KR20150073381A - Duplex stainless steel with excellent resistance to stress corrosion cracking - Google Patents

Duplex stainless steel with excellent resistance to stress corrosion cracking Download PDF

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KR20150073381A
KR20150073381A KR1020130161001A KR20130161001A KR20150073381A KR 20150073381 A KR20150073381 A KR 20150073381A KR 1020130161001 A KR1020130161001 A KR 1020130161001A KR 20130161001 A KR20130161001 A KR 20130161001A KR 20150073381 A KR20150073381 A KR 20150073381A
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stainless steel
phase
stress corrosion
corrosion resistance
phase stainless
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KR1020130161001A
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Korean (ko)
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유한진
최점용
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주식회사 포스코
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Abstract

The present invention relates to duplex stainless steel with excellent resistance to stress corrosion cracking comprising: 0.08 wt% or less of C, 0.2-3.0 wt% of Si, 2-4 wt% of Mn, 19-23 wt% of Cr, 0.3-2.5 wt% of Ni, 0.2-0.3 wt% of N, 0.5-2.5 wt% of Cu, 0.2 wt% or less of Mo, and the remainder consisting of Fe and inevitable impurities. Moreover, included are an austenite phase and a ferrite phase as a microstructure. A stress corrosion sensitivity index value is 0.06 or more with respect to an MgCl_2 aqueous solution whose boiling is 42%.

Description

[0001] DUPLEX STAINLESS STEEL WITH EXCELLENT RESISTANCE TO STRESS CORROSION CRACKING [0002]

The present invention relates to a two-phase stainless steel, and more particularly, to a two-phase stainless steel having a formability of an austenitic stainless steel of STS 304 and STS 316 and excellent in stress corrosion resistance.

In general, 18% Cr austenitic stainless steels such as STS 304 steels have been widely used as the base material for household and industrial equipment, with adequate corrosion resistance, weldability and excellent processability. On the other hand, the 18% Cr austenitic stainless steel has a problem that its use range is limited to relieve stress corrosion in a chloride atmosphere. For example, despite the excellent compatibility of 18% Cr austenitic stainless steels, ferritic stainless steels or two-phase stainless steels have been substituted for austenitic stainless steels such as STS 304 in applications where stress corrosion resistance is required.

The two-phase stainless steel is a stainless steel type having a microstructure composed of a mixture of austenite phase and ferrite phase, and exhibits both a characteristic of an austenite phase and a characteristic of a ferrite phase. A variety of two-phase stainless steels have been developed in accordance with the features including all the characteristics of the two-phase stainless steel, such as U.S. Patent Nos. 434094329, 5624504, and 6096441.

Two-phase stainless steels used in high corrosion resistance environments include Al2205 (UNS S 31803 or S32205) in Allegheny Ludlum nominally 22% Cr, 5.5% Ni, 3% Mo and 0.16% N, These steel types have better corrosion resistance than austenitic stainless steels such as STS 304 and STS 316. On the other hand, such a generally used two-phase stainless steel requires a large amount of expensive elements such as Ni and Mo, resulting in an increase in manufacturing cost, and the above-mentioned two-phase stainless steels have STS 304, STS 316 The stainless steel of the present invention is used only in a very limited range in order to open the moldability.

Accordingly, various researches have been conducted to develop a two-phase stainless steel having moldability and processability comparable to those of austenitic stainless steels of STS 304 and STS 316 which are used for general purposes, and which have excellent corrosion resistance and stress corrosion resistance . In addition, various studies have been conducted to lower the production cost and reduce expensive elements in order to use the two-phase stainless steel in a wide range of universal applications.

An object of the present invention is to provide a two-phase stainless steel excellent in stress corrosion resistance.

Another object of the present invention is to provide a two-phase stainless steel having a formability equivalent to STS 304 austenitic stainless steel and having excellent corrosion resistance in a high corrosion-resistant environment.

It is still another object of the present invention to provide a two-phase stainless steel having improved elongation and moldability by appropriately adjusting the addition amount of alloying elements such as Mn, Si, Cu, etc. by lowering the production cost by reducing expensive alloying elements such as Ni and Mo, It is to provide river.

