A production process control method for high purity stainless steel

Abstract

The present invention relates to the technical field of alloy smelting, and in particular to a production process control method for high-purity stainless steel, comprising: in the current AOD furnace refining process, sampling molten steel and obtaining the content of each element in the molten steel, obtaining the optimal stirring speed and optimal nitrogen-oxygen ratio of each element according to the content of each element and the historical refining curve; in the historical refining curve, under the optimal stirring speed and optimal nitrogen-oxygen ratio, according to the content change of each element at each addition, obtaining the loss coefficient of each element under the optimal stirring speed and optimal nitrogen-oxygen ratio. The optimal stirring speed and optimal nitrogen-oxygen ratio of all elements and the loss coefficient of each element are used to obtain the stirring speed and nitrogen-oxygen ratio of the molten steel in the current AOD furnace refining process. The present invention improves the production efficiency and purity of stainless steel.

Description

Technical Field

[0001] The invention relates to the technical field of alloy smelting, and in particular to a production process control method for high-purity stainless steel. Background Art

[0002] High-purity stainless steel is usually used in aerospace, petrochemical, automotive, food, medical, communication and other fields. Due to its application conditions, the control of harmful inclusions is much stricter than that of general materials. In order to solve the purity problem of stainless steel materials, AOD refining + electroslag remelting is generally used for production. This method has high production cost, high requirements for raw materials, low production efficiency and low yield rate. In order to obtain high-purity stainless steel and improve production efficiency, it is necessary to remove the electroslag remelting process and obtain high-purity stainless steel by optimizing AOD refining and other processes.

[0003] During AOD refining, elements such as nickel, chromium, and molybdenum need to be added to the molten steel. When adding these elements, the molten steel needs to be stirred and a nitrogen-oxygen mixture needs to be blown into it. When the stirring speed and the nitrogen-oxygen ratio are not appropriate, multiple additions may be required and the added elements may be lost, which may lead to insufficient stainless steel purity and reduced production efficiency. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a production process control method for high-purity stainless steel.

[0005] A production process control method for high purity stainless steel of the present invention adopts the following technical scheme:

[0006] An embodiment of the present invention provides a production process control method for high-purity stainless steel, wherein the production process includes an AOD furnace refining process, wherein several elements are added to the AOD furnace containing molten steel during the AOD refining process, and the molten steel is stirred, and a nitrogen-oxygen mixed gas is introduced into the molten steel. During each AOD furnace refining process, a content change curve of each element, a stirring speed change curve, and a nitrogen-oxygen ratio change curve are recorded; during all AOD furnace refining processes, the content change curves of all elements, the stirring speed change curves, and the nitrogen-oxygen ratio change curves are recorded as historical refining curves;

[0007] In the current AOD furnace refining process, the molten steel is sampled and the content of each element in the molten steel is obtained, and the optimal stirring speed and the optimal nitrogen-oxygen ratio of each element are obtained according to the content of each element and the historical refining curve. The optimal stirring speed and the optimal nitrogen-oxygen ratio refer to the stirring speed and nitrogen-oxygen ratio at the sampling time when the change rate of each element is the largest;

[0008] In the historical refining curve, under the optimal stirring speed and the optimal nitrogen-oxygen ratio, the loss coefficient of each element under the optimal stirring speed and the optimal nitrogen-oxygen ratio is obtained according to the content change of each element at each addition;

[0009] The optimal stirring speed and the optimal nitrogen-oxygen ratio of all elements and the loss coefficient of each element are used to obtain the stirring speed and the nitrogen-oxygen ratio of the molten steel in the current AOD furnace refining process.

[0010] Preferably, the step of obtaining the optimal stirring speed and the optimal nitrogen-oxygen ratio for each element comprises the following specific steps:

[0011] The historical refining curve includes a content change curve of each element in each AOD furnace refining process, the horizontal coordinate of the content change curve of each element is the sampling time of the molten steel, and the vertical coordinate is the content of each element in the sampled molten steel; the historical refining curve includes a stirring speed change curve in each AOD furnace refining process, the horizontal coordinate of the stirring speed change curve is the sampling time of the molten steel, and the vertical coordinate is the stirring speed of the molten steel; the historical refining curve includes a nitrogen-oxygen ratio change curve in each AOD furnace refining process, the horizontal coordinate of the nitrogen-oxygen ratio change curve is the sampling time of the molten steel, and the vertical coordinate is the nitrogen-oxygen ratio in the nitrogen-oxygen mixed gas;

[0012] In the current AOD furnace refining process, the content of each element in molten steel is recorded as aa;

[0013] In the historical refining curve, for each element, several contents with the smallest difference from aa are obtained, and the sampling times corresponding to the several contents with the smallest difference are recorded as the reference sampling times of each element in the current AOD furnace refining process;

[0014] Any reference sampling time is recorded as t, and the previous sampling time of sampling time t is recorded as t1; the content of each element at sampling time t in each AOD furnace refining process is recorded as ft; the content of each element at sampling time t1 is recorded as ft1. as the change rate of each element at sampling time t during the current AOD furnace refining process;

[0015] At all reference sampling times in all AOD furnace refining processes, the reference sampling time with the largest change rate of each element is obtained, and the stirring speed and nitrogen-oxygen ratio at the reference sampling time with the largest change rate are recorded as the optimal stirring speed and optimal nitrogen-oxygen ratio of each element.

[0016] Preferably, the method of obtaining the loss coefficient of each element at an optimal stirring speed and an optimal nitrogen-oxygen ratio according to the content change of each element at each addition comprises the following specific steps:

[0017] In the historical refining curve, the sampling time corresponding to the optimal stirring speed and nitrogen-oxygen ratio of each element is recorded as tmax, and the previous sampling time of sampling time tmax is recorded as t0; the content of each element at sampling time tmax is recorded as f1, and the content of each element at sampling time t0 is recorded as ft0; the target content of each element is recorded as F1, and the loss coefficient is .

