CN114764067B - Prediction method of austenite grain boundary cracks on the surface of continuous casting billet based on as-cast structure - Google Patents
Prediction method of austenite grain boundary cracks on the surface of continuous casting billet based on as-cast structure Download PDFInfo
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- 229910001566 austenite Inorganic materials 0.000 title claims abstract description 47
- 238000009749 continuous casting Methods 0.000 title claims abstract description 44
- 238000000034 method Methods 0.000 title claims abstract description 13
- 239000013078 crystal Substances 0.000 claims abstract description 80
- 230000035945 sensitivity Effects 0.000 claims abstract description 31
- 238000009826 distribution Methods 0.000 claims abstract description 9
- 239000002344 surface layer Substances 0.000 claims abstract description 9
- 238000004140 cleaning Methods 0.000 claims abstract description 4
- 230000001174 ascending effect Effects 0.000 claims abstract 3
- 230000002902 bimodal effect Effects 0.000 claims description 7
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 3
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims 1
- 229910017604 nitric acid Inorganic materials 0.000 claims 1
- 238000005266 casting Methods 0.000 description 25
- 229910000831 Steel Inorganic materials 0.000 description 8
- 239000010959 steel Substances 0.000 description 8
- 238000012512 characterization method Methods 0.000 description 6
- 238000010273 cold forging Methods 0.000 description 6
- 238000004458 analytical method Methods 0.000 description 4
- 238000005336 cracking Methods 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 229910002651 NO3 Inorganic materials 0.000 description 2
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000006355 external stress Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract
本发明公开了基于铸态组织的连铸小方坯表面奥氏体晶界裂纹预测方法，包括：1)对连铸坯表面进行清洁处理，通过金相显微镜得到连铸坯表层的铸态显微组织图像；2)用晶粒等效圆直径作为晶粒当量直径，将铸态显微组织图像的视域内所有晶粒的晶粒等效圆直径按递增顺序划分为多个等级，通过计算不同等级范围内晶粒面积百分比来表征奥氏体晶粒尺寸的分布情况；3)将混晶组织按晶粒等效圆直径划分为粗晶粒区和细晶粒区，在两区内均存在两个面积百分比的最大值，计算混晶指数；4)根据奥氏体晶粒尺寸、混晶指数，判断晶界裂纹敏感性。本发明在现有奥氏体晶界裂纹判据的基础上，引入混晶指数参数来实现对连铸坯表面奥氏体晶界裂纹敏感性的准确预测。
The present invention discloses a method for predicting austenite grain boundary cracks on the surface of a continuous casting billet based on as-cast structure, comprising: 1) cleaning the surface of the continuous casting billet, and obtaining an as-cast microstructure image of the surface layer of the continuous casting billet through a metallographic microscope; 2) using the grain equivalent circle diameter as the grain equivalent diameter, dividing the grain equivalent circle diameters of all grains in the field of view of the as-cast microstructure image into multiple levels in ascending order, and characterizing the distribution of austenite grain size by calculating the percentage of grain area within different levels; 3) dividing the mixed crystal structure into a coarse grain area and a fine grain area according to the grain equivalent circle diameter, and there are two maximum values of area percentage in both areas, and calculating the mixed crystal index; 4) judging the grain boundary crack sensitivity according to the austenite grain size and the mixed crystal index. The present invention introduces a mixed crystal index parameter on the basis of the existing austenite grain boundary crack criterion to realize accurate prediction of the austenite grain boundary crack sensitivity on the surface of the continuous casting billet.
Description
Technical Field
The invention relates to a continuous casting production technology, in particular to a continuous casting billet surface austenite grain boundary crack prediction method based on an as-cast structure.
Background
Grain boundary cracks on the surface of a continuous casting blank are an important factor for influencing the surface quality of the casting blank. This type of crack always develops along coarse austenite grain boundaries, propagates along the grain boundaries under external stress, and eventually forms surface macrocracks. The coarser the original austenite size, the more easily grain boundary cracks are generated on the surface of the continuous casting slab, namely, coarse original austenite grains are key factors for causing the grain boundary cracks to be generated on the surface of the continuous casting slab.
