Method for predicting precipitation of TiN inclusion in casting blank and casting blank production process

Abstract

The invention relates to the technical field of ferrous metallurgy, and discloses a method for predicting precipitation of TiN inclusions in a casting blank and a casting blank production process, the method comprises the following steps: S1, collecting steel grade components; s2, calculating the activity of Ti and N in the molten steel; s3, calculating the precipitation thermodynamic condition of the TiN inclusion in the molten steel according to the calculated activity of Ti and N in the molten steel; s4, the calculated precipitation thermodynamic condition of the TiN inclusion in the molten steel is compared with the liquidus temperature of the steel grade, and whether the TiN inclusion can be precipitated in the molten steel or not is judged; and S5, an inequality equation of the actual concentration product of nitrogen and titanium in the solid-liquid two-phase region in the molten steel solidification process and the equilibrium concentration product on the liquidus temperature is established, and whether TiN inclusions can be separated out of a casting blank obtained through molten steel solidification or not is judged. According to the method, the Ti and N contents in molten steel are associated with the solid fraction by considering the segregation problem according to the Ti and N content control requirements of the steel grade, and whether TiN inclusions are generated in a casting blank in the solidification process or not is predicted.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for predicting TiN inclusion precipitation in a casting billet and a casting billet production process. Background Art

[0002] TiN inclusions are square inclusions with sharp edges and corners, and are not easy to deform. They will not disappear after rolling and heat treatment. They have great damage to the fatigue performance and toughness of steel, especially for bearing steel and wheel steel with harsh service environment and strict performance requirements. Therefore, during the smelting process, the content of Ti and N in the molten steel must be strictly controlled to prevent the precipitation of TiN inclusions. At present, there are many studies on the precipitation of TiN in steel, mainly focusing on how to reduce the content of Ti and N in molten steel, or using numerical simulation to predict the size of TiN inclusions. However, there is no systematic study on whether TiN inclusions will precipitate in the ingot under the composition range of a given steel grade, the precipitation location, and how to control the precipitation of TiN inclusions.

[0003] In the existing literature, patent application CN109082493A-smelting process for reducing TiN inclusion content in high-titanium microalloyed high-strength steel, through pre-desulfurization of molten iron to control the sulfur content below 0.010% to reduce the desulfurization pressure of LF furnace, shorten the LF furnace refining cycle to reduce nitrogen absorption of molten steel, RH refining molten steel circulation within 1.5 minutes to achieve a vacuum degree of less than 1mbar, complete the composition adjustment within 3 minutes, continuous casting adopts dynamic light pressure and other measures to reduce the number and size of TiN inclusions in high-titanium microalloyed high-strength steel molten steel. Patent application CN108913844A-nitrogen control process for stranded wire steel series steel grades, through the selection of low-nitrogen auxiliary materials for smelting, LF furnace mouth positive pressure operation, LF furnace submerged arc refining, continuous casting protection casting and argon blowing throughout the steelmaking process, the nitrogen content in the steel is controlled below 60ppm, so that the TiN content in the steel is sharply reduced. Patent application CN109785907A - A method for controlling inclusions in high-strength and high-fatigue spring steel wire rods, which further refines the size of TiN inclusions by controlling the Ti content in molten iron, using low-Ti alloys, and using special ladle tanks to reduce the Ti content in steel. Patent application CN115896400A - A method for reducing titanium nitride inclusions in titanium-containing steels. When producing titanium-containing steels, the LF+RH dual process route is adopted. By adjusting the LF slag layer thickness, heating time, and slag viscosity, the LF nitrogen increase is reduced. By adjusting the circulating gas flow rate during the RH vacuum treatment process, the RH denitrification rate is increased, and titanium iron is added in the later stage of RH cycle denitrification to reduce the probability of titanium nitride formation. Patent application CN117004869A - A production method for controlling the size of TiN inclusions in steel, wherein the S in molten iron is controlled to ≤0.005% by KR desulfurization pretreatment, low-nitrogen scrap steel is selected, and the titanium content is controlled to ≤15ppm during converter tapping. During the tapping process, a slide plate is used to block slag and alloy the steel. By controlling the content of titanium and nitrogen in the molten steel, the equilibrium concentration product of TiN precipitated from the steel is controlled, and finally the size of TiN inclusions in the steel is reduced. The core idea of ​​the above technology is how to control the content of Ti and N elements in the steel as low as possible throughout the steelmaking process, so as to control the precipitation of TiN content in the steel. However, it is not specifically explained in advance on a theoretical level whether the corresponding steel type will produce TiN inclusions within the steel judgment range. If TiN inclusions will not be produced in theory within the composition control range, smelting using the above process method will cause a great waste of raw materials. In addition, the above scheme focuses on how to control the Ti and N content in the steel in the steelmaking and refining processes, and basically does not explain how to control TiN precipitation in the continuous casting process.

