US20200087745A1 - Ferritic stainless steel having excellent strength and corrosion resistance to acid and method of manufacturing the same - Google Patents
Ferritic stainless steel having excellent strength and corrosion resistance to acid and method of manufacturing the same Download PDFInfo
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- US20200087745A1 US20200087745A1 US16/473,044 US201716473044A US2020087745A1 US 20200087745 A1 US20200087745 A1 US 20200087745A1 US 201716473044 A US201716473044 A US 201716473044A US 2020087745 A1 US2020087745 A1 US 2020087745A1
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- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 45
- 239000002253 acid Substances 0.000 title claims abstract description 13
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 10
- 230000007797 corrosion Effects 0.000 title abstract description 7
- 238000005260 corrosion Methods 0.000 title abstract description 7
- 150000001247 metal acetylides Chemical class 0.000 claims abstract description 34
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims abstract description 33
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 24
- 239000010949 copper Substances 0.000 claims abstract description 24
- 239000011572 manganese Substances 0.000 claims abstract description 22
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 16
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 16
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims abstract description 13
- 229910052802 copper Inorganic materials 0.000 claims abstract description 13
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 12
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims abstract description 11
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims abstract description 11
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 11
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 11
- 239000012535 impurity Substances 0.000 claims abstract description 8
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 7
- 238000005098 hot rolling Methods 0.000 claims description 24
- 239000013078 crystal Substances 0.000 claims description 16
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 14
- 238000000034 method Methods 0.000 claims description 9
- 238000003303 reheating Methods 0.000 claims description 7
- 238000005097 cold rolling Methods 0.000 claims description 5
- 238000005096 rolling process Methods 0.000 claims description 5
- 230000000052 comparative effect Effects 0.000 description 55
- 229910000831 Steel Inorganic materials 0.000 description 33
- 239000010959 steel Substances 0.000 description 33
- 239000010960 cold rolled steel Substances 0.000 description 13
- 239000002244 precipitate Substances 0.000 description 13
- 238000000137 annealing Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 8
- 238000010438 heat treatment Methods 0.000 description 6
- 239000012467 final product Substances 0.000 description 5
- 238000009826 distribution Methods 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- 238000007670 refining Methods 0.000 description 4
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000005482 strain hardening Methods 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 238000004881 precipitation hardening Methods 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
Images
Classifications
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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
-
- 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
-
- 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
- C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
-
- 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
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- 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
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
-
- 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
-
- 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
-
- 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
- C21D8/0236—Cold rolling
-
- 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
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- 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
- C21D2211/005—Ferrite
Definitions
- the present disclosure relates to a ferritic stainless steel and a method of manufacturing the same, and more particularly, a ferritic stainless steel having an excellent strength and corrosion resistance to acid and a method of manufacturing the same.
- a ferritic stainless steel among stainless steels is widely used for building materials, kitchen containers, home appliances, parts of vehicle exhaust system, etc.
- the ferritic stainless steel has recently been applied to automotive battery cells. Automakers are demanding a higher strength and corrosion resistance than conventional ferritic stainless steels to secure long-term battery performance, and are demanding lower cost materials to lower the price of batteries.
- Methods of increasing the strength of the ferritic stainless steels to meet the automakers' demands include work hardening, solid solution strengthening, precipitation hardening, and the like.
- work hardening due to the characteristics of ferritic stainless steels without phase transformation, there is a problem that the workability is drastically lowered during work hardening.
- Mo and Nb which are excellent in solid solution strengthening, because they are expensive components.
- C which is a component damaging the workability of ferritic stainless steels
- C has been limited to 0.02 weight % or lower.
- the strength of the ferritic stainless steel can be improved due to the precipitation of carbides, and both a strength and workability can be secured when a certain degree of ductility is secured, due to recent development of processing technology.
- Patent Document 0001 Japan Patent Application Publication No. 2006-183081
- Embodiments of the present disclosure are directed to providing a ferritic stainless steel having an excellent strength and acid resistance by controlling alloy components of the ferritic stainless steel to control precipitates and crystal grains of the ferritic stainless steel.
- embodiments of the present disclosure are directed to providing a method of manufacturing a ferritic stainless steel having an excellent strength and acidacid resistance by controlling a slab reheating temperature, a reduction ratio, and a coiling temperature during hot rolling to control precipitates and crystal grains.
- a ferritic stainless steel having an excellent strength and acid resistance includes, by weight %, 0.1% to 0.2% of carbon (C), 0.005% to 0.05% of nitrogen (N), 0.01% to 0.5% of manganese (Mn), 12.0% to 19.0% of chrome (Cr), 0.01% to 0.5% of nickel (Ni), 0.3% to 1.5% of copper (Cu), the remainder iron (Fe), and other inevitable impurities, wherein a number of carbides having a diameter of 100 nm or more per unit area is 50 ea/100 ⁇ m 2 to 200 ea/100 ⁇ m 2 .
- an average crystal grain diameter may be 10 or less.
- a tensile strength may be 520 MPa or more.
- an elongation may be 20% or more.
