molten steel in the riser and no slag entrainment. By adding a heating agent to prolong the solidification time, the tiny Ti inclusions in the molten steel are promoted to float to the loose head area, reducing their residue inside the ingot. After pouring, carbonized rice husks are added to control the cooling process, avoid cracks and coarse inclusions, and ensure the stability of the ingot performance.

[0050] Furthermore, in the casting process, the amount of the heating agent added is 1.0 kg / t to 2.0 kg / t.

[0051] Specifically, the heating agent is an aluminum heating agent.

[0052] Furthermore, in the casting process, the time for reducing flow and compensating for shrinkage is 1.0 to 1.5 times the casting time of the main body.

[0053] Furthermore, in the casting process, the cooling includes mold cooling and air cooling, the mold cooling time is ≥1.5h, and air cooling follows the mold cooling.

[0054] Furthermore, the mass percentage of the chemical composition of the titanium-containing austenitic stainless steel is as follows: C≤0.08%, Mn≤2.0%, Si≤1.0%, S≤0.030%, P≤0.035%, Cr 17.0%~19.0%, Ti 5[C]~0.7%, Ni 10.0%~12.0%, with the balance being Fe and unavoidable impurities.

[0055] It should be noted that the [C] mentioned above refers to the C content in titanium-containing austenitic stainless steel, and the Ti content is 5 times to 0.7% of the C mass content.

[0056] To address the challenges of removing Ti inclusions due to their high stability, difficulty in flotation, lack of reaction with slag, and continuous precipitation during solidification, this invention employs a series of processes, including stepwise oxygen control and precise slag removal during AOD refining, and deep reduction under high-basicity slag conditions during LF refining. These processes significantly reduce the content of Ti-based inclusions and other harmful inclusions in molten steel, substantially improving its purity and meeting the stringent quality requirements of high-end fields such as nuclear power and advanced petrochemicals. Furthermore, this invention enhances the stability of the smelting process, reduces ineffective alloy consumption and production scrap rates, and saves overall production costs. It is suitable for large-scale industrial applications and provides a reliable technical solution for the high-quality preparation of titanium-containing austenitic stainless steel. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0058] To better illustrate the present invention, further examples are provided below.

[0059] Example 1

[0060] This invention provides a method for smelting 0Cr18Ni10Ti stainless steel:

[0061] S1, add scrap steel and metal raw materials in proportion, control the electric arc furnace temperature at 1650℃, until all raw materials in the furnace are turned into molten steel, take samples to analyze all elements, control the C mass content in the molten steel to be 1.8% and the Si mass content to be 0.4%, and tap the steel;

[0062] S2. Molten steel is added to an AOD furnace, along with quicklime and fluorite in a 2:1 mass ratio, totaling 50 kg / t. Slag is formed over 6 minutes. Then, a mixture of oxygen and argon is introduced in stages for blowing. Ferrochrome and ferronickel alloys are added according to the composition during the blowing process. The order of introduction, based on the volume ratio of oxygen to argon, is: 5:1 → 3:1 → 1:1 → 1:3 → 1:5. Each stage lasts 12 minutes, and the total flow rate of O2 and Ar is 1000 Nm³. 3 / h, according to the oxygen and argon volume ratio of 5:1, when the molten steel is heated to 1710℃, the oxygen-argon ratio is adjusted. Take a sample, and when the C mass content in the molten steel is 0.01% and the temperature is 1720℃, add FeSi alloy, control the Si mass content in the molten steel to be 0.32%, reduce for 7 minutes, remove 55% of the reduction slag in the furnace, then add 2.0 kg / t steel of aluminum granules, reduce for 8 minutes, and completely remove the reduction slag in the furnace. During the slag removal process, argon gas is used to protect the surface of the molten steel.

[0063] S3, add 38 kg / t quicklime and 20 kg / t fluorite to the molten steel, control the basicity of the reducing slag (R=CaO / SiO2) to 4, add 1.8 kg / t aluminum particles, reduce for 8 min, add metallic titanium according to the Ti content of 0.45% in the molten steel, maintain for 5 min after addition, tap the steel, and protect the surface of the molten steel with argon gas during the tapping process.

