A production method for reducing the size of non-metallic inclusions in spring steel by vitrification

Abstract

The present invention discloses a production method for reducing the size of non-metallic inclusions in spring steel by vitrification, which realizes the control of SiO2-Al2O3 type glassy inclusions with CaO and MgO content from the source. In terms of mass percentage, SiO2 accounts for more than 70%, and CaO+MgO+MnO≤10%. The crystallization transformation of inclusions is suppressed at a suitable heating temperature, and the rolling temperature is ensured to be above the softening temperature of the glassy inclusions, thereby achieving good deformation of the inclusions during the rolling process. The glassy inclusions mentioned in the present invention are mainly endogenous inclusions with small size, width ≤3μm after plastic deformation, and aspect ratio ≤5, which improves fatigue life while also ensuring the isotropy of the material.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking, and in particular relates to a production method for reducing the size of non-metallic inclusions in spring steel by vitrification. Background Art

[0002] Spring steel, cord steel, diamond wire steel, and other materials are subject to high deformation during drawing or high-frequency dynamic and alternating loads during operation. In these situations, stress concentration caused by large, non-deforming inclusions is a major cause of failure. Completely removing non-metallic inclusions from the molten steel is impossible. Therefore, inclusion plasticization is currently widely used, utilizing plastic deformation to reduce the size of inclusions. In this process, cord steel and diamond wire steel, due to their low alloy content, primarily contain MnO-SiO2-Al2O3-based non-metallic inclusions. Spring steel, however, requires significant alloying, and its non-metallic inclusions are primarily CaO-SiO2-Al2O3-based. The composition and size of these two types of inclusions must be controlled during production to ensure optimal plastic deformation and minimize adverse effects on performance and serviceability. It is important to note that even if non-metallic inclusions undergo plastic deformation, excessive length after deformation can reduce the material's isotropy. Many academic papers have mentioned that long strip inclusions lead to significant differences in the transverse and longitudinal impact properties of materials.

[0003] Patent CN 114752744 A (Method for Reducing the Characteristic Size of Inclusions in Bloom Silicon-Manganese Deoxidized Steel Bars and Wires) regulates the heating regime based on the TTT curve of the synthetic inclusions to ensure that the inclusions are located in the left glass zone, thereby achieving the goal of reducing the size of inclusions after rolling deformation. However, this method has a lag compared to adjustments made during the smelting process and is incompatible with the high-temperature, long-term heating process required for uniform composition before billeting. Patent CN 113680815 A (A Steel Rolling Method for Reducing the Size of Inclusions in Cord Steel Wire Rods) uses high-temperature heating and high rolling temperatures to increase the plastic deformation capacity of inclusions to reduce inclusion size. This method also has a lag, and the high-temperature, long-term heating before finishing is not conducive to decarburization and grain size control of the finished product.

[0004] Patent CN 110195145 B (a refined slag for vitrifying oxide inclusions in cord steel) suppresses the crystallization behavior of inclusions by adding alkali metal Na2CO3 to the refined slag, obtains glassy inclusions, and reduces the width of the inclusions.

[0005] Patent CN 109161632 B (Production Method for Controlling Large-Sized Hard Inclusions in Spring Steel Wire Rod) prevents the formation of large, high-melting-point Al2O3 hard inclusions by controlling the converter, LF refining, continuous casting, and heating and slugging processes. This is also a key control point for inclusion plasticization. However, the patent does not mention controlling the CaO and MgO content in the inclusions. The accompanying figures show that the CaO content in the inclusions ranges from 12-25%, with CaO + Al2O3 ≥ 25%. Therefore, although the inclusions undergo plastic deformation, their length after deformation is generally above 40μm, which is related to the increased CaO content, which increases the inclusion size. The literature "Effect of Calcium Treatment on Oxide Inclusions in Silicon-Deoxidized Spring Steel 55SiCr" and "A Potential Source of Magnesia-Silicon Olivine Inclusions in Silicon-Deoxidized 55SiCr" also mentions that increasing the CaO and MgO content in the inclusions increases the size. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a vitrified spring steel non-metallic inclusion and a production method thereof. Starting from the smelting process, the CaO and MgO contents in the inclusion are controlled in percentage by mass to ensure that SiO2 accounts for more than 70% of the inclusion and CaO+MgO+MnO ≤ 10%. This not only obtains a glassy inclusion composition that is not prone to crystallization, but also reduces the length and width of the inclusion after plastic deformation, thereby improving the fatigue life of the material while ensuring the isotropy of the material.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a production method for reducing the size of non-metallic inclusions in spring steel by vitrification, comprising the following steps:

