Patent Publication Number: US-2020299816-A1

Title: Non-magnetic austenitic stainless steel having excellent corrosion resistance and manufacturing method therefor

Description:
TECHNICAL FIELD 
     The present disclosure relates to a non-magnetic austenitic stainless steel, and more particularly, to a non-magnetic austenitic stainless steel with excellent corrosion resistance applicable to an environment requiring corrosion resistance together with non-magnetic properties, and a manufacturing method thereof. 
     BACKGROUND ART 
     Austenitic stainless steel, represented by STS304, has good corrosion resistance, and exhibits a non-magnetic austenite structure in annealing heat treatment, and is used as a non-magnetic steel in various devices. However, there are cases where cold working is performed depending on the application, and when cold working is applied to STS304 steel, due to the phase transformation to deformation induced martensite structure, it is difficult to maintain non-magnetic properties, which limits the application to materials. 
     Therefore, STS316L-based steel grades with higher austenite stability than STS304 are used for non-magnetic applications. However, in the case of STS316L-based steel grades, the Mo content is high, so a secondary phase such as σ or δ-ferrite is often present in the austenite matrix, and since the solidification starts from δ-ferrite during continuous casting of STS316L steel, it is difficult to decompose the secondary phases due to high Cr and Mo content in the center segregation region in the continuous casting slab, and thus the secondary phases tend to remain after hot rolling and final heat treatment. 
     When the secondary phases remain, it acts as a cause of increased magnetism in the area, and adversely affects the function of the device. Therefore, there is a need for a material capable of maintaining non-magnetic properties without these secondary phases. 
     Patent Document 1 refers to a high-strength non-magnetic austenitic stainless steel that maintains non-magnetic properties even after severe cold working and can significantly improve elastic limit stress by aging treatment. 
     However, the stainless steel of Patent Document 1 has a Mn content of 2 to 9%, so it is feared that corrosion resistance is reduced due to Mn, and its application is limited in applications requiring corrosion resistance. For the stabilization of the austenite phase, Ni-equivalent range was proposed to refer to maintaining non-magnetic properties even after cold working. However, since δ-ferrite, which affects non-magnetic properties, is not mentioned, it is necessary to solve the deterioration of non-magnetic properties due to δ-ferrite formation. 
     (Patent Document 0001) Korean Patent Publication No. 10-2015-0121061 (Oct. 28, 2015) 
     DISCLOSURE 
     Technical Problem 
     Therefore, it is an aspect of the present invention to provide a highly corrosion-resistant austenitic stainless steel with excellent non-magnetic properties by suppressing δ-ferrite formation during solidification by solving the above problems. 
     Technical Solution 
     In accordance with an aspect of the present disclosure, a non-magnetic austenitic stainless steel with excellent corrosion resistance includes, in percent (%) by weight of the entire composition, C: 0.05% or less, Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2% or less, the remainder of iron (Fe) and other inevitable impurities, and satisfies a following equation (1), and has a permeability of 1.02μ or less. 
       Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)
 
     Ni, C, Si, Mn, Cr, Mo, Cu, N mean the content (% by weight) of each element. 
     The austenitic stainless steel may further include: in percent (%) by weight, Cu: 3.0% or less. 
     The austenitic stainless steel may further include: in percent (%) by weight, Mo: 4.0% or less. 
     The austenitic stainless steel may further include: in percent (%) by weight, B: less than 0.01%. 
     The austenitic stainless steel may satisfy a calculated δ-ferrite fraction represented by the following equation (2) of 0% or less. 
       161*{[Cr+Mo+1.5*Si+18]/[Ni+30*(C+N)+0.5*(Cu+Mn)+36]+0.262}−161  (2)
 
     Cr, Mo, Si, Ni, C, N, Cu, Mn mean the content (% by weight) of each element The austenitic stainless steel may satisfy a pitting resistance equivalent number (PREN) represented by the following equation (3) of the range of 20 to 30. 
       Cr+3.3*Mo+30*N−Mn+Si  (3)
 
