Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/02—Hardening by precipitation
• • 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
  • C21D8/0205—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
  • 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
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
• • 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
  • C22C38/005—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
  • 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
• • 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
  • C22C38/46—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
• • 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
• • 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
• • 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 excellent in punching workability suitable for application to a flange or the like and a method for producing the same.
• an exhaust gas recirculation (EGR) system in which exhaust gas generated from an automobile engine is used again as intake air for the engine is being 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
• each exhaust system component is fastened via a flange in order to prevent gas leakage.
• the flange applied to such an exhaust system part needs to have sufficient rigidity. For this reason, a thick flange (for example, a plate thickness of 5 mm or more) is applied to such an exhaust system component.
• Patent Document 1 in mass%, C: 0.030% or less, Si: 2.00% or less, Mn: 2.00% or less, P: 0.050%
• a composition comprising S: 0.040% or less, Cr: 10.0 to 25.00%, N: 0.030% or less, Nb: 0.01 to 0.80%, the balance Fe and inevitable impurities.
• An Nb-containing ferritic stainless steel hot rolled coil having a thickness of 5.0 to 10.0 mm having a hardness of 190 HV or less and a Charpy impact value at 25 ° C. adjusted to 20 J / cm 2 or more is disclosed. .
• the present invention provides a ferritic stainless hot-rolled steel sheet and a method for producing the same that solve such problems, have sufficient corrosion resistance, and can suppress cracking when punching a thick flange with a crank press. For the purpose.
• the present inventors have performed a punching process to a thick flange without causing cracks by a processing method having a relatively high processing speed such as a crank press.
• the threshold stress intensity factor K IC of the steel sheet should be increased.
• the critical stress intensity factor K IC to 25 MPa ⁇ m 1/2 or more, even when a processing method with a high processing speed such as a crank press is performed, punching when punching into a thick flange is performed. It has been found that cracking at the end face can be effectively suppressed, and that it can be sufficiently put into practical use for a thick flange.
• the inventors of the present invention have made a detailed study in order to solve the problem.
• the workability is conventionally the Charpy impact value which have been used can not be accurately evaluated, but found to be able to accurately evaluate in critical stress intensity factor (Threshold stress Intensity factor)
• K IC is a toughness evaluation index plank fields. This is because with thin steel plates with a thickness of less than 5.0 mm, the plastic deformation region near the punched end surface during processing is larger than the plate thickness, so the fracture phenomenon associated with forming is uniquely handled by fracture mechanics.
• the plastic deformation region near the punched end surface during processing sufficiently satisfies the small-scale yield state where the thickness is sufficiently small relative to the plate thickness. Therefore, it can be considered that the fracture phenomenon associated with the predetermined processing can be handled by the stress intensity factor, which is a quantitative index of fracture mechanics, and particularly the critical value, that is, the critical stress intensity factor K IC can be accurately evaluated. .
• the present inventors have investigated in detail the relationship between the presence or absence of cracks and the critical stress intensity factor K IC when punching into a flange of a predetermined shape by a crank press.
• the critical stress intensity factor K IC 25 MPa ⁇ m 1/2 or more, it is possible to effectively suppress the occurrence of cracks at the punched end face when punching into a thick flange with a crank press. It has been found that it can be practically used for thick flanges.
• component composition in mass%, Ti: 0.01 to 0.30%, V: 0.01 to 0.20%, Zr: 0.01 to 0.20%, REM: 0.00.
