Rare earth microalloy treated hot-formed steel and smelting method thereof

Abstract

The invention discloses rare earth microalloy treated hot-formed steel and a smelting method thereof. The rare earth microalloy treated hot-formed steel comprises the following components in percentage by mass: 0.22%-0.25% of C, 0.10%-0.30% of Si, 1.30%-1.45% of Mn, less than or equal to 0.02% of P, less than or equal to 0.004% of S, less than or equal to 0.0050% of N, 0.15%-0.25% of Cr, 0.04%-0.08% of Als, 0.001%-0.003% of B, 0.020%-0.030% of Ti, 0.0050%-0.0070% of Ce and the balance of iron and inevitable impurities. Rare earth microalloying is matched with calcium treatment, reasonable component design is combined, it is guaranteed that the effects of metamorphic inclusions and microalloying are exerted, the form and size of the inclusions in the steel are optimized, the common water gap blocking problem of rare earth steel is solved, the hot-formed steel with good mechanical property and fatigue property is prepared, and the subsequent production requirement is met.

Description

Technical Field

[0001] The present invention relates to the technical field of materials and metallurgy, and more particularly to a rare earth microalloyed hot-forming steel and a smelting method thereof. Background Art

[0002] Traditionally, the mechanisms of rare earth (RE) action in steel are primarily believed to include purifying molten steel, modifying inclusions, and microalloying. Extensive theoretical research and process technology development efforts have been conducted both domestically and internationally regarding the mechanisms of rare earth action in steel and the development of rare earth steels, yielding fruitful results. With the rapid advancement of clean steelmaking technology, the mechanisms of rare earth action in steel are also evolving. The deoxidation and desulfurization-focused steel purification process has been phased out, while the inclusion modification process, which aims to spheroidize inclusions, has proven effective. The unique microalloying effect of rare earths is gradually attracting attention both domestically and internationally. Unlike calcium and magnesium treatments, rare earth treatment offers unique advantages in inclusion modification. The addition of rare earths to steel transforms high-hardness, angular inclusions (such as Al2O3) into low-hardness, nearly spherical RE2O2S and REAlO3 inclusions. Their thermal expansion coefficients and elastic moduli (especially RE2O2S) closely match those of the steel matrix, reducing stress concentration around the inclusions and minimizing their impact on steel matrix properties. Furthermore, literature research indicates that even in ultra-low sulfur steels with sulfur contents as low as 10 ppm, MnS inclusions that deform along the rolling direction still exist. Rare earth treatment significantly modifies these sulfides, significantly reducing the harmful effects of sulfide inclusions. Furthermore, rare earth elements can modify not only sulfide and oxide inclusions, but also complex oxide inclusions. Based on this, rare earth treatment is being used to alter and influence the aggregation characteristics and removal behavior of inclusions such as Al2O3 in steel, thereby controlling the spheroidization and dispersion of inclusions in steel.

[0003] However, at present, rare earth addition can only be done by adding rare earth wires in the crystallizer. The inclusions formed by the rare earth in the steel cannot float up and be removed, thereby polluting the molten steel; the added rare earth cannot be evenly distributed in the steel, and the rare earth microalloying effect cannot be stably exerted; the added rare earth will also react with the crystallizer protective slag, resulting in serious denaturation of the protective slag, thereby affecting the surface quality of the ingot. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a rare earth microalloyed hot-formed steel and a smelting method thereof. By combining rare earth microalloying with calcium treatment and reasonable composition design, the effects of metamorphic inclusions and microalloying are ensured, the shape and size of inclusions in the steel are optimized, the common problem of nozzle blockage in rare earth steel is solved, and the comprehensive performance of the steel is improved.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A rare earth microalloyed hot-forming steel comprises the following components in percentage by mass: C: 0.22% to 0.25%, Si: 0.10% to 0.30%, Mn: 1.30% to 1.45%, P≤0.02%, S≤0.004%, N≤0.0050%, Cr: 0.15% to 0.25%, Als: 0.04% to 0.08%, B: 0.001% to 0.003%, Ti: 0.020% to 0.030%, Ce: 0.0050% to 0.0070%, and the balance being iron and unavoidable impurities.

[0007] Optionally, the rare earth microalloyed hot-formed steel has a tensile strength of 1480 MPa to 1530 MPa and an elongation of 10.0% to 12.0%.

