Metal crack repairing method

Abstract

The invention provides a metal crack repairing method. The metal crack repairing method comprises the steps that S1, a to-be-repaired workpiece is obtained; s2, a welding gun is obtained, and the to-be-repaired workpiece is baked at the first temperature for the first time through the welding gun; s3, carrying out polishing treatment on the crack area, and carrying out ray and coloring detection; s4, punching treatment is conducted on the end points of the cracks; s5, the crack area is subjected to polishing treatment, so that a pit is formed; s6, the to-be-repaired workpiece is coated with a heat preservation material, and the surface, with the pits, of the to-be-repaired workpiece is heated through a heat source; and S7, molten metal is obtained, the molten metal is poured into the pit, the welding gun is adopted for heating the molten metal at the second temperature so that the molten metal can permeate into the grain boundary of the base metal, and after the molten metal and the pit form a whole, the step is repeated till the pit is filled. The problems of repeated cracking and crack propagation in crack repair of the metal workpiece in the prior art are solved.

Description

Technical Field

[0001] The invention relates to the technical field of casting equipment, and in particular to a metal crack repairing method. Background Art

[0002] In the use of highly brittle materials, especially the shells, bases, cylinders, connecting rods, etc. of large rotating equipment that have been subjected to high temperatures, conveyed harmful media, or cast parts, they are affected by the vibration of the unit, the erosion of harmful elements in the medium, or the pressure and temperature fluctuations of the conveyed medium during operation, which will cause the workpiece to crack or the body metal to peel off, affecting its use. In order to ensure its normal use, it must be repaired. However, due to the large size of these parts and the high brittleness of the parent material, the original high-temperature melting fusion repair technology will always cause repeated cracking and crack propagation, and even serious new cracks, which will eventually lead to repair failure and forced replacement, thereby doubling the production cost and labor intensity, and delaying production.

[0003] The current melting type fusion repair technology requires the use of high temperature to completely melt the metal workpiece locally and fuse it with the filler metal to form a closed joint, and then rapidly cool it in the air, causing the parent material grains to grow rapidly and then shrink rapidly, eventually causing gaps in the grain boundaries. Under the action of welding stress, the gaps between the grain boundaries continue to expand to form cracks, which are difficult to repair. Especially for extremely brittle materials, such as high-alloy steel, casting materials and other materials, if the heat treatment conditions are insufficient after insulation and preheating, it is very easy to cause large-scale cracks, which will eventually cause the workpiece or even the entire equipment to be scrapped.

[0004] That is to say, the crack repair of metal workpieces in the prior art has the problems of repeated cracking and crack propagation. Summary of the invention

[0005] The main purpose of the present invention is to provide a metal crack repair method to solve the problems of repeated cracking and crack propagation in the crack repair of metal workpieces in the prior art.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a metal crack repair method, comprising the following steps: step S1: obtaining a workpiece to be repaired and cleaning the workpiece to be repaired; step S2: obtaining a welding gun, and using the welding gun to bake the workpiece to be repaired at a first temperature and a first time; step S3: polishing the crack area of ​​the workpiece to be repaired, and performing X-ray and coloring detection; step S4: punching the end points of the cracks in the crack area; step S5: grinding the crack area of ​​the workpiece to be repaired to form a pit; step S6: using a heat-insulating material to cover at least part of the surface of the workpiece to be repaired, so that the surface of the workpiece to be repaired with the pit is exposed, and using a heat source to heat the surface of the workpiece to be repaired with the pit; step S7: obtaining molten metal, pouring the molten metal into the pit, using a welding gun to continuously heat the molten metal in the pit at a second temperature, so that the molten metal penetrates into the parent material grain boundary of the workpiece to be repaired, and repeating this step after the molten metal and the pit form a whole, until the pit is filled.

[0007] Furthermore, the metal crack repair method also includes steps after step S6: a temperature measuring step: setting a surface opposite to the surface with pits on the workpiece to be repaired as a temperature measuring surface, and using a temperature measuring gun to measure the temperature of the temperature measuring surface; a molten metal prefabrication step: melting a metal material with a melting point lower than that of the workpiece to be repaired to form molten metal.

