CN107835865B - Hot-rolled ferritic stainless steel sheet, hot-rolled annealed sheet, and methods for producing same - Google Patents

Hot-rolled ferritic stainless steel sheet, hot-rolled annealed sheet, and methods for producing same Download PDF

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CN107835865B
CN107835865B CN201680041261.5A CN201680041261A CN107835865B CN 107835865 B CN107835865 B CN 107835865B CN 201680041261 A CN201680041261 A CN 201680041261A CN 107835865 B CN107835865 B CN 107835865B
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steel sheet
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stainless steel
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CN107835865A (en
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吉野正崇
藤泽光幸
上力
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JFE Steel Corp
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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
    • 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
    • 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
    • C21D8/0247—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
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    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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    • 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
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • 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
    • 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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    • 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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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    • 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
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
    • 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
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

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Abstract

The invention provides a hot-rolled ferritic stainless steel sheet and a hot-rolled annealed sheet, which have sufficient corrosion resistance and can suppress deflection and distortion after forming, and methods for producing the same. A hot-rolled ferritic stainless steel sheet comprising, in mass%, 0.005 to 0.060% of C, 0.02 to 0.50% of Si, 0.01 to 1.00% of Mn, 0.04% or less of P, 0.01% or less of S, 15.5 to 18.0% of Cr, 0.001 to 0.10% of Al, 0.005 to 0.100% of N, 0.1 to 1.0% of Ni, and the balance of Fe and unavoidable impurities, wherein the absolute value of in-plane anisotropy of longitudinal modulus of elasticity calculated by the following formula (1) is 35GPa or less. I Δ E | (E)L－2×ED+EC) /2| … (1) Here, ELLongitudinal elastic modulus (GPa), E in a direction parallel to the rolling directionDLongitudinal elastic modulus (GPa), E in a direction of 45 DEG relative to the rolling directionCThe longitudinal elastic modulus (GPa) is taken as a direction perpendicular to the rolling direction.

Description

Hot-rolled ferritic stainless steel sheet, hot-rolled annealed sheet, and methods for producing same
Technical Field
The present invention relates to a hot-rolled ferritic stainless steel sheet and a hot-rolled annealed sheet having sufficient corrosion resistance and excellent rigidity, and methods for producing these.
Background
In recent years, the legislative regulations relating to automobile exhaust gas have been strengthened, and improvement of fuel economy has become a priority. Therefore, application of an Exhaust Gas Recirculation (EGR) system that uses Exhaust Gas generated by an engine of an automobile as intake air of the engine again is being promoted. The exhaust gas produced by the engine is supplied to the engine again after passing through an EGR cooler for reducing the temperature of the gas. When the exhaust gas is circulated, a flange needs to be provided between the members to prevent leakage of the gas. Among them, in a flange used for a connection portion with a component such as an EGR cooler that constantly vibrates during running of an automobile, a gap is generated between the components due to deflection of the flange caused by the vibration, and it is necessary to exhibit sufficient rigidity in order to prevent gas leakage caused by the generation of the gap. Thus, a thick (for example, 6mm or more thick) flange is used as the flange between members to which vibration is constantly applied during running of an automobile such as an EGR cooler.
Conventionally, ordinary steel has been used for such thick-walled flanges. However, with respect to components through which exhaust gas passes such as an EGR system, there is a concern about corrosion caused by exhaust gas. Therefore, applications of stainless steel having excellent corrosion resistance as compared with ordinary steel have been studied, and a ferritic stainless hot-rolled steel sheet having sufficient rigidity and a large sheet thickness (for example, a sheet thickness of 6mm or more) which can be applied to a thick flange has been demanded.
For example, patent document 1 discloses a hot-rolled ferritic stainless steel sheet containing, in mass%, 0.015% or less of C, 0.01 to 0.4% of Si, 0.01 to 0.8% of Mn, 0.04% or less of P, 0.01% or less of S, 14.0% or more and less than 18.0% of Cr, 0.05 to 1% of Ni, 0.3 to 0.6% of Nb, 0.05% or less of Ti, 0.020% or less of N, 0.10% or less of Al, 0.0002 to 0.0020% of B, and the balance of Fe and unavoidable impurities, wherein the contents of Nb, C and N are such that Nb/(C + N) is 16 or more, and the Charpy impact value at 0 ℃ is 10J/cm2The thickness is 5.0 to 9.0 mm.
In contrast, in recent years, there has been a strong demand for relatively inexpensive stainless steels (e.g., SUS430, 13Cr stainless steels, etc.) in which the content of C, N stabilizing elements such as Ti, Nb, etc. is reduced as much as possible.
Documents of the prior art
Patent document
Patent document 1 International publication No. 2014/157576
Disclosure of Invention
However, when the conventional hot-rolled ferritic stainless steel sheet containing no Ti or Nb is formed into the flange or the like, there is a problem that the steel sheet is easily bent or twisted during vibration or the like.
The present invention has been made to solve the above problems, and an object of the present invention is to provide a hot-rolled ferritic stainless steel sheet and a hot-rolled annealed sheet having sufficient corrosion resistance and capable of suppressing bending and twisting after forming, and methods for producing the same.
