KR20220082424A - Austenitic stainless steel with imporoved strength and corrosion resistance, and method for manufacturing the same - Google Patents

Abstract

An austenitic stainless steel with improved strength and corrosion resistance is disclosed. The disclosed austenitic stainless steels contain, in weight percent, C: 0.02 to 0.03%, Si: 0.3 to 0.8%, Mn: 1.0 to 1.8%, Ni: 6.5 to 7.0%, Cr: 17.0 to 18.0%, Cu: 0.15 to 0.15%. 0.5%, Mo: 0.5% or less (excluding 0), N: 0.12 to 0.16%, P: 0.1% or less (excluding 0), S: 0.01% or less (excluding 0), the remainder being Fe and unavoidable impurities Including, the following formula (1) is satisfied.
Formula (1): 15 ≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu)-18.5*Mo ≤ 25
Here, C, N, Si, Mn, Cr, Ni, Cu, and Mo mean the content (% by weight) of each element.

Description

AUSTENITIC STAINLESS STEEL WITH IMPOROVED STRENGTH AND CORROSION RESISTANCE, AND METHOD FOR MANUFACTURING THE SAME

The present invention relates to a method for manufacturing austenitic stainless steel, and in particular, to austenitic stainless steel with improved surface quality and improved surface quality while securing strength and elongation of the final cold rolled steel sheet by optimizing component conditions and cold rolling annealing conditions will be.

In general, stainless steel is classified according to its chemical composition or metal structure. According to the metal structure, stainless steel can be classified into austenite, ferrite, martensite, and dual phase.

Austenitic stainless steel is the most commonly used representative stainless steel due to its excellent properties such as formability, corrosion resistance, and weldability. Among them, STS 301 series, which is one of the representative steel types, has excellent corrosion resistance, workability, and weldability and is used for various purposes.

Austenitic stainless steels undergo phase transformation during machining. If the elements stabilizing the austenite phase are not sufficiently added, the austenite phase transforms into a martensite phase during plastic deformation, and work hardening according to the plastic deformation occurs.

However, there is a problem in that the surface quality cannot be secured due to the band-like stripes occurring on the surface of the cold-rolled steel sheet. These surface defects, such as band-shaped stripes, are caused by non-uniform growth of recrystallized grains due to non-equilibrium delta ferrite remaining non-uniformly in the process of transformation to austensite after solidification of delta ferrite during casting, and remain even after cold rolling annealing. .

Conventionally, it has been proposed to diffuse and remove delta-ferrite by reducing the deviation in the width direction of the steel sheet and increasing the heating temperature of the slab before hot rolling, which causes a non-uniform microstructure of the surface, but delta-ferrite is rolled And even in the annealing process, there is a problem of remaining non-uniformly without being completely removed.

Specifically, Japanese Laid-Open Publication No. 1999-012652 proposes a method for promoting diffusion and dissipation of delta ferrite by increasing the slab temperature before hot rolling, and by introducing low-speed cooling during continuous casting in Japanese Laid-Open Publication No. 1993-293601. Even by one method, the problem of gloss non-uniformity due to the band-like stripes on the surface still occurs.

On the other hand, Japanese Laid-Open Publication No. 2000-54081 proposes a method of adding Nb, B, Mo, etc. to refine the crystal grains on the surface of the cold-rolled material by controlling the distribution of oxides, but the manufacturing cost increases and surface defects remain. there is

Therefore, the development of austenitic stainless steel that can be applied to the exterior material of a railroad vehicle is required to secure the surface quality while ensuring the strength and elongation.

Embodiments of the present invention are intended to provide an austenitic stainless steel with improved surface quality and a method for manufacturing the same while ensuring the strength and elongation of the final cold-rolled annealed material.

The austenitic stainless steel with improved strength and corrosion resistance according to an embodiment of the present invention is, by weight, C: 0.02 to 0.03%, Si: 0.3 to 0.8%, Mn: 1.0 to 1.8%, Ni: 6.5 to 7.0% , Cr: 17.0 to 18.0%, Cu: 0.15 to 0.5%, Mo: 0.5% or less (excluding 0), N: 0.12 to 0.16%, P: 0.1% or less (excluding 0), S: 0.01% or less ( 0 is excluded), the remainder contains Fe and unavoidable impurities, and the following formula (1) is satisfied.

