WO2018216660A1

WO2018216660A1 - Method for manufacturing high manganese steel ingot

Info

Publication number: WO2018216660A1
Application number: PCT/JP2018/019526
Authority: WO
Inventors: 勇輔藤井; 中井　由枝; 信彦小田; 太小笠原; 菊池　直樹
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2017-05-25
Filing date: 2018-05-21
Publication date: 2018-11-29
Also published as: TWI685577B; KR102315999B1; KR20190142355A; EP3633051B1; JP6551626B2; EP3633051A1; EP3633051A4; TW201900897A; JPWO2018216660A1; CN110621793A

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 (step S100) for forming the hot metal into molten steel (melt (2)) with a low carbon concentration by a decarbonization treatment performed on the hot metal (melt (2)) in a converter furnace (1), a reduction step (step S102) 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 (1) after the decarbonization step, and a degassing step (step S104) for performing vacuum degassing treatment on the molten steel in a vacuum degassing device (5) 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 (1).

Description

Method for melting high manganese steel

The present invention relates to a method for melting high manganese steel.

Manganese has the advantage of improving the strength of the steel material by adding it to the steel. Manganese also has the advantage of reacting with sulfur remaining in the steel as an inevitable impurity to form MnS, preventing the formation of harmful FeS and suppressing the influence of sulfur in the steel material. For this reason, most of the steel material contains manganese. In recent years, low-carbon and high-manganese steels with low carbon content and high manganese content that have both high tensile strength and high workability have been developed to reduce the weight of structures. Widely used as steel plates and automotive steel plates.

In the steelmaking process, manganese sources used for adjusting the manganese concentration in molten steel include manganese ore, high carbon ferromanganese (carbon content: 7.5 mass% or less), medium carbon ferromanganese (carbon content: 2). 0.0 mass%), low carbon ferromanganese (carbon content: 1.0 mass% or less), silicomanganese (carbon content: 2.0 mass% or less), metal manganese (carbon content: 0.01 mass%) % Or less) is generally used. Moreover, these manganese sources become expensive as the carbon content decreases, except for manganese ore. Therefore, for the purpose of reducing the manufacturing cost, a method for melting manganese-containing steel using manganese ore or high carbon ferromanganese, which is an inexpensive manganese source, has been proposed.

For example, in Patent Document 1, as a method of melting high manganese steel, the carbon concentration is 1. when the steel is discharged to a ladle after rinsing with a bottom blowing gas after the completion of the converter blowing. There has been proposed a method in which high-carbon ferromanganese of 0% by mass or more is introduced, aluminum is introduced, deoxidation treatment is performed, and then RH gas degassing treatment is performed.
Further, in Patent Document 2, as a method for melting high manganese steel, manganese ore is used to decarburize and refine hot metal while reducing manganese ore, and after decarburization is finished, deoxidation of molten steel with aluminum is performed. There has been proposed a melting method in which molten steel is transported to a vacuum degassing facility without being treated, and a decarburization treatment is performed by blowing a mixed gas of oxygen gas and inert gas.
Furthermore, in Patent Document 3, as a method for melting high manganese steel, high Mn hot metal having a manganese concentration of 8% by mass or more is decarburized and refined under reduced pressure until the carbon concentration becomes 0.1% by mass or less. At this time, a method has been proposed in which a refining gas is used as a carrier gas and a powdery decarburization refining additive containing Mn oxide is sprayed onto the hot metal.

JP 2013-112855 A Japanese Patent No. 4534734 Japanese Patent Laid-Open No. 5-125428

By the way, in the smelting method of high manganese steels disclosed in Patent Documents 1 to 3, manganese ore introduced into the converter is reduced during decarburization and blowing of hot metal in the converter, or when the steel is removed from the converter or removed. The manganese concentration of the molten steel is increased by adding a manganese source to the molten steel during hot pot refining or vacuum degassing.
However, in such a smelting method, when a manganese source is added at the time of decarburization blowing or steeling, since the yield of the added manganese source is low, it is necessary to add a large amount of manganese source, and the processing time Increases in manganese and cost of manganese are problems. In addition, when a manganese source is added during steelmaking, ladle refining, or vacuum degassing refining, heat loss occurs due to dissolution of the manganese source, so it is necessary to raise the temperature of the molten steel in the process after the converter. Come. However, the heat treatment of molten steel using a ladle refining device or a vacuum degassing device is less efficient than the heat treatment in a converter and increases the cost of the treatment. In particular, in the case of high manganese steel having a manganese concentration of 5% by mass or more, these problems become significant.