As a result of conducting detailed studies to solve the problems, the present inventors have found that, when applied to a flange or the like, the absolute value | Δ E | of in-plane anisotropy of longitudinal elastic modulus represented by the following formula (1) may be reduced in a steel sheet in order to suppress deformation such as deflection or distortion during vibration. Further, it has been found that the absolute value of the in-plane anisotropy of the longitudinal elastic modulus is 35GPa or less, and thus the flange can be sufficiently put into practical use.
|ΔE|＝|(EL－2×ED+EC)/2|…(1)
Here, ELLongitudinal elastic modulus (GPa), E in a direction parallel to the rolling directionDLongitudinal elastic modulus (GPa), E in a direction of 45 DEG relative to the rolling directionCThe longitudinal elastic modulus (GPa) is taken as a direction perpendicular to the rolling direction.
In addition, EL、ED、ECCan be obtained by using the longitudinal elastic modulus measured by the transverse resonance method described in JIS Z2280-1993 under the temperature conditions of 23 ℃ for the rolling direction, the rolling direction of the steel sheet, the direction of 45 ℃ and the direction perpendicular to the rolling direction.
Further, it was found that in ferritic stainless steel having an appropriate composition, in particular, by appropriately controlling the rolling temperature range and the cumulative reduction ratio (100 [% ] - (final thickness/thickness before starting rolling of the final 3 passes) × 100 [% ] in the final 3 passes of the finish hot rolling step consisting of a plurality of passes, the in-plane anisotropy of the longitudinal elastic modulus can be significantly reduced.
The present invention has been completed based on the above findings, and the gist thereof is as follows.
[1] A hot-rolled ferritic stainless steel sheet having a composition comprising, in mass%, 0.005 to 0.060% of C, 0.02 to 0.50% of Si, 0.01 to 1.00% of Mn, 0.04% or less of P, 0.01% or less of S, 15.5 to 18.0% of Cr, 0.001 to 0.10% of Al, 0.005 to 0.100% of N, 0.1 to 1.0% of Ni, and the balance of Fe and unavoidable impurities,
the absolute value | Δ E | of the in-plane anisotropy of the longitudinal elastic modulus calculated by the following formula (1) is 35GPa or less.
|ΔE|＝|(EL－2×ED+EC)/2|…(1)
Here, ELLongitudinal elastic modulus (GPa), E in a direction parallel to the rolling directionDLongitudinal elastic modulus (GPa), E in a direction of 45 DEG relative to the rolling directionCThe longitudinal elastic modulus (GPa) is taken as a direction perpendicular to the rolling direction.
[2] The hot-rolled ferritic stainless steel sheet according to the above [1], which further comprises 1 or 2 or more selected from the group consisting of 0.1 to 1.0% by mass of Cu, 0.1 to 0.5% by mass of Mo, and 0.01 to 0.5% by mass of Co.
[3] The hot-rolled ferritic stainless steel sheet according to the above [1] or [2], which further comprises 1 or 2 or more selected from 0.01 to 0.25% by mass of V, 0.001 to 0.015% by mass of Ti, 0.001 to 0.025% by mass of Nb, 0.0002 to 0.0050% by mass of Mg, 0.0002 to 0.0050% by mass of B, 0.0002 to 0.0020% by mass of Ca, and 0.01 to 0.10% by mass of REM.
[4] A hot-rolled annealed ferritic stainless steel sheet characterized by being obtained by subjecting a hot-rolled ferritic stainless steel sheet according to any one of the above [1] to [3] to hot-rolled sheet annealing.
[5] A method for producing a hot-rolled ferritic stainless steel sheet according to any one of the above [1] to [3], wherein in a hot rolling step of performing a finish rolling of 3 or more passes, the final 3 passes of the finish rolling are performed at a temperature range of 900 to 1100 ℃ and a cumulative reduction of 25% or more.
[6] A method for producing a hot-rolled annealed ferritic stainless steel sheet, which comprises using the method for producing a hot-rolled ferritic stainless steel sheet according to [5], and further annealing the hot-rolled sheet at 800 to 900 ℃ after the hot-rolling step.
According to the present invention, a hot-rolled ferritic stainless steel sheet and a hot-rolled annealed sheet having sufficient corrosion resistance and capable of suppressing bending and twisting after forming can be obtained.
The sufficient corrosion resistance in the present invention means that when a salt spray cycle test (a test in which salt spray (35 ℃, 5 mass% NaCl, spray 2hr) → dry (60 ℃, 40%, 4hr) → wet (50 ℃, 95% or more relative humidity), as defined in JIS H8502) is performed for 8 cycles on a steel sheet whose surface has been polished and finished with #600 sandpaper and whose end surface portion has been sealed, the rust area ratio (rust area/total steel sheet area × 100 [% ]) of the steel sheet surface is 25% or less.
Detailed Description
The hot-rolled ferritic stainless steel sheet and the hot-rolled annealed sheet according to the present invention have a composition comprising, in mass%, 0.005 to 0.060% of C, 0.02 to 0.50% of Si, 0.01 to 1.00% of Mn, 0.04% or less of P, 0.01% or less of S, 15.5 to 18.0% of Cr, 0.001 to 0.10% of Al, 0.005 to 0.100% of N, 0.1 to 1.0% of Ni, and the balance of Fe and inevitable impurities, and the absolute value | Delta E | of the in-plane anisotropy of the longitudinal elastic modulus calculated by the following formula (1) is 35GPa or less.
|ΔE|＝|(EL－2×ED+EC)/2|…(1)
Here, E isLLongitudinal elastic modulus (GPa), E in a direction parallel to the rolling directionDLongitudinal elastic modulus (GPa), E in a direction of 45 DEG relative to the rolling directionCThe longitudinal elastic modulus (GPa) is taken as a direction perpendicular to the rolling direction.
