阅读说明：本技术 一种中厚板边部炸裂裂纹产生原因的判断方法 (Method for judging cause of edge cracking crack of medium plate ) 是由 李文双 孟宪成 俞飞 徐洪庆 乔志明 于 2020-12-29 设计创作，主要内容包括：本发明公开了一种中厚板边部炸裂裂纹产生原因的判断方法。该方法通过在中厚板、中间坯、连铸坯环节取样进行宏观形貌、微观金相、断口形貌等检测分析,根据中厚板边部炸裂裂纹的检验结果以及生产环节的各项工艺参数,进而判断其边部炸裂裂纹的产生原因。通过消除连铸坯角部横向裂纹,中厚板的边部炸裂裂纹得到明显改善。本发明通过分析总结各项检测结果,明确了中厚板边部炸裂裂纹的产生原因,提高了产品质量,创造了效益。(The invention discloses a method for judging the reason of the edge cracking crack of a medium plate. According to the method, the detection and analysis of macro morphology, micro metallographic phase, fracture morphology and the like are carried out by sampling in the links of the medium plate, the intermediate billet and the continuous casting billet, and the generation reason of the edge cracking crack of the medium plate is judged according to the detection result of the edge cracking crack of the medium plate and various process parameters of the production link. By eliminating transverse cracks at the corners of the continuous casting billet, the edge cracking cracks of the medium plate are obviously improved. According to the invention, various detection results are analyzed and summarized, the generation reason of the edge cracking crack of the medium plate is determined, the product quality is improved, and the benefit is created.)

1. A method for judging the cause of the edge cracking crack of a medium plate is characterized by comprising the following steps: the method comprises the following steps: 1) observing the macro morphology of the original crack defect of the medium plate; 2) metallographic observation of the crack sample; 3) carrying out acid pickling observation and crack fracture appearance observation after the continuous casting billet is subjected to corner cutting; the method specifically comprises the following steps:

observing the macro morphology of the original crack defect of the medium plate: observing and recording the distance from the edge part of the medium plate to the edge part, wherein the distance from the edge part of the medium plate to the edge part is 5-70 mm, the edge part of the medium plate to the edge part is distributed on two sides of the medium plate, the crack defect is only found on the upper surface of the medium plate through the turning plate, the defect is not found on the lower surface of the medium plate, the crack is distributed along the edge of the medium plate, and the whole steel plate is present;

metallographic observation of the crack sample: the gold phase sample is taken from the original crack defect and observed, the size of the sample is 15 multiplied by 15mm, and the following phenomena can be generally observed when the crack vicinity is observed through the crack interface of the medium plate sample: the cracks and the surface of the steel plate form a certain angle depthThe thickness of the tail part of the crack is 100-500 mu m below the surface layer of the steel plate, the tail part of the crack is smooth and does not expand to a matrix, the fiber streamline characteristic near the crack is obvious, the periphery of the crack is obviously decarburized, the periphery of the crack is obviously oxidized round points, the decarburizing temperature is above 900 ℃, and the decarburizing temperature is above 900 ℃ and stays for a period of time; the carbon atoms diffuse from inside to outside to form CO or CO with oxygen in the air₂Gas escape, leading to decarburization around the crack; the creation of oxidation dots near the crack ends is a result of internal oxidation; oxygen diffused into the steel is combined with strong oxidizing elements of silicon and manganese to form oxide particles rich in silicon and manganese; higher temperature and longer time are needed for forming the oxidation dots, the temperature is 950-1200 ℃, and the time is at least 0.5 h; the sharp crack end generally comes from casting blank defects, and the round crack end generally comes from rolling defects; the basic judgment of the generation reason can be carried out according to the observation of the vicinity of the crack of the metallographic specimen; the analysis is as follows corresponding to the above phenomena: 1) obvious decarburization exists near the cracks, a large number of oxidation round points exist, the roots of the cracks are sharp, the defects are generated only when the time and the temperature of the original defects in the heating furnace are higher and the time is longer, and the phenomenon can be judged that the original defects exist in the casting blank and the casting blank is further extended after being rolled; 2) decarburization exists near the crack, a large number of oxidation dots are not generated, the root of the crack is round and smooth, the defect is not long in time at a high temperature period, and the defect generally comes from steel rolling;

