JP2024101527A - Production method for chromium-containing steel - Google Patents

Abstract

To provide a production method for chromium-containing steel which improves production efficiency, suppresses chromium oxidation loss, and reduces alloy cost.SOLUTION: A production method for chromium-containing steel includes a step of combining a first molten metal prepared by subjecting blast furnace molten iron to molten iron pretreatment for converter decarburization with a second molten metal prepared by dissolving scrap or alloy iron containing chromium and refining it as necessary, and a chromium-containing raw material is intentionally not used in melting the first molten metal. It is preferable to include a step of subjecting a chromium-containing molten iron obtained by combining the first molten metal and the second molten metal to a decompression decarburization treatment after adjusting the carbon concentration as necessary, and to adjust the carbon concentration [C]i (mass%) in the molten metal before the decompression decarburization treatment so as to satisfy the equation {[N]i-[N]e≤0.28×([C]i-[C]e)-0.04} from the nitrogen concentration [N]i (mass%) in the molten metal before the decompression decarburization treatment, the target carbon concentration [C]e (mass%) and the target nitrogen concentration [N]e (mass%) in the molten metal after the decompression decarburization treatment.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing chromium-containing steel, and relates to a method for combining a molten metal to which chromium has not been intentionally added with a molten metal in which a chromium source has been dissolved.

For example, the electric furnace-AOD method and the converter-RHOB method are generally known as methods for producing stainless steel, that is, steel with a high content of chromium and nickel. In the former method, a raw material blend consisting mainly of stainless steel scrap and high carbon ferrochromium raw materials is melted in an electric furnace, and decarburization and refining are performed by AOD (Argon Oxygen Decarburization). In the latter method, molten iron is charged into a converter, nickel and chromium raw materials are added to the molten iron, and the molten iron is decarburized and refined, and the molten steel is finish-decarburized and the composition is adjusted to a desired composition by RHOB (RH Oxygen Blowing). However, each method has problems. In the electric furnace-AOD method, raw material costs are kept down by utilizing stainless steel scrap. On the other hand, since the heat size of an electric furnace is smaller than that of a converter, small lot production is required, and there is a problem of a large decrease in yield. In addition, the high energy and refractory costs of the electric furnace are a problem. On the other hand, the energy and refractory costs of the converter-RHOB process are relatively low. However, the raw material costs are high because stainless steel scrap cannot be used in large quantities, and the use of a large amount of molten iron results in a large amount of _CO2 emissions.

In light of this background, Patent Document 1 discloses a "combined molten metal" technology in which molten steel obtained in an electric furnace melting process is combined with molten pig iron and molten steel after blowing in a converter.

Patent Document 2 also discloses a method for producing high alloy steel, particularly high nickel steel, by combining molten steel. In order to prevent nickel contamination in the converter, high nickel steel is melted and refined in an electric furnace, and the molten steel after converter refining and the molten steel from the electric furnace are combined without deoxidization and with a [C] concentration of 0.05% by mass, which makes it possible to suppress re-P and N pickup.

Japanese Patent Application Publication No. 02-085334 Japanese Patent Application Publication No. 10-140227

However, the conventional technology has the following problems.
In the technology disclosed in Patent Document 1, the molten metal melted in an electric furnace and the converted hot metal are charged together into a converter, and the Cr source is charged after decarburization. Patent Document 1 states that decarburization blowing with less chromium loss can be achieved by charging ferrochromium in a state where the amount of hot metal charged is low and stirring power is earned, and then performing decarburization blowing. However, the chromium loss suppression technology obtained as an effect of this technology has a high chromium loss of 2% or more. In addition, the chromium source is basically charged in the converter, and no technology is disclosed for melting the chromium source mainly in an electric furnace. In addition, the converter is contaminated with chromium, and when melting steel types with strict chromium regulations after processing, the converter needs to be cleaned, which is a factor that increases costs.

