CN115401178A - Screw-down process determination method for improving internal quality of gear steel - Google Patents
Screw-down process determination method for improving internal quality of gear steel Download PDFInfo
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Abstract
The invention discloses a reduction process determination method for improving the internal quality of gear steel, which comprises the following steps: 1) Collecting field technical parameters and steel type parameters, and establishing a casting blank solidification heat transfer model; 2) Measuring the temperature of the site temperature, and verifying the casting blank solidification heat transfer model to ensure that the temperature difference between the site temperature and the casting blank solidification heat transfer model does not exceed a set value; 3) Calculating the appearance of a casting blank shell of a casting blank after the solidification tail end is mechanically reduced, applying the speed distribution of the casting blank after the solidification tail end is mechanically reduced to the section of the casting blank to obtain the solute transfer behavior at the solidification tail end of the casting blank, obtaining the reduction and a reduction interval through the change of the solute transfer behavior, comparing the obtained reduction interval with the calculation result of a casting blank solidification heat transfer model, and determining the final reduction interval; 4) Calculating the surface reduction of the steel grade; 5) And judging whether the surface reduction meets the condition, if so, entering the step 6), otherwise, returning to the step 4). The invention designs proper reduction amount and improves the internal quality of the casting blank.
Description
Technical Field
The invention relates to a steel continuous casting technology, in particular to a reduction process determination method for improving the internal quality of gear steel.
Background
In the process of solidification of the metal material, macro-micro segregation can be caused by selective crystallization, dendrite bridging, solidification shrinkage and the like, and the quality of the casting blank and the interior of a subsequent rolled material is seriously influenced by the loosening of a central shrinkage cavity. Macrosegregation will cause faults, material failure, and large amounts of carbides to aggregate to form cracks. The microcosmic segregation will cause banded structures in the subsequent rolling process, so that the materials have different mechanical properties in all directions, namely the properties along the direction of the banded structures are obviously superior to those in the vertical direction, and the plasticity, the toughness and the reduction of area of the steel are reduced. The central shrinkage and loosening can form cracks in the subsequent rolling process, and the product quality is seriously damaged. Therefore, the improvement of the internal quality of the casting blank has important significance.
Methods for improving the internal quality of a casting blank are researched more, wherein the reduction is carried out in the continuous casting process, namely, a certain reduction is carried out on each withdrawal and straightening unit of the casting blank in the continuous casting process, and a certain pressure is generated to compensate the solidification and shrinkage of the casting blank so as to achieve the purpose of improving the internal quality of the casting blank. However, only reasonable reduction interval and reduction can improve the internal quality of the casting blank, and unreasonable reduction parameters can only make the quality of the casting blank more serious.
In the existing patent application, for example, chinese patent CN101658911B discloses an on-line control method for bloom continuous casting dynamic soft reduction, which calculates the casting blank reduction by using the liquid core reduction and the reduction efficiency, and adjusts the roll gap. However, the patent has no thermodynamic coupling simulation calculation, and the reduction amount has an error.
For example, chinese patent CN105108096B discloses a method for determining dynamic light reduction of heavy rail steel bloom continuous casting, which determines the reduction by determining field process parameters, physical parameters, and thermodynamic properties of materials. However, the method is only suitable for heavy rail steel, and the surface temperature of the casting blank is not measured in the process parameters and the field process parameters are not corrected.
For example, chinese patent CN109396368B discloses a method for improving the internal quality of a high-carbon steel bloom continuous casting billet, which comprises the steps of firstly restricting the total rolling reduction to 10-25 mm, and distributing the rolling reduction by adopting a distribution coefficient mode. However, this patent does not consider the transfer efficiency of the reduction amount to the inside of the cast slab.
For example, chinese patent CN110523942A discloses a control method for improving internal defects of a bloom of high-carbon chromium bearing steel, which directly distributes rolling reduction under different solid phase ratios and may lack rationality.
For example, chinese patent CN110802207A discloses a continuous casting billet combined reduction method, which establishes a continuous casting billet solidification model to determine a solidification end point and a central solid phase rate, determines a critical solid phase rate formed by macrosegregation through a multiphase solidification coupling model, and predicts a critical solid phase rate of a position where central porosity starts to form through a solidification shrinkage analysis model, thereby determining a reduction interval and further determining an optimal reduction. However, this patent does not consider the influence of cracks which may occur when the reduction is too large on the quality of the cast slab.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a reduction process determination method for improving the internal quality of gear steel, which designs a proper reduction amount to improve the internal quality of a casting blank.
