CN113176292B - Judgment method for grain boundary embrittlement of casting blank - Google Patents
Judgment method for grain boundary embrittlement of casting blank Download PDFInfo
- Publication number
- CN113176292B CN113176292B CN202110308000.8A CN202110308000A CN113176292B CN 113176292 B CN113176292 B CN 113176292B CN 202110308000 A CN202110308000 A CN 202110308000A CN 113176292 B CN113176292 B CN 113176292B
- Authority
- CN
- China
- Prior art keywords
- grain boundary
- boundary embrittlement
- specific point
- time
- embrittlement
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Continuous Casting (AREA)
Abstract
The invention provides a method for judging grain boundary embrittlement of a casting blank, which comprises the following steps: drawing a temperature change curve of the continuous casting billet in the process from continuous casting to hot delivery by taking an optional point on the section of the casting billet vertical to the billet drawing direction as a specific point; acquiring a position corresponding to the characteristic temperature from the temperature change curve, and taking the position as a starting position of the transition of the specific point; corresponding the starting position of the transformation of the specific point to the 0 moment of the supercooling austenite isothermal transformation TTT curve to obtain a grain boundary embrittlement judgment diagram; and determining the position of the grain boundary embrittlement of the specific point in the drawing direction according to the intersection point position of the temperature change curve and the supercooling austenite isothermal transformation (TTT) curve in the grain boundary embrittlement judgment diagram. The method can solve the problems that in the prior art, a method capable of accurately determining the specific position of embrittlement of the surface region of the casting blank is lacked, measures for solving surface cracks of the casting blank are difficult to be taken pertinently, and the like.
Description
Technical Field
The invention belongs to the technical field of continuous casting and rolling, and particularly relates to a judgment method for grain boundary embrittlement of a casting blank.
Background
For microalloy steel, steel with carbon content of 0.4-0.55, particularly steel containing elements such as Cr, mn and the like, and steel with high Al and N content, microcracks appear on the surface and under the skin in the process of a lower cooling bed, or microcracks appear on the casting blank and under the skin under the condition of a hot delivery process, the appearance of the cracks is fine and basically occur along grain boundaries, and analysis shows that precipitates such as nitrides such as aluminum nitride, boron nitride and the like and carbonitrides can be separated out on the grain boundaries, so that the plasticity of the surface structure of the casting blank is seriously reduced, and the crack sensitivity is caused, and surface cracks appear due to overlarge surface thermal stress or mechanical stress (such as stress caused by bending, straightening or equipment misalignment) in the process of inserting line or heating or rolling in the later period, so that the treatment difficulty is brought.
At present, the production of crack sensitive steel grades such as microalloy steel and the like generally adopts slow cooling or even pit cooling, so that the production cost is higher due to factors such as production period, heat loss, long heating time and the like. The surface quenching technology can also be adopted to completely solve the occurrence of surface cracks in a mechanism way.
No matter what measures are taken to solve the problem of surface cracks, the specific position of embrittlement of the surface region of the casting blank needs to be accurately found to achieve the goal, the control precision of all measures is improved, and the adverse effect caused by the implementation time of the measures is avoided. However, a method capable of accurately determining a specific position where embrittlement occurs in the surface region of a cast slab is lacking.
Disclosure of Invention
In view of the above problems, the present invention aims to provide a method for determining embrittlement of grain boundaries of an ingot, so as to solve the problems that in the prior art, a method capable of accurately determining a specific position of embrittlement of a surface region of an ingot is lacked, measures for solving surface cracks of the ingot are difficult to be taken in a targeted manner, and the formation of surface cracks of the ingot due to embrittlement of the surface region of the ingot is difficult to avoid.
The invention provides a method for judging grain boundary embrittlement of a casting blank, which comprises the following steps:
drawing a temperature change curve of the continuous casting billet in the process from continuous casting to hot delivery by taking an optional point on the section of the casting billet vertical to the billet drawing direction as a specific point;
acquiring a position corresponding to the characteristic temperature from the temperature change curve, and taking the position as a starting position of the transition of the specific point;
corresponding the starting position of the transformation of the specific point to the 0 moment of the supercooling austenite isothermal transformation TTT curve to obtain a grain boundary embrittlement judgment diagram;
and determining the position of the grain boundary embrittlement of the specific point in the drawing direction according to the intersection point position of the temperature change curve and the supercooling austenite isothermal transformation (TTT) curve in the grain boundary embrittlement judgment diagram.
