KR20230059938A - Ferritic-austenitic two-phase stainless steel and the method for manufacturing the same - Google Patents

Abstract

In the present specification, ferritic stainless steel having improved elongation while omitting upper annealing and a manufacturing method thereof are disclosed.
Ferritic stainless steel according to an embodiment of the present invention, in weight%, C: 0.01% or more and 0.1% or less, Si: 0.01% or more and 1.0% or less, Mn: 0.01% or more and 1.5% or less, P: more than 0% 0.05% or less, S: more than 0% and 0.005% or less, Cr: 13.0% or more and 18.0% or less, N: 0.005% or more and 0.1% or less, Al: 0.005% or more and 0.2% or less, Ni: 0.08% or more and 0.15% or less, the balance Fe (iron) and other unavoidable impurities may be included.

Description

Ferritic-austenitic two-phase stainless steel and its manufacturing method

The present invention relates to a ferritic-austenitic two-phase stainless steel and a manufacturing method thereof, and more particularly, to a ferritic-austenitic two-phase stainless steel that secures high strength and high ductility, while minimizing the content of expensive elements to lower manufacturing costs. and a manufacturing method thereof.

Ferritic stainless steel is inexpensive and has good surface gloss, drawability, and oxidation resistance, so it is widely used in kitchen utensils, building exterior materials, home appliances, and electronic parts. On the other hand, austenitic stainless steel with good workability and corrosion resistance uses Fe (iron) as a base metal, contains Cr (chromium) and Ni (nickel) as main raw materials, and contains Mo (molybdenum) and Cu (copper), etc. Various types of steel are being developed to suit various uses by adding other elements of

However, since austenitic stainless steel contains expensive raw materials such as Ni and Mo, price competitiveness is poor. As an alternative to this, 400 series stainless steel has been discussed, but there are problems in that formability and impact characteristics are relatively poor and welds are weak.

On the other hand, duplex stainless steel in which austenite and ferrite phases are mixed has all the advantages of austenite and ferrite, and various types of duplex stainless steel have been developed.

As interest in stainless steel with reduced content of expensive elements such as Ni and Mo is steadily increasing, attempts to develop lean alloys are increasing. In addition, research on duplex stainless steel composed of a ferrite-austenite phase is also increasing.

In Patent Document 0001, an austenitic-ferritic stainless steel characterized by a low Ni content and a high N content is disclosed. In particular, Patent Document 0001 is characterized by controlling the stability of the austenite phase to form lean duplex stainless steel so that the elongation rate is high while maintaining high strength characteristics. However, Patent Document 0001 has a problem in that the manufacturing cost is relatively high because the contents of Mo and Ni, which are expensive elements, are still high.

Korean Patent Publication No. 10-2006-0074400 (published on July 3, 2006)

An object of the present invention for solving the above problems is to manage expensive elements, such as Ni, Cu, Mo, etc., as impurities and optimize alloy components, thereby reducing manufacturing costs while securing high strength and high elongation, ferrite- It is intended to provide an austenitic two-phase stainless steel and a manufacturing method thereof.

Ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention, in weight%, C: 0.01% or more and 0.04% or less, Si: 0.2% or more and 1.0% or less, Mn: 2.0% or more and 4.0% or less, P : more than 0% and less than 0.1%, S: more than 0% and less than 0.01%, Cr: 18.0% or more and 21.0% or less, N: 0.05% or more and 0.15% or less, the balance including Fe (iron) and other unavoidable impurities, the formula below The γ-phase stability index represented by (1) may satisfy -8 or less.

Formula (1): 133 + 109*[C] - 0.9*[Si] + 1.6*[Mn] - 7.1*[Cr] - 117*[N]

In the above formula (1), [C], [Si], [Mn], [Cr], and [N] mean the content (wt%) of each element.

In addition, the ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention may further include Ni: greater than 0% and 0.3% or less, Cu: greater than 0% and 0.3% or less, and Mo: greater than 0% and 0.3% or less. can

In addition, the ferrite-austenite two-phase stainless steel according to an embodiment of the present invention may include a ferrite phase of 60% or more and 80% or less in volume fraction.

In addition, the ferrite-austenite two-phase stainless steel according to an embodiment of the present invention may have an elongation of 30% or more.

In addition, the ferrite-austenite two-phase stainless steel according to an embodiment of the present invention may have a yield strength of 350 MPa or more.