[0008] Step 1: In a converter, the tapping temperature is controlled to be ≥1620°C, the initial oxygen content of the molten steel is 0.020-0.030% by mass, and the primary molten steel is poured into a special ladle. During the tapping process, low-aluminum and low-calcium ferrosilicon is first added, followed by low-aluminum ferromanganese and low-aluminum ferrochrome alloys. The amount of alloy added is controlled according to the lower limit of the chemical composition of the steel grade. After tapping is completed, the bottom argon gas is turned off, and 0.5-1.5kg / t of lime and 1.5-2.5kg / t of low-alkalinity synthetic slag are added to cover the surface of the molten steel. The amount of lime and low-alkalinity synthetic slag added is 2-4kg / t (0.5-1.5kg / t of lime and 1.5-2.5kg / t of low-alkalinity synthetic slag), and the alkalinity is 1.0-1.2 (the alkalinity of the low-alkalinity synthetic slag is 0.7-0.9, and the lime is used to adjust the alkalinity to 1.0-1.2). The ladle car is driven to the argon station;

[0009] Step 2: At the argon station, start bottom blowing argon with a flow rate of ≤100NL / min for 3-5min to promote the floating of inclusions to be absorbed by the slag, and then hoist them to the slag removal position;

[0010] Step 3: During the slag removal process, the bottom blowing argon is turned off throughout the process, and the surface slag is removed using a robotic arm. Then, according to the composition results of the previous process, low-aluminum and low-calcium ferrosilicon, low-aluminum ferromanganese, and low-aluminum ferrochrome are added to the chemical composition limit of the steel grade. Subsequently, low-basicity synthetic slag is added to cover the surface of the molten steel. The addition amount is 10-15kg / t, and the basicity is 0.7-0.9. The slag is then hoisted to the refining position.

[0011] Step 4: LF refining, power supply and temperature rise, bottom blowing argon flow rate ≤80NL / min, only carbon powder and ferrosilicon powder are used for diffusion deoxidation of slag surface, no additional alloy is added, the total refining time is controlled at 30-50min, the temperature is raised to 1516-1546℃ and hoisted for continuous casting;

[0012] Step 5: continuous casting;

[0013] Step 6: Heating and rolling, the billet heating temperature is 1000-1100℃, and the rolling temperature is 900-950℃.

[0014] Preferably, in terms of mass percentage, in the low-aluminum and low-calcium ferrosilicon in step 1, Al≤0.03%, Ca≤0.8%, in the low-aluminum ferromanganese, Al≤0.01%, and in the low-aluminum ferrochrome, Al≤0.01%.

[0015] Preferably, the special ladle is made of low-aluminum-magnesium carbon bricks (MgO≥85%, C≥12%, Al2O3≤1.0% by mass), and the slag line is coated with silica to resist slag erosion. The bottom of the ladle uses double-permeable bricks, which are arranged diagonally symmetrically to facilitate mixing of molten steel and floating of inclusions.

[0016] Preferably, the refractory materials in contact with the molten steel in step 5 are all low-aluminum refractory materials (zirconium-magnesium-carbon materials with high thermal shock stability, in which MgO+C+ZrO2≥95% by mass), and the ladle covering agent uses a magnesium covering agent (in which MgO≥85% by mass) to reduce the erosion of the ladle refractory materials.

