Isothermal quenching cooling method and isothermal quenching cooling device for nodular cast iron

Abstract

The invention relates to the technical field of quenching treatment, in particular to a nodular cast iron isothermal quenching cooling method and an isothermal quenching cooling device.The method comprises the steps that when nodular cast iron of the current batch is subjected to cooling treatment in a cooling stage before isothermal quenching in a salt bath furnace, a thermal image of the surface of the salt bath furnace is collected in real time; acquiring a first characteristic value of each nodular cast iron; obtaining a furnace wall area and a non-furnace wall area in each thermal image; obtaining an average temperature value of each non-furnace-wall area; acquiring a local high-temperature area in each thermal image; acquiring a high-temperature characteristic value of each thermal image; acquiring a second characteristic value of each nodular cast iron; and the optimal rotating speed of the stirring device is obtained when the next nodular cast iron of the nodular cast iron of the current batch is subjected to cooling treatment in the cooling stage before isothermal quenching. The invention aims to improve the isothermal quenching cooling quality of the nodular cast iron by adjusting the rotating speed of the stirring device during the isothermal quenching cooling of the nodular cast iron.

Description

Technical Field

[0001] The present application relates to the technical field of quenching treatment, and in particular to a ductile iron austempering cooling method and an austempering cooling device thereof. Background Art

[0002] Austempering cooling treatment of ductile iron is a method for preparing austempered ductile iron material, wherein the ductile iron, which has been heated to the austenitizing temperature and held at that temperature, is rapidly quenched into a salt bath furnace, where it is first cooled in the salt bath furnace in a cooling stage before austempering to cool the ductile iron to the bainite transformation temperature range, followed by a holding stage in austempering, and finally air-cooled to room temperature before being taken out of the furnace to obtain the austempered ductile iron material.

[0003] During the cooling stage before austempering of ductile iron, it is usually necessary to quickly cool the ductile iron to the bainite transformation temperature range to avoid the formation of pearlite or martensite. However, the overall cooling efficiency of the natural cooling of the salt bath furnace is low, which is difficult to meet the requirements of rapid cooling. Therefore, the existing method usually uses a stirring device to assist the rapid cooling of the salt bath furnace. However, since the nitrate component in the salt bath furnace is prone to aging and scaling problems, it is difficult to determine the appropriate stirring speed when stirring the salt bath furnace in the cooling stage before austempering, which in turn affects the cooling effect of the ductile iron in its cooling stage before austempering, thereby affecting the austempering quality of the ductile iron. Summary of the Invention

[0004] In view of the above, it is necessary to provide a method for austempering cooling of ductile iron and an austempering cooling device thereof. Compared with the traditional method for austempering cooling of ductile iron, the austempering cooling quality of ductile iron is improved by adjusting the rotation speed of the stirring device during austempering cooling of ductile iron: In a first aspect, an embodiment of the present application provides a method for austempering cooling of ductile iron, the method comprising the following steps: Conduct a stirring test on the salt bath furnace used for the current batch of ductile iron to obtain the critical speed value of the stirring device when cavitation occurs in the salt bath furnace; collect real-time thermal images of the salt bath furnace surface during the cooling stage before austempering of each batch of ductile iron in the salt bath furnace; and obtain the initial speed value of the stirring device during the cooling of the current batch of ductile iron; Obtaining the first characteristic value of each ductile iron by comparing the concentration of nitrate in the salt bath furnace before and after cooling the current batch of ductile iron; The furnace wall area and non-furnace wall area in each thermal image are obtained by the position distribution of the pixel points in each thermal image; the average temperature value of each non-furnace wall area is obtained by the temperature value distribution of the pixel points in each non-furnace wall area; the local high temperature area in each thermal image is obtained by the deviation of the temperature value of each pixel point in the furnace wall area in each thermal image compared with the average temperature value of the non-furnace wall area; the high temperature characteristic value of each thermal image is obtained by the proportion of the local high temperature area in each thermal image and the degree to which the temperature value of the pixel points in the local high temperature area exceeds the average temperature value of the non-furnace wall area; Obtaining a second characteristic value of each ductile iron by distributing the high-temperature characteristic values ​​of all thermal images of each ductile iron in the current batch during cooling; The optimal speed of the stirring device during the cooling treatment of the next ductile iron of each ductile iron in the current batch in the cooling stage before austempering is obtained through the second characteristic value, the critical speed value, the initial speed value and the first characteristic value.

[0005] In one embodiment, the process of obtaining the first characteristic value is: The difference between the concentration of nitrate in the salt bath furnace before cooling treatment of the current batch of ductile iron and the concentration of nitrate in the salt bath furnace after cooling treatment of each batch of ductile iron is recorded as the first difference; the first characteristic value is the ratio of the first difference to the concentration of nitrate in the salt bath furnace before cooling treatment of the current batch of ductile iron.

