A method and system for controlling NbN precipitation phase in a high-niobium and high-nitrogen nickel-based alloy during continuous casting

Abstract

The present invention belongs to the field of continuous casting technology, and specifically relates to a method and system for controlling NbN precipitation phase in a high-niobium and high-nitrogen nickel-based alloy during continuous casting, which can effectively control the precipitation of large-sized NbN phase in a high-niobium and high-nitrogen nickel-based alloy continuous casting wide and thick plates, reduce the difficulty of NbN remelting during homogenization, and facilitate the control of crack sensitivity of the ingot during continuous casting and hot rolling. Moreover, this method has strong portability in other high-niobium metal continuous casting processes and has good application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of continuous casting, and in particular to a method and system for controlling NbN precipitation phase in a continuous casting process of a high-niobium and high-nitrogen nickel-based alloy. Background Art

[0002] Nickel-based alloys with high niobium and high nitrogen content (Nb: 0.4~0.9wt%, N: 0.15~0.3wt%) have excellent heat resistance, corrosion resistance and good comprehensive mechanical properties, and are widely used in fields such as photovoltaic polysilicon cold hydrogenation high-parameter reactors. Nickel-based alloys are usually melted in a vacuum induction furnace and then produced through a double or even triple smelting process. However, its low yield rate and production efficiency, high cost, and unstable product quality seriously restrict the production specifications and application scope of the products. Compared with the traditional nickel-based alloy production process, the vertical bending continuous casting machine production process has a strong potential to further improve the rapid scale supply and produce large thickness and large unit weight products. Therefore, a domestic steel plant has recently conquered the production technology of high niobium and high nitrogen nickel-based alloys on vertical bending continuous casting machines.

[0003] For nickel-based alloys with complex alloy systems, although the high-temperature strength is more prominent after increasing the niobium and nitrogen content, they show stronger crack sensitivity and scrap rate during the continuous casting process. This is because high-niobium and high-nitrogen continuous casting billets are very likely to precipitate large-sized NbN phases at the columnar grain boundaries, which ultimately leads to the deterioration of the thermoplasticity of nickel-based alloy continuous casting billets. The frequency of longitudinal cracks in nickel-based alloy continuous casting billets produced by the current process is as high as over 25%, subcutaneous cracks are severe and unavoidable, and there is obvious stratification at 1 / 2 thickness of the billet, which greatly increases the difficulty of industrial promotion and application. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method and system for controlling the NbN precipitation phase of a high-niobium and high-nitrogen nickel-based alloy (wherein the mass percentages of niobium and nitrogen are respectively Nb: 0.4~0.9wt%, N: 0.15~0.3wt%) during continuous casting based on high-temperature confocal experimental simulation and finite element heat transfer model. The method directly avoids the precipitation of large-sized NbN phases at the columnar grain boundaries of the high-niobium and high-nitrogen nickel-based alloy before straightening, and significantly reduces the crack sensitivity of the high-niobium and high-nitrogen nickel-based alloy continuous casting billet during continuous casting.

[0005] According to one aspect of the present invention, the present invention provides the following technical solution:

[0006] A method for controlling NbN precipitation phase of a high-niobium and high-nitrogen nickel-based alloy during continuous casting, comprising the following steps:

[0007] S1. Collect actual continuous casting billet samples and obtain the thermoplastic deformation window of the continuous casting billet through hot stretching test;

[0008] S2. Through high-temperature confocal experiments, the continuous casting solidification process of the ingot from liquid to solid is simulated to obtain the kinetic curve of the precipitation behavior of the NbN precipitation phase at different temperatures;

[0009] S3. According to the thermoplastic deformation window of the continuous casting billet and the temperature range of the precipitation of the NbN precipitation phase, the temperature curve of the second cooling zone in the continuous casting process is determined to achieve the control of the NbN precipitation phase in the continuous casting process of the high niobium and high nitrogen nickel-based alloy.

[0010] As a preferred embodiment of the method for controlling the NbN precipitation phase of a high-niobium and high-nitrogen nickel-based alloy during continuous casting of the present invention, in step S1, the thermoplastic deformation window of the continuous casting billet is obtained by a Gleeble hot stretching test, and the hot stretching test specifically comprises: heating the sample to 1300°C at 20°C / s, keeping the temperature for 300s, cooling to the target temperature at 3°C / s, and heating for 0.001s. -1 The thermoplasticity was evaluated by the strain rate tensile test and the fracture shrinkage.

