CN116759020A - Prediction method for shrinkage cavity segregation diffusion in continuous casting billet heating process - Google Patents
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 96
- 238000005204 segregation Methods 0.000 title claims abstract description 81
- 238000000034 method Methods 0.000 title claims abstract description 33
- 238000009749 continuous casting Methods 0.000 title claims abstract description 24
- 238000009792 diffusion process Methods 0.000 title claims abstract description 20
- 238000005266 casting Methods 0.000 claims abstract description 18
- 239000000523 sample Substances 0.000 claims description 19
- 229910000831 Steel Inorganic materials 0.000 claims description 15
- 239000010959 steel Substances 0.000 claims description 15
- 239000012468 concentrated sample Substances 0.000 claims description 9
- 238000005520 cutting process Methods 0.000 claims description 4
- 238000004458 analytical method Methods 0.000 abstract description 5
- 229910052799 carbon Inorganic materials 0.000 description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- 238000000265 homogenisation Methods 0.000 description 4
- 238000005498 polishing Methods 0.000 description 4
- 238000009826 distribution Methods 0.000 description 3
- 238000005096 rolling process Methods 0.000 description 3
- 238000005070 sampling Methods 0.000 description 3
- 238000004364 calculation method Methods 0.000 description 2
- 210000001787 dendrite Anatomy 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000004321 preservation Methods 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
- G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T17/00—Three dimensional [3D] modelling, e.g. data description of 3D objects
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- G—PHYSICS
- G16—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS
- G16C—COMPUTATIONAL CHEMISTRY; CHEMOINFORMATICS; COMPUTATIONAL MATERIALS SCIENCE
- G16C60/00—Computational materials science, i.e. ICT specially adapted for investigating the physical or chemical properties of materials or phenomena associated with their design, synthesis, processing, characterisation or utilisation
Abstract
The invention discloses a prediction method for shrinkage cavity segregation diffusion in a continuous casting billet heating process, which comprises the following steps: 1) Scanning the appearance of the shrinkage cavity by using a field emission electron microscope to obtain the micro segregation ratio SR before heating the interior of the shrinkage cavity AH Calculating the micro segregation ratio SR before heating by adopting a formula (1) AH Time t'; 2) Calculating the micro segregation ratio SR after heating corresponding to different heating time t under the heating temperature according to the formula (2) BH . The method further determines the micro segregation degree in the continuous casting blank by analyzing the segregation ratio of micro segregation in the shrinkage cavity of the continuous casting blank, so that the proper heating process parameters can be determined according to the analysis. The method provides the specific parameter obtaining and calculating method, the analysis result is accurate and quick, and the method can effectively provide for the heat treatment process of the casting blank feeding processFor technical support.
Description
Technical Field
The invention relates to a continuous casting method, in particular to a prediction method for shrinkage cavity segregation diffusion in a continuous casting billet heating process.
Background
Because of the difference of solute distribution coefficients, macro-micro segregation is formed in the solidification process of molten steel, and meanwhile, central shrinkage cavities and looseness are generated under the actions of dendrite bridging and solidification shrinkage, and two metallurgical defects of segregation and shrinkage cavities are often accompanied. Macrosegregation will reduce the yield, mechanical properties and corrosion resistance of the casting blank and is prone to crack formation. Micro segregation will form a band-like structure in the subsequent rolling production process, affecting the mechanical properties and mechanical properties of the material. The central shrinkage cavity and the looseness can be easily expanded into cracks in the subsequent rolling production process, and the product quality is seriously affected. Therefore, the improvement of the internal quality of the casting blank has important significance. The heating process of the continuous casting blank feeding process is the most effective method for improving the micro segregation in the casting blank, namely, the casting blank is subjected to heating and heat preservation treatment before rolling, so that the micro segregation is subjected to diffusion homogenization, and the influence of the micro segregation of the casting blank on a rolled material is reduced.
