Key Takeaways & Executive Findings
- •• Supergravity fields achieve extreme removal of fine SiO2 and MnO inclusions from 304 stainless steel, with total oxygen content reduced from 240 to 28 ppm (88.33% removal) at gravity coefficient 500 and 600 s. • Inclusions migrate to the top of the sample and form large aggregates, while the bottom becomes significantly purified, showing a gradient distribution of inclusion volume fraction and number density. • The method outperforms conventional techniques (electroslag remelting, gas stirring, ceramic filtration) in removing small inclusions, offering a more effective and efficient purification approach. • The findings provide a promising industrial pathway for producing ultra-clean steel with enhanced mechanical properties and corrosion resistance.
Abstract
The extreme removal of SiO2 and MnO inclusions in 304 stainless steel in supergravity fields was investigated using an in-house high-temperature supergravity equipment. The influences of the gravity coefficient and separation time on the removal efficiency of the inclusions were studied. After supergravity treatment, the inclusions migrated to the top of the sample and formed large aggregates. Meanwhile, the lower part of the sample was purified considerably and appeared significantly cleaner than the raw material. At the gravity coefficient of 500 and separation time of 600 s, the total oxygen content at the bottom of the sample (position E) decreased from 240 to 28 ppm. This corresponded to a total oxygen removal rate of 88.33%. The volume fraction and number density of inclusions exhibited a gradient distribution along the supergravity direction, with values of 8.5% and 106 mm–2 at the top of the sample (position A) and 0.06% and 22 mm–2 at its bottom.
1. Introduction
With the increase in the demand for high-performance steel in advanced industry, improving the cleanliness of steel, particularly to reduce the content of inclusions, has become a key issue [1–3]. As non-metallic particles or compounds, inclusions can adversely affect the mechanical properties, surface quality, corrosion resistance, and overall steel performance [4–6]. These inclusions are vulnerable to stress concentration, which results in the formation of fatigue cracks [7–9] and surface defects during the rolling process [10–11]. Therefore, effectively removing and reducing the number and size of inclusions in steel are crucial for improving its performance [12].
The conventional inclusion removal techniques include electroslag remelting, gas stirring, and ceramic filtration. Electroslag remelting removes inclusions mainly through slag–metal interfacial reactions and physical filtration of the slag layer [13–14]. Wang et al. [15] effectively removed large-size inclusions (>5 μm) from the raw material (reduced their content from 21% to 5%). However, the removal effect on small-size inclusions (2–5 μm) was less significant (from 72% to 61%). Subsequently, Qi et al. [16] determined that after an axial static magnetic field (ASMF) was superimposed during electroslag remelting, the larger sized inclusions (>10 μm) were almost eliminated. However, the number of small sized inclusions was still high. Gas stirring removes inclusions by using gas bubbles to transport these to the surface of the steel. Guthrie and Isac [17] used small bubbles with a size of 1 mm to successfully capture large inclusions with sizes up to 50 μm. However, for small inclusions, the probability of being captured by bubbles is low, and the removal effect is not evident [18]. Moreover, the ascending speed of small bubbles is low, and the overall operation cycle is long and inefficient [19–21]. The ceramic filtration method is mainly applied to the steel inserted into a porous ceramic filter or makes the steel directly pass through the ceramic filter so that inclusions are adsorbed and captured by the filter to remove the impurities. Li et al. [22] used MgO filter to successfully remove inclusions with sizes of >5 µm. Here, the total oxygen content of steel removal rate was 77.3%. However, high-performance ceramic filter plates require complex manufacturing processes and high-purity raw materials. These increase the operating costs. Ceramic materials are straightforwardly cracked and damaged under high-temperature conditions and cannot be used frequently [23–25].
In addition, several external field enhancement methods, such as electromagnetic refining and supergravity, have been used to enhance the removal of inclusions. The electromagnetic refining method alters the steel flow pattern through the action of electromagnetic force, which induces the uplift and removal of inclusions. For example, numerical simulations have demonstrated that the application of electromagnetic stirring effectively reduces the trapping of inclusions and promotes their uplift to the surface of liquid steel by modifying the flow field [26]. It can effectively remove large inclusions and improve the purity of steel. However, it has the following disadvantages: the complexity involved in regulating the electromagnetic field strength, high equipment cost, and insufficient removal of small inclusions. Supergravity is a more effective strengthening technique than electromagnetic refining. It can significantly enhance the transfer of different substances and phase separation [27]. In a high-temperature melt, the ...
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Shuai Zhang, Lei Guo, Zhancheng Guo (2025). Extreme removal of fine inclusions from 304 stainless steel via high-temperature supergravity fields. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3127-5
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Frequently Asked Questions
What is the main objective of this study?
The study investigates the extreme removal of SiO2 and MnO inclusions from 304 stainless steel using high-temperature supergravity fields, focusing on the effects of gravity coefficient and separation time on removal efficiency.
What are the key results of the supergravity treatment?
At a gravity coefficient of 500 and separation time of 600 s, the total oxygen content at the bottom of the sample decreased from 240 to 28 ppm, achieving an 88.33% removal rate. Inclusions migrated to the top, forming aggregates, while the bottom became significantly purified.
How does supergravity compare to conventional inclusion removal methods?
Supergravity is more effective than conventional methods like electroslag remelting, gas stirring, and ceramic filtration, especially for removing small inclusions, and it offers a more efficient and cost-effective alternative.
What is the significance of the gradient distribution of inclusions?
The gradient distribution along the supergravity direction indicates that inclusions are effectively concentrated at the top, allowing for easy separation and yielding a highly purified lower portion, which is crucial for producing ultra-clean steel.
What are the potential industrial applications of this research?
This research provides a promising technique for producing high-purity stainless steel with improved mechanical properties and corrosion resistance, which is essential for advanced industrial applications.
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