EP2602351B1 - Ferritic stainless steel - Google Patents

Ferritic stainless steel Download PDF

Info

Publication number
EP2602351B1
EP2602351B1 EP11814699.2A EP11814699A EP2602351B1 EP 2602351 B1 EP2602351 B1 EP 2602351B1 EP 11814699 A EP11814699 A EP 11814699A EP 2602351 B1 EP2602351 B1 EP 2602351B1
Authority
EP
European Patent Office
Prior art keywords
black spots
stainless steel
amount
ferritic stainless
steel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
EP11814699.2A
Other languages
German (de)
French (fr)
Other versions
EP2602351A1 (en
EP2602351A4 (en
Inventor
Tooru Matsuhashi
Michio Nakata
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Stainless Steel Corp
Original Assignee
Nippon Steel and Sumikin Stainless Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Steel and Sumikin Stainless Steel Corp filed Critical Nippon Steel and Sumikin Stainless Steel Corp
Publication of EP2602351A1 publication Critical patent/EP2602351A1/en
Publication of EP2602351A4 publication Critical patent/EP2602351A4/en
Application granted granted Critical
Publication of EP2602351B1 publication Critical patent/EP2602351B1/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

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
    • C22C38/40—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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • 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
    • C21D8/0236—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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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
    • C22C38/02—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
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/22—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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/32—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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
    • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
    • F28F21/081—Heat exchange elements made from metals or metal alloys
    • F28F21/082—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys
    • F28F21/083—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys from stainless steel