In order to achieve the purpose, the invention adopts the following technical scheme:
a reduction process determination method for improving the internal quality of gear steel comprises the following steps:
1) Collecting field technical parameters and steel type parameters, and establishing a casting blank solidification heat transfer model;
2) Measuring the site temperature, and verifying the casting blank solidification heat transfer model, so that the temperature difference between the site temperature and the casting blank solidification heat transfer model does not exceed a set value;
3) Calculating the appearance of a casting blank shell of a casting blank after solidification tail end mechanical reduction, applying the speed distribution of the casting blank after the solidification tail end mechanical reduction on the section of the casting blank to obtain the solute transfer behavior at the solidification tail end position of the casting blank, obtaining the reduction and a reduction interval through the change of the solute transfer behavior, comparing the obtained reduction interval with the calculation result of the casting blank solidification heat transfer model, and determining the final reduction interval;
4) Calculating the surface reduction of the steel grade;
5) Judging whether the surface reduction meets the condition, if so, entering a step 6), and if not, returning to the step 4);
6) The rolling reduction determination was completed.
Preferably, the field technical parameters and steel type parameters comprise a field common pulling speed range, a superheat degree range, continuous casting machine parameters, electromagnetic stirring parameters, equipment reduction capacity, crystallizer length, secondary cooling water amount and steel type components.
Preferably, the casting blank solidification heat transfer model calculates a solidification end point position, a central solid phase ratio and a surface temperature of the obtained casting blank.
Preferably, the set value in the step 2) is 50 ℃.
Preferably, the temperature measuring positions of the field temperature are as follows:
and (4) discharging the two cooling zones and more than half of the positions between the two withdrawal and straightening machines, and detecting the temperature of the wide surface and the narrow surface of the casting blank according to the on-site temperature measurement condition.
Preferably, the step 3) further comprises:
calculating the shape of a casting blank shell after the solidification tail end is mechanically reduced by utilizing a thermal/force coupling model, establishing a casting blank geometric model by using the shape of the casting blank shell, introducing the casting blank geometric model into a multi-phase solidification coupling calculation model, applying the speed distribution after the solidification tail end is mechanically reduced on the section of the casting blank, and further solving a mass, momentum, energy and solute transmission equation under a phase coupling method to obtain the solute transmission behavior at the solidification tail end position of the casting blank;
and comparing the reduction process of different solidification end machines, obtaining reduction and reduction intervals through the change of the solute transport behavior, and determining the final reduction interval through the solid phase rate obtained by the casting blank solidification heat transfer model.
Preferably, the solid fraction f at the starting point of the selected region of the reduction interval s Not less than 0.3, and f is before the solidification end point at the end position of the selected area of the pressing-down interval s ＝0.95。
Preferably, the step 4) further comprises:
calculating the deformation condition of the surface and the liquid core of the casting blank in the reduction process by the heat/force coupling die type to obtain reduction efficiency eta, and calculating the liquid core reduction and the surface reduction required by the steel in the reduction interval;
when the reduction interval is exceeded and the solidification region is reached, the reduction efficiency eta is not calculated any more, and the reduction is limited by the capacity of the on-site reduction equipment.
Preferably, in the step 5), the determination conditions are as follows:
a) The method meets the requirements of on-site production and equipment and cannot exceed the equipment capacity;
b) Calculating the minimum rolling reduction required by predicting segregation improvement by using a multiphase solidification coupling model, comparing the minimum rolling reduction with the surface rolling reduction, if the surface rolling reduction is within the minimum rolling reduction, conforming the surface rolling reduction, continuing to perform next judgment, and returning to the step 4) to redesign the surface rolling reduction if the surface rolling reduction is not within the minimum rolling reduction;
c) Comparing the maximum green pressing force required by each roller in the surface reduction with the green pressing force of the field equipment, if the maximum green pressing force is consistent with the field equipment, continuing to perform next judgment, and if the maximum green pressing force is not consistent with the field equipment, returning to the step 4) to redesign the surface reduction;
d) Comparing the surface reduction with the risk of the caused cracks, if no risk exists, conforming, and if at risk, redesigning or extending the surface reduction in the step c);
e) The steps a) to d) should be satisfied simultaneously, and the surface rolling reduction is ensured to be consistent under different drawing speeds.
