JP6437062B2 - Duplex stainless steel and clad steel for clad steel - Google Patents

Description

  The present invention relates to a clad steel using a duplex stainless steel having excellent corrosion resistance as a laminated material, a clad steel that can be used as a tank for a chemical transport ship, a seawater desalination device, various containers, and the like, and for the clad steel The present invention relates to a duplex stainless steel used as a bonding material.

  Clad steel is composed of a base material and a laminated material. The base material is a relatively inexpensive steel such as carbon steel, and is responsible for the basic mechanical properties of clad steel such as strength and toughness. A relatively expensive steel is used for the laminated material, and special functions suitable for the use of the clad steel, such as corrosion resistance against a corrosive environment, are taken. There is a chemical transport ship tank as an application of clad steel made of stainless steel as a laminated material, and it is often used as a tank bulkhead at a part to be welded and joined with carbon steel outside the double hull. The stainless steel generally used as a laminated material of this clad steel is austenitic stainless steel including SUS316L, and there are few application examples using a duplex stainless steel.

  There is a disclosure about a method for producing clad steel using a duplex stainless steel as a laminated material (Patent Documents 1 and 2), and examples in which SUS304, SUS304L, SUS329J1, SUS329J3L, and SUS329J4L are combined are shown. When using the clad steel as it is rolled, it is necessary to suppress precipitates that deteriorate the corrosion resistance of the laminated material such as carbide and σ phase that are precipitated on the laminated material during hot rolling. In the disclosed manufacturing method, the corrosion resistance of the laminated material and the strength and toughness of the base material are ensured by the regulation of the rolling temperature and the regulation of the cooling method after rolling.

  From the viewpoint of reducing the susceptibility to precipitation of σ phase during hot rolling, a laminated material of duplex stainless steel and its clad steel material, which has a pitting corrosion temperature of 50 ° C. or more as defined by a formula for reducing the amount of Si to 0.15% or less, A manufacturing method disclosed in Patent Document 3 and combined with rolling conditions similar to the contents shown in Patent Documents 1 and 2 is disclosed.

  Duplex stainless steel has the demerit that it has high susceptibility to precipitation of sigma phase in the hot state due to its component characteristics of high Cr and Mo contents, and the above three patent documents show countermeasures against the problem. It is a thing.

  The duplex stainless steel also has a characteristic of high pitting corrosion resistance due to its component characteristics of high Cr and Mo contents. Factors that impair the pitting corrosion resistance of the duplex stainless steel used as a laminated material include a minute σ phase precipitated during the hot rolling described above and chromium nitride. These precipitates form a Cr-depleted region around the precipitate, and can be a starting point for pitting corrosion. On the other hand, as an inclusion that impairs the pitting corrosion resistance of stainless steel, sulfide can be cited. MnS and CaS are known as typical sulfides that impair pitting corrosion resistance. Therefore, as a method for increasing the pitting corrosion resistance of stainless steel, reducing the S content to a low value has been implemented as a universal component design.

  Duplex stainless steel is a stainless steel with poor hot workability, and even if the S content is reduced, ear cracks may occur during hot rolling. Therefore, various methods have been proposed as a countermeasure for hot workability, the amount of S is reduced to an extremely low value of 3 ppm or less (Patent Document 4), and Ca is further added to fix S in steel as CaS. (Non-Patent Document 1). However, when Ca is added, the CaS produced as described above may become a starting point of pitting corrosion and may reduce pitting corrosion resistance.

  On the other hand, Patent Document 5 discloses a method for improving the pitting corrosion resistance of stainless steel by appropriately adjusting the addition amounts of Al and Ca to generate oxide inclusions containing Ca. ing. However, Patent Document 5 does not disclose or suggest the relationship between the S content in steel and the formation of inclusions. Since S is inevitably mixed from the raw material and reacts with Ca in the steel, CaS is easily generated by the addition of Ca. Thus, by adding Ca, sulfide-based inclusions such as CaS are generated, and this CaS or the like may become a starting point of pitting corrosion and impair the corrosion resistance of the steel. Patent Document 5 does not disclose or suggest the problem of a decrease in corrosion resistance due to the formation of CaS. Therefore, the stainless steel disclosed in Patent Document 5 cannot be said to have sufficiently improved pitting corrosion resistance. .

  Moreover, although the laminated material of the clad steel which this invention makes object is used with hot processing, patent document 5 is disclosing only the stainless steel in which solution heat treatment is performed as a product example. Therefore, when the stainless steel disclosed in Patent Document 5 is used as the laminated material while being hot-worked, the presence of dislocations due to the work and the influence of other precipitates are assumed. Therefore, even if the stainless steel described in Patent Document 5 is directly applied as a laminated material of clad steel, the problem of the present invention has not been solved.

JP-A-60-216984 Japanese Patent Laid-Open No. 62-110880 JP 2014-114466 A JP-A-1-219144 Japanese Patent Publication No.54-24364

S. Tsuge.Effect of impurity and microalloying elements on the hot workability of duplex stainless steels.Proc. Int. Conf. On Stainless Steels, Chiba, Japan, 1991, p.799-806

  The present invention is a duplex stainless steel that is prevented from being deteriorated in corrosion resistance due to CaS, and has corrosion resistance and hot workability equivalent to solution heat treatment even when it is hot-rolled without being subjected to solution heat treatment. And it aims at provision of the clad steel which used the said duplex stainless steel as a bonding material.

  In order to solve the above-mentioned problems, the present inventors have first made 22Cr-3Mo-6Ni-, which is a typical duplex stainless steel, in order to clarify the solution for the duplex stainless steel targeted by the present invention. N-type SUS329J3L steel was used as a basic composition, and a melting material was produced in which the contents of Al, Ca, O, B, etc., which are said to improve hot productivity, were changed. In the melting experiment, in order to control the composition of oxides in steel, in addition to the commonly used MgO crucible, use a CaO crucible, use a flux with varying basicity for deoxidation and desulfurization, and add flux Various duplex stainless steels were dissolved by combining a change in amount, a deoxidizing agent, a desulfurizing agent addition amount, a change in addition time, and the like. Furthermore, in the same manner, melting of duplex stainless steel with other basic composition was added.