In addition, EL、ED、ECCan be obtained by using the longitudinal elastic modulus measured by the transverse resonance method described in JIS Z2280-1993 under the temperature conditions of 23 ℃ for the rolling direction, the rolling direction of the steel sheet, the direction of 45 ℃ and the direction perpendicular to the rolling direction.
The present invention will be described in detail below.
The hot-rolled ferritic stainless steel sheet and the hot-rolled annealed sheet according to the present invention are mainly used for thick flanges of EGR cooler parts for automobiles. The present inventors applied various hot rolled ferritic stainless steel sheets to thick flanges for EGR coolers and evaluated the performance thereof in detail. As a result, it was found that when a ferritic stainless hot-rolled steel sheet having an absolute value of in-plane anisotropy of longitudinal modulus of elasticity of more than 35GPa is used, large deflection and distortion due to vibration during automobile running are likely to occur.
Therefore, the present inventors have intensively studied a method for reducing the in-plane anisotropy of the longitudinal elastic modulus in a hot-rolled ferritic stainless steel sheet, particularly focusing on the rolling temperature and the reduction ratio in each pass of hot rolling consisting of a plurality of passes using a multistage stand. As a result, it was found that by performing the final 3-pass rolling in the multi-pass finish hot rolling composed of 3 or more passes at a temperature range of 900 to 1100 ℃ and a cumulative reduction of 25% or more (preferably 30% or more), the in-plane anisotropy of the longitudinal elastic modulus is greatly reduced, and the desired rigidity can be obtained.
The reason why the desired in-plane anisotropy of the longitudinal elastic modulus is exhibited by the above-described method will be described.
The modulus of elasticity in the longitudinal direction of a hot rolled ferritic stainless steel sheet strongly depends on the texture of the steel sheet. The texture of the hot-rolled steel sheet is formed by repeating the introduction of work strain by rolling and recrystallization, and therefore the texture can be controlled by the temperature at which rolling is performed and the amount of deformation thereof.
On the other hand, in the center portion of the thickness of the ingot before hot rolling of ferritic stainless steel, the elongated ferrite grains are continuously distributed along the casting direction. When such a stainless steel slab is hot-rolled by a conventional technique, the number of recrystallization sites is reduced in the center portion of the thickness compared to the surface portion of the steel sheet because the number of elongated grains is large and the grain boundary area is small.
When the steel sheet is rolled, the steel sheet is deformed and stretched mainly from the surface layer portion. Therefore, when the reduction ratio is small, the deformation amount at the plate thickness center portion becomes small, and rolling deformation is not substantially introduced at the plate thickness center portion.
In the hot rolling according to the conventional technique, the introduction of strain and recrystallization are repeated in the surface layer portion of the steel sheet, while the progress of recrystallization is greatly delayed in the center portion of the sheet thickness. Thus, the long ferrite grains having similar crystal orientations generated during casting are easily left without being broken, and the in-plane anisotropy of the longitudinal elastic modulus is increased after hot rolling.
As an optimum method for suppressing such in-plane anisotropy of longitudinal elastic modulus, the present inventors considered that the final 3 passes of finish hot rolling are conducted in a temperature range of 900 to 1100 ℃ in a temperature region where recrystallization actively occurs, and that a reduction with a cumulative reduction ratio of 25% or more as compared to the conventional one is applied.
Specifically, the present inventors examined systematically the influence of the temperature and reduction ratio at which each rolling pass was performed on the in-plane anisotropy of the longitudinal elastic modulus of a hot-rolled steel sheet produced by 7 passes of finish hot rolling. As a result, the following tendency was found: the in-plane anisotropy of the longitudinal elastic modulus of the hot-rolled steel sheet is not substantially affected by the temperature and reduction ratio of the first 4 passes, but strongly affected by the rolling temperature and reduction ratio of the final 3 passes. Therefore, the present inventors examined the influence of the rolling temperature and reduction in the final 3 passes and the cumulative reduction in the final 3 passes in further detail. As a result, it was found that the in-plane anisotropy of the longitudinal modulus of the hot-rolled steel sheet tends to be greatly reduced when the final 3-pass rolling is performed in the range of 900 to 1100 ℃, and the change amount of the in-plane anisotropy of the longitudinal modulus of the hot-rolled steel sheet at this time can be adjusted not to the reduction ratio of each pass but to the cumulative reduction ratio of the final 3-pass. That is, it is important to find out that the in-plane anisotropy of the longitudinal elastic modulus of the hot-rolled steel sheet is finished in a temperature range of 900 to 1100 ℃ and at a cumulative reduction of 25% or more.
The present inventors investigated the reason why the rolling temperature and reduction ratio in the rolling pass before the final 3 passes have little influence on the in-plane anisotropy of the longitudinal elastic modulus of the hot-rolled steel sheet. As a result, it was found that the thickness of the steel sheet before the start of rolling was large for the rolling pass before the final 3 passes, the rolling strain could not be introduced into the central portion of the thickness of the steel sheet even if the reduction ratio was increased, and the rolling temperature was high, so that the recrystallized grains generated after rolling excessively grew to coarse grains, and the anisotropy-eliminating effect of the metal structure due to the generation of recrystallized grains was significantly smaller than the cumulative effect in the final 3 passes.
