A method and apparatus for isothermal quenching and cooling of ductile iron

Abstract

This application relates to the field of quenching technology, specifically to an isothermal quenching cooling method and apparatus for ductile iron. The method includes: real-time acquisition of thermal images of the salt bath furnace surface during the cooling stage before isothermal quenching of each batch of ductile iron; acquisition of first characteristic values ​​for each ductile iron; acquisition of furnace wall and non-furnace wall regions in each thermal image; acquisition of the average temperature value of each non-furnace wall region; acquisition of local high-temperature regions in each thermal image; acquisition of high-temperature characteristic values ​​in each thermal image; acquisition of second characteristic values ​​for each ductile iron; and acquisition of the optimal rotation speed of the stirring device during the cooling stage before isothermal quenching of the next batch of ductile iron. This application aims to improve the quality of isothermal quenching cooling of ductile iron by adjusting the rotation speed of the stirring device during isothermal quenching.

Description

Technical Field

[0001] This application relates to the field of quenching technology, specifically to an isothermal quenching and cooling method for ductile iron and an isothermal quenching and cooling device thereof. Background Technology

[0002] Isothermal quenching is a method for preparing isothermal quenched ductile iron materials. The method involves rapidly quenching ductile iron, which has been heated to the austenitizing temperature and held at that temperature, into a salt bath furnace. In the salt bath furnace, the ductile iron is first cooled to the bainite transformation temperature range during the pre-quenching cooling stage. Then, it undergoes a holding stage during the isothermal quenching process. Finally, it is removed from the furnace and air-cooled to room temperature to obtain isothermal quenched ductile iron materials.

[0003] In the cooling stage before isothermal quenching of ductile iron, it is usually necessary to rapidly cool the ductile iron to the bainite transformation temperature range to avoid the formation of pearlite or martensite. However, the overall cooling efficiency of natural cooling in salt bath furnaces is low and cannot meet the requirements of rapid cooling. Therefore, existing methods usually use stirring devices to assist the rapid cooling of salt bath furnaces. However, due to the aging and scaling problems of nitrate components in salt bath furnaces, it is difficult to determine the appropriate stirring speed when stirring the salt bath furnace in the cooling stage before isothermal quenching. This affects the cooling effect of ductile iron in the cooling stage before isothermal quenching, thus affecting the isothermal quenching quality of ductile iron. Summary of the Invention

[0004] In view of the above, it is necessary to provide a method and apparatus for isothermal quenching and cooling of ductile iron. Compared with the traditional method, the quality of isothermal quenching and cooling of ductile iron is improved by adjusting the rotation speed of the stirring device during isothermal quenching and cooling.

[0005] In a first aspect, embodiments of this application provide an isothermal quenching and cooling method for ductile iron, the method comprising the following steps:

[0006] A stirring test was conducted 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; thermal images of the surface of the salt bath furnace were collected in real time during the cooling process of each ductile iron in the current batch before isothermal quenching; and the initial speed value of the stirring device was obtained when the current batch of ductile iron was being cooled.

[0007] The first characteristic value of each ductile iron was obtained by measuring the difference in nitrate concentration in the salt bath furnace before and after cooling treatment of the current batch of ductile iron.

[0008] By analyzing the positional distribution of pixels in each thermal image, the furnace wall region and non-furnace wall region in each thermal image are obtained; by analyzing the temperature value distribution of pixels in each non-furnace wall region, the average temperature value of each non-furnace wall region is obtained; by analyzing the deviation of the temperature value of each pixel in the furnace wall region in each thermal image from the average temperature value of the non-furnace wall region, the local high-temperature region in each thermal image is obtained; by analyzing the proportion of local high-temperature regions in each thermal image and the degree to which the temperature value of pixels in the local high-temperature region exceeds the average temperature value of the non-furnace wall region, the high-temperature feature value of each thermal image is obtained.

[0009] The second characteristic value of each ductile iron is obtained by analyzing the distribution of high-temperature characteristic values ​​of all thermal images during the cooling of each ductile iron in the current batch.

[0010] By using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value, the optimal speed of the stirring device is obtained when the next batch of ductile iron in the current batch undergoes cooling treatment during the cooling stage before isothermal quenching.

[0011] In one embodiment, the process of obtaining the first feature value is as follows:

[0012] 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 denoted 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.

