Austenitic stainless steel and manufacturing method therefor

Abstract

A method for manufacturing an austenitic stainless steel, according to the present invention, may comprise the steps of: preparing a steel comprising, by wt%, 0.001-0.050% of C, 0.1-1.0% of Si, 0.01-2.0% of Mn, P in an amount more than 0% and less than 0.05%, S in an amount more than 0% and less than 0.05%, 16.0-20.0% of Cr, 9.0-12.0% of Ni, 0.01-1.0% of Cu, 0.01-3.0% of Mo, 0.01-0.1% of N and the balance of Fe and other inevitable impurities, the steel having a value of formula (1) of 9.20 or more; heating the steel, and then hot rolling same so as to manufacture a hot-rolled material; performing solution heat treatment on the hot-rolled material and water-cooling same so as to manufacture a hot-rolled material; cold rolling the hot-rolled material at a reduction ratio of 55-75% so as to manufacture a cold-rolled material; and final-annealing the cold-rolled material at 900-1,000 °C. Formula (1): 0.2*[Cr]+0.5*[Ni]+0.25*[Mn]+0.3*[Mo]+0.4*[Cu]+3*([C]+[N]) In the formula, [Cr], [Ni], [Mn], [Mo], [Cu], [C] and [N] mean wt% of the respective elements.

Description

Austenitic stainless steel and method of manufacturing the same

[0001] The present invention relates to an austenitic stainless steel having excellent surface characteristics and a method for manufacturing the same by optimizing the alloy composition and manufacturing method.

[0002] Stainless steel is widely used in various fields, such as kitchenware, building materials, and industrial equipment, due to its excellent corrosion resistance and mechanical properties.

[0003] However, conventional austenitic stainless steels did not provide sufficient surface gloss and linearity, leading to a decline in appearance quality when applied to high-end home appliances or kitchenware. Additionally, work hardening during cold working reduced formability, making it difficult to manufacture products with complex shapes.

[0004] In particular, while manufacturing processes using diffusion bonding have recently been increasing for precision components such as heat exchangers and fuel cell separators, conventional stainless steel exhibits poor diffusion bonding properties due to the oxide film formed on its surface, making it difficult to secure bonding strength. This has been recognized as a critical issue that directly affects product reliability and lifespan.

[0005] With the recent increase in demand for precision components, there is a need to develop austenitic stainless steel that simultaneously satisfies appropriate strength and machinability along with excellent surface quality. Conventional general-purpose steels have struggled to satisfy these characteristics simultaneously, and it has been difficult to obtain target properties, particularly due to the difficulty in controlling grain size and texture during cold rolling and annealing processes.

[0006] Accordingly, the present invention aims to provide an austenitic stainless steel and a method for manufacturing the same, which can secure appropriate levels of strength and machinability while having excellent surface gloss and linearity through the optimization of alloy components and precise control of the manufacturing process.

[0007] One aspect of the present disclosure can provide an austenitic stainless steel having excellent surface properties by controlling the alloy composition components.

[0008] One aspect of the present disclosure can provide an austenitic stainless steel with excellent gloss and linearity while securing yield strength by controlling the manufacturing process.

[0009] The technical problems intended to be solved in this document are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which this invention belongs from the description below.

[0010] A method for manufacturing an austenitic stainless steel according to one embodiment of the present invention comprises the steps of: preparing a steel material having, in weight%, C: 0.001% to 0.050%, Si: 0.1% to 1.0%, Mn: 0.01% to 2.0%, P: greater than 0% and less than 0.05%, S: greater than 0% and less than 0.05%, Cr: 16.0% to 20.0%, Ni: 9.0% to 12.0%, Cu: 0.01% to 1.0%, Mo: 0.01% to 3.0%, N: 0.01% to 0.1%, and the remainder being Fe and other unavoidable impurities, wherein the value of the following formula (1) is 9.20 or higher; heating the steel material and then hot rolling it to produce a hot-rolled material; and performing solution heat treatment and water cooling on the hot-rolled material. The method may include the steps of manufacturing a hot-rolled material, cold-rolling the hot-rolled material with a reduction rate of 55% to 75% to manufacture a cold-rolled material, and finally annealing the cold-rolled material at 900°C to 1000°C.