[0008] Further, in step S7, a welding gun is used to continuously heat the molten metal in the pit at a second temperature so that the temperature of the pit reaches above 1312°C, so that the molten metal penetrates into the grain boundary of the parent material of the workpiece to be repaired, and the welding gun is moved to cool the molten metal and form a whole with the workpiece to be repaired.

[0009] Furthermore, in step S7, the molten metal is formed in the pit layer by layer in multiple times.

[0010] Furthermore, the metal crack repair method also includes a cooling step after step S7, wherein the cooling step is to remove the heat source and cool the workpiece to be repaired at a first cooling rate until the temperature of the workpiece to be repaired drops to 757.5°C, and then completely cover the workpiece to be repaired with an insulating material, and cool the workpiece to be repaired at a second cooling rate, wherein the second cooling rate is less than the first cooling rate, until the workpiece to be repaired is cooled to room temperature, and then the insulating material is removed.

[0011] Furthermore, the metal crack repair method also includes a detection step after the cooling step, and the detection step is to perform ultrasonic detection, color detection, and water pressure test on the repaired part of the workpiece to be repaired and the surrounding of the repaired part.

[0012] Further, in step S5, the pit is a U-shaped pit.

[0013] Furthermore, the length of the U-shaped pit is equal to the length of the crack, and the depth of the U-shaped pit is less than the depth of the crack.

[0014] Further, in step S2, the first temperature is less than or equal to 150° C., and the first time is greater than or equal to 62 hours.

[0015] Further, in step S6, there are multiple heat sources, and multiple heat sources are arranged at intervals on both sides of the pit.

[0016] By applying the technical solution of the present invention, the metal crack repair method includes the following steps S1 to S7, step S1: obtaining a workpiece to be repaired and cleaning the workpiece to be repaired; step S2: obtaining a welding gun, and using the welding gun to bake the workpiece to be repaired at a first temperature and a first time; step S3: polishing the crack area of ​​the workpiece to be repaired, and performing X-ray and coloring detection; step S4: punching the end points of the cracks in the crack area; step S5: grinding the crack area of ​​the workpiece to be repaired to form a pit; step S6: using a heat-insulating material to cover at least part of the surface of the workpiece to be repaired, so that the surface of the workpiece to be repaired with the pit is exposed, and using a heat source to heat the surface of the workpiece to be repaired with the pit; step S7: obtaining molten metal, pouring the molten metal into the pit, using a welding gun to continuously heat the molten metal in the pit at a second temperature, so that the molten metal penetrates into the parent material grain boundary of the workpiece to be repaired, and repeating this step after the molten metal and the pit form a whole, until the pit is filled.

[0017] By using a welding gun to bake the workpiece to be repaired at a first temperature and a first time in step S2, harmful gases and moisture inside the workpiece to be repaired can be removed, and the harmful gases and moisture inside the workpiece to be repaired can be prevented from entering the molten pool to produce defects such as pores, white spots, cracks, etc., so as to ensure that the subsequent processes can be carried out stably. By polishing the crack area of ​​the workpiece to be repaired in step S3, the workpiece to be repaired presents a metallic luster, and at the same time confirms the state of the crack gap and the situation of impurities in the gap, so as to take cleaning measures, and then performs radiation and coloring detection to determine the crack direction and specification size, so as to determine the direction in which the crack may expand. In step S4, the end points of the cracks in the crack area are punched, that is, positioning holes are processed at the end points of the cracks, so as to prevent the cracks from expanding infinitely during the grinding or repair process, which is conducive to preventing the cracks from spreading. In step S5, the crack area of ​​the workpiece to be repaired is polished to form a pit, so as to leave storage space for the subsequent molten metal and a channel for infiltration into the parent material grain boundary of the workpiece to be repaired, which is conducive to ensuring good subsequent bonding. In step S6, the surface of the workpiece to be repaired with the pit is heated by using a heat source to ensure that the overall temperature of the workpiece to be repaired is evenly increased, so that the temperature point where the grains of the base material of the workpiece to be repaired expand and produce tiny gaps is prevented from rapidly dissipating heat during the subsequent repair process, and it is slowly cooled to prevent the generation of new cracks. In step S7, the molten metal is obtained, poured into the pit, and the molten metal in the pit is continuously heated by a welding gun at a second temperature so that the molten metal penetrates into the base material grain boundary of the workpiece to be repaired. After the molten metal and the pit form a whole, this step is repeated until the pit is filled, thereby completing the repair work of the crack area on the workpiece to be repaired. The metal crack repair method of the present application can effectively avoid repeated cracking, crack propagation, and the appearance of new cracks, thereby ensuring that the workpiece can continue to be used, avoiding the situation of replacing the workpiece, and greatly saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0019] Figure 1 A flow chart showing a metal crack repair method according to an optional embodiment of the present invention;

[0020] Figure 2 Shows Figure 1 A state diagram of the metal crack repair method in the repair process.