[0013] In one embodiment, the process of acquiring the furnace wall region and non-furnace wall region in each thermal image is as follows:

[0014] The pixel at the center of each thermal image is denoted as the center pixel of each thermal image.

[0015] The pixels in each thermal image are arranged in descending order of their distance from the center pixel. The first preset number of pixels form the furnace wall region, and the area in each thermal image other than the furnace wall region is regarded as the non-furnace wall region.

[0016] In one embodiment, the process of obtaining the average temperature value is as follows:

[0017] A segmentation threshold is obtained for the temperature values ​​of all pixels in the non-furnace wall region of each thermal image. The average temperature value is the average of the temperature values ​​of all pixels in the non-furnace wall region of each thermal image whose temperature values ​​are less than or equal to the segmentation threshold.

[0018] In one embodiment, the process of obtaining the local high-temperature region is as follows:

[0019] The difference between the temperature value of each pixel in the furnace wall region and the average temperature value of the non-furnace wall region in each thermal image is recorded as the second difference. The local high temperature region is the region composed of pixels in the furnace wall region of each thermal image whose second difference is greater than 0.

[0020] In one embodiment, the process of obtaining the high-temperature characteristic value is as follows:

[0021] Calculate the ratio of the number of pixels in each local high-temperature region to the number of pixels in the corresponding thermal image;

[0022] Calculate the average of the second difference for all pixels within the local high-temperature region in each thermal image;

[0023] The high-temperature characteristic value is the product of the ratio and the average value.

[0024] In one embodiment, the second feature value is the maximum value among the high-temperature feature values ​​of all thermal images of each ductile iron in the current batch during cooling.

[0025] In one embodiment, the process of obtaining the optimal rotational speed is as follows:

[0026] The difference between the critical speed value and the initial speed value is recorded as the third difference.

[0027] Calculate the arithmetic mean of the first feature value and the second feature value;

[0028] Calculate the product of the third difference and the arithmetic mean;

[0029] The optimal speed is obtained by multiplying the initial speed value by the value.

[0030] In one embodiment, the optimal rotational speed is the sum of the rounded result of the product and the initial rotational speed value.

[0031] Secondly, this application also provides an isothermal quenching and cooling device for ductile iron, the device comprising: a salt bath furnace, a stirring device, and a control system for the stirring device;

[0032] Salt bath furnaces are used to cool ductile iron to the bainite transformation temperature range.

[0033] The stirring device is used to accelerate the cooling efficiency of ductile iron in a salt bath furnace when it is cooled to the bainite transformation temperature range.

[0034] The control system of the stirring device includes a data acquisition unit, a data processing unit, and a stirring control unit;

[0035] The data acquisition unit is used to perform stirring tests on the salt bath furnace used for the current batch of ductile iron, obtain the critical speed value of the stirring device when cavitation occurs in the salt bath furnace; acquire thermal images of the surface of the salt bath furnace in real time during the cooling process of each ductile iron in the current batch before isothermal quenching in the salt bath furnace; and obtain the initial speed value of the stirring device when the current batch of ductile iron is being cooled.

[0036] The data processing unit is used to obtain the first characteristic value of each ductile iron by the difference in nitrate concentration in the salt bath furnace before and after the cooling treatment of the current batch of ductile iron.

[0037] By analyzing the positional distribution of pixels in each thermal image, the furnace wall region and non-furnace wall region in each thermal image are obtained; by analyzing the temperature value distribution of pixels in each non-furnace wall region, the average temperature value of each non-furnace wall region is obtained; by analyzing the deviation of the temperature value of each pixel in the furnace wall region in each thermal image from the average temperature value of the non-furnace wall region, the local high-temperature region in each thermal image is obtained; by analyzing the proportion of local high-temperature regions in each thermal image and the degree to which the temperature value of pixels in the local high-temperature region exceeds the average temperature value of the non-furnace wall region, the high-temperature feature value of each thermal image is obtained.

[0038] The second characteristic value of each ductile iron is obtained by analyzing the distribution of high-temperature characteristic values ​​of all thermal images during the cooling of each ductile iron in the current batch.

[0039] By using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value, the optimal speed of the stirring device is obtained when the next batch of ductile iron in the current batch undergoes cooling treatment in the cooling stage before isothermal quenching.

[0040] The stirring control unit is used to adjust the speed of the stirring device to the optimal speed during the cooling process in the cooling stage before isothermal quenching of the next batch of ductile iron from the current batch.

