US20120009433A1 - Duplex stainless steel sheet with excellent press-formability - Google Patents

Duplex stainless steel sheet with excellent press-formability Download PDF

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US20120009433A1
US20120009433A1 US13/256,977 US201013256977A US2012009433A1 US 20120009433 A1 US20120009433 A1 US 20120009433A1 US 201013256977 A US201013256977 A US 201013256977A US 2012009433 A1 US2012009433 A1 US 2012009433A1
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stainless steel
formability
phases
steel sheet
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Masaharu Hatano
Akihiko Takahashi
Eiichiro Ishimaru
Ken Kimura
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Nippon Steel Stainless Steel Corp
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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
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • 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
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold 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
    • 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
    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • 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
    • C22C38/40—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
    • C22C38/60—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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • 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
    • 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
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12229—Intermediate article [e.g., blank, etc.]

Definitions

  • the present invention relates to duplex stainless steel sheet with excellent press-formability such as stretchability.
  • Austenitic stainless steel such as SUS304 is excellent in balance of corrosion resistance and workability, so is being used for a broad range of applications such as for kitchen appliances, household electric appliances, and electronic equipment.
  • austenitic stainless steel is much higher in elongation at break compared with ferritic stainless steel or duplex stainless steel, is excellent in stretchability, and is often preferred for press-formability of steel sheet.
  • austenitic stainless steel contains large amounts of the rare and expensive Ni, so has problems in general applicability and economy in the future.
  • duplex stainless steel which conserves on the amount of Ni has been known.
  • PLTs 1 to 3 disclose high strength duplex stainless steels for automotive use which contain Ni: 1 to 7%, Si: over 1 to 5%, N: 0.04 to 2%, and Cr: 17 to 22% and which have Mn, Cu, etc. added to adjust the Ni balance value and raise the Young's modulus.
  • These duplex stainless steels are characterized by high Si and low Ni and are provided with a high strength of a 0.2% proof stress of over 500 MPa and a high elongation.
  • PLT 4 and PLT 5 disclose austenitic-ferritic stainless steels with excellent formability which restrict the amount of Ni to 3% or less and adjust the C+N and ingredient balance in the austenite phases to obtain a high ductility.
  • PLT 6 discloses austenitic-ferritic stainless steel with excellent stretchability and crevice corrosion resistance which restricts the amount of Ni to 1% or less and the amount of Mn to 2% or less and adds an amount of N in 0.05 to 0.6% in range.
  • the amount of Ni is reduced by adding an amount of N in at least 0.08% or more.
  • PLT 7 has disclosed ferritic-austenitic stainless steels with excellent corrosion resistance and workability which make the upper limit of the amount of N 0.15% and thereby lower the amount of Ni.
  • These stainless steels set Cr+3Mo+10N ⁇ Mn ⁇ 18% from the viewpoint of the corrosion resistance and define the size, aspect ratio, and intergranular distance of austenite grains from the viewpoint of the workability.
  • the steels disclosed in the above publication have less than 50% of austenite phases and are mainly comprised of ferrite phases.
  • the steels disclosed in the above PLTs use quite a bit of N to conserve Ni and raise the strength. Much research is being performed on the effects of N on the mechanical properties of stainless steel and other ferrous metal materials. Addition of N has a large effect on the rise of the 0.2% proof stress. For example, in NPLT 1, if adding over 0.1% of N to the Fe—Cr—Ni—Mn alloy, at ordinary temperature, the 0.2% proof stress greatly exceeds 400 MPa. In actuality, the steels disclosed in PLTs 1 to 3 have 0.2% proof stresses of over 500 MPa. PLTs 4 to 7 do not describe a 0.2% proof stress, but from NPLT 1, it is easy to deduce that the value is over 400 MPa.
  • PLT 1 Japanese Patent Publication (A) No. 62-47461
  • PLT 2 Japanese Patent Publication (A) No. 62-47462
  • PLT 3 Japanese Patent Publication (A) No. 62-47463
  • PLT 4 Japanese Patent Publication (A) No. 2006-169622
  • PLT 5 Japanese Patent Publication (A) No. 2006-183129
  • PLT 6 Japanese Patent Publication (A) No. 2006-200035
  • NPLT 1 190th Nishiyama Commemorative Technical Course, November 2006, the Iron and Steel Institute of Japan, p. 60
  • the present invention has as its object to provide duplex stainless steel sheet with excellent press-formability provided with a 0.2% proof stress and Erichsen value equivalent to those of SUS304 and other austenitic stainless steel by controlling the steel ingredients, the Ni balance, and the austenite phase rate.
