Austenitic stainless steel containing tungsten

Abstract

This invention provides austenitic stainless steel with improved corrosion resistance and low-temperature shock absorption energy due to the addition of tungsten. [Solution] An austenitic stainless steel is provided, containing 16-20 weight ratios of chromium (Cr), 4.5-9 weight ratios of manganese (Mn), 3-6 weight ratios of nickel (Ni), 0.001-0.3 weight ratios of carbon (C), 0.1-0.35 weight ratios of nitrogen (N), tungsten (W) in a weight ratio of more than 0.0 and less than or equal to 2.0, with the remainder being iron (Fe) and other unavoidable impurities. According to the present invention, by adding a small amount of copper, the pitting potential is improved compared to existing 304LSTS, resulting in superior corrosion resistance, and it has the advantage of being price-competitive compared to existing austenitic stainless steel. Furthermore, the shock absorption energy at approximately -196°C may be 41J or more.

Description

[Technical Field]

[0001] The present invention relates to an austenitic stainless steel containing tungsten. [Background Art]

[0002] Existing 304L STS and 316L STS materials used for LNG carriers have stabilized the austenite phase down to temperatures below room temperature, but the addition of expensive nickel (Ni) imposes a cost burden. For this reason, the current situation is that it is necessary to develop a material with superior price competitiveness compared to 304L STS and 316L STS. For austenitic materials, it is necessary to reduce the content of high-cost nickel, and add inexpensive manganese (Mn), carbon (C) and nitrogen (N) elements so that the austenite phase can be stabilized even at room temperature. In addition, according to the regulations of the International Maritime Organization (IMO), materials used for LNG carriers must have an impact absorption energy of 41 J or more at -196°C, and it is necessary to develop a chemical composition for an austenitic stainless steel material whose corrosion resistance is equivalent or superior to that of 304L STS and 316L STS. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Korean Registered Patent No. 10-1198486 (published on July 4, 2012) [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] One object of the present invention is to provide an austenitic stainless steel with improved corrosion resistance and low-temperature impact absorption energy by adding tungsten.

[0005] Another object of the present invention is to provide an austenitic stainless steel containing nickel, manganese, carbon, and nitrogen in certain proportions to improve phase stability, shock absorption energy at cryogenic temperatures, workability, and corrosion resistance, as well as a method for producing the same. [Means for solving the problem]

[0006] To achieve the above objectives, the present invention provides an austenitic stainless steel containing 16-20 weight ratios of chromium (Cr), 4.5-9 weight ratios of manganese (Mn), 3-6 weight ratios of nickel (Ni), 0.001-0.3 weight ratios of carbon (C), 0.1-0.35 weight ratios of nitrogen (N), tungsten (W) in a weight ratio of more than 0.0 and less than or equal to 2.0, with the remainder being iron (Fe) and other unavoidable impurities. [Effects of the Invention]

[0007] According to the present invention, by adding a small amount of tungsten, the pitting potential is improved compared to existing 304L STS, resulting in superior corrosion resistance, and it has the advantage of being price-competitive compared to existing austenitic stainless steel. Furthermore, the shock absorption energy at approximately -196°C may be 41J or more.

[0008] Furthermore, the austenitic stainless steel according to the present invention is economical because it does not reduce or add expensive nickel and molybdenum content. It stabilizes the austenite phase up to room temperature by adding inexpensive manganese, carbon, and nitrogen, improves workability and corrosion resistance by adding carbon and nitrogen in a certain ratio, and improves the shock absorption energy at cryogenic temperatures compared to conventionally developed high-manganese stainless steel by controlling the composition ratio of nickel, manganese, carbon, and nitrogen. [Brief explanation of the drawing]

