Grain size control method in hot rolling process of ultra-pure austenite medical stainless steel

Abstract

The invention relates to the technical field of austenitic stainless steel production, in particular to a grain size control method in a hot rolling process of ultra-pure austenitic medical stainless steel, which comprises the following steps: smelting, refining and preheating a steel billet; a multi-pass rolling mode is adopted, and the temperature in the hot rolling process of each pass is regulated and controlled, specifically, for each pass, the temperature distribution deviation, the adjacent temperature deviation and the temperature comprehensive deviation degree at each collection moment are obtained; by comparing distribution of hot rolling temperature data in a scanning area at each acquisition moment with distribution of plate rolling thickness, pressure rate deviation distribution at each acquisition moment is obtained, and the temperature of a steel billet area corresponding to the scanning area at each acquisition moment in the next-pass hot rolling process is regulated and controlled. The grain size in the hot rolling process for preparing the stainless steel is controlled. According to the method, the stability and consistency of grain size control are improved by regulating and controlling the hot rolling temperature.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of austenitic stainless steel production, in particular to a grain size control method for an ultra-pure austenitic medical stainless steel hot rolling process. BACKGROUND

[0002] Medical stainless steel refers to stainless steel materials specially used in medical equipment, instruments or implants, which must have high purity, extremely narrow grain size control and no ferrite structure. Among them, the grain size is the key factor to determine the mechanical properties and processing consistency of the material, so the grain size needs to be strictly controlled during rolling.

[0003] In the prior art, the control of grain size is realized through the processing technology. The processing process of austenitic stainless steel is as follows: smelting billets, hot rolling production, solid solution treatment, straightening and shot blasting, pickling and passivation, and grinding production. However, the temperature in the hot rolling process will affect the uniformity of grain growth. If the temperature is set too high, the internal grains of the steel will grow unevenly, causing excessive grain coarsening and reducing the strength and toughness of the steel. If the temperature is set too low, the austenite conversion will not be complete, which will aggravate the oxidation of the material internal grain boundary and deteriorate the mechanical properties of the steel. However, in the hot rolling process, the rolling is mainly carried out by fixing the hot rolling temperature, so it is difficult to accurately control the grain size. Therefore, in order to prepare ultra-pure austenitic medical stainless steel, it is necessary to further optimize the control of grain size in the rolling process. SUMMARY

[0004] In view of the above, it is necessary to provide a grain size control method for an ultra-pure austenitic medical stainless steel hot rolling process. Compared with the traditional grain size control method for the hot rolling process of medical stainless steel, the stability and consistency of the grain size control are improved by adjusting the hot rolling temperature.

[0005] The grain size control method for an ultra-pure austenitic medical stainless steel hot rolling process provided by the application adopts the following technical scheme: One embodiment of the application provides a grain size control method for an ultra-pure austenitic medical stainless steel hot rolling process, which comprises the following steps: (1) smelting, refining and preheating the billet; (2) adopting a multi-pass rolling method to adjust the temperature in each pass of the hot rolling process, specifically: After each pass of hot rolling, the hot rolling temperature data and the plate rolling thickness of each sampling point in the scanning area are collected by a sensor arranged directly above the billet; for each pass, the temperature distribution deviation at each collection time is obtained by the maximum distribution range and the dispersion of the hot rolling temperature data in the scanning area at each collection time after hot rolling, and the temperature comprehensive deviation degree at each collection time is obtained by combining the adjacent pass temperature deviation obtained by comparing the hot rolling temperature data in the scanning area at each collection time and the adjacent collection time; the pressure ratio deviation distribution at each collection time is obtained by comparing the distribution of the hot rolling temperature data in the scanning area at each collection time and the distribution of the plate rolling thickness, and then the temperature of the billet region corresponding to the scanning area at each collection time in the next pass of hot rolling is regulated in combination with the temperature distribution deviation, so as to control the grain size of the hot rolling process of the prepared stainless steel.

[0006] In one embodiment, the initial heating temperature in the preheating process is 350℃, and the holding time is 3-4 hours.

[0007] In one embodiment, after heating to the initial temperature and holding, the temperature is raised to 800℃, and the holding time is 6-7 hours; then the temperature is raised to 1280-1310℃, and the holding time is 4-5 hours.

[0008] In one embodiment, in the process of the multi-pass rolling, the deformation amount is controlled to be 10-15% in the rolling process of each pass except the last pass, and the deformation amount is controlled to be 20-30% in the final pass rolling process.

[0009] In one embodiment, the temperature distribution deviation is obtained by: calculating the range and dispersion of the hot rolling temperature data of all sampling points in the scanning area at each collection time; the temperature distribution deviation is obtained by fusing the range and the dispersion.

[0010] In one embodiment, the adjacent pass temperature deviation is obtained by: calculating the difference value of the hot rolling temperature data of each same position sampling point between the scanning area at each collection time and the scanning area at the adjacent collection time; the adjacent pass temperature deviation is the mean value of all the difference values corresponding to each collection time.