Therefore, the present invention has been made paying attention to the above-mentioned problems, and when producing a high manganese steel containing 5 mass% or more of manganese, a high manganese yield can be obtained, and a high efficiency can be obtained. It aims at providing the manufacturing method of the high manganese steel which can be manufactured.

According to one aspect of the present invention, when steel containing 5 mass% or more of manganese is melted, the hot metal is decarburized in the converter to make the hot metal a molten steel with a low carbon concentration. After the decarburization step and the decarburization step, by adding a manganese source and a silicon source to the molten steel accommodated in the converter, after the reduction step of reducing the molten steel, after the reduction step, A degassing step of vacuum degassing the molten steel with a vacuum degassing device, and in the reduction step, the silicon source so as to satisfy the formula (1) according to the amount of the manganese source added. There is provided a method for melting high manganese steel characterized by adding

x _Mn : Manganese concentration in the manganese source (mass%)
_xSi : silicon concentration (mass%) in the silicon source
W _Mn : Amount of manganese source added (kg / t)
W _Si : Amount of silicon source added (kg / t)

According to one aspect of the present invention, a high manganese steel that can provide a high manganese yield and can be smelted with high efficiency when melting high manganese steel containing 5 mass% or more of manganese. A melting method is provided.

It is a flowchart which shows the melting method of the high manganese steel which concerns on 1 aspect of this invention. It is a schematic diagram which shows a converter. It is a schematic diagram which shows a vacuum degassing apparatus.

In the following detailed description, numerous specific details are set forth, illustrating embodiments of the present invention, in order to provide a thorough understanding of the present invention. However, it will be apparent that one or more embodiments may be practiced without such specific details. In the drawings, well-known structures and devices are schematically shown for simplicity.
<Method of melting high manganese steel>
A method for melting high manganese steel according to an embodiment of the present invention will be described with reference to FIGS. In this embodiment, the high manganese steel which is a molten steel which contains 5 mass% or more of manganese is melted by performing the refining process mentioned later with respect to the hot metal extracted from the blast furnace.

First, as shown in FIG.1 and FIG.2, the decarburization process which decarburizes the molten metal 2 (it is also called "molten iron") which is the molten metal accommodated in the converter 1 is performed (S100).
The molten metal 2 is molten iron discharged from the blast furnace, and after being discharged from the blast furnace, it is transferred to a steelmaking factory as a next process in a transfer container that can store molten iron such as a hot metal ladle or a torpedo car. In order to reduce the medium solvent such as lime source used in the converter 1, a dephosphorization process for reducing the phosphorus concentration of the hot metal is performed before charging the hot metal into the converter 1. preferable. In the dephosphorization process, an oxygen source such as solid oxygen such as iron oxide or gaseous oxygen and a medium solvent containing lime are added to the hot metal contained in the hot metal transfer container, and the hot metal becomes gaseous oxygen or a gas for stirring. The dephosphorization reaction proceeds as a result of stirring. 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 hot metal is lower than the upper limit concentration of the final component standard of the high manganese steel. Furthermore, since there is a concern about the increase in phosphorus concentration due to phosphorus pickup from the manganese source added in the post-process to the hot metal and recovery from the slag, the phosphorus concentration in the hot metal is 0.05 mass above the upper limit of the component standard. It is more preferable to carry out the dephosphorization treatment until it becomes about%, and then remove the slag generated by the treatment (also referred to as “removing”). Furthermore, in order to lower the phosphorus concentration of the hot metal below the upper limit of the component standard, desiliconization is performed before dephosphorization, and silicon that inhibits efficient dephosphorization reaction is removed in advance. Is preferred.

In the decarburization process, before performing the decarburization process, the molten metal 2 that is the molten iron conveyed in the conveying container is transferred to the molten iron ladle and then charged into the converter 1 that is the primary refining furnace. In addition, before charging the molten metal 2, scrap serving as an iron source may be charged into the furnace body 10.
The converter 1 is a conventional converter facility, and includes a furnace body 10, an upper blowing lance 11, a plurality of bottom blowing nozzles 12, and a chute 13, as shown in FIG. The furnace body 10 is a barrel-type or pear-type refining furnace having a furnace port as an opening at the top, and a refractory is provided inside. The upper blowing lance 11 is disposed above the furnace body 10 and configured to be movable up and down in the vertical direction (up and down direction in FIG. 2). A plurality of nozzle holes are formed at the lower end of the upper blowing lance 11, and the molten metal 2 in which the oxidizing gas containing at least oxygen supplied from a supply facility (not shown) is accommodated in the furnace body 10 from the plurality of nozzle holes. To spray. The plurality of bottom blowing nozzles 12 are provided at the bottom of the furnace body 10, and agitation gas that is an inert gas such as argon or nitrogen supplied from a supply device (not shown) is blown into the molten metal 2 accommodated in the furnace body 10. Thus, the molten metal 2 is stirred. The chute 13 is arranged above the furnace body 10, connected to a plurality of unillustrated furnace hoppers for storing various auxiliary materials such as lime-containing medium solvent and alloyed iron, and auxiliary materials cut out from each furnace hopper. Is added into the furnace body 10.