[0041] This application has at least the following beneficial effects:

[0042] This application determines the critical speed value of the stirring device when cavitation occurs in the salt bath furnace through stirring tests. The critical speed value is used as the upper limit of the stirring device speed, which can effectively avoid cavitation in the stirring area when the stirring device is stirring in the salt bath furnace. This can improve the cooling uniformity of the current batch of ductile iron during isothermal quenching in the salt bath furnace, thereby improving the final quenching quality of the current batch of ductile iron.

[0043] Furthermore, by calculating the first characteristic value, the degree of nitrate aging in the salt bath furnace after isothermal quenching and cooling of each ductile iron is assessed, which facilitates the subsequent adjustment of the stirring speed based on the degree of nitrate aging. By obtaining data from the furnace wall area and non-furnace wall area, key areas in the salt bath furnace where localized high temperatures may occur can be identified. Obtaining the average temperature value of the non-furnace wall area can serve as a benchmark for assessing temperature anomalies in the furnace wall area, making subsequent judgments on localized high-temperature areas more accurate and reliable. By identifying localized high-temperature areas, localized high-temperature phenomena caused by scaling on the furnace wall of the salt bath furnace can be accurately identified, providing a basis for quantifying the severity of localized high-temperature phenomena. By calculating the high-temperature characteristic value, the severity of localized high-temperature phenomena can be quantified. The second characteristic value reflects the maximum severity of localized high-temperature phenomena on the furnace wall caused by scaling during isothermal quenching and cooling of ductile iron in the salt bath furnace, which helps to adjust the stirring speed based on the maximum severity of localized high-temperature phenomena.

[0044] Furthermore, by using the first characteristic value, the second characteristic value, and the critical speed value, the optimal speed of the stirring device is obtained when the next ductile iron undergoes isothermal quenching and cooling. This not only effectively ensures that the subsequent ductile iron is rapidly cooled to the bainite transformation temperature range when using a salt bath furnace for isothermal quenching and cooling, but also improves the uniformity of cooling when the subsequent ductile iron is used for isothermal quenching and cooling in a salt bath furnace, thereby improving the quality of the subsequent ductile iron undergoing isothermal quenching and cooling. Attached Figure Description

[0045] To more clearly illustrate the technical solutions and advantages in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 A flowchart illustrating the steps of an isothermal quenching and cooling method for ductile iron, provided in one embodiment of this application;

[0047] Figure 2 This is a schematic diagram of the process for obtaining the optimal rotational speed. Detailed Implementation

[0048] In the description of the embodiments in this application, the words "exemplary," "or," and "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design schemes. Specifically, the use of the words "exemplary," "or," and "for example" is intended to present the relevant concepts in a specific manner.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. It should be understood that, unless otherwise stated, " / " in this application means "or".

[0050] 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.

[0051] The following description, in conjunction with the accompanying drawings, details a specific scheme for an isothermal quenching and cooling method for ductile iron and its isothermal quenching and cooling device provided in this application.

[0052] Please see Figure 1 The diagram illustrates a flowchart of an isothermal quenching and cooling method for ductile iron according to an embodiment of this application. The method includes the following steps:

[0053] Step 1: 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 thermal images of the surface of the salt bath furnace in real time during the cooling process of each batch of ductile iron in the current batch before isothermal quenching; obtain the initial speed value of the stirring device when the current batch of ductile iron is being cooled.

[0054] In this embodiment, a salt bath furnace is used for cooling treatment in the cooling stage before isothermal quenching of ductile iron. The nitrate in the salt bath furnace is composed of 60% potassium nitrate and 40% sodium nitrite, and the quenching temperature is 280°C. The composition of the nitrate and the quenching temperature can be set by the implementer according to the actual situation, and this application does not impose any special restrictions.

[0055] This application takes the control process of the stirring device speed during the cooling treatment in the cooling stage before isothermal quenching of the current batch of ductile iron as an example.

[0056] When using a stirring device to agitate the salt bath furnace, if the stirring speed exceeds the critical speed, cavitation will occur in the stirring area of ​​the salt bath furnace, leading to the generation of local bubbles or gas. If these bubbles adhere to the surface of the ductile iron, they will affect the uniformity of cooling during isothermal quenching in the salt bath furnace, thus reducing the final quenching quality of the ductile iron. Therefore, to avoid the above situation, before isothermal quenching the current batch of ductile iron, a stirring test is conducted 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 used for the current batch of ductile iron.

