A method for optimizing high-speed steel spheroidizing annealing process

Abstract

The present invention provides a method for optimizing the spheroidizing annealing process of high-speed steel, belonging to the field of high-speed steel microstructure and heat treatment process control. The method comprises: using thermodynamics to calculate the composition of M2C carbides and austenite Fcc in M42 high-speed steel at the spheroidizing annealing temperature; using kinetics to construct a dissolution model for M2C carbides in Fcc, inputting the high-speed steel spheroidizing annealing temperature, spheroidizing annealing time, Fcc composition, M2C composition, and Fcc / M2C interface energy into the dissolution model to calculate the dissolution rate of M2C carbides in the high-speed steel; and using the calculated dissolution rate to calculate the time required for complete dissolution of the M2C carbide tip position based on the statistically obtained M2C carbide tip position size from the high-speed steel microstructure. The present invention enables optimization of the high-speed steel spheroidizing annealing process based on thermodynamic and kinetic calculations.

Description

Technical Field

[0001] The present invention relates to the field of high-speed steel microstructure and heat treatment process control, and in particular to a high-speed steel spheroidizing annealing process optimization method. Background Art

[0002] High-speed steel (HSS) is a tool steel with high hardness, high wear resistance, and high heat resistance. It is widely used in high-speed cutting processes and can cut materials such as aluminum alloys, stainless steel, and titanium alloys. M42 HSS is a relatively advanced HSS grade. Its microstructure contains a large number of M2C-type carbides. The morphology of these carbides before spheroidizing annealing is irregular, and after deformation and crushing, the carbides have tip locations with a small radius of curvature. During the cutting service of HSS, stress concentration tends to occur at these tip locations, resulting in a shortened cutting tool life. The spheroidizing annealing process can preferentially dissolve the carbide tips, promoting the evolution of carbide particles into a spherical morphology, which is beneficial to improving the service performance of HSS. Therefore, selecting the appropriate spheroidizing annealing temperature and spheroidizing annealing time is the key to optimizing the spheroidizing annealing process for high-speed steel. Summary of the Invention

[0003] The embodiment of the present invention provides a method for optimizing the spheroidizing annealing process of high-speed steel, which can realize the optimization of the spheroidizing annealing process of high-speed steel based on thermodynamics and kinetic calculations.

[0004] The embodiment of the present invention provides a method for optimizing a high-speed steel spheroidizing annealing process, comprising:

[0005] The composition of M2C carbides and austenite Fcc in M42 high-speed steel at spheroidizing annealing temperature is calculated using thermodynamics.

[0006] A dissolution model of M2C carbides in Fcc was constructed using kinetics. The spheroidizing annealing temperature, spheroidizing annealing time, Fcc composition, M2C composition, and Fcc / M2C interface energy of high-speed steel were input into the dissolution model to calculate the dissolution rate of M2C carbides in high-speed steel.

[0007] Combined with the tip size of the M2C carbide obtained from the microstructure statistics of the high-speed steel, the time required for the complete dissolution of the tip of the M2C carbide is obtained using the calculated dissolution rate.

[0008] Furthermore, the composition of M2C carbides and austenite Fcc in M42 high-speed steel at the spheroidizing annealing temperature is calculated using thermodynamics, including:

[0009] The chemical composition and spheroidizing annealing temperature of M42 high-speed steel were input into the Thermo-Calc program. Only the austenite Fcc and carbide M2C phases were retained. The chemical compositions of austenite Fcc and M2C carbides were calculated under the point equilibrium mode, and the mass fractions of each chemical component in austenite Fcc and M2C carbides were recorded. Among them, the chemical composition of austenite Fcc is referred to as Fcc composition, and the chemical composition of M2C carbides is referred to as M2C composition.

[0010] Furthermore, the thermodynamic parameter library is a TCFE8 thermodynamic parameter library.

[0011] Furthermore, the dissolution model of M2C carbides in Fcc is constructed using kinetics, and the spheroidizing annealing temperature, spheroidizing annealing time, Fcc composition, M2C composition, and Fcc / M2C interface energy of the high-speed steel are input into the dissolution model to calculate the dissolution rate of M2C carbides in the high-speed steel. The calculation includes:

[0012] The dissolution model of M2C carbides in Fcc was constructed using the Dictra module in Thermo-Calc program.

