US20170283894A1 - Ferritic stainless steel having excellent ductility and method for manufacturing same - Google Patents

Ferritic stainless steel having excellent ductility and method for manufacturing same Download PDF

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US20170283894A1
US20170283894A1 US15/529,263 US201515529263A US2017283894A1 US 20170283894 A1 US20170283894 A1 US 20170283894A1 US 201515529263 A US201515529263 A US 201515529263A US 2017283894 A1 US2017283894 A1 US 2017283894A1
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ferritic stainless
stainless steel
less
precipitate
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Soo-ho Park
Jae-hong Shim
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Posco Holdings Inc
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Posco Co Ltd
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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
    • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
    • B22D11/002—Stainless steels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
    • B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
    • 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
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips 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
    • 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
    • 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
    • C21D8/0247—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
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • 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
    • 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
    • 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • 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
    • C21D2211/004—Dispersions; Precipitations
    • 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 ferritic stainless steel having a high degree of ductility and a method for manufacturing the ferritic stainless steel, and more particularly, to a new kind of ferritic stainless steel provided by improving ferritic stainless steel having poor ductility compared to austenitic stainless steel for use in applications requiring high ductility, and a method for manufacturing the ferritic stainless steel.
  • Ferritic stainless steels have a high degree of corrosion resistance even though the contents of expensive alloying elements in the ferritic stainless steels are low. That is, ferritic stainless steels are more competitive in price than austenitic stainless steels. Ferritic stainless steels are used in applications such as construction materials, transportation vehicles, or kitchen utensils. However, ferrite stainless steels have poor ductility and thus it is difficult to use ferritic stainless steels instead of austenitic stainless steels in many applications. Therefore, many efforts have been made to improve the ductility of ferritic stainless steels and thus to increase the applications of ferritic stainless steels.
  • An aspect of the present disclosure may provide ferritic stainless steel having a high degree of ductility and a method of manufacturing the ferritic stainless steel.
  • ferritic stainless steel may include, by wt %, C: 0.005% to 0.1%, Si: 0.01% to 2.0%, Mn: 0.01% to 1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10% to 30%, Ti: 0.005% to 0.5%, Al: 0.01% to 0.15%, N: 0.005% to 0.03%, and the balance of Fe and inevitable impurities, wherein the ferritic stainless steel may include 3.5 ⁇ 10 6 or fewer particles of an independent Ti(CN) precipitate per square millimeter (mm 2 ) of ferrite matrix.
  • ferritic stainless steel may include, by wt %, C: 0.005% to 0.1%, Si: 0.01% to 2.0%, Mn: 0.01% to 1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10% to 30%, Ti: 0.005% to 0.5%, Al: 0.01% to 0.15%, N: 0.005% to 0.03%, and the balance of Fe and inevitable impurities, wherein the ferritic stainless steel may include an independent Ti(CN) precipitate and a dependent Ti(CN) precipitate formed using a TiN inclusion as precipitation nuclei, and the ferritic stainless steel may have a P within a range of 60% or less, the P being defined by Formula 1 below:
  • N S refers to the number of independent Ti(CN) precipitate particles per unit area (mm 2 )
  • N C refers to the number of dependent Ti(CN) precipitate particles per unit area (mm 2 ).
  • the independent Ti(CN) precipitate may have a particle diameter of 0.01 ⁇ m or greater.
  • the independent Ti(CN) precipitate may have an average particle diameter of 0.15 ⁇ m or less.
  • the TiN inclusion may have an average particle diameter of 2 ⁇ m or greater.
  • the ferritic stainless steel may have an elongation of 34% or greater.
  • a method for manufacturing ferritic stainless steel may include casting molten steel as a slab, the molten steel including, by wt %, C: 0.005% to 0.1%, Si: 0.01% to 2.0%, Mn: 0.01% to 1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10% to 30%, Ti: 0.005% to 0.5%, Al: 0.01% to 0.15%, N: 0.005% to 0.03%, and the balance of Fe and inevitable impurities, wherein in the casting of the molten steel, the slab may be cooled at an average cooling rate of 5° C./sec or less (excluding 0° C./sec) within a temperature range of 1100° C. to 1200° C. based on a surface temperature of the slab.
  • the slab may be cooled at an average cooling rate of 5° C./sec or less (excluding 0° C./sec) within a temperature range of 1000° C. to 1250° C. based on the surface temperature of the slab.