[0011] Equation (1): 0.2*[Cr]+0.5*[Ni]+0.25*[Mn]+0.3*[Mo]+0.4*[Cu]+3*([C]+[N])

[0012] Here, [Cr], [Ni], [Mn], [Mo], [Cu], [C], and [N] represent the weight percentage of each element.

[0013] An austenitic stainless steel according to one embodiment of the present invention comprises, in weight percent, C: 0.001% to 0.050%, Si: 0.1% to 1.0%, Mn: 0.01% to 2.0%, P: greater than 0% and less than 0.05%, S: greater than 0% and less than 0.05%, Cr: 16.0% to 20.0%, Ni: 9.0% to 12.0%, Cu: 0.01% to 1.0%, Mo: 0.01% to 3.0%, N: 0.01% to 0.1%, and the remainder being Fe and other unavoidable impurities, wherein the value of the following formula (1) is 9.20 or higher, and the average grain size at the center of the thickness may be 10.0㎛ or less.

[0014] Equation (1): 0.2*[Cr]+0.5*[Ni]+0.25*[Mn]+0.3*[Mo]+0.4*[Cu]+3*([C]+[N])

[0015] Here, [Cr], [Ni], [Mn], [Mo], [Cu], [C], and [N] represent the weight percentage of each element.

[0016] According to the present disclosure, an austenitic stainless steel having excellent surface properties can be provided by controlling the grain size.

[0017] The effects obtainable from the present disclosure are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present disclosure belongs from the description below.

[0018] Preferred embodiments of the present invention are described below. However, embodiments of the present invention may be modified in various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field.

[0019] The terms used in this application are used merely to describe specific examples. For this reason, singular expressions include plural expressions unless the context clearly requires them to be singular. Additionally, it should be noted that terms such as “comprising” or “comprising” used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the existence of other features, steps, functions, components, or combinations thereof.

[0020] Meanwhile, unless otherwise defined, all terms used in this specification shall be understood to have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Accordingly, unless explicitly defined in this specification, specific terms should not be interpreted in an overly ideal or formal sense. For instance, singular expressions in this specification include plural expressions unless the context clearly indicates an exception.

[0021] Additionally, terms such as "about," "substantially," etc., in this specification are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the said sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content in which precise or absolute values ​​are mentioned to aid in understanding the invention.

[0022] A method for manufacturing stainless steel according to one embodiment of the present invention may include the step of preparing a steel material having, in weight%, C: 0.001% to 0.050%, Si: 0.1% to 1.0%, Mn: 0.01% to 2.0%, P: greater than 0% and less than 0.05%, S: greater than 0% and less than 0.05%, Cr: 16.0% to 20.0%, Ni: 9.0% to 12.0%, Cu: 0.01% to 1.0%, Mo: 0.01% to 3.0%, N: 0.01% to 0.1%, and the remainder being Fe and other unavoidable impurities, wherein the value of the following formula (1) is 9.20 or higher.

[0023] Equation (1): 0.2*[Cr]+0.5*[Ni]+0.25*[Mn]+0.3*[Mo]+0.4*[Cu]+3*([C]+[N])

[0024] Here, [Cr], [Ni], [Mn], [Mo], [Cu], [C], and [N] represent the weight percentage of each element.

[0025] The reasons for limiting the compositional range of each alloying element are described below. Unless otherwise noted, units are weight percent.

[0026] The content of C can be 0.001% to 0.050%.

[0027] C is an effective and inexpensive element for austenite stabilization. As an interstitial element, C increases yield strength through solid solution strengthening. Considering this, C can be added at a level of 0.001% or more. However, if the C content is excessive, Cr in the heat-affected zone after welding 23 Sensitization may occur due to grain boundary precipitation of C6 carbides, which can lead to a decline in ductility, toughness, and corrosion resistance. Considering this, the upper limit of C may be limited to 0.050%. Specifically, the C content may be 0.005% to 0.040%, and more specifically, 0.020% to 0.030%.

[0028] The Si content may be 0.1% to 1.0%.