In the prior published patent application, the patent CN201810804789.4 'microscopic structure simulation method of the casting blank' utilizes microscopic segregation and secondary dendrite spacing in a certain area of the casting blank, and predicts the required heating time and temperature by constructing an element concentration distribution diffusion model; however, the method can only obtain diffusion time and temperature, and can not predict the micro segregation ratio after diffusion. Patent CN202010394128.6, "a control method for promoting homogenization treatment of continuous casting billets", uses pulse current to improve diffusion mobility of solute atoms in the heating process of continuous casting billets, and effectively reduces intergranular solute segregation; however, the method only considers the inter-dendrite diffusion, and does not consider the micro segregation diffusion in the shrinkage cavity and the influence of the shrinkage cavity on the micro segregation diffusion. Patent application CN202111134925.1, "a high temperature diffusion heating process to mitigate carbon segregation in the micro-zone of the axle steel blank LZ50," provides a rational heating process to mitigate micro-segregation of the axle steel blank LZ50, which again does not predict micro-segregation after heating.
Disclosure of Invention
The invention aims to provide a prediction method for shrinkage cavity segregation diffusion in a continuous casting billet heating process.
In order to solve the technical problems, the invention adopts the following steps: the method comprises the following steps: 1) Scanning the appearance of the shrinkage cavity by using a field emission electron microscope to obtain the micro segregation ratio SR before heating the interior of the shrinkage cavity AH Calculating the micro segregation ratio SR before heating by adopting a formula (1) AH Time t';
in the formula (1), alpha is a steel grade-related parameter, and is 1 < C + > or C]/2；SR AH Is the micro segregation ratio before heating; r is the average diameter of shrinkage cavities, mum; d is the thermal diffusivity, cm 2 S; t' is the ratio SR of micro segregation before heating AH S, s;
2) Calculating the micro segregation ratio SR after heating corresponding to different heating time t under the heating temperature according to the formula (2) BH ；
In the formula (1), alpha is a steel grade-related parameter, and is 1 < C + > or C]/2；SR BH Is the micro segregation ratio after heating; r is the average diameter of shrinkage cavities, mum; d is the thermal diffusivity, cm 2 S; t is heating time, s; t' is the ratio SR of micro segregation before heating AH S, is provided.
Further, carrying out layered scanning on a sample of the continuous casting blank by using an ultrasonic scanning microscope, carrying out three-dimensional shrinkage cavity reconstruction on a layered scanning picture, finding out a shrinkage cavity concentrated part in the sample, and cutting out to form a shrinkage cavity concentrated sample; scanning the shrinkage cavity morphology of the shrinkage cavity concentrated sample by using a field emission electron microscope to obtain a micro segregation ratio SR before heating AH 。
Further, in the step 2), the micro segregation ratio SR after heating BH When the temperature is less than or equal to 1.5, the casting blank is considered to be homogenized.
The beneficial effects of adopting above-mentioned technical scheme to produce lie in: the invention analyzes the segregation ratio of the micro segregation in the shrinkage cavity of the continuous casting billet, so as to determine the micro segregation degree in the continuous casting billet, thereby determining proper heating process parameters according to the analysis. The invention provides the method for obtaining and calculating the specific parameters, the analysis result is accurate and quick, and the technical support can be effectively provided for the heat treatment process in the casting blank loading process.
Drawings
The invention will be described in further detail with reference to the drawings and the detailed description.
FIG. 1 is a sonogram of microscopic shrinkage cavity of a cross-section of a cast slab according to example 1 of the present invention;
FIG. 2 is a graph showing shrinkage cavity morphology and carbon element surface scanning before heating in example 1 of the present invention;
FIG. 3 is a graph showing the morphology of shrinkage cavities after heating and the surface scan of carbon element in example 1 of the present invention;
FIG. 4 is a SR in example 1 of the invention BH A graph of variation with heating temperature;
FIG. 5 is a SR in example 1 of the invention BH Graph of change with heating time.