Definitions

  • the present invention relates to a ferritic stainless steel that generates only a small amount of black spots in the TIG weld zone.
  • Ferritic stainless steel generally has properties such as a small expansion coefficient relative to the austenitic stainless steel and excellent resistance to stress corrosion cracking in addition to excellent corrosion resistance. Therefore, the ferritic stainless steel is widely used in tableware, kitchen equipment, building exterior materials such as roof materials, water or hot water container materials or the like. Further, there is increasing demand for replacement of austenitic stainless steel due to recent increasing price of nickel raw material, and the uses of ferritic stainless steel have expanded.
  • Patent Reference 3 discloses a technique of improving crevice corrosion resistance of the weld zone by adding a certain amount or more of Si in addition to combined addition of Al and Ti.
  • Patent Reference 4 discloses a technique to improve the corrosion resistance of a weld zone by satisfying 4Al + Ti ⁇ 0.32 (wherein each of Ti and Al denotes amount of each component in the steel), thereby reducing heat input during the welding and suppressing generation of scale in the weld zone, and improving corrosion resistance of the weld zone.
  • Patent Reference 5 there is a technique to improve the weather resistance and crevice corrosion resistance of not the weld zone but the material itself by intentionally adding P and appropriate amounts of Ca and Al (for example, see Patent Reference 5).
  • Ca and Al are added to control the shapes and distribution of non-metallic inclusions in the steel.
  • the most important feature of Patent Reference 5 is the addition of P in excess of 0.04%, and Patent Reference 5 describes nothing about an effect during welding.
  • JP 2006 263811 A discloses a ferritic stainless steel filler metal rod for TIG welding satisfying the conditions of Ti/Al ⁇ 5 and (Ti+Nb)/(C+N)>30.
  • black spots In the conventional ferritic stainless steel, dark spots (so called black spots or slag spots) occasionally occurred on the surfaces of back beads after the welding even though shielding conditions in the weld zone were controlled appropriately.
  • Elements such as Al, Ti, Si, Ca have a strong affinity to oxygen.
  • Black spots are oxides of these elements that are solidified on the surface of the weld metal during the solidification process of the weld metal formed by Tungsten Inert Gas (TIG) welding.
  • Tungsten Inert Gas (TIG) welding Tungsten Inert Gas
  • the black spot itself is an oxide
  • the black spots are generated in a large amount or generated in a continuously linked manner, the appearance of the weld material used without polishing the weld zone is worsened.
  • exfoliation of the black spots portion occasionally occurs during working of the weld zone.
  • problems such as deterioration of workability and/or occurrence of crevice corrosion in the interstitial area between the weld metal and the exfoliated black spots occasionally occur.
  • exfoliation of the black spots and the resultant deterioration of corrosion resistance occasionally occur in the member having a structure in which stress is loaded on the weld zone.
  • the corrosion resistance of the TIG weld zone it is important to not only improve the corrosion resistance of the weld bead portion itself and weld scale portion itself, but also to control the occurrence of black spots in the weld zone.
  • the scale that is generated during the welding and accompanies the change of color can be mostly suppressed by the method of enhancing shielding conditions during welding.
  • the black spots generated in the TIG weld zone could not be suppressed sufficiently in accordance with the prior arts even when the shielding conditions were enhanced.
  • an object of the present invention is to provide a ferritic stainless steel that is resistant to the generation of black spots in the TIG weld zone and exhibits excellent corrosion resistance and workability in the weld zone.
  • the inventors performed extensive research to suppress the amount of generation of black spots. As a result, the inventors found that the generation of black spots in the TIG weld zone could be suppressed by optimizing the amounts of Al, Ti, Si, and Ca, and reached the invention of the ferritic stainless steel in which black spots are generated only in a small amount.
  • a ferritic stainless steel according to the present invention that generates only a small amount of black spot satisfies the below described formula 1.
  • BI 3 ⁇ Al + Ti + 0.5 ⁇ Si + 200 ⁇ Ca ⁇ 0.8
  • Al, Ti, Si, and Ca in the formula 1 each denotes an amount of each element in the steel in mass %.
  • Al, Ti, Si, and Ca are elements that have a specifically strong affinity with oxygen and that generate black spots at the time of TIG welding. As the amount of Al, Ti, Si, and Ca contained in the steel increases, black spots are easily generated.
  • the coefficients of the amounts of Al, Ti, Si, and Ca in the above-described formula 1 are determined based on the degree (strength) of the effect of enhancing the generation of black spots and the amounts in the steel. Specifically, as it is shown in the following experimental example, Al is an element that is included in the black spot at the highest concentration and has a specifically large effect of enhancing the generation of black spots. Therefore, coefficient of the Al content in the above-described formula 1 is determined to be 3.
  • the coefficient of the Ca content is determined to be 200.
  • the generation of black spots is prominent.
  • the BI value is 0.8 or less
  • the generation of black spots in the TIG weld zone is sufficiently reduced, and an excellent corrosion resistance is obtained.
  • the BI value is 0.6 or less
  • the BI value is 0.4 or less
  • the generation of black spots is mostly suppressed, and it is possible to further improve the corrosion resistance of the TIG weld zone.
  • the black spot portion Under conditions in which a large amount of black spots tend to occur, the black spot portion has a large thickness. It is considered that such a portion is easily exfoliated at the time of working, and that severe working such as bulging causes the exfoliation and provides a starting point for corrosion. On the contrary, the black spots have thin thickness under conditions in which black spots are generated in a small amount. Therefore, it is considered that even when black spots are generated, the black spots are not exfoliated easily. Therefore, it is considered that corrosion resistance of the weld zone can be suppressed by suppressing the generation of black spots.
  • Al is important as an deoxidizing element and has an effect in grain-refinement of the microstructure of the steel by controlling the composition of non-metallic inclusion.
  • Al is an element that has the largest contribution to the generation of black spots.
  • excessive addition of Al causes coarsening of the non-metallic inclusions that may act as starting points of scratching in the product. Therefore, the upper limit of the amount of Al was determined to be 0.12%.
  • the steel contains 0.01% or more of Al with the purpose of deoxidization. More preferably, the amount of Al is 0.03% to 0.10%.
  • Ti is an very important element for fixing C and N and suppressing grain boundary corrosion in the weld zone, thereby improving workability.
  • excessive addition of Ti results in not only generation of black spots but also occurrence of surface scratches during the production process. Therefore, the range of the amount of Ti was determined to be 0.05% to 0.35%. More preferable range is 0.07% to 0.20%.
  • Si is an important element as an deoxidizing element and is effective in improvement of corrosion resistance and oxidation resistance.
  • excessive addition of Si results in not only enhancement of generation of black spots but also deterioration of workability and productivity. Therefore, the upper limit of the amount of Si was determined to be 1.0%.
  • the steel contains 0.01% or more of Si for the purpose of deoxidization.
  • the amount of Si is 0.05% to 0.55%.
  • Ca is very important as an deoxidizing element and is contained in the steel in small amount in the form of non-metallic inclusion.
  • Ca since Ca is oxidized very easily, Ca behaves as strong cause of generation of black spots in the time of welding.
  • the amount of Ca it is preferable to control the amount of Ca to be as small as possible, and the upper limit of the amount of Ca was determined to be 0.0015%. More preferably, the amount of Ca is 0.0012% or less.
  • the amount of C must be suppressed since C deteriorates grain boundary corrosion resistance and workability. Therefore the upper limit of C was determined to be 0.020%. On the other hand, excessive reduction of C causes an increase in the refining cost. Therefore, the amount of C is preferably 0.002% to 0.015%.
  • the amount of N is preferably 0.002% to 0.015%.
  • the amount of Mn was controlled to be 1.0% or less.
  • the steel contains 0.01% or more of Mn.
  • the amount of Mn is 0.05% to 0.5%, and more preferably, 0.05% to 0.3%.
  • Phosphorous (P) 0.001 to 0.035% by mass
  • the amount of P must be suppressed to low value since P deteriorates weldability and workability and makes the grain boundary corrosion easily occur. Therefore, the amount of P was controlled to be 0.035% or less. A more preferable amount of P is 0.001% to 0.02%.
  • the amount of S must be reduced since S generates water-soluble inclusions such as CaS and MnS that act as starting points of corrosion. Therefore, the amount of S is controlled to be 0.01% or less. On the other hand, excessive reduction of S results in deterioration of the cost. Therefore, the amount of S is preferably 0.0001% to 0.005%.
  • Cr is the most important element for ensuring corrosion resistance of the stainless steel. In order to stabilize the ferrite microstructure, it is necessary for the steel to contain 16.0% or more of Cr. On the other hand Cr deteriorates the workability and productivity of the steel. Therefore, the upper limit of Cr content was determined to be 25.0%. Preferably, the amount of Cr is 16.5% to 23.0%, and more preferably, 18.0% to 22.5%.
  • Nb has properties such that Nb may be added alone, or in combination with Ti. Where Nb and Ti are added in combination, it is preferable that the formula: (Ti+Nb)/(C+N) ⁇ 6 is satisfied, where Ti, Nb, C, and N in the formula each denote the amount in mass % of each element in the steel.
  • Nb fixes C and N, suppress grain boundary corrosion of weld-zone, and improves workability.
  • excessive addition of Nb deteriorates workability of the steel. Therefore, it is preferable to control the upper limit of the amount of Nb to be 0.6%.
  • the steel In order to improve the above-described properties by the content of Nb, it is preferable for the steel to contain 0.05% or more of Nb.
  • the amount of Nb is 0.15% to 0.55%.
  • the stainless steel sheet contains optionally one or more of 0.30 to 3.0% of Mo, 0.05 to 2.0% of Cn, 0.05 to 2.0% of Ni, 0.03 to 0.2% of V, 0.03 to 0.2% of Zr and 0.0001 to 0.005% of B.
  • Mo is an element that has an effect of repairing the passive film and is very effective in improvement of corrosion resistance.
  • Mo has an effect of improving pitting corrosion resistance of the steel.
  • Mo has an effect of improving the resistance to outflow rust.
  • increased Mo reduces workability and increases the cost. Therefore, if present, the upper limit of the amount of Mo is 3.0%.
  • the steel contains 0.30% or more of Mo.
  • the amount of Mo is 0.60% to 2.5%, more preferably, 0.9% to 2.0%.
