Method and system for predicting cracking tendency of magnesium alloy casting

Abstract

The present invention provides a method and system for predicting the cracking tendency of magnesium alloy casting, comprising: step 1: preparing magnesium alloy by smelting and casting process; step 2: determining the stretching temperature according to the lowest solidus temperature of the magnesium alloy; step 3: determining the stretching strain rate according to the linear contraction coefficient and cooling rate of the magnesium alloy at the stretching temperature; step 4: stretching the magnesium alloy by the stretching strain rate to determine the maximum strength of the magnesium alloy at the stretching temperature; step 5: predicting the cracking tendency of magnesium alloy casting by the maximum strength. Compared with the prior art, the present invention predicts the cracking tendency of magnesium alloy casting by the maximum strength of the magnesium alloy, and does not need to prepare a complex special evaluation mold for the cracking tendency. The prediction of the cracking tendency of magnesium alloy casting can be achieved by an ordinary high-temperature stretching machine, and the purpose of predicting the cracking tendency of magnesium alloy casting is achieved by simple and economical means.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloy casting, and in particular to a method and system for predicting cracking tendency of magnesium alloy casting. Background Art

[0002] As the lightest metal structural material, magnesium alloy has broad application prospects in the fields of transportation, electronic communications, and aerospace. At present, most magnesium alloys are formed by casting, and die-casting technology with low cost, high production efficiency and excellent dimensional accuracy has become the main means of production of magnesium alloys. Unfortunately, magnesium alloys shrink a lot and are prone to cracks during the casting process, which greatly limits the yield of magnesium alloy castings. Therefore, evaluating the cracking tendency of magnesium alloy castings is a must for producing high-quality magnesium alloy castings.

[0003] The cracking process of magnesium alloy casting is relatively complicated and it is difficult to predict it with a simple method. The existing technology requires the design of a special mold and a matching motor, stress sensor and data recorder to predict the cracking tendency of magnesium alloy casting. Therefore, there is a problem of complex prediction devices in the existing technology.

[0004] Patent document CN113340981A discloses a method for judging the tendency of stress corrosion cracking of chromium-nickel-iron alloy and predicting the degree of threat based on magnetic signals, which includes the following steps: in-situ detection of coercivity of the parts of chromium-nickel-iron alloy that are only subjected to film stress to obtain base point magnetic characteristic data; in-situ detection of coercivity of the parts of chromium-nickel-iron alloy suspected of high stress to obtain measured magnetic characteristic data; using the measured magnetic characteristic data to subtract the base point magnetic characteristic data to obtain magnetic characteristic increment data; calculating and using the statistical mean of the magnetic characteristic increment data to judge whether the suspected high stress parts have stress corrosion cracking tendency, and by comparing the size of the statistical mean of the magnetic characteristic increment of each part that has stress corrosion cracking tendency, the degree of stress corrosion cracking threat of each part can be determined. However, this method does not solve the problem of complex prediction devices in the prior art. Summary of the invention

[0005] In view of the defects in the prior art, the object of the present invention is to provide a method and system for predicting the cracking tendency of magnesium alloy casting.

[0006] A method for predicting cracking tendency of magnesium alloy casting provided by the present invention comprises:

[0007] Step 1: preparing magnesium alloy through melting and casting process;

[0008] Step 2: Determine the stretching temperature according to the lowest solidus temperature of the magnesium alloy;

[0009] Step 3: Determine the tensile strain rate according to the linear contraction coefficient of the magnesium alloy at the tensile temperature and the cooling rate;

[0010] Step 4: stretching the magnesium alloy by a tensile strain rate to determine the maximum strength of the magnesium alloy at the tensile temperature;

[0011] Step 5: Predict the cracking tendency of magnesium alloy castings through maximum strength.

[0012] Preferably, step 4 comprises:

[0013] Step 401: stretching the magnesium alloy at a tensile strain rate to obtain a tensile curve;

[0014] Step 402: Determine the maximum strength of the magnesium alloy at the tensile temperature through the tensile curve.

[0015] Preferably, step 5 comprises:

[0016] Step 501: obtaining a cracking tendency index of the magnesium alloy according to the inverse of the maximum strength;

[0017] Step 502: predicting the cracking tendency of magnesium alloy casting according to the cracking tendency index.