Detailed Description
The method for predicting shrinkage cavity segregation diffusion in the continuous casting billet heating process comprises the following process steps: 1) Sampling at the center of the continuous casting billet, and polishing the sample; the test sample is a cuboid test sample with smooth and flat surface, and the dimensions are that the length is less than or equal to 120mm, the width is less than or equal to 100mm, and the thickness is less than or equal to 20mm.
2) And carrying out layered scanning on the sample by using an ultrasonic scanning microscope, carrying out three-dimensional shrinkage cavity reconstruction on a layered scanning picture, counting the size range of shrinkage cavities in the casting blank, and determining the average equivalent volume size diameter of the shrinkage cavities, namely the average shrinkage cavity diameter R.
3) Analyzing the sample according to the average equivalent volume size diameter R to determine the concentrated part of shrinkage cavities in the sample; cutting the part of the sample with concentrated shrinkage cavities into cubes with the length, width and height not exceeding 15mm, and polishing to ensure that the cubes have no obvious scratches under a metallographic microscope view field of 200 times, thereby forming the shrinkage cavity concentrated sample.
4) The shrinkage cavity concentrated sample uses a field emission electron microscope to conduct shrinkage cavity morphology scanning, representative shrinkage cavities are selected according to the counted size range of the shrinkage cavities in the casting blank, and surface scanning is used for scanning the shrinkage cavities, and the micro segregation ratio SR (Segregation Ratio) in the shrinkage cavities, namely the micro segregation ratio SR after heating is calculated AH The method comprises the steps of carrying out a first treatment on the surface of the The SR is the maximum value of micro segregation in the shrinkage cavity and the minimum value of micro segregation in the shrinkage cavity. The representative shrinkage cavity is selected within the following size ranges: the size range is positioned in the middle of the total size range, the number of shrinkage cavities in the size range accounts for 30-50% of the total amount of shrinkage cavities, and the average diameter R of the shrinkage cavities is positioned in the size range.
5) Calculating the micro segregation ratio SR before heating by adopting a formula (1) AH Time t';
in the formula (1), alpha is a steel grade-related parameter, and is 1 < C + > or C]/2，The [ C ]]Is the carbon content in the continuous casting billet; SR (SR) AH Is the micro segregation ratio before heating; r is the average diameter of shrinkage cavities, and the unit is mu m; d is the thermal diffusivity in cm 2 S; t' is the ratio SR of micro segregation before heating AH In units of s.
6) Calculating the micro segregation ratio SR after heating corresponding to different heating time t under the heating temperature according to the formula (2) BH ；
In the formula (2), alpha is a steel grade-related parameter, and is 1 < C + > or C]/2；SR BH Is the micro segregation ratio after heating; r is the average diameter of shrinkage cavities, and the unit is mu m; d is the thermal diffusivity in cm 2 S; t is heating time, unit s; t' is the ratio SR of micro segregation before heating AH In units of s.
7) The micro segregation ratio SR after heating calculated by the process BH The smaller the size, the higher the homogenization degree of the casting blank; micro segregation ratio SR after heating BH When the temperature is less than or equal to 1.5, the casting blank is considered to reach the required homogenization degree, and the heating temperature and the heat preservation time at the moment are recorded and used as heating parameters in the subsequent continuous casting blank loading and conveying process. Optionally selecting a plurality of representative shrinkage cavities, respectively performing scanning calculation in the steps 4), 5) and 6), and finally calculating the micro segregation ratio SR after heating BH Average value of (1) using the SR BH The average value of (2) is predicted.
Example 1: the method for predicting shrinkage cavity segregation diffusion in the continuous casting billet heating process is specifically as follows.
