CN113600776A - Method for determining critical cooling rate in continuous casting process - Google Patents
Method for determining critical cooling rate in continuous casting process Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D11/00—Process control or regulation for heat treatments
- C21D11/005—Process control or regulation for heat treatments for cooling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/02—Hardening by precipitation
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
Abstract
The invention discloses a method for determining a critical cooling rate in a continuous casting process, which comprises the following steps: heating and melting a plurality of high titanium steel samples with the same titanium content; cooling the melted samples at different cooling rates respectively to the temperature of the samples out of the crystallizer; quenching the plurality of cooled samples; obtaining the sizes of carbides precipitated in the solidification process of a plurality of samples, and obtaining the thicknesses of ferrite films of the quenched samples; and determining samples meeting the carbide size standard and the ferrite film thickness standard, and taking the corresponding lowest cooling rate as the critical cooling rate of the high-titanium steel with the titanium content. The method can determine the critical cooling speed of the high titanium steel entering the high thermoplastic region.
Description
Technical Field
The invention relates to the technical field of metal casting, in particular to a method for determining a critical cooling rate in a continuous casting process.
Background
Titanium as a microalloy element can be dissolved in a solid solution in a steel matrix to play a role in solid solution strengthening, and can easily react with C, N, S in the steel to generate fine carbonitride, so that the aims of fine grain strengthening and precipitation strengthening are fulfilled, and the strength, toughness, welding performance and grain boundary corrosion resistance of the steel are finally improved. With the increase of the titanium content in the steel, the quantity and the size of the precipitated carbonitrides are gradually increased, and when the titanium content (mass fraction) in the steel exceeds 0.2%, a large amount of micron-nanoscale composite TiC particles can be generated in a matrix, so that the wear resistance and the strength of the steel are greatly improved, and the steel is widely applied to the fields of high-strength machinery, metallurgical mining and the like. At present, a large number of researchers have studied the influence of high titanium alloy content on the mechanical properties of steel, Xu et al have studied the influence of titanium content on titanium alloy steel, and the study finds that the strength of titanium alloy steel increases with the increase of titanium content, so that the titanium alloy steel can be inferred to replace niobium or vanadium alloy steel. By greatly improving the titanium content in the iron matrix, Huang et al obtain that the wear resistance of the high-titanium steel is 1.7 times that of the common wear-resistant steel through a three-body friction wear test.
A large number of researches show that during precipitation and precipitation of carbonitride of microalloy steel, the carbonitride is easy to nucleate and grow at grain boundaries, which undoubtedly reduces the bonding strength among the grains and causes the initiation of micro cracks, and which is also an important cause of frequent corner cracks during continuous casting bending and straightening of the microalloy steel. As the titanium content in the steel increases, the size and amount of TiC increases, resulting in a decrease in the high temperature thermoplasticity of the steel and a sharp increase in the risk of cracking. Therefore, the risk of corner cracks in the continuous casting process of the high titanium steel is far higher than that of the common microalloy steel. Meanwhile, the generation of a pro-eutectoid ferrite film at the initial austenite crystal boundary caused by the cooling process further improves the crack risk in the continuous casting process of the high titanium steel.
In the prior art, a series of micro-alloy steel casting blank corner crack control technologies are developed based on crack control theories such as a third brittleness temperature interval of micro-alloy steel, a casting blank surface layer control theory and the like, and in most of the crack control technologies, the diffusion precipitation of carbonitride is promoted by increasing the cooling rate of corners, a ferrite structure is refined, and a pro-eutectoid ferrite film is eliminated. Therefore, the critical cooling speed with the minimum continuous casting billet crack risk is determined, and the determination of the optimal structure of the continuous casting billet is a key factor for improving the thermoplasticity.
However, with the rapid increase of titanium content, the precipitation type, precipitation temperature interval and size of carbonitride thereof are greatly different from those of common microalloyed steel, the theory of the traditional microalloyed steel cannot be applied to high-titanium steel, and the traditional microalloyed steel technology is mainly qualitative analysis and has no quantitative data and determination method. Therefore, it is necessary to systematically study the precipitation of carbonitride and the transformation of ferrite film of high titanium steel and to establish the optimal thermoplastic critical cooling rate of high titanium steel.
