Treatment method for shrinkage porosity defect of steel casting

Abstract

The invention relates to a method for treating the shrinkage porosity defect of a steel casting. The method comprises the following steps: carrying out nondestructive testing on the steel casting, marking the position of the shrinkage porosity defect, preheating the shrinkage porosity defect and 70-90mm of the periphery to 100-120 DEG C, carrying out air gouging on the shrinkage porosity defect by using a welding machine as air gouging equipment, cooling to room temperature, and carrying out nondestructive testing to verify whether the shrinkage porosity defect is completely removed or not; a relief grinding tool is used for conducting relief grinding on the display area of the shrinkage porosity defect downwards, and air gouging trimming edges on the two sides of the defect are in smooth transition till the shrinkage porosity defect is completely removed; and welding and hydrogen removal treatment. According to the method, cracks are avoided at the defect positions of the casting, the quality is guaranteed, the production period is shortened, the repair qualification rate is increased, the repair frequency is reduced, and the casting quality is finally guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of steel casting, in particular to defect treatment of high alloy steel castings. Background Art

[0002] Steel castings, especially high alloy steel castings, are prone to shrinkage defects during their casting process. At present, shrinkage defects of high alloy steel castings are usually only treated by carbon arc gouging. However, the treatment method cannot effectively control the extension of defects by gouging, resulting in the defect size after gouging being larger than the non-destructive testing mark size, increasing the amount of subsequent welding; at the same time, since a lot of work is required to repeatedly treat shrinkage defects, repeated defect treatment fails, resulting in waste of resources and difficulty in treatment. Summary of the invention

[0003] Based on this, it is necessary to address the problem of shrinkage defects in high-alloy steel castings, overcome the problem that in the prior art, high-alloy defects are directly removed by gouging, which causes the defects to continue to extend within the scope of non-destructive testing standards, and repeatedly fail to meet the treatment standards. After welding, repeated welding occurs due to inadequate treatment of the defects themselves. A method for treating shrinkage defects in steel castings is proposed, in which a welding machine is used as gouging equipment. By gouging and grinding, the workload is minimized while ensuring that the defects are removed cleanly, so that the casting reaches a welding state, and the welding quality is improved by continuous arc priming welding.

[0004] This invention provides a method for treating shrinkage defects of steel castings, which is particularly suitable for treating shrinkage defects of high-alloy steel castings. The technical solution includes the following contents:

[0005] A method for treating shrinkage defects of steel castings comprises the following steps:

[0006] S1: Perform nondestructive testing on the steel casting to identify the location of the shrinkage defect, including the length, width and depth of the shrinkage defect;

[0007] S2: preheating the shrinkage defect and the surrounding 70mm to 90mm to 100℃ to 120℃, using a welding machine as an air gouging device to gouge the shrinkage defect to the depth marked in S1; S3: slowly cooling the steel casting to room temperature, polishing the surface of the defective position after treatment to a metallic luster, and performing nondestructive testing to verify whether the shrinkage defect is completely removed;

[0008] S4: If the nondestructive testing shows that the shrinkage defect is not completely removed, a grinding tool is used to grind downward the display area of ​​the shrinkage defect, and both sides of the defect are trimmed by air planing to achieve a smooth transition until the shrinkage defect is completely removed;

[0009] S5: welding process, using continuous arc welding to form a base layer, the base layer is two layers, after welding is completed, the welding base layer is fully hammered with a pneumatic shovel head to form a uniform hammered layer; and the hammered layer is polished and polished to make it bright, and then the middle part is filled with welding;

[0010] S6: The shrinkage defect position after the above steps is subjected to dehydrogenation treatment and is kept warm until post-weld heat treatment is performed.

[0011] In one embodiment, the nondestructive testing in S1 is performed by ultrasonic flaw detection.

[0012] In one embodiment, the welding machine in S2 uses a φ13mm carbon rod. Preheating is performed before gouging shrinkage defects. Gouging with a φ13mm carbon rod will cause shrinkage defects to extend at room temperature, causing the defect to exceed the non-destructive testing identification range. Gouging with a large-sized carbon rod will generate excessive heat input, causing shrinkage defects to extend, increasing the difficulty of defect treatment.