     Cr, Mo, N, Mn, Si mean the content (% by weight) of each element The austenitic stainless steel may satisfy a σ phase formation index represented by the following equation (4) of the range of 18 to 24. 
       Cr+Mo+3*Si  (4)
 
     Cr, Mo, Si mean the content (% by weight) of each element 
     The austenitic stainless may have a permeability of 1.012μ or less. 
     The average grain size of the stainless steel may be 70 μm or less. 
     In accordance with an aspect of the present disclosure, a manufacturing method of a non-magnetic austenitic stainless steel with excellent corrosion resistance, includes: hot rolling the slab comprising, in percent (%) by weight of the entire composition, C: 0.05% or less, Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2% or less, the remainder of iron (Fe) and other inevitable impurities and satisfying a σ phase formation index represented by the following equation (4) of the range of 18 to 24; and performing a solution heat treatment of the hot rolled material. 
     (4) Cr+Mo+3*Si Cr, Mo, Si mean the content (% by weight) of each element The slab may satisfy a following equation (1), and satisfy a calculated δ-ferrite fraction represented by a following equation (2) of 0% or less. 
       Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)
 
       161*{[Cr+Mo+1.5*Si+18]/[Ni+30*(C+N)+0.5*(Cu+Mn)+36]+0.262}161  (2)
 
     The solution heat treatment may be performed at 1,100 to 1,150° C. for 60 to 120 seconds. 
     Advantageous Effects 
     High corrosion-resistant non-magnetic austenitic stainless steel according to an embodiment of the present disclosure can be applied to a variety of non-magnetic components used in various devices. 
     In addition, since the non-magnetic property is determined by the components without an additional process of heat-treating the material for a long time in order to remove the magnetism by δ-ferrite, it is possible to provide non-magnetic austenitic stainless steel with a simple manufacturing process. 
     In addition, it is possible to prevent roughness deterioration due to an orange peel defect on the surface of the steel sheet. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a graph illustrating a correlation of permeability according to a difference between a Ni content and a Ni correction value (Ni adj ). 
     
    
    
     BEST MODE 
     A non-magnetic austenitic stainless steel with excellent corrosion resistance according to an embodiment of the present disclosure includes, in percent (%) by weight of the entire composition, C: 0.05% or less, Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2% or less, the remainder of iron (Fe) and other inevitable impurities, and satisfies a following equation (1), and has a permeability of 1.02μ or less. 
       Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)
 
     Ni, C, Si, Mn, Cr, Mo, Cu, N mean the content (% by weight) of each element. 
     MODES OF THE INVENTION 
     Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The following embodiments are provided to transfer the technical concepts of the present disclosure to one of ordinary skill in the art. However, the present disclosure is not limited to these embodiments, and may be embodied in another form. In the drawings, parts that are irrelevant to the descriptions may be not shown in order to clarify the present disclosure, and also, for easy understanding, the sizes of components are more or less exaggeratedly shown. 
     Also, when a part “includes” or “comprises” an element, unless there is a particular description contrary thereto, the part may further include other elements, not excluding the other elements. 
     An expression used in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. 
     Hereinafter, it describes a non-magnetic austenitic stainless steel which can secure non-magnetic properties even if it is manufactured in a normal process without requiring an additional process for decomposing δ-ferrite by controlling the content of δ-ferrite present in the microstructure of the steel and has superior corrosion resistance compared to commonly used STS316L stainless steel. 
     The present disclosure provides austenitic stainless steel which exhibits excellent non-magnetic properties only by controlling the alloy element components even without an additional heat treatment process, and a manufacturing method thereof. 
     A non-magnetic austenitic stainless steel with excellent corrosion resistance according to an embodiment of the present disclosure includes, in percent (%) by weight of the entire composition, C: 0.05% or less, Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2% or less, the remainder of iron (Fe) and other inevitable impurities, and satisfies a following equation (1). 
       Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)
 