[0064] After S4 and LF refining is completed, argon gas is turned on and stirred with a large amount of argon gas for 6 minutes to break the slag shell. The argon gas flow rate is 25L / min. Then, aluminum wire is fed into the molten steel according to the control of Al mass content of 0.12%. Power is turned on to raise the temperature. During the heating process, lime and fluorite are added to the furnace to form slag. The slag basicity (R=CaO / SiO2) is controlled at 4. When the slag turns white and the temperature reaches 1616℃, the power is turned off and samples are taken. The alloy content is finely adjusted according to the analysis results. Then, 0.20kg / t of silicon-calcium powder is added for deoxidation. The white slag is maintained for 22 minutes.

[0065] The molten steel composition meets the following requirements: C 0.043%, Mn 1.25%, Si 0.42%, S 0.0015%, P 0.02%, Cr 18.30%, Ti 0.41%, Ni 11.20%, Al 0.12%, N 0.014%, O 2ppm, with the balance being Fe and unavoidable impurities; soft blowing with argon is performed at a flow rate of 3L / min, ensuring that the molten steel is slightly agitated without being exposed, and the soft blowing time is 20min;

[0066] After the soft blowing process ends, the steel is unloaded from the ladle at a temperature of 1570℃.

[0067] S5, using risers for casting steel ingots. During the casting process, when the volume of molten steel entering the riser accounts for 1 / 2 of the total volume of the riser, the molten steel is subjected to flow reduction and feeding. When the volume of molten steel entering the riser accounts for 2 / 3 of the total volume of the riser, aluminum-based exothermic agent is added into the riser. After casting, 2.0 kg / t of carbonized rice husk is added. The overall feeding time is 1.2 times the casting time of the main body, the mold cooling time is 2.5 hours, and then the ingot is demolded and air-cooled to obtain the casting.

[0068] Example 2

[0069] This invention provides a method for smelting 0Cr18Ni10Ti stainless steel:

[0070] S1, add scrap steel and metal raw materials in proportion, control the electric arc furnace temperature at 1650℃, until all raw materials in the furnace are turned into molten steel, take samples to analyze all elements, control the C mass content in the molten steel to be 1.5% and the Si mass content to be 0.4%, and tap the steel;

[0071] S2. Molten steel is added to the AOD furnace, along with quicklime and fluorite in a 2:1 mass ratio, totaling 50 kg / t. Slagging is initiated over 6 minutes. Then, a mixture of oxygen and argon is introduced in stages for blowing. Ferrochrome and ferronickel alloys are added according to the composition during the blowing process. The order of introduction, based on the volume ratio of oxygen to argon, is: 4:1 → 2:1 → 0.5:1 → 1:4 → 1:6, with each stage lasting 8 minutes. The total flow rate of O2 and Ar is 1200 Nm³. 3 / h, according to the oxygen and argon volume ratio of 4:1, when the molten steel is heated to 1720℃, the oxygen-argon ratio is adjusted. Take a sample, and when the C mass content in the molten steel is 0.03% and the temperature is 1680℃, add FeSi alloy, control the Si mass content in the molten steel to be 0.4%, reduce for 5 minutes, remove 50% of the reduction slag in the furnace, then add 2.5kg / t steel aluminum granules, reduce for 5 minutes, and completely remove the reduction slag in the furnace. During the slag removal process, argon gas is used to protect the surface of the molten steel.

[0072] S3, add 35 kg / t quicklime and 25 kg / t fluorite to the molten steel, control the basicity of the reducing slag (R=CaO / SiO2) to 5, add 1.5 kg / t aluminum particles, reduce for 10 min, add metallic titanium according to the Ti content of 0.42% in the molten steel, keep for 3 min after addition, tap the steel, and protect the surface of the molten steel with argon gas during the tapping process.

[0073] After S4 and LF refining is completed, argon gas is turned on and stirred with a large amount of argon gas for 5 minutes to break the slag shell. The argon gas flow rate is 30L / min. Then, aluminum wire is fed into the molten steel according to the control of Al mass content of 0.15%. Power is turned on to raise the temperature. During the heating process, lime and fluorite are added to the furnace to form slag. The slag basicity (R=CaO / SiO2) is controlled at 3. When the slag turns white and the temperature reaches 1615℃, the power is turned off and samples are taken. The alloy content is finely adjusted according to the analysis results. Then, 0.25kg / t of silicon-calcium powder is added for deoxidation. The white slag is maintained for 20 minutes.

[0074] The molten steel composition meets the following requirements: C 0.04%, Mn 1.00%, Si 0.30%, S 0.0018%, P 0.025%, Cr 18.00%, Ti 0.40%, Ni 10.00%, Al 0.15%, N 0.02%, O 25ppm, with the balance being Fe and unavoidable impurities; soft blowing with argon is performed at a flow rate of 4L / min, ensuring that the molten steel is slightly agitated without being exposed, and the soft blowing time is 25min;

[0075] After the soft blowing process ends, the steel is unloaded from the ladle at a temperature of 1580℃.

