KR102015510B1 - Non-magnetic austenitic stainless steel with excellent corrosion resistance and manufacturing method thereof - Google Patents

Abstract

A nonmagnetic austenitic stainless steel having excellent corrosion resistance applicable to an environment where corrosion resistance is required along with excellent nonmagnetic characteristics and a method of manufacturing the same are disclosed.
Non-magnetic austenitic stainless steel having excellent corrosion resistance according to an embodiment of the present invention, in weight%, 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, remaining Fe and inevitable impurities, and satisfying the following formula (1).
(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

Description

Non-magnetic austenitic stainless steel with excellent corrosion resistance and its manufacturing method {NON-MAGNETIC AUSTENITIC STAINLESS STEEL WITH EXCELLENT CORROSION RESISTANCE AND MANUFACTURING METHOD THEREOF}

The present invention relates to a nonmagnetic austenitic stainless steel, and more particularly, to a nonmagnetic austenitic stainless steel excellent in corrosion resistance that can be applied to an environment in which corrosion resistance is required as well as nonmagnetic properties and a manufacturing method thereof.

The austenitic stainless steels represented by STS304 have good corrosion resistance, exhibit nonmagnetic austenitic structure in the annealing heat treatment state, and are used in various devices and devices as nonmagnetic steels. However, depending on the application, there are cases where cold working is performed. When cold working is applied to STS304 steel, it is difficult to maintain nonmagnetic properties due to the phase transformation into the processed organic martensite structure. do.

Therefore, steel grades of STS316L series having higher austenite stability than STS304 are used for nonmagnetic applications. However, in the case of STS316L steel grades, because of the high Mo content, secondary phases such as σ phase and δ-ferrite are often present in the austenitic matrix, and solidification starts from δ-ferrite during continuous casting of STS316L steel. In the central segregation region, it is difficult to decompose the secondary phases due to the high Cr and Mo contents, and thus tends to remain after hot rolling and final heat treatment.

If the secondary phases remain, this causes the magnetism in the area to increase, adversely affecting the function of the device. Therefore, there is a need for a material capable of maintaining nonmagnetic properties without these secondary phases.

Patent Document 1 refers to a high strength nonmagnetic austenitic stainless steel that can maintain nonmagnetic properties even after severe cold working and can significantly improve the elastic limit stress by aging treatment.

However, since the stainless steel of Patent Document 1 contains 2 to 9% of Mn, there is a fear of deterioration of corrosion resistance due to Mn, and application is limited in applications requiring corrosion resistance. In order to stabilize the austenite phase, the Ni equivalent formula is proposed to maintain nonmagnetic properties after cold working, but it does not mention δ-ferrite, which affects nonmagnetic properties. It is necessary to solve the deterioration of nonmagnetic properties.

Korean Unexamined Patent Publication No. 2015-0121061 (2015.10.28.)

Embodiments of the present invention to solve the above problems, to suppress the formation of δ-ferrite during solidification to provide a high corrosion-resistant austenitic stainless steel excellent in nonmagnetic properties.

Non-magnetic austenitic stainless steel having excellent corrosion resistance according to an embodiment of the present invention, in weight%, 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, remaining Fe and unavoidable impurities, satisfying the following formula (1), and the magnetic permeability is 1.02 mu or less.

(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

Here, Ni, C, Si, Mn, Cr, Mo, Cu, N means the content (wt%) of each element.

In addition, according to an embodiment of the present invention, by weight, Cu may further include 3.0% or less.

In addition, according to an embodiment of the present invention, in weight%, Mo: 4.0% or less may be further included.

In addition, according to an embodiment of the present invention, by weight, B may further include less than 0.01%.

Further, according to an embodiment of the present invention, the calculated δ-ferrite fraction represented by the following formula (2) may satisfy 0% or less.

(2) 161 * {[Cr + Mo + 1.5 * Si + 18] / [Ni + 30 * (C + N) + 0.5 * (Cu + Mn) + 36] + 0.262}-161

Here, Cr, Mo, Si, Ni, C, N, Cu, Mn means the content (wt%) of each element.