Disclosure of Invention
The invention mainly aims to provide a method for determining the critical cooling rate in the continuous casting process of high-titanium steel, so as to solve the problem that the traditional microalloyed steel theory cannot be applied to the high-titanium steel.
According to one aspect of the present invention, there is provided a method of determining a critical cooling rate of a continuous casting process, comprising: heating and melting a plurality of high titanium steel samples with the same titanium content; cooling the melted samples at different cooling rates respectively to the temperature of the samples out of the crystallizer; quenching the plurality of cooled samples; obtaining the sizes of carbides precipitated in the solidification process of a plurality of samples, and obtaining the thicknesses of ferrite films of the quenched samples; and determining samples meeting the carbide size standard and the ferrite film thickness standard, and taking the corresponding lowest cooling rate as the critical cooling rate of the high-titanium steel with the titanium content.
According to one embodiment of the invention, the heating temperature of the heating is 30-50 ℃ higher than the liquidus temperature of the sample, and the holding time is 3-5 min.
According to one embodiment of the invention, the liquidus temperature is obtained based on the alloy composition of the sample.
According to one embodiment of the invention, the following parameters of the sample are obtained based on the alloy composition of the sample: liquidus temperature, solidus temperature, density, thermophysical parameters; and obtaining the crystallizer-exiting temperature based on the plurality of parameters.
According to one embodiment of the invention, a plurality of said samples are selected from corner regions of a high titanium steel billet; and/or the cooling rate is 0.2-50 ℃/s.
According to one embodiment of the invention, a plurality of samples are divided into a plurality of groups, wherein the cooling rate of one group of samples is between 0.1 and 1 ℃/s, and the minimum difference of the cooling rates of the group of samples is between 0.1 and 0.3 ℃/s; and/or the cooling rates of one group of samples are 1-10 ℃/s, and the minimum difference of the cooling rates of the group of samples is 1-3 ℃/s; and/or the cooling rates of one group of samples are 10-50 ℃/s, and the minimum difference of the cooling rates of the group of samples is 5-20 ℃/s.
According to one embodiment of the invention, the carbide size criteria are: in a field of 250 micrometers multiplied by 250 micrometers, the proportion of carbide with the length less than or equal to 8 micrometers is 85-90%; and/or the ferritic film thickness standard is: the average ferrite film thickness is 2 μm or less.
According to an embodiment of the invention, the method further comprises: preparing high titanium steel to be measured by adopting the critical cooling rate, and performing a tensile test on the high titanium steel to be measured to obtain the reduction of area; verifying the critical cooling rate based on the reduction of area, wherein if the reduction of area is less than 60%, the critical cooling rate is verified to be false.
According to one embodiment of the invention, the obtaining of the high titanium steel to be tested comprises: heating the high titanium steel at 1350-1450 ℃ for 3-10 min; and cooling the heated high titanium steel to the crystallizer discharging temperature at the critical cooling rate.
According to one embodiment of the invention, the quenching comprises: an inert gas is sparged into the sample.
According to the method for determining the critical cooling rate in the continuous casting process, the critical cooling rate of high titanium steel with various titanium contents entering a high thermoplastic region can be determined, so that the production process is guided, and the crack risk of the high titanium steel continuous casting blank is reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 shows a schematic representation of TiC precipitated from high titanium steel, according to one embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the following embodiments of the present invention are described in further detail with reference to the accompanying drawings.
It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are used for distinguishing two entities with the same name but different names or different parameters, and it should be noted that "first" and "second" are merely for convenience of description and should not be construed as limitations of the embodiments of the present invention, and they are not described in any more detail in the following embodiments.