On the other hand, when the cumulative reduction ratio of the final 3 passes is increased to 25% or more as compared with the conventional case, the rolling strain is effectively introduced into the plate thickness center portion of the steel plate by the final 3 passes of rolling, and therefore the recrystallization sites at the plate thickness center portion are greatly increased. By carrying out such rolling in the range of 900 to 1100 ℃ in which recrystallization actively occurs, recrystallization in the center portion of the plate thickness is promoted, the grain structure of the elongated ferrite formed at the time of casting is effectively destroyed, and the in-plane anisotropy of the longitudinal elastic modulus after hot rolling is greatly reduced. Further, by performing the rolling at a rolling temperature of 1100 ℃ or lower, coarsening of recrystallized grains can be suppressed, and the effect of eliminating the anisotropy of the metal structure can be sufficiently exhibited. By this technique, the absolute value of the in-plane anisotropy of the longitudinal elastic modulus is set to 35GPa or less, and after molding into a thick flange or the like, large deformation such as bending or twisting at the time of vibration can be suppressed.
Further, the present inventors have found that, since the formability of the hot-rolled steel sheet is improved, when the hot-rolled steel sheet of the present invention is subjected to hot-rolled sheet annealing at 800 to 900 ℃ or lower to obtain a hot-rolled annealed sheet, the effect of reducing the in-plane anisotropy of the longitudinal elastic modulus exhibited by hot rolling is maintained in addition to the effect of improving the formability. The reason for this is found that the effect of reducing the in-plane anisotropy of the longitudinal elastic modulus of the present invention is caused by the destruction of the elongated ferrite grain structure in the center portion of the sheet thickness, and when the hot-rolled sheet is annealed in a predetermined temperature range after hot rolling, the elongated ferrite grains that promote the anisotropy of the steel sheet are not generated.
The thicknesses of the hot-rolled ferritic stainless steel sheet and the hot-rolled ferritic stainless steel annealed sheet of the present invention are not particularly limited, but are preferably 5.0 to 15.0mm because they are preferably applicable to thick flanges.
Next, the composition of the ferritic stainless steel sheet and the ferritic stainless hot-rolled annealed sheet of the present invention will be described.
Hereinafter, unless otherwise specified,% representing the composition of the components means mass%.
C:0.005～0.060％
Since the large amount of C causes a reduction in workability and a reduction in sensitization and toughness due to precipitation of Cr-based carbonitride, the C content is set to 0.060% as an upper limit. On the other hand, since extremely reducing the C content causes a significant increase in refining cost, the lower limit of the C content is set to 0.005% which is a level that does not cause a significant increase in production cost in normal refining. From the viewpoint of stable manufacturability in the steel-making process, the C content is preferably 0.010 to 0.050%. More preferably, the C content is in the range of 0.020 to 0.045%. Further preferably, the C content is in the range of 0.025 to 0.040%. More preferably, the C content is in the range of 0.030 to 0.040%.
Si:0.02～0.50％
Si is an element that acts as a deoxidizer during steel melting. In order to obtain this effect, Si needs to be contained by 0.02% or more. However, if the Si content exceeds 0.50%, the steel sheet is hardened, which increases the rolling load during hot rolling and lowers the manufacturability of the hot rolling process, which is not preferable. Therefore, the Si content is set to be in the range of 0.02 to 0.50%. The Si content is preferably in the range of 0.10 to 0.35%. Further preferably, the Si content is in the range of 0.10 to 0.30%.
Mn:0.01～1.00％
If Mn is contained excessively, the steel sheet is hardened, the rolling load during hot rolling increases, and the manufacturability in the hot rolling step is lowered, which is not preferable, as in Si. In addition, the amount of MnS produced may increase, and the corrosion resistance may decrease. Therefore, the upper limit of the Mn content is set to 1.00%. The lower limit of the Mn content is 0.01% from the viewpoint of the load on the refining step. The Mn content is preferably in the range of 0.10 to 0.90%. Further preferably, the Mn content is in the range of 0.45 to 0.85%.
P is less than 0.04%
Since P is an element that promotes grain boundary fracture due to grain boundary segregation, it is preferably small, and the upper limit of the content of P is set to 0.04%. The P content is preferably 0.03% or less. The P content is more preferably 0.01% or less.
S is less than 0.01%
S is an element which causes a reduction in ductility, corrosion resistance, and the like due to the presence of sulfide-based inclusions such as MnS, and particularly, if the S content exceeds 0.01%, these adverse effects are remarkably generated. Therefore, the S content is preferably as low as possible, and the upper limit of the S content is set to 0.01% in the present invention. The S content is preferably 0.007% or less. The S content is more preferably 0.005% or less.
Cr:15.5～18.0％
Cr is an element that forms a passive film on the surface of the steel sheet and has the effect of improving corrosion resistance. In order to obtain this effect, the Cr content needs to be 15.5% or more. However, if the Cr content exceeds 18.0%, the toughness of the steel sheet is significantly reduced, which is not preferable. Therefore, the Cr content is set to be in the range of 15.5 to 18.0%. The preferable Cr content is 16.0-17.0%. Further preferably, the Cr content is in the range of 16.0 to 16.5%.
Al:0.001～0.10％
Al is an element that functions as a deoxidizer, similarly to Si. In order to obtain this effect, 0.001% or more of Al needs to be contained. However, if the Al content exceeds 0.10%, Al is present2O3The Al-based inclusions increase, and the surface properties tend to decrease. Therefore, the Al content is set to be in the range of 0.001 to 0.10%. The Al content is preferably in the range of 0.001 to 0.07%. Further preferably, the Al content is in the range of 0.001 to 0.05%.
N:0.005～0.100％
When N is contained in a large amount, as in C, the workability is lowered, and the sensitization and toughness are lowered by the precipitation of Cr-based carbonitride, so the N content is set to an upper limit of 0.100%. On the other hand, since extremely lowering the N content causes a significant increase in refining cost as in C, the lower limit of the N content is set to 0.005% which is a level that does not cause a significant increase in production cost in normal refining. From the viewpoint of stable productivity in the steel-making step, the N content is preferably 0.010 to 0.075%. More preferably, the N content is in the range of 0.025 to 0.055%. Further preferably, the N content is in the range of 0.030 to 0.050%.