Preferably, in the step b), the segregation improvement uses carbon as a research element, and the improvement standard is that the macrosegregation is less than or equal to 1.08; and/or
In the step c), the maximum green pressing force is designed to be calculated by a heat/force coupling model, and the green pressing force with the maximum rolling reduction is selected as comparison; and/or
In the step d), the condition of forward and backward extension is that the distance between the solidification end point and the extension roller does not exceed one withdrawal and straightening machine position.
After the reduction process determination method for improving the internal quality of the gear steel is adopted for production, the casting blank segregation of the gear steel is effectively controlled, the segregation grades all reach 1 grade and are superior to comparison samples (the 2 grade and the 1 grade respectively account for 50 percent), the production requirement is met, the rate of certified products of the casting blank is improved, the banded structure of a subsequent rolled material is obviously improved, and the smooth process is ensured. The method for determining the gear steel pressing process has the advantages that the pressing amount is accurate, the dynamic pressing position control is favorably realized, and the effect is obvious; and considering that the influence of cracks possibly generated when the reduction is too large on the quality of the casting blank has the characteristic of small implementation risk, and the method is an effective means for solving the problems of internal cracks, center segregation and center porosity of the casting blank.
Drawings
FIG. 1 is a schematic flow diagram of a method for determining the reduction process of the present invention;
FIG. 2 is a schematic diagram of a solidification heat transfer simulation temperature compared with an actual test temperature in an embodiment of a reduction process determination method according to the present invention;
FIG. 3 is a schematic diagram of the selection of the reduction interval in an embodiment of the method for determining the reduction process of the present invention;
FIG. 4 is a schematic view showing the effect of the reduction on macrosegregation in an example of the method for determining the reduction process of the present invention;
FIG. 5 is a schematic view of the minimum reduction at which each roller is at risk of cracking in an embodiment of the reduction process determination method of the present invention;
FIG. 6 is a schematic view showing the effect of improving the quality of a cast slab (cross section) in an example of the reduction process determining method of the present invention;
FIG. 7 is a schematic view showing the effect of improving the quality of a cast slab in an example of the method for determining a reduction process according to the present invention (longitudinal section).
Detailed Description
In order to better understand the technical solutions of the present invention, the following technical solutions are further described with reference to the accompanying drawings and examples.
Referring to fig. 1, the method for determining the pressing process for improving the internal quality of the gear steel provided by the invention comprises the following steps:
1) Collecting field technical parameters and steel grade parameters, establishing a casting blank solidification heat transfer model, and obtaining the solidification end point position, the central solid phase rate and the surface temperature of a casting blank;
the field technical parameters and steel type parameters comprise a field common pulling speed range, a superheat degree range, a continuous casting machine parameter, an electromagnetic stirring parameter, equipment screw-down capacity, crystallizer length, secondary cooling water amount, steel type components and the like.
2) Measuring the temperature of the site by using an infrared thermometer, and verifying the casting blank solidification heat transfer model in the step 1) to ensure that the temperature difference between the site temperature and the casting blank solidification heat transfer model is not more than 50 ℃;
the temperature measurement positions of the field temperature are as follows:
and (4) discharging the casting blank from more than half of the position between the second cooling area and each withdrawal and straightening machine, and detecting the temperature of the wide surface and the narrow surface of the casting blank according to the on-site temperature measurement condition.
3) Calculating the shape of a casting blank shell after mechanical reduction of a solidification tail end by utilizing a thermal/force coupling model, establishing a casting blank geometric model by using the shape of the casting blank shell, introducing the casting blank geometric model into a multi-phase solidification coupling calculation model, applying the speed distribution after mechanical reduction of the solidification tail end on the section of a casting blank, and further solving a mass, momentum, energy and solute transfer equation under a phase coupling method to obtain a solute transfer behavior at the position of the solidification tail end of the casting blank;
comparing the reduction process of different solidification end machines, obtaining reduction and a reduction interval through solute transfer behavior change, and comparing the obtained reduction interval with the solid phase rate obtained by a casting blank solidification heat transfer model to further determine a final (optimal) reduction interval;
solid fraction f at starting point of selected area in reduction interval s More than or equal to 0.3, and f is before the solidification end point at the end position of the selection area of the pressing-down interval s =0.95, and the pressing zone should cover the place where the liquid phase speed is faster.