In addition, it is preferable that the drawing of the temperature change curve at a certain point in the process from continuous casting to hot delivery, with a point selected from a cross section of the cast slab in a direction opposite to the direction of billet withdrawal as the certain point, includes:
acquiring the position change and temperature change information of the specific point from the temperature change information in the process from continuous casting to hot conveying;
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 position of the casting blank section, which is positioned at the liquid level of the crystallizer, as an origin, 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 in the throwing process as an ordinate.
In addition, it is preferable that the characteristic temperature is an A3 temperature.
Preferably, the step of obtaining a grain boundary embrittlement judgment map by associating the start position of the transformation of the specific point with a time point 0 of the supercooled austenite isothermal transformation TTT curve 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 specific point is corresponding to the 0 moment of the supercooling austenite isothermal transformation TTT curve, drawing the temperature change curve after the starting position of the specific point and the supercooling austenite isothermal transformation TTT curve in the same graph to obtain a grain boundary embrittlement judgment 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 transition of the specific point, and V is the drawing speed.
Preferably, before determining a position of grain boundary embrittlement of the specific point in the direction of drawing from a position of an intersection of the temperature change curve and the supercooled austenite isothermal transformation TTT curve in the grain boundary embrittlement judgment map, the method further includes:
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;
and judging whether the grain boundary embrittlement of the specific point occurs in the drawing direction or not according to the grain boundary embrittlement judgment rule of the steel grade and the grain boundary embrittlement time.
Preferably, the steel grade grain boundary embrittlement judgment rule includes:
when the grain boundary embrittlement time is less than the grain boundary embrittlement standard time, the grain boundary embrittlement does not exist in the casting blank structure in the drawing direction of the specific point;
and when the grain boundary embrittlement time is more than or equal to the grain boundary embrittlement standard time, the casting blank structure in the drawing direction of the specific point has grain boundary embrittlement.
Preferably, the standard time for grain boundary embrittlement is set to 1.5 to 6min depending on the steel type.
Preferably, the determining, from a position of an intersection of the temperature change curve and the supercooled austenite isothermal transformation TTT curve in the grain boundary embrittlement judgment map, a position of grain boundary embrittlement in the drawing direction of the specific point includes:
setting the time corresponding to the intersection point of the ferrite precipitation starting curve and the temperature change curve to the time when the standard grain boundary embrittlement time is reached as the starting time of grain boundary embrittlement;
and determining the position of the grain boundary embrittlement of the specific point in the billet drawing direction in the processes from continuous casting to hot delivery according to the starting time of the grain boundary embrittlement by a grain boundary embrittlement position calculation formula.
In addition, preferably, the calculation formula of the grain boundary embrittlement position is:
M＝S1+t×V；
where M is the position of the specific point of grain boundary embrittlement during the process from continuous casting to hot delivery, S1 is the starting position of transformation at the specific point, t is the standard time of grain boundary embrittlement, and V is the speed of drawing.
According to the technical scheme, the judgment method for the embrittlement of the grain boundary of the casting blank provided by the invention is characterized in that a point which is selected from the section of the casting blank vertical to the blank drawing direction is taken as a specific point, a temperature change curve of the point in the process from continuous casting to hot delivery is drawn, the starting position of the transformation of the specific point is found through the characteristic temperature, and then the starting position of the transformation of the specific point corresponds to the 0 moment of a TTT curve of the isothermal transformation of supercooled austenite, so that a grain boundary embrittlement judgment diagram is obtained; and determining the position of the intersection point of the supercooling austenite isothermal transformation TTT curve and the temperature change curve in the drawing through grain boundary embrittlement so as to determine the grain boundary embrittlement position of the specific point in the drawing direction. The main mechanism of grain boundary embrittlement is that in the austenite decomposition process, enough ferrite forms a membranous structure on a grain boundary to cause the grain boundary to be embrittled, and fine hard nuclear particles such as carbide, carbide and carbonitride precipitated on the austenite grain boundary can intensify the grain boundary embrittlement effect brought by the ferritic membranous structure; the method can accurately judge and predict the opportunity of embrittlement at any position on the casting blank, thereby providing a basis for a process for solving embrittlement cracks of the grain boundary, achieving a goal, and determining the specific position of the casting blank, at which the grain boundary embrittlement occurs in the whole process flow, at any position within a certain depth from the center of the surface.