[0008] The present invention also discloses a smelting method of the rare earth microalloyed hot-forming steel as described above, comprising the following steps: molten iron pretreatment, converter smelting, LF refining, RH vacuum refining, and continuous casting;

[0009] In the converter smelting, the charge includes molten iron and scrap steel after the molten iron pretreatment; deoxidation and alloying are performed during the tapping process;

[0010] In the LF refining, the molten steel discharged from the converter smelting enters the LF furnace for refining treatment, and is sequentially subjected to refining and white slag making, deoxidation and desulfurization treatment, and alloy composition adjustment. When the LF refining station is discharged, the molten steel contains C: 0.22% to 0.25%, Si: 0.10% to 0.30%, Mn: 1.30% to 1.45%, P≤0.020%, S≤0.0040%, Cr: 0.15% to 0.25%, and Als: 0.04% to 0.08%.

[0011] During the RH vacuum refining, the molten steel after the LF refining is hoisted into the RH vacuum furnace for degassing, deoxidation alloying, rare earth alloying and calcium treatment in sequence;

[0012] During the continuous casting, the molten steel after the RH vacuum refining treatment is continuously cast, and the superheat degree of the tundish during pouring is 20° C. to 35° C.

[0013] Optionally, in the molten iron pretreatment, the molten iron is desulfurized, the S of the treated molten iron is ≤ 0.030%, the molten iron temperature is ≥ 1300°C, and then the molten iron after desulfurization is slag-skimmed, the slag volume of the treated molten iron is ≤ 20mm.

[0014] Optionally, in the converter smelting, the amount of molten iron added accounts for 85% to 90% of the total mass of the charge; the converter adopts top and bottom double blowing, the end oxygen content is 0.04% to 0.06%; the end temperature is 1630℃ to 1640℃, and the tapping time is 5min to 7min; the slide block slag tapping controls the ladle slag thickness to be ≤70mm; 0.8kg / t steel to 1.2kg / t steel of deoxidized aluminum balls are added during tapping, and the amount of alloy added to a ton of steel is: 2.0kg / t to 2.5kg / t of high Carbon ferrochrome, 8kg / t~12kg / t high carbon ferromanganese, 5kg / t~10kg / t silicon manganese alloy and 0.8kg / t~1.3kg / t coke butane recarburizer; the composition after alloying is C: 0.15%~0.20%, Si: 0.10%~0.20%, Mn: 1.10%~1.30%, P≤0.020%, S≤0.010%, Cr: 0.10%~0.20%, Als: 0.020%~0.040%.

[0015] Optionally, in the LF refining, 5kg / t steel to 8kg / t steel of active lime is used for slag making, white slag deep desulfurization treatment is used, 0.5kg / t steel to 1.0kg / t steel of aluminum balls are used for slag deoxidation, and according to the steel grade composition requirements, the following alloy addition amounts are added per ton of steel: 0.20kg / t to 0.60kg / t of low-carbon ferrochrome, 2.0kg / t to 4.0kg / t of high-carbon ferromanganese, and 0.20kg / t to 0.50kg / t of coke butane recarburizer; the LF refining endpoint temperature is 1610°C to 1630°C.

[0016] Optionally, in the RH vacuum refining, when the vacuum degree is ≤100 Pa, aluminum deoxidation is carried out after a cycle of 13min to 17min, and the mass content of Als is controlled to be 0.04% to 0.08%. After 2min to 4min, alloying treatment is carried out, and the amount of alloy steel added is 0.35kg / t to 0.45kg / t of ferrotitanium and 0.15kg / t to 0.20kg / t of ferroboron. After the final alloying under vacuum conditions for 3min to 5min, the vacuum degree is controlled to be ≤1000 Pa, and the aluminum is alloyed. The vacuum tank adds 0.85kg / t to 1.2kg / t of ferrocerium alloy to the molten steel in the vacuum chamber. After the molten steel is in a net circulation state for 5min to 8min, the vacuum chamber is broken and re-pressurized. After the ladle descends, argon blowing from the bottom of the ladle is turned on and the argon blowing flow rate is controlled to be 200NL / min to 400NL / min. The molten steel is then treated with calcium using a silicon calcium line with a feeding amount of 250m3 to 350m3. After feeding calcium, soft argon blowing is maintained for 5min to 8min, and then the steel is hoisted to the slab continuous casting for pouring the molten steel.

