WO2020071343A1 - オーステナイト系ステンレスクラッド鋼板および母材鋼板ならびにクラッド鋼板の製造方法 - Google Patents
オーステナイト系ステンレスクラッド鋼板および母材鋼板ならびにクラッド鋼板の製造方法Info
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- WO2020071343A1 WO2020071343A1 PCT/JP2019/038670 JP2019038670W WO2020071343A1 WO 2020071343 A1 WO2020071343 A1 WO 2020071343A1 JP 2019038670 W JP2019038670 W JP 2019038670W WO 2020071343 A1 WO2020071343 A1 WO 2020071343A1
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
- B32B15/011—Layered products comprising a layer of metal all layers being exclusively metallic all layers being formed of iron alloys or steels
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
- B23K20/04—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating by means of a rolling mill
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
- B23K20/22—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating taking account of the properties of the materials to be welded
- B23K20/227—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating taking account of the properties of the materials to be welded with ferrous layer
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
- B23K20/24—Preliminary treatment
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- C21D1/773—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material under reduced pressure or vacuum
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
- C21D3/02—Extraction of non-metals
- C21D3/06—Extraction of hydrogen
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0257—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with diffusion of elements, e.g. decarburising, nitriding
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- C—CHEMISTRY; METALLURGY
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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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
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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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
- C22C38/18—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
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2251/00—Treating composite or clad material
- C21D2251/02—Clad material
Definitions
- the present invention relates to a method for manufacturing an austenitic stainless clad steel sheet, a base steel sheet, and a clad steel sheet.
- a clad steel sheet is a steel sheet in which a plurality of different metals or alloys are joined.
- the metal to be coated is referred to as a bonding material, and the metal to be coated is referred to as a base material.
- a high corrosion-resistant alloy such as stainless steel is used as a material of a composite material
- carbon steel or low alloy steel is used as a material of a base material.
- corrosion resistance can be provided by a high corrosion resistant alloy
- strength and weldability with carbon steel can be provided by carbon steel or low alloy steel.
- clad steel sheet Applications of the clad steel sheet include chemical tanker tanks.
- Chemical tankers are carriers that carry various chemicals. For this reason, materials used for chemical tankers are required to have resistance to chemicals, and many of the tanks are made of stainless steel.
- a clad steel plate is used for the tank, for example, a stainless steel clad steel plate having stainless steel inside and carbon steel outside is used. By using such a stainless steel clad steel plate, corrosion resistance can be obtained and welding to the outer carbon steel shell can be facilitated.
- an assembly rolling method As a method of manufacturing a clad steel sheet, an assembly rolling method, a casting rolling method, an explosion pressure bonding method, a build-up welding method, and the like are known.
- the assembling rolling method of hot rolling the assembled material and bonding the interface is excellent in efficiently producing a large-sized product. For this reason, it is widely applied to the production of clad steel sheets.
- the assembling and rolling method has a problem in that the combination of steel types is limited, and a technique is required in order to provide interface adhesion.
- the base material in order to increase the strength toughness of the base material, it is effective to add rolling at a low temperature. In addition, it is also effective to perform water cooling after rolling to refine the ferrite transformation structure and improve the strength toughness.
- the heat treatment after the rolling is often omitted because the ferrite grains of the base material are coarsened and deformation is caused by a difference in coefficient of thermal expansion.
- Patent Document 1 discloses a manufacturing method in which the rolling reduction in a high-temperature range of 850 to 1050 ° C. is set to 30% or more to secure adhesion.
- the strength is increased by rolling to a low temperature of 750 to 850 ° C., and cooling by air cooling or water cooling is performed.
- the C content of the composite material is set to 0.03% or less because the stainless steel of the composite material may be sensitized by low-temperature rolling.
- Patent Document 2 discloses a production method in which the C content of the composite material is similarly set to 0.02% or less, and the reduction ratio at 1000 ° C. or more is set to 2.5 or more to secure adhesion.
- rolling is performed at 850 ° C. or less by 50% or more, and water cooling is performed.
- the C content of the composite material is set to 0.02% or less, and the components of the base material are adjusted to ensure toughness. Also disclosed is a method for producing a clad steel having a reduction ratio of 950 ° C. or higher with a reduction ratio of 1.5 or higher and having adhesion. In this manufacturing method, in order to improve the DWTT characteristic of the base material, the material is further rolled at 900 ° C. or less by 50% or more and water-cooled.
- the austenitic stainless steel component of the composite is C: 0.020% or less, and has a partially recrystallized structure, and has a shear strength with a base material of 300 MPa or more as an index of adhesion. Steel is disclosed.
- a reduction ratio of 1000 ° C. or more is 1.5 or more
- a rolling finish temperature is 850 ° C. or more
- accelerated cooling is further performed.
- adhesion is particularly important for clad steel sheets used in chemical tankers. This is because, in a chemical tanker, a decrease in adhesion and separation of the interface may cause an accident such as outflow of stored chemicals. Therefore, the clad steel sheet used for the chemical tanker is required to have particularly stable adhesion. Furthermore, in recent years, environmental regulations have been tightened, and it is also required to improve fuel efficiency. For this reason, it is also required to reduce the thickness of the tanker material, that is, the thickness of the clad steel plate, and to reduce the thickness and weight.