In addition, according to one embodiment of the present invention, the pitting equivalent index (PREN) represented by the following formula (3) may satisfy the range of 20 to 30.

(3) Cr + 3.3 * Mo + 30 * N-Mn + Si

Here, Cr, Mo, N, Mn, Si means the content (wt%) of each element.

In addition, according to an embodiment of the present invention, the σ phase formation index represented by the following formula (4) may satisfy the range of 18 to 24.

(4) Cr + Mo + 3 * Si

Here, Cr, Mo, and Si means content (weight%) of each element.

In addition, according to an embodiment of the present invention, the stainless steel may have a magnetic permeability of 1.012 μm or less.

In addition, according to an embodiment of the present invention, the average grain size of the stainless steel may be 70㎛ or less.

Non-magnetic austenitic stainless steel manufacturing method excellent in corrosion resistance according to an embodiment of the present invention, in weight%, C: 0.05% or less, Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24 Hot rolling a slab containing%, Ni: 10 to 16%, N: 0.2% or less, remaining Fe and inevitable impurities, and having an σ-phase formation index of 18 to 24 represented by the following formula (4): ; And solution heat treatment of the hot rolled material.

(4) Cr + Mo + 3 * Si

According to an embodiment of the present invention, the slab may satisfy the following Equation (1), and the calculated δ-ferrite fraction represented by the following Equation (2) may satisfy 0% or less.

(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

(2) 161 * {[Cr + Mo + 1.5 * Si + 18] / [Ni + 30 * (C + N) + 0.5 * (Cu + Mn) + 36] + 0.262}-161

In addition, according to one embodiment of the present invention, the solution heat treatment may be performed for 60 to 120 seconds at 1,100 to 1,150 ℃.

The highly corrosion-resistant nonmagnetic austenitic stainless steel according to the embodiment of the present invention can be variously applied for nonmagnetic parts used in various devices or devices.

In addition, since the nonmagnetic properties are determined by the components without the 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 a nonmagnetic austenitic stainless steel with a simple manufacturing process.

In addition, roughness deterioration due to an orange peel defect on the surface of the steel sheet can be prevented.

1 is a graph showing the magnetic permeability correlation according to the difference between the Ni content and the value of Ni correction formula (Ni _adj ).

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are presented to fully convey the spirit of the present invention to those skilled in the art. The invention is not limited to the examples presented herein but may be embodied in other forms. The drawings may omit illustrations of parts not related to the description in order to clarify the present invention, and may be exaggerated to some extent in order to facilitate understanding.

In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

Singular expressions include plural expressions unless the context clearly indicates an exception.

Hereinafter, by controlling the content of δ-ferrite present in the microstructure of the steel, there is no need for an additional process for decomposing δ-ferrite, even if manufactured in a conventional process, it is possible to secure nonmagnetic properties as well as the commonly used STS316L system. It describes a nonmagnetic austenitic stainless steel having better corrosion resistance than stainless steel.

The present invention provides an austenitic stainless steel exhibiting excellent nonmagnetic properties only by controlling alloy element components without undergoing an additional heat treatment, and a method of manufacturing the same.

Non-magnetic austenitic stainless steel having excellent corrosion resistance according to an embodiment of the present invention, in weight%, 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, remaining Fe and inevitable impurities, and satisfying the following formula (1).

(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

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

The content of C is 0.05% or less.

C is a strong austenitic stabilizing element and is an effective element for increasing the material strength by solid solution strengthening. However, the content of C is limited to 0.05% or less because it is easily combined with carbide-forming elements such as Cr, which is effective for corrosion resistance at the ferrite-austenite phase boundary to reduce the Cr content around the grain boundary to reduce corrosion resistance. In order to minimize the risk of carbide precipitation which may impair corrosion resistance, it is preferable 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 the corrosion resistance, but when excessive, it promotes precipitation of intermetallic compounds such as σ phase, thereby limiting mechanical properties and corrosion resistance related to impact toughness, and therefore limited to 1.0% or less.

The content of Mn is 0.5 to 2.0%.