[0029] Si is an element that acts as a deoxidizer during the steelmaking process and is effective in improving corrosion resistance. Considering this, Si can be added in an amount of 0.1% or more. However, if the Si content is excessive, a delta-ferrite phase may be formed due to a peritectic reaction during casting, which may reduce hot workability. Considering this, the upper limit of Si can be limited to 1.0% or less. Specifically, the Si content may be 0.2% to 1.0%, and more specifically, 0.46% to 0.6%.

[0030] Mn can be 0.01% to 2.0%.

[0031] Mn is an inexpensive element effective in increasing the austenite phase stability of work-induced martensite. Additionally, Mn is effective in increasing low-temperature impact toughness by suppressing heat-induced and work-induced martensite transformations. Considering this, Mn can be added in an amount of 0.01% or more. However, if the Mn content is excessive, the corrosion resistance and hot workability of the steel may decrease due to an increase in inclusions (MnS). Considering this, the upper limit of Mn can be limited to 2.0% or less. Specifically, the Mn content may be 0.20% to 1.80%, and more specifically, 1.10% to 1.30%.

[0032] The P content may be greater than 0% and less than 0.05%.

[0033] P is an impurity inevitably contained in steel that reduces corrosion resistance and hot workability, so it is added in the smallest possible amount. However, controlling the P content to be excessively low can lead to an increase in process costs. Considering this, the P content may be limited to greater than 0% and less than 0.05%, specifically greater than 0% and less than 0.03%.

[0034] The S content may be greater than 0% and less than 0.05%.

[0035] S, like P, is an impurity inevitably contained in steel that reduces corrosion resistance and hot workability, so it is added in the smallest possible amount. However, controlling the S content to be excessively low can lead to an increase in process costs. Considering this, the S content may be limited to greater than 0% and less than 0.05%, specifically greater than 0% and less than or equal to 0.03%.

[0036] The Cr content may be 16.0% to 20.0%.

[0037] Cr is an essential element for ensuring corrosion resistance and phase stability. Considering this, Cr can be added in an amount of 16.0% or more. However, if the Cr content is excessive, a delta-ferrite phase may be formed due to the peritectic reaction during casting, which may reduce hot workability. Considering this, the upper limit of Cr can be restricted to 20.0%. Specifically, the Cr content may be 16.0% to 19.0%. More specifically, it may be 16.2% to 18.5%.

[0038] The Ni content may be 9.0% to 12.0%.

[0039] Ni is a powerful element that stabilizes the austenite phase. In addition, Ni is a key element that enhances austenite phase stability and is effective in preventing a decrease in toughness at cryogenic temperatures by suppressing heat-induced and work-induced martensite transformations. Considering this, Ni may be added in an amount of 9.0% or more. However, if the Ni content is excessive, it may be a factor that reduces fine grain size. Considering this, the upper limit of Ni may be limited to 12.0%. Specifically, the Ni content may be 10.1% to 11.5%.

[0040] The content of Cu can be 0.01% to 1.0%.

[0041] Cu is an element effective in stabilizing the austenite phase. Additionally, Cu is an element effective in improving corrosion resistance in a reducing environment. Considering this, Cu can be added in an amount of 0.01% or more. However, if the Cu content is excessive, hot workability may be reduced due to Cu solidification segregation. Considering this, the upper limit of Cu can be limited to 1.00% or less. Specifically, the Cu content may be 0.01% to 0.8%, and more specifically, 0.2% to 0.3%.

[0042] The Mo content may be 0.01% to 3.0%.

[0043] Mo is an effective element for improving the corrosion resistance of stainless steel. However, Mo is an expensive element, and if its content is excessive, cold workability may decrease due to the increase in strength. Considering this, the upper limit of Mo may be limited to 3.0%. Specifically, the Mo content may be 1.0% to 3.0%. More specifically, it may be 1.8% to 2.2%.

[0044] The content of N can be 0.01% to 0.1%.

[0045] N is a very effective and inexpensive element for stabilizing the austenite phase. In addition, N is an effective element for increasing strength and improving corrosion resistance through solid solution strengthening. Considering this, N can be added in an amount of 0.01% or more. However, if the N content is excessive, it may reduce impact toughness at cryogenic temperatures. Considering this, the upper limit of N can be limited to 0.10%. Specifically, the N content may be 0.01% to 0.08%. More specifically, it may be 0.02% to 0.04%.

