Heat treatment method and device for improving hardness of ADI casting

Abstract

The invention relates to the technical field of casting heat treatment, in particular to a heat treatment method and device for improving the hardness of an ADI casting, and the method comprises the steps that temperature data of all positions of the surface of the ADI casting in the ADI casting heat treatment quenching process are obtained; the method comprises the following steps: acquiring significant values of rate difference and non-smooth degree of temperature change of each position in an initial quenching period, calculating an abnormal significant value of surface temperature change of a casting in each time window at each position, and a difference coefficient of a quenching temperature change state of each time window at each position; and then the stability consistency coefficient of the temperature state of each position in each time window is obtained, the stability consistency coefficient is used for calculating the lag influence coefficient of temperature control of each time window so as to optimize the temperature error in the quenching temperature control process of the PID controller, and then tempering treatment is carried out to complete heat treatment of the ADI casting. The ADI casting heat treatment method can improve the ADI casting heat treatment effect.

Description

Technical Field

[0001] The present application relates to the technical field of heat treatment of castings, and in particular to a heat treatment method and device for improving the hardness of ADI castings. Background Art

[0002] Austempering ductile iron (ADI) is a key step in the preparation of austempered ductile iron (ADI) materials. Specifically, the ductile iron is first heated to the austenitizing temperature and held at that temperature. It is then rapidly quenched into a salt bath. In the salt bath, the pre-austempering cooling phase takes place, cooling the ductile iron to the bainite transformation temperature. This phase is followed by the austempering holding phase, where the ductile iron is held at that temperature. Finally, tempering is performed to produce ADI materials with superior performance.

[0003] Ductile iron undergoes rapid cooling and a long period of holding process in a salt bath furnace, among which the cooling process and holding process of austempering have a greater impact on the hardness performance. Existing methods often use a stirring device to quickly cool down the salt bath furnace and maintain the temperature stability of the holding process. However, in the actual quenching process, the salt bath furnace is prone to aging and scaling of the quenching medium, which reduces the heat transfer performance and causes temperature fluctuations in the salt bath furnace, making it difficult to ensure the stability and consistency of the quenching quality of various parts of the ductile iron. The existing heat treatment method fails to fully consider the impact of changes in heat transfer performance and uneven stirring on temperature fluctuations, and is not stable enough in terms of temperature control during quenching, which easily leads to the problem of insufficient hardness of the casting after heat treatment. The present application improves the hardness performance of ADI castings by optimizing and adjusting the temperature of the holding process in the quenching stage.

[0004] Publication No. CN103088251B describes a ductile iron heat treatment method, which uses austempering for heat treatment, maintaining the heat in a salt bath of mixed molten salt for 2-3 hours to increase the hardness of the ductile iron. However, this insulation fails to fully account for temperature fluctuations caused by aging and scaling of the quenching medium, potentially resulting in insufficient hardness in the heat-treated casting. Summary of the Invention

[0005] In order to solve the above technical problems, the purpose of this application is to provide a heat treatment method and device for improving the hardness of ADI castings. The technical solutions adopted are as follows: The present invention provides a heat treatment method for improving the hardness of an ADI casting, comprising the following steps: Obtain temperature data at various locations on the surface of ADI castings during austempering during heat treatment of ADI castings; The initial quenching period of the casting quenching process is set, and the temperature data change differences between each position and other positions during the initial quenching period, as well as the smoothness of the temperature change during the initial quenching period, are used to obtain the significant values ​​of the temperature change rate difference and non-smoothness degree at each position during the initial quenching period. The outliers of the temperature data in each time window at each location of the casting are extracted. The deviation between the outliers and the average level of the temperature data in the time window, the degree of random fluctuation of the outliers, and the degree of discreteness of the time intervals between adjacent outliers are used to obtain the significant value of the abnormal temperature change of the casting surface in each time window at each location. According to the degree of difference in the temperature change trend between each position of the casting and other positions in the same time window, the difference coefficient of the quenching temperature change state of each position in each time window is obtained, and combined with the significant value of the abnormal temperature change of the casting surface, the stability consistency coefficient of the temperature state of each position in each time window is obtained; Combined with the significant values ​​of the temperature change rate differences and non-smoothness at various locations of the casting during the initial quenching period, as well as the stability consistency coefficient of the temperature state at each location within each time window, the hysteresis influence coefficient of the temperature control in each time window is obtained to optimize the temperature error during the quenching temperature control process of the PID controller. After that, the heat treatment of the ADI casting is completed through tempering treatment.

