CN113174467B - Method for predicting casting blank quenching structure and method for making casting blank quenching process - Google Patents
Method for predicting casting blank quenching structure and method for making casting blank quenching process Download PDFInfo
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- 238000001556 precipitation Methods 0.000 claims description 32
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- 229910001562 pearlite Inorganic materials 0.000 claims description 11
- 238000006243 chemical reaction Methods 0.000 claims description 8
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- 238000004519 manufacturing process Methods 0.000 description 7
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- 229910052799 carbon Inorganic materials 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 238000010583 slow cooling Methods 0.000 description 2
- 229910052582 BN Inorganic materials 0.000 description 1
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 description 1
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Abstract
The invention provides a method for predicting a quenching structure of a casting blank and a method for formulating a quenching process of the casting blank, which comprise the following steps: selecting specific points from the section of the casting blank vertical to the blank drawing direction, and drawing a temperature change curve of the specific points in the process of continuous casting, quenching and quenching; acquiring a position corresponding to the characteristic temperature from the temperature change curve, and taking the position as a starting position of austenite transformation at a specific point; corresponding the starting position of the austenite phase transformation at the specific point to the 0 moment of the supercooling austenite isothermal transformation TTT curve to obtain a quenching structure prediction graph; and determining the prediction result of the quenched structure corresponding to the specific point according to the intersection point position of the temperature change curve of the specific point and the supercooling austenite isothermal transformation TTT curve in the quenched structure prediction graph. The method can solve the problems that a method which can accurately predict the quenching structure and set a quenching process is lacked in the prior art.
Description
Technical Field
The invention belongs to the technical field of continuous casting and rolling, and particularly relates to a method for predicting a casting blank quenching structure and a method for formulating a casting blank quenching process.
Background
The hot charging and hot feeding of the continuous casting billet or the direct rolling can greatly reduce the production cost. With the increasingly fierce competition of the steel market, in the measure of further reducing the production cost, the continuous casting billet hot charging and hot delivery and even the direct rolling process obviously can reduce the energy consumption, reduce the time in a heating furnace and the like, and become the only effective cost control measure.
However, in microalloyed steel, steel containing 0.4 to 0.55 carbon, particularly containing Cr, mn and other elements, and steel containing relatively high content of Al and N, under the condition of the hot-conveying process, precipitates such as nitrides such as aluminum nitride and boron nitride, and carbonitrides are precipitated on the surface grain boundary of the casting blank at present, so that the plasticity of the surface structure of the casting blank is seriously reduced, the crack sensitivity is caused, and surface cracks appear in the heating or rolling process at the later stage, and the final material quality is unqualified. Therefore, the hot charging and hot feeding proportion of crack sensitive steel such as microalloy steel is very low and is less than 20 percent at present, and direct rolling cannot be realized.
At present, the production of crack sensitive steel grades such as microalloy steel and the like generally adopts slow cooling or even pit cooling, and related equipment is adopted, wherein the surface hardening technology can solve the problem of surface cracks of a casting blank in the hot charging and hot conveying process from the mechanism after continuous casting and cutting. For slow cooling and even pit cooling, the production cost is higher due to factors such as production period, heat loss and long heating time, and the productivity is greatly influenced.
For the adoption of the surface quenching technology, as the design idea of the quenching process cannot be solved, for example, aiming at a certain steel grade, the quenching position, the quenching depth, the specific quenching process standard and the like, the utilization rate of quenching equipment is low, even the quenching equipment is not used and abandoned, and the effect of improving the heat transfer ratio of the microalloyed steel is not achieved; meanwhile, a process model of an accurate mature system is not available for guiding the quenching structure prediction and the quenching process design.
Disclosure of Invention
In view of the above problems, the present invention aims to provide a method for establishing a quenching process for a casting blank, so as to solve the problems that a method for accurately predicting a quenching structure and establishing a quenching process is lacked in the prior art.