  • Nickel (Ni) If present, 0.05 to 2.0% or less by mass
  • Ni has an effect of suppressing active dissolution rate, and is excellent in repassivation properties because of the small hydrogen overvoltage. On the other hand, excessive addition of Ni deteriorates workability and destabilizes the ferrite microstructure. Therefore, if present, the upper limit of the amount of Ni is 2.0%. In order to improve the above-described properties by the content of Ni, if present, the steel contains 0.05% or more of Ni. Preferably, the amount of Ni is 0.1% to 1.2%, more preferably, 0.2% to 1.1%.
  • Copper (Cu) If present, 0.005 to 2.0% by mass
  • the upper limit of the amount is 2.0%.
  • steel contains 0.05% or more of Cu.
  • the amount of Cu is 0.2% to 1.5%, more preferably, 0.25% to 1.1%.
  • V and Zr improve weather resistance and crevice corrosion resistance.
  • V is added while suppressing the use of Cr and Mo, it is possible to ensure an excellent workability.
  • excessive addition of V and/or Zr deteriorates workability, and saturates the effect of improving corrosion resistance. Therefore, where V and/or Zr is contained, the upper limit of the amount is 0.2%.
  • the steel contains 0.03% or more of V and/or Zr. More preferably, the amount of V and/or Zr is 0.05% to 0.1%.
  • B is an element that strengthens grain boundary and is effective in improvement of secondary working embrittlement.
  • excessive addition of B causes reduction of ductility by solution-strengthening of ferrite. Therefore, where B is added, the lower limit is 0.0001%, and the upper limit is 0.005%. More preferably, the amount of B is controlled to be 0.0002% to 0.0020%.
  • Test pieces composed of ferritic stainless steel each having a chemical component (composition) shown in Table 1 were produced in accordance with the below described method. Firstly, a cast steel having a chemical component (composition) shown in Table 1 was molten by vacuum melting, and an ingot having a thickness of 40 mm was produced from the melt. The ingot was rolled to a thickness of 5 mm by hot rolling. After that, in accordance with the recrystallization behavior of each steel, the rolled steel was heat treated for one minute at a temperature of 800 to 1000°C. After removing a scale by grinding, steel plates having a thickness of 0.8 mm were produced by cold rolling. After removing the surface oxide scale by pickling (acid cleaning), test materials were obtained.
  • test pieces of Nos. 1 to 28 were produced.
  • the amount of each element is shown in mass %, and the balance is iron and unavoidable impurities.
  • the under-line shows that the value is outside the range of the present invention.
  • test pieces of Nos. 1 to 28 were subjected to TIG welding under the following welding conditions, and formation length ratio of black spot was measured in accordance with the following manner. In addition, corrosion experiment was performed for the test piece of Nos. 1 to 28.
  • Pieces of the same steel were butted and subjected to TIG welding with feed rate of 50 cm/min, and heat input of 550 to 650J/cm 2 .
  • Argon was used both in shielding of torch side and shielding of back side.
  • the formation length ratio of black spots was determined as a standard for showing the amount of generated black spots after the TIG welding.
  • the formation length ratio of black spots was obtained by integrating length of each black spot along the welding direction, and dividing the integrated value by the total welding length. Practically, photograph of a 10 cm length weld zone was taken by a digital camera, length of each black spot was measured, and ratio of the integrated length of black spots to the welding length was calculated using image processing.
  • TIG weld zones of test pieces were subjected to bulging and were used as test pieces for corrosion test. Erichsen test conditions in accordance with JIS2247 were used as the bulging conditions. The penetration side was used as the surface, and a punch of 20 mm ⁇ was used in the bulging. The working of each test piece was paused so as to adjust the working conditions with respect to the height of the bulge. The paused height (height of bulge) was standardized to 6 mm and 7 mm. Each test piece was subjected to continuous spray test of 5%NaCl in accordance with JIS Z 2371, and corrosion was evaluated by presence or absence of outflow rust in the test piece at 48 hours after the spray test.
  • formation length ratios of black spots were small, that is, amounts of generated black spots after the TIG welding were small in the test pieces Nos. 1 to 15, 19 to 21 that had chemical component (composition) within the range of the present invention and BI value of 0.8 or less.
  • Generation of black spots was suppressed in the test pieces No. 1 to 15 having a BI value of 0.6 or less. Further, generation of black spots was mostly suppressed in Nos. 1 to 13 having a BI value of 0.4 or less such that the ratio of formation length of black spots was 10% or less.
  • test pieces No. 1 to 21 which were worked to have a bulge height of 6mm using an Erichsen test machine, rust from the weld zone was not observed after the continuous spray test of 5%NaCl.
  • test pieces No. 1 to 21 which were more severely worked to have a bulge height of 7mm, rust was not observed in test pieces having BI value of 0.4 or less, and rust was observed in test pieces having BI value exceeding 0.4.
  • test pieces Nos. 22, 24, 26 to 28 having BI value exceeding 0.8 showed large formation length ratio of black spots after the TIG welding and rust from the weld zone was observed in each specimen in the corrosion test.
  • Magnified images of rust portions of test pieces Nos. 22, 24, 26 to 28 were observed using a magnifying glass.
  • exfoliation was observed in the boundary between the black spots and the weld bead portion.
  • Rust was generated in corrosion test of Nos. 22, 26, 27, and 28 in which concentrations of Al, Ti, Si, and Ca exceeded the regulated values. Occurrence of rust was observed in the corrosion test of the test piece No. 25 in which component ratio of Cr was less than 16% and the test piece No. 23 in which component ratio of Ti was less than 0.05%.
  • Test materials were produced in accordance with the same manner as test piece No.1 except for that steel plates of 1 mm thick were produced by cold-rolling of ferritic stainless steels having the below described chemical components (compositions). Test piece A and test piece B were obtained using the test materials.
  • test piece A and test piece B were subjected to TIG welding under the similar welding conditions as the test piece No. 1, and appearance of black spots generated in the back side during TIG welding was observed.
  • FIG. 1A and FIG. 1B The results are shown in FIG. 1A and FIG. 1B .
  • FIG. 1A is a photograph that shows an appearance of black spots generated in back side during TIG welding.
  • FIG. 1B is a schematic drawing that shows an appearance of black spots generated in back side during TIG welding and that corresponds to FIG. 1A .
  • FIG. 1A and FIG. 1B the left-side figures show a photograph and a drawing of test piece A in which BI value is 0.49, and the right-side figures show a photograph and a drawing of test piece B in which BI value is 1.07.
  • a FE (Field Emission) Auger Electron Spectroscopy was used in the AES analysis, and the analysis was performed until intensity of oxygen spectrum was almost not detected under conditions of an acceleration voltage of 10keV, a spot diameter of 40 nm, and a sputtering rate of 15 nm/min. Although a position dependent error may occur due to small spot of AES measurement, the results were applied as values showing approximate thickness.
  • FIG. 2A and FIG. 2B are graphs that show depth profile of elements (concentration distribution of elements in depth direction) in the black spot and the weld bead portion on the back side of the test piece as a result of AES analysis.
  • FIG. 2A is a result of weld bead portion
  • FIG. 2B is a result of a black spot.
  • the weld bead portion was an oxide having a thickness of several hundred ⁇ that mainly contained Ti, and also contained Al and Si.
  • the black spot was a thick oxide having a thickness of several thousand ⁇ that mainly contained Al, and also contained Ti, Si, and Ca. From the graph of black spot shown in FIG. 2B , it was confirmed that Al was contained in the black spot at the highest concentration and Ca was contained in the black spot at high concentration irrespective of its small amount in the steel.
  • Test materials of ferritic stainless steel having various component ratios (compositions) were produced in accordance with the production method similar to that of test piece A, where each steel had a basic composition of C: 0.002 to 0.015%, N: 0.02 to 0.015%, Cr: 16.5 to 23%, Ni: 0 to 1.5%, Mo: 0 to 2.5%, and also contained main components of black spots such as Al, Ti, Si, and Ca in different amount. Using the test materials, a plurality of test pieces was obtained.
  • test piece No. 1 The thus obtained plurality of test pieces were subjected to TIG welding under similar welding conditions as the test piece No. 1, and ratios of formation length of black spots were calculated in accordance with the same manner as the test piece No. 1.
  • the formation length ratio of black spots tended to increase in accordance with the increasing amounts of Al, Ti, Si, and Ca. Those elements are elements having specifically strong affinity with oxygen. It was found that Al had the highest effect, and Ca had a strong influence on black spots irrespective of its small amount in the steel. It was also confirmed that Ti and Si also contributed to the generation of black spots.
  • BI value shown by the below described formula 1 was calculated for the plurality of test pieces, and the relationship between the BI value and the ratio of formation length of black spots was examined.
  • BI 3 ⁇ Al + Ti + 0.5 ⁇ Si + 200 ⁇ Ca ⁇ 0.8
  • Al, Ti, Si, and Ca in the formula 1 respectively denotes an amount of each element in mass % of the steel.
  • FIG. 3 is a graph showing the relationship between the BI value and the ratio of formation length of black spots. As shown in FIG. 3 , it is recognized that the ratio of formation length of black spots increases with an increasing BI value.
  • FIG. 4 is a graph that shows a relationship between the BI values and the results of corrosion resistance evaluation after the spray test after working.
  • double circles (O) show excellent results
  • circles ( ⁇ ) show good results
  • crosses ( ⁇ ) show bad results.
  • corrosion did not occur in the specimen with bulge height of 6 mm where BI value was 0.8 or less.
  • BI value was 0.4 or less
  • specifically good results were achieved such that corrosion was not observed in the specimen with bulge height of 7 mm.
  • the ferritic stainless steel of the present invention can be appropriately used in members requiring corrosion resistance in a structure of, for example, exterior materials, building materials, water or hot water containers, consumer electronics, kitchen equipment, drain water collectors and heat exchanger of gas condensing boiler, various welded pipes or the like that are formed by TIG welding and used in general indoor or outdoor environment.
  • the ferritic stainless steel of the present invention is appropriately used in a member that is subjected to working after the welding. Since the ferritic stainless steel of the present invention is excellent not only in corrosion resistance but also in workability of TIG weld zone, the steel can be widely used in the usage suffering severe working conditions.