[0013] The spheroidizing annealing temperature, spheroidizing annealing time, Fcc composition, M2C composition and Fcc / M2C interface energy of high-speed steel are input into the dissolution model, and the dissolution rate of M2C carbides in high-speed steel is calculated in combination with the kinetic parameter library.

[0014] Furthermore, the kinetic parameter library is a MOBFE3 kinetic parameter library.

[0015] Furthermore, the tip position size of the M2C carbide obtained by combining the microstructure statistics of the high-speed steel and the time required for the tip position of the M2C carbide to be completely dissolved using the calculated dissolution rate include:

[0016] Based on the microstructure of high-speed steel before spheroidizing annealing, the M2C carbides were calibrated and the average size of the M2C carbide tips was obtained.

[0017] The time required for the complete dissolution of the M2C carbide tip was determined based on the calculated dissolution rate and the average size of the M2C carbide tip obtained from microstructural statistics.

[0018] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0019] In an embodiment of the present invention, the dissolution rate of M2C carbides at a specified spheroidizing annealing temperature is calculated using the Fcc and M2C compositions obtained by thermodynamic calculations and a dissolution model of M2C carbides in Fcc constructed using kinetics. Combined with the M2C tip position size obtained from microstructural statistics, the time required for complete dissolution of the M2C carbide tip position is accurately predicted, thereby achieving spheroidizing annealing process optimization for high-speed steel based on thermodynamic and kinetic calculations. This can reduce process optimization costs, improve process optimization efficiency, and avoid the consumption of a large amount of experimental work. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 A schematic diagram of the dissolution and material transport of M2C carbides provided in an embodiment of the present invention;

[0022] Figure 2 Schematic diagram of the local equilibrium between austenite Fcc and M2C carbides provided in an embodiment of the present invention;

[0023] Figure 3 A schematic flow chart of a method for optimizing a high-speed steel spheroidizing annealing process according to an embodiment of the present invention;

[0024] Figure 4 Schematic diagram of the M2C carbide dissolution model provided in an embodiment of the present invention;

[0025] Figure 5 A schematic diagram of the microstructure of M42 high-speed steel before spheroidizing annealing provided in an embodiment of the present invention;

[0026] Figure 6 A schematic diagram of a curve showing the change in the position of the Fcc / M2C interface over time obtained by kinetic calculations according to an embodiment of the present invention;

[0027] Figure 7 A schematic diagram of a curve showing the change in Fcc / M2C interface migration rate over time obtained from kinetic calculations provided in an embodiment of the present invention;

[0028] Figure 8 Schematic diagram of the microstructure of M42 high-speed steel after spheroidizing annealing provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0030] The theoretical basis of the embodiment of the present invention is that during the spheroidizing annealing of high-speed steel, the tips of large M2C particles (short for M2C carbides) have a smaller radius of curvature, which is equivalent to small M2C particles adhering to them. These M2C carbide tips will preferentially dissolve and precipitate on larger M2C particles, forming a continuous M2C coarsening process. Therefore, the elements dissolved in the Fcc matrix of M2C will continuously migrate to the surface of larger M2C (mass transfer), such as Figure 1 As shown. The mean free path (λ) between M2C and M6C dispersed carbide particles will affect the diffusion path of elements and the carbide coarsening rate, but the influence of M6C dispersed carbides is not considered in this example. Although the high-speed steel matrix contains Fcc, M2C and M6C, the interface between Fcc and M2C follows local equilibrium rather than global equilibrium, as shown in Figure 2 Therefore, the thermodynamic and kinetic calculations use the local equilibrium components of Fcc and M2C as the initial input, and introduce the contribution of the Fcc / M2C interface energy to the system energy, which promotes the migration of the Fcc interface toward the small particles of M2C, thereby achieving the effect of M2C dissolution.

[0031] like Figure 3 As shown, an embodiment of the present invention provides a method for optimizing a high-speed steel spheroidizing annealing process, comprising:

[0032] S101, Thermodynamic Calculation: Use thermodynamics to calculate the composition of M2C carbides and austenite Fcc in M42 high-speed steel at spheroidizing annealing temperature;

[0033] In this example, the chemical composition and spheroidizing annealing temperature of M42 high-speed steel were input into the Thermo-Calc program. Only the austenite Fcc and carbide M2C phases were retained. The chemical compositions of the austenite Fcc and M2C carbides were calculated in point equilibrium mode, and the mass fractions of the chemical components in the austenite Fcc and M2C carbides were recorded. The chemical composition of the austenite Fcc is referred to as the Fcc composition, and the chemical composition of the M2C carbides is referred to as the M2C composition.