Ni:0.1～1.0％
Ni is an element for improving corrosion resistance, and is effective when high corrosion resistance is required. This effect becomes remarkable when 0.1% or more is contained. However, if the content exceeds 1.0%, moldability is lowered, which is not preferable. Therefore, the Ni content is set to 0.1 to 1.0%. The Ni content is preferably in the range of 0.2 to 0.4%.
The remainder being Fe and unavoidable impurities.
The effects of the present invention can be obtained by the above composition, but the following elements may be contained in order to further improve the productivity and the material characteristics.
1 or more than 2 selected from 0.1-1.0% of Cu, 0.1-0.5% of Mo and 0.01-0.5% of Co
Cu:0.1～1.0％
Cu is an element for improving corrosion resistance, and is effective when high corrosion resistance is required. This effect becomes remarkable when Cu is contained by 0.1% or more. However, if the Cu content exceeds 1.0%, formability may be deteriorated. Therefore, Cu is contained in the alloy in an amount of 0.1 to 1.0%. The Cu content is preferably in the range of 0.2 to 0.4%.
Mo:0.1～0.5％
Like Ni and Cu, Mo is an element that improves corrosion resistance, and is effective when particularly high corrosion resistance is required. This effect becomes remarkable when 0.1% or more of Mo is contained. However, if the Mo content exceeds 0.5%, the steel sheet may be hardened, which may increase the rolling load during hot rolling and reduce the manufacturability in the hot rolling step. Therefore, Mo is contained in the range of 0.1 to 0.5%. The preferable Mo content is 0.2-0.3%.
Co:0.01～0.5％
Co is an element for improving toughness. The effect can be obtained by containing 0.01% or more. On the other hand, if the content exceeds 0.5%, moldability may be deteriorated. Therefore, the content of Co is set to be in the range of 0.01 to 0.5%.
1 or more than 2 selected from 0.01-0.25% of V, 0.001-0.015% of Ti, 0.001-0.025% of Nb, 0.0002-0.0050% of Mg, 0.0002-0.0050% of B, 0.0002-0.0020% of Ca and 0.01-0.10% of REM
V:0.01～0.25％
V is an element that forms carbonitrides more easily than Cr. V has an effect of suppressing sensitization due to precipitation of Cr carbonitride by precipitating C and N in the steel as V-based carbonitride during hot rolling. In order to obtain this effect, it is necessary to contain 0.01% or more of V. However, if the V content exceeds 0.25%, the processability may be lowered. Leading to an increase in manufacturing costs. Therefore, the content of V is set to be in the range of 0.01 to 0.25%. The preferable V content is 0.03-0.08%.
Ti:0.001～0.015％、Nb:0.001～0.025％
Like V, Ti and Nb are elements having high affinity for C and N, and have the effect of precipitating as carbides or nitrides during hot rolling and suppressing sensitization due to precipitation of Cr carbonitrides. In order to obtain this effect, it is necessary to contain 0.001% or more of Ti or 0.001% or more of Nb. However, if the Ti content exceeds 0.015% or the Nb content exceeds 0.030%, favorable surface properties may not be obtained due to excessive precipitation of TiN and NbC. Therefore, the content of Ti is in the range of 0.001 to 0.015%, and the content of Nb is in the range of 0.001 to 0.025%. The preferable Ti content is 0.003-0.010%. The preferable Nb content is 0.005 to 0.020%. Further preferably, the Nb content is in the range of 0.010 to 0.015%.
Mg:0.0002～0.0050％
Mg is an element having an effect of improving hot rolling workability. In order to obtain this effect, 0.0002% or more of Mg needs to be contained. However, if the Mg content exceeds 0.0050%, the surface quality may be reduced. Therefore, when Mg is contained, the content is set to be in the range of 0.0002 to 0.0050%. The preferable Mg content is in the range of 0.0005 to 0.0035%. Further preferably, the Mg content is in the range of 0.0005 to 0.0020%.
B:0.0002～0.0050％
B is an element effective for preventing low-temperature secondary work embrittlement. In order to obtain this effect, it is necessary to contain 0.0002% or more of B. However, if the B content exceeds 0.0050%, hot rolling workability may be reduced. Therefore, the content of B is set to be in the range of 0.0002 to 0.0050%. The B content is preferably in the range of 0.0005 to 0.0035%. Further preferably, the B content is in the range of 0.0005 to 0.0020%.
Ca:0.0002～0.0020％
Ca is an effective component for preventing clogging of the nozzle due to the crystallization of inclusions which are likely to occur during continuous casting. In order to obtain this effect, 0.0002% or more of Ca needs to be contained. However, if the Ca content exceeds 0.0020%, CaS is formed and the corrosion resistance is sometimes lowered. Therefore, the content of Ca is set to be in the range of 0.0002 to 0.0020%. Preferably, the Ca content is in the range of 0.0005 to 0.0015%. Further preferably, the Ca content is in the range of 0.0005 to 0.0010%.