[0076] S5, using risers for casting steel ingots. During the casting process, when the volume of molten steel entering the riser accounts for 1 / 3 of the total volume of the riser, the molten steel is subjected to flow reduction and feeding. When the volume of molten steel entering the riser accounts for 2 / 3 of the total volume of the riser, aluminum-based exothermic agent is added into the riser. After casting, 1.5 kg / t of carbonized rice husk is added. The overall feeding time is 1.5 times the casting time of the main body. The mold cooling time is 2.0 h. After that, the ingot is demolded and air-cooled to obtain the casting.

[0077] Example 3

[0078] This invention provides a method for smelting 0Cr18Ni10Ti stainless steel:

[0079] S1, add scrap steel and metal raw materials in proportion, control the electric arc furnace temperature at 1650℃, until all raw materials in the furnace are turned into molten steel, take samples to analyze all elements, control the C mass content in the molten steel to be 2.0% and the Si mass content to be 0.5%, and tap the steel;

[0080] S2. Molten steel is added to an AOD furnace, along with quicklime and fluorite in a 2:1 mass ratio, totaling 50 kg / t. Slagging is initiated over 6 minutes. Then, a mixture of oxygen and argon is introduced in stages for blowing. Ferrochrome and ferronickel alloys are added according to the composition during the blowing process. The order of introduction, based on the oxygen to argon volume ratio, is: 6:1 → 4:1 → 1.5:1 → 1:2 → 1:4. Each stage lasts 15 minutes, and the total flow rate of O2 and Ar is 800 Nm³. 3 / h, according to the oxygen and argon volume ratio of 6:1, when the molten steel is heated to 1700℃, the oxygen-argon ratio is adjusted. Take a sample, and when the C mass content in the molten steel is 0.02% and the temperature is 1750℃, add FeSi alloy, control the Si mass content in the molten steel to be 0.3%, reduce for 10 minutes, remove 60% of the reduction slag in the furnace, then add 1.5kg / t steel aluminum granules, reduce for 10 minutes, and completely remove the reduction slag in the furnace. During the slag removal process, argon gas is used to protect the surface of the molten steel.

[0081] S3, add 40 kg / t quicklime and 15 kg / t fluorite to the molten steel, control the basicity of the reducing slag (R=CaO / SiO2) to 3, add 2.0 kg / t aluminum particles, reduce for 7 min, add metallic titanium according to the Ti content of 0.52% in the molten steel, maintain for 6 min after addition, tap the steel, and protect the surface of the molten steel with argon gas during the tapping process;

[0082] After S4 and LF refining is completed, argon gas is turned on and stirred with a large amount of argon gas for 8 minutes to break the slag shell. The argon gas flow rate is 20L / min. Then, aluminum wire is fed into the molten steel according to the control of Al mass content of 0.08%. Power is turned on to raise the temperature. During the heating process, lime and fluorite are added to the furnace to form slag. The slag basicity (R=CaO / SiO2) is controlled at 5. When the slag turns white and the temperature reaches 1612℃, the power is turned off and samples are taken. The alloy content is finely adjusted according to the analysis results. Then, 0.15kg / t of silicon-calcium powder is added for deoxidation. The white slag is maintained for 20 minutes.

[0083] The molten steel composition meets the following requirements: C 0.05%, Mn 1.50%, Si 0.50%, S 0.002%, P 0.03%, Cr 18.50%, Ti 0.48%, Ni 12.00%, Al 0.08%, N 0.016%, O 21ppm, with the balance being Fe and unavoidable impurities; soft blowing with argon is performed at a flow rate of 2L / min, ensuring that the molten steel is slightly agitated without being exposed, and the soft blowing time is 20min;

[0084] After the soft blowing process ends, the steel is unloaded from the ladle at a temperature of 1560℃.

[0085] S5, using risers for casting steel ingots. During the casting process, when the volume of molten steel entering the riser accounts for 1 / 2 of the total volume of the riser, the molten steel is subjected to flow reduction and feeding. When the volume of molten steel entering the riser accounts for 3 / 4 of the total volume of the riser, aluminum-based exothermic agent is added into the riser. After casting, 3.0 kg / t of carbonized rice husk is added. The overall feeding time is 1.0 times the casting time of the main body. The mold cooling time is 1.5 hours. After that, the ingot is demolded and air-cooled to obtain the casting.

