Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—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
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—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
• • 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
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • 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
  • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
• • 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
  • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/36—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.7% by weight of carbon
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present invention relates to a Ti-containing ferritic stainless steel having good toughness, and also relates to a flange using the steel sheet.
• the Ti-containing ferritic stainless steel sheet has a problem that the toughness thereof tends to be reduced.
• a flange used in an automobile exhaust gas flow path there are large needs of a steel sheet having a large gauge thickness (for example, a sheet thickness of from 5.0 to 11.0 mm). With a large sheet thickness, the influence of the reduction in toughness tends to be conspicuous.
• a hot rolled steel sheet or a hot rolled and annealed steel sheet is generally applied to a steel sheet material with a large gauge thickness, and therefore the mainstream measures for improving the toughness have related to the hot rolling conditions (see PTLs 1 to 4).
• various types of steel are applied to a hot rolling line.
• the use of the dedicated operation condition that is different from the general ferritic stainless steel sheets, in the production of the Ti-containing ferritic stainless steel sheet may be a factor of deterioration of the overall productivity.
• An object of the invention is to provide a Ti-containing ferritic stainless steel sheet having good toughness that is capable of being obtained in the case where a general hot rolling condition is used, and a flange using the same.
• C and N represent the contents of C and N in the steel in terms of percentage by mass respectively.
• Ti-containing ferritic stainless steel sheet according to any one of the items (1) to (3), wherein the Ti-containing ferritic stainless steel sheet has the chemical composition further containing, in terms of percentage by mass, 0.0050% or less of B.
• a specimen having a known mass collected from the steel sheet is applied with a potential of from ⁇ 100 mV to 400 mV with respect to a saturated calomel electrode (SCE) to dissolve the matrix (metallic substrate) of the specimen completely, the liquid containing the undissolved matter is filtered with a membrane filter having a pore diameter of 0.05 ⁇ m, and the solid matter remaining on the filter is recovered as the extraction residue.
• SCE saturated calomel electrode
• a Ti-containing ferritic stainless steel sheet having good toughness can be achieved.
• the enhancement of the reliability by the improvement of the toughness is particularly large in a steel sheet having a large gauge thickness (for example, a sheet thickness of from 5.0 to 11.0 mm), in which the influence of the reduction in toughness tends to be conspicuous.
• the steel sheet can be produced without providing any particular restriction in the hot rolling condition, which therefore leads to the enhancement of the productivity of the continuous hot rolling line.
• a flange for an exhaust gas flow path excellent in toughness can be obtained by using the steel sheet as a material therefor.
• the invention targets a ferritic stainless steel containing the following component elements.
• the percentage for the chemical composition of the steel sheet is percentage by mass unless otherwise indicated.
• the C content i.e., the total amount of dissolved C and C present as a compound
• the C content is restricted to 0.030% or less.
• the C content is preferably 0.020% or less, and may be managed to 0.015% or less.
• An excessive decrease of C may increase the load on steel making and may increase the cost.
• a steel sheet having a C content of 0.003% or more is targeted herein.
• Si and Mn are effective as a deoxidizing agent, and in addition, have a function that enhances the high temperature oxidation resistance. It is more effective to ensure the content of 0.02% or more for Si and 0.10% or more for Mn. Large amounts of these elements contained may be a factor causing the embrittlement of the steel.
• the Si content is restricted to 2.0% or less, and more preferably 1.0% or less.
• the Mn content is also restricted to 2.0% or less, and more preferably 1.0% or less.
• P and S contained may be a factor that reduces the corrosion resistance.
• the P content is allowed to be up to 0.050%, and the S content is allowed to be up to 0.040%.
• An excessive decrease of P and S may increase the load on steel manufacturing and may not be economically effective.
• the P content may be controlled in a range of from 0.010 to 0.050%, and the S content may be controlled in a range of from 0.0005 to 0.040%.