• the ferritic stainless hot-rolled steel sheet according to any one of the above [1] to [3] containing [5] The method for producing a ferritic stainless steel hot-rolled steel sheet according to any one of [1] to [4] above, wherein the final three passes of finish rolling are performed in a hot rolling step in which finish rolling is performed for three or more passes. In a temperature range of 800 to 1100 ° C. and a cumulative rolling reduction ratio of the final three passes of 25% or more.
• the critical stress intensity factor K IC was obtained by taking a CT test piece compliant with ASTM E399 from the center of the plate width so that the fatigue precrack is in the direction perpendicular to the rolling direction and the stress axis is in the rolling parallel direction, and ASTM E399. It refers to the stress intensity factor obtained by testing according to the above.
• a ferritic stainless hot rolled steel sheet having sufficient corrosion resistance and excellent toughness capable of suppressing cracking when punching a thick flange with a clamp press can be obtained.
• sufficient corrosion resistance in the present invention refers to a salt spray cycle test ((salt spray (5 mass%) specified in JIS H8502) on a steel plate whose end face is sealed after polishing the surface to be evaluated with # 600 emery paper. (NaCl, 35 ° C., spraying 2 hr) ⁇ drying (60 ° C., 4 hr, relative humidity 40%) ⁇ wetting (50 ° C., 2 hr, relative humidity ⁇ 95%)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))
• the critical stress intensity factor K IC obtained by sampling in a direction perpendicular to the direction of stress and parallel to the rolling direction and testing in accordance with ASTM E399 is 25 MPa ⁇ m 1/2 or more.
• the ferritic stainless steel hot-rolled steel sheet of the present invention is, in mass%, C: 0.001 to 0.020%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.00%, P: 0.04% or less, S: 0.01% or less, Al: 0.001 to 0.50%, N: 0.001 to 0.020%, Cr: 11.0 to 24.0%, Ni: 0 .01 to 2.00%, Nb: 0.12 to 0.80%, the balance being a component composition of Fe and inevitable impurities, and a critical stress intensity factor K IC of 25 MPa ⁇ m 1/2 That's it.
• the ferritic stainless steel hot-rolled steel sheet of the present invention is, in mass%, C: 0.001 to 0.020%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.00. %, P: 0.04% or less, S: 0.01% or less, Al: 0.001 to 0.50%, N: 0.001 to 0.020%, Cr: 13.0 to 24.0% , Ni: 0.01-0.60%, Nb: 0.12-0.80%, with the balance being a component composition consisting of Fe and inevitable impurities, with a critical stress intensity factor K IC of 25 MPa ⁇ m 1/2 or more.
• the critical stress intensity factor K IC was obtained by collecting CT specimens in accordance with ASTM E399 from the center of the plate width so that the fatigue precrack is in the direction perpendicular to the rolling and the stress axis is in the direction parallel to the rolling, and in accordance with ASTM E399. Refers to the stress intensity factor obtained by testing.
• the present inventors have described in detail the cause of cracks generated by punching with a crank press into a flange having a hole with a diameter of 30 mm using various ferritic stainless steel hot-rolled steel sheets with a thickness of 5.0 mm. It was examined. As a result, in the above-mentioned steel plate where cracking occurred, in the vicinity of the central portion of the thickness of the punched end surface portion, a microcrack occurred in a direction perpendicular to the punching direction, and it was confirmed that cracking occurred due to its progress. I found it.
• the present inventors examined in detail the relationship between the occurrence and propagation of this microcrack and the material properties. As a result, it has been found that the growth of microcracks tends to occur as the critical stress intensity factor of the steel sheet decreases. Therefore, as a result of attempting to punch the flange using various ferritic stainless steel hot-rolled steel plates (plate thickness 5.0 mm), the critical stress intensity factor obtained by a predetermined measurement method is 25 MPa ⁇ m 1/2. It was found that no cracking occurred in the steel plate as described above, and it was likely to occur in a steel plate having a pressure lower than 25 MPa ⁇ m 1/2 .
• the present inventors conducted a detailed investigation of steel components and hot rolling conditions in order to examine a technique for improving the limit stress intensity factor in a ferritic stainless hot rolled steel sheet.