  • the method may further include: obtaining a hot-rolled sheet by performing a hot rolling process on the slab; and performing a hot band annealing process on the hot-rolled sheet within a temperature range of 450° C. to 1080° C. for 1 minute to 60 minutes.
  • the ferritic stainless steel of the present disclosure has a high degree of ductility.
  • FIG. 1 is a scanning electron microscope (SEM) image illustrating the microstructure of a hot-rolled sheet of Inventive Example 1.
  • FIG. 2 is a high magnification SEM image illustrating region A in FIG. 1 .
  • the inventors have reviewed various factors to improve the ductility of ferritic stainless steel and have acquired the following knowledge.
  • Ti titanium
  • Ti(CN) a large amount of Ti(CN) inevitably precipitates in the ferrite matrix of Ti-containing ferritic stainless steel, and the Ti(CN) precipitate becomes the main cause of ductility deterioration.
  • the Ti(CN) precipitate includes a Ti(CN) precipitate independently formed in the ferrite matrix (hereinafter referred to as an “independent Ti(CN) precipitate”) and a Ti(CN) precipitate formed with the help of particles of a TiN inclusion that are crystallized during a steel making process and function as precipitation nuclei (hereinafter referred to as a “dependent Ti(CN) precipitate”).
  • the dependent Ti(CN) precipitate does not have a significant effect on ductility deterioration when compared to the independent Ti(CN) precipitate.
  • ferritic stainless steel having a high degree of ductility will be described in detail according to an aspect of the present disclosure.
  • carbon (C) markedly affects the strength of steel
  • the content of carbon (C) in steel is excessively high, the strength of the steel may increase to an excessive degree, and the ductility of the steel may decrease. Therefore, the content of carbon (C) is limited to 0.1% or less.
  • the lower limit of the content of carbon (C) may be limited to 0.005%.
  • Silicon (Si) is an element added to molten steel during a steel making process to remove oxygen and stabilize ferrite. In the present disclosure, silicon (Si) is added in an amount of 0.01% or greater. However, if the content of silicon (Si) in steel is excessively high, the ductility of the steel may decrease due to hardening. Therefore, the content of silicon (Si) is limited to 2.0% or less.
  • Manganese (Mn) is an element effective in improving the corrosion resistance of steel.
  • manganese (Mn) is added in an amount of 0.01% or greater, more preferably, 0.5% or greater.
  • the content of manganese (Mn) in steel is excessively high, the generation of Mn-containing fumes markedly increases during a welding process, and thus the weldability of the steel decreases.
  • an MnS precipitate may be excessively formed to result in a decrease in the ductility of the steel. Therefore, the content of manganese (Mn) is limited to 1.5% or less, more preferably 1.0% or less.
  • Phosphorus (P) is an impurity inevitably included in steel, causing grain boundary corrosion during a pickling process and deteriorating the hot formability of the steel. Therefore, the content of phosphorus (P) is adjusted as low as possible. In the present disclosure, the upper limit of the content of phosphorus (P) is set to 0.05%.
  • S Sulfur
  • S an impurity inevitably included in steel, segregates along grain boundaries of the steel and deteriorates the hot formability of the steel. Therefore, the content of sulfur (S) is adjusted as low as possible.
  • the upper limit of the content of sulfur (S) is set to be 0.005%.
  • Chromium (Cr) is effective in increasing the corrosion resistance of steel.
  • chromium (Cr) is added in an amount of 10% or greater.
  • the content of chromium (Cr) is limited to 30% or less.
  • Titanium (Ti) fixes carbon (C) and nitrogen (N), thereby decreasing the amounts of carbon (C) and nitrogen (N) dissolved in steel.
  • titanium (Ti) is effective in improving the corrosion resistance of steel.
  • titanium (Ti) is added in an amount of 0.05% or greater, more preferably 0.1% or greater.
  • the content of titanium (Ti) is limited to 0.50% or less, more preferably 0.30% or less.
  • Aluminum (Al) is a powerful deoxidizer used to decrease the oxygen content of molten steel.
  • aluminum (Al) is added in an amount of 0.01% or greater.
  • the content of aluminum (Al) is limited to 0.15% or less, more preferably 0.1% or less.
  • Nitrogen (N) is an element facilitating recrystallization by precipitating austenite during a hot rolling process.
  • nitrogen (N) is added in an amount of 0.005% or greater.
  • the content of nitrogen (N) in steel is excessively high, the ductility of the steel decreases. Therefore, the content of nitrogen (N) is limited to 0.03% or less.
