TW201900897A - Smelting method of high manganese steel - Google Patents

Abstract

Provided is a method for manufacturing high manganese steel ingots with which ingots can be manufactured with high efficiency and a high manganese yield can be obtained when manufacturing ingots of high manganese steel that includes 5% by mass or more manganese. This method comprises, when ingots of steel that includes 5% by mass or more manganese are manufactured, a decarbonization step for forming the hot metal into molten steel with a low carbon concentration by a decarbonization treatment performed on the hot metal in a converter furnace, a reduction step for reducing treatment of the molten steel by adding a manganese source and a silicon source to the molten steel accommodated in the converter furnace after the decarbonization step, and a degassing step for performing vacuum degassing treatment on the molten steel in a vacuum degassing device after the reduction step. In the reduction step, the manganese source is added according to the target manganese concentration of the steel, and the silicon source is added so as to satisfy Equation.

Description

Smelting method of high manganese steel

The invention relates to a method for smelting high-manganese steel.

Manganese has the advantage of increasing the strength of the steel material by adding it to steel. In addition, manganese has the advantages of reacting with sulfur remaining in the steel as an unavoidable impurity to form MnS, preventing the generation of harmful FeS, and suppressing the influence of sulfur in the steel material. According to the situation, most steel materials contain manganese. In recent years, low-carbon and high-manganese steels with low carbon content and high manganese content have been developed for the purpose of reducing the weight of structures, and are widely used as steel plates for pipelines or Steel plates for automobiles, etc.

In the steel making step, as a manganese source for adjusting the manganese concentration in the molten steel, manganese ore or high-carbon ferromanganese alloy (carbon content: 7.5% by mass or less), medium-carbon ferromanganese alloy (carbon content: 2.0% by mass or less) are generally used. ), Low-carbon ferromanganese alloy (carbon content: 1.0% by mass or less), silicon-manganese alloy (carbon content: 2.0% by mass or less), metallic manganese (carbon content: 0.01% by mass or less), and the like. In addition, in these manganese sources, in addition to manganese ore, the lower the carbon content, the more expensive. Therefore, in order to reduce the manufacturing cost, a method for smelting a manganese-containing steel using a manganese ore or a high-carbon ferromanganese alloy as a cheap manganese source has been proposed.

For example, in Patent Document 1, as a method for smelting a high-manganese steel, a method is proposed in which, after the blowing of the converter is completed, the bottom blowing gas is subjected to a flushing treatment and the steel is discharged into a steel drum, A high-carbon ferromanganese alloy having a carbon concentration of 1.0% by mass or more is charged with aluminum and deoxidized, and thereafter, Rheinstahl Heraeus (RH) gas degassing is performed. In addition, Patent Document 2 proposes a smelting method as a method for smelting high-manganese steel: using manganese ore, decarburizing refining of molten iron while reducing the manganese ore, and after decarburization is completed, The molten steel is transported to a vacuum degassing device without performing a deoxidation treatment of the molten steel using aluminum, and a decarburization treatment is performed by spraying a mixed gas of oxygen and an inert gas. Furthermore, in Patent Document 3, as a method for smelting high-manganese steel, a method is proposed in which decarburization and refining of high-manganese molten iron having a manganese concentration of 8% by mass or more under reduced pressure is reduced to 0.1% by mass or less In the case of a high carbon concentration, a refining gas is used as a transport gas, and a powdery decarburization refining additive containing Mn oxide is sprayed onto the molten iron. [Prior Art Literature] [Patent Literature]

Patent Literature 1: Japanese Patent Laid-Open No. 2013-112855 Patent Literature 2: Japanese Patent No. 4534734 Patent Literature 3: Japanese Patent Laid-Open No. 5-125428

[Problems to be Solved by the Invention] In the method for smelting high-manganese steels in Patent Documents 1 to 3, the manganese ore input into the converter is reduced during the decarburization and blowing of molten iron in the converter, or The manganese source is added to the molten steel during tapping of the autoclave, during refining of the steel drum, and during vacuum degassing refining, thereby increasing the manganese concentration of the molten steel. However, in such a smelting method, when a manganese source is added during decarburization, blowing, or tapping, the yield of the added manganese source is low, so a large amount of manganese source needs to be added, which increases the processing time and The increase in the cost of manganese has become a problem. In addition, when a manganese source is added at the time of tapping, refining a steel barrel, or vacuum degassing refining, heat loss occurs due to the melting of the manganese source. Therefore, it is necessary to heat the molten steel in the process after the converter. However, compared with the heat treatment in a converter, the heat treatment of molten steel using a ladle refining device or a vacuum degassing device is inefficient, and an increase in the cost of the treatment becomes a problem. These problems are particularly noticeable in high-manganese steels with a manganese concentration of 5 mass% or more.