[0021] The above drawings include the following reference numerals:

[0022] 10. Workpiece to be repaired; 20. U-shaped pit; 30. Temperature measuring gun; 40. Temperature measuring point; 50. Liquid metal; 60. Welding gun; 70. Heat source. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs.

[0025] In the present invention, unless otherwise specified, the directional words used, such as "up, down, top, bottom", usually refer to the directions shown in the drawings, or to the components themselves in the vertical, perpendicular or gravity directions; similarly, for ease of understanding and description, "inside and outside" refer to the inside and outside relative to the outline of each component itself, but the above-mentioned directional words are not used to limit the present invention.

[0026] In order to solve the problems of repeated cracking and crack propagation in crack repair of metal workpieces in the prior art, the present invention provides a metal crack repair method.

[0027] like Figure 1 and Figure 2 As shown, the metal crack repair method includes the following steps S1 to S7:

[0028] Step S1: obtaining a workpiece 10 to be repaired and cleaning the workpiece 10 to be repaired;

[0029] Step S2: Obtain a welding gun 60, and use the welding gun 60 to bake the workpiece 10 to be repaired at a first temperature and for a first time;

[0030] Step S3: polishing the cracked area of ​​the workpiece 10 to be repaired, and performing X-ray and coloring inspection;

[0031] Step S4: punching the end points of the cracks in the crack area;

[0032] Step S5: grinding the cracked area of ​​the workpiece 10 to be repaired to form a pit;

[0033] Step S6: using a heat-insulating material to cover at least a portion of the surface of the workpiece 10 to be repaired, so that the surface of the workpiece 10 to be repaired with the pit is exposed, and using a heat source 70 to heat the surface of the workpiece 10 to be repaired with the pit;

[0034] Step S7: Obtain molten metal 50, pour the molten metal 50 into the pit, and use a welding gun 60 to continuously heat the molten metal 50 in the pit at a second temperature so that the molten metal 50 penetrates into the grain boundary of the parent material of the workpiece 10 to be repaired. After the molten metal 50 and the pit form a whole, repeat this step until the pit is filled.

[0035] By using a welding gun 60 to bake the workpiece 10 to be repaired at the first temperature and the first time in step S2, harmful gases and moisture inside the workpiece 10 to be repaired can be removed to prevent them from entering the molten pool and causing defects such as pores, white spots, cracks, etc., thereby ensuring that subsequent processes can be carried out stably. By polishing the crack area of ​​the workpiece 10 to be repaired in step S3, the workpiece 10 to be repaired presents a metallic luster, and at the same time confirms the state of the crack gap and the situation of impurities in the gap so as to take cleaning measures, and then performs X-ray and coloring detection to determine the crack direction and specification size so as to determine the direction in which the crack may expand. In step S4, the end points of the cracks in the crack area are punched, that is, positioning holes are processed at the end points of the cracks to prevent the cracks from infinitely expanding during the grinding or repair process, which is conducive to preventing the cracks from spreading. In step S5, the crack area of ​​the workpiece 10 to be repaired is polished to form a pit, so as to leave storage space for the subsequent molten metal 50 and a channel for penetrating into the grain boundary of the parent material of the workpiece 10 to be repaired, which is conducive to ensuring good subsequent bonding. In step S6, the surface of the workpiece 10 to be repaired with the pit is heated by using a heat source 70 to ensure that the overall temperature of the workpiece 10 to be repaired is evenly increased, so that the grains of the parent material of the workpiece 10 to be repaired expand and a temperature point of a small gap is generated, which is conducive to preventing the rapid dissipation of heat during the subsequent repair process, so that it is slowly cooled to prevent the generation of new cracks. In step S7, the molten metal 50 is obtained, poured into the pit, and the molten metal 50 in the pit is continuously heated by a welding gun 60 at a second temperature so that the molten metal 50 penetrates into the grain boundary of the parent material of the workpiece 10 to be repaired. After the molten metal 50 and the pit form a whole, this step is repeated until the pit is filled, thereby completing the repair work of the crack area on the workpiece 10 to be repaired. The metal crack repair method of the present application can effectively avoid repeated cracking, crack propagation and the appearance of new cracks, thereby ensuring that the workpiece can continue to be used, avoiding the need to replace the workpiece, and greatly saving costs.