4) Calculating the deformation condition of the surface of the casting blank and the liquid core in the reduction process by a heat/force coupling die to obtain reduction efficiency eta, and calculating the liquid core reduction and the surface reduction required by the steel in a reduction interval;
when the pressure exceeds the pressure reduction interval and reaches the solidification region, the pressure reduction efficiency eta is not calculated any more, the pressure reduction is limited by the capability of the on-site pressure reduction equipment, and the surface pressure reduction is recorded as a scheme A.
5) Scheme a should simultaneously satisfy the following conditions:
a) The method meets the requirements of on-site production and equipment, does not exceed the equipment capacity, and can reserve design allowance;
b) Calculating the minimum rolling reduction (marked as a scheme B) required by predicting segregation improvement by using a multiphase solidification coupling model, comparing the minimum rolling reduction with the scheme A, if the scheme A is within the scheme B, conforming the scheme A, continuing to perform the next judgment, and if the scheme A is not within the scheme B, returning to the step 4) to redesign the surface rolling reduction;
c) Comparing the maximum green pressing force required by each roller in the scheme A with the green pressing force of the field equipment, if the maximum green pressing force is consistent with the field equipment, continuing to perform next judgment, and if the maximum green pressing force is not consistent with the field equipment, returning to the step 4) to redesign the surface reduction;
d) Comparing the risk of the cracks in the scheme A with the risk of the cracks, if no risk exists, conforming, and if at risk, redesigning or extending the surface pressing amount in the step c);
e) The steps a) to d) should be satisfied simultaneously, and the surface rolling reduction is consistent under different pulling speeds.
In the step b), the segregation improvement takes carbon element as a research element, and the improvement standard is that the macrosegregation is less than or equal to 1.08; and/or
In the step c), the maximum green pressing force is designed to be calculated by a heat/force coupling model, and the green pressing force when the rolling reduction is maximum is selected as comparison; and/or
In the step d), the condition of forward and backward extension is that the distance between the solidification end point and the extension roller does not exceed one withdrawal and straightening machine position.
6) The rolling reduction determination is completed.
Examples
Taking a certain type of gear steel bloom as an example, the steel comprises the following components in percentage by weight: 0.18 to 0.22wt%, si:0.2 to 0.3wt%, mn:1.25 to 1.35wt%, P: 0to 0.15wt%, S:0.01 to 0.02wt percent. The casting superheat degree is 30 ℃, the drawing speed is 0.65-0.70 m/min, the section size is 320 multiplied by 425mm, and the secondary cooling water quantity adopts the common water quantity. The other processes are unchanged, and the reduction capable of improving the internal quality of the steel grade is determined, and the method comprises the following steps:
1) Establishing the steel grade solidification heat transfer model based on the field process to obtain parameters such as the solidification end point position, the central solid phase rate, the surface temperature and the like of the steel grade;
2) The combination of the temperature and the field temperature of the casting blank solidification heat transfer model shown in FIG. 2 shows that the difference between the calculated result and the field measured temperature is within a range, which indicates the accuracy of the calculated result;
3) And 3) obtaining the casting blank shell morphology of the casting blank after the solidification tail end mechanical reduction on the basis of the solidification heat transfer model in the step 2), establishing a casting blank geometric model by using the morphology, introducing the casting blank geometric model into a multi-phase solidification coupling calculation model, applying the speed distribution after the solidification tail end mechanical reduction on the casting blank section, and further solving a mass, momentum, energy and solute transmission equation under a phase coupling method to obtain the solute transmission behavior at the solidification tail end position of the casting blank. Obtaining the minimum rolling reduction and the optimum rolling reduction interval for segregation improvement, selecting the rolling reduction interval by combining the rolling reduction interval shown in figure 3, and selecting the rolling reduction interval as represented by a gray frame;
4) Calculating the liquid core reduction (see table 1 below), and calculating the reduction efficiency, the reduction efficiency (see table 2 below) and the surface reduction (see table 3 below) by using a reduction model;
TABLE 1 liquid core reduction distribution at different pulling speeds
TABLE 2 reduction efficiency distribution
TABLE 3 surface reduction distribution (protocol A)
5) Scheme a should simultaneously satisfy the following conditions:
a) Meets the requirements of on-site production and equipment. The rolling reduction is limited by field test conditions, the rolling reduction can not be further accurately controlled and needs to be controlled into an integer, and the rolling reduction is limited to be less than or equal to 5mm;