[0011] In one embodiment, the temperature comprehensive deviation degree is obtained by: calculating the cumulative value of the temperature distribution deviation and the adjacent pass temperature deviation at each collection time; the temperature comprehensive deviation degree is proportional to the cumulative value.

[0012] In one embodiment, the acquisition process of the press rate deviation distribution is as follows: respectively acquire all the clustering clusters of the hot rolling temperature data and the plate rolling thickness of all the sampling points in the scanning area at any acquisition time, calculate the average value of all the elements in each clustering cluster, sort all the clustering clusters of the hot rolling temperature data and all the clustering clusters of the plate rolling thickness according to the average value, and select the clustering cluster at the middle position from the sorted clustering clusters; count the intersection and the union of the sampling points corresponding to the two selected clustering clusters, and calculate the ratio of the number of elements in the intersection to the number of elements in the union; the difference between 1 and the ratio is taken as the press rate deviation distribution at the acquisition time.

[0013] In one embodiment, the temperature of the scanning area corresponding to the billet area at the next pass hot rolling process at each acquisition time is regulated, including: calculate the average value of the temperature comprehensive deviation and the press rate deviation distribution; calculate the product of the average value and the preset temperature allowable deviation; obtain the temperature of the scanning area corresponding to the billet area at the next pass hot rolling process at each acquisition time after each pass hot rolling by combining the product and the preset initial temperature in the next pass hot rolling process.

[0014] In one embodiment, the temperature of the scanning area corresponding to the billet area at the next pass hot rolling process at each acquisition time after each pass hot rolling is the cumulative sum of the product and the preset initial temperature in the next pass hot rolling process.

[0015] The present application has at least the following beneficial effects: The present application calculates the temperature distribution deviation through the range and dispersion of the hot rolling temperature, measures the deviation of temperature control from two aspects, provides accurate evaluation indexes for subsequent temperature regulation, helps to more accurately adjust the hot rolling temperature, and ensures the uniformity and stability of the temperature in the hot rolling process; by comparing the hot rolling temperatures at adjacent acquisition times, calculating the adjacent pass temperature deviation, evaluating the continuity of temperature change, helping to find the mutation or abnormal fluctuation of temperature, providing an important basis for evaluating the stability of the crystallization process in the hot rolling process, and then being able to timely adjust the temperature control strategy, optimize the crystallization conditions, and improve the precision and stability of the grain size control; and then comprehensively evaluating the temperature distribution deviation and the adjacent pass temperature deviation, evaluating the influence of the temperature in the hot rolling process on the grain growth, providing a more comprehensive basis for the temperature regulation in the hot rolling process, and being conducive to more accurately evaluating the influence of temperature change on the grain growth, and being able to more accurately adjust the hot rolling temperature in the next pass; Further, by analyzing the distribution of the rolling thickness of the plate and the distribution of the hot rolling temperature, the influence of the temperature deviation on the pressing rate of the billet is evaluated, which provides a more comprehensive reference for temperature regulation, further improves the accuracy of temperature regulation, reduces the uneven thickness caused by temperature deviation, ensures the stability and consistency of grain size control, and further adaptively regulates the temperature in the next hot rolling process, which can more accurately control the grain size and ensure that the grain size is within a small range, meet the demand of medical stainless steel with extremely narrow grain size, and improve the mechanical properties and processing consistency of the product. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0017] Figure 1 A step flow chart of a grain size control method for a hot rolling process of ultra-pure austenitic medical stainless steel provided by the present application is shown in the figure. Figure 2 A sensor deployment schematic diagram is shown in the figure. Figure 3 A temperature regulation flow chart is shown in the figure. DETAILED DESCRIPTION

[0018] In the description of the embodiments of the present application, the words "exemplary", "or", "for example" are used to mean example, illustration or description. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the words "exemplary", "or", "for example" are intended to present the relevant concept in a specific manner.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as understood by those skilled in the art to which the present application belongs. The terms used in the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application. It should be understood that, in the present application, unless otherwise specified, " / " means or.

[0020] In addition, it should be noted that the terms "first", "second" in the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence.

[0021] The specific scheme of the grain size control method for the hot rolling process of ultra-pure austenitic medical stainless steel provided by the present application will be described in detail below in combination with the drawings.

[0022] Embodiment 1 Embodiment 1 provides a grain size control method for a hot rolling process of an ultra-pure austenitic medical stainless steel, and specifically, refer to Figure 1 The method comprises the following steps: Step 1, billet processing.

[0023] In this embodiment, the steel billet has the following composition: the content of carbon C is 0.04wt%, the content of silicon Si is 0.61wt%, the content of manganese Mn is 0.87wt%, the content of phosphorus P is 0.03wt%, the content of sulfur S is 0.001wt%, the content of chromium Cr is 17.2wt%, the content of nickel Ni is 9.1wt%, the content of nitrogen N is 0.01wt%, the content of titanium Ti is 0.26wt%, and the balance is iron Fe.

[0024] The steel billet is smelted by an electric arc furnace (EAF), smelted by an AOD furnace (argon oxygen decarburization furnace), and refined by an LF furnace (LF furnace refining), and is cast by a vertical continuous casting machine. Before hot rolling, the steel billet is preheated, and temperature control is performed during preheating. The heating starting temperature is 350℃, and the temperature is maintained for 3 hours; then slowly heated to 800℃, and maintained for 6 hours; and then heated to 1280℃, and maintained for 4 hours.

