JP5329634B2 - Duplex stainless steel, duplex stainless steel cast, and duplex stainless steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inexpensive Sn-containing duplex stainless steel, duplex stainless steel slabs, and duplex stainless steel material having good hot productivity. <P>SOLUTION: The duplex stainless steel contains, by mass, 0.03% or less of C, 0.05-1.0% of Si, 0.1-4.0% of Mn, 0.05% or less of P, 0.0001-0.0010% of S, 23.0-28.0% of Cr, 2.0-6.0% of Ni, 0-1.0% of Co, 0.2-3.0% of Cu, 0.01-0.2% of Sn, 0.20-0.30% of N, 0.05% or less of Al, and 0.0010-0.0040% of Ca, wherein Ni+Co is 2.5% or more, with the balance comprising Fe and unavoidable impurities. The ratio Ca/O of the content of Ca to the content of O is 0.3-1.0. The duplex stainless steel slabs and duplex stainless steel material are also provided. <P>COPYRIGHT: (C)2013,JPO&amp;INPIT

Description

  The present invention relates to a duplex stainless steel containing a composite of Cu and Sn and having excellent corrosion resistance and is inexpensive, and can be used as a seawater desalination equipment, tanks for transport ships, various containers, etc. The present invention relates to a phase stainless steel slab and a duplex stainless steel material.

  General-purpose duplex stainless steel contains a large amount of Cr, Mo, Ni, and N, and has good corrosion resistance. However, containing expensive Mo and Ni increases the alloy cost, and the productivity is also good. It's hard to say. As a result, the price of the steel material is not so low, and it is difficult to say that it is often used instead of 316 series, 317 series stainless steel and the like. The duplex stainless steel targeted by the present invention has a pitting corrosion index PI (indicated by the mathematical sum of the contents of the right alloy element / PI = Cr + 3.3Mo + 16N) of more than 28 or more than 30, less than 40 (mass%). The steel has a corrosion resistance equivalent to that of a conventional duplex stainless steel having the above value, the alloy cost is lower than that of the conventional steel, the hot productivity is good, and the manufacturing cost is low. In particular, to develop inexpensive general-purpose duplex stainless steels that reduce the contents of expensive elements Ni and Mo by increasing the contents of N and Mn and adding Cu and Sn in combination. Was the object of the invention.

  As a duplex stainless steel containing Sn, a steel containing 0.01 to 0.1% of Sn as a selective element in a duplex stainless steel containing 25% or more of Cr (Patent Documents 1 and 2 below), an alloy element Steels containing 1% or less or 0.1% Sn in the saving duplex stainless steel (Patent Documents 3 and 4 below) are disclosed. Although these patent documents aim at improving the corrosion resistance by containing Sn, the relationship between the Sn content and the hot manufacturability of the steel material is not specifically described. In addition, steel with a N content of 0.2% or less is targeted.

  N is an element that lowers the hot workability of stainless steel, and ensuring the hot workability of the duplex stainless steel containing N at 0.2% or more at a desired level is less than 0.2%. More difficult than when duplex stainless steel is used. There is no technical document disclosing the hot workability of the duplex stainless steel containing 0.20% or more N and further containing Sn and Cu in combination.

  The present inventors pay attention to the possibility of improving acid resistance and pitting corrosion resistance by Sn and Cu, and the two-phase containing 0.20% or more of N, which has reduced the Mo and Ni contents targeted by the present invention. As a result of investigating the relationship between the contents of Sn and Cu, corrosion resistance and hot manufacturability in stainless steel, the corrosion resistance can be improved by containing 0.01 to 0.2% Sn and 0.2 to 3.0% Cu. Although these properties can be found, it is understood that these duplex stainless steels containing a large amount of Sn and Cu will decrease hot productivity, increase the frequency of steel yield reduction, and expect a significant cost increase. did.

  Looking back at the knowledge regarding the manufacturing technology of conventional Sn-containing duplex stainless steel hot rolled steel materials including Patent Documents 1 to 4, the temperature range of hot brittleness generation due to Sn contained in duplex stainless steel It was clear that there was little knowledge about the relationship with the Sn content and the relationship with the content of other elements.