     Hereinafter, the reason for the numerical limitation of the alloy component element content in the embodiment of the present disclosure will be described. In the following, unless otherwise specified, the unit is % by weight. 
     The content of C is 0.05% or less. 
     C is a strong austenite phase stabilizing element and is an effective element for increasing material strength by solid solution strengthening. However, when the content is excessive, it is easily combined with a carbide-forming element such as Cr effective for corrosion resistance at the ferrite-austenite phase boundary, thereby lowering the Cr content around the grain boundaries to reduce corrosion resistance. Therefore, the content of C is limited to 0.05% or less. In order to minimize the risk of carbide precipitation, which can inhibit corrosion resistance, it is desirable to limit the content of C to 0.03% or less. 
     The content of Si is 1.0% or less. 
     Si, which also acts as a ferrite phase stabilizing element, is effective in improving corrosion resistance, but when it is excessive, it promotes precipitation of intermetallic compounds such as σ phase, thereby reducing mechanical properties and corrosion resistance related to impact toughness, and is limited to 1.0% or less. 
     The content of Mn is 0.5 to 2.0%. 
     Mn is an austenite phase stabilizing element such as C and Ni, which can improve the N solubility, and is added by 0.5% or more. However, an increase in the Mn content is undesirable when corrosion resistance is required because it is involved in the formation of inclusions such as MnS, so it is preferable to limit the Mn content to 2.0% or less in order to secure corrosion resistance. 
     The content of Cr is 16.0 to 24.0%. 
     Cr is the most contained element of the corrosion resistance enhancing element of stainless steel, and must be included by 16% or more for the expression of corrosion resistance. However, Cr is a ferrite stabilizing element. As the Cr content increases, the ferrite fraction increases. Therefore, in order to obtain a non-magnetic property, since a large amount of Ni must be contained, the cost increases, and the formation of the σ phase is promoted, causing a decrease in mechanical properties and corrosion resistance. Therefore, it is preferable to limit the Cr content to 24% or less. 
     The content of Ni is 10.0 to 16.0%. 
     Ni is the most powerful element of the austenite phase stabilizing element and must be contained by 10% or more to obtain non-magnetic properties. However, since the increase in Ni content is directly related to the increase in the price of raw materials, it is preferable to limit Ni content to 16% or less. 
     The content of N is 0.2% or less. 
     N is an element useful for stabilizing the austenite phase as well as improving corrosion resistance in a chlorine atmosphere. However, it is preferable to limit N content to 0.2% or less, because the hot workability is reduced when a large amount is added to lower the yielding percentage of steel. 
     In addition, according to an embodiment of the present disclosure, by weight %, Cu of 3.0% or less may be further included. 
     Cu has the advantage of improving corrosion resistance in a sulfuric acid atmosphere, so it can be selectively added. However, in the chlorine atmosphere, there is a disadvantage of reducing the pitting resistance and lowering the hot workability, so it is limited to 3.0% or less. 
     In addition, according to an embodiment of the present disclosure, by weight %, Mo of 4.0% or less may be further included. 
     The content of Mo is 4.0% or less. 
     Mo is an element useful for improving corrosion resistance, and can be expected to improve corrosion resistance, so it can be selectively added. When adding, it is preferable to add 2.0% or more. However, Mo is a ferrite stabilizing element, and when added in large amounts, it is difficult to obtain a non-magnetic property due to an increase in the ferrite fraction and, in addition, the formation of the σ phase is promoted, leading to a decrease in mechanical properties and corrosion resistance. Therefore, the content of Mo is limited to 4.0% or less. 
     In addition, according to an embodiment of the present disclosure, by weight %, B may be further included less than 0.01%. 
     The content of B is less than 0.01%. 
     B has the effect of improving the hot workability, so it can be added in a range of less than 0.01%. However, when it is added more than that, since a low melting point boride compound is formed and rather hot workability is lowered, it is preferable to limit to less than 0.01%. 
     In various devices that use non-magnetic properties of steel, the permeability of the steel applied to the parts must be 1.02μ or less for normal device operation. In order to satisfy this, it is necessary to control the fraction of δ-ferrite formed during solidification of the steel. 
     In general, δ-ferrite present in the microstructure of austenitic stainless steel becomes magnetic due to the characteristics of the structure having a body-centered cubic structure, and austenite does not become magnetic due to the face-centered cubic structure. Therefore, it is possible to obtain a magnetic property of a desired size by controlling the fraction of δ-ferrite, and in the case of non-magnetic steel, it is necessary to make the fraction of δ-ferrite as low as possible or eliminate the fraction of δ-ferrite. 
     The fraction of δ-ferrite present in the microstructure of austenitic stainless steel can be determined by the content of various alloying elements, as shown in equation (2), which will be described later. In particular, it is possible to reduce the δ-ferrite fraction by adding an austenite stabilizing element. Since the Ni content is useful for stabilizing austenite without deteriorating other physical properties, the Ni content can be controlled to suppress the formation of δ-ferrite. 
     The Ni correction formula (hereinafter, Ni adj ) means a minimum Ni content that prevents δ-ferrite from being formed in a given composition component, and can be expressed as follows. 
       −2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  [Ni adj ]
 