[0006] Preferably, the method for determining the initial quenching period is: respectively obtaining the moment when the temperature of all positions near the surface of the casting material first reaches the preset isothermal quenching temperature, and the time period from the start of quenching to this moment is used as the initial quenching period.

[0007] Preferably, the method for obtaining the significant value of the difference in the rate of temperature change and the degree of non-smoothness at each position during the initial quenching period is: , where is the significant value of the temperature change rate difference and non-smoothness at the i-th position in the initial quenching period, is the difference coefficient of the temperature drop rate at the initial quenching stage at the i-th position, is the determination coefficient corresponding to the fitting curve of the temperature data of the initial quenching period at the i-th position.

[0008] Preferably, the first-order difference sequence of the temperature data of each position in the initial quenching period is counted, and the mean of the DTW distance between each position and the first-order difference sequence corresponding to all other positions in the initial quenching period is calculated as the difference coefficient of the temperature drop rate of each position in the initial quenching period.

[0009] Preferably, the method for obtaining the significant value of the abnormal temperature change of the casting surface in each time window at each position is: , where is the significant value of the abnormal temperature change of the casting surface in the jth time window at the i-th position, is the randomness of the casting surface temperature change in the jth time window at the i-th position, is the abnormal coefficient of the casting surface temperature variation within the jth time window at the i-th position.

[0010] Preferably, after the end of the initial quenching period, the preset time length is used as each time window, and the abnormal values ​​of the temperature data in the jth time window at the i-th position are counted, and the sum of the absolute values ​​of the differences between each abnormal value and the temperature mean in the time window is calculated as the abnormal coefficient of the temperature change amplitude of the casting surface in the j-th time window, and the product of the coefficient of variation of all abnormal values ​​in the j-th time window and the variance of the time intervals of all adjacent abnormal values ​​is used as the randomness of the casting surface temperature change in the j-th time window.

[0011] Preferably, the method for obtaining the difference coefficient of the quenching temperature change state in each time window of each position is: For the j-th time window of each position, the test statistic of each position in the j-th time window is extracted, the mean of the difference between the test statistics of each position and other positions corresponding to the j-th time window is calculated, and the mean of the difference between the average temperature of each position and other positions in the j-th time window is calculated. The product of the two means is used as the difference coefficient of the quenching temperature change state of the j-th time window of each position.

[0012] Preferably, the method for obtaining the stability consistency coefficient of the temperature state of each position in each time window is: , where is the stability consistency coefficient of the temperature state in the jth time window at the i-th position, is the significant value of the abnormal temperature change of the casting surface in the jth time window at the i-th position, is the difference coefficient of the quenching temperature change state in the jth time window at the i-th position.

[0013] Preferably, obtaining the hysteresis influence coefficient of the temperature control in each time window to optimize the temperature error in the quenching temperature control process of the PID controller includes: The significant values ​​of the temperature change rate difference and non-smoothness degree at each position in the initial quenching period and the stable consistency coefficient of the temperature state at each position in the j-th time window are arranged in time series to obtain the temperature state characteristic sequence of each position up to the j-th time window. The mean of the DTW distance between the temperature state characteristic sequences of all two positions up to the j-th time window is calculated as the hysteresis influence coefficient of the temperature control in the j-th time window. Optimized value of temperature error in the next time window The calculation formula is: ,in, is the temperature error in the current time window, It is the hysteresis influence coefficient of temperature control in the current time window.

[0014] An embodiment of the present application also provides a heat treatment device for improving the hardness of ADI castings, comprising a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of any one of the above-mentioned heat treatment methods for improving the hardness of ADI castings are implemented.

[0015] As can be seen from the above, the heat treatment method and device for improving the hardness of ADI castings provided by this application have at least the following beneficial effects: This application optimizes the temperature fluctuations that may occur during the austempering stage. By thoroughly analyzing the abnormal temperature drop characteristics during the initial quenching period, as well as the stability and uniformity of the casting surface temperature in a relatively stable state, and further considering the delay-related characteristics of the temperature change state at each location, a hysteresis effect coefficient is calculated. This hysteresis effect coefficient is used to optimize the overall parameters of the PID controller. This has the advantage of reducing the effects of variations in the salt bath's heat transfer performance and uneven stirring, improving the response to temperature changes, and thus ensuring temperature stability and consistency during the austempering process, which helps to improve the hardness of ADI castings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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.