  • the gist of the present invention is as follows:
  • a duplex stainless steel sheet with excellent press-formability characterized by containing, by mass %
  • Ni-bal. 30(C+N)+Ni+0.5Mn+0.3Cu ⁇ 1.1(Cr+1.5Si)+8.2 formula ⁇ 1>
  • a duplex stainless steel sheet with excellent press-formability as set forth in (3) characterized in that a 0.2% proof stress in a tensile test is less than 400 MPa and an elongation at break is 35% or more.
  • a duplex stainless steel sheet with excellent press-formability as set forth in (5) characterized in that a formed height found by an Erichsen test (Erichsen value) is 11 mm or more.
  • the present invention it is possible to provide a duplex stainless steel sheet with excellent press-formability which defines the ingredients of the steel, Ni balance, and austenite phase rate to obtain a 0.2% proof stress and Erichsen value equal to that of SUS304 or another austenitic stainless steel.
  • the remarkable effect is exhibited that the duplex stainless steel sheet of the present invention can be pressed-formed no different from SUS304 or other austenitic stainless steel sheet and Ni can be conserved.
  • FIG. 1 is a view showing the relationship between the Erichsen value and ingredients.
  • FIG. 2 is a view showing the relationship between the Erichsen value and Ni balance.
  • Table 1 shows representative ingredients of the test steel.
  • Duplex stainless steels of these ingredients were vacuum melted and used to produce 5 mm thick hot rolled sheets.
  • the hot rolled sheets were annealed at 1050° C. and then pickled to produce 0.6 mm thick cold rolled sheets.
  • the cold rolled sheets were annealed at 1050° C.
  • the cold rolled annealed sheets were measured for austenite ( ⁇ ) phase rate and were used for a JIS No. 13B tensile test and Erichsen test.
  • the ⁇ -phase rate was found by measurement of a phase map identifying the fcc and bcc crystal structures by the EBSP method at the sheet cross-sections.
  • the JIS No. 13B tensile test obtains a tensile test piece from the rolling direction, sets the tensile speed at 10 mm/min (range prescribed in JIS Z 2241), and measures the 0.2% proof stress (0.2% PS), tensile strength (TS), and elongation at break (EL).
  • the Erichsen test obtains a 90 mm square test piece, performs the Method B based on JIS Z 2247 (wrinkle pressure of 1 ton), and measures the deformed height when a crack runs through the sheet thickness (Erichsen value).
  • Table 2 shows the mechanical properties, Erichsen value (Er), and ⁇ -phase rate ( ⁇ ) obtained from sheets of typical test sheet ingredients compared with ferrite ( ⁇ ) and ⁇ single phase SUS430LX and SUS304 steels.
  • Er Erichsen value
  • ⁇ ⁇ -phase rate
  • N concentrates at the ⁇ -phases and raises the strength and work hardening. Therefore, if adding N, it can be easily predicted that the difference in strength between the ⁇ -phases and the ⁇ -phases would increase along with the working degree. The results of observation of [b] are believed to be due to the difference in strength between the ⁇ -phases and the ⁇ -phases.
  • the ingredients of the steel A feature low addition of N and Si.
  • N the strength and work hardening of the ⁇ -phases fall.
  • Si selectively forms a solid solution in the ⁇ -phases and raises the strength and work hardening of the ⁇ -phases. In this way, it is believed that by reducing the difference in strength of the ⁇ -phases and ⁇ -phases and making the high deformation ability ⁇ -phases the main phases, a good Erichsen value is obtained.
  • FIG. 1 shows the results.
  • an Erichsen value of 11 mm or more is indicated by “ ⁇ ” while a value of less than 11 mm is indicated by “ ⁇ ”.
  • An Erichsen value of 11 mm is difficult to reach with ⁇ -based stainless steel and was made a threshold value close to ⁇ -based stainless steel.
  • FIG. 1 it was learned that a high Erichsen value of 11 mm or more is obtained when the N is made 0.07% or less and adding Si in 0.5 to 3% in range.
  • FIG. 2 shows the Erichsen values of the ⁇ -based stainless steel by the same parameter.
  • ⁇ -based stainless steel there is a range of ingredients giving a good Erichsen value. The reason is the rise in the elongation due to work induced martensite transformation of the ⁇ -phases (transformation induced plasticity: TRIP).