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 flow chart of a method for judging grain boundary embrittlement of a casting blank according to an embodiment of the invention;
FIG. 2 is a graph showing temperature change trends at two specific points of 1mm and 10mm from the surface of a cast slab in a cross section of the cast slab in a continuous casting to hot delivery process according to example 1 of the present invention;
FIG. 3 is a temperature change trend graph showing temperature changes with time at two specific points of 1mm and 10mm from the surface of a cast slab on the cross section of the cast slab in the continuous casting to hot delivery process according to example 1 of the present invention;
FIG. 4 is a view showing the determination of the transition start position at two specific points of 1mm and 10mm 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 judgment of grain boundary embrittlement at two specific points of 1mm and 10mm from the surface of a cast slab on the cross section of the cast slab according to example 1 of the present invention;
FIG. 6 is a diagram showing determination of grain boundary embrittlement positions at two specific points of 1mm and 10mm from the surface of a cast slab on the cross section of the cast slab in example 1 of 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 the existing technology is lack of a method capable of accurately determining the specific position of embrittlement of the surface region of a casting blank, and the measures for solving the surface crack of the casting blank are difficult to be taken pertinently, so that the problems that the surface crack of the casting blank is formed due to the embrittlement of the surface region of the casting blank and the like are difficult to avoid, the judgment method for embrittlement of the grain boundary of the casting blank is 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 judging grain boundary embrittlement of an ingot, fig. 1 shows a flow of a method for judging grain boundary embrittlement of an ingot according to an embodiment of the present invention.
As shown in fig. 1, the method for judging grain boundary embrittlement of a casting blank provided by the invention comprises the following steps:
s1, drawing a temperature change curve of the continuous casting billet in the process from continuous casting to hot delivery by taking any point on a section of the casting billet vertical to the billet drawing direction as a specific point.
Specifically, a point is selected from a section of the cast slab perpendicular to the direction of drawing as a specific point, the specific point is arbitrarily selected, and a temperature change curve of the specific point in the processes from continuous casting to hot delivery is drawn.
Wherein, a temperature change curve of a certain point in the process from continuous casting to hot delivery is drawn by taking any one point on the section of the casting blank opposite to the casting blank drawing direction as the certain point, and the temperature change curve comprises the following steps:
acquiring the position change and temperature change information of a specific point from the temperature change information in the process from continuous casting to hot conveying;
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 position of the section of the casting blank, which is positioned at the liquid level of the crystallizer, as an origin, taking the distance from the specific point along the casting direction to the liquid level of the crystallizer as an abscissa and taking the temperature change of the specific point in the casting process as an ordinate.
The position of the section of the casting blank on the liquid level of the crystallizer is taken as an origin, so that the temperature change curve of a specific point and the subsequent determination of the grain boundary embrittlement position are convenient to draw.
And S2, acquiring a position corresponding to the characteristic temperature from the temperature change curve, and taking the position as a starting position of the transition of the specific point.
Specifically, the characteristic temperature is a characteristic temperature of the steel grade during the transformation of the steel grade, and may preferably be a starting temperature of austenite transformation. The characteristic temperature is previously obtained according to the steel grade.
Among them, the characteristic temperature is preferably an A3 temperature, but is not limited to the A3 temperature.
And S3, corresponding the starting position of the transformation of the specific point to the 0 moment of the supercooling austenite isothermal transformation TTT curve to obtain a grain boundary embrittlement judgment map.
Specifically, the amount of ferrite precipitated on the cast slab depends on the ferrite precipitation time before pearlite is formed, and whether grain boundary embrittlement occurs can be accurately determined by the precipitation time, and therefore, the point of intersection between the ferrite precipitation starting curve and the pearlite precipitation starting curve in the super-cooled austenite isothermal transformation TTT curve and the temperature change curve after the starting point of transformation of the specific point is the key for determining whether grain boundary embrittlement exists in the cast slab structure in the billet drawing direction of the specific point, and therefore, the starting point of transformation of the specific point is made to correspond to the 0 th time of the super-cooled austenite isothermal transformation TTT curve, and both are plotted in the same graph, thereby obtaining a grain boundary embrittlement determination graph.