comparing the scheme A, finding that the positions which are larger than 5mm in the scheme A and are not integers, returning to the step 4) again to obtain a new scheme A, redesigning all the exceeding parts to be 5mm, and then obtaining the new scheme A as shown in the following table 4;
TABLE 4 surface reduction distribution (protocol A)
b) Calculating the lowest value of the reduction required for predicting segregation improvement (the degree of carbon segregation is less than or equal to 1.08) by using a multiphase solidification coupling model;
referring to fig. 4, when the total pressure drop is 10mm, the calculated macrosegregation in the multiphase solidification coupling model is improved, that is, the total pressure drop of the newly designed scheme a should be controlled within 10mm, in order to prevent the pressure drop from being too large to meet the production requirement of the field process, the newly designed pressure drop scheme needs to have a margin, and the newly designed scheme a is shown in table 5 below;
TABLE 5 surface reduction distribution (protocol A)
The total reduction was designed to be 10mm only finally by improving the 10mm reduction required for calculation by macrosegregation. Meanwhile, if the total reduction value is not known without the calculation, the problem of inconsistent reduction values at different pulling speeds is caused, such as the total reduction values in table 4. This is disadvantageous in controlling the reduction amount during the continuous casting process and causes a problem of non-uniform cross section of the cast slab after reduction, so that a total reduction amount needs to be calculated by a macrosegregation solute transport calculation model. The improvement of macrosegregation in the pressing process plays an important role in designing the pressing amount;
c) Comparing the maximum green pressing force of the green pressing force required by the calculation of each roller in the scheme A with the green pressing force of the field equipment;
the pulling speed is 0.65m/min, the solidification end is pressed for 5mm, the compaction force is 140.3 tons, and is less than the maximum compaction force of 200 tons of field equipment, namely the equipment meets the requirement when the pressing amount before the solidification end is less than or equal to 5 mm.
d) Cracking the maximum rolling reduction of each roller in the scheme A;
as can be seen from fig. 4, when the rolling reduction is 1mm under the 3# roller, there is a risk of generating cracks, so the rolling reduction of the 3# roller should be less than 1mm, but the rolling reduction of the equipment can only be an integer, so the 3# roller does not roll, the designed rolling reduction interval is extended backward, and at the same time, the rolling reduction under different drawing speeds is consistent, and the design scheme of the final rolling reduction is shown in table 6 below;
TABLE 6 surface reduction distribution (protocol A)
6) The design of the reduction amount scheme is completed;
as shown by combining the graph 6 and the graph 7, the internal quality of the casting blank after reduction is better, the center porosity and segregation are obviously improved, the casting blank with the longitudinal section has no obvious V-shaped segregation, the design reduction effect is good, the reduction interval is accurately designed, the effective way of controlling the center segregation of the continuous casting bloom gear steel by the reduction process determination method is provided, and the reliable means of solving the internal cracks, the center segregation and the center porosity of the casting blank is provided.
It should be understood by those skilled in the art that the above embodiments are only for illustrating the present invention and are not to be used as a limitation of the present invention, and that changes and modifications to the above described embodiments are within the scope of the claims of the present invention as long as they are within the spirit and scope of the present invention.
Claims (10)
1. A reduction process determination method for improving the internal quality of gear steel is characterized by comprising the following steps:
1) Collecting field technical parameters and steel type parameters, and establishing a casting blank solidification heat transfer model;
2) Measuring the temperature of the site temperature, and verifying the casting blank solidification heat transfer model to ensure that the temperature difference between the site temperature and the casting blank solidification heat transfer model does not exceed a set value;
3) Calculating the appearance of a casting blank shell of a casting blank after solidification tail end mechanical reduction, applying the speed distribution of the casting blank after the solidification tail end mechanical reduction on the section of the casting blank to obtain the solute transfer behavior at the solidification tail end position of the casting blank, obtaining the reduction and a reduction interval through the change of the solute transfer behavior, comparing the obtained reduction interval with the calculation result of the casting blank solidification heat transfer model, and determining the final reduction interval;
4) Calculating the surface reduction of the steel grade;
5) Judging whether the surface reduction meets the condition, if so, entering the step 6), and if not, returning to the step 4);
6) The rolling reduction determination is completed.
