CN115508372A - Method for detecting microcracks on surface of thin strip steel - Google Patents
Method for detecting microcracks on surface of thin strip steel Download PDFInfo
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- CN115508372A CN115508372A CN202211184277.5A CN202211184277A CN115508372A CN 115508372 A CN115508372 A CN 115508372A CN 202211184277 A CN202211184277 A CN 202211184277A CN 115508372 A CN115508372 A CN 115508372A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/91—Investigating the presence of flaws or contamination using penetration of dyes, e.g. fluorescent ink
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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
- B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
- B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
- B22D11/0625—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels the two casting wheels being immersed in a molten metal bath and drawing out upwardly the casting strip
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/32—Polishing; Etching
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/34—Purifying; Cleaning
Abstract
The invention provides a method for detecting microcracks on the surface of thin strip steel. According to the method, firstly, a strip steel sample plate with a certain size is pre-stretched by 2% -6% in the width direction, the surface iron scale of the stretched sample plate is removed through acid cleaning, and a penetrant and a developer are sprayed on the surface of the strip steel after rinsing and drying. And finally, observing whether the surface of the strip steel has cracks or not by naked eyes and taking the cracks as a delivery judgment basis. The method is simple, convenient and quick to operate, and is beneficial to industrial large-scale crack detection.
Description
Technical Field
The invention relates to the field of band steel crack detection, and is mainly suitable for a method for detecting surface microcracks of hot-rolled thin band steel by using a double-roll thin strip casting and rolling technology.
Background
The hot rolled strip steel is generally coiled strip steel with the thickness of 0.7-20 mm, is widely used in industrial departments of automobiles, motors, chemical industry, shipbuilding and the like, and is also used as a raw material for producing cold rolled, welded pipes and cold bent section steel. In the application process, in addition to conventional mechanical properties, the requirements on the surface quality of the strip steel are higher and higher, and especially for the surface crack condition of a thin strip steel product below 2mm, the method plays an important role in the application of the product in the aspect of subsequent bending forming.
Patent document CN107478658A "crack detection method and apparatus" discloses a crack detection method and apparatus that mainly images a friction surface of a brake disc listed on a track to obtain a friction surface pattern; and identifying cracks in the friction surface pattern, and detecting the crack edges in the friction surface image by adopting different algorithms to obtain the number and the length of the cracks in the friction surface pattern. Patent document CN108287164A "a crack detection system" discloses a crack detection system including a mounting device, a crack detection device, and a data processing device. The crack detection device comprises a high-definition camera and a dot-matrix laser, and the high-precision crack detection is realized through machine vision and laser technology. Patent document CN210690430U, "a crack detection device", discloses a crack detection device, which performs pattern acquisition by rotating a workpiece by 360 degrees, so as to realize crack detection on the surface of the workpiece. The invention discloses a metal crack detection system and a crack detection sensor, and the metal crack detection system and the crack detection sensor are disclosed in the patent CN 111398316B.
The twin-roll casting thin strip steel is a green and environment-friendly strip steel production technology, the time for solidifying the molten steel into a casting strip is less than 0.2 second, and then the casting strip is subjected to hot rolling, cooling and coiling to form a coil, and a production line is only about 50 meters long. In particular, the process of twin roll casting is described in detail in patent application CN105473254B, "method of continuously casting thin strip", which is incorporated herein by reference in its entirety.
In the casting of thin strip using the twin roll casting process, the thickness of the thin strip that is ultimately formed is typically below 2mm, for example, between 0.7mm and 2 mm. Micro-cracks may occur in the cast strip/thin strip during early production of the cast strip due to the effects of the molten steel chemistry and/or when process parameters are not well controlled during casting.