  The hot workability of duplex stainless steel used as a bonding material based on this melted material is evaluated by the length of the ear cracks during hot rolling, and the pitting corrosion occurrence temperature and hardness of the bonding material are determined according to the ASTM G48 ferric chloride test. And Vickers hardness measurement, and using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer, the composition of the oxide present in the surface layer of the laminated material was determined.

  The inventors set the maximum length of the ear cracks generated on the left and right, respectively, for the above-mentioned rolled material of 12 mm thickness: about 400 mm length of the rolled regular portion of the duplex stainless steel plate of 12 mm thickness × 180 mm width × 600 mm length, respectively. The sum of the left and right maximum lengths was counted as the ear crack length. The result of making this result correspond to the measured value of the oxide composition (Ca / Al) on the surface of the laminated material is shown in FIG.

  The clad laminated material studied in this development is in a cooled state after hot working, and includes internal strain and fine precipitates, oxide inclusions, and sulfide inclusions in the process without heat treatment. ing. The pitting corrosion resistance of the laminated material is governed by the effects of these strains, precipitates and inclusions. To maintain the same pitting corrosion resistance as that of the solution heat-treated clad steel, the amount of precipitates and inclusions The present inventors thought that it was necessary to highly control the form and composition, and proceeded with research and development. As a result, the value of the weight ratio of Ca to Al (Ca / Al) in the oxide inclusions having a maximum diameter of 5 μm or more existing in the clad laminated material surface layer portion is 0.5 to 3.5. Knowing that the condition duplex stainless steel is used as a laminated material, the hot workability of the laminated material and the pitting corrosion resistance of the laminated material of clad steel can be achieved in the state of hot rolling or cold rolling. did.

  The inventors further changed various conditions in order to find a condition in which there is little ear cracking during rolling of the laminated material and the difference between the pitting corrosion occurrence temperature A and the pitting corrosion occurrence temperature B of the laminated material after clad rolling is small. Melting / casting / rolling experiments were conducted, and hot workability evaluation and pitting corrosion resistance evaluation were conducted energetically. Through the above experiments, the present invention was completed based on the obtained knowledge.