Wherein, the step of corresponding the starting position of the transformation of the specific point to the 0 moment of the TTT curve of the super-cooled austenite isothermal transformation to obtain a judgment diagram of the grain boundary embrittlement comprises the following steps:
converting a position abscissa in the temperature change curve into a time abscissa by a time coordinate conversion formula;
and (3) after the time abscissa of the starting position of the specific point for the transformation corresponds to the 0 moment of the supercooling austenite isothermal transformation TTT curve, drawing the temperature change curve after the starting position of the specific point for the transformation and the supercooling austenite isothermal transformation TTT curve in the same graph to obtain a grain boundary embrittlement judgment graph.
Since the abscissa of the temperature change curve of a specific point is a position (distance) coordinate, it is necessary to convert the abscissa of the position thereof into a time abscissa, the abscissa of the temperature change curve is easily converted from the position abscissa into the time abscissa by a time coordinate conversion formula based on the start position of the transition of the specific point, the position abscissa and the drawing speed, and then the time abscissa of the start position of the transition of the specific point is plotted in the same graph after corresponding to the time 0 of the super-cooled austenite isothermal transition TTT curve, thereby obtaining a grain boundary embrittlement judgment 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 transition of the specific point, and V is the drawing speed.
And S4, determining the position of the grain boundary embrittlement of the specific point in the drawing direction according to the intersection point position of the temperature change curve and the supercooling austenite isothermal transformation (TTT) curve in the grain boundary embrittlement judgment diagram.
Specifically, attention is mainly paid to the intersection points of the ferrite starting precipitation curve and the pearlite starting precipitation curve with the temperature change curve in the supercooled austenite isothermal transformation TTT curve, respectively, and since the amount of ferrite precipitation on an ingot depends on the ferrite precipitation time before pearlite is formed, whether grain boundary embrittlement occurs or not can be accurately determined by the precipitation time, and if grain boundary embrittlement occurs, the position of grain boundary embrittlement needs to be determined.
Before determining the position of grain boundary embrittlement of a specific point in a drawing direction according to the intersection point position of a temperature change curve and the supercooling austenite isothermal transformation (TTT) curve in a grain boundary embrittlement judgment diagram, the method further 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;
and judging whether the grain boundary embrittlement occurs at the specific point in the drawing direction or not according to the grain boundary embrittlement judgment rule of the steel grade and the grain boundary embrittlement time.
Wherein the judgment rule for the embrittlement of the grain boundary of the steel grade comprises the following steps:
when the grain boundary embrittlement time is less than the grain boundary embrittlement standard time, the grain boundary embrittlement does not exist in the casting blank structure in the drawing direction of the specific point;
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 casting blank structure in the drawing direction of the specific point.
Wherein the standard time of grain boundary embrittlement is set according to steel grades and is 1.5-6 min. The standard time for grain boundary embrittlement can be directly obtained according to the prior experience or detection.
Wherein, according to the intersection point position of the temperature change curve and the supercooling austenite isothermal transformation TTT curve in the grain boundary embrittlement judgment diagram, the step of determining the grain boundary embrittlement position of the specific point in the drawing direction comprises the following steps:
taking the time corresponding to the intersection point of the ferrite precipitation starting curve and the temperature change curve as the starting time of the grain boundary embrittlement, wherein the time is reached after the standard time of the grain boundary embrittlement;
and determining the position of the grain boundary embrittlement of the specific point in the billet drawing direction in the processes from continuous casting to hot delivery according to the starting time of the grain boundary embrittlement by a grain boundary embrittlement position calculation formula.
Wherein, the calculation formula of the embrittlement position of the grain boundary is as follows:
M＝S1+t×V；
where M is the position of the specific point of grain boundary embrittlement during the process from continuous casting to hot delivery, S1 is the starting position of transformation at the specific point, t is the standard time of grain boundary embrittlement, and V is the speed of drawing.
In order to better explain the method for judging the grain boundary embrittlement of the casting blank provided by the invention, the following specific examples are provided as follows:
example 1
In order to illustrate the method for judging the grain boundary embrittlement of the casting blank provided by the embodiment 1 of the invention, fig. 2 shows the temperature variation trend of two specific points, namely 1mm and 10mm away from the surface of the casting blank, on the cross section of the casting blank in the processes from continuous casting to hot delivery according to the embodiment 1 of the invention; FIG. 3 shows the temperature change tendency of the temperature change with time at two specific points of 1mm and 10mm from the surface of a cast slab on the cross section of the cast slab in the continuous casting to hot delivery process according to example 1 of the present invention; FIG. 4 shows the starting positions of transition at two specific points of 1mm and 10mm 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 shows the judgment of grain boundary embrittlement at two specific points of 1mm and 10mm from the surface of a cast slab on the cross section of the cast slab in example 1 according to the present invention; FIG. 6 shows grain boundary embrittlement positions at two specific points of 1mm and 10mm from the surface of a cast slab on the cross section of the cast slab in example 1 according to the present invention.
