CN115401178B - Reduction process determination method for improving internal quality of gear steel - Google Patents
Reduction process determination method for improving internal quality of gear steel Download PDFInfo
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Abstract
The invention discloses a pressing process determining method for improving the internal quality of gear steel, which comprises the following steps: 1) Collecting field technical parameters and steel parameters, and establishing a casting blank solidification heat transfer model; 2) Measuring the site temperature, verifying the casting blank solidification heat transfer model, and enabling the temperature difference between the site temperature and the casting blank solidification heat transfer model not to exceed a set value; 3) Calculating the shell shape of a casting blank after mechanical rolling of a solidification end, applying speed distribution after mechanical rolling of the solidification end to the section of the casting blank, obtaining solute transmission behavior at the position of the solidification end of the casting blank, obtaining rolling reduction and a rolling reduction interval through the change of the solute transmission behavior, comparing the obtained rolling reduction interval with the calculation result of a casting blank solidification heat transfer model, and determining a final rolling reduction interval; 4) Calculating the surface depression of the steel grade; 5) Judging whether the surface depression amount meets the condition, if so, entering the step 6), and if not, returning to the step 4). The invention designs proper rolling reduction and improves the internal quality of casting blanks.
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 solidification process of the metal material, macro-micro segregation can be caused by selective crystallization, dendrite bridging, solidification shrinkage and the like, and the problem that the internal quality of a casting blank and a follow-up rolled material is seriously affected by the loosening of a central shrinkage cavity is solved. Macrosegregation will cause faults, material failure, and massive carbide aggregation to form cracks. The micro segregation will cause the strip structure in the subsequent rolling process, so that the mechanical properties of the material are different in all directions, namely, the properties along the strip structure direction are obviously better than those along the vertical direction, and the plasticity, toughness and area shrinkage rate of the steel are reduced. The central shrinkage cavity and the looseness 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.
There have been many studies on a method for improving the internal quality of a cast slab, in which the reduction is performed during continuous casting, that is, a method for improving the internal quality of a cast slab is performed by applying a certain reduction amount to each withdrawal and straightening machine of the cast slab during continuous casting, and a certain pressure is generated to compensate for the internal solidification shrinkage of the cast slab, so as to achieve the purpose of improving the internal quality of the cast slab. However, only reasonable rolling interval and rolling reduction can improve the internal quality of the casting blank, and unreasonable rolling parameters can only make the quality of the casting blank more serious.
In the prior patent application, for example, chinese patent CN101658911B discloses an online control method for dynamic soft reduction of bloom continuous casting, which utilizes liquid core reduction and reduction efficiency to calculate casting blank reduction and adjust roll gap. However, the patent does not have thermodynamic coupling simulation calculation, and the reduction is error.
For example, chinese patent CN105108096B discloses a method for determining dynamic light rolling reduction of heavy rail steel bloom continuous casting, and the rolling reduction is determined by determining on-site process parameters, physical parameters and thermodynamic properties of materials. However, the method is only suitable for heavy rail steel, and the casting blank surface temperature is not measured and the on-site process parameters are not corrected in the process parameters.
For example, chinese patent CN109396368B discloses a method for improving the internal quality of high-carbon steel bloom continuous casting, first, the total rolling reduction is constrained to 10 mm-25 mm, and the distribution of rolling reduction is performed 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 high-carbon chromium bearing steel bloom, and the method can directly distribute the reduction under different solid phase rates, which may lack rationality.
For example, chinese patent CN110802207a discloses a method for combined rolling of continuous casting, which comprises establishing a continuous casting solidification model to determine solidification end point and central solid phase ratio, determining critical solid phase ratio formed by macrosegregation through a multiphase solidification coupling model, and predicting critical solid phase ratio of initial formation position of central porosity through a solidification shrinkage analysis model, thereby determining rolling interval and further determining optimal rolling reduction. However, this patent does not consider the influence of cracks, which may occur when the reduction is excessive, 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 determining method for improving the internal quality of gear steel, which designs proper reduction and improves the internal quality of casting blanks.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a pressing process determining method for improving the internal quality of gear steel comprises the following steps:
1) Collecting field technical parameters and steel parameters, and establishing a casting blank solidification heat transfer model;
2) Measuring 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 shell shape of a casting blank after mechanical rolling of a solidification end, applying speed distribution after mechanical rolling of the solidification end to the section of the casting blank, obtaining solute transmission behavior at the position of the solidification end of the casting blank, obtaining rolling reduction and a rolling reduction interval through the change of the solute transmission behavior, comparing the rolling reduction interval with the calculation result of the solidification heat transfer model of the casting blank, and determining a final rolling reduction interval;
4) Calculating the surface depression of the steel grade;
5) Judging whether the surface depression amount meets the condition, if so, entering the step 6), and if not, returning to the step 4);
6) The determination of the depression amount is completed.