According to one aspect of the present invention, embodiments of the present invention are directed to a method of manufacturing a semiconductor device, comprising, by weight%, 0.08% or less of C, 0.2% to 3.0% of Si, 2% 0.3 to 2.5% of N, 0.2 to 0.3% of N, 0.5 to 2.5% of Cu, and 0.2% of Mo or less and the balance of Fe and unavoidable impurities and contains austenite phase and ferrite phase in microstructure And stainless steel having excellent stress corrosion resistance with a stress corrosion sensitivity index value of 0.06 or more in a boiling 42% MgCl 2 aqueous solution.

The duplex stainless steel may further contain 0.1 to 1.0% W by weight.

In the two-phase stainless steel, Mo may be added as an impurity without being added.

The austenite phase may be 45% to 75% by volume fraction and the ferrite phase may be 25% to 55% by volume fraction.

The amount of fired organic martensite formed in the cold working of the two-phase stainless steel may be 5% or less.

The two-phase stainless steel has an average potential value of 300 mV or more and a maximum current value in an atmosphere of 5% sulfuric acid aqueous solution is 10 / / cm 2 ≪ / RTI >

The two-phase stainless steel may have an elongation of 50% or more, which is an index of moldability.

The two-phase stainless steel may have a yield strength of 500 MPa to 600 MPa and a tensile strength of 800 MPa to 900 MPa.

According to the present invention as described above, it is possible to provide a two-phase stainless steel having excellent stress corrosion resistance.

Further, according to the present invention, it is possible to provide a two-phase stainless steel having moldability at the level of STS 304 austenitic stainless steel and excellent corrosion resistance in a high corrosion-resistant environment.

Further, according to the present invention, there is provided a two-phase stainless steel in which an expensive alloying element such as Ni and Mo is reduced to lower the production cost, and an addition amount of an alloy element such as Mn, Si, Cu, etc. is appropriately controlled to improve elongation and formability can do.

1 is a graph showing the content of Ni and Mo according to the steel types 1 to 9.
2 is a graph showing elongation and stress corrosion sensitivity index values according to the steel types 1 to 9.

The details of other embodiments are included in the detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below, but may be embodied in various forms. In the following description, it is assumed that a part is connected to another part, But also includes a case in which other elements are electrically connected to each other in the middle thereof. In the drawings, parts not relating to the present invention are omitted for clarity of description, and like parts are denoted by the same reference numerals throughout the specification.

Hereinafter, the present invention will be described.

According to an embodiment of the present invention, a two-phase stainless steel having excellent stress corrosion resistance is characterized in that it comprises 0.08% or less of C, 0.2% to 3.0% of Si, 2% to 4% of Mn, 19% % Of Ni, 0.3 to 2.5% of Ni, 0.2 to 0.3% of N, 0.5 to 2.5% of Cu and 0.2% of Mo and the balance of Fe and unavoidable impurities. The microstructure contains austenite phase and ferrite including phase, and boiling (boiling) is the stress corrosion susceptibility value than 0.06 in 42% MgCl 2 aqueous solution. Further, in the above two-phase stainless steel, Mo is not intentionally added and may exist as an impurity in the process of producing the two-phase stainless steel. The duplex stainless steel may further contain 0.1 to 1.0% W by weight.

Hereinafter, the reason for limiting the components of the present invention will be described. In the following,% of the component content means% by weight.

Carbon (C) is an austenite-forming element, which is effective for increasing the strength of materials by solid solution strengthening. However, it is easily combined with carbide-forming elements such as Cr which is effective for corrosion resistance at the ferrite-austenite phase boundary, It is possible to reduce the corrosion resistance by lowering the content. Therefore, in order to maximize the corrosion resistance, the content of C is preferably 0.08% or less.

Silicon (Si) is an element which is partially added for the deoxidizing effect of Si and is concentrated in the ferrite when annealing with a ferrite forming element. Therefore, it can be added in an amount of 0.2% or more for proper ferrite phase fraction. On the other hand, if the content of Si is more than 3.0%, the hardness of the ferrite phase is rapidly increased to lower the elongation, making it difficult to secure the austenite phase for ensuring sufficient elongation. Also, when Si is excessive, slag fluidity during steelmaking may be reduced, and the steel may be combined with oxygen to form inclusions, thereby reducing corrosion resistance. Therefore, it is preferable that the Si content is included in the range of 0.2% to 3.0%.

