WO2017013850A1 - フェライト系ステンレス熱延鋼板および熱延焼鈍板、ならびにそれらの製造方法 - Google Patents
フェライト系ステンレス熱延鋼板および熱延焼鈍板、ならびにそれらの製造方法 Download PDFInfo
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- WO2017013850A1 WO2017013850A1 PCT/JP2016/003286 JP2016003286W WO2017013850A1 WO 2017013850 A1 WO2017013850 A1 WO 2017013850A1 JP 2016003286 W JP2016003286 W JP 2016003286W WO 2017013850 A1 WO2017013850 A1 WO 2017013850A1
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- C—CHEMISTRY; METALLURGY
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- 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
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- 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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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- 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
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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
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- 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
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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
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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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
- C22C38/44—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
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- 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
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- 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
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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
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
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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
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
Definitions
- the present invention relates to a ferritic stainless hot-rolled steel sheet and hot-rolled annealed sheet having sufficient corrosion resistance and excellent rigidity, and a method for producing them.
- an exhaust gas recirculation (EGR) system in which exhaust gas generated from an automobile engine is used again as engine intake air has been applied. Exhaust gas generated from the engine is supplied to the engine again after passing through an EGR cooler for lowering the gas temperature.
- EGR exhaust gas recirculation
- the flange used at the joint with a member such as an EGR cooler which is subject to vibration all the time when the vehicle is running, has sufficient rigidity to prevent gas leakage due to the generation of gaps between parts due to the deflection of the flange due to vibration.
- a thick-walled flange for example, a plate thickness: 6 mm or more
- a flange between members to which vibration is applied all the time when the vehicle is traveling such as an EGR cooler.
- Patent Document 1 includes mass%, C: 0.015% or less, Si: 0.01 to 0.4%, Mn: 0.01 to 0.8%, P: 0.04% or less, S: 0.01% or less, Cr: 14.0 to less than 18.0%, Ni: 0.05 to 1%, Nb: 0.3 to 0.6%, Ti: 0.05% or less, N: 0.020% or less, Al: 0.10% or less, B: 0.0002 to 0.0020%, the balance is Fe and inevitable impurities, and the content of Nb, C and N is Nb / ( A ferritic stainless hot rolled steel sheet satisfying C + N) ⁇ 16, a Charpy impact value at 0 ° C. of 10 J / cm 2 or more, and a plate thickness of 5.0 to 9.0 mm is disclosed.
- An object of the present invention is to provide a ferritic stainless steel hot-rolled steel sheet and hot-rolled annealed steel sheet that can solve such problems and have sufficient corrosion resistance and can be prevented from being bent and twisted after forming, and a method for producing the same.
- the present inventors have found that the following formula (1) is applied to a steel sheet in order to suppress deformation such as deflection and torsion during vibration after application to a flange or the like. It was found that the absolute value
- E L is the longitudinal elastic modulus (GPa) in the direction parallel to the rolling direction
- E D is the longitudinal elastic modulus (GPa) in the direction of 45 ° with respect to the rolling direction
- E C is the longitudinal elasticity in the direction perpendicular to the rolling direction.
- E L , E D , and E C are respectively determined by the transverse resonance method described in JIS Z 2280-1993 under the temperature condition of 23 ° C. in the rolling direction of the steel sheet, the 45 ° direction of rolling, and the direction perpendicular to the rolling direction. It can be obtained using the measured longitudinal elastic modulus.
- E L is the longitudinal elastic modulus (GPa) in the direction parallel to the rolling direction
- E D is the longitudinal elastic modulus (GPa) in the direction of 45 ° with respect to the rolling direction
- E C is the longitudinal elasticity in the direction perpendicular to the rolling direction.
- the component composition is selected from mass%, Cu: 0.1 to 1.0%, Mo: 0.1 to 0.5%, and Co: 0.01 to 0.5%.
- a ferritic stainless hot-rolled steel sheet and a hot-rolled annealed sheet that have sufficient corrosion resistance and can suppress deflection and twisting after forming can be obtained.
- sufficient corrosion resistance in the present invention refers to a salt spray cycle test (salt spray (35 ° C., 5% by mass) specified in JIS H8502 on a steel plate whose surface is polished and finished with # 600 emery paper and the end face is sealed. (NaCl, spraying 2 hr) ⁇ drying (60 ° C., relative humidity 40%, 4 hr) ⁇ wetting (50 ° C., relative humidity ⁇ 95%, 2
- the ferritic stainless steel hot-rolled steel sheet and hot-rolled annealed sheet according to the present invention are, in mass%, C: 0.005-0.060%, Si: 0.02-0.50%, Mn: 0.01-1. 00%, P: 0.04% or less, S: 0.01% or less, Cr: 15.5 to 18.0%, Al: 0.001 to 0.10%, N: 0.005 to 0.100 %, Ni: 0.1 to 1.0%, with the balance being a component composition consisting of Fe and inevitable impurities, the in-plane anisotropy of the longitudinal elastic modulus calculated by the following formula (1)
- is 35 GPa or less.
- E L is the longitudinal elastic modulus in the direction parallel to the rolling direction (GPa)
- modulus of longitudinal elasticity in the direction of E D is 45 ° to the rolling direction (GPa)
- E C is the rolling direction and the vertical direction
- E L , E D , and E C are respectively determined by the transverse resonance method described in JIS Z 2280-1993 under the temperature condition of 23 ° C. in the rolling direction of the steel sheet, the 45 ° direction of rolling, and the direction perpendicular to the rolling direction It can be obtained using the measured longitudinal elastic modulus.
- the ferritic stainless steel hot-rolled steel sheet and hot-rolled annealed sheet of the present invention are intended to be used mainly for thick-walled flanges used for EGR cooler parts of automobiles.