[0006] In one embodiment, the process of obtaining the furnace wall area and the non-furnace wall area in each thermal image is as follows: The pixel point at the center of each thermal image is recorded as the center pixel point of each thermal image; The pixels in each thermal image are arranged in descending order according to the distance from the central pixel, a preset number of pixels are used to form a furnace wall area, and the area other than the furnace wall area in each thermal image is used as a non-furnace wall area.

[0007] In one embodiment, the process of obtaining the average temperature value is as follows: A segmentation threshold of the temperature values ​​of all pixels in the non-furnace wall area of ​​each thermal image is obtained, and the average temperature value is the average of the temperature values ​​of all pixels in the non-furnace wall area of ​​each thermal image whose temperature is less than or equal to the segmentation threshold.

[0008] In one embodiment, the process of obtaining the local high temperature area is: The difference between the temperature value of each pixel point in the furnace wall area in each thermal image and the average temperature value of the non-furnace wall area is recorded as the second difference. The local high temperature area is the area composed of pixel points in the furnace wall area in each thermal image whose second difference value is greater than 0.

[0009] In one embodiment, the process of obtaining the high temperature characteristic value is as follows: Calculate the ratio of the number of pixels in each local high-temperature area to the number of pixels in the thermal image; Calculating an average value of the second difference values ​​corresponding to all pixels in the local high temperature area in each thermal image; The high temperature characteristic value is the product of the ratio and the average value.

[0010] In one embodiment, the second characteristic value is the maximum value among the high temperature characteristic values ​​of all thermal images of the ductile irons of the current batch during cooling.

[0011] In one embodiment, the process of obtaining the optimal rotation speed is as follows: Recording the difference between the critical speed value and the initial speed value as a third difference; Calculating the arithmetic mean of the first eigenvalue and the second eigenvalue; Calculating a product of the third difference and the arithmetic mean; The optimal rotational speed is obtained by multiplying the initial rotational speed value by the product.

[0012] In one embodiment, the optimal rotational speed is the sum of a rounded result of the product and the initial rotational speed value.

[0013] In a second aspect, an embodiment of the present application further provides a ductile iron austempering cooling device, the device comprising: a salt bath furnace, a stirring device, and a control system for the stirring device; Among them, the salt bath furnace is used to cool the ductile iron to the bainite transformation temperature range; The stirring device is used to accelerate the cooling efficiency of ductile iron when it is cooled to the bainite transformation temperature range in the salt bath furnace; The control system of the stirring device includes a data acquisition unit, a data processing unit and a stirring control unit; The data acquisition unit is used to perform a stirring test on the salt bath furnace used for the current batch of ductile iron to obtain the critical speed value of the stirring device when cavitation occurs in the salt bath furnace; to collect real-time thermal images of the surface of the salt bath furnace during the cooling stage before austempering of each batch of ductile iron in the salt bath furnace; and to obtain the initial speed value of the stirring device when the current batch of ductile iron is cooling; The data processing unit is used to obtain a first characteristic value of each ductile iron by comparing the concentration difference of nitrate in the salt bath furnace before and after cooling of the current batch of ductile iron; The furnace wall area and non-furnace wall area in each thermal image are obtained by the position distribution of the pixel points in each thermal image; the average temperature value of each non-furnace wall area is obtained by the temperature value distribution of the pixel points in each non-furnace wall area; the local high temperature area in each thermal image is obtained by the deviation of the temperature value of each pixel point in the furnace wall area in each thermal image compared with the average temperature value of the non-furnace wall area; the high temperature characteristic value of each thermal image is obtained by the proportion of the local high temperature area in each thermal image and the degree to which the temperature value of the pixel points in the local high temperature area exceeds the average temperature value of the non-furnace wall area; Obtaining a second characteristic value of each ductile iron by distributing the high-temperature characteristic values ​​of all thermal images of each ductile iron in the current batch during cooling; Obtaining, by using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value, an optimal speed of the stirring device during a cooling process in a cooling stage before austempering of the next ductile iron of each ductile iron of the current batch; The stirring control unit is used to adjust the rotation speed of the stirring device to the optimal rotation speed when performing a cooling treatment in a cooling stage before austempering on the next ductile cast iron of each ductile cast iron of the current batch.