[0004] Patent application CN114743604A - A method for predicting the precipitation of TiN inclusions in welding wire steel and a welding wire steel production process. The method proposes a welding wire steel production process. The method predicts whether TiN inclusions will precipitate during the welding wire steel production process under set process conditions by thermodynamic calculation. Specifically, the calculated temperature is compared with the liquidus temperature of the steel grade. If it is greater than the liquidus temperature, TiN inclusions will precipitate. If TiN inclusions are predicted to precipitate, the production process is adjusted; if no TiN inclusions are predicted to precipitate, welding wire steel is produced according to the preset process. This method can avoid the precipitation of TiN inclusions in liquid molten steel and is suitable for the case where the Ti and N contents in the molten steel are relatively high. If the Ti and N contents in the molten steel are low, the precipitation conditions cannot be met in the liquid molten steel. However, due to the existence of segregation, TiN inclusions will still precipitate during the solidification process. At this time, this method is not applicable.

[0005] Patent application CN109785907A - A method for predicting the precipitation of TiN inclusions during the solidification of molten steel. The method first collects the steel composition and solidification conditions, then calculates the heat and solute transfer during the solidification of the molten steel, the growth of the interface cell during the solidification, and the nucleation and growth of TiN during the solidification, and then establishes a mathematical model for the precipitation of TiN during the solidification of the Fe-C-Ti-N quaternary alloy; finally, according to the casting temperature, steel composition, and cold-speed continuous casting process conditions, the TiN precipitation law is predicted through the established TiN precipitation mathematical model, and the TiN precipitation information is displayed using data analysis and visualization processing software. In the simulation calculation of TiN precipitation, this method has a premise assumption that only TiN precipitation in the liquid phase is considered, but in the actual production process, due to the existence of segregation, most of the TiN inclusions are precipitated in the solid phase, so this assumption does not conform to reality; in addition, the accuracy of the simulation is not verified in the article. The above technical methods all describe the prediction of whether TiN inclusions will be generated in molten steel through thermodynamic calculations. Strictly speaking, if TiN inclusions are generated in molten steel, it means that the Ti and N content in the molten steel is too high. In actual production, in most cases, the Ti and N content in the molten steel meets the internal control standards, but TiN inclusions are found in the ingot inspection. The reason is that there is segregation of Ti and N elements, which is ignored by the above methods.

[0006] Patent application CN109082493A - Smelting process for reducing the content of TiN inclusions in high-titanium microalloyed high-strength steel, patent application CN108913844A - Nitrogen control process for stranded wire steel series, patent application CN109785907A - A method for controlling inclusions in high-strength and high-fatigue spring steel wire rods, patent application CN115896400A - A method for reducing titanium nitride inclusions in titanium-containing steels, patent application CN117004869A - A production method for controlling the size of TiN inclusions in steel. The above methods are about how to control the content of Ti and N elements in steel as low as possible throughout the entire steelmaking process, thereby achieving the precipitation of controlled TiN content in steel. There is no specific theoretical explanation on whether the corresponding steel type will produce TiN inclusions within the steel judgment range. Summary of the invention

[0007] The purpose of the present invention is to overcome the problem in the prior art that it is impossible to predict whether TiN inclusions will be generated in a cast billet and the precipitation position, and to provide a method for predicting the precipitation of TiN inclusions in a cast billet and a cast billet production process. The method combines the Ti and N content control requirements of the steel grade with the solid phase ratio in consideration of the existence of the segregation problem, and predicts whether TiN inclusions will be generated in the cast billet during the solidification process.