[0017] Preferably, the prepared spring steel has the following components by mass percentage: C 0.52-0.58%, Si 1.40-1.60%, Mn 0.60-0.80%, Cr 0.60-0.80%, P≤0.0012%, S≤0.008%, Al≤0.0020%, and the rest is Fe and unavoidable impurities.

[0018] Through smelting control, the control of SiO2-Al2O3 glassy inclusions with low CaO and MgO content is achieved from the source, of which SiO2 accounts for more than 70% and CaO+MgO+MnO ≤ 10%. The crystallization transformation of the inclusions is suppressed at a suitable heating temperature, while ensuring that the rolling temperature is above the softening temperature of the glassy inclusions, thereby achieving good deformation of the inclusions during the rolling process. The glassy inclusions mentioned in the present invention are mainly endogenous inclusions with small size, a width of ≤3μm after plastic deformation, and an aspect ratio of ≤5. This improves fatigue life while also ensuring the isotropy of the material.

[0019] The process principle of the present invention is as follows: Due to its composition requirements, spring steel needs to add a large amount of ferrosilicon, ferromanganese, and ferrochrome. These alloys will introduce impurity elements. Existing patents and academic literature have strict requirements on the aluminum in the alloy, but rarely mention the impact of calcium in the alloy on spring steel inclusions. In production practice, it has been found that when calcium treatment is not intentionally performed, CaO in non-metallic inclusions mainly comes from ferrosilicon alloy and slag. On the one hand, the present invention uses low-aluminum and low-calcium ferrosilicon alloy, sets the initial oxygen content of molten steel during tapping, and adds low-aluminum and low-calcium ferrosilicon alloy in a concentrated manner. The high concentration of local Si-Al-Ca-O is used to generate large-sized SiO2-Al2O3-CaO inclusions in advance. Argon is blown at the bottom of the ladle to promote their floating, and slag with higher basicity is added to the top to absorb such inclusions. On the other hand, the slag-steel interface transmission is reduced to prevent CaO from being brought into the molten steel. By controlling the bottom blowing of argon at the end of tapping, argon station, slag removal, and LF refining, the refined slag is prevented from being drawn into the molten steel and bringing in CaO. By adjusting the composition in advance, slag rolling caused by the addition of the alloy is avoided. At the same time, low-basicity synthetic slag is used in the LF refining process to reduce the activity of CaO in the slag.

[0020] MgO in non-metallic inclusions primarily comes from refractory erosion and slag. Traditionally, low-basicity steel smelting processes reduce refractory erosion by reducing ladle occupancy time and using high-quality refractory materials. However, spring steel, due to its high alloy content and high steel purity requirements, inevitably requires longer refining times. The present invention utilizes a specialized ladle with a silica coating at the slag line to reduce erosion from low-basicity slag. Furthermore, a magnesia coating (MgO ≥ 85%) is incorporated into the continuous casting tundish to minimize erosion of the tundish refractory materials.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) Through smelting control, the control of SiO2-Al2O3 type glassy inclusions with low CaO and MgO content is achieved from the source, wherein SiO2 accounts for more than 70% and CaO+MgO+MnO≤10%. (2) Matching the appropriate heating temperature suppresses the crystallization transformation of inclusions, ensuring that the rolling temperature is above the softening temperature of the glassy inclusions, and achieving good deformation of the inclusions during the rolling process. (3) The glassy inclusions mentioned in the present invention are mainly endogenous inclusions with small size, width ≤3μm after plastic deformation, and aspect ratio ≤5, which improves fatigue life while also ensuring the isotropy of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the inclusion morphology diagram of Example 1 of the present invention;

[0023] Figure 2 This is the inclusion morphology of comparative example 1;

[0024] Figure 3 This is the inclusion composition diagram of Example 1 and Comparative Example 1;

[0025] Figure 4 The inclusion size diagram of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0026] Example 1

[0027] A production method for reducing the size of non-metallic inclusions in spring steel by vitrification comprises the following steps:

