Titanium-containing austenitic stainless steel and preparation method thereof

Abstract

The invention discloses titanium-containing austenitic stainless steel and a preparation method thereof. The titanium-containing austenitic stainless steel is prepared from the following elements by taking the total mass of the titanium-containing austenitic stainless steel as 100 percent: 0.02 to 0.07 percent of C, 0.2 to 1.0 percent of Si, 1.0 to 2.0 percent of Mn, less than or equal to 0.035 percent of P, less than or equal to 0.005 percent of S, 16.0 to 22.0 percent of Cr, 10.0 to 14.0 percent of Ni, 2.0 to 3.0 percent of Mo, 0.15 to 0.40 percent of Ti, 0.01 to 0.05 percent of Al, 0.005 to 0.016 percent of N, 0.0005 to 0.0030 percent of Ca and the balance of Fe and inevitable impurity elements. The titanium-containing austenitic stainless steel has high strength, corrosion resistance and productivity.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel, and in particular relates to titanium-containing austenitic stainless steel and a preparation method thereof. Background Art

[0002] Common austenitic stainless steels such as 304 and 316 will become sensitized when they are heat treated in the sensitization temperature range or undergo welding heat cycles. That is, chromium carbides will precipitate on the grain boundaries, resulting in a decrease in the chromium content near the grain boundaries, which is called "chromium depletion". The chromium-depleted areas near the grain boundaries are more susceptible to corrosion due to the reduction of the corrosion-resistant element chromium, which is called "intergranular corrosion".

[0003] In order to prevent the occurrence of intergranular corrosion, the most common method is to reduce the carbon content in stainless steel, such as 304L and 316L, so as to reduce the precipitation of chromium carbides, avoid the occurrence of chromium deficiency, and thus prevent the occurrence of intergranular corrosion. However, it is well known that carbon is an effective solid solution strengthening element, so the result of low carbon is the reduction of stainless steel strength.

[0004] However, stainless steel used in certain applications, such as stainless steel for pressure vessels, needs to maintain high strength. Therefore, titanium-stabilized austenitic stainless steel that guarantees high strength and prevents intergranular corrosion is also active in commercial products, such as 321 and 316Ti. However, it is very difficult to control the inclusions of this type of steel, resulting in poor corrosion resistance, and it is very easy to cause nozzle nodules due to poor inclusion control during steelmaking and continuous casting. Prior art research shows that the main reason for the generation of inclusions is high Ti content. In practice, in order to ensure corrosion resistance and castability of molten steel, the carbon content is generally reduced, and the titanium content can be reduced according to the Ti / C requirements. However, the reduction in carbon and strength caused by such operation goes against the original intention of titanium-stabilized steel. Therefore, while maintaining high carbon and titanium content, effectively controlling inclusions and thereby ensuring the strength, corrosion resistance and productivity of stainless steel has become an urgent problem to be solved in this field. Summary of the invention

[0005] In order to solve at least one of the above technical problems, the object of the present invention is to provide a titanium-containing austenitic stainless steel and a preparation method thereof. The present invention can effectively control inclusions while maintaining high carbon and titanium content, so that the titanium-containing austenitic stainless steel has both high corrosion resistance and productivity.

[0006] To achieve the above object, the first aspect of the present invention provides a titanium-containing austenitic stainless steel, which is composed of the following elements, based on the total mass of the titanium-containing austenitic stainless steel being 100%: C 0.02-0.07%, Si 0.2-1.0%, Mn 1.0-2.0%, P≤0.035%, S≤0.005%, Cr 16.0-22.0%, Ni 10.0-14.0%, Mo 2.0-3.0%, Ti 0.15-0.40%, Al 0.01-0.05%, N 0.005-0.016%, Ca 0.0005-0.0030%, and the balance being Fe and unavoidable impurity elements;

[0007] The element contents in the titanium-containing austenitic stainless steel satisfy the following formulas (1) and (2):

[0008] log10(Ti)+log10(N)-0.07Ti-0.045Cr+3.28≤0 Formula (1);

[0009] Ti / (C+N)≥5.0 Formula (2);

[0010] Furthermore, the number of TiN inclusions in the austenite matrix of the titanium-containing austenitic stainless steel satisfies the following formula (3): non-nuclear TiN inclusions / (non-nuclear TiN inclusions+nuclear TiN inclusions)≥0.8 formula (3).

[0011] According to a specific embodiment of the present invention, preferably, the PREN of the titanium-containing austenitic stainless steel is ≥24, PREN=Cr+3.3Mo+16N.