However, compared to the crack defects on the surface of the steel sheet produced by the conventional hot rolling process, the size of the micro cracks that may be formed on the surface of the thin steel strip produced by twin roll casting is very small, and is generally invisible to the naked eye, and is difficult to detect by the conventional flaw detection method, and is also difficult to detect by the methods of the aforementioned many patents related to crack detection, but can generally be confirmed only by microscopic observation by means of electron microscopy, metallographic phase, and the like. However, microscopic detection methods such as electron microscopy and metallographic microscopy are expensive and difficult to operate, and only a small local area on the surface of thin strip steel can be detected, so that it is difficult to reflect the entire condition of the sample of thin strip steel. In addition, the detection of the microcracks on the surface of the thin strip steel does not need to acquire specific dimensions (such as depth, length and the like) of the microcracks; instead, it is only necessary to confirm the presence and density of the thin strip steel on the surface of the thin strip steel to determine whether the thin strip steel coil is qualified.
Therefore, there is a need for a method for detecting the entire microcracks on the surface of thin strip steel in a timely and rapid manner by a simple and convenient operation.
Disclosure of Invention
The invention provides a method for detecting surface microcracks of hot-rolled thin strip steel with the thickness of less than 2.0mm, which is suitable for the production of a double-roller casting and rolling technology, so that whether cracks exist on the surface of the product can be judged more intuitively through a simple and convenient operation means, and a reliable basis is provided for judging whether the strip steel is qualified.
Further, in the production of thin strip by twin roll casting, thin strip is continuously formed from molten steel, and for each furnace of molten steel, the strip is continuously cast without interruption, and usually 4 to 5 rolls of thin strip are produced per furnace of molten steel. In the production process, the quick and simple detection of the microcracks on the surface of the thin strip steel of the previous steel coil produced by the molten steel in the furnace can quickly feed back the microcracks to the current continuous casting process, timely and correspondingly adjust/correct the technological process and parameters of the previous procedure, reduce the judgment rate of products and improve the qualification rate of the subsequent continuous casting products of the molten steel in the furnace.
To achieve the above objects, the present invention provides a method for detecting microcracks on the surface of a thin strip steel formed by twin roll casting, comprising the steps of:
stretching: stretching a sample to be detected cut from the thin strip steel along a direction A vertical to the rolling direction of the thin strip steel;
surface cleaning: pickling a sample to be detected to remove a surface oxide layer of the sample to be detected, rinsing the sample to be detected, and drying or wiping the surface of the sample to be detected by air drying;
and (3) micro-crack detection: after spraying a penetrant on the surface of a sample to be detected and standing, removing the redundant penetrant on the surface of the sample to be detected, then spraying a developer on the surface of the sample to be detected and standing, and observing the surface of the sample to be detected through human eyes to identify microcracks on the sample to be detected.
In a preferred embodiment, the thin strip has a thickness of 2.0mm or less.
In a preferred embodiment, the sample to be detected of the thin strip steel is cut in a rolling direction a of the thin strip steel, a width W of the cut sample to be detected of the thin strip steel is substantially identical to a width of the thin strip steel and is in a range of 1180mm to 1650mm, and a length L of the cut sample to be detected of the thin strip steel is in a range of 200mm to 400 mm.
In a preferred embodiment, the elongation of the sample to be tested in the direction perpendicular to the rolling direction a of the thin strip is in the range of 2% to 6%.
In a preferred embodiment, the step of pickling the sample to be detected comprises soaking the sample to be detected in hydrochloric acid with the concentration of 20% -50% for 4-6 min.
In a preferred embodiment, in the step of detecting the microcracks, a penetrant is sprayed on the surface of the sample to be detected, after standing for 20-120 s, the redundant penetrant on the surface of the sample to be detected is removed, and then after a developer is sprayed on the surface of the sample to be detected and standing for 3-5 min, the surface of the sample to be detected is observed by human eyes to identify the microcracks thereon.
In a preferred embodiment, the penetrant comprises a red dye, and
in the step of detecting the microcracks, the surface of the sample to be detected is observed through human eyes, the position where the microcracks exist on the surface of the sample to be detected is red, and the position where the microcracks do not exist on the surface of the sample to be detected is white.
In a preferred embodiment, the drawing step, the surface cleaning step, the micro-crack detection step are performed in a sequential manner.