- the present inventors applied various ferritic stainless steel hot-rolled steel sheets to a thick flange for an EGR cooler, and evaluated the performance in detail. As a result, it has been found that when a ferritic stainless hot rolled steel sheet having an in-plane anisotropy of longitudinal elastic modulus exceeding 35 GPa is applied, large deflection and twist are likely to occur due to vibration during vehicle travel.
- the present inventors have developed a method for reducing the in-plane anisotropy of the longitudinal elastic modulus in a ferritic stainless steel hot-rolled steel sheet, in particular, the rolling temperature in each pass of hot rolling consisting of multiple passes using a multi-stage stand. And intensively studied focusing on the reduction ratio.
- the final 3 pass rolling in the multipass finishing hot rolling consisting of 3 passes or more is performed at a temperature range of 900 to 1100 ° C. and a cumulative reduction ratio of 25% or more (preferably 30% or more), thereby obtaining a longitudinal elastic modulus. It was found that the in-plane anisotropy was significantly reduced and the desired rigidity was obtained.
- the expanded ferrite grains are distributed along the casting direction in the central part of the thickness of the slab before hot rolling of the ferritic stainless steel.
- the center portion of the plate thickness has a large number of stretched grains and a small grain interfacial area, so that there are fewer recrystallization sites than the steel plate surface layer portion.
- the steel plate when a steel plate is rolled, the steel plate mainly deforms and extends from the surface layer portion. For this reason, when the rolling reduction is small, the amount of deformation in the central portion of the plate thickness is small, and almost no rolling strain is introduced into the central portion of the plate thickness.
- the introduction and recrystallization of strain are repeated in the surface layer portion of the steel sheet, while the progress of recrystallization is greatly delayed in the central portion of the plate thickness.
- the expanded ferrite grains having a similar crystal orientation generated during casting are likely to remain without being destroyed, and the in-plane anisotropy of the longitudinal elastic modulus is increased after hot rolling.
- the present inventors have set the final three passes of the finish hot rolling at 900 to 1100 ° C., which is a temperature range in which recrystallization occurs actively. It was devised to apply a greater reduction than the conventional range, with a cumulative reduction rate of 25% or more.
- the present inventors systematically affect the effect of the rolling temperature and rolling reduction of each rolling pass on the in-plane anisotropy of the longitudinal elastic modulus of hot-rolled steel sheet produced by 7-pass finishing hot rolling. Investigated. As a result, the in-plane anisotropy of the longitudinal elastic modulus of the steel sheet after hot rolling was hardly affected by the temperature and rolling reduction of the first 4 passes, whereas the rolling temperature and rolling reduction of the final 3 passes were not affected. It was found that there is a tendency to be strongly influenced. Therefore, the present inventors investigated in further detail the influence of the rolling temperature and rolling reduction in the final three passes and the cumulative rolling reduction in the final three passes.
- the in-plane anisotropy of the longitudinal elastic modulus of the hot-rolled steel sheet tends to be greatly reduced when the final three-pass rolling is performed in the range of 900 to 1100 ° C., and the longitudinal strength of the hot-rolled steel sheet at that time It has been found that the amount of change in the in-plane anisotropy of the elastic modulus can be arranged not by the rolling reduction rate of each pass but by the cumulative rolling reduction rate of the final three passes. That is, the in-plane anisotropy of the longitudinal elastic modulus in the hot-rolled steel sheet has been found to be important to complete the finish rolling in a temperature range of 900 to 1100 ° C. and a cumulative reduction ratio of 25% or more. .
- the present inventors investigated the reason why the rolling temperature and the rolling reduction of the rolling pass before the final three passes have little influence on the in-plane anisotropy of the longitudinal elastic modulus of the hot-rolled steel sheet.
- the plate thickness before rolling starts is large, and even if the rolling reduction is increased, the rolling strain is not sufficiently introduced to the central portion of the plate thickness, and the rolling temperature is high. For this reason, excessive growth of recrystallized grains generated after rolling occurs, resulting in coarse grains. Therefore, the effect of eliminating the anisotropy of the metal structure due to the formation of recrystallized grains is significantly larger than the cumulative effect in the final three passes. It was found that this was due to a small amount.
- the rolling strain is effectively introduced to the plate thickness central portion by rolling in the final three passes.
- the recrystallized sites in the area greatly increase.
- recrystallization at the center of the plate thickness is promoted, and the expanded ferrite grain structure formed during casting is effectively destroyed,
- the in-plane anisotropy of the longitudinal elastic modulus after hot rolling is greatly reduced.
- rolling temperature at 1100 degrees C or less, the coarsening of a recrystallized grain is suppressed and the cancellation effect of the metal structure anisotropy fully expresses.
- the absolute value of the in-plane anisotropy of the longitudinal elastic modulus can be 35 GPa or less, and deformation such as large deflection or torsion during vibration can be suppressed after molding into a thick flange or the like.
- the present inventors performed hot-rolled sheet annealing of the hot-rolled steel sheet of the present invention in the range of 800 to 900 ° C. or less to improve the formability of the hot-rolled steel sheet. It was found that in addition to the effect of improving the property, the effect of reducing the in-plane anisotropy of the longitudinal elastic modulus expressed by hot rolling is maintained.
- the effect of reducing the in-plane anisotropy of the longitudinal elastic modulus in the present invention is due to the fracture of the stretched ferrite grain structure in the center portion of the sheet thickness, and the hot rolled sheet in a predetermined temperature range after hot rolling It has been found that when annealed, no expanded ferrite grains that promote the anisotropy of the steel sheet are generated.
- the thickness of the ferritic stainless hot rolled steel sheet and ferritic stainless hot rolled annealed sheet of the present invention is not particularly limited, but is preferably a thickness that can be applied to a thick flange. 0.0 mm is preferable.
