CN116194235A - Method for producing cast sheet - Google Patents
Method for producing cast sheet Download PDFInfo
- Publication number
- CN116194235A CN116194235A CN202180064402.6A CN202180064402A CN116194235A CN 116194235 A CN116194235 A CN 116194235A CN 202180064402 A CN202180064402 A CN 202180064402A CN 116194235 A CN116194235 A CN 116194235A
- Authority
- CN
- China
- Prior art keywords
- molten steel
- vacuum degassing
- steel
- charge
- mass
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D1/00—Treatment of fused masses in the ladle or the supply runners before casting
-
- 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
-
- 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
-
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Treatment Of Steel In Its Molten State (AREA)
Abstract
The present invention provides a method for producing a cast sheet having high cleanliness by keeping titanium in molten steel at a low level during refining of steel and suppressing generation of TiN during casting. The method is a method for producing a cast slab by casting refined molten steel obtained by tapping steel from a converter or an electric furnace and subjecting the steel to at least vacuum degassing refining treatment in a ladle, wherein the ladle used in producing the cast slab is limited by the titanium content in the molten steel held in the ladle at least immediately before the steel receiving of the object charge, the titanium content in the molten steel after tapping of the object charge is set to 0.002 mass% or less, and the vacuum degassing apparatus for vacuum degassing refining treatment of the object charge is limited by the titanium content at the end of treatment in the vacuum degassing apparatus in the molten steel treated in the vacuum degassing apparatus at least immediately before the vacuum degassing refining treatment of the object charge.
Description
Technical Field
The present invention relates to a method for producing a cast sheet.
Background
Since steel materials used for bearings and crankshafts of automobiles are subjected to repeated stress, so-called "high-purity steel" is required in which nonmetallic inclusions serving as starting points of metal fatigue fracture are extremely small. Accordingly, various methods have been employed in the steel-making process to reduce oxide-based nonmetallic inclusions in steel in order to improve the fatigue properties of the steel.
For example, in the case of mass-produced steel, a method of promoting the floating and separation of oxide-based nonmetallic inclusions by vacuum degassing treatment is used, and a deoxidizer such as metallic Al is added to slag on molten steel present in a ladle to reduce the slag and thereby suppress Al generated by the reaction of the slag with Al in the molten steel 2 O 3 A method of forming the oxide-based nonmetallic inclusion in a mold of a continuous casting machine, and a method of arranging a magnetic field generating device directly below the mold to promote the floating and separation of the oxide-based nonmetallic inclusion in the mold.
For example, in patent document 1, attention is paid to Al which coarsens and causes adverse effects on fatigue life 2 O 3 An oxide, a method of adding an Mg alloy having an Mg content of more than 0.5 mass% and 30 mass% or less to a molten steel containing Si, mn and Al and having a C content of 0.2 mass% or more. According to patent document 1, al in molten steel is caused to be contained by adding an Mg alloy 2 O 3 Change to Al 2 O 3 MgO, thereby suppressing coarsening of the inclusions.
In addition, patent document 2 discloses the following process as a method for producing high-cleanliness bearing steel. First, an oxygen enrichment operation is performed in an electric furnace to form a peroxidized state in which the dissolved oxygen concentration in molten steel is 250ppm or more, and titanium and the like in the raw material are oxidized and transferred to slag. Subsequently, after the slag is discharged from the ladle, si deoxidation and Al deoxidation are sequentially performed to deoxidize the molten steel and the slag. Further, refining was performed in a ladle refining furnace and an RH vacuum degassing device in this order.
Further, as a method for producing a bearing steel requiring higher reliability and performance, patent document 3 discloses a method for producing an ultra-clean bearing steel, which uses a bearing steel containing no Mn exceeding 0.2 mass% as a base material, and remelts the base material by an electron beam melting method.
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open No. 5-311225
Patent document 2: japanese patent laid-open No. 6-145883
Patent document 3: japanese patent laid-open No. 7-109541
Disclosure of Invention
Problems to be solved by the invention
The prior art mentioned above is to achieve an improvement in rolling fatigue life by reducing the number or maximum diameter of oxides, sulfides. However, in order to further increase the life span and crush strength of the bearing material, it is necessary to reduce the amount of oxide inclusions and the maximum diameter of the amount of oxide inclusions, and also to reduce the amount of nitride inclusions. The nitride-based inclusions, which are problematic here, are fine TiN that is produced during solidification due to the reaction of titanium in molten steel with N dissolved in molten steel, and if the product of the titanium concentration and the N concentration, i.e., the product of the titanium concentration and the N concentration exceeds the crystallization limit, crystallization occurs. Therefore, in order to suppress the formation of TiN, it is necessary to reduce the concentration of both titanium and N in the molten steel, which is the cause of the formation, or to reduce the concentration of at least one of titanium and N to a value extremely close to zero.
Here, N is removed by removing N in the vacuum degassing refining step, but it is difficult to completely prevent absorption of N from nitrogen contained in the atmosphere into the molten steel, and therefore there is a limit in lowering of the N concentration in the molten steel. On the other hand, even if titanium is not intentionally added, it is sometimes unavoidable to mix (pick up) in the refining stage, and therefore it is difficult to maintain the titanium concentration in the molten steel at a low level at all times. As a result, the formation of TiN during casting cannot be completely suppressed, and it is difficult to further improve the fatigue life of steel requiring high fatigue strength such as bearing steel produced from the TiN as a raw material.
The present invention has been made in view of the above-described problems, and an object thereof is to provide a method for producing a cast sheet having high cleanliness by maintaining a low titanium content in molten steel during steel refining and suppressing TiN formation during casting. The content of a specific element such as titanium in molten steel is the mass of the specific element contained in molten steel per unit mass, and is expressed as a ratio (mass%) of the mass of the specific element in molten steel to the mass of molten steel. That is, the content of the specific element in the molten steel is the same as the concentration of the specific element in the molten steel.
Means for solving the problems
According to one aspect of the present invention, there is provided a method for producing a cast piece, which comprises casting refined molten steel obtained by subjecting the molten steel, which is tapped from a converter or an electric furnace and subjected to a steel-casting ladle, to at least a vacuum degassing refining treatment, wherein a ladle used for producing the cast piece is limited by a titanium content in the molten steel held in the ladle at least immediately before the steel-casting of the object charge, so that the titanium content in the molten steel after tapping of the object charge is 0.002 mass% or less, and a vacuum degassing apparatus for subjecting the object charge to the vacuum degassing refining treatment is limited by a titanium content at the end of the treatment in the vacuum degassing apparatus in the molten steel processed in the vacuum degassing apparatus at least immediately before the vacuum degassing refining treatment of the object charge.
Effects of the invention
According to one embodiment of the present invention, there is provided a method for producing a cast sheet having high cleanliness by maintaining the titanium content in molten steel at a low level during steel refining and suppressing the formation of TiN during casting.
Detailed Description
In the following detailed description, embodiments of the present invention are described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar symbols, and repetitive description thereof will be omitted. The drawings are schematic and include situations different from reality. The following embodiments illustrate apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is not to specify the materials, structures, arrangements, and the like of constituent members as follows. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.
As a factor that causes mixing of titanium into molten steel at the refining stage during refining of high fatigue strength steel and TiN formation during casting, the present inventors focused on the following factors (a) to (C). Then, the components (a) to (C) were extracted separately, and the influence on the mixing of titanium was examined sequentially.