[0011] As a preferred embodiment of the method for controlling the NbN precipitation phase of a high-niobium and high-nitrogen nickel-based alloy during the continuous casting process described in the present invention, wherein: in the step S2, the sample is melted by a high-temperature confocal experiment, the sample is cooled to 1250°C by simulating the average cooling rate of the continuous casting process, and then the sample temperature is quickly reduced to the target solid-state transition temperature, and then directly quenched to room temperature with argon after keeping the temperature for 10 minutes.

[0012] As a preferred embodiment of the method for controlling the NbN precipitation phase of a high-niobium and high-nitrogen nickel-based alloy during continuous casting described in the present invention, wherein: in the step S2, the volume fraction of the NbN precipitation phase is obtained by high-temperature confocal samples kept at different transition temperatures, and the specific operation includes: cutting the sample longitudinally to make a metallographic sample, and taking 10 backscattered images from left to right at the bottom of the sample with an electron microscope magnification of 500 times to count the volume fraction of the NbN precipitation phase.

[0013] A preferred embodiment of a method for controlling NbN precipitation phase in a continuous casting process of a high-niobium and high-nitrogen nickel-based alloy according to the present invention, wherein: in step S2, the precipitation kinetic behavior curve of the NbN precipitation phase is obtained by fitting the volume fraction of the precipitation phase at different temperatures by an improved JMAK model;

[0014] The traditional JMAK phase transition model is:

[0015]

[0016] Where, Y is the volume fraction of the precipitated phase;

[0017] t is the transition time;

[0018] n is the Avrami index, which is 1.5;

[0019] k is the solidification rate constant, , which is temperature related;

[0020] The improved JMAK model is used to fit the kinetic behavior of the precipitation phase at different temperatures:

[0021]

[0022] Where f(T) is a function of temperature T only.

[0023] The preferred embodiment of the method for controlling the NbN precipitation phase of a high-niobium and high-nitrogen nickel-based alloy during continuous casting of the present invention comprises the following steps: in step S2, f(T) is obtained by performing polynomial fitting on the volume fraction of the precipitated phase kept at different temperatures.

[0024] The preferred embodiment of the method for controlling the NbN precipitation phase of a high-niobium and high-nitrogen nickel-based alloy during continuous casting of the present invention, wherein: in the step S3, the temperature of the ingot is ensured to be within the thermoplastic temperature range during bending and straightening, and the temperature field of the ingot after entering the bending section is ensured to be within the upper limit of the NbN precipitation temperature, thereby determining the temperature curve of the second cooling zone of the continuous casting process.

[0025] A preferred embodiment of a method for controlling the NbN precipitation phase of a high-niobium and high-nitrogen nickel-based alloy during continuous casting of the present invention, wherein: in step S3, a temperature curve of the second cooling zone of the continuous casting process determined by high-temperature confocal experiment simulation is used to obtain the control result of the NbN precipitation phase.

[0026] According to another aspect of the present invention, the present invention provides the following technical solution:

[0027] A control system for NbN precipitation phase in a continuous casting process of a high-niobium and high-nitrogen nickel-based alloy, comprising:

[0028] Thermoplastic deformation window determination module collects actual continuous casting billet samples and obtains the thermoplastic deformation window of the continuous casting billet through hot stretching experiments;

[0029] The NbN precipitation behavior determination module simulates the continuous casting solidification process of the ingot from liquid to solid through high-temperature confocal experiments, and obtains the kinetic curves of the NbN precipitation behavior at different temperatures.

[0030] The module for determining the temperature curve of the second cooling zone in the continuous casting process determines the temperature curve of the second cooling zone in the continuous casting process according to the thermoplastic deformation window of the continuous casting billet and the temperature range of the precipitation of the NbN precipitation phase, so as to control the NbN precipitation phase of the high-niobium and high-nitrogen nickel-based alloy during the continuous casting process.

[0031] The beneficial effects of the present invention are as follows:

[0032] The present invention proposes a method and system for controlling NbN precipitation phase in the continuous casting process of high-niobium and high-nitrogen nickel-based alloys, which can effectively control the precipitation of large-sized NbN phases in the continuous casting wide and thick plates of high-niobium and high-nitrogen nickel-based alloys, reduce the difficulty of NbN remelting during homogenization, and facilitate the control of crack sensitivity of the ingot during continuous casting and hot rolling. Moreover, this method has strong portability in other high-niobium metal continuous casting processes and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0034] Figure 1 This is a schematic diagram of the continuous casting temperature field control of the present invention;

[0035] Figure 2 is the fracture shrinkage rate at different temperatures of the embodiment of the present invention;

[0036] Figure 3 is a precipitation kinetics curve of NbN precipitate phase in an embodiment of the present invention;

[0037] Figure 4 The temperature drop curve of the columnar crystal region of the ingot according to the embodiment of the present invention;

[0038] Figure 5 The NbN precipitation phase characteristics of the columnar crystal region of the ingot under the temperature curve of the second cooling zone of the embodiment of the present invention;

[0039] Figure 6 The NbN precipitation phase characteristics of the columnar crystal region of the ingot using the current production process are shown as a comparative example.