[0009] [Figure 1] This is an image of the microstructure of austenitic stainless steel according to the nickel and tungsten content of the embodiments of the present invention. [Figure 2]This is a graph showing the pitting potential evaluation results for an embodiment of the present invention. [Figure 3] This is a graph showing the shock absorption energy results for an embodiment of the present invention. [Figure 4] The image shows a phase map of the austenitic stainless steel according to the composition ratio of the embodiment of the present invention, and an image of the austenitic stainless steel corresponding to the phase map, taken with an optical microscope, with a scale bar of 75 μm. [Figure 5] This image shows a phase map based on the composition ratio of austenitic stainless steel according to an embodiment of the present invention, along with the shock absorption energy. [Figure 6] This shows the results of a machinability experiment on test specimens manufactured according to the composition ratio of the austenitic stainless steel in the embodiment of the present invention. [Figure 7] This shows the results of an anodic polarization experiment on a test specimen manufactured according to the composition ratio of the austenitic stainless steel in the embodiment of the present invention. [Figure 8] This image shows the results of a salt spray test on a test specimen manufactured according to the composition ratio of the austenitic stainless steel in the embodiment of the present invention. [Figure 9] This image shows the results of an intergranular corrosion test on a test specimen manufactured according to the composition ratio of the austenitic stainless steel in the embodiment of the present invention. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described in detail below with reference to the attached drawings. While the present invention can take on various forms through numerous modifications, specific embodiments will be illustrated in the drawings and described in detail in the text. However, it should be understood that this does not limit the present invention to any particular disclosure, but rather includes all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention. Similar reference numerals have been used for similar components in the illustration of each drawing. In the attached drawings, the dimensions of structures are shown enlarged for clarity of the present invention.

[0011] Terms such as "first," "second," etc., can be used to describe a variety of components, but the components should not be limited by such terms. The terms are used solely for the purpose of distinguishing one component from another. For example, the first component may be named the second component, and similarly, the second component may be named the first component, without departing from the scope of the rights of the present invention.

[0012] The terms used in this application are used solely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as “includes” or “having” are intended to specify the existence of features, figures, stages, operations, components, parts, or combinations thereof described in the specification, and should be understood not to preemptively exclude the possibility of the existence or addition of one or more other features, figures, stages, operations, components, parts, or combinations thereof.

[0013] On the other hand, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by a person of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meaning in the context of the relevant art, and not in an ideal or overly formal sense unless explicitly defined herein.

[0014] Austenitic stainless steel according to embodiments of the present invention may contain chromium (Cr) in a weight ratio of 16 to 20, manganese (Mn) in a weight ratio of 4.5 to 9, nickel (Ni) in a weight ratio of 3 to 6, carbon (C) in a weight ratio of 0.001 to 0.3, nitrogen (N) in a weight ratio of 0.1 to 0.35, tungsten (W) in a weight ratio of more than 0.0 and less than or equal to 2.0, the remainder being iron (Fe) and other unavoidable impurities.

[0015] In one embodiment, the austenitic stainless steel may comprise nickel and tungsten in a weight ratio of 4 to 9.

[0016] In one embodiment, the austenitic stainless steel may comprise nickel and tungsten in a weight ratio of 4.27 to 8.2.

[0017] In one embodiment, the austenitic stainless steel may comprise carbon and nitrogen in a weight ratio of 0.15 to 0.45.

[0018] The reason for the numerical limitation of the present invention will be described below. (1) Chromium (Cr): about 16 to 20 weight ratio Chromium is added because it can form a passive film on the surface of stainless steel to impart corrosion resistance. Therefore, in order to secure the corrosion resistance of the austenitic stainless steel and stabilize the austenite phase, chromium is required to be at about 16 weight ratio or more. If chromium exceeds about 20 weight ratio, a sigma phase that weakens corrosion resistance may be formed. Therefore, the austenitic stainless steel may comprise chromium in a weight ratio of about 16 to 20.

[0019] (2) Manganese: about 4.5 to 9 weight ratio Manganese can stabilize the austenite phase and increase the solid solubility of nitrogen. When manganese is added in an amount of about 4.5 weight ratio or more, the above effects can be obtained. However, if manganese exceeds about 9 weight ratio, it combines with impurities such as sulfur (S) and oxygen (O) to form manganese sulfide and manganese oxide, which may reduce the corrosion resistance and mechanical properties of the austenitic stainless steel. Therefore, the austenitic stainless steel may comprise manganese in a weight ratio of about 4.5 to 9.