Preferably, the on-site technical parameters and the steel grade parameters comprise an on-site common drawing speed range, a superheat degree range, a continuous casting machine parameter, an electromagnetic stirring parameter, equipment pressing capacity, a crystallizer length, secondary cooling water quantity and a steel grade component.
Preferably, the solidification end position, the central solid phase rate and the surface temperature of the casting blank are calculated by the casting blank solidification heat transfer model.
Preferably, the set value in the step 2) is 50 ℃.
Preferably, the temperature measuring position of the site temperature is:
and (3) outputting the second cooling area and more than half of the positions between the 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 includes:
calculating the shape of a casting blank shell after mechanical reduction of the solidification end by using a thermal/force coupling die, establishing a casting blank geometric model by using the shape of the casting blank shell, introducing the casting blank geometric model into a multiphase solidification coupling calculation model, applying the speed distribution after mechanical reduction of the solidification end to the section of the casting blank, and further solving the mass, momentum, energy and solute transfer equation under a phase coupling method to obtain the solute transfer behavior at the position of the solidification end of the casting blank;
comparing the rolling processes of different solidification tail end machines, obtaining rolling reduction and rolling reduction intervals through the change of solute transmission behaviors, and determining the final rolling reduction intervals through the solid phase ratio obtained by the casting blank solidification heat transfer model.
Preferably, the selected area starting point solid phase rate f of the pressing interval s Not less than 0.3, the selected area end position of the pressing interval is f before the solidification end point s ＝0.95。
Preferably, the step 4) further includes:
calculating deformation conditions of the surface of a casting blank and a liquid core in the rolling process by the thermal/force coupling die to obtain rolling efficiency eta, and calculating the rolling reduction of the liquid core and the surface rolling reduction required by the steel grade in the rolling interval;
when the reduction interval is exceeded and reaches the solidification region, the reduction efficiency eta is not calculated, and the reduction is limited by the on-site reduction equipment capacity.
Preferably, in the step 5), the judging conditions are as follows:
a) Meets the field production requirement and the equipment requirement, and does not exceed the equipment capacity;
b) Calculating the minimum rolling reduction required by the prediction segregation improvement by utilizing 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 carry out the next judgment, and if not conforming, returning to the step 4) to redesign the surface rolling reduction;
c) Comparing the maximum compaction force required by calculation of each roller in the surface reduction with the field device compaction force, if the maximum compaction force is matched with the field device compaction force, continuing to carry out the next step of judgment, and if the maximum compaction force is not matched with the field device compaction force, returning to the step 4), and redesigning the surface reduction;
d) Comparing the surface reduction with the risk of the crack caused by the surface reduction, if no risk exists, conforming, and if the risk exists, redesigning or extending the surface reduction in the step c) in a downstream manner;
e) The steps a) to d) should be satisfied simultaneously, and the surface reduction is ensured to be consistent under different pulling speeds.
Preferably, in the step b), the segregation improvement uses carbon element as a research element, and the improvement standard is that macro segregation is less than or equal to 1.08; and/or
In the step c), the maximum compaction force is designed by calculating a thermal/force coupling die type, and the compaction force with the maximum rolling reduction is selected as a comparison; and/or
In the step d), the condition of the backward extension is that the distance between the solidification end point and the delay roller is not more than one withdrawal and straightening machine position.
According to the method for determining the reduction process for improving the internal quality of the gear steel, after the process is adopted for production, the segregation of the gear steel casting blank is effectively controlled, the segregation rating is all 1 level and is superior to that of a comparison sample (50% of each of 2 level and 1 level), the production requirement is met, the casting blank quality is improved, the strip-shaped structure of the subsequent rolled material is obviously improved, and the process is ensured to be smooth. The method for determining the gear steel pressing process has accurate pressing amount, is favorable for realizing dynamic pressing position control and has obvious effect; in addition, the influence of cracks possibly generated when the rolling reduction is excessive on the quality of the casting blank is considered, and the method has the characteristic of small implementation risk and 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 chart of a method for determining a pressing process according to the present invention;
FIG. 2 is a schematic diagram of simulated temperatures of solidification heat transfer versus actual test temperatures in an embodiment of a method for determining a screw-down process according to the present invention;
FIG. 3 is a schematic diagram of the selection of the pressure interval in the embodiment of the method for determining the pressure process of the present invention;
FIG. 4 is a schematic view showing the effect of the amount of reduction in the embodiment of the method for determining the reduction process of the present invention on the improvement of macrosegregation;
FIG. 5 is a schematic diagram of the minimum reduction of risk of cracking of each roll 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 the embodiment 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 (vertical section) in the embodiment of the reduction process determining method of the present invention.