[0036] It should be noted that the metal crack repair method of the present application has a significant effect on the repair of various cracks generated by highly brittle materials, and can ensure that the highly brittle materials will not have cracks propagating or new cracks generated during the repair process, and can also ensure that after the repair, the cracks will not recur, thereby ensuring the high efficiency of the crack repair. It can improve the applicability and processability of the repaired part and the surrounding parent materials, avoid the scrapping of various equipment due to improper crack repair, and effectively reduce production costs and labor intensity.

[0037] In addition, the workpiece 10 to be repaired mentioned in the metal crack repair method of the present application can be a highly brittle material. The metal crack repair method of the present application is improved and designed in combination with the actual situation of crack repair of highly brittle materials on site, as well as the characteristics of high-temperature expansion of metal grains and strong permeability of heavy metal liquid 50. It is a repair method designed to overcome the disadvantages of the melting type fusion repair technology that the cracks of extremely brittle materials are prone to unlimited expansion, which eventually leads to the scrapping of the workpiece or even the entire equipment.

[0038] It should also be noted that during the repair process, the base material of the workpiece 10 to be repaired is not melted, but the filling metal liquid 50 penetrates into the body through the grain boundaries of the base material, and is slowly cooled by heat preservation for a long time to form a whole, thereby achieving the purpose of repair.

[0039] Specifically, in step S1, cleaning the workpiece 10 to be repaired includes: comprehensively cleaning the oil, dirt, paint and other harmful substances inside and outside the workpiece 10 to be repaired that are likely to cause rapid cooling and affect the repair quality, so as to avoid aggravated cooling during the repair process or cause cracks and other defects in the repaired part.

[0040] Specifically, in step S2, the first temperature is less than or equal to 150°C, and the first time is greater than or equal to 62 hours. In a specific embodiment of the present application, the first temperature is 150°C, and the first time is 62 hours, that is, the workpiece 10 to be repaired is baked at a low temperature of 150°C using a welding torch 60 for 62 hours to remove harmful gases and moisture inside the workpiece 10 to be repaired, and prevent them from entering the molten pool to cause defects such as pores, white spots, and cracks.

[0041] like Figure 2 As shown, the metal crack repair method further includes a temperature measurement step and a metal liquid prefabrication step after step S6:

[0042] Temperature measurement step: set the surface opposite to the surface with pits on the workpiece 10 to be repaired as the temperature measuring surface, set a plurality of spaced temperature measuring points 40 on the temperature measuring surface, and use a temperature measuring gun 30 to continuously measure the temperature of the temperature measuring points 40 on the temperature measuring surface to ensure that the overall temperature of the workpiece 10 to be repaired is uniform, and monitor the workpiece 10 to be repaired to reach a temperature of about 1312°C at which the base material grains expand and tiny gaps are generated.

[0043] Preparing molten metal step: melting a metal material having a melting point lower than the base material melting point of the workpiece 10 to be repaired by 420° C. to form molten metal 50, and storing the molten metal in a small container for future use.

[0044] Specifically, in step S5, the crack area of ​​the workpiece 10 to be repaired is polished to form a pit, which is a U-shaped pit 20, specifically a U-shaped groove, the length of the U-shaped pit 20 is equal to the total length of the crack, and the depth of the U-shaped pit 20 is less than 1.5mm to 2.5mm of the depth of the crack. Storage space is reserved for the molten metal 50 and a channel for infiltration into the grain boundary of the parent material of the workpiece 10 to be repaired, ensuring good subsequent bonding.