[0020] (3) Nickel: about 3 to 6 weight ratio Nickel can stabilize the austenite phase, increasing toughness and formability. It also improves shock absorption energy at approximately -196°C by minimizing the increase in pitting potential and interstitial element content. However, since nickel is an expensive element, adding excess nickel increases manufacturing costs. Therefore, the austenitic stainless steel can contain nickel in a weight ratio of approximately 3-6.

[0021] (4) Carbon: Approximately 0.001~0.3 weight ratio Carbon can stabilize the austenite phase and suppress martensitic transformation. However, carbon forms carbides, which reduces corrosion resistance. Therefore, the austenitic stainless steel can contain carbon in a weight ratio of approximately 0.001 to 0.3. Specifically, it can contain carbon in a weight ratio of 0.05 to 0.3.

[0022] (5) Nitrogen: Approximately 0.1-0.35 by weight Nitrogen can stabilize the austenite phase and can partially replace nickel. However, nitrogen forms nitrides, which reduce corrosion resistance and toughness. Therefore, the austenitic stainless steel may contain nitrogen at a weight ratio of approximately 0.1 to 0.35.

[0023] (6) Tungsten: Weight ratio of approximately 0.0 to 2.0 Tungsten, along with nickel, plays a role in improving the corrosion resistance of stainless steel. A tendency for the pitting potential to increase with increasing tungsten content was observed. At weight ratios of 4.7218 or higher Ni+2W content, the pitting potential was higher than that of 304L STS, and at weight ratios of 6.2590 or higher Ni+2W content, the pitting potential was equivalent to or higher than that of 316L STS. Therefore, it can be concluded that nickel and tungsten contribute to improving the corrosion resistance properties of stainless steel.

[0024] In one embodiment, the austenitic stainless steel may have a pitting potential of 250-500mV or 350-500mV at 16-20°C with a 3.5% NaCl solution.

[0025] In one embodiment, the austenitic stainless steel may have an impact absorption energy of 41 to 100 J or 60 to 100 J at approximately -196°C. If the impact absorption energy is less than approximately 41 J, it may not be suitable for LNG vessels.

[0026] In one embodiment, the austenitic stainless steel can satisfy the pitting potential expressed by the following formula 1 when the Ni+2W content is in the range of 4.27 to 8.2 by weight:

[0027] [Formula 1] E pit =0.05263(Ni+2W)+0.03769

[0028] In formula 1 above, Ni and W represent the weight percentage of each element.

[0029] In one embodiment, the austenitic stainless steel may contain nickel and manganese in a weight ratio of 8 to 15 or 8.5 to 15. When the total content of nickel and manganese and the total content of carbon and nitrogen as described above are satisfied, the austenitic stainless steel can stabilize the austenite phase even when the amount of nickel added is reduced.

[0030] For example, to stabilize the austenite phase while reducing the amount of nickel added, inexpensive manganese is added. However, manganese is only 0.5 times more effective than nickel in stabilizing the austenite phase. Therefore, carbon and nitrogen are added to compensate for this. Carbon and nitrogen are 15 times and 30 times more effective, respectively, in stabilizing the austenite phase than nickel. However, if the amount of carbon and nitrogen added increases excessively, there is a disadvantage in that the shock absorption energy at low temperatures decreases. Only by satisfying the aforementioned range can the austenite phase be stabilized and excellent shock absorption energy be exhibited at cryogenic temperatures.

[0031] Furthermore, in the austenitic stainless steel, the total carbon and nitrogen content may be 0.33% by weight or less, 0.3% by weight or less, 0.295% by weight or less, 0.285% by weight or less, 0.225% to 0.33% by weight, 0.255% to 0.3% by weight, or 0.25% to 0.295% by weight. By satisfying the above-mentioned total carbon and nitrogen content, excellent workability and cryogenic shock absorption energy can be achieved even if the manganese content is reduced.

[0032] Specifically, in the austenitic stainless steel, the weight ratio of carbon to the total weight of carbon and nitrogen [C / (C+N)] may be 0.1 to 0.7 or 0.2 to 0.5. By satisfying the weight ratio of carbon to the total content of carbon and nitrogen as described above, it is possible to exhibit corrosion resistance at the level of existing 304STS materials.