Therefore, the present invention has been made focusing on the above-mentioned problems, and an object thereof is to provide a high-manganese steel that can obtain a high manganese yield and can be efficiently smelted when smelting a high-manganese steel containing 5 mass% or more of manganese. 2. Smelting method of high manganese steel. [Means for solving problems]

According to one aspect of the present invention, a method for smelting high-manganese steel is provided. When smelting a steel containing more than 5% by mass of manganese, the method includes a step of decarburizing, and dehydrating molten iron in a converter. Carbon treatment, so that the molten iron becomes a molten steel with a low carbon concentration; a reduction step, after the decarburizing step, adding a manganese source and a silicon source to the molten steel contained in the converter, Thereby, the molten steel is subjected to reduction treatment; and a degassing step, after the reduction step, the molten steel is subjected to vacuum degassing treatment in a vacuum degassing device, and in the reduction step, according to The added amount of the manganese source is to add the silicon source in a manner satisfying the formula (1).

[Number 1] x _Mn : manganese concentration (mass%) in manganese source x _Si : silicon concentration (mass%) in silicon source W _Mn : added amount of manganese source (kg / t) W _Si : added amount of silicon source (kg / t) [Effect of the invention]

According to one aspect of the present invention, there is provided a smelting method of high-manganese steel that can obtain a high manganese yield and can be efficiently smelted when smelting a high-manganese steel containing 5 mass% or more of manganese.

In the following detailed description, in order to provide a complete understanding of the present invention, embodiments of the present invention are exemplified to describe many specific details. However, it is clear that more than one embodiment can be implemented even without the description of the specific details. In order to simplify the drawings, well-known structures and devices are omitted. <Smelting method of high manganese steel> A smelting method of high manganese steel according to an embodiment of the present invention will be described with reference to Figs. 1 to 3. In the present embodiment, the molten steel discharged from the blast furnace is subjected to a refining process described later, thereby smelting a high-manganese steel as molten steel containing 5% by mass or more of manganese.

First, as shown in FIGS. 1 and 2, a decarburization step (S100) of performing a decarburization treatment on the molten metal 2 (also referred to as “melted iron”) as the molten iron contained in the converter 1 is performed (S100). The melt 2 is molten iron milled out of the blast furnace. After being milled out of the blast furnace, the molten steel is transported to a steel making plant to be a next step by using a transport container capable of containing the molten iron such as a molten iron bucket or a torpedo car. In addition, in order to reduce a medium solvent such as a lime source used in the converter 1, it is preferable to perform a dephosphorization treatment to reduce the phosphorus concentration of the molten iron before the molten iron is charged into the converter 1. In the dephosphorization process, a solid oxygen such as iron oxide or a gaseous oxygen such as iron oxide and a medium solvent containing lime are added to the molten iron contained in the molten iron transport container, and the iron is reacted with the gaseous oxygen or a stirring gas. Water is stirred to perform a dephosphorization reaction. In addition, in the dephosphorization treatment, in order to minimize the medium solvent used in the converter 1, it is preferable that the phosphorus concentration of the molten iron is lower than the upper limit concentration of the final component specification of the high manganese steel. Furthermore, since it is feared that the phosphorus concentration rises due to the pick-up of phosphorus from the added manganese source toward the molten iron in the subsequent steps, or the re-phosphorization from the molten slag, it is more preferable to perform dephosphorization treatment until the molten iron The phosphorus concentration is about 0.05 mass% (mass%) lower than the upper limit of the component specification. Thereafter, the slag generated by the treatment is removed (also referred to as "slag removal"). Further, in order to make the phosphorus concentration of the molten iron lower than the upper limit value of the component specification, it is preferable to perform a desiliconization treatment before the dephosphorization treatment, and to remove silicon that hinders an efficient dephosphorization reaction in advance.

In the decarburization step, before performing the decarburization treatment, the molten metal 2 as the molten iron carried by the transport container is transferred into a molten iron bucket and then charged into the converter 1 as a primary refining furnace. In addition, a scrap that becomes an iron source may be loaded into the furnace body 10 before the melt 2 is charged. The converter 1 is a conventional converter equipment, and as shown in FIG. 2, the converter 1 includes a furnace body 10, a top-blown torch 11, a plurality of bottom-blown nozzles 12, and a chute 13. The furnace body 10 is a cylindrical or pear-type refining furnace having a furnace mouth as an opening in the upper portion, and a refractory material is provided inside. The top-blown torch 11 is arranged above the furnace body 10 and is configured to be vertically movable (up-down direction in FIG. 2). The top-blown torch 11 has a plurality of nozzle holes formed at the lower end, and an oxidizing gas containing at least oxygen supplied from a supply device (not shown) is sprayed into the melt 2 contained in the furnace body 10 from the plurality of nozzle holes. . A plurality of bottom-blown nozzles 12 are provided on the bottom of the furnace body 10, and blow agitation gas such as argon or nitrogen supplied from a supply device (not shown) as an inert gas into the melt 2 contained in the furnace body 10, and This stirs the melt 2. The chute 13 is arranged above the furnace body 10 and is connected to a plurality of furnace hoppers (not shown) storing various auxiliary materials such as a medium solvent containing lime or alloy iron, and the cut auxiliary materials are added from each furnace hopper to Inside the furnace body 10.