[0057] Taking any one of the ductile iron P in the current batch as an example, during the cooling process in the cooling stage before isothermal quenching of ductile iron P, 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 thermal images of the surface of the salt bath furnace in real time, wherein the value of the pixel in the thermal image is the temperature value.

[0058] In this embodiment, the sampling frequency of the infrared thermal imager is 10 frames per second. The sampling frequency is preset by the user and can be set by the implementer according to the actual situation. This application does not impose any special restrictions.

[0059] Simultaneously, a refractometer was used to measure the concentration of nitrates in the salt bath furnace before isothermal quenching of the current batch of ductile iron, and the concentration of nitrates in the salt bath furnace after isothermal quenching of the current batch of ductile iron P. The initial rotational speed of the stirring device during the isothermal quenching stage of the current batch of ductile iron was also obtained, wherein the initial rotational speed should be less than the critical rotational speed.

[0060] Each frame of thermal image is denoised using an image denoising algorithm to reduce the impact of environmental noise introduced during image acquisition and transmission on subsequent processing.

[0061] In this embodiment, the image denoising algorithm is a Gaussian filtering algorithm. Gaussian filtering algorithm is a well-known technology and will not be described in detail in this application. As other implementation methods, based on the ability to perform denoising processing on each frame of thermal image separately, implementers may use other existing technologies, such as median filtering algorithm, mean filtering algorithm, etc. This application does not impose any special restrictions.

[0062] To standardize the temperature values ​​of pixels in different frames of thermal images, the temperature values ​​of pixels in the acquired 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 with the ratio between the temperature value of each pixel and the austenitizing temperature value used in the current batch of ductile iron.

[0063] In this embodiment, the austenitizing temperature is 950°C. The austenitizing temperature is preset by the user and can be set by the implementer according to the actual situation. This application does not impose any special restrictions.

[0064] Step 2: Analyze the thermal images obtained during the cooling treatment of each batch of ductile iron and the changes in nitrate concentration in the salt bath furnace to determine the optimal speed of the stirring device during the cooling treatment stage before isothermal quenching of the next batch of ductile iron.

[0065] Step 2.1: Obtain the first characteristic value of each ductile iron by measuring the difference in nitrate concentration in the salt bath furnace before and after cooling treatment of the current batch of ductile iron.

[0066] Because ductile iron requires austenitizing before isothermal quenching in a salt bath furnace, and the austenitizing temperature is relatively high, the nitrates near the ductile iron in the furnace decompose into insoluble alkali metal compounds, such as sodium carbonate, upon heating. These compounds gradually accumulate in the furnace, leading to nitrate aging and a decrease in the concentration of effective components. Furthermore, the insoluble alkali metal compounds produced by nitrate decomposition alter the composition and structure of the furnace, increasing the melting point of the nitrates and reducing its cooling capacity. Therefore, to mitigate the decrease in furnace cooling capacity caused by accelerated nitrate aging after isothermal quenching of ductile iron, and to ensure that subsequent isothermal quenching of ductile iron in the salt bath furnace meets the requirement of rapid cooling to the bainite transformation temperature range, thereby improving the quality of subsequent isothermal quenching of ductile iron, the following treatment is implemented.

[0067] 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 the current batch of ductile iron P is denoted as the first difference. 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 is taken as the first characteristic value of ductile iron P. This value is used to evaluate the degree of aging of nitrate in the salt bath furnace after isothermal quenching and cooling of ductile iron P, compared to the degree of aging of nitrate in the salt bath furnace before isothermal quenching and cooling treatment of the current batch of ductile iron. The larger the first characteristic value, the greater the increase in the degree of aging, and the greater the decrease in the cooling capacity of the salt bath furnace after isothermal quenching and cooling of ductile iron P. Therefore, when subsequent ductile iron is subjected to isothermal quenching and cooling in a salt bath furnace, the rotation speed of the stirring device should be greater than the initial rotation speed of the stirring device. The first characteristic value is within the range of (0,1).