• the ferritic stainless steel having an appropriate component the final three passes in the hot rolling process in which finish rolling consisting of multiple passes is performed in the temperature range of 800 to 1100 ° C., and the cumulative reduction ratio of the final three passes.
• the thickness of the ferritic stainless hot rolled steel sheet of the present invention is not particularly limited, but is preferably 5.0 mm or more because it is desirable that the thickness be applicable to a thick flange.
• board thickness is although it does not specifically limit, 15.0 mm or less is preferable and 10.0 mm or less is more preferable.
• the present inventors diligently studied the method of effectively and sufficiently imparting the rolling strain to the plate thickness center portion of the steel sheet in the hot rolling process from both the steel component and hot rolling methods.
• the final three passes of finish hot rolling are controlled within an appropriate temperature range, and rolling is performed with a large cumulative reduction ratio, so that the rolling strain reaches the center of the plate thickness. It was found that it was given sufficiently and effectively.
• the final three passes of finish hot rolling are controlled within an appropriate temperature range, and rolling is performed at a large cumulative reduction ratio, thereby recovering rolling strain. It was found that the rolling strain was sufficiently and effectively applied to the center part of the sheet thickness while suppressing, and a predetermined critical stress intensity factor K IC was obtained.
• % indicating the component composition means mass%.
• the C content is in the range of 0.001 to 0.020%.
• the C content is preferably 0.003% or more, and more preferably 0.004% or more. Further, the C content is preferably 0.015% or less, and more preferably 0.012% or less.
• Si 0.05 to 1.00%
• Si has an effect of concentrating on an oxide film formed at the time of welding to improve the corrosion resistance of the welded portion, and is also an element useful as a deoxidizing element in the steel making process. These effects are obtained by containing 0.05% or more of Si, and the effect increases as the content increases.
• Si is contained in excess of 1.00%, the rolling load increases in the hot rolling process and a significant scale is generated.
• the pickling property decreases due to the formation of the Si concentrated layer on the steel sheet surface layer.
• the Si content is set to 0.05 to 1.00%.
• the Si content is preferably 0.10% or more.
• Si content becomes like this. Preferably it is 0.60% or less, More preferably, it is 0.40% or less.
• Mn 0.05 to 1.00% Mn has the effect of increasing the strength of the steel and also acts as a deoxidizer. In order to obtain the effect, it is necessary to contain 0.05% or more of Mn. However, if the Mn content exceeds 1.00%, precipitation of MnS, which is a starting point of corrosion, is promoted, and the corrosion resistance is lowered. Therefore, the Mn content is set to 0.05 to 1.00%.
• the Mn content is preferably 0.10% or more. Further, the Mn content is preferably 0.50% or less, and more preferably 0.30% or less.
• P 0.04% or less
• P is an element inevitably contained in steel. However, it is preferably reduced as much as possible because it is an element harmful to corrosion resistance and workability. In particular, when the P content exceeds 0.04%, workability is remarkably lowered due to solid solution strengthening. Therefore, the P content is 0.04% or less. Preferably, the P content is 0.03% or less.
• S 0.01% or less S is an element inevitably contained in steel like P. However, it is preferably reduced as much as possible because it is an element harmful to corrosion resistance and workability. In particular, when the S content exceeds 0.01%, the corrosion resistance significantly decreases. Therefore, the S content is 0.01% or less. Preferably, the S content is 0.008% or less. More preferably, the S content is 0.003% or less.
• Al 0.001 to 0.50%
• Al is an effective deoxidizer. Furthermore, since Al has a stronger affinity for N than Cr, when N penetrates into the welded portion, N is precipitated as Al nitride instead of Cr nitride, and has the effect of suppressing sensitization. These effects can be obtained by containing 0.001% or more of Al. However, it is not preferable to contain Al exceeding 0.50% because the penetration property during welding is lowered and the welding workability is lowered. Therefore, the Al content is in the range of 0.001 to 0.50%. The Al content is preferably 0.20% or less, and more preferably 0.10% or less.