[0028] Step 1: Converter, tapping temperature 1650 ° C, initial oxygen content of molten steel is 0.020% by mass, the primary molten steel is poured into a special ladle, and low aluminum and low calcium ferrosilicon (by mass percentage, Al ≤ 0.03%, Ca ≤ 0.8%) is preferentially added during the tapping process, followed by low aluminum ferromanganese (by mass percentage, Al ≤ 0.01%) and low aluminum ferrochrome (by mass percentage, Al ≤ 0.01%). The amount of alloy added is controlled according to the lower limit of the chemical composition of the steel grade, as shown in Tables 1 and 2. After tapping is completed, the bottom argon blowing is turned off, 0.5 kg / t lime and 1.5 kg / t low basicity synthetic slag are added to cover the surface of the molten steel, with an alkalinity of 1.2. The ladle car is driven to the argon station. The composition of the low basicity synthetic slag is shown in Table 3. The special ladle is made of low aluminum magnesium carbon bricks, and the slag line is coated with silicon dioxide to play a role in slag erosion resistance. The bottom of the ladle adopts double air-permeable bricks, which are arranged diagonally symmetrically to facilitate mixing of the molten steel and floating of inclusions.

[0029] Table 1 55SiCr alloying addition amount for steel tapping (kg / t)

[0030] Low aluminum and low calcium ferrosilicon Low aluminum ferromanganese Low aluminum ferrochrome 19.5 7.8 11.3

[0031] Table 2 Composition of 55SiCr steel after alloying (wt%)

[0032] C Si Mn Cr P S Al 0.50 1.42 0.61 0.61 0.0010 0.006 0.0015

[0033] Table 3 Composition of low basicity synthetic slag (wt%)

[0034] CaO SiO2 Al2O3 MgO Fe2O3 38-41 45-48 ≤1 ≤3 ≤0.7

[0035] Step 2: At the argon station, open the bottom blowing argon gas at a flow rate of 80NL / min for 3 minutes to promote the floating of inclusions and their absorption by the slag. Then close the bottom blowing argon gas and hoist the vessel to the slag removal position.

[0036] Step 3: Deslagging treatment: turn off the bottom blowing argon throughout the process, use a robotic arm to scrape off the surface slag, and add low-aluminum and low-calcium ferrosilicon, low-aluminum ferromanganese, and low-aluminum ferrochrome according to the composition results in Table 2 to the chemical composition limit of the steel grade, as shown in Table 4 and Table 5. Then add low-basicity synthetic slag to cover the surface of the molten steel. The addition amount is 10kg / t, and the basicity is 0.85 to the refining position;

[0037] Table 4 55SiCr secondary alloy addition amount (kg / t)

[0038] Low aluminum and low calcium ferrosilicon Low aluminum ferromanganese Low aluminum ferrochrome 0.8 0.5 0.7

[0039] Table 5 Composition of 55SiCr molten steel after secondary adjustment (wt%)

[0040]

[0041]

[0042] Step 4: LF refining, with a bottom blowing argon flow rate of 60NL / min throughout the whole process, only carbon powder and ferrosilicon powder are used for diffusion deoxidation of the slag surface, and no additional alloy is added. The refining time is 30min, and the temperature is raised to 1525℃ for continuous casting;

[0043] Step 5: Continuous casting: All refractory materials in contact with the molten steel are low-aluminum refractory materials (zirconium-magnesium-carbon materials with high thermal shock stability, calculated by mass percentage, MgO+C+ZrO2≥95%), and the tundish covering agent is a magnesia covering agent (calculated by mass percentage, MgO≥85%). The specific composition is shown in Table 6 to reduce the erosion of the tundish refractory materials;

[0044] Table 6 Magnesium coating composition (wt%)

[0045] MgO CaO <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[H2O]]> ≥85 ≤3 ≤5 ≤5 ≤2 ≤0.5

[0046] Step 6: Heating and rolling: the billet is heated and rolled, the heating temperature is 1030-1070℃, and the rolling temperature is 910-940℃.

[0047] The spring steel prepared in this embodiment has the following components by mass percentage: C 0.54%, Si 1.46%, Mn 0.69%, Cr 0.69%, P 0.0010%, S 0.006%, Al 0.0016%, and the remainder is Fe and unavoidable impurities.