The invention provides a method for predicting a casting blank quenching structure, which comprises the following steps:
selecting a specific point from a section of a casting blank vertical to the casting blank drawing direction, and drawing a temperature change curve of the specific point in the process of continuous casting, quenching and quenching;
acquiring a position corresponding to the characteristic temperature from the temperature change curve, and taking the position as a starting position of austenite transformation at the specific point;
corresponding the starting position of the austenite phase transformation at the specific point to the 0 moment of the supercooling austenite isothermal transformation TTT curve to obtain a quenching structure prediction graph;
and determining the prediction result of the quenched structure corresponding to the specific point according to the intersection point position of the temperature change curve of the specific point in the quenched structure prediction graph and the supercooling austenite isothermal transformation (TTT) curve.
In addition, it is preferable that the selecting of the specific point from the section of the cast slab perpendicular to the direction of drawing and the drawing of the temperature change curve thereof in the process after the continuous casting-quenching include:
selecting the specific point from the surface of the casting blank to the center of the section of the casting blank;
acquiring the position change and temperature change information of the specific point from the temperature change information of the process after continuous casting, quenching and quenching;
and according to the position change and the temperature change information of the specific point, drawing a temperature change curve of the specific point by taking the distance from the specific point to the liquid level of the crystallizer along the throwing direction as an abscissa and taking the temperature change of the specific point as an ordinate.
Preferably, in the process of obtaining a position corresponding to the characteristic temperature from the temperature change curve and setting the position as a starting position at which the austenite transformation at the specific point occurs,
when the quenching starting temperature of the casting blank is higher than A3 and lower than 50 ℃, taking the quenching starting temperature as a characteristic temperature;
when the quenching start temperature is equal to or lower than the A3 temperature, the A3 temperature is taken as a characteristic temperature.
Preferably, the step of associating the start position of the austenite transformation at the specific point with the time point 0 of the supercooled austenite isothermal transformation TTT curve to obtain the quenched structure prediction map includes:
converting a position abscissa in the temperature change curve into a time abscissa by a time coordinate conversion formula;
and after the time abscissa of the starting position of the austenite transformation at the specific point corresponds to the 0 moment of the supercooling austenite isothermal transformation TTT curve, drawing a temperature change curve after the starting position of the austenite transformation at the specific point and the supercooling austenite isothermal transformation TTT curve in the same graph to obtain a quenching structure prediction graph.
In addition, it is preferable that the time coordinate conversion formula is:
T＝(S-S1)/V
wherein T is the time on the time abscissa, S is the position coordinate of the specific point in the temperature change curve, S1 is the starting position of the austenite transformation of the specific point, and V is the drawing speed.
In addition, preferably, the determining of the prediction result of the quenched structure of the cast slab at the quenching depth to be measured in the drawing direction according to the intersection point position of the temperature change curve of the specific point in the quenched structure prediction graph and the supercooled austenite isothermal transformation TTT curve includes:
acquiring the time elapsed between the time corresponding to the intersection point of the ferrite initial precipitation curve and the pearlite initial precipitation curve and the temperature change curve respectively as the grain boundary embrittlement time;
judging whether grain boundary embrittlement occurs to a quench-cooled structure of the casting blank corresponding to the specific point in the drawing direction or not according to a steel grade grain boundary embrittlement judgment rule and the grain boundary embrittlement time; wherein the content of the first and second substances,
the judgment rule for the grain boundary embrittlement of the steel grade comprises the following steps:
when the grain boundary embrittlement time is less than the grain boundary embrittlement standard time, the quenching structure of the casting blank corresponding to the specific point in the drawing direction has no grain boundary embrittlement;
and when the grain boundary embrittlement time is greater than or equal to the grain boundary embrittlement standard time, the grain boundary embrittlement exists in the quenching structure of the casting blank corresponding to the specific point in the drawing direction.
In addition, it is preferable that, in obtaining the time elapsed between the respective times at which the ferrite precipitation starting curve and the pearlite precipitation starting curve correspond to the intersection points of the temperature change curves as the grain boundary embrittlement time,
if the ferrite precipitation starting curve and the temperature change curve have no intersection point, the quenching structure of the casting blank at the quenching depth corresponding to the specific point in the drawing direction has no grain boundary embrittlement.
Preferably, the standard time for grain boundary embrittlement is set in a range of 1.0 to 8.0min depending on the steel type.