[0040] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0041] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] like Figure 1As shown, the present invention proposes a control method and system for NbN precipitation phase in a continuous casting process of a high-niobium and high-nitrogen nickel-based alloy. First, the thermoplastic deformation window of the continuous casting billet is determined by a hot stretching experiment. Then, the precipitation kinetics curve of the NbN precipitation phase is obtained according to a high-temperature confocal experiment. Based on the thermoplastic deformation window of the continuous casting billet and the temperature range for the precipitation of the NbN precipitation phase, a new secondary cooling zone temperature curve is determined that can avoid the large-scale precipitation of the NbN precipitation phase before the continuous casting billet is bent and straightened.

[0043] According to one aspect of the present invention, the present invention provides the following technical solution:

[0044] A method for controlling NbN precipitation phase of a high-niobium and high-nitrogen nickel-based alloy during continuous casting, comprising the following steps:

[0045] S1. Collect actual continuous casting billet samples and obtain the thermoplastic deformation window of the continuous casting billet through hot stretching test;

[0046] S2. Through high-temperature confocal experiments, the continuous casting solidification process of the ingot from liquid to solid is simulated to obtain the kinetic curve of the precipitation behavior of the NbN precipitation phase at different temperatures;

[0047] S3. According to the thermoplastic deformation window of the continuous casting billet and the temperature range of the precipitation of the NbN precipitation phase, the temperature curve of the second cooling zone in the continuous casting process is determined to achieve the control of the NbN precipitation phase in the continuous casting process of the high niobium and high nitrogen nickel-based alloy.

[0048] Preferably, in step S1, the thermoplastic deformation window of the continuous casting billet is obtained by a Gleeble hot stretching test, which specifically includes: heating the sample to 1300°C at 20°C / s, keeping the temperature for 300s, cooling to the target temperature at 3°C / s, and heating for 0.001s. -1 The thermoplasticity was evaluated by the strain rate tensile test and the fracture shrinkage.

[0049] Preferably, in step S2, the sample is melted by a high-temperature confocal experiment, and the sample is cooled to 1250° C. by simulating the average cooling rate of the continuous casting process, and then the sample temperature is quickly reduced to the target solid-state transition temperature, and then directly quenched to room temperature with argon after keeping the temperature for 10 minutes.

[0050] Preferably, in step S2, the volume fraction of the NbN precipitated phase is obtained by high-temperature confocal samples kept at different transition temperatures, and the specific operations include: cutting the sample longitudinally to prepare a metallographic sample, and taking 10 backscattered images from left to right at the bottom of the sample with an electron microscope magnification of 500 times to count the volume fraction of the NbN precipitated phase.

[0051] Preferably, in step S2, the precipitation kinetic behavior curve of the NbN precipitation phase is obtained by fitting the volume fraction of the precipitation phase at different temperatures through an improved JMAK model;

[0052] The traditional JMAK phase transition model is:

[0053]

[0054] Where, Y is the volume fraction of the precipitated phase;

[0055] t is the transition time;

[0056] n is the Avrami index, which is 1.5;

[0057] k is the solidification rate constant, , which is temperature related;

[0058] The improved JMAK model is used to fit the kinetic behavior of the precipitation phase at different temperatures:

[0059]

[0060] Where f(T) is a function of temperature T only.

[0061] Preferably, in step S2, f(T) is obtained by performing polynomial fitting on the volume fraction of the precipitated phase kept at different temperatures.

[0062] Preferably, in step S3, the temperature of the ingot is ensured to be within the thermoplastic temperature range during bending and straightening, and the temperature field of the ingot after entering the bending section is ensured to be within the upper limit of the NbN precipitation temperature, thereby determining the temperature curve of the second cooling zone in the continuous casting process.

[0063] Preferably, in step S3, the control result of the NbN precipitation phase is obtained by using a temperature curve of the second cooling zone in the continuous casting process determined by high-temperature confocal experiment simulation.