(A) TiO contained in slag (converter slag or electric furnace slag) produced in refining of converter or electric furnace 2
(B) Titanium added to alloy in molten steel from converter or electric furnace tapping to end of vacuum degassing refining treatment
(C) Titanium contained in base metal attached to ladle and refining tank of vacuum degassing apparatus
(A) Converter slag or electric furnace slag
After pretreatment of molten iron such as desulfurization and dephosphorization, the molten iron discharged from the blast furnace is decarburized and refined by top-blowing or bottom-blowing oxygen in the converter. Slag produced in a converter contains various oxides and also contains titanium oxides mainly caused by titanium contained in molten iron. In addition, a cold iron source such as scrap is sometimes melted in an electric furnace to obtain molten steel. Slag generated in an electric furnace also contains various oxides, and if titanium-containing steel or the like is blended in scrap, the resulting slag also contains titanium oxides. At least a part of the converter slag or the electric furnace slag is carried out to a secondary refining step (heating stirring refining and vacuum degassing refining), and if conditions for reducing titanium oxide in the slag are reached in the secondary refining step, there is a possibility that titanium is mixed into the molten steel. However, under ordinary refining conditions, such conditions are rarely attained, and in practice, titanium inclusion due to converter slag or electric furnace slag is rarely found. Therefore, in the present embodiment, it is not necessary to take measures for preventing the mixing of titanium from the converter slag or the electric furnace slag, and it is preferable to take measures for reducing the amount of the converter slag or the electric furnace slag to be carried out to the secondary refining step, which will be described later, in the case where a large mixing amount of titanium into the molten steel due to other factors is expected.
(B) Alloy added to molten steel
Examples of the titanium-containing alloy include FeSi alloys. The present inventors have examined the titanium concentration in molten steel by changing the type of additive alloy used in vacuum degassing refining when high-purity steel is melted. As a result of the investigation, it was found that the titanium concentration in the molten steel reliably increased according to the pure titanium amount of the alloy added (alloy addition amount×titanium concentration of the alloy). That is, in order to maintain the titanium concentration in the molten steel in the refining stage at a low level all the time, if the amount of pure titanium of the added alloy is estimated on the premise that the mixing of titanium from the added alloy cannot be avoided, it is necessary to reduce the mixing amount of titanium due to other factors as much as possible. Of course, in order to reduce the amount of titanium mixed from the added alloy, it is preferable to use an alloy containing low concentration of titanium.
(C) Base metal attached to ladle and refining tank of vacuum degassing apparatus
The ladle used industrially in the steel production process is a molten steel holding vessel having a refractory material provided on the inner surface of a steel shell, and is repeatedly used in the production process. In the production process, various steels are generally repeatedly produced, and therefore, the ladle is repeatedly subjected to receiving (receiving) and discharging of molten steel several tens to several hundreds times from the start to the end of its use. At this time, in the ladle after the molten steel is discharged, a part of the last molten steel and slag that have not been completely discharged from the ladle is solidified and remains on the surface of the refractory in the ladle. These residual molten steel and slag (hereinafter, both will be collectively referred to as a base metal) contain an impurity element or an oxide thereof. The base metal is remelted by heat of molten steel when the molten steel to be charged next is received in a ladle, and therefore impurities or oxides thereof contained in the base metal are melted or mixed into the molten steel. Therefore, it is considered that, when a base metal charged last time is attached to a ladle used for refining molten steel for high fatigue strength steel (molten steel for high fatigue strength steel), if titanium is contained in the base metal, the concentration of titanium contained in the molten steel increases, and TiN inclusions are generated in cast pieces. Here, the charge (steelmaking charge) means a unit of treatment in refining treatment of molten steel. The next charge is a next charge to the target charge (target charge), and is a charge immediately after the treatment of the target charge. The last charge means the previous charge of the object charge, and is the charge immediately before the treatment of the object charge.
The present inventors have studied in detail the behavior of the titanium concentration in molten steel when refining molten steel for high fatigue strength steel. As a result, it is found that the titanium concentration in the molten steel increases in many cases from before the vacuum degassing refining treatment to after the vacuum degassing refining treatment. It is also known that, when a ladle used for refining molten steel for high fatigue strength steel receives molten steel having a high titanium content in the previous charge for refining molten steel for high fatigue strength steel (hereinafter also referred to as object refining) and when molten steel having a high titanium content in the previous charge for object refining is treated by a vacuum degassing apparatus used for object refining, an increase in titanium concentration before and after the vacuum degassing refining treatment becomes large. This is considered to indicate that the base metal adhering to the ladle and the base metal adhering to the inside of the tank of the vacuum degassing apparatus are melted in refining molten steel facing the high fatigue strength steel, and titanium in the base metal is mixed into the molten steel. Therefore, when refining molten steel for high fatigue strength steel, the production order is adjusted so that molten steel having a low titanium content is specified in molten steel refined in the previous process, and as a result, the amount of increase in titanium concentration in molten steel subject to refining is reduced, and TiN inclusions generated in cast pieces are also significantly reduced.
That is, in order to reduce TiN inclusions generated in cast slabs, it is important to maintain the titanium content in the molten steel in the refining stage at a low level at all times. However, if not only the titanium content in the molten steel is maintained at a low level but also the mixing of titanium from the base metal adhering to the ladle and the base metal adhering to the inside of the bath of the vacuum degassing apparatus is reduced, the effect of reducing the TiN inclusion generated in the cast slab becomes large. The reason for this is not clear, but the present inventors consider the following possibilities. That is, the surface of the base metal serving as a titanium source is often temporarily exposed to the atmosphere. Therefore, oxides containing an alloy component of iron and titanium are formed on the surface of the base metal, and if the base metal is melted, these oxides are suspended in the molten steel, and the cleanliness of the molten steel is lowered. It is considered that if the suspended oxide in the molten steel contains titanium oxide, the titanium content in the molten steel may increase, and it is needless to say that even a compound containing no titanium may become nuclei for formation of TiN inclusions during casting, and the nucleation frequency of TiN inclusions increases. In addition, it has been found that in order to suppress such a phenomenon, it is necessary to use a ladle having a low titanium content in molten steel of steel received in the previous charge of object refining and to use a vacuum degassing apparatus having a low titanium content in molten steel treated in the previous charge of object refining in refining of molten steel of high fatigue strength steel.
From the above, it was found that in order to reduce the mixing of titanium into molten steel for high fatigue strength steel and to suppress the formation of TiN during casting, it is effective to reduce the amount of converter slag or electric furnace slag carried over to the secondary refining step based on the verification of (a), to use an alloy having a low titanium concentration based on the verification of (B), and to reduce the mixing of titanium from the base metal adhering to the ladle and the refining vessel of the vacuum degassing apparatus based on the verification of (C).
Method for producing cast sheet
Hereinafter, a concrete embodiment of the present invention will be described by taking a case of producing a cast piece from converter molten steel as an example.
First, molten iron discharged from a blast furnace is charged in a molten iron holding/transporting vessel such as a ladle or a torpedo car, and transported to a converter for refining in a converter for the next step (transport step). In the transfer step, molten iron pretreatment such as desulfurization and dephosphorization may be performed on the molten iron during the transfer, if necessary.