Formula (1): 15 ≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu)-18.5*Mo ≤ 25

Here, C, N, Si, Mn, Cr, Ni, Cu, and Mo mean the content (% by weight) of each element.

In addition, according to an embodiment of the present invention, the following formula (2) may be satisfied.

Equation (2): 0.15 ≤ C+N ≤ 0.19

Here, C and N mean the content (% by weight) of each element.

In addition, according to an embodiment of the present invention, the elongation may be 45% or more.

Further, according to an embodiment of the present invention, the yield strength may be 300 MPa or more, and the tensile strength may be 700 MPa or more.

As another net weight % of the present invention, C: 0.02 to 0.03%, Si: 0.3 to 0.8%, Mn: 1.0 to 1.8%, Ni: 6.5 to 7.0%, Cr: 17.0 to 18.0%, Cu: 0.15 to 0.5% , Mo: 0.5% or less (excluding 0), N: 0.12 to 0.16%, P: 0.1% or less (excluding 0), S: 0.01% or less (excluding 0), the remainder contains Fe and unavoidable impurities; , preparing a slab satisfying the following formula (1); hot rolling the slab and hot rolling annealing; manufacturing a cold-rolled steel sheet by cold-rolling the hot-rolled annealed steel sheet; and cold-rolling and annealing the cold-rolled steel sheet at 1,000 to 1,100°C.

Formula (1): 15 ≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu)-18.5*Mo ≤ 25

Here, C, N, Si, Mn, Cr, Ni, Cu, and Mo mean the content (% by weight) of each element.

In addition, according to an embodiment of the present invention, the following formula (2) may be satisfied.

Equation (2): 0.15 ≤ C+N ≤ 0.19

In addition, according to an embodiment of the present invention, the cold rolling annealing may be performed for 10 seconds to 10 minutes.

According to an embodiment of the present invention, it is possible to provide an austenitic stainless steel with improved surface quality and a method for manufacturing the same while securing the strength and elongation of the final cold-rolled annealing material by optimizing component conditions and cold-rolling annealing conditions.

1 is a graph showing the correlation between strain, strength, and work hardening rate of an austenitic stainless steel according to an embodiment disclosed herein.
2 is a photograph showing the gloss unevenness generated on the surface of an austenitic stainless cold rolled steel sheet.

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 of ordinary skill in the art to which the present invention pertains. The present invention is not limited to the embodiments presented herein, and may be embodied in other forms. The drawings may omit the illustration of parts not related to the description in order to clarify the present invention, and slightly exaggerate the size of the components to help understanding.

Throughout the specification, when a part "includes" a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated. The singular expression includes the plural expression unless the context clearly dictates otherwise.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

The austenitic stainless steel with improved strength and corrosion resistance according to an embodiment of the present invention is, by weight, C: 0.02 to 0.03%, Si: 0.3 to 0.8%, Mn: 1.0 to 1.8%, Ni: 6.5 to 7.0% , Cr: 17.0 to 18.0%, Cu: 0.15 to 0.5%, Mo: 0.5% or less (excluding 0), N: 0.12 to 0.16%, P: 0.1% or less (excluding 0), S: 0.01% or less ( 0), and the remainder contains Fe and unavoidable impurities.

Hereinafter, the reason for numerical limitation of the content of the alloy component in the embodiment of the present invention will be described. Hereinafter, unless otherwise specified, the unit is % by weight.

The content of C is 0.02 to 0.03%.

Carbon (C) is an austenite phase stabilizing element. Since carbon greatly contributes to the strengthening effect not only in the solid solution strengthening effect but also in the martensitic phase transformation during processing, 0.02% or more can be added to secure the strength of the austenitic stainless steel. However, if the content is excessive, the upper limit may be limited to 0.03% because it may adversely affect ductility, toughness, corrosion resistance, etc. by inducing grain boundary precipitation of Cr carbides as well as lowering cold workability due to the solid solution strengthening effect.