[0018] Preferably, the optimal stirring speed and the optimal nitrogen-oxygen ratio of all elements and the loss coefficient of each element are used to obtain the stirring speed and the nitrogen-oxygen ratio of the molten steel in the current AOD furnace refining process, and the specific steps include the following:

[0019] The loss coefficient is recorded as x, exp(-x) is used as the attention factor of each element, the element whose attention factor is less than the first preset threshold tth1 is recorded as the element to be corrected, and the loss coefficient corresponding to the element to be corrected is recorded as Q1;

[0020] According to the content of the element to be corrected and the historical refining curve, the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio of each element to be corrected are obtained, wherein the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio refer to the stirring speed and the nitrogen-oxygen ratio at the sampling time when the change rate of each element is the second largest; wherein the maximum value of the change rate of the element to be corrected is recorded as q1, and the second maximum value of the change rate of the element to be corrected is recorded as q2; the loss coefficient of the element to be corrected at the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio is recorded as Q2;

[0021] Obtain a reference stirring speed of the element to be corrected according to w1 and the optimal stirring speed and the optimal nitrogen-oxygen ratio of the element to be corrected, as well as the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio;

[0022] The reference stirring speed of all elements to be corrected and the optimal stirring speed of other elements except the elements to be corrected are averaged to obtain the stirring speed of the molten steel during the current AOD furnace refining process; the reference nitrogen-oxygen ratio of all elements to be corrected and the optimal nitrogen-oxygen ratio of other elements except the elements to be corrected are averaged to obtain the nitrogen-oxygen ratio of the molten steel during the current AOD furnace refining process;

[0023] in ; exp() represents an exponential function with a natural constant as the base.

[0024] Preferably, the reference stirring speed of the element to be corrected is obtained according to w1 and the optimal stirring speed and the optimal nitrogen-oxygen ratio of the element to be corrected, as well as the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio, and the calculation formula included is:

[0025] The reference stirring speed vj of the element to be corrected is vj=exp(-w1)×vj1+(1-exp(-w1))×vj0, where vj0 and vj1 represent the optimal stirring speed and the suboptimal stirring speed of the element to be corrected, respectively;

[0026] The reference nitrogen-oxygen ratio vb of the element to be corrected is vb=exp(-w1)×vb1+(1-exp(-w1))×vb0, where vb0 and vb1 represent the optimal nitrogen-oxygen ratio and the suboptimal nitrogen-oxygen ratio of the element to be corrected, respectively.

[0027] Preferably, after adding elements to the molten steel during the AOD furnace refining process, the elements included in the molten steel and the target contents of the included elements are: the target content of C is 0.035%, the target content of Si is 0.35%, the target content of Mn is 3.9%, the target content of P is ≤0.024%, the target content of S is ≤0.005%, the target content of Ni is 10.3%, the target content of Cr is 20.1%, the target content of Mo is 2.3%, the target content of N is 0.35%, and the target content of Nb is 0.40%;

[0028] During the AOD furnace refining process, the amount of each element added is calculated by multiple drawing method based on the initial content and target content of each element in the molten steel, and then the alloy ingredients are poured into the molten steel and stirred;

[0029] The alloy ingredients contain each element that needs to be added, and the weight of the elements added to the alloy ingredients is equal to the required amount of each element to be added;

[0030] The alloy ingredients include: high carbon ferrochrome, Ni iron, pure nickel and ferromolybdenum; the added elements include Cr element, Ni element and Mo element; wherein the high carbon ferrochrome includes 60% of Cr element, the Ni iron includes 9% of Ni element, the pure nickel includes 99% of Ni element, and the ferromolybdenum includes 60% of Mo element.

[0031] Preferably, when the nitrogen-oxygen mixed gas is introduced into the molten steel, before the temperature of the AOD furnace is raised to 1680° C., the nitrogen-oxygen ratio of the nitrogen-oxygen mixed gas is set to 0.25;

[0032] During all the AOD furnace refining processes, from the first to the nth AOD furnace refining processes, when the temperature of the AOD furnace rises to 1680°C, the nitrogen-oxygen ratio in the nitrogen-oxygen mixed gas is w, and the method for obtaining w is: randomly selecting a value in the interval [1, 4] as the value of w; wherein n is a preset value.

[0033] Preferably, during the AOD furnace refining process, when the C content in the molten steel is lower than the target value, ferrosilicon and 99% electrolytic manganese are added to the molten steel, and 65% ferroniobium is added after removing the residue, and 500KG of lime and 300KG of fluorite are added for slag making and stirring; nitrogen is used throughout the stirring, and when the temperature reaches 1600-1620°C, the nitrogen content of the molten steel reaches 0.30%, and when the temperature reaches 1560-1580°C, the nitrogen content of the molten steel reaches 0.34% and steel is tapped; the additional amounts of ferrosilicon and the electrolytic manganese are calculated by the multi-drawing method.

[0034] Preferably, the AOD furnace refining process includes LF refining. During the LF refining process, argon stirring and alloy addition are used to make the content of various elements in the molten steel reach the target content of each element, and the molten steel temperature is adjusted to 1515-1525°C before casting.

[0035] Preferably, the LF refining process is followed by continuous casting, and a continuous casting machine is used for continuous casting during the continuous casting process. The matching relationship between superheat and pulling speed during the continuous casting process is: when the temperature is ≥1458°C and the superheat is ≥51°C, the pulling speed is set to 0.80M / MIN; when the temperature is between 1457~1452°C and the superheat is between 50~45°C, the pulling speed is set to 0.85M / MIN; when the temperature is between 1451~1447°C and the superheat is between 44~40°C, the pulling speed is set to 0.9M / MIN; when the temperature is between 1446~1442°C and the superheat is between 39~35°C, the pulling speed is set to 1.0M / MIN; when the temperature is between 1441~1437°C and the superheat is between 34~30°C, the pulling speed is set to 1.1M / MIN; when the temperature is ≤1436°C and the superheat is ≤29°C, the pulling speed is set to 1.2M / MIN.