The invention provides a method for formulating a casting blank quenching process, which comprises the following steps:
according to the method for predicting the quenching structure of the casting blank, the prediction results of the quenching structure from the surface of the casting blank to different positions of the center of the casting blank under at least two quenching working condition times are obtained;
according to the prediction results of the quenching structure from the surface of the casting blank to different positions of the center of the casting blank at each quenching working condition time, acquiring the position where the grain boundary embrittlement occurs at the maximum at the quenching working condition time, and taking the distance from the position to the surface of the casting blank as the quenching depth to obtain the corresponding data of the quenching working condition time and the quenching depth;
obtaining effective quenching time of a given quenching depth according to the corresponding data of the quenching working condition time and the quenching depth;
and formulating a quenching process of the casting blank according to the effective quenching time of the given quenching depth.
In addition, it is preferable that the time for the given quenching depth is 5mm to 15mm.
According to the technical scheme, the method for predicting the quenching structure of the casting blank and the method for making the quenching process of the casting blank provided by the invention have the advantages that the specific point is selected from the section of the casting blank vertical to the casting blank drawing direction, and the temperature change curve of the casting blank in the process of continuous casting, quenching and quenching is drawn; then, acquiring a position corresponding to the characteristic temperature from the temperature change curve, and taking the position as a starting position of austenite transformation at a specific point; then, the starting position of the austenite phase transformation at the specific point corresponds to the 0 moment of the supercooling austenite isothermal transformation TTT curve to obtain a quenching structure prediction graph; and obtaining the prediction result of the quenched structure corresponding to the specific point according to the intersection point position of the temperature change curve of the specific point in the quenched structure prediction graph and the supercooled austenite isothermal transformation (TTT) curve. The method for predicting the quenching structure of the casting blank can obtain the prediction results of the quenching structure at different depths of the quenched casting blank; the prediction method and the method for formulating the casting blank quenching process provided by the invention are based on the prediction method for the quenching structure of the casting blank provided by the invention, so that corresponding data of different quenching working condition time and quenching depth are obtained, and then various information required for formulating the quenching process is obtained according to the data, wherein the data mainly comprise effective quenching depth and effective quenching time.
To the accomplishment of the foregoing and related ends, one or more aspects of the invention comprise the features hereinafter fully described. The following description and the annexed drawings set forth in detail certain illustrative aspects of the invention. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Further, the present invention is intended to include all such aspects and their equivalents.
Drawings
Other objects and results of the present invention will become more apparent and more readily appreciated as the same becomes better understood by reference to the following description taken in conjunction with the accompanying drawings. In the drawings:
FIG. 1 is a flowchart of a method for predicting a casting blank quenched structure according to an embodiment of the present invention;
FIG. 2 is a flowchart of a method for establishing a casting blank quenching process according to an embodiment of the present invention;
FIG. 3 is a schematic view showing a temperature change tendency and austenite transformation at specific points of 1mm and 15mm from the surface of a cast slab in a cross section of the cast slab during quenching according to example 1 of the present invention;
FIG. 4 is a drawing of a prediction of a quenched structure at two specific points of 1mm and 15mm from the surface of a cast slab on the cross section of the cast slab according to example 1 of the present invention;
FIG. 5 is a graph showing ferrite precipitation times obtained in example 1 according to the present invention.
The same reference numbers in all figures indicate similar or corresponding features or functions.
Detailed Description
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) may be practiced without these specific details.
Aiming at the problems that a method capable of accurately predicting a quenching structure and formulating a quenching process is lacked in the prior art, a method for predicting a casting blank quenching structure and a method for formulating a casting blank quenching process are provided.
Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
In order to explain the method for predicting the quenched structure of a cast slab according to the present invention, fig. 1 shows a flow of the method for predicting the quenched structure of a cast slab according to the embodiment of the present invention.
As shown in fig. 1, the method for predicting a quenched structure of a cast slab according to the present invention includes the steps of:
s11, selecting specific points from the section of the casting blank vertical to the blank drawing direction, and drawing a temperature change curve of the specific points in the process of continuous casting, quenching and quenching.
Wherein, selecting specific points from the section of the casting blank vertical to the casting blank drawing direction, and drawing the temperature change curve of the casting blank in the process of continuous casting, quenching and quenching comprises the following steps:
selecting a specific point from the surface of the casting blank to the center of the section of the casting blank;
acquiring the position change and temperature change information of a specific point from the temperature change information of the process after continuous casting, quenching and quenching;
and according to the position change and the temperature change information of the specific point, drawing a temperature change curve of the specific point by taking the distance from the specific point to the liquid level of the crystallizer along the throwing direction as an abscissa and taking the temperature change of the specific point as an ordinate.