JP-A-3-158437 JP-A-4-072013 JP 2010-222593 A WO2009-119895 JP 2002-69592 A JP-A-7-118805

Effect of Cu and Ni on Hot Workability of Hot-rolled Mild Steel (ISIJVol.37 (1997) p.217-223)

  The present inventors have clarified the relationship between Sn and Cu contents and hot manufacturability, and by finding out the countermeasures, good hot manufacturability and inexpensive Sn-containing duplex stainless steel and duplex stainless steel slabs And it made it the subject to provide a duplex stainless steel material. Since such alloy element-saving general-purpose duplex stainless steel is expected to have a good balance between corrosion resistance and cost, it is considered that the possibility of being widely used in various fields is increased.

In order to solve the above-mentioned problems, the inventors of the present invention are intended to improve the Sn content and hot manufacturability of the alloy element-saving duplex stainless steel. Etc.,
Further, the Ni content, which is said to suppress embrittlement when Sn and Cu are added in combination, was changed, and a melting material further containing Co was prepared, and the following experiment was performed.

  Tensile test specimens are collected from cast slabs cast from molten materials, subjected to high-temperature tension at 1200 to 700 ° C., and hot ductility is evaluated by drawing (cross-sectional area reduction rate), and hot forging and hot rolling. Thus, a hot rolled steel sheet having a thickness of 12 mm was obtained, and the ear cracking property was evaluated. For some steels, the hot cracking heating temperature and the rolling temperature were changed to evaluate the ear cracking properties, and the correlation with high temperature ductility was obtained.

  As described in Patent Document 5 and Patent Document 6, when the slab drawing generally evaluated by high-temperature tension in the duplex stainless steel is less than 60%, the heat of the slab is often obtained. It is known that significant ear cracking occurs during hot rolling. For this reason, engineers in this field often refining, casting and hot working steel with the goal of at least 60% or more reduction of the slab at high temperatures. However, the inventors have reduced alloy element-saving duplex stainless steel containing 0.1% of Sn (base composition: 25% Cr-4% Ni-1.2% Mo-1.5% Cu-0). .25% N) When the high temperature ductility of the slab was evaluated, it was revealed by several melting experiments that the minimum value of the drawing value was less than 60%. Evaluation of high temperature ductility is performed by heating a parallel part of a round bar of 8 mmφ to 1200 ° C. using a high frequency, then lowering it to a temperature at which a fracture test is performed, pulling and breaking at that temperature at a rate of 20 mm / sec, and shrinking the cross section The rate is obtained. An example of the data is shown in FIG. From this, it was considered that there was little hope to obtain an inexpensive alloy element-saving duplex stainless steel with Sn added.

  The present inventors rarely observed the length of the ear cracks generated by hot rolling a slab of Mo, Ni content-saving Sn-containing general-purpose duplex stainless steel obtained by vacuum melting and casting. It has been discovered that there is a Sn-containing duplex stainless steel material with few ear cracks. In the hot rolling experiment, a slab having a thickness of 90 to 44 mm was heated to 1200 ° C. and then reduced to a thickness of 12 to 6 mm through a plurality of rolling passes, and the finish rolling temperature was controlled to about 900 ° C. Ear cracks occurred on the left and right, but the maximum length of each was added to evaluate the ear crack length. Even if the length of the steel ear cracks was arranged with the minimum value of the hot ductility drawing value of the slab (obtained at about 900 ° C. in FIG. 1), a clean correlation could not be obtained, but as shown in FIG. When the aperture value was arranged at 1000 ° C., it was revealed that a good correlation was exhibited regardless of the Sn content. In FIG. 2, ◯ plots correspond to Sn-A and Sn-B in FIG. 1, and ♦ plots are experimental results examined regardless of other Sn contents.

  In order to find out the conditions under which the above-mentioned steel material with few ear cracks can be obtained reliably, the present inventors conducted further melting, casting and rolling experiments with various element contents changed, evaluated the hot ductility of the slab, The steel ear cracks after rolling were evaluated vigorously. Through the above experiments, based on the obtained knowledge, the present invention has been completed which clearly shows an inexpensive Sn-containing duplex stainless steel.