• N 0.001 to 0.020%
• the workability and the corrosion resistance of the welded portion are significantly reduced. From the viewpoint of corrosion resistance, the lower the N content, the better.
• reducing the N content to less than 0.001% requires refining for a long time, which is not preferable because it causes an increase in manufacturing cost and a decrease in productivity. . Therefore, the N content is in the range of 0.001 to 0.020%.
• the N content is preferably 0.003% or more, and more preferably 0.005% or more.
• N content becomes like this. Preferably it is 0.015% or less, More preferably, it is 0.012% or less.
• Cr 11.0 to 24.0% Cr is the most important element for ensuring the corrosion resistance of stainless steel. If the content is less than 11.0%, sufficient corrosion resistance cannot be obtained in an automobile exhaust gas atmosphere. On the other hand, when Cr is contained exceeding 24.0%, the toughness is remarkably reduced due to the formation of the ⁇ (sigma) phase, and in the present invention, a predetermined critical stress intensity factor cannot be obtained. Therefore, the Cr content is in the range of 11.0 to 24.0%.
• the Cr content is preferably 13.0% or more, more preferably 14.0% or more, still more preferably 16.0% or more, and even more preferably 17.0% or more.
• Cr content becomes like this. Preferably it is 21.5% or less, More preferably, it is 20.0% or less, More preferably, it is 18.5% or less.
• Ni 0.01-2.00%
• Ni is an element that improves the corrosion resistance of stainless steel, and is an element that suppresses the progress of corrosion in a corrosive environment where a passive film is not formed and active dissolution occurs.
• Ni is a strong austenite generating element, and has the effect of suppressing ferrite formation at the weld and suppressing sensitization due to precipitation of Cr carbonitride. This effect is obtained by containing 0.01% or more of Ni, and increases as the Ni content increases. However, when the Ni content exceeds 2.00%, workability is lowered and stress corrosion cracking is likely to occur. Furthermore, since Ni is an expensive element, an increase in the content of Ni causes an increase in manufacturing cost, which is not preferable. Therefore, the Ni content is set to 0.01 to 2.00%.
• the Ni content is preferably 0.05% or more, more preferably 0.10% or more. Further, the Ni content is preferably 1.00% or less, more preferably 0.60% or less, further preferably 0.50% or less, and even more preferably 0.45% or less. .
• Nb 0.12 to 0.80% Nb combines with C or N in the hot rolling process and precipitates as Nb carbonitride.
• the precipitated Nb carbonitride has the effect of pinning dislocation movement and suppressing the rolling strain imparted by hot rolling from being eliminated by recovery. Thereby, the recovery
• the above effect is obtained when 0.12% or more of Nb is contained.
• the Nb content exceeds 0.80% the toughness may be lowered due to the generation of the Laves phase, and the rolling load in the hot rolling is significantly increased. Therefore, the hot rolling method provided by the present invention It becomes difficult to apply. Therefore, the Nb content is in the range of 0.12 to 0.80%.
• the Nb content is preferably 0.15% or more, more preferably 0.20% or more. Moreover, Nb content becomes like this. Preferably it is 0.75% or less, More preferably, it is 0.60% or less.
• the present invention is a ferritic stainless steel characterized in that it contains the above-mentioned essential components and the balance consists of Fe and inevitable impurities. Furthermore, as required, one or more selected from Cu, Mo, W and Co, or / or one selected from Ti, V, Zr, REM, B, Mg and Ca. Or 2 or more types can be contained in the following range.
• Cu 0.01 to 1.50%
• Cu is an element particularly effective for improving the corrosion resistance of the base material and the welded part when an aqueous solution or weakly acidic water droplets adhere. This effect is obtained when the content is 0.01% or more, and the effect increases as the Cu content increases. However, when Cu is contained exceeding 1.50%, hot workability may be reduced and surface defects may be induced. In addition, descaling after annealing may be difficult. Therefore, when Cu is contained, the Cu content is preferably in the range of 0.01 to 1.50%.
• the Cu content is more preferably 0.10% or more, and further preferably 0.30% or more. Further, the Cu content is more preferably 0.60% or less, and further preferably 0.45% or less.
• Mo 0.01-2.00%