Specifically, in the process of quenching the casting blank, a specific point is determined according to a quenching structure at the casting blank depth position to be predicted, the specific point is positioned on the section of the casting blank vertical to the drawing direction, and the distance between the specific point and the surface of the casting blank is the casting blank depth to be predicted.
And S12, acquiring a position corresponding to the characteristic temperature from the temperature change curve, and taking the position as a starting position of austenite transformation at a specific point.
Wherein, in the process of acquiring a position corresponding to the characteristic temperature from the temperature change curve and taking the position as a starting position of austenite transformation at a specific point,
when the quenching starting temperature of the casting blank is higher than A3 and lower than 50 ℃, taking the quenching starting temperature as a characteristic temperature;
when the quenching start temperature is equal to or lower than the A3 temperature, the A3 temperature is taken as the characteristic temperature.
Specifically, temperature change data of a casting blank quenching process, as well as a supercooled austenite isothermal transformation curve (TTT curve) of a steel type and a temperature-time-performance curve (TTP curve) of nitrides and carbonitrides of the steel type are obtained, and on the basis of the TTT curve, a position reaching a characteristic temperature in a temperature change curve at a casting blank depth (i.e., a specific point) to be studied is first found, and the characteristic temperature is determined according to actual conditions and is a known quantity.
And S13, corresponding the starting position of the austenite transformation at the specific point to the 0 moment of the supercooling austenite isothermal transformation TTT curve to obtain a quenching structure prediction graph.
Wherein, the starting position of the austenite transformation at the specific point corresponds to the 0 moment of the supercooling austenite isothermal transformation TTT curve, and the obtained quenching structure prediction graph comprises the following steps:
converting a position abscissa in the temperature change curve into a time abscissa by a time coordinate conversion formula;
and after the time abscissa of the starting position of the austenite transformation at the specific point corresponds to the 0 moment of the supercooling austenite isothermal transformation TTT curve, drawing the temperature change curve after the starting position of the austenite transformation at the specific point and the supercooling austenite isothermal transformation TTT curve in the same graph to obtain a quenching structure prediction graph.
Wherein, the time coordinate conversion formula is as follows:
T＝(S-S1)/V
wherein T is the time on the time abscissa, S is the position coordinate of the specific point in the temperature change curve, S1 is the starting position of the austenite transformation of the specific point, and V is the drawing speed.
Specifically, the abscissa of the temperature change curve of the specific point is a distance, so that the abscissa of the temperature change curve needs to be converted into a time coordinate according to a time coordinate conversion formula, and then the temperature change curve after the austenite transformation starting position of the specific point and the supercooled austenite isothermal transformation TTT curve are drawn into the same graph corresponding to the 0 th moment of the supercooled austenite isothermal transformation TTT curve, so as to obtain a quenching structure prediction graph.
And S14, determining the prediction result of the quenched structure corresponding to the specific point according to the intersection point position of the temperature change curve of the specific point in the quenched structure prediction graph and the supercooling austenite isothermal transformation (TTT) curve.
The method comprises the following steps of determining a prediction result of a quenching structure of a casting blank at a quenching depth to be measured in a drawing direction according to the intersection point position of a temperature change curve of a specific point in a quenching structure prediction graph and a supercooled austenite isothermal transformation (TTT) curve, wherein the prediction result comprises the following steps:
acquiring the time elapsed between the time corresponding to the intersection points of the ferrite precipitation starting curve and the pearlite precipitation starting curve and the temperature change curve respectively as the grain boundary embrittlement time;
judging whether the quenching structure of the casting blank corresponding to the specific point in the drawing direction generates grain boundary embrittlement or not according to the grain boundary embrittlement judgment rule of the steel type and the grain boundary embrittlement time; wherein the content of the first and second substances,
the judgment rule for the grain boundary embrittlement of steel grades comprises the following steps:
when the grain boundary embrittlement time is less than the grain boundary embrittlement standard time, the quenching structure of the casting blank corresponding to the specific point in the drawing direction has no grain boundary embrittlement;
and when the grain boundary embrittlement time is more than or equal to the grain boundary embrittlement standard time, the grain boundary embrittlement exists in the quenching structure of the casting blank corresponding to the specific point in the drawing direction.