[0012] The second aspect of the present invention provides a method for preparing the above-mentioned titanium-containing austenitic stainless steel, which comprises the following steps: subjecting the raw materials to electric arc furnace (EAF) melting, argon oxygen furnace (AOD) refining, vacuum smelting furnace (VOD) degassing, ladle refining furnace (LF) refining and continuous casting in sequence to obtain a continuously cast billet, which is the titanium-containing austenitic stainless steel.

[0013] According to a specific embodiment of the present invention, preferably, the arc furnace smelting process includes pre-desulfurization, and the pre-desulfurization includes: adding a desulfurizer to the molten steel under the conditions of blowing argon and stirring, the desulfurizer includes lime and fluorite, the amount of lime added is 10-15 kg / ton of molten steel, and the amount of fluorite added is 2-5 kg / ton of molten steel. More preferably, the S content in the molten steel obtained by the arc furnace smelting is less than 0.050 mass%.

[0014] According to a specific embodiment of the present invention, preferably, the process of argon-oxygen furnace refining includes: an oxidation period, a reduction period and tapping; in the oxidation period, top-blown oxygen is used to decarburize the molten steel, and when the C content in the molten steel is 0.02-0.07% by mass, the oxygen blowing is stopped, and the oxidation period is ended; then the reduction period is entered, argon is blown from the side for stirring, the argon flow rate is controlled at 18-25 L / min, and aluminum balls and ferrosilicon are added to the molten steel for composite deoxidation, and lime is added to adjust the basicity of the refined slag to 1.4-2.0, and the reduction period ends when the S content in the molten steel is less than 0.005% by mass and the Al content is 0.01-0.05% by mass; then the tapping temperature is controlled to 1620°C-1680°C for tapping into a ladle. More preferably, the preparation method further comprises the following steps: performing complete slag removal in the ladle, adding low-melting-point refined slag after the slag removal process, wherein the low-melting-point refined slag comprises CaO and SiO2 in a mass ratio of (0.8-1.0):1, and making it evenly cover the surface of the molten steel.

[0015] According to a specific embodiment of the present invention, preferably, the degassing process of the vacuum smelting furnace includes: evacuating, controlling the vacuum degree <100Pa and maintaining the pressure for 20 to 30 minutes, and stirring by blowing argon gas at the bottom during the degassing process. More preferably, the N content in the molten steel obtained by degassing the vacuum smelting furnace is 0.005 to 0.016 mass%.

[0016] According to a specific embodiment of the present invention, preferably, the refining process of the ladle refining furnace includes: controlling the temperature of the molten steel to 1495-1510°C, adding pure calcium cored wire, controlling the Ca content in the molten steel to 0.0005-0.0030% by mass, and blowing argon at the bottom and stirring for more than 25 minutes; then adding ferrotitanium, controlling the Ti content in the molten steel to 0.15-0.40% by mass, blowing argon and stirring for 2-10 minutes, and standing for more than 15 minutes.

[0017] According to a specific embodiment of the present invention, preferably, the continuous casting process includes: isolating the air in the tundish and the submerged nozzle by argon sealing.

[0018] According to a specific embodiment of the present invention, preferably, the preparation method further comprises the following steps: subjecting the continuously cast billet to heating, hot rolling, hot rolling annealing and pickling in sequence to obtain hot rolled steel, namely the titanium-containing austenitic stainless steel.

[0019] According to a specific embodiment of the present invention, preferably, the preparation method further comprises the following steps: subjecting the continuously cast billet to heating, hot rolling, hot rolling annealing and pickling, cold rolling and cold rolling annealing and pickling in sequence to obtain cold rolled steel, namely the titanium-containing austenitic stainless steel.

[0020] The present invention has at least the following beneficial effects:

[0021] The present invention can effectively control inclusions while maintaining high carbon and titanium content by designing the elements and content of austenitic stainless steel and combining the control of smelting process, so that the titanium-containing austenitic stainless steel of the present invention has both high strength and intergranular corrosion resistance, while also improving the productivity of continuous casting, and the titanium-containing austenitic stainless steel of the present invention also has high resistance to pitting corrosion in chloride ion environment. The titanium-containing austenitic stainless steel of the present invention can be applied to various occasions with strength requirements and intergranular corrosion resistance requirements, such as but not limited to pressure vessels such as dyeing and finishing equipment, automotive parts such as bellows, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a non-core TiN inclusion and a core TiN inclusion in a specific embodiment of the present invention.