In the decarburization step, the melt 2 contained in the furnace body 10 is stirred by the stirring gas blown from the bottom-blowing nozzle 12, and the melt 2 is sprayed from the top-blowing blow pipe 11 (also referred to as “ Oxygen supply ") An oxidizing gas is supplied to the melt 2 to perform decarburization treatment (also referred to as" decarburization blowing ") at atmospheric pressure. In the decarburization blowing, the decarburization reaction is performed by reacting the oxygen blown into the melt 2 through the top-blowing torch 11 and the carbon in the melt 2. When Cr or Ni is contained in the component specification of the high-manganese steel (when it must be added), during the decarburization and blowing process, auxiliary materials such as alloy iron containing Cr or Ni are passed through the chute 13. Added to melt 2. In the decarburization step, decarburization blowing is performed until the carbon concentration of the molten metal 2 becomes a predetermined range, and the molten metal 2 is changed from molten iron having a high carbon concentration to molten steel having a low carbon concentration. The predetermined range of the carbon concentration at this time is preferably 0.05% by mass or more and 0.2% by mass or less. The reason for this is that when the carbon concentration of the melt 2 after the decarburization step is less than 0.05% by mass, the oxygen potential of the melt 2 becomes high, resulting in a decrease in the yield of the manganese source. On the other hand, when the carbon concentration of the melt 2 after the decarburization step is more than 0.2% by mass, the decarburization treatment in the secondary refining step is required, and the treatment cost increases. When the carbon concentration of the melt 2 is within a predetermined range, the supply of the oxidizing gas into the furnace body 10 is stopped, and the decarburization step ends.

After the decarburization step, a reduction step of adding a manganese source and a silicon source to the furnace body 10 containing the melt 2 and performing a reduction treatment on the melt 2 as the molten steel is performed (S102). The manganese source is an ore, an alloy, or a metal containing manganese. As the manganese source, for example, manganese ore or high-carbon ferromanganese alloy, medium-carbon ferromanganese alloy, low-carbon ferromanganese alloy, silicon-manganese alloy, metal manganese, and the like can be used. A silicon source is an ore, alloy, or metal containing silicon. As the silicon source, for example, a ferrosilicon alloy or a silicon-manganese alloy can be used. The manganese source and the silicon source may be added from the furnace mouth through the chute 13, or may be added from the furnace mouth of the furnace body 10 using a waste chute (not shown) for loading waste. Furthermore, when a manganese source and a silicon source are added, a stirring gas is blown in from a plurality of bottom-blown nozzles 12 to add the molten solution 2 while stirring.

In the reduction step, a manganese source is added in an amount corresponding to a target manganese concentration as a component specification of the high manganese steel. That is, the amount of the manganese source to be added is determined by the manganese content of the manganese source or the carbon concentration of the melt 2 according to the target manganese concentration. In this case, the actual yield of the manganese source can also be considered. In addition, in the reduction step, it is not necessary to set the manganese concentration of the melt 2 as the target concentration, and the manganese concentration of the melt 2 can be set to a lower concentration than the target concentration in a manner to be adjusted in the degassing step described later. From the viewpoint of thermal efficiency, it is preferable to increase the amount of manganese source added in the reduction step as much as possible relative to the amount of manganese source added in the degassing step. Furthermore, from the viewpoint of reducing the cost of the treatment, it is preferable to use a manganese ore or a low-cost manganese source having a high carbon concentration as long as it does not affect the adjustment of components other than manganese such as carbon.

The silicon source is added in an amount to satisfy the following formula (1). (1) In the formula, x _Mn represents the manganese concentration (mass%) in the manganese source, x _Si represents the silicon concentration (mass%) in the silicon source, W _Mn represents the added amount (kg / t) of the manganese source, and W _Si Indicates the amount of silicon source added (kg / t). That is, the silicon source is added in an amount corresponding to the amount of the added manganese source.

[Number 2]

In addition, in the reduction step, after adding a manganese source and a silicon source, a stirring gas is blown in from a plurality of bottom-blowing nozzles 12, and the molten liquid 2 is stirred for a predetermined time. Here, since the oxygen potential of the melt 2 after the decarburization step is high, if a manganese source is added to the melt 2, the manganese in the manganese source does not remain in the melt 2 but is oxidized to become Manganese oxide (MnO) is included in the slag 3. However, in this embodiment, a silicon source is added in addition to the manganese source. Therefore, the manganese in the manganese source or the manganese oxide in the slag 3 generated by the decarburization step undergoes a reaction represented by the following formula (2). By being reduced, the manganese concentration of the melt 2 is increased. In addition, by preferentially oxidizing the silicon in the silicon source, the oxygen potential of the melt 2 decreases. This makes it easy for the manganese in the manganese source to remain in the melt 2, and the concentration of the manganese in the melt 2 becomes high. 2 (MnO) + [Si] = (SiO ₂ ) +2 [Mn]… (2)