That is, the gist of the present invention is as follows.
(1) By mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-4.0%,
P: 0.05% or less, S: 0.0001 to 0.0010%, Cr: 23.0 to 28.0%,
Ni: 2.0-6.0%, Co: 0-1.0%, Cu: 0.2-3.0%, Sn: 0.01-0.2%, N: 0.20-0. 30%, Al: 0.05% or less, Ca: 0.0010 to 0.0040%, Ni + Co is 2.5% or more, the balance is Fe and inevitable impurities, Ca and O content Duplex stainless steel having a Ca / O ratio of 0.3 to 1.0.
(2) The duplex stainless steel according to (1), further comprising one or more selected from Mo: 2.0% or less and W: 1.0% or less.
(3) Furthermore, it contains one or more selected from V: 0.05 to 0.5%, Nb: 0.01 to 0.15%, and Ti: 0.003 to 0.05%. The duplex stainless steel according to (1) or (2), wherein
(4) Further, it contains one or more selected from B: 0.0050% or less, Mg: 0.0030% or less, REM: 0.10% or less (1) to The duplex stainless steel according to any one of (3).
(5) A duplex stainless steel slab having the composition according to any one of (1) to (4) and having a fracture drawing value at 1000 ° C. of 70% or more.
(6) A duplex stainless steel material produced by hot working the duplex stainless steel cast according to (5).

  According to the present invention, it is possible to provide steel having improved corrosion resistance compared with conventional steel as seawater desalination equipment, tanks for transport ships, various containers, etc., and excellent balance with cost, contributing to industrial development. The place to do is extremely large.

It is a figure which illustrates the high temperature ductility of Sn containing and an Sn additive-free duplex stainless steel cast. It is a figure which shows the relationship between the ear crack length after hot rolling, and the aperture_diaphragm | restriction at 1000 degreeC.

  Below, the limitation reason as described in (1) of this invention is demonstrated first. In addition, content of each component shows the mass%.

  In the present invention, the stainless steel slab means steel in a state after casting and before being subjected to processing such as hot working or forging, and the stainless steel material is after the slab is processed by various methods. Slab, hot rolled steel sheet, cold rolled steel sheet, steel wire, steel pipe and the like. Stainless steel means all forms of steel such as slabs and steel materials. The above processing includes hot and cold processing.

  C limits the content to 0.03% or less in order to ensure the corrosion resistance of the stainless steel. If the content exceeds 0.03%, Cr carbide is generated during hot rolling, and the corrosion resistance and toughness deteriorate.

  Si is added at 0.05% or more for deoxidation. However, if it exceeds 1.0%, the toughness deteriorates. Therefore, the upper limit is limited to 1.0%. A preferable range is 0.2 to 0.7%.

  Mn has the effect of increasing the austenite phase and improving toughness. Moreover, since it has the effect which suppresses precipitation of nitride, it is preferable to add actively with this invention steel material. Add 0.1% or more for toughness of base metal and weld. However, if it exceeds 4.0%, corrosion resistance and toughness deteriorate. Therefore, the upper limit is limited to 4.0%. The preferred content is 1.0 to 3.5%, more preferably 2.0 to 3.0%.

  P is an element inevitably mixed from the raw material, and is limited to 0.05% or less in order to deteriorate hot workability and toughness. Preferably, it is 0.03% or less.

  S is an element inevitably mixed from the raw material, and also degrades hot workability, toughness, and corrosion resistance, so is limited to 0.0010% or less. Moreover, reducing to less than 0.0001% increases the cost for desulfurization refining. For this reason, it was determined as 0.0001 to 0.0010%. Preferably, it is 0.0002 to 0.0006%.

  Cr is contained at 23.0% or more in order to ensure basic corrosion resistance. On the other hand, if the content exceeds 28.0%, the ferrite phase fraction increases and the toughness and the corrosion resistance of the weld zone are impaired. Therefore, the Cr content is set to 23.0% or more and 28.0% or less. A preferable content is 24.0 to 27.5%.

  Ni is contained in an amount of 2.0% or more in order to stabilize the austenite structure, improve the corrosion resistance and toughness against various acids, and further suppress the decrease in hot workability due to the addition of Sn and Cu. By increasing the Ni content, the nitride precipitation temperature can be lowered. On the other hand, the steel according to the present invention, which is an expensive alloy and is intended for alloy element-saving duplex stainless steel, is limited to a content of 6.0% or less from the viewpoint of cost. The preferred content is 2.5 to 5.5%, more preferably 3.0 to 5.0%.

  Co is an element effective for enhancing the toughness and corrosion resistance of steel, and is an element that suppresses the decrease in hot workability due to the addition of Sn and Cu, and is desirably contained together with Ni. Moreover, when adding, it is preferable to make it contain 0.1% or more. If the content exceeds 1.0%, since it is an expensive element, an effect commensurate with the cost cannot be exhibited, so the upper limit was set to 1.0%. The preferable content in the case of adding is 0.1 to 0.5%.