After the transfer step, the molten iron is subjected to converter refining in a converter (primary refining step). In the primary refining step, decarburization refining of molten iron is performed by top-blowing or bottom-blowing oxygen using a small amount of quicklime or the like as a medium solvent as needed. Slag produced in a converter contains various oxides and titanium oxide. In order to reduce the carry-over of the converter slag to the next step and the mixing of titanium from the carried-over slag, it is preferable to use at least one of a slag outflow preventing means and a slag cutting means at the time of tapping from the converter. As means for preventing slag from flowing out during tapping in a converter, methods such as detecting slag flowing out by infrared rays or the like, and charging into a furnace of a dart type slag stopper can be used. Further, as slag cutting means, a plug, a sliding nozzle type slag stopper, or the like may be provided in the tap hole of the converter, and these may be used at the end of tapping. Further, the converter slag that flows out in this way can be further removed by removing slag after tapping from the converter to the ladle as a process of scraping the slag from the ladle using a scraper or the like. The smaller the amount of converter slag to be carried out to the subsequent step, the more preferable is 32 kg-slag/t-steel or less, and the more preferable is 25 kg-slag/t-steel or less. This is because the influence of the amount of influence of mixing titanium into the molten steel from the titanium oxide contained in the outflow slag can be minimized. In the description of the present embodiment, "t-steel" is the weight of molten steel in the target charge, "kg-slag" is the weight of slag in the target charge, and t (ton) is Metric Ton (MT).
As described above, the molten steel subjected to converter refining is tapped into a ladle as a molten steel holding vessel. In the present embodiment, restrictions are placed on the ladle used, and a ladle satisfying the conditions is used. The limitation of the ladle is that the ladle used for the charge for refining the object (hereinafter, also referred to as the object charge) is limited by the titanium content in the molten steel held at least immediately before the steel receiving of the object charge, and the titanium content in the molten steel after tapping is set to 0.002 mass% or less in the object charge. Specifically, the ladle used in the target charge is set to have an upper limit of the titanium content in the molten steel held at least immediately before the steel receiving of the target charge, and the ladle having a titanium content of not more than the upper limit in the molten steel held at least immediately before the steel receiving of the target charge is used for manufacturing the molten steel for high fatigue strength steel, and the titanium content in the molten steel after tapping of the target charge is set to not more than 0.002 mass%.
In addition, the aluminum content in the molten steel held immediately before the steel receiving of the object charge may also be limited. Specifically, the upper limit of the aluminum content in the molten steel held immediately before the steel receiving of the object charge may be set to 0.05 mass% or less. This is because if the aluminum content in the molten steel is more than 0.05 mass%, the oxide (TiO 2 ) Is reduced by aluminum in the molten steel, and the titanium concentration of the molten steel is increased.
The upper limit of the titanium content in the molten steel held immediately before the steel receiving of the object charge is preferably set to about 6 times or less the standard upper limit of the composition of the molten steel for producing the high fatigue strength steel, and if the usual amount of the base metal adhering to the ladle is taken into consideration, the titanium content in the molten steel held immediately before the steel receiving of the object charge is more preferably set to 0.020 mass% or less. By setting the upper limit of the titanium content in the molten steel held immediately before the steel receiving of the object charge to this range, the mixing of titanium into the molten steel can be prevented more reliably. Although the upper limit of the titanium content in the molten steel held immediately before the steel receiving of the object charge is set, the lower the titanium concentration in the molten steel is, the more the mixing of titanium can be prevented, and therefore, it is not necessary to set the lower limit of the titanium content in the molten steel held immediately before the steel receiving of the object charge.
In addition, the titanium content in the molten steel held in the last charge of the steel-receiving previous charge as the object charge may be affected not only when the titanium content in the molten steel held in the last charge of the previous charge (the charge twice before the object charge) is too high. Therefore, as for the ladle used, in addition to the limitation of the titanium content in the molten steel of the steel in the last charge of the object charge, the limitation of the titanium content in the molten steel of the steel in the last charge of the object charge may be used. In this case, the titanium content in the molten steel subjected to steel in the previous charge is preferably set to 0.020% by mass or less, and the effect on the mixing of titanium is smaller than in the molten steel subjected to steel in the previous charge, so that the upper limit may be set to a content of more than 0.020% by mass.
However, if the amount of the base metal adhering to the ladle (the amount of the adhering base metal to the ladle) and the titanium content (mass%) of the base metal adhering to the ladle (the adhering base metal to the ladle) are known, the amount of titanium mixed from the base metal adhering to the ladle can be estimated more accurately. However, it is generally difficult to accurately grasp the amount of the base metal adhering to the ladle (the amount of the adhering base metal to the ladle) and the titanium content (mass%) of the base metal adhering to the ladle (the adhering base metal to the ladle), and therefore, in the present invention, the ladle used in the subject charge is restricted by the titanium content in the molten steel held at least immediately before the steel receiving of the subject charge.
If the amount of the base metal grasped by measuring in advance the amount of the base metal or the like adhered to the ladle during the process prior to the production of the ladle charge, that is, the molten steel for high fatigue strength steel, the value may be used as the adhering base metal amount of the ladle. Alternatively, if the weight of the ladle before and after the previous treatment can be actually measured by a load cell or the like, the amount of the base metal to be adhered can be measured, and this value may be used. Here, the weight of the ladle before the previous treatment means the weight of the ladle before receiving the molten steel tapped from the converter in the previous treatment (the previous treatment of the ladle used for the object charge). The weight of the ladle after the previous treatment means the weight of the ladle after the molten steel is discharged after casting in the previous treatment. In addition, in the case of performing maintenance such as removal of the adhering base metal in the ladle after the molten steel is discharged, the weight after the maintenance may be used as the weight of the ladle after the previous treatment. That is, the weight of the ladle after the previous treatment is the weight of the ladle before the current treatment of molten steel is received from the converter.
The titanium content of the attached base metal of the ladle used when estimating the titanium mixing amount of the attached base metal from the ladle from the base metal attached to the ladle (attached base metal of the ladle) and the titanium content (mass%) of the base metal attached to the ladle (attached base metal of the ladle) may be set to be the titanium content (mass%) in the molten steel held at least immediately before the steel receiving (last charging) of the object charge. The conditions of the ladle used are preferably such that the titanium content of the adhering base metal of the ladle is about 6 times or less the upper limit of the component standard of the molten steel for high fatigue strength steel to be produced, and more preferably such that the titanium content of the adhering base metal of the ladle is 0.020 mass% or less, taking into consideration the usual base metal adhering amount of the ladle.
Then, the molten steel is transferred to a ladle refining furnace, and a heating and stirring refining treatment is performed, and then the molten steel is transferred to a vacuum degassing apparatus, and a vacuum degassing refining treatment (secondary refining step) is performed. In the heating and stirring refining treatment, refining such as heating, inclusion removal, deoxidation, component adjustment and the like is performed under an inert gas atmosphere. As the vacuum degassing apparatus, an RH vacuum degassing apparatus, a DH vacuum degassing apparatus, a VOD furnace, or the like can be used. In the following description, an example of vacuum degassing refining treatment using an RH vacuum degassing apparatus as a representative vacuum degassing apparatus will be described. The molten steel subjected to the secondary refining step, that is, the molten steel subjected to the vacuum degassing refining treatment is also referred to as refined molten steel.