     When the Ni content contained in the actual steel is greater than the value of Ni adj , δ-ferrite cannot be formed, thereby exhibiting non-magnetic properties. That is, in order to satisfy the non-magnetic property, it means that the content of Ni contained in the steel should be greater than Ni adj  combined with the content of C, Si, Mn, Cr, Mo, Cu, and N components. 
       Ni≥−2.7−5.8*C−1.77*Si−0.066*Mn+0.893*Cr+1.05*Mo−0.88*Cu−13.8*N  (1)
 
       FIG. 1  is a graph illustrating a correlation of permeability according to a difference between a Ni content and a Ni adj  value. Referring to  FIG. 1 , it can be seen that when the difference between the Ni content and the Ni adj  value included in the steel is positive, the permeability of the steel satisfies 1.02μ or less. 
     However, Ni is an expensive alloy element, and the more Ni is added, the higher the cost. Therefore, it is preferable to make the difference between the actual Ni content and the Ni adj  value less than 8%. 
     In addition, according to an embodiment of the present disclosure, the non-magnetic austenitic stainless steel with excellent corrosion resistance may satisfy the calculated δ-ferrite fraction represented by the following equation (2) of 0% or less. 
       161*{[Cr+Mo+1.5*Si+18]/[Ni+30*(C+N)+0.5*(Cu+Mn)+36]+0.262}−161  (2)
 
     The equation (2) is a formula that can predict the δ-ferrite content of steel through the content of each component when producing austenitic stainless steel in a normal steelmaking process. When the fraction of δ-ferrite calculated through equation (2) is 0% or less, the non-magnetic property to be achieved in the present disclosure may be satisfied. 
     The non-magnetic austenitic stainless steel of the present disclosure according to the equations (1) and/or (2) may exhibit a permeability of 1.02μ or less, and more preferably 1.012μ or less, thereby realizing a completely non-magnetic property. 
     On the other hand, in order to improve corrosion resistance of steel, it is effective to add alloy elements that improve corrosion resistance, such as Cr, Mo, Si, and N. In addition, when a large amount of Mn is added, since water-soluble inclusions such as MnS in steel are formed and corrosion resistance is lowered, it is necessary to control the Mn content. 
     In general, as an index indicating corrosion resistance of austenite stainless steel, pitting resistance equivalent number calculated by a combination of Cr, Mo, and N contents is applied. However, as described above, since the contents of Mn and Si also greatly affect corrosion resistance of steel, a new pitting resistance equivalent number considering these elements is also required. 
     According to an embodiment of the present disclosure, non-magnetic austenitic stainless steel with excellent corrosion resistance may satisfy a pitting resistance equivalent number (PREN) value represented by the following equation (3) of the range of 20 to 30. 
       Cr+3.3*Mo+30*N−Mn+Si  (3)
 
