CN115824738A - Microscopic analysis method for representing Q345B steel pipe folding cracks - Google Patents
Microscopic analysis method for representing Q345B steel pipe folding cracks Download PDFInfo
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- CN115824738A CN115824738A CN202211456663.5A CN202211456663A CN115824738A CN 115824738 A CN115824738 A CN 115824738A CN 202211456663 A CN202211456663 A CN 202211456663A CN 115824738 A CN115824738 A CN 115824738A
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Abstract
The invention discloses a microscopic analysis method for representing Q345B steel pipe folding cracks, which uses the technical means of metallographic microscope image acquisition function, image splicing, depth of field expansion and the like to represent the full appearance of the folding cracks, and shows the microscopic characteristics of the Q345B steel pipe folding cracks and the metallographic structure characteristics nearby the microscopic characteristics at a glance so as to judge the generation reasons of the folding cracks.
Description
Technical Field
The invention relates to the field of metal material detection, in particular to a microscopic analysis method for representing Q345B steel pipe folding cracks.
Background
The Q345B seamless steel pipe belongs to low-alloy high-strength structural steel, and is widely used for manufacturing structural parts and mechanical parts, such as petroleum drill pipes, automobile transmission shafts, bicycle frames, steel scaffold used in building construction and the like. The production process of the Q345B seamless steel pipe comprises the following steps: the method comprises the following steps of molten iron pretreatment, top and bottom combined blown converter, LF refining furnace, VD vacuum treatment, arc continuous casting machine, tube blank sawing, tube blank heating, mushroom punch, PQF continuous rolling mill, sizing mill, cooling bed and finishing. Before delivery, the steel pipe is required to have no visible defects of cracks, folds, scars, roll marks, delamination and the like on the inner and outer surfaces.
Q354B seamless steel tubes produced by a certain factory are punched and hot-rolled into phi 402mm multiplied by 16mm through phi 430mm round billets, and the outer wall of the tube has a folding crack defect, thereby seriously affecting the product quality.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a microscopic analysis method for representing Q345B steel pipe folding cracks, which is used for showing the microscopic characteristics of the Q345B steel pipe folding cracks and the metallographic structure characteristics nearby the microscopic characteristics at a glance so as to judge the generation reasons of the folding cracks.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention discloses a microscopic analysis method for representing Q345B steel pipe folding cracks, which mainly comprises the following steps:
1) Sampling
Judging the position of a crack source according to the macroscopic morphology of the folded crack, and taking a gold phase sample from the crack source;
2) Metallographic specimen preparation
Grinding a transverse or longitudinal detection surface of a crack source region of the sample, chamfering by using a grinder, roughly grinding, finely grinding by using abrasive paper, and mechanically polishing, wherein the detection surface of the sample is a mirror surface and has no water spots or stains; after the detection of the items of the non-metallic inclusions, the oxidized dots and the iron oxide is finished, corroding the sample by using a 4% nitric acid alcohol solution, and detecting the items of the microstructure, the grain size and the decarburization;
3) Microscopic examination
Inversely placing the prepared metallographic specimen on an objective table of a metallographic microscope, finding the position of a crack source, observing the depth and the length of the crack, nonmetallic inclusions at the crack, a microstructure and decarburization conditions, photographing and recording by using image acquisition software, and labeling a scale;
for the folding crack with the overlong length, splicing a plurality of view fields by adopting an image splicing means, and finally loading a scale;
for the folded crack with larger depth of field at the edge of the sample, a depth of field expansion means is adopted to superpose the depth of field of a plurality of fields, and finally a ruler is loaded;
4) Comprehensive analysis
The method comprehensively analyzes the reasons of the cracks by combining the original condition of the folded cracks, the macroscopic appearance of the cracks, the microscopic characteristics and the detection data, and feeds the reasons back to a production unit for guiding and optimizing the production process, reducing the generation rate of the cracks and improving the product quality.
Further, the step 1) is to avoid the influence of the cutting heat affected zone on the crack source zone when the sample is processed.
Further, in the step 3), the metallographic microscope is an Axio Observer metallographic microscope.
Compared with the prior art, the invention has the beneficial technical effects that:
the invention provides a microanalysis method for representing Q345B steel pipe folding cracks, which uses the technical means of metallographic microscope image acquisition function, image splicing, field depth expansion and the like to represent the overall appearance of the folding cracks and is beneficial to analyzing the generation reasons of the cracks.
Drawings
The invention is further illustrated in the following description with reference to the drawings.
FIG. 1 is a fold crack macrofeature;
FIG. 2 is an oxidation dot topography at the crack;
FIG. 3 is a general view of a fold crack;
FIG. 4 shows an abnormal structure on the near-surface side of a crack;
FIG. 5 shows a matrix structure.