Nitrogen (N) is one of the elements that contribute to the stabilization of austenite phase together with Ni in 2-phase stainless steel. It is one of the elements which is thickened in austenite phase during annealing heat treatment. The increase of N content is incidental to 2-phase stainless steel The corrosion resistance can be increased and the strength can be increased. On the other hand, the solubility of N varies depending on the content of Mn added. On the other hand, in order to improve the corrosion resistance, N is contained in an amount of not less than 0.2%, and if the N content is too low, it is difficult to secure an appropriate phase fraction. Therefore, it is preferable that the N content is included from 0.2% to 0.3%.

Manganese (Mn) is an element that increases nitrogen solubility and is an austenite forming element. Mn can be used as a substitute for expensive Ni. At this time, when the content of Mn is more than 4%, it becomes difficult to secure the corrosion resistance of STS 304 at the level of austenitic stainless steel. Further, when Mn is added in an excess amount, it has an effect on nitrogen solubility but forms MnS by binding with S, thereby deteriorating corrosion resistance. On the other hand, when the content of Mn is less than 2%, it is difficult to secure a proper austenite phase fraction even by controlling Ni, Cu, N and the like as the austenite forming elements, and the solubility of nitrogen added is low, Can not be obtained. Therefore, the content of Mn is preferably 2% to 4%.

Chromium (Cr) is a ferrite stabilizing element together with Si, which plays a major role in securing the ferrite phase of two-phase stainless steel and is an essential element for securing corrosion resistance. Increasing the content of Cr may increase the corrosion resistance of the two-phase stainless steel, but in order to maintain a predetermined phase fraction in relation to the austenite phase, it is necessary to increase the content of expensive Ni or other austenite phase forming elements, thereby increasing the production cost . Therefore, the content of Cr may be included from 19% to 23% in order to secure the corrosion resistance of STS 304 or higher while maintaining a predetermined phase fraction between the austenite phase and the ferrite phase in the duplex stainless steel.

Nickel (Ni) plays a major role in securing the austenite phase of the two-phase stainless steel as an austenite stabilizing element together with Mn, Cu, and N. In order to reduce the cost, it is possible to prevent the imbalance of the phase fraction that can be caused by the Ni reduction by increasing the Mn and N content of the austenite phase forming elements instead of maximally decreasing the expensive Ni content, It is possible to maintain a predetermined phase fraction balance. On the other hand, firing organic martensite may occur during the cold working of the above-mentioned two-phase stainless steel. In order to suppress the formation of martensite, it is necessary to secure the stability of austenite. . Further, when Ni is contained in an excessive amount, the percentage of austenite phase is increased and it is difficult to secure a predetermined austenite phase fraction. In particular, Ni is expensive, and therefore it is difficult to secure competitiveness compared to STS 304. Therefore, the Ni content is preferably 0.3% to 2.5%.

Copper (Cu) may be contained in an amount of 0.5% or more to 2.5% or less. If Cu is contained in an amount of less than 0.5%, corrosion resistance may be deteriorated, and if Cu is more than 2.5%, the hot workability of the two-phase stainless steel is lowered, Making it difficult to operate.

Mo (Mo) can be 0.2% or less. In the two-phase stainless steel according to the present embodiment, the Mo is not intentionally added and may be added as an impurity in the course of operating the two-phase stainless steel. The Mo is an expensive element, and an increase in the amount of Mo added can increase the production cost. In addition, in the present embodiment, it is possible to obtain the properties , The Mo is preferably contained at 0.2% or less, preferably 0%, which is added at the impurity level.

Tungsten (W) is an austenite-forming element and can be added to replace Mo as an element that improves corrosion resistance. On the other hand, the W may induce the formation of an intermetallic compound at 700 ° C to 1000 ° C during the heat treatment, resulting in deterioration of corrosion resistance and mechanical properties. When the content of W is more than 1%, the corrosion resistance and particularly the elongation rate are drastically reduced owing to the formation of intermetallic compounds. On the other hand, in order to secure predetermined corrosion resistance of the two-phase stainless steel, 0.1% or more of W should be added. Therefore, the content of W may be 0.1% to 1.0%.