[0033] Furthermore, when tool wear is measured using an end mill under dry conditions, the machinability of the austenitic stainless steel may be greater than 0 and less than 0.15 mm or greater than 0 and less than 0.125 mm.

[0034] Furthermore, the austenitic stainless steel may satisfy one or more of the following equations 2 to 5:

[0035] [Formula 2] (Ni+Mn)+165.94(C+N)≧49.47

[0036] [Formula 3] (Ni+Mn)-27.28(C+N)≧2.10

[0037] [Formula 4] (Ni+Mn)≧12.3

[0038] [Formula 5] (Ni+Mn)+13.133(C+N)≧1.73

[0039] In formulas 2 to 5 above, Ni, Mn, C, and N represent the weight percentages of nickel, manganese, carbon, and nitrogen, respectively.

[0040] Specifically, if the austenitic stainless steel satisfies one or more of the formulas selected from formulas 2 to 5, it can stabilize the austenite phase down to room temperature and exhibit excellent shock absorption energy at extremely low temperatures (-196°C).

[0041] Equations 2 and 5 were derived based on the phase map of austenitic stainless steel, representing the γ-phase stable region, and satisfy the region in which the austenite structure is stable at room temperature.

[0042] Equations 2 to 4 above were derived based on data showing the phase map and shock absorption energy of austenitic stainless steel, and are equations that simultaneously satisfy the γ phase stable region and shock absorption energy of 41 J or more.

[0043] The present invention will be described in detail below with reference to examples for the purpose of understanding it. However, the following examples are merely illustrative of the content of the present invention, and the scope of the present invention is not limited to these examples. The examples of the present invention are provided to give a more complete explanation of the present invention to a person with average knowledge of the art.

[0044] <Example 1> Nitrogen gas was injected into a vacuum induction melting furnace (VIM), and tungsten was added to steel with chemical components of Cr 16-20 wt%, Mn 4.5-9 wt%, Ni 3-6 wt%, C 0.05-0.3 wt%, and N 0.1-0.35 wt% to produce small steel ingots. After heating the small steel ingots to approximately 1200°C, they were hot-rolled to produce plate-shaped materials with a thickness of approximately 11.5 mm. The nitrogen content was adjusted by controlling the amount of nitrogen injected into the VIM and the reaction time. The Ni+2W content was set to approximately 4.9 by weight.

[0045] <Example 2> A small steel ingot was manufactured in the same manner as in Example 1, except that the Ni+2W content was set to approximately 5.5349 by weight.

[0046] <Example 3> A small steel ingot was manufactured in the same manner as in Example 1, except that the Ni+2W content was set to approximately 5.85 by weight.

[0047] <Example 4> A small steel ingot was manufactured in the same manner as in Example 1, except that the Ni+2W content was set to approximately 7.52 by weight.

[0048] <Comparative Example 1> A small steel ingot was manufactured in the same manner as in Example 1, except that the Ni+2W content was set to approximately 4.27 by weight.

[0049] <Comparative Example 2> A commercial 304L STS was used.

[0050] <Comparative Example 3> A commercial 316L STS was used.

[0051] <Experimental Example 1> Figure 1 shows an image of the microstructure observed in an embodiment of the present invention, which was observed using an optical microscope. Referring to Figure 1, it was confirmed that even when the tungsten content increased, only austenite structures were observed in the microstructure, and no delta-ferrite structures were observed. Furthermore, annealed twins were observed within the crystal grains, and the crystal grain boundaries appeared as straight lines, with no precipitates formed during cooling observed at the crystal grain boundaries.