[0025] Step 2, sectional hot rolling.

[0026] In this embodiment, a multi-pass rolling method is used, and a sectional stepped heating is used to eliminate internal stress of the steel billet, improve plasticity, improve metal organization, and avoid excessive grain growth. During the multi-pass rolling process, the temperature interval is controlled to be 1000℃-1310℃. At the same time, the deformation amount is controlled to be 10% during the rolling process of each pass except the last pass, and the deformation amount is controlled to be 20% during the final pass rolling process, so as to ensure that the total reduction rate is 80% during the hot rolling process, so that the thickness of the plate meets the production requirements.

[0027] During the hot rolling process, the steel is deformed at high temperature to soften and then recrystallize, thereby forming a single-phase organization. In actual hot rolling process, the hot rolling temperature is often set based on empirical value, but is affected by internal crystallization difference of the steel or deviation of the reduction rate, so that the hot rolling temperature deviates from the actual requirement, thereby causing the grain size of the prepared steel to be inconsistent with the requirement, and the control ability of the grain size is weak. Therefore, based on the hot rolling condition of the steel billet plate, automatic regulation and control of the temperature is realized, so as to improve the control precision of the grain size.

[0028] Step 2.1, after each pass of hot rolling, the hot rolling temperature data and the rolling thickness of each sampling point in the scanning area are collected by the sensors arranged above the billet.

[0029] In order to control the temperature in the process of hot rolling, sensors are arranged above the billet after each pass of hot rolling to collect relevant data in the process of hot rolling in real time. The arrangement of the sensors is shown in Figure 2 Figure 2 1 represents the sensor, 2 represents the roller of hot rolling, 3 represents the billet, 4 represents the movement direction of the billet, and 5 represents the scanning area of data collection. By arranging temperature sensors and thickness sensors, the hot rolling temperature data and the rolling thickness of each sampling point in the scanning area are collected in real time.

[0030] Based on the moving speed of the billet, the collection time interval of the hot rolling temperature data and the rolling thickness is controlled to control the next pass of hot rolling according to the result of each pass of hot rolling. In this embodiment, the j+1th pass of hot rolling is controlled according to the result of the jth pass of hot rolling. Specifically, if the distance from the center point of the scanning area after the jth pass of hot rolling to the contact center point of the j+1th roller and the billet is d, the unit is m, and the movement speed of the billet is v, the unit is m / s, then the collection time interval of the hot rolling temperature data and the rolling thickness is , the unit is s. Meanwhile, multiple sampling points are uniformly arranged in the scanning area.

[0031] In this embodiment, the number of sampling points in each scanning area is 16, and the implementer can set the number of sampling points according to the actual situation, and the present application does not make special limitation.

[0032] Step 2.2, for each pass, the temperature distribution deviation at each collection time is obtained by the maximum distribution range and the dispersion of the hot rolling temperature data in the scanning area at each collection time after hot rolling, and the adjacent temperature deviation at each collection time is obtained by comparing the hot rolling temperature data in the scanning area at each collection time and its adjacent collection time, and the temperature comprehensive deviation degree at each collection time is obtained.

[0033] In the process of hot rolling, the temperature is often controlled by adopting the method of quick rolling to reduce the rolling time, prevent the temperature from being out of control due to too long time, and avoid the problem of critical deformation. In addition, in the process of rolling, the temperature uniformity of the whole billet needs to be ensured as much as possible to eliminate the internal stress of the billet, optimize the metal organization, avoid the excessive growth of grains due to uneven temperature distribution, and make the control of grain size deviate.

[0034] ​Based on the above analysis, for the scanning area after the jth pass hot rolling, the scanning area is collected multiple times, and the hot rolling temperature data of multiple sampling points is collected each time. Taking the nth collection time as an example, if the temperature control is ideal, the hot rolling temperature data of multiple sampling points is closer. If the hot rolling temperature data of the sampling points in the scanning area at the nth collection time is larger, the temperature deviation in the jth pass hot rolling process is larger, and the temperature control effort of the j+1th pass hot rolling needs to be improved.

[0035] Based on the above analysis, the maximum distribution range and dispersion of the hot rolling temperature data in the scanning area at the nth collection time are obtained to obtain the temperature distribution deviation at the nth collection time, specifically: The range and dispersion of the hot rolling temperature data of all sampling points in the scanning area at the nth collection time are calculated. The temperature distribution deviation at the nth collection time is obtained by fusing the range and the dispersion.

[0036] In this embodiment, the dispersion is the average absolute deviation, wherein the calculation of the average absolute deviation is a known technology, and will not be described herein. As other embodiments, on the basis of being able to measure the distribution unevenness of the hot rolling temperature data, the implementer can use other existing technologies, such as standard deviation, coefficient of variation, etc., which are not specially limited by the present application.