[0008] In order to achieve the above object, the present invention provides a method for predicting the precipitation of TiN inclusions in a casting in a first aspect, the method comprising the following steps:

[0009] S1. Collect steel composition;

[0010] S2. Calculate the activities of Ti and N in the molten steel;

[0011] S3. Calculating the precipitation thermodynamic conditions of TiN inclusions in the molten steel according to the calculated activities of Ti and N in the molten steel;

[0012] S4, comparing the calculated precipitation thermodynamic conditions of TiN inclusions in the molten steel with the liquidus temperature of the steel grade to determine whether TiN inclusions will precipitate in the molten steel;

[0013] S5. Establish an inequality equation for the product of the actual nitrogen and titanium concentrations in the solid-liquid two-phase region during the solidification of the molten steel and the equilibrium concentration product at the liquidus temperature to determine whether TiN inclusions will precipitate in the ingot obtained by solidifying the molten steel.

[0014] In step S2 of the present invention, considering the interaction between the elements in the molten steel, the calculation formula for the activities of Ti and N in the molten steel is as follows:

[0015] a i =f i ·w[i] Formula (1)

[0016]

[0017] In formula (1) and formula (2), a i is the activity of element i; f i is the activity coefficient of element i; i is element Ti or N; j is the other elements in the molten steel except i; represents the interaction coefficient of element j to element i in the molten steel; w[i] is the mass fraction of element i in the molten steel; w[j] is the mass fraction of element j in the molten steel.

[0018] Because the temperature of the molten steel is usually 1873K, in a specific embodiment, what is calculated in the present invention is the activities of Ti and N in the molten steel at a temperature of 1873K.

[0019] Preferably, in step S3, the calculation formula of the precipitation thermodynamic condition of TiN inclusions in the molten steel is as follows:

[0020] △G=△G 4θ +RTln[aT iN / (a Ti ·a N )] Formula (3)

[0021] In formula (3), ΔG represents the actual Gibbs free energy of TiN formation in molten steel, ΔG = ΔG 4e +RTlnK, where K represents the reaction equilibrium constant, K = a TiN / (a Ti ·a N );△G 4θ represents the standard Gibbs free energy of formation of TiN in molten steel; R is the gas constant, the unit is J / (mol*K), in the specific implementation of the present invention, R=8.314J / (mol*K); a TiN is the activity of TiN. Since TiN has a high melting point, it can be considered as a pure substance. Therefore, in the present invention, a TiN =1; a Ti is the activity of element Ti; a N is the activity of element N.

[0022] Further, the chemical reaction formula for generating TiN is as follows:

[0023] Ti(s)=[Ti], and its standard formation Gibbs free energy is as follows:

[0024] △G 1θ =-25100-44.98T Formula (6)

[0025] 1 / 2N2(g)=[N], and its standard Gibbs free energy of formation is as follows:

[0026] △G 2θ =3600+13.89T Formula (7)

[0027] Ti(s)+1 / 2N2(g)=TiN(s), and its standard formation Gibbs free energy is as follows:

[0028] △G 3θ =-336300+93.26T Formula (8)

[0029] [Ti]+[N]=TiN(s), so combining equations (6) to (8) gives equation (4), which is the standard Gibbs free energy of formation of TiN in molten steel: 4θ The calculation formula is as follows:

[0030] △G 4θ =-314800+114.35T Formula (4)

[0031] In formula (4), T represents thermodynamic temperature, and its unit is K.

[0032] In the present invention, the equation (3) is set to 0, that is, ΔG = 0, and the thermodynamic temperature T at this time, that is, the thermodynamic condition for the precipitation of TiN inclusions in the molten steel, is calculated.