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: 0.1-6.0%, P: 0.05% or less, S: 0.0001 -0.0014%, Cr: 20.0-28.0%, Ni: 0.5-9.0%, Mo: 0.12-5.0 % , N : 0.05-0.35 %, in containing 0.001 to 0.004%, the balance being Fe and unavoidable impurities, the steel surface: a l: 0.003~0.05%, Ca : 0.0005~0.0040%, O maximum diameter 5μm or more sizes Ca and Al in a weight ratio of oxide inclusions in (Ca / Al) clad steel duplex stainless steel which is characterized in that 0.5 to 3.5.
(2) Further, by mass%, W: 3.0% or less, Co: 1.0% or less, Cu: 3.0% or less, V: 0.5% or less, Nb: 0.15% or less, Ti: The duplex stainless steel for clad steel according to (1), comprising at least one of 0.05% or less, B: 0.0050% or less, and Mg: 0.0030% or less.
( 3 ) A clad steel characterized in that the duplex stainless steel of (1) or (2 ) above is used as a combination material, and the base material is carbon steel.
( 4 ) By mass%, C: 0.03% or less, Si: 0.05 to 1.0%, Mn: 0.1 to 6.0%, P: 0.05% or less, S: 0.0001 -0.0014%, Cr: 20.0-28.0%, Ni: 0.5-9.0%, Mo: 0.12-5.0%, N: 0.05-0.35%, Al: 0.002 to 0.05%, O: 0.001 to 0.0052%, the balance consists of Fe and inevitable impurities,
Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. Pitting corrosion occurrence of duplex stainless steel having a composition in which the corrosion resistance index PREW represented by the formula (1) is in a range of −1.0 to +1.0, Ca is not added, and heat treatment for solution. Against temperature
The clad steel according to ( 3 ), wherein the pitting corrosion temperature of the laminated material is higher by −5 ° C. or more.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained.
(5) By mass%, C: 0.03% or less, Si: 0.05 to 1.0%, Mn: 0.1 to 6.0%, P: 0.05% or less, S: 0.0001 -0.0014%, Cr: 20.0-28.0%, Ni: 0.5-9.0%, Mo: 0.12-5.0%, N: 0.05-0.35%, Al: 0.002 to 0.05%, O: 0.001 to 0.0052%,
Further, by mass%, W: 3.0% or less, Co: 1.0% or less, Cu: 3.0% or less, V: 0.5% or less, Nb: 0.15% or less, Ti: 0.05 %, B: 0.0050% or less, Mg: at least one of 0.0030% or less, the balance consists of Fe and inevitable impurities,
Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. (1) A hole in a duplex stainless steel having a difference in corrosion resistance index PREW represented by the formula in the range of -1.0 to +1.0, having a composition to which Ca is not added, and subjected to solution heat treatment With respect to the eclipse temperature
The clad steel according to (3), wherein the pitting corrosion temperature of the laminated material is higher by −5 ° C. or more.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained.
(6) By mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-6.0%, P: 0.05% or less, S: 0.0001 -0.0014%, Cr: 20.0-28.0%, Ni: 0.5-9.0%, Mo: 0.12-5.0%, N: 0.05-0.35%, Al: 0.002 to 0.05%, O: 0.001 to 0.0052%, the balance consists of Fe and inevitable impurities,
Element Cr contained in the composition of the mating member, Mn, W, the difference of N, the content of M o and (percent), Cr: -1.0% ~ + 1.0 %, Mn: -1.0% ~ + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. Hardness of duplex stainless steel having a composition in which corrosion resistance index PREW represented by the following formula (1) is within a range of −1.0 to +1.0, Ca is not added, and solution heat treatment is performed. Against
1 . Having a 05 times 1.30 times the hardness characterized Rukoto (3) clad steel according to.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained.
(7) By mass%, C: 0.03% or less, Si: 0.05 to 1.0%, Mn: 0.1 to 6.0%, P: 0.05% or less, S: 0.0001 -0.0014%, Cr: 20.0-28.0%, Ni: 0.5-9.0%, Mo: 0.12-5.0%, N: 0.05-0.35%, Al: 0.002 to 0.05%, O: 0.001 to 0.0052%,
Further, by mass%, W: 3.0% or less, Co: 1.0% or less, Cu: 3.0% or less, V: 0.5% or less, Nb: 0.15% or less, Ti: 0.05 %, B: 0.0050% or less, Mg: at least one of 0.0030% or less, the balance consists of Fe and inevitable impurities,
Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. The difference in the corrosion resistance index PREW represented by the formula (1) is in the range of -1.0 to +1.0, the hardness of the duplex stainless steel having a composition to which Ca is not added and subjected to solution heat treatment. On the other hand,
The clad steel according to (3), having a hardness of 1.05 times or more and 1.30 times or less.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained.
(8) By mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-6.0%, P: 0.05% or less, S: 0.0001 -0.0014%, Cr: 20.0-28.0%, Ni: 0.5-9.0%, Mo: 0.12-5.0%, N: 0.05-0.35%, Al: 0.002 to 0.05%, O: 0.001 to 0.0052%, the balance consists of Fe and inevitable impurities,
Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. (1) A hole in a duplex stainless steel having a difference in corrosion resistance index PREW represented by the formula in the range of -1.0 to +1.0, having a composition to which Ca is not added, and subjected to solution heat treatment With respect to the eclipse temperature
The pitting corrosion occurrence temperature of the laminated material is higher than -5 ° C, and
The clad steel according to (3), which has a hardness of 1.05 times or more and 1.30 times or less of the hardness of the duplex stainless steel.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained.
(9) By mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-6.0%, P: 0.05% or less, S: 0.0001 -0.0014%, Cr: 20.0-28.0%, Ni: 0.5-9.0%, Mo: 0.12-5.0%, N: 0.05-0.35%, Al: 0.002 to 0.05%, O: 0.001 to 0.0052%,
Further, by mass%, W: 3.0% or less, Co: 1.0% or less, Cu: 3.0% or less, V: 0.5% or less, Nb: 0.15% or less, Ti: 0.05 %, B: 0.0050% or less, Mg: at least one of 0.0030% or less, the balance consists of Fe and inevitable impurities,
Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. (1) A hole in a duplex stainless steel having a difference in corrosion resistance index PREW represented by the formula in the range of -1.0 to +1.0, having a composition to which Ca is not added, and subjected to solution heat treatment With respect to the eclipse temperature
The pitting corrosion occurrence temperature of the laminated material is higher than -5 ° C, and
The clad steel according to (3), which has a hardness of 1.05 times or more and 1.30 times or less of the hardness of the duplex stainless steel.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained.

  According to the present invention, it is possible to provide clad steel with an excellent balance between cost and corrosion resistance in a state of hot rolling or cold rolling, and can be used for tanks of transport ships, seawater desalination equipment, various containers, etc. Therefore, the place that contributes to the development of the industry is extremely large.

The weight ratio (Ca / Al) of Ca and Al of oxide inclusions having a maximum diameter of 5 μm or more of the surface layer of the laminated material produced by hot rolling using duplex stainless steel having a basic composition of SUS329J3L It is a graph which shows the relationship of the ear crack length which generate | occur | produced in the steel material of thickness 12mm of the said laminated material. A secondary electron image obtained by observing oxide inclusions present on the surface of a duplex stainless steel laminated material with a scanning electron microscope and a maximum diameter of 5 μm or more obtained by energy dispersive X-ray analysis. It is a graph which shows the relationship between the weight ratio (Ca / Al) of Ca and Al of an oxide type inclusion, and the pitting corrosion generation temperature of the laminated material.

  In the present invention, the clad steel is composed of a base material and a laminated material, the base material is responsible for the basic mechanical properties of the clad steel, such as strength and toughness, and the laminated material is made of relatively expensive steel and is corroded. Steel with special functionality in application, such as corrosion resistance to the environment. The base material is made of relatively inexpensive steel such as carbon steel and is not particularly limited.

  In general, clad steel is manufactured by hot working or cold working, and has various forms such as a steel plate, a steel pipe, a wire, a forged material, and the present invention is also intended for these various forms of clad steel. There are clad steels that are finally annealed, pickled, or annealed / polished after the dimensions of the clad steel are determined by processing, but they are economical to use in the state of hot and cold work. Clad steel is the main subject of the present invention.

  Below, the component of the duplex stainless steel for laminated materials of clad steel of this invention is demonstrated first. In addition, content of each component shows the mass%.

  C limits the content to 0.03% or less in order to ensure the corrosion resistance of the duplex 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 0.8%.

  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 6.0%, corrosion resistance and toughness deteriorate. Therefore, the upper limit is limited to 6.0%. The preferred content is 0.3 to 4%, more preferably 0.5 to 3%.

  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 deteriorates hot workability, toughness and corrosion resistance, so is limited to 0.0014% 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 0.0014%. Preferably, it is 0.0002 to 0.0006%.

