CN113155861A - Method for detecting casting blank inclusions - Google Patents
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- CN113155861A CN113155861A CN202110234564.1A CN202110234564A CN113155861A CN 113155861 A CN113155861 A CN 113155861A CN 202110234564 A CN202110234564 A CN 202110234564A CN 113155861 A CN113155861 A CN 113155861A
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Abstract
The invention provides a method for detecting inclusions in a casting blank, which belongs to the technical field of continuous casting and comprises the steps of selecting a fixed-length casting blank to be subjected to inclusion detection as a casting blank to be detected, and carrying out surface quenching on the casting blank to be detected before grain boundary embrittlement; cutting a casting blank to be detected into a casting blank transverse sample with a set thickness along a blank drawing direction; performing low-power acid washing on the cross section of the casting blank transverse sample; observing whether a quenching area of a transverse sample of the casting blank has cracks or not; if cracks are generated in the quenching area of the transverse casting blank sample, judging that large-scale inclusions exist in the casting blank to be detected; the invention realizes the continuous analysis and detection of the inclusions on the whole fixed-length casting blank, thereby achieving the technical effects of improving the accuracy of the detection result and reducing the detection cost.
Description
Technical Field
The invention relates to the technical field of continuous casting, in particular to a method for detecting inclusions in a casting blank.
Background
The quality of the steel is influenced by oxide inclusions, and the quantity, the form, the size and the distribution position of the oxide inclusions have different damages to the quality of the steel; only through comprehensive and accurate analysis of inclusions in steel, the source, formation mechanism and distribution rule of the inclusions can be determined, and further, the steel making process is improved. Among them, the inclusions having a diameter of more than 50 μm become large inclusions, and the proportion of the large inclusions in the total amount of the inclusions is only 1%, but the large inclusions are very harmful to the quality of steel.
The detection and analysis of steel inclusions are completed by matching inclusion detection methods such as a microscope method, a small sample electrolysis method and a large sample electrolysis method with modes such as X-ray projection and sulfur imprint. The microscopic method comprises the steps of detecting the size, distribution position and quantity of inclusions on the surface of a polished steel sample by using an optical microscope, and then analyzing the type of the inclusions by using a metallographic photograph; the small sample point solution method and the large sample electrolysis method are used for detecting and analyzing inclusions by electrolyzing, elutriating, reducing, grading and bearing a steel sample with a certain weight; the disadvantages are as follows: only the steel sample area is detected, the whole casting blank cannot be continuously detected, the detection result is lack of continuity and has larger contingency, and the capturing effect of large inclusions is poor; the microscopy requires a large amount of steel samples, and has higher requirements on the surface smoothness of the steel samples, so that the detection cost is high; when the small sample electrolysis method and the large sample electrolysis method are used, a test period of 7 to 30 days is required for one steel sample.
In the prior art, large inclusions are detected on a steel sample by using ultrasonic waves or an OPA (in situ Analysis) technology; by utilizing the principle that the ultrasonic waves can be reflected when encountering the inclusions in the steel, the defects are displayed on a detection screen in the form of reflected waves, the number of the inclusions is judged according to the number of the defect waves, and the sizes of the inclusions are judged according to the height of the defect reflected waves. Although the detection time is shortened, professional detection personnel are required to be equipped, and the cost of the detection equipment is high.
Therefore, a method for detecting inclusions in a cast slab with low detection cost and high detection efficiency is needed.
Disclosure of Invention
The invention aims to provide a method for detecting inclusions in a casting blank, which aims to solve the problems of high detection cost and low detection efficiency of the conventional detection method.
The invention discloses a method for detecting inclusions in a casting blank, which comprises the following steps: selecting a fixed-length casting blank to be subjected to inclusion detection as a casting blank to be detected, and carrying out surface quenching on the casting blank to be detected before grain boundary embrittlement; when the temperature of the casting blank to be detected is cooled to 25 ℃, cutting the casting blank to be detected into a casting blank transverse sample with a set thickness along the blank drawing direction;
performing low-power acid washing on the cross section of the casting blank transverse sample;
observing whether a quenching area of a transverse sample of the casting blank has cracks or not;
and if cracks are generated in the quenching area of the transverse sample of the casting blank, judging that large-scale inclusions exist in the casting blank to be detected.