The content of Si is 0.3 to 0.8%.

Silicon (Si) acts as a deoxidizer during the steelmaking process and is an effective element to improve strength and corrosion resistance, and may be added in an amount of 0.3% or more. However, Si is an effective element for stabilizing the ferrite phase. When excessively added, it promotes the formation of delta ferrite in the cast slab, thereby lowering hot workability as well as ductility/toughness of steel due to the solid solution strengthening effect. Therefore, the upper limit is set to 0.8%. can be limited

The content of Mn is 1.0 to 1.8%.

Manganese (Mn) is an austenite phase stabilizing element, and may be added in an amount of 1.0% or more to improve the solubility of N and suppress excessive processing-induced martensite formation. However, if the content is excessive, the ductility, toughness and corrosion resistance of austenitic stainless steel may be lowered by excessive formation of S-based inclusions (MnS). It can be limited to 1.8%.

The content of Ni is 6.5 to 7.0%.

Nickel (Ni) is a strong austenite phase stabilizing element, and as its content increases, the austenite phase is stabilized to soften the material, and 6.5% or more can be added to suppress work hardening caused by the generation of strain-induced martensite. . However, if the content is excessive, the raw material cost increases, and the fraction of the processed martensite phase decreases due to the downward Md30, so the upper limit may be limited to 7.0%.

The content of Cr is 17.0 to 18.0%.

Although chromium (Cr) is a ferrite stabilizing element, it is effective in suppressing martensite phase formation, and 17% or more can be added as a basic element to secure corrosion resistance required for stainless steel. However, if the content is excessive, the manufacturing cost increases, and it is difficult to secure strength because the fraction of processing-induced martensite phase decreases due to Md30 downward, and as delta (δ) ferrite is formed in the slab, resulting in deterioration of hot workability. The upper limit can be limited to 18.0%.

The content of Cu is 0.15 to 0.5%.

Copper (Cu) is an austenite phase stabilizing element, and may be added in an amount of 0.15% or more to improve corrosion resistance. However, when the content is excessive, there are problems of liquefaction and low-temperature brittleness as well as an increase in cost. Accordingly, the upper limit may be limited to 0.5% in consideration of cost-efficiency and material properties of steel.

The content of Mo is 0.5% or less (excluding 0).

Molybdenum (Mo) is an effective element for improving corrosion resistance and greatly contributes to the solid solution strengthening effect. However, if it is excessive, since a decrease in hot workability may occur, it is preferable to limit the upper limit of Mo to 0.5% or less.

The content of N is 0.12 to 0.16%.

Nitrogen (N), like C, is an austenite phase forming element and is an effective element for improving the strength of materials by solid solution strengthening and processing-induced martensitic transformation. We want to control over 0.12%. However, when the content is excessive, the upper limit may be limited to 0.16% because surface cracks may be caused by the formation of N pores, and cold workability may be reduced by the solid solution strengthening effect.

The content of P is 0.1% or less (excluding 0).

Phosphorus (P) is an impurity that is unavoidably contained in steel and is an element that causes intergranular corrosion or inhibits hot workability. In the present invention, the upper limit of the P content is managed to 0.1% or less.

The content of S is 0.01% or less (excluding 0).

Sulfur (S) is an impurity that is unavoidably contained in steel, and is an element that segregates at grain boundaries and is a major cause of inhibiting hot workability, so it is desirable to control its content as low as possible. In the present invention, the upper limit of the S content is managed to 0.01% or less.

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 the normal manufacturing process, this cannot be excluded. Since these impurities are known to any person skilled in the art of manufacturing processes, all details thereof are not specifically mentioned in the present specification.

The exterior of railroad vehicles basically requires not only strength and corrosion resistance, but also price competitiveness. The present invention was to reduce the content of expensive austenite stabilizing elements such as Ni, and to add a large amount of an austenite stabilizing element N, which can compensate for this.