     The present inventors have found that the pitting resistance equivalent number including Mn and Si content represented by equation (3) well reflects the corrosion resistance of steel, and have confirmed that when the range of equation (3) is 20 to 30, corrosion resistance may be equal to or higher than that of conventional STS316L. 
     However, when the content of Cr, Mo, and Si increases, not only does the cost increase, but the formation of the σ phase promotes brittleness, and a Cr and Mo depletion region is formed, which adversely affects corrosion resistance. Therefore, it is necessary to set an appropriate Cr, Mo, Si content range that can minimize the formation of the σ phase while obtaining desired corrosion resistance. 
     According to an embodiment of the present disclosure, the non-magnetic austenitic stainless steel with excellent corrosion resistance may satisfy the σ phase formation index represented by the following equation (4) of the range of 18 to 24. 
       Cr+Mo+3*Si  (4)
 
     When the σ phase formation index is less than 18, the Cr and Mo content is so low that it is difficult to secure corrosion resistance of the steel, so it is limited to 18 or more. 
     By limiting the σ phase formation index to 24 or less, the σ phase fraction can be controlled to less than 1.0%, more preferably to 0.8% or less. When the σ phase formation index is greater than 24, decreased corrosion resistance and brittle material degradation due to excessive σ phase formation may occur. Non-magnetic properties may be further improved by securing a low σ phase fraction. 
     On the other hand, the σ phase formation control can suppress the formation of the σ phase by controlling the alloy component composition as in the present disclosure, but the formed σ phase may also be decomposed by controlling the solution heat treatment conditions. For the decomposition of the σ phase, it is effective to anneal for a long time at a high temperature, but in this case, the possibility of causing an orange peel defect on the surface increases due to excessive grain size growth. Here, the orange peel defect refers to a defect in which unevenness of roughness occurs on the surface when the steel is formed by coarse grain size, thereby damaging the beautiful surface. 
     According to an embodiment of the present disclosure, the average grain size of non-magnetic austenitic stainless steel with excellent corrosion resistance may be 70 μm or less. 
     For general 300-based austenitic stainless steel, solution heat treatment is performed at about 1,100° C. for about 60 to 100 seconds. In order to lower the incidence of defects in orange peel during molding, the average grain size of stainless steel should be 70 μm or less, and for this purpose, the average grain size of the non-magnetic austenitic stainless steel with excellent corrosion resistance of the present disclosure may be controlled to 70 μm or less by performing solution heat treatment of the hot rolled material at 1,100 to 1,150° C. for 60 to 120 seconds. 
     Hereinafter, it will be described in more detail through a preferred embodiment of the present disclosure. 
     Example 
     After the steel having the alloy composition shown in Table 1 was dissolved in a vacuum induction furnace, hot rolling was performed, and solution heat treatment was performed to prepare a hot rolled sheet having a thickness of 6 mm. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 composition (wt %) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 C 
                 Si 
                 Mn 
                 Cr 
                 Ni 
                 Mo 
                 Cu 
                 N 
                 B 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 S1 
                 0.030 
                 0.45 
                 1.3 
                 15.8 
                 15.8 
                 0.0 
                 1.5 
                 0.070 
                 0.0026 
               
               
                 S2 
                 0.034 
                 0.46 
                 1.2 
                 18.5 
                 15.4 
                 0.0 
                 1.2 
                 0.080 
                 0.0045 
               
               
                 S3 
                 0.025 
                 0.52 
                 1.2 
                 20.4 
                 16.0 
                 0.0 
                 1.3 
                 0.080 
                 0.0035 
               
               
                 S4 
                 0.028 
                 0.47 
                 1.4 
                 24.3 
                 15.4 
                 0.0 
                 1.6 
                 0.070 
                 0.0026 
               
               
                 S5 
                 0.021 
                 0.45 
                 1.3 
                 18.6 
                 14.3 
                 0.0 
                 2.1 
                 0.090 
                 0.0025 
               
               
                 S6 
                 0.024 
                 0.46 
                 1.1 
                 17.9 
                 14.5 
                 2.8 
                 0.0 
                 0.080 
                 0.0025 
               
               
                 S7 
                 0.026 
                 0.43 
                 1.2 
                 17.6 
                 10.5 
                 0.0 
                 2.5 
                 0.120 
                 0.0026 
               
               
                 S8 
                 0.030 
                 0.42 
                 1.2 
                 18.6 
                 13.5 
                 4.2 
                 2.6 
                 0.090 
                 0.0034 
               