[0048] Example 2

[0049] Step 1: Converter, tapping temperature 1680 ° C, initial oxygen content of molten steel is 0.030% by mass, the primary molten steel is poured into a special ladle, and low aluminum and low calcium ferrosilicon (by mass percentage, Al ≤ 0.03%, Ca ≤ 0.8%) is preferentially added during the tapping process, followed by low aluminum ferromanganese (by mass percentage, Al ≤ 0.01%) and low aluminum ferrochrome (by mass percentage, Al ≤ 0.01%). The amount of alloy added is controlled according to the lower limit of the chemical composition of the steel grade, as shown in Tables 1 and 2. After tapping is completed, the bottom argon blowing is turned off, 1.0 kg / t lime and 2.0 kg / t low basicity synthetic slag are added to cover the surface of the molten steel, with an alkalinity of 1.1. The ladle car is driven to the argon station. The composition of the low basicity synthetic slag is shown in Table 3. The special ladle is made of low aluminum magnesium carbon bricks, and the slag line is coated with silicon dioxide to play a role in slag erosion resistance. The bottom of the ladle adopts double air-permeable bricks, which are arranged diagonally symmetrically to facilitate mixing of the molten steel and floating of inclusions.

[0050] Table 1 55SiCr alloying addition amount for steel tapping (kg / t)

[0051] Low aluminum and low calcium ferrosilicon Low aluminum ferromanganese Low aluminum ferrochrome 19.8 7.9 11.5

[0052] Table 2 Composition of 55SiCr steel after alloying (wt%)

[0053] C Si Mn Cr P S Al 0.51 1.40 0.60 0.60 0.0009 0.007 0.0017

[0054] Table 3 Composition of low basicity synthetic slag (wt%)

[0055] CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO <![CDATA[Fe2O3]]> 38-41 45-48 ≤1 ≤3 ≤0.7

[0056] Step 2: At the argon station, open the bottom blowing argon gas at a flow rate of 80NL / min for 5 minutes to promote the floating of inclusions and their absorption by the slag. Then close the bottom blowing argon gas and hoist the vessel to the slag removal position.

[0057] Step 3: slag removal treatment: turn off the bottom blowing argon throughout the process, use a robotic arm to scrape off the surface slag, and add low-aluminum and low-calcium ferrosilicon, low-aluminum ferromanganese, and low-aluminum ferrochrome according to the composition results in Table 2 to the chemical composition limit of the steel grade, as shown in Table 4 and Table 5. Then add low-basicity synthetic slag to cover the surface of the molten steel. The addition amount is 15kg / t, and the basicity is 0.85. The slag is then hoisted to the refining position;

[0058] Table 4 55SiCr secondary alloy addition amount (kg / t)

[0059] Low aluminum and low calcium ferrosilicon Low aluminum ferromanganese Low aluminum ferrochrome 0.72 0.5 0.5

[0060] Table 5 Composition of 55SiCr molten steel after secondary adjustment (wt%)

[0061] C Si Mn Cr P S Al 0.55 1.45 0.68 0.68 0.0009 0.007 0.0017

[0062] Step 4: LF refining, with a bottom blowing argon flow rate of 60NL / min throughout the whole process, only carbon powder and ferrosilicon powder are used for diffusion deoxidation of the slag surface, and no additional alloy is added. The refining time is 50min, and the temperature is raised to 1525℃ for continuous casting;

[0063] Step 5: Continuous casting: All refractory materials in contact with the molten steel are low-aluminum refractory materials (zirconium-magnesium-carbon materials with high thermal shock stability, calculated by mass percentage, MgO+C+ZrO2≥95%), and the tundish covering agent is a magnesia covering agent (calculated by mass percentage, MgO≥85%). The specific composition is shown in Table 6 to reduce the erosion of the tundish refractory materials;

[0064] Table 6 Magnesium coating composition (wt%)

[0065] MgO CaO <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[H2O]]> ≥85 ≤3 ≤5 ≤5 ≤2 ≤0.5

[0066] Step 6: Heating and rolling: the billet is heated and rolled, the heating temperature is 1030-1070℃, and the rolling temperature is 910-940℃.