In addition, in the manufacturing method of ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention, in weight%, C: 0.01% or more and 0.04% or less, Si: 0.2% or more and 1.0% or less, Mn: 2.0% or more 4.0 % or less, P: more than 0% and less than 0.1%, S: more than 0% and less than 0.01%, Cr: 18.0% or more and less than 21.0%, N: 0.05% or more and less than 0.15%, the balance including Fe (iron) and other unavoidable impurities and preparing a slab having a γ-phase stability index represented by Equation (1) below that satisfies -8 or less; reheating the slab; preparing a hot-rolled steel sheet by hot-rolling the reheated slab and performing hot-rolling annealing; The method may include preparing a cold-rolled steel sheet by cold-rolling the hot-rolled steel sheet, and pickling after cold-rolling annealing.

Formula (1): 133 + 109*[C] - 0.9*[Si] + 1.6*[Mn] - 7.1*[Cr] - 117*[N]

In the above formula (1), [C], [Si], [Mn], [Cr], and [N] mean the content (wt%) of each element.

In addition, in the method for producing ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention, the slab contains Ni: more than 0% and 0.3% or less, Cu: more than 0% and 0.3% or less, Mo: more than 0% 0.3 % or less may be further included.

In addition, in the method for producing ferrite-austenite two-phase stainless steel according to an embodiment of the present invention, the hot rolling annealing may be performed at 1000 to 1250 ° C. for 1 to 60 minutes.

In addition, in the method for manufacturing ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention, the hot-rolled steel sheet may have a thickness of 3 to 20 mm.

In addition, in the method for producing ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention, the cold rolling annealing may be performed at 1000 to 1250 ° C. for 10 seconds to 60 minutes.

In addition, in the method for manufacturing ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention, the cold-rolled steel sheet may have a thickness of 0.1 to 5 mm.

According to an embodiment of the present invention, by managing expensive elements such as Ni, Cu, Mo, etc. as impurities and optimizing alloy components, ferrite-austenite two-phase, which can secure high strength and high elongation while reducing manufacturing cost Stainless steel and its manufacturing method can be provided.

1 is a graph showing the elongation according to the γ-phase stability index represented by Formula (1).
Figure 2 is a photograph taken with an optical microscope of the microstructure of the stainless steel according to Example 1.
Figure 3 is a photograph taken with an optical microscope of the microstructure of stainless steel according to Comparative Example 2.
Figure 4 is a photograph taken with an optical microscope of the microstructure of stainless steel according to Comparative Example 3.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are presented to sufficiently convey the spirit of the present invention to those skilled in the art. The present invention may be embodied in other forms without being limited to only the embodiments presented herein. In the drawings, in order to clarify the present invention, illustration of parts irrelevant to the description may be omitted, and the size of components may be slightly exaggerated to aid understanding.

Throughout the specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

Expressions in the singular number include plural expressions unless the context clearly dictates otherwise.

Hereinafter, the reason for limiting the numerical value of the alloy component content in the embodiments of the present invention will be described. Hereinafter, unless otherwise specified, units are % by weight.

Ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention, in weight%, C: 0.01% or more and 0.04% or less, Si: 0.2% or more and 1.0% or less, Mn: 2.0% or more and 4.0% or less, P : more than 0% and less than 0.1%, S: more than 0% and less than 0.01%, Cr: 18.0% or more and 21.0% or less, N: 0.05% or more and 0.15% or less, the balance may include Fe (iron) and other unavoidable impurities.

The content of C (carbon) may be 0.01% or more and 0.04% or less.

C is an austenite phase stabilizing element and can be used instead of expensive elements such as Ni. In addition, C is an effective element for increasing material strength by solid solution strengthening. Considering this, C may be added in an amount of 0.01% or more. However, when the content of C is excessive, segregation and coarse carbides are formed in the center of the material, thereby adversely affecting the subsequent hot rolling-annealing-cold rolling-cold rolling annealing process. In addition, when the content of C is excessive, since it can easily combine with carbide-forming elements such as Cr at the ferrite-austenite phase boundary, corrosion resistance may be inferior. Considering this, the upper limit of the C content may be limited to 0.04%.

The content of Si (silicon) may be 0.2% or more and 1.0% or less.

Si is an element added for a deoxidizing effect, and as a ferrite phase forming element, it can be concentrated in the ferrite phase during annealing heat treatment. Considering this, Si may be added in an amount of 0.2% or more. However, when the content of Si is excessive, the hardness of the ferrite phase is rapidly increased and the elongation rate may be lowered. In addition, when the content of Si is excessive, slag fluidity during steelmaking is reduced, and corrosion resistance may be reduced by forming inclusions by combining with oxygen. Considering this, the upper limit of the Si content may be limited to 1.0%.