[0034] In this embodiment, Fcc is equivalent to the Fcc phase, and Fcc is not a carbide.

[0035] In this embodiment, the thermodynamic calculation uses the TCFE8 thermodynamic parameter library, which stores the Gibbs free energy of the M42 high-speed steel system. The Thermo-Calc program calculates the chemical composition of each phase based on the principle of minimizing the Gibbs free energy.

[0036] S102, kinetic calculation: constructing a dissolution model of M2C carbides in Fcc using kinetics, inputting the spheroidizing annealing temperature, spheroidizing annealing time, Fcc composition, M2C composition, and Fcc / M2C interface energy of the high-speed steel into the dissolution model, and calculating the dissolution rate of M2C carbides in the high-speed steel. Specifically, the following steps may be included:

[0037] The dissolution model of M2C carbides in Fcc was constructed using the Dictra module in Thermo-Calc program.

[0038] The spheroidizing annealing temperature, spheroidizing annealing time, Fcc composition, M2C composition and Fcc / M2C interface energy of high-speed steel are input into the dissolution model, and the dissolution rate of M2C carbides in high-speed steel is calculated in combination with the kinetic parameter library.

[0039] In this embodiment, the dynamic calculation uses the MOBFE3 dynamic parameter library, which stores the atomic mobility parameters of austenite Fcc and M2C carbides in the M42 high-speed steel system.

[0040] In this embodiment, the calculation principle of carbide dissolution rate is:

[0041] During the thermodynamic calculation, the chemical composition of M42 high-speed steel and the spheroidizing annealing temperature are input to obtain the Fcc and M2C compositions. The thermodynamic calculation results (including the Fcc and M2C compositions), as well as the spheroidizing annealing temperature, spheroidizing annealing time, and Fcc / M2C interface energy are then input into the dissolution model. The Fcc / M2C interface energy is set to a positive value, indicating that small M2C particles are energetically unstable due to the interface scale effect and tend to dissolve in the Fcc. The dissolution model solves the kinetic equation and the diffusion flux conservation equation to obtain the Fcc / M2C interface position and interface migration rate of M2C carbides during the dissolution process. The interface migration rate varies with time and significantly slows down after reaching a certain value. This is because the matrix Fcc in the dissolution model is finite in size, and M2C elements gradually accumulate near the interface through diffusion, creating resistance to continued migration at the interface. Since the dissolution and precipitation process (coarsening process) of M2C carbides is continuous, the interface migration rate is based on the value before obvious slowdown, and the dissolution rate of M2C is equal to the Fcc / M2C interface migration rate at this time.

[0042] S103, combining the tip position size of the M2C carbide obtained from the microstructure statistics of the high-speed steel and using the calculated dissolution rate to obtain the time required for the tip position of the M2C carbide to be completely dissolved; specifically, the following steps may be included:

[0043] A1, Microstructure statistics: Based on the microstructure of high-speed steel before spheroidizing annealing, M2C carbides were calibrated and the average size of the M2C carbide tips was obtained.

[0044] In this embodiment, the microstructure of M42 high-speed steel can be photographed using the backscattered electron diffraction mode of a scanning electron microscope. The tip positions of the M2C carbides in the microstructure are counted using a ruler to obtain basic information such as the average size and maximum size of the tip positions of the M2C carbides.

[0045] A2. Optimization of spheroidizing annealing process: Based on the calculated dissolution rate and the average size of the M2C carbide tips obtained from microstructure statistics, the time required for complete dissolution of the M2C carbide tips is determined, providing guidance for adjusting the spheroidizing annealing time.

[0046] In this embodiment, the four process flows of thermodynamic calculation → kinetic calculation → microstructure statistics → spheroidizing annealing process optimization are used to accurately predict the tip dissolution behavior of M2C carbides during the spheroidizing annealing process of M42 high-speed steel.