  • the inventors discovered a balance of ingredients in which both the elongation and the Erichsen value effectively rise due to the TRIP phenomenon similar to that of ⁇ -based stainless steel in the range of ingredients described in [e] and [f] (range of Ni-bal). That is, the inventors obtained the new discovery that a high Erichsen value is obtained in an Ni-bal of ⁇ 7.5 to ⁇ 3.5 in range, more preferably ⁇ 6 to ⁇ 4 in range.
  • C raises the ⁇ -phase rate and concentrates in the ⁇ -phases to raise the stability of the ⁇ -phases. Therefore, it effectively acts to adjust the Ni-bal to express the press-formability targeted by the present invention.
  • 0.001% or more is preferably contained. However, if over 0.05%, the strength of the ⁇ -phases rises and facilitates increased sensitization due to grain boundary precipitation of the carbides leading to a drop in corrosion resistance. For this reason, the upper limit is made 0.05%, preferably 0.03% or less.
  • Si selectively forms a solid solution at the ⁇ -phases, raises the strength and work hardening of the ⁇ -phases, and reduces the difference in strengths of the ⁇ -phases and the ⁇ -phases to express the press-formability targeted by the present invention. It is an essentially added element for this. Further, it has the action of raising the stability of the ⁇ -phases and suppressing the martensite transformation in the cooling process after annealing. If undergoing martensite transformation, the ⁇ -phases become hard phases and the workability is remarkably impaired. To obtain the effect on the workability targeted by the present invention, as shown also in FIG. 1 , 0.5% or more is added. However, over 3% addition invites an increase in the hardening of the ⁇ -phases and a drop in the workability. For this reason, the upper limit is made 3%. The preferable range is 1.5 to 2.5%.
  • Mn raises the ⁇ -phase rate and concentrates at the ⁇ -phases to raise the stability of the ⁇ -phases. Therefore, it effectively acts to adjust the Ni-bal to express the press-formability targeted by the present invention.
  • 1% or more is added. However, if over 5%, in addition to a drop in the corrosion resistance, the strength of the ⁇ -phases rises and a drop in the press-formability is invited. For this reason, the upper limit is made 5%. From the viewpoints of the workability and the corrosion resistance, the preferable range is 2 to 4.5%, more preferably 3 to 4%.
  • Cr is an element forming ⁇ -phases and also has the action of securing the corrosion resistance and adjusting the stability of the ⁇ -phases to express the press-formability targeted by the present invention. Further, Cr, like Si, suppresses the martensite transformation of the ⁇ -phases in the cooling process after annealing. Therefore, to secure the stability of the ⁇ -phases and the action on the corrosion resistance etc., the content is made 16% or more. However, if over 21%, making the ⁇ -phases the main phases becomes difficult. This invites a drop in the workability targeted by the present invention. For this reason, the upper limit is made 21% or less. From the viewpoints of the workability and corrosion resistance, the preferable range is 16.5 to 18.5%.
  • Ni is an effective element forming ⁇ -phases and effectively acts to adjust the Ni-bal to express the press-formability targeted by the present invention. To obtain this effect, 1% or more is added. However, if over 6%, it cannot be said that the Ni is conserved and a rise in the material costs is incurred. For this reason, the upper limit is made 6%. From the viewpoints of the workability and costs, the preferable range is 2 to 5%, more preferably 2.5 to 4.5%.
  • Cu is an effective element forming ⁇ -phases in the same way as Ni and Mn and effectively acts to adjust the Ni-bal to express the press-formability targeted by the present invention. To obtain this effect, 1% or more is added. Further, it is also an element effective for improvement of the corrosion resistance by composite addition with Ni. To obtain this effect, 0.5% or more is added. However, if over 3%, a drop in the manufacturability and a rise in the material costs are incurred. For this reason, the upper limit is made 3%. From the viewpoints of the performance and manufacturability, the preferable range is 1.5 to 2.5%.
  • N like C and Ni, is an effective element for forming ⁇ -phases. It effectively acts to adjust the Ni-bal and expresses press-formability targeted by the present invention. For this reason, 0.001% or more is preferably contained. On the other hand, it has the action of raising the strength of the ⁇ -phases and the work hardening and enlarging the difference of strength of the ⁇ -phases and ⁇ -phases. For this reason, when actively utilizing the N in this way, this leads to a drop in the press-formability targeted by the present invention. Therefore, as shown in FIG. 1 as well, the upper limit is made 0.07%. From the viewpoint of the workability targeted by the present invention, the preferable range is 0.02 to 0.06%.