Taking a gear steel bloom of a certain model of Bao steel as an example, the contents of the components of the steel grade are (wt): 0.18 to 0.22 percent of C, 0.2 to 0.3 percent of Si, 1.25 to 1.35 percent of Mn, 0 to 0.15 percent of P, 0.01 to 0.02 percent of S, and the balance of Fe and unavoidable impurities; the cross-sectional dimension was 320X 425mm.
1) Sampling at the center of the continuous casting billet, and polishing the sample; the size of the sample is 120mm in length, 100mm in width and less than or equal to 20mm in thickness.
2) Carrying out ultrasonic scanning on the whole section to determine the position areas where the microcosmic shrinkage cavities exist in a large number, as shown in figure 1; and carrying out three-dimensional reconstruction on the scanning area, counting the size range of the shrinkage holes in the casting blank, wherein the size of the shrinkage holes is equivalent to the diameter of a sphere with the same size as the shrinkage holes, and determining the average equivalent size diameter R=116 mu m of the shrinkage holes.
The ultrasonic scanning instrument is KSI 400E, the probe is 10Hz, the section thickness is 20mm, and the scanning depth is 20mm.
3) Cutting and sampling (central area) at the place with more microcosmic shrinkage cavities, and polishing the shrinkage cavity concentrated sample; the size of the obtained shrinkage cavity concentrated sample is 15mm in length, 15mm in width and 15mm in height.
4) The statistical result of the step 2 shows that the shrinkage cavity range is less than 100 mu m and is 30.24%, the 100-300 mu m is 47.56%, and the 300-1000 mu m is 22.2%; selecting the 100-300 mu m with the highest duty ratio range as a representative size selection range of the shrinkage holes; searching shrinkage cavities on a sample by using an electronic probe, searching 9 shrinkage cavities at different positions, wherein the searched shrinkage cavities are all located in the size selection range, scanning each shrinkage cavity by using surface scanning, and calculating the micro segregation ratio SR inside each shrinkage cavity before high-temperature diffusion, wherein the micro segregation ratio SR is respectively: 2.469, 2.655, 1.707, 2.024, 2.783, 2.287, 2.457, 2.174, 2.455; the morphology and carbon element surface scanning diagram of the No. 7 shrinkage cavity are shown in FIG. 2.
5) The following is calculated by taking a 7# shrinkage cavity as an example, and other shrinkage cavities are calculated by the same process; the preset heating process comprises the following steps: heating temperature 1250 ℃ and heating time 90min; calculating the micro segregation ratio in the shrinkage cavity after heating by using the formula (1);
wherein α is a parameter related to the steel grade, α=1+0.22/2=1.11 for a steel grade having a carbon content of 0.22 wt%; SR (SR) AH Is the micro segregation ratio before heating; r is the average diameter of shrinkage cavities, 116 mu m; d is the thermal diffusivity, temperature and element dependent,the steel grade has a thermal diffusivity of 291.04 μm at 1250 DEG C 2 S; t' is the ratio SR of micro segregation before heating AH Time of (2); t' =252.8 s is calculated according to formula (1).
6) Calculating the micro segregation ratio SR after heating corresponding to different heating time t under the heating temperature according to the formula (2) BH ；
In the formula (2), alpha is 1.11; SR (SR) BH Is the micro segregation ratio after heating; r is the average diameter of shrinkage cavities, 116 mu m; d is the thermal diffusivity, 291.04 μm 2 S; t is heating time, 5400s; t' is the ratio SR of micro segregation before heating AH 252.8s. Obtaining the sample model to calculate the micro segregation ratio SR after heating BH 1.574. The micro segregation ratio SR before heating detected by each shrinkage cavity AH Calculated post-heating microsegregation ratio SR BH See table 1 below.