  • the ferritic stainless steel of the present disclosure may include 3.5 ⁇ 10 6 or fewer (excluding zero) independent Ti(CN) precipitate particles per square millimeter (mm 2 ) of ferrite matrix.
  • the Ti(CN) precipitate includes an independent Ti(CN) precipitate and a dependent Ti(CN) precipitate formed using TiN inclusion particles as precipitation nuclei.
  • the dependent Ti(CN) precipitate does not have a significant effect on ductility deterioration when compared to the independent Ti(CN) precipitate. Therefore, only the number of independent Ti(CN) precipitate particles is controlled in the present disclosure. If the number of independent Ti(CN) precipitate particles is outside the above-mentioned range, it may be difficult to obtain a desired degree of ductility.
  • a method of reducing the number of independent Ti(CN) precipitate particles is to increase the amount of Ti(CN) precipitating using TiN inclusion particles as precipitation nuclei.
  • a desired degree of ductility may be obtained by adjusting P defined by Formula 1 below within the range of 60% or less.
  • N S refers to the number of independent Ti(CN) precipitate particles per unit area (mm 2 )
  • N C refers to the number of dependent Ti(CN) precipitate particles per unit area (mm 2 ).
  • the independent Ti(CN) precipitate being the subject of control may be limited to having a particle diameter of 0.01 ⁇ m or greater. Since there is a limit to analyzing and quantifying independent Ti(CN) precipitate having a particle diameter of less than 0.01 ⁇ m, special consideration may not be given thereto.
  • the upper limit of the particle diameter of the independent Ti(CN) precipitate may not be specifically set. However, since it is difficult to form an independent Ti(CN) precipitate having a particle diameter of 2 ⁇ m or greater, the upper limit of the particle diameter of the independent Ti(CN) precipitate may be set to be 2 ⁇ m.
  • the independent Ti(CN) precipitate may have an average particle diameter of 0.15 ⁇ m or less. If the average particle diameter of the independent Ti(CN) precipitate is greater than 0.15 ⁇ m, surface defects may be formed even though the number of independent Ti(CN) precipitate particles is small.
  • the term “average particle diameter” refers to the average of equivalent circular diameters of particles measured by observing a cross-section of steel.
  • the average particle diameter of a TiN inclusion be within the range of 2 ⁇ m or greater.
  • the reason for this is that a relatively coarse TiN inclusion having an average particle diameter of 2 ⁇ m or greater forms nucleus forming sites more efficiently, and thus facilitates the precipitation of Ti(CN).
  • the upper limit of the average particle diameter of the TiN inclusion is not limited. However, if the TiN inclusion is excessively coarse, the total surface area of the TiN inclusion may be excessively small, and thus it may be difficult to increase the number of dependent Ti(CN) precipitate particles. Therefore, the upper limit of the average particle diameter of the TiN inclusion may be set to be 20 ⁇ m.
  • the ferritic stainless steel of the present disclosure has a high degree of ductility. According to an exemplary embodiment of the present disclosure, the ferritic stainless steel may have an elongation of 34% or greater.
  • the ferritic stainless steel of the present disclosure may be manufactured by various methods without limit.
  • the ferritic stainless steel may be manufactured as follows.
  • the method for manufacturing ferritic stainless steel includes casting molten steel having the above-described composition as a slab.
  • One of the technical features of the method is to maximally restrict the formation of an independent Ti(CN) precipitate by facilitating the diffusion of titanium (Ti), carbon (C), and nitrogen (N), and thus inducing the formation of a dependent Ti(CN) precipitate with the help of TiN inclusion particles functioning as precipitation nuclei.
  • a slab produced by casting molten steel is subjected to a cooling process to improve productivity.
  • relatively fine TiN inclusion particles are formed in the slab, and Ti(CN) precipitates randomly in the slab, thereby markedly increasing the number of independent Ti(CN) precipitate particles.
  • relatively rapid cooling of the slab limits the diffusion of alloying elements in the slab, and sufficient nucleus forming energy facilitates the formation of nuclei of a TiN inclusion and a Ti(CN) precipitate simultaneously across the slab.
  • the slab is cooled within the temperature range of 1100° C. to 1200° C. based on the surface temperature of the slab at an average cooling rate of 5° C./sec or less (excluding 0° C./sec), preferably 3° C./sec or less (excluding 0° C./sec), more preferably 2° C./sec (excluding 0° C./sec). That is, the inventors have tried to precipitate as much Ti(CN) as possible using TiN inclusion particles as precipitation nuclei by properly controlling the average cooling rate of a slab within the temperature range of 1100° C. to 1200° C., and thus to decrease the number of independent Ti(CN) precipitate particles.
