CN115505685B - Method for reducing oxidizing hazard of RH top slag of ultra-low carbon steel - Google Patents
Method for reducing oxidizing hazard of RH top slag of ultra-low carbon steel Download PDFInfo
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- CN115505685B CN115505685B CN202211079224.7A CN202211079224A CN115505685B CN 115505685 B CN115505685 B CN 115505685B CN 202211079224 A CN202211079224 A CN 202211079224A CN 115505685 B CN115505685 B CN 115505685B
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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
- C21C7/10—Handling in a vacuum
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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
- C21C7/0006—Adding metallic additives
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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
- C21C7/06—Deoxidising, e.g. killing
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention belongs to the technical field of steelmaking, and relates to a method for reducing the oxidative hazard of RH top slag of ultra-low carbon steel. According to the method, no slag forming material is added from converter tapping to before the ladle enters RH; adding slag forming materials into a vacuum chamber after RH aluminum adding final deoxidation, wherein the slag amount is calculated according to the slag forming thickness of 30-100 mm in a ladle; no deoxidizing modifier is added after RH is broken. The invention does not secondary pollution to molten steel, slag-forming materials added into the RH vacuum chamber enter the steel ladle through the lower part of the dipping pipe and are mainly adhered between the original top slag and the molten steel to form an isolation layer, thereby greatly reducing the oxidative hazard of the original top slag. The invention does not need to increase equipment, and has simple operation and strong universality.
Description
Technical Field
The invention belongs to the technical field of steelmaking, and relates to a method for reducing the oxidative hazard of RH top slag of ultra-low carbon steel.
Background
The ultra-low carbon steel used in the industries of automobiles, household appliances and the like has high requirements on the cleanliness of molten steel, and the control of the oxidizing property of RH top slag is very critical. Practice shows that the RH top slag has low oxidability, so that the number of inclusions in steel is small, the continuous casting aluminum loss is small, the molten steel has good castability, and the defect rate of the plate is low.
The slag in the converter is inevitably introduced into the ladle during tapping because of the high oxidizing property of the slag due to deep decarburization in the later stage of smelting. In order to complete the deep decarburization task, enough dissolved oxygen is required in the molten steel, and RH top slag is oxidized by oxygen in the molten steel, which is a difficulty in restricting the reduction of the oxidizing property of the ultra-low carbon steel slag. Therefore, in the tapping process, a deoxidizing modifier needs to be added into the top slag before the ladle enters RH, but the oxidizing property of the top slag is still higher after the RH treatment, and the method has larger hazard.
In the middle and later stages of RH treatment, the top slag surface is close to or even has crusted, and if the deoxidizing modifier is added again after RH deoxidation or after the treatment, the modification effect is not obvious. The method is characterized in that the RH outbound top slag TFe of the ultra-low carbon steel is controlled to be below 8 percent, and 80 percent of the heat is controlled to be below 6 percent, namely the current top level, so that the RH outbound top slag TFe is difficult to be stably controlled to be below 3 percent. Chinese patent application publication No. CN 109252010a discloses "smelting method for controlling oxidizing property of IF steel top slag", RH outbound top slag oxidizing TFe 6-8%; the Chinese patent application with publication number of CN 105755200A discloses a ladle top slag modification method, and the modified ladle top slag TFe is 3.9-6.7%. The technical effect achieved by these two patent applications also indicates the level of control of the RH outbound top slag TFe. At this time, the ladle argon blowing stirring can improve the modification effect, but can cause secondary pollution of molten steel, and is also not preferable.
In summary, the current method of reducing the oxidizing property of RH top slag by deoxidizing modification has not been ideal in controlling the oxidizing hazard of top slag.
Disclosure of Invention
In order to solve the technical problems, the invention provides a method for reducing the oxidization hazard of the RH top slag of the ultra-low carbon steel, which can not only greatly reduce the oxidization of the RH top slag under the condition of no secondary pollution to molten steel, but also isolate the top slag with high oxidization from the molten steel so as to reduce the hazard of the oxidization of the top slag.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
a method for reducing RH top slag oxidizing hazard of ultra-low carbon steel, which is characterized in that no slag forming material is added from converter tapping to before steel ladle enters RH; adding slag forming materials into a vacuum chamber after RH aluminum adding final deoxidation, wherein the slag amount is calculated according to the slag forming thickness of 30-100 mm in a ladle; no deoxidizing modifier is added after RH is broken.
The slag-forming material is lime, fluorite and bauxite or synthetic slag, and the granularity is 5-30 mm.
The slag-forming material comprises CaO/Al in slag after slag formation 2 O 3 =1.5±0.3 as control target.
When the slag forming thickness in the ladle is less than or equal to 70mm, adding slag forming materials for 2 times; when the slag forming thickness in the ladle is more than 70mm, adding slag forming materials for 3 times; each time interval is more than 1min.