  The amount of S in the duplex stainless steel is usually refined to 0.001% or less with the recent progress in smelting technology. In this case, when a strong sulfide-forming element is not added, sulfide that inhibits corrosion resistance is rarely generated, and pitting resistance is maintained high. On the other hand, in the steel of the present invention, Ca, which is a strong sulfide-forming element, is added. For this reason, a part of S in steel is combined with Ca to form CaS. The present invention for controlling the oxide composition so that this CaS does not become the starting point of pitting corrosion will be described in detail in the section describing the oxide composition rule.

  Cr is contained in an amount of 20.0% or more in order to ensure the basic corrosion resistance of the duplex stainless steel. 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 20.0% or more and 28.0% or less. A preferable content is 20.5 to 27.5%.

  Ni is contained in an amount of 0.5% or more in order to stabilize the austenite structure and improve the corrosion resistance and toughness against various acids. 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 9.0% or less from the viewpoint of cost. The preferred content is 1.0 to 8.0%, more preferably 1.5 to 7.5%.

  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. A more preferable lower limit is more than 1.5%, and further preferably 2.0% or more. On the other hand, it is an expensive element, and in the steel of the present invention, the upper limit is 5.0% from the viewpoint of suppressing the alloy cost of the steel. A more preferable upper limit is 4.0%, still more preferably 3.5%.

  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, 3.0% is contained at the upper limit.

  Co is an element effective for enhancing the toughness and corrosion resistance of steel, and is added as necessary. In addition, it is preferable to contain Co with Ni, and when adding, it is preferable to 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%.

  Cu is an element that enhances the corrosion resistance of stainless steel to acids and has an effect of improving toughness. In the present invention, Cu is added as necessary. In order to improve corrosion resistance, it is good to contain 0.1% or more. On the other hand, if the content exceeds 3.0%, the solid solubility exceeds the solid solubility during hot rolling, and εCu precipitates to cause embrittlement, so the upper limit was made 3.0%. A preferable content when Cu is contained is 0.5 to 2.0%.

  N is an effective element that improves the strength and corrosion resistance by dissolving in the austenite phase. For this reason, 0.05% or more is contained. 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 0.35% in the steel of the present invention, Cr nitride is precipitated and the toughness and corrosion resistance are impaired. In order to inhibit hot productivity, the upper limit of the content was set to 0.35%. A preferable content is 0.08 to 0.32%.

  Next, V, Nb, and Ti, which have a greater tendency to form nitrides than Cr, will be described. 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, 0.05% or more is contained. 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 the corrosion resistance, the content is 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%.

  B is an element that improves the hot workability of steel and is added as necessary. On the contrary, excessive addition lowers hot workability and toughness, so the upper limit of the content was set to 0.0050%.

  Al is a deoxidizing element for steel, and is contained together with 0.05% or more of Si in order to reduce oxygen in the steel. In the present invention, it is essential for controlling the oxide composition to enhance hot workability and pitting corrosion resistance, and it is necessary to contain 0.003% or more. 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 the hot manufacturability of steel in the present invention, and it is necessary to contain O and S in the steel as inclusions to improve the hot manufacturability. . In the steel of the present invention, 0.0005% or more is contained for that purpose. However, as described above, there is a problem that CaS is generated by the addition of Ca, so excessive addition reduces the pitting corrosion resistance. Therefore, the upper limit of the content is set to 0.0040%.

  Mg is an element that is added as necessary for improving the hot workability of the steel and refining the solidified structure. In the steel of the present invention, it is good to contain 0.0003% or more. Moreover, excessive addition reduces pitting corrosion resistance. Therefore, the upper limit of the content is set to 0.0030%.

  O is an inevitable impurity and is an important element constituting oxides that are representative of non-metallic inclusions, and the composition control of the oxides is hot in a duplex stainless steel used as a clad steel laminate. It is very important for improvement of manufacturability and pitting corrosion resistance of laminated materials. In the present invention for controlling the composition of the oxide, the oxygen content needs to be 0.001% or more, and the content is specified to be 0.001% or more. In addition, the formation of coarse clustered oxides causes surface defects. For this reason, the content needs to be limited low. For this reason, the upper limit of O content was defined as 0.004% or less.

  In addition, you may contain elements other than the above in the range which does not impair the effect of this invention. For example, in order to further improve the hot workability of the duplex stainless steel for clad steel of the present invention, REM can be added as necessary. REM is a general term for lanthanoid rare earth elements and is an element that shakes the effect of improving the hot workability of steel. REM includes elements such as Y, La, Ce, and Nd. One or more kinds can be added for the purpose of improving hot workability. In any case, excessive addition conversely reduces hot workability and toughness, so the upper limit of the content is preferably 0.10% as the total amount of REM. A preferable content is 0.005 to 0.05%.

  Next, the oxide inclusions to be measured on the steel surface of the duplex stainless steel for clad steel of the present invention will be described.

  The weight ratio of Ca to Al (Ca / Al) in oxide inclusions is an important index for improving the hot workability and corrosion resistance of the duplex stainless steel for clad steel of the present invention. The range of 0.5 to 3.5 was determined by development.

  Moreover, the pitting corrosion resistance of the duplex stainless steel for clad steel is dominated by relatively large oxide inclusions having a maximum diameter of 5 μm or more existing on the surface of the steel material and sulfide existing therearound. In the duplex stainless steel to which Ca is added, CaS is present in the steel and can easily dissolve in a corrosive environment to become a pitting corrosion origin. However, in the duplex stainless steel for clad steel according to the present invention containing Ca as an essential element, the weight ratio of Ca and Al in the oxide inclusions having a maximum diameter of 5 μm or more (Ca / Al). Is controlled to 0.5 to 3.5, pitting corrosion is prevented from occurring starting from sulfides such as CaS, and high pitting corrosion resistance is imparted.