In the present embodiment, the RH vacuum degasser to be used is limited, and the RH vacuum degasser in a state satisfying the conditions is used. The limitation of the RH vacuum degassing apparatus is to limit the titanium content (mass%) in the molten steel treated at least immediately before the treatment of the object charge.
Specifically, an RH vacuum degassing apparatus for treating molten steel having a low titanium content immediately before the treatment of an object charge is used for producing molten steel for high fatigue strength steel. The upper limit of the titanium content of the molten steel treated immediately before the treatment of the target charge is preferably set to about 6 times or less the standard upper limit of the composition of the molten steel for producing high fatigue strength steel, and if the usual amount of the base metal adhering to the RH vacuum degassing apparatus is taken into consideration, the titanium content in the molten steel treated in the vacuum degassing apparatus immediately before the vacuum degassing refining treatment of the target charge is more preferably set to 0.020 mass% or less. By setting the range to this level, the mixing of titanium into the molten steel can be prevented more reliably. For the value of the titanium content in the molten steel treated immediately before the treatment of the object charge, for example, the titanium content at the end of the treatment in the RH vacuum degassing apparatus in the molten steel of the last charge treated in the RH vacuum degassing apparatus immediately before the treatment of the object charge may be used.
In addition, the titanium content in the molten steel of the last charge of the target charge (the charge before the two times of the target charge) may be affected not only when the titanium content in the molten steel of the last charge of the charge immediately before the treatment in the RH vacuum degassing apparatus of the target charge is too high. Therefore, the limitation can also be made by the titanium content in the molten steel treated in the last charge. In this case, the conditions of the titanium content in the molten steel treated in the previous charge are preferably the same as those in the previous charge. However, since the molten steel treated in the previous charge has less influence on the mixing of titanium than the molten steel treated in the previous charge, the content of the molten steel can be set to be higher than that of the molten steel treated in the previous charge.
Further, the aluminum content of the molten steel treated immediately before the treatment of the object charge may be limited. Specifically, the upper limit of the aluminum content in the molten steel treated immediately before the treatment of the object charge may be set to 0.05 mass% or less. This is because if the aluminum concentration in the molten steel is more than 0.05 mass%, the oxide (TiO 2 ) Is reduced by aluminum in the molten steel, so that the titanium content of the molten steel is increased. For example, the aluminum content in the molten steel of the previous charge, which was treated in the RH vacuum degassing apparatus immediately before the treatment of the object charge, may be used as the value of the aluminum content in the molten steel, which was treated immediately before the treatment of the object charge, at the end of the treatment in the RH vacuum degassing apparatus.
However, if the amount of the base metal adhering to the refining vessel of the RH vacuum degassing device (the amount of the adhering base metal of the device) and the titanium content of the base metal adhering to the refining vessel of the RH vacuum degassing device (the amount of the adhering base metal of the device) (mass%) are known, the amount of titanium mixed from the base metal adhering to the device can be estimated more accurately. However, since it is generally difficult to accurately grasp the amount of the base metal adhering to the apparatus and the titanium content (mass%) of the adhering base metal of the apparatus, in the present invention, the RH vacuum degassing apparatus used for the object charge is limited by the titanium content in the molten steel treated at least immediately before the treatment of the object charge.
In the vacuum degassing refining process, if the amount of the base metal grasped by measuring the amount of the base metal attached in the previous process in advance is obtained, the obtained base metal can be used as the attached base metal amount of the apparatus. Alternatively, if the weight of the refining tanks (vacuum tanks and dip pipes) of the RH vacuum degassing device before and after the previous treatment can be actually measured by a load cell or the like, the amount of the base metal to be adhered can be measured, and this value can be used.
The concentration of titanium in the molten steel at the end of the vacuum degassing refining process in the last vacuum degassing refining process can be set by estimating the concentration of titanium in the attached base metal from the apparatus used when the amount of titanium mixed in the base metal attached to the apparatus based on the amount of attached base metal in the apparatus and the titanium content (mass%) of the attached base metal in the apparatus. The conditions of the RH vacuum degassing apparatus to be used are preferably such that the titanium content of the adhering base metal of the apparatus is about 6 times or less the upper limit of the component standard of the molten steel for high fatigue strength steel to be produced, and more preferably such that the titanium content of the adhering base metal of the apparatus is 0.020 mass% or less, considering the usual base metal adhering amount of the RH vacuum degassing apparatus.
After the secondary refining step, the refined molten steel (refined molten steel) is continuously cast, whereby a cast slab is produced as an intermediate product such as a billet, or a slab (casting step). The casting method in the casting step is not limited to continuous casting, and casting by the ingot casting method may be used.
By the above steps, a cast sheet is produced as a raw material of high fatigue strength steel.
< modification >
The present invention has been described above with reference to specific embodiments, but the present invention is not limited to these descriptions. Other embodiments of the present invention, including various modifications to the disclosed embodiments, will be apparent to those skilled in the art from consideration of the specification of the present invention. Accordingly, it should be understood that the embodiments of the invention described in the claims also include embodiments of these modifications described in the present specification, alone or in combination.
For example, in the above embodiment, the restrictions on the ladle and the refining tank of the vacuum degassing apparatus are performed in order to reduce the mixing of titanium, but the present invention is not limited to these examples. In addition to the restrictions on the ladle and the restrictions on the refining vessel of the vacuum degassing apparatus, it is preferable that at least the restrictions on the added alloyed iron, that is, the alloyed iron added from tapping to the end of the secondary refining step, be satisfied with (B) above.
In the above embodiment, in view of titanium contained in the added alloy, it is more preferable that the amount of increase in titanium concentration in the molten steel after tapping and until the vacuum degassing refining treatment is completed satisfies the following expression (1) for the object charge. In this case, the Ti content in the molten steel immediately before tapping of the subject charge is zero at or below the analysis limit, and when the molten steel is tapped from the converter, the Ti content in the molten steel at which the converter after the oxygen feed treatment has been completed is zero (at or below the analysis limit).
Δ[Ti]＝[Ti] LD +Σ(W t ×η t /100)+Δ[Ti] M ≤T 1 ×10…(1)
In the formula (1), Δti]The amount of increase in titanium content in molten steel (kg-Ti/t-steel) from after tapping to the end of vacuum degassing refining treatment was shown, [ Ti ]] LD Represents the titanium content (kg-Ti/t-steel) in the molten steel after tapping, W t Represents the addition amount (kg-alloy/t-steel) of the alloy added from tapping to the end of the vacuum degassing refining treatment in the target charge, η t Represents the titanium content (% by mass) of the alloy added from tapping to the end of the vacuum degassing refining treatment in the target charge, Δti] M Represents an increase in titanium content (kg-Ti/T-steel) in molten steel obtained from the outside of the alloy, T 1 The standard upper limit value (mass%) of the titanium component of the steel to be melted is shown. Two or more kinds of alloys containing titanium may be used, but in the formula (1), the addition amount W of each alloy t And titanium content eta t The multiplied values are added together.
Here, as the alloy containing titanium, feSi alloy is exemplified. In the case of adding the FeSi alloy, the grade (titanium content) of the FeSi alloy can be selected according to the amount of the FeSi alloy added in the ladle refining furnace and the RH vacuum degassing apparatus after tapping in the converter and the target titanium content of the molten steel.