Detailed Description
In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below 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 gear steel provided by the invention comprises the following steps:
1) Collecting field technical parameters and steel parameters, and establishing a casting blank solidification heat transfer model to obtain a solidification end point position, a central solid phase rate and a surface temperature of the casting blank;
the field technical parameters and the steel parameters comprise a field common pulling speed range, a superheat degree range, a continuous casting machine parameter, an electromagnetic stirring parameter, equipment pressing capacity, a crystallizer length, secondary cooling water quantity, steel components and the like.
2) Measuring the site temperature by an infrared thermometer, and verifying the casting blank solidification heat transfer model in the step 1), so that the temperature difference between the site temperature and the casting blank solidification heat transfer model is not more than 50 ℃;
the temperature measuring position of the site temperature is as follows:
and (3) outputting the second cooling area and more than half of the positions between the 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.
3) Calculating the shape of a casting blank shell after mechanical reduction of a solidification end by using a thermal/force coupling die, establishing a casting blank geometric model by using the shape of the casting blank shell, introducing the casting blank geometric model into a multiphase solidification coupling calculation model, applying the speed distribution after mechanical reduction of the solidification end to the section of the casting blank, and further solving the mass, momentum, energy and solute transmission equation under a phase coupling method to obtain the solute transmission behavior at the position of the solidification end of the casting blank;
comparing the mechanical pressing down processes of different solidification terminals, obtaining the pressing down amount and the pressing down interval through solute transmission behavior change, and comparing the obtained pressing down interval with the solid phase rate obtained by the solidification heat transfer model of the casting blank to further determine the final (optimal) pressing down interval;
area selection starting point solid phase ratio f of pressing interval s Not less than 0.3, the selected area end position of the pressing interval is f before the solidification end point s =0.95, while the hold-down zone should cover places where the liquid phase velocity is fast.
4) Calculating deformation conditions of the surface of a casting blank and a liquid core in the rolling process by using a thermal/force coupling die to obtain rolling efficiency eta, and calculating the rolling reduction of the liquid core and the surface rolling reduction required by the steel grade in a rolling interval;
when the reduction interval is exceeded and reaches the solidification region, the reduction efficiency eta is not calculated, the reduction is limited by the on-site reduction equipment capacity, and the surface reduction is recorded as a scheme A.
5) Scheme a should simultaneously satisfy the following conditions:
a) Meets the requirements of on-site production and equipment, does not exceed the equipment capacity, and can reserve design allowance;
b) Calculating the minimum reduction required for the improvement of the predictive segregation by utilizing a multiphase solidification coupling model (recorded as a scheme B), comparing the minimum reduction with a scheme A, if the scheme A is within the scheme B, conforming the scheme A, continuing to carry out the next judgment, and returning to the step 4) to redesign the surface reduction if the scheme A is not conforming;
c) Comparing the maximum compaction force required by calculation of each roller in the scheme A with the field device compaction force, if the maximum compaction force is matched with the field device compaction force, continuing to carry out the next step of judgment, and if the maximum compaction force is not matched with the field device compaction force, returning to the step 4), and redesigning the surface reduction;
d) Comparing the risk of the crack caused by the scheme A, if the risk is not met, redesigning or extending the surface reduction in the step c) in the following way if the risk is met;
e) The steps a) to d) should be satisfied simultaneously, and the consistent surface reduction under different pull rates is ensured.
In the step b), the segregation is improved by taking a carbon element as a research element, and the improvement standard is that macrosegregation is less than or equal to 1.08; and/or
In the step c), the maximum compaction force is designed and calculated by a thermal/force coupling die type, and the compaction force with the maximum rolling reduction is selected as comparison; and/or
In step d), the condition of the backward extension is that the distance between the solidification end point and the backward roller is not more than one withdrawal and straightening machine position.
6) The determination of the depression amount is completed.