  Although its mechanism of action has not been fully clarified, the liquidity in the micro pits generated by the dissolution of sulfide inclusions such as CaS is a low pH environment where the steel begins to dissolve. As an example, there is a possibility that an action of suppressing dissolution of steel is generated by dissolving an appropriate (Ca / Al) oxide and bringing liquidity to the alkali side. The Apart from some assumed mechanisms, the inventors cannot suppress the occurrence of pitting corrosion when (Ca / Al) is less than 0.5, while (Ca / Al) is 3 When the value exceeds .5, experimental results have been obtained in which the hot workability of the steel is likely to deteriorate. For this reason, (Ca / Al) was set to 0.5 to 3.5.

  In the present invention, the weight ratio of Ca and Al (Ca / Al) in the oxide inclusion is determined as follows. First, in the range of 5000 μm × 5000 μm of an arbitrary portion of the steel surface of the sample to be measured, the inclusion having a maximum diameter of 5 μm or more existing on the mirror surface of the steel surface layer is confirmed with an optical microscope, and then the scanning electron microscope is used. Place the sample to be measured in the sample chamber, irradiate the confirmed inclusions with an electron beam, and divide the energy of the reflected X-rays with a semiconductor detector to make oxide inclusions. Ca / Al contained is determined.

  As described above, when the inclusions are irradiated with an electron beam, the energy of X-rays such as oxygen, nitrogen, sulfur and the like is dispersed, so if the element showing the maximum value of these spectral intensities is oxygen, the analysis point Can be determined to be an oxide.

  The oxide inclusions to be measured for Ca / Al may be secondary particles in which primary particles composed of single-phase oxides having a maximum diameter of less than 5 μm are aggregated. In addition, the measurement of the Ca / Al is performed by analyzing two or more places on the specular surface of one oxide inclusion, and Ca / Al obtained by averaging them is defined as (Ca / Al) of the oxide inclusion. To do. The location to be analyzed may be two or three, and is not particularly limited. This is performed on five or more oxide inclusions, and the average value thereof is (Ca / Al) of oxide inclusions having a maximum diameter of 5 μm or more.

In addition, even if the oxide inclusion includes a compound which is not an oxide such as CaF ₂ , it may be a composite inclusion attached around the oxide. In such a case, the oxide inclusion Count as. In addition, even when the oxide inclusions are made of an oxide of a system containing only one of Ca and Al, generally Ca and Al are inevitably mixed. Therefore, Ca and Al do not become 0 at the analysis site of oxide inclusions.

CaO—Al ₂ O ₃ -based oxides are typical examples of oxide-based inclusions that may be present on the surface of the duplex stainless steel laminated material, but other examples include MgO-based oxides. Mg in steel is refractory containing MgO such as crucible and MgO contained in refining flux is reduced by various deoxidizers and dissolved in steel, and again MgO, MgO. It is generated when a process of precipitation as Al ₂ O ₃ , metal Mg, or Mg alloy is added.

  As a method for controlling the weight ratio of Ca and Al in the oxide inclusions, for example, in addition to a commonly used refractory container such as a MgO crucible, a refractory such as a CaO crucible is used. Using containers, changing the basicity of the flux for deoxidation / desulfurization, changing the addition amount of the flux, changing the addition amount and addition timing of the deoxidizer and desulfurization agent, etc. . Any one of these or a combination of two or more may be controlled.

  For example, in order to control the composition of oxide inclusions to a desired value, manufacturing conditions can be set with the following in mind. The composition of the oxide inclusions is governed by the activity of O and deoxidizing elements such as Ca, Mg, Al, and Si in the steel. If a flux with high basicity or a refractory with a high proportion of CaO is used, the activity of O decreases. Moreover, using a flux with a large CaO content and adding metal Ca or a Ca alloy increases the activity of Ca. Actually, a small amount of water contained in the refractory and the flux increases the activity of oxygen in the steel, often produces an oxide having a high Al ratio, and the ratio of CaO defined by the present invention is high. Controlling the oxide composition requires a careful refining process to remove the oxygen source.

  Next, the pitting corrosion resistance and surface hardness of the clad steel of the present invention will be described.

(Pitting corrosion resistance of the clad steel sheet of the present invention)
Although the duplex stainless steel of the present invention is not subjected to a solution heat treatment, its corrosion resistance is the element content that affects the corrosion resistance, and the PREW formula [ [Cr + 3.3 (Mo + 0.5W) + 16N-Mn] has a comparable composition and is comparable to a solution heat-treated steel. The “equivalent degree” means that the elements that affect the corrosion resistance have almost the same content, and the PREW values calculated by the PREW formula are almost the same. In addition, steel having the same level of elements that affect the corrosion resistance and having the same PREW value is defined as “equivalent steel”.

  Here, in the present invention, the “elements affecting the corrosion resistance” are each element constituting the PREW formula. Therefore, the “equivalent steel” in the present invention has a difference in the content of the elements Cr, Mn, W, N, and Mo as compared with the composition of the target steel. + 1.0%, Mn: -1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3 The steel is in the range of -1.0 to +1.0 with respect to the PREW value calculated by the PREW formula.

Steel without Ca is free of CaS and exhibits high corrosion resistance. The corrosion resistance of the clad steel of the present invention is equivalent to that of clad steel using an equivalent steel that is Ca-free and solution heat treated. That is, the corrosion resistance of the clad steel of the present invention is the pitting corrosion occurrence temperature A of the laminated material (that is, the duplex stainless steel of the present invention) that is not subjected to solution heat treatment, and the equivalent steel of the laminated material. and has a composition Ca is not added, the difference with respect to pitting temperature B ₀ of solid solution heat-treated duplex stainless steel is -5 ° C. or higher _{(a-B 0 ≧ -5)} .