The content of Mn (manganese) may be 2.0% or more and 4.0% or less.

Mn is an element effective in controlling molten metal fluidity and an element that increases deoxidizer and nitrogen solubility. In addition, Mn is an austenite forming element and can be used instead of expensive elements such as Ni. On the other hand, when Ni, Cu, and Mo are managed as impurities, a Mn content of a certain level or higher is required to secure an appropriate austenite phase fraction. Considering this, Mn may be added by 2.0% or more. However, when the Mn content is excessive, it is difficult to secure corrosion resistance as Mn is combined with S in steel to form MnS. In addition, when the Mn content is excessive, it becomes difficult to control the phase fraction due to the excessive austenite phase fraction. Considering this, the upper limit of the Mn content may be limited to 4.0%.

The content of P (phosphorus) may be greater than 0% and less than 0.1%.

P is an impurity inevitably contained in steel, and is an element that causes intergranular corrosion during pickling or impairs hot workability. Therefore, it is desirable to control the content of P as low as possible. Considering this, the upper limit of the P content may be limited to 0.1%.

The content of S (sulfur) may be greater than 0% and 0.01% or less.

S is an impurity inevitably contained in steel, and is an element that is segregated at grain boundaries and causes impairing hot workability. Therefore, it is desirable to control the content of S as low as possible. Considering this, the upper limit of the S content may be limited to 0.01%.

The content of Cr (chromium) may be 18.0% or more and 21.0% or less.

Cr is a ferrite phase stabilizing element together with Si, and is an element that is essentially added to improve corrosion resistance as well as play a major role in securing the ferrite phase. Considering this, Cr may be added by 18.0% or more. However, when the content of Cr is excessive, the formation of delta (δ) ferrite in the slab is promoted, elongation and impact toughness are lowered, and manufacturing cost is increased. Considering this, the upper limit of the Cr content may be limited to 21.0%.

The content of N (nitrogen) may be 0.05% or more and 0.15% or less.

N, together with C and Ni, is an element that contributes greatly to the stabilization of the austenite phase, and is an element that enriches the austenite phase during annealing heat treatment. In addition, N is an element capable of increasing corrosion resistance and high strength incidentally. Considering this, N may be added in an amount of 0.05% or more. However, when the content of N is excessive, surface defects due to generation of nitrogen pores during casting may be induced due to excessive solid solubility. Considering this, the upper limit of the N content may be limited to 0.15%.

The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in a normal manufacturing process, this cannot be excluded. Since these impurities are known to anyone skilled in the ordinary manufacturing process, not all of them are specifically mentioned in this specification.

The ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention may further include Ni: greater than 0% and 0.3% or less, Cu: greater than 0% and 0.3% or less, and Mo: greater than 0% and 0.3% or less. .

The content of Ni (nickel) may be more than 0% and 0.3% or less.

Ni is an austenite stabilizing element along with Mn, Cu and N, and is an element that plays a major role in increasing the stability of the austenite phase. However, in the present invention, Ni can be managed as an impurity for cost reduction, and the phase fraction balance can be maintained by increasing the contents of Mn and N. Considering this, the upper limit of the Ni content can be controlled to 0.3%.

The content of Cu (copper) may be greater than 0% and 0.3% or less.

Cu is an element that suppresses work hardening due to formation of a strain-induced martensite phase and contributes to softening of austenitic stainless steel. However, in the present invention, in order to reduce cost, it is possible to manage Cu as an impurity and maintain a phase fraction balance by increasing the contents of Mn and N. Considering this, the upper limit of the Ni content can be controlled to 0.3%.

The content of Mo (molybdenum) may be greater than 0% and 0.3% or less.

Mo is an element effective in improving corrosion resistance while stabilizing ferrite together with Cr. However, in the present invention, it is possible to maintain the balance of the phase fraction by managing Mo as an impurity and increasing the contents of Si and Cr for cost reduction. Considering this, the upper limit of the Mo content can be controlled to 0.3%.

The ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention may satisfy the γ-phase stability index (ASI, Austenitic phase Stability Index) of -8 or less represented by Equation (1) below.