Description

    TECHNICAL FIELD
  • The present invention relates to a ferritic stainless steel that generates only a small amount of black spots in the TIG weld zone.
    • BACKGROUND ART
  • Ferritic stainless steel generally has properties such as a small expansion coefficient relative to the austenitic stainless steel and excellent resistance to stress corrosion cracking in addition to excellent corrosion resistance. Therefore, the ferritic stainless steel is widely used in tableware, kitchen equipment, building exterior materials such as roof materials, water or hot water container materials or the like. Further, there is increasing demand for replacement of austenitic stainless steel due to recent increasing price of nickel raw material, and the uses of ferritic stainless steel have expanded.
  • Welding is an inevitable process in forming the above-described structure of stainless steel. Originally, ferritic stainless steel included a problem of sensitization in weld zone resulting in reduction of corrosion resistance due to the small solid-solubility limit of C and N. In order to solve the above-described problem, there has been proposed and widely practicalized a method of suppressing the sensitization of a weld metal zone by reduction of C and N contents, or by fixing of C and N by addition of stabilizing elements such as Ti and Nb, or the like (for example, see Patent Reference 1).
  • The following have been known with regards to the corrosion resistance of weld zone in the ferritic stainless steel. Corrosion resistance is deteriorated in the scale portion generated by heat input during the welding, and therefore, it is important to perform sufficient shielding with an inert gas compared to the austenitic stainless steel. Patent Reference 2 discloses a technique of adding Ti and Al such that the formula, P1=5Ti+20(Al-0.01) ≥ 5 (wherein Ti and Al in the formula denote amounts of respective elements in the steel) is satisfied, thereby forming an Al oxide film on the surface portion of the steel during welding to improve corrosion resistance of the weld-heat affected zone.
  • Patent Reference 3 discloses a technique of improving crevice corrosion resistance of the weld zone by adding a certain amount or more of Si in addition to combined addition of Al and Ti.
  • Patent Reference 4 discloses a technique to improve the corrosion resistance of a weld zone by satisfying 4Al + Ti ≤ 0.32 (wherein each of Ti and Al denotes amount of each component in the steel), thereby reducing heat input during the welding and suppressing generation of scale in the weld zone, and improving corrosion resistance of the weld zone.
  • The above-described prior arts have objects of improving corrosion resistance of the weld zone and weld heat affected zone.
  • In another method, there is a technique to improve the weather resistance and crevice corrosion resistance of not the weld zone but the material itself by intentionally adding P and appropriate amounts of Ca and Al (for example, see Patent Reference 5). In Patent Reference 5, Ca and Al are added to control the shapes and distribution of non-metallic inclusions in the steel. The most important feature of Patent Reference 5 is the addition of P in excess of 0.04%, and Patent Reference 5 describes nothing about an effect during welding.
    • Prior Art Reference Patent Reference
    • Patent Reference 1: Japanese Examined Patent Application, Second Publication No. S55-21102 .
    • Patent Reference 2: Japanese Unexamined Patent Application, First Publication No. H05-70899
    • Patent Reference 3: Japanese Unexamined Patent Application, First Publication No. 2006-241564
    • Patent Reference 4: Japanese Unexamined Patent Application, First Publication No. 2007-270290
    • Patent Reference 5: Japanese Unexamined Patent Application, First Publication No. H07-34205
  • JP 2006 263811 A discloses a ferritic stainless steel filler metal rod for TIG welding satisfying the conditions of Ti/Al<5 and (Ti+Nb)/(C+N)>30.
    • SUMMARY OF THE INVENTION Problems to be solved by the invention
  • In the conventional ferritic stainless steel, dark spots (so called black spots or slag spots) occasionally occurred on the surfaces of back beads after the welding even though shielding conditions in the weld zone were controlled appropriately. Elements such as Al, Ti, Si, Ca have a strong affinity to oxygen. Black spots are oxides of these elements that are solidified on the surface of the weld metal during the solidification process of the weld metal formed by Tungsten Inert Gas (TIG) welding. Weld conditions, especially the conditions of shielding with the inert gas have a strong influence on the generation of the black spots. Many black spots occur where the shielding is insufficient.
  • Since the black spot itself is an oxide, there is no problem in corrosion resistance and workability of the weld zone even when the weld zone is dotted with a small amount of black spots. However, where the black spots are generated in a large amount or generated in a continuously linked manner, the appearance of the weld material used without polishing the weld zone is worsened. In addition, exfoliation of the black spots portion occasionally occurs during working of the weld zone. Where the black spot portion is exfoliated, problems such as deterioration of workability and/or occurrence of crevice corrosion in the interstitial area between the weld metal and the exfoliated black spots occasionally occur. Even when the steel member is not worked after the welding, where a thick portion is formed by the black spots, exfoliation of the black spots and the resultant deterioration of corrosion resistance occasionally occur in the member having a structure in which stress is loaded on the weld zone.
  • Therefore, in order to improve the corrosion resistance of the TIG weld zone, it is important to not only improve the corrosion resistance of the weld bead portion itself and weld scale portion itself, but also to control the occurrence of black spots in the weld zone. The scale that is generated during the welding and accompanies the change of color can be mostly suppressed by the method of enhancing shielding conditions during welding. However, the black spots generated in the TIG weld zone could not be suppressed sufficiently in accordance with the prior arts even when the shielding conditions were enhanced.
  • In consideration of the above-explained circumstances, an object of the present invention is to provide a ferritic stainless steel that is resistant to the generation of black spots in the TIG weld zone and exhibits excellent corrosion resistance and workability in the weld zone.
    • Solution to the Problems
  • As described below, the inventors performed extensive research to suppress the amount of generation of black spots. As a result, the inventors found that the generation of black spots in the TIG weld zone could be suppressed by optimizing the amounts of Al, Ti, Si, and Ca, and reached the invention of the ferritic stainless steel in which black spots are generated only in a small amount.
  • The invention is defined in the claims.
    • Effect of the invention
  • According to the present invention, it is possible to provide a ferritic stainless steel in which black spots do not easily occur and that is excellent in corrosion resistance and workability of the weld zone.
    • BRIEF EXPLANATION OF DRAWINGS
    • FIG. 1A is a photograph that shows appearance of black spots that were generated in the back side during TIG welding.
    • FIG. 1B is a schematic drawing that corresponds to the photograph of FIG. 1A and shows an appearance of black spots that were generated in the back side during TIG welding.
    • FIG. 2A is a graph that shows a result of AES measurement of depth profile of elements (concentration distributions of elements in the depth direction) of the weld bead portion in the back side of a test piece.
    • FIG. 2B is a graph that shows a result of AES measurement of depth profile of elements (concentration distributions of elements in the depth direction) of a black spot in the back side of a test piece.
    • FIG. 3 is a graph that shows a relationship between the BI value and the formation length ratio of black spots.
    • FIG. 4 is a graph showing the relationship between the BI value and corrosion, where concentric double circles (⊚) show excellent results, circles (○ ) show good results, and crosses (×) show bad results.
    MODE FOR CARRYING OUT THE INVENTION
  • In the following, the present invention is explained in detail.
  • A ferritic stainless steel according to the present invention that generates only a small amount of black spot satisfies the below described formula 1. BI = 3 ⁢ Al + Ti + 0.5 ⁢ Si + 200 ⁢ Ca ≤ 0.8
    Figure imgb0001
     where Al, Ti, Si, and Ca in the formula 1 each denotes an amount of each element in the steel in mass %.