REM:0.01～0.10％
Rem (rare Earth metals) is an element that improves oxidation resistance, and particularly has the effect of inhibiting the formation of an oxide film in the weld zone and improving the corrosion resistance of the weld zone. In order to obtain this effect, REM needs to be contained at 0.01% or more. However, if REM is contained in an amount exceeding 0.10%, the workability such as pickling property during cold rolling annealing may be lowered. In addition, since REM is an expensive element, excessive inclusion thereof is not preferable because it increases the manufacturing cost. Therefore, the content of REM is set to be in the range of 0.01 to 0.10%. Preferably, the REM content is in the range of 0.01 to 0.05%.
Next, the methods for producing the ferritic stainless steel sheet and the ferritic stainless hot-rolled annealed sheet according to the present invention will be described.
The ferritic stainless steel sheet of the present invention is obtained by subjecting a steel slab having the above composition to hot rolling consisting of rough rolling and 3 or more passes of finish rolling, wherein the final 3 passes of finish rolling are performed at a temperature range of 900 to 1100 ℃ and a cumulative reduction of 25% or more.
The maximum number of passes of the finish rolling is not particularly limited from the viewpoint of obtaining a predetermined material, but if the maximum number of passes is more than 15 passes, the reduction in the temperature of the steel sheet due to the increase in the number of contacts with the reduction rolls is likely to occur, and external heating is necessary to maintain the temperature of the steel sheet within a predetermined temperature range, which may lead to a reduction in the productivity and an increase in the production cost. Therefore, the maximum number of passes is preferably 15 or less. More preferably, the maximum number of passes is 10 or less passes.
First, molten steel having the above-described composition is melted by a known method such as a converter, an electric furnace, or a vacuum melting furnace, and a steel material (ingot) is produced by a continuous casting method or an ingot-cogging method.
The slab is heated at 1100 to 1250 ℃ for 1 to 24 hours, or cast without heating, and directly subjected to hot rolling. In the present invention, the rough rolling is not particularly limited, but the cumulative reduction of the rough rolling is preferably 65% or more in order to effectively destroy the cast structure. Thereafter, the steel sheet is rolled to a predetermined thickness by a finish rolling, but the final 3 passes of the finish rolling are performed at a temperature range of 900 to 1100 ℃ and a cumulative reduction of 25% or more.
The final rolling temperature range of 3 passes is 900-1100 DEG C
In the final 3-pass finish rolling, it is necessary to effectively introduce rolling strain into the center of the sheet thickness and to cause sufficient recrystallization by increasing the cumulative reduction ratio. Therefore, the final finish rolling of the final 3 passes needs to be performed at a temperature range of 900 to 1100 ℃ at which recrystallization is sufficiently generated. When the rolling temperature of the final 3 passes is less than 900 ℃, recrystallization does not occur sufficiently, and in-plane anisotropy of a predetermined longitudinal elastic modulus cannot be obtained. On the other hand, if the rolling temperature of the final 3 passes exceeds 1100 ℃, the crystal grains are significantly coarsened, the in-plane anisotropy of the predetermined longitudinal elastic modulus is not obtained, and the toughness of the hot-rolled steel sheet is lowered, which is not preferable. The rolling temperature of the final 3 passes is preferably in the range of 900 to 1075 ℃. More preferably, the rolling temperature of the final 3 passes is 930 to 1050 ℃. In order to prevent an excessive rolling load from being applied to a specific pass of the final 3 passes, it is preferable that the rolling temperature range of the 1 st pass in the final 3 passes is 950 to 1100 ℃, the rolling temperature range of the 2 nd pass performed after the 1 st pass is 925 to 1075 ℃, and the rolling temperature range of the 3 rd pass performed after the 2 nd pass is 900 to 1050 ℃.
The final accumulated reduction rate of 3 passes is more than 25 percent
In order to effectively impart rolling strain to the center of the thickness of the steel sheet, a reduction with a cumulative reduction ratio of 25% or more is required for the final 3 passes of finish rolling. If the cumulative reduction ratio is less than 25%, the introduction of rolling strain into the center of the sheet thickness becomes insufficient, recrystallization at the center of the sheet thickness is delayed, and the in-plane anisotropy of the predetermined longitudinal elastic modulus cannot be obtained. Therefore, the cumulative rolling reduction is preferably 25% or more. More preferably, the cumulative rolling reduction is 30% or more. The cumulative rolling reduction is more preferably 35% or more. The upper limit of the cumulative reduction ratio is not particularly limited, but if the cumulative reduction ratio is excessively increased, the rolling load is increased to lower the productivity, and surface roughening may occur after rolling, and therefore, the upper limit is preferably 60% or less.
The cumulative reduction ratio was 100 [% ] multiplied by 100 [% ] of the final plate thickness/plate thickness before the start of the final 3-pass rolling.
In the method for producing a hot-rolled ferritic stainless steel sheet according to the present invention, the rolling temperature and the cumulative reduction ratio of the final 3 passes of the finish rolling are characterized in that, if the rolling temperature and the cumulative reduction ratio of the finish rolling are controlled to be 4 or more passes, the reduction ratio in each pass is small, and therefore the introduced strain hardly contributes to the reduction of the anisotropy of the longitudinal elastic modulus, and a sufficient effect of reducing the anisotropy of the longitudinal elastic modulus cannot be obtained. Further, if the rolling temperature and the cumulative reduction ratio of the finish rolling are controlled to be 2 passes or less, it is not preferable because the rolling load is significantly increased and the productivity is lowered in order to perform a large reduction of 25% or more of the cumulative reduction ratio in 2 passes. Therefore, in the method for producing a hot-rolled ferritic stainless steel sheet according to the present invention, the rolling temperature and the cumulative reduction ratio of the final 3 passes of the finish rolling are controlled.