Wherein, in the process of obtaining the time elapsed between the points of time corresponding to the respective intersection points of the ferrite precipitation starting curve and the pearlite precipitation starting curve with the temperature change curve as the grain boundary embrittlement time,
if the ferrite precipitation starting curve does not have an intersection point with the temperature change curve, the quenched structure of the casting blank in the drawing direction at the quenching depth corresponding to the specific point does not have grain boundary embrittlement.
Wherein the standard time of grain boundary embrittlement is set according to steel grades and is set within the range of 1.0-8.0 min.
Specifically, the super-cooled austenite isothermal transformation TTT curve includes a multi-element precipitation curve, in which the time elapsed from the ferrite precipitation starting curve to the pearlite precipitation starting temperature curve in the temperature variation curve is the ferrite precipitation time at the austenite grain boundary, which is called ferrite precipitation time, and the longer the ferrite precipitation time, the more the amount of ferrite precipitated at the austenite grain boundary, and when a standard amount is reached, the film-like ferrite is formed at the austenite grain boundary, so whether grain boundary embrittlement occurs is determined by the ferrite precipitation time and the time reaching the standard for forming the film-like ferrite at the grain boundary. And obtaining a prediction result of the quenched structure corresponding to the specific point by judging whether the grain boundary embrittlement occurs in the quenched structure corresponding to the specific point.
In order to explain the method for formulating the casting blank quenching process provided by the present invention, fig. 2 shows a flow of the method for formulating the casting blank quenching process according to the embodiment of the present invention.
As shown in fig. 2, the method for establishing the casting blank quenching process provided by the invention comprises the following steps:
s21, obtaining the prediction results of the quenching structures from the surface of the casting blank to different positions of the center of the casting blank under at least two quenching working condition times according to the method for predicting the quenching structures of the casting blank.
Specifically, the predicted casting blank depth can be 1mm, 2mm, 3mm and the like at 10S according to the predicted casting blank depth and the predicted results of the quenched structure of a plurality of different predicted depths at each quenching working condition time, for example, the predicted result of the quenched structure corresponding to 1mm is that no grain boundary embrittlement occurs, and the grain boundary embrittlement occurs at 10 mm.
S22, according to the prediction result of the quenching structure from the surface of the casting blank to different positions of the center of the casting blank in each quenching working condition time, obtaining the position where the grain boundary embrittlement occurs at the maximum in the quenching working condition time, and taking the distance from the position to the surface of the casting blank as the quenching depth to obtain the corresponding data of the quenching working condition time and the quenching depth.
Specifically, by the method, the result of predicting the quenching structure whether grain boundary embrittlement occurs at different positions from the surface of the casting blank to a certain depth is obtained, and the critical thickness of the grain boundary embrittlement is obtained from the result of predicting the quenching structure, namely the quenching depth. For example, in 10S, if no grain boundary embrittlement occurs at a position where the casting slab depth is predicted to be 8mm, it means that the quenching structure corresponding to the position has achieved the quenching effect, and if crystal embrittlement occurs at a position of 9mm, it means that the quenching structure corresponding to the position has not achieved the quenching effect, and 8mm is approximated to the quenching depth.
And S23, obtaining the effective quenching time of the given quenching depth according to the corresponding data of the quenching working condition time and the quenching depth.
Specifically, when a certain quenching process is set, the intended quenching depth, i.e., the given quenching depth or the effective quenching depth, is required to be given, the corresponding effective extraction time can be obtained according to the data obtained above, for example, the quenching depth of 10S is 8mm, the quenching depth of 20s is 12mm, the effective quenching depth or the effective quenching depth is 8mm, the effective quenching depth is 10S, and if the given quenching depth is 9mm, the effective quenching time is 10S-20S. Or conversely, the effective quenching depth is determined given the effective quenching time, similar to that described above, and will not be described further.
And S24, formulating a quenching process of the casting blank according to the effective quenching time of the given quenching depth.