Detailed Description
Examples
Q354B seamless steel tubes produced by a certain factory are punched and hot-rolled into phi 402mm multiplied by 16mm through phi 430mm round billets, and the outer wall of the tube has the defect of folding cracks, as shown in figure 1. And macroscopically observing that the defects are randomly distributed and expand along the rolling direction, and sampling at the defects to carry out microscopic detection and analysis in order to find the folding generation reason.
Grinding the transverse surface of the defect sample, observing the transverse surface under a metallographic microscope after polishing, and observing a crack which is about 30 degrees from the surface and is approximately parallel to the tail end of the defect and extends to the steel base. The cracks were filled with iron oxide and had oxidation circles in the vicinity, as shown in FIG. 2, and there were no abnormal nonmetallic inclusions in and around the cracks. After the corrosion by 4% nitric acid alcohol, the structure decarburization at the crack is observed under a mirror, and an abnormal martensite structure exists at the crack.
Because the visual field of a metallographic microscope is limited, the complete appearance of the crack cannot be expressed by adopting one visual field. Therefore, an image stitching means is used to form a picture of the whole appearance of the folded crack, and after a ruler is loaded, the crack length is estimated to be about 4.2mm and the depth is estimated to be about 0.7mm. Meanwhile, the difference between the abnormal structure near the surface of the crack and the matrix structure and the phenomenon of uneven grain size (i.e., mixed crystal) near the crack are also very obvious represented, as shown in fig. 3-5. This provides detailed and accurate data for determining the cause of the fold crack.
Comprehensive analysis shows that the vicinity of the crack has high-temperature oxidation characteristics such as iron oxide, oxidation dots, decarburization and the like. The steel billet surface has micro cracks, the periphery of the micro cracks is oxidized at high temperature after being heated by the heating furnace, and the outer wall folding defects are further formed in the subsequent rolling process. The abnormal martensite structure on the near-surface side of the outer wall folding crack is caused by the rapid cooling generated by water accumulation at the crack.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.
Claims (3)
1. A microscopic analysis method for representing Q345B steel pipe fold cracks is characterized in that: the method mainly comprises the following steps:
1) Sampling
Judging the position of a crack source according to the macroscopic morphology of the folded crack, and taking a gold phase sample from the crack source;
2) Metallographic specimen preparation
Grinding a transverse or longitudinal detection surface of a crack source region of the sample, chamfering by using a grinder, roughly grinding, finely grinding by using abrasive paper, and mechanically polishing, wherein the detection surface of the sample is a mirror surface and has no water spots or stains; after the detection of the items of the non-metallic inclusions, the oxidized dots and the iron oxide is finished, corroding the sample by using a 4% nitric acid alcohol solution, and detecting the items of the microstructure, the grain size and the decarburization;
3) Microscopic examination
The prepared metallographic specimen is inversely placed on an objective table of a metallographic microscope, the position of a crack source is found, the depth and the length of the crack, nonmetallic inclusions at the crack, the microstructure and the decarburization condition are observed, photographing record is carried out by using image acquisition software, and a ruler is marked;
for the folding crack with the overlong length, splicing a plurality of view fields by adopting an image splicing means, and finally loading a scale;
for the folded crack with larger depth of field at the edge of the sample, a depth of field expansion means is adopted to superpose the depth of field of a plurality of fields, and finally a ruler is loaded;
4) Comprehensive analysis
The original condition, the macroscopic appearance, the microscopic characteristics and the detection data of the folded cracks are combined, the reasons of the cracks are comprehensively analyzed, and the reasons are fed back to a production unit for guiding and optimizing the production process, reducing the crack generation rate and improving the product quality.
2. The method for the microscopic analysis of the folding cracks of a steel pipe characterized by Q345B according to claim 1, characterized in that: and 1) processing the sample to avoid the influence of the crack source area on the cutting heat affected zone.
3. The method for the microscopic analysis of the folding cracks of a steel pipe characterized by Q345B according to claim 1, characterized in that: and 3) the metallographic microscope is an Axio Observer metallographic microscope.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211456663.5A CN115824738A (en) | 2022-11-21 | 2022-11-21 | Microscopic analysis method for representing Q345B steel pipe folding cracks |
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| CN202211456663.5A CN115824738A (en) | 2022-11-21 | 2022-11-21 | Microscopic analysis method for representing Q345B steel pipe folding cracks |
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| CN202211456663.5A Pending CN115824738A (en) | 2022-11-21 | 2022-11-21 | Microscopic analysis method for representing Q345B steel pipe folding cracks |
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- 2022-11-21 CN CN202211456663.5A patent/CN115824738A/en active Pending
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