- % representing the component composition means mass%.
- 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%. More preferably, the C content is in the range of 0.025 to 0.040%. Even more preferably, the C content is in the range of 0.030 to 0.040%.
- Si 0.02 to 0.50%
- Si is an element that acts as a deoxidizer during steel melting. In order to obtain this effect, it is necessary to contain 0.02% or more of Si. However, if the Si content exceeds 0.50%, the steel sheet is hardened, the rolling load during hot rolling increases, and the manufacturability in the hot rolling process decreases, which is not preferable. Therefore, the Si content is in the range of 0.02 to 0.50%. Preferably, the Si content is in the range of 0.10 to 0.35%. More preferably, the Si content is in the range of 0.10 to 0.30%.
- Mn 0.01 to 1.00% If Mn is contained in an excessive amount in the same manner as Si, the steel sheet is hardened, the rolling load during hot rolling increases, and the manufacturability in the hot rolling process decreases, which is not preferable. Moreover, the production amount of MnS may increase and the corrosion resistance may decrease. Therefore, the upper limit of the Mn content is 1.00%. About the minimum of Mn content, it is set to 0.01% from a viewpoint of the load of a refining process. Preferably, the Mn content is in the range of 0.10 to 0.90%. More preferably, the Mn content is in the range of 0.45 to 0.85%.
- P 0.04% or less Since P is an element that promotes grain boundary fracture due to grain boundary segregation, it is desirable that P be less.
- the upper limit of the P content is 0.04%.
- the P content is 0.03% or less. More preferably, the P content is 0.01% or less.
- S 0.01% or less
- S is an element that exists as sulfide inclusions such as MnS and lowers ductility, corrosion resistance, etc., especially when the S content exceeds 0.01%. The adverse effect of the remarkably occurs. For this reason, the S content is desirably as low as possible.
- the upper limit of the S content is set to 0.01%.
- the S content is 0.007% or less. More preferably, the S content is 0.005% or less.
- Cr 15.5 to 18.0% Cr is an element having an effect of improving the corrosion resistance by forming a passive film on the surface of the steel sheet. In order to acquire this effect, it is necessary to make Cr content 15.5% or more. However, if the Cr content exceeds 18.0%, the toughness of the steel sheet is remarkably lowered, which is not preferable. Therefore, the Cr content is in the range of 15.5 to 18.0%. Preferably, the Cr content is in the range of 16.0 to 17.0%. More preferably, the Cr content is in the range of 16.0 to 16.5%.
- Al 0.001 to 0.10%
- Al is an element that acts as a deoxidizing agent similarly to Si. In order to obtain this effect, it is necessary to contain 0.001% or more of Al. However, when the Al content exceeds 0.10%, Al inclusions such as Al 2 O 3 increase, and the surface properties tend to be lowered. Therefore, the Al content is in the range of 0.001 to 0.10%. Preferably, the Al content is in the range of 0.001 to 0.07%. More preferably, the Al content is in the range of 0.001 to 0.05%.
- 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%. More preferably, the N content is in the range of 0.030 to 0.050%.
- Ni 0.1 to 1.0%
- Ni is an element that improves corrosion resistance, and it is effective to contain it particularly when high corrosion resistance is required. This effect becomes remarkable when the content is 0.1% or more. However, if the content exceeds 1.0%, the moldability is lowered, which is not preferable. Therefore, the Ni content is 0.1 to 1.0%. Preferably, the Ni content is in the range of 0.2-0.4%.
- the balance is Fe and inevitable impurities.
- Cu 0.1 to 1.0%
- Mo 0.1 to 0.5%
- Co 0.01 to 0.5%
- Cu 0.1 to 1 .0%
- Cu is an element that improves corrosion resistance, and it is effective to contain it particularly when high corrosion resistance is required. This effect becomes remarkable when the Cu content is 0.1% or more. However, if the Cu content exceeds 1.0%, the formability may deteriorate. Therefore, when Cu is contained, the content is made 0.1 to 1.0%.
- the Cu content is in the range of 0.2 to 0.4%.
- Mo 0.1 to 0.5%
- Mo is an element that improves the corrosion resistance like Ni and Cu, and it is effective to contain it particularly when high corrosion resistance is required. This effect becomes remarkable when the Mo content is 0.1% or more. However, if the Mo content exceeds 0.5%, the steel sheet becomes hard, the rolling load during hot rolling increases, and the manufacturability in the hot rolling process may decrease. Therefore, when it contains Mo, it is 0.1 to 0.5%.
- the Mo content is in the range of 0.2 to 0.3%.
- Co 0.01 to 0.5%
- Co is an element that improves toughness. This effect is obtained when the content is 0.01% or more. On the other hand, if the content exceeds 0.5%, moldability may be reduced. Therefore, if Co is contained, the content is made 0.01 to 0.5% in range.
- V 0.01 to 0.25%
- Ti 0.001 to 0.015%
- Nb 0.001 to 0.025%
- Mg 0.0002 to 0.0050%
- B 0.0002 to One or more selected from 0.0050%
- Ca 0.0002 to 0.0020%
- REM 0.01 to 0.10%
- V 0.01 to 0.25%
- V is an element that forms carbonitride more easily than Cr.
- V has the 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 acquire this effect, it is necessary to contain V 0.01% or more. However, if the V content exceeds 0.25%, workability may be reduced. Increases manufacturing costs. Therefore, when V is contained, the content is made 0.01 to 0.25%.
- the V content is in the range of 0.03 to 0.08%.
- Ti and Nb are elements having high affinity with C and N, and precipitate as carbide or nitride during hot rolling, and have the effect of suppressing sensitization due to precipitation of Cr carbonitride. 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%, good surface properties may not be obtained due to excessive precipitation of TiN and NbC. Therefore, when Ti is contained, the range is 0.001 to 0.015%, and when Nb is contained, the range is 0.001 to 0.025%.