acid pickling observation and crack fracture appearance observation after continuous casting billet corner cutting: two phenomena can be found through acid washing observation of the cutting angle of the casting blank: 1) the casting blank corner is intact, and no obvious transverse crack or longitudinal crack defect exists, which proves that the casting blank corner does not have quality problem, 2) the casting blank corner has crack defect, and the transverse crack generally appears at the wave trough of the casting blank vibration mark; if cracks exist at the corners of the casting blank, the cracks and fractures are analyzed, and the fact that no carbonitride exists in the fractures is found, which indicates that the phenomenon that the carbonitride expands the third brittle zone of the material does not exist, and the fact that a large amount of carbonitride exists in the fractures, indicates that the carbonitride precipitates at the grain boundaries, weakens the grain boundaries, expands the third brittle zone and is easy to crack in the straightening process.

Technical Field

The invention relates to the field of medium plate production, in particular to a method for judging the reason of the edge cracking crack of a medium plate.

Background

The quality control of the medium plate comprises internal quality control and surface quality control, the surface quality control is very important for the medium plate product as an important ring of the whole quality control, wherein an edge defect has important influence on the use of the medium plate, the damage of the edge crack defect is the greatest in the edge defect, the crack opening is large, the depth is deep, the phenomenon of incomplete cutting can be caused even if the edge cutting treatment can be carried out, and the subsequent welding process can not be stably and effectively welded to cause huge quality risks. Therefore, the method has very important significance for improving the quality of the medium plate by summarizing and judging the generation reason of the burst cracks at the edge of the medium plate.

It should be noted that the prior art discloses a method for judging the cause of the straight crack at the edge of the rolled plate, wherein the national patent number CN 102323388A, application date 2011.05.18, the hot rolled plate and the medium plate belong to two different fields, and the prior art judges the cause of the straight crack at the edge of the rolled plate, and the patent right of the prior art is ended; the invention belongs to the field of hot rolling medium plate, the edge cracking defect is completely different from the straight cracking defect, and the reason for the edge cracking crack cannot be judged according to the prior art, so that how to design a more scientific and more efficient method for judging the edge cracking crack defect of the medium plate is the problem to be solved by the invention.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a method for judging the cause of the edge cracking crack of a medium plate. By analyzing and summarizing various detection results, the generation reason of the edge cracking crack of the medium plate is determined, scientific explanation is provided for the generation mechanism of the defects, the product quality is improved, and benefits are created. ,

the invention is realized in this way, a method for judging the cause of the edge cracking crack of the medium plate, which is characterized in that: the method comprises the following steps: 1) observing the macro morphology of the original crack defect of the medium plate; 2) metallographic observation of the crack sample; 3) carrying out acid pickling observation and crack fracture appearance observation after the continuous casting billet is subjected to corner cutting; the method specifically comprises the following steps:

observing the macro morphology of the original crack defect of the medium plate: observing and recording the distance from the edge part of the medium plate to the edge part, wherein the distance from the edge part of the medium plate to the edge part is 5-70 mm, the edge part of the medium plate to the edge part is distributed on two sides of the medium plate, the crack defect is only found on the upper surface of the medium plate through the turning plate, the defect is not found on the lower surface of the medium plate, the crack is distributed along the edge of the medium plate, and the whole steel plate is present;