Furthermore, in the reduction step, it is preferable that the alkalinity (CaO / SiO) of the slag 3 is defined by a ratio of the concentration (mass%) of CaO in the slag 3 to the concentration (mass%) of SiO ₂ . ₂ ) Add lime to the furnace body 10 in a manner of 1.6 or more and 2.4 or more. This promotes the slag formation of the slag 3 and the desulfurization of the melt 2 represented by the following formula (3). 2 [S] + [Si] +2 (CaO) = 2 (CaS) + (SiO ₂ ) (3)

Furthermore, when the amount of silicon source added is lower than the range of formula (1), that is, when the amount of silicon source added is small, the reduction reaction of manganese oxide is not performed, so the manganese of melt 2 cannot be increased. concentration. On the other hand, when the amount of silicon source added is higher than the range of formula (1), that is, when the amount of silicon source is increased, the amount of lime used to adjust the alkalinity becomes too large, so refining The cost of processing increases. In addition, when a large amount of the silicon source is added, the silicon concentration of the melt 2 becomes high, and the upper limit of the component specification value may be exceeded. In this case, in the next step, a desilication treatment for reducing the silicon concentration of the melt 2 is required, which is not preferable.

Further, in the reduction step, when the reduction treatment is completed, the molten liquid 2 of the furnace body 10 is transferred (also referred to as "steel tapping") into a steel ladle. At this time, it is preferable to place the lime of 5 kg / t or more and 10 kg / t or less in advance in a steel drum in an amount per 1 t of the molten iron. By placing the lime in front of the steel bucket, it is possible to prevent white smoke from being generated during tapping, and to suppress an increase in the sulfur concentration of the melt 2 caused by resulfurization originating from the slag 3.

After the reduction step, a degassing step (S104) is performed in the vacuum degassing device 5 to perform a vacuum degassing treatment on the melt 2 as the molten steel. The vacuum degassing device 5 is a vacuum oxygen decarburization (VOD) type degassing device, and performs a degassing treatment by stirring the melt 2 contained in the steel drum 4 under reduced pressure. The vacuum degassing device 5 includes a vacuum tank 50, an exhaust pipe 51, a stirring gas supply path 52, a top-blown blow pipe 53, and a supply port 54. The vacuum tank 50 is a container that can hold the steel drum 4 inside, and has a removable top cover 500 so that the steel drum 4 can be taken out and put inside. The exhaust pipe 51 is provided on the side of the vacuum tank 50 and is connected to an exhaust device (not shown). The stirring gas supply path 52 is arranged inside from the outside of the vacuum tank 50, and the front end of the inside of the vacuum tank 50 is connected to the blowing inlet 40 of the steel tub 4. In the stirring gas supply path 52, a front end on the inner side of the vacuum tank 50 is connected to a stirring gas supply device (not shown), and a stirring gas such as argon supplied from the stirring gas supply device is supplied to the blowing inlet of the steel drum 4. 40. The top-blowing type blowing pipe 53 is inserted through the center of the upper cover 500 and is configured to be vertically movable (up-down direction in FIG. 3). In addition, a nozzle hole is formed at the lower end of the top-blowing type blow pipe 53, and an oxidizing gas containing at least oxygen supplied from a supply device (not shown) sprays the oxidizing gas from the nozzle hole to the melt contained in the steel barrel 4.液 2。 Liquid 2. The supply port 54 is an input port formed in the upper cover 500 and connected to a plurality of furnace upper hoppers (not shown) storing various auxiliary materials such as a medium solvent containing lime or alloy iron. The raw material is added to the melt 2 contained in the steel drum 4.

In the degassing step, after the steel drum 4 is accommodated in the vacuum tank 50, the molten liquid 2 is stirred by blowing stirring gas through the self-blow inlet 40, and exhausted from the exhaust pipe 51 using an exhaust device. The inside of the vacuum tank 50 is decompressed, and a vacuum degassing process is performed. By performing such a vacuum degassing treatment, the gas components (nitrogen or hydrogen, etc.) in the melt 2 are removed, the components of the melt 2 are homogenized, the inclusions of the melt 2 are removed, and the melt 2 Adjustment of temperature, etc. In addition, in the degassing step, when the vacuum degassing is performed, the auxiliary raw materials for component adjustment are supplied through the components of the melt 2 before or during the processing of the vacuum degassing so as to become the target component range. The port 54 is added to the melt 2. At this time, when the manganese concentration of the melt 2 before the vacuum degassing treatment is lower than the target concentration, a manganese source such as metal manganese, a high-carbon ferromanganese alloy, and a low-carbon ferromanganese alloy is added to the molten metal in an amount required for component adjustment. Liquid 2. In addition, when adjustment of components such as Al, Ni, Cr, Cu, Nb, Ti, V, Ca, B, and the like is required, a subsidiary raw material containing each component is added to the melt 2. Furthermore, for the purpose of desulfurization and the like, it is also possible to use a substance containing CaO or a substance containing MgO, a substance containing aluminum, a substance containing Al ₂ O _3, a substance containing SiO _{2 and} the like to adjust or promote the composition of the slag 3 The auxiliary material for the desulfurization reaction is added to the melt 2.