- the Ti content is preferably in the range of 0.003 to 0.010%.
- the Nb content is preferably in the range of 0.005 to 0.020%. More preferably, the Nb content is in the range of 0.010 to 0.015%.
- Mg 0.0002 to 0.0050%
- Mg is an element that has an effect of improving hot workability. In order to acquire this effect, 0.0002% or more of Mg needs to be contained. However, when the Mg content exceeds 0.0050%, the surface quality may deteriorate. Therefore, when Mg is contained, the content is made 0.0002 to 0.0050%.
- the Mg content is in the range of 0.0005 to 0.0035%. More preferably, the Mg content is in the range of 0.0005 to 0.0020%.
- B 0.0002 to 0.0050%
- B is an element effective for preventing embrittlement at low temperature secondary work. In order to obtain this effect, 0.0002% or more of B must be contained. However, when the B content exceeds 0.0050%, the hot workability may decrease. Therefore, when B is contained, the content is made 0.0002 to 0.0050%.
- the B content is in the range of 0.0005 to 0.0035%. More preferably, the B content is in the range of 0.0005 to 0.0020%.
- Ca 0.0002 to 0.0020%
- Ca is an effective component for preventing clogging of the nozzle due to crystallization of inclusions that are likely to occur during continuous casting.
- 0.0002% or more of Ca needs to be contained.
- the Ca content exceeds 0.0020%, CaS may be generated and the corrosion resistance may be reduced. Therefore, when Ca is contained, the content is made 0.0002 to 0.0020%.
- the Ca content is in the range of 0.0005 to 0.0015%. More 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 is particularly effective in suppressing the formation of an oxide film on the welded portion and improving the corrosion resistance of the welded portion. In order to obtain this effect, it is necessary to contain 0.01% or more of REM. However, if the content of REM exceeds 0.10%, productivity such as pickling at the time of cold rolling annealing may be lowered. Moreover, since REM is an expensive element, excessive inclusion is not preferable because it causes an increase in manufacturing cost. Therefore, when REM is contained, the content is made 0.01 to 0.10%. Preferably, the REM content is in the range of 0.01 to 0.05%.
- the final 3 passes of finishing rolling are performed in a temperature range of 900 to 1100 ° C. It is obtained by carrying out at a cumulative rolling reduction of 25% or more.
- the maximum number of passes of finish rolling is not particularly limited from the viewpoint of obtaining a predetermined material.
- the maximum number of passes exceeds 15 passes, the steel sheet temperature is likely to decrease due to an increase in the number of contacts with the rolling roll.
- the maximum number of paths is 15 paths or less. More preferably, the maximum number of paths is 10 paths or less.
- the molten steel having the above component composition is melted by a known method such as a converter, electric furnace, vacuum melting furnace or the like, and is made into a steel material (slab) by a continuous casting method or an ingot-bundling method.
- the slab is heated at 1100 to 1250 ° C. for 1 to 24 hours, or directly subjected to hot rolling as it is cast without heating.
- the rough rolling is not particularly limited, but it is preferable to set the cumulative rolling reduction in the rough rolling to 65% or more in order to effectively destroy the cast structure.
- the sheet is rolled to a predetermined thickness by finish rolling.
- the final three passes of finish rolling are performed in a temperature range of 900 to 1100 ° C. with a cumulative reduction ratio of 25% or more.
- Rolling temperature range for the final 3 passes 900-1100 ° C
- the final three-pass finish rolling it is necessary to effectively introduce rolling strain to the center of the plate thickness and to generate sufficient recrystallization by increasing the cumulative rolling reduction. Therefore, the final three-pass finish rolling must be performed in a temperature range of 900 to 1100 ° C. at which sufficient recrystallization occurs.
- the rolling temperature of the final three passes is less than 900 ° C., recrystallization does not occur sufficiently and in-plane anisotropy with a predetermined longitudinal elastic modulus cannot be obtained.
- the rolling temperature of the final three passes exceeds 1100 ° C., the crystal grains become extremely coarse, and in-plane anisotropy with a predetermined longitudinal elastic modulus cannot be obtained. Absent.
- the rolling temperature for the final three passes is in the range of 900-1075 ° C. More preferably, the rolling temperature in the final three passes is in the range of 930 to 1050 ° C.
- the rolling temperature range of the first pass in the final three passes is 950 to 1100 ° C., which is performed next to the first pass.
- the rolling temperature range of the second pass is preferably 925 to 1075 ° C.
- the rolling temperature range of the third pass performed after the second pass is preferably 900 to 1050 ° C.
- Cumulative rolling reduction of 25% or more in the final three passes In order to effectively impart rolling strain to the center of the plate thickness of the steel sheet, rolling of 25% or more is required as the cumulative rolling reduction for the final three passes of finish rolling. If the cumulative rolling reduction is less than 25%, the introduction of rolling strain into the center of the sheet thickness is insufficient, and recrystallization at the center of the sheet thickness is delayed, and in-plane anisotropy with a predetermined longitudinal elastic modulus cannot be obtained. . Therefore, it is preferable that the cumulative rolling reduction is 25% or more. More preferably, the cumulative rolling reduction is 30% or more. More preferably, the cumulative rolling reduction is 35% or more.
- the upper limit of the cumulative rolling reduction is not particularly limited, but if the cumulative rolling reduction is excessively increased, the rolling load increases and the productivity decreases, and surface roughness may occur after rolling. It is preferable to do.
- the cumulative rolling reduction is 100 ⁇ (final plate thickness / plate thickness before starting the final three-pass rolling) ⁇ 100 [%].