[0036] The beneficial effects of the technical solution of the present invention are:

[0037] The present invention obtains the optimal stirring speed and the optimal nitrogen-oxygen ratio of each element and the loss coefficient of each element under the optimal stirring speed and the optimal nitrogen-oxygen ratio in the current AOD furnace refining process. The optimal stirring speed and the optimal nitrogen-oxygen ratio of all elements and the loss coefficient of each element are used to obtain the stirring speed and the nitrogen-oxygen ratio of the molten steel in the current AOD furnace refining process. The present invention can make the added alloy quickly mixed and uniformly and reduce the number of additions in the oxygen blowing stirring process with a suitable stirring speed and a suitable nitrogen-oxygen ratio, and avoid the loss of elements in the added alloy when the stirring speed and the nitrogen-oxygen ratio do not match, such as the oxidation of elements in the alloy into slag, or the oxidation of the added alloy into slag or adsorption by the slag before it is completely melted or mixed evenly, and finally avoid the situation that the content of the added alloy elements reaches the target content after multiple additions, and avoid the waste of alloy ingredients, thereby improving the purity and production efficiency of the final stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] 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 these drawings without paying creative work.

[0039] Figure 1 A flow chart of the steps of a production process control method for high-purity stainless steel provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the production process control method of high-purity stainless steel proposed by the present invention, its specific implementation method, structure, characteristics and effects, in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0041] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0042] The specific scheme of the production process control method of high-purity stainless steel provided by the present invention is described in detail below with reference to the accompanying drawings.

[0043] Embodiment 1:

[0044] This embodiment provides a production process of high-purity stainless steel. Table 1 shows the target composition and content of the stainless steel produced in this embodiment. In addition to the elements shown in Table 1, the remaining elements are Fe. The production process is as follows:

[0045] Step S1, selecting ingredients.

[0046] Select the alloy type and quantity for batching and load them into 2~3 material tanks.

[0047] The selected alloy ingredients include high carbon ferrochrome, Ni iron and pure nickel. In the specific production, additional other alloy ingredients are added according to the function of the stainless steel to be produced. For example, the alloy ingredients in this embodiment include ferromolybdenum to increase the corrosion resistance and heat resistance of the stainless steel; for another example, the alloy ingredients in this embodiment include ferroniobium to improve the high temperature performance of the stainless steel.

[0048] This embodiment is described by taking two material tanks as an example. As an example, the quantity and metal element content of some alloy ingredients are shown in Table 2.

[0049] Step S2: initial refining in EAF furnace.

[0050] (1) Transfer the alloy from the material tank to the EAF furnace (electric arc furnace).

[0051] (2) Close the EAF furnace cover, turn on the power, and use electrical energy to melt the solid alloy into molten steel.

[0052] (3) Repeat the process of feeding the remaining alloy in the tank into the furnace for melting.

[0053] (4) When the temperature in the furnace reaches above 1600°C and all the solid alloy is melted, the power is turned off and the molten steel is poured into the mother liquid ladle for transfer.

[0054] Step S3: AOD furnace refining.

[0055] (1) Remove the residue on the surface of the mother liquor bag.

[0056] (2) The molten steel is poured into the AOD furnace (argon oxygen refining furnace).

[0057] (3) Take samples to confirm the composition, calculate the alloy according to the initial composition, and confirm the additional alloy.

[0058] As an example, the elements added to the alloy include: Ni, Cr, Mo, Nb, and Mn. The multiple drawing method is used for calculation so that Ni, Cr, Mo, Nb, and Mn are calculated to meet the target requirements.

[0059] As an example, Table 3 shows the initial content and target content of each element in the molten steel. In this embodiment, the target content of P is 0.024%, and the target content of S is 0.005%. In other embodiments, in order to further increase the toughness of stainless steel, the target content of P and the target content of S can be set lower, for example, to 0.02% and 0.003% respectively.

[0060] As an example, when the initial content of Mo is 0.06% and the target content is 2.3%, the method of calculating and adding Mo element by multiple drawing method is:

[0061] In this embodiment, the total amount of molten steel is 30 tons, of which the Mo element needs to be increased by 2.24%, and 60% of ferromolybdenum alloy is added in this embodiment. The weight of ferromolybdenum alloy to be added is 0.672 / 0.60=1.12 tons.

[0062] After the molybdenum-iron alloy is added, the molten steel is sampled again for testing to obtain the initial Mo content again, and the above process is repeated until the Mo content is equal to the target content.

[0063] As another example, when the initial Ni content is 10.9% and the target content is 10.3%, it is necessary to reduce the Ni element by 0.6%, that is, it is necessary to reduce the Cr element by 0.18 tons, and calculate the amount of low-Ni raw material to be added (for example, 9% Ni iron) to reduce the total Ni content by 0.18 tons. Then sample the molten steel again for testing to obtain the initial Ni content again. In this embodiment, spark direct reading spectroscopy (OES) is used to obtain the contents of various elements in the molten steel sample. Repeat the above process until the Ni content is equal to the target content. It should be noted that in the process of adding Ni, after adding the Ni element, if the initial Ni content is less than the target content, it is necessary to add high-Ni raw materials, for example, by adding 99% pure nickel to make the Ni content reach the target content.

[0064] In summary, in this embodiment, pure nickel (99%), high chromium (60%), ferromolybdenum (60%) and other alloy ingredients required for the calculation are added into the furnace for smelting in multiple times by the drawing method, and 2500 kg of lime is added for slag formation.

[0065] (4) While the alloy is being added, the molten steel is stirred so that the added alloy is melted and evenly mixed. In this embodiment, a physical stirring method is used for stirring.

[0066] (5) While adding the alloy as mentioned above, oxygen is blown into the AOD furnace. It should be noted that oxygen blowing is performed by blowing a nitrogen-oxygen mixture. Before the temperature in the AOD furnace reaches 1660-1680°C and after the temperature in the AOD furnace reaches 1660-1680°C (target temperature), the nitrogen-oxygen ratio in the nitrogen-oxygen mixture is different. In this embodiment, the ratio of nitrogen content to oxygen content in the nitrogen-oxygen mixture before the temperature in the AOD furnace reaches 1680°C is set to 1:4, that is, the nitrogen-oxygen ratio is 0.25. When the temperature in the AOD furnace reaches 1680°C (target temperature) and thereafter, the nitrogen-oxygen ratio is set to 1.0-4.0.

[0067] In other embodiments, the nitrogen-oxygen ratio can be changed when the temperature in the AOD furnace reaches 1660° C. or 1670° C.

[0068] (6) During the above-mentioned stirring and oxygen blowing process, the C content in the molten steel gradually decreases. The molten steel is sampled multiple times to obtain the C content in the molten steel.