[0014] This application has at least the following beneficial effects: The present application determines the critical speed value of the stirring device when cavitation occurs in the salt bath furnace through a stirring test. The critical speed value is used as the upper limit of the speed of the stirring device. This can effectively avoid the occurrence of cavitation in the stirring area when the stirring device is stirring in the salt bath furnace, thereby improving the cooling uniformity of the current batch of ductile iron during austempering cooling in the salt bath furnace, thereby improving the final quenching quality of the current batch of ductile iron. Furthermore, by calculating the first eigenvalue, the degree of aggravation of nitrate aging in the salt bath furnace after austempering and cooling of each ductile iron is evaluated, so as to facilitate the subsequent increase in the rotation speed of the stirring device according to the aggravation of nitrate aging; by obtaining the furnace wall area and the non-furnace wall area, the key areas in the salt bath furnace where local high temperature phenomena may occur can be identified; the average temperature value of the non-furnace wall area is obtained, which can be used as a benchmark for evaluating the temperature anomaly of the furnace wall area, making the subsequent judgment of the local high temperature area more accurate and reliable; by obtaining the local high temperature area, the local high temperature phenomenon caused by scaling on the salt bath furnace wall can be accurately identified, providing a basis for the subsequent quantification of the severity of the local high temperature phenomenon; by calculating the high temperature eigenvalue, the severity of the local high temperature phenomenon can be quantified; the second eigenvalue reflects the maximum severity of the local high temperature phenomenon on the salt bath furnace wall caused by scaling on the salt bath furnace wall when the salt bath furnace is austempering and cooling the ductile iron, which helps to subsequently increase the rotation speed of the stirring device according to the maximum severity of the local high temperature phenomenon; Furthermore, the optimal speed of the stirring device when the next ductile iron is austempering and cooling is obtained through the first eigenvalue, the second eigenvalue and the critical speed value. This can not only effectively ensure that the subsequent ductile iron is quickly cooled to the bainite transformation temperature range when austempering and cooling is performed in a salt bath furnace, but also improve the uniformity of cooling of the subsequent ductile iron when austempering and cooling is performed in a salt bath furnace, thereby improving the quality of the subsequent austempering and cooling of the ductile iron. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0016] Figure 1 A flowchart of a method for austempering cooling ductile iron according to one embodiment of the present application; Figure 2 Schematic diagram of the process of obtaining the optimal speed. DETAILED DESCRIPTION

[0017] In the description of the embodiments of this application, words such as "exemplary," "or," and "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary," "or," and "for example" is intended to present the relevant concepts in a concrete manner.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application relates. The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be understood that, unless otherwise indicated, " / " represents or.

[0019] It should also be noted that the terms "first" and "second" in this application are used to distinguish similar objects, rather than to describe a specific order or sequence.

[0020] The specific scheme of the austempering cooling method and austempering cooling device for ductile iron provided by the present application is described in detail below with reference to the accompanying drawings.

[0021] See also Figure 1, which shows a flowchart of a method for austempering cooling ductile iron provided by one embodiment of the present application, the method comprising the following steps: Step 1: Perform a stirring test on the salt bath furnace used for the current batch of ductile iron to obtain a critical speed value of the stirring device when cavitation occurs in the salt bath furnace; collect real-time thermal images of the surface of the salt bath furnace during the cooling stage before austempering of each batch of ductile iron in the salt bath furnace; and obtain an initial speed value of the stirring device when the current batch of ductile iron is cooled.

[0022] In this embodiment, for a salt bath furnace used for cooling treatment of ductile iron in the cooling stage before austempering, the nitrate salt in the salt bath furnace is composed of 60% potassium nitrate and 40% sodium nitrite, and the temperature during quenching is 280°C. The composition of the nitrate salt and the temperature during quenching can be set by the implementer according to actual conditions, and this application does not impose any special restrictions.

[0023] This application takes the process of controlling the rotational speed of the stirring device used in the cooling treatment of the current batch of ductile iron in the cooling stage before austempering as an example.

[0024] When a stirring device is used to stir the salt bath furnace, if the speed of the stirring device exceeds the critical speed, cavitation will occur in the stirring area of ​​the salt bath furnace, thereby causing local bubbles or gas to be generated. If the bubbles adhere to the surface of the ductile iron, it will affect the cooling uniformity of the ductile iron during austempering cooling in the salt bath furnace, thereby reducing the final quenching quality of the ductile iron. Therefore, in order to avoid the occurrence of the above situation, before austempering cooling the current batch of ductile iron, a stirring test is performed on the salt bath furnace used for the current batch of ductile iron using a stirring device to obtain the critical speed value of the stirring device when cavitation occurs in the salt bath furnace used for the current batch of ductile iron.

[0025] This application takes any ductile iron P from the current batch as an example. During the cooling treatment of the ductile iron P in the cooling stage before isothermal quenching, after the ductile iron P is completely immersed in the salt bath furnace, an infrared thermal imager located above the salt bath furnace and facing the surface of the salt bath furnace is used to collect a thermal image of the salt bath furnace surface in real time, wherein the value of the pixel point in the thermal image is the temperature value.

[0026] In this embodiment, the sampling frequency of the infrared thermal imager is 10 frames per second. The sampling frequency is preset manually and can be set by the implementer according to actual conditions. This application does not impose any special restrictions.