[0046] The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be incorporated during the ordinary manufacturing process, they cannot be excluded. As these impurities are known to any person skilled in the ordinary manufacturing process, all details thereof are not specifically mentioned in this specification.

[0047] The following explains Equation (1).

[0048] Equation (1): 0.2*[Cr]+0.5*[Ni]+0.25*[Mn]+0.3*[Mo]+0.4*[Cu]+3*([C]+[N])

[0049] Here, [Cr], [Ni], [Mn], [Mo], [Cu], [C], and [N] represent the weight percentage of each element.

[0050] Equation (1) above represents the stability of the austenite phase. Cr, Ni, Mn, Mo, Cu, C, and N constituting Equation (1) are elements that influence austenite stabilization. Equation (1) was derived to optimize the content of alloying elements so that an appropriate level of work-induced martensite transformation occurs, taking into account the deformation energy and work heat generated during cold rolling. In the present invention, to evaluate the stability of the austenite phase, the phase stability according to the content of each alloying element was calculated using the thermodynamic analysis program Thermo-Calc, and the austenite phase stability index of Equation (1) was derived. If the value of Equation (1) is less than 9.20, excessive work-induced martensite transformation occurs during cold rolling, which reduces the stability of the austenite phase and prevents the securing of the desired microstructure. Consequently, the target strength, gloss, and linearity cannot be secured simultaneously.

[0051] After manufacturing a steel material satisfying the above alloy composition and formula (1), it may undergo a series of heating, hot rolling, solution heat treatment, water cooling, cold rolling, and final annealing processes.

[0052] In general, deformation-induced martensite can develop in austenitic stainless steel during cold rolling. Deformation-induced martensite generally tends to develop differently depending on the stability of the austenite phase.

[0053] In austenitic stainless steel with low phase stability, ε-martensite bands develop during the initial deformation, and as the amount of deformation increases, α'-martensite may be formed from the intersections within the bands. Additionally, if a cold reduction rate (thickness reduction rate in the thickness direction) of 55% or more is applied, α'-martensite may be formed in a volume fraction of 60% or more within the total microstructure.

[0054] In addition, when the above cold-rolled material is subjected to annealing heat treatment at 900 to 1000°C, a reversion transformation from the work-induced martensite phase to the austenite phase occurs, and this reversion transformation may vary depending on the change in free energy from the martensite phase to the austenite phase during the annealing stage. At this time, the lower the driving force required for the reversion transformation, the easier the diffusion reversion transformation occurs at a lower temperature, allowing for a recrystallized structure.

[0055] Meanwhile, in addition to the driving force required for reverse transformation defined by the alloy composition system, the recrystallization tendency can also change depending on the annealing temperature and the amount of cold reduction. More specifically, the higher the amount of cold reduction, the greater the accumulated deformation energy within the material, making recrystallization more likely to occur; conversely, the higher the annealing temperature, the easier the diffusion and movement of dislocations become, making recrystallization more likely to occur.

[0056] In general, in grain refinement mechanisms utilizing reverse transformation, lower annealing temperatures tend to be more advantageous. This is because grain growth is inhibited at lower temperatures, making it easier to achieve a fine-grained structure.

[0057] However, in the case of alloy systems with low austenite phase stability, which is favorable for grain refinement, the driving force required for reverse transformation is generally low. This facilitates the occurrence of diffusion reverse transformation, thereby allowing for the easy realization of a recrystallized structure. Consequently, recrystallization occurs easily even at low annealing temperatures, and there may be a tendency for grain coarsening to be promoted as the annealing temperature increases. However, in actual operation, it is difficult to control the annealing temperature to a low level; therefore, for stable operation, it is advantageous to operate at a higher annealing temperature in terms of the material's calorific value and recrystallization.

[0058] Accordingly, the present invention increases the required driving force for reverse transformation to make it advantageous to operate at high annealing temperatures, and controls the annealing temperature and cold reduction amount to enable grain refinement at high temperatures, thereby providing a high-strength austenitic stainless steel with excellent resistance to stress corrosion cracking.