[0069] (7) When the C content in the molten steel reaches or is lower than the target content (the target content is shown in Table 3), ferrosilicon is added for stirring reduction, and the electrolytic manganese (99%) required for the formulation is added.

[0070] As an example, the method of adding ferrosilicon is:

[0071] The multiple drawing method is used to add ferrosilicon so that the sample content in the molten steel is lower than the target content (for example, 0.004%). The specific process of the multiple drawing method has been described above and will not be repeated again.

[0072] As another example, the amount of ferrosilicon added is calculated as:

[0073] The oxygen analyzer is used to measure the total oxygen content in the molten steel, including the dissolved oxygen and the oxygen content of the oxide in the molten steel. The total oxygen minus the decarburization and desiliconization oxygen is the oxidized oxygen; the decarburization and desiliconization oxygen refers to the amount of oxygen consumed during the decarburization and desiliconization process. The total amount of silicon required to remove the oxidized oxygen is calculated based on the silicon-oxygen chemical balance, and then the amount of silicon required for alloying is added to obtain the total silicon addition. Finally, the corresponding total silicon addition is added by adding ferrosilicon.

[0074] (8) Remove the residue in the molten steel, add the required ferroniobium (65%), and add 500 kg of lime and 300 kg of fluorite for slag making and stirring.

[0075] (9) Nitrogen is used throughout the subsequent smelting and stirring process. Steel is tapped when the following conditions are met: when the temperature reaches 1600-1620°C, the nitrogen content of the molten steel reaches 0.30%; when the temperature reaches 1560-1580°C, the nitrogen content of the molten steel reaches 0.34%.

[0076] Step S4: LF refining.

[0077] (1) The molten steel in the A0D furnace is transferred to the LF furnace (ladle refining furnace). Through argon stirring and trace alloy addition, the elements in the molten steel are fine-tuned to the target content. The target content of each element is shown in Table 3.

[0078] (2) The temperature of the molten steel is adjusted to a range of 1515-1525°C by stirring with argon gas and electrifying the electrodes for casting. In this embodiment, the temperature is adjusted to 1520°C for casting. In other embodiments, the temperature can be adjusted to 1515°C or 1525°C for casting.

[0079] Step S5: continuous casting.

[0080] The casting specification used in this embodiment is 220×220MM. That is, in the continuous casting process, the cross section of the ingot is a square with a side length of 220 mm.

[0081] The continuous casting machine is used to continuously cast the molten steel. In the continuous casting process, the ingot needs to be pulled out of the continuous casting machine at a suitable pulling speed.

[0082] The pulling speed in this embodiment depends on the temperature and superheat of the molten steel.

[0083] The matching relationship between the casting speed and the superheat in this embodiment is shown in Table 4. It should be noted that Table 4 cannot list the casting speeds at each temperature and superheat one by one. When the temperature and superheat used in other embodiments are not included in Table 4, the casting speeds at other temperatures and superheats can be obtained by using the data in Table 4 using the linear interpolation method. Linear interpolation is a well-known technology and will not be described in detail in this embodiment.

[0084] In addition, continuous casting vibration parameters play a key role in the continuous casting process. Reasonable parameter selection can significantly improve the quality and production efficiency of the cast billet. The continuous casting vibration parameters mainly include amplitude S, frequency F and negative sliding time Tn.

[0085]

[0086]

[0087]

[0088] It represents the actual pulling speed, its value is equal to V, and the unit is M / MIN. V represents the set pulling speed (see Table 4), and the unit is M / MIN. h represents the actual amplitude, and its value is equal to S.

[0089] In this embodiment, C1=1.8, C2=1.0, C3=70, C4=45, C5=0, .

[0090] During the continuous casting process, the water volume of the crystallizer is 105 cubic meters / hour to 115 cubic meters / hour. The current and frequency of electromagnetic stirring are set to 200A / 4HZ at the head end and continuous stirring. The water volume during secondary cooling is set to 0.2 liters per ton, and the distribution ratio is 44% for the full roller, 41% for the first stage, and 15% for the second stage.

[0091] The operation of continuous casting is as follows: open the water inlet of the large ladle, put the molten steel into the baked ladle, add the covering agent and the heat preservation agent, and measure the temperature to confirm; open the stopper rod, inject the steel flow into the crystallizer, wait for the molten steel to be immersed in the water inlet, add the protective slag, and start the vibration; slowly increase the pulling speed to match the superheat. Pull the billet out of the continuous casting machine and cut it by flame cutting according to the length requirements; the cut billet is placed on the cooling bed for uniform cooling; the billet in the collection area is lifted to the site by the hoist for pile cooling.

[0092] Table 1: Target composition and content of stainless steel

[0093]

[0094] Table 2: Alloy ingredients

[0095]

[0096] Table 3: Element starting content and target content

[0097]

[0098] Table 4: Superheat and casting speed matching table

[0099]

[0100] Embodiment 2:

[0101] This embodiment provides a control method for the above production process.

[0102] In the above production process, during AOD furnace refining, alloys need to be added to the molten steel multiple times so that the elements such as Ni, Cr, and Mo reach the target content. At the same time, the added alloy is quickly melted and mixed evenly by stirring the molten steel, and nitrogen and oxygen mixed gas is blown into the molten steel to reduce the C content. In this process, a suitable stirring speed and a suitable nitrogen-oxygen ratio can make the added alloy quickly mixed evenly and reduce the number of additions; if the stirring speed does not match the nitrogen-oxygen ratio, it will cause the elements in the added alloy to be lost, such as the elements in the alloy being oxidized into slag, or the added alloy being oxidized into slag or adsorbed by the slag before it is completely melted or mixed evenly, which ultimately requires multiple additions to make the added alloy element content reach the target content, and even affects the purity and production efficiency of the final stainless steel.

[0103] The production process control method of this embodiment controls the stirring speed and nitrogen-oxygen ratio after each alloy addition, so that the stirring speed matches the nitrogen-oxygen ratio to ensure that the added alloy elements can quickly and accurately reach the target content, thereby improving the purity of the stainless steel. Figure 1 As shown, the method comprises the following steps:

[0104] Step S201, in each AOD furnace refining process, record the content change curve of each element, the stirring speed change curve and the nitrogen-oxygen ratio change curve. In all AOD furnace refining processes, the recorded content change curves of all elements, the stirring speed change curves and the nitrogen-oxygen ratio change curves are recorded as historical refining curves.