[0023] Figure 2 1 is a scanning electron microscope image of a coreless TiN inclusion and a cored TiN inclusion in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0025] According to a specific embodiment of the first aspect of the present invention, the present invention provides a titanium-containing austenitic stainless steel, which is composed of the following elements, based on the total mass of the titanium-containing austenitic stainless steel as 100%: C 0.02-0.07%, Si 0.2-1.0%, Mn 1.0-2.0%, P≤0.035%, S≤0.005%, Cr 16.0-22.0%, Ni 10.0-14.0%, Mo2.0-3.0%, Ti 0.15-0.40%, Al 0.01-0.05%, N 0.005-0.016%, Ca 0.0005-0.0030%, and the balance is Fe and unavoidable impurity elements;

[0026] The element contents in the titanium-containing austenitic stainless steel satisfy the following formulas (1) and (2):

[0027] log10(Ti)+log10(N)-0.07Ti-0.045Cr+3.28≤0 Formula (1);

[0028] Ti / (C+N)≥5.0 Formula (2);

[0029] Furthermore, the number of TiN inclusions in the austenite matrix of the titanium-containing austenitic stainless steel satisfies the following formula (3): non-nuclear TiN inclusions / (non-nuclear TiN inclusions+nuclear TiN inclusions)≥0.8 formula (3).

[0030] It can be understood by those skilled in the art that the element symbols in formula (1) and formula (2) represent the mass percentage values ​​of the corresponding elements in the titanium-containing austenitic stainless steel.

[0031] like Figure 1 As shown, the nucleated TiN inclusions are TiN formed by heterogeneous nucleation, and the nucleation point is the oxide inclusion. The nucleated TiN inclusions are TiN formed by homogeneous nucleation, and the whole is pure TiN.

[0032] In some embodiments, the PREN of the titanium-containing austenitic stainless steel is ≥ 24, PREN = Cr + 3.3Mo + 16N. It can be understood by those skilled in the art that PREN refers to pitting corrosion resistance equivalent, and the element symbols (i.e., Cr, Mo, and N) in the PREN calculation formula represent the mass percentage values ​​of the corresponding elements in the titanium-containing austenitic stainless steel. The higher the PREN, the stronger the material's pitting corrosion resistance. The present invention controls the PREN to be above 24, so that the material has better pitting corrosion resistance.

[0033] The C element is an austenite forming element and an austenite stabilizing element. A too low C content will affect the stability of austenite, and the C element is also one of the most important solid solution strengthening elements in stainless steel materials. The present invention controls the lower limit of the C content to 0.02% by mass, which can make the stainless steel have a higher strength. The C element is also a carbide forming element of Cr. If the C content is too high, it is very easy to cause sensitization problems during welding thermal cycles, and further cause intergranular corrosion in a corrosive environment. In the present invention, Ti is added for stabilization, so the intergranular corrosion caused by the precipitation of Cr carbides is not focused on. However, the present invention controls the upper limit of the C content to 0.07% by mass, which can avoid the casting problem caused by high Ti content.

[0034] Si is a deoxidizing element. The present invention controls the lower limit of the Si content to 0.2 mass %, which can ensure a sufficient deoxidizing effect. At the same time, Si is a ferrite element. The present invention controls the upper limit of the Si content to 1.0 mass %, which can avoid the problem that too high Si content is not conducive to the stability of austenite, and avoids the situation that too high Si content leads to too high ferrite content in the weld, affecting the mechanical properties and corrosion resistance of the weld.

[0035] The Mn element is a strong austenite stabilizing element. The present invention controls the lower limit of the Mn content to 1.0 mass %, which can better maintain the stability of austenite. At the same time, the present invention controls the upper limit of the Mn content to 2.0 mass %, which can avoid the corrosion resistance problem caused by excessive Mn content.

[0036] The most important role of Cr is to ensure corrosion resistance. Cr is conducive to improving pitting resistance. However, Cr is a ferrite-forming element. Excessive addition of Cr requires a simultaneous increase in the content of austenite elements, especially the content of Ni, which will increase production costs. The present invention controls the Cr content to 16.0-22.0 mass %, while ensuring corrosion resistance and achieving a better balance with the content of austenite elements.

[0037] Like C, N is a strong austenite forming and stabilizing element, and is also an interstitial element, which has a strong solid solution strengthening effect. The present invention controls the lower limit of N content to 0.005% by mass, which can significantly improve the strength of austenitic steel and is also conducive to improving the corrosion resistance of the material. However, too high N content in Ti-containing steel will cause the TiN precipitation temperature to increase, causing problems such as continuous casting nozzle blockage that seriously affect productivity. The present invention controls the upper limit of N content to 0.016% by mass, so that stainless steel has better productivity.

[0038] Ni is an important element in austenitic stainless steel, and is a strong austenite forming and stabilizing element. The present invention controls the lower limit of Ni content to 10.0%, which is conducive to the material obtaining good strength and toughness matching. At the same time, the present invention controls the upper limit of Ni content to 14.0%, avoiding the problem that too high Ni content will greatly increase production costs, and avoiding the situation that too high Ni content will reduce the solubility of C element in austenite, promote carbide precipitation, and reduce corrosion resistance. At the same time, it is avoided that too high Ni content will reduce the δ ferrite content in the weld and increase the risk of solidification cracks.