  • Al, Ti, Si, and Ca are elements that have a specifically strong affinity with oxygen and that generate black spots at the time of TIG welding. As the amount of Al, Ti, Si, and Ca contained in the steel increases, black spots are easily generated. The coefficients of the amounts of Al, Ti, Si, and Ca in the above-described formula 1 are determined based on the degree (strength) of the effect of enhancing the generation of black spots and the amounts in the steel. Specifically, as it is shown in the following experimental example, Al is an element that is included in the black spot at the highest concentration and has a specifically large effect of enhancing the generation of black spots. Therefore, coefficient of the Al content in the above-described formula 1 is determined to be 3.
  • Ca is an element that is included in the black spot at a high concentration regardless of its small content in the steel and that has a large effect of enhancing the generation of black spots. Therefore, the coefficient of the Ca content is determined to be 200.
  • Where the above-described BI value exceeds 0.8, the generation of black spots is prominent. On the other hand, where the BI value is 0.8 or less, the generation of black spots in the TIG weld zone is sufficiently reduced, and an excellent corrosion resistance is obtained. Where the BI value is 0.6 or less, it is possible to suppress the generation of black spots more effectively. Further, where the BI value is 0.4 or less, the generation of black spots is mostly suppressed, and it is possible to further improve the corrosion resistance of the TIG weld zone.
  • Under conditions in which a large amount of black spots tend to occur, the black spot portion has a large thickness. It is considered that such a portion is easily exfoliated at the time of working, and that severe working such as bulging causes the exfoliation and provides a starting point for corrosion. On the contrary, the black spots have thin thickness under conditions in which black spots are generated in a small amount. Therefore, it is considered that even when black spots are generated, the black spots are not exfoliated easily. Therefore, it is considered that corrosion resistance of the weld zone can be suppressed by suppressing the generation of black spots.
  • Next, component compositions of the ferritic stainless steel according to the present invention are explained in detail.
  • Firstly, each of the elements for regulating the above described formula 1 is explained.
    • Aluminum (Al): 0.01 to 0.12% by mass
  • Al is important as an deoxidizing element and has an effect in grain-refinement of the microstructure of the steel by controlling the composition of non-metallic inclusion. However, Al is an element that has the largest contribution to the generation of black spots. In addition, excessive addition of Al causes coarsening of the non-metallic inclusions that may act as starting points of scratching in the product. Therefore, the upper limit of the amount of Al was determined to be 0.12%. The steel contains 0.01% or more of Al with the purpose of deoxidization. More preferably, the amount of Al is 0.03% to 0.10%.
    • Titanium (Ti): 0.05% to 0.35% by mass
  • Ti is an very important element for fixing C and N and suppressing grain boundary corrosion in the weld zone, thereby improving workability. However, excessive addition of Ti results in not only generation of black spots but also occurrence of surface scratches during the production process. Therefore, the range of the amount of Ti was determined to be 0.05% to 0.35%. More preferable range is 0.07% to 0.20%.
    • Silicon (Si): 0.01 to 1.0% by mass
  • Si is an important element as an deoxidizing element and is effective in improvement of corrosion resistance and oxidation resistance. However, excessive addition of Si results in not only enhancement of generation of black spots but also deterioration of workability and productivity. Therefore, the upper limit of the amount of Si was determined to be 1.0%. The steel contains 0.01% or more of Si for the purpose of deoxidization. Preferably, the amount of Si is 0.05% to 0.55%.
    • Calcium (Ca): present up to 0.0015% by mass
  • Ca is very important as an deoxidizing element and is contained in the steel in small amount in the form of non-metallic inclusion. On the other hand, since Ca is oxidized very easily, Ca behaves as strong cause of generation of black spots in the time of welding. In addition, there is a case in that Ca causes generation of water-soluble inclusion, thereby deteriorating corrosion resistance. Therefore, it is preferable to control the amount of Ca to be as small as possible, and the upper limit of the amount of Ca was determined to be 0.0015%. More preferably, the amount of Ca is 0.0012% or less.
  • Next, the other elements constituting the ferritic stainless steel according to the present invention is explained.
    • Carbon (C): 0.002 to 0.020% by mass
  • The amount of C must be suppressed since C deteriorates grain boundary corrosion resistance and workability. Therefore the upper limit of C was determined to be 0.020%. On the other hand, excessive reduction of C causes an increase in the refining cost. Therefore, the amount of C is preferably 0.002% to 0.015%.
    • Nitrogen (N): 0.002 to 0.025% by mass
  • In the same manner as C, N deteriorates grain boundary corrosion resistance and the workability of the steel. Therefore, it is necessary to reduce the amount of N. Therefore, upper limit of the amount of N was determined to be 0.025%. On the other hand, excessive reduction of N causes an increase in the refining cost. Therefore, the amount of N is preferably 0.002% to 0.015%.
    • Manganese (Mn): 0.01 to 1.0% by mass
  • Although Mn is an important element as a deoxidizing element, excessive addition of Mn tends to cause generation of MnS that acts as a starting point of corrosion, and destabilizes the ferrite microstructure. Therefore, the amount of Mn was controlled to be 1.0% or less. For the purpose of deoxidization, the steel contains 0.01% or more of Mn. Preferably, the amount of Mn is 0.05% to 0.5%, and more preferably, 0.05% to 0.3%.
    • Phosphorous (P): 0.001 to 0.035% by mass
  • The amount of P must be suppressed to low value since P deteriorates weldability and workability and makes the grain boundary corrosion easily occur. Therefore, the amount of P was controlled to be 0.035% or less. A more preferable amount of P is 0.001% to 0.02%.
    • Sulfur (S): 0.0001 to 0.01% by mass
  • The amount of S must be reduced since S generates water-soluble inclusions such as CaS and MnS that act as starting points of corrosion. Therefore, the amount of S is controlled to be 0.01% or less. On the other hand, excessive reduction of S results in deterioration of the cost. Therefore, the amount of S is preferably 0.0001% to 0.005%.
    • Chromium (Cr): 16.0% to 25.0% by mass
  • Cr is the most important element for ensuring corrosion resistance of the stainless steel. In order to stabilize the ferrite microstructure, it is necessary for the steel to contain 16.0% or more of Cr. On the other hand Cr deteriorates the workability and productivity of the steel. Therefore, the upper limit of Cr content was determined to be 25.0%. Preferably, the amount of Cr is 16.5% to 23.0%, and more preferably, 18.0% to 22.5%.
    • Niobium (Nb): 0.05∼0.6% by mass
  • Nb has properties such that Nb may be added alone, or in combination with Ti. Where Nb and Ti are added in combination, it is preferable that the formula: (Ti+Nb)/(C+N) ≥ 6 is satisfied, where Ti, Nb, C, and N in the formula each denote the amount in mass % of each element in the steel.
  • In the same manner as Ti, Nb fixes C and N, suppress grain boundary corrosion of weld-zone, and improves workability. On the other hand, excessive addition of Nb deteriorates workability of the steel. Therefore, it is preferable to control the upper limit of the amount of Nb to be 0.6%. In order to improve the above-described properties by the content of Nb, it is preferable for the steel to contain 0.05% or more of Nb. Preferably, the amount of Nb is 0.15% to 0.55%.
  • In the invention, the stainless steel sheet contains optionally one or more of 0.30 to 3.0% of Mo, 0.05 to 2.0% of Cn, 0.05 to 2.0% of Ni, 0.03 to 0.2% of V, 0.03 to 0.2% of Zr and 0.0001 to 0.005% of B.
    • Molybdenum (Mo): If present, 0.30 to 3.0% by mass
  • Mo is an element that has an effect of repairing the passive film and is very effective in improvement of corrosion resistance. By being added in combination with Cr, Mo has an effect of improving pitting corrosion resistance of the steel. By being added in combination with Ni, Mo has an effect of improving the resistance to outflow rust. On the other hand, increased Mo reduces workability and increases the cost. Therefore, if present, the upper limit of the amount of Mo is 3.0%. In order to improve the above-described properties by the content of Mo, if present, the steel contains 0.30% or more of Mo. Preferably, the amount of Mo is 0.60% to 2.5%, more preferably, 0.9% to 2.0%.
    • Nickel (Ni): If present, 0.05 to 2.0% or less by mass