  In the critical pitting temperature test (ASTM G48 method), a test piece is immersed in a solution of 6% ferric chloride and hydrochloric acid, and a hole having a depth of 0.025 mm or more is raised while raising the test temperature. This is a test to find the lowest temperature at which pitting occurs. Among these, the E method is a test immersed for 24 hours at each temperature, and is a test often used for measuring the pitting corrosion resistance of stainless steel. The pitting corrosion resistance of the duplex stainless steel targeted by the present invention is in a wide range from a steel type having a pitting corrosion temperature of about 5 ° C. to a high temperature of about 80 ° C. The composition of the oxide in the duplex stainless steel laminated material to which Ca is added is not preferred, and the composition tends to be the starting point of pitting corrosion or the hot rolling conditions are not preferred, and the σ phase and nitride are contained in the laminated material. Is deposited to some extent, the pitting corrosion occurrence temperature A is lower by about 10 to 20 ° C. than the original pitting corrosion occurrence temperature B. The pitting corrosion occurrence temperature B is obtained by performing a solution heat treatment on a laminated material of duplex stainless steel to which no Ca is added.

(Surface hardness of the clad steel of the present invention)
Since the clad steel of the present invention is made into a final product while being hot-rolled, the surface hardness can be secured more than that subjected to solution heat treatment. Therefore, the surface hardness of the clad steel of the present invention is such that the hardness C of the laminated material (that is, the duplex stainless steel of the present invention) that has not been subjected to solution heat treatment is equivalent steel of the laminated material. It is 1.05 times or more and 1.30 times or less with respect to the hardness D ₀ of the duplex stainless steel having a composition to which Ca is not added and subjected to solution heat treatment. When the hardness C is less than 1.05 times the hardness D ₀ , the pitting corrosion resistance becomes insufficient because the metal structure is equivalent to that of the solution-treated duplex stainless steel. In addition, when hot rolling is performed so that the hardness C is more than 1.30 times the hardness D ₀ , the effect of processing strain and fine precipitates are generated. It becomes impossible to ensure the state of B ₀ ≧ −5 ″.

  As described above, the clad steel of the present invention is characterized in that the laminated material in the state of hot rolling is superior in surface hardness to the laminated material subjected to solution heat treatment. The hardness is preferably obtained by determining the surface hardness, and may be measured by embedding a cross section with a resin. As a hardness measurement method, Vickers hardness, Rockwell hardness, Brinell hardness and the like can be applied.

  The duplex stainless steel for clad steel of the present invention can be produced as a laminated material under the appropriate hot rolling conditions already disclosed.

  As described above, the duplex stainless steel for clad steel according to the present invention described above is characterized in that it has good hot workability and pitting corrosion resistance as a laminated material, and is economical in the industrial field targeted by the present invention. Can provide a clad steel.

Examples are described below. The inventors prepared test steels having chemical compositions shown in Table 1-1 (invention example) and Table 1-2 (comparative example) by 25 kg of vacuum melting. An MgO crucible was mainly used, and a CaO crucible was partially used. In some dissolutions, 500 to 1000 g of CaO—Al ₂ O ₃ —CaF ₂ refining fluxes with various changes in basicity were added at various timings, melted and held, and refined to approach deoxidation equilibrium. . The remainder of the components described in Table 1-1 and Table 1-2 is Fe and inevitable impurity elements. Moreover, since the part which content is not described about the component shown in Table 1-1 and Table 1-2 (part indicated by the sign "-") does not intentionally add the corresponding element component, Indicates that no measurement was performed.

  The maximum length of the ear cracks generated on the left and right is machined from a slab cast from a melted material into a rolled material 60 mm thick x 160 mm wide x 150 mm long, hot rolled to a thickness of 12 mm at a rolling finishing temperature of 850 ° C. Observed and evaluated the hot workability of the melt. That is, the maximum length of the ear cracks generated on the left and right sides of each of the rolling regular portions of about 400 mm length of the duplex stainless steel sheet of 12 mm thickness × 180 mm width × 600 mm length is measured, and the sum of the left and right maximum lengths is calculated. It was counted as the crack length. FIG. 1 shows the correspondence between the SUS329J3L steel grade and the value of the oxide composition (Ca / Al) on the surface of the laminated material.

  Next, the oxidized scale on the surface of the steel plate is removed by grinding, and welding assembly is performed with a carbon steel having a plate thickness of 68 mm and a carbon content of 0.12%. Welded and assembled as the inner side, and made a material of a sandwich type clad steel plate of 160 mm thickness × 170 mm width × 300 mm length.

  After heating the material of each clad steel plate to 1200 ° C., it is rolled to a thickness of 40 mm at the rolling finishing temperature shown in Table 2-1 or Table 2-2, and from the water cooling start temperature shown in Table 2-1 or Table 2-2. Spray water cooling was performed, and water cooling was stopped at 550 ° C. After rolling, the clad steel plate was separated into two pieces to obtain a duplex stainless steel clad steel plate having a thickness of 20 mm (base material 17 mm, laminated material 3 mm).

  The clad steel sheet laminated material is taken out by machining, and 3 pieces each of 3 mm thick x 25 mm wide x 50 mm long pitting corrosion temperature measurement test specimens, which are wet-polished with emery paper # 120, are collected. At the same time, one surface hardness test piece was cut out.

  The pitting corrosion resistance of the laminated material was evaluated by measuring a test piece for measuring pitting corrosion temperature of 3 mm thickness × 25 mm width × 50 mm length of ASTM G48 in a state in which the entire surface was wet-polished with emery paper # 120. According to the method, it was immersed for 24 hours at a predetermined temperature, and the depth of the generated pitting corrosion was measured. When pitting corrosion of a depth of 0.025 mm or more has not occurred, the test temperature is increased by 5 ° C., the next test is performed, and this is repeated to obtain the pitting corrosion generating temperature for each test piece. The value of the lowest temperature among the pitting corrosion occurrence temperatures was defined as the pitting corrosion occurrence temperature A. FIG. 2 shows a result of arranging the results of the pitting corrosion occurrence temperature of the SUS329J3L-based laminated material with (Ca / Al) of the oxide-based inclusions on the surface of the laminated material.