The weight content of C in the ultra-low carbon steel is less than or equal to 0.02 percent.
The beneficial effects of adopting above-mentioned technical scheme to produce lie in: the slag-forming material of the invention is added after RH final deoxidation and can be melted into non-oxidizing slag. Slag-forming materials added into the RH vacuum chamber enter the steel ladle through the lower part of the dipping pipe and are mainly adhered between the original top slag and molten steel to form an isolation layer, so that the oxidative hazard of the original top slag is greatly reduced. The larger the slag making amount is, the thicker the slag layer is, and the smaller the influence of the original top slag oxidizing property on the bottom slag and molten steel is. When TFe in the bottom slag of the top slag is less than or equal to 3%, the oxidizing hazard of the top slag is small and is basically eliminated; when TFe in the bottom slag is less than or equal to 0.5%, the oxidizing hazard of RH top slag can be completely eliminated. After the RH molten steel of the invention is discharged, the TFe of the top slag is reduced by 40-70% compared with the conventional deoxidization modification process, and the TFe in the bottom slag of the top slag is less than or equal to 3%.
The invention can be used singly and matched with the conventional deoxidization and modification (namely, only the deoxidization modifier for converter tapping is reserved and the tapping slag charge and the outbound modifier are cancelled), so that better effect can be achieved.
The slag-forming material added into the RH vacuum chamber has isolation effect, and the modifier is not needed to be added after the slag-forming material is broken.
The invention does not need to increase equipment, and has simple operation and strong universality.
Detailed Description
A method for reducing the oxidative damage of RH top slag of ultra-low carbon steel is suitable for ultra-low carbon steel with the C weight content less than or equal to 0.02 percent. The method is produced by adopting a process flow of molten iron desulfurization-converter-RH-slab continuous casting, and is specifically implemented in the following manner (the part which is not illustrated here is operated conventionally):
(1) The converter stops slag and taps, and no slag forming material is added from tapping to before the ladle enters RH.
(2) Adding slag-forming materials lime, fluorite and bauxite or synthetic slag with granularity of 5-30 mm into a vacuum chamber for slag formation after RH aluminum addition final deoxidation, wherein the slag mixture ratio is CaO/Al in slag after slag formation 2 O 3 =1.5±0.3 and is easily fused into control target calculation. The slag charge quantity is calculated according to the thickness of slag formed in a steel ladle of 30-100 mm, and the concrete adding quantity can be comprehensively determined by combining TFe value in slag, steel grade castability and quality requirement; the TFe value in the slag is high, the steel grade has poor castability and high quality requirement, and is added according to the upper limit, otherwise, the TFe value in the slag is added according to the lower limit. When the slag forming thickness in the ladle is less than or equal to 70mm, adding slag forming materials for 2 times; when the slag forming thickness in the ladle is more than 70mm, adding slag forming materials for 3 times; and (3) melting by using molten steel circulation in the RH vacuum chamber at intervals of more than 1min each time, so as to ensure that molten steel enters the ladle after melting.
(3) No deoxidizing modifier is added after RH is broken.
After the RH molten steel comes out, TFe in top slag and bottom slag is less than or equal to 3%, and TFe in top slag is reduced by 40-70% compared with the conventional deoxidization modification process.
Example 1
According to the method, IF steel with the weight content of C less than or equal to 0.005% is smelted in a converter-RH-slab continuous casting production line. The main operation is as follows:
no slag forming material is added from converter tapping to RH entering; adding 2460kg of slag forming materials into a vacuum chamber after adding aluminum into RH final deoxidization for 2min, wherein the thickness of slag layer in a ladle is increased by 68mm, wherein the weight of lime is 1280kg, bauxite is 880kg and fluorite is 300 kg; the slag forming material was added in 2 batches of 1230kg each, with 2min intervals. No modifier is added after the breaking.
Calculating the weight content of TFe in the whole top slag after RH station outlet to be 2.6%; taking out the lower slag sample, wherein the TFe weight content is 0.9%, caO/Al 2 O 3 1.4; the molten steel has good castability, and the full casting continuous casting 7 furnaces have no water gap.
Example 2
According to the method, SPHE steel with the weight content of C of 0.010% is smelted and produced in a converter-RH-slab continuous casting production line. The main operation is as follows:
no slag forming material is added from converter tapping to RH entering; TFe in RH inbound slag is 4.8%, 1540kg of slag forming material is added into a vacuum chamber after RH final deoxidization and aluminum addition are carried out for 2min, wherein 740kg of lime, 600kg of synthetic slag and 200kg of fluorite are added, and the thickness of a slag layer in a ladle is increased by 42mm; the slag forming material was added in 2 batches of 770kg each, with 1min intervals. No modifier is added after the breaking.
Calculating the weight content of TFe in the whole top slag after RH station outlet to be 2.4%; taking out the lower slag sample, wherein the TFe weight content is 1.1%, caO/Al 2 O 3 1.3; the molten steel has good castability, and the full casting continuous casting 7 furnaces have no water gap.
