A method for regulating the morphology of sulfides using pulsed current
By inserting electrodes into molten steel and applying pulsed current, the morphology of sulfides can be regulated to be spherical, blocky, or spindle-shaped, thus solving the problem of sulfide morphology control in wind power steel plates, improving fatigue life, and avoiding the introduction of foreign inclusions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANDONG IRON & STEEL CO LTD
- Filing Date
- 2024-12-27
- Publication Date
- 2026-07-14
AI Technical Summary
Existing technologies cannot effectively control the morphology of sulfide inclusions in steel plates used for wind power, leading to stress concentration and crack propagation, which affects fatigue life.
The method of controlling the morphology of sulfides by pulsed current involves inserting electrodes into molten steel and applying pulsed current to promote the formation of spherical, blocky, and spindle-shaped sulfides during solidification, while inhibiting the formation of chain-like and elongated morphologies.
It improves the fatigue life of steel plates used in wind power, avoids the introduction of foreign inclusions, and is simple and easy to implement.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of iron and steel metallurgy technology, and particularly relates to a method for regulating the morphology of sulfides using pulsed current. Background Technology
[0002] Due to the unique service environment and harsh working conditions of wind turbine steel plates, higher fatigue life has always been the goal pursued by all high-end wind turbine steel plates. Non-metallic inclusions are a key challenge that seriously restricts the improvement of fatigue life in steel. The fundamental reason is that the difference in properties between inclusions and the matrix disrupts the continuity of the matrix. The presence of inclusions causes localized stress around the inclusions during processing, manufacturing, and service environments, which can easily lead to cracks forming inside or on the surface of the steel components. Stress concentration during service causes the cracks to further propagate and deteriorate, ultimately causing fatigue failure of wind turbine equipment.
[0003] Most existing technologies focus on reducing the size of inclusions and ensuring their uniform distribution to prevent small inclusions from agglomerating and growing into large clusters, thus reducing the damage caused by large inclusions to the steel. While brittle non-metallic inclusions severely impair fatigue strength, fine, dispersed ductile non-metallic inclusions (sulfides) can positively impact the fatigue life of steel. Currently, controlling the morphology of sulfide inclusions in fatigue-resistant wind turbine steel plates is particularly challenging, with continuously cast billets containing unfavorable morphologies such as chain-like, elongated, and irregular shapes. If the unfavorable morphology of sulfide inclusions could be transformed into favorable morphologies such as spherical, blocky, and spindle-shaped inclusions, the fatigue life of wind turbine steel plates would be significantly improved. Summary of the Invention
[0004] In view of this, the technical problem to be solved by the present invention is to provide a method for regulating the morphology of sulfides using pulsed current. This method can regulate the nucleation mechanism of sulfides in sulfur-containing steel and promote the formation of spherical, blocky, and spindle-shaped sulfides.
[0005] This invention provides a method for controlling the morphology of sulfides using pulsed current, comprising the following steps:
[0006] S1) Provide molten steel; the molten steel contains sulfides;
[0007] S2) Insert two electrodes into the molten steel and apply a pulsed current until the molten steel is completely solidified; the voltage of the pulsed current is 10-100V; the pulsed current is 10-500A; and the frequency of the pulsed current is 1-5000Hz.
[0008] Preferably, in step S1), molten steel is obtained by melting sulfur-containing steel and holding it at a certain temperature; the holding time is at least 20 minutes.
[0009] Preferably, the sulfide is selected from one or more of manganese sulfide, calcium sulfide, ferrous sulfide, and sulfur oxides formed by their polymerization.
[0010] Preferably, the sulfur content in the molten steel is 0.05% to 0.1% by mass;
[0011] The main components of the molten steel, by mass percentage, also include: Fe: 80%–82%; Cr: 0.15%–0.2%; V: 0.02%–0.06%; Si: 0.2%–0.3%; Mn: 0.5%–0.8%; Ni: 0.05%–0.08%.
[0012] Preferably, the sulfur content in the molten steel is 0.07% by mass;
[0013] The main components of the molten steel, by mass percentage, also include: Fe: 81.31%; Cr: 0.18%; V: 0.04%; Si: 0.26%; Mn: 0.65%; Ni: 0.06%.
[0014] Preferably, the electrode is selected from graphite electrodes or pure iron electrodes;
[0015] The distance between the two electrodes is in the ratio of 0.6 to 0.8 to the surface diameter of the molten steel.
[0016] The ratio of the depth of the electrode inserted into the molten steel to the depth of the molten steel is 0.9 to 1.