- a critical current density I crit in a 5% sulfuric acid atmosphere may be 10 mA or less.
- a method of manufacturing a ferritic stainless steel having an excellent strength and acid resistance includes hot-rolling and cold-rolling a ferritic stainless steel slab including, by weight %, 0.1% to 0.2% of Carbon (C), 0.005% to 0.05% of nitrogen (N), 0.01% to 0.5% of manganese (Mn), 12.0% to 19.0% of chrome (Cr), 0.01% to 0.5% of nickel (Ni), 0.3% to 1.5% of copper (Cu), the remainder iron (Fe), and other inevitable impurities, wherein a value of Equation (1) during the hot rolling satisfies 1,000 or less, Equation (1) being 15*RHT/R4+CT, where RHT (° C.) represents a slab reheating temperature, R4(%) represents a reduction ratio of R4 stand of rough rolling, and CT (° C.) represents a coiling temperature.
- Equation (1) may satisfy 800 to 1,000.
- RHT may be below 1,250° C.
- R4 may be above 40%, and CT may be below 650° C.
- a number of carbides having a diameter of 100 nm or more per unit area of a cold-rolled plate may be 50 ea/100 ⁇ m 2 to 200 ea/100 ⁇ m 2 , and an average crystal grain diameter of the cold-rolled plate may be 10 ⁇ m or less.
- the strength and acid resistance of the ferritic stainless steel may be improved by controlling alloy components and hot rolling conditions to control precipitates and crystal grains.
- FIG. 1 is a graph for explaining a correlation between hot rolling conditions of a ferritic stainless steel and a number of carbides of a cold-rolled steel plate.
- FIG. 2 is a picture showing a distribution of precipitates in a ferritic stainless cold-rolled steel plate according to an embodiment of the present disclosure, taken by a transmission electron microscope (TEM).
- TEM transmission electron microscope
- FIG. 3 is a picture showing a distribution of precipitates in a ferritic stainless cold-rolled steel plate according to a comparative example of the present disclosure, taken by a TEM.
- FIG. 4 is a graph for explaining a correlation between a number of carbides and a tensile strength of a cold-rolled steel plate made of a ferritic stainless steel.
- a ferritic stainless steel having an excellent strength and acid resistance may include, by weight %, 0.1% to 0.2% of carbon (C), 0.005% to 0.05% of nitrogen (N), 0.01% to 0.5% of manganese (Mn), 12.0% to 19.0% of chrome (Cr), 0.01% to 0.5% of nickel (Ni), 0.3% to 1.5% of copper (Cu), the remainder iron (Fe), and other inevitable impurities.
- An amount of carbon (C) may be, by weight %, 0.1% to 0.2%.
- an amount of austenite generated during hot-rolling may be reduced so that ferritic band structures remain without being destroyed and the size of crystal grains increases.
- the tensile strength of the final cold rolled product may be lowered to less than 500 MPa.
- carbides of materials may increase excessively to deteriorate the elongation of the final product, and the carbides may fall off to deteriorate surface quality and corrosion resistance.
- An amount of nitrogen (N) may be, by weight %, 0.005% to 0.05%.
- a refining time may increase and the lifecycle of refractories may be reduced, resulting in an increase of manufacturing cost.
- an equiaxed structure ratio of a slab may be lowered due to a low degree of subcooling upon casting.
- the amount of nitrogen (N) exceeds 0.05%, there is a high possibility that pinholes are made due to nitrogen during slab casting, the number of Cr 2 N precipitates per unit area in the final cold rolled product may increase, and accordingly, a Cr depleted zone formed around the Cr 2 N precipitates forms a large number of pits on the surface of the final cold rolled product, resulting in poor surface quality.
- An amount of manganese (Mn) may be, by weight %, 0.01% to 0.5%. When the amount of manganese (Mn) is less than 0.01%, refining cost may increase, and when the amount of manganese (Mn) exceeds 0.5%, an elongation and corrosion resistance may be lowered.
- An amount of chrome (Cr) may be, by weight %, 12.0% to 19.0%.
- amount of chrome (Cr) is less than 12.0%, corrosion resistance may deteriorate, whereas when the amount of chrome (Cr) exceeds 19.0%, an elongation may be lowered, and hot-rolling sticking defects may be generated.
- An amount of nickel (Ni) may be, by weight %, 0.01% to 0.5%.
- amount of nickel (Ni) is less than 0.01%, refining cost may increase, whereas when the amount of nickel (Ni) exceeds 0.5%, the impurities of the materials may increase, which lowers an elongation.
- An amount of copper (Cu) may be, by weight %, 0.3% to 1.5%.
- the critical current density I crit may exceed 10 mA in a 5% sulfuric acid atmosphere so that sufficient acid resistance may not be secured.
- the amount of copper (Cu) exceeds 1.5%, material cost may increase significantly, and furthermore, the hot workability and the elongation of the final product may be lowered.
- the number of carbides having a diameter of 100 nm or more per unit area may be 50 ea/100 ⁇ m 2 .