  It is known from Non-Patent Document 1 that Ni has an action of increasing the solid solubility of Cu and suppressing the generation of a liquid phase having a low melting point due to the addition of Cu and Sn. Co is an element belonging to the same group as Ni. Therefore, increasing the sum of the contents of Ni and Co is considered to suppress a decrease in hot workability due to Cu and Sn. When the present inventors arranged the hot workability of the steel subject to the present invention by the sum of the contents of Ni and Co, it was found that the ear cracking property of the steel material is increased when it is less than 2.5%. For this reason, the range of Ni + Co was set to 2.5% or more.

  Cu is an element that increases the corrosion resistance of stainless steel to acids, and has the effect of improving toughness. In this invention, in order to improve corrosion resistance, it is contained 0.2% or more with 0.01% or more of Sn. If the content exceeds 3.0%, the solid solubility will be exceeded during hot rolling, and εCu will precipitate and embrittlement will occur, so the upper limit was made 3.0%. A preferable content when Cu is contained is 0.5 to 2.0%.

  Sn is contained in order to improve the corrosion resistance of the steel of the present invention. For this purpose, a content of at least 0.01% is necessary. Furthermore, it is preferable to make it contain 0.02% or more. On the other hand, Sn is an element that hinders the hot manufacturability of steel. In the alloying element type saving duplex stainless steel targeted by the present invention, especially at the interface between the ferrite phase and the austenite phase at 900 ° C. or lower. Reduce strength. The degree of the reduction depends on the contents of S, Ca, and O. However, even if other limitations in the present invention are added, if the content exceeds 0.2%, the hot productivity cannot be prevented from being lowered. The upper limit of the content was set to 0.2%.

  N is an effective element that improves the strength and corrosion resistance by dissolving in the austenite phase. For this reason, it is contained by 0.20% or more. Since it is possible to reduce Ni by increasing the amount of N, it is an element to be actively added. On the other hand, the upper limit of the content must be limited within the solid solubility limit of N. The solid solubility limit of N increases with the Cr and Mn contents. However, when the content of N exceeds 0.30% in the steel of the present invention, Cr nitride precipitates and the toughness and corrosion resistance are impaired. In order to inhibit hot manufacturability, the upper limit of the content was set to 0.30%. A preferable content is 0.20 to 0.28%.

  Al is a deoxidizing element of steel, and is contained together with 0.05% or more of Si in order to reduce oxygen in the steel as necessary. In the Sn-containing steel, the reduction of the oxygen amount is essential for securing hot productivity, and for this purpose, the content of 0.003% or more is necessary. On the other hand, Al is an element having a relatively large affinity with N, and if added excessively, AlN is generated and inhibits the toughness of stainless steel. The degree depends on the N content, but when Al exceeds 0.05%, the toughness deteriorates remarkably, so the upper limit of the content is set to 0.05%. Preferably it is 0.04% or less.

  Ca is an important element for hot manufacturability of steel, and it is necessary to contain O and S in the steel as inclusions to improve hot manufacturability. In the steel of the present invention, 0.0010% or more is contained for that purpose. Moreover, excessive addition reduces pitting corrosion resistance. Therefore, the upper limit of the content is set to 0.0040%.

  The ratio Ca / O of the content of O and Ca is an important component index for improving the hot manufacturability and corrosion resistance of the steel of the present invention. In order to improve the hot manufacturability of the Sn-containing steel, the lower limit of Ca / O is limited. The high temperature ductility of the Sn-containing steel decreases particularly at a temperature of 900 ° C. or less, but if the Ca / O value is less than 0.3, the high temperature ductility at 1000 ° C. also decreases, and hot productivity is greatly impaired. For this reason, Ca / O is limited to 0.3 or more in the steel of the present invention. On the other hand, when Ca is excessively added and Ca / O exceeds 1.0, pitting corrosion resistance is impaired. Moreover, when Ca becomes excessive, the high temperature ductility over 1000-1100 degreeC will also be impaired. For this reason, the upper limit of Ca / O was set to 1.0. Preferably it is 0.4-0.8.

  O is an unavoidable impurity, and its upper limit was not particularly defined. However, O is an important element constituting an oxide that is representative of non-metallic inclusions, and the composition control of the oxide improves hot manufacturability. Very important to. In addition, the formation of coarse clustered oxides causes surface defects. For this reason, the content needs to be limited low. In the present invention, as described above, the O content is limited by setting the ratio of the Ca content and the O content to 0.3 or more. The upper limit of the O content is preferably 0.005% or less.