[0017] Figure 1 This is a flow chart of the steps of a heat treatment method for improving the hardness of ADI castings provided in this application. DETAILED DESCRIPTION

[0018] To further illustrate the technical means and effectiveness of this application's implementation of the intended invention, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effectiveness of a heat treatment method and apparatus for improving the hardness of ADI castings proposed in this application. In the following description, references to different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0019] Unless otherwise specified and limited, terms such as "comprises", "includes" or any other variants thereof are intended to cover non-exclusive inclusion, so that a circuit structure, article or device comprising a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the article or device comprising the element. In addition, the term "and\or" used herein includes any and all combinations of one or more related listed items. All technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs.

[0020] The following describes in detail a specific scheme of a heat treatment method and device for improving the hardness of ADI castings provided by the present application with reference to the accompanying drawings.

[0021] See also Figure 1 , which shows a flow chart of the steps of a heat treatment method for improving the hardness of ADI castings provided by one embodiment of the present application, including the following steps: Step 1: Obtain the temperature data of various positions on the surface of the ADI casting during the austempering process of the ADI casting heat treatment.

[0022] In this embodiment, the heat treatment process of ADI castings generally includes several stages of austenitization, austempering and tempering. Among them, austenitization is the process of heating the alloy to the austenite phase region to transform the ferrite and cementite in the alloy into austenite. In this embodiment, a box-type resistance furnace is used to heat the casting material to - In this embodiment, the casting material is heated to 900°C. It should be noted that the specific temperature selection needs to be adjusted according to the chemical composition and organizational state of the casting. For example, when the silicon and phosphorus content in the casting is high, a higher austenitizing temperature should be selected; and when it contains copper, nickel, and molybdenum alloy elements, the austenitizing temperature can be appropriately lowered. After austenite is formed, it is necessary to maintain it at the austenitizing temperature for a certain period of time to homogenize the composition and organization of the austenite. After heating to the austenitizing temperature, the casting is kept warm for 2-4 hours to ensure that the interior is completely austenitized. Preferably, in this embodiment, the casting is kept warm for 3 hours.

[0023] After austenitization, the casting material is quickly transferred to a salt bath furnace for austempering. Since the nitrate salt bath has good thermal stability and heat transfer performance, it can improve the temperature uniformity of the casting during austempering. The quenching medium used in this embodiment is a mixed salt of 50% KNO3 + 50% NaNO2. The austempering temperature is generally - Different austempering temperatures will result in different structures and properties. Within the above temperature range, the lower the austempering temperature, the less the retained austenite content in the structure. The elongation and toughness of the ADI casting decrease significantly with increasing temperature, while its hardness gradually increases. Therefore, the austempering temperature is preset to , set the quenching time to 2 hours.

[0024] The hardness of ADI castings is easily affected by the austempering temperature. It is very important to ensure the stability and balance of the surface temperature of ADI castings during the long austempering process. In the actual quenching process, the quenching medium may age and scale, resulting in a decrease in its heat transfer performance. In addition, improper stirring can easily cause differences in the salt bath temperature, making it difficult to achieve accurate temperature control. Therefore, in this embodiment, thermocouple temperature sensors are placed at equal intervals at multiple locations near the surface of the ADI casting to monitor the temperature changes on the casting surface in real time, and the time interval for temperature data collection is set to 1 second. By analyzing the temperature state and change characteristics under the influence of the decrease in the heat transfer performance of the salt bath and uneven stirring, the stability of the austempering temperature is improved, thereby increasing the hardness of the ADI casting.

[0025] Step 2: Set the initial quenching period during the casting quenching process, and use the difference in temperature data changes between each position and other positions during the initial quenching period, as well as the smoothness of the temperature change during the initial quenching period, to obtain the significant values ​​of the temperature change rate difference and non-smoothness of each position during the initial quenching period.

[0026] Aging quenching media can affect their heat transfer properties. During the stirring process, varying heat transfer properties of the quenching media can cause heat transfer, leading to short-term, rapid, random variations in the surface temperature of the ADI casting. This, in turn, can cause quenching temperature variations and instability. Immediately after transfer to the salt bath furnace, the ADI casting is gradually cooled from the austenitizing temperature to the quenching temperature. A rapid or slow drop in the casting's surface temperature can affect mechanical properties, and varying heat transfer properties can lead to varying cooling rates in different parts of the casting. Therefore, the greater the difference in the rate of temperature drop at different locations during quenching, the greater the impact on casting hardness.