Mn is an austenite stabilizing element such as C and Ni, which can improve the N solid solubility and is added at 0.5% or more. However, an increase in Mn content is not preferable when corrosion resistance is required due to involvement of inclusions such as MnS, and therefore, 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 basic element among the corrosion resistance improving elements of stainless steel, and at least 16% or more must be included in order to develop corrosion resistance. However, Cr is a ferrite stabilizing element.As the Cr content increases, the ferrite fraction increases, so that a large amount of Ni must be included in order to obtain nonmagnetic properties, and the cost increases, and the formation of σ phase is promoted, which causes a decrease in mechanical properties and corrosion resistance. do. Therefore, the Cr content is preferably limited to 24% or less.

The content of Ni is 10.0 to 16.0%.

Ni is the strongest element among the austenite phase stabilizing elements and should be contained at least 10% in order to obtain nonmagnetic properties. However, since the increase in Ni content is directly related to the rise in raw material prices, it is desirable to limit the amount to 16% or less.

The content of N is 0.2% or less.

N is an element useful for stabilizing austenite phase as well as improving corrosion resistance in a chlorine atmosphere. However, since the hot workability is reduced when a large amount is added to lower the steel's real number ratio, it is preferable to limit it to 0.2% or less.

In addition, according to an embodiment of the present invention, by weight, Cu may further include 3.0% or less.

Cu has the advantage of improving the corrosion resistance in sulfuric acid atmosphere, so selective addition is possible. However, in the chlorine atmosphere there is a disadvantage in reducing the formal resistance, and the hot workability is limited to 3.0% or less.

In addition, according to an embodiment of the present invention, in weight%, Mo: 4.0% or less may be further included.

The content of Mo is 4.0% or less.

Mo is an element useful for improving the corrosion resistance and can be added selectively since it can anticipate the effect of improving corrosion resistance, and at the time of addition, it is preferable to add 2.0% or more. However, Mo is a ferrite stabilizing element, the ferrite fraction is increased when a large amount is difficult to obtain non-magnetic properties, the formation of σ phase is promoted to cause mechanical properties and corrosion resistance is limited to 4.0% or less.

In addition, according to an embodiment of the present invention, by weight, B may further include less than 0.01%.

The content of B is less than 0.01%.

B has an effect of improving the hot workability, it can be added in less than 0.01% range. However, when added more, it is preferable to form a boride compound having a low melting point and to decrease the hot workability, so it is limited to less than 0.01%.

For various equipment or devices that utilize the nonmagnetic properties of steel, the permeability value of steel applied to the part must be less than 1.02μ for the normal operation of the device. In order to satisfy this, the fraction of δ-ferrite formed during solidification of the steel must be controlled.

In general, the δ-ferrite present in the microstructure of the austenitic stainless steel is magnetic due to the characteristics of the structure having a body-centered cubic structure, and the austenite is not a magnet in the face-centered cubic structure. Therefore, the magnetic properties of the desired size can be obtained by controlling the fraction of δ-ferrite, and in the case of nonmagnetic steel, it is necessary to lower or eliminate the fraction of δ-ferrite as much as possible.

The fraction of δ-ferrite present in the microstructure of the austenitic stainless steel can be determined by the content of various alloying elements, as can be seen in Equation (2) below. In particular, by adding an austenite stabilizing element, the δ-ferrite fraction can be reduced. Since the Ni content is useful for stabilizing austenite without deteriorating other physical properties, the formation of δ-ferrite can be suppressed by controlling the Ni content.

The Ni correction formula (hereinafter, Ni _adj ) means a minimum Ni content such that δ-ferrite is not formed in a given compositional component system, and may be expressed as follows.

[Ni _adj ]

-2.7-5.8 * C-1.77 * Si-0.066 * Mn + 0.893 * Cr + 1.05 * Mo-0.88 * Cu-13.8 * N

When the Ni content contained in the steel is larger than the value of Ni _adj , δ-ferrite cannot be formed, thereby exhibiting nonmagnetic properties. That is, in order to satisfy the nonmagnetic property, it means that the content of Ni contained in the steel must be greater than Ni _adj combined with the contents of C, Si, Mn, Cr, Mo, Cu, and N components.

(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 is a graph showing the magnetic permeability correlation according to the difference between Ni content and Ni _adj value. Referring to FIG. 1, when the difference between the Ni content and the Ni _adj value included in the steel is positive, the permeability of the steel satisfies 1.02 μ or less.