[0017] Preferably, the frequency of the pulse current is 1 to 500 Hz; the pulse current is 300 to 500 A.
[0018] Preferably, the duration of the applied pulse current is 20 to 120 minutes.
[0019] Preferably, the sulfides in the steel ingot after the molten steel has completely solidified are in one or more of the following forms: spherical, blocky, and spindle-shaped.
[0020] Preferably, the diameter of the spherical shape is 5-50 μm; the length, width and height of the block shape are each 5-50 μm; the length of the spindle shape is 5-100 μm; and the diameter of the spindle shape is 1-30 μm.
[0021] This invention provides a method for controlling the morphology of sulfides using pulsed current, comprising the following steps: S1) providing molten steel containing sulfides; S2) inserting two electrodes into the molten steel and applying a pulsed current until the molten steel is completely solidified; the voltage of the pulsed current is 10–100V; the pulsed current is 10–500A; and the frequency of the pulsed current is 1–5000Hz. Compared with the prior art, this invention utilizes the low-frequency effect of pulsed current to generate a uniformly distributed current field in the sulfur-containing molten steel, increasing the probability of spontaneous nucleation of sulfides and promoting the precipitation of sulfides during solidification. This results in sulfides precipitating and growing in blocky, spherical, and spindle-shaped forms, inhibiting the formation of elongated and chain-like sulfides, and preventing stress concentration and cracking during the service of sulfur-containing steel. This achieves control of sulfide morphology by pulsed current during solidification, and the operation method is simple and easy to implement. It avoids the risks of introducing additional foreign inclusions through alloying methods to control sulfides, has practical application value, and is easy to promote and apply. Attached Figure Description
[0022] Figure 1 This is a sulfide morphology distribution diagram of the steel ingot obtained in Example 1 of the present invention;
[0023] Figure 2 This is a sulfide morphology distribution diagram of the steel ingot obtained in Comparative Example 1 of the present invention. Detailed Implementation
[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0025] This invention provides a method for controlling the morphology of sulfides using pulsed current, comprising the following steps: S1) providing molten steel; the molten steel contains sulfides; S2) inserting two electrodes into the molten steel and applying a pulsed current until the molten steel is completely solidified; the voltage of the pulsed current is 10-100V; the pulsed current is 10-500A; and the frequency of the pulsed current is 1-5000Hz.
[0026] This invention utilizes the low-frequency effect of pulsed current to generate a uniformly distributed current field within molten sulfur-containing steel, increasing the probability of spontaneous nucleation of sulfides and promoting their precipitation during solidification. This results in sulfides precipitating and growing in blocky, spherical, or spindle-shaped forms, while inhibiting the formation of elongated or chain-like sulfides. This prevents stress concentration and cracking during the service life of sulfur-containing steel, achieving control of sulfide morphology by pulsed current during solidification. The method is simple and easy to implement, avoiding the risks associated with alloying methods that control sulfides and introduce additional inclusions. It has practical application value and is easy to promote and apply.
[0027] In this invention, there are no special restrictions on the source of any raw materials; they can be commercially available.
[0028] In this invention, molten steel is first provided; the molten steel is preferably obtained by melting sulfur-containing steel, more specifically, by melting sulfur-containing steel and holding it at a certain temperature; the melting temperature is preferably 1500℃~1600℃, more preferably 1550℃; the melting is preferably carried out in a smelting furnace; the heating rate of the melting is preferably 5~15℃ / min, more preferably 8~12℃ / min, and even more preferably 10℃ / min; the heating time of the melting is preferably 1~5h, more preferably 2~4h, and even more preferably 3h; the holding time is preferably at least 20m. The molten steel is preferably 20-60 min, more preferably 20-50 min, even more preferably 20-40 min, and most preferably 30 min; the molten steel contains sulfides; the sulfides are preferably one or more of manganese sulfide, calcium sulfide, ferrous sulfide, and sulfur oxides formed by their polymerization; the sulfides in the molten steel are one or more of chain-like, elongated, or irregular forms that have adverse effects on performance; the mass content of sulfur in the molten steel is preferably 0.05%-0.1%, more preferably 0.06%-0.08%, and even more preferably 0.07%.
[0029] In one specific embodiment of the present invention, the main components of the molten steel, by mass percentage, further include: Fe: 80%–82%; Cr: 0.15%–0.2%; V: 0.02%–0.06%; Si: 0.2%–0.3%; Mn: 0.5%–0.8%; Ni: 0.05%–0.08%.