[0037] It should be noted that fusion refers to combining multiple independent variables in a way to enhance the overall effect, which can be realized by calculating the sum, calculating the product, etc., which is not specially limited by the present application.

[0038] In this embodiment, the sum of the range and the dispersion is taken as the temperature distribution deviation at the nth collection time.

[0039] It should be noted that the temperature distribution deviation measures the deviation of the temperature control in the jth pass hot rolling from two aspects, wherein the range can reflect the overall temperature deviation, and the dispersion measures the distribution unevenness of the hot rolling temperature data of all sampling points. The larger the calculated temperature distribution deviation is, the higher the imbalance degree of the matching between the temperature control and the rolling requirement in the jth pass hot rolling is.

[0040] In addition, since the processing process of the billet is a continuous casting type processing process, the temperature control of the billet has a certain continuity, that is, the temperature distribution in the scanning area at the nth collection time should be close to the temperature distribution in the scanning area at the n-1th collection time. If the hot rolling temperature data deviation of the adjacent two collection times is larger, the crystallization of the billet at the adjacent two collection times is larger, and the temperature control effort of the j+1th pass hot rolling needs to be increased.

[0041] Based on the above analysis, by comparing the hot rolling temperature data in the scanning area at the n-th acquisition time and the adjacent acquisition time thereof, the adjacent temperature deviation at the n-th acquisition time is obtained, and the expression is: , wherein, indicates the adjacent temperature deviation at the n-th acquisition time; M indicates the total number of sampling points in a single scanning area; indicates the difference value between the hot rolling temperature data of the i-th sampling point in the scanning area at the n-th acquisition time and the hot rolling temperature data of the i-th sampling point in the scanning area at the adjacent acquisition time.

[0042] In this embodiment, the difference value is the absolute value of the difference, and as other embodiments, on the basis of measuring the difference between the hot rolling temperature data, the implementer can use other calculation methods, such as the square of the difference, the ratio, etc., which are not specially limited in this application.

[0043] In this embodiment, in the process of calculating the adjacent temperature deviation, the adjacent acquisition time of the n-th acquisition time refers to the n-1-th acquisition time.

[0044] It should be noted that the adjacent temperature deviation mainly evaluates the crystallization difference of the billet at the adjacent acquisition time through the difference between the hot rolling temperature data of the corresponding sampling points at the adjacent acquisition time; the greater the difference between the hot rolling temperature data, the greater the crystallization difference of the billet at the adjacent acquisition time.

[0045] Further, the temperature comprehensive deviation degree at the n-th acquisition time is obtained by combining the temperature distribution deviation at the n-th acquisition time and the adjacent temperature deviation, and specifically: The cumulative value of the temperature distribution deviation at the n-th acquisition time and the adjacent temperature deviation is calculated; The temperature comprehensive deviation degree at the n-th acquisition time is proportional to the cumulative value.

[0046] In this embodiment, the expression of the temperature comprehensive deviation degree at the n-th acquisition time is: ; wherein, indicates the temperature comprehensive deviation degree at the n-th acquisition time; indicates the temperature distribution deviation at the n-th acquisition time; indicates the adjacent temperature deviation at the n-th acquisition time; indicates the preset temperature allowable deviation, which is in ℃, and indicates the allowable temperature deviation of the billet surface. Generally, the allowable temperature deviation range of the billet surface is ±25℃, so in this embodiment, the value of is 50℃, and the temperature allowable deviation is used for non-dimensional conversion.

[0047] It should be noted that: by the distribution of hot rolling temperature data at the nth acquisition time and the temperature difference with the adjacent acquisition time, the temperature deviation in the jth pass hot rolling process is evaluated; the greater the calculated temperature comprehensive deviation degree, the greater the temperature control deviation of the scanning area corresponding to the billet region at the nth acquisition time in the jth pass hot rolling process.

[0048] Step 2.3, by comparing the distribution of hot rolling temperature data in the scanning area at each acquisition time and the distribution of plate rolling thickness, the rolling rate deviation distribution at each acquisition time is obtained.

[0049] In the hot rolling process, the material of the billet is mainly softened by heating, so that the uniform softening deformation of the billet is realized by rolling. When the temperature deviation occurs, the hardness of the billet material will be different, so that the thickness of the billet during rolling will be different, so it is necessary to analyze the rolling thickness of the billet, that is, the rolling rate, to realize the hot rolling temperature control.

[0050] For the temperature distribution and thickness distribution at the nth acquisition time, the hot rolling temperature data of all sampling points in the scanning area at the nth acquisition time and the plate rolling thickness of each cluster are obtained, the average value of all elements in each cluster is calculated, all clusters of hot rolling temperature data are arranged in descending order according to the average value, and the cluster at the middle position is recorded as the temperature distribution cluster. The cluster before the temperature distribution cluster may represent the cluster of hot rolling temperature data that causes the grain to grow excessively due to too high temperature, and the cluster after the temperature distribution cluster may represent the cluster of hot rolling temperature data that causes incomplete austenite transformation due to too low temperature, and the temperature distribution cluster is closer to the ideal hot rolling temperature range. All clusters of plate rolling thickness are arranged in descending order according to the average value, and the cluster at the middle position is recorded as the thickness distribution cluster. The cluster before the thickness distribution cluster may represent the cluster of plate rolling thickness that causes local thickness to exceed the standard due to uneven rolling, and the cluster after the thickness distribution cluster may represent the cluster of plate rolling thickness that causes material performance to decline due to excessive local rolling, and the thickness distribution cluster is closer to the ideal rolling thickness.

