A calculation method and storage medium for the pulse time of vacuum carburizing

Abstract

The present invention provides a method for calculating the pulse time of vacuum carburizing and a storage medium, belonging to the technical field of vacuum carburizing. The refined control of the carbon concentration during the carburizing process is the basis for regulating the structure and properties of carburized parts. The present invention takes the infiltrated mass as the carburizing target and can accurately calculate the time of all strong carburizing processes and diffusion processes of vacuum carburizing under the condition of a fixed number of pulses. The error between the infiltrated mass of the workpiece obtained according to the above-mentioned vacuum carburizing pulse time and the target value is less than 0.1%, which is a significant improvement compared with the 5% calculation error of the traditional algorithm (the current algorithm with the carburized layer depth as the calculation target), providing a process method support for the refined control of the carburizing process.

Description

Technical Field

[0001] The present invention relates to the technical field of vacuum carburizing, and in particular to a calculation method and a storage medium for the pulse time of vacuum carburizing. Background Art

[0002] Vacuum low-pressure carburizing is a clean, efficient and green surface strengthening technology, which has been widely used in the fields of aerospace, rail transit, automobiles, industrial robots, etc. With the development of vacuum low-pressure carburizing technology, the carburizing method has gradually developed from the traditional "one-stage" or "two-stage" to "pulse type". Pulse carburizing means "inflating - holding pressure - pumping - holding pressure" periodically during the carburizing process. Compared with "one-stage" or "two-stage" carburizing, pulse carburizing can reduce the generation of carbon black and realize the refined control of the carburizing process.

[0003] From the perspective of microscopic mechanism, the "inflating - holding pressure - pumping" of one pulse is usually called the strong carburizing process, and the subsequent "holding pressure" is called the diffusion process. During the strong carburizing process, the carbon concentration of the material is increased by supplying the carburizing medium, and the surface carbon concentration reaches the high point; during the diffusion process, the surface carbon concentration of the material is reduced by the diffusion of carbon in the material, and the surface carbon concentration reaches the low point. Obviously, the strong carburizing time and the diffusion time are important process parameters to ensure that the target carbon concentration distribution of the carburized workpiece is achieved, and they are also the core parameters to be calculated in the vacuum carburizing process.

[0004] The infiltration quality is an important integral quantity in the vacuum carburizing process, and can be used as the goal of carburizing together with the carburized layer depth. The infiltration quality can be measured by the weight difference method, which is convenient and does not require damaging the workpiece. At the same time, the amount of carbon that the carburizing medium needs to provide has a linear relationship with the infiltration quality of carbon. However, there is currently no calculation method for calculating the carburizing process (the time series of the strong carburizing - diffusion process) with the infiltration quality as the carburizing target. If the current algorithm with the carburized layer depth as the calculation target is used, the calculation accuracy is insufficient. Summary of the Invention

[0005] The purpose of the present invention is to provide a calculation method and a storage medium for the pulse time of vacuum carburizing, and the calculation method prepared by the present invention has small errors.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a calculation method for the pulse time of vacuum carburizing, including the following steps:

[0008] (1) Determine the target surface carbon concentration C d , the target infiltrated carbon mass m d , material parameters, the number of carburizing pulses n, the left value C l,l of the low point of the target surface carbon concentration, the right value C of the low point of the target surface carbon concentrationl,r and the error E; the matrix carbon concentration < the C l,l < the C l,r < the austenite saturation carbon concentration;

[0009] (2) Obtain the mass m of the infiltrated carbon when the low point of the surface carbon concentration is C d according to C l,l , material parameters, n, and C l,l . If m l < m l , reduce C d and repeat step (2) until m l,l ≥ m l ; d ;

[0010] If m > m d , proceed to step (3);

[0011] (3) Obtain the mass m of the infiltrated carbon when the low point of the surface carbon concentration is C d according to C l,r , material parameters, n, and C l,r . If m r > m r , increase C d and repeat step (3) until m l,r ≤ m r ; d ;

[0012] If m r ≤ m d , proceed to step (4);

[0013] (4) Calculate C l,l according to C l,r and C l,m ;

[0014] The C l,m = xC l,l + (1 - x)C l,r , where 0 < x < 1;

[0015] (5) According to C d , material parameters, n, and the mass m of the infiltrated carbon when the low point of the surface carbon concentration is C l,m , the sum of the strong carburizing time and the diffusion time of all carburizing pulses is the pulse time; m ;

[0016] If |m m - m d | ≤ E, C l,m is the low point of the surface carbon concentration, and the sum of the strong carburizing time and the diffusion time of all carburizing pulses is the pulse time;

[0017] If |m m -m d | > E and m m > m d , then C l,m = C l,l , repeat steps (4) and (5) until |m m -m d | ≤ E;

[0018] If |m m -m d | > E and m m < m d , then C l,m = C l,r , repeat steps (4) and (5) until |m m -m d | ≤ E.