[0033] Further in step S4 of the present invention, the calculated precipitation thermodynamic conditions of TiN inclusions in the molten steel are compared with the liquidus temperature of the steel grade. When the calculated precipitation thermodynamic conditions of TiN inclusions in the molten steel are greater than the liquidus temperature of the steel grade, it indicates that TiN inclusions will precipitate in the molten steel; when the calculated precipitation thermodynamic conditions of TiN inclusions in the molten steel are less than the liquidus temperature of the steel grade, it indicates that TiN inclusions will not precipitate in the molten steel.

[0034] The liquidus temperature of the steel grade in the present invention can be found according to the steel grade smelting operation instruction manual.

[0035] However, it is well known to those skilled in the art that TiN inclusions can be generated in the molten steel and can also be generated in the process of solidifying the molten steel into a cast billet. Even if no TiN inclusions are generated in the molten steel, TiN inclusions may be generated in the process of solidifying the molten steel into a cast billet (in the actual solidification process of the molten steel, as the temperature decreases, the solubility of N and Ti in the steel gradually decreases, and there will be segregation and enrichment of N and Ti at the crystallization front. At a certain temperature, when the actual concentration product of N and Ti is higher than the lower limit of the equilibrium concentration product w[Ti]·w[N] (w[Ti] represents the mass fraction of the element Ti in the molten steel, and w[N] represents the mass fraction of the element N in the molten steel), the formation of TiN inclusions becomes possible. Therefore, in the actual solidification process of the molten steel, there are conditions for the formation of TiN inclusions in the solid-liquid two-phase region), so it is also necessary to determine whether TiN inclusions will be generated in the cast billet; and usually if TiN inclusions are generated in the molten steel, then TiN inclusions will inevitably be generated in the solidification process, so it is necessary to further accurately predict the formation timing of TiN inclusions.

[0036] Among them, the relationship between the content of Ti and N in the molten steel and the solid phase ratio is expressed by equations (9) and (10):

[0037]

[0038] In formula (9) and formula (10), [N] represents the mass fraction of N in the liquid phase during the solidification of the molten steel; [Ti] represents the mass fraction of Ti in the liquid phase during the solidification of the molten steel.

[0039] The actual concentration product Q of N and Ti in the solid-liquid two-phase region during the solidification of molten steel TiN for:

[0040] Q TiN =[Ti] / % ·[N] / % Formula (11)

[0041] Combining equations (9) to (11), we can obtain the actual concentration product of N and Ti in the solid-liquid two-phase region during the solidification of molten steel:

[0042]

[0043] When the concentration product of N and Ti during solidification is higher than the lower limit of the equilibrium concentration product w[Ti]·w[N] at a certain temperature, the formation of TiN inclusions becomes possible. Because the equilibrium concentration product increases with the increase of temperature, the equilibrium concentration product of TiN at any temperature in the solid-liquid two-phase region must be less than the equilibrium concentration product at the liquidus temperature. Therefore, as long as the actual concentration product of TiN at a certain temperature between the two-phase region is greater than the equilibrium concentration product at the liquidus temperature, it will inevitably precipitate. When the formation reaction of TiN reaches the equilibrium critical point, the actual formation Gibbs free energy of TiN in the steel liquid is △G=0 (Formula (3)). Based on this, the functional relationship between the mass fraction of Ti and N in the steel and the temperature T is calculated as follows:

[0044] Ln{w[Ti]·w[N]}=13.78-37863.84 / T (13)

[0045] Substituting the liquidus temperature of the molten steel into equation (13), the equilibrium concentration product at the liquidus temperature can be obtained as:

[0046] w[Ti]·w[N]=e 13.78-37863.84 / T (14)

[0047] Let equation (12)>equation (14), that is, equation (5) is obtained. Therefore, in step S5, the inequality equation for the product of the actual nitrogen and titanium concentrations in the solid-liquid two-phase region during the solidification of the molten steel and the equilibrium concentration product at the liquidus temperature is established as follows:

[0048]

[0049] In formula (5), [N]0 represents the mass fraction of N in the initial liquid steel phase; [Ti]0 represents the mass fraction of Ti in the initial liquid steel phase; f s Indicates the solidification percentage (solid phase ratio); K N represents the equilibrium solute distribution coefficient of N; K Ti represents the equilibrium solute distribution coefficient of Ti; in the present invention, K N =0.32, K Ti =0.40.