Specifically, the establishment of the general casting blank quenching process comprises effective quenching time and effective quenching depth, and the reasonable quenching process can be established according to the above contents.
Preferably, the time for a given quenching depth is 5mm to 15mm.
In order to better explain the method for predicting the quenching structure of the casting blank and the method for making the quenching process of the casting blank provided by the invention, the following specific examples are provided as follows:
example 1
In order to explain the method for predicting the quenching structure of the casting blank and the method for making the quenching process of the casting blank provided by the embodiment 1 of the invention, fig. 3 shows the temperature change trend of two specific points 1mm and 15mm away from the surface of the casting blank on the cross section of the casting blank and the austenite transformation and transformation of the specific points in the quenching process according to the embodiment 1 of the invention; FIG. 4 is a graph showing the prediction of the quenched structure at two specific points of 1mm and 15mm from the surface of a cast slab on the cross section of the cast slab according to example 1 of the present invention; fig. 5 is a graph showing ferrite precipitation time obtained in example 1 according to the present invention.
As shown in fig. 3 to 5, the method for predicting the quenching structure of a casting blank and the method for establishing the quenching process of a casting blank provided by the present invention are used to predict the quenching structure corresponding to two specific points of 1mm and 15mm away from the surface of the casting blank on the cross section of the casting blank and establish the process based on the prediction method.
The method mainly comprises the steps of continuously casting 180mm multiplied by 180mm small square billets in a certain steel mill, taking 40Cr as an example of steel grades, directly carrying out hot delivery on casting billets, and configuring a surface quenching technology because the direct hot delivery easily causes surface grain boundary microcracks in the traditional process. And the quenching adopts box-type cooling, and after the casting blank is cut, the casting blank is placed into a quenching box for quenching in a hoisting mode. The casting machine 40Cr production pulling speed is 1.4m/min, the cutting position is 25m, and the cut casting blank is equivalent to the continuation distance coordinate of the casting flow according to time.
The temperature changes of different positions of the casting blank before and after quenching are shown in figure 3, the A3 temperature of the 40Cr steel grade measured through a model is 778 ℃, in figure 3, the A3 temperature of the steel grade is taken as a characteristic temperature, the austenite transformation starting position of the casting blank at a position 1mm away from the surface is 29.12m, and the austenite transformation starting position of the casting blank at a position 15mm away from the surface is 29.65m.
As the temperature changes rapidly in the quenching process, the selection of the characteristic temperature can be carried out within a certain range, and as shown in figure 3, the austenite phase transition starting position of the casting blank at a position 1mm away from the surface can be simply selected as the quenching starting position, namely the position corresponding to the turning point of obvious quenching at a position 1mm away from the surface of the casting blank; the austenite phase transition starting position of the casting blank at the position 15mm away from the surface can be simply selected as the position corresponding to the quenching turning point with the temperature, and also can be simply selected as the austenite phase transition starting position the same as the casting blank at the position 1mm away from the surface.
The subsequent temperature conversion time coordinates of the cast slab at the austenite transformation start position at 1mm and 15mm from the surface in fig. 3 and the TTT curve of the 40Cr steel type are plotted in the same graph, as shown in fig. 4.
From fig. 4, the structure of the casting blank after quenching at different depth positions can be predicted, and it can be seen that: the casting blank structure at the position 1mm away from the surface is martensite, bainite, ferrite and pearlite, and a temperature curve is not intersected with a ferrite precipitation starting curve, so that the problems of membranous ferrite and grain boundary embrittlement do not exist, namely, the problem of grain boundary embrittlement of the casting blank structure at the position 1mm away from the surface is solved after a quenching process; on the other hand, the casting blank structure at a position 15mm away from the surface is ferrite + pearlite, the temperature curve, the ferrite precipitation starting curve and the pearlite precipitation starting curve are intersected, the ferrite precipitation time is provided, and more detailed judgment needs to be carried out as to whether grain boundary membranous ferrite is always present.
In fig. 5, the time interval between the temperature curve of the casting blank at a position 15mm away from the surface and the intersection of the temperature curve and the ferrite precipitation starting curve and the pearlite precipitation starting curve is ferrite precipitation time, specifically, 0.85min to 1.95min, and the ferrite precipitation time is 1.1min.