In addition, as shown in Table 2-1 and Table 2-2, pitting corrosion is also carried out in the same manner for a laminated material obtained by solution heat treatment of a clad steel plate using a Ca-free laminated material for each equivalent steel. The generation temperature _B0 was determined.

For example, Invention Examples No. a1 to a3, a5 to a8 and Comparative Examples No. a0 and a11 to a15 are in the relationship of equivalent steel. Accordingly, the comparative example No. a0 is subjected to solution heat treatment to produce a duplex stainless steel laminated material, and then the clad steel plate is produced by the production method described above using the laminated material, and the clad steel plate produced as described above. by the method, the present invention example No.A1～a3, A5 to A8 and Comparative example No.A0, was determined pitting temperature B ₀ about A11 to A15.

Equivalent steel b1~b3 and b0, b11, pitting temperature B ₀ of b12 is a pitting temperature of clad plate of the mating material of Comparative Example No.B0. Similarly, steel numbers c0 to c2 are equivalent steels, and steel numbers d0 to d2 are equivalent steels. Steel numbers e and e0, steel numbers f and f0, steel numbers g and g0, steel numbers h and h0, steel numbers i and i0, and steel numbers j and j0 are in the same steel relationship. For even these equivalent steel, with steel numbers c0, d0, e0, f0, g0, h0, i0, j0, was determined pitting temperature B ₀ for each equivalent steel. The solution heat treatment temperature is set to an appropriate temperature for each steel type and is in the range of 1000 to 1100 ° C.

  The value of the oxide composition (Ca / Al) on the surface of the laminated material was measured as follows. First, a test piece of 3 mm thickness x 10 mm width x 20 mm length is cut out by machining, the surface corresponding to the surface layer portion is prevented from dissolving inclusions such as oxides and sulfides, and mirror-polished with diamond abrasive grains. I did it. Next, in a 5000 μm × 5000 μm range of an arbitrary portion of the steel surface, inclusions having a maximum diameter of 5 μm or more present on the mirror surface of the steel surface layer were confirmed with an optical microscope, and then a sample was put into a scanning electron microscope. The confirmed inclusions were irradiated with an electron beam, and the energy of the reflected X-rays was dispersed with a semiconductor detector to obtain the weight ratio of the metal elements excluding the light elements, which was confirmed by the method described above. Ca / Al contained in five or more oxide inclusions was obtained, and the average value (Ca / Al) was obtained. The results are shown in Table 2-1 and Table 2-2. The oxide inclusions were observed to be oxides, sulfides, partially nitrides, etc., but were mainly C-based oxides that were not expanded. In Table 2-2, when (Ca / Al) is 0.04 or less, 0.0 is written.

After the surface of the surface hardness test piece was wet-polished with emery paper # 600, the surface hardness C was measured with a Vickers hardness of 10 kg. Also, under the same conditions as the pitting corrosion occurrence temperature measurement, a clad steel plate using a Ca-free additive material for each equivalent steel is subjected to a solution heat treatment material, and the subsequent additive material is taken out by machining in the same manner. the surface hardness D ₀ was measured. Based on the above results, (A-B ₀ ) and (C / D ₀ ) were determined and shown in Tables 2-1 and 2-2.

From the examples shown in Table 2-1 and Table 2-2, the duplex stainless steel sheet for the laminated material of the clad steel sheet disclosed by the present invention has an ear crack length of 3 mm or less and good hot workability, It is clear that the pitting corrosion occurrence temperature (A-B ₀ ) of the clad steel sheet laminated material is −5 ° C. or higher and the corrosion resistance is good. Further, since the surface hardness of the laminated material is in the state of being rolled with C / D ₀ being 1.05 or more and 1.30 or less, it has good corrosion resistance without being subjected to heat treatment, so that the final annealing can be omitted, which is economical. Clearly, a clad steel plate can be provided.

  As can be seen from the above examples, according to the present invention, it is clear that the hot workability is good, the corrosion resistance of the clad steel laminated material is improved, and the clad steel can be obtained using an economical duplex stainless steel as the laminated material. became.

  The duplex stainless steel of the present invention is a clad steel with good hot workability, excellent pitting corrosion resistance when applied as a laminated material, and excellent balance between corrosion resistance and cost, widely used in various fields can do. According to the present invention, it is possible to provide a clad steel having good corrosion resistance and a low price using a duplex stainless steel as a combined material, and can be used as a tank for a transport ship, seawater desalination equipment, various containers, etc. The place to do is extremely large.

Claims (9)

In mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-6.0%, P: 0.05% or less, S: 0.0001-0. 0014%, Cr: 20.0~28.0%, Ni: 0.5~9.0%, Mo: 0.12~ 5.0%, N: 0.05~0.35%, A l: 0.003 to 0.05%, Ca: 0.0005 to 0.0040%, O : 0.001 to 0.004%, the balance is made of Fe and inevitable impurities, and the maximum diameter on the steel surface is 5 μm. A duplex stainless steel for clad steel, wherein the weight ratio of Ca to Al (Ca / Al) in the oxide inclusions of the above size is 0.5 or more and 3.5 or less. Further, by mass%, W: 3.0% or less, Co: 1.0% or less, Cu: 3.0% or less, V: 0.5% or less, Nb: 0.15% or less, Ti: 0.05 2. The duplex stainless steel for clad steel according to claim 1, comprising at least one of:% or less, B: 0.0050% or less, and Mg: 0.0030% or less. A clad steel characterized in that the duplex stainless steel according to claim 1 or 2 is used as a laminated material, and a base material is carbon steel. In mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-6.0%, P: 0.05% or less, S: 0.0001-0. 0014%, Cr: 20.0 to 28.0%, Ni: 0.5 to 9.0%, Mo: 0.12 to 5.0%, N: 0.05 to 0.35%, Al: 0 0.002 to 0.05%, O: 0.001 to 0.0052%, with the balance being Fe and inevitable impurities,
Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. (1) A hole in a duplex stainless steel having a difference in corrosion resistance index PREW represented by the formula in the range of -1.0 to +1.0, having a composition to which Ca is not added, and subjected to solution heat treatment With respect to the eclipse temperature
The clad steel according to claim 3 , wherein a pitting corrosion temperature of the laminated material is higher by -5 ° C or more.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained. In mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-6.0%, P: 0.05% or less, S: 0.0001-0. 0014%, Cr: 20.0 to 28.0%, Ni: 0.5 to 9.0%, Mo: 0.12 to 5.0%, N: 0.05 to 0.35%, Al: 0 0.002 to 0.05%, O: 0.001 to 0.0052%,
Further, by mass%, W: 3.0% or less, Co: 1.0% or less, Cu: 3.0% or less, V: 0.5% or less, Nb: 0.15% or less, Ti: 0.05 %, B: 0.0050% or less, Mg: at least one of 0.0030% or less, the balance consists of Fe and inevitable impurities,
  Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. (1) A hole in a duplex stainless steel having a difference in corrosion resistance index PREW represented by the formula in the range of -1.0 to +1.0, having a composition to which Ca is not added, and subjected to solution heat treatment With respect to the eclipse temperature
The clad steel according to claim 3, wherein a pitting corrosion temperature of the laminated material is higher by -5 ° C or more.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained. In mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-6.0%, P: 0.05% or less, S: 0.0001-0. 0014%, Cr: 20.0 to 28.0%, Ni: 0.5 to 9.0%, Mo: 0.12 to 5.0%, N: 0.05 to 0.35%, Al: 0 0.002 to 0.05%, O: 0.001 to 0.0052%, with the balance being Fe and inevitable impurities,
Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. The difference in the corrosion resistance index PREW represented by the formula (1) is in the range of -1.0 to +1.0, the hardness of the duplex stainless steel having a composition to which Ca is not added and subjected to solution heat treatment. On the other hand,
1 . Clad steel according to claim 3, characterized in Rukoto that have a 1.30 times or less of the hardness of 05 times or more.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained. In mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-6.0%, P: 0.05% or less, S: 0.0001-0. 0014%, Cr: 20.0 to 28.0%, Ni: 0.5 to 9.0%, Mo: 0.12 to 5.0%, N: 0.05 to 0.35%, Al: 0 0.002 to 0.05%, O: 0.001 to 0.0052%,
Further, by mass%, W: 3.0% or less, Co: 1.0% or less, Cu: 3.0% or less, V: 0.5% or less, Nb: 0.15% or less, Ti: 0.05 %, B: 0.0050% or less, Mg: at least one of 0.0030% or less, the balance consists of Fe and inevitable impurities,
Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. The difference in the corrosion resistance index PREW represented by the formula (1) is in the range of -1.0 to +1.0, the hardness of the duplex stainless steel having a composition to which Ca is not added and subjected to solution heat treatment. On the other hand,
The clad steel according to claim 3, having a hardness of 1.05 times or more and 1.30 times or less.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained. In mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-6.0%, P: 0.05% or less, S: 0.0001-0. 0014%, Cr: 20.0 to 28.0%, Ni: 0.5 to 9.0%, Mo: 0.12 to 5.0%, N: 0.05 to 0.35%, Al: 0 0.002 to 0.05%, O: 0.001 to 0.0052%, with the balance being Fe and inevitable impurities,
Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. (1) A hole in a duplex stainless steel having a difference in corrosion resistance index PREW represented by the formula in the range of -1.0 to +1.0, having a composition to which Ca is not added, and subjected to solution heat treatment With respect to the eclipse temperature
The pitting corrosion occurrence temperature of the laminated material is higher than -5 ° C, and
The clad steel according to claim 3, wherein the clad steel has a hardness of 1.05 times or more and 1.30 times or less of the hardness of the duplex stainless steel.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained. In mass%, C: 0.03% or less, Si: 0.05-1.0%, Mn: 0.1-6.0%, P: 0.05% or less, S: 0.0001-0. 0014%, Cr: 20.0 to 28.0%, Ni: 0.5 to 9.0%, Mo: 0.12 to 5.0%, N: 0.05 to 0.35%, Al: 0 0.002 to 0.05%, O: 0.001 to 0.0052%,
Further, by mass%, W: 3.0% or less, Co: 1.0% or less, Cu: 3.0% or less, V: 0.5% or less, Nb: 0.15% or less, Ti: 0.05 %, B: 0.0050% or less, Mg: at least one of 0.0030% or less, the balance consists of Fe and inevitable impurities,
  Differences from the contents (%) of elements Cr, Mn, W, N, and Mo contained in the composition of the laminated material are Cr: −1.0% to + 1.0%, Mn: −1.0% to + 1.0%, W: -0.6% to + 0.6%, N: -0.06% to + 0.06%, Mo: -0.3% to + 0.3%. (1) A hole in a duplex stainless steel having a difference in corrosion resistance index PREW represented by the formula in the range of -1.0 to +1.0, having a composition to which Ca is not added, and subjected to solution heat treatment With respect to the eclipse temperature
The pitting corrosion occurrence temperature of the laminated material is higher than -5 ° C, and
The clad steel according to claim 3, wherein the clad steel has a hardness of 1.05 times or more and 1.30 times or less of the hardness of the duplex stainless steel.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N-Mn (1)
However, the element symbol in a formula means content (mass%) of the said element, and 0 is substituted when an element is not contained.

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