In the invention of (2), elements that additionally enhance the corrosion resistance are defined. The reason for the limitation will be described.
Mo is a very effective element that additionally increases the corrosion resistance of stainless steel, and can be contained as necessary. In order to improve corrosion resistance, it is preferable to contain 0.2% or more. On the other hand, it is an expensive element, and in the steel of the present invention, the upper limit is set to a content of 2.0% from the viewpoint of suppressing the alloy cost of the steel.
W, like Mo, is an element that additionally improves the corrosion resistance of stainless steel, and can be added as necessary. For the purpose of enhancing the corrosion resistance in the steel of the present invention, 1.0% is contained at the upper limit. A preferable content is 0.1 to 0.8%.

  Next, the contents defined in (3) will be described for elements that have a greater tendency to form nitrides than Cr. V, Nb, and Ti can be added as necessary, and when contained in a very small amount, the corrosion resistance tends to be improved.

  The nitrides and carbides formed by V are generated during the hot working and cooling of the steel material, and have the effect of increasing the corrosion resistance. Although sufficient confirmation has not been made for this reason, there is a possibility of suppressing the generation rate of chromium nitride at 700 ° C. or lower. In order to improve this corrosion resistance, it is desirable to contain 0.05% or more. If the content exceeds 0.5%, coarse V-based carbonitrides are produced and the toughness deteriorates. Therefore, the upper limit is limited to 0.5%. The preferable content when added is in the range of 0.1 to 0.3%.

  Nitride and carbide formed by Nb are produced during the hot working and cooling of the steel material, and have the effect of enhancing the corrosion resistance. Although sufficient confirmation has not been made for this reason, there is a possibility of suppressing the generation rate of chromium nitride at 700 ° C. or lower. In order to improve this corrosion resistance, it is desirable to contain 0.01% or more. On the other hand, excessive addition causes precipitation as an undissolved precipitate during heating before hot rolling, which impairs toughness, so the upper limit of its content was set to 0.15%. The preferable content range in the case of adding is 0.03% to 0.10%.

  Ti is an element that forms oxides, nitrides, and sulfides in an extremely small amount, and solidifies the steel and refines the crystal grains of the high-temperature heating structure. Further, like V and Nb, it also has a property of substituting for a part of chromium nitride chromium. A Ti precipitate is formed when the content is 0.003% or more. On the other hand, if it exceeds 0.05% and is contained in the duplex stainless steel, coarse TiN is generated and the toughness of the steel is inhibited. For this reason, the upper limit of the content was set to 0.05%. A suitable content of Ti is 0.005 to 0.020%.

  Furthermore, in order to further improve the hot workability described in (4) of the present invention, B, Mg, and REM to be contained as necessary are limited as follows.

  B, Mg, and REM are all elements that improve the hot workability of steel, and it is desirable to add one or more of them for that purpose. Since excessive addition of B, Mg, and REM decreases hot workability and toughness, the upper limit of the content is determined as follows. B is 0.0050%, Mg is 0.0030%, and REM is 0.10%. The preferred contents are B: 0.0005 to 0.0030%, Mg: 0.0001 to 0.0015%, and REM: 0.005 to 0.05%, respectively. Here, REM is the total content of lanthanoid rare earth elements such as La and Ce.

  As described above, by having the characteristics described in any one of (1) to (4) of the present invention described above, it is possible to remarkably improve the hot productivity of general-purpose duplex stainless steel containing Sn, At the slab stage, the fracture drawing value at 1000 ° C. is 70% or more. Moreover, it is possible to obtain a duplex stainless steel material with high yield and few surface defects by subjecting the slab to processing including hot working.

  Examples are described below. Table 1 shows the chemical composition of the test steel. The remainder of the components listed in Table 1 is Fe and inevitable impurity elements. Moreover, the part in which content is not described about the component shown in Table 1 shows that it is an impurity level, REM means a lanthanoid type rare earth element, and content shows the sum total of these elements.