[0030] In a specific embodiment of the present invention, the main components of the molten steel, by mass percentage, further include: Fe: 81%–81.5%; Cr: 0.16%–0.2%; V: 0.03%–0.05%; Si: 0.25%–0.3%; Mn: 0.6%–0.7%; Ni: 0.05%–0.07%.
[0031] In one specific embodiment of the present invention, the main components of the molten steel, by mass percentage, further include: Fe: 81.31%; Cr: 0.18%; V: 0.04%; Si: 0.26%; Mn: 0.65%; Ni: 0.06%.
[0032] Two electrodes are inserted into molten steel, and a pulsed current is applied until the steel completely solidifies. The electrodes are preferably graphite or pure iron electrodes. The ratio of the electrode diameter to the distance between the two electrodes is preferably 1:2 to 1:5, more preferably 1:2 to 1:4, and even more preferably 1:3. The ratio of the distance between the two electrodes to the surface diameter of the molten steel is preferably 0.6 to 0.8, more preferably 0.6 to 0.7. The ratio of the electrode insertion depth to the depth of the molten steel is preferably 0.9 to 1, more preferably 0.9 to 0.98. The preferred values are 0.9–0.96, further preferably 0.9–0.94, and most preferably 0.92; the voltage of the pulse current is preferably 10–100V, more preferably 15–100V, further preferably 20–100V, further preferably 20–95V, further preferably 30–95V, further preferably 35–95V, further preferably 40–95V, and most preferably 42–95V; in some embodiments provided by the present invention, the voltage of the pulse current is specifically 15V, 42V, 20V, and 66V. The voltage is 80V or 95V; the pulse current is preferably 10-500A, more preferably 50-500A, even more preferably 80-500A, even more preferably 100-500A, even more preferably 150-500A, even more preferably 250-500A, and most preferably 300-500A; the pulse current is specifically 100A, 450A, 200A, 150A, 250A, or 500A; the frequency of the pulse current is 1-5000Hz, preferably 10-5000Hz, more preferably... The frequency is 50–5000 Hz, more preferably 80–5000 Hz, and most preferably 100–5000 Hz; the frequency of the pulse current is specifically 4000 Hz, 100 Hz, 800 Hz, 5000 Hz, 2000 Hz, or 200 Hz; the duration of applying the pulse current is preferably 20–120 min, more preferably 30–120 min; in some embodiments provided by the present invention, the duration of applying the pulse current is specifically 30 min, 120 min, or 60 min.
[0033] In a specific embodiment of the present invention, the electrode is a graphite electrode. When the frequency of the pulse current is 1-500Hz and the pulse current is 300-500A, the proportion of undesirable sulfide forms is less than 10%; when the frequency of the pulse current is 500-5000Hz and the pulse current is 10-300A, the proportion of undesirable sulfide forms is greater than 10%.
[0034] In another specific embodiment provided by the present invention, the electrode is a pure iron electrode. When the frequency of the pulse current is 1 to 500 Hz and the pulse current is 300 to 500 A, the proportion of undesirable sulfide forms is less than 5%; when the frequency of the pulse current is 500 to 5000 Hz and the pulse current is 10 to 300 A, the proportion of undesirable sulfide forms is greater than 5%.
[0035] According to the present invention, the morphology of the sulfides in the steel ingot after complete solidification of the molten steel is preferably one or more of spherical, blocky, and spindle-shaped. More specifically, the diameter of the spherical shape is preferably 5-50 μm, more preferably 5-40 μm, even more preferably 5-30 μm, and most preferably 10-30 μm; the length, width, and height of the blocky shape are each preferably 5-50 μm, more preferably 5-40 μm, even more preferably 5-30 μm, and most preferably 10-30 μm; the length of the spindle-shaped shape is preferably 5-100 μm, more preferably 10-100 μm, even more preferably 30-100 μm, and most preferably 50-100 μm; the diameter of the spindle-shaped shape is preferably 1-30 μm, more preferably 5-30 μm, even more preferably 5-20 μm, and most preferably 5-10 μm.