               
                 S9 
                 0.037 
                 0.48 
                 1.3 
                 18.1 
                 12.6 
                 2.1 
                 1.5 
                 0.220 
                 0.003 
               
               
                 S10 
                 0.032 
                 0.45 
                 1.3 
                 18.2 
                 13.5 
                 2.5 
                 1.6 
                 0.100 
                 0.002 
               
               
                 S11 
                 0.026 
                 0.45 
                 1.2 
                 17.9 
                 14.2 
                 2.6 
                 1.4 
                 0.050 
                 0.0021 
               
               
                 S12 
                 0.028 
                 0.46 
                 0.5 
                 18.1 
                 13.8 
                 0.0 
                 0.0 
                 0.070 
                 0.0026 
               
               
                 S13 
                 0.029 
                 0.47 
                 1.3 
                 18.4 
                 13.9 
                 0.0 
                 0.6 
                 0.080 
                 0.0026 
               
               
                 S14 
                 0.027 
                 0.41 
                 2.2 
                 18.1 
                 13.9 
                 0.0 
                 0.0 
                 0.080 
                 0.0032 
               
               
                 S15 
                 0.024 
                 0.42 
                 1.2 
                 18.1 
                 14.5 
                 2.1 
                 0.3 
                 0.080 
                 0.0025 
               
               
                 S16 
                 0.026 
                 0.75 
                 1.3 
                 18.4 
                 14.0 
                 2.0 
                 0.4 
                 0.090 
                 0.003 
               
               
                 S17 
                 0.035 
                 1.12 
                 1.1 
                 18.7 
                 13.9 
                 2.3 
                 0.6 
                 0.110 
                 0.0026 
               
               
                   
               
            
           
         
       
     
     In some of the S1 to S17 steel types listed in Table 1, the solution heat treatment conditions were varied to change the grain size, and when the steel with each grain size was formed, the incidence of orange peel defects was investigated and shown in Table 2 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                   
                 orange 
               
               
                   
                 average 
                 peel 
               
            
           
           
               
               
               
               
            
               
                   
                 solution heat treatment 
                 grain 
                 incidence 
               
            
           
           
               
               
               
               
               
            
               
                   
                 temperature(° C.) 
                 time(sec) 
                 size(μm) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Inventive 
                 1 
                 S2 
                 1,150 
                 90 
                 23.48 
                 &lt;1.0 
               
               
                 Example 
                 2 
                 S3 
                 1,150 
                 90 
                 30.45 
                 &lt;1.0 
               
               
                   
                 3 
                 S5 
                 1,150 
                 90 
                 25.63 
                 &lt;1.0 
               
               
                   
                 4 
                   
                 1,100 
                 90 
                 22.89 
                 &lt;1.0 
               
               
                   
                 5 
                   
                 1,150 
                 180 
                 50.88 
                 3.2 
               
               
                   
                 6 
                   
                 1,180 
                 90 
                 53.48 
                 3.5 
               
               
                   
                 7 
                 S6 
                 1,150 
                 90 
                 30.89 
                 &lt;1.0 
               
               
                   
                 8 
                 S7 
                 1,150 
                 90 
                 38.52 
                 &lt;1.0 
               
               
                   
                 9 
                 S10 
                 1,150 
                 90 
                 23.58 
                 &lt;1.0 
               
               
                   
                 10 
                 S11 
                 1,150 
                 90 
                 25.25 
                 &lt;1.0 
               
               
                   
                 11 
                 S12 
                 1,150 
                 90 
                 26.84 
                 &lt;1.0 
               
               
                   
                 12 
                 S13 
                 1,150 
                 90 
                 21.35 
                 &lt;1.0 
               
               
                 Comparative 
                 13 
                 S1 
                 1,150 
                 90 
                 21.93 
                 &lt;1.0 
               
               
                 Example 
                 14 
                 S4 
                 1,150 
                 90 
                 27.56 
                 &lt;1.0 
               
               
                   