[0027] First, the moment at which the temperature at all locations near the casting surface first reaches the preset austempering temperature is determined. The period from the start of quenching to this moment is defined as the initial quenching period. Taking the temperature data collected at the i-th location as an example, a first-order difference sequence of the temperature data at that location during the initial quenching period is obtained. Each value in this first-order difference sequence reflects the temperature change between adjacent moments. In other words, each element in the first-order difference sequence can be used to characterize the temperature change rate at each moment.

[0028] Then, the DTW distance between each position and the first-order difference sequence corresponding to each other position in the initial quenching period is calculated respectively, and the mean of all the DTW distances is used as the difference coefficient of the temperature drop rate in the initial quenching period of each position. The difference coefficient of the temperature drop rate in the initial quenching period of the i-th position is recorded as D, which is used to reflect the degree of difference in the temperature drop rate between this position and other positions in the initial quenching period.

[0029] Furthermore, variations in the heat transfer effect of the quenching medium or the influence of the stirring state can cause the temperature drop process to be non-smooth due to random variations, affecting the mechanical properties of ADI castings. To address this, a quadratic polynomial fitting technique was used to obtain a fitting curve for the temperature data during the initial quenching period. The coefficient of determination of this fitting curve was calculated. The coefficient of determination corresponding to the fitting curve for the temperature data during the initial quenching period at the i-th position is denoted as R. A higher degree of fit indicates a smoother temperature change. This value reflects the smoothness of the temperature change at the corresponding position during the initial quenching period.

[0030] Furthermore, in this embodiment, the significant values ​​of the temperature change rate difference and non-smoothness degree at each position during the initial quenching period are obtained, and the formula is: , where is the significant value of the temperature change rate difference and non-smoothness at the i-th position in the initial quenching period, is the difference coefficient of the temperature drop rate at the initial quenching stage at the i-th position, is the determination coefficient corresponding to the fitting curve of the temperature data of the initial quenching period at the i-th position.

[0031] The larger the A is, the greater the difference in temperature change rate between the i-th position and other positions in the initial quenching period, and the less smooth the temperature change in the initial quenching period.

[0032] Step 3: Extract the outliers of the temperature data in each time window at each location of the casting. Use the deviation between the outliers and the average level of the temperature data in the time window, as well as the degree of random fluctuation of the outliers and the degree of discreteness of the time intervals between adjacent outliers to obtain the significant value of the abnormal temperature change of the casting surface in each time window at each location.

[0033] Furthermore, considering that the surface temperature of the ADI casting reaches a relatively stable state, it will fluctuate around the set isothermal quenching temperature. As mentioned above, the decrease in heat transfer performance or uneven stirring of the quenching medium will affect the stability and consistency of its surface temperature, making its fluctuation have rapid and random characteristics. In order to obtain the short-term change characteristics after the end of the initial quenching period, preferably, in this embodiment, a time window with a duration of 2 minutes is set after the end of the initial quenching period. Taking the jth time window at the i-th position as an example, the SOS (Stochastic Outlier Selection) detection algorithm is used to obtain the abnormal value of the temperature data in the j-th time window. The obtained abnormal value fluctuation amplitude and the frequency of occurrence of abnormal value points reflect the degree of temperature change fluctuation and random characteristics. Therefore, the difference between each abnormal value and the mean of all temperatures in the time window is calculated respectively, and the cumulative sum of the absolute values ​​of all the differences is used as the abnormal coefficient of the casting surface temperature change amplitude in the j-th time window at the i-th position, which is recorded as . Income The larger the value is, the greater the magnitude of the instantaneous temperature anomaly is within the time window.