[0050] Further, f in formula (5) s To solve, when f in equation (5) s When there is no solution, it means that TiN inclusions will not precipitate in the ingot obtained by solidification of molten steel; when f in equation (5) s When there is a solution, it means that TiN inclusions will precipitate in the ingot obtained by solidification of molten steel, and the obtained f s Determine the precipitation position of TiN inclusions in the ingot (for example, when f sWhen it is greater than a certain value, it means that TiN inclusions will precipitate when the solid phase ratio reaches this value. At this time, the ingot is cut along the cross section, and TiN inclusions will be generated at the position where the cross-sectional area of ​​the ingot is this value).

[0051] A second aspect of the present invention provides a casting billet production process, which comprises the following steps: before casting billet production, first use the method for predicting TiN inclusion precipitation in the casting billet as mentioned above to predict whether TiN inclusion precipitation will occur during the casting billet production process under a preset process; if TiN inclusion precipitation is predicted, adjust the smelting process; if no TiN inclusion precipitation is predicted, perform casting billet production according to the preset process.

[0052] In a preferred embodiment, the present invention adjusts the smelting process from the electric furnace, LF furnace, and continuous casting process to prevent the generation of TiN inclusions. Specifically, the adjustment of the smelting process includes the following operations:

[0053] a. The ratio of molten iron to the electric furnace is controlled at more than 55%, and the scrap steel is low-nitrogen scrap steel;

[0054] b. Use graphite low-nitrogen recarburizer to reduce the nitrogen content of raw materials brought into molten steel;

[0055] c. The order of adding alloys to steel is from weak to strong. When the steel output reaches 1 / 3, silicon-manganese alloy is added, and when the steel output reaches 2 / 3, aluminum-iron alloy is added;

[0056] d. During refining operation, the furnace cover must fall to the lower limit to ensure slight positive pressure operation;

[0057] e. During the refining process, large argon stirring is prohibited. The argon flow rate during the temperature rise operation is 200-300NL / min, and the slag layer thickness is greater than 150mm to ensure submerged arc operation. It is prohibited to add alloys and aluminum wires during the temperature rise;

[0058] f. Calcium treatment is carried out when refining leaves the station, and the argon flow rate does not exceed 200NL / min to prevent molten steel from splashing and causing nitrogen increase;

[0059] g. Asbestos gaskets shall be added to the long shroud of each ladle in continuous casting. The long shroud must be vertical and argon gas shall be passed through the long shroud to protect the pouring. The argon gas flow control standard is that the molten steel does not turn over;

[0060] h. The thickness of the slag layer covering the tundish is greater than 50mm, isolating the air and preventing nitrogen from increasing in the molten steel;

[0061] i. Continuous casting increases cooling intensity. The cooling water flow rate of the crystallizer is 3000-4000L / min. The secondary cooling curve adopts C curve + (30-50%) cooling intensity.

[0062] The scheme of the present invention combines the segregation of Ti and N components in molten steel with the solid phase ratio, predicts whether TiN inclusions will precipitate in the ingot during solidification and the precipitation position, and adjusts the smelting process to prevent the generation of TiN inclusions in the ingot, thereby improving the quality of the ingot. The scheme is suitable for all steel types that have requirements for TiN inclusions. DETAILED DESCRIPTION

[0063] The specific embodiments of the present invention are described in detail below by way of examples. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0064] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0065] The steel type in the following embodiments is 25MnCrNiMoA, whose chemical composition is shown in Table 1. Its liquidus temperature is 1501° C. (1774K) according to the operation instructions.