Patent Document 2 discloses a technique for combining high-nickel steel. However, this technique requires a certain amount of decarburization in an electric furnace when producing high-chromium molten metal using an inexpensive ferrochromium source (such as high-carbon ferrochromium) in an electric furnace to produce chromium-containing steel. If this technique is to be applied to the production of chromium-containing steel, preferential decarburization of chromium molten metal in an electric furnace under atmospheric conditions becomes difficult as the metal becomes lower in the C range, and it is thermodynamically difficult to obtain molten metal with a [C] concentration of 0.05% by mass or less. Therefore, this is not a suitable process for producing chromium-containing steel.

The present invention was made in consideration of the above circumstances, and aims to propose a method for producing chromium-containing steel that improves production efficiency, suppresses chromium oxidation loss, and reduces alloy costs.

The method for producing chromium-containing steel according to the present invention, which advantageously solves the above problems, includes a step of combining a first molten metal obtained by subjecting blast furnace hot metal to hot metal pretreatment and decarburizing in a converter with a second molten metal obtained by melting chromium-containing scrap or ferroalloys and refining them as necessary, and is characterized in that no chromium-containing raw material is intentionally used in the production of the first molten metal.

The method for producing chromium-containing steel according to the present invention is as follows:
(a) a step of subjecting the chromium-containing molten iron obtained by combining the first molten metal and the second molten metal to a reduced pressure decarburization treatment after adjusting the carbon concentration as necessary;
(b) adjusting the carbon concentration [C] _i (mass%) in the molten metal before the reduced pressure decarburization treatment so as to satisfy the following formula 1 based on the nitrogen concentration [N] i (mass%) in the molten metal before the reduced pressure decarburization treatment, the target carbon concentration [C] _e (mass%) in the molten metal after the reduced pressure decarburization treatment _, and the target nitrogen concentration [N] _e (mass%);
(c) the carbon concentration [C] _i in the molten metal before the reduced pressure decarburization treatment is more than 0.05 mass%;
(d) The composition of the chromium-containing steel includes, on a mass basis, Cr: 7% or more, C: 0.005% or more, and N: 0.05% or less;
This may be a more preferable solution.
[Formula 1]
[N] _i - [N] _e ≦0.28×([C] _i - [C] _e ) -0.04

According to the method for producing chromium-containing steel of the present invention, blast furnace molten iron and electric furnace molten iron are combined to produce chromium-containing steel. This improves production efficiency and reduces chromium oxidation loss and alloy costs compared to production using the electric furnace-AOD process and converter-RHOB process. Furthermore, the nitrogen concentration can be reduced by decarburizing the combined chromium-containing molten steel under reduced pressure.

FIG. 1 is a flow diagram of a method for producing a chromium-containing steel according to one embodiment of the present invention. 1 is a graph showing the relationship between the amount of carbon removed in steel Δ[C] (mass %) and the amount of nitrogen removed in steel Δ[N] (mass %) in a reduced pressure decarburization treatment of chromium-containing molten steel.

First, before describing the embodiments of the present invention, an outline of the invention will be described to facilitate understanding of the invention. The technology described in Patent Document 2 is an example of a technology related to the present invention. The technology described in Patent Document 2 is mainly a technology for melting high Ni steel, and the prerequisites for both converter and electric furnace are suppression of CO gas generation, suppression of N absorption, and prevention of re-P. Therefore, it is assumed that the steel is not deoxidized, that is, the increase in the [O] (oxygen) concentration in the molten steel and the [C] concentration of the molten steel is 0.05 mass% or less. On the other hand, the technology according to the present invention is a technology for high Cr steel. First, in the electric furnace melting process of high Cr molten metal in the combined melting process, decarburization is performed in an air atmosphere. Therefore, in order to suppress Cr loss in the electric furnace, deoxidation is performed to recover Cr, and a molten metal with a high [C] concentration is produced. When the combined melting of the converter melt and the electric furnace melt is performed in the air, the combined melt has a high concentration of Cr, which has a high affinity for nitrogen, so the N concentration of the molten metal after the combination is absorbed N to the saturated nitrogen concentration. In this respect, the prerequisites for the combined molten metal are different from those of the technology described in Patent Document 2. Due to this difference, the [C] concentration of the molten steel obtained by converter refining using the technology described in Patent Document 2 is 0.05 mass% or less, and the molten metal of the high alloy steel melted in an electric furnace is also 0.05 mass% or less. In other words, the technology described in Patent Document 2 makes the [C] concentration of the molten metal after combined molten metal 0.05 mass% or less. In contrast, in the present invention, it is preferable in principle to make the carbon concentration in the molten metal before the reduced pressure decarburization treatment more than 0.05 mass% (e.g., 0.3 mass%).