- the carbides may be M 23 C 6 type carbide-based metal precipitates.
- deformed structures may need to be sufficiently formed in a hot rolled material during a hot rolling process.
- the deformed structures are not sufficiently formed, it is difficult to increase the amount of carbides because carbide precipitation sites are not sufficient.
- a slab reheating temperature, a rough rolling reduction ratio and a hot rolled coil coiling temperature may need to be controlled during a hot rolling process, and details thereof will be described later.
- the number of carbides having a diameter of 100 nm or more per unit area can reach 50 ea/100 ⁇ m 2 or more.
- a tensile strength of 520 MPa or more can be secured.
- the number of carbides having a diameter of 100 nm or more is less than 50 ea/100 ⁇ m 2 , coarsening may occur due to the small amount of carbides, which lowers the tensile strength.
- the ferritic stainless steel may have an average crystal grain diameter of 10 ⁇ m or less.
- the ferritic stainless steel according to an embodiment of the present disclosure may have a tensile strength of 520 MPa or more.
- the ferritic stainless steel according to an embodiment of the present disclosure may have an elongation of 20% or more.
- the ferritic stainless steel according to an embodiment of the present disclosure may have critical current density I crit of 10 mA or less in a 5% sulfuric acid atmosphere.
- a method of manufacturing a ferritic stainless steel, according to an embodiment of the present disclosure, for manufacturing the ferritic stainless steel according to an embodiment of the present disclosure may include hot-rolling and cold-rolling a ferritic stainless steel slab including, by weight %, 0.1% to 0.2% of carbon (C), 0.005% to 0.05% of nitrogen (N), 0.01% to 0.5% of manganese (Mn), 12.0% to 19.0% of chrome (Cr), 0.01% to 0.5% of nickel (Ni), 0.3% to 1.5% of copper (Cu), the remainder iron (Fe) and other inevitable impurities, wherein a value of Equation (1) during the hot rolling satisfies 1,000 or less:
- RHT (° C.) represents a slab reheating temperature
- R4(%) represents a reduction ratio of a R4 stand of rough rolling
- CT (° C.) represents a coiling temperature
- the ferritic stainless steel slab may be produced through continuous casting of molten steel containing the above-mentioned components. Thereafter, the slab may be hot-rolled and a hot-rolled coil having a thickness of 2 mm to 10 mm may be produced through hot rolling.
- the slab reheating temperature (RHT) may be less than 1,250° C.
- the reduction ratio of the R4 stand of the rough rolling may be 40% or more
- the coiling temperature (CT) may be less than 650° C.
- the hot rolling conditions may be set such that the value of Equation (1) satisfies 1,000 or less.
- FIG. 1 is a graph for explaining a correlation between hot rolling conditions of a ferritic stainless steel and the number of carbides of a cold-rolled steel plate.
- Equation (1) when a value of Equation (1) is 1,000 or less, the number of carbides having a diameter of 100 nm or more is 50 ea/100 ⁇ m 2 or more.
- the coiling temperature is as high as 650° C. or higher, coarsening of precipitates occurs, and a desired number of carbides may not be obtained. As a result, crystal grains become coarse, and a desired tensile strength may not be obtained in the final product.
- Equation (1) may satisfy 800 to 1,000.
- Equation (1) When the value of Equation (1) is less than 800, a temperature during hot rolling may be too low, resulting in a poor plate shape.
- the hot-rolled plate is subjected to an annealing process, and carbides are sufficiently precipitated through annealing at 700° C. to 900° C. in the annealing process.
- the annealing heat treatment may be performed by a BAF annealing process.
- a cold rolled plate having a thickness of less than 2 mm is produced through cold rolling, and final heat treatment may be performed through heat treatment at a temperature of 800° C. to 900° C.
- the number of carbides having a diameter of 100 nm or more per unit area may be 50 ea/100 ⁇ m 2 or more and an average crystal grain diameter may be 10 ⁇ m or less.
- Slabs of inventive steels 1 to 4 and comparative steels 1 to 9 satisfying components of Table 1 were produced through continuous casting and reheated according to hot rolling conditions of Table 2, and then a hot-rolled coil of 5 mmt was produced through hot rolling. Then, annealing heat treatment was performed at 900° C. in a BAF annealing process. Thereafter, a cold rolled steel plate having a thickness of 1 mmt was prepared by cold rolling, heat treatment was conducted at 900° C., and a final product was produced by surface short ball treatment and pickling with sulfuric acid and hydrogen peroxide.
- the number of carbides having a diameter of 100 nm or more per unit area, an average crystal grain diameter, a tensile strength, an elongation, and critical current density in a 5% sulfuric acid atmosphere were measured and shown in Table 3 below.
- a TEM replica for the final cold rolled plate was made, and the number of carbide precipitates per unit area (100 ⁇ m 2 ) was measured.
- FIG. 2 is a picture showing a distribution of precipitates in a ferritic stainless steel cold-rolled steel plate according to an embodiment of the present disclosure, taken by a transmission electron microscope (TEM).