[0017] Optionally, the mass content of cerium in the ferrocerium alloy is 19% to 21%.

[0018] The implementation of the present invention will have the following beneficial effects:

[0019] The present invention combines rare earth microalloying with calcium treatment, combined with rational composition design, to ensure the effective utilization of both modified inclusions and microalloying, optimize the morphology and size of inclusions in the steel, resolve the common nozzle clogging problem of rare earth steel, and improve the overall performance of the steel. Specifically, by adding a certain amount of Ce, inclusions are modified while simultaneously exerting their microalloying effect. The unique microalloying properties of rare earths can modify not only sulfide and oxide inclusions, but also complex oxide inclusions. Based on this, rare earth treatment is used to alter and influence the aggregation characteristics and removal behavior of inclusions such as Al2O3 in high-quality steels, such as hot-formed steels. This achieves controlled spheroidization and dispersion of inclusions in the steel, reducing the average size of inclusions. The industrial trial-produced rare earth hot-stamped steel exhibits a slight increase in strength and significant improvement in plasticity. The difference in microhardness between the undeformed and deformed zones after hot stamping is significantly reduced, resulting in the production of rare earth microalloyed hot-formed steel with excellent mechanical and fatigue properties, meeting subsequent production requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a comparison chart of the average inclusion number density and average size of Example 1 of the present invention and Comparative Examples 1-2. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0022] Example 1

[0023] The rare earth microalloyed hot forming steel of this embodiment (production furnace number is 2319121, brand is PHS1500) includes the following components in mass percentage: C: 0.22%, Si: 0.22%, Mn: 1.41%, P: 0.017%, S: 0.003%, N: 0.0029%, Cr: 0.19%, Als: 0.051%, B: 0.0022%, Ti: 0.020%, Ce: 0.0056%, and the balance is iron and unavoidable impurities.

[0024] The smelting method of rare earth microalloyed hot-formed steel of this embodiment comprises the following steps:

[0025] S1. In the molten iron pretreatment, the molten iron is desulfurized, and the S of the treated molten iron is 0.0026%, and the molten iron temperature is 1345°C. The molten iron after desulfurization is then skimmed, and the amount of slag after treatment is 18mm.

[0026] S2. During converter smelting, the amount of molten iron added accounts for 88% of the total mass of the charge; the converter adopts top and bottom combined blowing, and the end-point oxygen content is 0.0447%; the end-point temperature is 1638℃, and the tapping time is 5.5 minutes; the slide plate slag blocking control controls the ladle slag thickness to 60mm during tapping; 0.85kg / t of deoxidized aluminum balls are added to the tapping, and the alloy addition per ton of steel is: 2.27kg / t of high-carbon ferrochrome, 11.45kg / t of high-carbon ferromanganese, 5.68kg / t of silicon-manganese alloy and 1.11kg / t of coke butane recarburizer; its composition after alloying is C: 0.17%, Si: 0.18%, Mn: 1.14%, P: 0.015%, S: 0.010%, Cr: 0.16%; Als: 0.03%.

[0027] In S3 and LF refining, the LF furnace uses active lime to make slag, and "white slag" deep desulfurization operation is carried out. The amount of lime added is 7.6kg / t steel, and 0.57kg / t steel of aluminum balls are used for slag deoxidation. According to the requirements of steel grade composition, the alloy steel addition amount is supplemented: 0.25kg / t low carbon ferrochrome, 3.73kg / t high carbon ferromanganese, and 0.38kg / t of coke butane recarburizer. The tested composition is C: 0.22%, Si: 0.21%, Mn: 1.43%, P: 0.016%, S: 0.003%, Cr: 0.18%, Als: 0.057%, and the end temperature of LF refining is 1626℃.

[0028] During S4 and RH vacuum refining, RH is degassed. When the vacuum degree is 87 Pa, aluminum is deoxidized after a 15-minute circulation, and the mass content of Als is controlled to 0.06%. After 3 minutes, alloying treatment is performed, and the following alloy additions per ton of steel are added: 0.37 kg / t of ferrotitanium (70% content) and 0.17 kg / t of ferroboron. After final alloying under vacuum conditions for 2 minutes, the vacuum degree is controlled to be ≤1000 Pa, and 0.86 kg / t of ferrocerium alloy (cerium content of 20% by mass) is added from the vacuum feed tank to the molten steel in the vacuum chamber. After the molten steel is in a net circulation state for 7 minutes, the vacuum chamber is pierced and re-pressurized. After the ladle is lowered, argon blowing from the ladle bottom is started, and the argon blowing flow rate is controlled to 280 NL / min. The molten steel is then calcium treated using a silicon calcium line with a feeding amount of 300 m3. After calcium feeding, soft argon blowing is maintained for 7 minutes. The molten steel is then hoisted to the slab continuous casting for pouring the molten steel. The superheat of the tundish during pouring is 33°C.

[0029] Example 2

[0030] The rare earth microalloyed hot forming steel of this embodiment (production furnace number is 2319126, brand is PHS1500) includes the following components in mass percentage: C: 0.23%, Si: 0.19%, Mn: 1.38%, P: 0.020%, S: 0.002%, N: 0.0032%, Cr: 0.18%, Als: 0.06%, B: 0.0019%, Ti: 0.028%, Ce: 0.0065%, and the balance is iron and unavoidable impurities.

[0031] The smelting method of rare earth microalloyed hot-formed steel of this embodiment comprises the following steps:

[0032] S1. In the molten iron pretreatment, the molten iron is desulfurized, and the S of the treated molten iron is 0.0028%, and the temperature of the molten iron is 1321°C. The molten iron after desulfurization is then skimmed, and the amount of slag after treatment is 16mm.

[0033] S2. During converter smelting, the amount of molten iron added accounts for 85% of the total mass of the charge; the converter adopts top and bottom combined blowing, the end point oxygen content is 0.0489%; the end point temperature is 1633℃, and the tapping time is 6 minutes; the slide plate slag blocking control ladle slag thickness to 70mm; 0.82kg / t steel of deoxidized aluminum balls are added during tapping, and the alloy addition amount per ton of steel is: 2.0kg / t high carbon ferrochrome, 11.43kg / t high carbon ferromanganese, 5.65kg / t silicon manganese alloy and 1.10kg / t coke butane recarburizer; the composition after alloying is C: 0.18%, Si: 0.17%, Mn: 1.24%, P: 0.012%, S: 0.010%, Cr: 0.15%, Als: 0.04%.

[0034] In S3 and LF refining, the LF furnace uses active lime to make slag, and "white slag" deep desulfurization operation is carried out. The amount of lime added is 5.4kg / t steel, and 0.54kg / t steel of aluminum balls are used for slag deoxidation. According to the requirements of steel grade composition, the alloy steel addition amount is additionally: 0.54kg / t low carbon ferrochrome, 2.1kg / t high carbon ferromanganese, and 0.25kg / t of coke butane recarburizer. The inspection composition is C: 0.22%, Si: 0.19%, Mn: 1.34%, P: 0.019%, S: 0.002%, Cr: 0.18%, Als: 0.047%, and the end temperature of LF refining is 1619℃.

[0035] In S4 and RH vacuum refining, RH is degassed. When the vacuum degree is 80 Pa, aluminum is deoxidized after 15 minutes of circulation, and the mass content of Als is controlled to be 0.055%. After 3 minutes, alloying treatment is carried out, and the amount of alloy steel added is: 0.43 kg / t of titanium iron (70% content) and 0.15 kg / t of boron iron. After the final alloying for 4 minutes under vacuum conditions, the vacuum degree is controlled to be ≤1000 Pa, and the molten steel in the vacuum chamber is fed from the vacuum tank to the vacuum chamber. 0.98 kg / t of ferrocerium alloy (cerium content of 20% by mass) was added, and after the molten steel was in a net circulation state for 7 minutes, the vacuum chamber was broken and re-pressurized. After the ladle was lowered, argon blowing from the bottom of the ladle was started, and the argon blowing flow rate was controlled to 300 NL / min. The molten steel was then calcium treated using a silicon calcium wire with a feeding amount of 350 m3. After calcium feeding, soft argon blowing was maintained for 7 minutes, and then the steel was hoisted to the slab continuous casting for pouring the molten steel. The superheat of the ladle during pouring was 28°C.

[0036] Comparative Example 1

[0037] This embodiment is a preparation example of hot-formed steel without adding rare earth (production furnace number is 2420007, brand is PHS1500), including the following components in mass percentage: C: 0.24%, Si: 0.18%, Mn: 1.38%, P: 0.020%, S: 0.004%, N: 0.0032%, Cr: 0.17%, Als: 0.06%, B: 0.0019%, Ti: 0.028%, and the balance is iron and unavoidable impurities.

[0038] The smelting method of this comparative example comprises the following steps:

[0039] D1. In the molten iron pretreatment, the molten iron is desulfurized, and the S of the treated molten iron is 0.0030%, and the molten iron temperature is 1310°C. The molten iron after desulfurization is then skimmed, and the amount of slag after treatment is 20mm.

[0040] D2. During converter smelting, the amount of molten iron added accounts for 90% of the total mass of the charge; the converter adopts top and bottom combined blowing, the end-point oxygen content is 0.0473%; the end-point temperature is 1645℃, and the tapping time is 5 minutes; the slide plate slag blocking is used to control the ladle slag thickness to 65mm during tapping; 0.80kg / t of deoxidized aluminum balls are added during tapping, and the alloy addition per ton of steel is: 1.90kg / t of high-carbon ferrochrome, 11.26kg / t of high-carbon ferromanganese, 5.1kg / t of silicon-manganese alloy, and 0.55kg / t of coke butane recarburizer; the alloying composition is C: 0.21%, Si: 0.17%, Mn: 1.05%, P: 0.019%, S: 0.019%, Cr: 0.16%, and Als: 0.08%.

[0041] In D3 and LF refining, the LF furnace uses active lime to make slag and "white slag" deep desulfurization operation. The lime addition amount is 4.6kg / t steel. The slag deoxidation uses 0.48kg / t steel aluminum balls. According to the steel grade composition requirements, the alloy steel addition amount is additionally: 0.50kg / t low carbon ferrochrome, 2.0kg / t high carbon ferromanganese, and 0.28kg / t coke butane recarburizer. The inspection composition is C: 0.24%, Si: 0.18%, Mn: 1.35%, P: 0.020%, S: 0.004%, Cr: 0.18%, Als: 0.037%. The LF refining endpoint temperature is 1625℃.

[0042] During D4 and RH vacuum refining, RH is degassed. When the vacuum degree is 80 Pa, aluminum is deoxidized after 12 minutes of circulation, and the mass content of Als is controlled to be 0.055%. After 3 minutes, alloying treatment is carried out, and the following alloy steel addition amounts are added: 0.40 kg / t of ferrotitanium (70% content) and 0.17 kg / t of ferroboron; the vacuum degree is controlled to be ≤200 Pa, and after the molten steel is in a net circulation state for 6 minutes, the vacuum chamber is broken and re-pressurized. After the ladle is lowered, it is subsequently hoisted to the slab continuous casting for pouring the molten steel. The superheat of the ladle during pouring is 32°C.

[0043] Test Case

[0044] The performance tests of the products obtained in the examples of the present invention and the comparative examples are shown in Table 1 and Figure 1 shown.

[0045] Table 1 Performance data of Comparative Example 1 and Examples 1-2

[0046] Tensile strength (MPa) Elongation (%) Example 1 1513 11.45 Example 2 1525 11.66 Comparative Example 1 1510 11.06

[0047] like Figure 1 As shown, Figure 1 The graphs of average inclusion number density and average size of Example 1 and Comparative Example 1 show that the inclusion density of Example 1 is significantly higher than that of Comparative Example 1, and the inclusion size of Example 1 is significantly smaller than that of Comparative Example 1. The technical effect of Example 2 is the same as that of Example 1.

[0048] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A rare earth microalloyed hot-formed steel, characterized in that: The invention comprises the following components in mass percentage: C: 0.22% to 0.25%, Si: 0.10% to 0.30%, Mn: 1.30% to 1.45%, P≤0.02%, S≤0.004%, N≤0.0050%, Cr: 0.15% to 0.25%, Als: 0.04% to 0.08%, B: 0.001% to 0.003%, Ti: 0.020% to 0.030%, Ce: 0.0050% to 0.0070%, and the balance is iron and unavoidable impurities.

2. The rare earth microalloyed hot-formed steel according to claim 1, characterized in that: The rare earth microalloyed hot-forming steel has a tensile strength of 1480 MPa to 1530 MPa and an elongation of 10.0% to 12.0%.

3. A smelting method for rare earth microalloyed hot-forming steel according to any one of claims 1 to 2, characterized in that: The following steps are involved: Hot metal pretreatment, converter smelting, LF refining, RH vacuum refining, continuous casting; In the converter smelting, the charge includes molten iron and scrap steel after the molten iron pretreatment; deoxidation and alloying are performed during the tapping process; In the LF refining, the molten steel discharged from the converter smelting enters the LF furnace for refining treatment, and is sequentially subjected to refining and white slag making, deoxidation and desulfurization treatment, and alloy composition adjustment. When the LF refining station is discharged, the molten steel contains C: 0.22% to 0.25%, Si: 0.10% to 0.30%, Mn: 1.30% to 1.45%, P≤0.020%, S≤0.0040%, Cr: 0.15% to 0.25%, and Als: 0.04% to 0.08%. During the RH vacuum refining, the molten steel after the LF refining is hoisted into the RH vacuum furnace for degassing, deoxidation alloying, rare earth alloying and calcium treatment in sequence; During the continuous casting, the molten steel after the RH vacuum refining treatment is continuously cast, and the superheat degree of the tundish during pouring is 20° C. to 35° C.

4. The smelting method according to claim 3, characterized in that: In the molten iron pretreatment, the molten iron is desulfurized, the S of the treated molten iron is less than or equal to 0.030%, and the molten iron temperature is greater than or equal to 1300° C. The desulfurized molten iron is then skimmed, and the slag volume of the treated molten iron is less than or equal to 20 mm.

5. The smelting method according to claim 3, characterized in that: During the converter smelting, the amount of molten iron added accounts for 85% to 90% of the total mass of the furnace charge; the converter adopts top and bottom combined blowing, the end point oxygen content is 0.04% to 0.06%; the end point temperature is 1630° C. to 1640° C., and the tapping time is 5 minutes to 7 minutes; the slide plate is used to block the slag during tapping to control the ladle slag thickness to be ≤70 mm; 0.8 kg / t to 1.2 kg / t of deoxidized aluminum balls are added during tapping, and 2.0 kg / t to 2.5 kg / t of high carbon chromium is added to each ton of alloy steel. Iron, 8kg / t-12kg / t high carbon ferromanganese, 5kg / t-10kg / t silicon manganese alloy and 0.8kg / t-1.3kg / t coke butane recarburizer; the composition after alloying is C: 0.15%-0.20%, Si: 0.10%-0.20%, Mn: 1.10%-1.30%, P≤0.020%, S≤0.010%, Cr: 0.10%-0.20%, Als: 0.020%-0.040%.

6. The smelting method according to claim 3, characterized in that: In the LF refining, 5kg / t-8kg / t of steel active lime is used for slagging, white slag deep desulfurization treatment is used, 0.5kg / t-1.0kg / t of steel aluminum balls are used for slag deoxidation, and according to the requirements of the steel grade composition, the following alloy addition amounts are added per ton of steel: 0.20kg / t-0.60kg / t of low-carbon ferrochrome, 2.0kg / t-4.0kg / t of high-carbon ferromanganese, and 0.20kg / t-0.50kg / t of coke butane recarburizer; and the LF refining endpoint temperature is 1610°C-1630°C.

7. The smelting method according to claim 3, characterized in that: In the RH vacuum refining, when the vacuum degree is ≤100 Pa, aluminum deoxidation is carried out after a cycle of 13 to 17 minutes, and the mass content of Als is controlled to be 0.04% to 0.08%. After 2 to 4 minutes, alloying treatment is carried out, and the amount of alloy steel added is 0.35 kg / t to 0.45 kg / t of ferrotitanium and 0.15 kg / t to 0.20 kg / t of ferroboron. After the final alloying under vacuum conditions for 3 to 5 minutes, the vacuum degree is controlled to be ≤1000 Pa, and the vacuum is removed. The material tank adds 0.85kg / t~1.2kg / t of ferrocerium alloy into the molten steel in the vacuum chamber. After the molten steel is in a net circulation state for 5min~8min, the vacuum chamber is broken and re-pressurized. After the ladle descends, the argon blowing from the bottom of the ladle is turned on and the argon blowing flow rate is controlled to be 200NL / min~400NL / min. The molten steel is then treated with calcium using a silicon calcium line with a feeding amount of 250m~350m. After feeding calcium, soft argon blowing is maintained for 5min~8min, and then the steel is hoisted to the slab continuous casting for pouring the molten steel.

8. The smelting method according to claim 7, characterized in that: The mass content of cerium element in the ferrocerium alloy is 19% to 21%.

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