Examples
Taking a gear steel bloom of a certain model as an example, the contents of various components of the steel grade are C:0.18 to 0.22 weight percent, si:0.2 to 0.3 weight percent, mn:1.25 to 1.35 weight percent, P: 0to 0.15 weight percent, S:0.01 to 0.02 weight percent. The casting superheat degree is 30 ℃, the pulling speed is 0.65-0.70 m/min, the cross section size is 320 multiplied by 425mm, and the secondary cooling water quantity adopts the common water quantity. The rest processes are unchanged, and the reduction of the internal quality of the steel grade can be improved is determined, wherein the steps are as follows:
1) Setting up a steel solidification heat transfer model based on a field process to obtain parameters such as a solidification end point position, a central solid phase rate, a surface temperature and the like of the steel;
2) The diagram of the calculated temperature and the on-site temperature test result of the casting blank solidification heat transfer model is shown in combination with fig. 2, and the difference between the calculated temperature and the on-site measured temperature is within a range, so that the accuracy of the calculated result is shown;
3) And 2) obtaining the appearance of a casting blank shell after mechanical reduction of a solidification end on the basis of the solidification heat transfer model in the step 2), establishing a casting blank geometric model by using the appearance, introducing the casting blank geometric model into a multiphase solidification coupling calculation model, applying the speed distribution after mechanical reduction of the solidification end on the section of the casting blank, and further solving the mass, momentum, energy and solute transmission equation under a coupling method to obtain the solute transmission behavior at the position of the solidification end of the casting blank. Obtaining the minimum reduction and the optimal reduction interval of the segregation improvement, and selecting the reduction interval in combination with the representation shown in fig. 3, wherein the selection of the reduction interval is represented by gray boxes;
4) Calculating the liquid core rolling reduction (see table 1 below), calculating rolling efficiency by using a rolling model, rolling efficiency (see table 2 below), and surface rolling reduction (see table 3 below);
TABLE 1 liquid core reduction distribution at different pull rates
TABLE 2 reduction efficiency distribution
TABLE 3 surface reduction distribution (scheme A)
5) Scheme a should simultaneously satisfy the following conditions:
a) Meets the requirements of on-site production and equipment. The rolling reduction cannot be further and accurately controlled by limiting the field test conditions, the rolling reduction is required to be controlled to be an integer, and the rolling reduction is limited to be less than or equal to 5mm;
comparing the scheme A, finding that the scheme A has a place larger than 5mm and is not an integer, returning to the step 4) again to obtain a new scheme A, and redesigning more than part of the scheme A to be 5mm, wherein the new scheme A is shown in the following table 4;
TABLE 4 surface reduction distribution (scheme A)
b) Calculating the minimum value of the reduction required by the predicted segregation improvement (carbon segregation degree is less than or equal to 1.08) by utilizing a multiphase solidification coupling model;
referring to fig. 4, when the total rolling reduction is 10mm, macrosegregation is improved in the multiphase solidification coupling model, that is, the total rolling reduction of the newly designed scheme a should be controlled within 10mm, and in order to prevent the rolling reduction from being too large to meet the production requirement of the field process, the newly designed rolling reduction scheme needs to have a margin, and the newly designed scheme a is shown in the following table 5;
TABLE 5 surface reduction distribution (scheme A)
The total reduction was designed to be 10mm only after the reduction of 10mm required for the calculation by macrosegregation improvement. Meanwhile, without this calculation, the value of the total reduction cannot be known, which would lead to the problem that the reduction is not uniform at different pull rates, such as the total reduction in table 4. This is disadvantageous for controlling the reduction in the continuous casting process and causes the problem of inconsistent cross section of the cast slab after reduction, so that it is necessary to calculate a total reduction by a macrosegregation solute transport calculation model. Macrosegregation improvement in the pressing process plays an important role in designing the pressing quantity;
c) Comparing the maximum compaction force of the compaction force required by each roller in the scheme A with the compaction force of the field equipment;
the pulling speed is 0.65m/min, the pressing force of the solidification end is 5mm, the required pressing force is 140.3ton, and the maximum pressing force of the field device is less than 200ton, namely, the equipment meets the requirement when the pressing force is less than or equal to 5mm before the solidification end.
d) The maximum rolling reduction crack risk of each roller in the scheme A;
as can be seen from fig. 4, when the rolling reduction is 1mm under the 3# roller, the cracking risk is generated, so the rolling reduction of the 3# roller is less than 1mm, but the rolling reduction of the equipment is only an integer, so the 3# roller does not press, the designed rolling reduction interval is extended backward, the rolling reduction is consistent under different pulling speeds, and the final rolling reduction design scheme is shown in the following table 6;
TABLE 6 surface reduction distribution (scheme A)
6) The design of the reduction scheme is completed;
as shown in the combination of figures 6 and 7, the internal quality of the casting blank after reduction is better, the central porosity and segregation are obviously improved, the vertical section casting blank has no obvious V-shaped segregation, the design reduction effect is good, the reduction interval design is accurate, and the effective way for controlling the central segregation of the gear steel of the continuous casting bloom by the reduction process determination method disclosed by the invention is a reliable means for solving the internal cracks, the central segregation and the central porosity of the casting blank.