The two-phase stainless steel may include austenite phase and ferrite phase as microstructures. The austenite phase may be 45% to 75% by volume fraction and the ferrite phase may be 25% to 55% by volume fraction. When the volume fraction of the austenite phase is less than 45%, excessive austenitization of the austenite forming element occurs within the austenite phase. In addition, when the volume fraction of the austenite phase is less than 45%, sufficient tensile strength of the two-phase stainless steel can be secured by increasing the austenite strength by suppressing the firing organic martensite transformation amount. However, And it is not possible to secure more than 50% of the elongation rate of the STS 304 level. On the other hand, when the austenite phase is more than 75%, the surface cracking occurs during hot rolling and the hot workability is lowered, and the phase fraction of the ferrite phase is not balanced, so that the physical properties of the two-phase stainless steel can be lost. Therefore, it is preferable that the austenite phase has a volume fraction of 45% to 75%.

Further, it is most preferable that the duplex stainless steel comprises only an austenite phase and a ferrite phase. On the other hand, in the two-phase stainless steel, a part of the austenite phase may be transformed into sintered organic martensite during cold working. For example, when the duplex stainless steel is composed of only an austenite phase and a ferrite phase, the ferrite phase may be remained outside the austenite phase, and therefore, the ferrite phase is most preferably 25% to 55% in volume fraction.

Also, the amount of sintered organic martensite formed in cold working of the duplex stainless steel may be 5% or less. The calcined organic martensite is a phase formed when the unstable austenite is deformed, and can induce work hardening to increase the elongation of the two-phase stainless steel. The two-phase stainless steel according to one embodiment of the present invention is adjusted by using an appropriate distribution of alloying elements in order to secure a predetermined stability of the austenite phase so that when the tensile deformation of the two-phase stainless steel is carried out before and after the local necking, Respectively. If the sintered organic martensite is formed abruptly, rapid work hardening is caused, whereby the two-phase stainless steel is cured and the elongation can be drastically reduced. Therefore, it is necessary to control the amount of fired organic martensite, and the amount of fired organic martensite formed when the two-phase stainless steel is cold-worked. When the amount of fired organic martensite is 5% or less, it corresponds to STS 304 Or more, an elongation of 50% or more, preferably an elongation of 55% or more can be secured.

The two-phase stainless steel according to the present embodiment may have a yield strength of 500 MPa to 600 MPa and a tensile strength of 800 MPa to 900 MPa. It is preferable that the yield strength and the tensile strength satisfy a predetermined range. When the yield strength is less than 500 MPa or the tensile strength is less than 800 MPa, the load load of the product manufactured using the two- The thickness of the two-phase stainless steel should be increased to satisfy a predetermined load load suitable for the product. Increasing the thickness can reduce the efficiency of the process and increase the unit cost. On the other hand, when the yield strength is higher than 600 MPa or the tensile strength is higher than 900 MPa, cracks may be generated in the process of forming the two-phase stainless steel, and overloading of the press may occur. Therefore, the two-phase stainless steel according to the present embodiment preferably has a yield strength of 500 MPa to 600 MPa and a tensile strength of 800 MPa to 900 MPa.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the scope of the present invention is not limited by the following examples.

(Temperature, pressure, time) in a 50 kg vacuum dissolving facility using each of stainless steels having component contents (weight%) as shown in Table 1 below to make 120 mm thick ingots. Each of the produced ingots was hot rolled (rolled condition) and cold rolled to obtain cold rolled plates under the same conditions.

In Table 1, Grade 1 to Grade 5 are comparative examples of two-phase stainless steel (Grade 6 to Grade 9) according to an embodiment of the present invention, and Grade 1 and 2 are austenitic stainless steels STS 304 and STS 304, STS 316L, and the steel types 3 to 5 are ordinary two-phase stainless steel STS 329LA, STS 329LD and STS 2507, respectively. Steel types 6 to 9 are steel types satisfying the composition range, the austenite phase fraction, and the sintered martensite-based amount according to the embodiment of the present invention.

The mechanical properties (formability) of each of the steel types 1 to 5 fabricated according to Table 2 were confirmed and the corrosion resistance was evaluated.