However, in the case of reducing Ni and adding a large amount of N in order to secure price competitiveness as described above, work hardening occurs rapidly and hot workability cannot be ensured, so that manufacturing is not easy. In consideration of the above, it is necessary to secure the elongation of the austenitic stainless steel.

The elongation of the snitic stainless steel is correlated with the martensitic transformation rate during the plastic deformation process. 1 is a graph showing the correlation between strain, strength, and work hardening rate of an austenitic stainless steel according to a disclosed embodiment.

Referring to FIG. 1 , in the case of a material having a large work hardening, the strength increases, but the elongation decreases. On the other hand, in the case of a material having low work hardening, it can be seen that the elongation increases but the strength decreases.

Austenitic stainless steel undergoes martensitic transformation by plastic working at a temperature higher than or equal to the martensitic transformation initiation temperature (Ms). The upper limit temperature at which phase transformation occurs by such processing is represented by the Md value, and is a measure of the degree of phase transformation occurring by processing.

In particular, when 30% strain is applied, the temperature (°C) at which 50% of the phase transformation to martensite occurs is defined as Md ₃₀ . When the Md ₃₀ value is high, it is easy to generate the processing-induced martensite phase, whereas when the Md ₃₀ value is low, it can be determined that the processing-induced martensite phase is relatively difficult to form. In general, the Md ₃₀ value is used as an index to judge the austenite stability of general austenitic stainless steels, 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29 It can be calculated through the Nohara regression equation expressed as *(Ni+Cu)-18.5*Mo.

If the Md ₃₀ value is low, work hardening is also suppressed, but the cost increases due to the addition of alloying elements.

In the present invention, the following formula (1) was derived in consideration of the phase transformation caused by the deformation of the austenitic stainless steel.

Formula (1): 15 ≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu)-18.5*Mo ≤ 25

Here, C, N, Si, Mn, Cr, Ni, Cu, and Mo mean the content (% by weight) of each element.

In the present invention, in order to secure strength through plastic organic martensite transformation during temper rolling, it was attempted to secure the Md ₃₀ value above 15°C. On the other hand, when the Md ₃₀ value increases, the austenitic stainless steel exhibits abrupt strain-induced martensitic transformation behavior due to external deformation, and accordingly, there is a problem in that the elongation of the austenitic stainless steel decreases. In the present invention, Md A value of ₃₀ is limited to 25°C or lower.

On the other hand, in order to secure the strength of the austitic stainless steel, it is necessary to maximize the contents of the interstitial elements C and N. On the other hand, as C+N increases, the rolling force increases during hot rolling, which makes manufacturing difficult. Therefore, it is necessary to control the range of C+N values by considering the strength of the final cold rolled material and the limit of the rolling force during hot rolling. there is

According to an embodiment of the present invention, the C + N content satisfies 0.15 to 0.19%.

By controlling the content of C + N to 0.15% or more, it is possible to realize an increase in the strength of the processing-induced martensite phase. Even if each of the ranges of C of 0.02 to 0.03% and N of 0.12 to 0.16% are satisfied, when the C + N content is less than 0.15%, it is difficult to secure the yield strength of the final cold rolled material of 300 MPa or more and the tensile strength of 700 MPa or more.

The austenitic stainless steel according to the present invention that satisfies the alloy element composition range and relational expression can secure a yield strength of 300 MPa or more and a tensile strength of 700 MPa or more, as well as an elongation of 45% or more.

Next, a method for manufacturing an austenitic stainless steel with improved strength according to another aspect of the present invention will be described.

A method of manufacturing an austenitic stainless steel having improved strength and corrosion resistance according to an embodiment of the present invention,

By weight%, C: 0.02 to 0.03%, Si: 0.3 to 0.8%, Mn: 1.0 to 1.8%, Ni: 6.5 to 7.0%, Cr: 17.0 to 18.0%, Cu: 0.15 to 0.5%, Mo: 0.5% or less (excluding 0), N: 0.12 to 0.16%, P: 0.1% or less (excluding 0), S: 0.01% or less (excluding 0), the remainder including Fe and unavoidable impurities, the following formula (1 ) to manufacture a slab that satisfies; hot rolling the slab and hot rolling annealing; manufacturing a cold-rolled steel sheet by cold-rolling the hot-rolled annealed steel sheet; and cold-rolling and annealing the cold-rolled steel sheet at 1,000 to 1,100°C.