The following is a detailed description of the embodiments of the present invention. The following embodiments are intended to exemplify equipment and methods for embodying the technical ideas of the present invention, and are not intended to specify the configuration as described below. In other words, the technical ideas of the present invention can be modified in various ways within the technical scope described in the claims.

The manufacturing flow of chromium-containing steel according to one embodiment of the present invention is shown in FIG. 1. When producing one heat of chromium-containing steel, the blast furnace hot metal S1 is adjusted in composition by a combination of one or more of desiliconization, dephosphorization, and desulfurization treatments in the hot metal pretreatment step S2 as necessary. In the first combining step S4, the blast furnace hot metal S1 may be combined with the molten iron produced in the first electric furnace melting step S3 before being charged into the converter, but this is not necessary. When the first combining step S4 is performed, it is preferable to avoid the addition of chromium alloys that cause oxidation loss by the subsequent oxygen blowing of the converter in the first electric furnace melting step S3, and to melt the molten iron into an alloy other than chromium or molten iron with the same composition as general carbon steel. In other words, chromium-containing raw materials are not intentionally used in the melting of the molten metal here. "Intentionally not using chromium-containing raw materials" includes cases where no chromium-containing raw materials are added during converter blowing, as well as cases where chromium-containing raw materials are not actively added at a predetermined ratio or more. The predetermined ratio of the chromium concentration [Cr] in the molten metal on a mass basis is, for example, less than 1% at most, preferably 0.5%, more preferably 0.3%, and even more preferably 0.2%. In the converter blowing S5, blowing is performed without charging raw materials containing chromium. However, a chromium source that is not intentionally added may be included. The molten metal after the converter blowing is deoxidized. On the other hand, in the second electric furnace melting step S6, melting is performed in the electric furnace, mainly using chromium raw materials such as ferrochromium and chromium-containing steel scrap. The second electric furnace melting step S6 may be performed multiple times from the viewpoint of the heat size of the electric furnace or the scrap blending ratio. However, when performing multiple melting processes in the electric furnace, it is preferable to wait in equipment that can maintain heating, such as VAD (Vacuum Arc Degassing) or LF (Ladle Furnace), in consideration of temperature drop.

In the second electric furnace melting process S6, it is preferable to use high-carbon ferrochrome ([C] to 10% by mass, [Cr] to 70% by mass) to reduce raw material costs. Scrap containing chromium-containing products and other alloys may also be melted. Here, since it is preferable that the final carbon concentration [C] of the electric furnace molten metal is low, decarburization is performed as necessary when using raw materials with a high C content. The electric furnace molten metal discharged through the second electric furnace melting process S6 is received in a ladle and then transported, and in the second combining process S7, it is combined with the ladle that received the molten steel that has been subjected to converter blowing S5. When the molten steel after converter blowing S5 and the electric furnace molten metal are combined in the second combining process S7, if the dissolved oxygen concentration in the molten iron is high, CO gas will be generated due to the CO generation reaction during the combination, which may cause operational problems. Therefore, in the second electric furnace melting step S6, the molten metal may not be deoxidized during electric furnace refining, but it is preferable to deoxidize the molten metal using a deoxidizer when tapping or before combining after tapping, or to deoxidize the molten metal during refining in the furnace. Also, the blending ratio in the second combining step S7 is preferably in the range of 1 part of the molten metal from S5 to 0.15 to 0.50 parts of the molten metal from S6. For example, when combining molten metal from a converter with a capacity of 200 to 350 tonnes with molten metal from an electric furnace with a capacity of 30 to 100 tonnes, a higher ratio of converter molten steel is better when producing chromium-containing steel that minimizes alloy costs by prioritizing yield, i.e., the amount of production per run.