Steel grade C Cr Mn Ni Si Cu N Mo W One 0.07 18.3 One 8.3 0.6 0 0.04 0 0 Comparative Example 2 0.14 18 0.7 12.1 0.65 0 0.02 2.1 0 3 0.03 21.3 1.8 2.1 0.78 0.5 0.18 0.6 0 4 0.03 20.1 2.4 2.5 0.5 0.2 0.16 1.4 0 5 0.02 25 0.8 7 0.3 0.2 0.28 3.8 0 6 0.054 19.93 3.03 0.35 2 0.5 0.202 0 0 Example 7 0.051 20.12 3.03 2.05 2 0.8 0.234 0 0 8 0.051 19.87 2.91 0.5 0.865 One 0.24 0 0 9 0.047 21.33 3.04 1.02 1.53 One 0.23 0 0.48

Mechanical properties (formability) Corrosion resistance Steel grade Yield strength The tensile strength Elongation Official potential Bipolar polarization
(Maximum current value, / / cm2) Stress corrosion sensitivity index value (Mpa) (Mpa) (%) (mV) One 280 640 54 290 ○ (15) 0.018 Comparative Example 2 285 562 47 400 ○ (10) 0.021 3 627 807 38 330 (11) 0.033 4 522 715 35 650 ○ (10) 0.036 5 585 850 35 No-pit ◎ (8) 0.065 6 520 810 56 340 ◎ (8) 0.075 7 540 845 60 345 ◎ (8) 0.079 Example 8 510 811 58 320 ◎ (9) 0.091 9 500 800 55 330 ◎ (9) 0.105

1 is a graph showing the content of Ni and Mo according to the steel types 1 to 9.

Referring to FIG. 1, it was confirmed that the content of Ni in the steel types 1 to 5 was 2.1 wt% or more, and on the average was 6.4 wt%. In the steel types 6 to 9, Ni was 2.05 wt% , It was confirmed that it was about 0.98 wt%. Further, referring to the content of Mo, it can be confirmed that the molten steel of the steel types 2 to 5, which are comparative examples except for the steel type 1, is about 2 wt% in terms of Mo, and the steel types 6 to 9 in the examples are 0 wt% of Mo. That is, it can be confirmed that the contents of Ni and Mo in the steel types 6 to 9 of the examples are lower than those of the steel types 1 to 5.

Table 2 shows tensile tests at room temperature in order to evaluate the mechanical properties and formability of the steel types 1 to 9. In the room temperature tensile test, tensile tests were conducted at a speed of 1 mm / min using stainless steel having the components of the steel types 1 to 9 shown in Table 1, and the yield strength, tensile strength and elongation were measured for each steel type .

The two-phase stainless steels 3 to 5, which are general-purpose two-phase stainless steels, and the two-phase stainless steels according to the embodiment of the present invention have relatively low tensile strength and yield strength than the steels 6 to 9 in the case of the austenitic stainless steels 1 and 2 . In the elongation rate, the austenitic stainless steels 1 and 2 have a relatively high value of about 50%, while the general two-phase stainless steels 3 to 5 have a very low elongation of 40% or less. On the other hand, in the case of the two-phase stainless steels according to the embodiment of the present invention, in the case of the steel types 6 to 9, the tensile strength and the yield strength were higher than those of the steel types 1 and 2 and the elongation rates were similar to those of the steel types 1 and 2 It is confirmed that the elongation is 55% or more as shown in Table 2, and it is preferable that the elongation is 55% or more.

Also, referring to Table 1 and Table 2, the formal potential, anodic polarization and stress corrosion sensitivity index values were confirmed to confirm the corrosion resistance. The formal potential was measured by anodic polarization test at a scanning rate of 20 mV / sec in aqueous 3.5% sodium chloride (NaCl) solution at a temperature of 30 ° C. The formula potential is used as a measure for evaluating the resistance of the alloy to formal resistance, which means that the higher the official stiffness, the better the local corrosion resistance of the alloy.