[0086] Comparative Example 1

[0087] This comparative example provides a smelting method for 0Cr18Ni10Ti stainless steel. The only difference from Example 1 is that the basicity of the slag in the AOD refining process S3 and the LF refining process S4 is changed to R(CaO / SiO2) = 1.5. The rest are exactly the same and will not be described again here.

[0088] Comparative Example 2

[0089] This comparative example provides a smelting method for 0Cr18Ni10Ti stainless steel. The only difference from Example 1 is that the basicity of the slag in the LF refining process S4 is changed to R(CaO / SiO2) = 1.5. The rest are exactly the same and will not be described again here.

[0090] Comparative Example 3

[0091] This comparative example provides a smelting method for 0Cr18Ni10Ti stainless steel. The only difference from Example 1 is that in the AOD refining process, FeSi is added for reduction and then all the slag is directly removed, and Al is not added for reduction. The specific steps are as follows:

[0092] S1, same as in Example 1;

[0093] S2. Molten steel is added to an AOD furnace, along with quicklime and fluorite in a 2:1 mass ratio, totaling 50 kg / t. Slag is formed over 6 minutes. Then, a mixture of oxygen and argon is introduced in stages for blowing. Ferrochrome and ferronickel alloys are added according to the composition during the blowing process. The order of introduction, based on the volume ratio of oxygen to argon, is: 5:1 → 3:1 → 1:1 → 1:3 → 1:5. Each stage lasts 12 minutes, and the total flow rate of O2 and Ar is 1000 Nm³. 3 / h, according to the oxygen and argon volume ratio of 5:1, when the molten steel is heated to 1710℃, the oxygen-argon ratio is adjusted. Take a sample, and when the C mass content in the molten steel is 0.01% and the temperature is 1720℃, add FeSi alloy, control the Si mass content in the molten steel to be 0.32%, reduce for 7 minutes, and then completely remove the reduction slag in the furnace. During the slag removal process, argon gas is used to protect the surface of the molten steel.

[0094] S3~S5 are the same as in Example 1.

[0095] Comparative Example 4

[0096] This comparative example provides a smelting method for 0Cr18Ni10Ti stainless steel. The only difference from Example 1 is that the titanium metal is added before tapping from the AOD refining furnace instead of before tapping from the LF furnace. 0.25 kg / t of silicon-calcium powder is added for deoxidation. After the white slag is maintained for 20 minutes, the titanium metal is added, followed by soft blowing. After the soft blowing is completed, the steel is tapped from the ladle. The rest is exactly the same and will not be described in detail here.

[0097] The ingots produced in Examples 1 to 3 and Comparative Examples 1 to 4 were rolled and heat-treated using conventional processes for 0Cr18Ni10Ti stainless steel in the prior art. The inclusion grade, impact performance and other tests were then performed, and the results are shown in Table 1.

[0098] In the rolling process, the initial rolling temperature is controlled at 1050℃, the final rolling temperature at 850℃, the heat treatment temperature at 1020℃, and water cooling is performed after the heat treatment is completed.

[0099] Table 1

[0100]

[0101] As shown in the table above, the inclusion levels of the ingots produced in Examples 1 to 3 are significantly better than those in Comparative Examples 1 to 4. This demonstrates that the control of high-basicity slag in AOD refining and LF refining in the embodiments of the present invention, as well as the timing of partial slag removal and addition of metallic titanium after FeSi total reduction, play an important role in controlling the inclusion content in 0Cr18Ni10Ti stainless steel. The above data fully verify the core value of the above process combination of the present invention in improving the inclusion quality of 0Cr18Ni10Ti stainless steel and thus enhancing the comprehensive performance of the material. It also provides key quality assurance for the application of this steel in harsh working conditions such as nuclear power and high-end chemical industry.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of smelting a titanium-containing austenitic stainless steel, characterized in that, The electric furnace smelting, the AOD refining, the LF refining and the casting process are included; The AOD refining process comprises the following steps: The slagging auxiliary material is added to the molten steel obtained by the electric furnace smelting to perform slagging and decarburization, and then the mixed gas of O2 and Ar is introduced to perform blowing, when the mass content of C in the molten steel is 0.01%~0.03% and the temperature of the molten steel is 1680℃~1750℃, the FeSi alloy is added to reduce, then the reduction slag of 50%~60% of the total amount of the reduction slag is removed, then the first group of aluminum particles is added, and the remaining reduction slag in the furnace is completely removed after the reduction is completed, thereby obtaining the primary reduction molten steel; The reduction slag material is added to the primary reduction molten steel, the basicity R of the reduction slag is controlled to be 3~5, then the second group of aluminum particles is added to reduce, thereby obtaining the secondary reduction molten steel; The Ti is added to the secondary reduction molten steel before the AOD refining is completed, thereby obtaining the AOD refining molten steel; The LF refining process comprises the following steps: After the argon is introduced into the AOD refining molten steel to break the slag shell, the aluminum wire is fed, then the power is supplied to heat, the slagging auxiliary material is added during the heating process, the basicity R of the slag is controlled to be 3~5, when the slag is white and the temperature is greater than or equal to 1600℃, the alloy is added to fine tune the composition, then the silicon calcium powder is added to perform deoxidation, and the white slag is kept for greater than or equal to 20 minutes.