                 15 
                 S5 
                 1,180 
                 120 
                 74.58 
                 15.8 
               
               
                   
                 16 
                   
                 1,180 
                 180 
                 86.72 
                 22.9 
               
               
                   
                 17 
                 S8 
                 1,150 
                 90 
                 24.69 
                 &lt;1.0 
               
               
                   
                 18 
                 S9 
                 1,150 
                 90 
                 23.75 
                 &lt;1.0 
               
               
                   
                 19 
                 S14 
                 1,150 
                 90 
                 26.84 
                 &lt;1.0 
               
               
                   
                 20 
                 S17 
                 1,150 
                 90 
                 31.24 
                 &lt;1.0 
               
               
                   
               
            
           
         
       
     
     As shown in Table 2, the S5 steel grades used in Comparative Examples 15 and 16 satisfy all the components of the present disclosure, but the solution heat treatment temperature was performed at 1,180° C. exceeding 1,150° C. for 120 seconds or more and the average grain size exceeded 70 μm, and the orange peel defect after molding was more than 15%. 
     As the solution heat treatment temperature changed, the grain size of the steel changed. As the heat treatment temperature and time increased, it was found that the average grain size increased. When the average grain size was 70 μm or more, it was found that the incidence of orange peel defects was 15% or more, significantly increasing compared to other heat treatment conditions. 
     In addition, for the S1 to S17 steel grades described in Table 1, the calculated values according to equations (1) to (4), permeability, and σ phase fraction were measured and are shown in Table 3 below. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 measured 
                   
                   
                   
                   
                 measured 
               
               
                   
                   
                 δ-ferrite 
                   
                   
                   
                   
                 σ phase 
               
               
                   
                 equation 
                 fraction 
                 equation 
                 permeability 
                 equation 
                 equation 
                 fraction 
               
               
                   
                 (1) 
                 (%) 
                 (2) 
                 (μ) 
                 (3) 
                 (4) 
                 (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Inventive 
                 1 
                 S2 
                 4.8 
                 0 
                 −11.9 
                 1.003 
                 20.2 
                 19.9 
                 0.06 
               
               
                 Example 
                 2 
                 S3 
                 3.9 
                 0 
                 −7.0 
                 1.004 
                 22.1 
                 22.0 
                 0.11 
               
               
                   
                 3 
                 S5 
                 4.5 
                 0 
                 −10.4 
                 1.003 
                 20.5 
                 20.0 
                 0.16 
               
               
                   
                 4 
                   
                 4.5 
                 0 
                 −10.4 
                 1.004 
                 20.5 
                 20.0 
                 0.08 
               
               
                   
                 5 
                   
                 4.5 
                 0 
                 −10.4 
                 1.003 
                 20.5 
                 20.0 
                 0.06 
               
               
                   
                 6 
                   
                 4.5 
                 0 
                 −10.4 
                 1.004 
                 20.5 
                 20.0 
                 0.15 
               
               
                   
                 7 
                 S6 
                 0.4 
                 0 
                 −1.7 
                 1.005 
                 28.9 
                 22.1 
                 0.09 
               
               
                   
                 8 
                 S7 
                 2.3 
                 0 
                 −8.2 
                 1.012 
                 20.4 
                 18.9 
                 0.03 
               
               
                   
                 9 
                 S10 
                 1.2 
                 0 
                 −3.4 
                 1.004 
                 28.6 
                 22.1 
                 0.06 
               
               
                   
                 10 
                 S11 
                 1.1 
                 0 
                 −1.5 
                 1.003 
                 27.2 
                 21.9 
                 0.17 
               
               
                   
                 11 
                 S12 
                 2.3 
                 0 
                 −7.0 
                 1.006 
                 20.2 
                 19.5 
                 0.05 
               
               
                   
                 12 
                 S13 
                 2.9 
                 0 
                 −8.4 
                 1.001 
                 20.0 
                 19.8 
                 0.11 
               
               
                 Comparative 
                 13 
                 S1 
                 7.7 
                 0 
                 −20.1 
                 1.001 
                 17.7 
                 17.2 
                 0.03 
               