[0105] During each A0D refining process, multiple molten steel sampling is required to obtain the content of elements such as Ni, Cr, and Mo. After each molten steel sampling, the content of each element and the sampling time of the molten steel are recorded. The molten steel sampling time in this embodiment is accurate to year, month, day, hour, minute, and second. All sampling times during each A0D refining process are used as the horizontal coordinate, and the content of each element is used as the vertical coordinate. The content of each element during each A0D refining process constitutes a content change curve. In this embodiment, only the content change curve of the added element is recorded.

[0106] At the same time, the stirring speed and nitrogen-oxygen ratio of the molten steel between each sampling time and the previous sampling time are recorded. When a sampling time does not have a previous sampling time, the sampling time is not considered. The stirring speed during each A0D refining process constitutes a stirring speed change curve, and the nitrogen-oxygen ratio during each A0D refining process constitutes a nitrogen-oxygen ratio change curve.

[0107] In this embodiment, the time interval between two adjacent samplings is 20 minutes. In other embodiments, the time of each sampling can be determined artificially, and this embodiment does not specifically limit it.

[0108] During all AOD furnace refining processes, the recorded content change curves of all elements, stirring speed change curves and nitrogen-oxygen ratio change curves are recorded as historical refining curves.

[0109] In this embodiment, during all AOD furnace refining processes, during the first to nth AOD furnace refining processes, after the temperature of the AOD furnace rises to 1680°C, during a period of time after the last alloy addition to the next alloy addition, the nitrogen-oxygen ratio in the nitrogen-oxygen mixed gas is w, and w is obtained by randomly selecting a value in the interval [1, 4] as the value of w; wherein n is a preset value, and this embodiment is described by taking n=10 as an example. During the first to nth AOD furnace refining processes, during a period of time after the last alloy addition to the next alloy addition, the stirring speed is p (indicates revolutions per minute), and p is obtained by randomly selecting a value in the interval [200, 400] as the value of p.

[0110] In other embodiments, during all AOD furnace refining processes, from the first to the nth AOD furnace refining process, after the temperature of the AOD furnace is heated to 1680° C., the nitrogen-oxygen ratio and the stirring speed can be manually set or modified according to the specific smelting process.

[0111] The stirring speed and nitrogen-oxygen ratio after the nth AOD furnace refining process are calculated according to the change in the content of each element under different stirring speeds and nitrogen-oxygen ratios in the previous n times and in accordance with the subsequent method.

[0112] Step S202: In the current AOD furnace refining process, sample the molten steel and obtain the content of each element in the molten steel, and obtain the optimal stirring speed and optimal nitrogen-oxygen ratio of each element according to the content of each element and the historical refining curve.

[0113] In this embodiment, the optimal stirring speed and the optimal nitrogen-oxygen ratio of each element are represented by the stirring speed and nitrogen-oxygen ratio used when the content of each element changes fastest during the period between two additional additions of alloy, that is, during the period from the last additional addition of alloy ingredients to the next additional addition of alloy ingredients.

[0114] It should be noted that, since this embodiment is mainly aimed at the alloy ingredients added in the oxygen blowing and decarburization stage, each element in this embodiment refers to the elements in the alloy ingredients added in the oxygen blowing and decarburization stage.

[0115] As an example, the optimal stirring speed and the optimal nitrogen-oxygen ratio for each element are obtained as follows:

[0116] In the current AOD furnace refining process, the content of each element in molten steel is recorded as aa;

[0117] In the historical refining curve, for each element, such as Cr, Ni, and Mo, several element contents with the smallest difference from aa (that is, the absolute value of the difference) are obtained, and the sampling times corresponding to the several element contents with the smallest difference are recorded as the reference sampling times of each element in the current AOD furnace refining process;

[0118] Any reference sampling time is recorded as t, and the previous sampling time of sampling time t is recorded as t1; the content of each element at sampling time t in each AOD furnace refining process is recorded as ft; the content of each element at sampling time t1 is recorded as ft1. as the change rate of each element at sampling time t during the current AOD furnace refining process;

[0119] At all reference sampling times in all AOD furnace refining processes, the reference sampling time with the largest change rate of each element is obtained, and the stirring speed and nitrogen-oxygen ratio at the reference sampling time with the largest change rate are recorded as the optimal stirring speed and optimal nitrogen-oxygen ratio of each element.

[0120] Step S203, in the historical refining curve, according to the content change of each element at each addition under the optimal stirring speed and the optimal nitrogen-oxygen ratio of each element, the loss coefficient of each element under the optimal stirring speed and the optimal nitrogen-oxygen ratio is obtained.

[0121] The optimal stirring speed and optimal nitrogen-oxygen ratio of each element are obtained above. Considering that the optimal stirring speed and optimal nitrogen-oxygen ratio of each element may be different for different elements, it is impossible to directly obtain the stirring speed and nitrogen-oxygen ratio of the molten steel in the current AOD furnace refining process based on the optimal stirring speed and optimal nitrogen-oxygen ratio of all elements.

[0122] This embodiment takes into account that when the alloy is added by the drawing method multiple times, after each addition of the alloy, the elements in the added alloy will be lost due to inappropriate stirring speed and nitrogen-oxygen ratio, which will result in a small number of alloy additions failing to reach the target element content, and multiple alloy additions are required to increase the element content (or the element content is diluted by adding alloy), which ultimately not only reduces the production efficiency of stainless steel, but also causes the situation where the element content cannot be equal to the target content, thereby making the purity of the produced stainless steel unqualified.

[0123] This embodiment describes the loss of elements when adding alloy at the optimal stirring speed and the optimal nitrogen-oxygen ratio through the loss coefficient of each element at the optimal stirring speed and the optimal nitrogen-oxygen ratio, thereby avoiding the situation in which the alloy elements are obviously lost at the stirring speed and nitrogen-oxygen ratio of the molten steel during the current AOD furnace refining process.