[0064] According to another aspect of the present invention, the present invention provides the following technical solution:

[0065] A control system for NbN precipitation phase in a continuous casting process of a high-niobium and high-nitrogen nickel-based alloy, comprising:

[0066] Thermoplastic deformation window determination module collects actual continuous casting billet samples and obtains the thermoplastic deformation window of the continuous casting billet through hot stretching experiments;

[0067] The NbN precipitation behavior determination module simulates the continuous casting solidification process of the ingot from liquid to solid through high-temperature confocal experiments, and obtains the kinetic curves of the NbN precipitation behavior at different temperatures.

[0068] The module for determining the temperature curve of the second cooling zone in the continuous casting process determines the temperature curve of the second cooling zone in the continuous casting process according to the thermoplastic deformation window of the continuous casting billet and the temperature range of the precipitation of the NbN precipitation phase, so as to control the NbN precipitation phase of the high-niobium and high-nitrogen nickel-based alloy during the continuous casting process.

[0069] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0070] Example

[0071] A method for controlling NbN precipitation phase of a high-niobium and high-nitrogen nickel-based alloy during continuous casting, comprising the following steps:

[0072] S1. Collect samples of columnar crystal area of ​​actual continuous casting billet, and perform Gleeble hot stretching test. Stretch the samples every 50℃ in the range of 800℃~1300℃, and calculate the cross-sectional shrinkage of the samples at different stretching temperatures. The results are as follows: Figure 2 As shown in the figure, it can be found that the plastic processing temperature range of high niobium and high nitrogen nickel-based alloy is 950℃~1200℃. This means that the ingot must be cooled to this temperature range before bending and straightening.

[0073] S2. Through high temperature confocal experiment, the columnar crystal area sample was heated and melted to liquid state, and then cooled to 1050, 1000, 950 and 900℃ respectively at an average cooling rate of 20℃ / min during continuous casting, and then kept warm for 10 minutes, and then the sample was quenched by argon. After the sample was longitudinally sectioned, 10 SEM photos of the bottom of the sample were taken under an electron microscope at 500 times, and the volume fraction of NbN was calculated, such as Figure 3 As shown, the modified JMAK model is used to fit the kinetic transformation curves of NbN at different temperatures:

[0074]

[0075] From the kinetic curve of NbN precipitation phase, we can know that the phase transition temperature range of NbN is 1089℃~889℃, among which the precipitation is fastest at 986℃~934℃.

[0076] S3. According to the plastic range of the ingot and the temperature range of the NbN precipitation phase, determine the temperature curve of the second cooling zone in the continuous casting process, such as Figure 4 As shown. The high temperature confocal experiment simulated the continuous casting cooling process and obtained the control results of the precipitation phase (such as Figure 5 as shown).

[0077] Depend on Figure 4It can be seen that the optimized temperature curve of the second cooling zone in the continuous casting process shows that when the billet enters the bending section and the straightening section, the billet shell temperature is 1150℃ and 1100℃ respectively, both of which are within the plastic range (950℃~1200℃). In addition, in the bending section, the billet shell temperature is at the upper limit of the NbN precipitation temperature (1089℃), which can avoid the decrease in the plasticity of the billet due to the large amount of NbN precipitation during the straightening of the billet, resulting in a large number of straightening cracks. The billet is rapidly cooled to below 900℃ in the horizontal section, so that the billet quickly passes through the NbN precipitation temperature range. At the same time, after the sample is melted by the high-temperature confocal experiment, the second cooling zone is simulated according to the optimized temperature curve of the second cooling zone in the continuous casting process to check the effectiveness of the temperature curve. Figure 5 (a) and (b) show the morphology and size distribution characteristics of NbN in the embodiment, respectively, and (c) is a local magnified image and surface scan result of NbN morphology. Figure 5 It can be found that the NbN precipitated phase in the embodiment is fine and discretely distributed, with an average size of about 3.87 μm.

[0078] Comparative Example

[0079] The difference from the embodiment is that the temperature curve of the casting billet currently produced in industrialization is adopted. Figure 4 It can be found that the current production process causes the billet to stay in the NbN precipitation temperature range for too long after entering the bending section, causing a large amount of large-sized NbN phases to precipitate before the billet is straightened. In addition, during the straightening section, the billet temperature is in the third brittle zone, which leads to the appearance of straightening cracks. Figure 6 (a) and (b) show the morphology and size distribution characteristics of NbN in the comparative example, and (c) is a local magnified image and surface scan result of NbN morphology. Figure 6 It can be found that the NbN precipitated phase using the existing process has an irregular morphology, and the average size of the NbN phase reaches 12.12µm, which is much larger than the embodiment process.