However, since Ni increases the cost as the alloy element is expensive, it is desirable that the difference between the actual Ni content and the Ni _adj value is 8% or less.

According to one embodiment of the present invention, the non-magnetic austenitic stainless steel having excellent corrosion resistance may satisfy a calculated δ-ferrite fraction represented by the following formula (2) of 0% or less.

(2) 161 * {[Cr + Mo + 1.5 * Si + 18] / [Ni + 30 * (C + N) + 0.5 * (Cu + Mn) + 36] + 0.262}-161

Equation (2) is a formula for predicting the δ-ferrite content of the steel through the content of each component when producing austenitic stainless steel in a conventional steelmaking process, the δ-ferrite calculated through the formula (2) If the fraction is 0% or less, it can satisfy the nonmagnetic properties to be achieved in the present invention.

The nonmagnetic austenitic stainless steel of the present invention according to the formulas (1) and / or (2) may exhibit a magnetic permeability of 1.02μ or less, and more preferably 1.012μ or less, thereby enabling realization of fully nonmagnetic properties. .

On the other hand, in order to improve the corrosion resistance of steel, it is effective to add corrosion resistance improving alloy elements such as Cr, Mo, Si, N. In addition, when a large amount of Mn is added, it is necessary to form a water-soluble inclusion such as MnS in steel to lower corrosion resistance and to control Mn content.

In general, as an indicator of corrosion resistance of austenitic stainless steel, a pitting resistance index calculated by a combination of Cr, Mo, and N contents is applied. However, as described above, since the Mn and Si contents also have a great influence on the corrosion resistance of the steel, a new pitting resistance index is also required considering these elements.

According to an embodiment of the present invention, the non-magnetic austenitic stainless steel having excellent corrosion resistance may satisfy a PREN value of 20 to 30 represented by the following Equation (3).

(3) Cr + 3.3 * Mo + 30 * N-Mn + Si

The inventors have found that the pitting resistance index including Mn and Si content, which is represented by Eq. (3), well reflects the corrosion resistance of steel, and when Eq. (3) is in the range of 20 to 30, compared with conventional STS316L. It was confirmed that it can have more than equivalent corrosion resistance.

However, if the Cr, Mo, Si content is increased, not only increases the cost but also promotes the formation of σ phase to cause brittleness, and form a Cr and Mo depleted region, rather adversely affect the corrosion resistance. Therefore, it is necessary to set the appropriate Cr, Mo, Si content range that can minimize the formation of σ phase while obtaining the desired corrosion resistance.

According to one embodiment of the present invention, the nonmagnetic austenitic stainless steel having excellent corrosion resistance may satisfy the range of 18 to 24 represented by the? Phase formation index represented by the following formula (4).

(4) Cr + Mo + 3 * Si

If the sigma phase formation index is less than 18, since the Cr and Mo contents are so low, the corrosion resistance of the steel is difficult to secure, so it is limited to 18 or more.

By restricting the? phase formation index to 24 or less, the? phase fraction can be controlled to less than 1.0%, more preferably 0.8% or less. If the σ phase formation index is more than 24, problems of deterioration of corrosion resistance and brittle material due to excessive σ phase formation may occur. By securing a low σ phase fraction, the nonmagnetic properties can be further improved.

On the other hand, the? Phase formation control can suppress the formation of the? Phase by controlling the alloy component composition as in the present invention, but the formed? Phase can also be decomposed by controlling the solution heat treatment conditions. It is effective to anneal for a long time at a high temperature for decomposition of the σ phase, but in that case, the crystal grains grow excessively, which increases the possibility of causing orange peel defects on the surface. Herein, the orange peel defect means a defect that causes unevenness of roughness on the surface when forming steel by coarse grain size, thereby damaging the beautiful surface.

According to one embodiment of the present invention, the average grain size of the nonmagnetic austenitic stainless steel having excellent corrosion resistance may be 70 μm or less.