[0124] As an example, the loss coefficient of each element at the optimal stirring speed and the optimal nitrogen-oxygen ratio is obtained as follows:

[0125] The sampling time corresponding to the optimal stirring speed and the optimal nitrogen-oxygen ratio of each element is recorded as tmax, and the previous sampling time of sampling time tmax is recorded as t0; in the historical refining curve, the content of each element at sampling time tmax is obtained, recorded as f1, and the content of each element at sampling time t0 is recorded as ft0; the target content of each element is recorded as F1, where F1 is obtained from Table 3.

[0126] Loss coefficient .

[0127] The larger the value is, the less the content of the element increases significantly at sampling time tmax. The larger the value, the greater the difference between the element content at sampling time tmax and the target content. Larger.

[0128] Loss coefficient The larger the value, the more it means that in the historical AOD furnace refining process, after each element is added to the alloy by the pulling method, and at the optimal stirring speed and optimal nitrogen-oxygen ratio of each element, even if the required alloy ingredients are added, the difference between the content of each element and the target content in the molten steel sampled at the tmax moment is still large, indicating that the optimal stirring speed and optimal nitrogen-oxygen ratio of each element will still cause obvious loss of each element. Loss coefficient The smaller it is, it means that in the historical AOD furnace refining process, after each element was supplemented with alloys through the drawing method, and at the optimal stirring speed and optimal nitrogen and oxygen ratio of each element, after the required alloys were added, the difference between the content of each element in the molten steel sampled at tmax and the target content was smaller, indicating that the optimal stirring speed and optimal nitrogen and oxygen ratio of each element will not cause obvious loss of each element.

[0129] Step S204, using the optimal stirring speed and the optimal nitrogen-oxygen ratio of all elements and the loss coefficient of each element, the stirring speed and nitrogen-oxygen ratio of the molten steel in the current AOD furnace refining process are obtained.

[0130] The stirring speed and nitrogen-oxygen ratio of molten steel in the current AOD furnace refining process refer to: in the current AOD furnace refining process, after the molten steel is sampled, the stirring speed of the molten steel and the nitrogen-oxygen ratio of the molten steel are then blown in. Under this stirring speed and nitrogen-oxygen ratio, the added alloy can be kept as free of loss as possible, melted and mixed quickly, and the loss can be reduced.

[0131] As an example, the method for obtaining the stirring speed and nitrogen-oxygen ratio of molten steel in the current AOD furnace refining process is as follows:

[0132] exp(-x) is used as the concern factor of each element, and the concern factors of all elements are normalized. In this embodiment, the softmax method is used for normalization, so that the sum of the normalized concern factors is equal to 1. The normalized concern factors are used as the weights of the optimal stirring speed and the optimal nitrogen-oxygen ratio of each element. The optimal stirring speeds of all elements are weighted and summed according to the weight of each element to obtain the stirring speed of the molten steel in the current AOD furnace refining process; the optimal nitrogen-oxygen ratios of all elements are weighted and summed according to the weight of each element to obtain the nitrogen-oxygen ratio in the current AOD furnace refining process. exp() represents an exponential function with a natural constant as the base.

[0133] In summary, in the AOD furnace refining process currently being carried out, the stirring speed and nitrogen-oxygen ratio of the molten steel before the next molten steel sampling can be obtained after each sampling of the molten steel (after sampling the molten steel, the alloy calculated by the drawing method needs to be added). The AOD furnace refining process (specifically, the process of adding alloys through multiple drawing and matching during the oxygen blowing stage) can automatically change or control the stirring speed of the molten steel and the nitrogen-oxygen ratio of the nitrogen-oxygen mixed gas, which can not only make the element content change quickly, but also reduce the loss of elements as much as possible, thereby improving the production efficiency of stainless steel and improving the purity of stainless steel.

[0134] Embodiment three:

[0135] This embodiment provides another method for obtaining the stirring speed and nitrogen-oxygen ratio of molten steel during the current AOD furnace refining process. The specific process is as follows:

[0136] After obtaining the normalized attention factor of each element, the element whose attention factor is less than the first preset threshold th1 is recorded as the element to be corrected, and the loss coefficient corresponding to the element to be corrected is recorded as Q1. This embodiment is described by taking th1=0.5 as an example, and th1 can be set to other values ​​in other embodiments.

[0137] At all sampling times in all AOD furnace refining processes (including the AOD furnace refining process currently being performed), obtain the sampling time with the second largest change rate of the element to be corrected, and record the stirring speed and nitrogen-oxygen ratio at the sampling time with the second largest change rate as the suboptimal stirring speed and suboptimal nitrogen-oxygen ratio of the element to be corrected;

[0138] The maximum value of the rate of change of the element to be corrected is recorded as q1, and the second maximum value of the rate of change of the element to be corrected is recorded as q2.

[0139] The loss coefficient of the element to be corrected under the suboptimal stirring speed and suboptimal nitrogen-oxygen ratio is obtained, which is recorded as Q2 (similar to step S203).

[0140] make , The larger the value is, the larger the loss coefficient of the element to be corrected under the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio is, and the element change rate corresponding to the element to be corrected under the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio is smaller. At this time, the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio of the element to be corrected are not sufficient to change the content of the element to be corrected efficiently and with low loss compared with the optimal stirring speed and the optimal nitrogen-oxygen ratio. The smaller it is, it means that the loss coefficient of the element to be corrected at the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio is relatively small, and the element change rate corresponding to the element to be corrected at the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio is larger. At this time, the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio of the element to be corrected can change the content of the element to be corrected with high efficiency and low loss compared with the optimal stirring speed and the optimal nitrogen-oxygen ratio.

[0141] In this embodiment, the reference stirring speed vj of the element to be corrected is set to be exp(-w1)×vj1+(1-exp(-w1))×vj0, where vj0 and vj1 represent the optimal stirring speed and the suboptimal stirring speed of the element to be corrected, respectively. This formula makes the reference stirring speed closer to the optimal stirring speed when w1 is larger, and vice versa.

[0142] In this embodiment, the reference nitrogen-oxygen ratio vb of the element to be corrected is set to be exp(-w1)×vb1+(1-exp(-w1))×vb0, wherein vb0 and vb1 represent the optimal nitrogen-oxygen ratio and the suboptimal nitrogen-oxygen ratio of the element to be corrected, respectively.

