CN110472322B - Method for predicting pearlite steel microstructure based on thermodynamics and kinetics - Google Patents
Method for predicting pearlite steel microstructure based on thermodynamics and kinetics Download PDFInfo
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Abstract
The invention provides a method for predicting a pearlite steel microstructure based on thermodynamics and kinetics, and belongs to the field of pearlite steel microstructure calculation. The method utilizes thermodynamics to calculate a quasi-equilibrium phase diagram of the pearlite steel and extracts eutectoid point components, eutectoid point temperature, eutectoid phase species and formation temperature. And then performing kinetic calculation by taking parameters such as pearlite steel components, cooling speed, formation temperature of the pro-eutectoid phase, temperature of a eutectoid point, model size and the like as input to obtain a pro-eutectoid phase interface position and a pearlite lamellar spacing curve, and converting the pro-eutectoid phase content and the pearlite lamellar spacing. According to the thermodynamics, kinetics and data extraction method, the microstructure characteristic parameters under the conditions of appointed pearlite steel components and cooling speed can be predicted, so that the microstructure prediction of the pearlite steel is realized, and the tedious and time-consuming experimental process is avoided or reduced.
Description
Technical Field
The invention relates to the technical field of calculation of pearlite steel microstructure, in particular to a method for predicting the pearlite steel microstructure based on thermodynamics and kinetics.
Background
The pearlite steel has high strength, high wear resistance and high toughness, can be used for tire steel wires, bridge cables and spring members, and is widely applied to national economic construction. Pearlite is a mechanical mixture of ferrite and cementite resulting from the eutectoid decomposition of the parent phase austenite, which usually occurs during continuous cooling on the stelmor cooling line. In the pearlite microstructure, the proeutectoid phase composition and the pearlite lamellar spacing are critical microstructural characteristic parameters.
The influence of the pearlite steel component and the cooling speed on the proeutectoid phase component and the pearlite sheet interlayer spacing is researched through an experimental method, so that the time and the labor are consumed, and the whole parameter range is difficult to cover. The current Calphad method exhibits powerful material design capabilities, and thermodynamic and kinetic calculations fall within the category of Calphad methods. Thermo-Calc is a phase diagram thermodynamic and diffusion dynamics calculation program developed based on the Calphad concept, has become a calculation system with complete data, powerful functions and complete structure through the development of nearly 40 years, and is the most widely used thermodynamic and dynamics calculation software in the world. The invention realizes the pearlite steel microstructure prediction based on thermodynamics and kinetics by using thermodynamics and kinetics methods and combining Thermo-Calc program.
Disclosure of Invention
The invention aims to provide a method for predicting the microstructure of pearlitic steel based on thermodynamics and kinetics, which utilizes thermodynamics to calculate a quasi-equilibrium phase diagram of the pearlitic steel and extracts eutectoid point components, eutectoid point temperature, eutectoid phase species and formation temperature. And then performing kinetic calculation by taking parameters such as pearlite steel components, cooling speed, formation temperature of the pro-eutectoid phase, temperature of a eutectoid point, model size and the like as input to obtain a pro-eutectoid phase interface position and a pearlite lamellar spacing curve, and converting the pro-eutectoid phase content and the pearlite lamellar spacing. According to the thermodynamics, kinetics and data extraction method, the microstructure characteristic parameters under the conditions of appointed pearlite steel components and cooling speed can be predicted, so that the microstructure prediction of the pearlite steel is realized.
The method comprises the following steps:
(1) thermodynamic calculation:
inputting the components of the pearlite steel into a Thermo-Calc program, calculating by using a quasi-equilibrium mode to obtain a quasi-equilibrium phase diagram of the pearlite steel, and obtaining eutectoid point components, eutectoid point temperature, eutectoid phase species and formation temperature information based on the assistance of the quasi-equilibrium phase diagram;
(2) and (3) kinetic calculation:
inputting the pearlite steel components, the cooling speed, the formation temperature of the pro-eutectoid phase, the temperature of a eutectoid point and the size parameters of the model into a Thermo-Calc program, respectively constructing an interface migration kinetic model and a competitive growth kinetic model, and calculating to obtain the interface position of the pro-eutectoid phase and a pearlite lamella spacing curve;
(3) and (3) microstructure prediction:
and (3) predicting the microstructure of the pearlitic steel by utilizing the content of the pro-eutectoid phase and the pearlite interlamellar spacing obtained in the step (1) and the step (2).