In the degassing step, it is preferable to perform the melt 2 under the condition that the stirring power ε (W / t) represented by the following formula (4) is 300 W / t or more and 1300 W / t or less. Stir. When the stirring power ε is less than 300 W / t, since the stirring power becomes small, it takes time for the denitrification treatment or dehydrogenation treatment, and the processing time for the vacuum degassing treatment is extended, which is not satisfactory. In addition, when the stirring power ε is greater than 1300 W / t, the entrainment amount of the slag 3 toward the melt 2 is increased, and the defect rate due to slag-based inclusions is increased, which is not satisfactory. In the formula (4), Q _n represents the flow rate of the stirring gas (Nm ³ / min), T _l represents the temperature (K) of the melt 2, W _m represents the weight (t) of the melt 2, and ρ _l represents The density of the melt 2 (kg / m ³ ), h is the depth of the melt 2 in the steel bucket 4, that is, the height of the liquid surface (m), P ₁ is the environmental pressure (Torr), and η is the energy transfer efficiency (-), T _n represents the temperature (K) of the stirring gas. In addition, 1 Torr is (101325/760) Pa.

[Number 3]

Furthermore, in the degassing step, when the temperature of the melt 2 is lower than the target temperature after the completion of the degassing step, a temperature increasing treatment for increasing the temperature of the melt 2 may be performed in the vacuum degassing treatment. In the temperature increasing process, after adding aluminum to the melt 2 from the supply port 54, an oxygen-containing oxidizing gas is sprayed into the melt 2 from a top-blowing torch 53. Thereby, the aluminum in the molten metal 2 and the oxygen of the oxidizing gas are reacted, whereby the temperature of the molten metal 2 can be raised. In addition, in the temperature increasing treatment, it is preferable that the jet flow of the oxidizing gas sprayed from the top-blown torch 53 calculated by the equations (5) and (6) is performed so as to be 10 kPa or more and 50 kPa or less. Dynamic pressure P (kPa) is controlled. By controlling the dynamic pressure P within the above range, even if the evaporation of manganese originating from the melt 2 is suppressed to a minimum, the melt 2 can be efficiently heated. In the formula (5), ρ _g represents the density of the oxidizing gas (kg / Nm ³ ), and U represents the flow rate (m / sec) of the oxidizing gas ejected from the nozzle of the top-blown torch 53 at the tip of the nozzle. In the formula (6), F represents the flow rate (Nm ³ / h) of the oxidizing gas, and S represents the cross-sectional area (m ² ) of the nozzle of the top-blown torch 53.

[Number 4]

The molten steel which has a target component concentration is subjected to smelting by passing through a degassing step. Furthermore, after the degassing step, the molten steel to be smelted is continuously cast, thereby manufacturing a slab of high-manganese steel having a predetermined shape such as a slab.

<Modifications> The present invention has been described with reference to specific embodiments, but it is not intended to limit the invention by these descriptions. For those skilled in the art, by referring to the description of the present invention, other embodiments of the present invention including various modifications will be clarified together with the disclosed embodiments. Therefore, it should be understood that the embodiments of the invention described in the scope of the patent application also include the embodiments including the modifications described in the present specification either individually or in combination.

For example, in the said embodiment, although the vacuum degassing apparatus 5 was made into the refining apparatus of a VOD system, this invention is not limited to the said example. For example, the vacuum degassing device 5 may be an RH-type degassing device or a Dortmund Horder (DH) -type degassing device. In addition, when the vacuum degassing device is a RH-type degassing device, in order to suppress the evaporation of manganese, it is preferable that the pressure in the tank space of the vacuum tank be 50 Torr to 100 Torr under the following conditions ( 7) The annular flow rate Q (t / min) of the molten steel represented by the formula is set to be 150 t / min or more and 200 t / min or less. In addition, when denitrification or dehydrogenation of molten steel is required, the treatment can be carried out in a tank with a pressure of less than 50 Torr, but it is preferably 50 Torr or more and 100 Torr or less after denitrification and dehydrogenation. The space pressure in the tank is processed. (7) In the formula, K represents a constant, G represents a flow rate (NL / min) of a blow-in gas for returning from a dipping tube, D represents an inner diameter (m) of the dipping tube, and P ₂ represents an external pressure (Torr ), P ₃ represents the space pressure (Torr) in the vacuum tank.

[Number 5]

Moreover, in the said embodiment, although only the molten steel 2 which is the molten steel manufactured by the converter 1 was used as the molten metal 2 processed by the vacuum degassing device 5, this invention is not limited to the said example. For example, the molten steel produced by the converter 1 may be mixed with molten steel smelted by other refining furnaces and used as the molten liquid 2 processed by the vacuum degassing device 5. In this case, by increasing the manganese concentration of the molten steel smelted in another refining furnace, the manganese concentration of the molten steel produced in the converter 1 can be reduced.