[0068] Step 2.2: Obtain the furnace wall region and non-furnace wall region in each thermal image by the positional distribution of pixels in each thermal image; obtain the average temperature value of each non-furnace wall region by the temperature value distribution of pixels in each non-furnace wall region; obtain the local high temperature region in each thermal image by the deviation of the temperature value of each pixel in the furnace wall region from the average temperature value of the non-furnace wall region; obtain the high temperature feature value of each thermal image by the proportion of the local high temperature region in each thermal image and the degree to which the temperature value of the pixels in the local high temperature region exceeds the average temperature value of the non-furnace wall region.

[0069] During austenitization, ductile iron surfaces come into contact with air and form oxide scale. This scale peels off during isothermal quenching in the salt bath furnace under the scouring action of liquid nitrates. This scale, along with refractory alkali metal compounds formed from the thermal decomposition of nitrates, continuously deposits in the furnace, gradually forming a blocky scale on the furnace wall. As the scale slowly solidifies, nitrates near the furnace wall adhere to it. This scale hinders heat transfer, affecting the furnace wall's heat dissipation. Consequently, areas near the furnace wall are more prone to localized overheating due to scale formation, leading to uneven temperature distribution and uneven cooling during isothermal quenching of ductile iron in the salt bath furnace. To reduce the excessively high local temperature of the salt bath furnace wall caused by scaling after isothermal quenching of ductile iron, and to improve the uniformity of cooling of subsequent isothermal quenching of ductile iron in the salt bath furnace, thereby improving the quality of subsequent isothermal quenching of ductile iron, the following treatment is performed.

[0070] (1) Obtain the furnace wall area and non-furnace wall area in each thermal image by the position distribution of pixels in each thermal image.

[0071] Since the furnace wall area of ​​the salt bath furnace is generally located at the edge of the acquired thermal image, the pixel at the center of each thermal image is recorded as the center pixel of each thermal image, which is used 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 from the center pixel. The first preset number of pixels form the furnace wall area, and the area in each thermal image other than the furnace wall area is regarded as the non-furnace wall area.

[0072] In this embodiment, the distance between each pixel in the thermal image and the center pixel is the Euclidean distance.

[0073] In this embodiment, the preset quantity is the product of the number of pixels in each thermal image and 10%. Here, 10% is only one embodiment of this application. Implementers can set its specific value according to the actual situation. This application does not impose any special restrictions.

[0074] (2) Obtain the average temperature value of the non-furnace wall region in each thermal image by the distribution of the temperature values ​​of the pixels in the non-furnace wall region in each thermal image.

[0075] Since the temperature of austenitized ductile iron is higher than that of the salt bath furnace, a threshold segmentation algorithm is used to obtain the segmentation threshold of the temperature values ​​of all pixels in the non-furnace wall region of each thermal image. The average temperature value of the non-furnace wall region of each thermal image with a temperature value less than or equal to the segmentation threshold is taken as the average temperature value of the non-furnace wall region of 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 region in the salt bath furnace.

[0076] In this embodiment, the Otsu threshold segmentation algorithm is used to obtain the segmentation threshold of the temperature value of all pixels 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, based on the ability to obtain the segmentation threshold of the temperature value of all pixels in each non-furnace wall area, the implementer may use other existing technologies, such as iterative threshold segmentation, global threshold segmentation, etc., which will not be described in detail in this application.

[0077] (3) By comparing the temperature values ​​of each pixel in the furnace wall region with the average temperature value of the non-furnace wall region in each thermal image, the local high temperature region in each thermal image is obtained; by the proportion of the local high temperature region in each thermal image and the degree to which the temperature value of the pixel in the local high temperature region exceeds the average temperature value of the non-furnace wall region, the high temperature feature value of each thermal image is obtained.

[0078] The difference between the temperature value of each pixel within the furnace wall region and the average temperature value of the non-furnace wall region in each thermal image is recorded as the second difference. This difference is used to assess whether the salt bath furnace location corresponding to each pixel within the furnace wall region is in a localized high-temperature area. The region formed by pixels within the furnace wall region in each thermal image where the second difference is greater than 0 is considered the localized high-temperature area in each thermal image. Since the pixels corresponding to localized high-temperature areas on the furnace wall of the salt bath furnace are usually clustered rather than discrete in the thermal images, all discrete pixels in the localized high-temperature areas of each thermal image are removed to reduce the impact of noise-affected pixels on the severity assessment of the localized high-temperature phenomenon on the furnace wall of the salt bath furnace in subsequent assessments. The method for determining discrete pixels in the image is a known technique, and the specific process will not be elaborated in this application.