2. The smelting method of the titanium-containing austenitic stainless steel according to claim 1, characterized by, The mass content of C in the molten steel obtained by the electric furnace smelting is 1.5%~2.0%, and the mass content of Si is less than or equal to 0.5%.

3. The method of smelting a titanium-containing austenitic stainless steel according to claim 1, characterized in that, In the AOD refining process, the blowing specifically comprises the following steps: The mixed gas of O2 and Ar is sequentially introduced into the molten steel in the order of the volume ratio of O2 to Ar being (4-6):1, (2-4):1, (0.5-1.5):1, 1:(2-4), 1:(4-6), and the blowing time of each stage is 8-15 minutes; the total flow of O2 and Ar is 800 Nm 3 / h~1200 Nm 3 / h.

4. The method of smelting a titanium-containing austenitic stainless steel according to claim 1, characterized in that, In the AOD refining process, the reduction time after the FeSi alloy is added is 5min~10min.

5. The method of smelting a titanium-containing austenitic stainless steel according to claim 1, characterized in that, In the AOD refining process, the reduction time after the first group of aluminum particles is added is 5min~10min; and / or In the AOD refining process, the FeSi alloy is added according to the control of the mass content of Si in the molten steel being 0.3%~0.4%; and the addition amount of the first group of aluminum particles is 1.5kg / t~2.5kg / t.

6. The method of smelting a titanium-containing austenitic stainless steel according to claim 1, characterized in that, In the AOD refining process, the reduction slag material comprises lime and fluorite, and the addition amount of the reduction slag material is 50kg / t~65kg / t; and / or In the AOD refining process, the addition amount of the second group of aluminum particles is 1.5kg / t~2.0kg / t; and / or In the AOD refining process, the reduction time after the second group of aluminum particles is added is 7min~10min; and / or In the AOD refining process, after the Ti is added, the molten steel is kept for 3min~6min to be discharged.

7. The method of smelting a titanium-containing austenitic stainless steel according to claim 1, characterized in that, In the LF refining process, the aluminum wire is added according to the control of the mass content of Al in the molten steel being 0.08%~0.15%; And / or In the LF refining process, the addition amount of the silicon calcium powder is 0.15kg / t~0.25kg / t; and / or The tapping temperature of the LF refining process is 1560℃~1580℃.

8. The method of smelting a titanium-containing austenitic stainless steel according to claim 1, characterized in that, The casting process specifically comprises the following steps: During the casting process, when the volume of the molten steel entering the riser accounts for 1 / 3~1 / 2 of the total volume of the riser, the molten steel is subjected to flow reduction and feeding; when the volume of the molten steel entering the riser accounts for 2 / 3~3 / 4 of the total volume of the riser, the heating agent is added into the riser, after the casting is completed, the carbonized rice husk is added, cooled, demolded, thereby obtaining the cast ingot.

9. The method of smelting a titanium-containing austenitic stainless steel according to claim 8, characterized in that, In the pouring process, the adding amount of the heat agent is 1.0 kg / t~2.0 kg / t; and / or In the pouring process, the time of the flow reduction feeding is 1.0~1.5 times of the pouring body time.

10. The method of smelting a titanium-containing austenitic stainless steel according to claim 1, characterized in that, The chemical composition of the titanium-containing austenitic stainless steel contains, by mass percent, C≤0.08%, Mn≤2.0%, Si≤1.0%, S≤0.030%, P≤0.035%, Cr 17.0%~19.0%, Ti 5[C]~0.7%, Ni 10.0%~12.0%, and the balance of Fe and inevitable impurities.

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