- the above can promote the diffusion of elements between interfaces and enhance the adhesion.
- the shear strength which is an index indicating the adhesiveness of the interface
- the shear strength varies greatly and sometimes shows a considerably low value depending on the position.
- an object of the present invention is to provide a method for producing an austenitic stainless clad steel sheet, a base material steel sheet, and a clad steel sheet having high strength and good and stable interface adhesion.
- the present invention has been made to solve the above-described problems, and has the following austenitic stainless clad steel sheet, a base material steel sheet, and a method for producing a clad steel sheet.
- a clad steel sheet including a base material and a bonding material joined to the base material The base material is made of carbon steel or low alloy steel, The carbon equivalent Ceq of the base material represented by the following formula (i) is 0.38 or less, and the tensile strength of the base material is 490 MPa or more and 620 MPa or less,
- the composite material is made of austenitic stainless steel, An austenitic stainless clad steel sheet having an average shear strength of 400 MPa or more and a standard deviation of the shear strength of 20 MPa or less at a bonding interface between the base material and the composite material.
- Ceq C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 (i)
- the symbol of the element in the above formula (i) represents the content (% by mass) of each element contained in the steel, and is zero if not contained.
- the chemical composition of the base material is represented by mass%, C: 0.08 to 0.10%, Si: 0.10 to 0.50%, Mn: 1.30 to 1.60%, P: 0.035% or less, S: 0.035% or less, Nb: 0.02 to 0.05%, Ti: 0.005 to 0.020%, Al: 0.01-0.05%, N: 0.006% or less, and Ni: 0 to 0.20%,
- step (c) hot rolling is performed by setting the rolling reduction in a temperature range of 1000 ° C. or more to 3 or more and the rolling reduction in a temperature range of less than 1000 ° C. to 30% or more.
- the temperature range of 700 to 400 ° C. is reduced at a cooling rate of less than 1.0 ° C./s, and the temperature range of 400 to 200 ° C. is 0.4 ° C./s or less. Cooling at the cooling rate of The method for producing an austenitic stainless clad steel sheet according to (4) or (5).
- a base steel sheet used in the method for producing an austenitic stainless steel clad steel sheet according to (6) Chemical composition in mass% C: 0.08 to 0.10%, Si: 0.10 to 0.50%, Mn: 1.30 to 1.60%, P: 0.035% or less, S: 0.035% or less, Nb: 0.02 to 0.05%, Ti: 0.005 to 0.020%, Al: 0.01-0.05%, N: 0.006% or less, and Ni: 0 to 0.20%, A base material steel sheet.
- the present inventors have conducted the following studies on the above problems. As a result, the following findings (a) to (c) were obtained.
- the cause of the location where the shear strength is low may be caused by the presence of hydrogen existing in the steel material.
- hydrogen is concentrated by diffusion or the like in pores existing at the boundary between the base material steel plate and the base material steel plate and becomes gaseous hydrogen.
- (C) In order to suppress the generation of voids, it is effective to appropriately control the amount of hydrogen at the boundary.
- the hydrogen dissolved in the steel described above is mixed with the molten steel in the order of ppm and remains in the steel, and it is desirable that the hydrogen be appropriately removed before rolling by a treatment such as a heat treatment described below. .
- An austenitic stainless clad steel sheet according to the present invention includes a base material and a composite material joined to the base material.
- the base material is made of carbon steel or low alloy steel described below.
- the joining material is made of austenitic stainless steel.
- the base material steel sheet before joining by hot rolling is referred to as a base material steel sheet
- the joining material steel sheet before joining is referred to as a combination material steel sheet.
- the chemical composition of the base material and the base material steel plate, and of the composite material and the composite material steel plate do not change before and after rolling, and their chemical compositions are the same.
- Base material 2-1 Chemical composition of base material
- the base material is made of carbon steel or low alloy steel.
- Examples of the carbon steel or the low alloy steel include a steel material for a welded structure, a boiler, a carbon steel for a pressure vessel, and a steel material for shipbuilding.
- the carbon equivalent Ceq is an index related to weldability, and is important in ships such as chemical tankers because the hull is assembled by welding.
- the carbon equivalent Ceq is set to 0.38 or less from the viewpoint of weldability. Further, the carbon equivalent Ceq of the base material is preferably set to 0.365 or less.
- the carbon equivalent Ceq is represented by the following formula (i).
- the following equation (i) is described in Section 1.5 of the K Rules of the Steel Ship (issued by The Japan Maritime Association), and the above numerical value is described as KA36 in Section 3.1.
- Ceq C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 (i)
- the symbol of the element in the above formula (i) represents the content (% by mass) of each element contained in the steel, and is zero if not contained.
- the tensile strength of the base material is in the range of 490 to 620 MPa required for the base material of the clad steel plate used for the chemical tanker. The range of the tensile strength is described in the above-mentioned KA36 of the K Rules of Steel Ships, which is the highest strength level of the stainless steel clad steel plate used.