[0051] In this embodiment, K-means algorithm is used to obtain three clusters of hot rolling temperature data and plate rolling thickness. The K-means algorithm is a known technology, and this application will not be repeated. As other embodiments, as long as the hot rolling temperature data and plate rolling thickness can be clustered, the implementer can use other existing feasible technologies, and this application does not make special limitations. Three is only one embodiment of this application, and the implementer can set its specific value according to the actual situation, and this application does not make special limitations.

[0052] Ideally, the sampling point of the hot rolling temperature close to the ideal hot rolling temperature range is the same as the sampling point of the rolling thickness close to the ideal rolling thickness. If the sampling points corresponding to the temperature distribution clustering cluster and the thickness distribution clustering cluster are more different in the actual hot rolling process, the deviation of the pressing rate of the billet is larger when the temperature distribution is uneven.

[0053] Based on the above analysis, by comparing the sampling points to which the elements in the temperature distribution clustering cluster and the thickness distribution clustering cluster belong, the pressing rate deviation distribution at the nth acquisition time is obtained, and the expression is: In the formula, The pressing rate deviation distribution at the nth acquisition time is represented by The set composed of the sampling points to which all elements in the temperature distribution clustering cluster at the nth acquisition time belong is represented by The set composed of the sampling points to which all elements in the thickness distribution clustering cluster at the nth acquisition time belong is represented by And The intersection operation and the union operation in the set operation are represented by and respectively; and the statistical quantity operation is represented by num().

[0054] It should be noted that the pressing rate deviation distribution measures the influence of the temperature deviation on the pressed thickness of the billet through the intersection and union ratio between the temperature distribution clustering cluster and the corresponding sampling points. When the pressed thickness is inconsistent, the grain stretching size in the billet will be inconsistent, which will affect the recrystallization degree of the grain.

[0055] Step 2.4, by the pressing rate deviation distribution and the temperature distribution deviation at each acquisition time, the temperature of the billet region corresponding to the scanning region at the next pass hot rolling process is controlled to control the grain size of the hot rolling process of the prepared stainless steel.

[0056] Further, by the hot rolling of the jth pass, the temperature in the j+1th pass hot rolling process is controlled, specifically: by the temperature distribution deviation and the pressing rate deviation distribution at the nth acquisition time, combined with the preset temperature allowable deviation, the temperature of the billet region corresponding to the scanning region at the nth acquisition time in the j+1th pass hot rolling process is controlled, and the expression is: In the formula, The temperature of the billet region corresponding to the scanning region at the nth acquisition time after the jth pass hot rolling in the j+1th pass hot rolling process is represented by The preset initial temperature in the j+1th pass hot rolling process is represented by The value of in this embodiment is 1240℃; , respectively represent the temperature comprehensive deviation degree and the pressure rate deviation distribution at the n-th collection moment after the j-th hot rolling; represents the preset temperature allowable deviation.

[0057] It should be noted that the temperature of the steel billet region corresponding to the scanning region at the n-th collection moment after the j-th hot rolling is regulated in the j+1-th hot rolling process through the temperature distribution and the thickness distribution. The temperature regulation flow chart is shown in Figure 3 .

[0058] Step 3, solution treatment.

[0059] The obtained hot-rolled plate is subjected to solution treatment in a normalizing furnace, and the solution treatment is carried out in a step-by-step manner, the holding rate is 2.8 min / mm, and the rapid cooling is carried out in a water cooling manner.

[0060] Step 4, sampling test.

[0061] In order to verify whether the treated stainless steel plate meets the requirements, a sampling test is carried out for performance measurement, and the stainless steel plate is subjected to plate shape straightening and shot blasting before the performance measurement, and then online sampling is carried out.

[0062] Step 5, pickling and passivation.

[0063] In order to remove the oxide skin formed on the surface of the plate after heat treatment, expose the pure metal surface, form a passivation film, and improve the corrosion resistance of the plate, pickling is required. In the pickling process, the stainless steel plate is pickled at a temperature of 50℃ with 150g / L sulfuric acid; in the passivation process, the pickled stainless steel plate is passivated at a temperature of 35℃ with mixed acid, wherein the mixed acid is mixed by 200g / L nitric acid and 20g / L hydrofluoric acid; the stainless steel plate after passivation treatment is surface cleaned with fresh water and dried with hot air at 100℃.

[0064] Step 6, grinding production.

[0065] In order to further reduce surface defects, in the stainless steel processing process, the surface is polished with a grinding wheel to remove visible defects, while ensuring that the thickness of the polished steel meets the corresponding standard requirements, and the polishing point is required to be rectangular.

[0066] Example 2 The grain size control method of the hot rolling process of the ultra-pure austenitic medical stainless steel provided in Example 2 is specific, please refer to Figure 1 , which comprises the following steps: Step 1, billet treatment.