  • Ni has an effect of suppressing active dissolution rate, and is excellent in repassivation properties because of the small hydrogen overvoltage. On the other hand, excessive addition of Ni deteriorates workability and destabilizes the ferrite microstructure. Therefore, if present, the upper limit of the amount of Ni is 2.0%. In order to improve the above-described properties by the content of Ni, if present, the steel contains 0.05% or more of Ni. Preferably, the amount of Ni is 0.1% to 1.2%, more preferably, 0.2% to 1.1%.
    • Copper (Cu): If present, 0.005 to 2.0% by mass
  • In the same manner as Ni, Cu reduces the active dissolution rate, and has an effect of enhancing repassivation. However, an excessive addition of Cu deteriorates the workability. Therefore, where Cu is added, the upper limit of the amount is 2.0%. In order to improve the above-described property by the content of Cu, if present, steel contains 0.05% or more of Cu. Preferably, the amount of Cu is 0.2% to 1.5%, more preferably, 0.25% to 1.1%.
    • Vanadium (V) and/or zirconium (Zr): If present, 0.003 to 0.2% by mass
  • V and Zr improve weather resistance and crevice corrosion resistance. In addition, where V is added while suppressing the use of Cr and Mo, it is possible to ensure an excellent workability. On the other hand, excessive addition of V and/or Zr deteriorates workability, and saturates the effect of improving corrosion resistance. Therefore, where V and/or Zr is contained, the upper limit of the amount is 0.2%. In order to improve the above-described properties by the content of V and/or Zr, the steel contains 0.03% or more of V and/or Zr. More preferably, the amount of V and/or Zr is 0.05% to 0.1%.
    • Boron (B): If present, 0.0001 to 0.005% or less by mass
  • B is an element that strengthens grain boundary and is effective in improvement of secondary working embrittlement. On the other hand, excessive addition of B causes reduction of ductility by solution-strengthening of ferrite. Therefore, where B is added, the lower limit is 0.0001%, and the upper limit is 0.005%. More preferably, the amount of B is controlled to be 0.0002% to 0.0020%.
    • EXAMPLE
  • Test pieces composed of ferritic stainless steel each having a chemical component (composition) shown in Table 1 were produced in accordance with the below described method. Firstly, a cast steel having a chemical component (composition) shown in Table 1 was molten by vacuum melting, and an ingot having a thickness of 40 mm was produced from the melt. The ingot was rolled to a thickness of 5 mm by hot rolling. After that, in accordance with the recrystallization behavior of each steel, the rolled steel was heat treated for one minute at a temperature of 800 to 1000°C. After removing a scale by grinding, steel plates having a thickness of 0.8 mm were produced by cold rolling. After removing the surface oxide scale by pickling (acid cleaning), test materials were obtained. Using the test materials, test pieces of Nos. 1 to 28 were produced. In the chemical component (composition) shown in Table 1, the amount of each element is shown in mass %, and the balance is iron and unavoidable impurities. The under-line shows that the value is outside the range of the present invention. Table 1
    No. C Si Mn P S Cr Al Ti Ca N Mo Nb Ni Cu B V Zr Fe and unavoidable impurities
    1 0.004 0.10 0.11 0.007 0.001 18.0 0.04 0.20 0.0002 0.008 Balance reference
    2 0.005 0.11 0.20 0.015 0.003 18.2 0.06 0.12 0.0002 0.007 0.52 Balance reference
    3 0.008 0.09 0.20 0.011 0.002 19.7 0.04 0.12 0.0003 0.012 0.20 Balance inventive
    4 0.011 0.10 0.11 0.009 0.001 22.9 0.03 0.10 0.0003 0.010 0.31 0.05 Balance inventive
    5 0.012 0.11 0.18 0.009 0.001 18.7 0.03 0.16 0.0004 0.011 1.81 0.28 Balance inventive
    6 0.005 0.08 0.20 0.008 0.001 22.5 0.07 0.09 0.0002 0.008 1.18 0.18 Balance inventive
    7 0.007 0.10 0.14 0.010 0.002 19.0 0.04 0.14 0.0004 0.010 0.99 0.22 Balance inventive
    8 0.010 0.13 0.15 0.010 0.002 18.4 0.04 0.16 0.0002 0.010 1.90 0.23 0.12 0.20 0.10 Balance inventive
    9 0.004 0.12 0.18 0.009 0.003 22.6 0.05 0.13 0.0003 0.011 0.82 0.25 0.15 0.15 0.08 Balance inventive
    10 0.007 0.51 0.25 0.010 0.002 19.1 0.01 0.07 0.0002 0.009 0.45 0.28 0.44 Balance inventive
    11 0.004 0.10 0.16 0.009 0.001 20.9 0.03 0.06 0.0002 0.009 0.25 0.0007 Balance inventive
    12 0.007 0.12 0.25 0.010 0.002 19.1 0.06 0.12 0.0002 0.009 0.95 0.21 1.02 0.06 Balance inventive
    13 0.014 0.04 0.22 0.020 0.003 17.5 0.04 0.08 0.0005 0.014 0.51 0.12 Balance inventive
    14 0.003 0.45 0.27 0.011 0.002 19.4 0.05 0.09 0.0003 0.006 0.17 0.40 0.50 0.0004 0.12 Balance inventive
    15 0.009 0.08 0.09 0.008 0.002 18.5 0.08 0.08 0.0004 0.008 0.55 Balance inventive
    16 0.004 0.12 0.20 0.022 0.002 23.0 0.12 0.19 0.0002 0.008 0.55 Balance reference
    17 0.005 0.15 0.21 0.020 0.003 19.2 0.04 0.30 0.0009 0.009 0.25 0.39 Balance reference
    18 0.004 0.10 0.14 0.007 0.001 17.1 0.04 0.22 0.0003 0.009 Balance reference
    19 0.004 0.12 0.12 0.008 0.003 23.7 0.06 0.15 0.0005 0.011 1.85 0.21 Balance inventive
    20 0.013 0.62 0.25 0.020 0.003 17.6 0.06 0.07 0.0004 0.014 0.38 Balance inventive
    21 0.005 0.09 0.28 0.015 0.002 23.8 0.08 0.21 0.0010 0.010 0.19 0.0008 0.09 Balance inventive
    22 0.010 0.25 0.20 0.030 0.003 23.0 0.15 0.19 0.0015 0.012 0.22 Balance comparative
    23 0.006 0.65 0.21 0.015 0.002 18.5 0.05 0.02 0.0010 0.009 0.41 0.25 0.39 Balance comparative
    24 0.004 0.20 0.22 0.020 0.003 21.5 0.09 0.34 0.0010 0.010 1.05 0.11 Balance comparative
    25 0.006 0.26 0.16 0.025 0.001 15.9 0.09 0.21 0.0009 0.014 0.0010 Balance comparative
    26 0.010 0.25 0.20 0.020 0.002 17.9 0.03 0.40 0.0015 0.011 2.01 Balance comparative
    27 0.015 1.01 0.31 0.002 0.002 18.0 0.04 0.19 0.0014 0.014 0.36 Balance comparative
    28 0.012 0.28 0.23 0.018 0.003 23.5 0.10 0.21 0.0019 0.012 1.56 0.18 0.08 Balance comparative
  • The thus obtained test pieces of Nos. 1 to 28 were subjected to TIG welding under the following welding conditions, and formation length ratio of black spot was measured in accordance with the following manner. In addition, corrosion experiment was performed for the test piece of Nos. 1 to 28.
    • Welding conditions
  • Pieces of the same steel were butted and subjected to TIG welding with feed rate of 50 cm/min, and heat input of 550 to 650J/cm2. Argon was used both in shielding of torch side and shielding of back side.
    • Ratio of formation length of black spot
  • The formation length ratio of black spots was determined as a standard for showing the amount of generated black spots after the TIG welding. The formation length ratio of black spots was obtained by integrating length of each black spot along the welding direction, and dividing the integrated value by the total welding length. Practically, photograph of a 10 cm length weld zone was taken by a digital camera, length of each black spot was measured, and ratio of the integrated length of black spots to the welding length was calculated using image processing.
    • Corrosion test
  • TIG weld zones of test pieces were subjected to bulging and were used as test pieces for corrosion test. Erichsen test conditions in accordance with JIS2247 were used as the bulging conditions. The penetration side was used as the surface, and a punch of 20 mm φ was used in the bulging. The working of each test piece was paused so as to adjust the working conditions with respect to the height of the bulge. The paused height (height of bulge) was standardized to 6 mm and 7 mm. Each test piece was subjected to continuous spray test of 5%NaCl in accordance with JIS Z 2371, and corrosion was evaluated by presence or absence of outflow rust in the test piece at 48 hours after the spray test. Where the outflow rust was not observed in the bulged test piece with bulging height of 6 mm after the continuous spray test of 5%NaCl, the result was evaluated as "GOOD". Where the outflow rust was not observed in the bulged test piece with bulging height of 7 mm after the same spray test, the result was evaluated as "EXCELLENT". Where the outflow rust occurred after the continuous spray test, the result was evaluated as BAD.
  • BI values determined from the chemical component in Table 1, formation length ratio of black spots, and the results of corrosion test are shown in Table 2. Table 2
    No. BI Formation length ratio of black spots (%) Results of corrosion test
    1 0.40 10 EXCELLENT reference
    2 0.40 7 EXCELLENT reference
    3 0.35 3 EXCELLENT inventive
    4 0.30 0 EXCELLENT inventive
    5 0.39 9 EXCELLENT inventive
    6 0.38 7 EXCELLENT inventive
    7 0.39 9 EXCELLENT inventive
    8 0.39 10 EXCELLENT inventive
    9 0.40 8 EXCELLENT inventive
    10 0.40 9 EXCELLENT inventive
    11 0.24 0 EXCELLENT inventive
    12 0.40 9 EXCELLENT inventive
    13 0.32 7 EXCELLENT inventive
    14 0.53 22 GOOD inventive
    15 0.44 15 GOOD inventive
    16 0.65 41 GOOD reference
    17 0.68 49 GOOD reference
    18 0.45 19 GOOD reference
    19 0.49 20 GOOD inventive
    20 0.64 39 GOOD inventive
    21 0.70 45 GOOD inventive
    22 1.07 78 BAD comparative
    23 0.70 45 BAD comparative