At present, the grain boundary crack sensitivity of the continuous casting billet is mainly predicted by the critical size of the original austenite crystal grains, and when the size of the original austenite crystal grains is larger than 1mm, the grain structure crack sensitivity is strong, and the continuous casting billet is easy to generate grain boundary cracks; when the original austenite grain size is smaller than 1mm, the sensitivity of grain structure cracks is weak, and the continuous casting billet is not easy to generate grain boundary cracks. However, it was found by analysis of the actual cast slab surface that austenite grains smaller than 1mm exist in the austenite structure at the cracks, and that austenite grains larger than 1mm do not have grain boundary cracks. This indicates that there is a shortage of susceptibility to predicting grain boundary cracking at the surface of a continuous casting billet based on the prior austenite grain size alone. Therefore, it is very necessary to perfect the existing crack sensitivity criterion to improve the prediction accuracy of the grain boundary crack sensitivity of the surface of the continuous casting billet.
The austenitic structure of the surface layer of the continuous casting blank is observed, and the sizes of crystal grains are mixed and randomly distributed, the shapes of the crystal grains in the structure are different, small crystal grains are mixed in a large crystal grain group, or the large crystal grains are mixed in a small crystal grain group to surround the phenomenon, namely a mixed crystal structure. As in literature "Characterisation of bimodal grain structures in HSLA steels"(Debalay Chakrabarti,et al.Materials Characterization,2007,58:423-438.), quantitative characterization of mixed crystal structure by mixed crystal index is proposed, but the relationship between mixed crystal index and austenite grain boundary crack is not studied.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide a continuous casting billet surface austenite grain boundary crack prediction method based on an as-cast structure, and on the basis of the existing austenite grain boundary crack criterion, mixed crystal index parameters are introduced to realize accurate prediction of the sensitivity of austenite grain boundary cracks on the continuous casting billet surface.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a continuous casting billet surface austenite grain boundary crack prediction method based on an as-cast structure comprises the following steps:
1) Cleaning the surface of a continuous casting billet, and obtaining an as-cast microstructure image of the surface layer of the continuous casting billet through a metallographic microscope;
2) Dividing the equivalent circle diameters of the crystal grains in the view field of the as-cast microstructure image into a plurality of grades according to an increasing sequence by taking the equivalent circle diameters of the crystal grains as equivalent diameters of the crystal grains, calculating area percentages of the crystal grains in different grade ranges, and drawing by taking the equivalent circle diameters of the crystal grains in different grades as an abscissa and the corresponding area percentages of the crystal grains as an ordinate to obtain a bimodal distribution image of a mixed crystal structure;
3) Dividing the mixed crystal structure into a coarse grain region and a fine grain region according to the bimodal distribution image in the step 2), wherein the maximum value of the area percentage exists in the coarse grain region and the fine grain region, and calculating the peak height ratio to obtain a mixed crystal index;
4) And judging the sensitivity of the grain boundary crack according to the austenitic grain size and the mixed crystal index.
Preferably, in the step 1), the surface of the continuous casting blank is cleaned by using nitrate alcohol.
Preferably, in the step 2), the equivalent circle diameters of the grains are divided into 15 grades in increasing order.
Preferably, in the step 4), the grain boundary crack sensitivity is determined as follows:
When the equivalent circle diameter of the crystal grains is larger than 1mm critical diameter and the mixed crystal index is larger than 0.5, crystal boundary cracks are easy to generate on the surface of a casting blank, and the sensitivity of the crystal boundary cracks is strong;
When the equivalent circle diameter of the crystal grains is larger than 1mm critical diameter and the mixed crystal index is smaller than 0.5, grain boundary cracks are not easy to generate on the surface of a casting blank, and the sensitivity of the grain boundary cracks is weak;
When the equivalent circle diameter of the crystal grains is smaller than the critical diameter of 1mm and the mixed crystal index is larger than 0.7, crystal boundary cracks are easy to generate on the surface of a casting blank, and the sensitivity of the crystal boundary cracks is strong;
when the equivalent circle diameter of the crystal grains is smaller than 1mm critical diameter and the mixed crystal index is smaller than 0.7, grain boundary cracks are not easy to generate on the surface of a casting blank, and the sensitivity of the grain boundary cracks is weak.
The continuous casting billet surface austenite grain boundary crack prediction method based on the cast structure provided by the invention has the advantages of high accuracy, simplicity and strong applicability, so that the accuracy of judging the sensitivity of the austenite grain boundary crack on the surface of the continuous casting billet is increased from 64.1% to 97.4%, and the accurate prediction of the sensitivity of the grain boundary crack is realized.
Drawings
FIG. 1 is a schematic diagram of the austenitic grain boundary crack sensitivity criterion of the continuous casting billet surface austenitic grain boundary crack prediction method of the present invention with respect to the continuous casting billet surface austenitic grain boundary crack.
