Method for healing internal defects of steel ingot by using ultrahigh pressure

Abstract

The invention discloses a method for healing internal defects of a steel ingot by using ultrahigh pressure, which comprises the following steps: cleaning the surface of the steel ingot to be treated, placing the cleaned steel ingot in a press, after reaching a preset temperature and a preset pressure intensity, carrying out heat-preservation and pressure-preservation compression for a period of time to remove the internal defects, and taking out the steel ingot after the compression is completed; the preset pressure intensity is 4-10 GPa; when the preset temperature is room temperature, the compression time is 7-10 hours, and when the preset temperature is 600-800 DEG C, the compression time is 20-60 minutes. According to the method, the internal defects of the bearing steel are healed by adopting an ultrahigh pressure technology below the recrystallization temperature, grain growth and phase change caused by high-temperature compression are avoided, oxidation and decarburization of the material surface are avoided, and defect closing can be realized under the condition that the temperature is not obviously increased, so that the defect volume is reduced or eliminated, and the yield of the bearing steel is improved. Defects in the casting are repaired, and the mechanical property is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of physical simulation of material thermal processing, and in particular relates to a method for healing internal defects of a steel ingot by using ultra-high pressure. Background Art

[0002] As advanced equipment develops towards high power, high performance and high reliability, the demand for basic steel materials also shows a trend of large specifications, high quality and diversification. This trend leads to the increase in the size of steel ingots, which inevitably increases the appearance of internal defects (cracks, looseness, shrinkage, etc.). Especially for large and extra-large cross-section ingots, the presence of these defects seriously affects the mechanical properties and service life of the material. Therefore, the development of effective defect healing technology is crucial for the preparation of high-quality steel materials.

[0003] At present, one of the main solutions to such problems is to repair defects through hot working methods. Such methods usually heat the material to the recrystallization temperature or above, and apply appropriate pressure to promote metal flow, thereby closing or filling internal defects (such as cracks, looseness, shrinkage cavities, etc.).

[0004] However, traditional thermoplastic deformation methods often require higher temperatures (over 950°C), and the pressure of general forging machines is relatively small (generally between 500 and 3,000 tons). Repeated upsetting and stretching are required to achieve a good healing effect, but this will cause serious shape changes in the steel. High temperatures may not only lead to coarse grains, but also induce phase changes; at the same time, long-term exposure to high temperatures can easily cause surface oxidation and even decarburization, which will have an adverse effect on the performance of the final product. Although the degree of defect healing can be optimized by adjusting the traditional thermoplastic deformation process parameters, traditional methods are still difficult to completely eliminate or have limited improvement for certain specific types of defects (for defects with greater depth or complex morphology).

[0005] In view of the above situation, it is particularly important to explore new and more efficient technical solutions that can overcome the bottlenecks of existing technologies. Therefore, the present invention provides a method for healing internal defects of steel ingots using ultra-high pressure, and uses ultra-high pressure technology to treat defects inside the steel ingot. This method uses ultra-high pressure instead of relying solely on the effect of temperature, and can achieve better defect repair effects at lower temperatures, while reducing the negative effects caused by high temperatures, and this method can heal defects without changing the shape of the steel. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a method for healing internal defects of steel ingots using ultra-high pressure. The ultra-high pressure technology is used to close the defects without significantly increasing the temperature, thereby reducing or eliminating the defect volume, repairing the defects inside the casting, and improving the mechanical properties. The problem of grain growth and phase change caused by high-temperature compression in traditional methods is solved, and oxidation and decarburization of the material surface are avoided.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for healing internal defects of a steel ingot using ultrahigh pressure, the method specifically comprising: cleaning the surface of the steel ingot to be treated, placing the cleaned steel ingot in a press, and after reaching a preset temperature and a preset pressure, compressing it for a period of time to remove its internal defects; the preset pressure is 4 to 10 GPa, preferably 5 GPa.

[0009] Furthermore, the present invention provides a method for healing internal defects of a steel ingot using ultra-high pressure, which may also have the following characteristics: the preset temperature is 600-800°C, preferably 700°C, and the compression time is 20-60 minutes, preferably 30 minutes.

[0010] Furthermore, the present invention provides a method for healing internal defects of a steel ingot using ultra-high pressure, which may also have the following characteristics: the heating process to reach a preset temperature is: heating from room temperature to 400°C at a heating rate of 1 to 3°C / s, and heating from 400°C to 600 to 800°C at a heating rate of 1 to 3°C / s; the pressurization rate to reach a preset pressure is 1 to 2 GPa / min, preferably 1 GPa / min.

[0011] Furthermore, the present invention provides a method for healing internal defects of steel ingots using ultra-high pressure, which may also have the following characteristics: after compression is completed, the temperature and pressure are lowered, and the cooling rate is 10 to 20°C / s and the pressure reduction rate is 1 to 3Mpa / min.