Obviously, if the standard time for forming the grain boundary film ferrite of the steel grade is 1min, the casting blank has grain boundary embrittlement at a position 15mm away from the surface; if the standard time for the formation of the grain boundary film-like ferrite of this steel grade is 2min, grain boundary embrittlement does not occur in the cast slab at a distance of 15mm from the surface.
According to the method for predicting the quenching structure of the casting blank, disclosed by the embodiment of the invention, whether the structure of the casting blank is embrittled at different depth positions from the surface to the center in any quenching process can be obtained, so that the effective quenching thickness corresponding to the process can be obtained. For example, a casting blank 14mm away from the surface has no grain boundary embrittlement, while a casting blank 15mm away from the surface has grain boundary embrittlement, which indicates that the effective quenching depth under the quenching process is 14mm.
Further, according to the method for predicting the quenching structure of the casting blank of the present invention, the quenching depths of different quenching times (each quenching time is a quenching process) can be obtained, and the quenching process time can be determined in reverse under the condition that the process requirement of the quenching depth is known. For example, the method of the invention can obtain the quenching depth of 6mm for 15S, 10mm for 20S, 13mm for 30S and 16mm for 40S, and if the quenching depth is required to be more than 10mm in the process, the quenching time is required to be more than 20S to meet the requirement of the quenching depth.
According to the method for predicting the quenching structure of the casting blank and the method for formulating the quenching process of the casting blank, provided by the invention, the specific point is selected from the section of the casting blank vertical to the billet drawing direction, and the temperature change curve of the casting blank in the process after continuous casting, quenching and quenching is drawn; then, acquiring a position corresponding to the characteristic temperature from the temperature change curve, and taking the position as a starting position of austenite transformation at a specific point; then, corresponding the starting position of the austenite phase transformation of the specific point to the 0 moment of the supercooling austenite isothermal transformation TTT curve to obtain a quenching structure prediction graph; and obtaining the prediction result of the quenched structure corresponding to the specific point according to the intersection point position of the temperature change curve of the specific point in the quenched structure prediction graph and the supercooled austenite isothermal transformation (TTT) curve. The method for predicting the quenching structure of the casting blank can obtain the prediction result of the quenching structure at different depths of the quenched casting blank; the prediction method and the method for formulating the casting blank quenching process provided by the invention are based on the prediction method for the quenching structure of the casting blank provided by the invention, so that corresponding data of different quenching working condition time and quenching depth are obtained, and then various information required for formulating the quenching process is obtained according to the data, wherein the data mainly comprise effective quenching depth and effective quenching time.
The method for predicting a quenched structure of a cast slab and the method for preparing a quenching process of a cast slab according to the present invention are described above by way of example with reference to the accompanying drawings. However, it will be appreciated by those skilled in the art that various modifications may be made to the method for predicting a quenched structure of a cast slab and the method for producing a quenched structure of a cast slab proposed by the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention should be determined by the contents of the appended claims.
Claims (9)
1. A method for predicting a casting blank quenching structure is characterized by comprising the following steps:
selecting a specific point from a section of a casting blank vertical to the casting blank drawing direction, and drawing a temperature change curve of the specific point in the process of continuous casting, quenching and quenching;
acquiring a position corresponding to the characteristic temperature from the temperature change curve, and taking the position as a starting position of austenite transformation at the specific point;
corresponding the starting position of the austenite phase transformation at the specific point to the 0 moment of the supercooling austenite isothermal transformation TTT curve to obtain a quenching structure prediction graph; wherein, specifically include:
converting a position abscissa in the temperature change curve into a time abscissa by a time coordinate conversion formula; after the time abscissa of the starting position of the austenite transformation at the specific point corresponds to the 0 moment of the supercooling austenite isothermal transformation TTT curve, drawing the temperature change curve after the starting position of the austenite transformation at the specific point and the supercooling austenite isothermal transformation TTT curve in the same graph to obtain a quenching structure prediction graph;
and determining the prediction result of the quenched structure corresponding to the specific point according to the intersection point position of the temperature change curve of the specific point in the quenched structure prediction graph and the supercooling austenite isothermal transformation (TTT) curve.