metallographic observation of the crack sample: the gold phase sample is taken from the original crack defect and observed, the size of the sample is 15 multiplied by 15mm, and the following phenomena can be generally observed when the crack vicinity is observed through the crack interface of the medium plate sample: the crack and the surface of the steel plate form a certain angle and penetrate into the surface of the steel plate to be 100-500 mu m below, the tail of the crack is smooth and does not expand to a matrix, the vicinity of the crack has obvious fiber streamline characteristics, obvious decarburization exists around the crack, obvious oxidation round points exist around the crack, the temperature of the decarburization needs to be above 900 ℃, and the decarburization needs to stay for a period of time at the temperature of above 900 ℃; the carbon atoms diffuse from inside to outside to form CO or CO with oxygen in the air₂Gas escape, leading to decarburization around the crack; the creation of oxidation dots near the crack ends is a result of internal oxidation; oxygen diffused into the steel is combined with strong oxidizing elements of silicon and manganese to form oxide particles rich in silicon and manganese; higher temperature and longer time are needed for forming the oxidation dots, the temperature is 950-1200 ℃, and the time is at least 0.5 h; the sharp crack end generally comes from casting blank defects, and the round crack end generally comes from rolling defects; the basic judgment of the generation reason can be carried out according to the observation of the vicinity of the crack of the metallographic specimen; the analysis is as follows corresponding to the above phenomena: 1) obvious decarburization exists near the cracks, a large number of oxidation round points exist, the roots of the cracks are sharp, the defects are generated only when the time and the temperature of the original defects in the heating furnace are higher and the time is longer, and the phenomenon can be judged that the original defects exist in the casting blank and the casting blank is further extended after being rolled; 2) decarburization exists near the crack, a large number of oxidation dots are not generated, the root of the crack is round and smooth, the defect is not long in time at a high temperature period, and the defect generally comes from steel rolling;

acid pickling observation and crack fracture appearance observation after continuous casting billet corner cutting: two phenomena can be found through acid washing observation of the cutting angle of the casting blank: 1) the casting blank corner is intact, and no obvious transverse crack or longitudinal crack defect exists, which proves that the casting blank corner does not have quality problem, 2) the casting blank corner has crack defect, and the transverse crack generally appears at the wave trough of the casting blank vibration mark; if cracks exist at the corners of the casting blank, the cracks and fractures are analyzed, and the fact that no carbonitride exists in the fractures is found, which indicates that the phenomenon that the carbonitride expands the third brittle zone of the material does not exist, and the fact that a large amount of carbonitride exists in the fractures, indicates that the carbonitride precipitates at the grain boundaries, weakens the grain boundaries, expands the third brittle zone and is easy to crack in the straightening process.

The invention has the beneficial effects that:

the invention provides a method for judging the cause of an edge cracking crack of a medium plate. By analyzing and summarizing various detection results, the generation reason of the edge cracking crack of the medium plate is determined, scientific explanation is provided for the generation mechanism of the defects, the product quality is improved, and benefits are created.

Drawings

FIG. 1 is a schematic view of edge cracking;

FIG. 2 is a crack metallographic structure diagram;

FIG. 3 is a metallographic structure of cracks (not corroded);

FIG. 4 is a schematic view of rolled intermediate billet cracking;

FIG. 5 is a schematic diagram of the pickling profile of a corner of a casting blank;

FIG. 6 shows the cross-fracture morphology at the corner of a cast slab.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

A method for judging the cause of the edge cracking crack of a medium plate comprises the following steps: 1) observing the macro morphology of the original crack defect of the medium plate; 2) metallographic observation of the crack sample; 3) carrying out acid pickling observation and crack fracture appearance observation after the continuous casting billet is subjected to corner cutting; the method specifically comprises the following steps:

observing the macro morphology of the original crack defect of the medium plate: the edge cracking crack of the medium plate is 5-70 mm away from the edge and distributed on two sides of the medium plate, the cracking crack defect is only found on the upper surface (corresponding to the inner arc of a casting blank) of the steel plate through the turning plate, the defect is not found on the lower surface (corresponding to the outer arc of the casting blank), the crack is distributed along the edge of the medium plate, and the whole steel plate is present.