[0067] The spring steel prepared in this embodiment has the following components by mass percentage: C 0.55%, Si 1.45%, Mn 0.68%, Cr 0.68%, P 0.0009%, S 0.007%, Al 0.0017%, and the remainder is Fe and unavoidable impurities.

[0068] Comparative Example 1

[0069] A method for producing spring steel comprises the following steps:

[0070] (1) Converter, high carbon steel tapping, tapping temperature 1600 ℃, initial oxygen content of molten steel is 0.012% by mass, primary molten steel is poured into magnesium carbon ladle, low aluminum ferrosilicon (by mass percentage, Al≤0.03%, Ca≥1%), low aluminum ferromanganese (by mass percentage, Al≤0.01%), low aluminum ferrochrome (by mass percentage, Al≤0.01%) are added in sequence during tapping, the amount of alloy added and the composition of molten steel after alloying are shown in Table 1 and Table 2, low basicity synthetic slag (see Table 3) is directly added once during tapping to cover the surface of molten steel, the amount added is 10-12 kg / t, the basicity is 0.85, and the ladle is hoisted to LF refining;

[0071] Table 1 55SiCr alloying addition amount for steel tapping (kg / t)

[0072] Low aluminum ferrosilicon Low aluminum ferromanganese Low aluminum ferrochrome 17.8 7.1 10.2

[0073] Table 2 Composition of 55SiCr steel after alloying (wt%)

[0074] C Si Mn Cr P S Al 0.50 1.30 0.50 0.50 0.0010 0.006 0.0015

[0075] Table 3 Composition of low basicity synthetic slag (wt%)

[0076] CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO <![CDATA[Fe2O3]]> 38-41 45-48 ≤1 ≤3 ≤0.7

[0077] (2) LF refining: in the early stage, the temperature is raised and the composition is adjusted. The bottom blowing is carried out with large argon stirring at a flow rate of 200 NL / min. In order to achieve the steel grade composition, the total amount of alloy to be added is ≥3 kg / t, as shown in Table 3 and Table 4. After the composition adjustment is completed, the bottom blowing argon flow rate is reduced to 100 NL / min. The total refining time is 75 min. After soft blowing for ≥20 min, it is hoisted to the continuous casting position.

[0078] Table 3 55SiCr secondary alloy addition amount (kg / t)

[0079] Low aluminum and low calcium ferrosilicon Low aluminum ferromanganese Low aluminum ferrochrome 2.6 1.1 1.8

[0080] Table 4 Composition of 55SiCr steel liquid after secondary adjustment (wt%)

[0081] C Si Mn Cr P S Al 0.55 1.45 0.68 0.68 0.0010 0.006 0.0016

[0082] (3) Continuous casting: all refractory materials in contact with molten steel are low-aluminum refractory materials (MgO+C ≥ 95%), and the tundish covering agent uses a low-basicity tundish covering agent, the composition of which is shown in Table 5;

[0083] Table 5 Low alkalinity coating agent composition (wt%)

[0084] CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO <![CDATA[Fe2O3]]> <![CDATA[CaO / SiO2]]> 40-43 42-45 ≤2 ≤5 ≤2.5 0.9-1.1

[0085] (4) Heating and rolling: heating temperature 1030-1070℃, rolling temperature 910-940℃.

[0086] The spring steel prepared in this embodiment has the following components by mass percentage: C 0.55%, Si 1.45%, Mn 0.68%, Cr 0.68%, P 0.0010%, S 0.006%, Al 0.0016%, and the remainder is Fe and unavoidable impurities.