• Mo is an element that remarkably improves the corrosion resistance of stainless steel. This effect is obtained when the content is 0.01% or more, and the effect improves as the content increases. However, if the Mo content exceeds 2.00%, the rolling load at the time of hot rolling increases, and the manufacturability may decrease, or the steel sheet strength may increase excessively. Moreover, since Mo is an expensive element, a large content increases the manufacturing cost. Therefore, when Mo is contained, the Mo content is preferably 0.01 to 2.00%. The Mo content is more preferably 0.10% or more. Further, the Mo content is more preferably 1.40% or less. However, in the Ti-containing steel, Mo also has an effect of reducing toughness.
• the Mo content is preferably 0.30 to 1.40% or less.
• the Mo content is more preferably 0.40% or more.
• the Mo content is more preferably 0.90% or less.
• W 0.01-0.20% W, like Mo, has the effect of improving corrosion resistance. This effect is obtained by containing 0.01% or more of W. However, if it exceeds 0.20% and W is contained, the strength increases, and the productivity may decrease due to an increase in rolling load. Therefore, when W is contained, the W content is preferably in the range of 0.01 to 0.20%. The W content is more preferably 0.05% or more. Further, the W content is more preferably 0.15% or less.
• Co 0.01-0.20%
• Co is an element that improves toughness. This effect is obtained by containing 0.01% or more of Co. On the other hand, if the Co content exceeds 0.20%, workability may be reduced. Therefore, when Co is contained, the Co content is preferably in the range of 0.01 to 0.20%.
• Ti 0.01 to 0.30%
• Ti is an element having a higher affinity for C and N than Cr, and is precipitated as a carbide or nitride, and has an effect of suppressing sensitization due to the precipitation of Cr carbonitride. In order to obtain this effect, it is necessary to contain 0.01% or more of Ti. However, if the Ti content exceeds 0.30%, it may be impossible to obtain good surface properties due to excessive precipitation of TiN. Therefore, when Ti is contained, the Ti content is preferably in the range of 0.01 to 0.30%. The Ti content is more preferably 0.03% or more, and still more preferably 0.10% or more. Further, the Ti content is more preferably 0.20% or less, and still more preferably 0.15% or less.
• V 0.01-0.20%
• V forms carbonitride with C and N, suppresses sensitization during welding and improves the corrosion resistance of the weld. This effect is obtained when the V content is 0.01% or more.
• the V content is preferably 0.01 to 0.20%.
• the V content is more preferably 0.05% or more. Further, the V content is more preferably 0.15% or less.
• Zr 0.01-0.20%
• Zr has an effect of suppressing sensitization by combining with C and N. This effect is obtained by containing 0.01% or more of Zr.
• the Zr content exceeds 0.20%, the workability may be significantly reduced. Therefore, when Zr is contained, the Zr content is preferably in the range of 0.01 to 0.20%. The Zr content is more preferably 0.10% or less.
• REM 0.001 to 0.100% REM (Rare Earth Metals) has an effect of improving the oxidation resistance, and suppresses formation of a Cr-deficient region immediately below the oxide film by suppressing formation of an oxide film (weld temper color) in the welded portion. This effect is acquired by containing REM 0.001% or more.
• productivity such as pickling at the time of cold rolling annealing, may be reduced. Therefore, when REM is contained, the REM content is preferably in the range of 0.001 to 0.100%.
• the REM content is more preferably 0.050% or less.
• B 0.0002 to 0.0025%
• B is an element effective for improving secondary work embrittlement resistance after deep drawing. This effect is obtained by making the B content 0.0002% or more. On the other hand, if the B content exceeds 0.0025%, workability and toughness may be reduced. Therefore, when B is contained, the B content is preferably in the range of 0.0002 to 0.0025%. The B content is more preferably 0.0003% or more. Further, the B content is more preferably 0.0006% or less.
• Mg 0.0005 to 0.0030%
• Mg is an element that improves the equiaxed crystal ratio of the slab and is effective in improving workability and toughness. This effect is obtained by containing 0.0005% or more of Mg.
• the Mg content is preferably in the range of 0.0005 to 0.0030%.
• the Mg content is more preferably 0.0010% or more.
• the Mg content is more preferably 0.0020% or less.
• Ca 0.0005 to 0.0030%