In the decarburization step, oxidizing gas is injected from the top blowing lance 11 into the molten metal 2 (also referred to as “acid feeding”) while stirring the molten metal 2 accommodated in the furnace body 10 with the stirring gas blown from the bottom blowing nozzle 12. Then, decarburization treatment (also referred to as “decarburization blowing”) is performed under atmospheric pressure by supplying oxygen to the molten metal 2. In the decarburization blowing, the decarburization reaction proceeds by the oxygen blown into the molten metal 2 by the top blowing lance 11 and the carbon in the molten metal 2 reacting. In addition, when Cr and Ni are included in the component standard of the high manganese steel (when addition is essential), during the decarburization blowing, an auxiliary raw material such as alloy iron containing Cr or Ni is added to the chute 13. Is added to the molten metal 2. In the decarburization step, decarburization blowing is performed until the carbon concentration of the molten metal 2 falls within 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. At this time, the predetermined range of the carbon concentration is preferably 0.05% by mass or more and 0.2% by mass or less. This is because when the carbon concentration of the molten metal 2 after the decarburization step is less than 0.05% by mass, the oxygen potential of the molten metal 2 is increased and the yield of the manganese source is decreased. On the other hand, when the carbon concentration of the molten metal 2 after the decarburization process is greater than 0.2% by mass, a decarburization process in the secondary refining process is necessary, and the processing cost increases. And if the carbon concentration of the molten metal 2 becomes a predetermined range, supply of the oxidizing gas into the furnace body 10 will be stopped, and a decarburization process will be complete | finished.

After the decarburization step, a manganese source and a silicon source are added into the furnace body 10 in which the molten metal 2 is accommodated, and a reduction step is performed in which the molten metal 2 that is molten steel is reduced (S102). Manganese sources are ores, alloys and metals containing manganese. As the manganese source, for example, manganese ore, high carbon ferromanganese, medium carbon ferromanganese, low carbon ferromanganese, silicomanganese, metal manganese, and the like can be used. The silicon source is an ore, an alloy, or a metal containing silicon (silicon). As the silicon source, for example, ferrosilicon or silicomanganese can be used. The manganese source and the silicon source may be added from the furnace port via the chute 13 or may be added from the furnace port of the furnace body 10 using a scrap chute (not shown) used for charging the scrap. Good. Further, when adding the manganese source and the silicon source, the molten metal 2 is added while being stirred by blowing a stirring gas from the plurality of bottom blowing nozzles 12.

In the reduction process, the manganese source is added in an amount corresponding to the target manganese concentration, which is a component standard of high manganese steel. That is, the addition amount of the manganese source is determined by the manganese content of the manganese source, the carbon concentration of the molten metal 2 and the like according to the target manganese concentration. At this time, the record of the yield of the manganese source may be considered. In the reduction process, it is not necessary to set the manganese concentration of the molten metal 2 to a target concentration, and the manganese concentration of the molten metal 2 is set to a lower concentration than the target concentration so that it can be adjusted in the degassing step described later. May be. From the viewpoint of thermal efficiency, it is preferable to increase the addition amount of the manganese source in the reduction step as much as possible relative to the addition amount of the manganese source in the degassing step. Furthermore, from the viewpoint of reducing the cost for processing, it is preferable to use manganese ore or an inexpensive manganese source with a high carbon concentration as much as possible, as long as there is no effect on the adjustment of components other than manganese such as carbon.

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

In addition, in the reduction process, after adding the manganese source and the silicon source, the stirring gas is blown from the plurality of bottom blowing nozzles 12, and the molten metal 2 is stirred for a predetermined time.
Here, since the molten metal 2 after the decarburization step has a high oxygen potential, when a manganese source is added to the molten metal 2, manganese in the manganese source is oxidized and not oxidized in the molten metal 2, and manganese oxide (MnO ) And included in the slag 3. However, in this embodiment, since the silicon source is added in addition to the manganese source, manganese in the manganese source and manganese oxide in the slag 3 generated by the decarburization process are reduced by the reaction represented by the following formula (2). By doing so, the manganese concentration of the molten metal 2 becomes high. Moreover, the oxygen potential of the molten metal 2 is lowered by preferentially oxidizing silicon in the silicon source. Thereby, the manganese in a manganese source becomes easy to yield in the molten metal 2, and the manganese concentration of the molten metal 2 becomes high.
2 (MnO) + [Si] = (SiO ₂ ) +2 [Mn] (2)