[0067] The billets are smelted by an electric arc furnace (EAF), smelted by an AOD furnace (argon oxygen decarburization furnace) and refined by an LF furnace (LF furnace refining), and cast by a vertical continuous casting machine. Before hot rolling, the billets are preheated, and temperature control is performed during the preheating process. The heating starting temperature is 350℃, and the temperature is kept for 3.5 hours. Then the temperature is slowly increased to 800℃, and the temperature is kept for 6.5 hours. Then the temperature is continuously increased to 1295℃, and the temperature is kept for 4.5 hours. The remaining operations are the same as those in Example 1.

[0068] Step 2, sectional hot rolling.

[0069] In this embodiment, a multi-pass rolling method is used, and a sectional stepped heating is used to eliminate internal stress of the billets, improve plasticity, improve metal organization and avoid excessive grain growth. During the multi-pass rolling process, the temperature interval is controlled to be 1000℃-1310℃. At the same time, the deformation amount is controlled to be 12% during the rolling process of each pass except the last pass, and the deformation amount is controlled to be 25% during the rolling process of the final pass, so as to ensure that the total reduction rate is 88% during the hot rolling process, and the thickness of the plate meets the production requirements.

[0070] Step 3, solid solution treatment.

[0071] The obtained hot-rolled plate is subjected to solid solution treatment by using a normalizing furnace, and the solid solution treatment is performed in a sectional manner, the holding rate is 2.8min / mm, and the rapid cooling is performed by using water cooling.

[0072] Step 4, sampling test.

[0073] In order to verify whether the treated stainless steel plate meets the requirements, a sampling test is performed to measure the mechanical properties, and the plate shape straightening and shot blasting are performed on the stainless steel plate before the measurement of the mechanical properties, and then the online sampling is performed.

[0074] Step 5, pickling and passivation.

[0075] In order to remove the oxide skin formed on the surface of the plate after heat treatment, expose the pure metal surface, form a passivation film and improve the corrosion resistance of the plate, pickling is required. In the pickling process, the stainless steel plate is pickled by 275g / L sulfuric acid at a temperature of 62℃; in the passivation process, the pickled stainless steel plate is passivated by mixed acid at a temperature of 45℃, wherein the mixed acid is mixed by 275g / L nitric acid and 45g / L hydrofluoric acid; the stainless steel plate after passivation treatment is surface cleaned by fresh water, and hot air is dried at 200℃.

[0076] Step 6, grinding production.

[0077] In order to further reduce surface defects, in the stainless steel processing process, the surface is polished by using a grinding wheel to remove visible defects, while ensuring that the thickness of the polished steel meets the corresponding standard requirements, and the polished point is rectangular.

[0078] Example 3 Example 3 provides a grain size control method for the hot rolling process of ultra-pure austenitic medical stainless steel. For details, please refer to Figure 1 The method comprises the following steps: Step 1, billet treatment.

[0079] The steel billet is smelted by an electric arc furnace (EAF), an AOD furnace (argon oxygen decarburization furnace), and an LF furnace (LF furnace refining), and is cast by a vertical continuous casting machine. Before hot rolling, the steel billet is preheated, and temperature control is performed during preheating. The heating starting temperature is 350°C, and the temperature is maintained for 4 hours; then slowly heated to 800°C, and maintained for 7 hours; continue to heat to 1310°C, and maintain for 5 hours. The remaining operations are consistent with Example 1.

[0080] Step 2, sectional hot rolling.

[0081] In this embodiment, a multi-pass rolling method is used, and a sectional stepped heating is used to eliminate internal stress of the steel billet, improve plasticity, improve metal organization, and avoid excessive grain growth. During the multi-pass rolling process, the temperature interval is controlled to be 1000°C-1310°C. At the same time, the deformation amount is controlled to be 15% during the rolling process of each pass except the last pass, and the deformation amount is controlled to be 30% during the final pass rolling process, so as to ensure that the total reduction rate is 97% during the hot rolling process, so that the thickness of the plate meets the production requirements.

[0082] Step 3, solid solution treatment.

[0083] The obtained hot-rolled plate is subjected to solid solution treatment by using a normalizing furnace, and is subjected to sectional solid solution treatment, the temperature holding rate is 2.8 min / mm, and the water cooling method is used for rapid cooling.

[0084] Step 4, sampling test.

[0085] In order to verify whether the treated stainless steel plate meets the requirements, a sampling test is performed to measure the mechanical properties, and the plate shape is straightened and shot blasted before measuring the mechanical properties, and then online sampling is performed.

[0086] Step 5, pickling and passivation.

[0087] In order to remove the oxide skin formed on the surface of the plate after heat treatment, expose the pure metal surface, form a passivation film, and thus improve the corrosion resistance of the plate, pickling is required. In the pickling process, the stainless steel plate is pickled at a temperature of 75°C with 400 g / L sulfuric acid; in the passivation process, the pickled stainless steel plate is passivated at a temperature of 55°C with mixed acid, wherein the mixed acid is prepared by mixing 350 g / L nitric acid and 70 g / L hydrofluoric acid; and the passivated stainless steel plate is surface cleaned with fresh water and dried with hot air at 300°C.