Formula (1): 133 + 109*[C] - 0.9*[Si] + 1.6*[Mn] - 7.1*[Cr] - 117*[N]

In the above formula (1), [C], [Si], [Mn], [Cr], and [N] mean the content (wt%) of each element.

Cr and Si are elements that stabilize the ferrite phase, and C, N, and Mn are elements that stabilize the austenite phase. However, in the two-phase stainless steel, each element can sensitively affect the change in the phase fraction of the two phases constituting the microstructure. Also, phase fraction changes can lead to changes in the stability of ferrite and austenite phases. Therefore, in order to achieve phase fraction balance through optimization of alloy components, it is necessary to control the contents of Cr, Si, C, N, and Mn. Considering this, the value of Equation (1) may be -8 or less.

In addition, the ferrite-austenite two-phase stainless steel according to an embodiment of the present invention may include a ferrite phase of 60% or more and 80% or less in volume fraction. By controlling the ferrite phase and austenite phase fractions, it is possible to maintain the properties of the two-phase stainless steel and suppress the formation of thermal martensite after annealing.

Meanwhile, the ferrite-austenite structure referred to in the present invention means that the ferrite phase and the austenite phase occupy most of the structure, and does not mean that the structure is formed only of the ferrite phase and the austenite phase.

For example, that the ferrite phase and the austenite phase occupy most of the structure may mean that the sum of the ferrite phase and the austenite phase accounts for 95% or more of the structure forming the stainless steel, and the ferrite phase and the austenite phase The rest except for may be occupied by the martensite phase in which the austenite phase is transformed. However, it is not limited thereto.

In addition, the ferrite-austenite two-phase stainless steel according to an embodiment of the present invention may have an elongation of 30% or more and a yield strength of 350 MPa or more.

Next, a method for manufacturing ferrite-austenite two-phase stainless steel according to another aspect of the present invention will be described.

In the manufacturing method of ferrite-austenitic two-phase stainless steel according to an embodiment of the present invention, in weight%, C: 0.01% or more and 0.04% or less, Si: 0.2% or more and 1.0% or less, Mn: 2.0% or more and 4.0% or less , P: more than 0% and less than 0.1%, S: more than 0% and less than 0.01%, Cr: 18.0% or more and 21.0% or less, N: 0.05% or more and 0.15% or less, the balance including Fe (iron) and other unavoidable impurities, Preparing a slab having a γ-phase stability index represented by Equation (1) below that satisfies -8 or less; reheating the slab; preparing a hot-rolled steel sheet by hot-rolling the reheated slab and performing hot-rolling annealing; The method may include preparing a cold-rolled steel sheet by cold-rolling the hot-rolled steel sheet, and pickling after cold-rolling annealing.

Formula (1): 133 + 109*[C] - 0.9*[Si] + 1.6*[Mn] - 7.1*[Cr] - 117*[N]

In the above formula (1), [C], [Si], [Mn], [Cr], and [N] mean the content (wt%) of each element.

In addition, in the method for producing ferritic-austenitic two-phase stainless steel according to an embodiment of the present invention, the slab contains Ni: more than 0% and 0.3% or less, Cu: more than 0% and 0.3% or less, Mo: more than 0% 0.3 % or less may be further included.

The component range of each alloy composition and the reason for limiting the numerical values of Equation (1) are as described above, and each manufacturing step will be described in detail below.

First, after manufacturing a slab satisfying the alloy composition and formula (1), a series of reheating, hot rolling, hot rolling annealing, cold rolling, cold rolling annealing and pickling may be performed.

The hot rolling annealing may be performed at 1000 to 1250 ° C for 1 to 60 minutes.

When the hot rolling annealing temperature is low or the running time is short, the elongation rate may be inferior due to the high residual martensite fraction. However, when the hot rolling annealing temperature is high or the running time is too long, the strength may decrease due to grain coarsening. In consideration of this, the hot rolling annealing may be performed at 1000 to 1250 ° C for 1 to 60 minutes, preferably, at 1000 to 1100 ° C for 1 to 60 minutes.

The hot-rolled steel sheet manufactured through the hot rolling and the hot rolling annealing may have a thickness of 3 to 20 mm.

The cold rolling annealing may be performed at 1000 to 1250 ° C for 10 seconds to 60 minutes.