As a result of the evaluation of the formal dislocation as an index of corrosion resistance, the austenitic stainless steels 1 (STS 304) and 2 (STS 316L) were 290 mV and 400 mV, respectively, and the general two-phase stainless steels 3 and 4 329LA and STS 329LD) were 330mV and 650mV, respectively, and STS 2507 showed no-pit formation. On the other hand, in the case of the steel type 6 to the steel type 9 according to the embodiment of the present invention, it was confirmed that the formula potential was higher than that of the steel type 1 at about 300 mV or higher.

Anodic polarization was measured by anodic polarization test at a scanning rate of 20 mV / sec in a 0.5% sulfuric acid aqueous solution at 30 ° C. When the value at which the maximum current flows during the anodic polarization test is referred to as an activation current density, the active current density is an index of corrosion resistance in an aqueous sulfuric acid solution. The activation current density is determined based on the values of STS 304 and STS 316, which are austenitic stainless steels, of 10 to 15 / / cm 2 . That is, when the active current density has a value higher than 15 / / cm 2 , it is represented by X. When the current density of STS 304 and STS 316 is similar to 10 15 A / cm 2 , / cm < 2 & gt ;. It was confirmed that the steel types 1 and 2 of the austenitic stainless steel and the steel types 3 to 4 of the general-purpose two-phase stainless steel have values substantially similar to those of the standard STS 304. On the other hand, it was confirmed that the two-phase stainless steels 6 to 9 according to the present invention had better corrosion resistance in the sulfuric acid atmosphere than the steels 1 to 4. It was confirmed that the maximum current value in the 5% sulfuric acid atmosphere of the two-phase stainless steel according to the embodiment of the present invention is 10 uA / cm 2 or less.

2 is a graph showing elongation and stress corrosion sensitivity index values according to the steel types 1 to 9.

Stress corrosion resistance properties were evaluated to confirm stress corrosion sensitivity index values. Stress corrosion resistance was measured using a 42% aqueous solution of magnesium chloride (MgCl2) at 140 DEG C according to ASTM G129. Table 2 shows the fracture strain ratio, which is a value obtained by dividing the fracture strain of the austenitic stainless steel in the aqueous magnesium chloride solution by the fracture strain of the austenitic stainless steel in the air, as the stress corrosion sensitivity index. The higher the stress corrosion sensitivity index value, the higher the resistance to stress corrosion. As a result of evaluating the stress corrosion resistance, it was confirmed that the stress corrosion sensitivity index values of the steel types 1 and 2 which are austenitic stainless steels are 0.018 and 0.021, which are very low. In addition, it was confirmed that 0.035, 0.036, and 0.065, respectively, were obtained in the case of the two-phase stainless steel steels 3 to 5 used for general purposes, respectively, as compared with the steels 1 and 2. On the other hand, it was confirmed that the duplex stainless steel according to the embodiment of the present invention has 0.075, 0.079, 0.091, and 0.105, respectively, which is about 3.5 times to 6 times higher than the steel types 1 and 2.

In the case of steel type 5, the elongation rate is relatively low. On the other hand, when the formula does not occur at the formal potential and the anodic polarization and stress corrosion sensitivity index values are confirmed, it is confirmed that the internal resistance and the stress corrosion resistance are excellent there was. On the other hand, in the case of the steel type 5, there is a problem that the production cost is increased by an expensive element of Ni and Mo added in a large amount.

That is, it was confirmed that the two-phase stainless steels 6 to 9 according to the embodiment of the present invention have higher yield strength and tensile strength than the austenitic stainless steels 1 and 2 and have similar elongation. Further, it can be seen that the steel type 6 to the steel type 9 according to the embodiment of the present invention have a similar yield strength and tensile strength, but a higher elongation, as compared with the two-phase stainless steels 3 to 5 there was.

From the viewpoint of corrosion resistance, it was confirmed that the steel type 6 to the steel type 9 according to the embodiment of the present invention had a much higher stress corrosion sensitivity index value than those of the austenitic stainless steels 1 and 2, Stress corrosion sensitivity index values were higher than stainless steel. It was also confirmed that the anode polarization characteristics were also excellent in the steel types 6 to 9 according to the examples of the present invention.