[0013] Furthermore, during air gouging, the angle of the carbon rod is 25° to 45°, and as the angle increases, the air gouging depth increases; the burning angle of the front end of the carbon rod is 55° to 60°, which allows the carbon rod to burn fully without generating excessive resistance, and the groove is set to be small inside and large outside, which is conducive to welding.

[0014] In one embodiment, the nondestructive testing in S3 uses magnetic particle testing to verify defect removal.

[0015] In one of the embodiments, an alloy head grinding tool is used in S4 to remove the defect. When grinding downward, the tool is perpendicular to the display area of ​​the shrinkage defect and the tool is ground downward by 5 mm to 10 mm each time for non-destructive testing and verification.

[0016] In one embodiment, when the depth of the grinding defect is greater than 20 mm, an air planing device is used to plane and trim the two sides of the grinding defect to make a smooth transition, and then the grinding is continued downward, and the air planing and trimming are performed once every 20 mm of downward grinding. This process is repeated.

[0017] In one of the embodiments, the welding of the base layer described in S5 uses a welding rod with a diameter of Φ3.2mm, and the welding current is selected to be 90A-120A manual welding single pass without swinging. The welding joint is left outside the defect, and each weld pass covers 1 / 3 of the previous weld pass. The thickness of the base layer is ≤2mm. The base welding requires that each weld seam is welded uninterruptedly and the welding is completed in one time. The welding joint is left outside the defect. The welding joint position is the part where welding defects are most likely to occur. Each weld pass covers about 1 / 3 of the previous weld pass to ensure full fusion and avoid welding unfused defects. A small current is used for welding during the base layer process. A total of two layers of base layers are used to ensure that the bottom of the defect is fully fused with the welding layer, and the welding stress generated by low welding heat input welding is minimized.

[0018] In one embodiment, the welding of the middle part in S5 adopts metal-metal gas shielded welding with a welding current of 180A to 270A; for manual arc welding, the welding material diameter is φ4.0 electrode, and the welding current is controlled at 130A to 170A.

[0019] In one embodiment, the dehydrogenation in S6 is carried out at 300°C to 350°C for 2 to 4 hours; the temperature for continuous insulation is controlled at 100°C to 150°C.

[0020] The beneficial effects of the present invention are:

[0021] The present application provides a method for treating shrinkage defects of high-alloy steel castings, which is particularly used for treating casting defects such as shrinkage of high alloys. Due to the material characteristics of the castings, using conventional treatment methods to gouge defects will cause the defects to be repeatedly treated unqualified, and the defects may extend beyond the non-destructive mark. Using the method of the present invention, the present invention uses a welding machine to replace the gouging equipment in the prior art, and uses a φ13mm carbon rod to remove defects by moving the gouging equipment and grinding, thereby avoiding cracks in the defects of the castings, ensuring quality while shortening the production cycle, and using manual welding and hammering to reduce the occurrence of cracks in the welding heat affected zone caused by welding, thereby improving the rework pass rate, reducing the number of reworks, and ultimately ensuring the quality of the castings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the air planing process in the present invention;

[0023] Figure 2 It is a schematic diagram of the relief grinding process in the present invention;

[0024] Figure 3 It is a schematic diagram of the welding process in the present invention.

[0025] 1-Carbon rod; 2-Shrinkage defect area; 3-Casting body; 4-Grinding area; 5-Air planing trimming area; 6-Base layer 1; 7-Base layer 2; 8-Hammer layer DETAILED DESCRIPTION

[0026] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0027] In one embodiment, a high alloy steel casting has a shrinkage defect. To solve this problem, the following treatment is performed:

[0028] Step 1: Nondestructive testing is used to identify the shrinkage defect location. Ultrasonic testing is used to perform flaw detection on both sides of the defect. The size of the defective position is marked on the casting with a white paint pen, including the length, width, depth and other parameters of the defect. The defect detection length is 20mm, the width is 20mm, and the depth is 30mm. Mark on the casting according to the actual size to identify the shrinkage defect area 2 on the casting body 1.