• Ca has an effect of refining inclusions generated during smelting and continuous casting, and is an effective component for preventing nozzle clogging in continuous casting.
• the effect is acquired by containing 0.0005% or more of Ca.
• the Ca content exceeds 0.0030%, the corrosion resistance may decrease due to the formation of CaS. Therefore, when Ca is contained, the Ca content is preferably in the range of 0.0005 to 0.0030%.
• the Ca content is more preferably 0.0015% or less, and further preferably 0.0010% or less.
• the ferritic stainless steel hot rolled steel sheet according to the present invention has a limit stress intensity factor K IC of 25 MPa ⁇ m 1/2 or more.
• the crack at the time of performing a punching process with a clamp press can be suppressed.
• the critical stress intensity factor K IC is preferably 30 MPa ⁇ m 1/2 or more, more preferably 35 MPa ⁇ m 1/2 or more, and further preferably 40 MPa ⁇ m 1/2 or more.
• the thick flange is not particularly limited, and examples thereof include a flange having a plate thickness of 5.0 mm or more. As the flange, for example, a flange having a plate thickness of 5.0 to 15.0 mm is preferable, and a flange having a plate thickness of 5.0 to 10.0 mm is more preferable.
• the temperature is the surface temperature of a steel slab, hot-rolled steel sheet, or the like measured with a surface thermometer or the like.
• the ferritic stainless steel hot-rolled steel sheet of the present invention uses a steel slab having the above component composition, and in hot rolling comprising rough rolling and finishing rolling of 3 or more passes, the final 3 passes of finishing rolling are performed in a temperature range of 800 to It can be obtained by setting the final three passes to a cumulative rolling reduction of 25% or more at 1100 ° C.
• 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.
• hot rolling there is no particular limitation for rough rolling.
• the cast structure is effectively destroyed before finish hot rolling, it is superior to refinement of crystal grains in subsequent finish hot rolling.
• the cumulative rolling reduction in rough rolling is 65% or more because it can be expected to further improve toughness due to refinement of the metal structure after hot rolling.
• the sheet is rolled to a predetermined plate thickness by finish hot rolling, but the final three passes of finish rolling are performed in a temperature range of 800 to 1100 ° C., and the cumulative reduction ratio is 25% or more.
• Rolling temperature range for the final three passes of finish hot rolling 800-1100 ° C Cumulative rolling reduction in the final three passes of finish hot rolling: 25% or more
• the temperature and cumulative rolling reduction in the final three passes of finishing hot rolling are appropriate. It is necessary to effectively impart rolling strain to the central portion of the plate thickness while suppressing excessive recovery during rolling.
• the cumulative reduction ratio in the final three passes of finish hot rolling is set to 25% or more.
• 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. However, if the cumulative rolling reduction is excessively increased, the rolling load may increase and the productivity may be lowered.
• the rolling temperature of the final three passes of finish hot rolling is less than 800 ° C.
• the rolling load increases remarkably as the steel plate temperature decreases, which is not preferable for production.
• the rolling temperature of the final three passes exceeds 1100 ° C.
• the rolling strain imparted by rolling is eliminated by excessive recovery, and a predetermined limit stress intensity factor cannot be obtained. Therefore, the rolling temperature for the final three passes is in the range of 800 to 1100 ° C.
• the rolling temperature in the final three passes is in the range of 800 to 1050 ° C. More preferably, the rolling temperature in the final three passes is in the range of 850 to 1000 ° C.
• the rolling temperature range of the first pass among the final three passes is 950 to 1100 ° C., and this first pass
• the rolling temperature range for the second pass to be performed next is preferably 925 to 1075 ° C.
• the rolling temperature range for the third pass to be performed next to the second pass is preferably 875 to 1050 ° C.