- the tensile strength of the base material is determined by removing the bonding material from the clad steel plate, collecting a tensile test piece, and performing a tensile test based on JIS Z 2241: 2011.
- the laminated material of the austenitic stainless clad steel sheet according to the present invention is made of austenitic stainless steel. Thereby, corrosion resistance to the chemicals stored in the tank inner wall can be provided.
- SUS316L is a typical type of austenitic stainless steel.
- the steel type is not particularly limited as long as it is an austenitic stainless steel other than the same steel type.
- examples of the steel type include SUS304 and SUS317L.
- the average value of the shear strength at the joint interface between the base metal and the composite material, and the standard deviation of the shear strength value Evaluate stable adhesion. This is because, even when the average value of the shear strength is high, if there is a portion where the shear strength is low, there is a possibility that peeling may occur at the interface of the clad steel sheet. Therefore, in order to evaluate stable adhesion, the standard deviation of the value of the shear strength is also used for the evaluation.
- the average value of the shear strength at the joint interface between the base material and the composite material is 400 MPa or more, and more preferably 420 MPa or more.
- the shear strength increases as the tensile strength of the base material or the composite increases. Therefore, in the clad steel sheet according to the present invention, the average value of the shear strength is set in the above range in consideration of the tensile strength of the base material and the composite material.
- the standard deviation of the shear strength at the bonding interface is as small as possible.
- the standard deviation of the shear strength is 20 MPa or less, and preferably 18 MPa or less.
- the shear strength is measured in accordance with JIS G 0601: 2012, and the number of tests is 10 or more. Generally, when the number of tests is less than 10, it is considered that an appropriate standard deviation cannot be obtained.
- As the test piece a plate-shaped test piece in which a projection of a matching material is left on a base material described in JIS G0601: 2012 is used.
- the hydrogen content of the base metal and the cladding material in the clad steel sheet is controlled in the following range in order to obtain stable adhesion at the bonding interface between the base metal and the cladding material. Is preferred.
- the content of hydrogen in the base material of the clad steel sheet is preferably 1.0 ppm or less, more preferably 0.8 ppm or less, and even more preferably 0.6 ppm or less. Further, the hydrogen content in the cladding material of the clad steel sheet is preferably 3.0 ppm or less, more preferably 2.5 ppm or less, and even more preferably 2.3 ppm or less.
- the metal structure is mainly in an austenitic phase.
- the austenite phase has a characteristic that the amount of dissolved hydrogen is large and the diffusion rate of hydrogen is small compared to the ferrite phase which is a metal structure of carbon steel. Therefore, the hydrogen content of the composite material made of austenitic stainless steel is higher than the hydrogen content of the base metal.
- a method for measuring the hydrogen content there are a melting method, a heating method, and the like defined in JIS Z 2614: 1990.
- the hydrogen content is measured by using an inert gas melting method and a thermal conductivity method specified in JIS Z 2614: 1990.
- the above-described base material steel plate and composite material steel plate may be manufactured by a conventional method. Specifically, after smelting by a known method such as a converter, an electric furnace, or a vacuum melting furnace, the slab is controlled to a predetermined chemical composition by a continuous casting method or an ingot-bulking method. The obtained slab is hot-rolled under a condition usually used to obtain a hot-rolled steel sheet. Subsequently, annealing, pickling, polishing, and the like may be performed on the obtained hot-rolled steel sheet as necessary.
- ⁇ It is preferable to perform vacuum evacuation from a vacuum evacuation hole provided in the base material steel plate of the clad rolled material in advance so that the degree of vacuum of the lamination surface becomes a high vacuum of 0.1 Torr or less. After evacuation, the hole in the base steel plate is sealed. In addition, since the above-mentioned hole for evacuation is open from the side of the base material steel plate in the above-mentioned material to the lamination surface, the lamination surface of the clad rolled material can be made high vacuum. In the evacuation, it is preferable to heat the clad rolled material to a temperature range of 200 to 450 ° C.
- the degree of vacuum of the lamination surface exceeds 0.1 Torr, poor bonding between the base material and the composite material may occur after rolling. Further, the content of hydrogen in the base material and the composite material after rolling cannot be sufficiently reduced, and the shear strength decreases. For this reason, the degree of vacuum on the lamination surface is preferably set to 0.1 Torr or less, more preferably 0.01 Torr or less. The lower the degree of vacuum of the lamination surface is, the better, but even if it is reduced to 0.005 Torr or less, the effect of improving the bonding strength is small.
- the heating temperature at the time of evacuation is lower than 200 ° C., hydrogen remains in the base material and the composite material after rolling. This is presumably because in a temperature range of less than 200 ° C., the diffusion rate of hydrogen is low, and hydrogen cannot be sufficiently removed. For this reason, the heating temperature is preferably set to 200 ° C. or higher.
- the heating temperature at the time of evacuation exceeds 450 ° C.