In the above embodiment, the primary refining step of performing converter refining, the secondary refining step of performing heating and stirring refining treatment and vacuum degassing refining treatment were performed, but the present invention is not limited to this example. For example, in the primary refining step, molten steel may be produced using equipment such as an electric furnace, not a converter, as a refining furnace. In the secondary refining step, only the vacuum degassing refining treatment may be performed without performing the treatment in the ladle refining furnace.
As an example of the high fatigue strength steel, a bearing steel specified as SUJ2 in JIS (japanese industrial standard) G4805 is given. The components of the composition range are as follows: the carbon concentration is 0.95 to 1.10 mass%, the silicon concentration is 0.15 to 0.35 mass%, the manganese concentration is 0.50 mass%, the phosphorus concentration is 0.025 mass%, the sulfur concentration is 0.025 mass%, the chromium concentration is 1.30 to 1.60 mass%, the molybdenum concentration is 0.08 mass%, the nickel concentration is 0.25 mass%, and the copper concentration is 0.25 mass%.
As the bearing steel specified in other standards, there are bearing steel specified as 100Cr6 in ISO (international organization for standardization) 683-17 standard, bearing steel specified as GCr15 in GB (national standard in china), bearing steel specified as 52100 in ASTM (american society for testing and materials) a295 standard, bearing steel specified as 100Cr6 in DIN (german society for standardization) standard, and the like. The composition ranges of the bearing steel specified as 100Cr6 in the ISO (international organization for standardization) 683-17 standard are: the carbon concentration is 0.95 to 1.10 mass%, the silicon concentration is 0.15 to 0.35 mass%, the manganese concentration is 0.25 to 0.45 mass%, the phosphorus concentration is 0.030 mass%, the sulfur concentration is 0.025 mass% or less, and the chromium concentration is 1.35 to 1.65 mass%.
Further, the chromium-molybdenum steel material (SCM material) specified in JIS G4053 also requires fatigue strength according to the application. As an example of the SCM material, the chromium-molybdenum steel material specified as SCM420 contains the following components: the carbon concentration is 0.18 to 0.23 mass%, the silicon concentration is 0.15 to 0.35 mass%, the manganese concentration is 0.60 to 0.90 mass%, the phosphorus concentration is less than 0.030 mass%, the sulfur concentration is less than 0.030 mass%, the nickel concentration is less than 0.25 mass%, the chromium concentration is 0.90 to 1.20 mass%, and the molybdenum concentration is 0.15 to 0.25 mass%.
As chromium molybdenum steel materials specified in other standards, there are steel materials specified as 25CrMo4 in ISO (international organization for standardization) standards, EN (european commission for standardization) standards, DIN (german standards institute for standardization) standards, etc., steel materials specified as 30CrMn in GB (chinese national standard), steel materials specified as 4130 in ASTM (american society for testing and materials) a29 standards, and the like.
Further, a carbon steel material (SC material) for machine structural use specified in JIS G4051 is also required to have fatigue strength according to the application. As an example of the SC material, the chromium-molybdenum steel material specified in S53C contains: the carbon concentration is 0.50 to 0.56 mass%, the silicon concentration is 0.15 to 0.35 mass%, the manganese concentration is 0.60 to 0.90 mass%, the phosphorus concentration is less than 0.030 mass%, and the sulfur concentration is less than 0.035 mass%.
Effect of the embodiments >
(1) In the method for producing a cast piece according to one embodiment of the present invention, a refined molten steel obtained by subjecting molten steel tapped from a converter or an electric furnace and subjected to a steel-casting ladle to at least vacuum degassing refining treatment is cast, wherein the ladle used in a target charge for producing the cast piece is restricted by the titanium content in the molten steel held in the ladle at least immediately before the steel-casting of the target charge so that the titanium content in the molten steel after tapping of the target charge is 0.002 mass% or less, and a vacuum degassing apparatus for subjecting the target charge to vacuum degassing refining treatment is restricted by the titanium content at the end of treatment in the vacuum degassing apparatus in the molten steel treated in the vacuum degassing apparatus at least immediately before the vacuum degassing refining treatment of the target charge.
According to the configuration of (1) above, in addition to the mixing of titanium from the base metal adhering to the ladle and the vacuum degassing equipment, the mixing of oxide on the surface of the base metal can be suppressed, and therefore, the titanium content in the molten steel can be maintained at a low level during refining, and the cleanliness of the molten steel can be maintained, and thus, the formation of TiN can be suppressed, and a cast sheet with high cleanliness can be produced.
(2) In the configuration of (1) above, the molten steel tapped from the converter or the electric furnace and received into the ladle is subjected to the heating and stirring refining treatment and the vacuum degassing refining treatment in this order, and the refined molten steel thus obtained is cast.
According to the constitution of the above (2), the same effects as those of the above (1) can be obtained also in the process of performing the refining heating stirring refining treatment and the vacuum degassing refining treatment after tapping.
(3) In the configuration of (1) or (2), the titanium content in the molten steel held immediately before receiving the steel of the object charge is set to 0.020% by mass or less with respect to the ladle used in the object charge.
According to the configuration of (3), mixing of titanium from the adhering base metal of the ladle can be suppressed, and a cast piece with high cleanliness can be produced.
(4) In the configuration of (3), the aluminum content in the molten steel held immediately before the steel receiving of the object charge is set to 0.050 mass% or less for the ladle used in the object charge.
According to the configuration of (4), since reduction of titanium oxide contained in the adhering base metal of the ladle by aluminum can be suppressed, mixing of titanium from the adhering base metal of the ladle can be further suppressed, and a cast sheet with high cleanliness can be produced.
(5) In any one of the configurations (1) to (4), the titanium content at the end of the treatment in the vacuum degassing apparatus in the molten steel treated in the vacuum degassing apparatus immediately before the vacuum degassing refining treatment of the object charge is set to 0.020 mass% or less in the vacuum degassing apparatus for the vacuum degassing refining treatment of the object charge.
According to the constitution of (5), mixing of titanium into the adhesion base metal from the refining vessel of the vacuum degassing apparatus can be suppressed, and a cast sheet with high cleanliness can be produced.
(6) In the configuration of (5) above, the aluminum content at the end of the treatment in the vacuum degassing apparatus in the molten steel treated in the vacuum degassing apparatus immediately before the vacuum degassing refining treatment of the object charge is set to 0.050 mass% or less in the vacuum degassing apparatus for the vacuum degassing refining treatment of the object charge.
According to the configuration of (6), since reduction of titanium oxide contained in the adhering base metal of the refining vessel of the vacuum degassing apparatus by aluminum can be suppressed, mixing of titanium from the adhering base metal of the refining vessel of the vacuum degassing apparatus can be further suppressed, and a cast sheet with high cleanliness can be produced.
(7) In any one of the configurations (1) to (6), the Ti content in the molten steel immediately before tapping of the subject charge is zero below the analysis limit, and the amount of increase in the Ti content in the molten steel from the time after tapping to the time when the vacuum degassing refining treatment is completed satisfies the following expression (1).
