Semi-solid negative pressure purification method for ultrahigh-clean steel pipe melt

Abstract

The invention relates to the technical field of stainless steel pipe manufacturing, in particular to a semi-solid negative pressure purification method for an ultra-high clean steel pipe melt. The ultra-high-cleanliness steel pipe is obtained through pretreatment, precise semi-solid temperature regulation and control, high-vacuum negative-pressure environment construction, electromagnetic stirring pulping, solid fraction and spheroidization degree regulation and control, inclusion directional separation and scum removal, purity detection and subsequent conveying and rolling. According to the method, the synergistic effect of hydrogen removal, impurity removal and grain optimization is achieved, the method is applied to purification of various stainless steel melts, the overall purity of the melts is improved, and the preparation requirement of the ultra-high-cleanliness stainless steel pipe is met.

Description

Technical Field

[0001] This invention relates to the field of stainless steel pipe manufacturing technology. Background Technology

[0002] In modern industry, ultra-high cleanliness stainless steel pipes are widely used for gas and liquid transportation in semiconductor devices, optical fibers, and biomedicine due to their excellent corrosion resistance, mechanical properties, and purity, as well as in the manufacture of precision components for integrated circuits and aerospace. These applications place stringent requirements on stainless steel pipes, requiring them to achieve ultra-low carbon content, sufficient mechanical properties, and that the Cr and Ni metal compositions meet relevant standards. Furthermore, the content of harmful elements such as P, S, Mn, and Al, as well as O and H, in the material needs to be reduced to extremely low levels.

[0003] Melt purity is a core factor determining the quality of the final steel pipe product, directly affecting its mechanical properties (such as strength and toughness), corrosion resistance, and service life. However, traditional steel pipe melt purification technologies suffer from several key drawbacks in practical applications: First, low hydrogen removal efficiency, with residual hydrogen easily leading to hydrogen embrittlement during subsequent processing or use; second, difficulty in removing inclusions, as traditional filtration or refining processes have limited effectiveness in removing inclusions; and third, poor grain morphology, with traditional processes producing melts often exhibiting dendritic grains, resulting in uneven mechanical properties in the final product. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a semi-solid negative pressure purification method for ultra-high clean steel pipe melt.

[0005] The technical solution adopted by the present invention to achieve the above objectives is: a method for purifying ultra-high clean steel pipe melt semi-solid negative pressure, comprising the following steps:

[0006] S1. Select stainless steel melt as raw material, heat the stainless steel melt to the semi-solid temperature range of the corresponding steel grade, so that the stainless steel melt forms a semi-solid state where solid and liquid coexist.

[0007] S2. Construct a high vacuum negative pressure environment and evacuate the semi-solid stainless steel melt;

[0008] S3. After vacuuming, use an electromagnetic stirrer to stir the semi-solid stainless steel melt.

[0009] S4. Take samples of the stirred semi-solid stainless steel melt for testing. Repeat steps S1-S4 for any semi-solid stainless steel melt that fails the test until it passes the test. Semi-solid stainless steel melt that passes the test will proceed to the rolling process.

[0010] S5. Select a suitable rolling process to prepare the steel pipe. After rolling is completed, an ultra-high cleanliness steel pipe is obtained.

[0011] Preferably, step S1 further includes pretreatment, in which the surface of the stainless steel melt is purged with inert gas to remove surface air.

[0012] Preferably, in step S1, a medium-frequency induction heating furnace is used to heat the stainless steel melt to form a semi-solid state of "50%-70% liquid + 50%-30% solid".

[0013] Preferably, in step S2, during the vacuuming process, the vacuum level is first evacuated from atmospheric pressure to 10³-10¹Pa and maintained for a period of time; then the vacuuming continues until the vacuum level reaches 10⁻¹-10⁻³Pa and is maintained for a period of time.

[0014] Preferably, in step S3, a low-frequency electromagnetic stirrer is used to stir the stainless steel melt, with an input power of 80-120kW, and the stirring time is 20-40 minutes.