As shown in the figures 2 to 6 together, the judgment method for the grain boundary embrittlement of the casting blank provided by the invention is adopted to judge the grain boundary embrittlement and determine the position of the grain boundary embrittlement in the drawing direction at two specific points 1mm and 10mm away from the surface of the casting blank on the section of the casting blank.
The method mainly comprises the steps of continuously casting 180mm small square billets in a certain steel mill, finding that microcracks appear on the surface and under the surface of the casting blank after steel type 40Cr passes through an overturning cooling bed and is discharged, observing crack structures under a metallographic phase, finding that cracks crack along a grain boundary, and obviously leading to grain boundary embrittlement.
The casting machine 40Cr production pulling speed is 1.4m/min, the cutting position is 25m, the casting blank can enter a turnover cooling bed after passing through a cutting roller way and a steel pushing process after being cut (similarly, if the casting blank is directly hot-fed, the casting blank can pass through the cutting roller way, the steel pushing process, a loosening roller way and other process flows after being cut), in order to show the method provided by the invention more clearly, the situation that the casting blank is completely a turnover cooling bed area after being cut at the 25m position is simplified.
The present example shows the judgment of the embrittlement of the grain boundary from the temperature change of the cast slab at two specific points of 1mm and 10mm from the surface of the cast slab. Obviously, the time of the casting blank in the turnover cooling bed area in the embodiment can be converted into a coordinate with the distance as an X axis through the pulling speed, so that the casting blank and the casting blank in the casting flow keep the same coordinate, as shown in FIG. 2; meanwhile, the temperature coordinate of the casting blank in the casting flow can be converted into a time coordinate through the pulling speed, so that the time sequence of the temperature coordinate is the same as that of the turning cooling bed area, the time coordinate is the same, and the temperature change curve is shown in figure 3.
The characteristic temperature of A3 on the TTT curve of the 40Cr is 778 ℃. Taking the distance coordinates of fig. 1 as an example, the starting positions of transition of two specific points can be found according to the characteristic temperature A3, as shown in fig. 4, it can be seen that, the starting position of transition corresponding to a casting slab at a specific point 1mm away from the surface is located at 29.736m away from the mold liquid surface, and the starting position of transition corresponding to a casting slab at a specific point 10mm away from the surface is located at 32.016m away from the mold liquid surface.
The portions after the transition start positions of the slab temperatures at two specific points 1mm and 10mm from the surface are plotted into the TTT curve of the 40Cr steel grade of this example, as shown in fig. 5, in which the transition start positions correspond to the 0 th time of the TTT curve, while the slab temperatures at two specific points 1mm and 10mm from the surface are partially converted into time coordinates after the transition start positions, i.e., (position-transition start position)/pulling rate.
As can be seen from fig. 5, the intersection points of the temperature variation curves of the casting slab at the positions 1mm and 10mm from the surface and the ferrite precipitation starting curve are substantially the same, as shown by point a in the figure, the intersection points of the temperature variation curves of the casting slab at the positions 1mm and 10mm from the surface and the pearlite precipitation starting curve are completely the same, as shown by point B in the figure, the time from point a to point B is the time from the point 1mm from the surface and the point 10mm from the ferrite precipitation starting curve to the pearlite precipitation starting curve, which is the grain boundary embrittlement time of the present invention, the point corresponding time to point a is 5.9min, and the point corresponding time to point B is 9.7min, so the grain boundary embrittlement time of the casting slab at the positions 1mm and 10mm from the surface is (9.7 min-5.9 min) =3.8min in this example.
The standard time of grain boundary embrittlement of the steel under corresponding working conditions is about 2.5min, and obviously, the standard time of grain boundary embrittlement obtained from the graph 5 is 3.8min and is obviously longer than the standard time of grain boundary embrittlement, so that according to the existing working conditions, casting blanks at positions 1mm and 10mm away from the surface are subjected to grain boundary embrittlement in the subsequent turnover cooling bed process, and cracks are possibly caused.