[0059] The heating described above may be performed at 1150°C to 1350°C for 1 to 3 hours. The heating can re-decompose coarse precipitates generated during steel manufacturing and control the internal grain size to an appropriate size. If the heating temperature is below 1150°C, complete redissolution of precipitates is difficult, making it difficult to inhibit grain growth in subsequent processes; if it exceeds 1350°C, grains may grow excessively, potentially degrading mechanical properties. If the heating time is less than 1 hour, sufficient redissolution of precipitates does not occur, and if it exceeds 3 hours, grain coarsening may occur, potentially degrading product properties.

[0060] Next, the heated ingot can be hot-rolled to produce a hot-rolled material.

[0061] Subsequently, the hot-rolled material may undergo solution heat treatment at 1000°C to 1200°C for 1 to 30 minutes. If the solution temperature is below 1000°C, complete solid solution of precipitates does not occur, resulting in reduced workability during subsequent cold rolling; if it exceeds 1200°C, excessive grain growth may occur, potentially degrading the mechanical properties and surface quality of the final product. Additionally, if the solution time is less than 1 minute, sufficient solid solution does not occur, and if it exceeds 30 minutes, grain coarsening may occur along with intensified surface oxidation. The solution heat treatment is a process in which the hot-rolled material is heated to the solid solution range and then rapidly cooled to maintain the solid solution state down to room temperature. By performing solution heat treatment, the strength and workability of the steel can be improved.

[0062] After the above solution heat treatment, a hot-rolled material can be manufactured by performing a water cooling treatment.

[0063] The above hot-rolled material can be cold-rolled to produce a cold-rolled material by cold-rolling it with a reduction rate of 55% to 75%. During the above cold-rolling, the change in free energy (△G) from the austenite phase to the martensite phase at room temperature γ→α (25℃)) can be -2.4 kJ / mol or less. By controlling the above free energy amount and cold rolling with a reduction rate of 55% to 75%, most of the microstructure can be transformed into martensite, thereby compensating for austenite phase stability and simultaneously achieving grain refinement. Furthermore, within the above range, TRIP transformation occurs sufficiently during cold rolling, and in terms of grain refinement, the amount of TRIP transformation increases due to internal heat generation, which can further improve strength. Next, the above cold-rolled material is finally annealed at 900℃ to 1000℃, and during the final annealing, the change in free energy from the martensite phase to the austenite phase at high temperatures (△G α→γ (950℃)) By controlling the driving force required for reverse transformation to 0.4 kJ / mol or less to facilitate diffusion reverse transformation, the reverse transformation recrystallization from martensite to austenite can be easily performed.

[0064] In one embodiment of the present invention, the method for manufacturing austenitic stainless steel may have a value of 7.80 or less in the following formula (2).

[0065] Formula (2): (Reduction rate (%) / 100) * exp(1 / (Annealing temperature (°C)) * Grain size (㎛)

[0066] Equation (2) above is an equation derived for the recrystallization of austenite. Since the manufacturing process proceeds at a relatively high annealing temperature, the grain size may become somewhat larger. In order to secure the desired physical properties in the present invention, it is necessary to control the reduction ratio, annealing temperature, and grain size. Equation (2) was derived to secure optimal recrystallization behavior by simultaneously considering the deformation energy introduced during cold rolling and the grain growth during annealing. In the present invention, the austenite recrystallization index of Equation (2) was derived by experimentally analyzing the change in grain size under various reduction ratio and annealing temperature conditions. If the value of Equation (2) above exceeds 7.80, the critical driving force required for recrystallization is not secured, resulting in non-uniform recrystallization, and thus the desired recrystallization structure cannot be obtained. Consequently, the target strength and surface quality cannot be secured simultaneously.

[0067] In a method for manufacturing austenitic stainless steel according to one embodiment of the present invention, the value of the following formula (3) may be 70.00 or less. Since it is necessary to control the composition of the alloy and the manufacturing process in order to produce austenite with excellent surface properties, if the value of the above formula (3) is controlled to be 70.00 or less, the austenite stability and recrystallization behavior are optimized, thereby enabling the simultaneous securing of a uniform microstructure, excellent gloss, and linearity.

[0068] In one embodiment of the present invention, the method for manufacturing austenitic stainless steel may have a value of 4.70 or higher in the following formula (4).

[0069] Formula (4): Yield strength (MPa) * Gloss (GU, 20°) * 10 -4

[0070] Here, glossiness refers to the average value of GU(20°), and yield strength refers to the stress value at a strain of 0.2%.