Advantageous technical effects
Compared with the prior art, the invention has the advantages that:
(1) The crack condition of the surface of the thin strip steel is simply judged by observing through human eyes by a simpler and more convenient operation means;
(2) The microcrack condition on the surface of the thin strip steel with a large area can be detected so as to reflect the overall condition of the sample of the thin strip steel;
(3) The method can quickly judge the surface crack condition of the produced thin strip steel, feed back the surface crack condition to the preorder procedure in time, correct/adjust the technological process and parameters of the preorder procedure in time, reduce the judgment rate of products and improve the qualification rate of subsequent continuous casting products.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly described below. It is to be expressly understood that the drawings in the following description are directed to only some embodiments of the invention and are not intended as a definition of the limits of the invention.
FIG. 1 is a schematic side view of a twin roll caster system of the present invention;
fig. 2 is a partial cross-sectional view of the casting rolls installed into roll cassettes in a casting position through the twin roll caster of fig. 1.
Fig. 3 is a schematic diagram of a tensile test performed on thin strip steel.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without any inventive step, are within the scope of protection of the invention.
Unless defined otherwise, technical or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
Referring now to fig. 1 and 2, there is shown a twin roll continuous caster comprising a main frame 10, the main frame 10 upstanding from a floor and supporting a pair of casting rolls 12, the pair of casting rolls 12 being mounted in roll cassettes 11 for ease of operation and movement.
A twin roll caster for continuously casting thin metal strip comprises a pair of counter-rotating casting rolls 12 each having a casting surface 12A forming a nip 18 therebetween. Molten metal passes from ladle 13 through tundish 14 and then through refractory outlet shroud 15 to transition ladle 16 and then to distributor 17 positioned between casting rolls 12 above nip 18. The molten metal so delivered forms a molten pool 19 supported above the nip above the casting surfaces 12A of the casting rolls 12.
The casting rolls 12 are internally cooled (e.g., internally water cooled) so that as the casting rolls 12 rotate relative to each other, the molten metal in the molten bath 19 rotationally contacts the casting surfaces 12A and cools and solidifies on the casting surfaces 12A. During casting, the metal shells that cool and solidify on the casting surfaces 12A of the casting rolls 12 are brought together at the nip 18 between the casting rolls to form a thin cast strip delivered downwardly from the nip.
The thin strip formed from the twin roll caster is rolled in the direction a, rolled by rolls, cooled, and coiled to form a coil of thin strip. In order to ensure that the quality of the thin strip steel product in the formed thin strip steel coil is qualified and meets the performance requirements, a detection sample needs to be cut from the thin strip steel coil and micro cracks on the sample to be detected need to be detected.
Firstly, a section of thin strip steel is cut along the rolling direction A of the thin strip steel and is used as a sample to be detected. The width W of the sample to be tested is generally consistent with the width of the thin strip steel, and is approximately in the range of 1180mm to 1650 mm; the length L of the sample to be examined, i.e. its length in the rolling direction a of the thin strip, is preferably taken in the range of 200mm to 1000mm, more preferably 200mm to 400mm, in order to be able to reflect the surface quality and the micro-crack condition of the entire width of the thin strip as a whole. Of course, in alternative embodiments, any section of the thin strip steel may be cut as the sample to be tested, rather than cutting the sample to be tested along the entire width of the thin strip steel.
The method for detecting the microcracks on the surface of the sample to be detected based on interception comprises the following steps:
(1) Stretching of
As shown in fig. 3, both ends of a sample to be tested are fixed by a jig 101 of a stretcher (not shown) and stretched by the stretcher in a stretching direction perpendicular to the rolling direction a of the thin strip at a certain stretching ratio.
In particular, since the microcrack defects that may be formed on the surface of the thin strip produced by twin roll casting generally include elongated microcracks in the rolling direction a of the thin strip, for example, the length of the microcracks in the rolling direction a is generally 1mm to 5mm, and the width in the direction perpendicular to the rolling direction a is generally only 0.5mm or less, it is difficult to detect by a conventional flaw detection method and to visually observe it.
In the technical scheme of the invention, the sample to be detected is stretched along the stretching direction vertical to the rolling direction A, so that the slender microcrack can be expanded along the width direction (namely the stretching direction vertical to the rolling direction A), and the microcrack can be detected more easily.