[0079] Furthermore, the ratio of the number of pixels in each local high-temperature region to the number of pixels in the corresponding thermal image is calculated to assess the proportion of local high-temperature regions on the salt bath furnace wall. The average of the second difference corresponding to all pixels in the local high-temperature regions of each thermal image is calculated, and the product of the ratio and the average value is used as the high-temperature feature value of each thermal image. The high-temperature feature value is used to assess the severity of the local high-temperature phenomenon on the salt bath furnace wall appearing in the thermal image; the larger the high-temperature feature value, the higher the severity of the local high-temperature phenomenon on the salt bath furnace wall appearing in the thermal image.

[0080] Step 2.3: Obtain the second characteristic value of each ductile iron by means of the distribution of high temperature characteristic values ​​of all thermal images of each ductile iron in the current batch during cooling.

[0081] The maximum value among all high-temperature characteristic values ​​of the thermal images collected during the cooling process before isothermal quenching of ductile iron P is used as the second characteristic value of ductile iron P. This value is used to evaluate the maximum severity of local high-temperature phenomena on the furnace wall caused by scale formation during isothermal quenching of ductile iron P in a salt bath furnace. The larger the second characteristic value, the greater the maximum severity of local high-temperature phenomena. In order to improve the cooling uniformity of ductile iron during isothermal quenching in a salt bath furnace, the rotation speed of the stirring device should be higher. The second characteristic value is within the range of (0,1).

[0082] Step 2.4: Using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value, obtain the optimal speed of the stirring device during the cooling process of the next ductile iron in the current batch before isothermal quenching.

[0083] Furthermore, by using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value, the optimal speed of the stirring device is obtained during the cooling treatment of the next batch of ductile iron before isothermal quenching in each batch of ductile iron. The expression is:

[0084] In the formula, V represents the optimal rotational speed of the stirring device during the cooling process before isothermal quenching of the next batch of ductile iron P; v2 represents the initial rotational speed of the stirring device during the cooling of the current batch of ductile iron; round() represents the rounding function; v1 represents the critical rotational speed of the stirring device when cavitation occurs in the salt bath furnace used for the current batch of ductile iron; s represents the average of the first and second characteristic values ​​of ductile iron P. v1-v2 is recorded as the third difference. A schematic diagram of the process for obtaining the optimal rotational speed is shown below. Figure 2 As shown.

[0085] During the cooling process of the next ductile iron in the current batch of ductile iron P before isothermal quenching, the speed of the stirring device is adjusted to the optimal speed. After the next ductile iron in the salt bath furnace is cooled to the bainite transformation temperature range by the stirring device, the ductile iron is subjected to the holding treatment during the isothermal quenching holding stage. Finally, it is taken out of the furnace and air-cooled to room temperature to obtain isothermal quenched ductile iron material.

[0086] Based on the same inventive concept as the above method, this application embodiment also provides an isothermal quenching and cooling device for ductile iron, including: a salt bath furnace, a stirring device, and a control system for the stirring device;

[0087] Salt bath furnaces are used to cool ductile iron to the bainite transformation temperature range.

[0088] The stirring device is used to accelerate the cooling efficiency of ductile iron in a salt bath furnace when it is cooled to the bainite transformation temperature range.

[0089] The control system of the stirring device includes a data acquisition unit, a data processing unit, and a stirring control unit;

[0090] The data acquisition unit is used to perform stirring tests on the salt bath furnace used for the current batch of ductile iron, obtain the critical speed value of the stirring device when cavitation occurs in the salt bath furnace; acquire thermal images of the surface of the salt bath furnace in real time during the cooling process of each ductile iron in the current batch before isothermal quenching in the salt bath furnace; and obtain the initial speed value of the stirring device when the current batch of ductile iron is being cooled.

[0091] The data processing unit is used to obtain the first characteristic value of each ductile iron by the difference in nitrate concentration in the salt bath furnace before and after the cooling treatment of the current batch of ductile iron.

[0092] By analyzing the positional distribution of pixels in each thermal image, the furnace wall region and non-furnace wall region in each thermal image are obtained; by analyzing the temperature value distribution of pixels in each non-furnace wall region, the average temperature value of each non-furnace wall region is obtained; by analyzing the deviation of the temperature value of each pixel in the furnace wall region in each thermal image from the average temperature value of the non-furnace wall region, the local high-temperature region in each thermal image is obtained; by analyzing the proportion of local high-temperature regions in each thermal image and the degree to which the temperature value of pixels in the local high-temperature region exceeds the average temperature value of the non-furnace wall region, the high-temperature feature value of each thermal image is obtained.