[0066] Table 1

[0067]

[0068] The interaction coefficients of other elements in the molten steel with Ti and N elements at a temperature of 1873K are shown in Table 2.

[0069] Table 2

[0070]

[0071]

[0072] Example 1

[0073] Before the slab production, the following steps are used to predict whether TiN inclusions will be precipitated during the slab production process under the preset process:

[0074] S1. Collect the steel grade composition. The chemical composition of the steel grade is shown in Table 1.

[0075] S2. Calculate the activities of Ti and N in the molten steel. The calculation formula for the activities of Ti and N in the molten steel is as follows:

[0076] a i =f i ·w[i] Formula (1)

[0077]

[0078] In formula (1) and formula (2), a i is the activity of element i; f i is the activity coefficient of element i; i is element Ti or N; j is the other elements in the molten steel except i; represents the interaction coefficient of element j to element i in the molten steel; w[i] is the mass fraction of element i in the molten steel; w[j] is the mass fraction of element j in the molten steel;

[0079] Substituting the mass fraction of each element in 25MnCrNiMoA steel (Table 1) and the interaction coefficient of each element in the molten steel with Ti and N at 1873K (Table 2) into equations (1) and (2), the activity coefficients of Ti and N in the molten steel are obtained: Ti and f N and activity a Ti and a N They are respectively (the interaction coefficients of elements not recorded in Table 2 with Ti and N elements are negligible):

[0080] lgf Ti =-0.003253, the activity coefficient f of Ti Ti =0.9925, the activity of Ti Ti =0.01489

[0081] lgf N =-0.006056, the activity coefficient f of N N =0.9862, the activity of N N =0.0095;

[0082] S3. Calculating the precipitation thermodynamic conditions of TiN inclusions in the molten steel according to the calculated activities of Ti and N in the molten steel;

[0083] The calculation formula for the thermodynamic conditions of precipitation of TiN inclusions in molten steel is as follows:

[0084] △G=△G 4θ +RTln[a TiN / (a Ti ·a N )] Formula (3)

[0085] In formula (3), ΔG represents the actual formation Gibbs free energy of TiN in molten steel; ΔG 4θ represents the standard Gibbs free energy of formation of TiN in molten steel; R is the gas constant, R = 8.314 J / (mol*K); a TiN is the activity of TiN, a TiN =1;

[0086] Standard Gibbs free energy of formation of TiN in molten steel △G 4θ The calculation formula is as follows:

[0087] △G 4θ =-314800+114.35T Formula (4)

[0088] In formula (4), T represents the thermodynamic temperature;

[0089] The a calculated in step S2 Ti and a N Substituting into equation (3) and setting △G = 0, the thermodynamic temperature T (i.e., the thermodynamic condition for the precipitation of TiN inclusions in molten steel) is calculated to be 1367°C;

[0090] S4, comparing the precipitation thermodynamic condition of TiN inclusions in the molten steel calculated in step S3 with the liquidus temperature of the steel grade, at this time, the precipitation thermodynamic condition of TiN inclusions in the molten steel is 1367°C, which is less than the liquidus temperature of 1501°C, so TiN inclusions will not precipitate in the molten steel at this time;

[0091] S5. Establish an inequality equation for the product of the actual nitrogen and titanium concentrations in the solid-liquid two-phase region during the solidification of the molten steel and the equilibrium concentration product at the liquidus temperature to determine whether TiN inclusions will precipitate in the ingot obtained by solidifying the molten steel;

[0092] Among them, the inequality equation for the product of the actual nitrogen and titanium concentrations in the solid-liquid two-phase region during the solidification of molten steel and the equilibrium concentration product at the liquidus temperature is as follows:

[0093]

[0094] In formula (5), [N]0 represents the mass fraction of N in the initial liquid steel phase; [Ti]0 represents the mass fraction of Ti in the initial liquid steel phase; f s Indicates the solidification percentage; K N represents the equilibrium solute distribution coefficient of N; K Ti represents the equilibrium solute distribution coefficient of Ti, K N =0.32, K Ti =0.40;