- the strength of the base steel sheet, carbon steel or low alloy steel rapidly decreases, and the gap due to the difference in thermal expansion from the combined steel sheet causes voids in the laminated surface. May occur.
- the shear strength may decrease. Therefore, the heating temperature is preferably set to 450 ° C. or less.
- the heating temperature during hot rolling is preferably set to 1050 ° C. or higher.
- the heating temperature during hot rolling is preferably set to 1250 ° C. or less.
- the reduction ratio in the temperature range of 1000 ° C. or more is preferably 3 or more, and the reduction ratio in the temperature range of less than 1000 ° C. is preferably 30% or more.
- the rolling reduction in the temperature range of 1000 ° C. or higher is a value obtained by dividing the material thickness of the clad rolled material before rolling by the thickness of the clad steel sheet at 1000 ° C. If the rolling reduction in the temperature range of 1000 ° C. or higher is less than 3, recrystallization is promoted at the interface between the base material and the composite material, and it is difficult to provide stable and high adhesion. For this reason, it is preferable that the rolling reduction in the temperature range of 1000 ° C. or more is 3 or more.
- the rolling reduction at less than 1000 ° C. is obtained by dividing the thickness reduction by rolling in a temperature range of less than 1000 ° C. by the thickness of the clad steel sheet at 1000 ° C. to obtain a percentage.
- the temperature of the base material is substantially lower than the recrystallization temperature. Rolling in this temperature range accumulates ductile strain, which refines the crystal grains as transformation nuclei during the ferrite-pearlite transformation, and thus can obtain high strength and toughness.
- the rolling reduction at the time of rolling at less than 1000 ° C. is preferably set to 30% or more.
- Cooling Subsequently, as cooling after hot rolling, it is preferable to cool the temperature range of 700 to 400 ° C. at a cooling rate of less than 1.0 ° C./s, and to cool the temperature range of 400 to 200 ° C. to 0.4 ° C./s. It is preferable to cool at a cooling rate of s or less.
- a clad steel sheet having good and stable interface with good adhesion at the interface can be obtained.
- a minute mixed layer with a composite material may be formed. In such a minute mixed layer, when quenching is performed, it is possible, although very rarely, to cause separation due to hydrogen due to another factor.
- the microparts having high hardenability generated by mixing the components of the composite material and the base material become a hard martensite structure at the time of quenching, causing delayed fracture due to hydrogen and generating cracks.
- the base material undergoes ferrite transformation.
- the temperature range of 700 to 400 ° C. is set to a cooling rate of 1.0 ° C./s or more, the metal structure of the base material transforms into a ferrite phase. Time is not enough. After ferrite transformation occurs, hydrogen does not diffuse sufficiently. Therefore, it is preferable that the cooling rate be less than 1.0 ° C./s in the temperature range of 700 to 400 ° C.
- the diffusion rate of hydrogen is lower than the above temperature range. Therefore, if the temperature range of 400 to 200 ° C. is cooled at a cooling rate of more than 0.4 ° C./s, it is difficult to promote the diffusion of hydrogen. Therefore, it is preferable to set the cooling rate to 0.4 ° C./s or less in the temperature range of 400 to 200 ° C. In a temperature range of less than 200 ° C., the diffusion rate of hydrogen is reduced to a negligible level, so the cooling rate is not particularly limited.
- the chemical composition of the base material steel plate is not limited as long as the base material after rolling has a predetermined carbon equivalent and tensile strength. However, when the production is performed by a method of performing slow cooling after rolling as described in 6-4 (cooling) described later, when there is a possibility that the ferrite structure becomes coarse and the strength and toughness are reduced, the chemical shown below is used. It is preferable to use a base steel sheet containing a composition.
- C 0.08 to 0.10%
- the C content is preferably set to 0.08% or more.
- the C content is preferably set to 0.10% or less.
- Si 0.10 to 0.50% Si is an element necessary for deoxidation. Therefore, the Si content is preferably set to 0.10% or more. However, if the content of Si exceeds 0.50%, the toughness is deteriorated, and further, the KA36 prescribed in the K Rules of the Steel Ship (issued by the Japan Maritime Association) is deviated. For this reason, the Si content is preferably set to 0.50% or less.
- Mn 1.30-1.60%
- the Mn content is preferably set to 1.30% or more.
- the Mn content is preferably set to 1.60% or less.
- P 0.035% or less P is also contained in the raw material and is an impurity element that is inevitably mixed. If P is excessively contained, the weldability and the like are reduced, so that the smaller the P content, the better.
- the P content is preferably at most 0.035%, more preferably at most 0.02%. On the other hand, excessively reducing P increases the production cost, so that the P content is preferably 0.005% or more.
- S 0.035% or less
- S is an impurity element unavoidably mixed. Further, it may combine with Mn to form an inclusion and serve as a base point of rust in some cases. Therefore, the S content is preferably set to 0.035% or less. From the viewpoint of improving corrosion resistance, the S content is more preferably set to 0.010% or less. On the other hand, excessively reducing S increases the production cost, so the S content is preferably 0.001% or more.
- Nb 0.02 to 0.05%
- the Nb content is preferably at least 0.02%, more preferably at least 0.030%.
- the Nb content is preferably set to 0.05% or less.
- Ti 0.005 to 0.020%
- the Ti content is preferably set to 0.005% or more.
- the Ti content is preferably set to 0.020% or less, and more preferably set to 0.015% or less.
- Al 0.01-0.05%
- Al is usually contained as a deoxidizing agent.
- the Al content is preferably set to 0.01% or more.
- the toughness decreases. Therefore, the Al content is preferably set to 0.05% or less.
- N 0.006% or less N precipitates as Ti nitride together with Ti and suppresses austenite grain coarsening, but the content is inevitably contained at a level unavoidable. Specifically, the N content is preferably set to 0.006% or less. If the content exceeds the above range, nitrides are formed with Al and the like in addition to Ti, and the toughness is reduced.
- Ni 0 to 0.20%
- Ni is an element that improves the low-temperature toughness of steel and the like, and is particularly effective when used in a low-temperature environment. For this reason, you may make it restrictively contain as needed. However, when Ni is excessively contained, the raw material cost is significantly increased and a martensite phase is generated at the clad interface. Therefore, the Ni content is preferably set to 0.20% or less, more preferably 0.10% or less. On the other hand, in order to obtain the above effects, the Ni content is preferably at least 0.010%, more preferably at least 0.020%. Further, it is preferable to set the manufacturing conditions as described above.
- elements such as Cr, Cu, Mo, V, and Ca may be contained.
- Cr has a strength improving effect. Therefore, when Cr is contained, the Cr content is preferably in the range of 0.01 to 0.20%.
- Cu has an effect of improving strength toughness. For this reason, when it is contained, the Cu content is preferably in the range of 0.01 to 0.35%.
- Mo has a strength improving effect. Therefore, when Mo is contained, the Mo content is preferably in the range of 0.01 to 0.08%.
- V has a crystal grain refinement effect. Therefore, when it is contained, the V content is preferably in the range of 0.02 to 0.10%.
- Ca has a toughness improving effect. Therefore, when Ca is contained, the Ca content is preferably in the range of 0.001 to 0.004%.
- the balance is Fe and inevitable impurities.
- "inevitable impurities” are ore, raw materials such as scrap, and components that are mixed due to various factors in the manufacturing process when industrially manufacturing a base steel sheet, and do not adversely affect the present invention. Means acceptable within the range.
- ⁇ ⁇ Austenitic stainless steel having the chemical composition shown in Table 1 was melted into a steel slab and subjected to hot rolling, annealing, and pickling steps to obtain a 20 mm thick austenitic stainless steel composite steel plate.
- the composite material after rolling had the same composition except for hydrogen.
- a carbon steel having a chemical composition shown in Table 2 was melted into a billet and subjected to hot rolling and descaling processes to obtain a carbon steel base steel plate having a thickness of 120 mm.
- the base material after rolling had the same composition except for hydrogen.
- the vacuum was evacuated from the evacuation hole until the degree of vacuum on the lamination surface became the degree of vacuum shown in Table 3, and then the hole was sealed.
- the obtained clad rolled material was heated at a heating temperature as shown in Table 3, a reduction ratio of 1000 ° C. or more, a reduction rate of 1000 ° C. or less, and an average cooling rate of 700 ° C. to 400 ° C. and 400 to 200 ° C. , Rolling, cooling, etc., to finally obtain an austenitic stainless clad steel plate having a thickness of 23 to 34 mm.
- the shear strength test was carried out in accordance with JIS G 0601: 2012, and a total of 10 test pieces were formed from the 300 mm ends and the center of the clad steel sheet. A test piece having a thickness of 13 mm was sampled and measured. Further, the shaving amount when shaping the joint material to produce a test piece was set to an amount obtained by adding 0 to 0.1 mm to the plate thickness of the joint material, and the base material was adjusted so as not to scrape beyond 0.1 mm. The test piece was sandwiched between specified jigs to apply a load and peeled off, and the shear strength was determined from the load.
- a No. 14A tensile test specimen conforming to JIS Z 2241: 2011 is sampled from the base material in the sheet width direction, and a tensile force of 10 N / mm 2 sec to the yield point and a tension of 0.008 / sec after the yield point The test was performed at a speed to determine the tensile strength.
- Hydrogen analysis was performed by taking samples from each of the base material portion and the composite material, and measuring the hydrogen content using the inert gas melting method and the thermal conductivity method specified in JIS Z 2614: 1990.
- Table 3 shows the conditions and measurement results.
- No. Nos. 1 to 6 are examples of the present invention, in which the amount of hydrogen in the composite material and the base material is sufficiently low, satisfying the specified base material tensile strength, and the interface shear strength with the composite material is excellent in both average and standard deviation. I got
- the steel content G is a base material, such as the steel content G, as in No. 16, when the slow cooling described in 6-4 is performed, the strength becomes insufficient. When performing the slow cooling, it is desirable to make the C content higher. However, in the case of this base material, steel type No. If the quenching is performed as in 17, a predetermined strength can be obtained.