[0034] Furthermore, in order to obtain the random characteristics of its abnormal fluctuations, the coefficient of variation of all abnormal values ​​is calculated. The larger the obtained coefficient of variation, the stronger the randomness of the variation range of the abnormal quenching temperature value. Then the time intervals of all adjacent abnormal values ​​in the time window are obtained, and the variance of all time intervals is calculated. The larger the variance, the greater the degree of discreteness of the time intervals between adjacent abnormal values, which further reflects the randomness of the position distribution of the abnormal values ​​in the time window. The product of the obtained coefficient of variation and the variance is taken as the randomness of the casting surface temperature change, which is recorded as , income The larger the value, the more obvious the random characteristics of the abnormal temperature change in the time window. The abnormal significance value of the casting surface temperature change in the jth time window at the i-th position is calculated using the formula: , where is the significant value of the abnormal temperature change of the casting surface in the jth time window at the i-th position, are the abnormal coefficient of the casting surface temperature variation in the jth time window at the i-th position and the random degree of the casting surface temperature variation. The larger the value is, the greater the instantaneous abnormal fluctuation amplitude of temperature change in the time window is, and the distribution of abnormal values ​​is more random.

[0035] Step 4: According to the degree of difference in the temperature change trend between each position of the casting and other positions in the same time window, the difference coefficient of the quenching temperature change state of each time window of each position is obtained. Combined with the significant value of the abnormal temperature change of the casting surface, the stability consistency coefficient of the temperature state of each position in each time window is obtained.

[0036] Furthermore, after the quenching temperature reaches a steady state, the heat transfer properties and uneven stirring of the quenching medium can cause differences in quenching temperatures in different parts of the ADI casting, thereby affecting the overall hardness of the casting material. The large thermal inertia of the salt bath furnace causes a delayed response of the casting surface temperature to changes in the salt bath temperature, resulting in different overall change trends. Therefore, the consistency of the temperature state in different parts can be reflected by whether the temperature change trends at different locations are similar. Compared with simply comparing the temperature data differences at different locations, this can reduce the interference of random outliers to a certain extent.

[0037] Therefore, taking the i-th position as an example, the Mann-Kendall algorithm is used to obtain the change trend characteristics of the temperature data corresponding to the i-th position in the j-th time window, output the test statistic of the i-th position in the j-th time window, calculate the mean of the difference between the i-th position and the test statistics corresponding to the j-th time window of other positions, and calculate the mean of the difference between the i-th position and the average temperature of other positions in the j-th time window. The product of the two means is used as the difference coefficient of the quenching temperature change state of the i-th position in the j-th time window, which is recorded as . Income The larger it is, the worse the consistency of the surface temperature state between this location and other locations is.

[0038] Among them, the obtained significant value of the abnormal temperature change of the casting surface reflects the stability characteristics of the temperature state at each position, and the difference coefficient of the quenching temperature change state reflects the consistency characteristics of the temperature at each position with other positions. In a good heat treatment process, the surface temperature of the ADI casting needs to have good stability and consistency at the same time. Therefore, the stability consistency coefficient of the temperature state at the i-th position in the j-th time window is calculated as follows: , where is the stability consistency coefficient of the temperature state in the jth time window at the i-th position, is the significant value of the abnormal temperature change of the casting surface in the jth time window at the i-th position, is the difference coefficient of the quenching temperature change state in the jth time window at the i-th position, and the obtained It reflects the stability and consistency of temperature changes at that location.

[0039] Step 5: Combine the significant values ​​of the temperature change rate differences and non-smoothness at each location of the casting during the initial quenching period, as well as the stability consistency coefficient of the temperature state at each location within each time window, to obtain the hysteresis influence coefficient of the temperature control in each time window. This is used to optimize the temperature error during the quenching temperature control process of the PID controller. After tempering, the heat treatment of the ADI casting is completed.

[0040] In a salt bath furnace for austempering, there is a hysteresis between the temperature state of the ADI casting and the control of the stirring unit, resulting in a certain delay-related characteristic in the temperature states at different locations. The closer the surface temperature change characteristics at different locations, the more timely and effective the stirring unit's temperature control within the salt bath furnace. Taking the i-th position as an example, the difference in the rate of temperature change and the significance of the degree of non-smoothness at each position during the initial quenching period are arranged in time series, along with the stability consistency coefficient of the temperature state at each position within the j-th time window. This yields a characteristic sequence of the temperature state at each position up to the j-th time window. The mean of the DTW distances between all temperature state characteristic sequences at any two positions up to the j-th time window is calculated as the hysteresis influence coefficient of the temperature control in the j-th time window. The larger the hysteresis influence coefficient, the greater the hysteresis influence of the stirring unit's control on the ADI casting temperature during the austempering process up to the j-th time window.