[0027] At the same time, a refractometer is used to measure the concentration of nitrate in the salt bath furnace before cooling treatment during the cooling stage before austempering of the current batch of ductile iron, and the concentration of nitrate in the salt bath furnace after cooling treatment during the cooling stage before austempering of the ductile iron P. An initial speed value of the stirring device during the cooling treatment of the current batch of ductile iron during the cooling stage before austempering is also obtained, wherein the initial speed value should be less than the critical speed value.

[0028] The image denoising algorithm is used to perform denoising on each frame of the acquired thermal image to reduce the impact of environmental noise introduced during the image acquisition and transmission process on subsequent processing.

[0029] In this embodiment, the image denoising algorithm is a Gaussian filtering algorithm. The Gaussian filtering algorithm is a well-known technology and will not be described in detail in this application. As other implementation methods, on the basis of being able to perform denoising processing on each frame of thermal image separately, the implementer can adopt other existing technologies, such as median filtering algorithm, mean filtering algorithm, etc., and this application does not impose any special restrictions.

[0030] In order to standardize the temperature values ​​of the pixels in different frames of thermal images, the temperature values ​​of the pixels in the thermal images are converted to the range of (0, 1). Specifically, the temperature value of each pixel in each frame of thermal image is replaced by the ratio between the temperature value of each pixel and the austenitizing temperature used by the current batch of ductile iron.

[0031] In this embodiment, the austenitizing temperature is 950° C. The austenitizing temperature is preset manually and can be set by the implementer according to actual conditions. This application does not impose any special restrictions.

[0032] Step 2: Analyze the thermal images obtained during the cooling treatment of each ductile iron batch in the current batch and the concentration change of nitrate in the salt bath furnace to obtain the optimal speed of the stirring device during the cooling treatment of the next ductile iron batch in the cooling stage before austempering.

[0033] Step 2.1: Obtain the first characteristic value of each ductile iron by comparing the concentration difference of nitrate in the salt bath furnace before and after the cooling treatment of the current batch of ductile iron.

[0034] Because ductile iron requires austenitization before being placed in a salt bath for austempering, and the austenitization temperature is relatively high, after the ductile iron is placed in the salt bath, the nitrate salts near the ductile iron in the salt bath will be decomposed by heat into insoluble alkali metal compounds, such as sodium carbonate. These insoluble alkali metal compounds will gradually accumulate in the salt bath, causing the nitrate salts in the salt bath to age, which in turn causes the concentration of the active ingredients in the salt bath to decrease. The insoluble alkali metal compounds produced by the decomposition of the nitrate salts will change the composition and structure of the salt bath, causing the melting point of the nitrate salts in the salt bath to increase, thereby reducing the cooling capacity of the salt bath. Therefore, in order to reduce the degree of reduction in the cooling capacity of the salt bath caused by the increased aging of the nitrate salts after austempering in the salt bath, and to ensure that the ductile iron can meet the requirements of rapid cooling to the bainite transformation temperature range during subsequent austempering in the salt bath, thereby improving the quality of subsequent austempering of the ductile iron, the following treatment is performed.

[0035] The difference between the concentration of nitrate in the salt bath furnace before the cooling treatment of the current batch of ductile iron P and the concentration of nitrate in the salt bath furnace after the cooling treatment of the current batch of ductile iron P is recorded as the first difference value. The ratio of the first difference value to the concentration of nitrate in the salt bath furnace before the cooling treatment of the current batch of ductile iron P is used as the first characteristic value of the ductile iron P. This is used to evaluate the degree of aging of the nitrate in the salt bath furnace after austempering of the ductile iron P, compared to the degree of aging of the nitrate in the salt bath furnace before the austempering of the current batch of ductile iron. The larger the first characteristic value, the greater the increase in aging, and the greater the degree of reduction in the cooling capacity of the salt bath furnace after the austempering of the ductile iron P. Therefore, when the ductile iron is subsequently austempered in the salt bath furnace, the speed of the stirring device should be greater than the initial speed of the stirring device. The first characteristic value is in the range of (0,1).

[0036] Step 2.2, obtain the furnace wall area and non-furnace wall area in each thermal image through the position distribution of pixel points in each thermal image; obtain the average temperature value of each non-furnace wall area through the temperature value distribution of pixel points in each non-furnace wall area; obtain the local high temperature area in each thermal image through the deviation of the temperature value of each pixel point in the furnace wall area in each thermal image compared with the average temperature value of the non-furnace wall area; obtain the high temperature characteristic value of each thermal image through the proportion of local high temperature areas in each thermal image and the degree to which the temperature value of the pixel points in the local high temperature area exceeds the average temperature value of the non-furnace wall area.