Wherein, the eutectoid point component and the eutectoid point temperature in the step (1) are respectively the horizontal axis component and the vertical axis temperature corresponding to the unique intersection point in the quasi-equilibrium phase diagram, and the pre-eutectoid phase forming temperature is the maximum value of the intersection point of the pearlite steel component line and the quasi-equilibrium phase diagram.
When the pearlite steel component in the step (1) is lower than the eutectoid point component, firstly, the eutectoid phase is ferrite; when the pearlite steel component is higher than the eutectoid point component, the eutectoid phase is cementite first.
In the step (2), the content of the proeutectoid phase is obtained according to the position of the proeutectoid phase interface and the size of the model, wherein the content of the proeutectoid phase is 100 percent (the position of the proeutectoid phase interface/the size of the model).
In the step (2), the pearlite interlamellar spacing is obtained according to the pearlite interlamellar spacing curve, and the pearlite interlamellar spacing is (maximum value of the pearlite interlamellar spacing curve + minimum value of the pearlite interlamellar spacing curve) × 0.5.
And (2) performing thermodynamic calculation in the step (1) by adopting a TCFE thermodynamic database, an SSOL thermodynamic database or a self-constructed thermodynamic database.
And (3) adopting a MOBFE dynamics database, a MOB general dynamics database or a self-constructed dynamics database for dynamics calculation in the step (2).
The technical scheme of the invention has the following beneficial effects:
in the scheme, information such as eutectoid point components, eutectoid point temperature, eutectoid phase species and formation temperature is extracted according to a pearlite steel quasi-equilibrium phase diagram calculated by thermodynamics; combining the pearlite steel components and the cooling speed, and obtaining the content of the pro-eutectoid phase and the pearlite lamellar spacing through kinetic calculation; finally, the pearlite steel microstructure prediction based on calculation is realized, and the tedious and time-consuming experimental process is avoided or reduced.
Drawings
FIG. 1 is a schematic diagram of a thermodynamically calculated quasi-equilibrium phase diagram of a pearlitic steel microstructure based on the method of the present invention for thermodynamically and kinetically predicting pearlitic steel microstructure;
FIG. 2 is a schematic view of the kinetically calculated pro-eutectoid phase interface position of the method for predicting pearlite steel microstructure based on thermodynamics and kinetics according to the present invention;
FIG. 3 is a schematic view of a kinetically calculated pearlite interlamellar spacing curve for the method of the present invention for predicting the microstructure of pearlitic steel based on thermodynamics and kinetics;
FIG. 4 is a SEM micrograph of sample number 1 according to an embodiment of the present invention;
FIG. 5 is a SEM micrograph of sample number 2 according to an embodiment of the present invention;
FIG. 6 is a SEM micrograph of sample number 3 in example of the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
The invention provides a method for predicting a pearlite steel microstructure based on thermodynamics and kinetics.
The method comprises the following steps:
(1) thermodynamic calculation:
inputting the components of the pearlite steel into a Thermo-Calc program, calculating by using a quasi-equilibrium mode to obtain a quasi-equilibrium phase diagram of the pearlite steel, and obtaining eutectoid point components, eutectoid point temperature, eutectoid phase species and formation temperature information based on the assistance of the quasi-equilibrium phase diagram; the eutectoid point component and the eutectoid point temperature are the horizontal axis component and the vertical axis temperature corresponding to the unique intersection point in the quasi-equilibrium phase diagram, respectively, and the pro-eutectoid phase formation temperature is the maximum value of the intersection point of the pearlite steel component line and the quasi-equilibrium phase diagram. When the pearlite steel component is lower than the eutectoid point component, the eutectoid phase is ferrite firstly; when the pearlite steel component is higher than the eutectoid point component, the eutectoid phase is cementite first.
(2) And (3) kinetic calculation:
inputting the pearlite steel components, the cooling speed, the formation temperature of the pro-eutectoid phase, the temperature of a eutectoid point and the size parameters of the model into a Thermo-Calc program, respectively constructing an interface migration kinetic model and a competitive growth kinetic model, and calculating to obtain the interface position of the pro-eutectoid phase and a pearlite lamella spacing curve; and (3) obtaining the content of the pre-eutectoid phase according to the position of the pre-eutectoid phase interface and the size of the model, wherein the content of the pre-eutectoid phase is (the position of the pre-eutectoid phase interface/the size of the model) × 100%. The pearlite interlamellar spacing was determined from the pearlite interlamellar spacing curve, and the pearlite interlamellar spacing was 0.5 (maximum pearlite interlamellar spacing curve + minimum pearlite interlamellar spacing curve).