The invention provides a method for determining a critical cooling rate in a continuous casting process, which comprises the following steps:
heating and melting a plurality of high titanium steel samples with the same titanium content;
cooling the melted samples at different cooling rates respectively to the temperature of the samples out of the crystallizer;
quenching the plurality of cooled samples;
obtaining the sizes of carbides precipitated in the solidification process of a plurality of samples, and obtaining the thicknesses of ferrite films of the quenched samples;
and determining samples meeting the carbide size standard and the ferrite film thickness standard, and taking the corresponding lowest cooling rate as the critical cooling rate of the high-titanium steel with the titanium content.
According to the method for determining the critical cooling rate in the continuous casting process, the critical cooling rate of high titanium steel with various titanium contents entering a high thermoplastic region can be determined, so that the production process is guided, and the crack risk of the high titanium steel continuous casting blank is reduced.
In the embodiment of the invention, the high titanium steel refers to steel containing more than 0.1% of titanium by mass fraction. The crystallizer outlet temperature refers to the temperature of a casting blank discharged from a crystallizer in the continuous casting process, the specific temperature is different along with different components and process conditions, generally is 850-780 ℃, and the crystallizer outlet temperature can be obtained by simulating the actual continuous casting process.
In one embodiment, a plurality of the samples are selected from corner regions of a high titanium steel billet, so as to research how to improve the thermoplasticity of the corner regions and reduce the occurrence of cracks aiming at the problem of corner cracking. The sample can be a small cylinder with the diameter of 2mm and the height of 5mm so as to match the requirements of related detection equipment and ensure the detection accuracy. The high titanium steel casting blank corner area can be processed into small cylinders with the diameter of 2mm and the height of 5mm by adopting a linear cutting technology. The sample can be polished before heating, so that the change of the tissue morphology of the sample can be observed through a high-temperature microscope during the heating process of the sample.
In the step of heating the high titanium steel sample, the sample is put into Al prepared in advance2O3Heating in a crucible at a temperature 30-50 ℃ higher than the liquidus temperature of the sample, and keeping the temperature for 3-5 min, thereby ensuring that the sample can be fully melted. High titanium steels of different compositions have different liquidus temperatures, wherein the contents of carbon and titanium affect the liquidus temperature among other things. In an embodiment of the invention, the liquidus temperature is obtained based on the alloy composition of the sample. Alloy components of the high titanium steel can be brought into Jmat-pro software to calculate the liquidus temperature of the high titanium steel. The sample may be heated using a high temperature focusing microscope and the rate of temperature rise may be 5 ℃/s.
And after the heat preservation is carried out for 3-5 min to ensure that the samples are fully melted, cooling the multiple samples to the temperature of the crystallizer according to different cooling rates. In an embodiment of the present invention, the following parameters of the sample are obtained based on the alloy composition of the sample: liquidus temperature, solidus temperature, density, thermophysical parameters; and obtaining the crystallizer-exiting temperature based on the plurality of parameters. Specifically, alloy components of the high titanium steel are introduced into Jmat-pro software to calculate the solidus temperature, the liquidus temperature and the density of the high titanium steel, and thermophysical parameters such as specific heat capacity and latent heat of the high titanium steel, and the parameters are introduced into MSC.
The cooling rate can be 0.2-50 ℃/s, and the critical cooling rate is tested and searched within the numerical range. In one embodiment, a plurality of the samples are divided into a plurality of groups, wherein the cooling rate of one group of samples is between 0.1 and 1 ℃/s, and the minimum difference of the cooling rates of the group of samples is between 0.1 and 0.3 ℃/s; and/or the cooling rates of one group of samples are 1-10 ℃/s, and the minimum difference of the cooling rates of the group of samples is 1-3 ℃/s; and/or the cooling rates of one group of samples are 10-50 ℃/s, and the minimum difference of the cooling rates of the group of samples is 5-20 ℃/s. The minimum difference is a minimum difference among differences between each two of a plurality of different cooling rate values, regardless of setting the same cooling rate value. The number of samples may be 15 to 20. The cooling rate values of the samples of each group can be set according to gradients, the gradients of different groups are different, the smaller the value is, the smaller the gradient is, and the larger the value is, the larger the gradient is, so that the critical cooling rate can be found out quickly and accurately. For example, the samples may be divided into three groups, with the cooling rate for the first group of samples set at 0.2 ℃/s, 0.4 ℃/s, 0.6 ℃/s, and so forth; the cooling rate of the second group of samples is set according to 1 ℃/s, 3 ℃/s, 5 ℃/s and the like; the cooling rates for the third set of samples were set at 10 deg.C/s, 15 deg.C/s, 20 deg.C/s, etc.