[0037] When ductile iron is austenitized, its surface will come into contact with air to form oxide scale, and the oxide scale will flake off under the scouring of liquid nitrate in the salt bath furnace when the ductile iron is austempered and cooled, and will continuously deposit in the salt bath furnace with refractory alkali metal compounds generated by the thermal decomposition of nitrate in the salt bath furnace, resulting in the gradual formation of a layer of block scale on the furnace wall of the salt bath furnace. In the process of slow condensation of the scale, the nitrate near the furnace wall of the salt bath furnace will adhere to the scale, and the appearance of scale will hinder the transfer of heat and affect the heat dissipation of the salt bath furnace wall. As a result, compared with the rest of the salt bath furnace, the area at the salt bath furnace wall is more likely to have a local overtemperature due to the formation of scale, which in turn causes uneven temperature distribution in the salt bath furnace, resulting in uneven cooling of the ductile iron during austempering and cooling in the salt bath furnace. In order to reduce the degree of excessively high local temperature of the salt bath furnace wall caused by scaling after austempering cooling of ductile iron in a salt bath furnace, and to improve the uniformity of cooling of subsequent ductile iron during austempering cooling in a salt bath furnace, thereby improving the quality of subsequent austempering cooling of ductile iron, the following treatment is carried out.

[0038] (1) Obtain the furnace wall area and non-furnace wall area in each thermal image through the position distribution of pixel points in each thermal image.

[0039] Since the furnace wall area of ​​the salt bath furnace is generally located at the edge area of ​​the collected thermal image, the pixel point at the center of each thermal image is recorded as the center pixel point of each thermal image to characterize the center position of the salt bath furnace. The pixels in each thermal image are arranged in descending order according to the distance between them and the center pixel point. A preset number of pixels form the furnace wall area, and the area other than the furnace wall area in each thermal image is regarded as the non-furnace wall area.

[0040] In this embodiment, the distance between the pixel points in each thermal image and the central pixel point is the Euclidean distance.

[0041] In this embodiment, the preset number is the product of the number of pixels in each thermal image and 10%, where 10% is only an embodiment of the present application. The implementer can set the specific value according to the actual situation, and this application does not impose any special restrictions.

[0042] (2) The average temperature value of the non-furnace wall area in each thermal image is obtained by the temperature value distribution of the pixel points in the non-furnace wall area in each thermal image.

[0043] Since the temperature of the austenitized ductile iron will be higher than the temperature of the salt bath furnace, the threshold segmentation algorithm is used to obtain the segmentation threshold of the temperature values ​​of all pixels in the non-furnace wall area of ​​each thermal image. The average of the temperature values ​​of all pixels in the non-furnace wall area of ​​each thermal image with a temperature value less than or equal to the segmentation threshold is used as the average temperature value of the non-furnace wall area in each thermal image, so as to reduce the influence of the temperature near the ductile iron in the salt bath furnace on the evaluation of the average temperature of the non-furnace wall area in the salt bath furnace.

[0044] In this embodiment, the Otsu threshold segmentation algorithm is used to obtain the segmentation threshold of the temperature values ​​of all pixel points in each non-furnace wall area. The Otsu threshold segmentation algorithm is a well-known technology and will not be described in detail in this application. As other implementation methods, on the basis of being able to obtain the segmentation threshold of the temperature values ​​of all pixel points in each non-furnace wall area, the implementer may adopt other existing technologies, such as iterative threshold segmentation, global threshold segmentation, etc., which will not be described in detail in this application.

[0045] (3) The local high temperature area in each thermal image is obtained by the deviation of the temperature value of each pixel point in the furnace wall area in each thermal image compared with the average temperature value of the non-furnace wall area; the high temperature characteristic value of each thermal image is obtained by the proportion of the local high temperature area in each thermal image and the degree to which the temperature value of the pixel point in the local high temperature area exceeds the average temperature value of the non-furnace wall area.

[0046] The difference between the temperature of each pixel in the furnace wall area of ​​each thermal image and the average temperature of the non-furnace wall area is recorded as a second difference, which is used to assess whether the salt bath furnace location corresponding to each pixel in the furnace wall area is in a local high temperature area. The area within the furnace wall area of ​​each thermal image consisting of pixels where the second difference value is greater than 0 is considered the local high temperature area in each thermal image. Because the pixels corresponding to the local high temperature area on the salt bath furnace wall in the thermal image are typically clustered rather than discrete, all discrete pixels in the local high temperature area of ​​each thermal image are removed to reduce the impact of noise-induced pixels on the severity assessment of the local high temperature phenomenon in the salt bath furnace wall when the thermal image is subsequently evaluated. The method for determining discrete pixels in the image is well known in the art, and the specific process will not be repeated in this application.

[0047] Furthermore, the ratio of the number of pixels within each local high-temperature region to the number of pixels within the corresponding thermal image is calculated to assess the proportion of the local high-temperature region on the salt bath furnace wall. The average value of the second difference corresponding to all pixels within the local high-temperature region in each thermal image is calculated, and the product of the ratio and the average value is used as the high-temperature characteristic value for each thermal image. The high-temperature characteristic value is used to assess the severity of the local high-temperature phenomenon on the salt bath furnace wall appearing in the thermal image. A larger high-temperature characteristic value indicates a higher severity of the local high-temperature phenomenon on the salt bath furnace wall appearing in the thermal image.