  All the steels were cast pieces with a thickness of 100 mm, and the fracture drawing was evaluated first. In the evaluation, the parallel part of the 8 mmφ round bar was heated to 1200 ° C. using a high frequency and then lowered to the temperature (1000 ° C.) at which the breaking test was performed. Shrinkage was determined. Table 2 shows that the drawing at break was 70% or more as ◯, 60 to less than 70% as Δ, and less than 60% as x. The slab was made into a 60 mm thick steel slab by hot forging, and this was used as a hot rolled material. Hot rolling is performed at a predetermined temperature of 1150 to 1250 ° C., and then performed by a two-stage rolling mill in a laboratory. After rolling, the sheet thickness is adjusted at 25 mm, and finish rolling is performed from 1000 ° C. to 900 ° C. The final finish rolling was carried out so that the final plate thickness was 12 mm and the plate width was 120 mm. The maximum value of the ear crack generated in the left and right ears of this hot-rolled steel sheet was measured, and the sum of the left and right maximum values was obtained. Table 2 shows the sum of the ear cracks evaluated as ○ when 5 mm is less than 5 mm, Δ when 10 mm is exceeded, and x.

  Further, this steel sheet was subjected to solution heat treatment. In the solution heat treatment, a steel plate was inserted into a heat treatment furnace set at 1050 ° C., extracted after a soaking time of 5 minutes, and then cooled to room temperature.

The corrosion resistance of the steel sheet was evaluated by the corrosion rate in sulfuric acid.
Corrosion rate in sulfuric acid is 3mm thick x 25mm wide x 25mm long test piece, 6h immersion test in 15%, 40 ° C sulfuric acid containing 2000ppm Cl ion. The weight loss rate was determined. ○ the corrosion rate is less than 0.1g / m ² · hr in sulfuric acid, △ a 0.1~0.3g / m ² · hr, the evaluation result of evaluating as × 0.3g / m ² · hr than It is shown in Table 2.

Impact characteristics were measured with Charpy specimens taken long in the width direction. The test piece was a full size, 2 mm V notch was processed in the rolling direction, two tests were conducted at -20 ° C., and the impact characteristics were evaluated by the average value. Impact value 100 J / cm ² than the ○, the 50~100J / cm ² △, was evaluated as × less than 50 J / cm ^2, as described in Table 2.

  As shown in the examples shown in Table 2, the alloy element-saving general-purpose duplex stainless steel Nos. 1 to 23 satisfying the conditions of the present invention have good hot manufacturability, corrosion resistance and impact properties, while Steel Nos. AK and MT which do not satisfy the conditions of the invention were inferior in hot manufacturability, corrosion resistance and impact properties. Moreover, although the comparative example L satisfy | fills a characteristic, since Co is contained in large quantities, it is inferior in terms of cost. Comparative Example U is S31803 steel, which has good hot manufacturability, corrosion resistance, and manufacturability. However, the contents of Ni and Mo are high and the cost intended by the present invention is inferior.

As can be seen from the above examples, according to the present invention, it was clarified that the addition of Sn and Cu improves the corrosion resistance, and provides an alloy element-saving general-purpose duplex stainless steel with good hot productivity and low cost.

According to the present invention, it is possible to provide a low-cost alloy element-saving general-purpose duplex stainless steel material with improved corrosion resistance, which contributes to the industry such as seawater desalination equipment, tanks for transport ships, various containers, etc. However, it is extremely large.

Claims (6)

% By mass
C: 0.03% or less,
Si: 0.05 to 1.0%,
Mn: 0.1 to 4.0%,
P: 0.05% or less,
S: 0.0001 to 0.0010%,
Cr: 23.0-28.0%,
Ni: 2.0-6.0%,
Co: 0 to 1.0%,
Cu: 0.2-3.0%,
Sn: 0.01-0.2%
N: 0.20 to 0.30%,
Al: 0.05% or less,
Ca: 0.0010 to 0.0040% is contained, Ni + Co is 2.5% or more, the balance is made of Fe and inevitable impurities, and the Ca / O content ratio Ca / O is 0.3 to 1 Duplex stainless steel that is 0.0. Furthermore,
Mo: 2.0% or less,
The duplex stainless steel according to claim 1, comprising one or more selected from W: 1.0% or less. Furthermore,
V: 0.05-0.5%
Nb: 0.01 to 0.15%,
The duplex stainless steel according to claim 1 or 2, comprising one or more selected from Ti: 0.003 to 0.05%. Furthermore,
B: 0.0050% or less,
Mg: 0.0030% or less,
The duplex stainless steel according to any one of claims 1 to 3, comprising one or more selected from REM: 0.10% or less.   A duplex stainless steel slab having the composition according to any one of claims 1 to 4 and having a fracture drawing value at 1000 ° C of 70% or more. A duplex stainless steel material produced by hot working the duplex stainless steel slab according to claim 5.

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