[0012] Furthermore, the present invention provides a method for healing internal defects of steel ingots using ultra-high pressure, which may also have the following characteristics: the preset temperature is room temperature, the compression time is 7 to 10 hours, preferably 8 hours; the pressurization rate to reach the preset pressure is 1 to 2 GPa / min, preferably 1 GPa / min.

[0013] Furthermore, the present invention provides a method for healing internal defects of a steel ingot using ultra-high pressure, which may also have the following characteristics: after the compression is completed, the pressure is reduced, and the pressure reduction rate is 1 to 3 MPa / min.

[0014] Furthermore, the present invention provides a method for healing internal defects of a steel ingot using ultra-high pressure, which may also have the following characteristics: the composition of the steel ingot to be treated includes, by mass percentage, the following: C 0.42%, Si 0.31%, Mn 0.76%, P0.011%, S 0.002%, Cu 0.02%, Ni 0.02%, Cr 1.14%, V 0.005%, Mo 0.21%, Nb0.0014%, Al 0.024%, Ti 0.0032%, N 0.0037%, O 0.0012%, H0.00005%, and the rest is Fe element.

[0015] Furthermore, the present invention provides a method for healing internal defects of a steel ingot using ultra-high pressure, and may also have the following characteristics: the steel ingot to be treated is a cylindrical steel ingot of Φ6×8mm.

[0016] Furthermore, the present invention provides a method for healing internal defects of a steel ingot using ultra-high pressure, and may also have the following characteristics: the press is a CS-1V type six-sided top press, and the compressed gas is air.

[0017] Furthermore, the present invention provides a method for healing internal defects of a steel ingot using ultra-high pressure, which may also have the following characteristics: after the compression treatment is completed, Micro CT detection is performed on the treated steel ingot, and the changes in the internal defects of the steel ingot before and after the compression treatment are compared, and the ratio of the defect volume after the compression treatment to the defect volume before the compression treatment is used to characterize the degree of healing of the internal defects.

[0018] Furthermore, the present invention provides a method for healing internal defects of a steel ingot using ultra-high pressure, and may also have the following characteristics: the surface cleaning method is to clean the surface of the steel ingot to be treated with acetone.

[0019] Beneficial effects:

[0020] (1) The present invention changes the microstructure of the material by applying ultra-high pressure, without relying on high temperature. It can be carried out at a lower temperature, and even at room temperature to achieve defect healing. This treatment method can avoid the dynamic recrystallization and rapid grain growth of the material during the defect healing process, and at the same time can inhibit the defect growth behavior caused by the Kirkendall effect under high temperature treatment conditions, thereby achieving efficient closure of internal defects in steel.

[0021] (2) The present invention is suitable for components that require precise control of material structure without causing excessive macroscopic deformation, such as defect repair of high-end castings such as wind power bearings. The ultra-high pressure treatment of the present invention can significantly increase the density of the material, reduce the porosity, and thus improve the mechanical properties of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1This is a schematic diagram of the internal defect distribution of the steel ingot before compression treatment revealed by Micro CT scanning in Example 1 of the present invention;

[0023] Figure 2 This is a schematic diagram of the internal defect distribution of the steel ingot after compression treatment in Example 1 of the present invention revealed by Micro CT scanning;

[0024] Figure 3 This is a schematic diagram of the internal defect distribution of the steel ingot before compression treatment revealed by Micro CT scanning in Example 2 of the present invention;

[0025] Figure 4 This is a schematic diagram of the internal defect distribution revealed by Micro CT scanning of the steel ingot after compression treatment in Example 2 of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] The experimental methods used in the following examples are conventional methods unless otherwise specified, and the reagents, methods and equipment used are conventional reagents, methods and equipment in the art unless otherwise specified.

[0028] Example 1

[0029] The present embodiment provides a method for healing internal defects of a steel ingot using ultrahigh pressure, wherein the components of the steel ingot include, by mass percentage, C 0.42%, Si 0.31%, Mn 0.76%, P 0.011%, S 0.002%, Cu 0.02%, Ni0.02%, Cr 1.14%, V 0.005%, Mo 0.21%, Nb 0.0014%, Al 0.024%, Ti 0.0032%, N0.0037%, O 0.0012%, H 0.00005%, and the rest is Fe element.

[0030] Internal defect elimination methods specifically include:

[0031] (1) The steel ingot to be processed is processed into a small cylinder of Φ6×8mm with a smooth surface and no major scratches. The surface of the cylindrical sample is cleaned with acetone;

[0032] (2) The cleaned steel ingot was placed in a CS-1V six-sided top press and pressurized to 5 GPa at a pressurization rate of 1 GPa / min. At the same time, the temperature was raised from room temperature to 400°C at a heating rate of 2°C / s, and from 400°C to 700°C at a heating rate of 1°C / s. After reaching 5 GPa and 700°C, the steel ingot was kept at this temperature and pressure and compressed for 30 minutes.