[0048] Step 2.3: Obtain the second characteristic value of each ductile iron through the distribution of the high temperature characteristic values ​​of all thermal images of each ductile iron in the current batch during cooling.

[0049] The maximum value of the high-temperature eigenvalues ​​of all thermal images collected during the cooling treatment of the ductile iron P in the cooling stage before austempering is counted, and the maximum value is used as the second eigenvalue of the ductile iron P. This is used to evaluate the maximum severity of the local high-temperature phenomenon on the salt bath furnace wall caused by scaling during the austempering cooling of the ductile iron P using the salt bath furnace. The larger the second eigenvalue, the greater the maximum severity of the local high-temperature phenomenon. In order to improve the uniformity of the subsequent cooling of the ductile iron during austempering cooling in the salt bath furnace, the speed of the stirring device should be increased during the subsequent austempering cooling of the ductile iron using the salt bath furnace. The second eigenvalue is in the range of (0,1).

[0050] Step 2.4: Obtain the optimal speed of the stirring device during the cooling process of the next ductile iron of each ductile iron in the current batch in the cooling stage before austempering by using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value.

[0051] Furthermore, the optimal speed of the stirring device during the cooling process of the next ductile iron of each ductile iron in the current batch before austempering is obtained by using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value. The expression is: ; Wherein, V represents the optimal speed of the stirring device during the cooling stage before austempering of the next ductile iron of the current batch of ductile iron P; v2 represents the initial speed value of the stirring device during cooling of the current batch of ductile iron; round() represents the rounding function; v1 represents the critical speed value of the stirring device when cavitation occurs in the salt bath furnace obtained by performing a stirring test on the salt bath furnace used for the current batch of ductile iron; s represents the average of the first and second eigenvalues ​​of the ductile iron P. Let v1-v2 be the third difference. The schematic diagram of the process of obtaining the optimal speed is shown in the figure below. Figure 2 shown.

[0052] When the next ductile cast iron of the current batch of ductile cast iron P is subjected to a cooling treatment in the cooling stage before austempering, the rotational speed of the stirring device is adjusted to the optimal rotational speed, and after the next ductile cast iron in the salt bath furnace is cooled to the bainite transformation temperature range by using the stirring device, the ductile cast iron is subjected to a heat preservation treatment in the heat preservation stage during austempering, and finally taken out of the furnace and air-cooled to room temperature to obtain an austempering ductile cast iron material.

[0053] Based on the same inventive concept as the above method, the embodiment of the present application further provides a ductile iron austempering cooling device, comprising: a salt bath furnace, a stirring device, and a control system for the stirring device; Among them, the salt bath furnace is used to cool the ductile iron to the bainite transformation temperature range; The stirring device is used to accelerate the cooling efficiency of ductile iron when it is cooled to the bainite transformation temperature range in the salt bath furnace; The control system of the stirring device includes a data acquisition unit, a data processing unit and a stirring control unit; The data acquisition unit is used to perform a stirring test on the salt bath furnace used for the current batch of ductile iron to obtain the critical speed value of the stirring device when cavitation occurs in the salt bath furnace; to collect real-time thermal images of the surface of the salt bath furnace during the cooling stage before austempering of each batch of ductile iron in the salt bath furnace; and to obtain the initial speed value of the stirring device when the current batch of ductile iron is cooling; The data processing unit is used to obtain a first characteristic value of each ductile iron by comparing the concentration difference of nitrate in the salt bath furnace before and after cooling of the current batch of ductile iron; The furnace wall area and non-furnace wall area in each thermal image are obtained by the position distribution of the pixel points in each thermal image; the average temperature value of each non-furnace wall area is obtained by the temperature value distribution of the pixel points in each non-furnace wall area; the local high temperature area in each thermal image is obtained by the deviation of the temperature value of each pixel point in the furnace wall area in each thermal image compared with the average temperature value of the non-furnace wall area; the high temperature characteristic value of each thermal image is obtained by the proportion of the local high temperature area in each thermal image and the degree to which the temperature value of the pixel points in the local high temperature area exceeds the average temperature value of the non-furnace wall area; Obtaining a second characteristic value of each ductile iron by distributing the high-temperature characteristic values ​​of all thermal images of each ductile iron in the current batch during cooling; Obtaining, by using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value, an optimal speed of the stirring device during a cooling process in a cooling stage before austempering of the next ductile iron of each ductile iron of the current batch; The stirring control unit is used to adjust the rotation speed of the stirring device to the optimal rotation speed when performing a cooling treatment in a cooling stage before austempering on the next ductile cast iron of each ductile cast iron of the current batch.