- the base steel type was H and the C content was too high, so that the strength was increased and the weld toughness was reduced.
- the base material steel types were I, J, and K, and Mn, Nb, and Ti were too low, respectively, so that the crystal grains of the base material were coarsened, resulting in low strength and low toughness.
- the base material steel types are L and M, and these are examples of the present invention because they satisfy the specified range of the present invention.
- Al and N are too high, respectively, nitrides are precipitated, and toughness is lowered. .
- an austenitic clad steel sheet having a sufficiently high tensile strength and stably high interfacial adhesion is provided for a clad steel sheet using austenitic stainless steel as a composite material, carbon steel or a low alloy steel as a base material. It greatly contributes to the industrial and environmental aspects.
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Abstract
Description
前記母材は、炭素鋼または低合金鋼からなり、
下記(i)式で示される前記母材の炭素当量Ceqが0.38以下で、かつ前記母材の引張強さが490MPa以上620MPa以下であり、
前記合せ材は、オーステナイト系ステンレス鋼からなり、
前記母材と前記合せ材との接合界面におけるせん断強度の平均値が400MPa以上で、かつ、前記せん断強度の標準偏差が20MPa以下である、オーステナイト系ステンレスクラッド鋼板。
Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15 ・・・(i)
但し、上記(i)式中の元素記号は、鋼中に含まれる各元素の含有量(質量%)を表し、含有されない場合はゼロとする。
C:0.08~0.10%、
Si:0.10~0.50%、
Mn:1.30~1.60%、
P:0.035%以下、
S:0.035%以下、
Nb:0.02~0.05%、
Ti:0.005~0.020%、
Al:0.01~0.05%、
N:0.006%以下、および
Ni:0~0.20%、
を含有する、上記(1)または(2)に記載のオーステナイト系ステンレスクラッド鋼板。
(a)表面を有しかつ前記表面につながる穴が予め設けられた、炭素鋼または低合金鋼である母材鋼板と、表面を有しかつオーステナイト系ステンレス鋼である合せ材鋼板とを積層し、前記表面同士を当接させることで積層面を形成させ、前記積層面の周囲を溶接することで封止し、クラッド圧延素材とする工程と、
(b)前記クラッド圧延素材を200~450℃の温度に加熱しながら、前記積層面につながる前記穴から、前記積層面における真空度が0.1Torr以下となるように真空引きする工程と、
(c)前記(b)の工程の後に、前記クラッド圧延素材を1050~1250℃の温度範囲で加熱し、熱間圧延を行う工程と、
を有する、オーステナイト系ステンレスクラッド鋼板の製造方法。
上記(4)に記載のオーステナイト系ステンレスクラッド鋼板の製造方法。
上記(4)または(5)に記載のオーステナイト系ステンレスクラッド鋼板の製造方法。
化学組成が、質量%で、
C:0.08~0.10%、
Si:0.10~0.50%、
Mn:1.30~1.60%、
P:0.035%以下、
S:0.035%以下、
Nb:0.02~0.05%、
Ti:0.005~0.020%、
Al:0.01~0.05%、
N:0.006%以下、および
Ni:0~0.20%、
を含有する、母材鋼板。
本発明に係るオーステナイト系ステンレスクラッド鋼板は、母材と、母材に接合された合せ材とを備える。母材は、後述する炭素鋼または低合金鋼からなる。また、合せ材はオーステナイト系ステンレス鋼からなる。なお、以下、説明のために、熱間圧延による接合前における母材の素材鋼板を母材鋼板、接合前における合せ材の素材鋼板を合せ材鋼板と呼ぶ。母材と母材鋼板、合せ材と合せ材鋼板は、基本的には水素を除き、圧延前後で化学組成は変化せず、その化学組成は同一となる。
2-1.母材の化学組成
母材は炭素鋼または低合金鋼からなる。炭素鋼または低合金鋼としては、例えば、溶接構造用鋼材、ボイラ、圧力容器用炭素鋼、造船用鋼材等が例示される。
炭素当量Ceqとは、溶接性に関わる指標であり、ケミカルタンカーのような船舶では船体を溶接で組み上げていくため、重要である。本発明に係る母材においては、溶接性の観点から、炭素当量Ceqは、0.38以下とする。また、母材の炭素当量Ceqは、0.365以下とするのが好ましい。
Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15 ・・・(i)
但し、上記(i)式中の元素記号は、鋼中に含まれる各元素の含有量(質量%)を表し、含有されない場合はゼロとする。
母材の引張強さは、ケミカルタンカーに用いられるクラッド鋼板の母材に必要な490以上620MPa以下の範囲とする。当該引張強さの範囲は、上述の鋼船規則K編のKA36に記載されており、使用されるステンレスクラッド鋼板としては最も高強度なレベルである。
本発明に係るオーステナイト系ステンレスクラッド鋼板の合せ材はオーステナイト系ステンレス鋼からなる。これにより、タンク内壁に貯蔵する薬品類への耐食性を具備させることができる。オーステナイト系ステンレス鋼としては、SUS316Lが代表的な鋼種である。しかしながら、同鋼種以外であっても、オーステナイト系ステンレス鋼であれば、鋼種は特に限定されない。鋼種としては、上記以外にも、例えば、SUS304,SUS317L等が例示される。
本発明に係るクラッド鋼板では、母材と合せ材との接合界面におけるせん断強度の平均値、およびせん断強度値の標準偏差を用い、良好でかつ安定した密着性を評価する。これは、せん断強度の平均値が高い場合であっても、一部にせん断強度が低い箇所があると、クラッド鋼板の界面において剥離を生じる可能性があるためである。このため、安定した密着性を評価するため、せん断強度の値の標準偏差についても評価に用いる。
本発明に係るクラッド鋼板では、母材と合せ材との接合界面において、安定した密着性を得るため、クラッド鋼板における母材および合せ材の含有水素量を以下の範囲に制御するのが好ましい。
以下において、本発明に係るクラッド鋼板の製造方法について説明する。
6-1.母材鋼板および合せ材鋼板の製造方法
上記母材鋼板および合せ材鋼板は、常法により製造すればよい。具体的には、転炉、電気炉、真空溶解炉等の公知の方法で、溶製した後、連続鋳造法あるいは造塊-分塊法により、所定の化学組成に制御したスラブにする。得られたスラブを通常用いられる条件で熱間圧延し、熱延鋼板とする。続いて、得られた熱延鋼板に対し、必要に応じて、焼鈍、酸洗、研磨などを実施してもよい。
真空引き用の穴を予め設けた、炭素鋼または低合金鋼である母材鋼板と、オーステナイト系ステンレス鋼板である合せ材鋼板とを積層する。続いて、積層させた母材鋼板と合せ材鋼板とが当接している面(以下、「積層面」と記載する。)の周囲を溶接することで、母材鋼板および合せ材鋼板の四周を封止し、クラッド圧延素材とする。この際、溶接は、アーク溶接、レーザー溶接、電子ビーム溶接などの方法を用いればよく、その方法は特に限定されない。
続いて、真空引きおよび加熱がされたクラッド圧延を1050~1250℃の温度範囲で加熱し、熱間工程を行うことが好ましい。
続いて、熱間圧延後の冷却として、700~400℃の温度域を1.0℃/s未満の冷却速度で冷却するのが好ましく、400~200℃の温度域を0.4℃/s以下の冷却速度で、冷却するのが好ましい。
母材鋼板は、圧延後の母材において所定の炭素当量と引張強度とを有する限りにおいて、その化学組成を限定するものではない。しかしながら、後述する6-4(冷却)に示す、圧延後に徐冷を行う方法で製造を行う場合、フェライト組織が粗大化し、強度および靭性低下を招く可能性がある場合には、以下に示す化学組成を含む母材鋼板を用いることが好ましい。
Cは、母材の強度を確保するために必要な元素である。このため、C含有量は0.08%以上とするのが好ましい。しかしながら、Cを、0.10%を超えて含有させると、溶接性および低温靭性が劣化するため、C含有量は、0.10%以下とするのが好ましい。
Siは、脱酸のため必要な元素である。このため、Si含有量は0.10%以上とするのが好ましい。しかしながら、Siを、0.50%を超えて含有させると靭性が劣化し、さらに、鋼船規則K編(財団法人日本海事協会発行)に定められたKA36の規定から外れることになる。このため、Si含有量は0.50%以下とするのが好ましい。
Mnは、含有させることで、強度および靭性が向上する。このため、Mn含有量は1.30%以上とするのが好ましい。しかしながら、Mnを、1.60%を超えて含有させると、溶接性を低下させ、さらに、上述したKA36の規定から外れることになる。このため、Mn含有量は1.60%以下とするのが好ましい。
Pは、原料にも含有されており、不可避的に混入する不純物元素である。Pを過度に含有させると、溶接性等を低下させるため、P含有量は少ないほど好ましい。P含有量は0.035%以下とするのが好ましく、0.02%以下とすることがより好ましい。一方、Pを過度に低減することは、製造コストを増加させるため、P含有量は0.005%以上とするのが好ましい。
Sは、不可避的に混入する不純物元素である。また、Mnと結合して介在物を形成し、発銹の基点となる場合がある。このため、S含有量は、0.035%以下とするのが好ましい。耐食性が向上の観点から、S含有量は0.010%以下とすることがより好ましい。一方、Sを過度に低減することは、製造コストを増加させるため、S含有量は0.001%以上であるのが好ましい。
Nbは、含有させることで、母材結晶粒の微細化を促進し、強度、靭性いずれも向上させる。このため、Nb含有量は0.02%以上とするのが好ましく、0.030%以上であるのがより好ましい。しかしながら、Nbを、0.05%を超えて含有させると、Nb炭化物の析出によりかえって靭性が低下し、さらに上述のKA36の規定を外れることになる。このため、Nb含有量は0.05%以下とするのが好ましい。
Tiは、含有させることで、Ti窒化物として析出し、ステンレス鋼合せ材の鋭敏化を防止する。そして、母材と合せ材とを圧延する際に、1150℃といった高温加熱を行っても、母材オーステナイト粒の粗大化を抑制することができる。このため、Ti含有量は0.005%以上とするのが好ましい。しかしながら、Tiを、0.020%を超えて含有させると、Ti窒化物の析出により靭性が低下し、さらに、上述のKA36の規定を外れることになる。このため、Ti含有量は、0.020%以下とするのが好ましく、0.015%以下とするのがより好ましい。
Alは、通常脱酸剤として含有させる。この効果を得るためには、Al含有量は0.01%以上とするのが好ましい。しかしながら、Alを、0.05%を超えて含有させると靭性が低下する。このため、Al含有量は0.05%以下とするのが好ましい。
Nは、TiとともにTi窒化物として析出し、オーステナイト粒の粗大化を抑制するが、その含有量は不可避的に含有されるレベルで十分である。具体的には、N含有量は、0.006%以下とするのが好ましい。上記範囲を超えて含有される場合、Tiに加え、Al等と窒化物を生成し、靭性が低下する。
Niは、鋼の低温靭性等を向上させ、特に低温環境で使用される場合に有効な元素である。このため、必要に応じて限定的に含有させてもよい。しかしながら、Niを過剰に含有させると、原料コストの大幅な増加、およびクラッド界面にマルテンサイト相の生成を促す。このため、Ni含有量は、0.20%以下とするのが好ましく、0.10%以下とするのがより好ましい。一方、上記効果を得るためには、Ni含有量は0.010%以上であるのが好ましく、0.020%以上であるのがより好ましい。さらに、上述のような製造条件とするのが好ましい。
Claims (7)
- 母材と、前記母材に接合された合せ材とを備えるクラッド鋼板であって、
前記母材は、炭素鋼または低合金鋼からなり、
下記(i)式で示される前記母材の炭素当量Ceqが0.38以下で、かつ前記母材の引張強さが490MPa以上620MPa以下であり、
前記合せ材は、オーステナイト系ステンレス鋼からなり、
前記母材と前記合せ材との接合界面におけるせん断強度の平均値が400MPa以上で、かつ、前記せん断強度の標準偏差が20MPa以下である、オーステナイト系ステンレスクラッド鋼板。
Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15 ・・・(i)
但し、上記(i)式中の元素記号は、鋼中に含まれる各元素の含有量(質量%)を表し、含有されない場合はゼロとする。 - 前記母材の含有水素量が1.0ppm以下で、かつ前記合せ材の含有水素量が3.0ppm以下である、請求項1に記載のオーステナイト系ステンレスクラッド鋼板。
- 前記母材の化学組成が、質量%で、
C:0.08~0.10%、
Si:0.10~0.50%、
Mn:1.30~1.60%、
P:0.035%以下、
S:0.035%以下、
Nb:0.02~0.05%、
Ti:0.005~0.020%、
Al:0.01~0.05%、
N:0.006%以下、および
Ni:0~0.20%、
を含有する、請求項1または2に記載のオーステナイト系ステンレスクラッド鋼板。 - 請求項1~3のいずれかに記載のオーステナイト系ステンレスクラッド鋼板の製造方法であって、
(a)表面を有しかつ前記表面につながる穴が予め設けられた、炭素鋼または低合金鋼である母材鋼板と、表面を有しかつオーステナイト系ステンレス鋼である合せ材鋼板とを積層し、前記表面同士を当接させることで積層面を形成させ、前記積層面の周囲を溶接することで封止し、クラッド圧延素材とする工程と、
(b)前記クラッド圧延素材を200~450℃の温度に加熱しながら、前記積層面につながる前記穴から、前記積層面における真空度が0.1Torr以下となるように真空引きする工程と、
(c)前記(b)の工程の後に、前記クラッド圧延素材を1050~1250℃の温度範囲で加熱し、熱間圧延を行う工程と、
を有する、オーステナイト系ステンレスクラッド鋼板の製造方法。 - 前記(c)の工程において、1000℃以上の温度域での圧下比を3以上とし、1000℃未満の温度域での圧下率を30%以上として、熱間圧延を行う、
請求項4に記載のオーステナイト系ステンレスクラッド鋼板の製造方法。 - 前記(c)の工程における熱間圧延後、700~400℃の温度域を1.0℃/s未満の冷却速度で、400~200℃の温度域を0.4℃/s以下の冷却速度で、冷却する、
請求項4または5に記載のオーステナイト系ステンレスクラッド鋼板の製造方法。 - 請求項6に記載のオーステナイト系ステンレスクラッド鋼板の製造方法に用いられる母材鋼板であって、
化学組成が、質量%で、
C:0.08~0.10%、
Si:0.10~0.50%、
Mn:1.30~1.60%、
P:0.035%以下、
S:0.035%以下、
Nb:0.02~0.05%、
Ti:0.005~0.020%、
Al:0.01~0.05%、
N:0.006%以下、および
Ni:0~0.20%、
を含有する、母材鋼板。
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