Claims

1. A production method for reducing the size of non-metallic inclusions in spring steel by vitrification, characterized in that The following steps are involved: Step 1: In a converter, the tapping temperature is controlled to be ≥1620°C, the initial oxygen content of the molten steel is 0.020-0.030% by mass, and the primary molten steel is poured into a ladle. During the tapping process, low-aluminum and low-calcium ferrosilicon is first added, followed by low-aluminum ferromanganese and low-aluminum ferrochrome. The amount of alloy added is controlled according to the lower limit of the chemical composition of the steel grade. After tapping is completed, the bottom argon blowing is turned off, and lime and low-alkalinity synthetic slag are added to cover the surface of the molten steel. The amount of lime and low-alkalinity synthetic slag added is 2-4 kg / t, and the alkalinity is 1.0-1.

2. The ladle car is driven to the argon station. Step 2: At the argon station, start bottom blowing argon with a flow rate of ≤100NL / min for 3-5min to promote the floating of inclusions to be absorbed by the slag, and then hoist them to the slag removal position; Step 3: During the slag removal process, the bottom blowing argon is turned off throughout the process, and the surface slag is removed using a robotic arm. Then, according to the composition results of the previous process, low-aluminum and low-calcium ferrosilicon, low-aluminum ferromanganese, and low-aluminum ferrochrome are added to the chemical composition limit of the steel grade. Subsequently, low-basicity synthetic slag is added to cover the surface of the molten steel. The addition amount is 10-15kg / t, and the basicity is 0.7-0.

9. The slag is then hoisted to the refining position. Step 4: LF refining, power supply and temperature rise, bottom blowing argon flow rate ≤80NL / min, carbon powder and ferrosilicon powder are used to diffuse deoxidize the slag surface, no additional alloy is added, the total refining time is controlled at 30-50min, the temperature is raised to 1516-1546℃ and hoisted for continuous casting; Step 5: continuous casting; Step 6: Heating and rolling, the billet heating temperature is 1000-1100℃, and the rolling temperature is 900-950℃.

2. The method for reducing the size of non-metallic inclusions in spring steel by vitrification as claimed in claim 1, characterized in that: In step 1, by mass percentage, Al≤0.03% and Ca≤0.8% in the low-aluminum and low-calcium ferrosilicon, Al≤0.01% in the low-aluminum ferromanganese, and Al≤0.01% in the low-aluminum ferrochrome.

3. The method for reducing the size of non-metallic inclusions in spring steel by vitrification as claimed in claim 1, characterized in that: In step 1, the ladle is made of low-aluminum-magnesium carbon bricks, and the slag line is coated with silica to resist slag erosion. The bottom of the ladle uses double-permeable bricks, which are arranged diagonally symmetrically to facilitate mixing of molten steel and floating of inclusions.

4. The method for reducing the size of non-metallic inclusions in spring steel by vitrification as claimed in claim 1, characterized in that: In step 5, the refractory materials in contact with the molten steel are all low-aluminum refractory materials, and the tundish covering agent uses a magnesium covering agent to reduce the corrosion of the tundish refractory materials.

5. The method for reducing the size of non-metallic inclusions in spring steel by vitrification as claimed in claim 1, characterized in that: The prepared spring steel has the following components by mass percentage: C 0.52-0.58%, Si 1.40-1.60%, Mn 0.60-0.80%, Cr 0.60-0.80%, P≤0.0012%, S≤0.008%, Al≤0.0020%, and the rest is Fe and inevitable impurities.

6. The method for reducing the size of non-metallic inclusions in spring steel by vitrification according to claim 1, characterized in that: In step 1, the amount of lime added is 0.5-1.5 kg / t, the amount of low-alkalinity synthetic slag added is 1.5-2.5 kg / t, the alkalinity of the low-alkalinity synthetic slag is 0.7-0.9, and the alkalinity is adjusted to 1.0-1.2 by adding lime.

7. The method for reducing the size of non-metallic inclusions in spring steel by vitrification as claimed in claim 1, characterized in that: In terms of mass percentage, the glassy inclusions SiO2 in the prepared spring steel account for more than 70%, CaO+MgO+MnO≤10%, the glassy inclusions have a width of ≤3μm, and an aspect ratio of ≤5.

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