[0054] In summary, the present application determines the critical speed value of the stirring device when cavitation occurs in the salt bath furnace through a stirring test. Using the critical speed value as the upper limit of the speed of the stirring device can effectively avoid cavitation in the stirring area when the stirring device is stirring in the salt bath furnace, thereby improving the cooling uniformity of the current batch of ductile iron during austempering cooling in the salt bath furnace, thereby improving the final quenching quality of the current batch of ductile iron; Furthermore, by calculating the first eigenvalue, the degree of aggravation of nitrate aging in the salt bath furnace after austempering and cooling of each ductile iron is evaluated, so as to facilitate the subsequent increase in the rotation speed of the stirring device according to the aggravation of nitrate aging; by obtaining the furnace wall area and the non-furnace wall area, the key areas in the salt bath furnace where local high temperature phenomena may occur can be identified; the average temperature value of the non-furnace wall area is obtained, which can be used as a benchmark for evaluating the temperature anomaly of the furnace wall area, making the subsequent judgment of the local high temperature area more accurate and reliable; by obtaining the local high temperature area, the local high temperature phenomenon caused by scaling on the salt bath furnace wall can be accurately identified, providing a basis for the subsequent quantification of the severity of the local high temperature phenomenon; by calculating the high temperature eigenvalue, the severity of the local high temperature phenomenon can be quantified; the second eigenvalue reflects the maximum severity of the local high temperature phenomenon on the salt bath furnace wall caused by scaling on the salt bath furnace wall when the salt bath furnace is austempering and cooling the ductile iron, which helps to subsequently increase the rotation speed of the stirring device according to the maximum severity of the local high temperature phenomenon; Furthermore, the optimal speed of the stirring device when the next ductile iron is austempering and cooling is obtained through the first eigenvalue, the second eigenvalue and the critical speed value. This can not only effectively ensure that the subsequent ductile iron is quickly cooled to the bainite transformation temperature range when austempering and cooling is performed in a salt bath furnace, but also improve the uniformity of cooling of the subsequent ductile iron when austempering and cooling is performed in a salt bath furnace, thereby improving the quality of the subsequent austempering and cooling of the ductile iron.

[0055] The flowcharts and block diagrams in the accompanying drawings show the possible implementation architectures, functions and operations of the systems, methods and computer program products according to the embodiments of the present disclosure. In this regard, each box in the flowchart or block diagram can represent a module, program segment or part of the code, and the module, program segment or part of the code contains one or more executable instructions for implementing the specified logical functions. In some alternative implementations, the functions marked in the box can also occur in an order different from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, or they can sometimes be executed in the opposite order, which can depend on the functions involved. In the descriptions corresponding to the flowcharts and block diagrams in the accompanying drawings, the operations or steps corresponding to different boxes can also occur in an order different from that disclosed in the description, and sometimes there is no specific order between different operations or steps. For example, two consecutive operations or steps can actually be executed substantially in parallel, or they can sometimes be executed in the opposite order, which can depend on the functions involved. Each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented by a dedicated hardware-based system that performs the specified function or action, or may be implemented by a combination of dedicated hardware and computer instructions.

[0056] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and that the present application can be implemented in other specific forms without departing from the basic characteristics of the present application. Therefore, from all perspectives, the above embodiments of the present application should be regarded as exemplary and non-restrictive.

Claims

1. A method for austempering cooling of ductile iron, characterized in that: The method comprises the following steps: Conduct a stirring test on the salt bath furnace used for the current batch of ductile iron to obtain the critical speed value of the stirring device when cavitation occurs in the salt bath furnace; collect real-time thermal images of the salt bath furnace surface during the cooling stage before austempering of each batch of ductile iron in the salt bath furnace; and obtain the initial speed value of the stirring device during the cooling of the current batch of ductile iron; Obtaining the first characteristic value of each ductile iron by comparing the concentration of nitrate in the salt bath furnace before and after cooling the current batch of ductile iron; The furnace wall area and non-furnace wall area in each thermal image are obtained by the position distribution of the pixel points in each thermal image; the average temperature value of each non-furnace wall area is obtained by the temperature value distribution of the pixel points in each non-furnace wall area; the local high temperature area in each thermal image is obtained by the deviation of the temperature value of each pixel point in the furnace wall area in each thermal image compared with the average temperature value of the non-furnace wall area; the high temperature characteristic value of each thermal image is obtained by the proportion of the local high temperature area in each thermal image and the degree to which the temperature value of the pixel points in the local high temperature area exceeds the average temperature value of the non-furnace wall area; Obtaining a second characteristic value of each ductile iron by distributing the high-temperature characteristic values ​​of all thermal images of each ductile iron in the current batch during cooling; The optimal speed of the stirring device during the cooling treatment of the next ductile iron of each ductile iron in the current batch in the cooling stage before austempering is obtained through the second characteristic value, the critical speed value, the initial speed value and the first characteristic value.