[0029] Step 2: Gouging

[0030] According to the above marks and parameters, use carbon arc gouging to gouge along the marked position to minimize the gouging amount. Figure 1 Before defect treatment, natural gas heating is used to preheat the shrinkage defect area 2 and the surrounding 70mm range to above 100℃. Normal temperature gouging will cause the shrinkage defect to extend, making the defect exceed the identification range of non-destructive testing. Figure 1 As shown, this embodiment abandons the use of conventional gouging equipment and uses a welding machine as gouging equipment. A φ13mm carbon rod is selected for gouging. A certain angle is formed between the carbon rod 3 and the shrinkage defect area 2. The angle is controlled at 25° to 45°. If the angle increases, the gouging depth increases, affecting the surface quality of the casting. When gouging, the front end of the carbon rod 3 is burned at an angle of 60° to ensure that the carbon rod is fully burned without generating excessive resistance. The groove is set to be small inside and large outside, which is conducive to welding. The defects are gouged to a non-destructive marking depth.

[0031] Step 3: Cool down and recheck

[0032] After the shrinkage defect area 2 is air-planed, it is slowly cooled to room temperature. Water cooling or air cooling and other compulsory measures are not allowed during cooling. The cracks caused by shrinkage in high-alloy products are more sensitive, and too fast cooling speed will cause cracks. After room temperature, use a grinding tool to grind the defect surface until the metallic luster is visible, and then use magnetic particle inspection to detect the bottom of the defect to verify whether the defect has been removed completely. After verification, there are still defects such as cracks, and the defect area is marked, that is, the grinding area 4 is marked, and the next step of processing is continued.

[0033] Step 4: Grind away defects

[0034] Use alloy head relief grinding tools to perform relief grinding according to the markings. Figure 2 , continue to grind 5mm vertically downward from the bottom of the grinding area 4, and continue to use magnetic particle inspection to confirm whether the defect is removed cleanly. Use magnetic particle inspection to check whether the defect is removed cleanly when the grinding depth is 5mm each time. If the defect is not completely removed, continue to repeat the grinding process. When the grinding exceeds 20mm, use the air planing equipment to perform air planing and smooth trimming on both sides of the defect, and the air planing and trimming area 5 is trimmed and smoothly transitioned. Repeat this process until the defect is cleaned. The grinding process is a cold treatment process, which can ensure that the crack defect caused by the defect will no longer extend. Since the extension of the crack is generated during the air planing process, the depth of the newly added crack by air planing is generally within 20mm. Therefore, magnetic particle inspection verification is used for each grinding of 5 to 10mm, so that the defect can be processed as soon as possible. After the magnetic particle detects the defect, grind 5 to 10mm vertically downward from the bottom of the defect each time along the defect position. When the grinding defect depth is greater than 20mm, use the air planing equipment to air planer and trim the two sides of the grinding defect for a smooth transition. The smooth transition of air planing is because the depth of defects caused by grinding is not conducive to welding. If smooth transition is performed after all defects have been processed and qualified, new cracks will appear in the air planing.

[0035] Step 5: Soldering

[0036] After all defects are dealt with, welding begins. First, use a small-size electrode with a diameter of Φ3.2mm to prime the area to be welded. After preheating the area to be welded to above 180℃, use a φ3.2 electrode to perform continuous arc prime welding for at least two layers. Figure 3 , welding forms two layers of base layer, base layer 1 6 and base layer 2 7, the layer thickness of base layer 1 6 and base layer 2 7 is ≤ 2mm. The welding current is selected to be 90A ~ 120A manual welding single pass without swinging, requiring each weld to be welded continuously and completed in one time. Leave the weld joint outside the defect. The weld joint position is the part where welding defects are most likely to occur. Each weld pass covers about 1 / 3 of the previous weld pass to ensure full fusion and avoid welding unfused defects. A small current is used for welding during the primer process. A total of two primer layers are used to ensure that the bottom of the defect is fully fused with the welding layer. The welding stress generated by welding with low welding heat input is minimized.

[0037] After welding is completed, the pneumatic shovel head is used to hammer the welding area and grind the pneumatic shovel head into a flat shape. After the base layer is welded, the pneumatic shovel head is used to fully hammer the welding base layer and form a uniform hammering layer 8. The purpose of hammering is to make the structure of the weld area denser and eliminate part of the welding stress. Then use an electric grinding tool to grind the base layer to make it bright, and then fill the middle part. In this embodiment, gas shielded welding is used for filling welding, and the welding current is selected to be 230-270A.