    24 0.91 86 BAD comparative
    25 0.79 60 BAD comparative
    26 0.92 89 BAD comparative
    27 1.10 83 BAD comparative
    28 1.03 88 BAD comparative
  • As shown in Table 2, formation length ratios of black spots were small, that is, amounts of generated black spots after the TIG welding were small in the test pieces Nos. 1 to 15, 19 to 21 that had chemical component (composition) within the range of the present invention and BI value of 0.8 or less. Generation of black spots was suppressed in the test pieces No. 1 to 15 having a BI value of 0.6 or less. Further, generation of black spots was mostly suppressed in Nos. 1 to 13 having a BI value of 0.4 or less such that the ratio of formation length of black spots was 10% or less. In test pieces No. 1 to 21 which were worked to have a bulge height of 6mm using an Erichsen test machine, rust from the weld zone was not observed after the continuous spray test of 5%NaCl. In test pieces No. 1 to 21 which were more severely worked to have a bulge height of 7mm, rust was not observed in test pieces having BI value of 0.4 or less, and rust was observed in test pieces having BI value exceeding 0.4.
  • On the other hand, the test pieces Nos. 22, 24, 26 to 28 having BI value exceeding 0.8 showed large formation length ratio of black spots after the TIG welding and rust from the weld zone was observed in each specimen in the corrosion test. Magnified images of rust portions of test pieces Nos. 22, 24, 26 to 28 were observed using a magnifying glass. As a result, exfoliation was observed in the boundary between the black spots and the weld bead portion. Rust was generated in corrosion test of Nos. 22, 26, 27, and 28 in which concentrations of Al, Ti, Si, and Ca exceeded the regulated values. Occurrence of rust was observed in the corrosion test of the test piece No. 25 in which component ratio of Cr was less than 16% and the test piece No. 23 in which component ratio of Ti was less than 0.05%.
  • Experimental example 1, not within the scope of the present invention.
  • Test materials were produced in accordance with the same manner as test piece No.1 except for that steel plates of 1 mm thick were produced by cold-rolling of ferritic stainless steels having the below described chemical components (compositions). Test piece A and test piece B were obtained using the test materials.
    • Chemical component (composition) Test piece A
  • C: 0.007%, N: 0.011%, Si: 0.12%, Mn: 0.18%, P: 0.22%, S: 0.001%, Cr: 19.4%, Al 0.06%, Ti: 0.15%, Ca: 0.000,5%, balance: iron and unavoidable impurities.
    • Test piece B
  • C: 0.009%, N: 0.010%. Si: 0.25%. Mn: 0.15%, P: 0.21%, S: 0.001%, Cr: 20.2%, Al: 0.15%, Ti: 0.19%, Ca: 0.0015%, balance: iron and unavoidable impurities.
  • The thus obtained test piece A and test piece B were subjected to TIG welding under the similar welding conditions as the test piece No. 1, and appearance of black spots generated in the back side during TIG welding was observed.
  • The results are shown in FIG. 1A and FIG. 1B.
  • FIG. 1A is a photograph that shows an appearance of black spots generated in back side during TIG welding. FIG. 1B is a schematic drawing that shows an appearance of black spots generated in back side during TIG welding and that corresponds to FIG. 1A.
  • In FIG. 1A and FIG. 1B, the left-side figures show a photograph and a drawing of test piece A in which BI value is 0.49, and the right-side figures show a photograph and a drawing of test piece B in which BI value is 1.07.
  • As shown by the arrows in FIG. 1A and FIG. 1B, spot-like black spots are observed dispersingly both in the test piece A with BI value of 0.49 and test piece B with BI value of 1.07. However, it is recognized that the black spots are generated in larger amount in test piece B (right-side photograph) having a larger BI value.
  • Two portions selected from the weld bead portion and the black spot portion of the test piece B with a BI value of 1.07 were subjected to auger electron spectroscopy (AES). The results are shown in FIG. 2A and FIG. 2B.
  • A FE (Field Emission) Auger Electron Spectroscopy was used in the AES analysis, and the analysis was performed until intensity of oxygen spectrum was almost not detected under conditions of an acceleration voltage of 10keV, a spot diameter of 40 nm, and a sputtering rate of 15 nm/min. Although a position dependent error may occur due to small spot of AES measurement, the results were applied as values showing approximate thickness.
  • FIG. 2A and FIG. 2B are graphs that show depth profile of elements (concentration distribution of elements in depth direction) in the black spot and the weld bead portion on the back side of the test piece as a result of AES analysis. FIG. 2A is a result of weld bead portion, and FIG. 2B is a result of a black spot.
  • As shown in FIG. 2A. the weld bead portion was an oxide having a thickness of several hundred Å that mainly contained Ti, and also contained Al and Si. On the other hand, as shown in FIG. 2B, the black spot was a thick oxide having a thickness of several thousand Å that mainly contained Al, and also contained Ti, Si, and Ca. From the graph of black spot shown in FIG. 2B, it was confirmed that Al was contained in the black spot at the highest concentration and Ca was contained in the black spot at high concentration irrespective of its small amount in the steel.
    • Experimental example 2
  • Test materials of ferritic stainless steel having various component ratios (compositions) were produced in accordance with the production method similar to that of test piece A, where each steel had a basic composition of C: 0.002 to 0.015%, N: 0.02 to 0.015%, Cr: 16.5 to 23%, Ni: 0 to 1.5%, Mo: 0 to 2.5%, and also contained main components of black spots such as Al, Ti, Si, and Ca in different amount. Using the test materials, a plurality of test pieces was obtained.
  • The thus obtained plurality of test pieces were subjected to TIG welding under similar welding conditions as the test piece No. 1, and ratios of formation length of black spots were calculated in accordance with the same manner as the test piece No. 1.
  • As a result, the formation length ratio of black spots tended to increase in accordance with the increasing amounts of Al, Ti, Si, and Ca. Those elements are elements having specifically strong affinity with oxygen. It was found that Al had the highest effect, and Ca had a strong influence on black spots irrespective of its small amount in the steel. It was also confirmed that Ti and Si also contributed to the generation of black spots.
  • Based on the results, it was found that there was a strong possibility of generation of black spots even under shielding conditions where large amounts of Al, Ti, Si, and Ca were added, and that Al and Ti had strong influence on generation of black spots.
  • BI value shown by the below described formula 1 was calculated for the plurality of test pieces, and the relationship between the BI value and the ratio of formation length of black spots was examined. BI = 3 ⁢ Al + Ti + 0.5 ⁢ Si + 200 ⁢ Ca ≤ 0.8
    Figure imgb0002
     where Al, Ti, Si, and Ca in the formula 1 respectively denotes an amount of each element in mass % of the steel.
  • The results are shown in FIG. 3. FIG. 3 is a graph showing the relationship between the BI value and the ratio of formation length of black spots. As shown in FIG. 3, it is recognized that the ratio of formation length of black spots increases with an increasing BI value.
  • Each of the plurality of test pieces was subjected to corrosion test in accordance with the same manner as the test piece No. 1. The results are shown in FIG. 4. FIG. 4 is a graph that shows a relationship between the BI values and the results of corrosion resistance evaluation after the spray test after working. In the figure, double circles (Ⓞ) show excellent results, circles ( ○) show good results, and crosses (×) show bad results. As shown in FIG. 4, corrosion did not occur in the specimen with bulge height of 6 mm where BI value was 0.8 or less. Especially, where BI value was 0.4 or less, specifically good results were achieved such that corrosion was not observed in the specimen with bulge height of 7 mm.
    • INDUSTRIAL APPLICABILITY
  • The ferritic stainless steel of the present invention can be appropriately used in members requiring corrosion resistance in a structure of, for example, exterior materials, building materials, water or hot water containers, consumer electronics, kitchen equipment, drain water collectors and heat exchanger of gas condensing boiler, various welded pipes or the like that are formed by TIG welding and used in general indoor or outdoor environment. Specifically, the ferritic stainless steel of the present invention is appropriately used in a member that is subjected to working after the welding. Since the ferritic stainless steel of the present invention is excellent not only in corrosion resistance but also in workability of TIG weld zone, the steel can be widely used in the usage suffering severe working conditions.