The carbide precipitated in the solidification process of the high titanium steel sample can be observed in situ by a high-temperature confocal microscope, and the size and content of the carbide and a precipitation temperature interval are obtained. During solidification, the precipitated carbides change in size until they stabilize at the point of complete precipitation. The whole solidification process of the sample can be shot, and the required carbide size and content can be obtained from the shot video. The carbide may specifically be TiC. Fig. 1 shows a schematic diagram of TiC precipitated from a high titanium steel according to an embodiment of the present invention, specifically, a structure photograph of the high titanium steel (mass fraction of Ti is 0.37%) obtained at four different cooling rates of 0.6 ℃/s, 0.8 ℃/s, 3.0 ℃/s and 5.0 ℃/s when TiC precipitation is complete, from which the size and content of TiC can be obtained.
In the whole test process, one size change of micron-sized TiC in the whole high-titanium steel solidification process can be observed in situ, and a precipitation temperature interval is formed. The in-situ observation method by using the high-temperature confocal microscope is only suitable for high-titanium alloy steel, namely steel with the mass fraction of Ti in the steel being more than or equal to 0.1%, because micron-sized carbonitride is generated in the high-temperature solidification stage of the steel, the steel can be observed under the high-temperature confocal microscope (the resolution is 0.1 mu m), and in the microalloy steel, namely the steel with the mass fraction of each microalloy element being less than 0.1%, the generated carbonitride is nano-sized carbonitride, and the carbonitride cannot be distinguished by the confocal microscope.
In an embodiment of the invention, said quenching comprises: and (3) spraying inert gas to the sample so that the sample is rapidly cooled. The temperature of the inert gas may be normal temperature. The tissue of the sample can be changed during the continuous cooling process of the sample, and the tissue shape of the sample is kept for a required period by quenching, so that the sample can be observed conveniently.
After quenching, the sample was ground, polished, and etched with 4% nital (4% by volume nitric acid, 96% by volume alcohol), after which the ferrite film thickness of the sample was observed.
The size of carbide, the precipitation temperature interval and the thickness of ferrite film can be counted, and analyzed and compared to obtain the critical cooling rate. In an embodiment of the invention, the carbide size criteria are: in a field of 250 micrometers multiplied by 250 micrometers, the proportion of carbide with the length less than or equal to 8 micrometers is 85-90%; the thickness standard of the ferrite film is as follows: the average ferrite film thickness is 2 μm or less. Selecting one or more samples meeting the carbide size standard and the ferrite film thickness standard, and corresponding to one or more cooling rates, and selecting the lowest cooling rate as the critical cooling rate of the high-thermoplastic region of the high-titanium steel.
In a further embodiment, the method further comprises:
preparing high titanium steel to be measured by adopting the critical cooling rate, and performing a tensile test on the high titanium steel to be measured to obtain the reduction of area;
verifying the critical cooling rate based on the reduction of area, wherein if the reduction of area is less than 60%, the critical cooling rate is verified to be false.
According to a Suzuki general criterion for dividing a brittle area of a casting blank with the reduction of area of 60%, more than 60% of the brittle area is a high-plasticity area, and less than 60% of the brittle area is a low-plasticity area. Therefore, if the reduction of area of the high titanium steel obtained based on the critical cooling rate is less than 60%, it indicates that the high titanium steel does not enter the high plasticity zone at this time, that is, the obtained critical cooling rate does not belong to the critical cooling rate entering the high plasticity zone, that is, the result is incorrect.