Δ[Ti]＝[Ti] LD +Σ(W t ×η t /100)+Δ[Ti] M ≤T 1 ×10…(1)
Wherein, in the formula (1),
delta [ Ti ]: an increase in titanium content (kg-Ti/t-steel) in the molten steel from the time of tapping to the time of completion of the vacuum degassing refining treatment;
[Ti] LD : titanium content (kg-Ti/t-steel) in the molten steel after tapping;
W t : an amount of alloy added (kg-alloy/t-steel) from tapping to the end of the vacuum degassing refining treatment in the target charge;
η t : titanium content (mass%) of the alloy added from tapping to the end of the vacuum degassing refining treatment in the object charge;
Δ[Ti] M : an increase in titanium content in molten steel mixed from outside the alloy (kg-Ti/t-steel);
T 1 : titanium concentration standard upper limit value (mass%) of steel to be melted.
According to the configuration of (7), since mixing of titanium from the added alloy is also suppressed, the titanium content in the molten steel can be maintained at a low level during refining, and thus the formation of TiN is suppressed, and a cast sheet with high cleanliness can be produced.
(8) In any one of the above configurations (2) to (7), the amount of the slag flowing out of the ladle during tapping from the converter or the electric furnace to the weight of the molten steel in the target charge is set to 25 kg-slag/t-steel or less at a time before the heating and stirring refining treatment.
According to the configuration of (8), since outflow of slag generated in the primary refining process to the ladle can be sufficiently suppressed, mixing of titanium due to titanium contained in the slag can be suppressed.
(9) In any one of the above configurations (1) to (8), the titanium content in the refined molten steel after continuous casting is 0.0020 mass% or less.
In the present description, the steel (high fatigue strength steel) requiring high fatigue strength is described as an example, but the present invention is not limited to high fatigue strength steel, and can be used for refining a steel grade in which it is not desired to mix titanium into molten steel.
Examples
The primary refining step in the converter, the secondary refining step in the ladle refining furnace and the RH vacuum degassing apparatus, and the casting step in the continuous casting machine were performed in the same manner as in the above-described embodiment, using a solid machine having a primary charged molten steel amount of about 200 tons, to produce a billet cast piece as a raw material of bearing steel of high fatigue strength steel. The bearing steel comprises the following components: the carbon concentration is 0.90 mass% or more and 1.10 mass% or less, the silicon concentration is 0.15 mass% or more and 0.25 mass% or less, the manganese concentration is 0.45 mass% or less, the phosphorus concentration is 0.0020 mass% or less, the sulfur concentration is 0.0050 mass% or less, the aluminum concentration is 0.030 mass% or less, the chromium concentration is 1.4 mass% or more and 1.7 mass% or less, the nitrogen concentration is 0.0050 mass% or less, the titanium concentration is 0.0020 mass% or less, and the balance is iron and unavoidable impurities.
When tapping molten steel from a converter to a ladle, a carburizing agent, an alloy, and lime are added to the molten steel. In addition, during tapping, slag outflow is detected using infrared rays or the like, and slag outflow from the converter is prevented using a dart type slag stopper. Next, in the heating and stirring refining treatment, refining is performed using a predetermined flux, and Al is added to perform deoxidation. Further, molten steel is fed to the RH vacuum degassing device, and the temperature, composition, and the like of the molten steel are adjusted in the RH vacuum degassing device. Then, a billet cast piece (300 mm×400mm cross section) was produced by continuous casting. Subsequently, the square billet casting was subjected to heat treatment, and then rolled into a billet having a diameter of 215 mm. Further, the slab was hot rolled to obtain a steel bar having a diameter of 60mm, and the steel bar was annealed to obtain a round bar.
In the examples, the weight of a ladle receiving molten steel from a converter was measured before receiving the steel, and the amount of the base metal attached was measured. Further, the titanium content of the adhesion base metal was obtained from the titanium content in the molten steel at the time of casting in the previous treatment. The amount of the base metal adhering to the RH vacuum degassing device was measured by measuring the weights of the vacuum tank and the dip pipe of the RH vacuum degassing device before and after the previous vacuum degassing refining treatment. The titanium content of the adhered base metal was obtained from the titanium content in the molten steel at the end of the vacuum degassing refining treatment in the previous treatment. In this case, the previous treatment in the ladle and the previous treatment in the RH vacuum degasser are not limited to the same steel grade, and in many cases, different previous treatments are performed.
Further, the amount of FeSi alloy added and the titanium content in the secondary refining step of the heating and stirring refining treatment and the vacuum degassing refining treatment are considered. In the examples, the amounts of the matrix metal adhered to the ladle and the steel grade treated last, the amounts of the matrix metal adhered to the RH vacuum degassing apparatus and the steel grade treated last, and the amounts of the FeSi alloy added in the secondary refining step and the titanium content were varied for the respective test operations. The respective conditions and test results are shown in table 1. The utilization ratio of titanium in the molten steel in the FeSi alloy added in the vacuum degassing refining treatment was assumed to be 100%. In table 1, the titanium content of the ladle base metal (attached base metal of the ladle) and the RH base metal (attached base metal of the apparatus) are the titanium content in the molten steel at the time of casting in the charge of immediately before receiving steel and the titanium content in the molten steel after the vacuum degassing refining treatment of the immediately before charge, respectively.
The longitudinal sections of the 1/4 thick portion and the 1/2 thick portion of the round bar of the product obtained at the time of melting in each test were observed by microscopic examination. The area to be inspected is set to 3000mm 2 . The composition of the inclusions was specified by SEM (scanning electron microscope) and EDX (energy dispersive X-ray spectrometry) together with the inclusion measurement by microscopy, and the size and number of TiN-based inclusions were measured to evaluate cleanliness.
In examples 1 and 2 of the present invention, a high-grade FeSi alloy having a titanium content of 0.05 mass% or less was used as the FeSi alloy used in the RH vacuum degasser. In the present invention examples 1 and 2, the secondary refining step was performed on the molten steel treated before the ladle and the primary charge of the RH vacuum degassing apparatus, while the molten steel was limited to the steel grade having a titanium content of 0.040 mass% or less.
In examples 3 to 5 of the present invention, the secondary refining step was performed on all of the molten steels treated before the primary charging in the ladle and the RH vacuum degassing device, while limiting the content of titanium to a steel grade of 0.020% by mass or less. In examples 3 to 5 of the present invention, a common grade FeSi alloy having a titanium content of about 0.20 mass% was used as the FeSi alloy used in the RH vacuum degasser.
In the present invention examples 11 and 12, as in the present invention examples 3 to 5, the secondary refining step was performed on the molten steel treated before the primary charging of the ladle and the RH vacuum degassing apparatus while limiting the titanium content to the steel grade of 0.020% by mass or less. Further, as the FeSi alloy used in the RH vacuum degasser, a FeSi alloy of normal grade having a titanium content of about 0.20 mass% was used. However, the secondary refining step was performed using a steel grade having an aluminum content standard of more than 0.050 mass% of the molten steel treated before the primary charging of the ladle or the RH vacuum degassing device. In examples other than examples 11 and 12 of the present invention, the secondary refining step was performed with the steel grade having an aluminum content standard of 0.050 mass% or less of the molten steel treated before the primary charging of the ladle and the RH vacuum degassing device.
In example 6 of the present invention, a high-grade FeSi alloy having a titanium content of 0.05 mass% or less was used as the FeSi alloy used in the RH vacuum degasser. In addition, in the present invention example 6, the secondary refining step was performed on the molten steel treated before the ladle and the primary charge of the RH vacuum degassing apparatus, while the molten steel was limited to a more severe steel grade in which the titanium content standard was 0.010 mass% or less.