The stretching ratio of the sample to be tested during the stretching process is selected from the range of 2% to 6%, preferably in the range of 3% to 5%. The excessive selection of the elongation rate may cause the generation of cracks which do not exist originally on the surface of the thin strip steel and even the fracture of the thin strip steel; too small a selection of the stretching ratio may result in insufficient broadening of the microcracks and thus failure of detection by subsequent steps, both of which may result in inaccurate detection results.
(2) Surface cleaning
The surface of a sample to be detected is subjected to acid cleaning (for example, the sample is soaked in a hydrochloric acid solution with the concentration of 20-50% for 4-6 min) to remove a surface oxide layer, and then the surface of the sample to be detected is rinsed clean with hydrochloric acid through rinsing (for example, a weak base solution), and then the surface of the sample to be detected is dried through air drying or wiping.
The step is used for removing the oxide layer on the surface of the sample to be detected, so that microcracks on the surface of the sample are more clearly shown and the sample is easy to detect.
(3) Microcrack detection
Placing the stretched and surface-cleaned sample to be detected on a detection table, spraying a penetrant on the surface of the sample to be detected, standing for a period of time (such as 20-120 s), allowing the penetrant to permeate into microcracks on the surface of the sample to be detected due to capillary action, and removing or wiping redundant penetrant on the surface of the sample after permeation is finished.
And then, spraying a developer on the surface of the sample to be detected, standing for a period of time (such as 3-5 min), wherein the capillary action of the developer can adsorb the penetrant infiltrated into the microcracks, so that the penetrant at the microcracks is infiltrated back to the surface of the thin strip steel again to form an amplified defect display. The positions with cracks and the positions without cracks are in obviously different colors, so that the existence of microcracks on the surface of the thin strip steel and the density of cracks can be visually judged by observing the surface of the thin strip steel through human eyes, and whether the product is qualified is judged.
For example, in an alternative embodiment, the penetrant is added with a brightly colored red dye to provide a sharp contrast with the background (e.g., white background) of the developer for easy observation by the human eye. For example, after the penetrant and the developer are sprayed in sequence, the part of the thin strip steel surface where the microcrack exists is red, and the part of the thin strip steel surface where the microcrack does not exist is white, so that the existence of the microcrack on the thin strip steel surface can be judged simply through human eye observation.
Through the above method, the present invention can easily detect the presence or absence of micro cracks on the surface of a thin strip (having a thickness of 2.0mm or less) produced by twin roll casting without detecting the depth of the cracks. The method is simple and easy to operate, short in time, high in efficiency and suitable for industrial production large-batch crack detection work.
It should be noted that, although the three steps of the detection method according to the present invention are indicated in a sequential manner in the foregoing method as (1) stretching, (2) surface cleaning, and (3) micro-crack detection, the order of the steps is not meant to limit the order of the three steps. For example, in the aforesaid detection method, the sample to be detected may be subjected to (2) the operation of surface cleaning, then to (1) the operation of stretching, and finally to (3) the operation of microcrack detection, without departing from the scope of protection defined by the claims of the present invention.
In a preferred embodiment, the aforementioned three steps of (1) stretching, (2) surface cleaning, (3) microcrack detection are performed in a sequential manner, i.e. (1) stretching step is performed before (2) surface cleaning step. The operation sequence of the stretching step can destroy the compact oxide film on the surface of the strip steel before the acid cleaning, thereby facilitating the acid cleaning and reducing the acid cleaning time, and being more beneficial to the detection of microcracks.
The solution according to the invention is further illustrated below by means of two exemplary embodiments.
The first embodiment is as follows:
stretching: the sample to be tested was placed in a tensile testing machine for a tensile test with an elongation of 2%.
Surface cleaning: and (3) pickling the stretched sample to remove surface iron oxide scales, and rinsing and blow-drying the sample.
And (3) micro-crack detection: and (3) placing the sample on a detection table, spraying a proper amount of penetrant on the surface of the sample, standing for 20s, removing redundant penetrant on the surface of the sample, then spraying developer, standing for 3min, observing the surface of the sample, and further determining whether the product is qualified.