[0041] To minimize the impact of salt bath furnace temperature fluctuations on the hardness of ADI castings, this embodiment uses a PID controller to adjust the stirring unit in real time. The resulting hysteresis coefficient is used to optimize the PID controller's response rate. The PID controller in this embodiment has a self-tuning function that automatically adjusts PID parameters to achieve optimal control. The proportional term parameter in the PID controller is tuned based on the error between the measured temperature and a preset target temperature, the austempering temperature. A larger error indicates a faster controller response. The delay between the real-time measured temperature data and the actual temperature state of the ADI casting surface causes the error obtained during the tuning process to be inaccurate, making it difficult to reflect the actual temperature difference in a timely manner. A larger hysteresis coefficient indicates a greater hysteresis effect on the stirring unit's adjustment. In this case, the controller's response speed needs to be increased. During the proportional term parameter tuning process, a larger error is set to improve the system's response rate. Conversely, a smaller error is set to avoid overshoot or oscillation in the adjustment.

[0042] Specifically, for the hysteresis effect coefficient of the temperature control in each time window, the sigmoid function is used to normalize the hysteresis effect coefficient of the temperature control in the current time window, and the result is recorded as , During the quenching temperature adjustment process, the specific formula for temperature error optimization is: ,in Optimize the temperature error value for the next time window, is the hysteresis influence coefficient of temperature control in the current time window, is the temperature error in the current time window, which is calculated by the difference between the actual temperature in the current time window and the preset target temperature. Furthermore, in this embodiment, the proportional term parameter for the next time window is obtained based on the optimized temperature error. A PID controller is then used to adjust the quenching temperature based on the proportional term parameter for the next time window, ensuring the stability of the salt bath furnace temperature and thereby improving the hardness of the ADI casting. It should be noted that the specific control process of the PID controller and the calculation process of the proportional term parameter are well known to those skilled in the art and will not be further described in this embodiment.

[0043] In order to further adjust the stability of retained austenite, improve mechanical properties and reduce internal stress, in this embodiment, after the ADI casting is austempered, it is transferred to a tempering furnace for tempering. The castings in the tempering furnace are evenly placed to avoid contact with each other to ensure uniform heating. The tempering temperature range is set to - In this embodiment, the tempering temperature is 350°C. When the casting reaches the set tempering temperature, it starts to be kept warm for a time range of 1-4 hours. In this embodiment, the holding time is 2 hours. It should be noted that in actual application scenarios, the implementer can set the specific tempering temperature and holding time according to actual conditions.

[0044] At this point, the heat treatment of the ADI casting can be completed according to the above process of this embodiment.

[0045] Based on the same inventive concept as the above method, an embodiment of the present application also provides a heat treatment device for improving the hardness of ADI castings, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of any one of the above-mentioned heat treatment methods for improving the hardness of ADI castings are implemented.

[0046] It should be understood that the order in which the embodiments of the present application are presented is for illustrative purposes only and does not necessarily represent the superiority or inferiority of the embodiments. Furthermore, the foregoing descriptions of specific embodiments of this specification are provided. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential sequence shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0047] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0048] The above content is only an implementation method of the present application and is not intended to limit the scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the scope of protection of the present application.

Claims

1. A heat treatment method for improving the hardness of ADI castings, characterized in that: The following steps are involved: Obtain temperature data at various locations on the surface of ADI castings during austempering during heat treatment of ADI castings; The initial quenching period of the casting quenching process is set, and the temperature data change differences between each position and other positions during the initial quenching period, as well as the smoothness of the temperature change during the initial quenching period, are used to obtain the significant values ​​of the temperature change rate difference and non-smoothness degree at each position during the initial quenching period. The outliers of the temperature data in each time window at each location of the casting are extracted. The deviation between the outliers and the average level of the temperature data in the time window, the degree of random fluctuation of the outliers, and the degree of discreteness of the time intervals between adjacent outliers are used to obtain the significant value of the abnormal temperature change of the casting surface in each time window at each location. According to the degree of difference in the temperature change trend between each position of the casting and other positions in the same time window, the difference coefficient of the quenching temperature change state of each position in each time window is obtained, and combined with the significant value of the abnormal temperature change of the casting surface, the stability consistency coefficient of the temperature state of each position in each time window is obtained; Combined with the significant values ​​of the temperature change rate differences and non-smoothness at various locations of the casting during the initial quenching period, as well as the stability consistency coefficient of the temperature state at each location within each time window, the hysteresis influence coefficient of the temperature control in each time window is obtained to optimize the temperature error during the quenching temperature control process of the PID controller. After that, the heat treatment of the ADI casting is completed through tempering treatment.