Further, in the embodiment described above, after adding a manganese source and a silicon source in the reduction step, it is assumed that agitating gas is blown in from a plurality of bottom blowing nozzles 12 and the melt 2 is stirred for a predetermined time. The invention is not limited to the examples. In the reduction step, in addition to the blowing of the stirring gas, the oxidizing gas originating from the top-blown torch 11 may be sprayed. In particular, when it is necessary to raise the temperature of the melt 2, the heat treatment may be performed by an oxidation reaction using an oxidizing gas.

Further, in the above-mentioned embodiment, it is assumed that the molten iron is subjected to dephosphorization treatment before the decarburization treatment, but the present invention is not limited to the examples. For example, before the decarburization treatment, in addition to the dephosphorization treatment, a desulfurization treatment that reduces the sulfur concentration in the molten iron may be performed. Depending on the equipment configuration, the desulfurization treatment may be performed before or after the dephosphorization treatment. Furthermore, in the said embodiment, although it is set as the dephosphorization process to the molten iron contained in the molten iron carrying container, this invention is not limited to the said example. The dephosphorization treatment may be, for example, a method in which a molten iron contained in a converter-type refining furnace is sprayed with an oxidizing gas from a top-blown torch to perform a treatment.

<Effects of Embodiments> (1) Regarding the smelting method of high manganese steel according to one aspect of the present invention, when smelting a steel containing 5 mass% or more of manganese, the method includes a decarburization step (step S100), and In the converter 1, molten iron (melt 2) is subjected to decarburization treatment, thereby the molten iron is made into molten steel (melt 2) with a low carbon concentration; a reduction step (step S102), and after the decarburization step, manganese is removed. The source and the silicon source are added to the molten steel contained in the converter 1, thereby reducing the molten steel; and a degassing step (step S104), after the reducing step, the molten steel is processed in the vacuum degassing device 5. Vacuum degassing, and in the reduction step, a manganese source is added according to the target manganese concentration of the steel, so that the silicon source is added in a manner satisfying the formula (1).

According to the configuration of (1), since the reduction reaction of the formula (2) can be promoted, the manganese in the added manganese source easily remains in the melt 2. In addition, since the manganese source is added in the converter 1, the heat loss (the decrease in the temperature of the melt 2) caused by the addition of the manganese source can be suppressed. Furthermore, after the manganese source is added, the melt 2 can be subjected to a heat treatment in the converter 1, so the heat treatment can be performed efficiently. Furthermore, it is possible to suppress the addition of an excess silicon source in an amount sufficient to promote the reduction reaction, and it is not necessary to perform a desiliconization process in the degassing step, so that the degassing treatment can be efficiently performed in a short treatment time. As the degassing treatment time becomes longer, not only the cost of the treatment increases, but also the production efficiency decreases. That is, according to the configuration of (1), when high-manganese steel containing 5% by mass or more of manganese is smelted, a high manganese yield can be obtained, and high-manganese steel can be efficiently smelted.

(2) In the configuration of (1), as the vacuum degassing device 5, a device for stirring molten steel by blowing stirring gas from the bottom of a ladle containing molten steel is used in the degassing step. The vacuum degassing treatment was performed while stirring the molten steel under the condition that the stirring power ε represented by the formula (4) was 300 W / t or more and 1300 W / t or less. According to the configuration of (2), the time required for the denitrification process or the dehydrogenation process can be shortened, and further, the entrapment of the slag 3 into the melt 2 can be suppressed. Therefore, the processing time of the vacuum degassing process can be shortened. [Example 1]

Next, Example 1 performed by the present inventors will be described. In Example 1, the molten iron that was milled from the blast furnace was subjected to a desiliconization treatment and a dephosphorization treatment, and the phosphorus concentration was set to 0.010% by mass. In the same manner as the embodiment, the hot metal is subjected to a decarburization step, a reduction step, and a degassing step, thereby smelting a high-manganese steel having a manganese concentration of 5 mass% or more. In addition, the components of the smelted high manganese steel are carbon concentration: 0.145 mass% or more and 0.155 mass% or less, manganese concentration: 24 mass% or more and 25 mass% or less, and silicon concentration: 0.1 mass% or more and 0.2 mass% or less. , Sulfur concentration: 0.002 mass% or less, nitrogen concentration: 100 ppm or less, hydrogen concentration: 5 ppm or less.