[0018] Preferably, step 401 includes:

[0019] Step 4011: heating the magnesium alloy to a stretching temperature at a preset speed;

[0020] Step 4012: Stretching the magnesium alloy at a tensile strain rate using a high temperature stretching machine to obtain a stretching curve.

[0021] Preferably, step 2 comprises:

[0022] Step 201: subtract the upper limit difference from the lowest solidus temperature to obtain the upper limit of the stretching temperature;

[0023] Step 202: subtract the lower limit difference from the lowest solidus temperature to obtain the lower limit value of the stretching temperature;

[0024] Step 203: Determine the stretching temperature according to the upper limit value of the stretching temperature and the lower limit value of the stretching temperature.

[0025] A magnesium alloy casting cracking tendency prediction system provided by the present invention comprises:

[0026] Module M1: Preparation of magnesium alloy through melting and casting process;

[0027] Module M2: Determine the stretching temperature based on the lowest solidus temperature of the magnesium alloy;

[0028] Module M3: Determine the tensile strain rate based on the linear contraction coefficient of the magnesium alloy at the tensile temperature and the cooling rate;

[0029] Module M4: Stretching magnesium alloy by tensile strain rate to determine the maximum strength of magnesium alloy at the tensile temperature;

[0030] Module M5: Prediction of cracking tendency of magnesium alloy castings by maximum strength.

[0031] Preferably, module M4 comprises:

[0032] Submodule M401: stretching magnesium alloy by tensile strain rate to obtain tensile curve;

[0033] Submodule M402: Determine the maximum strength of magnesium alloy at the tensile temperature through the tensile curve.

[0034] Preferably, module M5 comprises:

[0035] Submodule M501: Obtain the cracking tendency index of magnesium alloy according to the inverse of the maximum strength;

[0036] Submodule M502: Predict the cracking tendency of magnesium alloy casting based on the cracking tendency index.

[0037] Preferably, the submodule M401 includes:

[0038] Unit D4011: Heating a magnesium alloy to a stretching temperature at a predetermined rate;

[0039] Unit D4012: Magnesium alloy is stretched at a tensile strain rate using a high temperature stretching machine to obtain a tensile curve.

[0040] Preferably, module M2 comprises:

[0041] Submodule M201: Subtract the upper limit difference from the lowest solidus temperature to obtain the upper limit of the stretching temperature;

[0042] Submodule M202: subtract the lower limit difference from the lowest solidus temperature to obtain the lower limit of the stretching temperature;

[0043] Submodule M203: Determine the stretching temperature according to the upper and lower limits of the stretching temperature.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. The present invention is based on the deduction that the cracking of magnesium alloy castings during the casting process is caused by the local tensile stress caused by the thermal shrinkage of the solidified part being greater than the maximum stress that the alloy can withstand at this time. It is proposed that the anti-casting cracking performance of the magnesium alloy is proportional to its maximum strength at high temperature, so the inverse of the maximum strength can be used to predict the cracking tendency of the magnesium alloy. The method can simply and efficiently predict the cracking tendency of the magnesium alloy.

[0046] 2. The present invention can predict the cracking tendency of magnesium alloy casting by using a common high-temperature stretching machine, thus achieving the purpose of simplicity and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0048] Figure 1 It is a schematic diagram of the process of the present invention;

[0049] Figure 2 are high temperature tensile curves of three magnesium alloys of the present invention;

[0050] Figure 3 It is a comparison chart of the relative value of the cracking tendency index of the present invention and the relative value of the cracking tendency index given by the standard cracking tendency evaluation device. DETAILED DESCRIPTION

[0051] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0052] Figure 1 It is a schematic diagram of the process of the present invention, such as Figure 1 As shown, the present invention provides a method for predicting the cracking tendency of magnesium alloy casting, comprising the following steps:

[0053] Step 1: Prepare magnesium alloy through melting and casting process.