[0039] The Mo element can significantly improve the pitting corrosion resistance and crevice corrosion resistance of stainless steel, and the addition of Mo is beneficial to high temperature strength. In some high temperature service environments such as dyeing and finishing equipment, it helps to stabilize the strength of the structure; however, Mo will promote the precipitation of intermetallic phases in austenitic stainless steel, which has an adverse effect on the corrosion resistance and mechanical properties of the steel. The present invention controls the Mo content to 2.0-3.0% by mass, so that the stainless steel has better high temperature strength and corrosion resistance.

[0040] The Al element is a strong deoxidizer, and in particular, in the smelting of steel containing Ti, in order to protect Ti from being oxidized, the use of Al can be more effective in deoxidation. The present invention controls the Al content to 0.01-0.05% by mass, reduces the high melting point spinel inclusions formed by the Al deoxidation product in the molten steel, and further reduces the effective nucleation points provided by such inclusions for the heterogeneous nucleation of TiN, thereby reducing the precipitation of TiN, thereby improving the pouring performance of the molten steel.

[0041] The Ca element is an inclusion modifying element. After Al deoxidation, the Al inclusions contained in the molten steel have a high melting point, which will lead to heterogeneous nucleation of TiN, reduce the casting performance of the molten steel and reduce the corrosion resistance of the material. Therefore, the present invention performs appropriate Ca treatment on the Al deoxidized steel, and controls the Ca content to 0.0005-0.0030% by mass, reduces the melting point of inclusions, and is conducive to improving the casting performance of the molten steel and the corrosion resistance of the material.

[0042] P and S are impurity elements. Among them, S element easily forms sulfide, which affects the corrosion resistance of the material. Therefore, it is more strictly managed than P element. In the present invention, the P content is controlled to be ≤0.035 mass % and the S content is controlled to be ≤0.005 mass %.

[0043] According to a specific embodiment of the second aspect of the present invention, the present invention provides a method for preparing the above-mentioned titanium-containing austenitic stainless steel, which comprises the following steps: subjecting the raw materials to electric arc furnace (EAF) melting, argon oxygen furnace (AOD) refining, vacuum smelting furnace (VOD) degassing, ladle refining furnace (LF) refining and continuous casting in sequence to obtain a continuously cast billet, which is the titanium-containing austenitic stainless steel.

[0044] Those skilled in the art will appreciate that the raw materials include alloys and / or pure metals.

[0045] Those skilled in the art can understand that the processes of electric arc furnace melting, argon oxygen furnace refining, vacuum smelting furnace degassing and ladle refining furnace refining all belong to the stainless steel smelting process.

[0046] In some embodiments, the arc furnace smelting process includes pre-desulfurization, which includes: adding a desulfurizer to the molten steel under the conditions of blowing argon and stirring, the desulfurizer includes lime and fluorite, the amount of lime added is 10-15 kg / ton of molten steel, and the amount of fluorite (CaF2) added is 2-5 kg / ton of molten steel. Specifically, the added lime is high-grade lime (CaO mass content>90%). More preferably, the S content in the molten steel obtained by the arc furnace smelting is less than 0.050 mass%.

[0047] In some embodiments, the argon-oxygen furnace refining process includes: an oxidation period, a reduction period and steel tapping; in the oxidation period, top-blown oxygen is used to decarburize the molten steel. When the C content in the molten steel is 0.02-0.07 mass%, the oxygen blowing is stopped and the oxidation period is ended; then the reduction period is entered, argon is side-blown for stirring, the argon flow rate is controlled at 18-25 L / min, and aluminum balls and ferrosilicon are added to the molten steel for composite deoxidation, and lime is added to adjust the alkalinity of the refined slag to 1.4-2.0. When the S content in the molten steel is less than 0.005 mass% and the Al content is 0.01-0.05 mass%, the reduction period ends; then the steel tapping temperature is controlled to 1620°C-1680°C and the steel is tapped into a ladle. The oxidation period is mainly used for decarburization of molten steel; the reduction period is mainly used for deoxidation, desulfurization and slag making of molten steel. The function of adding aluminum balls is Al deoxidation, and the function of adding ferrosilicon is Si deoxidation. The added lime is high-grade lime (CaO mass content>90%). The side blowing of argon gas and stirring can promote the floating of deoxidation and desulfurization products. The preferred amount of aluminum balls added is 8-10 kg / ton of molten steel, and the preferred amount of ferrosilicon added is 12-16 kg / ton of molten steel. In the process of argon oxygen furnace refining, the contents of Si, Mn, P, Cr, Ni and Mo in molten steel are controlled within the scope of the present invention. Preferably, the preparation method further comprises the following steps: performing complete slag removal in the ladle, adding low-melting-point refined slag after the slag removal treatment, wherein the low-melting-point refined slag comprises CaO and SiO2 in a mass ratio of (0.8-1.0):1, and making it evenly cover the surface of the molten steel, and the amount of the low-melting-point refined slag added is based on the slag surface being uniform, and the argon gas stirring slightly turns the slag surface but does not expose the molten steel.