When the cold rolling annealing temperature is low or the running time is short, the elongation may be inferior due to high residual martensite fraction. However, if the cold rolling annealing temperature is high or the execution time is too long, the strength may decrease due to grain coarsening, and the thickness of the surface oxide layer becomes thick, so that the pickling time for removing the oxide layer becomes long or the oxide layer is sufficiently removed. may not support In consideration of this, the cold rolling annealing may be performed at 1000 to 1250 ° C for 10 seconds to 60 minutes, preferably, at 1000 to 1100 ° C for 10 seconds to 60 minutes.

The cold-rolled steel sheet manufactured through the cold rolling, the cold rolling annealing, and the pickling may have a thickness of 0.1 to 5 mm.

Hereinafter, the present invention will be described in more detail through examples. However, the description of these examples is only for exemplifying the practice of the present invention, and the present invention is not limited by the description of these examples. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

{Example}

For the various alloy composition ranges shown in Table 1 below, slabs with a thickness of 150 mm were prepared in a vacuum induction melting furnace. The prepared slab was reheated at 1250° C., hot-rolled to a sheet width of 200 mm and thickness of 3.2 mm, air-cooled, and hot-rolled annealing was performed at 1100° C. for 1 minute to prepare a hot-rolled steel sheet. Next, the hot-rolled steel sheet was cold-rolled to a thickness of 1.2 mm, followed by cold-rolling annealing at 1050° C. for 30 seconds, and pickling to prepare a cold-rolled steel sheet.

division alloy component C Si Mn P S Cr N Example 1 0.019 0.41 3.93 0.02 <0.003 19.5 0.11 Example 2 0.028 0.4 3.6 0.021 <0.003 19.7 0.085 Comparative Example 1 0.021 0.22 1.98 0.014 <0.003 18 0.09 Comparative Example 2 0.021 0.3 2.85 0.02 <0.003 18.8 0.1 Comparative Example 3 0.019 0.28 2.65 0.021 <0.003 17.9 0.088 Comparative Example 4 0.02 0.38 3.2 0.02 <0.003 18.3 0.1 Comparative Example 5 0.02 0.5 3.93 0.021 <0.003 18.7 0.11 Comparative Example 6 0.021 0.52 3.16 0.018 <0.003 18.1 0.1 Comparative Example 7 0.021 0.45 3.04 0.014 <0.003 18.1 0.093

Table 2 below shows the volume fraction of the ferrite phase, the value of Equation (1), microstructure, yield strength and elongation.

The volume fraction of the ferrite phase was measured using a ferrite content meter, model name Ferritescope MP30 manufactured by Fisher.

The value of Equation (1) represents the γ-phase stability index value represented by Equation (1) below.

Formula (1): 133 + 109*[C] - 0.9*[Si] + 1.6*[Mn] - 7.1*[Cr] - 117*[N]

In the above formula (1), [C], [Si], [Mn], [Cr], and [N] mean the content (wt%) of each element.

The microstructure was measured by dividing ferrite (F), austenite (A), and martensite (M) using an optical microscope manufactured by Himax Tech.

Yield strength and elongation were tested at room temperature at a tensile speed of 20 mm per minute by taking specimens with a gage length of 50 mm and a width of 12.5 mm from a cold-rolled steel sheet with a thickness of 1.2 mm through a tensile tester from Zwick Roell. performed and measured. After each test was performed 3 times for each example, the average value was shown.

division ferrite phase
Volume fraction (%) Equation (1) microstructure Yield strength (MPa) elongation rate
(%) Example 1 71.8 -10.3 F+A 381 33.7 Example 2 78.4 -8.4 F+A 361 36.5 Comparative Example 1 69.7 -0.1 F+M 391 15.3 Comparative Example 2 70.9 -5.6 F+M+A 334 21.6 Comparative Example 3 67.5 1.7 F+M 392 15.8 Comparative Example 4 65.4 -1.7 F+M 366 18.3 Comparative Example 5 66.2 -4.6 F+M+A 386 23.3 Comparative Example 6 65.3 -0.3 F+M 400 17.5 Comparative Example 7 65.9 0.4 F+M 344 20.6

Referring to Table 2, Examples 1 and 2 satisfy the alloy composition, component range, formula (1) and manufacturing process presented in the present invention, so the volume fraction of the ferrite phase satisfies 60% or more and 80% or less, and the yield The strength satisfies 350 MPa or more, and the elongation rate satisfies 30% or more.

However, in Comparative Examples 2 and 5, the value of Equation (1) did not satisfy -8 or less, so that not only the ferrite phase and the austenite phase but also the martensite phase were measured as microstructures. Therefore, Comparative Examples 2 and 5 did not satisfy the elongation rate of 30% or more and were inferior.