2. A reduction process determining method for improving internal quality of gear steel according to claim 1, characterized in that: the field technical parameters and steel type parameters comprise a field common pulling speed range, a superheat degree range, continuous casting machine parameters, electromagnetic stirring parameters, equipment pressing capacity, crystallizer length, secondary cooling water amount and steel type components.
3. A reduction process determining method for improving internal quality of gear steel according to claim 1, characterized in that: and the casting blank solidification heat transfer model calculates the solidification end point position, the central solid phase rate and the surface temperature of the casting blank.
4. A reduction process determining method for improving internal quality of gear steel according to claim 1, characterized in that: the set value in step 2) was 50 ℃.
5. A reduction process determining method for improving internal quality of gear steel according to claim 4, wherein the temperature measuring positions of the field temperature are as follows:
and (4) discharging the casting blank from more than half of the position between the second cooling area and each withdrawal and straightening machine, and detecting the temperature of the wide surface and the narrow surface of the casting blank according to the on-site temperature measurement condition.
6. A reduction process determining method for improving the internal quality of gear steel according to claim 3, wherein said step 3) further comprises:
calculating the shape of a casting blank shell after the solidification tail end is mechanically reduced by utilizing a thermal/force coupling model, establishing a casting blank geometric model by using the shape of the casting blank shell, introducing the casting blank geometric model into a multi-phase solidification coupling calculation model, applying the speed distribution after the solidification tail end is mechanically reduced on the section of the casting blank, and further solving a mass, momentum, energy and solute transmission equation under a phase coupling method to obtain the solute transmission behavior at the solidification tail end position of the casting blank;
and comparing the mechanical reduction processes of different solidification ends, obtaining reduction and reduction intervals through the change of the solute transport behavior, and determining the final reduction interval through the solid phase rate obtained by the casting blank solidification heat transfer model.
7. A reduction process determining method for improving internal quality of gear steel according to claim 6, characterized in that: solid fraction f at starting point of selected area of the reduction interval s Not less than 0.3, and f is before the solidification end point at the end position of the selected area of the pressing-down interval s ＝0.95。
8. A reduction process determining method for improving the internal quality of gear steel according to claim 6, wherein said step 4) further comprises:
calculating the deformation condition of the surface and the liquid core of the casting blank in the reduction process by the heat/force coupling die type to obtain reduction efficiency eta, and calculating the liquid core reduction and the surface reduction required by the steel in the reduction interval;
when the reduction interval is exceeded and the solidification region is reached, the reduction efficiency eta is not calculated any more, and the reduction is limited by the capability of the on-site reduction equipment.
9. A reduction process determining method for improving internal quality of gear steel according to claim 8, wherein in the step 5), the judgment conditions are as follows:
a) The method meets the requirements of on-site production and equipment and cannot exceed the equipment capacity;
b) Calculating the minimum rolling reduction required by predicting segregation improvement by using a multiphase solidification coupling model, comparing the minimum rolling reduction with the surface rolling reduction, if the surface rolling reduction is within the minimum rolling reduction, conforming the surface rolling reduction, continuing to perform next judgment, and returning to the step 4) to redesign the surface rolling reduction if the surface rolling reduction is not within the minimum rolling reduction;
c) Comparing the maximum green pressing force required by each roller in the surface reduction with the green pressing force of the field equipment, if the maximum green pressing force is consistent with the field equipment, continuing to perform next judgment, and if the maximum green pressing force is not consistent with the field equipment, returning to the step 4) to redesign the surface reduction;
d) Comparing the surface reduction with the risk of the caused cracks, if no risk exists, conforming, and if at risk, redesigning or extending the surface reduction in the step c);
e) The steps a) to d) should be satisfied simultaneously, and the surface rolling reduction is ensured to be consistent under different drawing speeds.
10. A reduction process determining method for improving internal quality of gear steel according to claim 9, characterized in that:
in the step b), the segregation improvement takes carbon element as a research element, and the standard of the segregation improvement is that the macrosegregation is less than or equal to 1.08; and/or
In the step c), the maximum green pressing force is designed to be calculated by a heat/force coupling model, and the green pressing force with the maximum rolling reduction is selected as comparison; and/or
In the step d), the condition of forward and backward extension is that the distance between the solidification end point and the extension roller does not exceed one withdrawal and straightening machine position.
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