- the rolling temperature and cumulative rolling reduction of the final three passes of finish rolling are controlled, and the rolling temperature and cumulative rolling reduction of finish rolling are controlled. If the final four passes or more, since the rolling reduction rate in each pass is small, the introduced strain hardly contributes to the reduction of the anisotropy of the longitudinal elastic modulus, and there is a sufficient effect of reducing the anisotropy of the longitudinal elastic modulus. I can't get it.
- the rolling temperature and the cumulative reduction ratio of the finish rolling are controlled to the final two passes or less, the rolling load is significantly increased and the productivity is lowered because the large reduction with the cumulative reduction ratio of 25% or more is performed in two passes. This is not preferable. Therefore, in the method for producing a ferritic stainless steel hot-rolled steel sheet according to the present invention, the rolling temperature and cumulative rolling reduction of the final three passes of finish rolling are controlled.
- the steel sheet After finishing rolling, the steel sheet is cooled, and then the steel sheet is wound to form a hot-rolled steel strip.
- the coiling temperature is not particularly limited, but in the case of a steel component in which an austenite phase is generated during hot rolling, when the coiling temperature is less than 500 ° C., the austenite phase is transformed into a martensite phase, The rolled steel sheet may become hard and formability may deteriorate. Therefore, the winding process is preferably performed at 500 ° C. or higher.
- the ferritic stainless steel hot-rolled annealed sheet may be obtained by performing hot-rolled sheet annealing in the range of 800 to 900 ° C. after the hot rolling step.
- Hot-rolled sheet annealing temperature 800-900 ° C
- the hot-rolled sheet annealing temperature is less than 800 ° C.
- recrystallization does not occur sufficiently, so that the work structure by hot rolling remains and the effect of improving formability cannot be obtained.
- the temperature exceeds 900 ° C. an anustenite phase is generated during annealing, and the anisotropy of the longitudinal elastic modulus increases, that is, the in-plane anisotropy of the predetermined longitudinal elastic modulus that has been developed in the hot-rolled steel sheet disappears. There is.
- the temperature range is preferably set to 800 to 900 ° C.
- maintenance time and method of hot-rolled sheet annealing You may implement by either box annealing (batch annealing) or continuous annealing.
- the obtained hot-rolled steel sheet or the steel sheet subjected to hot-rolled sheet annealing may be subjected to descaling treatment by shot blasting or pickling as necessary. Furthermore, in order to improve the surface properties, grinding or polishing may be performed.
- a molten stainless steel having the chemical composition shown in Table 1 is melted by refining a converter with a capacity of 150 ton and strong stirring and vacuum oxygen decarburization (SS-VOD), and a steel slab having a width of 1000 mm and a thickness of 200 mm by continuous casting. did.