[0015] Preferably, in step S3, the initial stirring frequency is 1-5Hz, and the later stirring frequency is 20-30Hz.

[0016] Preferably, in step S3, the stainless steel melt that has been electromagnetically stirred and slurried is introduced into an inclined guide channel. The inclined guide channel is equipped with a high-temperature resistant filter layer, and a scum scraper is used to scrape off the scum on the surface of the guide channel.

[0017] Preferably, in step S4, the detection items include:

[0018] Hydrogen content detection: Gas chromatography is used for detection, and the hydrogen content is required to be ≤1.5ppm;

[0019] Inclusion detection: Inclusions are observed using a metallographic microscope. The inclusion size is required to be ≤10μm and the number density is ≤3 inclusions / mm².

[0020] Total oxygen content: Detected using an oxygen and nitrogen analyzer, the total oxygen content must be ≤8ppm;

[0021] Solid phase uniformity: Using image analysis, the deviation is required to be ≤ ±5%.

[0022] Preferably, in step S4, the qualified semi-solid stainless steel melt is transported to the rolling process through an insulated conveying pipeline.

[0023] The beneficial effects of this invention are as follows:

[0024] This invention significantly reduces the hydrogen content in the melt by creating a high-vacuum negative pressure environment, thereby significantly improving hydrogen removal efficiency. It combines electromagnetic stirring and solid fraction control to cause inclusions to collide and aggregate into clusters, facilitating separation and effectively removing impurities from the melt. Furthermore, it breaks down dendritic primary crystals, transforming them into spherical or near-spherical particles, reducing inclusion encapsulation and improving grain uniformity and purity. By adjusting process parameters such as the semi-solid temperature range and stirring parameters, this invention can be applied to the purification of various types of stainless steel melts, meeting the preparation requirements of ultra-high cleanliness steel pipes of different materials, thus having a wide range of applications. Finally, this invention achieves a synergistic effect of "hydrogen removal + impurity removal + grain optimization," improving the overall purity of the melt and meeting the preparation requirements of ultra-high cleanliness stainless steel pipes. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall process of an embodiment of the present invention. Detailed Implementation

[0026] Embodiments of the present invention provide a method for purifying ultra-high cleanliness steel pipe molten semi-solid negative pressure, such as... Figure 1 As shown, it includes the following steps:

[0027] S1. Select stainless steel melt as raw material. Pretreatment: Purge the surface of the stainless steel melt with inert gas for a certain period to remove surface air. The stainless steel melt can be 304 stainless steel, 321 stainless steel, 316 stainless steel, etc. In this embodiment, 304 stainless steel is used. The inert gas can be argon or nitrogen, and the purging time depends on actual requirements.

[0028] For different types of stainless steel, such as 321 and 316 stainless steel, this invention can purify the melt of various types of stainless steel by adjusting the semi-solid temperature range, stirring frequency and vacuum degree, thus expanding the scope of application of the technology and meeting the preparation requirements of ultra-high clean steel pipes of different materials.

[0029] The pretreated stainless steel melt is placed in a medium-frequency induction heating furnace equipped with a temperature sensor. The stainless steel melt is first heated to 1450℃ by gradually increasing the temperature to ensure complete melting and eliminate initial solid inclusions. Then, the temperature is slowly reduced, and combined with the real-time temperature data from the temperature sensor, the temperature of the stainless steel melt is precisely controlled to a semi-solid range of 1410-1420℃. Within this temperature range, the melt forms a mixed state of "50%-70% liquid + 50%-30% solid". The solid particles can act as a solid-phase carrier for inclusions and can also inhibit excessive grain growth during subsequent processing.

[0030] S2. Transfer the molten stainless steel in the semi-solid region to a vacuum pumping device. The vacuum pumping device is equipped with a temperature compensation device to create a high vacuum negative pressure environment. The vacuum pumping operation is carried out in two stages:

[0031] Rough vacuuming stage: The vacuum level in the vacuuming device chamber is evacuated from atmospheric pressure to 10³-10¹Pa and maintained for 10 minutes to initially remove the gas in the stainless steel melt.