Furthermore, in the reduction step, the basicity (CaO / SiO ₂ ) of the slag 3 defined by the ratio of the CaO concentration (mass%) to the SiO ₂ concentration (mass%) in the slag 3 is 1.6 or more. It is preferable to add lime to the furnace body 10 so as to be 2.4 or more. Thereby, hatching of the slag 3 and desulfurization of the molten metal 2 shown by the following formula (3) are promoted.
2 [S] + [Si] +2 (CaO) = 2 (CaS) + (SiO ₂ ) (3)

In addition, when the addition amount of the silicon source is lower than the range of the formula (1), that is, when the addition amount of the silicon source is small, the reduction reaction of manganese oxide does not proceed, so the manganese concentration of the molten metal 2 may be increased. become unable. On the other hand, when the addition amount of the silicon source becomes higher than the range of the formula (1), that is, when the addition amount of the silicon source is large, the addition amount of lime for adjusting the basicity becomes too large. The cost is high. Moreover, when there is much addition amount of a silicon source, the silicon concentration of the molten metal 2 becomes high and may exceed the upper limit of a component specification value. In such a case, it is necessary to perform a silicon removal treatment for reducing the silicon concentration of the molten metal 2 in the next step, which is not preferable.

Furthermore, in the reduction process, when the reduction process is completed, the molten metal 2 of the furnace body 10 is transferred to the ladle (also referred to as “tapping steel”). At this time, it is preferable that lime of 5 kg / t or more and 10 kg / t or less is previously placed in the pan in an amount per 1 t of the molten metal. Preliminary lime in the ladle can prevent the generation of white smoke at the time of steelmaking and suppress the increase in the sulfur concentration of the molten metal 2 due to the sulfurization from the slag 3.

After the reduction process, a degassing process is performed in which the vacuum degassing apparatus 5 performs a vacuum degassing process on the molten metal 2 that is molten steel (S104). The vacuum degassing device 5 is a VOD type degassing device, and performs degassing processing by stirring the molten metal 2 accommodated in the ladle 4 under reduced pressure. The vacuum degassing apparatus 5 includes a vacuum chamber 50, an exhaust pipe 51, a stirring gas supply path 52, an upper blowing lance 53, and a supply port 54. The vacuum chamber 50 is a container that can accommodate the ladle 4 therein, and has a detachable upper lid 500 so that the ladle 4 can be taken in and out. The exhaust pipe 51 is provided on the side surface of the vacuum chamber 50 and is connected to an exhaust device (not shown). The stirring gas supply path 52 is arranged from the outside to the inside of the vacuum chamber 50, and the tip on the inner side of the vacuum chamber 50 is connected to the blowing port 40 of the ladle 4. The stirring gas supply path 52 is connected to a stirring gas supply device (not shown) at the inner end of the vacuum chamber 50, and a stirring gas such as argon gas supplied from the stirring gas supply device is blown into the inlet of the ladle 4. 40. The upper blowing lance 53 is inserted into the center of the upper lid 500 and is configured to be able to move up and down in the vertical direction (vertical direction in FIG. 3). Further, the upper blowing lance 53 has a nozzle hole formed at the lower end, and an oxidizing gas containing at least oxygen supplied from a supply facility (not shown) is supplied from the nozzle hole to the molten metal 2 accommodated in the ladle 4. Inject. The supply port 54 is formed in the upper lid 500 and is connected to a plurality of furnace hoppers (not shown) that store various auxiliary materials such as a solvate containing lime and iron alloy, and takes out the auxiliary materials cut out from each of the furnace hoppers. It is an inlet for adding to the molten metal 2 accommodated in the pan 4.

In the degassing step, after the ladle 4 is accommodated in the vacuum chamber 50, the molten gas 2 is stirred by blowing the stirring gas from the blowing port 40, and then the exhaust pipe 51 is evacuated using the exhaust device. Vacuum degassing treatment is performed by reducing the pressure in the chamber 50. By performing such vacuum degassing treatment, the removal of gas components (such as nitrogen and hydrogen) in the molten metal 2, the homogenization of the components of the molten metal 2, the removal of inclusions in the molten metal 2, the temperature of the molten metal 2 Make adjustments. Further, in the degassing step, when performing the vacuum degassing process, the auxiliary component for component adjustment is set so as to be within the target component range according to the components of the molten metal 2 before or during the vacuum degassing process. The raw material is added to the molten metal 2 through the supply port 54. At this time, if the manganese concentration of the molten metal 2 before the vacuum degassing treatment is lower than the target concentration, the amount of manganese source such as metal manganese, high carbon ferromanganese, low carbon ferromanganese, etc. necessary for component adjustment Only add to molten metal 2. Further, when it is necessary to adjust the components such as Al, Ni, Cr, Cu, Nb, Ti, V, Ca, B, etc., auxiliary materials containing each component are added to the molten metal 2. Further, for the purpose of desulfurization and the like, secondary materials used for adjusting the composition of slag 3 and promoting desulfurization reaction, such as CaO-containing material, MgO-containing material, aluminum-containing material, Al ₂ O ₃ -containing material, SiO ₂ -containing material May be added to the molten metal 2.