[0052] Figure 2 is a graph showing the pitting potential of the embodiments according to the present invention. Figure 2 shows the results of measuring the pitting potential of austenitic stainless steel with a Ni+2W content varied from 4 wt% to 8.5 wt% (including Examples 1 to 4 and Comparative Examples 1 to 3) under the conditions of 3.5 wt% NaCl, 16 to 20°C, 0.2 mV / s (potential sweep rate), and SiC1500 grit (Surface finish). Referring to Figure 2, it was observed that the pitting potential gradually increased as the Ni+2W content increased. This confirmed that the embodiments according to the invention have a superior pitting potential and excellent corrosion resistance compared to existing 304L STS. Specifically, we confirmed that a Ni+2W content of 4.7218 wt% or more can ensure a pitting potential equivalent to or better than that of 304L STS, and a Ni+2W content of 6.2590 wt% or more can ensure a pitting potential equivalent to or better than that of 316L STS.

[0053] Figure 3 is a graph showing the shock absorption energy results for the embodiments according to the present invention. The shock absorption energy was measured using a Charpy impact tester (Tinius Olsen, IT542E) according to ISO 148-1: Metal Charpy impact test. For LNG vessels, the shock absorption energy at approximately -196°C must be approximately 41 J or more. All of Examples 1 to 4 recorded a shock absorption energy of approximately 60 J or more, and it was confirmed that the shock absorption energy at low temperatures gradually increased as the Ni+2W content increased.

[0054] <Example 5> 1) Manufacturing of small steel ingots After charging the raw materials Fe, Cr, Mn, Ni, and C into a crucible, the crucible was placed inside a chamber, and a vacuum was created to remove water vapor, oxygen, and nitrogen present inside the chamber.

[0055] After injecting high-purity Ar and high-purity nitrogen (N) gases into a vacuum, an electric current was passed through an induction heating furnace to heat the inside of the crucible to 1530°C. This caused the raw materials to melt, and the introduced elements were uniformly distributed. At this time, the nitrogen concentration in the molten steel was controlled by adjusting the gas pressure. After melting, the molten steel was poured into a mold to produce rectangular steel ingots (44-45mm × 28-30mm × 67-70mm).

[0056] 2) Rolling A rolling process was used to manufacture a plate shape from a small steel ingot. The small steel ingot was maintained at 1200°C for 2 hours, and then plastically deformed in a rolling process to create a flat, long plate shape. During this process, the small steel ingot was heated to maintain low processing stresses in order to shape it into a plate.

[0057] 3) Heat treatment The flattened plates were subjected to normalizing heat treatment, which involved heating to 1130°C, maintaining the temperature for 1 hour, and then water cooling.

[0058] <Experimental Example 2> To confirm the phase stability of the austenitic stainless steel according to the present invention, austenitic stainless steel fabricated with each component was observed using an optical microscope, and a phase map of the austenitic stainless steel was shown. The results are shown in Figure 4 and Table 1.

[0059] [Table 1] [Table 1-1] [Table 1-2] [Table 1-3]

[0060] Figure 4 is a phase map of austenitic stainless steel based on its composition ratio, created based on the results in Table 1. Table 1 shows the results of observing the microstructure of each sample based on its composition ratio using an optical microscope. Figure 4 confirms that the austenite phase is stabilized up to room temperature when the nickel and manganese (Ni+Mn) content is 6% by weight or more, and the carbon and nitrogen (C+N) content is 0.225% by weight or more. Specifically, based on the phase map, mathematical formulas corresponding to the γ phase stable region were derived, which are shown in the following formulas 1 and 2. When formulas 1 and 2 are satisfied, the austenite phase can be stabilized up to room temperature.

[0061] [Formula 1] (Ni+Mn)+165.94(C+N)≧49.47

[0062] [Formula 2] (Ni+Mn)+13.133(C+N)≧1.73

[0063] In equations 1 and 2, Ni represents the weight percentage of nickel, Mn represents the weight percentage of manganese, C represents the weight percentage of carbon, and N represents the weight percentage of nitrogen.

[0064] <Experimental Example 3> To confirm the shock absorption properties of the austenitic stainless steel according to the present invention, the shock absorption energy was measured, and based on the shock absorption energy and the phase map obtained in Experimental Example 2, the composition ratio of austenitic stainless steel having a certain level of shock absorption energy while maintaining phase stability at room temperature was determined. The results are shown in Figure 5 and Table 2.

[0065] The shock absorption energy was obtained through the following shock tests.