Wherein, the obtaining of the high titanium steel to be measured comprises the following steps:
heating the high titanium steel at 1350-1450 ℃ for 3-10 min;
and cooling the heated high titanium steel to the crystallizer discharging temperature at the critical cooling rate.
The corner area of the casting blank can be selected, the casting blank is processed into a cylindrical stretching sample with the diameter of 10mm and the height of 120mm by linear cutting, and the two ends of the cylindrical stretching sample are processed into the diameterHeating 10mm screw thread to 1400 deg.C/s at 10 deg.C/s by thermal simulation tester, holding for 5min, cooling to crystallizer temperature at critical cooling speed, such as 780 deg.C, and strain rate of 0.001s-1And (4) performing high-temperature stretching.
The invention relates to a method for determining the optimal thermoplastic critical cooling rate of high-titanium steel in a continuous casting process. The method is used for improving the size, distribution and quantity of the solidification structure and the carbonitride of the high titanium steel by utilizing the cooling speed in the continuous casting process of the high titanium steel (particularly for the steel with titanium more than 0.3 percent in the steel), has obvious effect, can be popularized and applied to the production of the high titanium steel, and can provide technical reserve for the research and development of high titanium variety steel.
The following description is based on specific examples.
Example 1
(1) Introducing alloy components of high-titanium steel with 0.37% of titanium content (mass fraction) into Jmat-pro software to calculate the solidus temperature, liquidus temperature and density of the high-titanium steel and the thermophysical parameters of the high-titanium steel, such as specific heat capacity, latent heat and the like, and introducing the parameters into MSC.Marc limited software to simulate the temperature of a crystallizer in the actual continuous casting process of the high-titanium steel continuous casting billet, so as to obtain the temperature of the crystallizer, wherein the temperature of the crystallizer is 810 ℃;
(2) selecting the corner area position of a high titanium steel casting blank, processing the high titanium steel casting blank into a small cylinder with the diameter of 2mm and the height of 5mm by adopting a linear cutting technology, and putting Al which is prepared in advance into the small cylinder after polishing2O3Heating to 30 ℃ above the liquidus temperature at a heating rate of 5 ℃/s by using a high-temperature focusing microscope in a crucible, and keeping the temperature for 3 min;
(3) to be Al2O3After the high titanium steel in the crucible is melted, cooling different samples to 810 ℃ at cooling rates of 0.2 ℃/s, 0.4 ℃/s, 0.6 ℃/s, 0.8 ℃/s, 3 ℃/s and 5 ℃/s respectively, and then quenching; in-situ observation is carried out on the micron-sized TiC in the whole high-titanium steel solidification process, and the size and the content of TiC completely separated out are obtained;
(4) grinding and polishing the quenched sample, corroding the sample by using 4% nitric acid alcohol, and observing the thickness of the ferrite film of the sample;
(5) and (4) counting the TiC size and the ferrite film thickness in the step (3) and the step (4). Wherein 85% of TiC is observed to be less than or equal to 8 μm in length in a visual field of 250 μm multiplied by 250 μm, the average ferrite film thickness is less than or equal to 2 μm, and the lowest cooling speed meeting the cooling speed under the condition is taken as the critical cooling speed of the high-thermoplastic region of the high-titanium steel.
Table 1 shows the TiC size content of the samples at different cooling rates and the results of the reduction of area for each sample. As can be seen from Table 1, the TiC size content of the sample with the cooling rate of 0.6 ℃/s, 0.8 ℃/s and 3 ℃/s does not meet the standard, and the corresponding reduction of area is less than 60%, which indicates that the sample is in a low plasticity zone; and the TiC size content of the sample with the cooling rate of 5 ℃/s meets the standard, the corresponding reduction of area is more than 60 percent, and the sample is verified to be in a high plasticity zone.