  • Mo may be suitably added for improving the corrosion resistance.
  • 0.1% or more is preferably added.
  • the content is made 1% or less. From the viewpoints of the corrosion resistance and economy, the preferable range when added is respectively 0.2 to 0.8%.
  • Nb, V, and Ti improve the corrosion resistance and express effects similar to Si. That is, by solution strengthening of the ⁇ -phases, the strength difference of the ⁇ -phases and the ⁇ -phases is reduced to improve the press-formability and suppress the martensite transformation of the ⁇ -phases in the cooling process after annealing. These may be suitably added to obtain the above effects.
  • the contents are preferably respectively 0.05% or more. However, if over 0.5%, the economy is liable to be impaired. For this reason, when added, the contents are respectively made 0.5% or less. From the viewpoints of the above effects and economy, the preferable ranges when added are respectively 0.1 to 0.3%.
  • Sn, Sb, and W may be suitably added for improving the corrosion resistance.
  • the hot workability and other aspects of the manufacturability are sometimes impaired.
  • the contents are respectively made 1% or less.
  • the preferable ranges when added are respectively 0.1 to 0.6%.
  • Al is a powerful deoxidizing agent and may be suitably added. To obtain the above effect, 0.001% or more is preferably added. However, if over 0.1%, nitrides are formed and surface flaws or a drop in corrosion resistance is liable to be incurred. For this reason, when added, the content is made 0.1% or less. From the viewpoints of the above effects and manufacturability, the preferable range when added is 0.005 to 0.05%.
  • B, Ca, and Mg may be suitably added for improving the hot workability.
  • preferably 0.0002% or more are respectively added.
  • the corrosion resistance sometimes remarkably falls.
  • the contents are respectively made 0.01% or less.
  • the preferable ranges when added are 0.0005 to 0.01%.
  • La, Ce, Zr, Y, and other rare earth metals (REM) also have actions of improving the hot workability in the same way as B, Ca, and Mg. Therefore, they may be suitably added. To obtain these effects, 0.001% or more are preferably respectively added. However, if over 0.3%, sometimes the economy is impaired. For this reason, when added, the contents are made 0.3% or less. From the viewpoints of the above effects and economy, the preferable ranges when added are 0.002 to 0.1%.
  • P, S, and O may also be included as unavoidable impurities.
  • P, S, and O are elements harmful to the hot workability and corrosion resistance.
  • P is preferably made 0.1% or less, more preferably 0.05% or less.
  • S is preferably made 0.01% or less, more preferably 0.005% or less, still more preferably less than 0.002%.
  • O is preferably made 0.01% or less, more preferably 0.005% or less, still more preferably less than 0.002%.
  • a parameter relating to the production of the ⁇ -phases and ⁇ -phases defined by the Ni-bal of the following formula ⁇ 1> from the amounts of C, N, Ni, Mn, Cu, Cr, and Si is prescribed in range to obtain the press-formability targeted by the present invention.
  • the Erichsen value made the parameter of the press-formability reaches the target value of the Erichsen value of 11 mm of the present invention in the range of an Ni-bal of ⁇ 7.5 to ⁇ 3.5.
  • the contents of the elements are adjusted so as to give an Ni-bal of ⁇ 7.5 to ⁇ 3.5 in range.
  • the value is made ⁇ 6 to ⁇ 4 in range so that the Erichsen value becomes a maximal value.
  • Ni-bal. 30(C+N)+Ni+0.5Mn+0.3Cu ⁇ 1.1(Cr+1.5Si)+8.2 ⁇ 1>
  • the duplex stainless steel sheet of the present invention has the ingredients and Ni-bal explained in section (A) and defines the ⁇ -phase rate for improving the press-formability.
  • the ⁇ -phase rate has a general correlation with the Ni-bal. That is, the ⁇ -phase rate tends to increase along with the rise of the Ni-bal.
  • the ⁇ -production ability in the final annealing temperature region explained later does not necessarily correspond straight with the coefficients of the elements in the Ni-bal. For this reason, to obtain a press-formability targeted by the present invention, it is necessary to define both the Ni-bal and the ⁇ -phase rate.
  • the ⁇ -phase rate can be found by the EBSP method.