[0088] Step 6, grinding production.

[0089] In order to further reduce surface defects, in the stainless steel processing process, a grinding wheel is used to polish the surface to remove visible defects, while ensuring that the thickness of the polished steel meets the corresponding standard requirements, and the polished point is rectangularized.

[0090] Further, after selecting the stainless steel plate sample for performance testing, the technical parameters of the stainless steel plate sample are measured, and the specific measurement method is: Grain size measurement: based on the test standard ASTM E112-2013 "Standard Test Method for Determining Average Grain Size", the grain size of the stainless steel plate produced in Example 1 is measured.

[0091] Grain size difference: based on the test standard ASTM E112-2013 "Standard Test Method for Determining Average Grain Size", by measuring the primary and secondary grain size grades in Example 1, the absolute value of the difference between the two is taken as the grain size difference of the stainless steel plate sample.

[0092] Mechanical property test: based on the test standard ASTM A370-2018 "Test Methods and Definitions for Mechanical Testing of Steel Products", the mechanical properties of the stainless steel plate produced in Example 1 are measured, including yield strength, tensile strength, elongation and hardness.

[0093] In order to verify the effectiveness of the present application, a plurality of comparative examples are constructed, specifically: Comparative Example 1: coarse rolling and fine rolling of the steel billet are realized at 1000°C, the remaining operations are consistent with Example 1, and the technical parameters of the stainless steel plate are measured in the same way.

[0094] Comparative Example 2: coarse rolling and fine rolling of the steel billet are realized at 1200°C, the remaining operations are consistent with Example 1, and the technical parameters of the stainless steel plate are measured in the same way.

[0095] Comparative Example 3: coarse rolling and fine rolling of the steel billet are realized at 1300°C, the remaining operations are consistent with Example 1, and the technical parameters of the stainless steel plate are measured in the same way.

[0096] Comparative Example 4: Rough rolling of the steel billet was achieved at 1300℃, fine rolling was performed at 1000℃, and the technical parameters of the stainless steel plate were measured in the same way.

[0097] After obtaining the technical parameters of the stainless steel plates produced in Example 1 and Comparative Examples 1, 2, 3, and 4, a comparison table of technical parameters was constructed, as shown in Table 1.

[0098] Table 1 Comparison table of technical parameters Number Grain size Grain size difference Yield strength Tensile strength Elongation Hardness Example 1 7 / 7 0 268 630 70 175 Comparative Example 1 4 / 6 2 205 560 68 149 Comparative Example 2 5 / 6 1 219 585 62 152 Comparative Example 3 5 / 6 1 222 575 65 150 Comparative Example 4 6.5 / 6.5 0 250 600 67 162 As can be seen from Table 1, the grain size of the medical stainless steel produced in Example 1 meets the requirements (ASTM A240M-2019, ≤7 grade), and the difference in grain size is not more than 1. The stainless steel produced in Example 1 has a narrow grain size control and can meet the production requirements of medical use, and has better mechanical properties.

[0099] In summary, by calculating the temperature distribution deviation through the range and dispersion of the hot rolling temperature, the deviation of temperature control is measured from two aspects, which provides accurate evaluation indexes for subsequent temperature regulation, helps to more accurately adjust the hot rolling temperature, and ensures the uniformity and stability of the temperature in the hot rolling process; by comparing the hot rolling temperature at adjacent collection times and calculating the adjacent temperature deviation, the continuity of temperature change is evaluated, which helps to find the mutation or abnormal fluctuation of temperature, provides an important basis for evaluating the stability of the crystallization process in the hot rolling process, and then the temperature control strategy can be adjusted in time to optimize the crystallization conditions and improve the precision and stability of grain size control; then, by comprehensively evaluating the temperature distribution deviation and the adjacent temperature deviation, the influence of temperature on grain growth in the hot rolling process is evaluated, which provides a more comprehensive basis for temperature regulation in the hot rolling process, and is conducive to more accurately evaluating the influence of temperature change on grain growth, which can more accurately adjust the hot rolling temperature in the next pass; Further, by analyzing the distribution of the plate rolling thickness and the distribution of the hot rolling temperature, the influence of temperature deviation on the reduction rate of the steel billet is evaluated, which provides a more comprehensive reference for temperature regulation, further improves the precision of temperature regulation, reduces the thickness unevenness caused by temperature deviation, and ensures the stability and consistency of grain size control; then, the temperature in the next hot rolling process is adaptively regulated, which can more accurately control the grain size, ensure that the grain size is within a small range, meet the requirements of medical stainless steel with extremely narrow grain size, and improve the mechanical properties and processing consistency of the product.

[0100] The computer program instructions can also be loaded onto a computer, other programmable data processing apparatus, or other processing devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other processing devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0101] It is apparent that a person skilled in the art can make a variety of modifications to the application described herein without departing from the spirit and scope of the application. Therefore, the described embodiments are to be considered in all respects as illustrative and not restrictive.