[0019] Preferably, the material parameters include surface transfer coefficient, diffusion coefficient and matrix carbon content.

[0020] Preferably, the difference between the C l,l and the matrix carbon concentration is 0.1 wt%.

[0021] Preferably, the difference between the austenite saturated carbon concentration and the C l,r is 0.1 wt%.

[0022] Preferably, the calculation methods of the infiltration mass m, strong infiltration time and diffusion time in steps (2), (3) and (5) include solving Fick's law by finite difference method, solving Fick's law by finite element method or analytical equation.

[0023] The present invention also provides a storage medium storing a computer program for executing the calculation method described in the above technical solution of the claims.

[0024] The present invention provides a calculation method for vacuum carburizing pulse time, comprising the following steps:

[0025] (1) Determine the target surface carbon concentration C d , the target infiltrated carbon mass m d , material parameters, number of carburizing pulses n, left value C l,l of the low point of the target surface carbon concentration, right value C l,r of the low point of the target surface carbon concentration, error E; matrix carbon concentration < the C l,l < the C l,r < austenite saturated carbon concentration;

[0026] (2) According to C d , material parameters, n and C l,lObtain the infiltration carbon mass m when the low surface carbon concentration point is C l,l ; if m l < m l < m d , reduce C l,l , and repeat step (2) until m l ≥ m d ;

[0027] If m > m d , proceed to step (3);

[0028] (3) According to C d , material parameters, n, and C l,r Obtain the infiltration carbon mass m when the low surface carbon concentration point is C l,r ; if m r > m r > m d , increase C l,r , and repeat step (3) until m r ≤ m d ;

[0029] If m r ≤ m d , proceed to step (4);

[0030] (4) Calculate C l,l based on C l,r and C l,m ;

[0031] The said C l,m = xC l,l +(1 - x)C l,r , where 0 < x < 1;

[0032] (5) According to C d , material parameters, n, and the infiltration carbon mass m when the low surface carbon concentration point is C l,m ; the sum of the strong carburizing time and diffusion time of all carburizing pulses is the pulse time; m

[0033] If |m m - m d | ≤ E, C l,m is the low surface carbon concentration point, and the sum of the strong carburizing time and diffusion time of all carburizing pulses is the pulse time;

[0034] If |m m - m d | > E and m m > m d > m, then C l,m = C l,l , and repeat steps (4) and (5) until |mm -m d | ≤ E;

[0035] If |m m -m d | > E and m m < m d , then C l,m = C l,r , repeat steps (4) and (5) until |m m -m d | ≤ E.

[0036] (1) The refined control of the carbon concentration during the carburizing process is the basis for the regulation of the structure and properties of carburized parts. The present invention takes the infiltration mass as the carburizing target and can accurately calculate the time of all strong carburizing processes and diffusion processes in vacuum carburizing under a fixed number of pulses. The error between the infiltration mass of the workpiece obtained based on the above-mentioned vacuum carburizing pulse time and the target value is less than 0.1%, which is a significant improvement compared to the 5% calculation error of the traditional algorithm (the current algorithm that takes the carburized layer depth as the calculation target), providing a process method support for the refined control of the carburizing process.

[0037] (2) Carburizing needs to be carried out at high temperatures, which is a process with high energy consumption. The infiltration mass calculated by the traditional method is often higher than the target infiltration mass. The higher the infiltration mass, the greater the deviation value, and the longer the calculated process time. The deviation value of the present invention is low, which can avoid the above problems, not only reduce the process time, improve the carburizing efficiency, but also reduce the holding time of the workpiece at the carburizing temperature and reduce energy consumption.

[0038] (3) In the traditional calculation method, the number of carburizing pulses is not adjustable. The number of pulses of the present invention is preset. By changing the number of pulses, the time of all strong carburizing processes and diffusion processes in vacuum carburizing can be obtained. The present invention can, for vacuum carburizing equipment, obtain the corresponding pulse carburizing process time by adjusting the number of pulses. Therefore, the present invention has stronger adjustability in the actual carburizing equipment and process operation, and is more in line with the actual production requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flowchart of the calculation method of the present invention;

[0040] Figure 2 is the changing trend of C l,m with the increase of the number of cycles during the calculation process;

[0041] Figure 3 is the changing trend of the infiltration mass with the increase of the number of cycles during the calculation process;