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 predicting austenite grain boundary cracks on the surface of a continuous casting billet based on an as-cast structure provided by the invention comprises the following steps:
1) Cleaning the surface of the continuous casting billet by using nitrate alcohol, and obtaining an as-cast microstructure image of the surface layer of the continuous casting billet through a metallographic microscope;
2) Dividing the Equivalent Circle Diameter (ECD) of all grains in the view of the as-cast microstructure image into 15 grades in increasing order by taking the equivalent circle diameter (see the reference ECD in figure 1) of the grains as the equivalent circle diameter of the grains, calculating the area percentage of the grains in the range of different grades (the ratio of the area of the grains in the different grades to the total area of the grains), and plotting the Equivalent Circle Diameter (ECD) of the grains in the different grades as the abscissa and the corresponding area percentage of the grains as the ordinate to obtain a bimodal distribution image (two maximum points of the area percentage of the grains);
3) Dividing the mixed crystal structure into a coarse grain region and a fine grain region according to the Equivalent Circle Diameter (ECD) of the grains according to the bimodal distribution image in the step 2) (usually taking the equivalent circle diameter corresponding to the minimum grain area percentage between the two peaks as a breakpoint), wherein the maximum value of the area percentage exists in the coarse grain region and the fine grain region (namely the two peaks), and calculating the peak height ratio to be the mixed crystal index (see the reference number PHR in figure 1);
4) Judging the sensitivity of the grain boundary crack according to the austenitic grain size and the mixed crystal index, wherein the sensitivity is as follows:
when the Equivalent Circle Diameter (ECD) of the crystal grains is larger than 1mm critical diameter and the mixed crystal index (PHR) is larger than 0.5, the surface of the casting blank is easy to generate grain boundary cracks, and the sensitivity of the grain boundary cracks is strong;
When the Equivalent Circle Diameter (ECD) of the crystal grains is larger than 1mm critical diameter and the mixed crystal index (PHR) is smaller than 0.5, the surface of the casting blank is not easy to generate grain boundary cracks, and the sensitivity of the grain boundary cracks is weak;
when the Equivalent Circle Diameter (ECD) of the crystal grains is smaller than the critical diameter of 1mm and the mixed crystal index (PHR) is larger than 0.7, the surface of the casting blank is easy to generate grain boundary cracks, and the sensitivity of the grain boundary cracks is strong;
when the Equivalent Circle Diameter (ECD) of the crystal grains is smaller than 1mm critical diameter and the mixed crystal index (PHR) is smaller than 0.7, the surface of the casting blank is not easy to generate grain boundary cracks, and the sensitivity of the grain boundary cracks is weak.
In an ideal state, the grain size is in unimodal distribution, the mixed crystal index (PHR) is zero (peak height ratio=0), the grain size is uniform, and the austenitic structure of the surface layer of the casting blank has higher high-temperature plasticity; the higher the mixed crystal index (PHR), the more serious the mixed crystal, the more uneven the grain size distribution, the worse the high-temperature plasticity of the casting blank, the stronger the sensitivity of cracks on the surface of the casting blank, and the more easily the cracks are generated in the continuous casting process.
Examples 1 to 3 below are examples of continuous casting billets (brands: 10B21, SCM440, SWRCH22A, section 160 mm. Times.160 mm) of cold-headed alloy steel actually produced in a certain factory. The original austenite grain size is counted and the mixed crystal index is calculated through the observation and analysis of the as-cast structure of the original austenite grains on the surface of the cold heading steel casting blank, such as grain boundary cracks, surface depressions, deep vibration marks and normal positions.
Example 1
10B21 continuous casting billet
In this example 10B21 alloy cold forging steel continuous casting billet (specification: section 160 mm. Times.160 mm), as-cast structure observation analysis of surface layer original austenite grains at the surface grain boundary crack, surface dent, deep vibration mark and normal position of cold forging steel casting billet, the original austenite grain size was counted and mixed crystal index was calculated.