In Comparative Examples 1, 3, 4, 6 and 7, the value of Formula (1) was found to be considerably high. Therefore, in Comparative Examples 1, 3, 4, 6, and 7, ferrite phase and martensite phase were measured as microstructures. Therefore, Comparative Examples 1, 3, 4, 6 and 7 were very inferior in elongation.

1 is a graph showing elongation according to the γ-phase stability index represented by Formula (1).

Referring to FIG. 1, it can be seen that when the γ-phase stability index represented by Formula (1) is -8 or less, an elongation of 30% or more can be secured.

2 is a photograph of the microstructure of stainless steel according to Example 1 taken with an optical microscope, and FIGS. 3 and 4 are photographs of the microstructure of stainless steel according to Comparative Examples 2 and 3 taken with an optical microscope. .

2, 3 and 4, in the case of the stainless steel according to Example 1, the microstructure is composed of ferrite and austenite, and in the case of the stainless steel according to Comparative Example 2, the microstructure is ferrite, austenite and It is composed of martensite, and in the case of Comparative Example 3, it can be seen that the microstructure is composed of ferrite and martensite.

Claims (11)

In weight percent, C: 0.01% or more and 0.04% or less, Si: 0.2% or more and 1.0% or less, Mn: 2.0% or more and 4.0% or less, P: 0% or more and less than 0.1%, S: 0% or more and less than 0.01%, Cr : 18.0% or more and 21.0% or less, N: 0.05% or more and 0.15% or less, the balance including Fe (iron) and other unavoidable impurities,
A ferritic-austenitic two-phase stainless steel that satisfies -8 or less in the γ-phase stability index represented by Equation (1) below:
Formula (1): 133 + 109*[C] - 0.9*[Si] + 1.6*[Mn] - 7.1*[Cr] - 117*[N]
(In the above formula (1), [C], [Si], [Mn], [Cr], [N] means the content (wt%) of each element). The method of claim 1,
Ni: more than 0% and 0.3% or less, Cu: more than 0% and 0.3% or less, and Mo: more than 0% and 0.3% or less, ferritic-austenitic two-phase stainless steel. The method of claim 1,
A ferritic-austenitic two-phase stainless steel comprising, by volume fraction, a ferrite phase of 60% or more and 80% or less. The method of claim 1,
A ferritic-austenitic two-phase stainless steel with an elongation greater than 30%. The method of claim 1,
A ferritic-austenitic two-phase stainless steel with a yield strength greater than 350 MPa. In weight percent, C: 0.01% or more and 0.04% or less, Si: 0.2% or more and 1.0% or less, Mn: 2.0% or more and 4.0% or less, P: 0% or more and less than 0.1%, S: 0% or more and less than 0.01%, Cr : 18.0% or more and 21.0% or less, N: 0.05% or more and 0.15% or less, the balance including Fe (iron) and other unavoidable impurities, and the γ-phase stability index represented by the formula (1) below satisfies -8 or less Preparing a;
reheating the slab;
preparing a hot-rolled steel sheet by hot-rolling the reheated slab and performing hot-rolling annealing;
A method for producing a ferritic-austenite two-phase stainless steel comprising the step of cold rolling the hot-rolled steel sheet, cold-rolling and then pickling to prepare a cold-rolled steel sheet:
Formula (1): 133 + 109*[C] - 0.9*[Si] + 1.6*[Mn] - 7.1*[Cr] - 117*[N]
(In the above formula (1), [C], [Si], [Mn], [Cr], [N] means the content (% by weight) of each element). The method of claim 6,
The slab, Ni: more than 0% to 0.3% or less, Cu: more than 0% to 0.3% or less, Mo: more than 0% to 0.3% or less, ferritic-austenitic two-phase stainless steel manufacturing method. The method of claim 6,
The hot rolling annealing is performed at 1000 to 1250 ° C. for 1 to 60 minutes, ferrite-austenite two-phase stainless steel manufacturing method. The method of claim 6,
The hot-rolled steel sheet has a thickness of 3 to 20 mm, ferrite-austenite two-phase stainless steel manufacturing method. The method of claim 6,
The cold rolling annealing is performed at 1000 to 1250 ° C. for 10 seconds to 60 minutes, ferrite-austenite two-phase stainless steel manufacturing method. The method of claim 6,
The cold-rolled steel sheet has a thickness of 0.1 to 5 mm, ferrite-austenite two-phase stainless steel manufacturing method.

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