(3) And (3) microstructure prediction:
and (3) predicting the microstructure of the pearlitic steel by utilizing the content of the pro-eutectoid phase and the pearlite interlamellar spacing obtained in the step (1) and the step (2).
The principle of the invention is as follows:
1) the data extraction principle of the quasi-equilibrium phase diagram. The pearlite steel components are input into a Thermo-Calc program, and a quasi-equilibrium phase diagram of the pearlite steel is obtained by utilizing a quasi-equilibrium mode calculation, and is shown in figure 1. In the quasi-equilibrium phase diagram, only two lines exist, and the phase diagram is divided into 4 regions, namely an austenite region, a ferrite region, a cementite region, and a pearlite region. The horizontal axis component corresponding to the unique intersection point A of the two lines in the quasi-equilibrium phase diagram is a eutectoid component, and the vertical axis temperature corresponding to the intersection point A is the eutectoid temperature. The composition line of the pearlite steel is shown by a broken line in the figure, and the temperature of the vertical axis corresponding to the maximum value B of the intersection point of the composition line and the quasi-equilibrium phase diagram is the pro-eutectoid phase formation temperature. When the component line is positioned at the left end of the eutectoid point A, the eutectoid phase is ferrite; when the component line is located at the right end of the eutectoid point A, the eutectoid phase is cementite.
2) The principle of foreeutectoid phase content prediction. The pearlite steel composition, the cooling rate, the eutectoid point temperature a, the pro-eutectoid phase formation temperature B, the model size and other parameters are input into a Thermo-Calc program, an interface migration kinetic model is constructed, and the pro-eutectoid phase interface position D is obtained through calculation, as shown in fig. 2. For the content of the pro-eutectoid phase, the value is (D/model size) × 100%, wherein the model size is the prior austenite average grain size.
3) Prediction principle of pearlite interlamellar spacing. Inputting parameters such as pearlite steel components, cooling speed, eutectoid point temperature A, proeutectoid phase formation temperature B, model size and the like into a Thermo-Calc program, constructing a competitive growth kinetic model, and calculating to obtain a pearlite sheet interlayer spacing curve, as shown in FIG. 3. Wherein the maximum value of the pearlite interlamellar spacing curve is E, the minimum value of the pearlite interlamellar spacing curve is F, and the value of the pearlite interlamellar spacing is (E + F) × 0.5.
4) Thermodynamic principles of calculation. The thermodynamic calculations in the present invention require the use of a TCFE thermodynamic database, an SSOL thermodynamic database, or a self-building thermodynamic database. The Gibbs free energy of a pearlite steel system is stored in a thermodynamic database, and a quasi-equilibrium phase diagram is obtained by calculation according to the Gibbs free energy minimization principle and on the assumption of rapid diffusion of carbon atoms through a Thermo-Calc program.
5) And (4) a kinetic calculation principle. The kinetic calculation in the invention needs to use a MOBFE kinetic database, a MOB general kinetic database or a self-constructed kinetic database. Atom mobility parameters are stored in a dynamics database, and a Thermo-Calc program calculates and obtains a proeutectoid phase interface position and a pearlite lamellar spacing curve by solving a dynamics equation and a diffusion flux conservation equation, so that the proeutectoid phase interface position and the pearlite lamellar spacing curve are converted into the proeutectoid phase content and the pearlite lamellar spacing.
The following description is given with reference to specific examples.
The embodiment of the invention researches the content of pro-eutectoid ferrite and the interlayer spacing of pearlite plates of the pearlite steel under the conditions of different cooling speeds.
The chemical composition of the pearlitic steel is shown in table 1.
Table 1: chemical composition of pearlite steel in wt%
| Serial number | Fe | C | Mn | Si | P | S | O |
| 1 | Bal. | 0.82 | 0.52 | 0.20 | 0.01 | 0.005 | 0.002 |
| 2 | Bal. | 0.82 | 0.52 | 0.20 | 0.01 | 0.005 | 0.002 |
| 3 | Bal. | 0.82 | 0.52 | 0.20 | 0.01 | 0.005 | 0.002 |
The information of the quasi-equilibrium phase diagram of the pearlitic steel is shown in table 2.
Table 2: eutectoid composition, eutectoid temperature, proeutectoid phase species, and formation temperature in quasi-equilibrium phase diagram
| Serial number | Co-segregation point component | Temperature of eutectoid point | Species of proeutectoid phase | Temperature of formation of proeutectoid phase |
| 1 | 0.87wt％C | 975K | Ferrite | 989K |
| 2 | 0.87wt％C | 975K | Ferrite | 989K |
| 3 | 0.87wt％C | 975K | Ferrite | 989K |
The pro-eutectoid ferrite content and pearlite plate interlayer distance experimental measurements of the pearlitic steel are shown in table 3.