[0054] Specifically, three kinds of magnesium alloys were prepared by ordinary smelting and casting process. The three kinds of magnesium alloys include: magnesium-aluminum alloy (Mg-7.5Al (mass ratio)), magnesium-cerium alloy (Mg-3.0Ce (mass ratio)) and magnesium-cerium-aluminum alloy (Mg-9Ce-6.5Al (mass ratio)), wherein Mg-7.5Al (mass ratio) means that the mass ratio of aluminum in the magnesium alloy is 7.5%; Mg-3.0Ce (mass ratio) means that the mass ratio of cerium in the magnesium alloy is 3.0%; Mg-9Ce-6.5Al (mass ratio) means that the mass ratio of cerium in the magnesium alloy is 9% and the mass ratio of aluminum is 6.5%. Among them, the pouring temperature when preparing the magnesium alloy ingot is 720°C, and the temperature of the cylindrical metal mold is 150°C.

[0055] Furthermore, conventional high temperature tensile rods are machined from magnesium alloy ingots using wire cutting and CNC lathes.

[0056] Step 2: Determine the stretching temperature based on the lowest solidus temperature of the magnesium alloy.

[0057] In the present invention, the stretching temperature range of high temperature stretching is 300°C-550°C, which is higher than the lowest solidus temperature T in the same batch of alloys. min Low 15℃-40℃, that is, at (T min -40) to (T min -15).

[0058] Specifically, the stretching temperature is determined to ensure that the high temperature stretching test is safe and representative.

[0059] Preferably, step 2 comprises: step 201: subtracting the upper limit difference from the lowest solidus temperature to obtain the upper limit value of the stretching temperature; step 202: subtracting the lower limit difference from the lowest solidus temperature to obtain the lower limit value of the stretching temperature; step 203: determining the stretching temperature according to the upper limit value of the stretching temperature and the lower limit value of the stretching temperature.

[0060] In the present invention, there is no limitation on the setting of the upper limit difference and the lower limit difference. For example, the upper limit difference can be set to 15° C. and the lower limit difference can be set to 40° C.

[0061] In the present invention, there is no limitation on the method of determining the stretching temperature based on the upper limit value of the stretching temperature and the lower limit value of the stretching temperature. For example, a value between the upper limit value of the stretching temperature and the lower limit value of the stretching temperature can be randomly selected as the stretching temperature, or the middle value between the upper limit value of the stretching temperature and the lower limit value of the stretching temperature can be taken as the stretching temperature.

[0062] An optional embodiment first determines the lowest solidus temperature based on the solidus temperatures of three magnesium alloys, namely Mg-7.5Al, Mg-3.0Ce and Mg-9Ce-6.5Al. Among the three magnesium alloys, the solidus temperature of the Mg-7.5Al alloy is 436°C, which is the lowest solidus temperature. Then, based on the lowest solidus temperature, the stretching temperature is determined to be 420°C to ensure that the high-temperature stretching test is safe and representative.

[0063] Step 3: Determine the tensile strain rate according to the linear contraction coefficient of the magnesium alloy at the tensile temperature and the cooling rate.

[0064] The present invention does not limit the setting of the cooling rate, and can be set according to the cooling conditions of the specific casting. For example, the present invention prepares a standard restraint rod casting by a common smelting and casting process. The restraint rod casting is prepared using a special casting cracking tendency assessment mold mentioned in a published paper (Journal of Materials Science & Technology, 2022, 105: 68-80.) to obtain the standard cracking tendency values ​​of the three magnesium alloys for comparison with the indicators in the present invention. The standard restraint rod casting prepared at a pouring temperature of 720°C and a mold temperature of 270°C has a cooling rate of about 5K / s at about 420°C, and the linear shrinkage coefficient of the magnesium alloy at this temperature is about (30×10 -6 ) / K, so it can be calculated that the tensile strain rate required for the tensile test is 1.5×10 -4 s -1 .

[0065] The tensile strain rate of the high temperature stretching in the present invention is 10 -5 s -1 -10 -2 s -1 between.

[0066] Specifically, the tensile strain rate is calculated from the cooling rate corresponding to the selected tensile temperature. Where α is the linear expansion coefficient. The high temperature linear expansion coefficient of magnesium alloy is about 30×10 -6 / K, c is the cooling rate.