Further, preferably, the grain boundary embrittlement time of the sized casting blank is the time of the first intersection point position of the supercooled austenite isothermal cooling transformation curve and the temperature change curve of the casting blank;
the supercooled austenite isothermal cooling transformation curve comprises a ferrite starting generation curve, a pearlite ending generation curve and a bainite starting generation curve; the temperature change curves comprise a temperature change curve of a set depth from the wide surface to the surface, a temperature change curve of a set depth from the corner part to the surface and a temperature change curve of a set depth from the narrow surface to the surface.
Further, preferably, the surface quenching mode is spray quenching or quenching box type quenching;
when spray quenching is adopted, the quenching time of the casting blank to be detected in a spray area is not less than 60 seconds, and the spray water flow density is not less than 1000L/(m)2·min)。
Further, it is preferable that when the quenching is carried out in a quenching chamber type, the quenching depth is not less than 10mm, and the quenching time is not less than 50 seconds.
Further, it is preferable that the predetermined thickness of the cast slab is 10mm to 20 mm.
Further, preferably, in the process of low-power acid washing of the cross section of the casting blank transverse sample, the acid liquor volume ratio of the hydrochloric acid solution is 1: 0.5-1.5, the acid etching temperature is 60-80 ℃, and the acid etching time is 5-35 min.
Further, it is preferable that whether or not cracks are generated in the quenching area where the transverse sample of the casting slab is observed; if cracks are generated in the quenching area of the transverse sample of the casting blank, after the step of judging that large-scale inclusions exist in the casting blank to be detected, the method further comprises the following steps:
acquiring the shape information of the crack, and detecting and analyzing the crack through an electronic energy spectrum to acquire an electronic energy spectrum analysis result;
and judging the type of the inclusion in the casting blank to be detected according to the shape information of the crack and the analysis result of the electronic energy spectrum.
Further, preferably, the shape information of the crack is input as parameter information into a pre-established casting blank inclusion detection model, a type parameter of the inclusion in the casting blank to be detected is obtained, and the type of the inclusion is judged.
As described above, the method for detecting inclusions in a casting slab according to the present invention determines whether large inclusions exist or not by cracks generated in a cross section of a horizontal sample of the casting slab, and further determines the types of the inclusions by data information of the cracks, and has the following advantageous effects:
1. the continuous analysis and detection of the inclusions on the whole fixed-length casting blank can be realized, the discontinuity and the contingency of the detection result are eliminated, and the accuracy of the detection result is further improved;
2. the detection aim can be realized by using conventional production equipment without preparing a special detection instrument, and the detection method is scientific, reasonable, simple and feasible, so that the detection cost is reduced.
To the accomplishment of the foregoing and related ends, one or more aspects of the invention comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects of the invention. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Further, the present invention is intended to include all such aspects and their equivalents.
Drawings
Other objects and results of the present invention will become more apparent and more readily appreciated as the same becomes better understood by reference to the following description and appended claims, taken in conjunction with the accompanying drawings. In the drawings:
FIG. 1 is a scene diagram of cutting a fixed-length casting blank according to an embodiment of the method for detecting inclusions in the casting blank;
FIG. 2 is a graph showing the effect of low-acid pickling of a cast slab cross sample according to the method for detecting inclusions in a cast slab of the embodiment of the present invention;
FIG. 3 is a graph showing the crack effect of the method for detecting inclusions in a cast slab according to the embodiment of the present invention;
fig. 4 is a schematic view of a large inclusion according to the method for detecting an ingot casting inclusion according to the embodiment of the present invention.
Detailed Description
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) may be practiced without these specific details.
According to the method for detecting the large-sized inclusion of the casting blank, which is low in cost and high in detection efficiency, whether the large-sized inclusion exists in the casting blank to be detected is judged and analyzed according to the fact that the casting blank is cracked under the condition that the quenching strength is sufficiently high once the large-sized inclusion exists in the surface area of the casting blank.
Various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
Fig. 1 to 4 collectively illustrate a method for detecting inclusions in a cast slab. Specifically, fig. 1 is a scene diagram illustrating cutting of a fixed-length casting blank according to the method for detecting inclusions in a casting blank of the present invention; FIG. 2 is a diagram showing the effect of a casting slab after low-acid pickling according to the method for detecting inclusions in a casting slab of the present invention; FIG. 3 is a diagram showing the crack effect of a casting slab cross sample according to the method for detecting inclusions in a casting slab of the present invention; FIG. 4 is a schematic view showing large inclusions in a cast slab cross sample in the method for detecting inclusions in a cast slab according to the present invention.