Table 3: determining the content of pro-eutectoid ferrite in pearlite steel and the interlayer spacing of pearlite sheet according to a scanning electron microscope
The calculated pro-eutectoid ferrite content and pearlite plate interlayer distance value of the pearlite steel are shown in table 4.
Table 4: the pearlite steel pro-eutectoid ferrite content and the pearlite sheet interlayer spacing obtained by the thermodynamic and kinetic calculation method provided by the invention
| Serial number | Rate of cooling | Content of proeutectoid ferrite | Interlayer spacing of pearlite sheet |
| 1 | 5℃/s | 1.5％ | 0.28μm |
| 2 | 10℃/s | 1.3％ | 0.20μm |
| 3 | 15℃/s | 1.0％ | 0.15μm |
FIGS. 4, 5 and 6 are SEM photographs of sample No. 1, sample No. 2 and sample No. 3, respectively. Therefore, according to the thermodynamic and kinetic calculation method provided by the invention, the proeutectoid phase composition and the pearlite interlamellar spacing of the pearlite steel can be accurately calculated, and the microstructure of the pearlite steel can be reasonably predicted.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (4)
1. A method for predicting the microstructure of pearlitic steel based on thermodynamics and kinetics is characterized in that: the method comprises the following steps:
(1) thermodynamic calculation:
inputting the components of the pearlite steel into a Thermo-Calc program, calculating by using a quasi-equilibrium mode to obtain a quasi-equilibrium phase diagram of the pearlite steel, and obtaining eutectoid point components, eutectoid point temperature, eutectoid phase species and formation temperature information based on the assistance of the quasi-equilibrium phase diagram;
(2) and (3) kinetic calculation:
inputting the pearlite steel components, the cooling speed, the formation temperature of the pro-eutectoid phase, the temperature of a eutectoid point and the size parameters of the model into a Thermo-Calc program, respectively constructing an interface migration kinetic model and a competitive growth kinetic model, and calculating to obtain the interface position of the pro-eutectoid phase and a pearlite lamella spacing curve;
(3) and (3) microstructure prediction:
predicting the microstructure of the pearlite steel by utilizing the content of the pro-eutectoid phase and the pearlite inter-lamellar spacing obtained in the step (1) and the step (2);
the eutectoid point component and the eutectoid point temperature in the step (1) are respectively the horizontal axis component and the vertical axis temperature corresponding to the unique intersection point in the quasi-equilibrium phase diagram, and the formation temperature of the pre-eutectoid phase is the maximum value of the intersection point of the pearlite steel component line and the quasi-equilibrium phase diagram;
in the step (2), the content of the proeutectoid phase is obtained according to the position of the proeutectoid phase interface and the size of the model, wherein the content of the proeutectoid phase is 100 percent (the position of the proeutectoid phase interface/the size of the model);
in the step (2), the pearlite interlamellar spacing is obtained according to the pearlite interlamellar spacing curve, and the pearlite interlamellar spacing is (maximum value of the pearlite interlamellar spacing curve + minimum value of the pearlite interlamellar spacing curve) × 0.5.
2. The method for thermodynamically and kinetically predicting a pearlitic steel microstructure according to claim 1, wherein: when the pearlite steel component in the step (1) is lower than the eutectoid point component, firstly, the eutectoid phase is ferrite; when the pearlite steel component is higher than the eutectoid point component, the eutectoid phase is cementite first.
3. The method for thermodynamically and kinetically predicting a pearlitic steel microstructure according to claim 1, wherein: the thermodynamic calculation in the step (1) adopts a TCFE thermodynamic database, an SSOL thermodynamic database or a self-constructed thermodynamic database.
4. The method for thermodynamically and kinetically predicting a pearlitic steel microstructure according to claim 1, wherein: and (3) adopting a MOBFE dynamics database, a MOB general dynamics database or a self-constructed dynamics database for dynamics calculation in the step (2).
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| CN107858492A (en) * | 2017-10-25 | 2018-03-30 | 刘澄 | Change the alloy carburizing steel preprocess method of netted acicular ferrite in microscopic structure |
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| CN107858492A (en) * | 2017-10-25 | 2018-03-30 | 刘澄 | Change the alloy carburizing steel preprocess method of netted acicular ferrite in microscopic structure |
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