Claims

1. A method of controlling the grain size of an ultra-pure austenitic medical stainless steel in a hot rolling process, characterized in that, The method comprises the following steps: (1) smelting, refining and preheating the billet; (2) controlling the temperature in each pass hot rolling process by adopting a multi-pass rolling mode, specifically: After each pass hot rolling, the hot rolling temperature data and the plate rolling thickness of each sampling point in the scanning area are collected by the sensor arranged directly above the billet; for each pass, the temperature distribution deviation at each collection time is obtained by the maximum distribution range and the dispersion of the hot rolling temperature data in the scanning area at each collection time after hot rolling; the adjacent pass temperature deviation at each collection time is obtained by comparing the hot rolling temperature data in the scanning area at each collection time and the adjacent collection time; the temperature comprehensive deviation degree at each collection time is obtained by combining the temperature distribution deviation and the adjacent pass temperature deviation; the rolling rate deviation distribution at each collection time is obtained by comparing the distribution of the hot rolling temperature data and the distribution of the plate rolling thickness in the scanning area at each collection time, and the temperature of the billet region corresponding to the scanning area at each collection time in the next pass hot rolling process is controlled to control the grain size of the hot rolling process for preparing stainless steel.

2. A method of controlling the grain size of an ultra-pure austenitic medical stainless steel in a hot rolling process according to claim 1, characterized in that, The initial heating temperature in the preheating process is 350 DEG C, and the holding time is 3-4 hours.

3. A method of controlling the grain size of an ultra-pure austenitic medical stainless steel in a hot rolling process according to claim 2, characterized in that, After heating to the initial temperature and holding in the preheating process, the temperature is raised to 800 DEG C, and the holding time is 6-7 hours; then the temperature is raised to 1280-1310 DEG C, and the holding time is 4-5 hours.

4. The method of controlling the grain size of an ultra-pure austenitic medical stainless steel in a hot rolling process according to claim 1, wherein the steel is heated to a temperature of 1,100°C to 1,200°C. In the process of multi-pass rolling, the deformation amount is controlled to be 10-15% in the rolling process of each pass except the last pass, and the deformation amount is controlled to be 20-30% in the final pass rolling process.

5. The method of controlling the grain size of an ultra-pure austenitic medical stainless steel in a hot rolling process according to claim 1, wherein the steel is heated to a temperature of 1,100°C to 1,200°C. The temperature distribution deviation is obtained by fusing the range and the dispersion. The adjacent pass temperature deviation is obtained by: The difference value of the hot rolling temperature data of each same position sampling point between the scanning area at each collection time and the scanning area at the adjacent collection time is calculated.

6. The method of controlling the grain size of an ultra-pure austenitic medical stainless steel in a hot rolling process according to claim 1, wherein the steel is heated to a temperature of 1,100°C to 1,200°C. The adjacent pass temperature deviation is the average value of all the difference values at the corresponding collection time. The temperature comprehensive deviation degree is obtained by: The cumulative value of the temperature distribution deviation and the adjacent pass temperature deviation at each collection time is calculated.

7. The method of controlling the grain size of an ultra-pure austenitic medical stainless steel in a hot rolling process according to claim 1, wherein the steel is heated to a temperature of 1,100°C to 1,200°C. The temperature comprehensive deviation degree is proportional to the cumulative value. The rolling rate deviation distribution is obtained by: The hot rolling temperature data and the plate rolling thickness of all sampling points in the scanning area at any collection time are respectively obtained, the average value of all elements in each cluster is calculated, all clusters of the hot rolling temperature data and all clusters of the plate rolling thickness are sorted according to the average value, and the cluster at the middle position is selected; 8. The method of controlling the grain size of an ultra-pure austenitic medical stainless steel in a hot rolling process according to claim 1, wherein the steel is heated to a temperature of 1,100°C to 1,200°C. The intersection and the union of the sampling points corresponding to the two selected clusters are counted, and the ratio of the number of elements in the intersection to the union is calculated; The difference between 1 and the ratio is taken as the rolling rate deviation distribution at the any collection time. The temperature of the billet region corresponding to the scanning area at each collection time in the next pass hot rolling process is controlled, which comprises: ​ 9. The method of controlling the grain size of an ultra-pure austenitic medical stainless steel in a hot rolling process according to claim 1, wherein the steel is heated to a temperature of 1,100°C to 1,200°C. ​ calculating a mean value of the temperature comprehensive deviation degree and the rolling rate deviation distribution; calculating a product of the mean value and a preset temperature allowable deviation; obtaining a temperature of a steel billet region corresponding to the scanning region at each acquisition time after each pass hot rolling in a next pass hot rolling process by combining the product and a preset initial temperature in the next pass hot rolling process.

10. The method of controlling the grain size of an ultra-pure austenitic medical stainless steel in a hot rolling process according to claim 9, wherein the steel is heated to a temperature of 1,100°C to 1,200°C. The temperature of the steel billet region corresponding to the scanning region at each acquisition time after each pass hot rolling in the next pass hot rolling process is a cumulative sum of the product and the preset initial temperature in the next pass hot rolling process.

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