[0047] In this embodiment, the dissolution rate of M2C carbides at a specified spheroidizing annealing temperature is calculated using the Fcc and M2C compositions obtained by thermodynamic calculations and the dissolution model of M2C carbides in Fcc constructed using kinetics. Combined with the M2C tip position size obtained from microstructural statistics, the time required for complete dissolution of the M2C carbide tip position is accurately predicted, thereby achieving spheroidizing annealing process optimization for high-speed steel based on thermodynamic and kinetic calculations. This can reduce process optimization costs, improve process optimization efficiency, and avoid the consumption of a large amount of experimental work.

[0048] In order to verify the effectiveness of the high-speed steel spheroidizing annealing process optimization method described in the embodiment of the present invention, this embodiment studies the M2C carbide dissolution rate and the time required for complete dissolution of a specified M2C tip position during spheroidizing annealing of M42 high-speed steel at 900°C.

[0049] In this embodiment, the chemical composition of the provided M42 high-speed steel is shown in Table 1;

[0050] Table 1 Chemical composition of M42 high speed steel, unit is wt.%

[0051]

[0052] In this embodiment, when performing thermodynamic and kinetic calculations, the chemical composition of M42 high-speed steel is simplified, and the effects of trace elements Si, Mn, P, S and non-M2C stabilizing elements W and V are ignored. The simplified chemical composition of M42 high-speed steel is obtained, as shown in Table 2.

[0053] Table 2 Simplified chemical composition of M42 high-speed steel, unit is wt.%

[0054] element Fe Mo Cr Co C content Bal. 9 4 8 1

[0055] In this embodiment, the chemical compositions of austenite Fcc and M2C carbides were calculated using the Thermo-Calc program in combination with the TCFE8 thermodynamic parameter library. The calculation results are shown in Table 3.

[0056] Table 3 Chemical composition of austenitic Fcc and M2C carbides, in wt.%

[0057] Fcc <![CDATA[M2C]]> Fe 85.501 6.020 Mo 1.855 77.575 Cr 3.413 9.637 Co 8.816 0.155 C 0.415 6.613

[0058] In this embodiment, the dissolution model of M2C carbide in Fcc is constructed using kinetics, as shown in Figure 4 As shown, the dots are model grid points, the arrows are Fcc / M2C interfaces (Boundary), and λ is the mean free path of M2C carbide particles. During the kinetic calculation, it is necessary to input the spheroidizing annealing temperature, spheroidizing annealing time, Fcc composition, M2C composition, and Fcc / M2C interface energy. In this embodiment, the spheroidizing annealing temperature is 900°C, and the spheroidizing annealing time is generally no more than 5 hours. This model provides some redundancy and sets the spheroidizing annealing time to 8 hours; the Fcc composition and M2C composition are derived from the calculation results in Table 3, and the Fcc / M2C interface energy is set to 2×10 8 J. The left end of the dissolution model is set to M2C with a scale of 2 μm, indicating the average size of the M2C tip position; the middle end of the dissolution model is set to austenite Fcc with a scale of 10 μm; the right end of the dissolution model is set to M2C with a scale of 5 μm; the number of grid points in the dissolution model is set to 50.

[0059] In this embodiment, the microstructure of M42 high speed steel before spheroidizing annealing is shown in FIG. Figure 5 The statistical results show that the volume fraction of M2C in the high-speed steel structure is 4.5%, the average size of the M2C tip is 1.97μm, and the maximum size is 5.23μm. Figure 5 The English meanings below are: EHT represents the electric field acceleration voltage, WD represents the focal length, Signal A=aBSD1 represents the scanning mode is backscattered electron diffraction, Mag represents the magnification, Date represents the date, and Time represents the specific time.

[0060] In this embodiment, the curve of the Fcc / M2C interface position (Position of interface) changing with time obtained by kinetic calculation is as follows Figure 6 As shown, from Figure 6 It can be seen that the position of the Fcc / M2C interface gradually decreases and migrates toward the M2C end, indicating that the M2C at the tip position dissolves.

[0061] In this embodiment, the curve of the Fcc / M2C interface migration rate (Velocity of interface) obtained by kinetic calculation over time is shown as follows: Figure 7 As shown, from Figure 7 It can be observed that the interfacial migration rate slows down significantly after reaching 0.2 nm / s (point A), indicating the emergence of significant interfacial resistance. In this dissolution model calculation, an interfacial migration rate of 0.2 nm / s is used, i.e., an M2C dissolution rate of 0.2 nm / s.