The temperature of the molten iron may drop significantly due to the second combining step S7. Therefore, it is preferable to go through a heating step S8 such as LF. Since the heat is raised in the heating step such as LF, there is a concern that P and Mn may be picked up from the slag brought into the casting ladle. Depending on the P and Mn standards, it is preferable to add a slag removal step before this heating step S8, but this is not always necessary.

In the second electric furnace melting process S6, the electric furnace molten metal is combined in a deoxidized state, so air entrainment increases during the second combining process S7 in the atmosphere, causing nitrogen pick-up in the atmosphere. At this time, chromium in the molten metal has the property of lowering the nitrogen activity, and nitrogen is picked up to a saturated state by the second combining process S7 in the atmosphere. Therefore, denitrification treatment is essential to obtain a nitrogen concentration [N] (mass%) that meets the product specifications. Denitrification treatment is carried out using reduced pressure equipment such as an RH type vacuum treatment device.

In this embodiment, the decarburization process and the denitrification process are performed in parallel in the reduced pressure decarburization step S9. For example, it is known that the denitrification process proceeds with the CO generation reaction in the reduced pressure decarburization process. FIG. 2 shows the relationship between the reduced pressure decarburization amount Δ[C] (mass%) and the denitrification amount Δ[N] (mass%) when the chromium-containing molten steel is subjected to reduced pressure decarburization using an RH type vacuum processing apparatus. The chromium-containing molten steel used in FIG. 2 had a range of [Cr]: 10.2 to 13.5 mass%. Here, the reduced pressure decarburization amount Δ[C] (mass%) is the difference between the carbon concentration [C] _i (mass%) in the molten metal before the reduced pressure decarburization process and the carbon concentration [C] _f (mass%) in the molten metal after the reduced pressure decarburization process. In addition, the denitrification amount Δ[N] (mass%) is the difference between the nitrogen concentration [N] _i (mass%) in the molten metal before the reduced pressure decarburization process and the nitrogen concentration [N] _f (mass%) in the molten metal after the reduced pressure decarburization process. From this result, the following formula 1 is derived for obtaining the carbon concentration before the reduced pressure decarburization treatment to obtain the target nitrogen concentration.
[Formula 1]
[N] _i - [N] _e ≦0.28×([C] _i - [C] _e ) -0.04
Here, [N] _i is the nitrogen concentration (mass%) in the molten metal before the reduced pressure decarburization treatment,
[N] _e is the target nitrogen concentration (mass%) after reduced pressure decarburization treatment,
[C] _i is the carbon concentration (mass%) in the molten metal before the reduced pressure decarburization treatment,
[C] _e is the target carbon concentration (mass%) of the molten metal after reduced pressure decarburization treatment
Represents.

A certain amount of decarburization is required to obtain a certain amount of decarburization. In other words, if the steel carbon concentration [C] _i (mass%) is not certain before the start of the reduced pressure decarburization treatment, the decarburization treatment cannot be performed from the nitrogen concentration [N] _i in the steel picked up to the saturated state to the target nitrogen concentration [N] _e (mass%). In order to ensure the carbon concentration [C] _i (mass%) in the steel at the start of the reduced pressure decarburization treatment, it is preferable to increase the carbon concentration [C] at the electric furnace tapping point, or to add an alloy or the like to carburize the steel before the start of the reduced pressure treatment (before the start of the decarburization) or in the heating step S8 before the start of the reduced pressure treatment. In addition, it is preferable to make the carbon concentration [C] of the molten steel after the converter blowing S5 more than 0.05 mass%. If the carbon concentration [C] _i in the steel at the start of the reduced pressure decarburization treatment is excessively high, excessive decarburization is required to achieve the carbon concentration standard for chromium-containing steel, so it is preferable to make the carbon concentration sufficient for the decarburization treatment.

In the reduced pressure decarburization treatment using the RH type vacuum treatment device, oxygen sending decarburization and vacuum decarburization can be performed. For example, when the treatment is performed under conditions of a temperature T or higher calculated based on the preferential decarburization temperature of stainless steel (Equation 2 below), the oxidation loss of chromium can be minimized. Therefore, it is preferable to set the molten steel temperature T at which decarburization starts to be equal to or higher than the temperature calculated by Equation 2. The chromium-containing molten steel whose composition has been adjusted in this way in the RH type vacuum treatment device may be directly transported to the casting step S11 and cast. It is also preferable to move to the casting step S11 via a ladle refining step S10 such as LF in order to reduce the slag in which chromium has been oxidized in the reduced pressure decarburization treatment.
[Formula 2]
log {(a _Cr ^2/3・P _CO )/a _C }=8.48-13520/T
Here, a _Cr is the activity of chromium in the chromium-containing molten steel,
_PCO is the partial pressure of carbon monoxide in the atmosphere (atm),
a _C is the activity of carbon in chromium-containing molten steel,
T is the temperature of the chromium-containing molten steel (K)
Represents.

In the above embodiment, an example is described in which an RH type vacuum processing device is used in the reduced pressure decarburization process S9, but this is not limited to this. This embodiment can be applied to any equipment capable of reduced pressure decarburization. Ingot-making decomposition method or continuous casting method can be applied to the casting process S11. From the viewpoint of yield, continuous casting method is preferable.

When carrying out the combined hot-melt method in the manufacturing method of chromium-containing steel according to the present embodiment, there are no particular upper or lower limits on the contents of Cr, C, and N. However, it is preferable to apply the method to chromium-containing steel containing Cr: 7% or more, C: 0.005% or more, and N: 0.05% or less by mass. If the Cr content is less than 7%, it is cheaper to add the chromium raw material in a converter or ladle refining than to melt the chromium raw material using an electric furnace. Note that although there is no particular upper limit for the Cr content, the upper limit of the Cr content of steel that can be realistically produced from the standpoint of standards is generally about 30%. In order to make the C content less than 0.005%, excessive decarburization treatment is required when the Cr content is in the above range, and there is a risk that the chromium yield will decrease due to oxidation loss. On the other hand, although there is no particular upper limit for the C content, the upper limit of the C content of steel that can generally be assumed is about 0.5%. If the N content exceeds 0.05%, there is a risk that the low-temperature toughness will deteriorate. Other elements can be included as necessary.

Example 1
Based on the manufacturing method of chromium-containing steel according to the embodiment, 13Cr steel was manufactured according to the flow chart of FIG. 1. The target composition of the 13Cr steel was [C] _e : 0.20 mass%, [N] _e : 0.030 mass% or less, and [Cr] _e : 13.0 mass%. The blast furnace hot metal S1 was subjected to hot metal pretreatment step S2 and converter blowing S5 to obtain 240 t of molten steel. The composition of the molten steel did not contain Cr, and the carbon concentration [C] was 0.03 mass%. In the second electric furnace melting step S6, high carbon ferrochromium and 13Cr billet scrap were used as the main raw materials and arc melted in an electric furnace with a capacity of 50 t per melting. After melting, oxygen supply decarburization was performed under atmospheric pressure to adjust the carbon concentration in the molten metal. The composition of the obtained chromium-containing molten metal was [C]: 2 mass%, [Cr]: 66 mass%. In the second combining step S7, 240 t of chromium-free molten steel and 50 t of chromium-containing molten metal were combined under atmospheric pressure to obtain 290 t of molten metal. The composition of the molten metal after the combining was [C] _i : 0.37 mass%, [N] _i : 0.0458 mass%, and [Cr] _i : 11.38 mass%. In the reduced pressure decarburization step S9, the molten metal was subjected to reduced pressure decarburization treatment using an RH type vacuum treatment device. The molten metal was subjected to oxygen supply decarburization treatment for 30 minutes under reduced pressure conditions of 80 to 100 Torr (10666 to 13332 Pa), and then to vacuum decarburization treatment under reduced pressure conditions of 5 Torr (667 Pa) or less. The composition of the molten metal after the reduced pressure decarburization treatment was [C] _f : 0.15 mass%, [N] _f : 0.0098 mass%, and [Cr] _f : 11.02 mass%. Then, in the ladle refining process S10, the chromium content that had migrated to the slag as a chromium loss was reduced, and at the same time, an alloy was added to adjust the composition so as to satisfy the target composition standard. Finally, in the casting process S11, continuous casting was performed to produce a semi-finished billet.

In this embodiment, chromium contamination of the converter and oxidation loss of chromium were avoided by blowing blast furnace molten iron with no intentional addition of chromium, and raw material costs were reduced by melting 13Cr billet scraps together as raw materials in the second electric furnace melting process S6. Therefore, 13Cr steel could be manufactured with high production capacity.

Example 2
13Cr steel was produced in the same flow as in Example 1. The target composition of the 13Cr steel was [C] _e : 0.015 mass%, [N] _e : 0.020 mass% or less, and [Cr] _e : 12.5 mass%. The blast furnace hot metal S1 was subjected to hot metal pretreatment process S2 and converter blowing S5 to obtain 200 t of molten steel. The composition of the molten steel did not contain Cr, and the carbon concentration [C] was 0.01 mass%. In the second electric furnace melting process S6, arc melting was performed twice in an electric furnace with a capacity of 50 t per time, using high carbon ferrochromium and 13Cr billet scrap as the main raw materials. After melting, oxygen supply decarburization was performed under atmospheric pressure to adjust the carbon concentration in the molten metal. The total amount of molten metal from the two melting processes was 90 t, with 50 t of chromium-containing molten metal with [C]: 0.60 mass% and [Cr]: 28 mass%, and 40 t of chromium-containing molten metal with [C]: 1.31 mass% and [Cr]: 55 mass%. In the second combining process S7, 200 t of molten steel not containing chromium and 90 t of chromium-containing molten metal were combined under atmospheric pressure to obtain 290 t of molten metal. The composition of the molten metal after the combination was [C] _i : 0.30 mass%, [N] _i : 0.0645 mass%, and [Cr] _i : 12.41 mass%. In the heating process S8, the required carbon concentration [C] before the reduced pressure decarburization process was calculated based on formula 1, and a recarburizer was added to obtain the carbon concentration in the steel [C] _i : 0.36 mass%. In the reduced pressure decarburization process S9, the molten metal was subjected to reduced pressure decarburization treatment using an RH type vacuum treatment device. The molten metal was decarburized for 60 minutes under reduced pressure conditions of 80 to 100 Torr (10,666 to 13,332 Pa), and then decarburized in vacuum under reduced pressure conditions of 5 Torr (667 Pa) or less. The composition of the molten metal after the reduced pressure decarburization treatment was [C] _f : 0.005 mass%, [N] _f : 0.0070 mass%, and [Cr] _f : 11.02 mass%. Then, in the ladle refining step S10, the chromium content that had moved to the slag as chromium loss was reduced, and at the same time, an alloy was added to adjust the composition so as to satisfy the standard of the target composition. Finally, the molten metal was continuously cast in the casting step S11 to produce a billet of a semi-finished product.

In this embodiment, chromium contamination of the converter and oxidation loss of chromium were avoided by blowing blast furnace molten iron with no intentional addition of chromium, and raw material costs were reduced by melting 13Cr billet scraps together as raw materials in the second electric furnace melting process S6. Therefore, 13Cr steel could be manufactured with high production capacity.

Comparative Example
13Cr steel was produced in the same flow as in Example 2. The composition of the 200 t molten steel subjected to converter blowing S5 was Cr-free and had a carbon concentration [C] of 0.01 mass%. In the second electric furnace melting step S6, 50 t of chromium-containing molten metal with [C]: 0.56 mass% and [Cr]: 29 mass% was produced by two electric furnace meltings, and 40 t of chromium-containing molten metal with [C]: 1.25 mass% and [Cr]: 55 mass% was produced, and the total amount of molten metal from the two meltings was 90 t. In the second combining step S7, 200 t of molten steel not containing chromium and 90 t of chromium-containing molten metal were combined under atmospheric pressure to produce 290 t of molten metal. The composition of the molten metal after the combination was [C] _i : 0.28 mass%, [N] _i : 0.0610 mass%, and [Cr] _i : 12.59 mass%. In the heating step S8, no carburization was performed, and the molten metal was subjected to the reduced pressure decarburization step S9 as it was. In the reduced pressure decarburization step S9, the molten metal was subjected to reduced pressure decarburization treatment in an RH type vacuum treatment device. The molten metal was subjected to oxygen supply decarburization treatment for 60 minutes under reduced pressure conditions of 80 to 100 Torr (10666 to 13332 Pa), and then subjected to vacuum decarburization treatment under reduced pressure conditions of 5 Torr (667 Pa) or less. The composition of the molten metal after the reduced pressure decarburization treatment was [C] _f : 0.007 mass %, [N] _f : 0.0215 mass %, and [Cr] _f : 11.74 mass %. As a result, the nitrogen concentration was higher than the standard, and the composition was out of the range.

In this specification, [M] represents a component element M in the chromium-containing molten iron or chromium-containing alloy. The unit of pressure "atm" is 101325 Pa. The unit of pressure "Torr" is 133.3 Pa. The unit of mass "t" is 10 ³ kg.

Claims (5)

A method for producing chromium-containing steel, comprising a step of combining a first molten metal obtained by subjecting blast furnace hot metal to hot metal pretreatment and decarburization in a converter with a second molten metal obtained by melting chromium-containing scrap or ferroalloys and refining them as necessary, and wherein no chromium-containing raw materials are intentionally used in the production of the first molten metal. The method for producing chromium-containing steel according to claim 1, further comprising a step of subjecting the chromium-containing molten iron obtained by combining the first molten metal and the second molten metal to a reduced pressure decarburization treatment, after adjusting the carbon concentration as necessary. 3. The _{method for producing a chromium-containing steel according to claim 2, wherein the carbon concentration [C]i (mass%) in the molten metal before the reduced pressure decarburization treatment is adjusted so as to satisfy the following formula 1 from the nitrogen concentration [N]i ( mass} %) in the molten metal before the reduced pressure decarburization treatment, the target carbon concentration [C] _e (mass%) in the molten metal after the reduced pressure decarburization treatment, and the target nitrogen concentration [N]e (mass%).
[Formula 1]
[N] _i - [N] _e ≦0.28×([C] _i - [C] _e ) -0.04 The method for producing a chromium-containing steel according to claim 3, wherein the carbon concentration [C] _i in the molten metal before the reduced pressure decarburization treatment is more than 0.05 mass%. The method for producing a chromium-containing steel according to any one of claims 1 to 4, wherein the component composition of the chromium-containing steel contains, on a mass basis, Cr: 7% or more, C: 0.005% or more, and N: 0.05% or less.

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