[0071] According to the manufacturing method of the present invention, a stainless steel with excellent surface characteristics having a glossiness (GU, 20°) of 140 or higher can be manufactured. In addition, since a yield strength of 290 MPa or higher can be secured, the value of Equation (4) can be controlled to 4.70 or higher.

[0072] An austenitic stainless steel according to one embodiment of the present invention may satisfy the alloy composition and the value of Equation (1). The reason for controlling the alloy composition and Equation (1) may be as described above.

[0073] According to one embodiment of the present invention, the average grain size at the center of the thickness of the austenitic stainless steel may be 10.0 μm or less. The austenitic stainless steel according to one embodiment of the present invention can secure desired diffusion bondability, yield strength, and glossiness by refining the grains. In the present invention, grain size refers to the diameter of a circle assumed to have an area equal to the grain area. In addition, the average grain size is (measured area x number of grains) 1 / 2 It can be calculated as follows. The grain size can be measured based on a plane parallel to the cross-section perpendicular to rolling (TD plane). In this case, the grain size was evaluated using an image analyzer equipped with an analysis program that assumes multiple hexagons are connected (grain measurement method of ASTM E112). Additionally, in the present invention, the center of thickness refers to the center in the thickness direction relative to the surface of the cross-section.

[0074] In one embodiment of the present invention, the austenitic stainless steel may have a value of 4.70 or higher in the following formula (4).

[0075] Formula (4): Yield strength (MPa) * Gloss (GU, 20°) * 10 -4

[0076] Here, glossiness refers to the average value of GU(20°), and yield strength refers to the stress value at a strain of 0.2%.

[0077] An austenitic stainless steel according to one embodiment of the present invention may have a glossiness (GU, 20°) of 140 or higher.

[0078] An austenitic stainless steel according to one embodiment of the present invention may have a yield strength of 290 MPa or more.

[0079] An austenitic stainless steel according to one embodiment of the present invention may have a linearity of 17.0 or higher.

[0080] The present invention will be explained in more detail below through the following examples. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited thereto.

[0081] Examples

[0082] Ingots were manufactured in a vacuum induction furnace for various alloy composition ranges shown in Table 1 below. The manufactured ingots were heated at 1250°C for 2 hours and then hot-rolled to a thickness of 10.0 mm to produce hot-rolled materials. The hot-rolled materials were solution-heat-treated at 1100°C for 10 minutes and then water-cooled to produce hot-rolled materials. The hot-rolled materials were cold-rolled at a reduction rate of 55% to 75% to produce cold-rolled materials with a thickness of 3 mm to 5 mm. The cold-rolled materials were subjected to final annealing heat treatment at 900°C to 1000°C.

[0083] Steel Grade (Weight%) CSIMnPSCrNiMoCuN Formula (1) Steel Grade 10.020.46 1.20.020.003 18.110.12.20.30.049.93 Steel Grade 20.030.5 11.30.030.003 17.5 11.520.20.02 10.41 Steel Grade 30.020.48 1.20.030.003 16.5 11.22.10.30.03 10.10 Steel Grade 40.020.5 1.10.020.003 18.5 10.11.80.20.049.83 Steel Grade 50.030.51.10.030.00318.510.51.90.30.0410.13 Steel Type 60.020.61.10.030.00316.210.12.10.30.029.44 Steel Type 70.020.491.20.020.00317.59.120.30.029.19 Steel Type 80.020.491.20.020.003189.52.10.30.029.52

[0084] The values ​​of Equation (1) for the steel grades in Table 1 above were calculated and presented. Equation (1): 0.2*[Cr]+0.5*[Ni]+0.25*[Mn]+0.3*[Mo]+0.4*[Cu]+3*([C]+[N])

[0085] Here, [Cr], [Ni], [Mn], [Mo], [Cu], [C], and [N] represent the weight percentage of each element.

[0086] Table 2 below shows the manufacturing process, the average grain size at the center of the thickness, the values ​​of Equation (2) to Equation (4), and the yield strength, glossiness, and linearity accordingly.