  • the EBSP method for example, as described in Microscope; Seiichi Suzuki, vol. 39, no. 2, 121 to 124, designates crystal data of the ⁇ -phases (fcc) and ⁇ -phases (bcc) and displays a phase distribution map color coding the individual phases. Due to this, it becomes possible to find the ⁇ -phase rate. Further, it is possible to obtain a grasp of the state of dispersion of the ⁇ -phases and the ⁇ -phases. For example, the samples are examined from the cross-sections in the sheet thickness directions under a measurement ratio of 500.
  • the lower limit of the ⁇ -phase rate is made 50% for securing the press-formability targeted by the present invention.
  • the rate is preferably 60% or more.
  • the ⁇ -phase rate exceeds 95%, large amounts of Ni, Mn, and Cu have to be added. This is a problem from the viewpoints of conserving Ni and economy. Furthermore, differentiation from ⁇ -based stainless steel is also not easy. For this reason, the upper limit is made 95%. From the viewpoint of conserving Ni and economy, the preferable range is 60 to 80%.
  • NPLT 2 reports the metal microstructure of duplex stainless steel characterized by a high Si and low Ni in relation to development of PLTs 1 to 3. These steels aim at a rise of the 0.2% proof stress to secure strength for automotive use as explained in the Background Art. In general, the 0.2% proof stress of the ⁇ -phases is smaller than that of the ⁇ -phases. For this reason, to raise the 0.2% proof stress, it is preferable to provide a duplex microstructure wherein the ⁇ -phases are the main phases.
  • the metal microstructure shown in NPLT 2 is a duplex stainless steel with an amount of Cr over 17% where the ⁇ -phases constitute the main phases (53.3 to 75.0% ⁇ ). Therefore, the metal microstructure of the present invention targeted by the press-formability of the steel sheet differs from the metal microstructure of the steel disclosed in PLTs 1 to 3.
  • the duplex stainless steel sheet of the present invention is mainly comprised of ⁇ -phases and has a balance of ⁇ -phases. If the amount of Cr or the amount of Si is low, the ⁇ -phases sometimes undergo martensite transformation in the cooling process after annealing. Martensite phases may also be unavoidably included to an extent not obstructing the press-formability targeted by the present invention.
  • the form of dispersion of the ⁇ -phases when making ⁇ the main phases is not particularly limited.
  • the ⁇ -phases are preferably finely dispersed.
  • the less than 50 ⁇ m ⁇ -phases are preferably dispersed in fibrous shapes or grain shapes in the sheet thickness direction.
  • the duplex stainless steel sheet of the present invention has the ingredients and Ni-bal explained in section (A) and defines the ⁇ -phase rate explained in section (B) so as to improve the press-formability.
  • the mechanical properties and Erichsen value of the steel sheets satisfying these provisions are preferably the following values so as to enable a press-formability no different from that of SUS304 or other austenitic stainless steel sheet.
  • the 0.2% proof stress is preferably made less than 400 MPa to make it an extent no different from SUS304 or other austenitic stainless steel.
  • 400 MPa or more if envisioning an actual press, there is a fear of insufficient power of the press or wear and damage to the die. More preferably, the value is made 350 MPa or less.
  • the lower limit is not particularly defined, but if considering amount of C+N or amount of alloy added, the more preferable range is 250 to 350 MPa.
  • the elongation at break is preferably 35% or more to obtain a high Erichsen value as explained in the explanation of the test steels A, B, and C in Table 2 and [g].
  • the value is more preferably 40% or more, still more preferably 45% or more.
  • the Erichsen value is important as a parameter of the press-formability such as the stretchability.
  • the value is preferably 11 mm or more, more preferably 12 mm or more.
  • the upper limit is not particularly provided, but making it over 15 mm is difficult under conditions prescribed in Method B of JIS Z 2241 (wrinkle pressure of 1 tons).
  • the method of production is not particularly limited.
  • the final cold rolling and final annealing conditions have an effect on the ⁇ -phase rate and the dispersed state of the microstructure.
  • the reduction rate of the cold rolling is preferably 40% or more from the viewpoint of fine dispersion of the ⁇ -phases as the second phase.
  • the final annealing is preferably heated to 950 to 1150° C. in range in order to main the ⁇ -phases the main phases. If over 1150° C., the amount of production of the ⁇ -phases increases and the microstructure is liable to coarsen. If less than 950° C., the recrystallization and softening of the ⁇ -phases are liable to become insufficient.