- the slab was heated at 1200 ° C. for 1 h, and then subjected to reverse rough rolling using a three-stage stand as hot rolling to obtain a steel plate of about 40 mm, and then the final three passes (fifth pass) of 7-pass finish rolling. , 6th pass, 7th pass) were performed under the conditions shown in Table 2 to obtain hot-rolled steel sheets.
- some hot-rolled steel sheets (No. 25, 26, and 38 in Table 2) were subjected to hot-rolled sheet annealing that was furnace-cooled after holding for 8 hours under the conditions shown in Table 2 after hot rolling. I got a plate.
- the obtained hot-rolled steel sheet and hot-rolled annealed sheet were evaluated as follows.
- Photograph the surface of the specimen after 8 cycles of salt spray cycle test measure the rusting area on the specimen surface by image analysis, and calculate the rusting rate (( Rust area / total area of test piece) ⁇ 100 [%]) was calculated.
- a rusting rate of 10% or less was determined to pass with excellent corrosion resistance ()), more than 10% to 25% or less passed ( ⁇ ), and more than 25% to reject (x).
- the ferritic stainless steel hot-rolled steel sheet obtained by the present invention is particularly suitable for applications requiring rigidity and corrosion resistance, for example, application to flanges of EGR coolers.
Abstract
Description
|ΔE|=|(EL-2×ED+EC)/2| ・・・(1)
ここで、ELは圧延方向に平行な方向の縦弾性率(GPa)、EDは圧延方向に対して45°の方向の縦弾性率(GPa)、ECは圧延方向と垂直方向の縦弾性率(GPa)である。
また、EL、ED、ECは、それぞれ、鋼板の圧延方向、圧延45°方向、圧延方向と垂直方向について、23℃の温度条件下、JIS Z 2280-1993に記載の横共振法により測定した縦弾性率を用いて得ることができる。
[1]質量%で、C:0.005~0.060%、Si:0.02~0.50%、Mn:0.01~1.00%、P:0.04%以下、S:0.01%以下、Cr:15.5~18.0%、Al:0.001~0.10%、N:0.005~0.100%、Ni:0.1~1.0%を含有し、残部がFeおよび不可避的不純物からなる成分組成を有し、
下式(1)で算出される縦弾性率の面内異方性の絶対値|ΔE|が35GPa以下であるフェライト系ステンレス熱延鋼板。
|ΔE|=|(EL-2×ED+EC)/2| ・・・(1)
ここで、ELは圧延方向に平行な方向の縦弾性率(GPa)、EDは圧延方向に対して45°の方向の縦弾性率(GPa)、ECは圧延方向と直角方向の縦弾性率(GPa)である。
[2]成分組成として、質量%で、さらに、Cu:0.1~1.0%、Mo:0.1~0.5%、Co:0.01~0.5%のうちから選ばれる1種または2種以上を含有する上記[1]に記載のフェライト系ステンレス熱延鋼板。
[3]成分組成として、質量%で、さらに、V:0.01~0.25%、Ti:0.001~0.015%、Nb:0.001~0.025%、Mg:0.0002~0.0050%、B:0.0002~0.0050%、Ca:0.0002~0.0020%、REM:0.01~0.10%のうちから選ばれる1種または2種以上を含有する上記[1]または[2]に記載のフェライト系ステンレス熱延鋼板。
[4]上記[1]~[3]のいずれかに記載のフェライト系ステンレス熱延鋼板に熱延板焼鈍を施して得られるフェライト系ステンレス熱延焼鈍板。
[5]上記[1]~[3]のいずれかに記載のフェライト系ステンレス熱延鋼板の製造方法であって、3パス以上の仕上げ圧延を行う熱間圧延工程において、仕上げ圧延の最終3パスを温度範囲900~1100℃、累積圧下率25%以上で行うフェライト系ステンレス熱延鋼板の製造方法。
[6]上記[5]に記載のフェライト系ステンレス熱延鋼板の製造方法を用い、
前記熱間圧延工程後に、さらに800~900℃で熱延板焼鈍を行うフェライト系ステンレス熱延焼鈍板の製造方法。
|ΔE|=|(EL-2×ED+EC)/2| ・・・(1)
なお、ここで、ELは圧延方向に平行な方向の縦弾性率(GPa)、EDは圧延方向に対して45°の方向の縦弾性率(GPa)、ECは圧延方向と垂直方向の縦弾性率(GPa)である。
以下、特に断らない限り、成分組成を表す%は質量%を意味する。
Cを多量に含有する場合、加工性の低下やCr系炭窒化物の析出による鋭敏化および靭性の低下を招くため、C含有量は0.060%を上限とする。一方、C含有量を極度に低下させることは精錬コストの著しい上昇を招くため、C含有量の下限は常法の精錬において製造コストの著しい上昇を招かないレベルである0.005%とする。製鋼工程における安定製造性の観点から、C含有量は0.010~0.050%とすることが好ましい。より好ましくは、C含有量は0.020~0.045%の範囲である。さらに好ましくは、C含有量は0.025~0.040%の範囲である。さらにより好ましくは、C含有量は0.030~0.040%の範囲である。
Siは、鋼溶製時に脱酸剤として作用する元素である。この効果を得るためには0.02%以上のSiの含有が必要である。しかし、Si含有量が0.50%を超えると、鋼板が硬質化して熱間圧延時の圧延負荷が増大し、熱間圧延工程における製造性が低下するため好ましくない。そのため、Si含有量は0.02~0.50%の範囲とする。好ましくは、Si含有量は0.10~0.35%の範囲である。さらに好ましくは、Si含有量は0.10~0.30%の範囲である。