[0038] Step 6: Post-heat dehydrogenation

[0039] After the defect welding is completed, natural gas is used to dehydrogenate the defective position. The dehydrogenation temperature is controlled at 300℃~350℃ and the dehydrogenation is kept for 2 hours. This step can effectively eliminate the hydrogen element in the weld to avoid hydrogen-induced cracks in the later stage. After the dehydrogenation is completed, the temperature is lowered to 100℃~150℃ and kept warm until stress relief heat treatment is performed. Post-weld stress relief heat treatment is performed according to the heat treatment process of the casting.

[0040] In this example, according to the defect size, a welding machine is used for air planing, combined with a scraping and grinding method to remove the defect, and the defect is repaired by manual welding and hammering. The present invention can effectively solve the casting quality problem that occurs when the shrinkage defect of high-alloy castings is treated. This embodiment is used to solve the shrinkage defect of steel castings. The casting quality meets the requirements, no cracks are seen at the defective parts of the castings, the production cycle is effectively shortened, the rework pass rate is high, and no secondary rework is performed.

[0041] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0042] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for treating shrinkage defects of steel castings, characterized in that: The steps include: S1: Perform nondestructive testing on the steel casting to identify the location of the shrinkage defect, including the length, width and depth of the shrinkage defect; S2: preheat the shrinkage defect and the surrounding 70 mm to 90 mm to 100° C. to 120° C., use a welding machine as an air gouging device to gouge the shrinkage defect to the depth marked in S1; S3: slowly cooling the steel casting from room temperature to room temperature, polishing the surface of the defective position after treatment to a metallic luster, and performing nondestructive testing to verify whether the shrinkage defect is completely removed; S4: If the nondestructive testing shows that the shrinkage defect is not completely removed, use a grinding tool to grind the display area of ​​the shrinkage defect downward, and air planer trim the edges on both sides of the defect to make a smooth transition until the shrinkage defect is completely removed; S5: welding process, using continuous arc welding to form a base layer, the base layer is two layers, after welding is completed, the welding base layer is fully hammered to form a uniform hammered layer; the hammered layer is scraped and polished to brighten, and then the middle part is filled with welding; S6: The position treated in the above steps is subjected to dehydrogenation treatment and is kept warm until post-weld heat treatment is performed.

2. A method for treating shrinkage defects of steel castings according to claim 1, characterized in that: The non-destructive testing in S1 is performed by ultrasonic flaw detection.

3. The method for treating shrinkage defects of steel castings according to claim 1, characterized in that: The welding machine in S2 uses a carbon rod of φ13 mm.

4. A method for treating shrinkage defects of steel castings according to claim 2, characterized in that: During air planing, the angle of the carbon rod is 25° to 45°, and the burning angle of the front end of the carbon rod is 55° to 60°.

5. The method for treating shrinkage defects of steel castings according to claim 1, characterized in that: The non-destructive testing in S3 uses magnetic particle testing to verify defect removal.

6. A method for treating shrinkage defects of steel castings according to claim 1, characterized in that: When grinding downward in S4, the non-destructive testing is performed vertically to the display area of ​​the shrinkage defect, and grinding downward 5 mm to 10 mm each time.

7. A method for treating shrinkage defects of steel castings according to claim 6, characterized in that: When the depth of the grinding defect is greater than 20mm, use air planing equipment to air planer and trim the two sides of the defect to make a smooth transition, and then grind downwards, and repeat this process repeatedly.

8. A method for treating shrinkage defects of steel castings according to claim 1, characterized in that: The welding of the base layer described in S5 uses an electrode with a diameter of Φ3.2mm, and the welding current is selected to be 90A~120A manual welding single pass without swinging. The welding joint is left outside the defect, and each weld pass covers 1 / 3 of the previous weld pass. The thickness of the base layer is ≤2mm.

9. A method for treating shrinkage defects of steel castings according to claim 1, characterized in that: The welding of the middle part of S5 adopts metal-metal gas shielded welding with a welding current of 180A to 270A; manual arc welding is adopted with a welding rod of φ4.0 in diameter and a welding current controlled at 130A to 170A.

10. A method for treating shrinkage defects of steel castings according to claim 1, characterized in that: The dehydrogenation in S6 is carried out at 300°C to 350°C for 2 to 4 hours; the continuous insulation temperature is controlled at 100°C to 150°C.

Images