[0042] Figure 4 is the carburizing time diagram when different numbers of pulses are adopted. Detailed implementation mode

[0043] The present invention provides a calculation method for the pulse time of vacuum carburizing, comprising the following steps:

[0044] (1) Determine the target surface carbon concentration C d , the target infiltrated carbon mass m d , material parameters, the number of carburizing pulses n, the left value C l,l of the low point of the target surface carbon concentration, the right value C l,r of the low point of the target surface carbon concentration, and the error E; the matrix carbon concentration < the C l,l < the C l,r < the austenite saturation carbon concentration;

[0045] (2) Obtain the infiltrated carbon mass m d when the low point of the surface carbon concentration is C l,l according to C l,l , material parameters, n and C l . If m l < m d , reduce C l,l , and repeat step (2) until m l ≥ m d ;

[0046] If m > m d , continue to step (3);

[0047] (3) Obtain the infiltrated carbon mass m d when the low point of the surface carbon concentration is C l,r according to C l,r , material parameters, n and C r . If m r > m d , increase C l,r , and repeat step (3) until m r ≤ m d ;

[0048] If m r ≤ m d , continue to step (4);

[0049] (4) Calculate C l,l according to C l,r and C l,m ;

[0050] The C l,m = xC l,l + (1 - x)C l,r , where 0 < x < 1;

[0051] (5) According to C d, material parameters, n, and the low point of the surface carbon concentration is C l,m The mass m of the infiltrated carbon when m The sum of the strong carburizing time and the diffusion time of all carburizing pulses is the pulse time;

[0052] If |m m - m d | ≤ E, C l,m is the low point of the surface carbon concentration, and the sum of the strong carburizing time and the diffusion time of all carburizing pulses is the pulse time;

[0053] If |m m - m d | > E and m m > m d , then C l,m = C l,l , repeat steps (4) and (5) until |m m - m d | ≤ E;

[0054] If |m m - m d | > E and m m < m d , then C l,m = C l,r , repeat steps (4) and (5) until |m m - m d | ≤ E.

[0055] (1) Determine the target surface carbon concentration C d , the target infiltrated carbon mass m d , material parameters, the number of carburizing pulses n, the left value C l,l of the low point of the target surface carbon concentration, the right value C l,r of the low point of the target surface carbon concentration, and the error E.

[0056] In the present invention, the matrix carbon concentration < the C l,l < the C l,r < the austenite saturation carbon concentration; the C l,l The difference from the matrix carbon concentration is preferably 0.1 wt%.

[0057] In the present invention, the difference between the austenite saturation carbon concentration and C l,r is preferably 0.1 wt%

[0058] In the present invention, the material parameters preferably include the surface transfer coefficient, the diffusion coefficient, and the matrix carbon content.

[0059] (2) According to C d , material parameters, n, and C l,lObtain the mass m of the infiltrated carbon when the low point of the surface carbon concentration is C l,l ; if m l < m l < m d , reduce C l,l , and repeat step (2) until m l ≥ m d ;

[0060] If m > m d , continue to step (3).

[0061] In the present invention, the reduced C l,l still needs to satisfy the requirement that the matrix carbon concentration < the C l,l < the C l,r < the austenite saturation carbon concentration.

[0062] (3) According to C d , material parameters, n, and C l,r obtain the mass m of the infiltrated carbon when the low point of the surface carbon concentration is C l,r ; if m r > m r > m d , increase C l,r , and repeat step (3) until m r ≤ m d ;

[0063] If m r ≤ m d , continue to step (4);

[0064] In the present invention, the increased C l,r still needs to satisfy the requirement that the matrix carbon concentration < the C l,l < the C l,r < the austenite saturation carbon concentration.

[0065] (4) Calculate C l,l based on C l,r and C l,m ;

[0066] The C l,m = xC l,l + (1 - x)C l,r , where 0 < x < 1; preferably, x is 1 / 2.

[0067] (5) According to C d , material parameters, n, and the mass m of the infiltrated carbon when the low point of the surface carbon concentration is C l,m ; the sum of the strong carburizing time and the diffusion time of all carburizing pulses is the pulse time; m If |m

[0068] If |mm -m d |≤E, C l,m That is the low point of the surface carbon concentration. The sum of the strong carburizing time and the diffusion time of all carburizing pulses is the pulse time;

[0069] If |m m -m d |>E and m m >m d , then C l,m =C l,l , repeat steps (4) and (5) until |m m -m d |≤E;

[0070] If |m m -m d |>E and m m <m d , then C l,m =C l,r , repeat steps (4) and (5) until |m m -m d |≤E.