2. A heat treatment method for improving the hardness of ADI castings according to claim 1, characterized in that: The method for determining the initial quenching period is: respectively obtaining the time corresponding to the first time the temperature of all positions near the surface of the casting material reaches the preset austempering temperature, and the time period from the start of quenching to this time is used as the initial quenching period.

3. A heat treatment method for improving the hardness of ADI castings according to claim 1, characterized in that: The method for obtaining the significant value of the difference in the rate of temperature change and the degree of non-smoothness at each position during the initial quenching period is as follows: , where is the significant value of the temperature change rate difference and non-smoothness at the i-th position in the initial quenching period, is the difference coefficient of the temperature drop rate at the initial quenching stage at the i-th position, is the determination coefficient corresponding to the fitting curve of the temperature data of the initial quenching period at the i-th position.

4. A heat treatment method for improving the hardness of ADI castings according to claim 3, characterized in that: The first-order difference sequence of the temperature data of each position in the initial period of quenching is counted, and the mean of the DTW distance between each position and the first-order difference sequence corresponding to all other positions in the initial period of quenching is calculated as the difference coefficient of the temperature drop rate of each position in the initial period of quenching.

5. A heat treatment method for improving the hardness of ADI castings according to claim 1, characterized in that: The method for obtaining the significant value of the abnormal temperature change of the casting surface in each time window at each position is as follows: , where is the significant value of the abnormal temperature change of the casting surface in the jth time window at the i-th position, is the randomness of the casting surface temperature change in the jth time window at the i-th position, is the abnormal coefficient of the casting surface temperature variation within the jth time window at the i-th position.

6. A heat treatment method for improving the hardness of ADI castings according to claim 5, characterized in that: After the initial quenching period, the preset time length is used as each time window, and the abnormal values ​​of the temperature data in the jth time window at the i-th position are counted. The sum of the absolute values ​​of the differences between each abnormal value and the temperature mean in the time window is calculated as the abnormal coefficient of the temperature change amplitude of the casting surface in the j-th time window, and the product of the coefficient of variation of all abnormal values ​​in the j-th time window and the variance of the time intervals of all adjacent abnormal values ​​is used as the randomness of the casting surface temperature change in the j-th time window.

7. A heat treatment method for improving the hardness of ADI castings according to claim 1, characterized in that: The method for obtaining the difference coefficient of the quenching temperature change state in each time window of each position is: For the j-th time window of each position, the test statistic of each position in the j-th time window is extracted, the mean of the difference between the test statistics of each position and other positions corresponding to the j-th time window is calculated, and the mean of the difference between the average temperature of each position and other positions in the j-th time window is calculated. The product of the two means is used as the difference coefficient of the quenching temperature change state of the j-th time window of each position.

8. A heat treatment method for improving the hardness of ADI castings according to claim 1, characterized in that: The method for obtaining the stability consistency coefficient of the temperature state of each position in each time window is: , where is the stability consistency coefficient of the temperature state in the jth time window at the i-th position, is the significant value of the abnormal temperature change of the casting surface in the jth time window at the i-th position, is the difference coefficient of the quenching temperature change state in the jth time window at the i-th position.

9. A heat treatment method for improving the hardness of ADI castings according to claim 1, characterized in that: The step of obtaining the hysteresis influence coefficient of the temperature control in each time window to optimize the temperature error during the quenching temperature control process of the PID controller includes: The significant values ​​of the temperature change rate difference and non-smoothness degree at each position in the initial quenching period and the stable consistency coefficient of the temperature state at each position in the j-th time window are arranged in time series to obtain the temperature state characteristic sequence of each position up to the j-th time window. The mean of the DTW distance between the temperature state characteristic sequences of all two positions up to the j-th time window is calculated as the hysteresis influence coefficient of the temperature control in the j-th time window. Optimized value of temperature error in the next time window The calculation formula is: ,in, is the temperature error in the current time window, It is the hysteresis influence coefficient of temperature control in the current time window.

10. A heat treatment device for improving the hardness of ADI castings, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the steps of the heat treatment method for improving the hardness of ADI castings as described in any one of claims 1 to 9 are implemented.

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