[0143] In this embodiment, the reference stirring speed of all elements to be corrected and the optimal stirring speed of other elements are averaged to obtain the stirring speed of molten steel during the current AOD furnace refining process. The reference nitrogen-oxygen ratio of all elements to be corrected and the optimal nitrogen-oxygen ratio of other elements are averaged to obtain the nitrogen-oxygen ratio of molten steel during the current AOD furnace refining process.

[0144] Embodiment 4:

[0145] Based on the third embodiment, this embodiment provides a method for obtaining the stirring speed and nitrogen-oxygen ratio of molten steel in the current AOD furnace refining process:

[0146] Update the loss coefficient of the element to be corrected to x1=exp(-w1)×Q2+(1-exp(-w1))×Q1.

[0147] The element to be corrected is obtained again according to the loss coefficient of the element to be corrected, that is, the attention factor of the element to be corrected is obtained according to the loss coefficient of the element to be corrected, and the element to be corrected is obtained again according to the normalized attention factor.

[0148] When the elements to be corrected obtained in this embodiment are included in the elements to be corrected obtained in the third embodiment, and belong to the elements to be corrected obtained in the third embodiment but do not belong to the elements to be corrected obtained in this embodiment, such elements to be corrected are no longer marked as correction elements.

[0149] For the element to be corrected obtained in this embodiment, the following operations are performed: the method in the third embodiment is executed, and the "second largest change rate" and "second largest change rate" in the third embodiment are replaced with the value of the third largest change rate. The "optimal stirring speed" and "optimal nitrogen-oxygen ratio" in the third embodiment are replaced with the "reference stirring speed" and "reference nitrogen-oxygen ratio" obtained in the third embodiment, and the stirring speed and nitrogen-oxygen ratio of the molten steel in the current AOD furnace refining process are obtained again.

[0150] The above process of this embodiment gradually reduces the number of correction elements by allowing the maximum value, the second largest value, and the third largest value of the change rate to participate in the calculation, so that in the current AOD furnace refining process, the stirring speed of the molten steel and the nitrogen-oxygen ratio can reduce the loss of all elements as much as possible, rather than blindly pursuing the maximum element change rate of the element, that is, reducing the loss of elements by sacrificing part of the production efficiency.

[0151] The same can be done in other embodiments, and the method in Embodiment 4 can be repeatedly executed, and the value with the fourth largest change rate and the value with the fifth largest change rate can be gradually included in the calculation, until there is no element to be corrected or the value with the smallest change rate is also included in the calculation and stops.

[0152] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A production process control method for high-purity stainless steel, wherein the production process includes an AOD furnace refining process, wherein several elements are added to the AOD furnace containing molten steel, the molten steel is stirred, and a nitrogen-oxygen mixed gas is introduced into the molten steel, wherein: During each AOD furnace refining process, the content change curve of each element, the stirring speed change curve and the nitrogen-oxygen ratio change curve are recorded; during all AOD furnace refining processes, the content change curves of all elements, the stirring speed change curves and the nitrogen-oxygen ratio change curves are recorded as historical refining curves; In the current AOD furnace refining process, the molten steel is sampled and the content of each element in the molten steel is obtained, and the optimal stirring speed and the optimal nitrogen-oxygen ratio of each element are obtained according to the content of each element and the historical refining curve. The optimal stirring speed and the optimal nitrogen-oxygen ratio refer to the stirring speed and nitrogen-oxygen ratio at the sampling time when the change rate of each element is the largest; In the historical refining curve, under the optimal stirring speed and the optimal nitrogen-oxygen ratio, the loss coefficient of each element under the optimal stirring speed and the optimal nitrogen-oxygen ratio is obtained according to the content change of each element at each addition; Using the optimal stirring speed and the optimal nitrogen-oxygen ratio of all elements and the loss coefficient of each element, the stirring speed and nitrogen-oxygen ratio of the molten steel in the current AOD furnace refining process are obtained; The specific steps of obtaining the optimal stirring speed and the optimal nitrogen-oxygen ratio for each element are as follows: The historical refining curve includes a content change curve of each element in each AOD furnace refining process, the horizontal coordinate of the content change curve of each element is the sampling time of the molten steel, and the vertical coordinate is the content of each element in the sampled molten steel; the historical refining curve includes a stirring speed change curve in each AOD furnace refining process, the horizontal coordinate of the stirring speed change curve is the sampling time of the molten steel, and the vertical coordinate is the stirring speed of the molten steel; the historical refining curve includes a nitrogen-oxygen ratio change curve in each AOD furnace refining process, the horizontal coordinate of the nitrogen-oxygen ratio change curve is the sampling time of the molten steel, and the vertical coordinate is the nitrogen-oxygen ratio in the nitrogen-oxygen mixed gas; In the current AOD furnace refining process, the content of each element in molten steel is recorded as aa; In the historical refining curve, for each element, several contents with the smallest difference from aa are obtained, and the sampling times corresponding to the several contents with the smallest difference are recorded as the reference sampling times of each element in the current AOD furnace refining process; Any reference sampling time is recorded as t, and the previous sampling time of sampling time t is recorded as t1; the content of each element at sampling time t in each AOD furnace refining process is recorded as ft; the content of each element at sampling time t1 is recorded as ft1. as the change rate of each element at sampling time t during the current AOD furnace refining process; At all reference sampling times in all AOD furnace refining processes, obtain the reference sampling time with the largest change rate of each element, and record the stirring speed and nitrogen-oxygen ratio at the reference sampling time with the largest change rate as the optimal stirring speed and optimal nitrogen-oxygen ratio of each element; The specific steps of obtaining the loss coefficient of each element at the optimal stirring speed and the optimal nitrogen-oxygen ratio according to the content change of each element at each addition are as follows: In the historical refining curve, the sampling time corresponding to the optimal stirring speed and nitrogen-oxygen ratio of each element is recorded as tmax, and the previous sampling time of sampling time tmax is recorded as t0; the content of each element at sampling time tmax is recorded as f1, and the content of each element at sampling time t0 is recorded as ft0; the target content of each element is recorded as F1, and the loss coefficient is The method of using the optimal stirring speed and the optimal nitrogen-oxygen ratio of all elements and the loss coefficient of each element to obtain the stirring speed and nitrogen-oxygen ratio of molten steel in the current AOD furnace refining process includes the following specific steps: The loss coefficient is recorded as x, exp(-x) is used as the attention factor of each element, the element whose attention factor is less than the first preset threshold tth1 is recorded as the element to be corrected, and the loss coefficient corresponding to the element to be corrected is recorded as Q1; According to the content of the element to be corrected and the historical refining curve, the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio of each element to be corrected are obtained, wherein the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio refer to the stirring speed and the nitrogen-oxygen ratio at the sampling time when the change rate of each element is the second largest; wherein the maximum value of the change rate of the element to be corrected is recorded as q1, and the second maximum value of the change rate of the element to be corrected is recorded as q2; the loss coefficient of the element to be corrected at the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio is recorded as Q2; Obtain a reference stirring speed of the element to be corrected according to w1 and the optimal stirring speed and the optimal nitrogen-oxygen ratio of the element to be corrected, as well as the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio; The reference stirring speed of all elements to be corrected and the optimal stirring speed of other elements except the elements to be corrected are averaged to obtain the stirring speed of the molten steel during the current AOD furnace refining process; the reference nitrogen-oxygen ratio of all elements to be corrected and the optimal nitrogen-oxygen ratio of other elements except the elements to be corrected are averaged to obtain the nitrogen-oxygen ratio of the molten steel during the current AOD furnace refining process; in exp() represents an exponential function with a natural constant as the base; The reference stirring speed of the element to be corrected is obtained according to w1 and the optimal stirring speed and the optimal nitrogen-oxygen ratio of the element to be corrected, as well as the suboptimal stirring speed and the suboptimal nitrogen-oxygen ratio, and the calculation formula included is: The reference stirring speed vj of the element to be corrected = exp(-w1) × vj1 + (1-exp(-w1)) × vj0, where vj0 and vj1 represent the optimal stirring speed and the suboptimal stirring speed of the element to be corrected, respectively; The reference nitrogen-oxygen ratio vb of the element to be corrected is exp(-w1)×vb1+(1-exp(-w1))×vb0, wherein vb0 and vb1 represent the optimal nitrogen-oxygen ratio and the suboptimal nitrogen-oxygen ratio of the element to be corrected, respectively.