[0071] In the present invention, the calculation method of the infiltrated carbon mass m described in steps (2), (3) and (5) preferably includes solving Fick's law by the finite difference method, solving Fick's law by the finite element method or calculating the carbon concentration distribution after carburizing by an analytical equation, and more preferably the calculation method in Application No. 202310591341.X.

[0072] The present invention also provides a storage medium storing a computer program for executing the calculation method described in the above solution.

[0073] The flowchart of the calculation method of the present invention is as Figure 1 shown.

[0074] The following describes in detail a calculation method and a storage medium for the vacuum carburizing pulse time provided by the present invention with reference to embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0075] Embodiment 1

[0076] Target surface carbon concentration: 0.8 wt%, target infiltrated carbon mass 0.019 kg / m 2 ; The material parameters are as follows: surface transfer coefficient: 5×10 -8 m / s, diffusion coefficient: 1×10 -11 m 2 / s, austenite saturated carbon concentration: 1.6 wt%, matrix carbon concentration: 0.2 wt%, density: 7.8×10 3 kg / m3 ; The number of pulses is 10, the left value is 0.3 wt%, the right value is 1.5 wt%, and the error is 1e -6 kg / m 2 . Carburizing gas: acetylene.

[0077] (1) Determine the target surface carbon concentration C d , the target infiltrated carbon mass m d , material parameters, the number of carburizing pulses n, the left value C l,l of the low point of the target surface carbon concentration, and the right value C l,r of the low point of the target surface carbon concentration; the matrix carbon concentration < the C l,l < the C l,r < the austenite saturation carbon concentration;

[0078] (2) Obtain the infiltrated carbon mass m d when the low point of the surface carbon concentration is C l,l according to C l,l , material parameters, n, and C l . If m l < m d , reduce C l,l and repeat step (2) until m l ≥ m d ;

[0079] If m > m d , proceed to step (3);

[0080] (3) Obtain the infiltrated carbon mass m d when the low point of the surface carbon concentration is C l,r according to C l,r , material parameters, n, and C r . If m r > m d , increase C l,r and repeat step (3) until m r ≤ m d ;

[0081] If m r ≤ m d , proceed to step (4);

[0082] (4) Calculate the average value C l,l according to C l,r and C l,m ;

[0083] The C l,m = (C l,l + C l,r ) / 2;

[0084] (5) According to Cd and the mass m of the infiltrated carbon when the material parameters, n, and the low point of the surface carbon concentration are C l,m ; the sum of the strong carburizing time and the diffusion time of all carburizing pulses is the pulse time; m

[0085] If |m m - m d | ≤ E, then C l,m is the low point of the surface carbon concentration, and the sum of the strong carburizing time and the diffusion time of all carburizing pulses is the pulse time;

[0086] If |m m - m d | > E and m m > m d , then C l,m = C l,l , and repeat steps (4) and (5) until |m m - m d | ≤ E;

[0087] If |m m - m d | > E and m m d < m l,m , then C l,r = C m , and repeat steps (4) and (5) until |m d - m d | ≤ E.

[0088] The method of "calculating the vacuum carburizing pulse time according to C l,m , material parameters, n, and C l,r (C l,l or C 1 )":

[0089] Step 1: For the strong carburizing process, assume a carburizing time t (t > 0), solve Fick's law according to the finite difference method, and obtain the surface carbon concentration at the carburizing time t; if the surface carbon concentration is lower than the austenite saturation carbon concentration, increase t; if the surface carbon concentration is higher than the austenite saturation carbon concentration, decrease t; repeat the above process until the time t when the surface carbon concentration of the workpiece reaches the austenite saturation carbon concentration during the strong carburizing process 1 is obtained, and the carbon concentration distribution at the carburizing time t 1 is obtained by solving Fick's law and used as the initial value of the carbon concentration distribution for the next process.

[0090] Step 2: For the diffusion process, assume a carburizing time t, solve Fick's law according to the finite difference method, and obtain the surface carbon concentration at the carburizing time t; if the surface carbon concentration is higher than the low point C of the pulse carburizing surface carbon concentrationl,m , then increase t; if the surface carbon concentration is lower than the low point C of the pulsed carburizing surface carbon concentration l,m , then decrease t; repeat the above process until the time t when the surface carbon concentration of the workpiece reaches the low point C of the pulsed carburizing surface carbon concentration during the diffusion process l,m is obtained 2 , and the carburizing time is obtained as t by solving Fick's law 2 for the carbon concentration distribution, which is used as the initial value of the carbon concentration distribution for the next process.

[0091] Step 3: Loop steps 1 and 2 eight times to obtain t 3 ~t 18 , and then execute step 1 again to obtain t 19 .