  • the cooling after annealing is preferably a cooling rate of air cooling or more (about 3° C./sec or more) for suppressing martensite transformation of the ⁇ -phases in the case of a small amount of Cr, amount of Si, etc.
  • Duplex stainless steels having the ingredients shown in Table 3 were smelted and hot rolled to produce 4.0 to 5.0 mm thick hot rolled sheets.
  • Steel No. 1 to Steel No. 22 have ingredients and Ni-bal's prescribed by the present invention.
  • Steel Nos. 23 and 24 have the ingredients prescribed by the present invention, but have Ni-bal's outside the present invention.
  • Steel Nos. 25 to 27 have Ni-bal's prescribed by the present invention, but have ranges of ingredients outside of the present invention.
  • These hot rolled sheets were annealed and pickled, then cold rolled to 0.7 mm thickness and final annealed at 1050° C.
  • Nos. 23 and 24 have an elongation of less than 35% or a ⁇ -phase rate of less than 50% and failed to reach Erichsen values of 11 mm or more targeted by the present invention. Due to this, it is learned that even if satisfying the ingredients prescribed in the present invention, when outside the Ni-bal range, the Erichsen value targeted by present invention is not reached.
  • Nos. 25 to 27 have 0.2% proof stresses of over 400 MPa or ⁇ -phase rates of less than 50% and failed to reach Erichsen values of 11 mm or more targeted by the present invention. Due to this, it is learned that even if satisfying the Ni-bal range prescribed in the present invention, when outside the ranges of ingredients, the Erichsen value targeted by present invention is not reached.

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US13/256,977 2009-03-19 2010-03-17 Duplex stainless steel sheet with excellent press-formability Abandoned US20120009433A1 (en)

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JP2009067767A JP5335503B2 (ja) 2009-03-19 2009-03-19 プレス成形性に優れた二相ステンレス鋼板
PCT/JP2010/055147 WO2010107132A1 (fr) 2009-03-19 2010-03-17 Tôle d'acier inoxydable duplex ayant une excellente aptitude au moulage à la presse

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US (1) US20120009433A1 (fr)
EP (1) EP2410068B1 (fr)
JP (1) JP5335503B2 (fr)
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CN (1) CN102356173B (fr)
ES (1) ES2720184T3 (fr)
WO (1) WO2010107132A1 (fr)

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WO2013058274A1 (fr) 2011-10-21 2013-04-25 新日鐵住金ステンレス株式会社 Acier inoxydable duplex, brame d'acier inoxydable duplex et matériau d'acier inoxydable duplex
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CN103938115A (zh) * 2014-03-03 2014-07-23 黄忠波 一种双相不锈钢合金材料
CN103938116A (zh) * 2014-03-03 2014-07-23 黄忠波 一种双相不锈钢合金材料及其制备方法
CN104451455A (zh) * 2014-11-15 2015-03-25 柳州市潮林机械有限公司 一种双相不锈钢管材
JP6530923B2 (ja) * 2015-02-17 2019-06-12 日鉄日新製鋼株式会社 耐食性に優れたステンレス鋼板およびその製造方法
CN105420626A (zh) * 2015-11-25 2016-03-23 铜陵市经纬流体科技有限公司 一种高耐腐蚀抗磨损的不锈钢泵阀铸件及其制备方法
KR101746404B1 (ko) * 2015-12-23 2017-06-14 주식회사 포스코 내식성 및 가공성이 향상된 린 듀플렉스 스테인리스강 및 이의 제조 방법
CN108690939B (zh) * 2017-04-10 2021-02-19 宝钢德盛不锈钢有限公司 一种高成形含氮奥氏体不锈钢及其制造方法
CN109972060B (zh) * 2019-05-07 2020-10-09 四川维珍高新材料有限公司 一种低镍高强度双相不锈钢材料及其制备方法
WO2021205943A1 (fr) * 2020-04-07 2021-10-14 日本製鉄株式会社 Tôle d'acier
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ES2720184T3 (es) 2019-07-18
EP2410068A1 (fr) 2012-01-25
JP2010222593A (ja) 2010-10-07
CN102356173B (zh) 2013-11-13
CN102356173A (zh) 2012-02-15
KR101538750B1 (ko) 2015-07-27
KR20140102326A (ko) 2014-08-21
EP2410068B1 (fr) 2019-02-20
WO2010107132A1 (fr) 2010-09-23
KR20110123772A (ko) 2011-11-15
EP2410068A4 (fr) 2017-05-03

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