[0095] Substituting the N content, Ti content and liquidus temperature of 25MnCrNiMoA steel recorded in Table 1 into formula (5), that is, setting T = 1774K, [N]0 to 0.0060%, [Ti]0 to 0.015%, and f s Solve and find f s >0.89, f sAt this time, there is a solution, that is, TiN inclusions will precipitate in the ingot obtained by solidification of molten steel, and when the solid phase ratio is greater than 89%, TiN inclusions will precipitate in the ingot. At this time, the ingot is cut along the cross section, and TiN inclusions will be generated at the position where the cross-sectional area of ​​the ingot is 89%;

[0096] S6. According to the result of step S5, TiN inclusions will be precipitated in the casting process under the preset process, and the smelting process needs to be adjusted. The adjustment of the smelting process includes the following operations:

[0097] a. The ratio of molten iron into the electric furnace is controlled at 60%, and the scrap steel is low-nitrogen scrap steel;

[0098] b. LF furnace uses graphite low nitrogen recarburizer to reduce the nitrogen content of raw materials brought into molten steel;

[0099] c. The order of adding alloys to steel is from weak to strong. When the steel output reaches 1 / 3, silicon-manganese alloy is added, and when the steel output reaches 2 / 3, aluminum-iron alloy is added;

[0100] d. During the LF furnace refining operation, the furnace cover must fall to the lower limit position to ensure the whole process of micro-positive pressure operation;

[0101] e. During the refining process, large argon stirring is prohibited. During the temperature rise operation, the argon flow rate is 250NL / min, the slag layer thickness is 160mm, and the submerged arc operation is guaranteed. It is prohibited to add alloy and aluminum wire during the temperature rise;

[0102] f. Calcium treatment is carried out when the LF furnace is leaving the refining station, and the argon flow rate is 100NL / min to prevent molten steel from splashing and causing nitrogen increase;

[0103] g. Asbestos gaskets shall be added to the long shroud of each ladle in continuous casting. The long shroud must be vertical and argon gas shall be passed through the long shroud to protect the pouring. The argon gas flow control standard is that the molten steel does not turn over;

[0104] h. The thickness of the slag layer covering the tundish is 60mm, which isolates the air and prevents nitrogen addition to the molten steel;

[0105] i. Continuous casting increases cooling intensity, allowing the molten steel to solidify quickly and shortening the time it takes for the molten steel to drop from the liquidus temperature to the solidus temperature. The crystallizer cooling water flow rate is 4000L / min, and the secondary cooling curve uses C curve + 30% cooling intensity;

[0106] After adjusting the smelting process according to the above operation, ingots were produced, and the nitrogen content in the slag was controlled below 35ppm. Metallographic samples were taken from the ingots obtained by solidification of the molten steel, and the samples were tested with ASPEX equipment, and no TiN inclusions were found.

[0107] According to the above results, it can be seen that the method of the present invention can effectively predict whether TiN inclusions will precipitate in the ingot during solidification and the precipitation position, and timely adjust the smelting process to prevent the formation of TiN inclusions in the ingot and improve the quality of the ingot.

[0108] It should be understood that parts not elaborated in detail in this specification belong to the prior art.

[0109] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for predicting TiN inclusion precipitation in a casting, characterized in that: The method comprises the following steps: S1. Collect steel composition; S2. Calculate the activities of Ti and N in the molten steel; S3. Calculating the precipitation thermodynamic conditions of TiN inclusions in the molten steel according to the calculated activities of Ti and N in the molten steel; S4, comparing the calculated precipitation thermodynamic conditions of TiN inclusions in the molten steel with the liquidus temperature of the steel grade to determine whether TiN inclusions will precipitate in the molten steel; S5. Establish an inequality equation for the product of the actual nitrogen and titanium concentrations in the solid-liquid two-phase region during the solidification of the molten steel and the equilibrium concentration product at the liquidus temperature to determine whether TiN inclusions will precipitate in the ingot obtained by solidifying the molten steel.