- FIG. 3 is a picture showing a distribution of precipitates in a ferritic stainless steel cold-rolled steel plate according to a comparative example of the present disclosure, taken by a TEM.
- TEM transmission electron microscope
- FIG. 2 is a picture showing a cold-rolled steel plate according to Embodiment 2
- FIG. 3 is a picture showing a cold-rolled steel plate according to Comparative Example 2.
- a value of 15*RHT/R4+CT according to the relational expression relating to a slab reheating temperature, a R4 reduction ratio, and a coiling temperature upon hot rolling exceeds 1,000, as in Comparative Examples 1 to 4, so that sufficient deformed structures for a hot rolling material are not formed and thus carbide precipitation sites are not sufficient although a carbon content is sufficient.
- FIG. 4 is a graph for explaining a correlation between the number of carbides and the tensile strength of a cold-rolled steel plate made of a ferritic stainless steel.
- FIG. 4 is a graph showing the numbers of carbides and tensile strengths of the cold-rolled steel plates according to the embodiments and the comparative examples. Referring to FIG. 4 , it is confirmed that as the number of carbides increases, the tensile strength tends to increase accordingly.
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Abstract
Description
- The present disclosure relates to a ferritic stainless steel and a method of manufacturing the same, and more particularly, a ferritic stainless steel having an excellent strength and corrosion resistance to acid and a method of manufacturing the same.
- A ferritic stainless steel among stainless steels is widely used for building materials, kitchen containers, home appliances, parts of vehicle exhaust system, etc.
- The ferritic stainless steel has recently been applied to automotive battery cells. Automakers are demanding a higher strength and corrosion resistance than conventional ferritic stainless steels to secure long-term battery performance, and are demanding lower cost materials to lower the price of batteries.
- Methods of increasing the strength of the ferritic stainless steels to meet the automakers' demands include work hardening, solid solution strengthening, precipitation hardening, and the like. However, due to the characteristics of ferritic stainless steels without phase transformation, there is a problem that the workability is drastically lowered during work hardening. Also, it is difficult to utilize Mo and Nb, which are excellent in solid solution strengthening, because they are expensive components.
- Conventionally, carbon (C), which is a component damaging the workability of ferritic stainless steels, has been limited to 0.02 weight % or lower. However, when a large amount of C is added, the strength of the ferritic stainless steel can be improved due to the precipitation of carbides, and both a strength and workability can be secured when a certain degree of ductility is secured, due to recent development of processing technology.
- However, in the case in which hot rolling is performed at a high temperature, a reduction ratio is low, and a coiling temperature is high even when a large amount of C is added, carbides are precipitated not finely but coarsely in the deformed structure. As a result, there is a problem that it is difficult to refine the crystal grains and to secure a desired strength.
- (Patent Document 0001) Japan Patent Application Publication No. 2006-183081
- Embodiments of the present disclosure are directed to providing a ferritic stainless steel having an excellent strength and acid resistance by controlling alloy components of the ferritic stainless steel to control precipitates and crystal grains of the ferritic stainless steel.
- In addition, embodiments of the present disclosure are directed to providing a method of manufacturing a ferritic stainless steel having an excellent strength and acidacid resistance by controlling a slab reheating temperature, a reduction ratio, and a coiling temperature during hot rolling to control precipitates and crystal grains.
- A ferritic stainless steel having an excellent strength and acid resistance according to an embodiment of the present disclosure includes, by weight %, 0.1% to 0.2% of carbon (C), 0.005% to 0.05% of nitrogen (N), 0.01% to 0.5% of manganese (Mn), 12.0% to 19.0% of chrome (Cr), 0.01% to 0.5% of nickel (Ni), 0.3% to 1.5% of copper (Cu), the remainder iron (Fe), and other inevitable impurities, wherein a number of carbides having a diameter of 100 nm or more per unit area is 50 ea/100 μm2 to 200 ea/100 μm2.
- In addition, according to an embodiment of the present disclosure, an average crystal grain diameter may be 10 or less.
- In addition, according to an embodiment of the present disclosure, a tensile strength may be 520 MPa or more.
- In addition, according to an embodiment of the present disclosure, an elongation may be 20% or more.
- In addition, according to an embodiment of the present disclosure, a critical current density Icrit in a 5% sulfuric acid atmosphere may be 10 mA or less.
- A method of manufacturing a ferritic stainless steel having an excellent strength and acid resistance according to an embodiment of the present disclosure includes hot-rolling and cold-rolling a ferritic stainless steel slab including, by weight %, 0.1% to 0.2% of Carbon (C), 0.005% to 0.05% of nitrogen (N), 0.01% to 0.5% of manganese (Mn), 12.0% to 19.0% of chrome (Cr), 0.01% to 0.5% of nickel (Ni), 0.3% to 1.5% of copper (Cu), the remainder iron (Fe), and other inevitable impurities, wherein a value of Equation (1) during the hot rolling satisfies 1,000 or less, Equation (1) being 15*RHT/R4+CT, where RHT (° C.) represents a slab reheating temperature, R4(%) represents a reduction ratio of R4 stand of rough rolling, and CT (° C.) represents a coiling temperature.