[0048] In some embodiments, the degassing process of the vacuum smelting furnace includes: evacuating, controlling the vacuum degree to <100Pa and maintaining the pressure for 20 to 30 minutes, and stirring by blowing argon gas at the bottom during the degassing process. The degassing of the vacuum smelting furnace is mainly used to denitrify the molten steel and promote the floating of inclusions. Preferably, the N content in the molten steel obtained by degassing the vacuum smelting furnace is 0.005 to 0.016% by mass. The present invention uses a VOD furnace vacuum degassing to ensure a lower N content in the molten steel and can remove inclusions.

[0049] In some embodiments, the refining process of the ladle refining furnace includes: controlling the temperature of the molten steel to 1495-1510°C, adding pure calcium cored wire according to the Al content in the vacuum degassed steel composition, the amount of pure calcium cored wire added is preferably 4 times the mass of Al in the molten steel ± 20kg, controlling the Ca content in the molten steel to 0.0005-0.0030% by mass, and blowing argon at the bottom and stirring for more than 25 minutes; then adding ferrotitanium, controlling the Ti content in the molten steel to 0.15-0.40% by mass, blowing argon and stirring for 2-10 minutes, and standing for more than 15 minutes. Among them, the refining of the ladle refining furnace is mainly used for controlling the composition and temperature adjustment of the molten steel. In the refining process of the ladle refining furnace, the content of each element in the molten steel needs to be controlled within the scope of the present invention, so raw materials (including alloys and / or pure metals) can be added in the process.

[0050] In some embodiments, the continuous casting process includes: isolating the air in the tundish and the submerged nozzle by argon sealing. The present invention adopts argon sealing in the continuous casting process to prevent the molten steel from absorbing gases such as nitrogen. Preferably, in the continuous casting process, the tundish temperature is controlled at 1490-1510°C, the casting target speed is controlled at 1.0±0.2m / min, the cooling water temperature of the crystallizer is controlled at 25±10°C, the water volume on the narrow side of the crystallizer is controlled at 500±10L / min, the water volume on the wide side of the crystallizer is controlled at 3400±20L / min, the temperature of the continuous casting billet spray cooling water is controlled at 25±10°C, and the spray cooling water specific water volume is controlled at 0.6±0.05_L / (ton·min).

[0051] In some embodiments, the preparation method further comprises the following steps: subjecting the continuous casting billet to heating, hot rolling, hot rolling annealing and pickling in sequence to obtain hot rolled steel, namely the titanium-containing austenitic stainless steel. The present invention does not impose any special restrictions on the specific conditions of these steps, which can be routinely adjusted by those skilled in the art.

[0052] In some embodiments, the preparation method further comprises the following steps: subjecting the continuous casting billet to heating, hot rolling, hot rolling annealing and pickling, cold rolling, and cold rolling annealing and pickling in sequence to obtain cold rolled steel, namely the titanium-containing austenitic stainless steel. The present invention does not impose any special restrictions on the specific conditions of these steps, and they can be routinely adjusted by those skilled in the art.

[0053] In the present invention, the equipment used in each step of the preparation method are all equipment in the prior art, and the present invention does not impose any special restrictions on the structures of these equipment.

[0054] The present invention will be specifically described below by way of examples, but the present invention is not limited to these examples and can of course be implemented with various modifications within the scope of the gist of the present invention.

[0055] Example 1

[0056] This embodiment provides a titanium-containing austenitic stainless steel, which is composed of the following elements, based on the total mass of the titanium-containing austenitic stainless steel being 100%, C 0.020%, Si 0.98%, Mn 1.96%, P 0.0166%, S 0.0048%, Cr 16.05%, Ni 10.09%, Mo 2.87%, Ti 0.15%, Al 0.010%, N 0.0083%, Ca 0.0005%, and the remainder being Fe and unavoidable impurity elements. The element contents in the titanium-containing austenitic stainless steel satisfy the following formulas (1) and (2):

[0057] log10(Ti)+log10(N)-0.07Ti-0.045Cr+3.28≤0 Formula (1);

[0058] Ti / (C+N)≥5.0 Formula (2);

[0059] Furthermore, the number of TiN inclusions in the austenite matrix of the titanium-containing austenitic stainless steel satisfies the following formula (3): non-nuclear TiN inclusions / (non-nuclear TiN inclusions+nuclear TiN inclusions)≥0.8 formula (3).