[0032] Fine vacuuming stage: After the initial vacuuming, vacuuming continues until the vacuum level reaches 10⁻¹-10⁻³ Pa, and is maintained for 30 minutes. Under high vacuum negative pressure, the solubility of hydrogen in the stainless steel melt significantly decreases, dropping to 0.1-0.3 mL / 100g. Hydrogen atoms aggregate to form tiny bubbles with a diameter of 5-10 μm. These bubbles rise rapidly to the surface of the stainless steel melt under buoyancy, achieving efficient hydrogen removal. During the vacuuming process, a temperature compensation device maintains the temperature of the stainless steel melt at 1410-1420℃ to prevent the semi-solid state of the stainless steel melt from being destroyed due to temperature drop.

[0033] S3. Stir the molten stainless steel using a low-frequency electromagnetic stirrer. The input power of the low-frequency electromagnetic stirrer should be adjusted according to the melt volume; in this example, the input power is 80-120kW. Stir for 20-40 minutes, divided into two stages:

[0034] Crystal breaking stage: The stirring frequency is controlled at 1-5Hz in the initial stage to break up the coarse dendritic primary crystals that have formed in the melt;

[0035] Homogenization stage: In the later stage of stirring, the frequency is adjusted to 20-30Hz. High-frequency stirring makes the solid and liquid phases in the melt more uniformly mixed, and at the same time promotes the collision and polymerization of inclusions, which facilitates subsequent separation.

[0036] During electromagnetic stirring, the solid fraction is stabilized between 0.3 and 0.7 by controlling the temperature, with an optimal solid fraction of 0.5. At this state, the melt's fluidity and inclusion adhesion are optimally balanced. Simultaneously, the sphericity of the solid particles is adjusted by controlling the electromagnetic stirring frequency, ensuring a sphericity shape factor ≥1.1. During this process, dendritic primary crystals transform into spherical or near-spherical particles, reducing the encapsulation of inclusions within the grains. Furthermore, the stirring convection promotes collisions between inclusions larger than 5 μm, agglomerating them into 20-50 μm clusters, facilitating subsequent separation.

[0037] The molten stainless steel, prepared by electromagnetic stirring, is introduced into an inclined guide channel equipped with a high-temperature resistant filter layer. The flow velocity is controlled at 0.5-1 m / s, ensuring smooth slurry flow while providing sufficient time for inclusion separation. A scum scraper is used to remove scum from the surface of the guide channel every 5 minutes. During slurry flow, rising hydrogen bubbles generate a "dragging" force, carrying inclusion clusters attached to the surface of spherical solid particles to the slurry surface, forming scum that is then scraped off by the scum scraper. Simultaneously, the high-temperature resistant filter layer filters out any remaining small inclusions that do not float to the surface.

[0038] S4. Sample and test the semi-solid stainless steel melt flowing out of the inclined guide channel. The test items include:

[0039] Hydrogen content detection: Gas chromatography is used for detection, and the hydrogen content is required to be ≤1.5ppm;

[0040] Inclusion detection: Inclusions are observed using a metallographic microscope. The inclusion size is required to be ≤10μm and the number density is ≤3 inclusions / mm².

[0041] Total oxygen content: Detected using an oxygen and nitrogen analyzer, the total oxygen content must be ≤8ppm;

[0042] Solid phase uniformity: Using image analysis, the deviation is required to be ≤ ±5%.

[0043] For semi-solid stainless steel melt that fails the test, repeat steps S1-S4 until it passes the test; for semi-solid stainless steel melt that passes the test, proceed to the rolling process.