In the case of a general 300 series austenitic stainless steel, the solution heat treatment is performed for about 60 to 100 seconds at about 1,100 ℃. In order to reduce the orange peel defect occurrence rate during molding, the average grain size of the stainless steel should be 70 µm or less. For this purpose, the non-corrosive austenitic stainless steel having excellent corrosion resistance of the present invention is a hot rolled material for 60 to 120 seconds at 1,100 to 1,150 ° C. By solution heat treatment, average grain size can be controlled to 70 micrometers or less.

Hereinafter will be described in more detail through a preferred embodiment of the present invention.

Example

After the steel having the alloy composition shown in Table 1 was dissolved in a vacuum induction melting furnace, hot rolling was performed, and solution heat treatment was performed to prepare a hot rolled sheet having a thickness of 6 mm.

division Composition (% by weight) 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

division Solution heat treatment Average
Grain size (㎛) Orange peel
Incidence rate (%) Temperature (℃) Time in seconds foot
persons
Yes One S2 1,150 90 23.48 <1.0 2 S3 1,150 90 30.45 <1.0 3 S5 1,150 90 25.63 <1.0 4 1,100 90 22.89 <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 <1.0 8 S7 1,150 90 38.52 <1.0 9 S10 1,150 90 23.58 <1.0 10 S11 1,150 90 25.25 <1.0 11 S12 1,150 90 26.84 <1.0 12 S13 1,150 90 21.35 <1.0 ratio
School
Yes 13 S1 1,150 90 21.93 <1.0 14 S4 1,150 90 27.56 <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 <1.0 18 S9 1,150 90 23.75 <1.0 19 S14 1,150 90 26.84 <1.0 20 S17 1,150 90 31.24 <1.0

As shown in Table 2, the S5 steel grades used in Comparative Examples 15 and 16 satisfy all of the component systems of the present invention, but the average crystal grain size was 70 µm at 120 ° C. or higher at 1,180 ° C. where the solution heat treatment temperature exceeded 1,150 ° C. It exceeded, and the orange peel defect after molding more than 15% occurred.

As the solution heat treatment temperature is changed, the grain size of the steel changes, and as the heat treatment temperature and time increase, the average grain size increases. When the average grain size is 70 µm or more, the orange peel defect occurrence rate is 15% or more. It can be seen that the increase significantly compared to other heat treatment conditions.

In addition, for the S1 to S17 steel grades described in Table 1, the calculated values, permeability and σ phase fraction according to equations (1) to (4) were measured and shown in Table 3 below.

division Formula (1) Actual measurement
δ-ferrite
Fraction (%) Formula (2) Permeability
(μ) Formula (3) Formula (4) Actual measurement
σ phase
Fraction (%) foot
persons
Yes One S2 4.8 0 -11.9 1.003 20.2 19.9 0.06 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 ratio
School
Yes 13 S1 7.7 0 -20.1 1.001 17.7 17.2 0.03 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 Equation (1) is positive, the permeability was found to be 1.02 μm or less, particularly the examples of the present invention satisfy 1.012 μ or less, and the calculation according to Equation (2) When the δ-ferrite fraction is 0% or less, it can be seen that the measured δ-ferrite fraction is 0%. In addition, when the σ phase formation index was 24 or more, the σ phase fraction was more than 0.8%, which was close to 1.0%, indicating that the σ phase fraction increased significantly compared to other steel grades.

Comparative Example 13 had a low PREN (Equation (3)) value due to the lack of Cr content and did not meet the corrosion resistance requirements, and the σ phase formation index (Equation (4)) did not even reach 18.

Comparative Example 14 was not satisfied with the formulas (1) and (2) due to the S4 steel grade containing excess Cr, the σ phase fraction was high, the magnetic permeability was measured to be 1.042μ, and the nonmagnetic properties of the present invention was unsatisfactory. . The σ phase formation index also exceeded 24, indicating that the σ phase fraction was close to 1.0%. It was found that σ phase formation was promoted by increasing Cr content to form Cr depleted regions.

In Comparative Example 17, the S8 steel grade containing excessive Mo did not satisfy the formulas (1) and (2), and the σ-phase fraction was high, so that the magnetic permeability was measured to be 1.026 μ, thereby dissatisfying the nonmagnetic properties of the present invention. , the σ phase formation index also exceeded 24, and the σ phase fraction was close to 1.0%. It was found that σ phase formation was promoted by increasing Mo content to form Mo depletion region. This confirms that the Mo should be added at 4.0% or less.