2. A ductile iron austempering cooling method according to claim 1, characterized in that: The process of obtaining the first eigenvalue is as follows: The difference between the concentration of nitrate in the salt bath furnace before cooling treatment of the current batch of ductile iron and the concentration of nitrate in the salt bath furnace after cooling treatment of each batch of ductile iron is recorded as the first difference; the first characteristic value is the ratio of the first difference to the concentration of nitrate in the salt bath furnace before cooling treatment of the current batch of ductile iron.

3. A ductile iron austempering cooling method according to claim 1, characterized in that: The process of obtaining the furnace wall area and non-furnace wall area in each thermal image is as follows: The pixel point at the center of each thermal image is recorded as the center pixel point of each thermal image; The pixels in each thermal image are arranged in descending order according to the distance from the central pixel, a preset number of pixels are used to form a furnace wall area, and the area other than the furnace wall area in each thermal image is used as a non-furnace wall area.

4. A method for austempering and cooling ductile iron according to claim 1, characterized in that: The process of obtaining the average temperature value is as follows: A segmentation threshold of the temperature values ​​of all pixels in the non-furnace wall area of ​​each thermal image is obtained, and the average temperature value is the average of the temperature values ​​of all pixels in the non-furnace wall area of ​​each thermal image whose temperature is less than or equal to the segmentation threshold.

5. The method for austempering cooling of ductile iron according to claim 1, wherein: The process of obtaining the local high temperature area is as follows: The difference between the temperature value of each pixel point in the furnace wall area in each thermal image and the average temperature value of the non-furnace wall area is recorded as the second difference. The local high temperature area is the area composed of pixel points in the furnace wall area in each thermal image whose second difference value is greater than 0.

6. A method for austempering and cooling ductile iron according to claim 5, characterized in that: The process of obtaining the high temperature characteristic value is as follows: Calculate the ratio of the number of pixels in each local high-temperature area to the number of pixels in the thermal image; Calculating an average value of the second difference values ​​corresponding to all pixels in the local high temperature area in each thermal image; The high temperature characteristic value is the product of the ratio and the average value.

7. A method for austempering and cooling ductile iron according to claim 1, characterized in that: The second characteristic value is the maximum value among the high temperature characteristic values ​​of all thermal images of the ductile irons of the current batch when they are cooled.

8. A method for austempering and cooling ductile iron according to claim 1, characterized in that: The process of obtaining the optimal speed is as follows: Recording the difference between the critical speed value and the initial speed value as a third difference; Calculating the arithmetic mean of the first eigenvalue and the second eigenvalue; Calculating a product of the third difference and the arithmetic mean; The optimal rotational speed is obtained by multiplying the initial rotational speed value by the product.

9. A method for austempering and cooling ductile iron according to claim 8, characterized in that: The optimal rotational speed is the sum of the rounded calculation result of the product and the initial rotational speed value.

10. A ductile iron austempering cooling device, using the ductile iron austempering cooling method according to claim 1, characterized in that: The device comprises: a salt bath furnace, a stirring device and a control system for the stirring device; Among them, the salt bath furnace is used to cool the ductile iron to the bainite transformation temperature range; The stirring device is used to accelerate the cooling efficiency of ductile iron when it is cooled to the bainite transformation temperature range in the salt bath furnace; The control system of the stirring device includes a data acquisition unit, a data processing unit and a stirring control unit; The data acquisition unit is used to perform a stirring test on the salt bath furnace used for the current batch of ductile iron to obtain the critical speed value of the stirring device when cavitation occurs in the salt bath furnace; to collect real-time thermal images of the surface of the salt bath furnace during the cooling stage before austempering of each batch of ductile iron in the salt bath furnace; and to obtain the initial speed value of the stirring device when the current batch of ductile iron is cooling; The data processing unit is used to obtain a first characteristic value of each ductile iron by comparing the concentration difference of nitrate in the salt bath furnace before and after cooling of the current batch of ductile iron; The furnace wall area and non-furnace wall area in each thermal image are obtained by the position distribution of the pixel points in each thermal image; the average temperature value of each non-furnace wall area is obtained by the temperature value distribution of the pixel points in each non-furnace wall area; the local high temperature area in each thermal image is obtained by the deviation of the temperature value of each pixel point in the furnace wall area in each thermal image compared with the average temperature value of the non-furnace wall area; the high temperature characteristic value of each thermal image is obtained by the proportion of the local high temperature area in each thermal image and the degree to which the temperature value of the pixel points in the local high temperature area exceeds the average temperature value of the non-furnace wall area; Obtaining a second characteristic value of each ductile iron by distributing the high-temperature characteristic values ​​of all thermal images of each ductile iron in the current batch during cooling; Obtaining, by using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value, an optimal speed of the stirring device during a cooling process in a cooling stage before austempering of the next ductile iron of each ductile iron of the current batch; The stirring control unit is used to adjust the rotation speed of the stirring device to the optimal rotation speed when performing a cooling treatment in a cooling stage before austempering on the next ductile cast iron of each ductile cast iron of the current batch.

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