[0087] Formula (2): (Reduction rate (%) / 100) * exp(1 / (Annealing temperature (°C)) * Grain size (㎛)

[0088] Equation (3): Value of Equation (1) * Value of Equation (2)

[0089] Formula (4): Yield strength (MPa) * Gloss (GU, 20°) * 10 -4

[0090] Here, glossiness refers to the average value of GU(20°), and yield strength refers to the stress value at a strain of 0.2%.

[0091] The average grain size was measured by photographing the center of the thickness using a scanning electron microscope (SEM).

[0092] Yield strength was determined by preparing plate-shaped subsize tensile specimens in accordance with JIS 13B standards and performing a tensile test at room temperature using a Zwick Roell tensile testing machine at a tensile speed of 20 mm per minute. The stress value at a strain of 0.2% was expressed as the yield strength.

[0093] Glossiness was measured using micro-TRI-gloss under a 20° incident angle condition, and the glossiness (GU) of the specimen surface was measured 5 times per specimen, and the average value was used.

[0094] The linearity (GU) of the specimen surface was measured using wave-scan under an incident angle of 20°, and the average value was used after 5 measurements per specimen. A higher linearity value indicates superior image clarity of the surface.

[0095] Classification Steel Type Annealing Temperature (°C) Reduction Rate (%) Grain Size (㎛) Formula (2) Formula (3) Formula (4) YS 0.2(MPa) Gloss (GU, 20) Lineability Example 1 Steel Type 1950708.15.6856.365.2133615518.5 Example 2 Steel Type 2945658.55.5357.555.1733815319.2 Example 3 Steel Type 3930708.35.8258.745.3633516018.8 Example 4 Steel Type 4950609.25.5354.294.9233014917.4 Example 5 Steel Type 5960709.36.5265.984.7832514718.3 Example 6 Steel Type 6950707.95.5452.234.9032015317.3 Comparative Example 1 Steel Type 11150702517.52173.932.502609610.4 Comparative Example 2 Steel Type 21100652314.96155.702.432709011.3 Comparative Example 3 Steel Type 31100702215.41155.682.362658910.2 Comparative Example 4 Steel Type 41050601911.41112.112.522809011.6 Comparative Example 5 Steel Type 51100702416.82170.252.572709512.3 Comparative Example 6 Steel Type 61150702517.52165.262.362658910.2 Comparative Example 7 Steel Type 7 71100703021.02193.172.572709510.5 Comparative Example 8 Steel Type 894560137.8174.334.3030314216.5 Comparative Example 9 Steel Type 81100602816.82160.082.512709311.5

[0096] According to Table 2, in the case of Examples 1 to 6, the composition content, manufacturing process, and values ​​of Equations (1) to (4) were satisfied, and it was confirmed that the yield strength, glossiness, and linearity were satisfied. On the other hand, in the case of Comparative Examples 1 to 6, the annealing temperature in the manufacturing process was high, and the values ​​of Equations (2) to (4) were not satisfied, so the grain size exceeded 10 μm and became coarse, and the desired yield strength, glossiness, and linearity were not satisfied.

[0097] In the case of Comparative Example 7, the annealing temperature during the manufacturing process was high, and since Equations (1) to (4) were not satisfied, the grain size was coarse and the desired yield strength, glossiness, and linearity were not satisfied.

[0098] In the case of Comparative Example 8, the alloy composition and Equation (1) were satisfied, but Equations (2) to (4) were not satisfied, so the desired yield strength and gloss were not secured.

[0099] In the case of Comparative Example 9, it was confirmed that the crystal grains became coarse due to the high annealing temperature.

[0100] Although embodiments of the invention disclosed above have been illustrated and described, the disclosed invention is not limited to the specific embodiments described above, and various modifications may be made by those skilled in the art to which the disclosed invention belongs without departing from the essence claimed in the claims.