[0080] Therefore, the present invention measures the hot plastic processing window and the NbN rapid precipitation temperature curve of the high-niobium and high-nitrogen nickel-based alloy, and proposes an optimized secondary cooling zone temperature curve of the high-niobium and high-nitrogen nickel-based alloy. The present invention can greatly control the growth of the NbN precipitate phase in the secondary cooling zone, thereby avoiding a sharp decrease in plasticity and an increase in crack sensitivity of the nickel-based alloy continuous casting billet before straightening.

[0081] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for controlling NbN precipitation phase in a high-niobium and high-nitrogen nickel-based alloy during continuous casting, characterized in that: The steps include: S1. Collect actual continuous casting billet samples and obtain the thermoplastic deformation window of the continuous casting billet through hot stretching test; S2. Through high-temperature confocal experiments, the continuous casting solidification process of the ingot from liquid to solid was simulated to obtain the kinetic curve of the precipitation behavior of the NbN precipitation phase at different temperatures; the precipitation kinetic behavior curve of the NbN precipitation phase was obtained by fitting the volume fraction of the precipitation phase at different temperatures through the improved JMAK model; the improved JMAK model is used to fit the kinetic behavior of the precipitation phase at different temperatures: In the formula, f(T) is a function only about temperature T; Y is the volume fraction of the precipitated phase; t is the transformation time; n is the Avrami index, which is 1.5; f(T) is obtained by polynomial fitting of the volume fraction of the precipitated phase at different temperatures; S3. According to the thermoplastic deformation window of the continuous casting billet and the temperature range of the NbN precipitation phase, the billet temperature is ensured to be within the thermoplastic temperature range during bending and straightening, and the temperature field after the billet enters the bending section is ensured to be within the upper limit of the NbN precipitation temperature. The billet is rapidly cooled to below 900°C in the horizontal section so that the billet quickly passes through the NbN precipitation temperature range, thereby determining the temperature curve of the second cooling zone in the continuous casting process, and realizing the control of the NbN precipitation phase of the high niobium and high nitrogen nickel-based alloy in the continuous casting process.

2. The method for controlling NbN precipitation phase in a continuous casting process of a high-niobium and high-nitrogen nickel-based alloy according to claim 1, characterized in that: In step S1, the thermoplastic deformation window of the continuous casting billet is obtained by a Gleeble hot stretching test, which specifically includes: heating the sample to 1300°C at 20°C / s, keeping the temperature for 300s, cooling to the target temperature at 3°C / s, and heating for 0.001s. -1 The thermoplasticity was evaluated by the strain rate tensile test and the fracture shrinkage.

3. The method for controlling NbN precipitation phase in a continuous casting process of a high-niobium and high-nitrogen nickel-based alloy according to claim 1, characterized in that: In step S2, the sample is melted by a high-temperature confocal experiment, and the sample is cooled to 1250° C. by simulating the average cooling rate of the continuous casting process, and then the sample temperature is quickly reduced to the target solid-state transition temperature. After keeping the temperature for 10 minutes, it is directly quenched to room temperature with argon gas.

4. The method for controlling NbN precipitation phase in a continuous casting process of a high-niobium and high-nitrogen nickel-based alloy according to claim 3, characterized in that: In step S2, the volume fraction of the NbN precipitated phase is obtained by heat-insulating high-temperature confocal samples at different transition temperatures. The specific operation includes: cutting the sample longitudinally to prepare a metallographic sample, and taking 10 backscattered images from left to right at the bottom of the sample with an electron microscope magnification of 500 times to calculate the volume fraction of the NbN precipitated phase.

5. The method for controlling NbN precipitation phase in a continuous casting process of a high-niobium and high-nitrogen nickel-based alloy according to claim 1, characterized in that: In the step S3, the control result of the NbN precipitation phase is obtained by using the temperature curve of the second cooling zone in the continuous casting process determined by the high temperature confocal experiment simulation.

6. A control system for NbN precipitation phase in a high-niobium and high-nitrogen nickel-based alloy during continuous casting, characterized in that: A control method for implementing any one of claims 1 to 5, comprising: Thermoplastic deformation window determination module collects actual continuous casting billet samples and obtains the thermoplastic deformation window of the continuous casting billet through hot stretching experiments; The NbN precipitation behavior determination module simulates the continuous casting solidification process of the ingot from liquid to solid through high-temperature confocal experiments, and obtains the kinetic curves of the NbN precipitation behavior at different temperatures. The module for determining the temperature curve of the second cooling zone in the continuous casting process determines the temperature curve of the second cooling zone in the continuous casting process according to the thermoplastic deformation window of the continuous casting billet and the temperature range of the precipitation of the NbN precipitation phase, so as to control the NbN precipitation phase of the high-niobium and high-nitrogen nickel-based alloy during the continuous casting process.

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