TABLE 1 TiC ratio and reduction of area of not more than 8 μm at different cooling rates
| Cooling rate | 0.6℃/s | 0.8℃/s | 3.0℃/s | 5.0℃/s |
| TiC proportion less than or equal to 8 mu m | 6％ | 18％ | 54％ | 90％ |
| Reduction of area | 16％ | 23％ | 47％ | 61％ |
Example 2
(1) Introducing alloy components of high-titanium steel with 0.20% of titanium content (mass fraction) into Jmat-pro software to calculate solidus temperature, liquidus temperature and density of the high-titanium steel and thermophysical parameters such as specific heat capacity and latent heat of the high-titanium steel, and introducing the parameters into MSC.Marc limited software to simulate the temperature of a crystallizer in the actual continuous casting process of the high-titanium steel continuous casting billet, so as to obtain the temperature of the crystallizer which is 790 ℃;
(2) selecting the corner area position of a high titanium steel casting blank, processing the high titanium steel casting blank into a small cylinder with the diameter of 2mm and the height of 5mm by adopting a linear cutting technology, and putting Al which is prepared in advance into the small cylinder after polishing2O3Heating to 40 ℃ above the liquidus temperature at a heating rate of 5 ℃/s by using a high-temperature focusing microscope in a crucible, and keeping the temperature for 5 min;
(3) to be Al2O3After the high titanium steel in the crucible is melted, cooling different samples to 790 ℃ at cooling rates of 0.6 ℃/s, 0.8 ℃/s, 3 ℃/s, 5 ℃/s and 10 ℃/s respectively, and then quenching; in-situ observation is carried out on the micron-sized TiC in the whole high-titanium steel solidification process, and the size and the content of TiC completely separated out are obtained;
(4) grinding and polishing the quenched sample, corroding the sample by using 4% nitric acid alcohol, and observing the thickness of the ferrite film of the sample;
(5) and (4) counting the TiC size and the ferrite film thickness in the step (3) and the step (4). Wherein 85% of TiC is observed to be less than or equal to 8 μm in length in a visual field of 250 μm multiplied by 250 μm, the average ferrite film thickness is less than or equal to 2 μm, the lowest cooling speed meeting the cooling speed under the condition is taken as the critical cooling speed of the high-thermoplastic region of the high-titanium steel, and the thermal simulation thermoplastic test is used for verifying the TiC.
Example 3
(1) Introducing alloy components of high-titanium steel with 0.31% of titanium content (mass fraction) into Jmat-pro software to calculate the solidus temperature, liquidus temperature and density of the high-titanium steel and the thermophysical parameters of the high-titanium steel, such as specific heat capacity, latent heat and the like, and introducing the parameters into MSC.Marc limited software to simulate the temperature of a crystallizer in the actual continuous casting process of the high-titanium steel continuous casting billet, so as to obtain the temperature of the crystallizer of 780 ℃;
(2) selecting the corner area position of a high titanium steel casting blank, processing the high titanium steel casting blank into a small cylinder with the diameter of 2mm and the height of 5mm by adopting a linear cutting technology, and putting Al which is prepared in advance into the small cylinder after polishing2O3Heating to 50 ℃ above the liquidus temperature at a heating rate of 5 ℃/s by using a high-temperature focusing microscope in a crucible, and keeping the temperature for 5 min;
(3) to be Al2O3After the high titanium steel in the crucible is melted, cooling different samples to 780 ℃ at cooling rates of 0.2 ℃/s, 0.4 ℃/s, 0.6 ℃/s, 0.8 ℃/s, 3 ℃/s, 5 ℃/s, 10 ℃/s and 15 ℃/s respectively, and then quenching; in-situ observation is carried out on the micron-sized TiC in the whole high-titanium steel solidification process, and the size and the content of TiC completely separated out are obtained;
(4) grinding and polishing the quenched sample, corroding the sample by using 4% nitric acid alcohol, and observing the thickness of the ferrite film of the sample;
(5) and (4) counting the TiC size and the ferrite film thickness in the step (3) and the step (4). Wherein 85% of TiC is observed to be less than or equal to 8 μm in length in a visual field of 250 μm multiplied by 250 μm, the average ferrite film thickness is less than or equal to 2 μm, and the lowest cooling speed meeting the cooling speed under the condition is taken as the critical cooling speed of the high-thermoplastic region of the high-titanium steel.