TABLE 1 Austenitic grain size characterization parameters and grain boundary cracking relations for casting surface
| Sample preparation | Maximum austenite grain size (μm) | Mixed crystal index | With or without cracks |
| 1# | 1188 | 0.96 | Has the following components |
| 2# | 1572 | 1.12 | Has the following components |
| 3# | 1042 | 0.41 | Without any means for |
| 4# | 1082 | 0.68 | Has the following components |
| 5# | 1576 | 1.04 | Has the following components |
| 6# | 936 | 0.94 | Has the following components |
| 7# | 865 | 0.51 | Without any means for |
| 8# | 874 | 1.12 | Has the following components |
| 9# | 927 | 0.68 | Without any means for |
| 10# | 742 | 0.61 | Without any means for |
In the above table 1, when the prior austenite grain size (grain equivalent circular diameter ECD) is greater than 1mm and the mixed crystal index (PHR) is greater than 0.5, grain boundary cracks are generated on the surface of the cast slab; when the mixed crystal index is less than 0.5, no grain boundary crack is generated. When the original austenite grain size is smaller than 1mm and the mixed crystal index is larger than 0.7, grain boundary cracks are easy to occur on the surface of the casting blank; when the mixed crystal index is less than 0.7, no grain boundary crack is generated on the surface of the casting blank. Meets the austenitic grain boundary crack sensitivity criterion proposed by the invention.
Example 2
SCM440 continuous casting billet
The SCM440 alloy cold forging steel continuous casting billet (specification: section 160mm×160 mm) of the embodiment is used for observing and analyzing the as-cast structure of surface layer original austenite grains at the surface grain boundary cracks, surface pits, deep vibration marks and normal positions of the cold forging steel casting billet, counting the sizes of the original austenite grains and calculating the mixed crystal index.
TABLE 2 Austenitic grain size characterization parameters and grain boundary cracking relations for casting surface
| Sample preparation | Maximum austenite grain size (μm) | Mixed crystal index | With or without cracks |
| 1# | 1129 | 0.43 | Without any means for |
| 2# | 1239 | 0.51 | Has the following components |
| 3# | 1104 | 0.35 | Without any means for |
| 4# | 1135 | 0.82 | Has the following components |
| 5# | 668 | 0.32 | Without any means for |
| 6# | 623 | 0.26 | Without any means for |
| 7# | 558 | 0.06 | Without any means for |
| 8# | 686 | 0.47 | Without any means for |
| 9# | 794 | 1.33 | Has the following components |
In the above table 2, when the prior austenite grain size (grain equivalent circular diameter ECD) is greater than 1mm and the mixed crystal index (PHR) is greater than 0.5, grain boundary cracks are generated on the surface of the cast slab; when the mixed crystal index is less than 0.5, no grain boundary crack is generated. When the original austenite grain size is smaller than 1mm and the mixed crystal index is larger than 0.7, grain boundary cracks are easy to occur on the surface of the casting blank; when the mixed crystal index is less than 0.7, no grain boundary crack is generated on the surface of the casting blank. Meets the austenitic grain boundary crack sensitivity criterion proposed by the invention.
Example 3
SWRCH22A continuous casting billet
The SWRCH22A alloy cold forging steel continuous casting billet (specification: section 160mm×160 mm) of this example was subjected to observation and analysis of as-cast structure of surface layer original austenite grains at the surface grain boundary cracks, surface pits, deep vibration marks and normal positions of the cold forging steel casting billet, and the original austenite grain sizes were counted and the mixed crystal indexes were calculated.
TABLE 3 Austenitic grain size characterization parameters and grain boundary cracking relations for casting surface
| Sample preparation | Maximum austenite grain size (μm) | Mixed crystal index | With or without cracks |
| 1# | 1867 | 0.56 | Has the following components |
| 2# | 1267 | 0.45 | Has the following components |
| 3# | 667 | 1.01 | Has the following components |
| 4# | 798 | 0.86 | Has the following components |
| 5# | 886 | 0.47 | Without any means for |
| 6# | 894 | 1.31 | Has the following components |
In Table 3 above, when the prior austenite grain size (grain equivalent circular diameter ECD) is greater than 1mm and the mixed crystal index (PHR) is greater than 0.5, grain boundary cracks are generated on the surface of the cast slab; when the mixed crystal index is less than 0.5, grain boundary cracks are also generated. When the original austenite grain size is smaller than 1mm and the mixed crystal index is larger than 0.7, grain boundary cracks are easy to occur on the surface of the casting blank; when the mixed crystal index is less than 0.7, no grain boundary crack is generated on the surface of the casting blank. Meets the austenitic grain boundary crack sensitivity criterion proposed by the invention.
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.
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| CN107014813A (en) * | 2017-05-24 | 2017-08-04 | 东北大学 | A kind of steel continuous casting billet solidifies arborescent structure detection method |
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