In the degassing step, it is preferable to stir the molten metal 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. When the stirring power ε is less than 300 W / t, the stirring power becomes small, so that it takes time for the denitrification process and the dehydrogenation process, and the processing time for the vacuum degassing process is extended, which is not preferable. On the other hand, when the stirring power ε is larger than 1300 W / t, the amount of slag 3 entrapped in the molten metal 2 increases, and the defect rate due to slag inclusions increases, which is not preferable. In the equation (4), Q _n is the flow rate of the stirring gas (Nm ³ / min), T _l is the temperature (K) of the molten metal 2, W _m is the weight (t) of the molten metal 2, and ρ _l is the molten metal 2 Density (kg / m ³ ), h is the height of the molten metal surface (m) which is the depth of the molten metal 2 in the ladle 4, P ₁ is the atmospheric pressure (Torr), η is the energy transfer efficiency (−), T _n Indicates the temperature (K) of the stirring gas. One Torr is (101325/760) Pa.

Furthermore, in the degassing step, when the temperature of the molten metal 2 is lower than the target temperature after the degassing step, a temperature increasing process for raising the temperature of the molten metal 2 may be performed during the vacuum degassing process. In the temperature raising process, after adding aluminum to the molten metal 2 from the supply port 54, an oxidizing gas containing oxygen is injected from the upper blowing lance 53 onto the molten metal 2. Thereby, the temperature of the molten metal 2 can be raised because the aluminum in the molten metal 2 and oxygen of oxidizing gas react. In the temperature raising process, the dynamic pressure P (kPa) of the oxidizing gas jet injected from the top blowing lance 53, calculated from the equations (5) and (6), is 10 kPa or more and 50 kPa or less. It is preferable to control as described above. By controlling the dynamic pressure P within the above range, the molten metal 2 can be efficiently heated while minimizing the evaporation of manganese from the molten metal 2. In equation (5), ρ _g is the density of the oxidizing gas (kg / Nm ³ ), and U is the flow velocity (m / sec) of the oxidizing gas jetted from the nozzle of the top blowing lance 53 at the nozzle tip. Each is shown. In the equation (6), F represents the flow rate of the oxidizing gas (Nm ³ / h), and S represents the cross-sectional area (m ² ) of the nozzle of the top blowing lance 53.

By passing through the degassing process, molten steel with a predetermined target component concentration is produced. In addition, after the degassing step, a molten slab or the like is continuously cast to produce a high-manganese steel slab having a predetermined shape such as a slab.

<Modification>
Although the present invention has been described above with reference to specific embodiments, it is not intended that the present invention be limited by these descriptions. By referring to the description of the present invention, other embodiments of the present invention will be apparent to those skilled in the art, including various modifications along with the disclosed embodiments. Therefore, it should be understood that the embodiments of the present invention described in the claims also include embodiments including these modifications described in the present specification alone or in combination.

For example, in the above embodiment, the vacuum degassing apparatus 5 is a VOD type refining apparatus, but the present invention is not limited to such an example. For example, the vacuum degassing device 5 may be an RH degassing device or a DH degassing device. When the vacuum degassing apparatus is an RH type degassing apparatus, in order to suppress the evaporation of manganese, the molten steel represented by the following formula (7) is used under the condition that the space pressure in the vacuum tank is 50 Torr to 100 Torr. The reflux amount Q (t / min) is preferably 150 t / min or more and 200 t / min or less. If denitrification or dehydrogenation of the molten steel is required, the treatment may be performed at a tank internal pressure of less than 50 Torr, but after the denitrification and dehydrogenation, the treatment is performed at a tank internal pressure of 50 Torr or more and 100 Torr or less. It is preferable to carry out. In the equation (7), K is a constant, G is the flow rate (NL / min) of the recirculation gas blown from the dip tube, D is the inner diameter (m) of the dip tube, P ₂ is the external pressure (Torr), P Reference numeral ₃ represents the internal space pressure (Torr) of the vacuum chamber.