Example 3
According to the method, SPHE steel with the weight content of C less than or equal to 0.020% is smelted in a converter-RH-slab continuous casting production line. The main operation is as follows:
no slag forming material is added from converter tapping to RH entering; TFe in RH inbound slag is 4.5%, 1090kg of slag forming material is added into a vacuum chamber after RH final deoxidization and aluminum addition are carried out for 3min, wherein 630kg of lime, 210kg of bauxite and 250kg of fluorite are added into a ladle, and the thickness of a slag layer is increased by 30mm; the slag forming material was added in 2 batches of 545kg each, with 1 minute intervals. No modifier is added after the breaking.
Calculating RThe weight content of TFe in the whole top slag after H comes out of the station is 2.9%; taking out the lower slag sample, wherein the TFe weight content is 1.3%, caO/Al 2 O 3 1.4; the molten steel has good castability, and the full casting continuous casting 7 furnaces have no water gap.
Example 4
According to the method, IF steel with the weight content of C less than or equal to 0.003% is smelted in a converter-RH-slab continuous casting production line. The main operation is as follows:
no slag forming material is added from converter tapping to RH entering; TFe in RH inbound slag is 7.2%, 3000kg of slag forming material is added into a vacuum chamber after RH final deoxidization and aluminum addition are carried out for 3min, wherein the thickness of slag layer in a ladle is increased by 82mm, and the slag layer comprises 1700 kg of lime kg, 790kg of bauxite and 510kg of fluorite; the slag forming material was added in 3 batches of 1000kg each, with 2min intervals. No modifier is added after the breaking.
Calculating the weight content of TFe in the whole top slag after RH station outlet to be 2.6%; taking out the lower slag sample, wherein the TFe weight content is 0.5%, caO/Al 2 O 3 1.7; the molten steel has good castability, and the full casting continuous casting 7 furnaces have no water gap.
Example 5
According to the method, IF steel with the weight content of C less than or equal to 0.003% is smelted in a converter-RH-slab continuous casting production line. The main operation is as follows:
no slag forming material is added from converter tapping to RH entering; TFe in RH inbound slag is 7.8%, 3640kg of slag forming material is added into a vacuum chamber after RH final deoxidization and aluminum addition are carried out for 4min, wherein the thickness of slag layer in a ladle is increased by 100mm, and the slag layer comprises 2050kg of lime, 980kg of bauxite and 610kg of fluorite; the slag forming material was added in 3 batches of 1213.3kg each, with 2min intervals. No modifier is added after the breaking.
Calculating the weight content of TFe in the whole top slag after RH station outlet to be 2.5%; taking out the lower slag sample, wherein the TFe weight content is 0.4%, caO/Al 2 O 3 1.75; the molten steel has good castability, and the full casting continuous casting 7 furnaces have no water gap.
According to statistics, IF steel is produced by adopting the method on the basis of conventional operation in a certain steel plant, RH outlet top slag TFe is reduced by 40-70% compared with a conventional deoxidization modification process, bottom slag TFe is totally lower than 3%, total oxygen content of molten steel is reduced by 2-6ppm compared with a conventional deoxidization modification process, a water gap is not replaced by a full pouring 7-time furnace, and a water gap is replaced by a conventional deoxidization modification process generally 2-4-time furnace.
Claims (5)
1. A method for reducing the oxidative damage of RH top slag of ultra-low carbon steel is characterized in that,
before tapping from the converter to the ladle and entering RH, no slag-forming material is added;
adding slag forming materials into a vacuum chamber after RH aluminum adding final deoxidation, enabling the slag forming materials added into the RH vacuum chamber to enter a steel ladle through the lower part of a dipping pipe, and calculating the slag amount according to the slag forming thickness of 30-100 mm in the steel ladle;
no deoxidizing modifier is added after RH is broken.
2. The method for reducing the oxidative damage to ultra-low carbon steel RH top slag according to claim 1, wherein the slag forming material is lime, fluorite and bauxite, or lime, fluorite and synthetic slag, having a particle size of 5-30 mm.
3. The method for reducing the oxidative damage of RH top slag of ultra-low carbon steel according to claim 2, wherein the slag forming material comprises the following components in proportion to CaO/Al in slag after slag forming 2 O 3 =1.5±0.3 as control target.
4. The method for reducing the oxidative damage of RH top slag of ultra-low carbon steel according to claim 3, wherein when the slag thickness in the steel ladle is less than or equal to 70mm, the slag forming material is added in 2 times; when the slag forming thickness in the ladle is more than 70mm, adding slag forming materials for 3 times; each time interval is more than 1min.
5. The method of reducing the oxidative damage to an RH top slag of ultra-low carbon steel as claimed in any one of claims 1 to 4 wherein said ultra-low carbon steel comprises less than or equal to 0.02% C by weight.
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