[0060] The values ​​of formula (1), formula (2), formula (3) and PREN of the titanium-containing austenitic stainless steel are shown in Tables 1 and 2.

[0061] The preparation method of titanium-containing austenitic stainless steel in this embodiment at least includes smelting, and the smelting includes: melting the raw materials through an electric arc furnace (EAF) → refining in an argon oxygen furnace (AOD) → degassing in a vacuum smelting furnace (VOD) → refining in a ladle refining furnace (LF) → continuous casting into slabs.

[0062] Specifically, the process of electric arc furnace smelting includes pre-desulfurization, which includes: adding a desulfurizer to molten steel under the condition of blowing argon and stirring, wherein the desulfurizer is high-grade lime (CaO mass content>90%) and fluorite (CaF2), the addition amount of high-grade lime is 10-15 kg / ton of molten steel, the addition amount of fluorite (CaF2) is 2-5 kg / ton of molten steel, and the S content in the molten steel obtained by electric arc furnace smelting is less than 0.050 mass%;

[0063] Then the molten steel is put into an argon oxygen furnace for refining. The argon oxygen furnace refining process includes: oxidation period, reduction period and steel tapping; in the oxidation period, top blowing oxygen is used to decarburize the molten steel. When the C content in the molten steel is 0.02 mass%, oxygen blowing is stopped to complete decarburization and end the oxidation period; then the molten steel is put into the reduction period for deoxidation, desulfurization and slag making, and argon is blown from the side for stirring. The argon flow rate is controlled at 18-25L / min to promote the floating of deoxidation and desulfurization products, and aluminum balls and ferrosilicon are added to the molten steel for composite deoxidation. The amount of aluminum balls added is 8-10kg / ton of molten steel, and the amount of ferrosilicon added is 1 2-16kg / ton molten steel, and adding high-grade lime (CaO mass content>90%) to adjust the basicity of the refined slag to 1.4-2.0, when the S content in the molten steel is less than 0.005 mass% and the Al content is 0.01-0.05 mass%, the reduction period ends; then the tapping temperature is controlled to be 1620°C-1680°C and the steel is tapped into a ladle; the ladle is completely slag-stripped, and after the slag-stripping treatment, low-melting-point refined slag is added, the low-melting-point refined slag includes CaO and SiO2 in a mass ratio of (0.8-1.0):1, and the slag is evenly covered on the surface of the molten steel;

[0064] Then it enters the vacuum smelting furnace for vacuum denitrification and promotes the floating of inclusions. The degassing process of the vacuum smelting furnace includes: vacuuming, controlling the vacuum degree <100Pa and maintaining the pressure for 20 to 30 minutes, blowing argon gas at the bottom for stirring during the degassing process, and after breaking the vacuum, the N content of the molten steel is detected to be 0.0083%;

[0065] Then, the steel enters the ladle refining furnace for composition control and temperature adjustment. The refining process of the ladle refining furnace includes: controlling the temperature of the molten steel to 1495-1510°C, adding pure calcium cored wire for calcium treatment, the amount of pure calcium cored wire added is 4 times the mass of Al in the molten steel ± 20kg, controlling the Ca content in the molten steel to 0.0005-0.0030% by mass, and blowing argon gas at the bottom and weakly stirring for more than 25 minutes; then adding ferrotitanium, controlling the Ti content in the molten steel to 0.15% by mass, blowing argon gas and softly stirring for 2-10 minutes, and standing for more than 15 minutes; in the process of refining in the ladle refining furnace, it is necessary to control the content of each element in the molten steel within the scope of the present invention, so raw materials (including alloys and / or pure metals) can be added in the process;

[0066] Then, continuous casting is carried out, which adopts protective casting. Argon sealing is used to isolate the air in the tundish and the immersed nozzle. During the continuous casting process, the tundish temperature is controlled at 1490-1510°C, the casting target speed is controlled at 1.0±0.2m / min, the cooling water temperature of the crystallizer is controlled at 25±10°C, the water volume on the narrow side of the crystallizer is controlled at 500±10L / min, the water volume on the wide side of the crystallizer is controlled at 3400±20L / min, the spray cooling water temperature of the continuous casting billet is controlled at 25±10°C, and the spray cooling water volume ratio is controlled at 0.6±0.05_L / (ton·min) to obtain a continuously cast billet.

[0067] Afterwards, the continuous casting billet can be selectively subjected to heating → hot rolling → hot rolling annealing and pickling to obtain a hot rolled product; or, the continuous casting billet can be selectively subjected to heating → hot rolling → hot rolling annealing and pickling → cold rolling → cold rolling annealing and pickling to obtain a cold rolled product.