Mnは、Siと同様に過剰に含有すると鋼板が硬質化して熱間圧延時の圧延負荷が増大し、熱間圧延工程における製造性が低下するため好ましくない。また、MnSの生成量が増加して耐食性が低下する場合がある。そのため、Mn含有量の上限を1.00%とする。Mn含有量の下限については、精錬工程の負荷の観点から0.01%とする。好ましくは、Mn含有量は0.10~0.90%の範囲である。さらに好ましくは、Mn含有量は0.45~0.85%の範囲である。
Pは、粒界偏析による粒界破壊を助長する元素であるため少ない方が望ましく、P含有量の上限を0.04%とする。好ましくは、P含有量は0.03%以下である。さらに好ましくは、P含有量は0.01%以下である。
Sは、MnSなどの硫化物系介在物となって存在して延性や耐食性等を低下させる元素であり、特にS含有量が0.01%を超えた場合にそれらの悪影響が顕著に生じる。そのため、S含有量は極力低い方が望ましく、本発明ではS含有量の上限を0.01%とする。好ましくは、S含有量は0.007%以下である。さらに好ましくは、S含有量は0.005%以下である。
Crは、鋼板表面に不動態皮膜を形成して耐食性を向上させる効果を有する元素である。この効果を得るためには、Cr含有量を15.5%以上とする必要がある。しかし、Cr含有量が18.0%を超えると、鋼板の靭性が著しく低下するため好ましくない。そのため、Cr含有量は15.5~18.0%の範囲とする。好ましくは、Cr含有量は16.0~17.0%の範囲である。さらに好ましくは、Cr含有量は16.0~16.5%の範囲である。
Alは、Siと同様に脱酸剤として作用する元素である。この効果を得るためには、0.001%以上のAlの含有が必要である。しかし、Al含有量が0.10%を超えると、Al2O3等のAl系介在物が増加し、表面性状が低下しやすくなる。そのため、Al含有量は0.001~0.10%の範囲とする。好ましくは、Al含有量は0.001~0.07%の範囲である。さらに好ましくは、Al含有量は0.001~0.05%の範囲である。
Nを多量に含有する場合、Cと同様に加工性の低下やCr系炭窒化物の析出による鋭敏化および靭性の低下を招くため、N含有量は0.100%を上限とする。一方、N含有量を極度に低下させることはCと同様に精錬コストの著しい上昇を招くため、N含有量の下限は常法の精錬において製造コストの著しい上昇を招かないレベルである0.005%とする。製鋼工程における安定製造性の観点から、N含有量は0.010~0.075%とすることが好ましい。より好ましくは、N含有量は0.025~0.055%の範囲である。さらに好ましくは、N含有量は0.030~0.050%の範囲である。
Niは耐食性を向上させる元素であり、特に高い耐食性が要求される場合には含有することが有効である。この効果は0.1%以上の含有で顕著となる。しかし、含有量が1.0%を超えると成形性が低下するため好ましくない。そのため、Ni含有量は0.1~1.0%とする。好ましくは、Ni含有量は0.2~0.4%の範囲である。
Cu:0.1~1.0%
Cuは耐食性を向上させる元素であり、特に高い耐食性が要求される場合には含有することが有効である。この効果は0.1%以上のCuの含有で顕著となる。しかし、Cu含有量が1.0%を超えると成形性が低下する場合がある。そのため、Cuを含有する場合は、0.1~1.0%とする。好ましくは、Cu含有量は0.2~0.4%の範囲である。
MoはNiおよびCuと同様に耐食性を向上させる元素であり、特に高い耐食性が要求される場合には含有することが有効である。この効果は0.1%以上のMoの含有で顕著となる。しかし、Mo含有量が0.5%を超えると鋼板が硬質化して熱間圧延時の圧延負荷が増大し、熱間圧延工程における製造性が低下する場合がある。そのため、Moを含有する場合は、0.1~0.5%とする。好ましくは、Mo含有量は0.2~0.3%の範囲である。
Coは靭性を向上させる元素である。この効果は0.01%以上の含有によって得られる。一方、含有量が0.5%を超えると成形性を低下させる場合がある。そのため、Coを含有する場合の含有量は、0.01~0.5%の範囲とする。
V:0.01~0.25%
VはCrよりも炭窒化物を形成しやすい元素である。Vは熱間圧延時に鋼中のCおよびNをV系の炭窒化物として析出させることにより、Cr炭窒化物の析出による鋭敏化を抑制する効果がある。この効果を得るためにはVを0.01%以上含有する必要がある。しかし、V含有量が0.25%を超えると加工性が低下する場合がある。製造コストの上昇を招く。そのため、Vを含有する場合は0.01~0.25%の範囲とする。好ましくは、V含有量は0.03~0.08%の範囲である。
TiおよびNbはVと同様に、CおよびNとの親和力の高い元素であり、熱間圧延時に炭化物あるいは窒化物として析出し、Cr炭窒化物の析出による鋭敏化を抑制する効果がある。この効果を得るためには、0.001%以上のTi、あるいは0.001%以上のNbを含有する必要がある。しかし、Ti含有量が0.015%を超える、あるいはNb含有量が0.030%を超えると、TiNおよびNbCの過剰な析出により良好な表面性状を得ることができない場合がある。そのため、Tiを含有する場合は0.001~0.015%の範囲、Nbを含有する場合は0.001~0.025%の範囲とする。Ti含有量は、好ましくは0.003~0.010%の範囲である。Nb含有量は、好ましくは、0.005~0.020%の範囲である。さらに好ましくは、Nb含有量は0.010~0.015%の範囲である。
Mgは、熱間加工性を向上させる効果がある元素である。この効果を得るためには0.0002%以上のMgの含有が必要である。しかし、Mg含有量が0.0050%を超えると表面品質が低下する場合がある。そのため、Mgを含有する場合は0.0002~0.0050%の範囲とする。好ましくは、Mg含有量は0.0005~0.0035%の範囲である。さらに好ましくは、Mg含有量は0.0005~0.0020%の範囲である。
Bは、低温二次加工脆化を防止するのに有効な元素である。この効果を得るためには0.0002%以上のBの含有が必要である。しかし、B含有量が0.0050%を超えると熱間加工性が低下する場合がある。そのため、Bを含有する場合は0.0002~0.0050%の範囲とする。好ましくは、B含有量は0.0005~0.0035%の範囲である。さらに好ましくは、B含有量は0.0005~0.0020%の範囲である。
Caは、連続鋳造の際に発生しやすい介在物の晶出によるノズルの閉塞を防止するのに有効な成分である。その効果を得るためには0.0002%以上のCaの含有が必要である。しかし、Ca含有量が0.0020%を超えるとCaSが生成して耐食性が低下する場合がある。そのため、Caを含有する場合は0.0002~0.0020%の範囲とする。好ましくは、Ca含有量は0.0005~0.0015%の範囲である。さらに好ましくは、Ca含有量は0.0005~0.0010%の範囲である。