[0067] Step 4: Stretch the magnesium alloy by tensile strain rate to determine the maximum strength of the magnesium alloy at the tensile temperature.

[0068] Preferably, step 4 comprises: step 401: stretching the magnesium alloy at a tensile strain rate to obtain a stretching curve;

[0069] Step 402: Determine the maximum strength of the magnesium alloy at the tensile temperature through the tensile curve.

[0070] Preferably, step 401 comprises: step 4011: heating the magnesium alloy to a stretching temperature at a preset speed; step 4012: stretching the magnesium alloy at a tensile strain rate using a high-temperature stretching machine to obtain a stretching curve.

[0071] Specifically, the present invention adopts a common high temperature tensile test to evaluate the cracking tendency of magnesium alloy casting.

[0072] During the magnesium alloy casting process, the cracking of the casting is caused by the local tensile stress σ caused by the thermal contraction of the solidified part, which is greater than the maximum stress σ that the magnesium alloy can withstand at this time. max Resulting in that when σ>σ max The temperature of the solidified part during this process is usually between 300-550℃. Under the same casting process, the thermal shrinkage of magnesium alloy is basically the same, that is, the local tensile stress σ caused by thermal shrinkage is max Therefore, the resistance of magnesium alloy to casting cracking and its maximum strength at high temperature σ max is proportional to, that is, the σ of magnesium alloy max The larger the value, the better the resistance to casting cracking. Therefore, the tendency of magnesium alloy casting cracking is the inverse of its maximum strength at high temperature. Proportional, The larger the value, the higher the cracking tendency of magnesium alloy. As an indicator for evaluating the cracking tendency of magnesium alloy casting. max The high temperature tensile test is conducted at a temperature 15°C to 40°C lower than the lowest solidus temperature Tmin in the same batch of alloys; the tensile strain rate is calculated from the cooling rate corresponding to the selected tensile temperature. Where α is the linear expansion coefficient. The high temperature linear expansion coefficient of magnesium alloy is about 30×10 -6 / K, c is the cooling rate. Among them, the maximum pressure is the maximum strength in the present invention.

[0073] In an optional embodiment, Figure 2 are the high temperature tensile curves of the three magnesium alloys of the present invention, such as Figure 2 As shown, the horizontal axis is engineering strain, the unit is %, and the vertical axis is engineering stress, the unit is megapascal (MPa). Figure 2 The three curves in the figure are, from top to bottom: the high temperature tensile curve of Mg-9Ce-6.5Al, the high temperature tensile curve of Mg-3.0Ce and the high temperature tensile curve of Mg-7.5Al. Figure 2 It can be seen that the maximum intensity σ corresponding to Mg-9Ce-6.5Al, Mg-3.0Ce and Mg-7.5Al maxThe tensile tests were carried out using a conventional high-temperature tensile machine. The three magnesium alloys were first fixed, and then the samples were heated to 420°C at a rate of 15K / min and kept warm for 10 minutes to ensure uniform heating of the samples. -4 s -1 The strain rate is used to obtain Figure 2 The tensile curves shown in the figure can be used to obtain the maximum strength σ of the three magnesium alloys. max .

[0074] Step 5: Predict the cracking tendency of magnesium alloy castings through maximum strength.

[0075] Preferably, step 5 comprises: step 501: obtaining a cracking tendency index of the magnesium alloy according to the inverse of the maximum strength; step 502: predicting the cracking tendency of the magnesium alloy casting according to the cracking tendency index.

[0076] Specifically, the cracking tendency index is the inverse of the maximum strength, i.e.