It should be particularly noted that the various components or steps in the above embodiments can be mutually intersected, replaced, added or deleted, and therefore, the combination formed by the reasonable permutation and combination conversion shall also belong to the protection scope of the present invention, and the protection scope of the present invention shall not be limited to the embodiments.
The above is an exemplary embodiment of the present disclosure, and the order of disclosure of the above embodiment of the present disclosure is only for description and does not represent the merits of the embodiment. It should be noted that the discussion of any embodiment above is exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, of embodiments of the invention is limited to those examples, and that various changes and modifications may be made without departing from the scope, as defined in the claims. The functions, steps and/or actions of the method claims in accordance with the disclosed embodiments described herein need not be performed in any particular order. Furthermore, although elements of the disclosed embodiments of the invention may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.
Those of ordinary skill in the art will understand that: the discussion of any embodiment above is meant to be exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, of embodiments of the invention is limited to these examples; within the idea of an embodiment of the invention, also technical features in the above embodiment or in different embodiments may be combined and there are many other variations of the different aspects of an embodiment of the invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omissions, modifications, substitutions, improvements, and the like that may be made without departing from the spirit and principles of the embodiments of the present invention are intended to be included within the scope of the embodiments of the present invention.
Claims (10)
1. A method of determining a critical cooling rate for a continuous casting process, comprising:
heating and melting a plurality of high titanium steel samples with the same titanium content;
cooling the melted samples at different cooling rates respectively to the temperature of the samples out of the crystallizer;
quenching the plurality of cooled samples;
obtaining the sizes of carbides precipitated in the solidification process of a plurality of samples, and obtaining the thicknesses of ferrite films of the quenched samples;
and determining samples meeting the carbide size standard and the ferrite film thickness standard, and taking the corresponding lowest cooling rate as the critical cooling rate of the high-titanium steel with the titanium content.
2. The method according to claim 1, wherein the heating temperature is 30-50 ℃ higher than the liquidus temperature of the sample, and the holding time is 3-5 min.
3. The method of claim 2, wherein the liquidus temperature is obtained based on the alloy composition of the sample.
4. The method of claim 1, wherein the following parameters of the sample are obtained based on the alloy composition of the sample: liquidus temperature, solidus temperature, density, thermophysical parameters; and
obtaining the crystallizer-exiting temperature based on the plurality of parameters.
5. The method of claim 1, wherein a plurality of the samples are selected from corner regions of a high titanium steel billet; and/or
The cooling rate is 0.2-50 ℃/s.
6. The method of claim 1, wherein a plurality of said samples are divided into a plurality of groups,
wherein the cooling rate of one group of samples is between 0.1 and 1 ℃/s, and the minimum difference of the cooling rates of the group of samples is between 0.1 and 0.3 ℃/s; and/or
The cooling rate of one group of samples is 1-10 ℃/s, and the minimum difference of the cooling rates of the group of samples is 1-3 ℃/s; and/or
The cooling rate of one group of samples is 10-50 ℃/s, and the minimum difference of the cooling rates of the group of samples is 5-20 ℃/s.
7. The method of claim 1,
the carbide size standard is as follows: in a field of 250 micrometers multiplied by 250 micrometers, the proportion of carbide with the length less than or equal to 8 micrometers is 85-90%; and/or
The thickness standard of the ferrite film is as follows: the average ferrite film thickness is 2 μm or less.
8. The method of claim 1, further comprising:
preparing high titanium steel to be measured by adopting the critical cooling rate, and performing a tensile test on the high titanium steel to be measured to obtain the reduction of area;
verifying the critical cooling rate based on the reduction of area, wherein if the reduction of area is less than 60%, the critical cooling rate is verified to be false.
9. The method of claim 8, wherein the obtaining the high titanium steel to be tested comprises:
heating the high titanium steel at 1350-1450 ℃ for 3-10 min;
and cooling the heated high titanium steel to the crystallizer discharging temperature at the critical cooling rate.
10. The method of claim 1, wherein the quenching comprises: an inert gas is sparged into the sample.
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