Claims

1. A step of preparing a steel material comprising, in weight%, C: 0.001% to 0.050%, Si: 0.1% to 1.0%, Mn: 0.01% to 2.0%, P: greater than 0% and less than 0.05%, S: greater than 0% and less than 0.05%, Cr: 16.0% to 20.0%, Ni: 9.0% to 12.0%, Cu: 0.01% to 1.0%, Mo: 0.01% to 3.0%, N: 0.01% to 0.1%, and the remainder being Fe and other unavoidable impurities, wherein the value of the following formula (1) is 9.20 or higher; A step of manufacturing a hot-rolled material by heating the above steel material and then hot-rolling it; A step of manufacturing a hot-rolled material by solution heat treatment and water cooling of the above hot-rolled material; A step of manufacturing a cold-rolled material by cold-rolling the above hot-rolled material at a reduction rate of 55% to 75%; and A method for manufacturing austenitic stainless steel comprising the step of finally annealing the above cold-rolled material at 900°C to 1000°C. Equation (1): 0.2*[Cr]+0.5*[Ni]+0.25*[Mn]+0.3*[Mo]+0.4*[Cu]+3*([C]+[N]) (Here, [Cr], [Ni], [Mn], [Mo], [Cu], [C], and [N] represent the weight percent of each element.) 2. In Claim 1, A method for manufacturing austenitic stainless steel in which the value of the following formula (2) is 7.80 or less. Formula (2): (Reduction rate (%) / 100) * exp(1 / (Annealing temperature (°C)) * Grain size (㎛) 3. In Claim 1, A method for manufacturing austenitic stainless steel in which the value of the following formula (3) is 70.00 or less. Equation (3): Value of Equation (1) * Value of Equation (2) Equation (1): 0.2*[Cr]+0.5*[Ni]+0.25*[Mn]+0.3*[Mo]+0.4*[Cu]+3*([C]+[N]) Formula (2): (Reduction rate (%) / 100) * exp(1 / (Annealing temperature (°C)) * Grain size (㎛) (Here, [Cr], [Ni], [Mn], [Mo], [Cu], [C], and [N] represent the weight percent of each element.) 4. In Claim 1, A method for manufacturing austenitic stainless steel in which the value of the following formula (4) is 4.70 or higher. Formula (4): Yield strength (MPa) * Gloss (GU, 20°) * 10 -4 (Here, glossiness refers to the average GU(20°) value, and yield strength refers to the stress value at a strain of 0.2%.) 5. In Claim 1, The change in free energy from the austenite phase to the martensite phase at room temperature during the above cold rolling (△G γ→α A method for manufacturing austenitic stainless steel in which (25℃)) is -2.4 kJ / mol or less.

6. In Claim 1, The amount of change in free energy from the martensite phase to the austenite phase at high temperature during the above final annealing (△G α→γ A method for manufacturing austenitic stainless steel in which (950℃)) is 0.4 kJ / mol or less.

7. In Claim 1, A method for manufacturing austenitic stainless steel, wherein the heating is performed at 1150℃ to 1350℃ for 1 hour to 3 hours.

8. In Claim 1, A method for manufacturing austenitic stainless steel, wherein the above solution heat treatment is performed at 1000℃ to 1200℃ for 1 minute to 30 minutes.

9. In weight%, it comprises C: 0.001% to 0.050%, Si: 0.1% to 1.0%, Mn: 0.01% to 2.0%, P: greater than 0% and less than 0.05%, S: greater than 0% and less than 0.05%, Cr: 16.0% to 20.0%, Ni: 9.0% to 12.0%, Cu: 0.01% to 1.0%, Mo: 0.01% to 3.0%, N: 0.01% to 0.1%, and the remainder being Fe and other unavoidable impurities, The value of the following equation (1) is 9.20 or greater, and Austenitic stainless steel with an average grain size of 10.0㎛ or less at the center of the thickness. Equation (1): 0.2*[Cr]+0.5*[Ni]+0.25*[Mn]+0.3*[Mo]+0.4*[Cu]+3*([C]+[N]) (Here, [Cr], [Ni], [Mn], [Mo], [Cu], [C], and [N] represent the weight percent of each element.) 10. In Claim 9, Austenitic stainless steel having a value of 4.70 or higher in the following formula (4). Formula (4): Yield strength (MPa) * Gloss (GU, 20°) * 10 -4 (Here, glossiness refers to the average GU(20°) value, and yield strength refers to the stress value at a strain of 0.2%.) 11. In Claim 9, Austenitic stainless steel with a glossiness (GU, 20°) of 140 or higher.

12. In Claim 9, Austenitic stainless steel with a yield strength of 290 MPa or higher.

13. In Claim 9, Austenitic stainless steel with a linearity of 17.0 or higher.