• Cr is important for ensuring the corrosion resistance as a stainless steel. Cr is also effective for enhancing the high temperature oxidation resistance. For exhibiting these functions, the Cr content is necessarily 10.0% or more. A large amount of Cr contained may harden the steel to impair the improvement of the toughness of the hot rolled steel sheet having a large gauge thickness in some cases. A steel sheet having a Cr content of 19.0% or less is targeted herein.
• N is a factor that reduces the toughness of the hot rolled steel as similar to C.
• the N content i.e., the total amount of dissolved N and N present as a compound
• the N content is restricted to 0.030% or less.
• the N content is preferably 0.020% or less, and may be managed to 0.015% or less.
• An excessive decrease of N may increase the load on steel manufacturing and may increase the cost.
• the N content may be controlled in a range of 0.003% or more.
• Ti forms a Ti carbonitride through bonding with C and N to suppress the segregation of a Cr carbonitride at the grain boundaries, and thus is an element that is considerably effective for retaining the corrosion resistance and the high temperature oxidation resistance of the steel.
• a ferritic stainless steel having a Ti content that is 4 times or more the total content of C and N in terms of percentage by mass is targeted herein.
• An excessive large Ti content is not preferred since the reduction of the toughness of the hot rolled steel sheet may be promoted.
• the Ti content is restricted to 0.80% or less, and Ti is more preferably contained in an amount in a range of 0.50% or less.
• the “carbonitride” means a compound containing a metal element bonded to at least one of C and N.
• the Ti carbonitride for example, TiC, TiN, and Ti(C,N) are encompassed therein.
• Al is effective as a deoxidizing agent. For achieving the function sufficiently, it is effective to add Al to make an Al content of 0.010% or more. A large amount of Al contained may be a factor that reduces the toughness. The Al content is restricted to 0.20% or less.
• Mo is effective for enhancing the corrosion resistance, and may be added depending on necessity. In this case, a Mo content of 0.01% or more is more effective. A large amount of Mo contained may adversely affect the toughness in some cases.
• the Mo content is necessarily in a range of from 0 to 1.50%, and may be managed to a range of from 0 to 0.50%.
• the B is effective for enhancing the secondary workability, and may be added depending on necessity. In this case, it is more effective to ensure the content thereof to 0.0005% or more. However, when the B content exceeds 0.0050%, the uniformity of the metal structure may be impaired due to the formation of Cr 2 B to reduce the workability in some cases.
• the B content may be in a range of from 0 to 0.0050%.
• the extraction residue that is recovered by the aforementioned electrolytic extraction method contains a Ti carbonitride as a major component.
• Ti is an element that is added to fix C and N as described above.
• C has an increased proportion thereof that is solid-dissolved in the matrix without bonding to Ti, as compared to N.
• Ti is not generally consumed for the formation of the carbonitride, but Ti that does not form the carbonitride is present in the steel sheet.
• the toughness of the steel sheet having a large gauge thickness e.g., a sheet thickness of from 5.0 to 11.0 mm
• the metal structure is controlled in such a state that the content R (% by mass) of the extraction residue recovered by the electrolytic extraction method and the contents of C and N in the steel satisfy the following expression (1).
• unforeseen troubles due to the reduction of the toughness which may be a problem in passing the sheet in cold rolling or in working a steel sheet having a large gauge thickness as a base material to a component, can be avoided.
• C and N represent the contents of C and N in the steel in terms of percentage by mass respectively.
• the term “5.0C” corresponds to the mass proportion of TiC on the assumption that C in the steel is entirely bonded to Ti
• the term “4.4N” corresponds to the mass proportion of TiN on the assumption that N in the steel is entirely bonded to Ti.
• the term “ ⁇ 0.025” corresponds to the value obtained by converting the maximum amount of the solid-dissolved C and the solid-dissolved N that is allowable for the toughness improvement effect provided sufficiently, to the amount of the Ti carbonitride. However, it is considered that N is bonded preferentially to Ti than C, and therefore the term “ ⁇ 0.025” may be substantially regarded as the allowable amount of the solid-dissolved C.