Moreover, in the said embodiment, although only the molten metal 2 which is the molten steel manufactured with the converter 1 was used as the molten metal 2 processed with the vacuum degassing apparatus 5, this invention is not limited to this example. For example, the molten steel manufactured in the converter 1 may be used as the molten metal 2 to be processed by the vacuum degassing device 5 by combining the molten steel melted in another refining furnace. In this case, the manganese concentration of the molten steel manufactured by the converter 1 can be lowered by increasing the manganese concentration of the molten steel melted in another refining furnace.

Furthermore, in the above-described embodiment, the manganese gas and the silicon source are added to the reduction step, and then the stirring gas is blown from the plurality of bottom blowing nozzles 12 to stir the molten metal 2 for a predetermined time. Is not limited to such an example. In the reduction step, oxidizing gas from the top blowing lance 11 may be injected in addition to blowing the stirring gas. In particular, when it is necessary to raise the temperature of the molten metal 2, the heat treatment may be performed by an oxidation reaction with an oxidizing gas.

Furthermore, in the said embodiment, although dephosphorization processing was performed to hot metal before decarburization processing, this invention is not limited to this example. For example, before the decarburization treatment, in addition to the dephosphorization treatment, a desulfurization treatment for reducing the sulfur concentration in the hot metal may be performed. The desulfurization process may be performed before the dephosphorization process or after the dephosphorization process depending on the equipment configuration.
Furthermore, in the said embodiment, although the dephosphorization process was performed with respect to the hot metal accommodated in the hot metal conveyance container, this invention is not limited to this example. The dephosphorization treatment may be, for example, a method of performing treatment by injecting an oxidizing gas from an upper blowing lance to hot metal accommodated in a converter type refining furnace.

<Effect of embodiment>
(1) The method for melting high manganese steel according to one aspect of the present invention is to decarburize hot metal (molten metal 2) in converter 1 when melting steel containing 5 mass% or more of manganese. By adding a manganese source and a silicon source to the molten steel housed in the converter 1 after the decarburization step (step S100) in which the molten iron has a low carbon concentration (molten metal 2) and the decarburization step Thus, a reduction process (Step S102) for reducing the molten steel, and a degassing process (Step S104) for performing a vacuum degassing process on the molten steel in the vacuum degassing apparatus 5 after the reduction process, In the reduction step, a manganese source is added according to the target manganese concentration of the steel, and a silicon source is added so as to satisfy equation (1).

According to the configuration of (1) above, since the reduction reaction of the formula (2) can be promoted, manganese in the added manganese source can be easily retained in the molten metal 2. Further, since the manganese source is added in the converter 1, heat loss (decrease in the temperature of the molten metal 2) due to the addition of the manganese source can be suppressed. Furthermore, since the molten metal 2 can be subjected to a heat treatment in the converter 1 after the addition of the manganese source, the heat treatment can be efficiently performed. Furthermore, it is possible to suppress the addition of an excessive silicon source more than an amount sufficient for promoting the reduction reaction, and it is not necessary to perform a desiliconization process in the degassing process. Can do. When the degassing treatment time is lengthened, the cost for the treatment is increased and the production efficiency is lowered. That is, according to the structure of said (1), when melting high manganese steel containing 5 mass% or more of manganese, a high manganese yield can be obtained and high manganese steel is melted with high efficiency. Can do.

(2) In the configuration of the above (1), as the vacuum degassing device 5, a device for stirring the molten steel by blowing a stirring gas from the bottom of the ladle containing the molten steel is used. The vacuum degassing process is performed while stirring the molten steel under the condition that the stirring power ε represented by the above is 300 W / t or more and 1300 W / t or less.
According to the configuration of (2) above, the time required for the denitrification process and the dehydrogenation process can be shortened, and further, the slag 3 can be prevented from being caught in the molten metal 2. For this reason, the processing time of a vacuum degassing process can be shortened.

Next, Example 1 performed by the present inventors will be described. In Example 1, the hot metal discharged from the blast furnace was subjected to hot metal pretreatment of desiliconization treatment and dephosphorization treatment, so that the phosphorus concentration was 0.010% by mass. Similar to the above embodiment, a high manganese steel having a manganese concentration of 5% by mass or more was melted by performing a decarburization process, a reduction process, and a degassing process on the hot metal. The components of the molten high manganese steel are as follows: carbon concentration: 0.145 mass% to 0.155 mass%, manganese concentration: 24 mass% to 25 mass%, silicon concentration: 0.1 mass% or more It was 0.2 mass% or less, sulfur concentration: 0.002 mass% or less, nitrogen concentration: 100 ppm or less, and hydrogen concentration: 5 ppm or less.