[0077] Figure 3 The figure is a comparison chart of the relative value of the cracking tendency index of the present invention and the relative value of the cracking tendency index given by the standard cracking tendency evaluation device, such as Figure 3 As shown, the horizontal axis is three kinds of magnesium alloys, the vertical axis corresponding to the bar graph is the relative value obtained by the standard cracking tendency evaluation device, and the vertical axis corresponding to the broken line is the relative value obtained by the standard cracking tendency evaluation device. The relative value of cracking tendency obtained. In the present invention, the restraint rod casting is manufactured by an ordinary smelting and casting process. The restraint rod casting is prepared using a special casting cracking tendency evaluation mold mentioned in a published paper (Journal of Materials Science & Technology, 2022, 105: 68-80.) It is used to obtain the standard cracking tendency values ​​of the three magnesium alloys for comparison with the indicators in the present invention. The pouring temperature during the preparation of the restraint rod casting is 720°C and the mold temperature is 270°C. Based on the prepared restraint rod casting, the standard casting cracking tendency value is calculated, such as Figure 3 As shown in Figure 2, the hot cracking sensitivity (HCS) of the standard cracking tendency of Mg-7.5Al, Mg-3.0Ce and Mg-9Ce-6.5Al are 112, 104 and 80 respectively, and the relative ratio is 112:104:80. The maximum strength σ obtained in step 5 max Calculate the magnesium alloy casting cracking tendency index proposed by the present invention like Figure 3As shown, the relative ratio of the casting cracking tendency index of Mg-7.5Al, Mg-3.0Ce and Mg-9Ce-6.5Al calculated by the present invention is 112:100:76. By comparing the cracking tendency trend calculated by the present invention with the standard cracking tendency trend, it can be found that the method described in the present invention can effectively predict the casting cracking tendency of magnesium alloys.

[0078] The present invention provides a magnesium alloy casting cracking tendency prediction system, comprising:

[0079] Module M1: Magnesium alloy is prepared by melting and casting process.

[0080] Module M2: Determine the stretching temperature based on the lowest solidus temperature of the magnesium alloy.

[0081] Preferably, module M2 comprises: submodule M201: subtracting the upper limit difference from the lowest solidus temperature to obtain the upper limit value of the stretching temperature; submodule M202: subtracting the lower limit difference from the lowest solidus temperature to obtain the lower limit value of the stretching temperature; submodule M203: determining the stretching temperature according to the upper limit value of the stretching temperature and the lower limit value of the stretching temperature.

[0082] Module M3: Determine the tensile strain rate based on the linear contraction coefficient of the magnesium alloy at the tensile temperature and the cooling rate.

[0083] Module M4: Stretching magnesium alloys by tensile strain rate to determine the maximum strength of magnesium alloys at the tensile temperature.

[0084] Preferably, module M4 comprises: submodule M401: stretching the magnesium alloy at a tensile strain rate to obtain a stretching curve; submodule M402: determining the maximum strength of the magnesium alloy at the stretching temperature through the stretching curve.

[0085] Preferably, the submodule M401 comprises: a unit D4011: heating the magnesium alloy to a stretching temperature at a preset speed; and a unit D4012: stretching the magnesium alloy at a stretching strain rate by a high-temperature stretching machine to obtain a stretching curve.

[0086] Module M5: Prediction of cracking tendency of magnesium alloy castings by maximum strength.

[0087] Preferably, module M5 comprises: submodule M501: obtaining a cracking tendency index of the magnesium alloy according to the inverse of the maximum strength; submodule M502: predicting the cracking tendency of magnesium alloy casting according to the cracking tendency index.

[0088] The technical problems solved by the present invention are:

[0089] 1. The existing technology requires the preparation of a complex special cracking tendency assessment mold to predict the cracking tendency.

[0090] The technical principle of the present invention is:

[0091] According to the theory, the cracking of magnesium alloy castings during the casting process is caused by the local tensile stress caused by the thermal contraction of the solidified part being greater than the maximum stress that the alloy can withstand at this time, that is, σ>σ max The temperature of the solidified part during this process is usually between 300-550℃. Under the same casting process, the thermal shrinkage of magnesium alloy is basically the same, so σ is constant; therefore, the anti-casting cracking performance of magnesium alloy is proportional to its maximum strength at high temperature, so its cracking tendency can be used Evaluation, where σ max It can be obtained by ordinary high temperature tensile test. The invention does not need to prepare a complex special evaluation mold for cracking tendency, and can evaluate the cracking tendency of magnesium alloy casting by ordinary high temperature stretching.

[0092] Compared with the prior art, the present invention has the following beneficial effects:

[0093] 1. The present invention is based on the deduction that the cracking of magnesium alloy castings during the casting process is caused by the local tensile stress caused by the thermal shrinkage of the solidified part being greater than the maximum stress that the alloy can withstand at this time. It is proposed that the anti-casting cracking performance of the magnesium alloy is proportional to its maximum strength at high temperature, so the inverse of the maximum strength can be used to predict the cracking tendency of the magnesium alloy. The method can simply and efficiently predict the cracking tendency of the magnesium alloy.

[0094] 2. The present invention can predict the cracking tendency of magnesium alloy casting by using a common high-temperature stretching machine, thus achieving the purpose of simplicity and economy.

[0095] Those skilled in the art know that, in addition to implementing the system, device and its various modules provided by the present invention in a purely computer-readable program code, it is entirely possible to implement the same program in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers and embedded microcontrollers by logically programming the method submodule M. Therefore, the system, device and its various modules provided by the present invention can be considered as a hardware component, and the modules included therein for implementing various programs can also be considered as structures within the hardware component; the modules for implementing various functions can also be considered as both software programs for implementing methods and structures within hardware components.

[0096] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for predicting cracking tendency of magnesium alloy casting, characterized in that: include: Step 1: preparing the magnesium alloy by a smelting and casting process; Step 2: Determine the stretching temperature according to the lowest solidus temperature of the magnesium alloy; Step 3: determining the tensile strain rate according to the linear contraction coefficient and cooling rate of the magnesium alloy at the tensile temperature; Step 4: stretching the magnesium alloy at the tensile strain rate to determine the maximum strength of the magnesium alloy at the stretching temperature; Step 5: predicting the cracking tendency of the magnesium alloy casting according to the maximum strength; The step 4 comprises: Step 401: stretching the magnesium alloy at the tensile strain rate to obtain a tensile curve; Step 402: determining the maximum strength of the magnesium alloy at the stretching temperature through the stretching curve; The step 5 comprises: Step 501: obtaining a cracking tendency index of the magnesium alloy according to the inverse of the maximum strength; Step 502: predicting the cracking tendency of the magnesium alloy casting according to the cracking tendency index; The step 401 includes: Step 4011: heating the magnesium alloy to the stretching temperature at a preset speed; Step 4012: stretching the magnesium alloy at the tensile strain rate using a high temperature stretching machine to obtain the tensile curve; The step 2 comprises: Step 201: subtract the upper limit difference from the lowest solidus temperature to obtain the upper limit of the stretching temperature; Step 202: subtracting the lower limit difference from the lowest solidus temperature to obtain a lower limit value of the stretching temperature; Step 203: Determine the stretching temperature according to the upper limit value of the stretching temperature and the lower limit value of the stretching temperature.

2. A magnesium alloy casting cracking tendency prediction system, characterized in that: include: Module M1: preparing the magnesium alloy through a smelting and casting process; Module M2: determining the stretching temperature according to the lowest solidus temperature of the magnesium alloy; Module M3: determining the tensile strain rate according to the linear contraction coefficient and cooling rate of the magnesium alloy at the tensile temperature; Module M4: stretching the magnesium alloy at the tensile strain rate to determine the maximum strength of the magnesium alloy at the tensile temperature; Module M5: predicting the cracking tendency of the magnesium alloy casting according to the maximum strength; The module M4 comprises: Submodule M401: stretching the magnesium alloy at the tensile strain rate to obtain a tensile curve; Submodule M402: determining the maximum strength of the magnesium alloy at the stretching temperature through the stretching curve; The module M5 comprises: Submodule M501: obtaining a cracking tendency index of the magnesium alloy according to the inverse of the maximum strength; Submodule M502: predicting the cracking tendency of the magnesium alloy casting according to the cracking tendency index; The submodule M401 includes: Unit D4011: heating the magnesium alloy to the stretching temperature at a preset speed; Unit D4012: stretching the magnesium alloy at the tensile strain rate by a high temperature stretching machine to obtain the tensile curve; The module M2 comprises: Submodule M201: subtract the upper limit difference from the lowest solidus temperature to obtain the upper limit of the stretching temperature; Submodule M202: subtract the lower limit difference from the lowest solidus temperature to obtain the lower limit value of the stretching temperature; Submodule M203: Determine the stretching temperature according to the stretching temperature upper limit value and the stretching temperature lower limit value.

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