In example 7 of the present invention, a high-grade FeSi alloy having a titanium content of 0.05 mass% or less was used as the FeSi alloy used in the RH vacuum degasser. In addition, in the present invention example 7, the secondary refining step was performed on the molten steel treated before the primary charging of the ladle and the RH vacuum degassing apparatus, with the steel types limited to the titanium composition standard of 0.020 mass% or less and 0.010 mass% or less, respectively.
In example 8 of the present invention, a high-grade FeSi alloy having a titanium content of 0.05 mass% or less was used as the FeSi alloy used in the RH vacuum degasser. In addition, in example 8 of the present invention, the secondary refining step was performed on the molten steel treated before the primary charging of the ladle and the RH vacuum degassing apparatus, with the steel types limited to the titanium composition standard of 0.010 mass% or less and 0.020 mass% or less, respectively.
In example 9 of the present invention, a common-grade FeSi alloy having a titanium content of 0.20 mass% or less was used as the FeSi alloy used in the RH vacuum degasser. In addition, in example 9 of the present invention, the secondary refining step was performed on the molten steel treated before the ladle and the primary charge of the RH vacuum degassing apparatus, while the molten steel was limited to a more severe steel grade having a titanium content of 0.010 mass% or less.
In example 10 of the present invention, a high-grade FeSi alloy having a titanium content of 0.05 mass% or less was used as the FeSi alloy used in the RH vacuum degasser. In addition, in the present invention example 10, the secondary refining step was performed on the molten steel treated before the ladle and the primary charge of the RH vacuum degassing apparatus, while the molten steel was limited to a more severe steel grade having a titanium content of 0.010 mass% or less. However, in the present invention example 10, since the titanium content in the raw molten iron was high, the titanium content after tapping was 0.019 mass% higher than that in the other invention examples. Therefore, slag is removed after tapping from the converter to the ladle, and the slag amount is reliably made to be 25 kg-slag/t-steel or less.
In comparative example 1, as the FeSi alloy used in the RH vacuum degassing apparatus, a FeSi alloy of normal grade having a titanium content of about 0.20 mass% was used, and the secondary refining step was performed on the molten steel treated before the primary charging of the ladle, with the steel grade limited to a titanium content standard of 0.020 mass% or less. On the other hand, the molten steel treated before one charge of the RH vacuum degassing device is not limited to the titanium component standard, and the titanium content is about 0.15 mass%.
In comparative example 2, as the FeSi alloy used in the RH vacuum degassing apparatus, a FeSi alloy of normal grade having a titanium content of about 0.20 mass% was used, and the secondary refining step was performed on the molten steel treated before the primary charging in the RH vacuum degassing apparatus, with the steel grade limited to a titanium content standard of 0.020 mass% or less. On the other hand, in the molten steel treated before one charge of the ladle, there is no limitation on the composition standard of titanium, and the titanium content is about 0.08 mass%.
In comparative example 3, as the FeSi alloy used in the RH vacuum degassing apparatus, a high-grade FeSi alloy having a titanium content of about 0.05 mass% was used, and the secondary refining step was performed on the molten steel treated before the primary charging of the ladle, with the steel grade limited to a titanium content standard of 0.020 mass% or less. On the other hand, the molten steel treated before one charge of the RH vacuum degassing device is not limited to the titanium component standard, and the titanium content is about 0.15 mass%.
In comparative example 4, as the FeSi alloy used in the RH vacuum degassing apparatus, a high-grade FeSi alloy having a titanium content of about 0.05 mass% was used, and the secondary refining step was performed on the molten steel treated before the primary charging in the RH vacuum degassing apparatus, with the steel grade limited to a titanium content of 0.020 mass% or less. On the other hand, in the molten steel treated before one charge of the ladle, there is no limitation on the composition standard of titanium, and the titanium content is about 0.08 mass%.
In comparative example 5, as the FeSi alloy used in the RH vacuum degassing apparatus, a high-grade FeSi alloy having a titanium content of about 0.05 mass% was used. In addition, the secondary refining step was performed on the molten steel treated before the primary charging of the ladle and the RH vacuum degassing apparatus, while the molten steel was limited to a steel grade having a titanium content of 0.040 mass% or less. However, since the titanium content in the secondary raw material is high, the titanium content of the molten steel after tapping is as high as 0.0026 mass%, which deviates from the upper limit of the component standard.
In comparative examples 6 and 7, a high-grade FeSi alloy having a titanium content of about 0.05 mass% was used as FeSi alloy used in the RH vacuum degasser. However, the secondary refining step is performed on molten steel treated before the primary charging of the ladle and the RH vacuum degassing device without limiting the titanium component standard.
In the item "whether or not (1) is satisfied" in table 1, "Σ" indicates that the condition satisfies (1) and "×" indicates that the condition does not satisfy (1).
In examples 1 to 10 of the present invention, the ladle used in the subject charge was restricted by the titanium content in the molten steel held at least immediately before the subject charge was subjected to the steel receiving, the titanium content in the molten steel after tapping was set to 0.002 mass% or less, and the RH vacuum degassing apparatus for performing the vacuum degassing refining treatment of the subject charge was restricted by the titanium content at the end of the vacuum degassing refining treatment in the molten steel subjected to the treatment in the charge immediately before the treatment of the subject charge. As a result, in the present invention, the titanium content in the molten steel cast after the completion of the vacuum degassing refining treatment was controlled to be not more than the upper limit of the composition standard of the titanium to be melted, and the number of nitride-based inclusions was not more than 5 per 100mm 2 No TiN inclusions of 15 μm or more were found.
In particular, by limiting the base metal of the ladle and the base metal of the RH vacuum degasser, a great tendency was observed in the effect of reducing the number of nitride-based inclusions. However, in examples 11 and 12 of the present invention, the ladle used in the subject charge was limited by the titanium content in the molten steel held at least immediately before the subject charge was subjected to the steel receiving operation, and the RH vacuum degassing device for performing the vacuum degassing refining operation of the subject charge was limited by the titanium content in the molten steel subjected to the treatment in the charge immediately before the vacuum degassing refining operation of the subject charge, but the aluminum concentration in any molten steel was higher than 0.050 mass%. As a result, the base metal of the ladle and the base metal of the RH vacuum degasser were limited, but the effect of reducing the nitride-based inclusions was slightly smaller.
On the other hand, in the comparative example, the titanium content in the molten steel to be cast exceeded the upper limit of the composition standard of titanium to be melted in many cases, and in either case, it was: the number of nitride inclusions is 10 or more per 100mm 2 On the other hand, tiN inclusions having a size of 15 μm or more were found to be high-order and had poor cleanliness.
Claims (9)
1. A method for producing a cast piece by casting refined molten steel obtained by subjecting molten steel tapped from a converter or an electric furnace and fed into a ladle to at least vacuum degassing refining treatment, wherein,
with respect to a ladle used in a subject charge for producing the cast slab, the titanium content in molten steel held in the ladle at least immediately before steel receiving of the subject charge is used for limiting,
the titanium content in the molten steel after tapping of the object charge is set to 0.002 mass% or less,
with respect to a vacuum degassing apparatus that performs the vacuum degassing refining treatment on the object charge, a limitation is made on the titanium content at the end of the treatment in the vacuum degassing apparatus in molten steel that is treated in the vacuum degassing apparatus at least immediately before the vacuum degassing refining treatment of the object charge.