The grain boundary embrittlement time determined by the figure 5 is known to cause grain boundary embrittlement, and a specific embrittlement time or position is determined, namely the time when the temperature change curve passes through the standard time of grain boundary embrittlement from the boundary of the ferrite starting precipitation curve to the rear, as shown in the figure 6, namely the time point A of the casting blank temperature change curve at the positions 1mm and 10mm away from the surface from the boundary of the ferrite starting precipitation curve to the rear C of the standard time of grain boundary embrittlement after 2.5min, and the corresponding time point is 8.4min, namely the starting time of the grain boundary embrittlement of the casting blank.
As can be seen from fig. 6, a point a of the temperature curve can be found on the TTT, and then a point C time is found, and if the point B time is greater than the point C time, grain boundary embrittlement occurs in the casting blank corresponding to the temperature curve; and if the time of the point B is less than the time of the point C, the casting blank corresponding to the temperature curve does not have grain boundary embrittlement.
From the time point C of the starting time of the grain boundary embrittlement during continuous casting to the offline or during the whole hot delivery process, the specific precise position of the grain boundary embrittlement during casting at the 1mm and 10mm positions from the surface can be found, and it is obvious that although the time point C of the grain boundary embrittlement during casting at the 1mm and 10mm positions from the surface is 8.4min, the specific precise positions of the grain boundary embrittlement during casting at the 1mm and 10mm positions from the surface are different because the starting positions of the transformation (shown in FIG. 4). The concrete precise embrittlement position of the casting blank crystallizer at a position 1mm away from the surface is a transition starting position 29.736m + embrittlement time 8.4min multiplied by a pulling speed 1.4m/min, namely a position 41.496m in the whole process flow; the specific precise embrittlement position of the casting blank crystallizer at a position 1mm away from the surface is a transition starting position 32.016m + embrittlement time 8.4min multiplied by a pulling speed of 1.4m/min, namely a position 43.776m in the whole process flow.
According to the method for judging the grain boundary embrittlement of the casting blank, provided by the invention, a temperature change curve of the casting blank in the process from continuous casting to hot delivery is drawn by taking any point on the section of the casting blank perpendicular to the direction of drawing as a specific point, the starting position of the transformation of the specific point is found through the characteristic temperature, and then the starting position of the transformation of the specific point corresponds to the 0 moment of the isothermal transformation TTT curve of the supercooled austenite, so that a grain boundary embrittlement judgment graph is obtained; and judging the intersection point position of the supercooling austenite isothermal transformation TTT curve and the temperature change curve in the drawing through grain boundary embrittlement, thereby determining the grain boundary embrittlement position of the specific point in the drawing direction. The main mechanism of grain boundary embrittlement is that in the austenite decomposition process, enough ferrite is formed on a grain boundary to form a membranous structure, so that the grain boundary is embrittled, and fine hard nuclear particles such as carbide, carbonitride and the like precipitated on the austenite grain boundary can aggravate the grain boundary embrittlement effect brought by the ferritic membranous structure; the method can accurately judge and predict the opportunity of embrittlement at any position on the casting blank, thereby providing a basis for a process for solving embrittlement cracks of the grain boundary, achieving a goal, and determining the specific position of the casting blank, at which the grain boundary embrittlement occurs in the whole process flow, at any position within a certain depth from the center of the surface.
The judgment method of grain boundary embrittlement of a cast slab proposed according to the present invention is described above by way of example with reference to the accompanying drawings. However, it will be understood by those skilled in the art that various modifications may be made to the method for judging grain boundary embrittlement 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 (8)
1. A judgment method for embrittlement of casting blank grain boundaries is characterized by comprising the following steps:
drawing a temperature change curve of the continuous casting billet in the process from continuous casting to hot delivery by taking an optional point on the section of the casting billet vertical to the billet drawing direction as a specific point;
acquiring a position corresponding to the characteristic temperature from the temperature change curve, and taking the position as a starting position of the transition of the specific point;
corresponding the starting position of the transformation of the specific point to the 0 moment of the supercooling austenite isothermal transformation TTT curve to obtain a grain boundary embrittlement judgment diagram; 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 specific point for the transformation corresponds to the 0 moment of the supercooling austenite isothermal transformation TTT curve, drawing a temperature change curve after the starting position of the specific point for the transformation and the supercooling austenite isothermal transformation TTT curve in the same graph to obtain a grain boundary embrittlement judgment graph;
determining the position of grain boundary embrittlement of the specific point in the throwing direction according to the intersection point position of the temperature change curve and the supercooling austenite isothermal transformation (TTT) curve in the grain boundary embrittlement judgment diagram; wherein, before determining the position of the grain boundary embrittlement of the specific point in the drawing direction, the method further comprises the following steps:
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;
and judging whether the grain boundary embrittlement occurs at the specific point in the drawing direction or not according to the grain boundary embrittlement judgment rule of the steel grade and the grain boundary embrittlement time.