[0036] According to the present invention, when no electrode is inserted into the molten steel and no pulse current is applied, the amount of undesirable sulfides accounts for 30% to 50% of the total sulfides; when a graphite electrode is inserted and no pulse current is applied, the amount of undesirable sulfides accounts for 70% to 90% of the total sulfides; when a graphite electrode is inserted and a pulse current is applied, the amount of undesirable sulfides accounts for 10% to 20% of the total sulfides, and the amount of one or more improved sulfides in spherical, blocky, or spindle-shaped forms accounts for 80% to 90% of the total sulfides; when a non-graphite electrode (such as a pure iron electrode) is inserted and no pulse current is applied, the situation is the same as when no electrode is inserted; when a non-graphite electrode (such as a pure iron electrode) is inserted and a pulse current is applied, the amount of undesirable sulfides accounts for 5% to 10% of the total sulfides; and the amount of one or more improved sulfides in spherical, blocky, or spindle-shaped forms accounts for 90% to 95% of the total sulfides.
[0037] To further illustrate the present invention, the following describes in detail a method for regulating the morphology of sulfides using pulsed current, in conjunction with embodiments.
[0038] All reagents used in the following examples are commercially available.
[0039] Example 1
[0040] A method for controlling the speciation of sulfides using pulsed current includes the following steps:
[0041] S1. Sulfur-containing steel liquid was obtained by melting sulfur-containing steel in a smelting furnace. Its main components, by mass percentage, were: Fe: 81.31%; Cr: 0.18%; V: 0.04%; Si: 0.26%; Mn: 0.65%; Ni: 0.06%; S: 0.07%. The heating rate was 10℃ / min; the heating time was 3 hours; the smelting temperature was 1550℃; and the holding time was 30 minutes.
[0042] S2. Insert two preheated graphite electrodes into the sulfur-containing molten steel, and stop heating the molten steel. The electrode diameter is 10 mm; the electrode spacing is 30 mm; the electrode insertion depth is 35 mm; the molten steel depth is approximately 38 mm; and the bottom area is approximately 2000 mm². 2 Then, a pulsed current was applied to the sulfur-containing molten steel through the electrode for 30 minutes until the molten steel was completely solidified. The pulse voltage was 15V, the pulse frequency was 4000Hz, and the pulse current was 100A, thus obtaining a steel ingot.
[0043] The sulfide morphology distribution of the steel ingot prepared in Example 1 is as follows: Figure 1 As shown, by Figure 1 It can be seen that the morphology of sulfides is mainly spherical, massive and spindle-shaped. According to statistics, the number of sulfides with unfavorable morphology accounts for 19% of the total number of sulfides.
[0044] Example 2
[0045] A method for controlling the speciation of sulfides using pulsed current includes the following steps:
[0046] S1. Sulfur-containing steel liquid was obtained by melting sulfur-containing steel in a smelting furnace. Its main components were Fe: 81.31%; Cr: 0.18%; V: 0.04%; Si: 0.26%; Mn: 0.65%; Ni: 0.06%; S: 0.07%. The heating rate was 10℃ / min; the heating time was 3h; the smelting temperature was 1550℃; and the holding time was 30min.
[0047] S2. Insert two preheated graphite electrodes into the sulfur-containing molten steel, and stop heating the molten steel. The electrode diameter is 10 mm; the electrode spacing is 30 mm; the electrode insertion depth is 35 mm; the molten steel depth is approximately 38 mm; and the bottom area is approximately 2000 mm². 2 Then, a pulsed current was applied to the sulfur-containing molten steel through the electrode for 2 hours until the molten steel was completely solidified. The pulse voltage was 42V, the pulse frequency was 100Hz, and the pulse current was 450A, thus obtaining a steel ingot.
[0048] The sulfide morphology of the steel ingot prepared in Example 2 was mainly spherical, blocky and spindle-shaped. According to statistics, the number of unfavorable sulfide morphologies accounted for 10% of the total sulfide.
[0049] Example 3
[0050] A method for controlling the speciation of sulfides using pulsed current includes the following steps:
[0051] S1. Sulfur-containing steel liquid was obtained by melting sulfur-containing steel in a smelting furnace. Its main components were Fe: 81.31%; Cr: 0.18%; V: 0.04%; Si: 0.26%; Mn: 0.65%; Ni: 0.06%; S: 0.07%. The heating rate was 10℃ / min; the heating time was 3h; the smelting temperature was 1550℃; and the holding time was 30min.
[0052] S2. Insert two preheated graphite electrodes into the sulfur-containing molten steel, and stop heating the molten steel. The electrode diameter is 10 mm; the electrode spacing is 30 mm; the electrode insertion depth is 35 mm; the molten steel depth is approximately 38 mm; and the bottom area is approximately 2000 mm². 2 Then, a pulsed current was applied to the sulfur-containing molten steel through the electrode for 1 hour until the molten steel was completely solidified. The pulse voltage was 20V, the pulse frequency was 800Hz, and the pulse current was 200A, thus obtaining a steel ingot.