[0044] S5. The qualified semi-solid stainless steel molten material is transported to the rolling process via an insulated conveying pipeline, ensuring that the temperature of the stainless steel molten material is maintained within the semi-solid range of 1410-1420℃ during transportation to prevent changes in its state due to temperature drop. Before rolling, the temperature of the semi-solid stainless steel molten material is adjusted to the entry temperature of 1400-1410℃. A suitable rolling process is selected to prepare the steel pipe, such as cold rolling or hot rolling. After rolling, ultra-high cleanliness steel pipes are obtained.

[0045] This invention has been described through embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this invention.

Claims

1. A method for purifying ultra-high cleanliness steel pipe molten semi-solid under negative pressure, characterized in that, Includes the following steps: S1. Select stainless steel melt as raw material, heat the stainless steel melt to the semi-solid temperature range of the corresponding steel grade, so that the stainless steel melt forms a semi-solid state where solid and liquid coexist. S2. Construct a high vacuum negative pressure environment and evacuate the semi-solid stainless steel melt; S3. After vacuuming, use an electromagnetic stirrer to stir the semi-solid stainless steel melt. S4. Take samples of the stirred semi-solid stainless steel melt for testing. Repeat steps S1-S4 for any semi-solid stainless steel melt that fails the test until it passes the test. Semi-solid stainless steel melt that passes the test will proceed to the rolling process. S5. Select a suitable rolling process to prepare the steel pipe. After rolling is completed, an ultra-high cleanliness steel pipe is obtained.

2. The ultra-high cleanliness steel pipe molten semi-solid negative pressure purification method according to claim 1, characterized in that, Step S1 also includes pretreatment, which involves purging the surface of the stainless steel melt with inert gas to remove surface air.

3. The ultra-high cleanliness steel pipe molten semi-solid negative pressure purification method according to claim 1, characterized in that, In step S1, a medium-frequency induction heating furnace is used to heat the stainless steel melt to form a semi-solid state of "50%-70% liquid + 50%-30% solid".

4. The ultra-high cleanliness steel pipe molten semi-solid negative pressure purification method according to claim 1, characterized in that, In step S2, during the vacuuming process, the vacuum level is first evacuated from atmospheric pressure to 10³-10¹Pa and maintained for a period of time; then the vacuuming continues until the vacuum level reaches 10⁻¹-10⁻³Pa and is maintained for a period of time.

5. The ultra-high cleanliness steel pipe molten semi-solid negative pressure purification method according to claim 1, characterized in that, In step S3, a low-frequency electromagnetic stirrer is used to stir the stainless steel melt, with an input power of 80-120kW, for 20-40 minutes.

6. The ultra-high cleanliness steel pipe molten semi-solid negative pressure purification method according to claim 5, characterized in that, In step S3, the stirring frequency is 1-5Hz in the initial stage and 20-30Hz in the later stage.

7. The ultra-high cleanliness steel pipe molten semi-solid negative pressure purification method according to claim 1, characterized in that, In step S3, the stainless steel melt that has been electromagnetically stirred and pulped is introduced into an inclined guide channel. The inclined guide channel is equipped with a high-temperature resistant filter layer, and a scum scraper is used to scrape off the scum on the surface of the guide channel.

8. The ultra-high cleanliness steel pipe molten semi-solid negative pressure purification method according to claim 1, characterized in that, In step S4, the detection items include: Hydrogen content detection: Gas chromatography is used for detection, and the hydrogen content is required to be ≤1.5ppm; Inclusion detection: Inclusions are observed using a metallographic microscope. The inclusion size is required to be ≤10μm and the number density is ≤3 inclusions / mm². Total oxygen content: Detected using an oxygen and nitrogen analyzer, the total oxygen content must be ≤8ppm; Solid phase uniformity: Using image analysis, the deviation is required to be ≤ ±5%.

9. The ultra-high cleanliness steel pipe molten semi-solid negative pressure purification method according to claim 1, characterized in that, In step S4, the qualified semi-solid stainless steel melt is transported to the rolling process through an insulated conveying pipeline.

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