[0062] In this embodiment, according to the statistical results of the microstructure of M42 high-speed steel before spheroidizing annealing, the average size of the M2C tip is 1.97 μm. Therefore, the time required for most of the M2C tip positions to completely dissolve is: average size / dissolution rate = 1.97 / (0.2 ÷ 1000) s = 9850 s = 2.7 h, which is approximately equal to 3 hours. According to the calculation results, spheroidizing annealing of M42 high-speed steel at 900 ° C for 3 hours can eliminate the tip morphology of most carbides. The microstructure of M42 high-speed steel after spheroidizing annealing at 900 ° C for 3 hours is shown in the figure. Figure 8 As shown in the experimentally characterized high-speed steel microstructure, the M2C tips are fully dissolved, and the particle corners are relatively smooth, indicating that the carbide tip morphology has been significantly improved. Therefore, the high-speed steel spheroidizing annealing process optimization method provided by the embodiment of the present invention can accurately calculate the carbide dissolution rate of M42 high-speed steel at a specified temperature and the time required for complete dissolution of a specified carbide tip size, thus achieving the optimization of the M42 high-speed steel spheroidizing annealing process.

[0063] By using the high-speed steel spheroidizing annealing process optimization method provided in an embodiment of the present invention, different spheroidizing annealing temperatures can be designed, and the corresponding M2C dissolution rates and spheroidizing annealing times can be calculated respectively, thereby optimizing the high-speed steel spheroidizing annealing process and controlling the time cost / heating cost.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for optimizing the spheroidizing annealing process of high-speed steel, characterized in that: include: The composition of M2C carbides and austenite Fcc in M42 high-speed steel at spheroidizing annealing temperature is calculated using thermodynamics. A dissolution model of M2C carbides in Fcc was constructed using kinetics. The spheroidizing annealing temperature, spheroidizing annealing time, Fcc composition, M2C composition, and Fcc / M2C interface energy of high-speed steel were input into the dissolution model to calculate the dissolution rate of M2C carbides in high-speed steel. Combined with the size of the tip of the M2C carbide obtained from the microstructure statistics of the high-speed steel, the time required for the tip of the M2C carbide to completely dissolve is obtained using the calculated dissolution rate; The method of constructing a dissolution model of M2C carbides in Fcc by using kinetics, inputting the spheroidizing annealing temperature, spheroidizing annealing time, Fcc composition, M2C composition, and Fcc / M2C interface energy of the high-speed steel into the dissolution model, and calculating the dissolution rate of M2C carbides in the high-speed steel includes: The dissolution model of M2C carbides in Fcc was constructed using the Dictra module in Thermo-Calc program. The spheroidizing annealing temperature, spheroidizing annealing time, Fcc composition, M2C composition, and Fcc / M2C interface energy of high-speed steel are input into the dissolution model, and the dissolution rate of M2C carbides in high-speed steel is calculated in combination with the kinetic parameter library. Wherein, the kinetic parameter library is the MOBFE3 kinetic parameter library.

2. The high speed steel spheroidizing annealing process optimization method according to claim 1, characterized in that: The composition of M2C carbides and austenite Fcc in M42 high-speed steel at the spheroidizing annealing temperature calculated by thermodynamics includes: The chemical composition and spheroidizing annealing temperature of M42 high-speed steel were input into the Thermo-Calc program. Only the austenite Fcc and carbide M2C phases were retained. The chemical compositions of austenite Fcc and M2C carbides were calculated under the point equilibrium mode, and the mass fractions of each chemical component in austenite Fcc and M2C carbides were recorded. The chemical composition of austenite Fcc is referred to as Fcc composition, and the chemical composition of M2C carbides is referred to as M2C composition.

3. The high speed steel spheroidizing annealing process optimization method according to claim 2, characterized in that: Thermodynamic calculations were performed using the TCFE8 thermodynamic parameter library.

4. The high speed steel spheroidizing annealing process optimization method according to claim 1, characterized in that: The tip position size of the M2C carbide obtained by combining the microstructure statistics of the high-speed steel and the time required for the complete dissolution of the tip position of the M2C carbide using the calculated dissolution rate include: Based on the microstructure of high-speed steel before spheroidizing annealing, the M2C carbides were calibrated and the average size of the M2C carbide tips was obtained. The time required for the complete dissolution of the M2C carbide tip was determined based on the calculated dissolution rate and the average size of the M2C carbide tip obtained from microstructural statistics.

Images