The method for detecting the casting blank inclusion comprises the steps S1-S5.
S1, selecting a fixed-length casting blank to be subjected to inclusion detection as a casting blank to be detected, and carrying out surface quenching on the casting blank to be detected before grain boundary embrittlement; and when the temperature of the casting blank to be detected is cooled to 25 ℃, cutting the casting blank to be detected into a casting blank transverse sample with a set thickness along the drawing direction.
As shown in FIG. 1, in the case of continuous casting of a bloom in a certain domestic factory, the slab has a cross section of 200mm × 280mm and a fixed-length slab of 6m length, and large inclusions are detected in a slab of a specific fixed length in this heat.
The method comprises the following steps that the grain boundary embrittlement moment of a fixed-length casting blank is the moment of a first intersection point position of a supercooled austenite isothermal cooling transformation curve and a temperature change curve of the casting blank; the supercooled austenite isothermal cooling transformation curve comprises a ferrite starting generation curve, a pearlite ending generation curve and a bainite starting generation curve; the temperature change curves comprise a temperature change curve of a set depth from the wide surface to the surface, a temperature change curve of a set depth from the corner part to the surface and a temperature change curve of a set depth from the narrow surface to the surface.
It should be noted that grain boundary embrittlement occurs in the structure of a sized cast slab to be subjected to large-size inclusion detection, and cracks occurring after quenching may be caused by large-size inclusions or by grain boundary embrittlement. Therefore, a fixed-length casting blank before the grain boundary embrittlement time needs to be selected as a casting blank to be detected. And the grain boundary embrittlement moment of the fixed-length casting blank is the moment of the first intersection point position of the supercooled austenite isothermal cooling transformation curve and the temperature change curve of the casting blank. The specific execution flow refers to CN107641683B, a method for designing a continuous casting and rolling quenching process. Specifically, the grain boundary embrittlement time needs to be accurately determined, and then the interference of grain boundary embrittlement cracks on the casting blank inclusion detection method is avoided.
The surface quenching mode is spray quenching or quenching box type quenching; in the specific implementation process, in order to further obtain a strong quenching effect, a quenching box type quenching is selected. When the quenching box type quenching is adopted, the quenching depth is not less than 10mm, and the quenching time is not less than 50 seconds. In addition, when spray quenching is adopted, the quenching time of the casting blank to be detected in a spray area is not less than 60 seconds, and the spray water flow density is not less than 1000L/(m)2Min). Wherein the quenching depth is the thickness from a quenching ring visible to the naked eye in the macrostructure to the surface of the casting blank, but not a structure boundary corresponding to a metallographic structure.
In a specific embodiment, the casting blank to be detected is cut into a casting blank transverse sample with a set thickness along the drawing direction. The cutting direction is cutting along the throwing direction. The thickness is set to 10mm to 20 mm. Through a large number of sample tests, the length of the cracks caused by the obtained large-sized inclusions is not more than 15mm, the cracks are distributed on the casting blank transverse sample, and in order to further improve the continuity of the detection result, the thickness of the casting blank transverse sample needs to be smaller than the length of the cracks caused by the large-sized inclusions.
And S2, performing low-power acid washing on the cross section of the casting blank transverse sample.
In a specific implementation, the cross section of the slab cross is acid washed less often in order to increase the observability of cracks. In the low-power acid washing process, the acid liquor volume ratio of the hydrochloric acid solution is 1: 0.5-1.5, the acid etching temperature is 60-80 ℃, and the acid etching time is 5-35 min.
Carrying out a hot pickling experiment on the cross section of the casting blank transverse sample by using a hydrochloric acid aqueous solution with an acid liquor volume ratio of 1: 0.5-1.5, wherein the acid etching temperature is in a range of 60-80 ℃, and the acid etching time is 5-35 min; after hot pickling, taking a picture by using a high-definition digital camera to obtain the overall appearance of the solidification structure of the continuous casting slab with the cross section; as shown in fig. 2 and 3. Because different components of the continuous casting billet have different reaction degrees on the acid etching solution, the solidified structure appearance of the cross section of the continuous casting billet is presented after acid cleaning; the method is convenient for taking clear pictures and then selecting the measuring points.
S3, observing whether a quenching area of the transverse sample of the casting blank has cracks or not; and if cracks are generated in the quenching area of the transverse sample of the casting blank, judging that large-scale inclusions exist in the casting blank to be detected.