[0092] Step 4: Assume a carburizing time t, solve Fick's law according to the finite difference method, and obtain the surface carbon concentration at the carburizing time t; if the surface carbon concentration is higher than C d , then increase t; if the surface carbon concentration is lower than C d , then decrease t; repeat the above process until the time t when the surface carbon concentration is C d is obtained 20 , and the carbon concentration distribution at the carburizing time t is obtained by solving Fick's law. Integral calculation is performed according to the carbon concentration distribution to obtain the infiltrated mass m. The time t 20 recorded in all the previous steps is the pulsed carburizing time. 1~20 The pulsed carburizing time is finally obtained as follows:

[0093] Table 1 Pulsed carburizing time of Example 1

[0094] are the changing trends of C

[0095]

[0096] Result analysis:

[0097] Figure 2 and Figure 3 during the calculation process respectively. It can be seen from the figure that with the increase of the number of cycles, the infiltrated mass gradually approaches the target infiltrated mass, and finally the error between the two is less than E, meeting the condition for the end of the algorithm, and the optimal C l,m is obtained. Then, according to C l,m , the pulsed carburizing time can be calculated. l,m In this example, when the target infiltrated mass is 0.019 kg / m

[0098] 2 ​, the infiltration mass calculated by the traditional algorithm is 0.0203 kg, with an error of 6%, and the total infiltration time is 202 min; the infiltration mass obtained by the method of the present invention is 0.01899 kg, with an error of 0.052%, and the total infiltration time is 177 min. Compared with the traditional algorithm, the process time calculated by the method in the present invention is shortened by 12.4%, effectively improving the process efficiency.

[0099] Figure 4 It is the carburizing time diagram when different pulse numbers are adopted. It can be seen that as the pulse number set during the calculation of the process increases, the process time gradually shortens. The more the pulse number, the shorter the strong carburizing time, and the higher the requirements for the inflation, pressure holding, and air extraction rates of the equipment. Therefore, the pulse number can be determined according to the actual situation of the equipment.

[0100] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for calculating vacuum carburizing pulse time, characterized in that: It includes the following steps: (1) Determine the target surface carbon concentration Cd, the target infiltrated carbon mass md, material parameters, the number of carburizing pulses n, the left value Cl,l of the low point of the target surface carbon concentration, the right value Cl,r of the low point of the target surface carbon concentration, and the error E; the matrix carbon concentration < Cl,l < Cl,r < austenite saturation carbon concentration; (2) Obtain the infiltrated carbon mass ml when the low point of the surface carbon concentration is Cl,l according to Cd, material parameters, n, and Cl,l. If ml < md, reduce Cl,l and repeat step (2) until ml ≥ md; If m > md, proceed to step (3); (3) Obtain the infiltrated carbon mass mr when the low point of the surface carbon concentration is Cl,r according to Cd, material parameters, n, and Cl,r. If mr > md, increase Cl,r and repeat step (3) until mr ≤ md; If mr ≤ md, proceed to step (4); (4) Calculate Cl,m according to Cl,l and Cl,r; Cl,m = xCl,l + (1 - x)Cl,r, where 0 < x < 1; (5) According to Cd, material parameters, n, and the infiltrated carbon mass mm when the low point of the surface carbon concentration is Cl,m, the sum of the strong carburizing time and the diffusion time of all carburizing pulses is the pulse time; If |mm - md| ≤ E, Cl,m is the low point of the surface carbon concentration, and the sum of the strong carburizing time and the diffusion time of all carburizing pulses is the pulse time; If |mm - md| > E and mm > md, then Cl,m = Cl,l, and repeat steps (4) and (5) until |mm - md| ≤ E; If |mm - md| > E and mm < md, then Cl,m = Cl,r, and repeat steps (4) and (5) until |mm - md| ≤ E.

2. The calculation method according to claim 1, characterized in that: The material parameters include the surface transfer coefficient, the diffusion coefficient, and the matrix carbon content.

3. The calculation method according to claim 1, characterized in that: The difference between Cl,l and the matrix carbon concentration is 0.1 wt%.

4. The calculation method according to claim 1, characterized in that: The difference between the austenite saturation carbon concentration and Cl,r is 0.1 wt%.

5. The calculation method according to claim 1, characterized in that: The calculation methods of the infiltrated carbon mass, the strong carburizing time, and the diffusion time in steps (2), (3), and (5) include solving Fick's law by the finite difference method, solving Fick's law by the finite element method, or an analytical equation.

6. The calculation method according to claim 1, characterized in that: The x is 1 / 2.

7. A storage medium, characterized in that: Store a computer program for executing the calculation method described in any one of claims 1 to 6.

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