[0053] The sulfide morphology of the steel ingot prepared in Example 3 was mainly spherical, blocky and spindle-shaped. According to statistics, the number of unfavorable sulfide morphologies accounted for 16% of the total sulfide.
[0054] Example 4
[0055] A method for controlling the speciation of sulfides using pulsed current includes the following steps:
[0056] S1. Sulfur-containing steel liquid was obtained by melting sulfur-containing steel in a smelting furnace. Its main components were Fe: 81.31%; Cr: 0.18%; V: 0.04%; Si: 0.26%; Mn: 0.65%; Ni: 0.06%; S: 0.07%. The heating rate was 10℃ / min; the heating time was 3h; the smelting temperature was 1550℃; and the holding time was 30min.
[0057] S2. Insert two preheated pure iron electrodes into the sulfur-containing molten steel, and stop heating the molten steel. The electrode diameter is 10 mm; the electrode spacing is 30 mm; the electrode insertion depth is 35 mm; the molten steel depth is approximately 38 mm; and the bottom area is approximately 2000 mm². 2 Then, a pulsed current was applied to the sulfur-containing molten steel through the electrode for 30 minutes until the molten steel was completely solidified. The pulse voltage was 66V, the pulse frequency was 5000Hz, and the pulse current was 150A, thus obtaining a steel ingot.
[0058] The sulfide morphology of the steel ingot prepared in Example 4 was mainly spherical, blocky and spindle-shaped. According to statistics, the number of unfavorable sulfide morphologies accounted for 10% of the total sulfide.
[0059] Example 5
[0060] A method for controlling the speciation of sulfides using pulsed current includes the following steps:
[0061] S1. Sulfur-containing steel liquid was obtained by melting sulfur-containing steel in a smelting furnace. Its main components were Fe: 81.31%; Cr: 0.18%; V: 0.04%; Si: 0.26%; Mn: 0.65%; Ni: 0.06%; S: 0.07%. The heating rate was 10℃ / min; the heating time was 3h; the smelting temperature was 1550℃; and the holding time was 30min.
[0062] S2. Insert two preheated pure iron electrodes into the sulfur-containing molten steel, and stop heating the molten steel. The electrode diameter is 10 mm; the electrode spacing is 30 mm; the electrode insertion depth is 35 mm; the molten steel depth is approximately 38 mm; and the bottom area is approximately 2000 mm². 2 Then, a pulsed current was applied to the sulfur-containing molten steel through the electrode for 1 hour until the molten steel was completely solidified. The pulse voltage was 80V, the pulse frequency was 2000Hz, and the pulse current was 250A, thus obtaining a steel ingot.
[0063] The sulfide morphology of the steel ingot prepared in Example 5 was mainly spherical, blocky and spindle-shaped. According to statistics, the number of unfavorable sulfide morphologies accounted for 7% of the total sulfide.
[0064] Example 6
[0065] A method for controlling the speciation of sulfides using pulsed current includes the following steps:
[0066] S1. Sulfur-containing steel liquid was obtained by melting sulfur-containing steel in a smelting furnace. Its main components were Fe: 81.31%; Cr: 0.18%; V: 0.04%; Si: 0.26%; Mn: 0.65%; Ni: 0.06%; S: 0.07%. The heating rate was 10℃ / min; the heating time was 3h; the smelting temperature was 1550℃; and the holding time was 30min.
[0067] S2. Insert two preheated pure iron electrodes into the sulfur-containing molten steel, and stop heating the molten steel. The electrode diameter is 10 mm; the electrode spacing is 30 mm; the electrode insertion depth is 35 mm; the molten steel depth is approximately 38 mm; and the bottom area is approximately 2000 mm². 2 Then, a pulsed current was applied to the sulfur-containing molten steel through the electrode for 2 hours until the molten steel was completely solidified. The pulse voltage was 95V, the pulse frequency was 200Hz, and the pulse current was 500A, thus obtaining a steel ingot.
[0068] The sulfide morphology of the steel ingot prepared in Example 6 was mainly spherical, blocky and spindle-shaped. According to statistics, the number of unfavorable sulfide morphologies accounted for 5% of the total sulfide.
[0069] Comparative Example 1
[0070] The difference from Example 1 is that a graphite electrode is inserted but no pulsed current is applied.