• the method for producing a ferritic stainless hot rolled steel sheet according to the present invention is characterized in that a large reduction is applied after controlling the temperature range in the final three passes of finishing hot rolling consisting of three or more passes. If rolling with a large reduction is performed over the final four passes or more, even if the cumulative reduction rate is the same, the reduction rate will be distributed to each pass, so the strain applied to the center of the plate thickness will be insufficient, and each pass Since the accumulated conveyance time increases, recovery during conveyance between the passes is facilitated, the effect of applying strain is reduced, and it becomes difficult to obtain a predetermined limit stress intensity factor.
• the rolling temperature and cumulative rolling reduction of the finish rolling are controlled.
• the manufacturing method of the ferritic stainless steel hot-rolled steel sheet of the present invention it is important to control the rolling temperature and cumulative rolling reduction of the final three passes of finish hot rolling, and if it is finish rolling of 3 passes or more Any number of finishing rolls may be performed, but if the maximum number of passes is more than 15 passes, the steel plate temperature is likely to decrease due to an increase in the number of contacts with the rolling roll, and the steel plate temperature is kept within a predetermined temperature range.
• the maximum number of passes is preferably 15 passes or less because it may lead to a decrease in manufacturability or an increase in manufacturing costs, such as heating from the outside required for maintenance. More preferably, the maximum number of paths is 10 paths or less.
• the steel sheet After finishing hot 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 when the coiling temperature is more than 450 ° C. to less than 500 ° C., embrittlement due to 475 ° C. embrittlement may occur. Therefore, the winding temperature is preferably 450 ° C. or lower or 500 ° C. or higher. It is more preferable to perform accelerated cooling such as brackish water cooling after the final rolling and then perform a winding process at 450 ° C. or lower because it is possible to further suppress the elimination of rolling distortion due to recovery after winding.
• the hot-rolled steel sheet obtained in the present invention may be hot-rolled steel sheet by performing hot-rolled sheet annealing. Since the hot-rolled steel sheet provided by the present invention is excellent in toughness, conventionally, it is possible to perform hot-rolled sheet annealing in a continuous annealing line that is avoided due to fear of fracture due to low toughness. Moreover, the obtained hot-rolled annealed steel sheet may be subjected to cold rolling and cold-rolled sheet annealing thereafter.
• 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 hour, 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 3 passes (5th pass) of the final rolling consisting of 7 passes. , 6th pass, 7th pass) were performed under the conditions shown in Table 2 to obtain hot-rolled steel sheets.
• Photograph the evaluation surface of the test piece after 5 cycles of the salt spray cycle test measure the surface area of the evaluation surface of the test piece by image analysis, and determine the rate of occurrence from the ratio to the total area of the test piece ((test (Spring area in the piece / total area of the test piece) ⁇ 100 [%]) was calculated.
• a cracking rate of 10% or less was passed with excellent corrosion resistance ( ⁇ ), 10% to 25% or less was accepted ( ⁇ ), and 25% or more was rejected (x).
• the ferritic stainless steel hot-rolled steel sheet obtained by the present invention is particularly excellent in punching workability by a crank press, and is manufactured by punching using a crank press or other methods, and requires high workability and corrosion resistance. It is particularly suitable for application to thick flanges.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Heat Treatment Of Steel (AREA)

Priority Applications (6)

Applications Claiming Priority (2)

Publications (1)

Family

ID=62979289

Family Applications (1)

Country Status (7)

Cited By (2)

Families Citing this family (8)

Citations (4)

Family Cites Families (9)

• 2018
  • 2018-01-12 US US16/480,785 patent/US20200002779A1/en not_active Abandoned
  • 2018-01-12 WO PCT/JP2018/000559 patent/WO2018139207A1/ja unknown
  • 2018-01-12 JP JP2018521321A patent/JP6384640B1/ja active Active
  • 2018-01-12 CN CN201880008313.8A patent/CN110225988B/zh active Active
  • 2018-01-12 MX MX2019008874A patent/MX2019008874A/es unknown
  • 2018-01-12 EP EP18745041.6A patent/EP3556880A4/en active Pending
  • 2018-01-12 KR KR1020197021747A patent/KR102274976B1/ko active IP Right Grant

Patent Citations (4)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events