[0068] Embodiments 2 to 6

[0069] Examples 2 to 6 respectively provide a titanium-containing austenitic stainless steel, the elemental compositions of these stainless steels are shown in Table 1, and the values ​​of formula (1), formula (2), formula (3) and PREN of these stainless steels are shown in Tables 1 and 2.

[0070] The preparation methods of titanium-containing austenitic stainless steels of Examples 2 to 6 are basically the same as those of Example 1, except that the contents of the elements are different, and therefore the amounts of raw materials and treatment agents are different. Those skilled in the art can adjust the amounts of the raw materials and treatment agents within the scope of the present invention based on the preparation method of Example 1 and the element contents in Table 1.

[0071] Comparative Examples 1 to 3

[0072] Comparative Examples 1 to 3 respectively provide a titanium-containing stainless steel, the elemental composition of these stainless steels is shown in Table 1, and the formula (1), formula (2), formula (3) and PREN values ​​of these stainless steels are shown in Tables 1 and 2.

[0073] The preparation methods of titanium-containing stainless steel of Comparative Examples 1 to 3 are basically the same as that of Example 1, except that: the contents of each element are different, so the addition amounts of raw materials and treatment agents are different. Specifically, the differences between the preparation methods of titanium-containing stainless steel of Comparative Examples 1 to 3 and Example 1 mainly include: to ensure complete deoxidation, during the reduction period of the argon oxygen furnace refining process, the addition amount of aluminum balls is higher than that of Example 1, and is controlled to be greater than 10 kg / ton of molten steel, so that the Al content in the products of Comparative Examples 1 to 3 is greater than 0.05% by mass. In addition, the contents of Cr, Ti, and N in Comparative Examples 2 to 3 are controlled according to the range of the present invention, but are not comprehensively controlled according to PI=log10(Ti)+log10(N)-0.07Ti-0.045Cr+3.28≤0.

[0074] Whether the submerged nozzle of the tundish in the continuous casting process of the above-mentioned embodiments and comparative examples is blocked was observed and recorded. The results are shown in Table 1.

[0075] Table 1

[0076]

[0077] Note: PI in Table 1 refers to the value of log10(Ti)+log10(N)-0.07Ti-0.045Cr+3.28. The elements in Table 1 are elements other than the balance Fe and unavoidable impurity elements.

[0078] The cross section of the continuous casting billet of the above-mentioned embodiment and comparative example at 1 / 4 width and 1 / 4 thickness is taken as a sample. After the sample is ground and polished, a scanning electron microscope is used to observe and analyze the inclusions, and the number of non-nuclear TiN and nucleated TiN in the inclusions is counted, and then the ratio is calculated according to formula (3). Among them, the field of view (100 times) randomly selected for TiN quantity statistics in each embodiment and comparative example is more than 10, and the average value is taken after statistics and calculation as the value of formula (3). The values ​​of formula (3) of the above-mentioned embodiment and comparative example are shown in Table 2. Figure 2 The scanning electron microscope images of the non-core TiN inclusions and the core TiN inclusions in Example 1. A person skilled in the art can easily distinguish the non-core TiN inclusions and the core TiN inclusions by scanning electron microscope.

[0079] The continuous casting billets of the above-mentioned embodiment and comparative example were subjected to heating, hot rolling, hot rolling annealing and pickling, cold rolling, cold rolling annealing and pickling under the same conditions to obtain cold-rolled white coil materials.

[0080] The pitting potential of cold rolled white coils was measured according to GB / T 17899-1999 standard, and the corresponding current density on the anodic polarization curve was 100μA / cm 2 The potential value is used to represent the pitting potential, recorded as E'b100 The pitting potential results are shown in Table 2.

[0081] Table 2

[0082]

[0083] It can be seen from Tables 1 and 2 that by controlling the elements and contents of austenitic stainless steel within the scope of the present invention, and by controlling the values ​​of formula (1), formula (2), formula (3) and PREN within the scope of the present invention, the titanium-containing austenitic stainless steel of the present invention has both high corrosion resistance and continuous casting productivity. At the same time, since the titanium-containing austenitic stainless steel of the present invention has high carbon and titanium content, it has high strength.