Comparative Example 18 had a high PREN value due to an excessively high content of S9 steel, which did not meet the corrosion resistance requirements.

Comparative Example 19 did not meet the corrosion resistance requirements due to the low PREN value due to the S14 steel grade containing excessive Mn, it can be seen that the corrosion resistance was not secured due to inclusions formed by the increase of Mn content.

Comparative Example 20 exhibited an σ phase formation index exceeding 24 due to S17 steel containing excessive Si, and a magnetic permeability of 1.028 despite satisfying equations (1) and (2) due to the magnetic phase σ phase. High in μ. This was confirmed that Si is effective in improving the corrosion resistance, but when excessive, it promotes the precipitation of intermetallic compounds such as σ phase and thus lowers the corrosion resistance and nonmagnetic properties, so that it should be added at 1.0% or less.

As described above, exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and a person of ordinary skill in the art may be within the scope and spirit of the following claims. It will be understood that various changes and modifications are possible.

Claims (12)

By weight, C: greater than 0 and 0.05% or less, Si: greater than 0 and 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2% or less, remaining Fe and Contains inevitable impurities,
The average grain size is 70 µm or less, the magnetic permeability is 1.012 µm or less,
A nonmagnetic austenitic stainless steel excellent in corrosion resistance that satisfies the following formula (1) and satisfies the pneumatic equivalence index (PREN) represented by the following formula (3) in the range of 20 to 30:
(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
(In this case, Ni, C, Si, Mn, Cr, Mo, Cu, N means content (wt%) of each element)
(3) Cr + 3.3 * Mo + 30 * N-Mn + Si
(In this case, Cr, Mo, N, Mn, Si means the content (wt%) of each element) The method of claim 1,
Non-magnetic austenitic stainless steel having excellent corrosion resistance further comprising Cu: 3.0% by weight. The method of claim 1,
Non-magnetic austenitic stainless steel excellent in corrosion resistance, further comprising Mo: 4.0% by weight. The method of claim 1,
A nonmagnetic austenitic stainless steel having excellent corrosion resistance further comprising B: less than 0.01% by weight. The method of claim 1,
The said stainless steel is a nonmagnetic austenitic stainless steel excellent in corrosion resistance that the calculated δ-ferrite fraction represented by the following formula (2) satisfies 0% or less.
(2) 161 * {[Cr + Mo + 1.5 * Si + 18] / [Ni + 30 * (C + N) + 0.5 * (Cu + Mn) + 36] + 0.262}-161
Here, Cr, Mo, Si, Ni, C, N, Cu, Mn means content (wt%) of each element. delete The method of claim 1,
The stainless steel is a non-magnetic austenitic stainless steel excellent in corrosion resistance that satisfies the range of 18 to 24, the σ phase formation index represented by the following formula (4).
(4) Cr + Mo + 3 * Si
Here, Cr, Mo, and Si mean content (wt%) of each element. delete delete By weight, C: greater than 0 and 0.05% or less, Si: greater than 0 and 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2% or less, remaining Fe and Contains inevitable impurities,
Hot rolling a slab that satisfies the following formula (1) and satisfies the range of 18 to 24 represented by the? Phase formation index represented by the following formula (4); And
And heat-treating the hot rolled material at 1,100 to 1,150 ° C. for 60 to 120 seconds.
A method for producing a nonmagnetic austenitic stainless steel having excellent corrosion resistance in which the calculated δ-ferrite fraction represented by the following formula (2) satisfies 0% or less.
(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
(2) 161 * {[Cr + Mo + 1.5 * Si + 18] / [Ni + 30 * (C + N) + 0.5 * (Cu + Mn) + 36] + 0.262}-161
(In this case, Ni, C, Si, Mn, Cr, Mo, Cu, N means content (wt%) of each element)
(4) Cr + Mo + 3 * Si
Here, Cr, Mo, and Si mean content (wt%) of each element.
delete delete

Images