It should be noted that cracks caused by the presence of large inclusions are relatively noticeable and visible to the naked eye. Therefore, whether or not cracks occurred can be determined by visual observation.
And S4, acquiring the shape information of the crack, detecting and analyzing the crack through an electronic energy spectrum, and acquiring an electronic energy spectrum analysis result.
Specifically, the shape information of the crack includes data information such as the number of cracks, the size of the crack, the distribution of the crack, the occurrence position of the crack, and the specific shape and size of the large inclusion at the crack.
It is noted that electron spectroscopy (photoelectron spectroscopy) measures the kinetic energy (and hence the binding energy) of photoelectrons that are ejected from a sample by unilateral radiation using the principle of the photoelectric effect, the intensity of the photoelectrons, and the angular distribution of these electrons. And acquiring specific element composition information of the inclusions through an electronic energy spectrum.
And S5, judging the type of the inclusion in the casting blank to be detected according to the shape information of the crack and the analysis result of the electronic energy spectrum.
The type and the source of the large-scale inclusions are judged according to the acquired information, and the production process is further improved according to the judgment. According to the invention, the transverse sample of the casting blank cut on the casting blank with the priority of fixed length is not more than 20mm, so that the continuity and completeness of cracks can be met, and the accuracy of large-scale inclusion detection is further improved.
Still take the continuous casting production of bloom in a certain factory in China as an example, the operation process of the method for detecting the inclusions in the casting blank is specifically explained; the section of the large square billet is 200mm multiplied by 280mm, the length of the fixed-length casting billet is 6m, and large-scale inclusion detection is carried out on the specific fixed-length casting billet of the furnace.
1. Firstly, the method for determining the grain boundary embrittlement time of the fixed-length casting blank is used for determining the production process of the casting machine, so that the situation that the crystallizer embrittlement of the casting blank is not generated after the casting blank is cut is ensured.
2. And (3) carrying out quenching box type surface quenching on the fixed-length casting blank to be detected with the inclusion, wherein the quenching time is 60 seconds.
3. As shown in figure 1, the casting blank to be sized is cooled to room temperature (25 ℃), and then cut into continuous casting blank transverse samples with the thickness of 20mm at intervals.
4. The casting slab cross samples were pickled at low power, wherein the low power results for one casting slab cross sample are shown in fig. 2.
As can be seen from FIG. 2, the macroscopic quench ring had a thickness of 25mm to 40mm from the center to the corners, and cracks appeared in the quench thickness region at the lower left corner, indicating the presence of large inclusions.
5. As shown in FIG. 3, when the details of the crack are observed, the maximum length of the crack is within 15 mm; as shown in FIG. 4, when the specific morphology of the crack is observed, it can be seen that the morphology of the large inclusion is a spherical structure with a diameter of about 60 μm.
6. The large-scale inclusion is subjected to electron energy spectrum analysis, the electron energy spectrum analysis result is shown in table 1, and the large-scale inclusion contains high Al content, which indicates that the large-scale inclusion mainly comprises the components of the casting powder and possibly comes from the slag entrapment of the crystallizer. Table 1 is as follows:
| element(s) | wt％ | σ |
| Al | 48.0 | 0.4 |
| Fe | 15.6 | 0.2 |
| C | 15.5 | 0.6 |
| O | 14.8 | 0.3 |
| Cu | 5.8 | 0.2 |
In a specific embodiment, the shape information of the crack is used as parameter information and input into a pre-established casting blank inclusion detection model, the type parameter of the inclusion in the casting blank to be detected is obtained, and the type of the inclusion is judged.
As an improvement, the determination process for the crack is realized by using a machine-learned casting block inclusion detection model. Specifically, the casting blank inclusion detection model is obtained by adopting a plurality of groups of data and utilizing machine learning training, wherein the machine learning is a way for realizing artificial intelligence, has certain similarity with data mining, is a multi-field cross subject, and relates to a plurality of subjects such as probability theory, statistics, approximation theory, convex analysis, computational complexity theory and the like. Compared with the method for finding mutual characteristics among big data by data mining, the machine learning focuses on the design of an algorithm, so that a computer can automatically learn rules from the data and predict unknown data by using the rules.
First, a large inclusion crack data set is needed, and the data set comprises a large number of data of corresponding relations between various cracks and various large inclusions. And training a casting blank inclusion detection model by using the large inclusion crack data set. And inputting the shape information of the crack to be tested as parameter information into a pre-established casting blank inclusion detection model, calculating the model according to a correlation algorithm at the moment, outputting corresponding information, and finally outputting type judgment of the large-scale inclusion.