2. The method for controlling the production process of high-purity stainless steel according to claim 1, characterized in that: After adding elements to the molten steel during the AOD furnace refining process, the elements included in the molten steel and the target contents of the included elements are: the target content of C is 0.035%, the target content of Si is 0.35%, the target content of Mn is 3.9%, the target content of P is ≤0.024%, the target content of S is ≤0.005%, the target content of Ni is 10.3%, the target content of Cr is 20.1%, the target content of Mo is 2.3%, the target content of N is 0.35%, and the target content of Nb is 0.40%; During the AOD furnace refining process, the amount of each element added is calculated by multiple drawing method based on the initial content and target content of each element in the molten steel, and then the alloy ingredients are poured into the molten steel and stirred; The alloy ingredients contain each element that needs to be added, and the weight of the elements added to the alloy ingredients is equal to the required amount of each element to be added; The alloy ingredients include: high carbon ferrochrome, Ni iron, pure nickel and ferromolybdenum; the added elements include Cr element, Ni element and Mo element; wherein the high carbon ferrochrome includes 60% of Cr element, the Ni iron includes 9% of Ni element, the pure nickel includes 99% of Ni element, and the ferromolybdenum includes 60% of Mo element.

3. The production process control method of high purity stainless steel according to claim 1, characterized in that: When the nitrogen-oxygen mixed gas is introduced into the molten steel, before the temperature of the AOD furnace is raised to 1680° C., the nitrogen-oxygen ratio of the nitrogen-oxygen mixed gas is set to 0.25; During all the AOD furnace refining processes, from the first to the nth AOD furnace refining processes, when the temperature of the AOD furnace rises to 1680°C, the nitrogen-oxygen ratio in the nitrogen-oxygen mixed gas is w, and the method for obtaining w is: randomly selecting a value in the interval [1, 4] as the value of w; wherein n is a preset value.

4. The method for controlling the production process of high-purity stainless steel according to claim 1, characterized in that: During the AOD furnace refining process, when the C content in the molten steel is lower than the target value, ferrosilicon and 99% electrolytic manganese are added to the molten steel, and 65% ferroniobium is added after removing the residue, and 500KG of lime and 300KG of fluorite are added for slag making and stirring; nitrogen is used entirely during stirring, and when the temperature reaches 1600-1620°C, the nitrogen content of the molten steel reaches 0.30%, and when the temperature reaches 1560-1580°C, the nitrogen content of the molten steel reaches 0.34% before steel is tapped; the additional amounts of ferrosilicon and the electrolytic manganese are calculated by the multi-drawing method.

5. The method for controlling the production process of high-purity stainless steel according to claim 1, characterized in that: The AOD furnace refining process includes LF refining. During the LF refining process, argon stirring and alloy addition are used to make the content of various elements in the molten steel reach the target content of each element. The molten steel temperature is adjusted to 1515-1525°C before casting.

6. The method for controlling the production process of high-purity stainless steel according to claim 5, characterized in that: The LF refining process is followed by continuous casting, in which a continuous casting machine is used for continuous casting. The matching relationship between superheat and pulling speed during the continuous casting process is: when the temperature is ≥1458°C and the superheat is ≥51°C, the pulling speed is set to 0.80M / MIN; when the temperature is between 1457 and 1452°C and the superheat is between 50 and 45°C, the pulling speed is set to 0.85M / MIN; when the temperature is between 1451 and 1447°C and the superheat is between 44 and 40°C, the pulling speed is set to 0.9M / MIN; when the temperature is between 1446 and 1442°C and the superheat is between 39 and 35°C, the pulling speed is set to 1.0M / MIN; when the temperature is between 1441 and 1437°C and the superheat is between 34 and 30°C, the pulling speed is set to 1.1M / MIN; when the temperature is ≤1436°C and the superheat is ≤29°C, the pulling speed is set to 1.2M / MIN.

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