It will be appreciated by persons skilled in the art that the above embodiments are provided for illustration only and not for limitation of the invention, and that variations and modifications of the above described embodiments are intended to fall within the scope of the claims of the invention as long as they fall within the true spirit of the invention.
Claims (4)
1. A pressing process determining method for improving the internal quality of gear steel is characterized by comprising the following steps:
1) Collecting field technical parameters and steel parameters, and establishing a casting blank solidification heat transfer model, wherein the field technical parameters and the steel parameters comprise a field common pulling speed range, a superheat degree range, a continuous casting machine parameter, an electromagnetic stirring parameter, equipment pressing capacity, a crystallizer length, secondary cooling water quantity and steel components; calculating the solidification end position, the central solid phase ratio and the surface temperature of the casting blank by the casting blank solidification heat transfer model;
2) Measuring 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 shell shape of a casting blank after mechanical rolling of a solidification end, applying speed distribution after mechanical rolling of the solidification end to the section of the casting blank, obtaining solute transmission behavior at the position of the solidification end of the casting blank, obtaining rolling reduction and a rolling reduction interval through the change of the solute transmission behavior, comparing the rolling reduction interval with the calculation result of the solidification heat transfer model of the casting blank, and determining a final rolling reduction interval;
4) Calculating the surface depression of the steel grade;
5) Judging whether the surface depression amount meets the condition, if so, entering the step 6), and if not, returning to the step 4);
6) The determination of the amount of depression is completed,
the step 3) further comprises:
calculating the shape of a casting blank shell after mechanical reduction of the solidification end by using a thermal/force coupling die, establishing a casting blank geometric model by using the shape of the casting blank shell, introducing the casting blank geometric model into a multiphase solidification coupling calculation model, applying the speed distribution after mechanical reduction of the solidification end to the section of the casting blank, and further solving the mass, momentum, energy and solute transfer equation under a phase coupling method to obtain the solute transfer behavior at the position of the solidification end of the casting blank;
comparing different solidification tail end mechanical pressing processes, obtaining pressing quantity and pressing interval through the change of solute transmission behavior, and determining the final pressing interval through the solid phase rate obtained by the casting blank solidification heat transfer model;
the step 4) further comprises:
calculating deformation conditions of the surface of a casting blank and a liquid core in the rolling process by the thermal/force coupling die to obtain rolling efficiency, and calculating the required liquid core rolling reduction and the surface rolling reduction of the steel grade in the rolling interval;
when the reduction interval is exceeded and reaches the solidification region, the reduction efficiency is not calculated any more, the reduction is limited by the on-site reduction equipment capacity,
in the step 5), the judgment conditions are as follows:
a) Meets the field production requirement and the equipment requirement, and does not exceed the equipment capacity;
b) Calculating the minimum rolling reduction required by the prediction segregation improvement by utilizing 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 carry out the next judgment, and if not conforming, returning to the step 4) to redesign the surface rolling reduction;
c) Comparing the maximum compaction force required by calculation of each roller in the surface reduction with the field device compaction force, if the maximum compaction force is matched with the field device compaction force, continuing to carry out the next step of judgment, and if the maximum compaction force is not matched with the field device compaction force, returning to the step 4), and redesigning the surface reduction;
d) Comparing the surface reduction with the risk of the crack caused by the surface reduction, if no risk exists, conforming, and if the risk exists, redesigning or extending the surface reduction in the step c) in a downstream manner;
e) Steps a) to d) should be satisfied simultaneously, and ensure that the surface reduction amounts are consistent at different pull rates,
in the step b), the segregation is improved by taking a carbon element as a research element, and the improvement standard is that macro segregation is less than or equal to 1.08; and/or
In the step c), the maximum compaction force is designed by calculating a thermal/force coupling die type, and the compaction force with the maximum rolling reduction is selected as a comparison; and/or
In the step d), the condition of the backward extension is that the distance between the solidification end point and the delay roller is not more than one withdrawal and straightening machine position.
2. The method for determining the reduction process for improving the internal quality of gear steel according to claim 1, wherein: the set value in step 2) is 50 ℃.
3. The method for determining the reduction process for improving the internal quality of gear steel according to claim 2, wherein the temperature measuring position of the site temperature is:
and (3) outputting the second cooling area and more than half of the positions between the 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.
4. The method for determining the reduction process for improving the internal quality of gear steel according to claim 1, wherein: the solid phase rate of the initial point of the selected area in the pressing intervalf s Not less than 0.3, the selected area end position of the pressing interval is positioned before the solidification end pointf s =0.95。
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