In the method for producing a hot-rolled ferritic stainless steel sheet according to the present invention, any number of passes of finish rolling can be performed as long as 3 passes or more of finish rolling is performed so as to control the final 3 passes of rolling temperature and the cumulative reduction ratio.
After finishing rolling, the steel sheet is cooled, and then wound to produce a hot-rolled steel strip. In the present invention, the coiling temperature is not particularly limited, but when the coiling temperature is less than 500 ℃ in the case of a steel component that generates an austenite phase during hot rolling, the austenite phase may be transformed into a martensite phase, and the hot-rolled steel sheet may be hardened, resulting in a reduction in formability. Therefore, the winding treatment is preferably performed at 500 ℃ or higher.
In the present invention, in-plane anisotropy having a desired corrosion resistance and a desired longitudinal elastic modulus can be obtained at the time point when the hot rolling step is completed, but for the purpose of improving formability, a hot rolled sheet is annealed at 800 to 900 ℃ after the hot rolling step to obtain a hot rolled annealed ferritic stainless steel sheet.
The annealing temperature of the hot rolled plate is 800-900 DEG C
When the annealing temperature of the hot-rolled sheet is less than 800 ℃, recrystallization does not sufficiently occur, and therefore the worked structure by hot rolling remains, and the effect of improving formability is not obtained. On the other hand, if the temperature exceeds 900 ℃, an austenite phase is formed during annealing, and the anisotropy of the longitudinal elastic modulus becomes large, that is, the in-plane anisotropy of the predetermined longitudinal elastic modulus exhibited by the hot-rolled steel sheet may disappear. Further, when the cooling rate after annealing of the hot-rolled sheet at more than 900 ℃ is high, the austenite phase is transformed into the martensite-site phase, and the steel sheet is hardened, so that the formability may be deteriorated. Therefore, the temperature range is preferably 800 to 900 ℃ when annealing the hot rolled sheet. The holding time and method of hot-rolled sheet annealing are not particularly limited, and may be performed by either box annealing (batch annealing) or continuous annealing.
The hot-rolled steel sheet or the steel sheet annealed by the hot-rolled sheet (hot-rolled annealed sheet) thus obtained may be subjected to descaling treatment by shot blasting or acid pickling, if necessary. In addition, grinding, polishing, etc. may be performed to improve the surface properties.
Examples
The present invention will be described in detail below with reference to examples.
Stainless steel molten steel having a chemical composition shown in Table 1 was melted by refining in a converter having a capacity of 150 tons and a strong stirring/vacuum oxygen decarburization (SS-VOD) treatment, and was continuously cast into a steel ingot having a width of 1000mm and a thickness of 200 mm. This ingot was heated at 1200 ℃ for 1 hour, and then subjected to reverse rough rolling using a 3-stage stand as hot rolling to obtain a steel sheet of about 40mm, and then subjected to final 3 passes (5 th, 6 th, and 7 th) of 7 passes of finish rolling under the conditions shown in table 2 to obtain a hot-rolled steel sheet. In addition, a hot rolled steel sheet (nos. 25, 26, and 38 in table 2) was partially hot rolled, held for 8 hours under the conditions described in table 2, and then subjected to furnace-cooled hot plate annealing to obtain a hot annealed sheet.
The hot-rolled steel sheet and the hot-rolled annealed sheet thus obtained were evaluated as follows.
(1) Evaluation of in-plane anisotropy
Test pieces 60mm long × 10mm wide × 2mm thick were sampled from the center of the plate thickness within ± 1mm with the long axes of the parallel rolling direction, the 45 ° rolling direction, and the right angle rolling direction. The longitudinal elastic modulus at 23 ℃ of the collected test piece was measured by the transverse resonance method described in JIS Z2280-1993, and the absolute value (| Δ E |) of the in-plane anisotropy of the longitudinal elastic modulus was calculated from the following formula (1).
|ΔE|＝|(EL－2×ED+EC)/2|(1)
Here, ELLongitudinal elastic modulus (GPa), E in a direction parallel to the rolling directionDLongitudinal elastic modulus (GPa), E in a direction of 45 DEG relative to the rolling directionCIn the rolling directionLongitudinal elastic modulus (GPa) in the vertical direction.
When the in-plane anisotropy | Δ E | of the longitudinal elastic modulus is 35GPa or less, it is determined that the bending and twisting after the flange or the like is molded can be sufficiently suppressed, and it is acceptable (○). when the in-plane anisotropy | Δ E | of the longitudinal elastic modulus exceeds 35GPa, it is not acceptable (x).
(2) Evaluation of Corrosion resistance
A60X 100mm test piece was taken from a hot-rolled steel sheet, and a test piece was prepared by polishing and trimming the surface with #600 sandpaper and sealing the end face, and subjected to a salt water spray cycle test defined in JIS H8502. The salt spray cycle test was carried out for 8 cycles with 1 cycle of salt spray (5 mass% NaCl, 35 ℃, spray 2hr) → dry (60 ℃, 4hr, relative humidity 40%) → wet (50 ℃, 2hr, relative humidity ≥ 95%).
The surface of the test piece after the 8-cycle salt spray cycle test was photographed, the rust area on the surface of the test piece was measured by image analysis, and the rust rate ((rust area in the test piece/total area of the test piece) × 100 [% ]) was calculated from the ratio to the total area of the test piece, and when the rust rate was 10% or less, the corrosion resistance was particularly excellent as pass (◎), when more than 10% and 25% or less were pass (○), and when more than 25% were fail (x).
The evaluation results are shown in table 2 together with hot rolling conditions.