2. The method for determining grain boundary embrittlement of a cast slab according to claim 1, wherein the step of plotting a temperature change curve of a specific point in a process from continuous casting to hot delivery, with an optional point on a cross section of the cast slab opposite to a direction of drawing as the specific point, comprises:
acquiring the position change and temperature change information of the specific point from the temperature change information in the process from continuous casting to hot conveying;
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 position of the casting blank section, which is positioned at the liquid level of the crystallizer, as an origin, 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 in the throwing process as an ordinate.
3. The method for determining grain boundary embrittlement of cast slab according to claim 1, wherein the characteristic temperature is A3 temperature.
4. The method for judging grain boundary embrittlement of casting slabs according to claim 1, wherein the time coordinate transformation 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 transition of the specific point, and V is the drawing speed.
5. The method for judging grain boundary embrittlement of cast slab according to claim 1, wherein the steel grade grain boundary embrittlement judgment rule includes:
when the grain boundary embrittlement time is less than the grain boundary embrittlement standard time, the grain boundary embrittlement does not exist in the casting blank structure in the drawing direction of the specific point;
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 casting blank structure in the drawing direction of the specific point.
6. The method for judging the grain boundary embrittlement of the casting slab according to claim 5, wherein the standard time for the grain boundary embrittlement is set to be 1.5-6 min according to the steel grade.
7. The method for judging the grain boundary embrittlement of the casting blank according to claim 1, wherein the step of determining the position of the grain boundary embrittlement of the specific point in the drawing direction according to the intersection point position of the temperature change curve and the super-cooled austenite isothermal transformation (TTT) curve in the grain boundary embrittlement judgment map comprises:
setting the time corresponding to the intersection point of the ferrite precipitation starting curve and the temperature change curve as the starting time of grain boundary embrittlement after the standard time of grain boundary embrittlement;
and determining the position of the grain boundary embrittlement of the specific point in the billet drawing direction in the process from continuous casting to hot delivery according to the starting time of the grain boundary embrittlement by using a grain boundary embrittlement position calculation formula.
8. The method for judging the grain boundary embrittlement of the casting blank according to claim 7, wherein the calculation formula of the grain boundary embrittlement position is as follows:
M = S1+t×V；
where M is the position of the specific point of grain boundary embrittlement during the process from continuous casting to hot delivery, S1 is the starting position of transformation at the specific point, t is the standard time of grain boundary embrittlement, and V is the speed of drawing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110308000.8A CN113176292B (en) | 2021-03-23 | 2021-03-23 | Judgment method for grain boundary embrittlement of casting blank |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110308000.8A CN113176292B (en) | 2021-03-23 | 2021-03-23 | Judgment method for grain boundary embrittlement of casting blank |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN113176292A CN113176292A (en) | 2021-07-27 |
| CN113176292B true CN113176292B (en) | 2023-03-17 |
Family
ID=76922295
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202110308000.8A Active CN113176292B (en) | 2021-03-23 | 2021-03-23 | Judgment method for grain boundary embrittlement of casting blank |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN113176292B (en) |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1322257A (en) * | 1998-08-12 | 2001-11-14 | 斯瓦戈洛克公司 | Selective case hardening processes at low temperature |
| JP2003343981A (en) * | 2002-05-29 | 2003-12-03 | Koyo Thermo System Kk | Continuous heat treatment furnace and heat treatment method |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5910846B2 (en) * | 1979-02-16 | 1984-03-12 | 新日本製鐵株式会社 | High temperature slab direct rolling method |