In the decarburization step, as in the above-mentioned embodiment, the melt 2 as the molten iron that has been subjected to the pretreatment of the molten iron is subjected to the decarburization treatment, and the decarburization and blowing is performed until the carbon concentration becomes 0.05% by mass. Made of molten steel. In the reduction step, a high-carbon ferromanganese alloy and metallic manganese are added as a manganese source, and a ferrosilicon alloy is added as a silicon source to the melt 2 as the molten steel subjected to the decarburization treatment. Then, while the molten liquid 2 is being stirred by the stirring gas, the supply of oxygen from the top-blown torch 11 is continuously performed to perform a reduction treatment, thereby dissolving the manganese source, thereby increasing the manganese concentration of the molten liquid 2. The addition amount of the silicon source is set to satisfy the formula (1). In addition, a manganese source and lime are added together in the reduction step. The manganese concentration of the melt 2 at the end of the reduction treatment was approximately 24% by mass. Further, in the reduction step, when the melt 2 is transferred (steel) from the converter 1 to the steel drum 4, about 0.8 kg of metal aluminum is added per 1 ton of molten steel with respect to the melt 2 of the produced steel.

In the degassing step, similarly to the above-mentioned embodiment, a vacuum degassing device 5 of the VOD method is used to degas the molten steel 2 having a reduction step of 150 tons as molten steel. In the degassing step, the Ar gas at a flow rate of 2000 Nl / min is blown into the melt 2 from the blowing inlet 40 of the steel drum 4 and stirred, and the pressure in the tank space of the vacuum tank 50 is set to 2 Torr for degassing. In the degassing step, in the degassing treatment, metal manganese and a high-carbon ferromanganese alloy are added to the melt 2 to adjust the composition.

In addition, in Example 1, for comparison, smelting of high-manganese steel was performed even when the addition amount of the silicon source in the reduction step did not satisfy the formula (1) (Comparative Example 1). The conditions other than the addition amount of the silicon source in the reduction step in Comparative Example 1 are the same as in Example 1. As a result of Example 1, Table 1 shows the addition amount of the silicon source in the reduction step, the Mn yield, the silicon concentration of the melt 2 during tapping, and the time required for the degassing treatment in the degassing step. Furthermore, in Table 1, 0.013 × W _Mn × x _Mn / x _Si represents the lower limit value of the range shown by the formula (1), and 0.150 × W _Mn × x _Mn / x _Si represents the upper limit of the range shown by the formula (1) Limit. As shown in Table 1, in Example 1, the six conditions of Example 1-1 to Example 1-6 in which the amount of silicon source added W _Si falls within the range of the formula (1), and the addition of silicon source The high-manganese steel was smelted under a total of 10 conditions of the four conditions of Comparative Example 1-1 to Comparative Example 1-4, where the amount W _{Si was} outside the range of the formula (1). In addition, the Mn yield in Table 1 indicates how much manganese contained in the manganese source used in the reduction step was added to the melt 2, that is, the manganese component contained in the manganese source was compared to the melt 2 before and after the reduction step. How much the increase in manganese concentration contributes.

[Table 1]

As shown in Table 1, under the conditions of Comparative Example 1-1 and Comparative Example 1-2, the manganese yield was lower than 46% as compared with other conditions. This is considered to be because the addition amount of the silicon source was small, and therefore the reduction reaction of the slag 3 represented by the formula (2) was not sufficiently performed. In Comparative Examples 1-1 and 1-2, since the yield of Mn is low, it is necessary to add a silicon source in the degassing step for reduction treatment, and then adjust the composition and temperature, which is required for the degassing step. The time is longer than that of Examples 1-1 to 1-6.

In addition, under the conditions of Comparative Examples 1-3 and Comparative Examples 1-4, although the manganese yield was high, the silicon concentration at the time of tapping exceeded 0.20% by mass as the upper limit of the specification. The reason for this is considered to be that the melt 2 was supplied with silicon in an amount greater than the amount consumed in the reduction reaction of the slag 3 represented by the formula (2) or the desulfurization reaction represented by the formula (3). In Comparative Examples 1-3 and 1-4, the silicon concentration at the time of tapping was high. Therefore, the degassing treatment was required in the degassing treatment step. The time required for the degassing step was longer than that in Examples 1-1 to 1-2. Examples 1-6 are long. Furthermore, in the desiliconization process, an oxidizing gas is sprayed into the melt 2 from the top-blown torch 53, whereby the silicon contained in the melt 2 is oxidized and removed. On the other hand, under the conditions of Examples 1-1 to 1-6, a high yield of manganese can be obtained in the reduction step, and a silicon source is not added more than necessary, thereby reducing the silicon during tapping. concentration. Therefore, the time required for the degassing step can be shortened. [Example 2]

Next, Example 2 performed by the present inventors will be described. In Example 2, the same smelting method as in Examples 1-4 was used to perform smelting of high-manganese steel under a plurality of conditions where the stirring power ε in the degassing step was changed. In addition, the components of the smelted high manganese steel are carbon concentration: 0.145 mass% or more and 0.155 mass% or less, manganese concentration: 24 mass% or more and 25 mass% or less, and silicon concentration: 0.1 mass% or more and 0.2 mass% or less. , Sulfur concentration: 0.002 mass% or less, nitrogen concentration: 100 ppm or less, hydrogen concentration: 5 ppm or less.

Specifically, as in the decarburization step, as in Example 1-4, the decarburization treatment was performed on the melt 2 as the molten iron that was subjected to the pretreatment of the molten iron in the converter 1, and decarburization and blowing were performed until the carbon The molten steel was produced until the concentration became 0.05% by mass. Next, as a reduction step, a silicon source of 35 kg / t was added to perform a reduction treatment on the melt 2 in the same manner as in Example 1-4. The manganese concentration of the melt 2 at the end of the reduction treatment was approximately 24% by mass. Further, as a degassing step, the melt 2 was degassed in the vacuum degassing device 5 in the same manner as in Example 1-4. In the degassing step, the flow rate of the Ar gas blown from the blowing inlet 40 of the steel drum 4 is adjusted, whereby the degassing treatment is performed under a plurality of conditions in which the stirring power ε is arbitrarily changed.

As a result of Example 2, Table 2 shows the addition amount of the silicon source in the reduction step, the Mn yield, the silicon concentration of the melt 2 during tapping, the stirring power in the degassing step, and the amount in the degassing step. Time required for degassing. As shown in Table 2, in Example 2, the high-manganese steel was smelted under 10 conditions of Examples 2-1 to 2-10 with different stirring powers in the degassing step. The stirring power ε in the degassing step in Example 1-4 corresponds to Example 2-1. In addition, in Examples 2-1 to 2-10, the smelting conditions other than the above were the same as those in Example 1-4.

[Table 2]

As shown in Table 2, under the conditions of Examples 2-3 to 2-8 under which the stirring power ε is 300 W / t or more and 1300 W / t or less, the stirring power ε is less than 300 W / t. As compared with Examples 2-1, 2-2, or Examples 2-9 and 2-10 in which the stirring power ε exceeded 1300 W / t, it was confirmed that the time required for the degassing treatment was shorter. The reason is considered to be that the appropriate stirring power was applied to the melt 2 and the stirring was performed, thereby promoting dehydrogenation, denitrification, and inclusion inclusions in the vacuum degassing treatment.

On the other hand, under the conditions of Examples 2-1 and 2-2 where the stirring power ε is less than 300 W / t, because the stirring is weak, dehydrogenation or denitrification takes time, so it becomes necessary for degassing treatment. The result of longer time. In addition, under the conditions of Examples 2-9 and 2-10 where the stirring power ε exceeds 1300 W / t, the stirring was too strong, so the amount of slag 3 entrained into the melt 2 was increased, so that the melt 2 Since it takes time for the slag-based inclusions to float out, the time required for the degassing treatment becomes longer.

1‧‧‧ converter

10‧‧‧furnace

11, 53‧‧‧ Top-blowing blowpipe

12‧‧‧ bottom blow nozzle

13‧‧‧chute

2‧‧‧ melt

3‧‧‧ slag

4‧‧‧Steel bucket

40‧‧‧ blowing inlet

5‧‧‧Vacuum degassing device

50‧‧‧vacuum tank

500‧‧‧ Upper cover

51‧‧‧ exhaust pipe

52‧‧‧ Stirring gas supply path

54‧‧‧ supply port

S100‧‧‧Decarbonization step

S102‧‧‧Restore steps

S104‧‧‧Degassing step

FIG. 1 is a flowchart showing a method for smelting a high-manganese steel according to an aspect of the present invention. Fig. 2 is a schematic diagram showing a converter. Fig. 3 is a schematic diagram showing a vacuum degassing device.

Claims (2)

A method for smelting high-manganese steel, characterized in that, when smelting a steel containing more than 5 mass% of manganese, the method includes: a decarburization step of performing decarburization treatment on molten iron in a converter, thereby making the iron Water becomes molten steel with a low carbon concentration; a reduction step, after the decarburization step, a manganese source and a silicon source are added to the molten steel contained in the converter, thereby reducing the molten steel A treatment; and a degassing step, after the reduction step, performing vacuum degassing treatment on the molten steel in a vacuum degassing device, and in the reduction step, according to the amount of the manganese source added to meet (1) adding the silicon source in a manner; x _Mn : manganese concentration (mass%) in manganese source x _Si : silicon concentration (mass%) in silicon source W _Mn : added amount of manganese source (kg / t) W _Si : added amount of silicon source (kg / t). The method for smelting high-manganese steel according to item 1 of the scope of patent application, wherein, as the vacuum degassing device, agitating gas is blown from the bottom of a steel ladle containing the molten steel to stir the vacuum A device for melting steel, and in the degassing step, the molten steel is stirred while the stirring power ε represented by the formula (4) is 300 W / t or more and 1300 W / t or less. Vacuum degassing; Q: flow rate of stirring gas (Nm ³ / min) T _l : temperature of molten steel (K) W _m : weight of molten steel (t) ρ _l : density of molten steel (kg / m ³ ) h: height of liquid surface (M) P ₂ : ambient pressure (Torr) η: energy transfer efficiency (-) T _n : temperature (K) of stirring gas.