[ Table 1]
Figure BDA0001546211440000151
[ Table 2]
Figure BDA0001546211440000161
In Nos. 1 to 21 and 25 to 34 in which the steel composition, hot rolling condition and hot rolled sheet annealing condition satisfy the ranges of the present invention, the absolute value (| Δ E |) of in-plane anisotropy of longitudinal elastic modulus was as small as 35GPa or less, and a desired rigidity was obtained. Further, the corrosion resistance of the obtained hot-rolled steel sheet or hot-rolled annealed sheet was evaluated, and it was confirmed that the rust percentage was 25% or less and the steel sheet had sufficient corrosion resistance.
In particular, in Nos. 14 to 17 using steel C containing 0.52 mass% of Ni and 0.4 mass% of Cu and No.32 using steel J containing 0.3 mass% of Mo, the rust percentage was 10% or less, and further excellent corrosion resistance was obtained.
In sample No.22 having a final 3-pass cumulative reduction ratio lower than the range of the present invention, a large number of long crystal grains remain in the central portion of the plate thickness, and therefore the in-plane anisotropy of the longitudinal elastic modulus becomes large, and a predetermined | Δ E | cannot be obtained.
In sample No.23 in which the final temperature of only the 7 th pass in the final 3-pass rolling was lower than the range of the present invention, and sample No.24 in which the rolling temperature of the final 3-pass was all lower than the range of the present invention, although rolling was performed at a predetermined cumulative reduction ratio, recrystallization at the center portion of the plate thickness became insufficient, and a predetermined | Δ E |, was not obtained. In addition, in sample No.37 in which the rolling temperature of the final 3 passes was all over the range of the present invention, the crystal grains were coarsened and the predetermined | Δ E | could not be obtained.
In sample No.38 in which the annealing temperature of the hot-rolled sheet exceeded the range of the present invention, austenite was generated during annealing of the hot-rolled sheet, and therefore the predetermined | Δ E |, could not be obtained. It was confirmed that, when the steel sheets of Nos. 22 to 24, 37 and 38, in which the predetermined | Δ E | was not obtained, were applied to the thick flange, the steel sheets were bent or twisted during vibration.
In steel M No.35 in which the Cr content was less than the range of the present invention, no sufficient passive film was formed on the steel sheet surface, and the desired corrosion resistance was not obtained.
In the case of No.36 using steel N in which the Cr content exceeded the range of the present invention, cracks occurred in the slab during cooling after casting, and thus, fracture occurred during the hot rolling process, and a predetermined evaluation could not be performed.
Industrial applicability of the invention
The hot rolled ferritic stainless steel sheet obtained by the present invention is particularly suitable for applications requiring rigidity and corrosion resistance, for example, for application to a flange of an EGR cooler.

Claims (6)

1. A hot-rolled ferritic stainless steel sheet characterized by having the following composition: contains 0.016 to 0.060 wt% of C, 0.02 to 0.50 wt% of Si, 0.01 to 1.00 wt% of Mn, 0.04 wt% or less of P, 0.01 wt% or less of S, 15.5 to 18.0 wt% of Cr, 0.001 to 0.10 wt% of Al, 0.025 to 0.100 wt% of N, 0.1 to 1.0 wt% of Ni, and the balance of Fe and unavoidable impurities,
and is obtained by performing the final 3 passes of finish rolling at a temperature range of 953 to 1100 ℃ and a cumulative reduction ratio of 25% to 39% in a hot rolling step of performing the finish rolling of 3 passes or more,
the absolute value | Delta E | of the in-plane anisotropy of the longitudinal elastic modulus calculated by the following formula (1) is 35GPa or less,
|ΔE|＝|(EL－2×ED+EC)/2|…(1)
here, ELModulus of elasticity in the longitudinal direction in a direction parallel to the rolling direction, EDIs a longitudinal elastic modulus in a direction of 45 DEG relative to the rolling direction, ECFor a longitudinal modulus of elasticity at right angles to the direction of calendering, said EL、ED、ECThe unit of (a) is GPa.
2. The hot-rolled ferritic stainless steel sheet according to claim 1, further comprising 1 or 2 or more selected from the group consisting of 0.1 to 1.0% by mass of Cu, 0.1 to 0.5% by mass of Mo, and 0.01 to 0.5% by mass of Co.
3. The hot-rolled ferritic stainless steel sheet according to claim 1 or 2, further comprising 1 or 2 or more selected from the group consisting of 0.01 to 0.25% by mass of V, 0.001 to 0.015% by mass of Ti, 0.001 to 0.025% by mass of Nb, 0.0002 to 0.0050% by mass of Mg, 0.0002 to 0.0050% by mass of B, 0.0002 to 0.0020% by mass of Ca, and 0.01 to 0.10% by mass of REM.
4. A hot-rolled annealed ferritic stainless steel sheet characterized by being obtained by subjecting a hot-rolled ferritic stainless steel sheet according to any one of claims 1 to 3 to hot-rolled sheet annealing.
5. A method for producing a hot-rolled ferritic stainless steel sheet according to any one of claims 1 to 3, wherein the hot-rolled steel sheet is subjected to 3 or more passes of finish rolling, and the final 3 passes of the finish rolling are performed at a temperature range of 953 to 1100 ℃ and a cumulative reduction ratio of 25% to 39%.
6. A method for producing a hot-rolled annealed ferritic stainless steel sheet, characterized in that the method for producing a hot-rolled ferritic stainless steel sheet according to claim 5 is used, and after the hot-rolling step, hot-rolled sheet annealing is further performed at 800 to 889 ℃.
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