The two-phase stainless steel according to the present embodiment has elongation and stress corrosion resistance characteristics superior to those of two-phase stainless steel used for general use, and has elongation similar to that of austenitic stainless steels STS 304 and STS 316L, It is confirmed that the stress corrosion resistance of the stainless steel is very improved. Therefore, the two-phase stainless steel according to the present embodiment can be used for a wide variety of applications such as manufacturing a food processing container which was not applicable due to the low elongation of a two-phase stainless steel used for general purpose due to the excellent elongation and corrosion resistance and a heat exchanger for a water heater, And can be effectively applied in an acidic atmosphere and a chloride atmosphere in which austenitic stainless steel can not be applied due to the improved corrosion resistance.

The two-phase stainless steel according to the present invention can reduce the production cost by reducing the content of expensive Ni and not adding expensive Mo, and can control the addition amount of alloying elements such as N, Mn, Si, Cu, By controlling the phase fraction of austenite and ferrite at the time of treatment and the partition coefficient of the alloying element, it is possible to improve moldability and corrosion characteristics by securing the moldability similar to that of STS 304 and STS 316L.

It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing detailed description, and all changes or modifications derived from the meaning and scope of the claims and the equivalents thereof are included in the scope of the present invention Should be interpreted.

Claims (8)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.08% or less of C, 0.2 to 3.0% of Si, 2 to 4% of Mn, 19 to 23% of Cr, 0.3 to 2.5% of Ni, 0.2 to 0.3% Cu: 0.5% ~ 2.5%, Mo: 0.2% or less, and the remainder Fe and inevitable impurities, and comprising an austenite phase and a ferrite phase in the microstructure, the boiling (boiling) the stress corrosion susceptibility in the MgCl 2 solution Two-phase stainless steel having excellent stress corrosion resistance with an index value of 0.06 or more. The method according to claim 1,
Wherein the two-phase stainless steel further comprises 0.1% to 1.0% W by weight, and W is excellent in stress corrosion resistance. The method according to claim 1,
In the above two-phase stainless steel, Mo is present at 0%, and the two-phase stainless steel having excellent stress corrosion resistance. The method according to claim 1,
Wherein the austenite phase has a volume fraction of 45% to 75%, and the ferrite phase has a volume fraction of 25% to 55%. The method according to claim 1,
The two-phase stainless steel is a two-phase stainless steel excellent in stress corrosion resistance with an amount of sintered organic martensite formed in cold working of 5% or less. The method according to claim 1,
Wherein the two-phase stainless steel has a formaldehyde value of 300 mV or more and a maximum current value of 10 μA / cm 2 or less in a 5% sulfuric acid aqueous solution atmosphere. The method according to claim 1,
The two-phase stainless steel is a two-phase stainless steel excellent in stress corrosion resistance with an elongation of 50% or more, which is an index of formability. The method according to claim 1,
The two-phase stainless steel has a yield strength of 500 MPa to 600 MPa and a tensile strength of 800 MPa to 900 MPa.
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* Cited by examiner, † Cited by third party
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WO2017111250A1 (en) * 2015-12-23 2017-06-29 주식회사 포스코 Lean duplex stainless steel having improved corrosion resistance and machinability, and manufacturing method therefor
CN113025891A (en) * 2021-02-08 2021-06-25 江阴兴澄特种钢铁有限公司 Duplex stainless steel S32101 steel plate and manufacturing method thereof

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017111250A1 (en) * 2015-12-23 2017-06-29 주식회사 포스코 Lean duplex stainless steel having improved corrosion resistance and machinability, and manufacturing method therefor
CN108368592A (en) * 2015-12-23 2018-08-03 株式会社Posco Economizing type two phase stainless steel with improved corrosion resistance and processability and its manufacturing method
JP2019501286A (en) * 2015-12-23 2019-01-17 ポスコＰｏｓｃｏ Lean duplex stainless steel with improved corrosion resistance and workability and method for producing the same
EP3395996A4 (en) * 2015-12-23 2019-03-06 Posco Lean duplex stainless steel having improved corrosion resistance and machinability, and manufacturing method therefor
CN113025891A (en) * 2021-02-08 2021-06-25 江阴兴澄特种钢铁有限公司 Duplex stainless steel S32101 steel plate and manufacturing method thereof
CN113025891B (en) * 2021-02-08 2022-07-22 江阴兴澄特种钢铁有限公司 Duplex stainless steel S32101 steel plate and manufacturing method thereof

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