2. The method for predicting the slab quenching structure according to claim 1, wherein the step of selecting a specific point from a cross section of the slab perpendicular to the slab drawing direction and plotting a temperature change curve thereof in the process after the continuous casting-quenching comprises:
selecting the specific point from the surface of the casting blank to the center of the section of the casting blank;
acquiring the position change and temperature change information of the specific point from the temperature change information of the process after continuous casting, quenching and quenching;
and according to the position change and the temperature change information of the specific point, drawing a temperature change curve of the specific point by taking the distance from the specific point to the liquid level of the crystallizer along the billet drawing direction as an abscissa and taking the temperature change of the specific point as an ordinate.
3. The method of predicting a slab quenching structure according to claim 1, wherein in a process of obtaining a position corresponding to a characteristic temperature from the temperature change curve and setting the position as a starting position at which austenite transformation occurs at the specific point,
when the quenching starting temperature of the casting blank is higher than A3 and lower than 50 ℃, taking the quenching starting temperature as a characteristic temperature;
and when the quenching starting temperature is less than or equal to the A3 temperature, taking the A3 temperature as a characteristic temperature.
4. The method for predicting a quenched structure of a cast slab according to claim 1, wherein the time coordinate conversion formula is:
T = (S-S1)/V
wherein T is the time on the time abscissa, S is the position coordinate of the specific point in the temperature change curve, S1 is the starting position of the austenite transformation of the specific point, and V is the drawing speed.
5. The method for predicting the quenched structure of the casting blank according to claim 1, wherein determining the prediction result of the quenched structure of the casting blank in the casting direction at the quenching depth to be measured according to the intersection position of the temperature change curve of a specific point in the quenched structure prediction graph and the supercooled austenite isothermal transition (TTT) curve comprises:
acquiring the time elapsed between the ferrite precipitation starting curve and the pearlite precipitation starting curve and the time corresponding to the intersection point of the temperature change curve respectively as the grain boundary embrittlement time;
judging whether the quenching structure of the casting blank corresponding to the specific point in the drawing direction generates grain boundary embrittlement or not according to a steel grade grain boundary embrittlement judgment rule and the grain boundary embrittlement time; wherein the content of the first and second substances,
the judgment rule for the grain boundary embrittlement of the steel grade comprises the following steps:
when the grain boundary embrittlement time is less than the grain boundary embrittlement standard time, the quenching structure of the casting blank corresponding to the specific point in the drawing direction has no grain boundary embrittlement;
and when the grain boundary embrittlement time is greater than or equal to the grain boundary embrittlement standard time, the grain boundary embrittlement exists in the quenching structure of the casting blank corresponding to the specific point in the drawing direction.
6. The method of predicting a quenched structure of a cast slab according to claim 5, wherein the method of predicting a quenched structure of a cast slab according to claim 1,
in the process of obtaining the time elapsed between the times corresponding to the respective intersection points of the ferrite precipitation starting curve and the pearlite precipitation starting curve with the temperature change curve as the grain boundary embrittlement time,
if the ferrite precipitation starting curve and the temperature change curve have no intersection point, the quenching structure of the casting blank at the quenching depth corresponding to the specific point in the drawing direction has no grain boundary embrittlement.
7. The method for predicting a casting blank quench structure according to claim 5, wherein the standard time for grain boundary embrittlement is set in a range of 1.0 to 8.0min depending on a steel type.
8. A method for making a casting blank quenching process is characterized by comprising the following steps:
according to the method for predicting the quenching structure of the casting blank as claimed in any one of claims 1 to 7, obtaining the prediction results of the quenching structure from the surface of the casting blank to different positions of the center of the casting blank under at least two quenching working conditions;
according to the prediction results of the quenching structures at different positions from the surface of the casting blank to the center of the casting blank under each quenching working condition time, obtaining the position where the grain boundary embrittlement occurs at the maximum under the quenching working condition time, and taking the distance from the position to the surface of the casting blank as the quenching depth to obtain the corresponding data of the quenching working condition time and the quenching depth;
obtaining effective quenching time of a given quenching depth according to the corresponding data of the quenching working condition time and the quenching depth;
and formulating a quenching process of the casting blank according to the effective quenching time of the given quenching depth.
9. The method for establishing a slab quenching process according to claim 8,
the time of the given quenching depth is 5mm to 15mm.
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