Specifically, a casting blank inclusion detection model is obtained according to original sample data training, and the probability of the large inclusion type corresponding to the crack data is judged according to the crack data information.
The improved grain boundary embrittlement time determination of the present embodiment may be realized by a machine learning model, the grain boundary embrittlement time determination model and the casting blank inclusion detection model are both classification models, and the grain boundary embrittlement time determination model and the casting blank inclusion detection model may be the same or different. The specific type of the classification model is, for example, a discriminant analysis model, an SVM model, a logistic model, a decision tree model, or the like.
In summary, the invention relates to a method for detecting inclusions in a casting blank, which determines whether large inclusions exist or not through cracks generated on the cross section of a transverse sample of the casting blank, and further determines the types of the inclusions through data information of the cracks, so that continuous analysis and detection of the inclusions on the whole fixed-length casting blank can be realized, discontinuity and contingency of detection results are eliminated, and accuracy of the detection results is further improved; the detection aim can be realized by using conventional production equipment without preparing a special detection instrument, and the detection method is scientific, reasonable, simple and feasible, thereby achieving the technical effect of reducing the detection cost.
However, it will be appreciated by those skilled in the art that various modifications may be made to the method for detecting inclusions in a cast slab provided by the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention should be determined by the contents of the appended claims.
Claims (8)
1. A method for detecting inclusions in a casting blank is characterized by comprising the following steps:
selecting a fixed-length casting blank to be subjected to inclusion detection as a casting blank to be detected, and carrying out surface quenching on the casting blank to be detected before grain boundary embrittlement;
when the temperature of the casting blank to be detected is cooled to 25 ℃, cutting the casting blank to be detected into a casting blank transverse sample with a set thickness along the casting drawing direction;
performing low-power acid washing on the cross section of the casting blank transverse sample;
observing whether a quenching area of the casting blank transverse sample generates cracks or not;
and if cracks are generated in the quenching area of the transverse sample of the casting blank, judging that large-scale inclusions exist in the casting blank to be detected.
2. The method for detecting inclusions in a cast slab according to claim 1,
the grain boundary embrittlement moment of the fixed-length casting blank is the moment of the first intersection point position of the supercooled austenite isothermal cooling transformation curve and the temperature change curve of the casting blank;
wherein the supercooled austenite isothermal cooling transformation curve includes a ferrite start generation curve, a pearlite end generation curve, and a bainite start generation curve; the temperature change curves comprise a temperature change curve of a set depth from the wide surface to the surface, a temperature change curve of a set depth from the corner part to the surface and a temperature change curve of a set depth from the narrow surface to the surface.
3. The method for detecting inclusions in a casting blank according to claim 1, wherein the surface quenching is spray quenching or quench box quenching;
when spray quenching is adopted, the quenching time of the casting blank to be detected in a spray area is not less than 60 seconds, and the spray water flow density is not less than 1000L/(m)2·min)。
4. The method for detecting inclusions in a cast slab according to claim 3, wherein the quenching depth is not less than 10mm and the quenching time is not less than 50 seconds when the quenching is carried out in a quenching chamber type.
5. The method for detecting inclusions in a cast slab according to claim 1, wherein the predetermined thickness of the slab sample is 10mm to 20 mm.
6. The method for detecting the inclusions in the casting blank according to claim 1, wherein in the low-power pickling process of the cross section of the casting blank transverse sample, the acid liquor volume ratio of a hydrochloric acid solution is 1: 0.5-1.5, the acid etching temperature is 60-80 ℃, and the acid etching time is 5-35 min.
7. The method for detecting inclusions in a cast slab according to claim 1, wherein whether or not cracks occur in the quenching area of the cross sample of the cast slab is observed; if cracks are generated in the quenching area of the transverse casting blank sample, after the step of judging that large-scale inclusions exist in the casting blank to be detected, the method further comprises the following steps:
acquiring the shape information of the crack, and detecting and analyzing the crack through an electronic energy spectrum to acquire an electronic energy spectrum analysis result;
and judging the type of the inclusions in the casting blank to be detected according to the shape information of the cracks and the analysis result of the electronic energy spectrum.
8. The method according to claim 7, wherein the shape information of the crack is input as parameter information to a pre-established casting blank inclusion detection model, a type parameter of the inclusion in the casting blank to be detected is obtained, and the type of the inclusion is determined.
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