- In addition, according to an embodiment of the present disclosure, the value of Equation (1) may satisfy 800 to 1,000.
- In addition, according to an embodiment of the present disclosure, RHT may be below 1,250° C. R4 may be above 40%, and CT may be below 650° C.
- In addition, according to an embodiment of the present disclosure, a number of carbides having a diameter of 100 nm or more per unit area of a cold-rolled plate may be 50 ea/100 μm2 to 200 ea/100 μm2, and an average crystal grain diameter of the cold-rolled plate may be 10 μm or less.
- According to the embodiments of the present disclosure, the strength and acid resistance of the ferritic stainless steel may be improved by controlling alloy components and hot rolling conditions to control precipitates and crystal grains.
-
FIG. 1 is a graph for explaining a correlation between hot rolling conditions of a ferritic stainless steel and a number of carbides of a cold-rolled steel plate. -
FIG. 2 is a picture showing a distribution of precipitates in a ferritic stainless cold-rolled steel plate according to an embodiment of the present disclosure, taken by a transmission electron microscope (TEM). -
FIG. 3 is a picture showing a distribution of precipitates in a ferritic stainless cold-rolled steel plate according to a comparative example of the present disclosure, taken by a TEM. -
FIG. 4 is a graph for explaining a correlation between a number of carbides and a tensile strength of a cold-rolled steel plate made of a ferritic stainless steel. - Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The following embodiments are provided to sufficiently transfer the technical concepts of the disclosure to one of ordinary skill in the art. However, the disclosure is not limited to these embodiments, and may be embodied in another form. In the drawings, parts that are irrelevant to the descriptions may be not shown in order to clarify the disclosure, and also, for easy understanding, the widths, lengths, thicknesses, etc. of components are more or less exaggeratedly shown. Like numbers refer to like elements throughout this specification.
- A ferritic stainless steel having an excellent strength and acid resistance, according to an exemplary embodiment of the present disclosure, may include, by weight %, 0.1% to 0.2% of carbon (C), 0.005% to 0.05% of nitrogen (N), 0.01% to 0.5% of manganese (Mn), 12.0% to 19.0% of chrome (Cr), 0.01% to 0.5% of nickel (Ni), 0.3% to 1.5% of copper (Cu), the remainder iron (Fe), and other inevitable impurities.
- Carbon (C): 0.1% to 0.2%
- An amount of carbon (C) may be, by weight %, 0.1% to 0.2%. When the amount of carbon (C) is less than 0.1%, an amount of austenite generated during hot-rolling may be reduced so that ferritic band structures remain without being destroyed and the size of crystal grains increases. As a result, the tensile strength of the final cold rolled product may be lowered to less than 500 MPa. Also, when the amount of carbon (C) exceeds 0.2%, carbides of materials may increase excessively to deteriorate the elongation of the final product, and the carbides may fall off to deteriorate surface quality and corrosion resistance.
- Nitrogen (N): 0.005% to 0.05%
- An amount of nitrogen (N) may be, by weight %, 0.005% to 0.05%. When the amount of nitrogen (N) is less than 0.005%, a refining time may increase and the lifecycle of refractories may be reduced, resulting in an increase of manufacturing cost. Also, an equiaxed structure ratio of a slab may be lowered due to a low degree of subcooling upon casting. Meanwhile, when the amount of nitrogen (N) exceeds 0.05%, there is a high possibility that pinholes are made due to nitrogen during slab casting, the number of Cr2N precipitates per unit area in the final cold rolled product may increase, and accordingly, a Cr depleted zone formed around the Cr2N precipitates forms a large number of pits on the surface of the final cold rolled product, resulting in poor surface quality.
- Manganese (Mn): 0.01% to 0.5%
- An amount of manganese (Mn) may be, by weight %, 0.01% to 0.5%. When the amount of manganese (Mn) is less than 0.01%, refining cost may increase, and when the amount of manganese (Mn) exceeds 0.5%, an elongation and corrosion resistance may be lowered.
- Chrome (Cr): 12.0% to 19.0%
- An amount of chrome (Cr) may be, by weight %, 12.0% to 19.0%. When the amount of chrome (Cr) is less than 12.0%, corrosion resistance may deteriorate, whereas when the amount of chrome (Cr) exceeds 19.0%, an elongation may be lowered, and hot-rolling sticking defects may be generated.
- Nickel (Ni): 0.01% to 0.5%
- An amount of nickel (Ni) may be, by weight %, 0.01% to 0.5%. When the amount of nickel (Ni) is less than 0.01%, refining cost may increase, whereas when the amount of nickel (Ni) exceeds 0.5%, the impurities of the materials may increase, which lowers an elongation.
- Copper (Cu): 0.3% to 1.5%
- An amount of copper (Cu) may be, by weight %, 0.3% to 1.5%. When the amount of copper (Cu) is less than 0.3%, the critical current density Icrit may exceed 10 mA in a 5% sulfuric acid atmosphere so that sufficient acid resistance may not be secured. When the amount of copper (Cu) exceeds 1.5%, material cost may increase significantly, and furthermore, the hot workability and the elongation of the final product may be lowered.
- In order to obtain a desired tensile strength in a final cold-rolled product of a ferritic stainless steel, it is necessary to secure a large number of fine carbides, and refining of crystal grains is required.
- In the ferritic stainless steel having the excellent strength and acid resistance, according to an embodiment of the present disclosure, the number of carbides having a diameter of 100 nm or more per unit area may be 50 ea/100 μm2.
- For example, the carbides may be M23C6 type carbide-based metal precipitates.
- In order to increase the number of carbides per unit area, deformed structures may need to be sufficiently formed in a hot rolled material during a hot rolling process. When the deformed structures are not sufficiently formed, it is difficult to increase the amount of carbides because carbide precipitation sites are not sufficient.
- In order to sufficiently form deformed structures in the hot rolled material, a slab reheating temperature, a rough rolling reduction ratio and a hot rolled coil coiling temperature may need to be controlled during a hot rolling process, and details thereof will be described later.
- That is, through the control of hot rolling process conditions, the number of carbides having a diameter of 100 nm or more per unit area can reach 50 ea/100 μm2 or more. By securing a large number of fine carbides, a tensile strength of 520 MPa or more can be secured. When the above-mentioned process conditions are not satisfied, a sufficient amount of carbides cannot be obtained because of the generation of coarse carbides.
- For example, when the number of carbides having a diameter of 100 nm or more is less than 50 ea/100 μm2, coarsening may occur due to the small amount of carbides, which lowers the tensile strength.
- For example, the ferritic stainless steel may have an average crystal grain diameter of 10 μm or less.
- For example, the ferritic stainless steel according to an embodiment of the present disclosure may have a tensile strength of 520 MPa or more.
- For example, the ferritic stainless steel according to an embodiment of the present disclosure may have an elongation of 20% or more.
- For example, the ferritic stainless steel according to an embodiment of the present disclosure may have critical current density Icrit of 10 mA or less in a 5% sulfuric acid atmosphere.
- A method of manufacturing a ferritic stainless steel, according to an embodiment of the present disclosure, for manufacturing the ferritic stainless steel according to an embodiment of the present disclosure, may include hot-rolling and cold-rolling a ferritic stainless steel slab including, by weight %, 0.1% to 0.2% of carbon (C), 0.005% to 0.05% of nitrogen (N), 0.01% to 0.5% of manganese (Mn), 12.0% to 19.0% of chrome (Cr), 0.01% to 0.5% of nickel (Ni), 0.3% to 1.5% of copper (Cu), the remainder iron (Fe) and other inevitable impurities, wherein a value of Equation (1) during the hot rolling satisfies 1,000 or less:
-
15*RHT/R4+CT Equation (1), - where, RHT (° C.) represents a slab reheating temperature, R4(%) represents a reduction ratio of a R4 stand of rough rolling, and CT (° C.) represents a coiling temperature.
- The ferritic stainless steel slab may be produced through continuous casting of molten steel containing the above-mentioned components. Thereafter, the slab may be hot-rolled and a hot-rolled coil having a thickness of 2 mm to 10 mm may be produced through hot rolling.
- For example, the slab reheating temperature (RHT) may be less than 1,250° C., the reduction ratio of the R4 stand of the rough rolling may be 40% or more, and the coiling temperature (CT) may be less than 650° C. In this case, the hot rolling conditions may be set such that the value of Equation (1) satisfies 1,000 or less.
-
FIG. 1 is a graph for explaining a correlation between hot rolling conditions of a ferritic stainless steel and the number of carbides of a cold-rolled steel plate. - Referring to
FIG. 1 , it is seen that when a value of Equation (1) is 1,000 or less, the number of carbides having a diameter of 100 nm or more is 50 ea/100 μm2 or more. - When the hot rolling condition of Equation (1) is not satisfied although a carbon content is sufficient, deformed structures are not sufficiently formed in the hot rolled material so that carbide precipitation sites are not sufficiently formed.
- Particularly, when the coiling temperature is as high as 650° C. or higher, coarsening of precipitates occurs, and a desired number of carbides may not be obtained. As a result, crystal grains become coarse, and a desired tensile strength may not be obtained in the final product.
- For example, the value of Equation (1) may satisfy 800 to 1,000.
- When the value of Equation (1) is less than 800, a temperature during hot rolling may be too low, resulting in a poor plate shape.
- The hot-rolled plate is subjected to an annealing process, and carbides are sufficiently precipitated through annealing at 700° C. to 900° C. in the annealing process. For example, the annealing heat treatment may be performed by a BAF annealing process. After the annealing heat treatment, a cold rolled plate having a thickness of less than 2 mm is produced through cold rolling, and final heat treatment may be performed through heat treatment at a temperature of 800° C. to 900° C.
- For example, in the cold rolled plate, the number of carbides having a diameter of 100 nm or more per unit area may be 50 ea/100 μm2 or more and an average crystal grain diameter may be 10 μm or less.
- Hereinafter, the present disclosure will be described in more detail through embodiments.
- Slabs of inventive steels 1 to 4 and comparative steels 1 to 9 satisfying components of Table 1 were produced through continuous casting and reheated according to hot rolling conditions of Table 2, and then a hot-rolled coil of 5 mmt was produced through hot rolling. Then, annealing heat treatment was performed at 900° C. in a BAF annealing process. Thereafter, a cold rolled steel plate having a thickness of 1 mmt was prepared by cold rolling, heat treatment was conducted at 900° C., and a final product was produced by surface short ball treatment and pickling with sulfuric acid and hydrogen peroxide.
-
TABLE 1 C N Mn Cr Ni Cu Inventive Steel 1 0.103 0.014 0.13 14.3 0.11 0.67 Inventive Steel 2 0.171 0.016 0.11 17.2 0.09 0.45 Inventive Steel 3 0.122 0.006 0.24 16.7 0.13 1.21 Inventive Steel 4 0.125 0.008 0.19 16.5 0.12 1.05 Comparative Steel 1 0.133 0.012 0.23 17.5 0.15 1.79 Comparative Steel 2 0.147 0.015 0.24 16.9 0.17 0.14 Comparative Steel 3 0.227 0.022 0.15 17.1 0.21 0.84 Comparative Steel 4 0.232 0.017 0.14 17.6 0.11 0.66 Comparative Steel 5 0.042 0.046 0.21 16.2 0.11 0.12 Comparative Steel 6 0.051 0.042 0.15 15.2 0.13 0.23 Comparative Steel 7 0.047 0.041 0.17 16.9 0.14 0.77 Comparative Steel 8 0.062 0.015 0.16 17.3 0.13 0.81 Comparative Steel 9 0.085 0.015 0.25 18.1 0.15 0.67 -
TABLE 2 RHT Steel (° C.) CT (° C.) R4 (%) 15 * RHT/R4 + CT Embodiment 1 Inventive Steel 1 1,130 550 45 927 Embodiment 2 Inventive Steel 2 1,130 550 45 927 Embodiment 3 Inventive Steel 3 1,180 550 45 943 Embodiment 4 Inventive Steel 4 1,180 580 45 973 Comparative Inventive Steel 1 1,250 550 30 1,175 Example 1 Comparative Inventive Steel 2 1,180 650 30 1,240 Example 2 Comparative Inventive Steel 3 1,180 580 30 1,170 Example 3 Comparative Inventive Steel 4 1,250 550 40 1,019 Example 4 Comparative Comparative 1,130 550 45 927 Example 5 Steel 1 Comparative Comparative 1,130 580 45 957 Example 6 Steel 2 Comparative Comparative 1,180 550 45 943 Example 7 Steel 3 Comparative Comparative 1,180 580 45 973 Example 8 Steel 4 Comparative Comparative 1,180 650 30 1,240 Example 9 Steel 5 Comparative Comparative 1,130 550 45 927 Example 10 Steel 6 Comparative Comparative 1,180 550 45 943 Example 11 Steel 7 Comparative Comparative 1,180 650 45 1,043 Example 12 Steel 8 Comparative Comparative 1,250 650 30 1,275 Example 13 Steel 9 - With respect to the final cold-rolled steel plate, the number of carbides having a diameter of 100 nm or more per unit area, an average crystal grain diameter, a tensile strength, an elongation, and critical current density in a 5% sulfuric acid atmosphere were measured and shown in Table 3 below.
- A TEM replica for the final cold rolled plate was made, and the number of carbide precipitates per unit area (100 μm2) was measured.
-
TABLE 3 Critical Current Density in a 5% The number of Average crystal Sulfuric Acid Carbides Grain Diameter Tensile Strength Atmosphere (ea/100 μm2) (μm) Elongation (%) (MPa) (mA) Embodiment 1 91 6.8 25.7 529 5.6 Embodiment 2 124 5.9 23.9 531 7.2 Embodiment 3 72 7.4 25.3 542 3.7 Embodiment 4 75 8.1 26.7 537 3.5 Comparative 32 10.8 27.6 498 8.5 Example 1 Comparative 45 11.6 25.3 508 5.9 Example 2 Comparative 37 10.5 26.7 515 4.2 Example 3 Comparative 41 12.1 27.2 498 4.5 Example 4 Comparative 81 6.5 18.8 554 3.1 Example 5 Comparative 107 5.4 25.7 527 14.5 Example 6 Comparative 227 4.8 18.5 567 6.9 Example 7 Comparative 305 5.3 19.2 572 7.5 Example 8 Comparative 13 18.1 30.1 457 15.6 Example 9 Comparative 19 17.3 29.8 453 13.8 Example 10 Comparative 28 20.6 28.9 476 6.3 Example 11 Comparative 21 14.1 27.7 481 5.4 Example 12 Comparative 26 12.0 26.3 491 4.2 Example 13 -
FIG. 2 is a picture showing a distribution of precipitates in a ferritic stainless steel cold-rolled steel plate according to an embodiment of the present disclosure, taken by a transmission electron microscope (TEM).FIG. 3 is a picture showing a distribution of precipitates in a ferritic stainless steel cold-rolled steel plate according to a comparative example of the present disclosure, taken by a TEM. -
FIG. 2 is a picture showing a cold-rolled steel plate according to Embodiment 2, andFIG. 3 is a picture showing a cold-rolled steel plate according to Comparative Example 2. - Referring to
FIGS. 2 and 3 , a value of 15*RHT/R4+CT according to the relational expression relating to a slab reheating temperature, a R4 reduction ratio, and a coiling temperature upon hot rolling exceeds 1,000, as in Comparative Examples 1 to 4, so that sufficient deformed structures for a hot rolling material are not formed and thus carbide precipitation sites are not sufficient although a carbon content is sufficient. - Furthermore, when the coiling temperature is high as in Comparative Example 2, coarsening of precipitates occurs so that a desired number of carbides may not be obtained.
- When the copper content is excessive as in Comparative Example 5, the elongation of the final product becomes 18.8%, which means that the elongation deteriorates. When the copper content is small as in Comparative Example 6, the critical current density Icrit is 14.5 mA so that sufficient acid resistance may not be secured.
- When the carbon content is excessive as in Comparative Examples 7 and 8, the number of carbides increases and an elongation decreases. When the carbon content is small as in Comparative Examples 9 to 13, it is confirmed that the crystal grain size increases and the tensile strength is lowered to less than 500 MPa.
-
FIG. 4 is a graph for explaining a correlation between the number of carbides and the tensile strength of a cold-rolled steel plate made of a ferritic stainless steel. -
FIG. 4 is a graph showing the numbers of carbides and tensile strengths of the cold-rolled steel plates according to the embodiments and the comparative examples. Referring toFIG. 4 , it is confirmed that as the number of carbides increases, the tensile strength tends to increase accordingly. - While the present disclosure has been particularly described with reference to exemplary embodiments, it should be understood by those of skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the present disclosure.
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US9353424B2 (en) * | 2013-03-14 | 2016-05-31 | Nippon Steel & Sumitomo Metal Corporation | High strength steel sheet excellent in delayed fracture resistance and low temperature toughness, and high strength member manufactured using the same |
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JPS52108314A (en) * | 1976-03-09 | 1977-09-10 | Nippon Steel Corp | Highly tough ferritic stainless steel having improved hydrogen-induced crack resistance |
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JPH01159319A (en) * | 1987-12-16 | 1989-06-22 | Kawasaki Steel Corp | Production of high-corrosion resistance ferritic stainless steel having excellent moldability |
JPH05179357A (en) * | 1991-12-27 | 1993-07-20 | Sumitomo Metal Ind Ltd | Production of cold rolled ferritic stainless steel sheet |
TW429270B (en) * | 1996-03-15 | 2001-04-11 | Ugine Sa | Process for producing a ferritic stainless steel having an improved corrosion resistance, especially resistance to intergranular and pitting corrosion |
JP2000178694A (en) * | 1998-12-09 | 2000-06-27 | Nippon Steel Corp | Ferritic stainless steel excellent in surface property and workability and its production |
JP4285843B2 (en) | 1999-07-21 | 2009-06-24 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel with excellent shape freezing property during bending and its manufacturing method |
CN1226442C (en) * | 2002-11-18 | 2005-11-09 | 烨联钢铁股份有限公司 | Austenitic stainless steel having low nickel content |
JP4082205B2 (en) * | 2002-12-20 | 2008-04-30 | Jfeスチール株式会社 | Ferritic stainless steel sheet excellent in workability and ridging resistance and method for producing the same |
JP2007186764A (en) * | 2006-01-13 | 2007-07-26 | Nisshin Steel Co Ltd | Free-cutting ferritic stainless steel |
CN101008043B (en) * | 2006-01-27 | 2010-05-12 | 宝山钢铁股份有限公司 | Process for producing ferritic stainless steel |
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JP4915923B2 (en) * | 2007-02-09 | 2012-04-11 | 日立金属株式会社 | Ferritic stainless cast steel and cast member with excellent acid resistance |
JP2011001564A (en) * | 2008-03-21 | 2011-01-06 | Nisshin Steel Co Ltd | Ferritic stainless steel sheet having excellent roughening resistance and method for producing the same |
JP5375069B2 (en) | 2008-12-15 | 2013-12-25 | Jfeスチール株式会社 | Ferritic stainless steel plate with excellent corrosion resistance on the shear end face |
CN103643157B (en) * | 2013-11-26 | 2015-11-18 | 攀钢集团江油长城特殊钢有限公司 | A kind of copper-bearing ferritic Stainless Steel Disc unit and manufacture method thereof |
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US9353424B2 (en) * | 2013-03-14 | 2016-05-31 | Nippon Steel & Sumitomo Metal Corporation | High strength steel sheet excellent in delayed fracture resistance and low temperature toughness, and high strength member manufactured using the same |
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