[0066] Test specimens were taken from sound areas of the plates (shrinkage holes were present in the top portion of the steel ingot), and standard specimen sizes (10 × 10 × 55 mm) were taken in the rolling direction. Notches (2 mm V-notches) were machined perpendicular to the rolling surface, and six impact test specimens were machined from each plate.

[0067] Impact tests were conducted at -196°C. Test specimens were immersed at -196°C for 30 minutes, then tested in an impact testing machine according to ASTM A370-20 standards. Two specimens were tested at each test temperature.

[0068] [Table 2]

[0069] Figure 5 is an image showing the phase map and shock absorption energy of austenitic stainless steel based on its composition ratio. As can be seen in Figure 5, stability is improved when the nickel and manganese (Ni+Mn) content is 8% by weight or more, and the carbon and nitrogen (C+N) content is 0.225% by weight or more.

[0070] Table 2 shows the results of impact absorption energy measurements for test specimens manufactured according to the composition ratio of austenitic stainless steel.

[0071] Table 2 shows that austenitic stainless steel satisfies the requirements for structural stability at room temperature and shock absorption energy of 41 J or more at low temperatures (-196°C). It was confirmed that when the nickel and manganese (Ni+Mn) content is 8.5% by weight or more, and the carbon and nitrogen (C+N) content is 0.225% by weight or more, the austenitic structural stability and shock absorption energy of 41 J or more are satisfied.

[0072] <Experimental Example 4> To confirm the machinability of the austenitic stainless steel according to the present invention, machinability tests were conducted on test specimens of austenitic stainless steel with different composition ratios and on 316 stainless steel (STS), and the results are shown in Figure 6.

[0073] The aforementioned machinability experiment was conducted using an end mill under dry conditions, with tool wear measured and evaluated after 5 passes. The machining conditions are shown in Table 3 below. The composition ratio of each test specimen is shown in Table 4, in weight percent.

[0074] [Table 3]

[0075] [Table 4]

[0076] Figure 6 shows the results of machinability experiments on test specimens manufactured according to the composition ratio of austenitic stainless steel. As can be seen in Figure 6, it was confirmed that machinability is excellent when the sum of carbon and nitrogen (C+N) is 0.33% by weight or less.

[0077] <Experimental Example 5> To confirm the corrosion resistance of the austenitic stainless steel according to the present invention, anodic polarization tests, salt spray tests, and intergranular corrosion tests were conducted on test specimens of austenitic stainless steel according to their composition ratio, as well as on existing commercial materials, 304 stainless steel (STS) and 316 stainless steel (STS). The results are shown in Figures 7 to 9 and Table 5.

[0078] The aforementioned anodic polarization test was conducted in accordance with ASTM G5, using a 3.5 wt% NaCl (seawater) solution and maintaining a temperature of 25°C.

[0079] The aforementioned salt spray test was conducted according to KS D 9502:2020, and the test was carried out by KTR (certified testing). The solution used was (50±5) g / L NaCl, and the temperature was maintained at 35±2°C for 500 hours. The size of the test specimen was W24 × L(40-50) × T(2-3) mm 3 Three samples were tested for each alloy.

[0080] The aforementioned intergranular corrosion test evaluated the degree of sensitization of the grain boundaries in accordance with ASTM A262-15 (2021), and after immersion in 10% oxalic acid (25°C), a measurement of 1 mA·cm was taken. -2 After applying the solution for 90 seconds to corrode the sample, the presence or absence of intergranular corrosion was determined by observing the surface.

[0081] [Table 5]

[0082] Figure 7 shows the results of anodic polarization experiments on test specimens manufactured according to the composition ratio of austenitic stainless steel. As can be seen from Figure 7 and Table 5, the pitting potential of the economical austenitic stainless steel according to the present invention is equivalent to or higher than that of 304 stainless steel, and a pitting potential almost similar to that of 316 stainless steel was confirmed.