2. The method for producing a cast slab according to claim 1, wherein the molten steel tapped from the converter or the electric furnace and subjected to the steel into the ladle is subjected to a heating and stirring refining treatment and the vacuum degassing refining treatment in this order, and the refined molten steel thus obtained is cast.
3. The method for producing a cast slab according to claim 1 or 2, wherein the titanium content in the molten steel held immediately before the steel receiving of the object charge is set to 0.020% by mass or less with respect to a ladle used in the object charge.
4. The method for producing a cast slab according to claim 3, wherein the aluminum content in the molten steel held immediately before the steel receiving of the object charge is set to 0.050 mass% or less for the ladle used in the object charge.
5. The method for producing a cast sheet according to any one of claims 1 to 4, wherein, in the vacuum degassing apparatus for performing the vacuum degassing refining treatment of the object charge, the titanium content at the end of the treatment in the vacuum degassing apparatus in the molten steel that is treated in the vacuum degassing apparatus immediately before the vacuum degassing refining treatment of the object charge is made to be 0.020 mass% or less.
6. The method for producing a cast sheet according to claim 5, wherein, for the vacuum degassing apparatus that performs the vacuum degassing refining treatment of the object charge, the aluminum content at the end of the treatment in the vacuum degassing apparatus in the molten steel that is treated in the vacuum degassing apparatus immediately before the vacuum degassing refining treatment of the object charge is made to be 0.050 mass% or less.
7. The method for producing a cast sheet according to any one of claims 1 to 6, wherein,
the Ti content in the molten steel of the object charge immediately before tapping from the converter or the electric furnace is zero below an analysis limit,
the amount of increase in the titanium content in the molten steel from the time of tapping of the target charge to the time of ending the vacuum degassing refining treatment satisfies the following expression (1),
Δ[Ti]＝[Ti] LD +Σ(W t ×η t /100)+Δ[Ti] M ≤T 1 ×10…(1)
wherein, in the formula (1),
delta [ Ti ]: an increase in titanium content (kg-Ti/t-steel) in the molten steel from the time of tapping to the time of completion of the vacuum degassing refining treatment;
[Ti] LD : titanium content (kg-Ti/t-steel) in the molten steel after tapping;
W t : an amount of alloy added (kg-alloy/t-steel) from tapping to the end of the vacuum degassing refining treatment in the target charge;
η t : titanium content (mass%) of the alloy added from tapping to the end of the vacuum degassing refining treatment in the object charge;
Δ[Ti] M : an increase in titanium content in molten steel mixed from outside the alloy (kg-Ti/t-steel);
T 1 : titanium concentration standard upper limit value (mass%) of steel to be melted.
8. The method for producing a cast slab according to any one of claims 2 to 7, wherein the amount of slag flowing out of the converter or the electric furnace into the ladle at the time of tapping is set to 25 kg-slag/t-steel or less with respect to the weight of molten steel in the target charge at a time before the heating and stirring refining treatment.
9. The method for producing a cast sheet according to any one of claims 1 to 8, wherein a titanium content in the refined molten steel that is continuously cast is 0.0020 mass% or less.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2020-162684 | 2020-09-28 | ||
| JP2020162684 | 2020-09-28 | ||
| PCT/JP2021/035664 WO2022065511A1 (en) | 2020-09-28 | 2021-09-28 | Slab manufacturing method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN116194235A true CN116194235A (en) | 2023-05-30 |
Family
ID=80845485
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202180064402.6A Pending CN116194235A (en) | 2020-09-28 | 2021-09-28 | Method for producing cast sheet |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JP7248153B2 (en) |
| CN (1) | CN116194235A (en) |
| WO (1) | WO2022065511A1 (en) |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH06145883A (en) * | 1992-11-02 | 1994-05-27 | Daido Steel Co Ltd | High purity bearing steel and its production |
| JP4257368B2 (en) * | 2007-06-05 | 2009-04-22 | 株式会社神戸製鋼所 | Manufacturing method of high cleanliness steel |
| JP5176587B2 (en) * | 2008-02-22 | 2013-04-03 | 新日鐵住金株式会社 | Manufacturing method of high clean steel slab |
| CN107312906B (en) * | 2017-07-10 | 2019-06-14 | 西王金属科技有限公司 | A kind of smelting process of the ultrapure low titanium bearing steel of low cost |
-
2021
- 2021-09-28 JP JP2021576544A patent/JP7248153B2/en active Active
- 2021-09-28 CN CN202180064402.6A patent/CN116194235A/en active Pending
- 2021-09-28 WO PCT/JP2021/035664 patent/WO2022065511A1/en active Application Filing
Also Published As
| Publication number | Publication date |
|---|---|
| JPWO2022065511A1 (en) | 2022-03-31 |
| WO2022065511A1 (en) | 2022-03-31 |
| JP7248153B2 (en) | 2023-03-29 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA2798852C (en) | Steel for steel tube with excellent sulfide stress cracking resistance | |
| JP5803824B2 (en) | Method of melting carburized bearing steel | |
| CN105567907A (en) | Method for controlling plastic inclusions of austenitic stainless steel | |
| CN110004371B (en) | Wear-resistant steel and smelting method | |
| CN114574770B (en) | Preparation method of high-strength fatigue-resistant 60Si2MnA spring steel | |
| WO2012079415A1 (en) | Steel used for railway locomotive axle and the manufacturing method thereof | |
| CN103468866A (en) | Refining technology for molten medium-high carbon steel | |
| CN111286677B (en) | Ultralow-sulfur low-aluminum high-nitrogen steel and smelting method | |
| CN113025781B (en) | Method for producing low-carbon low-silicon ultralow-sulfur steel by adopting LF (ladle furnace) single-link process | |
| CN112695258B (en) | High-capacity smelting and component regulation and control method for ultra-high manganese TWIP steel | |
| CN116875912B (en) | High-purity high-carbon steel wire rod and production method thereof | |
| CN103225009A (en) | Method for producing high-cleanness steel | |
| WO2014191783A1 (en) | Production process of ultra high purity microalloyed steel containing sulphure, affecting metallurgical resulphurization processes | |
| CN114351035B (en) | Argon station pre-refining method for improving purity of bearing steel | |
| JP7248153B2 (en) | Method for manufacturing slab | |
| CN116806273A (en) | Nickel alloy with excellent surface properties and method for producing same | |
| CN115917014A (en) | Method for manufacturing high-cleanliness steel | |
| CN109778073B (en) | Free-cutting steel for automobile synchronizer and preparation method thereof | |
| WO2021256159A1 (en) | Method for producing cast slab that serves as material for steel with high fatigue strength | |
| CN112575144B (en) | Method for improving flaw detection qualification rate of medium plate | |
| JP5387045B2 (en) | Manufacturing method of bearing steel | |
| JP6984803B1 (en) | Manufacturing method of slabs used as a material for high fatigue strength steel | |
| CN117965840B (en) | Converter phosphorus control smelting method of low-temperature steel and production method of high-quality low-temperature steel | |
| CN115449599B (en) | Molten steel calcium deoxidization method | |
| US20230323492A1 (en) | Degassing method for manufacturing steel |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |