Method for producing chromium-containing steel

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

[Technical Field]

[0001] The present invention relates to a method for producing chromium-containing steel, and 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. [Background technology]

[0002] For example, the electric furnace-AOD process and the converter-RHOB process are commonly known as methods for producing stainless steel, i.e., steel with high chromium and nickel contents. In the former process, a raw material blend consisting primarily of stainless steel scrap and high-carbon ferrochromium materials is melted in an electric furnace, followed by decarburization and refinement using argon oxygen decarburization (AOD). In the latter process, molten pig iron is charged into a converter, and nickel and chromium materials are added to the molten iron to decarburize and refine the molten iron. The resulting molten steel is then subjected to final decarburization and composition adjustment using RH oxygen blowing (RHOB). However, each process has its own drawbacks. The electric furnace-AOD process reduces raw material costs by utilizing stainless steel scrap. On the other hand, the electric furnace's smaller heat size compared to the converter results in small-lot production, resulting in significant yield reductions. In addition, the high energy and refractory costs associated with the electric furnace are a problem. In contrast, the converter-RHOB process has relatively low energy and refractory costs. However, stainless steel scrap cannot be used in large quantities, which results in high raw material costs, and the use of a large amount of molten iron results in high CO2 emissions.

[0003] In light of this background, Patent Document 1 discloses a "combined melt" 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.

[0004] Patent Document 2 also discloses a method for producing high alloy steel, particularly high-nickel steel, by combining molten metal. In order to prevent nickel contamination in a converter, high-nickel steel is melted and refined in an electric furnace, and the molten steel after converter refining and the molten metal in the electric furnace are combined without deoxidization to produce a combined molten metal with a [C] concentration of 0.05% by mass, thereby making it possible to suppress re-P and N pickup. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 02-085334 [Patent Document 2] Japanese Patent Application Publication No. 10-140227 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the conventional technology has the following problems. In the technology disclosed in Patent Document 1, molten metal melted in an electric furnace and converted hot metal are charged together into a converter, and a Cr source is added after decarburization. Patent Document 1 claims that decarburization blowing with minimal chromium loss can be achieved by adding ferrochromium while increasing stirring power under conditions where the hot metal charge amount is low. However, the chromium loss reduction technology achieved by this technology results in a high chromium loss of 2% or more. Furthermore, the chromium source is generally charged in a converter, and no technology is disclosed for melting the chromium source primarily in an electric furnace. In addition, the converter is contaminated with chromium, and when melting steel grades subject to strict chromium restrictions after processing, the converter must be cleaned, which increases costs.

[0007] Furthermore, 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 a high-chromium molten metal using an inexpensive ferrochromium source (such as high-carbon ferrochromium) in order to produce chromium-containing steel. When attempting to apply this technique to the production of chromium-containing steel, preferential decarburization of chromium molten metal in an electric furnace under atmospheric conditions becomes more difficult as the carbon content decreases, making it thermodynamically difficult to obtain a molten metal with a carbon concentration of 0.05% by mass or less. Therefore, this process is not suitable for producing chromium-containing steel.

[0008] The present invention has been made in view 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. [Means for solving the problem]

[0009] The method for producing a chromium-containing steel according to the present invention, which advantageously solves the above-mentioned problems, includes a step of combining a first molten metal obtained by subjecting blast furnace hot metal to hot metal pretreatment and decarburizing it 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.

[0010] The method for producing chromium-containing steel according to the present invention is as follows: (a) the method includes a step of subjecting the chromium-containing molten iron obtained by combining the first molten metal and the second molten metal to a decarburization treatment under reduced pressure after adjusting the carbon concentration as necessary; (b) Nitrogen concentration in the molten metal before decompression treatment [N] i (mass%), target carbon concentration of molten metal after decompression treatment [C] e (mass%) and target nitrogen concentration [N] e (mass%) to satisfy the following formula 1: i (% by mass), (c) Carbon concentration in the molten metal before decompression treatment [C] iis more than 0.05% by mass, (d) The chemical composition of the chromium-containing steel contains, by mass, 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 [Effects of the Invention]

[0011] According to the method for producing chromium-containing steel of the present invention, blast furnace hot metal and electric furnace hot metal 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 the converter-RHOB process. Furthermore, the nitrogen concentration of the combined chromium-containing molten steel can be reduced by decarburizing it under reduced pressure. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flow diagram of a method for producing a chromium-containing steel according to one embodiment of the present invention. [Figure 2] 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. DETAILED DESCRIPTION OF THE INVENTION

[0013] First, prior to describing the embodiments of the present invention, an outline of the invention will be provided to facilitate understanding. Patent Document 2 is a technology related to the present invention. The technology described in Patent Document 2 is primarily concerned with the melting of high-Ni steel, and both converter and electric furnace processes require the suppression of CO gas generation, N absorption, and re-phosphorization. Therefore, it is assumed that the steel is not deoxidized, i.e., the [O] (oxygen) concentration in the molten steel is increased, and the [C] concentration of the molten steel is 0.05 mass% or less. On the other hand, the technology of the present invention is concerned with high-Cr steel. First, in the combined melting process, high-Cr molten metal is decarburized in an air atmosphere during electric furnace melting. Therefore, to suppress Cr loss in the electric furnace, deoxidation is performed to recover Cr and produce a molten metal with a high [C] concentration. When converter melt and electric furnace melt are combined in the air, the combined molten metal contains a high concentration of Cr, which has a high affinity for nitrogen, and N absorption occurs until the nitrogen concentration of the combined molten metal reaches the saturated nitrogen concentration. In this respect, the prerequisites for combining the molten metal differ 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 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 aims to make the [C] concentration of the molten metal after combining the molten metal 0.05 mass% or less. In contrast, in the present invention, it is theoretically preferable to make the carbon concentration in the molten metal before reduced pressure decarburization treatment greater than 0.05 mass% (e.g., 0.3 mass%).

[0014] The following is a detailed description of embodiments of the present invention. The following embodiments are intended to exemplify equipment and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope defined in the claims.

[0015] FIG. 1 shows a production flow of chromium-containing steel according to one embodiment of the present invention. To produce one heat of chromium-containing steel, blast furnace hot metal S1 is optionally subjected to one or more of desiliconization, dephosphorization, and desulfurization treatments in a hot metal pretreatment step S2 to adjust its composition. In a first combining step S4, the blast furnace hot metal S1 may be combined with molten iron produced in a first electric furnace melting step S3 before being charged into a converter, but this is not required. When the first combining step S4 is performed, it is preferable to avoid the addition of chromium alloys, which would cause oxidation loss during the subsequent oxygen blowing in the converter, and instead melt the molten iron into a non-chromium alloy or a molten iron with a composition equivalent to that of general carbon steel. In other words, no chromium-containing raw materials are intentionally used in the production of the molten metal. "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 intentionally added in amounts greater than a predetermined ratio. The predetermined chromium concentration [Cr] in the molten metal by mass is, for example, less than 1% at most, preferably 0.5%, more preferably 0.3%, and even more preferably 0.2%. In converter blowing S5, blowing is performed without adding any chromium-containing raw materials. However, chromium sources that are not intentionally added may be included. The molten metal after converter blowing is deoxidized. Meanwhile, in the second electric furnace melting step S6, chromium raw materials, such as ferrochromium and chromium-containing steel scrap, are melted in an electric furnace. The second electric furnace melting step S6 may be performed multiple times depending on the heat size or scrap content of the electric furnace. However, when performing multiple melting processes in an electric furnace, it is preferable to wait in equipment capable of maintaining heat, such as a VAD (Vacuum Arc Degassing) or LF (Ladle Furnace), in consideration of temperature drop.

[0016] In the second electric furnace melting process S6, it is preferable to use high-carbon ferrochrome ([C] ~ 10 mass%, [Cr] ~ 70 mass%) to reduce raw material costs. Also, scrap containing chromium-containing products or other alloys may be melted in combination. Here, since a low final carbon concentration [C] of the electric furnace molten metal is preferable, decarburization treatment is performed as necessary when using raw materials with a high C content. The electric furnace molten metal tapped through the second electric furnace melting process S6 is received in a ladle and then transported. 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 from 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 metal is high, a CO gas is generated by the CO generation reaction during the combining, which can 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 furnace refining. Furthermore, the blending ratio in the second combining step S7 is preferably 1:1, and the molten metal from S6 is preferably in the range of 0.15 to 0.50. For example, when combining molten steel from a converter furnace with a capacity of 200 to 350 tonnes with molten steel from an electric furnace with a capacity of 30 to 100 tonnes, a higher ratio of molten steel from the converter furnace is preferable in order to produce chromium-containing steel that prioritizes yield, i.e., production volume per run, and minimizes alloy costs.

[0017] The second mixing step S7 may result in a large temperature drop in the molten iron. Therefore, it is preferable to use a heating step S8, such as a LF. Because the temperature is increased in the heating step S8, there is concern about the pickup of P and Mn from the slag carried into the casting ladle. Depending on the P and Mn specifications, it is preferable to add a slag removal step before this heating step S8, but this is not always necessary.

[0018] In the second electric furnace melting process S6, the electric furnace molten metal is deoxidized before being combined. This causes significant air entrainment during the second combining process S7 in the atmosphere, resulting in nitrogen pick-up from the atmosphere. At this time, chromium in the molten metal has the property of lowering nitrogen activity, so nitrogen is picked up to a saturated state during the second combining process S7 in the atmosphere. Therefore, denitrification is essential to achieve a nitrogen concentration [N] (mass%) that meets product specifications. Denitrification is carried out using reduced-pressure equipment such as an RH-type vacuum treatment device.

[0019] In this embodiment, decarburization and denitrification are carried out in parallel in the reduced pressure decarburization step S9. For example, it is known that denitrification proceeds in conjunction with the CO generation reaction during reduced pressure decarburization. Figure 2 shows the relationship between the amount of decarburization under reduced pressure Δ[C] (mass%) and the amount of denitrification Δ[N] (mass%) when chromium-containing molten steel is subjected to reduced pressure decarburization using an RH-type vacuum processing device. The chromium-containing molten steel used in Figure 2 had a [Cr] in the range of 10.2 to 13.5 mass%. Here, the amount of decarburization under reduced pressure Δ[C] (mass%) is calculated by multiplying the carbon concentration [C] in the molten steel before reduced pressure decarburization. i (mass%) and carbon concentration in the molten metal after decompression treatment [C] f The nitrogen removal amount Δ[N] (mass%) is the difference between the nitrogen concentration [N] in the molten metal before the decompression decarburization treatment and the nitrogen removal amount Δ[N] (mass%). i (mass%) and nitrogen concentration in the molten metal after decompression treatment [N] f From this result, the following formula 1 is derived to obtain the carbon concentration before the reduced pressure decarburization treatment in order to obtain the target nitrogen concentration. [Formula 1] [N] i -[N] e ≦0.28×([C] i -[C] e )-0.04 where [N] i is the nitrogen concentration in the molten metal before decompression treatment (mass%), [N] e is the target nitrogen concentration (mass%) after decompression decarburization treatment, [C] i is the carbon concentration in the molten metal before decompression treatment (mass%), [C] e is the target carbon concentration (mass%) of the molten metal after decompression treatment Represents.

[0020] To obtain a certain amount of denitrification, a certain amount of decarburization is required. That is, a certain carbon concentration in steel [C] is required before the start of the decarburization treatment. i Nitrogen concentration in steel (mass%) [N] i to target nitrogen concentration [N] e Denitrification treatment cannot be performed up to (mass%). Carbon concentration in steel at the start of reduced pressure decarburization treatment [C] i In order to ensure this (mass%), it is preferable to increase the carbon concentration [C] at the time of tapping from the electric furnace or to add an alloy or the like to the molten steel before the start of the reduced pressure treatment (before the start of decarburization) or in the heating step S8 before the start of the reduced pressure treatment to recarburize it. In addition, it is preferable that the carbon concentration [C] of the molten steel after the converter blowing S5 exceeds 0.05 mass%. Note that the carbon concentration [C] in the steel at the start of the reduced pressure decarburization treatment i If the carbon concentration is too high, excessive decarburization treatment will be required to achieve the carbon concentration standard for chromium-containing steel, so it is preferable to set the carbon concentration to a level that is necessary and sufficient for denitrification treatment.

[0021] In the reduced-pressure decarburization process using an RH-type vacuum processing device, oxygen-flow decarburization and vacuum decarburization can be performed. For example, when the process is performed at a temperature equal to or higher than the temperature T 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 begins 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 processing device may be directly transported to the casting process S11 and cast. Furthermore, in order to reduce the slag in which chromium has oxidized during the reduced-pressure decarburization process, it is preferable to proceed to the casting process S11 via a ladle refining process S10 such as an LF. [Formula 2] log{(a Cr 2 / 3 P CO ) / a C}=8.48-13520 / T where a Cr is the activity of chromium in chromium-containing molten steel, P CO 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.

[0022] In the above embodiment, an example in which an RH-type vacuum processing device is used in the reduced pressure decarburization step S9 has been described, but this is not limiting. This embodiment can be applied to any equipment capable of reduced pressure decarburization. The casting step S11 can be applied with an ingot-making decomposition method or a continuous casting method. From the viewpoint of yield, a continuous casting method is preferred.

[0023] When implementing the combined melting method in the manufacturing method of chromium-containing steel according to this embodiment, there are no particular upper or lower limits on the Cr, C, and N contents. However, it is preferable to apply this method to chromium-containing steel containing, by mass, 7% or more Cr, 0.005% or more C, and 0.05% or less N. If the Cr content is less than 7%, it is cheaper to add the chromium raw material in a converter or ladle refining process than to melt the chromium raw material using an electric furnace. While there is no specific upper limit for the Cr content, the upper limit for the Cr content of steel that can be realistically produced from a standard perspective is generally about 30%. To achieve a C content of less than 0.005%, excessive decarburization is required within the above Cr content range, which may result in a decrease in chromium yield due to oxidation loss. On the other hand, although there is no specific upper limit for the C content, the upper limit for the C content of steel that can generally be expected is about 0.5%. If the N content exceeds 0.05%, low-temperature toughness may be degraded. Other elements may be added as needed. [Example]

[0024] Example 1 Based on the method for producing chromium-containing steel according to the embodiment described above, a 13Cr steel was produced in accordance with the flow shown in FIG. 1. The target composition of the 13Cr steel was [C] e :0.20 mass%, [N] e : 0.030 mass% or less and [Cr] eThe carbon content of the molten metal was 13.0% by mass. The blast furnace hot metal S1 was subjected to hot metal pretreatment process S2 and converter blowing S5 to obtain 240 t of molten steel. The molten steel was free of Cr and had a carbon concentration [C] of 0.03% by mass. In the second electric furnace melting process S6, high-carbon ferrochromium and 13Cr billet scrap were arc-melted in an electric furnace with a capacity of approximately 50 t per melt. After melting, the carbon content of the molten metal was adjusted by oxygen-flow decarburization under atmospheric pressure. The resulting chromium-containing molten metal had a composition of [C]: 2% by mass, [Cr]: 66% by mass. In the second combining process 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 combined molten metal was [C]: 0.03% by mass. i :0.37% by mass, [N] i : 0.0458 mass% and [Cr] i 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 blowing decarburization treatment for 30 minutes under reduced pressure conditions of 80 to 100 Torr (10666 to 13332 Pa), and then vacuum decarburization treatment was performed under reduced pressure conditions of 5 Torr (667 Pa) or less. The chemical composition of the molten metal after the reduced pressure decarburization treatment was [C] f :0.15% by mass, [N] f : 0.0098 mass% and [Cr] f The chromium content was 11.02% by mass. Then, in the ladle refining process S10, the chromium content that had transferred to the slag as a chromium loss was reduced, and at the same time, alloy was added to adjust the composition so that the target composition specifications were met. Finally, in the casting process S11, continuous casting was performed to produce a semi-finished billet.

[0025] In this example, chromium-free molten iron was blown into a converter to avoid chromium contamination in the converter and oxidation loss of chromium, and raw material costs were reduced by melting 13Cr billet scrap as raw material in the second electric furnace melting step S6, enabling the production of 13Cr steel with high production capacity.

[0026] Example 2 13Cr steel was produced in the same manner as in Example 1. The target composition of the 13Cr steel was [C]e :0.015% by mass, [N] e : 0.020 mass% or less and [Cr] e The carbon content was 12.5% ​​by mass. Blast furnace hot metal S1 was subjected to hot metal pretreatment process S2 and converter blowing S5, producing 200 tons of molten steel. The molten steel contained no Cr and had a carbon concentration [C] of 0.01% by mass. In the second electric furnace melting process S6, arc melting was performed twice in an electric furnace with a capacity of approximately 50 tons per melting, using high-carbon ferrochromium and 13Cr billet scrap as the main raw materials. After melting, the carbon concentration of the molten metal was adjusted by oxygen-flow decarburization under atmospheric pressure. 50 tons of molten metal containing chromium [C]: 0.60% by mass and [Cr]: 28% by mass was obtained, and 40 tons of molten metal containing chromium [C]: 1.31% by mass and [Cr]: 55% by mass was obtained, resulting in a total of 90 tons of molten metal from the two melting processes. In the second combining step S7, 200 t of chromium-free molten steel and 90 t of chromium-containing molten metal were combined under atmospheric pressure to obtain 290 t of molten metal. The chemical composition of the combined molten metal was [C] i :0.30 mass%, [N] i : 0.0645 mass% and [Cr] i In the heating step S8, the required carbon concentration [C] before the reduced pressure decarburization treatment was calculated based on Equation 1, and the recarburizer was added to obtain the carbon concentration [C] in the steel. i 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 blowing decarburization treatment for 60 minutes under reduced pressure conditions of 80 to 100 Torr (10666 to 13332 Pa), and then vacuum decarburization treatment was performed under reduced pressure conditions of 5 Torr (667 Pa) or less. The chemical composition of the molten metal after the reduced pressure decarburization treatment was [C] f :0.005% by mass, [N] f : 0.0070 mass% and [Cr] f The chromium content was 11.02% by mass. Then, in the ladle refining process S10, the chromium content that had transferred to the slag as a chromium loss was reduced, and at the same time, alloy was added to adjust the composition so that the target composition specifications were met. Finally, in the casting process S11, continuous casting was performed to produce a semi-finished billet.

[0027] In this example, chromium-free molten iron was blown into a converter to avoid chromium contamination in the converter and oxidation loss of chromium, and raw material costs were reduced by melting 13Cr billet scrap as raw material in the second electric furnace melting step S6, enabling the production of 13Cr steel with high production capacity.

[0028] (Comparative Example) 13Cr steel was produced using the same flow as in Example 2. The chemical composition of 200 t of 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, two electric furnace melting operations were performed to produce 50 t of chromium-containing molten metal with [C]: 0.56 mass% and [Cr]: 29 mass%, and 40 t of chromium-containing molten metal with [C]: 1.25 mass% and [Cr]: 55 mass%, for a total of 90 t of molten metal from the two melting operations. In the second combining step S7, 200 t of chromium-free molten steel and 90 t of chromium-containing molten metal were combined under atmospheric pressure to produce 290 t of molten metal. The chemical composition of the combined molten metal was [C]: 0.56 mass% and 29 mass% of chromium. i :0.28% by mass, [N] i : 0.0610 mass% and [Cr] i The carbon content was 12.59 mass%. In the heating step S8, no carburization was performed, and the molten metal was directly subjected to the reduced pressure decarburization step S9. 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 blowing decarburization treatment under reduced pressure conditions of 80 to 100 Torr (10666 to 13332 Pa) for 60 minutes, and then vacuum decarburization treatment was performed under reduced pressure conditions of 5 Torr (667 Pa) or less. The chemical composition of the molten metal after the reduced pressure decarburization treatment was [C] f :0.007% by mass, [N] f : 0.0215 mass% and [Cr] f The nitrogen concentration was 11.74% by mass. As a result, the nitrogen concentration was higher than the standard and was not included in the ingredients.

[0029] In this specification, [M] represents the component element M in 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 Let's say it's kg.

Claims

1. In producing chromium-containing steel having a composition containing, by mass, C: 0.005% or more and N: 0.05% or less, 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, decarburizing in a converter, and then deoxidizing the first molten metal with a second molten metal obtained by melting chromium-containing scrap or ferroalloys and then deoxidizing the second molten metal; and a step of subjecting the first molten metal and the second molten metal to reduced pressure decarburization to produce chromium-containing molten iron having a carbon concentration of more than 0.05% by mass, wherein the chromium concentration of the first molten metal is less than 1% by mass.

2. Nitrogen concentration in molten metal before decompression treatment [N] ｉ (mass%), target carbon concentration of molten metal after reduced pressure decarburization treatment [C] ｅ (mass%) and target nitrogen concentration [N] ｅ (mass%) to satisfy the following formula 1: carbon concentration [C] in the molten metal before decompression treatment ｉ The method for producing a chromium-containing steel according to claim 1, wherein the Cr content is adjusted to 0.05% by mass. [Formula 1] [N] ｉ -[N] ｅ ≦0.28×([C] ｉ -[C] ｅ )-0.04

3. A method for producing chromium-containing steel as described in claim 1, which comprises at least one of refining the second molten metal and adjusting the carbon concentration of the chromium-containing molten iron before subjecting it to a reduced pressure decarburization treatment.

4. A method for producing chromium-containing steel as described in claim 2, which comprises at least one of refining the second molten metal and adjusting the carbon concentration of the chromium-containing molten iron before subjecting it to a reduced pressure decarburization treatment.

5. 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, 7% or more of Cr.

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