2. The method according to claim 1, characterized in that In step S2, the calculation formula of Ti and N activities in the molten steel is as follows: a i = f i · w[i] Equation (1) In formula (1) and formula (2), a i is the activity of element i; f i is the activity coefficient of element i; i is element Ti or N; j is the other elements in the molten steel except i; represents the interaction coefficient of element j to element i in the molten steel; w[i] is the mass fraction of element i in the molten steel; w[j] is the mass fraction of element j in the molten steel.

3. The method according to claim 1 or 2, characterized in that: In step S3, the calculation formula of the thermodynamic conditions for the precipitation of TiN inclusions in the molten steel is as follows: △G = △G 4θ + RTln[a TiN / (a Ti ·a N )] Equation (3) In formula (3), ΔG represents the actual formation Gibbs free energy of TiN in molten steel; ΔG 4θ represents the standard Gibbs free energy of formation of TiN in molten steel; R is the gas constant; a TiN is the activity of TiN; a Ti is the activity of element Ti; a N is the activity of element N.

4. The method according to claim 3, characterized in that Standard Gibbs free energy of formation of TiN in molten steel △G 4θ The calculation formula is as follows: △G 4θ =-314800+114.35T Formula (4) In formula (4), T represents the thermodynamic temperature.

5. The method according to claim 1, characterized in that: In step S4, when the calculated precipitation thermodynamic conditions of TiN inclusions in the molten steel are greater than the liquidus temperature of the steel grade, it indicates that TiN inclusions will precipitate in the molten steel; when the calculated precipitation thermodynamic conditions of TiN inclusions in the molten steel are less than the liquidus temperature of the steel grade, it indicates that TiN inclusions will not precipitate in the molten steel.

6. The method according to claim 1, characterized in that In step S5, the established inequality equation for the product of the actual nitrogen and titanium concentrations in the solid-liquid two-phase region during the solidification of the molten steel and the equilibrium concentration product at the liquidus temperature is as follows: In formula (5), [N]0 represents the mass fraction of N in the initial liquid steel phase; [Ti]0 represents the mass fraction of Ti in the initial liquid steel phase; f s Indicates the solidification percentage; K N represents the equilibrium solute distribution coefficient of N; K Ti represents the equilibrium solute distribution coefficient of Ti.

7. The method according to claim 6, characterized in that For f in formula (5), s To solve, when f in equation (5) s When there is no solution, it means that TiN inclusions will not precipitate in the ingot obtained by solidification of molten steel; when f in equation (5) s When there is a solution, it means that TiN inclusions will precipitate in the ingot obtained by solidification of the molten steel.

8. The method according to claim 7, characterized in that When f in formula (5) s When there is a solution, according to the solved f s Determine the precipitation position of TiN inclusions.

9. A casting process, characterized in that: The ingot production process comprises the following steps: before ingot production, first use the method for predicting TiN inclusion precipitation in ingot as described in any one of claims 1 to 8 to predict whether TiN inclusion precipitation will occur during ingot production under a preset process; if TiN inclusion precipitation is predicted, adjust the smelting process; if no TiN inclusion precipitation is predicted, produce ingot according to the preset process.

10. The casting process according to claim 9, characterized in that: The adjustment of the smelting process includes the following operations: a. The ratio of molten iron into the electric furnace should be controlled above 55%; b. Use graphite carburizer; c. The order of adding alloys to steel is from weak to strong; d. During refining operation, the furnace cover falls to the lower limit; e. During the refining process, the argon flow rate is 200-300NL / min during the temperature increase operation, and the slag layer thickness is greater than 150mm; f. Calcium treatment is carried out when the refining leaves the station, and the argon flow rate does not exceed 200NL / min; g. Asbestos gaskets are added to the shroud of each ladle in continuous casting, the shroud is vertical, and argon is passed through the shroud to protect the pouring; h. The thickness of the tundish covering slag layer is greater than 50mm; i. Continuous casting increases cooling intensity. The cooling water flow rate of the crystallizer is 3000-4000L / min. The secondary cooling curve adopts C curve + (30-50%) cooling intensity.

Images