7) According to a preset heating process: heating temperature 1250 ℃ and heating time 90min; heating the shrinkage cavity concentrated sample, and then performing surface scanning through an electronic probe to obtain a heated actual micro segregation ratio SR Actual practice is that of The morphology of the No. 7 shrinkage cavity and the carbon element surface scanning chart are shown in FIG. 3; the results are shown in Table 1;
table 1: example 1 micro segregation ratio of sample
| Shrinkage cavity | 1# | 2# | 3# | 4# | 5# | 6# | 7# | 8# | 9# |
| SR AH | 2.469 | 2.655 | 1.707 | 2.024 | 2.783 | 2.287 | 2.457 | 2.174 | 2.455 |
| SR Actual practice is that of | 1.504 | 1.497 | 1.388 | 1.684 | 1.642 | 1.552 | 1.604 | 1.422 | 1.661 |
| SR BH | 1.502 | 1.500 | 1.500 | 1.506 | 1.505 | 1.516 | 1.538 | 1.542 | 1.606 |
| Error% | 0.133 | -0.200 | 8.069 | -11.620 | -8.343 | -2.320 | -4.115 | 8.439 | -3.311 |
Taking the 7# shrinkage cavity as an example for illustration, the SR calculated by the method BH 1.538, and the actual micro segregation ratio SR after heating obtained by electron probe surface scanning Actual practice is that of 1.604, the error was-4.115%.
8) The same casting blank can be provided with a plurality of samples, the steps 1) to 5) are respectively adopted to carry out analysis and calculation under different heating processes, and the calculated SR BH The value is established with the corresponding heating temperature and heating time to obtain the SR shown in FIG. 4 BH Plot of change with heating temperature, SR shown in FIG. 5 BH Graph of change with heating time. FIG. 3 is a diagram showing the distribution of elements after heating the inside of the shrinkage cavity in the present embodiment; as shown in fig. 3, 4 and 5, when the micro segregation in the shrinkage cavity is heated at different temperatures, the micro segregation in the shrinkage cavity is diffused, and the micro segregation in the shrinkage cavity of the casting blank is also causedSegregation uniformity (SR) BH And 1.5) is different, whereby different heating temperatures and times matched to the temperatures can be selected according to the prediction result.
Claims (3)
1. The method for predicting shrinkage cavity segregation diffusion in the continuous casting billet heating process is characterized by comprising the following steps: 1) Scanning the appearance of the shrinkage cavity by using a field emission electron microscope to obtain the micro segregation ratio SR before heating the interior of the shrinkage cavity AH Calculating the micro segregation ratio SR before heating by adopting a formula (1) AH Time t';
in the formula (1), alpha is a steel grade-related parameter, and is 1 < C + > or C]/2；SR AH Is the micro segregation ratio before heating; r is the average diameter of shrinkage cavities, mum; d is the thermal diffusivity, cm 2 S; t' is the ratio SR of micro segregation before heating AH S, s;
2) Calculating the micro segregation ratio SR after heating corresponding to different heating time t under the heating temperature according to the formula (2) BH ；
In the formula (2), alpha is a steel grade-related parameter, and is 1 < C + > or C]/2；SR BH Is the micro segregation ratio after heating; r is the average diameter of shrinkage cavities, mum; d is the thermal diffusivity, cm 2 S; t is heating time, s; t' is the ratio SR of micro segregation before heating AH S, is provided.
2. The method for predicting shrinkage cavity segregation diffusion in the heating process of a continuous casting billet according to claim 1, wherein: using an ultrasonic scanning microscope to conduct layered scanning on a sample of the continuous casting blank, conducting three-dimensional shrinkage cavity reconstruction on a layered scanning picture, and finding out a shrinkage cavity concentrated part in the sampleDividing and cutting to form a shrinkage cavity concentrated sample; scanning the shrinkage cavity morphology of the shrinkage cavity concentrated sample by using a field emission electron microscope to obtain a micro segregation ratio SR before heating AH 。
3. The prediction method of shrinkage cavity segregation diffusion during heating of a continuous casting billet according to claim 1 or 2, wherein: in the step 2), the micro segregation ratio SR after heating BH When the temperature is less than or equal to 1.5, the casting blank is considered to be homogenized.
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