[0093] The second characteristic value of each ductile iron is obtained by analyzing the distribution of high-temperature characteristic values ​​of all thermal images during the cooling of each ductile iron in the current batch.

[0094] By using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value, the optimal speed of the stirring device is obtained when the next batch of ductile iron in the current batch undergoes cooling treatment in the cooling stage before isothermal quenching.

[0095] The stirring control unit is used to adjust the speed of the stirring device to the optimal speed during the cooling process in the cooling stage before isothermal quenching of the next batch of ductile iron from the current batch.

[0096] In summary, this application determines the critical speed value of the stirring device when cavitation occurs in the salt bath furnace through stirring tests. Using the critical speed value as the upper limit of the stirring device speed can effectively avoid cavitation in the stirring area when the stirring device is stirring in the salt bath furnace. This can improve the cooling uniformity of the current batch of ductile iron during isothermal quenching in the salt bath furnace, thereby improving the final quenching quality of the current batch of ductile iron.

[0097] Furthermore, by calculating the first characteristic value, the degree of nitrate aging in the salt bath furnace after isothermal quenching and cooling of each ductile iron is assessed, which facilitates the subsequent adjustment of the stirring speed based on the degree of nitrate aging. By obtaining data from the furnace wall area and non-furnace wall area, key areas in the salt bath furnace where localized high temperatures may occur can be identified. Obtaining the average temperature value of the non-furnace wall area can serve as a benchmark for assessing temperature anomalies in the furnace wall area, making subsequent judgments on localized high-temperature areas more accurate and reliable. By identifying localized high-temperature areas, localized high-temperature phenomena caused by scaling on the furnace wall of the salt bath furnace can be accurately identified, providing a basis for quantifying the severity of localized high-temperature phenomena. By calculating the high-temperature characteristic value, the severity of localized high-temperature phenomena can be quantified. The second characteristic value reflects the maximum severity of localized high-temperature phenomena on the furnace wall caused by scaling during isothermal quenching and cooling of ductile iron in the salt bath furnace, which helps to adjust the stirring speed based on the maximum severity of localized high-temperature phenomena.

[0098] Furthermore, by using the first characteristic value, the second characteristic value, and the critical speed value, the optimal speed of the stirring device is obtained when the next ductile iron undergoes isothermal quenching and cooling. This not only effectively ensures that the subsequent ductile iron is rapidly cooled to the bainite transformation temperature range when using a salt bath furnace for isothermal quenching and cooling, but also improves the uniformity of cooling when the subsequent ductile iron is used for isothermal quenching and cooling in a salt bath furnace, thereby improving the quality of the subsequent ductile iron undergoing isothermal quenching and cooling.

[0099] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to embodiments of this disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than that shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending 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 blocks may also occur in a different order than disclosed in the description, and sometimes there is no specific order between different operations or steps. For example, two consecutive operations or steps may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. Each block in a block diagram and / or flowchart, and combinations of blocks in a block diagram and / or flowchart, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0100] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from its essential characteristics. Therefore, the embodiments described above should be considered exemplary and non-limiting in all respects.