[0045] Specifically, the above-mentioned heat-insulating material is heat-insulating cotton. In step S6, the heat-insulating material is used to cover at least part of the surface of the workpiece 10 to be repaired, leaving only the position for the heat source 70 of the U-shaped pit 20 to heat. There are multiple heat sources 70, and multiple heat sources 70 are arranged at intervals on both sides of the pit. In a specific embodiment of the present application, the number of heat sources 70 is four, and two heat sources 70 are arranged at intervals on both sides of the U-shaped pit 20. The heat source 70 is used to continuously heat the surface around the U-shaped pit 20 to ensure the uniformity of the temperature near the U-shaped pit 20, so as to prevent the heat from dissipating quickly during the repair process and ensure the effect of constant temperature.

[0046] refer to Figure 2 Two heat sources 70 are used to fully heat the left side of the U-shaped pit 20, and the other two heat sources 70 are used to fully heat the right side of the U-shaped pit 20, ensuring that the average heating rate is 150°C / h, ensuring that the overall temperature of the workpiece 10 to be repaired is evenly increased.

[0047] In a specific embodiment of the present application, the heat source 70 may be a spray gun or other tools for heating.

[0048] Specifically, in step S7, after pouring the molten metal 50 into the pit, the welding gun 60 is used to continuously heat the molten metal 50 in the pit and the pit walls on both sides of the pit at the second temperature, so that the temperature of the pit reaches above the temperature point 1312°C, so that the parent material grains of the workpiece 10 to be repaired continue to expand, the grain boundary gaps are enlarged, the fluidity of the molten metal 50 is increased, and the flowing molten metal 50 gradually penetrates into the parent material grain boundaries of the workpiece 10 to be repaired, and the fluidity is increased by continuously heating so that it gradually penetrates into the tiny gaps between the expanded grains, and the welding gun 60 is slowly moved, so that the molten metal 50 that penetrates into the parent material grain boundaries of the workpiece 10 to be repaired is slowly cooled and forms a whole with the workpiece 10 to be repaired. The above-mentioned second temperature can be set according to actual conditions, as long as the temperature of the pit can reach above the temperature point 1312°C.

[0049] Specifically, in step S7, the molten metal 50 is formed in the pit layer by layer for multiple times. That is, the molten metal 50 is to be infiltrated into the grain boundary of the parent material of the workpiece 10 to be repaired in layers. That is, after the molten metal 50 and the pit form a whole, the next layer of molten metal 50 is poured in, and the operation is repeated until the pit is filled. This arrangement ensures grain refinement, reduces the probability of defect formation, and further improves the structural strength of the repaired part.

[0050] Specifically, after the pit is filled, the metal crack repair method also includes a cooling step after step S7. The cooling step is to slowly remove multiple heat sources 70 in turn, so that the workpiece 10 to be repaired is cooled at a first cooling rate to ensure that the overall temperature of the workpiece 10 to be repaired is evenly and slowly reduced until the temperature of the workpiece 10 to be repaired drops to 757.5°C. The workpiece 10 to be repaired is completely wrapped with insulation cotton, and the workpiece 10 to be repaired is cooled at a second cooling rate to slowly cool the workpiece 10 to be repaired. The second cooling rate is less than the first cooling rate. After 72 hours, until the workpiece 10 to be repaired is cooled to room temperature or normal temperature, the insulation material is removed.

[0051] In a specific embodiment of the present application, the first cooling rate is 20°C / h on average, and the second cooling rate is 5°C / h on average.

[0052] Specifically, the metal crack repair method further includes a detection step after the cooling step, wherein the detection step is to perform ultrasonic detection, color detection, and water pressure test on the repaired part and the surrounding of the repaired part of the workpiece 10 to be repaired. The ultrasonic detection result is qualified at level 1, the color detection result is qualified at level 1, and there is no leakage in the water pressure test of 1.25 times the design pressure.

[0053] The advantages of the metal crack repair method of the present application are described below in combination with specific applications, taking a reciprocating compressor cylinder seat as an example. The cylinder seat has a thickness of 55mm, a height of 856mm, and a diameter of 1216mm. During operation, the cooling water channel is blocked and cannot circulate and discharge normally. When it is shut down in winter, it freezes and cracks. The cracks are penetrating cracks with a length of 684mm. In order to save costs, crack repair is arranged. Previously, the melting type fusion repair technology was used for repair, but because the melting temperature was too high and the parent material was gray cast iron, the brittleness was high, and the repair process repeatedly cracked, eventually leading to failure. In order to solve the problem as soon as possible, a metal crack repair method using grain boundary infiltration of molten metal 50 was developed. After it was put into use, the effect was significantly improved. Although there are still some micro defects, there is no crack propagation phenomenon, and no new cracks have appeared. The repaired cylinder seat is still in operation. The cost savings are about 6.775 million yuan.