Example two:
surface cleaning: and (3) removing surface iron oxide scales of the sample to be detected through acid washing, and then rinsing and blow-drying.
Stretching: the surface-cleaned sample was placed in a tensile testing machine to perform a tensile test at a tensile rate of 5%.
And (3) micro-crack detection: and (3) placing the sample on a detection table, spraying a proper amount of penetrant on the surface of the sample, standing for 2min, removing redundant penetrant on the surface of the sample, then spraying developer, standing for 5min, observing the surface of the sample, and further determining whether the product is qualified.
The above detailed description of embodiments of the disclosure, presented in connection with the drawings, is not intended to limit the scope of the claimed disclosure, but is merely representative of selected embodiments of the disclosure. The drawings are only for schematically illustrating the components according to the present invention, and the dimensions, proportions and the like thereof are not intended to actually limit the true proportional relationship of the components.
The foregoing is directed to embodiments of the present invention and it is noted that various modifications and adaptations of the invention may occur to those skilled in the art without departing from the scope and spirit of the invention.
Claims (8)
1. Method for detecting micro-cracks on the surface of thin strip steel, characterized in that it comprises the steps of:
stretching: stretching a sample to be detected cut from the thin strip steel along a direction (A) vertical to the rolling direction of the thin strip steel;
surface cleaning: pickling the sample to be detected to remove a surface oxide layer of the sample to be detected, rinsing the sample to be detected, and drying or wiping the surface of the sample to be detected;
and (3) micro-crack detection: spraying a penetrating agent on the surface of a sample to be detected and standing, removing the redundant penetrating agent on the surface of the sample to be detected, then spraying a developing agent on the surface of the sample to be detected and standing, and observing the surface of the sample to be detected through human eyes to identify microcracks on the surface of the sample to be detected.
2. The method for detecting micro-cracks on the surface of thin strip steel according to claim 1, characterized in that,
the thickness of the thin strip steel is less than 2.0 mm.
3. The method for detecting micro-cracks on the surface of thin strip steel according to claim 1, characterized in that,
the sample to be detected of the thin strip steel is cut along the rolling direction (A) of the thin strip steel, the width (W) of the sample to be detected of the cut thin strip steel is basically consistent with the width of the thin strip steel and is in the range of 1180 mm-1650 mm, and the length (L) of the sample to be detected of the cut thin strip steel is in the range of 200-400 mm.
4. The method for detecting micro-cracks on the surface of thin strip steel according to claim 1, characterized in that,
the elongation of the sample to be detected in the direction (A) perpendicular to the rolling direction of the thin strip steel is within the range of 2-6%.
5. The method for detecting micro-cracks on the surface of thin strip steel according to claim 1, characterized in that,
the step of carrying out acid washing on the sample to be detected comprises the step of soaking the sample to be detected in hydrochloric acid with the concentration of 20% -50% for 4-6 min.
6. Method for detecting micro-cracks on the surface of thin strip steel according to claim 1,
in the step of detecting the microcracks, spraying a penetrant on the surface of a sample to be detected, standing for 20-120 s, removing the redundant penetrant on the surface of the sample to be detected, then spraying a developer on the surface of the sample to be detected, standing for 3-5 min, and observing the surface of the sample to be detected through human eyes to identify the microcracks on the sample to be detected.
7. Method for detecting micro-cracks on the surface of thin strip steel according to claim 1,
the penetrating agent comprises a red dye, and
in the step of detecting the microcracks, the surface of the sample to be detected is observed through human eyes, the position of the surface of the sample to be detected, where the microcracks exist, is red, and the position of the surface of the sample to be detected, where the microcracks do not exist, is white.
8. Method for detecting micro-cracks on the surface of thin strip steel according to any one of claims 1 to 7,
the drawing step, the surface cleaning step, and the microcrack detection step are performed in a sequential manner.
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| CN202211184277.5A CN115508372A (en) | 2022-09-27 | 2022-09-27 | Method for detecting microcracks on surface of thin strip steel |
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