[0033] (3) After the compression is completed, the temperature and pressure are lowered, the temperature lowering rate is 10-20°C / s, and the pressure lowering rate is 1Mpa / min; after the temperature and pressure are lowered, the steel ingot is taken out;

[0034] (4) Micro CT testing was performed on the treated steel ingots to compare the volume changes of the internal defects of the steel ingots before and after compression treatment. The ratio of the defect volume after compression treatment to the defect volume before compression treatment was used to characterize the degree of healing of the internal defects.

[0035] The results show that the volume of the defect before compression treatment is 113274889.54μm 3 , the volume of the defect after compression treatment is 71734.50μm 3 , the degree of healing of internal defects of castings = 99.94%.

[0036] Example 2

[0037] The present embodiment provides a method for healing internal defects of a steel ingot using ultrahigh pressure, wherein the components of the steel ingot include, by mass percentage, C 0.42%, Si 0.31%, Mn 0.76%, P 0.011%, S 0.002%, Cu 0.02%, Ni0.02%, Cr 1.14%, V 0.005%, Mo 0.21%, Nb 0.0014%, Al 0.024%, Ti 0.0032%, N0.0037%, O 0.0012%, H 0.00005%, and the rest is Fe element.

[0038] Internal defect elimination methods specifically include:

[0039] (1) The steel ingot to be processed is processed into a small cylinder of Φ6×8mm with a smooth surface and no major scratches. The surface of the cylindrical sample is cleaned with acetone;

[0040] (2) The cleaned steel ingot was placed in a CS-1V six-sided top press and pressurized to 5 GPa at a pressurization rate of 1 GPa / min. After reaching 5 GPa, the pressure was maintained and compressed at room temperature for 8 h;

[0041] (3) After the compression is completed, the pressure is reduced at a rate of 1 MPa / min. After the pressure reduction is completed, the steel ingot is taken out;

[0042] (4) Micro CT testing was performed on the treated steel ingots to compare the volume changes of the internal defects of the steel ingots before and after compression treatment. The ratio of the defect volume after compression treatment to the defect volume before compression treatment was used to characterize the degree of healing of the internal defects.

[0043] The results show that the volume of the defect before compression treatment is 149096240.04μm 3 , the volume of the defect after compression treatment is 2236646.88μm 3 , the degree of healing of internal defects of castings = 98.50%.

[0044] The present invention changes the microstructure of the material by applying extremely high pressure without relying on high temperature. It can be carried out at a relatively low temperature and can even achieve defect healing at room temperature. This treatment method has little effect on the grain size, phase composition, etc. of the material. It mainly improves the material properties by changing the state of internal defects. It can repair and close defects without destroying the overall structure of the material, and solves the problems of grain growth, phase change, material surface oxidation, decarburization, etc. caused by high-temperature treatment in the prior art.

[0045] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for healing internal defects of a steel ingot using ultrahigh pressure, characterized in that: The method specifically comprises: cleaning the surface of the steel ingot to be processed, placing the cleaned steel ingot in a press, and after reaching a preset temperature and a preset pressure, compressing it for a period of time to remove its internal defects; the preset pressure is 4 to 10 GPa.

2. The method for healing internal defects of steel ingots using ultrahigh pressure according to claim 1, characterized in that: The preset temperature is 600-800° C., and the compression time is 20-60 minutes.

3. The method for healing internal defects of steel ingots using ultrahigh pressure according to claim 2, characterized in that: The heating process to reach the preset temperature is: heating from room temperature to 400°C at a heating rate of 1 to 3°C / s, and heating from 400°C to 600 to 800°C at a heating rate of 1 to 3°C / s; The pressurization rate to reach the preset pressure is 1 to 2 GPa / min.

4. The method for healing internal defects of a steel ingot using ultrahigh pressure according to claim 3, characterized in that: After the compression is completed, the temperature and pressure are lowered, with a cooling rate of 10 to 20°C / s and a pressure reduction rate of 1 to 3Mpa / min.

5. The method for healing internal defects of steel ingots using ultrahigh pressure according to claim 1, characterized in that: The preset temperature is room temperature, the compression time is 7 to 10 hours, and the pressurization rate to reach the preset pressure is 1 to 2 GPa / min.

6. The method for healing internal defects of steel ingots using ultrahigh pressure according to claim 5, characterized in that: After the compression is completed, the pressure is reduced at a rate of 1 to 3 MPa / min.

7. The method for healing internal defects of steel ingots using ultrahigh pressure according to claim 1, characterized in that: The press is a CS-1V six-sided top press, and the compressed gas is air.

8. The method for healing internal defects of steel ingots using ultrahigh pressure according to claim 1, characterized in that: After the compression treatment is completed, Micro CT detection is performed on the treated steel ingot to compare the changes in the internal defects of the steel ingot before and after the compression treatment. The ratio of the defect volume after the compression treatment to the defect volume before the compression treatment is used to characterize the degree of healing of the internal defects.

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