               
                 Example 
                 14 
                 S4 
                 −0.1 
                 0.9 
                 5.2 
                 1.042 
                 25.5 
                 25.7 
                 0.97 
               
               
                   
                 15 
                 S5 
                 4.5 
                 0 
                 −10.4 
                 1.003 
                 20.5 
                 20.0 
                 0.05 
               
               
                   
                 16 
                   
                 4.5 
                 0 
                 −10.4 
                 1.003 
                 20.5 
                 20.0 
                 0.12 
               
               
                   
                 17 
                 S8 
                 −0.3 
                 0.3 
                 2.5 
                 1.026 
                 34.4 
                 24.1 
                 0.94 
               
               
                   
                 18 
                 S9 
                 2.4 
                 0 
                 −10.2 
                 1.002 
                 30.8 
                 21.6 
                 0.17 
               
               
                   
                 19 
                 S14 
                 2.6 
                 0 
                 −9.8 
                 1.002 
                 18.7 
                 19.3 
                 0.03 
               
               
                   
                 20 
                 S17 
                 1.8 
                 0 
                 0.0 
                 1.028 
                 28.7 
                 24.4 
                 0.84 
               
               
                   
               
            
           
         
       
     
     As shown in Table 3, when the Ni-Ni adj  value represented by the equation (1) is positive, it was found that permeability satisfies 1.02μ or less, particularly, the examples of the present disclosure satisfy 1.012μ or less. When the calculated δ-ferrite fraction according to equation (2) is 0% or less, it was found that the measured δ-ferrite fraction was 0%. In addition, when the σ phase formation index is 24 or more, the σ phase fraction is 0.8% or more, which is close to 1.0%, indicating that the σ phase fraction is significantly increased compared to other steel types. 
     Comparative Example 13 did not satisfy the corrosion resistance requirement due to the low PREN (Eq. (3)) value due to the S1 steel grade having insufficient Cr content, and the σ phase formation index (Eq. (4)) was also less than 18. 
     Comparative Example 14 does not satisfy the equations (1) and (2) due to the S4 steel grade containing excessive Cr, and has a high σ phase fraction, so the permeability was measured to be 1.042μ, and the desired non-magnetic property of the present disclosure was not satisfied. The σ phase formation index also exceeded 24, indicating that the σ phase fraction was close to 1.0%. It was found that the σ phase formation was promoted by the increase of the Cr content, thereby forming a Cr depletion region. 
     Comparative Example 17 does not satisfy the equations (1) and (2) due to the S8 steel grade containing excessive Mo, and has a high σ phase fraction, so the permeability was measured to be 1.026μ, and the desired non-magnetic property of the present disclosure was not satisfied. The σ phase formation index also exceeded 24, indicating that the σ phase fraction was close to 1.0%. It was found that the σ phase formation was promoted by the increase of the Mo content, thereby forming a Mo depletion region. Through this, it was confirmed that when adding additional Mo, it should be added at 4.0% or less. 
     Comparative Example 18 did not meet the corrosion resistance requirement due to the high PREN value due to the S9 steel grade containing N excessively. 
     Comparative Example 19 did not satisfy the corrosion resistance requirement due to the low PREN value due to the S14 steel grade containing excessive Mn, and it was found that corrosion resistance was not secured due to inclusion formation due to an increase in the Mn content. 
     In Comparative Example 20, the σ phase formation index exceeded 24 due to the S17 steel containing excessive Si, and the permeability was high as 1.028μ despite satisfying equations (1) and (2) due to the σ phase, which is a magnetic secondary phase. It was confirmed that Si is effective in improving corrosion resistance, but when it is excessive, it promotes precipitation of intermetallic compounds such as σ phase, thereby lowering corrosion resistance and non-magnetic properties, and thus should be added at 1.0% or less. 
     While the present disclosure has been particularly described with reference to exemplary embodiments, it should be understood by those of skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The austenitic stainless steel according to the present disclosure may be applied as a non-magnetic component of various electronic devices, and may secure non-magnetic properties without an additional process such as heat treatment for a long time.