The explanation for the reason for numerical limitation of the content of alloying elements is as described above.

Stainless steel having the above composition is manufactured as a slab by continuous casting or ingot casting, and a series of manufacturing processes of hot rolling, hot rolling annealing, cold rolling and cold rolling annealing are performed.

Hot rolling and hot annealing may be performed by a conventional method, and are not particularly limited. For example, the slab may be hot-rolled at a temperature of 1,100 to 1,200 °C, which is a normal rolling temperature, and the hot-rolled steel sheet may be hot-rolled annealed at a temperature range of 800 to 1,100 °C. At this time, the hot-rolling annealing may be performed for 10 seconds to 10 minutes.

Hereinafter, heat treatment conditions during cold rolling and cold annealing among the methods for manufacturing austenitic stainless steel with improved strength and corrosion resistance according to the present invention will be described in detail.

The hot-rolled annealing material may be manufactured into a final product through cold rolling and cold-rolling annealing.

The exterior of railroad vehicles used in places exposed to the naked eye basically requires not only strength and corrosion resistance, but also surface quality.

2 is a photograph showing the gloss unevenness generated on the surface of the existing STS 301 cold-rolled steel sheet. Referring to FIG. 2 , it can be seen that the microstructure of the white part is uniform, whereas the microstructure of the black part has a large amount of defects indicated by arrows. These defects appear in the form of segregation and are visually recognized as black band-like streaks, thereby deteriorating the surface quality of the cold-rolled steel sheet.

Band-like streaks are generated by inducing non-uniform growth of recrystallized grains by non-equilibrium delta ferrite remaining non-uniformly in the process of transformation to austenite after solidification of delta ferrite during casting, and it remains after cold rolling annealing.

Therefore, in order to secure a uniform surface quality in the final cold-rolled annealing material, after cold rolling, a heat treatment capable of inducing uniform solidification in the width direction in the continuous casting process or suppressing the formation of non-equilibrium delta ferrite during the cold rolling annealing process Optimization of conditions is required.

In the present invention, as a method for reducing band-shaped stripe gloss defects, it was attempted to minimize grain growth by cold rolling annealing heat treatment at a relatively low temperature of 1,100° C. or less.

If the temperature range is excessively high during cold rolling annealing, grain growth occurs unevenly due to delta ferrite and non-uniform fine precipitates inside the material, which is expressed as band-like streaks. Therefore, in the present invention, in order to reduce the band-like stripes of the final cold-rolled annealing material, the cold-rolled annealing temperature is to be controlled to 1,100° C. or less.

On the other hand, when the cold rolling annealing temperature is excessively low, the elongation is lowered and there is a problem that a uniform material distribution cannot be secured.

In addition, cold rolling annealing according to an embodiment of the present invention may be performed at a temperature of 1,000 to 1,100° C. for 10 seconds to 10 minutes.

In this way, when the alloy component, component relational expression, and cold rolling annealing conditions are controlled, price competitiveness, strength, elongation and corrosion resistance can be secured, and uniform surface glossiness can be secured even in the final cold rolled annealing material.

Hereinafter, the present invention will be described in more detail through examples.

For the various alloy component ranges shown in Table 1 below, molten steel was melted in an electric furnace and then subjected to a steelmaking process in AOD, and slabs were manufactured in a vertical bending type casting machine. Next, after 2 hours of heat treatment in a reheating furnace at 1245° C., hot rolling was performed to a thickness of 4 to 6 mm, annealing heat treatment at 1100° C. for 30 seconds, and then pickling in mixed acid (nitric acid + hydrofluoric acid) to prepare a hot rolled material.