Claims

1. A titanium-containing austenitic stainless steel, wherein: Taking the total mass of the titanium-containing austenitic stainless steel as 100%, it is composed of the following elements: C 0.02-0.07%, Si 0.2-1.0%, Mn 1.0-2.0%, P≤0.035%, S≤0.005%, Cr 16.0-22.0%, Ni 10.0-14.0%, Mo 2.0-3.0%, Ti 0.15-0.40%, Al 0.01-0.05%, N0.005-0.016%, Ca 0.0005-0.0030%, and the balance is Fe and unavoidable impurity elements; The element contents in the titanium-containing austenitic stainless steel satisfy the following formulas (1) and (2): log10(Ti)+log10(N)-0.07Ti-0.045Cr+3.28≤0 Formula (1); Ti / (C+N)≥5.0 Formula (2); Furthermore, the number of TiN inclusions in the austenite matrix of the titanium-containing austenitic stainless steel satisfies the following formula (3): non-nuclear TiN inclusions / (non-nuclear TiN inclusions+nuclear TiN inclusions)≥0.8 formula (3).

2. The titanium-containing austenitic stainless steel according to claim 1, wherein: The PREN of the titanium-containing austenitic stainless steel is ≥24, PREN=Cr+3.3Mo+16N.

3. A method for preparing titanium-containing austenitic stainless steel according to claim 1 or 2, wherein: The preparation method comprises the following steps: subjecting the raw materials to arc furnace melting, argon oxygen furnace refining, vacuum smelting furnace degassing, ladle refining furnace refining and continuous casting in sequence to obtain a continuous casting billet, namely the titanium-containing austenitic stainless steel.

4. The method for preparing titanium-containing austenitic stainless steel according to claim 3, wherein: The arc furnace smelting process includes pre-desulfurization, which includes: adding a desulfurizer to the molten steel under the conditions of blowing argon and stirring, the desulfurizer includes lime and fluorite, the amount of lime added is 10-15 kg / ton of molten steel, and the amount of fluorite added is 2-5 kg / ton of molten steel; Preferably, the S content in the molten steel obtained by smelting in the electric arc furnace is 0.050 mass % or less.

5. The method for preparing titanium-containing austenitic stainless steel according to claim 3, wherein: The argon-oxygen furnace refining process includes: an oxidation period, a reduction period and steel tapping; in the oxidation period, top-blown oxygen is used to decarburize the molten steel, and when the C content in the molten steel is 0.02-0.07 mass%, oxygen blowing is stopped, and the oxidation period ends; then the reduction period is entered, argon is blown from the side for stirring, the argon flow rate is controlled at 18-25 L / min, and aluminum balls and ferrosilicon are added to the molten steel for composite deoxidation, and lime is added to adjust the basicity of the refined slag to 1.4-2.0, and the reduction period ends when the S content in the molten steel is less than 0.005 mass% and the Al content is 0.01-0.05 mass%; then the steel tapping temperature is controlled to be 1620° C.-1680° C. and the steel is tapped into a ladle; Preferably, the preparation method further comprises the following steps: performing complete slag removal in the ladle, adding low-melting-point refined slag after the slag removal process, wherein the low-melting-point refined slag comprises CaO and SiO2 in a mass ratio of (0.8-1.0):1, and making it evenly cover the surface of the molten steel.

6. The method for preparing titanium-containing austenitic stainless steel according to claim 3, wherein: The degassing process of the vacuum smelting furnace includes: evacuating, controlling the vacuum degree to be less than 100Pa and maintaining the pressure for 20 to 30 minutes, and blowing argon gas at the bottom for stirring during the degassing process; Preferably, the N content in the molten steel obtained by degassing in the vacuum smelting furnace is 0.005-0.016 mass %.

7. The method for preparing titanium-containing austenitic stainless steel according to claim 3, wherein: The refining process of the ladle refining furnace includes: controlling the temperature of the molten steel to 1495-1510° C., adding pure calcium cored wire, controlling the Ca content in the molten steel to 0.0005-0.0030% by mass, and blowing argon gas at the bottom and stirring for more than 25 minutes; then adding ferrotitanium, controlling the Ti content in the molten steel to 0.15-0.40% by mass, blowing argon gas and stirring for 2-10 minutes, and standing for more than 15 minutes.

8. The method for preparing titanium-containing austenitic stainless steel according to claim 3, wherein: The continuous casting process includes: using argon sealing to isolate the air in the tundish and the submerged nozzle.

9. The method for preparing titanium-containing austenitic stainless steel according to claim 3, wherein: The preparation method further comprises the following steps: subjecting the continuous casting billet to heating, hot rolling, hot rolling annealing and pickling in sequence to obtain hot rolled steel, namely the titanium-containing austenitic stainless steel.

10. The method for preparing titanium-containing austenitic stainless steel according to claim 3, wherein: The preparation method further comprises the following steps: subjecting the continuous casting billet to heating, hot rolling, hot rolling annealing and pickling, cold rolling and cold rolling annealing and pickling in sequence to obtain cold rolled steel, namely the titanium-containing austenitic stainless steel.

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