  • the inventors have found that if a slab is cooled under the conditions described above, the number of independent Ti(CN) precipitate particles is reduced to a target value or less. The reason for this may be that since slow cooling guarantees a sufficient time period for alloying elements to move, large amounts of Ti, C, and N diffuse toward TiN inclusion particles and precipitate in the form of Ti(CN) using the TiN inclusion particles as precipitation nuclei.
  • the average cooling rate of the slab may be controlled using any method or apparatus.
  • a heat insulating material may be disposed around a cast strand.
  • the method of controlling the average cooling rate of the slab is not limited.
  • the slab may be cooled slowly at a constant cooling rate within the above-mentioned temperature range, or the slab may be cooled at a relatively high cooling rate after the slab is constantly maintained at a particular temperature within the temperature range.
  • the temperature range within which the slab is slowly cooled may be widened to a range of 1000° C. to 1250° C. to induce the formation of a coarse TiN inclusion and enable the coarse TiN inclusion to function as nucleus forming sites more effectively for the precipitation of Ti(CN).
  • the method may further include: forming a hot-rolled sheet by performing a finish hot rolling process on the slab; and performing a hot band annealing process on the hot-rolled sheet.
  • Hot band annealing process perform within the range of 450° C. to 1080° C. for 60 minutes or less.
  • the hot band annealing process is performed to improve the ductility of the hot-rolled sheet. Owing to the hot band annealing process, the independent Ti(CN) precipitate may be dissolved again, and dissolved alloying elements may be diffused, thereby further decreasing the number of independent Ti(CN) precipitate particles. To this end, the hot band annealing process may be performed at a temperature of 450° C. or higher. However, if the temperature of the hot band annealing process is higher than 1080° C., or the duration of the band annealing process is longer than minutes, the dependent Ti(CN) precipitate may be dissolved again, and thus the above-mentioned effects may be decreased. The lower limit of the duration of the band annealing process is not limited. For example, it may be preferable that the band annealing process be performed for 1 minute or longer to obtain sufficient effects.
  • the annealed hot-rolled sheet may be subjected to a cold rolling process and a cold rolled sheet annealing process to produce a cold-rolled steel sheet.
  • Molten steels having the compositions shown in Table 1 were prepared and were cast at a constant speed under the conditions shown in Table 2 in order to produce slabs.
  • the slabs were subjected to a hot rolling process and a hot band annealing process to obtain hot-rolled sheets.
  • the slab cooling rate is an average cooling rate measured based on the surface temperature of a slab within the temperature range of 1100° C. to 1200° C.
  • the hot-rolled sheets were photographed using a transmission electron microscope (TEM), and the number and ratio (P) of independent Ti(CN) precipitate particles having a particle diameter of 0.01 ⁇ m or greater were measured using an image analyzer.
  • samples were taken from the hot-rolled sheets based on a direction making an angle of 90° with the rolling direction of the hot-rolled sheets according to JIS 13B, and the elongation of the samples was measured. Results of the measurements are shown in Table 3.
  • FIG. 1 is a scanning electron microscope (SEM) image illustrating the microstructure of a hot-rolled sheet of Inventive Example 1
  • FIG. 2 is a higher magnification SEM image illustrating region A in FIG. 1 .
  • a particle shown in the center of region A in FIG. 1 corresponds to a TiN inclusion particle crystallized during a steel making process.
  • FIG. 2 illustrating region A on an enlarged scale, a large amount of Ti(CN) has precipitated on the TiN inclusion particle functioning as a precipitation nucleus.

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US15/529,263 2014-12-26 2015-04-30 Ferritic stainless steel having excellent ductility and method for manufacturing same Abandoned US20170283894A1 (en)

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KR10-2014-0190545 2014-12-26
KR20140190545 2014-12-26
KR10-2015-0061378 2015-04-30
KR1020150061378A KR101553607B1 (ko) 2014-12-26 2015-04-30 연성이 우수한 페라이트계 스테인리스 강재 및 그 제조방법
PCT/KR2015/004410 WO2016104883A1 (ko) 2014-12-26 2015-04-30 연성이 우수한 페라이트계 스테인리스 강재 및 그 제조방법

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