Thereafter, cold rolling was performed in ZRM to a thickness of 2 mm, and the final cold rolled annealing material was manufactured through a cold rolling annealing and pickling process. The yield strength, tensile strength and elongation of the cold rolled annealed material were measured by a tensile test. Specifically, the room temperature tensile test was conducted in accordance with the ASTM standard, and the measured yield strength (Yield Strength, MPa), tensile strength (Tensile Strength, MPa) and elongation (Elongation, %) were described in Table 1 below. .

C Si Mn Ni Cr N Mo Cu C+N Md30 YS(MPa) TS(MPa) Elongation (%) Example 1 0.0196 0.372 1.342 6.53 17.14 0.156 0.08 0.187 0.18 24.5 401 769 47 Example 2 0.021 0.56 1.58 6.46 17.4 0.15 0.1 0.2 0.17 20.7 327 747 51 Example 3 0.021 0.55 1.6 6.46 17.3 0.14 0.1 0.49 0.16 18.2 322 709 52 Example 4 0.019 0.52 1.42 7.08 17.2 0.12 0.1 0.21 0.14 21.6 307 711 51 Comparative Example 1 0.027 0.65 1.3 7.2 17.1 0.125 0.1 0.3 0.15 10.6 310 710 53 Comparative Example 2 0.02 0.4 1.42 6.6 17 0.15 0.09 0.19 0.17 25.8 331 743 44 Comparative Example 3 0.016 0.41 1.38 6.55 17.2 0.13 0.1 0.21 0.15 35.1 303 766 41 Comparative Example 4 0.0202 0.376 1.357 6.48 17.02 0.136 0.09 0.209 0.16 35.6 350 798 42 Comparative Example 5 0.0202 0.376 1.357 6.48 17.02 0.152 0.09 0.19 0.17 28.7 370 801 43 Comparative Example 6 0.026 0.5 1.41 6.52 17.2 0.165 0.1 0.21 0.191 14.1 450 730 51

Referring to Table 1, in the case of Examples 1 to 4 satisfying the alloy composition and the values of Formula (1) and the ranges of values of Formula (2) presented by the present invention, yield strength of 300 MPa or more, tensile strength of 700 MPa or more It was confirmed that not only strength can be secured, but excellent elongation of 45% or more can be secured. In addition, the amount of Ni content, which is an expensive austenite stabilizing element, can be reduced, so that price competitiveness of austenitic stainless steel can be secured.

In Comparative Example 1, the Md ₃₀ value was less than 15, and yield strength of 300 MPa or more, tensile strength of 700 MPa or more, and elongation of 45% or more could be secured, but price competitiveness could not be secured because 7% or more of Ni was added. It is a case of organizing as a comparative example.

Comparative Examples 2 to 5 were steel grades belonging to the alloy composition proposed by the present invention, satisfying the range of Equation (2), and yield strength of 300 MPa or more and tensile strength of 700 MPa or more by solid solution strengthening, but Since the value of (1) exceeded 25, it was not possible to secure an elongation of 45% or more, and the surface material was poor.

In Comparative Example 6, the value of Equation (2) exceeded 0.19, and the rolling force in the hot rolling process exceeded 4,000 tons, so it was not easy to manufacture to a desired thickness.

Next, the cold rolled steel sheet having the composition of Example 1 was subjected to cold rolling annealing under the temperature conditions shown in Table 2 below, and then the surface material and the degree of band-like streaks were described.

After cold rolling annealing and pickling, it was visually determined that the surface material was uniform.

The degree of band-like stripes was classified into grades 1 to 5 in Table 2 below, and grades 1 and 2 were judged as pass.

yield strength The tensile strength elongation stripes surface material (MPa) (MPa) (%) (Rating) Annealing temperature 900 355 789 42.5 Grade 1 X (℃) 950 344 790 44 Grade 1 X 1000 339 790 46 Grade 1 O 1050 328 784 46 Grade 1 O 1100 311 783 46.5 2nd grade O 1120 313 787 46.8 3rd grade X 1140 307 789 47 4th grade X

2 is a photograph showing the gloss non-uniformity generated on the surface of the austenitic stainless steel cold-rolled steel sheet, and corresponds to the 4th grade in Table 2 above.