| JPH05223726A (en) * | 1992-02-14 | 1993-08-31 | Toshiba Corp | Method for detecting secular embrittlement |
| JPH08283895A (en) * | 1995-04-13 | 1996-10-29 | Nippon Steel Corp | Method for preventing surface defect at edging of cast slab |
| CN102560047B (en) * | 2012-02-29 | 2013-03-20 | 首钢总公司 | Method for controlling grain-boundary embrittlement of high-carbon steel coil rods |
| CN107641683B (en) * | 2017-08-22 | 2019-04-05 | 中冶连铸技术工程有限责任公司 | A kind of method of continuous casting and rolling quenching technological design |
| CN107695313B (en) * | 2017-08-22 | 2019-10-11 | 中冶连铸技术工程有限责任公司 | A kind of method and arrangement of nozzles method solving slab Corner Crackss |
-
2021
- 2021-03-23 CN CN202110308000.8A patent/CN113176292B/en active Active
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1322257A (en) * | 1998-08-12 | 2001-11-14 | 斯瓦戈洛克公司 | Selective case hardening processes at low temperature |
| JP2003343981A (en) * | 2002-05-29 | 2003-12-03 | Koyo Thermo System Kk | Continuous heat treatment furnace and heat treatment method |
Non-Patent Citations (7)
| Title |
|---|
| Tomohito TANAKA* etal.Mechanism of Grain Boundary Embrittlement in Fe–Ni–S Alloys .2013,第53卷(第7期),第1289–1291页. * |
| 侯建德,傅智敏,黄金印.物质热稳定性评估方法研究.(第02期),全文. * |
| 吴乾章,陈庆汉,田万春.晶体生长与品质鉴定.(第01期),全文. * |
| 周晨光,周镇国,邵扬道.感应加热和连续冷却对U71Mn轨钢组织和性能的影响.(第01期),全文. * |
| 常桂华;曹亚丹;吕志升;修国涛;张维维;.连铸坯的高温力学性能分析.(第06期),全文. * |
| 杨慧贤 等.压力容器用钢表面裂纹分析与控制.2017,第42卷(第第42卷期),第177-190页. * |
| 汪学瑶.当代合金结构钢的发展.(第06期),全文. * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN113176292A (en) | 2021-07-27 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN102492894B (en) | The corrosion-resistant martensitic steel of high-dimensional stability and steel structure material preparation method thereof | |
| CN102363859B (en) | Method for producing wear-resisting steel plate | |
| CA2804320C (en) | Austenite-ferrite stainless steel of improved machinability | |
| CN103769424B (en) | The control method of steekle mill surface of steel plate red scale | |
| CN105925894B (en) | A kind of high-strength anti-lamellar tearing Q500D Z35 Hydropower Units steel plates of super thick and its manufacture method | |
| CN104046914B (en) | A kind of non-hardened and tempered steel and production technique thereof | |
| CN103556069B (en) | A kind of gas cylinder seamless large-diameter pipes and manufacture method thereof | |
| CN101927432B (en) | Manufacturing method of high-manganese strip steel with high strength and plasticity | |
| CN102168227B (en) | Super-thick quenched-tempered steel plate with 60kg-grade tensile strength and production method of the super-thick quenched-tempered steel plate | |
| GB1562104A (en) | Production of seamless steel pipe | |
| CN105586537A (en) | High-strength steel plate for ocean engineering and production method thereof | |
| CN107641683B (en) | A kind of method of continuous casting and rolling quenching technological design | |
| CN102337478A (en) | Excellent 100 kg-grade quenched and tempered steel plate with strong toughness and plasticity, and manufacturing method thereof | |
| CN104726769A (en) | Maximum-thickness S355G10+N steel plate for ocean platform and production method of steel plate | |
| CN103882346B (en) | R4 level mooring chain steel and preparation method thereof | |
| CN105648324A (en) | Large-thickness rack steel plate and production method thereof | |
| CN103556055A (en) | Hot-rolled H-shaped steel for marine natural gas extraction platform structure and production method of hot-rolled H-shaped steel | |
| CN113174467B (en) | Method for predicting casting blank quenching structure and method for making casting blank quenching process | |
| CN112981232B (en) | 12Cr2Mo1VR steel plate with low compression ratio and high flaw detection quality requirement for continuous casting billet finished product and production process thereof | |
| CN103212588B (en) | Method of reducing defect that slag is clamped under surface when carbon manganese steel is rolled in a hot mode | |
| CN101333629A (en) | Method for producing medium-high-carbon high-strength steel based on sheet bar technology | |
| CN113176292B (en) | Judgment method for grain boundary embrittlement of casting blank | |
| JP2002086252A (en) | Continous casting method | |
| CN106811679A (en) | A kind of method for eliminating high carbon steel billet surface imperfection oscillation mark | |
| CN105714187B (en) | Production method of 30CrMnSiA hot rolled steel strip |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |