CN111378811B - Process method for smelting high-purity steel by using VD (vacuum distillation) vacuum treatment equipment - Google Patents

Process method for smelting high-purity steel by using VD (vacuum distillation) vacuum treatment equipment Download PDF

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CN111378811B
CN111378811B CN202010367426.6A CN202010367426A CN111378811B CN 111378811 B CN111378811 B CN 111378811B CN 202010367426 A CN202010367426 A CN 202010367426A CN 111378811 B CN111378811 B CN 111378811B
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steel
refining
vacuum
argon
slag
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CN111378811A (en
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翟万里
印传磊
郑力宁
田春阳
李润
张洪才
林鹏
刘从德
蒋栋初
徐亚鹏
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Jiangsu Lihuai Steel Co ltd
Jiangsu Shagang Group Huaigang Special Steel Co Ltd
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Jiangsu Lihuai Steel Co ltd
Jiangsu Shagang Group Huaigang Special Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/064—Dephosphorising; Desulfurising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28—Manufacture of steel in the converter
    • C21C5/30—Regulating or controlling the blowing
    • C21C5/35—Blowing from above and through the bath
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/072—Treatment with gases
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
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  • Treatment Of Steel In Its Molten State (AREA)

Abstract

The invention discloses a process method for smelting high-purity steel by using VD (vacuum distillation) vacuum treatment equipment, which comprises the following steps of: KR molten iron desulphurization: ensuring that the S in the molten iron is less than or equal to 30ppm before the molten iron enters the furnace; blowing by a top-bottom combined blown converter: the mass percentage omega C of converter tapping C is more than or equal to 0.08%, and the whole course of external refining and argon refining is weakly stirred; calcium-aluminum-silicon furnace slag with alkalinity of 2.0-4.5 is adopted; the VD treatment adopts high vacuum for a long time of 20-35 min to maintain the strength, and the strength of bottom stirring argon is controlled in time intervals according to a strong → weak → strong mode in the treatment process; after VD is broken, the purity of the molten steel is further improved by adopting the methods of removing large-particle impurities by soft blowing and removing small-particle impurities by standing the molten steel. According to the method, a special VD treatment process stirring control mode is adopted and an appropriate refining slag system and soft blowing operation method are adopted, so that the slag entrapment of the molten steel can be effectively reduced, the removal effect of non-metallic inclusions is improved, and the method is suitable for the production of various low-carbon, medium-carbon and high-carbon steel grades with the carbon content of 0.15-1.05%.

Description

Process method for smelting high-purity steel by using VD (vacuum distillation) vacuum treatment equipment
Technical Field
The invention relates to the field of steelmaking process, in particular to a process method for smelting high-purity steel by using VD (vacuum distillation) vacuum treatment equipment.
Background
The high-end special steel is a key material required by major equipment manufacturing and national key engineering, is widely applied to the fields of aviation, automobiles, engineering machinery, energy exploitation, railway transportation and the like, and the quality control level of the high-end special steel represents the industrial development level and the strength of the manufacturing industry of the country. White spots in steel, namely hydrogen-induced cracks, are one of the defects of the most harmful steel, and once no effective rescue measures are generated, steel parts are often directly scrapped, so that the defects in the production process of the steel are avoided to the utmost extent. The control level of purity of molten steel such as non-metallic inclusion, total oxygen content, residual hydrogen content and the like in steel directly determines the fatigue property, tensile property, corrosion property, welding property, processing property and the like of the steel, and the fatigue life of a steel part is exponentially increased along with the reduction of the total oxygen content and the size reduction of the non-metallic inclusion in the steel.
Vacuum degassing has become one of the production processes necessary for producing high-end steel products because the hydrogen content of molten steel can be greatly reduced by vacuum treatment of molten steel, and the probability of white spots in steel can be greatly reduced. At present, two vacuum degassing modes of VD and RH are mainly available in the world. Compared with RH and VD, the vacuum degassing and desulfurizing device has strong degassing and desulfurizing capacity and less investment and is sought by a plurality of domestic steel mills. However, in the molten steel treatment process of VD, steel slag is violently mixed and flushed, so that severe slag rolling is caused, and the control of inclusions in steel has a large difference from RH. For high-end special steel with higher requirements on B-type and Ds-type inclusions in steel, the control effect cannot be achieved by VD treatment.
In order to solve the problem of inclusion control by adopting a VD (vacuum distillation) treatment process, domestic steelmaking workers continuously carry out process research work, but the process flow adopted by the research is relatively complex and mainly focuses on a few high-carbon steels such as high-carbon chromium bearing steel and the like. The high-carbon steel determines that the primary smelting furnace can control the C content of the steel to be at a higher level due to the steel type characteristics, has obvious advantages in the aspect of controlling T.O and nonmetallic inclusions in the steel, and cannot necessarily achieve expected effects when the adopted process method is popularized to medium-low carbon steel with lower carbon content. For example, the method for smelting high-carbon chromium bearing steel by using VD (vacuum degassing) process disclosed by patent CN 108118115A can control Ds and B mixed impurities within 1.0 level, but the control process is only limited to high-carbon bearing steel, and two times of vacuum refining are required in the production process, so that the organization complexity of the production process is increased, and the unstable control risk is increased. Patent CN 104087719B discloses a smelting process of high-carbon bearing steel, and its control process is limited to high-carbon bearing steel equally, and adopts under the very high concise slag system condition of basicity, can inevitably produce the condition of excessive sediment in VD treatment process, is unfavorable for the stable execution of VD treatment process technology, increases molten steel dehydrogenation control risk. CN 108950130A discloses a large-scale production smelting method of low-oxygen high-purity steel, which is suitable for controlling the purity of molten steel of steel types with different carbon contents, but can only ensure that the T.O of the molten steel is less than or equal to 15ppm, and also adopts the process thought of twice vacuum refining, thereby increasing the difficulty of production organization and greatly improving the production cost.
Disclosure of Invention
The invention aims to provide a process method for smelting high-purity steel by using VD (vacuum distillation) vacuum treatment equipment, which solves the problem of large-particle B-type and Ds-type impurities generated by producing special steel by using VD vacuum treatment and realizes the stable purity production of high-end special steel.
The technical scheme adopted by the invention is as follows:
a process method for smelting high-purity steel by using VD (vacuum distillation) vacuum treatment equipment comprises the following steps:
1) pre-desulfurization of molten iron: low-sulfur molten iron is adopted, KR stirring desulfurization is carried out, and S in the molten iron before entering the furnace is ensured to be less than or equal to 30 ppm;
2) converting in a converter: smelting by using a top-bottom combined blown converter with the specification of 90T, ensuring that the mass percentage omega C of the tapped C is more than or equal to 0.08 percent, and precipitating and deoxidizing the tapped C by using aluminum;
3) LF refining: the refining time is 60-150 min, the flow of the stirring argon is 50-600 NL/min, the slag components are adjusted by adopting a deoxidation slagging auxiliary material, the alkalinity of the refined final slag is 2.0-4.5, and the mass percent omega Al of a refining ladle Al is controlled to be 0.030% -0.060%;
4) VD vacuum treatment: the VD treatment time is within the range of 20-35 min, argon gas is blown at the bottom in the treatment process for stirring, and the strength is performed according to 'strong → weak → strong', and the method specifically comprises the following steps: and weak stirring with the flow rate of below 50NL/min is adopted in the process from the beginning of VD treatment to the high vacuum, after the high vacuum is achieved, strong stirring with the flow rate of 500-600 NL/min is adopted in the first one-third time period in the high vacuum maintaining process, then weak stirring with the flow rate of 50-160 NL/min is adopted in the first one-third to seven-eighth time period, strong stirring with the flow rate of 300-500 NL/min is adopted in the last one-eighth time period in the high vacuum maintaining process, and the high vacuum is broken after the high vacuum maintaining time meets the control requirement.
5) Soft blowing and standing: and removing impurities in the steel by combining soft blowing and molten steel standing, carrying out soft blowing after VD treatment is finished, wherein the soft blowing time is 10-20 min, removing larger particle impurities, and standing the molten steel for 20-35 min after the soft blowing is finished, so that floating of small particle impurities is promoted.
The invention has the further improvement scheme that in the step 1), molten iron with the mass percent of S being less than or equal to 0.025 percent is adopted as a raw material.
According to a further improvement scheme of the invention, in the step 2), free oxygen of molten steel tapped from the converter is controlled within 500ppm, when the tapping amount is approximately one third, aluminum blocks are added into a ladle according to the proportion of 1.25-1.65 kg/t for rapid deoxidation, and the mass percentage of Al refined to a station is controlled to be 0.050% -0.080%.
The invention further improves the scheme that in the step 3), different argon stirring strengths are implemented in stages in the LF refining process, and specifically the argon stirring strengths are as follows: in the process of heating the molten steel, the flow of argon is 100-400 NL/min, the flow of argon is 300-600 NL/min when chemical components are adjusted, and the flow of argon is 50-200 NL/min when the molten steel waits.
The further improvement scheme of the invention is that in the step 3), lime and premelted refining slag are added for slagging in 500-plus-one furnace respectively after aluminum deoxidation in the converter tapping process, silicon carbide is adopted for slag surface deoxidation in the LF refining process, the silicon carbide dosage is 180-plus-one furnace, and at least 200kg of quartz sand is adopted for furnace slag component adjustment to form calcium-aluminum-silicon series molten steel top slag before VD treatment, wherein the mass percentages of the components are as follows: CaO: 42% -55% of SiO2：12％～21％、MgO：8％～15％、Al2O3：20％～30％、S：0.2％～1.0％、Tfe：0～0.8％。
The invention has the beneficial effects that:
the first, the invention relates to a process method for smelting high-purity steel by using VD vacuum treatment equipment, which adopts a special VD treatment stirring control mode and is assisted by a proper refining slag system and soft blowing operation method, thereby reducing the slag entrapment of molten steel, improving the removal effect of non-metallic inclusions, and being suitable for the production of various low, medium and high carbon steel types with the carbon content of 0.15-1.05%.
Secondly, the process method for smelting high-purity steel by using the VD vacuum treatment equipment adopts a calcium-silicon-aluminum refining slag system with the alkalinity R2 of 2.0-4.5, ensures good fluidity and deoxidation and inclusion adsorption capacity of slag under the conditions of LF refining and VD vacuum treatment process, and is beneficial to separating steel slag after VD treatment.
Thirdly, the process method for smelting high-purity steel by using the VD vacuum treatment equipment limits the specific stirring argon flow in different smelting stages in the LF refining process, adopts stronger stirring to ensure the uniformity of chemical components and normal temperature rise when the chemical components are adjusted and the temperature rise operation is carried out by using electrodes, avoids overlarge stirring strength of molten steel, and effectively reduces slag entrapment in the LF refining process; the molten steel is stirred weakly when waiting, the floating of nonmetallic inclusion is promoted, and the excessive secondary oxidation in the molten steel refining process is avoided.
Fourthly, according to the process method for smelting high-purity steel by using the VD vacuum treatment equipment, a strong-weak-strong control mode is adopted for argon blowing stirring strength in the VD treatment process, strong stirring is adopted for blowing off the slag surface of molten steel for a certain time in the early stage of a high vacuum maintaining process for strengthening dehydrogenation and denitrification, a longer-time weak stirring mode is adopted in the middle stage to keep a continuous degassing effect and simultaneously promote the slag strongly stirred and rolled in the early stage to fully float and remove, and strong stirring and solidification degassing effects are adopted in the later stage for short time, so that the strong stirring time required by degassing in the VD treatment process can be effectively reduced, the slag mixing impact strength in the treatment process is reduced, the slag rolling is reduced, and meanwhile, the floating and removal of impurities in the molten steel in the treatment process is promoted.
Fifthly, according to the process method for smelting high-purity steel by using the VD vacuum treatment equipment, after the VD vacuum treatment is finished and the vacuum is broken, the small-particle inclusion is removed by carrying out long-time standing treatment on the molten steel after the removal effect of the large-particle inclusion is consolidated by using short-time soft blowing on the basis of stirring control in the VD treatment process, and the inclusion removal efficiency is obviously improved.
Sixth, the invention relates to a process for smelting high-purity steel by using VD vacuum treatment equipment, through the production practice of high-carbon steel, medium-carbon steel and low-carbon steel, the purity of molten steel can be controlled at the following level: T.O in the steel is less than or equal to 10.0ppm, and the average content is 7.0 ppm; the steel rarely finds the oxide of the B-type inclusion in a strip string shape, and the grade is less than or equal to 1.0 grade; ds-type inclusions not smaller than 1.0 are not found.
Drawings
FIG. 1 is a scanning electron microscope image of a 2.0-grade B-type inclusion of a product obtained by the prior art.
FIG. 2 is a scanning electron microscope image of class B inclusions in class 1.0 of the product obtained in example 1 of the present invention.
FIG. 3 is a scanning electron microscope image of class B0.5 inclusions of a product obtained in example 5 of the present invention.
FIG. 4 is a scanning electron microscope image of class 0B inclusions in a product obtained in example 9 of the present invention.
FIG. 5 is a scanning electron microscope image of Ds type 2.5 inclusion inclusions of a product obtained by the prior art.
FIG. 6 is a scanning electron microscope image of Ds inclusion inclusions of 1.0 grade obtained from example 1 of the present invention.
FIG. 7 is a scanning electron microscope image of 0.5-grade Ds inclusion inclusions of a product obtained in example 5 of the present invention.
FIG. 8 is a scanning electron microscope image of Ds 0 inclusion inclusions of a product obtained in example 9 of the present invention.
The above are scanning electron micrographs of the type B inclusions and the type Ds inclusions of the product obtained in example 1/5/9 of the present invention and those of the prior art. Compared with the prior art, the size of the nonmetallic inclusion in the product obtained by the invention is obviously reduced. The non-metallic inclusions in the products obtained in examples 2 and 3, examples 4 and 6 and examples 7 and 8 were also significantly reduced in size compared to the prior art (not shown).
Detailed Description
Prior Art
42CrMo4 alloy steel, wherein the mass percent omega [ C ] of C in the steel is 0.42%, and the alloy steel is produced by adopting a molten iron desulphurization → LD → LF → VD technological process. The method specifically comprises the following steps:
1) molten iron with the mass percentage of S being 0.035% is adopted as a raw material, KR is used for stirring and desulphurization, and the content of S in the molten iron before charging is 53 ppm;
2) smelting by using a 90T top-blown converter, wherein the mass percent omega C of the steel tapping C is 0.06 percent, the free oxygen content of the molten steel during the steel tapping is 700ppm, aluminum blocks are added according to the proportion range of 1.33kg/T during about 40 tons of steel tapping for precipitation and deoxidation, and the mass percent omega Al of Al refined to a station is 0.012 percent;
3) LF refining and slagging: adding lime 500 kg/furnace and premelted refining slag 600 kg/furnace for slagging after aluminum deoxidation in the converter tapping process, wherein calcium carbide is adopted for slag surface deoxidation in the LF refining process, the using amount is 150 kg/furnace, the binary alkalinity R2 of the calcium-aluminum-silicon molten steel top slag before VD treatment is 9.7, and the mass percentages of the components are as follows: CaO: 57.69% and SiO2：5.95％、MgO：3.28％、Al2O3：35.29％、S：0.42％、Tfe：0.37％；
4) The LF refining time is 50min, the argon flow is 600NL/min in the molten steel temperature rising process, the argon flow is 800NL/min when chemical components are adjusted, the waiting time except the molten steel temperature rising and component adjusting is 360NL/min, aluminum particles are adopted in the LF refining process to supplement aluminum, and the Al content is 0.023% when ladle hanging is carried out;
5) VD vacuum treatment: and controlling the high vacuum maintaining time of VD treatment for 12min, wherein the whole argon flow is 550NL/min after VD reaches high vacuum, and the vacuum is broken after the high vacuum is maintained for 12 min.
6) Soft blowing: and immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, wherein the argon flow is 30NL/min, and the soft blowing time is 20 min.
The 42CrMo4 steel obtained by the steps 1) to 6) has the oxygen content T.O of 13.8ppm, the B-type inclusion grade of 2.0 grade and the Ds-type inclusion grade of 2.5 grade.
The invention aims at the process of low-carbon steel
For low carbon gear steel 20CrMo, the mass percent omega [ C ] of C in the steel is 0.20%, and the steel is produced by adopting the process flow of molten iron desulphurization → LD → LF → VD. The method specifically comprises the following steps:
1) molten iron with the mass percentage of S being less than or equal to 0.022 percent is adopted as a raw material, KR is used for stirring and desulfurizing, and the S content of the molten iron before charging is less than or equal to 20 ppm;
2) smelting by using a top-bottom combined blowing converter with the specification of 90T, wherein the mass percent omega C of the tapping C is within the range of 0.08-0.12%, the free oxygen content of molten steel is 300-500 ppm during tapping, aluminum cakes are added into the converter for quick deoxidation according to the proportion range of 1.40-1.65 kg/T before the tapping amount is 30T, and the mass percent omega Al of Al refined to a station is within the range of 0.060-0.080%;
3) LF refining and slagging: lime and premelted refining slag are added into the furnace for slagging respectively at 500kg, silicon carbide is adopted for slag surface deoxidation in the LF refining process, the consumption is 160-180 kg per furnace, quartz sand is adopted for 200kg per furnace for adjusting the components of the slag, the binary alkalinity R2 of the top slag of the calcium-aluminum-silicon molten steel before VD treatment is within the range of 3.0-4.5, and the mass percentages of the components are as follows: CaO: 49% -55% of SiO2：12％～16％、MgO：8％～12％、Al2O3：20％～25％、S：0.3％～0.8％、Tfe：0.4～0.8％；
4) Controlling the LF refining time and the stirring strength, controlling the refining time to be 80-130 min, controlling the argon flow to be 150-350 NL/min in the temperature rising process of the molten steel, adjusting the argon flow to be 300-450 NL/min when chemical components are adjusted, controlling the argon flow to be 50-100 NL/min in the waiting time except for the temperature rising and component adjustment of the molten steel, not supplementing aluminum in the LF refining process, and enabling the Al content to be 0.040% -0.060% in ladle hanging;
5) VD vacuum treatment: controlling VD processing time for 25min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and (3) adopting the flow of 20-30 NL/min in the process from the beginning of VD treatment to the high vacuum, keeping the flow of argon of 500-550 NL/min within 7min after the high vacuum is achieved, keeping the flow of argon of 50-120 NL/min within the time period of keeping the high vacuum of 7-22 min, blowing off the slag surface, keeping the flow of argon of 300-380 NL/min within the time period of keeping the high vacuum of 22-25 min, and breaking the vacuum after the high vacuum is kept for 25 min.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, controlling the soft blowing time to be within the range of 10-16 min according to the production rhythm, and standing the molten steel for 20min after the soft blowing is finished, wherein the flow of the argon is 20-30 NL/min.
In the 20CrMo steel obtained by the steps 1) to 6), the T.O is in the range of 7.2-10.0 ppm, and the grades of B-type and Ds-type inclusions are controlled within 1.0 grade.
Example 1
20CrMo, the mass percent omega [ C ] of C in the steel is 0.20%, and the steel is produced by adopting the technological process of molten iron desulphurization → LD → LF → VD. The method specifically comprises the following steps:
1) molten iron with the mass percentage of S being 0.019% is used as a raw material, KR is used for stirring and desulfurization, and the content of S in the molten iron before entering a furnace is 16 ppm;
2) smelting by using a top-bottom combined blown converter with the specification of 90T, wherein the mass percent omega C of the steel tapping C is 0.08 percent, the free oxygen content of the molten steel is 500ppm during the steel tapping, an aluminum cake is added into the converter for fast deoxidation according to the proportion of 1.65kg/T before the steel tapping amount reaches 30T, and the mass percent omega Al of Al refined to a station is 0.067 percent;
3) LF refining and slagging: lime and premelted refining slag are added into the furnace for slagging respectively at 500kg, silicon carbide is adopted for slag surface deoxidation in the LF refining process, the consumption is 180kg per furnace, quartz sand is adopted for 200kg per furnace for adjusting the components of the slag, the binary alkalinity R2 of the top slag of the calcium-aluminum-silicon molten steel before VD treatment is 3.2, and the mass percentages of the components are as follows: CaO: 51% SiO2：16％、MgO：11％、Al2O3：21％、S：0.32％、Tfe：0.68％；
4) The LF refining time is 120min, the argon flow in the molten steel temperature rising process is 210NL/min, the argon flow when chemical components are adjusted is 330NL/min, the waiting time except the molten steel temperature rising and component adjusting is 55NL/min, the LF refining process does not supplement aluminum, and the Al content is 0.043% during ladle hanging;
5) VD vacuum treatment: controlling VD processing time for 25min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and (3) adopting the flow of 20NL/min in the process from the beginning of VD treatment to the high vacuum, keeping the flow of argon of 520NL/min within 7min after the high vacuum is achieved, keeping the flow of argon of 70NL/min within a time period of high vacuum of 7-22 min, keeping the flow of argon of 300NL/min within a time period of high vacuum of 22-25 min, and breaking the vacuum after the high vacuum is kept for 25 min.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, wherein the argon flow is 22NL/min, the soft blowing time is 13min, and the molten steel is kept stand for 20min after the soft blowing is finished.
The 20CrMo steel obtained by the steps 1) to 6) has the oxygen content T.O of 9.6ppm and the grades of B-type and Ds-type inclusions in the steel are 1.0 grade.
Example 2
20CrMo, the mass percent omega [ C ] of C in the steel is 0.20%, and the steel is produced by adopting the technological process of molten iron desulphurization → LD → LF → VD. The method specifically comprises the following steps:
1) molten iron with the mass percentage omega S of 0.021% of S is taken as a raw material, KR is used for stirring and desulfurization, and the content of S in the molten iron before entering a furnace is 20 ppm;
2) smelting by using a top-bottom combined blown converter with the specification of 90T, wherein the mass percent omega C of the discharged steel C is 0.10 percent, the free oxygen content of molten steel is 330ppm during the discharging, aluminum cakes are added into the converter to perform rapid deoxidation according to the proportion of 1.49kg/T before the discharging amount is 30T, and the mass percent omega Al of Al refined to a station is 0.071 percent;
3) LF refining and slagging: lime and premelted refining slag are added into the furnace for slagging respectively at 500kg, silicon carbide is adopted for slag surface deoxidation in the LF refining process, the consumption is 170kg per furnace, quartz sand is adopted for 200kg per furnace for adjusting the components of the slag, the binary alkalinity R2 of the top slag of the calcium-aluminum-silicon molten steel before VD treatment is 3.85, and the mass percentages of the components are as follows: CaO: 50% SiO2：13.5％、MgO：10％、Al2O3：25％、S：0.7％、Tfe：0.8％；
4) The LF refining time is 105min, the argon flow is 260NL/min in the molten steel temperature rising process, the argon flow is 400NL/min when chemical components are adjusted, the waiting time except the molten steel temperature rising and component adjusting is 70NL/min, the LF refining process does not supplement aluminum, and the Al content is 0.052% in ladle hanging;
5) VD vacuum treatment: controlling VD processing time for 25min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and (3) adopting the flow rate of 25NL/min in the process from the beginning of VD treatment to the high vacuum, keeping the argon flow rate of 530NL/min within 7min after the high vacuum is achieved, keeping the argon flow rate of 90NL/min within a time period of 7-22 min for the high vacuum, keeping the argon flow rate of 340NL/min within a time period of 22-25 min for the high vacuum, and breaking the vacuum after the high vacuum is kept for 25 min.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, wherein the argon flow is 26NL/min, the soft blowing time is 15min, and after the soft blowing is finished, standing the molten steel for 20 min.
The 20CrMo steel obtained by the steps 1) to 6) has the oxygen content T.O of 8.3ppm and the grade of B-type and Ds-type inclusions in the steel is 1.0 grade.
Example 3
20CrMo, the mass percent omega [ C ] of C in the steel is 0.20%, and the steel is produced by adopting the technological process of molten iron desulphurization → LD → LF → VD. The method specifically comprises the following steps:
1) molten iron with the mass percentage omega S of 0.022% of S is adopted as a raw material, KR is used for stirring and desulfurizing, and the S content of the molten iron before entering a furnace is 19 ppm;
2) smelting by using a top-bottom combined blown converter with the specification of 90T, wherein the mass percent omega C of the steel tapping C is 0.11 percent, the free oxygen content of the molten steel is 310ppm during the steel tapping, an aluminum cake is added into the converter to be rapidly deoxidized according to the proportion of 1.43kg/T before the steel tapping amount reaches 30T, and the mass percent omega Al of Al refined to a station is 0.073 percent;
3) LF refining and slagging: lime and premelted refining slag are added into the furnace for slagging respectively at 500kg, silicon carbide is adopted for slag surface deoxidation in the LF refining process, the consumption is 160kg per furnace, quartz sand is adopted for 200kg per furnace for adjusting the components of the slag, the binary alkalinity R2 of the top slag of the calcium-aluminum-silicon molten steel before VD treatment is 4.3, and the mass percentages of the components are as follows: CaO: 55% SiO2：12.8％、MgO：8.3％、Al2O3：22.64％、S：0.76％、Tfe：0.5％；
4) The LF refining time is 90min, the argon flow is 310NL/min in the temperature rising process of the molten steel, the argon flow is 430NL/min when chemical components are adjusted, the waiting time except the temperature rising and component adjusting of the molten steel is 90NL/min, the LF refining process does not supplement aluminum, and the Al content is 0.047% during ladle hanging;
5) VD vacuum treatment: controlling VD processing time for 25min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and (3) adopting the flow of 30NL/min in the process from the beginning of VD treatment to the high vacuum, keeping the argon flow rate within 540NL/min after the high vacuum is reached and within 7min, keeping the argon flow rate within 100NL/min within a time period of high vacuum of 7-22 min, keeping the argon flow rate within 360NL/min within a time period of high vacuum of 22-25 min, and breaking the vacuum after the high vacuum is kept for 25 min.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, wherein the argon flow is 28NL/min, the soft blowing time is 16min, and after the soft blowing is finished, standing the molten steel for 20 min.
The 20CrMo steel obtained by the steps 1) to 6) has the oxygen content T.O of 7.7ppm and the grades of B-type and Ds-type inclusions in the steel are 1.0 grade.
Process for medium carbon steel
For medium-carbon large-scale forging alloy steel 42CrMo4, the mass percent omega [ C ] of C in the steel is 0.42%, and the steel is produced by adopting the technological process of molten iron desulphurization → LD → LF → VD. The method specifically comprises the following steps:
1) molten iron with the mass percent of S being less than or equal to 0.025 percent is adopted as a raw material, KR is used for stirring and desulfurization, and the S content of the molten iron before charging is less than or equal to 30 ppm;
2) smelting by using a top-bottom combined blowing converter with the specification of 90T, wherein the mass percent omega C of the tapping C is in the range of 0.09% -0.15%, the free oxygen content of molten steel is 220-400 ppm during tapping, aluminum blocks are added before the tapping amount is 30T according to the proportion range of 1.30-1.50 kg/T for precipitation and deoxidation, and the mass percent omega Al of Al refined to a station is in the range of 0.053% -0.070%;
3) LF refining and slagging: adding 450kg of lime into the converter and 500kg of premelted refining slag into the converter for slagging after aluminum deoxidation in the tapping process of the converter, wherein silicon carbide is adopted for slag surface deoxidation in the LF refining process, the dosage is 130-150 kg per furnace, and quartz sand 200 is adoptedAdjusting the components of the slag in kg/furnace, wherein the binary alkalinity R2 of the top slag of the calcium-aluminum-silicon molten steel before VD treatment is within the range of 2.6-3.8, and the mass percentages of the components are as follows: CaO: 47% -53% of SiO2：14％～18％、MgO：9％～13％、Al2O3：22％～27％、S：0.3％～0.9％、Tfe：0.2～0.6％；
4) Controlling the LF refining time and the stirring strength, controlling the refining time to be 60-120 min, controlling the argon flow to be 200-350 NL/min in the temperature rising process of the molten steel, adjusting the argon flow to be 400-550 NL/min when chemical components are adjusted, controlling the argon flow to be 80-150 NL/min in the waiting time except for the temperature rising and component adjustment of the molten steel, not supplementing aluminum in the LF refining process, and enabling the Al content to be 0.036% -0.053% in the ladle hanging process;
5) VD vacuum treatment: controlling VD processing time to be 28min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and (3) adopting the flow of 30-40 NL/min in the process from the beginning of VD treatment to the high vacuum, blowing off the slag surface within 9min of the argon flow of 530-570 NL/min after the high vacuum is reached, keeping the argon flow of 70-130 NL/min in the time period of 9-25 min of high vacuum, keeping the argon flow of 350-400 NL/min in the time period of 25-28 min of high vacuum, and keeping the high vacuum for 28min to break the air.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, controlling the soft blowing time to be within the range of 15-20 min according to the production rhythm, and standing the molten steel for 25min after the soft blowing is finished, wherein the flow of the argon is 25-35 NL/min.
The 42CrMo4 steel obtained by the steps 1) to 6) has T.O within the range of 6.1-9.2 ppm, B-type inclusion grade within 1.0 grade and Ds-type inclusion grade within 0.5 grade.
Example 4
42CrMo4 alloy steel, wherein the mass percent omega [ C ] of C in the steel is 0.42%, and the alloy steel is produced by adopting a molten iron desulphurization → LD → LF → VD technological process. The method specifically comprises the following steps:
1) molten iron with the mass percentage omega S of 0.020% is adopted as a raw material, KR is used for stirring and desulfurizing, and the content of S in the molten iron before entering a furnace is 22 ppm;
2) smelting by using a top-bottom combined blown converter with the specification of 90T, wherein the mass percent omega C of the tapping C is 0.10 percent, the free oxygen content of molten steel is 340ppm during tapping, an aluminum block is added before the tapping amount reaches 30T according to the proportion range of 1.45kg/T for precipitation and deoxidation, and the mass percent omega Al of Al refined to a station is 0.059 percent;
3) LF refining and slagging: adding 450kg of lime into the converter and 500kg of premelted refining slag into the converter for slagging after aluminum deoxidation in the converter tapping process, wherein silicon carbide is adopted for slag surface deoxidation in the LF refining process, the consumption is 150kg per furnace, the slag components are adjusted by adopting 200kg of quartz sand per furnace, the binary alkalinity R2 of the calcium-aluminum-silicon molten steel top slag before VD treatment is 2.9, and the mass percentages of the components are as follows: CaO: 50.2% SiO2：17.3％、MgO：9.3％、Al2O3：22.32％、S：0.43％、Tfe：0.58％；
4) The LF refining time is 110min, the argon flow is 230NL/min in the molten steel temperature rising process, the argon flow is 460NL/min when chemical components are adjusted, the waiting time except the molten steel temperature rising and component adjusting is 90NL/min, the LF refining process does not supplement aluminum, and the Al content is 0.039% during ladle hanging;
5) VD vacuum treatment: controlling VD processing time to be 28min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and (3) adopting the flow of 32NL/min in the process from the beginning of VD treatment to the high vacuum, keeping the high vacuum within 9min, blowing off the slag surface by the argon flow of 540NL/min, keeping the high vacuum within 9-25 min, keeping the high vacuum within 25-28 min, keeping the argon flow of 360NL/min, and keeping the high vacuum for 28min to break the vacuum.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, controlling the flow of argon at 27NL/min, controlling the soft blowing time at 16min, and standing the molten steel for 25min after the soft blowing is finished.
The 42CrMo4 steel obtained by the steps 1) to 6) has the oxygen content T.O of 8.5ppm, the B-type inclusion grade of 1.0 grade and the Ds-type inclusion grade of 0.5 grade.
Example 5
42CrMo4 alloy steel, wherein the mass percent omega [ C ] of C in the steel is 0.42%, and the alloy steel is produced by adopting a molten iron desulphurization → LD → LF → VD technological process. The method specifically comprises the following steps:
1) molten iron with the mass percentage omega S of 0.022% of S is adopted as a raw material, KR is used for stirring and desulfurizing, and the S content of the molten iron before charging is 26 ppm;
2) smelting by using a top-bottom combined blown converter with the specification of 90T, wherein the mass percent omega C of the tapping C is 0.12 percent, the free oxygen content of molten steel during tapping is 280ppm, an aluminum block is added before the tapping amount reaches 30T according to the proportion range of 1.37kg/T for precipitation and deoxidation, and the mass percent omega Al of Al refined to a station is 0.064 percent;
3) LF refining and slagging: adding 450kg of lime into the converter and 500kg of premelted refining slag into the converter for slagging after aluminum deoxidation in the converter tapping process, wherein silicon carbide is adopted for slag surface deoxidation in the LF refining process, the using amount of the silicon carbide is 140kg per furnace, the slag components are adjusted by adopting 200kg of quartz sand per furnace, the binary alkalinity R2 of the calcium-aluminum-silicon molten steel top slag before VD treatment is 3.3, and the mass percentages of the components are as follows: CaO: 49.2% of SiO2：14.8％、MgO：10.3％、Al2O3：24.58％、S：0.66％、Tfe：0.46％；
4) The LF refining time is 90min, the argon flow is 300NL/min in the molten steel temperature rising process, the argon flow is 490NL/min when chemical components are adjusted, the argon flow is 110NL/min when the molten steel is waited for the time except for temperature rising and component adjustment, the LF refining process does not supplement aluminum, and the Al content is 0.042% when the ladle is hung;
5) VD vacuum treatment: controlling VD processing time to be 28min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and the flow rate is 35NL/min in the process from the beginning of VD treatment to the high vacuum, the argon flow rate is 550NL/min within 9min after the high vacuum is achieved, the slag surface is blown away by the argon flow rate of 100NL/min within the time period of high vacuum maintenance of 9-25 min, the argon flow rate is 380NL/min within the time period of high vacuum maintenance of 25-28 min, and the high vacuum is broken for 28 min.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, controlling the flow of argon to be 30NL/min, controlling the soft blowing time to be 17min, and standing the molten steel for 25min after the soft blowing is finished.
The 42CrMo4 steel obtained by the steps 1) to 6) has the oxygen content T.O of 7.4ppm, the B-type inclusion grade of 0.5 grade and the Ds-type inclusion grade of 0.5 grade.
Example 6
42CrMo4 alloy steel, wherein the mass percent omega [ C ] of C in the steel is 0.42%, and the alloy steel is produced by adopting a molten iron desulphurization → LD → LF → VD technological process. The method specifically comprises the following steps:
1) molten iron with the mass percentage omega S of 0.025 percent of S is adopted as a raw material, KR is used for stirring and desulfurization, and the content of S in the molten iron before charging is 30 ppm;
2) smelting by using a top-bottom combined blown converter with the specification of 90T, wherein the mass percent omega C of the steel tapping C is 0.14 percent, the free oxygen content of the molten steel is 250ppm during the steel tapping, an aluminum block is added before the steel tapping amount reaches 30T according to the proportion range of 1.32kg/T for precipitation and deoxidation, and the mass percent omega Al of Al refined to a station is 0.066 percent;
3) LF refining and slagging: adding 450kg of lime into the converter and 500kg of premelted refining slag into the converter for slagging after aluminum deoxidation in the converter tapping process, wherein silicon carbide is adopted for slag surface deoxidation in the LF refining process, the consumption is 130kg per furnace, the slag components are adjusted by adopting 200kg of quartz sand into the furnace, the binary alkalinity R2 of the calcium-aluminum-silicon molten steel top slag before VD treatment is 3.7, and the mass percentages of the components are as follows: CaO: 52.9% SiO2：14.3％、MgO：9.1％、Al2O3：22.6％、S：0.78％、Tfe：0.32％；
4) The LF refining time is 70min, the argon flow is 340NL/min in the molten steel temperature rising process, the argon flow is 530NL/min when chemical components are adjusted, the waiting time except the molten steel temperature rising and component adjusting is 140NL/min, the LF refining process does not supplement aluminum, and the Al content is 0.040% during ladle hanging;
5) VD vacuum treatment: controlling VD processing time to be 28min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and in the process from the beginning of VD treatment to high vacuum, the flow rate is 40NL/min, the argon flow rate is 560NL/min within 9min after high vacuum is achieved, the slag surface is blown away by the argon flow rate of 120NL/min within the time period of high vacuum maintenance of 9-25 min, the argon flow rate of 400NL/min within the time period of high vacuum maintenance of 25-28 min, and the high vacuum is broken for 28 min.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, controlling the flow of argon to be 30NL/min, controlling the soft blowing time to be 19min, and standing the molten steel for 25min after the soft blowing is finished.
The 42CrMo4 steel obtained by the steps 1) to 6) has the oxygen content T.O of 6.5ppm, the B-type inclusion grade of 0.5 grade and the Ds-type inclusion grade of 0 grade.
Process for high carbon steel
For B6 series high-carbon wear-resistant ball steel, the mass percent omega C of C in the steel is 0.82%, and the steel is produced by adopting the process flow of molten iron desulphurization → LD → LF → VD. The method specifically comprises the following steps:
1) molten iron with the mass percent of S being less than or equal to 0.020 percent is adopted as a raw material, KR is used for stirring and desulfurizing, and the S content of the molten iron before entering the furnace is less than or equal to 20 ppm;
2) smelting by using a top-bottom combined blowing converter with the specification of 90T, wherein the mass percent omega C of the tapping C is in the range of 0.10-0.15%, the free oxygen content of molten steel is 150-350 ppm during tapping, aluminum blocks are added according to the proportion range of 1.25-1.40 kg/T before the tapping amount is 30T for precipitation and deoxidation, and the mass percent omega Al of Al refined to a station is in the range of 0.050-0.066%;
3) LF refining and slagging: adding 400kg of lime and 450kg of premelted refining slag after aluminum deoxidation in the converter tapping process for slagging, wherein silicon carbide is adopted for slag surface deoxidation in the LF refining process, the using amount is 100-130 kg/furnace, 200kg of quartz sand is adopted for furnace slag component adjustment, the binary alkalinity R2 of the calcium-aluminum-silicon molten steel top slag before VD treatment is within the range of 2.2-3.1, and the mass percentages of the components are as follows: CaO: 42% -47% of SiO2：15％～19％、MgO：10％～14％、Al2O3：25％～30％、S：0.1％～0.4％、Tfe：0.5～0.8％；
4) Controlling the LF refining time and the stirring strength, controlling the refining time to be 100-150 min, controlling the argon flow to be 250-400 NL/min in the temperature rising process of the molten steel, adjusting the argon flow to be 500-600 NL/min when chemical components are adjusted, controlling the argon flow to be 120-200 NL/min in the waiting time except for the temperature rising and component adjustment of the molten steel, not supplementing aluminum in the LF refining process, and enabling the Al content to be 0.030% -0.048% in the ladle hanging process;
5) VD vacuum treatment: controlling VD processing time for 32min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: the flow rate is 40-50 NL/min in the process from the beginning of VD treatment to the high vacuum, the flow rate of argon is 550-600 NL/min within 11min after the high vacuum is achieved, the flow rate of argon is 100-150 NL/min within the time period of high vacuum maintenance for 11-28 min, the slag surface is blown off, the flow rate of argon is 400-500 NL/min within the time period of high vacuum maintenance for 28-32 min, and the high vacuum is broken for 32 min.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, controlling the soft blowing time to be within the range of 15-20 min according to the production rhythm, and standing the molten steel for 30min after the soft blowing is finished, wherein the flow of the argon is 35-45 NL/min.
In the B6 series high-carbon steel obtained by the steps 1) to 6), the T.O is in the range of 4.0-6.6 ppm, and the grade of the B-type and Ds-type inclusions is controlled within 0.5.
Example 7
B6 steel, wherein the mass percent omega C of C in the steel is 0.82%, and the steel is produced by adopting the technological process of molten iron desulphurization → LD → LF → VD. The method specifically comprises the following steps:
1) molten iron with the mass percentage omega S of 0.018 percent of S is used as a raw material, KR is used for stirring and desulfurizing, and the content of S in the molten iron before charging is 15 ppm;
2) smelting by using a top-bottom combined blown converter with the specification of 90T, wherein the mass percent omega C of the tapping C is 0.11 percent, the free oxygen content of molten steel during tapping is 320ppm, an aluminum block is added before the tapping amount reaches 30T according to the proportion range of 1.38kg/T for precipitation and deoxidation, and the mass percent omega Al of Al refined to a station is 0.055 percent;
3) LF refining and slagging: adding lime 400 kg/furnace and premelted refining slag 450 kg/furnace for slagging after aluminum deoxidation in the converter tapping process, wherein silicon carbide is adopted for slag surface deoxidation in the LF refining process, the consumption is 130 kg/furnace, the slag components are adjusted by adopting quartz sand 200 kg/furnace, the binary alkalinity R2 of the calcium-aluminum-silicon molten steel top slag before VD treatment is within the range of 2.4, and the mass percentages of the components are as follows: CaO: 43.4% of SiO2：18.1％、MgO：12.5％、Al2O3：25.0％、S：0.27％、Tfe：0.73％；
4) Controlling the LF refining time and the stirring strength, controlling the refining time to be 150min, controlling the argon flow to be 290NL/min in the temperature rising process of the molten steel, adjusting the argon flow to be 520NL/min when chemical components are adjusted, controlling the argon flow to be 130NL/min when the molten steel is not heated and is not adjusted to be components, not supplementing aluminum in the LF refining process, and controlling the Al content to be 0.037% in ladle hanging;
5) VD vacuum treatment: controlling VD processing time for 32min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and adopting the flow rate of 42NL/min in the process from the beginning of VD treatment to the high vacuum, keeping the argon flow rate of 550NL/min within 11min after the high vacuum is reached, blowing off the slag surface by the argon flow rate of 110NL/min within the time period of keeping the high vacuum for 11-28 min, keeping the argon flow rate of 430NL/min within the time period of keeping the high vacuum for 28-32 min, and keeping the high vacuum for 32min to break the vacuum.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, controlling the flow of argon to be 38NL/min, controlling the soft blowing time to be 17min, and standing the molten steel for 30min after the soft blowing is finished.
In the B6 series high-carbon steel obtained by the steps 1) to 6), the oxygen content T.O in the steel is 6.1ppm, and the grade of the B-type and Ds-type inclusions is 0.5 grade.
Example 8
B6 steel, wherein the mass percent omega C of C in the steel is 0.82%, and the steel is produced by adopting the technological process of molten iron desulphurization → LD → LF → VD. The method specifically comprises the following steps:
1) molten iron with the mass percentage omega S of 0.019% of S is used as a raw material, KR is used for stirring and desulfurization, and the content of S in the molten iron before entering a furnace is 18 ppm;
2) smelting by using a top-bottom combined blown converter with the specification of 90T, wherein the mass percent omega C of the steel tapping C is 0.14 percent, the free oxygen content of the molten steel during the steel tapping is 210ppm, an aluminum block is added before the steel tapping amount reaches 30T according to the proportion range of 1.29kg/T for precipitation and deoxidation, and the mass percent omega Al of Al refined to a station is 0.064 percent;
3) LF refining and slagging: adding lime 400 kg/furnace and premelted refining slag 450 kg/furnace for slagging after aluminum deoxidation in the converter tapping process, wherein silicon carbide is adopted for slag surface deoxidation in the LF refining process, the using amount is 120 kg/furnace, the slag components are adjusted by adopting quartz sand 200 kg/furnace, the binary alkalinity R2 of the calcium-aluminum-silicon molten steel top slag before VD treatment is within the range of 2.7, and the mass percentages of the components are as follows: CaO: 45.4% of SiO2：16.8％、MgO：11.3％、Al2O3：25.6％、S：0.33％、Tfe：0.57％；
4) Controlling the LF refining time and the stirring strength, controlling the refining time to be 110min, controlling the argon flow to be 330NL/min in the temperature rising process of the molten steel, adjusting the argon flow to be 540NL/min when chemical components are adjusted, controlling the argon flow to be 170NL/min when the molten steel is not heated and is not adjusted to be components, not supplementing aluminum in the LF refining process, and enabling the Al content to be 0.045% in ladle hanging;
5) VD vacuum treatment: controlling VD processing time for 32min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and adopting the flow of 46NL/min in the process from the beginning of VD treatment to the high vacuum, keeping the argon flow 580NL/min within 11min after the high vacuum is reached, blowing off the slag surface by the argon flow 130NL/min within the time period of keeping the high vacuum for 11-28 min, keeping the argon flow 470NL/min within the time period of keeping the high vacuum for 28-32 min, and keeping the high vacuum for 32min to break the vacuum.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, controlling the flow of argon to be 42NL/min, controlling the soft blowing time to be 18min, and standing the molten steel for 30min after the soft blowing is finished.
In the B6 series high-carbon steel obtained by the steps 1) to 6), the oxygen content T.O in the steel is 5.3ppm, the grade of B-type inclusion is 0.5 grade, and the grade of Ds-type inclusion is 0 grade.
Example 9
B6 steel, wherein the mass percent omega C of C in the steel is 0.82%, and the steel is produced by adopting the technological process of molten iron desulphurization → LD → LF → VD. The method specifically comprises the following steps:
1) molten iron with the mass percentage omega S of 0.020% is adopted as a raw material, KR is used for stirring and desulfurizing, and the content of S in the molten iron before entering a furnace is 20 ppm;
2) smelting by using a top-bottom combined blown converter with the specification of 90T, wherein the mass percent omega C of the steel tapping C is 0.15 percent, the free oxygen content of the molten steel is 170ppm during the steel tapping, an aluminum block is added before the steel tapping amount reaches 30T according to the proportion range of 1.25kg/T for precipitation and deoxidation, and the mass percent omega Al of the Al refined to the station is 0.060 percent;
3) LF refining and slagging: adding lime 400 kg/furnace and premelted refining slag 450 kg/furnace for slagging after aluminum deoxidation in the converter tapping process, wherein silicon carbide is adopted for slag surface deoxidation in the LF refining process, the using amount is 100 kg/furnace, the slag components are adjusted by adopting quartz sand 200 kg/furnace, the binary alkalinity R2 of the calcium-aluminum-silicon molten steel top slag before VD treatment is 3.0, and the mass percentages of the components are as follows: CaO: 45.9% of SiO2：15.3％、MgO：10.1％、Al2O3：27.5％、S：0.43％、Tfe：0.77％；
4) Controlling the LF refining time and the stirring strength, controlling the refining time to be 140min, controlling the argon flow to be 380NL/min in the temperature rising process of the molten steel, adjusting the argon flow to be 590NL/min when chemical components are adjusted, controlling the argon flow to be 200NL/min when the molten steel is not heated and is not adjusted to be components, not supplementing aluminum in the LF refining process, and controlling the Al content to be 0.039% in ladle hanging;
5) VD vacuum treatment: controlling VD processing time for 32min, wherein the mode of bottom blowing argon stirring intensity in the processing process is as follows: and (3) adopting the flow of 50NL/min in the process from the beginning of VD treatment to the high vacuum, keeping the high vacuum within 11min, blowing away the slag surface by the argon flow of 150NL/min within 11-28 min, keeping the high vacuum within 28-32 min, and breaking the vacuum by the argon flow of 480NL/min within 32 min.
6) Soft blowing and standing: immediately adjusting the argon blowing mode to a soft blowing mode after the VD breaks the air, controlling the flow of argon to be 45NL/min, controlling the soft blowing time to be 20min, and standing the molten steel for 30min after the soft blowing is finished.
In the B6 series high-carbon steel obtained by the steps 1) to 6), the oxygen content T.O in the steel is 4.6ppm, the grade of B-type inclusions is 0 grade, and the grade of Ds-type inclusions is 0 grade.

Claims (5)

1. A process method for smelting high-purity steel by using VD (vacuum distillation) vacuum treatment equipment is characterized by comprising the following steps of:
1) pre-desulfurization of molten iron: low-sulfur molten iron is adopted, KR stirring desulfurization is carried out, and S in the molten iron before entering the furnace is ensured to be less than or equal to 30 ppm;
2) converting in a converter: smelting by using a top-bottom combined blown converter with the specification of 90T, ensuring that the mass percentage omega C of the tapped C is more than or equal to 0.08 percent, and precipitating and deoxidizing the tapped C by using aluminum;
3) LF refining: the refining time is 60-150 min, the flow of the stirring argon is 50-600 NL/min, the deoxidation and slagging auxiliary material is adopted to adjust the components of the slag, the alkalinity of the final refining slag is 2.0-4.5, the mass percent omega Al of the refining ladle Al is controlled to be 0.030% -0.060%,
adding 500kg of lime and 500kg of premelted refining slag respectively after aluminum deoxidation in the converter tapping process, performing slag formation in an LF (ladle furnace) refining process by adopting silicon carbide for slag surface deoxidation, wherein the silicon carbide consumption is 180kg per furnace, and at least 200kg of quartz sand is adopted for furnace slag component adjustment to form calcium-aluminum-silicon molten steel top slag before VD treatment;
4) VD vacuum treatment: controlling VD processing time within the range of 20-35 min according to the requirements of specific alloy components of steel grades, bottom blowing argon gas for stirring in the processing process, and controlling the stirring strength according to a mode of 'strong → weak → strong', wherein the specific steps are as follows: after the VD treatment is started to reach the high vacuum, weak stirring with the flow rate of below 50NL/min is adopted, after the high vacuum is reached, strong stirring with the flow rate of 500-600 NL/min is adopted in the first one-third time period in the high vacuum maintaining process, then weak stirring with the flow rate of 50-160 NL/min is adopted in the third to seventh eighth time period, strong stirring with the flow rate of 300-500 NL/min is adopted in the last one-eighth time period in the high vacuum maintaining process, and the high vacuum is broken after the high vacuum maintaining time reaches the control requirement;
5) soft blowing and standing: and removing impurities in the steel by combining soft blowing and molten steel standing, carrying out soft blowing after VD treatment is finished, wherein the soft blowing time is 10-20 min, removing larger particle impurities, and standing the molten steel for 20-35 min after the soft blowing is finished, so that floating of small particle impurities is promoted.
2. The process method for smelting high-purity steel by using VD vacuum processing equipment as claimed in claim 1, characterized in that: in the step 1), molten iron with the mass percent of S being less than or equal to 0.025 percent is used as a raw material.
3. The process method for smelting high-purity steel by using VD vacuum processing equipment as claimed in claim 1, characterized in that: in the step 2), the free oxygen of the molten steel tapped from the converter is controlled within 500ppm, when the tapping amount is approximately one third, aluminum blocks are added into a ladle according to the proportion of 1.25-1.65 kg/t for rapid deoxidation, and the mass percent of Al refined to a station is controlled to be 0.050% -0.080%.
4. The process method for smelting high-purity steel by using VD vacuum processing equipment as claimed in claim 1, characterized in that: in the step 3), different argon stirring strengths are implemented in stages in the LF refining process, and specifically: in the process of heating the molten steel, the flow of argon is 100-400 NL/min, the flow of argon is 300-600 NL/min when chemical components are adjusted, and the flow of argon is 50-200 NL/min when the molten steel waits.
5. The process method for smelting high-purity steel by using VD vacuum processing equipment as claimed in claim 1, characterized in that: the top slag of the calcium-aluminum-silicon molten steel comprises CaO and SiO2、MgO、Al2O3S and Tfe, wherein the mass percent of each component is as follows: CaO: 42% -55% of SiO2：12%～21%、MgO：8%～15%、Al2O3：20%～30%、S：0.2%～1.0%、TFe ：0~0.8%。
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CN113528748B (en) * 2021-06-18 2022-11-18 首钢集团有限公司 Method for controlling fine inclusions in ultra-low sulfur steel
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