[0071] The sulfide morphology distribution of the steel ingot prepared in Comparative Example 1 is as follows: Figure 2 As shown, by Figure 2 It is evident that the sulfide forms are mainly unfavorable forms such as chain-like, elongated, and irregular shapes. According to statistics, unfavorable sulfide forms account for 81% of the total number of sulfides.
[0072] Comparative Example 2
[0073] The difference from Example 2 is that a pure iron electrode is inserted but no pulsed current is applied.
[0074] The sulfide morphology of the steel ingot prepared in Comparative Example 2 still has a large number of undesirable morphologies such as chain-like, elongated, and irregular shapes, and the number of undesirable sulfide morphologies accounts for 38% of the total sulfide morphology.
[0075] Table 1 Results of steel ingot preparation conditions and sulfide content
[0076]
[0077] As can be seen from the above embodiments and comparative examples, the sulfide morphology in the steel ingot prepared using Comparative Example 1 is mainly unfavorable, consisting of chain-like, elongated, and irregular shapes. This is because the electrode inserted into the molten steel is a graphite electrode, which increases the carbon content in the molten steel. The increased carbon content leads to the transformation of the sulfide morphology into unfavorable chain-like, elongated, and irregular shapes. However, using the same graphite electrode, the sulfide morphology in the steel ingots prepared in Examples 1-3 of this invention is mainly favorable, consisting of spherical, blocky, and spindle-shaped shapes. Even with the avoidance of carbon's influence on sulfide morphology, Comparative Example 2 still contains a large number of unfavorable sulfide morphologies. However, by using a pure iron electrode and avoiding the introduction of carbon into the molten steel, the sulfide morphology in the steel ingots prepared in Examples 4-6 of this invention is mainly spherical, blocky, and spindle-shaped, and the proportion of unfavorable sulfide morphologies is significantly reduced. Pulsed current applied during the solidification stage of sulfur-containing steel can regulate the transformation of sulfide morphology from unfavorable chain-like, elongated, and irregular shapes to favorable spherical, blocky, and spindle-shaped shapes.
[0078] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for controlling the morphology of sulfides using pulsed current, characterized in that, Includes the following steps: S1) Provide molten steel; the molten steel contains sulfides; S2) Two electrodes are inserted into the molten steel, and a pulsed current is applied until the steel is completely solidified. Utilizing the low-frequency effect of the pulsed current, a uniformly distributed current field is generated within the sulfur-containing molten steel, increasing the probability of spontaneous nucleation of sulfides and promoting their precipitation during solidification. This results in sulfides precipitating and growing in blocky, spherical, or spindle-shaped forms, while inhibiting the formation of elongated or chain-like sulfides. The voltage of the pulsed current is 42~95 V; the pulsed current is 450~500 A; the frequency of the pulsed current is 100~200 Hz; and the duration of the pulsed current application is 20~120 min. The electrode is selected from graphite electrodes or pure iron electrodes; The distance between the two electrodes is in the ratio of 0.6 to 0.8 to the surface diameter of the molten steel. The ratio of the depth of the electrode inserted into the molten steel to the depth of the molten steel is 0.9~1; After the molten steel has completely solidified, the sulfides in the steel ingot can be in one or more of the following forms: spherical, blocky, and spindle-shaped. The diameter of the spherical shape is 5~50 μm; the length, width and height of the block shape are each 5~50 μm; the length of the spindle shape is 5~100 μm; and the diameter of the spindle shape is 1~30 μm.
2. The method according to claim 1, characterized in that, In step S1), molten steel is obtained by melting sulfur-containing steel and holding it at a constant temperature; the holding time is at least 20 minutes.
3. The method according to claim 1, characterized in that, The sulfide is selected from one or more of manganese sulfide, calcium sulfide, ferrous sulfide, and sulfur oxides formed by their polymerization.
4. The method according to claim 1, characterized in that, The sulfur content in the molten steel is 0.05% to 0.1% by mass. The main components of the molten steel, by mass percentage, include: Fe: 80%~82%; Cr: 0.15%~0.2%; V: 0.02%~0.06%; Si: 0.2%~0.3%; Mn: 0.5%~0.8%; Ni: 0.05%~0.08%.
5. The method according to claim 1, characterized in that, The mass content of sulfur in the molten steel is 0.07%; The main components of the molten steel, by mass percentage, also include: Fe: 81.31%; Cr: 0.18%; V: 0.04%; Si: 0.26%; Mn: 0.65%; Ni: 0.06%.