[0054] Obviously, the above-described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0055] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0056] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A metal crack repair method, characterized in that: The steps include: Step S1: obtaining a workpiece to be repaired (10), and cleaning the workpiece to be repaired (10); Step S2: obtaining a welding gun (60), and using the welding gun (60) to bake the workpiece (10) to be repaired at a first temperature and for a first time; Step S3: polishing the cracked area of ​​the workpiece (10) to be repaired, and performing X-ray and colorimetric testing; Step S4: punching the end points of the cracks in the crack area; Step S5: grinding the cracked area of ​​the workpiece (10) to be repaired to form a pit; Step S6: using a heat-insulating material to cover at least a portion of the surface of the workpiece (10) to be repaired, so that the surface of the workpiece (10) to be repaired having the pit is exposed, and using a heat source (70) to heat the surface of the workpiece (10) to be repaired having the pit; Step S7: obtaining molten metal (50), pouring the molten metal (50) into the pit, using the welding gun (60) to continuously heat the molten metal (50) in the pit at a second temperature, so that the molten metal (50) penetrates into the grain boundary of the parent material of the workpiece (10) to be repaired, and repeating this step after the molten metal (50) and the pit form a whole, until the pit is filled.

2. The metal crack repairing method according to claim 1, characterized in that: The metal crack repairing method further comprises the following steps after step S6: Temperature measurement step: setting a surface opposite to the surface of the workpiece (10) to be repaired having the pit as a temperature measurement surface, and using a temperature measuring gun (30) to measure the temperature of the temperature measurement surface; Prefabricate the molten metal step: melt the metal material with a melting point lower than that of the workpiece (10) to be repaired to form the molten metal (50).

3. The metal crack repairing method according to claim 1, characterized in that: In the step S7, the welding gun (60) is used to continuously heat the molten metal (50) in the pit at a second temperature so that the temperature of the pit reaches above 1312° C., so that the molten metal (50) penetrates into the grain boundary of the parent material of the workpiece (10) to be repaired, and the welding gun (60) is moved to cool the molten metal (50) and form a whole with the workpiece (10) to be repaired.

4. The metal crack repairing method according to claim 1, characterized in that: In the step S7, the molten metal (50) is formed in the pit layer by layer in multiple times.

5. The metal crack repairing method according to claim 1, characterized in that: The metal crack repairing method further comprises a cooling step after step S7. The cooling step is to remove the heat source (70) and cool the workpiece (10) to be repaired at a first cooling rate until the temperature of the workpiece (10) to be repaired drops to 757.5°C, and then completely cover the workpiece (10) to be repaired with a heat-insulating material, and cool the workpiece (10) to be repaired at a second cooling rate, wherein the second cooling rate is lower than the first cooling rate, until the workpiece (10) to be repaired is cooled to room temperature, and then the heat-insulating material is removed.

6. The metal crack repairing method according to claim 5, characterized in that: The metal crack repairing method further comprises a detection step after the cooling step, The detection step is to perform ultrasonic detection, color detection, and water pressure test on the repaired part of the workpiece (10) to be repaired and the surrounding area of ​​the repaired part.

7. The metal crack repairing method according to claim 1, characterized in that: In the step S5, the pit is a U-shaped pit (20).

8. The metal crack repairing method according to claim 7, characterized in that: The length of the U-shaped pit (20) is equal to the length of the crack, and the depth of the U-shaped pit (20) is less than the depth of the crack.

9. The metal crack repairing method according to claim 1, characterized in that: In the step S2, the first temperature is less than or equal to 150° C., and the first time is greater than or equal to 62 hours.

10. The metal crack repairing method according to claim 1, characterized in that: In the step S6, the heat source (70) is multiple, and the two sides of the pit are respectively provided with multiple heat sources (70) arranged at intervals.

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