Referring to Table 2, when cold rolling annealing was performed at 1,000 to 1,100° C., which is the temperature range suggested by the present invention, good material and surface quality were derived.

On the other hand, when the cold rolling annealing temperature was less than 1,000 ℃, grain growth was suppressed and band stripes were not expressed, but the elongation was lowered, so that a uniform material distribution could not be secured.

On the other hand, when the cold rolling annealing temperature exceeds 1,100 ℃, it was not possible to secure the surface quality due to the band-like streaks due to grain growth.

According to the disclosed embodiment, by controlling the alloy element composition range and relational expression, it is possible not only to secure a yield strength of 300 MPa or more, a tensile strength of 700 MPa or more, and an elongation of 45% or more, but also increase the amount of Ni content, which is an expensive austite stabilizing element. This can lower the price of austenitic stainless steels.

In addition, according to the disclosed embodiment, by optimizing the cold-rolled annealing conditions, it is possible to minimize grain growth to prevent local grain boundary erosion of the hot-rolled annealed pickling steel sheet, thereby ensuring uniform surface quality even in the final cold-rolled annealing material.

In the foregoing, exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and those of ordinary skill in the art may not depart from the concept and scope of the claims described below. It will be appreciated that various modifications and variations are possible.

Claims (7)

By weight%, C: 0.02 to 0.03%, Si: 0.3 to 0.8%, Mn: 1.0 to 1.8%, Ni: 6.5 to 7.0%, Cr: 17.0 to 18.0%, Cu: 0.15 to 0.5%, Mo: 0.5% or less (excluding 0), N: 0.12 to 0.16%, P: 0.1% or less (excluding 0), S: 0.01% or less (excluding 0), the remainder including Fe and unavoidable impurities,
Austenitic stainless steel with improved strength and corrosion resistance satisfying the following formula (1).
Formula (1): 15 ≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu)-18.5*Mo ≤ 25
Here, C, N, Si, Mn, Cr, Ni, Cu, and Mo mean the content (% by weight) of each element. The method of claim 1,
Austenitic stainless steel with improved strength and corrosion resistance satisfying the following formula (2).
Equation (2): 0.15 ≤ C+N ≤ 0.19
Here, C and N mean the content (% by weight) of each element. The method of claim 1,
Austenitic stainless steel with improved strength and corrosion resistance with an elongation of 45% or more. The method of claim 1,
Austenitic stainless steel with improved strength and corrosion resistance with a yield strength of 300 MPa or more and a tensile strength of 700 MPa or more. By weight%, C: 0.02 to 0.03%, Si: 0.3 to 0.8%, Mn: 1.0 to 1.8%, Ni: 6.5 to 7.0%, Cr: 17.0 to 18.0%, Cu: 0.2 to 0.5%, Mo: 0.5% or less (excluding 0), N: 0.12 to 0.16%, P: 0.1% or less (excluding 0), S: 0.01% or less (excluding 0), the remainder including Fe and unavoidable impurities, the following formula (1 ) to manufacture a slab that satisfies;
hot rolling the slab and hot rolling annealing;
manufacturing a cold-rolled steel sheet by cold-rolling the hot-rolled annealed steel sheet; and
Cold-rolled annealing the cold-rolled steel sheet at 1,000 to 1,100 ℃; A method of manufacturing austenitic stainless steel with improved strength and corrosion resistance, comprising a.
Formula (1): 15 ≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu)-18.5*Mo ≤ 25
Here, C, N, Si, Mn, Cr, Ni, Cu, and Mo mean the content (% by weight) of each element. 6. The method of claim 5,
A method of manufacturing an austenitic stainless steel having improved strength and corrosion resistance satisfying the following formula (2).
Equation (2): 0.15 ≤ C+N ≤ 0.19
Here, C and N mean the content (% by weight) of each element. 6. The method of claim 5,
The cold-rolled annealing is a method of manufacturing an austenitic stainless steel having improved strength and corrosion resistance, which is performed for 10 seconds to 10 minutes.

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