[0083] Figure 8 is an image showing the results of a salt spray test on test specimens manufactured according to the composition ratio of austenitic stainless steel. As can be seen in Figure 8 and Table 5, it was confirmed that the specimens did not suffer damage or change in mass despite being exposed to salt water for 500 hours. In particular, the corrosion resistance of the austenitic stainless steel of the present invention was evaluated and compared with that of existing commercial materials, STS304 and STS316, and it was confirmed that the austenitic stainless steel of the present invention has corrosion resistance equal to or better than that of STS316.

[0084] Figure 9 is an image showing the results of intergranular corrosion tests on test specimens manufactured according to the composition ratio of austenitic stainless steel. As can be seen in Figure 9, it was confirmed that intergranular corrosion does not occur in the economical austenitic stainless steel according to the present invention.

[0085] This demonstrates that the austenitic stainless steel of the present invention has strong corrosion resistance.

[0086] While preferred embodiments of the present invention have been described above with reference to the present invention, those skilled in the art will understand that the present invention can be modified and altered in various ways without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. Austenitic stainless steel containing 16-20 weight ratios of chromium (Cr), 4.5-9 weight ratios of manganese (Mn), 3-6 weight ratios of nickel (Ni), 0.001-0.3 weight ratios of carbon (C), 0.1-0.35 weight ratios of nitrogen (N), tungsten (W) in a weight ratio of more than 0.0 and less than or equal to 2.0, with the remainder being iron (Fe) and other unavoidable impurities.

2. The austenitic stainless steel according to claim 1, wherein the austenitic stainless steel contains nickel and tungsten in a weight ratio of 4 to 9.

3. The austenitic stainless steel according to claim 2, wherein the austenitic stainless steel contains nickel and tungsten in a weight ratio of 4.27 to 8.

2.

4. The austenitic stainless steel according to claim 1, wherein the austenitic stainless steel contains carbon and nitrogen in a weight ratio of 0.15 to 0.

45.

5. The austenitic stainless steel according to claim 1, wherein the austenitic stainless steel has a pitting potential of 250 to 500 mV at 16 to 20°C with a 3.5% NaCl solution.

6. The austenitic stainless steel according to claim 5, wherein the austenitic stainless steel has a pitting potential of 350 to 500 mV at 16 to 20°C with a 3.5% NaCl solution.

7. The austenitic stainless steel according to claim 1, wherein the austenitic stainless steel has an impact absorption energy of 60 to 100 J at -196°C.

8. The austenitic stainless steel according to claim 1 satisfies the pitting potential expressed by the following formula 1: [Formula 1] E ｐｉｔ =0.05263(Ni+2W)+0.03769 In formula 1 above, Ni and W represent the weight percentage of each element.

9. The austenitic stainless steel according to claim 4, wherein the austenitic stainless steel contains nickel and manganese in a weight ratio of 8 to 15.

10. The austenitic stainless steel according to claim 9, wherein the austenitic stainless steel contains nickel and manganese in a weight ratio of 8.5 to 15, and carbon and nitrogen in a weight ratio of 0.225 to 0.

33.

11. The austenitic stainless steel according to claim 10, wherein when tool wear is measured using an end mill under dry conditions, the machinability of the austenitic stainless steel is greater than 0 and less than or equal to 0.15 mm.

12. The austenitic stainless steel according to any one of claims 1 to 11, wherein the weight ratio of carbon to the total weight of carbon and nitrogen [C / (C+N)] is 0.1 to 0.

7.

13. The austenitic stainless steel according to claim 9, satisfying one or more conditions selected from the following formulas 2 to 5: [Formula 2] (Ni+Mn)+165.94(C+N)≧49.47 [Formula 3] (Ni+Mn)-27.28(C+N)≧2.10 [Formula 4] (Ni+Mn)≧12.3 [Formula 5] (Ni+Mn)+13.133(C+N)≧1.73 In formulas 2 to 5 above, Ni, Mn, C, and N represent the weight percent of nickel, manganese, carbon, and nitrogen, respectively.

14. The austenitic stainless steel according to claim 13, satisfying the conditions of formulas 2 and 5.

15. The austenitic stainless steel according to claim 13, satisfying the conditions of formulas 2 to 4.

16. The austenitic stainless steel according to claim 4, wherein the total content of carbon and nitrogen is 0.33% by weight or less.

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