In the decarburization step, as in the above-described embodiment, the molten metal 2 that has been subjected to the hot metal pretreatment is decarburized, and decarburized and blown until the carbon concentration reaches 0.05% by mass to obtain molten steel. .
In the reduction step, high-carbon ferromanganese and metal manganese were added as a manganese source to molten metal 2 that was a decarburized molten steel, and ferrosilicon was added as a silicon source. Then, while stirring the molten metal 2 with the stirring gas, the acid supply from the top blowing lance 11 was continued and the reduction treatment was performed to dissolve the manganese source and increase the manganese concentration of the molten metal 2. The addition amount of the silicon source satisfies the formula (1). In the reduction step, lime was added together with the manganese source. The manganese concentration of the molten metal 2 at the end of the reduction treatment was approximately 24% by mass. Furthermore, in the reduction process, when transferring the molten metal 2 from the converter 1 to the ladle 4 (tapping steel), about 0.8 kg of metal aluminum was added per ton of molten steel to the molten metal 2 to be tapped. .

In the degassing step, the degassing process was performed on the molten metal 2 that was 150 tons of molten steel that had undergone the reduction step, using the VOD type vacuum degassing device 5 as in the above embodiment. In the degassing step, degassing was performed by blowing the Ar gas at a flow rate of 2000 Nl / min into the molten metal 2 from the inlet 40 of the ladle 4 and stirring the molten metal 2 while setting the internal space pressure of the vacuum chamber 50 to 2 Torr. In the degassing step, metal manganese and high carbon ferromanganese were added to the molten metal 2 during the degassing process to adjust the components.

Moreover, in Example 1, as a comparison, high manganese steel was melted even under conditions where the addition amount of the silicon source did not satisfy the formula (1) in the reduction step (Comparative Example 1). In Comparative Example 1, the conditions other than the addition amount of the silicon source in the reduction step were the same as those in Example 1.
Table 1 shows the amount of silicon source added in the reduction step, the Mn yield, the silicon concentration of the molten metal 2 during steel output, and the time required for the degassing process in the degassing step as the results of Example 1. In Table 1, 0.013 × W _Mn × x _Mn / x _Si is the lower limit value of the range shown in Formula (1), and 0.150 × W _Mn × x _Mn / x _Si is the range shown in Formula (1). The upper limit value of each is shown. As shown in Table 1, in Example 1, Examples 1-1 to 1-6 of 6 conditions amount _{W Si} of the silicon source is within the range of (1), and the amount _{W Si} of the silicon source A high manganese steel was melted under a total of 10 conditions including 4 conditions of Comparative Examples 1-1 to 1-4 in which the value was outside the range of the formula (1). Further, the Mn yield in Table 1 indicates how much manganese contained in the manganese source used in the reduction process was added to the molten metal 2, that is, the manganese content in the manganese source was that of the molten metal 2 before and after the reduction process. It shows how much it contributed to the increase in manganese concentration.

As shown in Table 1, under the conditions of Comparative Examples 1-1 and 1-2, the manganese yield was as low as 46% or less compared to the other conditions. This is considered to be caused by the fact that the reduction reaction of the slag 3 represented by the formula (2) did not proceed sufficiently because the addition amount of the silicon source was small. In Comparative Examples 1-1 and 1-2, since the Mn yield was low, it was necessary to perform a reduction treatment by adding a silicon source in the degassing step, and then to adjust the components and temperature, which was necessary for the degassing step. The time was longer than in Examples 1-1 to 1-6.

Further, under the conditions of Comparative Examples 1-3 and 1-4, the manganese yield was high, but the silicon concentration at the time of steel output exceeded the standard upper limit of 0.20% by mass. This is considered to be because more silicon than the amount consumed by the reduction reaction of the slag 3 represented by the formula (2) and the desulfurization reaction represented by the formula (3) was supplied to the molten metal 2. In Comparative Examples 1-3 and 1-4, since the silicon concentration at the time of steel output was high, it was necessary to perform the desiliconization process in the degassing process, and the time required for the degassing process was as described in Examples 1-1 to 1. Longer than -6. In the silicon removal process, the silicon contained in the molten metal 2 is oxidized and removed by injecting an oxidizing gas from the top blowing lance 53 onto the molten metal 2.
On the other hand, under the conditions of Examples 1-1 to 1-6, a high manganese yield can be obtained in the reduction process, and the silicon concentration at the time of steel output can be lowered by not adding a silicon source more than necessary. It was. For this reason, the time required for the degassing step could be shortened.