• the Ti-containing ferritic stainless steel sheet having a solid-dissolved C amount decreased to satisfy the expression (1) can be achieved by adding a heat treatment step in a particular temperature range, to an ordinary production process of a stainless steel sheet.
• a hot rolled steel sheet is produced in an ordinary method, and the hot rolled steel sheet is annealed to provide an annealed steel sheet.
• the temperature of the annealing of the hot rolled sheet may be, for example, more than 950° C. and 1,150° C. or less, and is more preferably more than 1,000° C. and 1,150° C. or less.
• the resulting annealed steel sheet is subjected to a heat treatment by retaining the steel sheet in a temperature range of 750° C. or more and 1,000° C.
• the retaining temperature is more preferably 750° C. or more and 950° C. or less, and may be managed to 750° C. or more and 900° C. or less.
• the retaining time may be set in a range of 60 minutes or less, and more preferably 10 minutes or less. It has been found that the heat treatment introduced provides the structure state satisfying the expression (1). The optimum conditions for the retaining temperature and the retaining time may be comprehended by performing a preliminary experiment corresponding to the condition for the annealing performed before the heat treatment and the chemical composition.
• Steels having the chemical compositions shown in Table 1 were made, hot rolled under condition for an ordinary ferritic stainless steel sheet, and annealed at 1,080° C. in an annealing and acid pickling line, so as to provide an annealed steel sheet.
• Steel sheets that were obtained by subjecting the annealed steel sheets to a heat treatment or steel sheets that were not subjected to a heat treatment were used as test steel sheets.
• the conditions of the heat treatment are shown in Table 2.
• a specimen was collected from the test steel sheet, and the value R thereof was obtained by the “Method for obtaining Content R of Extraction Residue in Steel” described in the foregoing.
• a U-notch impact test specimen was produced form the test steel sheet and subjected to a Charpy impact test at temperatures of 70° C. or less with an interval of 10° C. according to JIS Z2242:2005.
• the application direction of the impact with a hammer i.e., the depth direction of the U-notch
• the lowest temperature that provides an impact value of 150 J/cm 2 or more in the tests with an interval of 10° C. is defined as DBTT.
• the DBTT is 30° C. or less in the steel sheet having a large gauge thickness (for example, a sheet thickness of from 5.0 to 11.0 mm) of the Ti-containing steel species having the aforementioned chemical composition, it can be evaluated that the reliability in the aspect of the toughness is significantly improved. Accordingly, the specimens having DBTT of 30° C. or less are judged as “good” (passing for toughness improvement), and the other specimens are judged as “poor” (not passing for the toughness improvement).
• Nos. 6 to 10 as Comparative Examples correspond to ordinary hot rolled annealed steel sheets.
• the value [A]-[B] in Table 2 is a negative value and does not satisfy the expression (1).
• the structure state satisfying the expression (1) is obtained by performing the appropriate heat treatment. It is understood that these steel sheets are significantly improved in toughness as compared to Comparative Examples.

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• Chemical & Material Sciences (AREA)
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• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
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• Treatment Of Steel In Its Molten State (AREA)

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• 2017
  • 2017-02-07 CN CN201780018427.6A patent/CN109072372B/zh active Active
  • 2017-02-07 KR KR1020187030797A patent/KR102685247B1/ko active IP Right Grant
  • 2017-02-07 WO PCT/JP2017/004348 patent/WO2017163636A1/ja active Application Filing
  • 2017-02-07 RU RU2018132200A patent/RU2728362C2/ru active
  • 2017-02-07 MY MYPI2018703422A patent/MY186193A/en unknown
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  • 2017-02-07 EP EP17769683.8A patent/EP3434800A4/en active Pending
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