REM(Rare Earth Metals)は耐酸化性を向上させる元素であり、特に溶接部の酸化皮膜の形成を抑制し溶接部の耐食性を向上させる効果がある。この効果を得るためには0.01%以上のREMの含有が必要である。しかし、0.10%を超えてREMを含有すると冷延焼鈍時の酸洗性などの製造性を低下させる場合がある。また、REMは高価な元素であるため、過度な含有は製造コストの増加を招くため好ましくない。そのため、REMを含有する場合は0.01~0.10%の範囲とする。好ましくは、REM含有量は0.01~0.05%の範囲である。
最終3パスの仕上げ圧延では、累積圧下率を大きくすることにより、板厚中央へ圧延ひずみを効果的に導入するとともに十分な再結晶を生じさせる必要がある。そのため、最終3パスの仕上げ圧延は再結晶が十分に生じる900~1100℃の温度範囲で行う必要がある。最終3パスの圧延温度が900℃未満の場合、再結晶が十分に生じず所定の縦弾性率の面内異方性が得られない。一方、最終3パスの圧延温度が1100℃を超えると、結晶粒が著しく粗大化し所定の縦弾性率の面内異方性が得られないことに加え、熱延鋼板の靭性が低下するため好ましくない。好ましくは、最終3パスの圧延温度は900~1075℃の範囲である。より好ましくは、最終3パスの圧延温度は930~1050℃の範囲である。また、最終3パスにおける特定パスで過度の圧延負荷がかかることを防ぐため、最終3パスのうち、第1パス目の圧延温度範囲を950~1100℃、この第1パスの次に行われる第2パス目の圧延温度範囲を925~1075℃、この第2パスの次に行われる第3パス目の圧延温度範囲を900~1050℃とすることが好ましい。
鋼板の板厚中央へ圧延ひずみを効果的に付与するためには、仕上げ圧延の最終3パスについて、累積圧下率で25%以上の圧下が必要である。累積圧下率が25%未満では、板厚中央への圧延ひずみの導入が不十分となって板厚中央部の再結晶が遅滞し、所定の縦弾性率の面内異方性が得られない。そのため、累積圧下率を25%以上とすることが好ましい。より好ましくは、累積圧下率は30%以上である。さらに好ましくは、累積圧下率は35%以上である。なお、累積圧下率の上限は特に限定されないが、累積圧下率を過度に大きくすると圧延負荷が上昇して製造性が低下するとともに、圧延後に表面肌荒れが発生する場合があるため、60%以下とすることが好ましい。
熱延板焼鈍温度を800℃未満とした場合、再結晶が十分に生じないため、熱間圧延による加工組織が残存し成形性の向上効果が得られない。一方、900℃を超えると焼鈍時にオーステナイト相が生成して縦弾性率の異方性が大きくなり、すなわち熱延鋼板で発現していた所定の縦弾性率の面内異方性が消失する場合がある。また、900℃超で熱延板焼鈍を行った後の冷却速度が速い場合、オーステナイト相がマルテンサイト相へと変態して鋼板が硬質化するためにかえって成形性が低下する場合がある。そのため、熱延板焼鈍を行う場合には温度範囲を800~900℃とすることが好ましい。なお、熱延板焼鈍の保持時間および手法に特に限定はなく、箱焼鈍(バッチ焼鈍)、連続焼鈍のどちらで実施してもかまわない。
圧延平行方向、圧延45°方向および圧延直角方向を長手として60mm長さ×10mm幅×2mm厚の試験片を、板厚中央±1mm内の位置からそれぞれ採取した。採取した試験片についてJIS Z 2280-1993に記載の横共振法により23℃における縦弾性率を測定し、下式(1)により縦弾性率の面内異方性の絶対値(|ΔE|)を算出した。
|ΔE|=|(EL-2×ED+EC)/2| (1)
ここで、ELは圧延方向に平行な方向の縦弾性率(GPa)、EDは圧延方向に対して45°の方向の縦弾性率(GPa)、ECは圧延方向と垂直方向の縦弾性率(GPa)である。
縦弾性率の面内異方性|ΔE|が35GPa以下である場合を、フランジ等への成形後のたわみやねじれを十分に抑制可能であると判断し、合格(○)とした。縦弾性率の面内異方性|ΔE|が35GPa超である場合を、不合格(×)とした。
熱延鋼板から、60×100mmの試験片を採取し、表面を#600エメリーペーパーにより研磨仕上げした後に端面部をシールした試験片を作製し、JIS H 8502に規定された塩水噴霧サイクル試験に供した。塩水噴霧サイクル試験は、塩水噴霧(5質量%NaCl、35℃、噴霧2hr)→乾燥(60℃、4hr、相対湿度40%)→湿潤(50℃、2hr、相対湿度≧95%)を1サイクルとして、8サイクル行った。
塩水噴霧サイクル試験を8サイクル実施後の試験片表面を写真撮影し、画像解析により試験片表面の発錆面積を測定し、試験片全面積との比率から発錆率((試験片中の発錆面積/試験片全面積)×100 [%])を算出した。発錆率が10%以下を特に優れた耐食性で合格(◎)、10%超25%以下を合格(○)、25%超を不合格(×)とした。
Claims (6)
- 質量%で、C:0.005~0.060%、Si:0.02~0.50%、Mn:0.01~1.00%、P:0.04%以下、S:0.01%以下、Cr:15.5~18.0%、Al:0.001~0.10%、N:0.005~0.100%、Ni:0.1~1.0%を含有し、残部がFeおよび不可避的不純物からなる成分組成を有し、
下式(1)で算出される縦弾性率の面内異方性の絶対値|ΔE|が35GPa以下であるフェライト系ステンレス熱延鋼板。
|ΔE|=|(EL-2×ED+EC)/2| ・・・(1)
ここで、ELは圧延方向に平行な方向の縦弾性率(GPa)、EDは圧延方向に対して45°の方向の縦弾性率(GPa)、ECは圧延方向と直角方向の縦弾性率(GPa)である。 - 成分組成として、質量%で、さらに、Cu:0.1~1.0%、Mo:0.1~0.5%、Co:0.01~0.5%のうちから選ばれる1種または2種以上を含有する請求項1に記載のフェライト系ステンレス熱延鋼板。
- 成分組成として、質量%で、さらに、V:0.01~0.25%、Ti:0.001~0.015%、Nb:0.001~0.025%、Mg:0.0002~0.0050%、B:0.0002~0.0050%、Ca:0.0002~0.0020%、REM:0.01~0.10%のうちから選ばれる1種または2種以上を含有する請求項1または2に記載のフェライト系ステンレス熱延鋼板。
- 請求項1~3のいずれかに記載のフェライト系ステンレス熱延鋼板に熱延板焼鈍を施して得られるフェライト系ステンレス熱延焼鈍板。
- 請求項1~3のいずれかに記載のフェライト系ステンレス熱延鋼板の製造方法であって、3パス以上の仕上げ圧延を行う熱間圧延工程で、仕上げ圧延の最終3パスを温度範囲900~1100℃、累積圧下率25%以上で行うフェライト系ステンレス熱延鋼板の製造方法。
- 請求項5に記載のフェライト系ステンレス熱延鋼板の製造方法を用い、
前記熱間圧延工程後に、さらに800~900℃で熱延板焼鈍を行うフェライト系ステンレス熱延焼鈍板の製造方法。
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WO2018074164A1 (ja) * | 2016-10-17 | 2018-04-26 | Jfeスチール株式会社 | フェライト系ステンレス熱延焼鈍鋼板およびその製造方法 |
CN110546294A (zh) * | 2017-04-27 | 2019-12-06 | 杰富意钢铁株式会社 | 铁素体系不锈钢热轧退火钢板及其制造方法 |
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