Next, Example 2 performed by the present inventors will be described. In Example 2, high manganese steel was melted by a melting method similar to that in Example 1-4 under a plurality of conditions in which the stirring power ε in the degassing step was changed. The components of the molten high manganese steel are as follows: carbon concentration: 0.145 mass% to 0.155 mass%, manganese concentration: 24 mass% to 25 mass%, silicon concentration: 0.1 mass% or more It was 0.2 mass% or less, sulfur concentration: 0.002 mass% or less, nitrogen concentration: 100 ppm or less, and hydrogen concentration: 5 ppm or less.

Specifically, as in the decarburization step, similarly to Example 1-4, the decarburization process was performed on the molten metal 2 that was the hot metal that had been subjected to the hot metal pretreatment in the converter 1, and the carbon concentration was 0.05 mass%. Until then, decarburization was blown into molten steel. Next, as a reduction process, similarly to Example 1-4, a 35 kg / t silicon source was added and the molten metal 2 was subjected to a reduction treatment. The manganese concentration of the molten metal 2 at the end of the reduction treatment was approximately 24% by mass. Further, as a degassing step, the molten metal 2 was degassed by the vacuum degassing apparatus 5 as in Example 1-4. In the degassing step, the degassing process was performed under a plurality of conditions in which the stirring power ε was arbitrarily changed by adjusting the flow rate of Ar gas blown from the blowing port 40 of the ladle 4.

As a result of Example 2 shown in Table 2, the amount of silicon source added in the reduction process, the Mn yield, the silicon concentration of the molten metal 2 during steel output, the stirring power in the degassing process, and the time required for degassing in the degassing process Indicates. As shown in Table 2, in Example 2, high manganese steel was melted under 10 conditions of Examples 2-1 to 2-10 having different stirring power in the degassing step. The stirring power ε in the degassing step in Example 1-4 corresponds to that in Example 2-1. In Examples 2-1 to 2-10, the other melting conditions were the same as those in Example 1-4.

As shown in Table 2, under the conditions of Examples 2-3 to 2-8 in which the stirring power ε is 300 W / t or more and 1300 W / t or less, Example 2-1 in which the stirring power ε is less than 300 W / t , 2-2 and stirring power ε exceeding 1300 W / t, it was confirmed that the time required for the degassing treatment was shortened compared to Examples 2-9 and 2-10. This is considered to be because dehydrogenation, denitrogenation, and floating of inclusions in the vacuum degassing process were promoted by applying an appropriate stirring power to the molten metal 2 to perform stirring.

On the other hand, in the conditions of Examples 2-1 and 2-2 in which the stirring power ε was less than 300 W / t, since the stirring was weak, it took time for dehydrogenation and denitrogenation. The result became longer. Further, in the conditions of Examples 2-9 and 2-10 in which the stirring power ε exceeds 1300 W / t, since the stirring was too strong, the amount of slag 3 entrapped in the molten metal 2 increased, and the slag system in the molten metal 2 Since it took time to raise the inclusions, the time required for the degassing treatment was increased.

DESCRIPTION OF SYMBOLS 1 Converter 10 Furnace 11 Top blowing lance 12 Bottom blowing nozzle 13 Chute 2 Molten metal 3 Slag 4 Ladle 40 Blowing port 5 Vacuum degassing apparatus 50 Vacuum tank 51 Exhaust pipe 52 Stirring gas supply path 53 Top blowing lance 54 Supply port

Claims

When melting steel containing 5 mass% or more of manganese,
In the converter, by decarburizing the hot metal, the decarburization step to make the hot metal a molten steel with a low carbon concentration,
After the decarburization step, a reduction step of reducing the molten steel by adding a manganese source and a silicon source to the molten steel accommodated in the converter;
After the reduction step, a degassing step of performing vacuum degassing treatment on the molten steel in a vacuum degassing device;
With
In the reduction step, the silicon source is added so as to satisfy the formula (1) according to the amount of the manganese source added.

x Mn : Manganese concentration in the manganese source (mass%)
xSi : silicon concentration (mass%) in the silicon source
W Mn : Amount of manganese source added (kg / t)
W Si : Amount of silicon source added (kg / t)
As the vacuum degassing device, using a device for stirring the molten steel by blowing a stirring gas from the bottom of the ladle containing the molten steel,
In the degassing step, a vacuum degassing process is performed while stirring the molten steel under a condition that the stirring power ε represented by the formula (4) is 300 W / t or more and 1300 W / t or less. Item 2. A method for melting high manganese steel according to Item 1.

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: Hot water surface height (m)
P 2 : Atmospheric pressure (Torr)
η: Energy transfer efficiency (-)
T n : Stirring gas temperature (K)