Metallographic observation of the crack sample: the gold phase sample is taken from the original crack defect and observed, the size of the sample is 15 multiplied by 15mm, and the following phenomena can be generally observed when the crack vicinity is observed through the crack interface of the medium plate sample: the cracks and the surface of the steel plate form a certain angle and penetrate into the surface of the steel plate to be 100-500 mu m below, the tail parts of the cracks are smooth and do not expand to a matrix, the fiber streamline characteristics near the cracks are obvious, obvious decarburization exists around the cracks, obvious oxidation round points exist around the cracks, generally, the decarburization needs to be carried out at a higher temperature (above 900 ℃) and stay for a period of time at the higher temperature. The carbon atoms diffuse from inside to outside to form CO or CO with oxygen in the air₂The gas escapes, resulting in decarburization around the crack. The creation of an oxidation dot near the end of the crack is a result of internal oxidation. Oxygen diffused into the steel combines with the strong oxidizing elements silicon and manganese to form oxide particles enriched with silicon and manganese. Generally, higher temperature and longer time are needed for forming the oxidation dots, the temperature is 950-1200 ℃, and the time is at least 0.5 h; the sharp crack ends generally originate from casting defects and the rounded crack ends generally originate from rolling defects.

The basic judgment of the cause of the crack can be made by observing the vicinity of the crack in the metallographic specimen. The above phenomena are summarized as follows: 1) obvious decarburization exists near the crack, a large number of oxidation round points exist, the root of the crack is sharp, the defect is caused by the phenomenon that the time and the temperature of the original defect in a heating furnace are higher and the time is longer than that of a factory, and the phenomenon can be generally observed to judge that the casting blank has the original defect and then extends further after being rolled; 2) decarburization exists near the crack, a large number of oxidation dots are not generated, the root of the crack is round and smooth, the defect is not long in time at a high temperature period, and the defect generally comes from rolled steel.

The edge cracking metallographic morphology is as follows: obvious decarburization exists around the crack, a large number of oxidation round points exist, the root of the crack is sharp, the existence of the crack before rolling is indicated, the appearance is a typical characteristic of the genetic crack of the casting blank, and therefore the problem of the casting blank continuous casting link is judged.

Acid pickling observation and crack fracture appearance observation after continuous casting billet corner cutting: two phenomena can be found through acid washing observation of the cutting angle of the casting blank: 1) the casting blank has intact corners and no obvious transverse crack or longitudinal crack defect, which proves that the quality problem does not exist in the corners of the casting blank, and 2) the cracks exist in the corners of the casting blank, and the transverse crack generally appears at the wave trough of the vibration mark of the casting blank.

If cracks exist at the corners of the casting blank, the cracks and fractures are analyzed, and the fact that no carbonitride exists in the fractures is found, which indicates that the phenomenon that the carbonitride expands the third brittle zone of the material does not exist, and the fact that a large amount of carbonitride exists in the fractures, indicates that the carbonitride precipitates at the grain boundaries, weakens the grain boundaries, expands the third brittle zone and is easy to crack in the straightening process.

In summary, the judgment of the cracking of the edge of the medium plate mainly comprises 3 processes of 1 observation of the macro morphology of the original defect, 2 observation of the metallographic phase of the crack sample, and 3 observation of the pickling after the corner cutting of the continuous casting slab and the appearance observation of the fracture of the crack. The method is characterized in that the crack is macroscopically observed to be distributed at the positions 5-70 mm away from the edges on two sides of a steel plate and only exists on the upper surface, the lower surface is not, obvious decarburization and oxidation round points exist near the crack when the metallographic observation is carried out, the root of the crack is sharp, the defect is judged to be from a casting blank, the transverse crack exists at the corner of the casting blank finally through the observation of the cutting angle of the casting blank and the analysis of the fracture, a large amount of carbonitride exists at the fracture, and the reason for judging the occurrence of the crack defect of the edges of the medium plate is as follows: the presence of carbonitride in the steel enlarges the third brittle zone of the material, and tensile stress is generated in the inner arc during the straightening of the cast blank, so that transverse cracks are generated at the inner arc corners of the cast blank, and the cracks are not welded in the subsequent rolling process.