Claims

1. A method for isothermal quenching and cooling of ductile iron, characterized in that, The method includes the following steps: A stirring test was conducted 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; thermal images of the surface of the salt bath furnace were collected in real time during the cooling process of each ductile iron in the current batch before isothermal quenching; and the initial speed value of the stirring device was obtained when the current batch of ductile iron was being cooled. The first characteristic value of each ductile iron was obtained by measuring the difference in nitrate concentration in the salt bath furnace before and after cooling treatment of the current batch of ductile iron. By analyzing the positional distribution of pixels in each thermal image, the furnace wall region and non-furnace wall region in each thermal image are obtained; by analyzing the temperature value distribution of pixels in each non-furnace wall region, the average temperature value of each non-furnace wall region is obtained; by analyzing the deviation of the temperature value of each pixel in the furnace wall region in each thermal image from the average temperature value of the non-furnace wall region, the local high-temperature region in each thermal image is obtained; by analyzing the proportion of local high-temperature regions in each thermal image and the degree to which the temperature value of pixels in the local high-temperature region exceeds the average temperature value of the non-furnace wall region, the high-temperature feature value of each thermal image is obtained. The second characteristic value of each ductile iron is obtained by analyzing the distribution of high-temperature characteristic values ​​of all thermal images during the cooling of each ductile iron in the current batch. By using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value, the optimal speed of the stirring device is obtained when the next batch of ductile iron in the current batch undergoes cooling treatment in the cooling stage before isothermal quenching. The process of obtaining the first feature value 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 denoted 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. The process of obtaining the local high-temperature region is as follows: The difference between the temperature value of each pixel in the furnace wall area and the average temperature value of the non-furnace wall area in each thermal image is recorded as the second difference. The local high temperature area is the area composed of pixels in the furnace wall area of ​​each thermal image whose second difference is greater than 0. The process for obtaining the high-temperature characteristic value is as follows: Calculate the ratio of the number of pixels in each local high-temperature region to the number of pixels in the corresponding thermal image; Calculate the average of the second difference for all pixels within the local high-temperature region in each thermal image; The high-temperature characteristic value is the product of the ratio and the average value; The second characteristic value is the maximum value among the high-temperature characteristic values ​​of all thermal images during the cooling of each ductile iron in the current batch; The process for obtaining the optimal rotational speed is as follows: The difference between the critical speed value and the initial speed value is recorded as the third difference. Calculate the arithmetic mean of the first feature value and the second feature value; Calculate the product of the third difference and the arithmetic mean; The optimal speed is obtained by multiplying the initial speed value by the value. The optimal rotational speed is the sum of the rounded result of the product and the initial rotational speed value.

2. The isothermal quenching and cooling method for ductile iron as described in claim 1, characterized in that, The process of acquiring the furnace wall region and non-furnace wall region in each thermal image is as follows: The pixel at the center of each thermal image is denoted as the center pixel of each thermal image. The pixels in each thermal image are arranged in descending order of their distance from the center pixel. The first preset number of pixels form the furnace wall region, and the area in each thermal image other than the furnace wall region is regarded as the non-furnace wall region.

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

4. A ductile iron isothermal quenching and cooling device, employing the ductile iron isothermal quenching and cooling method described in claim 1, characterized in that, The device includes: a salt bath furnace, a stirring device, and a control system for the stirring device; Salt bath furnaces are used to cool ductile iron to the bainite transformation temperature range. The stirring device is used to accelerate the cooling efficiency of ductile iron in a salt bath furnace when it is cooled to the bainite transformation temperature range. 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 stirring tests on the salt bath furnace used for the current batch of ductile iron, obtain the critical speed value of the stirring device when cavitation occurs in the salt bath furnace; acquire thermal images of the surface of the salt bath furnace in real time during the cooling process of each ductile iron in the current batch before isothermal quenching in the salt bath furnace; and obtain the initial speed value of the stirring device when the current batch of ductile iron is being cooled. The data processing unit is used to obtain the first characteristic value of each ductile iron by the difference in nitrate concentration in the salt bath furnace before and after the cooling treatment of the current batch of ductile iron. By analyzing the positional distribution of pixels in each thermal image, the furnace wall region and non-furnace wall region in each thermal image are obtained; by analyzing the temperature value distribution of pixels in each non-furnace wall region, the average temperature value of each non-furnace wall region is obtained; by analyzing the deviation of the temperature value of each pixel in the furnace wall region in each thermal image from the average temperature value of the non-furnace wall region, the local high-temperature region in each thermal image is obtained; by analyzing the proportion of local high-temperature regions in each thermal image and the degree to which the temperature value of pixels in the local high-temperature region exceeds the average temperature value of the non-furnace wall region, the high-temperature feature value of each thermal image is obtained. The second characteristic value of each ductile iron is obtained by analyzing the distribution of high-temperature characteristic values ​​of all thermal images during the cooling of each ductile iron in the current batch. By using the second characteristic value, the critical speed value, the initial speed value, and the first characteristic value, the optimal speed of the stirring device is obtained when the next batch of ductile iron in the current batch undergoes cooling treatment in the cooling stage before isothermal quenching. The stirring control unit is used to adjust the speed of the stirring device to the optimal speed during the cooling process in the cooling stage before isothermal quenching of the next batch of ductile iron from the current batch.

Images