In the embodiment, the practical application of the invention is as follows: edge defects of 1 ten thousand tons occur during the production of Q245R container panels by a certain company, causing severe quality loss, and edge burst crack defects account for 95% of the total defects. Through detection of multiple links of the medium plate and the intermediate blank, transverse cracks at the inner arc corners of the casting blank are found to be the main cause of defects, and through pertinence improvement of the quality of the corners of the casting blank, the defects of cracking at the edges of the medium plate are finally eliminated.

Referring to the attached figure 1, through observation of the macroscopic morphology of the original crack defects, the cracks at the crack distribution edge part are about 50mm away from the edge part and distributed at two sides of the medium plate, the cracks are found to exist only on the upper surface (corresponding to the inner arc of the casting blank) of the steel plate through the turning plate, the defects are not found on the lower surface (corresponding to the outer arc of the casting blank), the cracks are distributed along the edge of the medium plate, and the whole steel plate exists.

Referring to fig. 2 and 3, the following phenomena are observed when the gold phase sample is taken at the original crack defect: the crack and the surface of the steel plate form a certain angle and extend into the position 300 mu m below the surface layer of the steel plate, obvious fiber streamline characteristics are arranged near the crack, obvious decarburization is arranged around the crack, and obvious oxidation round points are arranged around the crack, the defect is caused by the fact that the time and the temperature of an original defect in a heating furnace are higher, and a time comparison factory can only generate the defect, which indicates that the crack exists before rolling, and the appearance is the typical characteristic of the genetic crack of a casting blank, so that the problem of the continuous casting link of the casting blank is judged.

Referring to the attached drawings 4 and 5, after the angle of the continuous casting billet is cut, the crack defect exists at the corner of the casting billet through acid cleaning observation and crack fracture appearance observation, and the transverse crack generally appears at the trough of the oscillation mark of the casting billet, so that the original transverse crack defect exists in the casting billet. Referring to FIG. 6, when the crack fracture is analyzed, a large amount of carbonitride exists in the fracture, which indicates that the carbonitride is precipitated at grain boundaries, the grain boundaries are weakened, the third brittle zone is enlarged, and cracks are easy to occur in the straightening process.

From the analysis, the existence of the original transverse crack at the corner of the casting blank is the main reason of the current edge cracking defect of the medium plate.

The reason for the transverse crack of the inner arc corner of the continuous casting blank is as follows: the stress position of the inner arc corner is mainly in the straightening stage of a continuous casting billet, 3 brittle zones generally exist between 600 ℃ and a melting point of a steel material, a straightening temperature range belongs to a third brittle zone of the material, the third brittle zone is further expanded due to the existence of the third brittle zone and the precipitation of carbonitride at a grain boundary, the inner arc of the casting billet is subjected to tensile stress in the straightening process, the high-temperature strain of the material exceeds the plastic limit, and corner transverse cracking can occur.

The measures and the implementation effects of controlling the transverse cracking of the corner of the continuous casting billet are as follows: the secondary cooling strength is reduced, the secondary cooling uniformity is improved, and the temperature of the casting blank in a straightening area is increased; reducing the nitrogen content in the molten steel to reduce the precipitation of carbonitrides; the equipment precision is improved, and the walking stress of the casting blank in the continuous casting process is eliminated; the molten steel quality is improved, the soft blowing time is ensured, and the impurities are completely floated.

The Q245R container plate has edge cracking defects, and the main reason is judged to be caused by transverse cracking of the corner of the casting blank by using the method. Through adjusting the continuous casting tool and the continuous casting process, the corner transverse crack defect of the continuous casting billet is finally eliminated, and the edge cracking crack defect of the medium plate is effectively controlled.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.