Claims (10)

  1. A ferritic stainless steel for being welded by TIG welding consisting of, in mass %,
    0.002 to 0.020 % of C,
    0.002 to 0.025% of N,
    0.01 to 1.0% of Si,
    0.01 to 1.0% of Mn,
    0.001 to 0.035% of P,
    0.0001 to 0.01% of S,
    16.0 to 25.0% of Cr,
    0.01 to 0.12% of Al,
    0.05 to 0.35% of Ti,
    0.05 to 0.6% of Nb,
    present up to 0.0015% of Ca, and optionally one or more of 0.30 to 3.0 % of Mo, 0.05 to 2.0 % of Cu, 0.05 to 2.0 % of Ni,
    0.03 to 0.2% of V, 0.03 to 0.2% Zr and 0.0001 to 0.005% of B,
    the balance consisting of Fe and unavoidable impurities, wherein the following formula 1 is satisfied, BI = 3 ⁢ Al + Ti + 0.5 ⁢ Si + 200 ⁢ Ca ≤ 0.8
    Figure imgb0003
    where Al, Ti, Si, and Ca in the formula 1 each denotes an amount of each element in mass % of the steel.
  2. A ferritic stainless steel according to claim 1, containing, in mass %, 0.30 to 3.0% of Mo.
  3. A ferritic stainless steel according to claim 1 or 2, containing, in mass %, one or two selected from 0.05 to 2.0% of Cu and 0.05 to 2.0% of Ni.
  4. A ferritic stainless steel according to claim 1 or 2, containing, in mass %, one or two selected from 0.03 to 0.2% of V and 0.03 to 0.2% of Zr.
  5. A ferritic stainless steel according to claim 3, containing, in mass %, one or two selected from 0.03 to 0.2% of V and 0.03 to 0.2% of Zr.
  6. A ferritic stainless steel according to claim 1 or 2, containing, in mass %, 0.0001 to 0.005% of B.
  7. A ferritic stainless steel according to claim 3, containing, in mass %, 0.005% of B.
  8. A ferritic stainless steel according to claim 4, containing, in mass %, 0.0001 to 0.005% of B.
  9. A ferritic stainless steel according to claim 5, containing, in mass %, 0.0001 to 0.005% of B.
  10. Use of a ferritic stainless steel according to any one of claims 1 to 9 in members being welded by TIG welding.
EP11814699.2A 2010-08-06 2011-08-04 Ferritic stainless steel Active EP2602351B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2010177998A JP5793283B2 (en) 2010-08-06 2010-08-06 Ferritic stainless steel with few black spots
PCT/JP2011/067850 WO2012018074A1 (en) 2010-08-06 2011-08-04 Ferritic stainless steel

Publications (3)

Publication Number Publication Date
EP2602351A1 EP2602351A1 (en) 2013-06-12
EP2602351A4 EP2602351A4 (en) 2017-04-05
EP2602351B1 true EP2602351B1 (en) 2019-10-02

Family

ID=45559570

Family Applications (1)

Application Number Title Priority Date Filing Date
EP11814699.2A Active EP2602351B1 (en) 2010-08-06 2011-08-04 Ferritic stainless steel

Country Status (8)

Country Link
US (1) US20130129560A1 (en)
EP (1) EP2602351B1 (en)
JP (1) JP5793283B2 (en)
KR (1) KR20130034042A (en)
CN (1) CN103052731A (en)
AU (1) AU2011286685A1 (en)
TW (1) TWI526549B (en)
WO (1) WO2012018074A1 (en)

Families Citing this family (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6071608B2 (en) 2012-03-09 2017-02-01 新日鐵住金ステンレス株式会社 Ferritic stainless steel plate with excellent oxidation resistance
JP5793459B2 (en) 2012-03-30 2015-10-14 新日鐵住金ステンレス株式会社 Heat-resistant ferritic stainless steel cold-rolled steel sheet excellent in workability, ferritic stainless hot-rolled steel sheet for cold-rolled material, and production method thereof
FI124995B (en) * 2012-11-20 2015-04-15 Outokumpu Oy Ferritic stainless steel
WO2014087648A1 (en) * 2012-12-07 2014-06-12 Ｊｆｅスチール株式会社 Ferritic stainless steel sheet
MX2015013765A (en) 2013-03-27 2016-02-26 Nippon Steel & Sumikin Sst Hot-rolled ferritic stainless-steel plate, process for producing same, and steel strip.
JP5987821B2 (en) * 2013-12-27 2016-09-07 Ｊｆｅスチール株式会社 Ferritic stainless steel
JP5935792B2 (en) * 2013-12-27 2016-06-15 Ｊｆｅスチール株式会社 Ferritic stainless steel
US10272513B2 (en) * 2014-07-31 2019-04-30 Jfe Steel Corporation Ferritic stainless steel sheet for plasma arc welding and welding method therefor
US20190106775A1 (en) * 2016-03-29 2019-04-11 Jfe Steel Corporation Ferritic stainless steel sheet
ES2835273T3 (en) * 2016-06-27 2021-06-22 Jfe Steel Corp Ferritic stainless steel sheet
CN109563596A (en) * 2016-09-02 2019-04-02 杰富意钢铁株式会社 Ferrite-group stainless steel
WO2018043309A1 (en) 2016-09-02 2018-03-08 Ｊｆｅスチール株式会社 Ferritic stainless steel
JP2019044255A (en) * 2017-09-07 2019-03-22 Ｊｆｅスチール株式会社 Ferritic stainless steel sheet
JP7042057B2 (en) 2017-10-25 2022-03-25 日鉄ステンレス株式会社 Stainless steel materials and welded structural members with excellent slag spot generation suppression ability and their manufacturing methods
TWI801538B (en) * 2018-03-27 2023-05-11 日商日鐵不銹鋼股份有限公司 Ferritic stainless steel, method for producing the same, ferritic stainless steel sheet, method for producing the same, and members for fuel cell
ES2927078T3 (en) * 2018-12-21 2022-11-02 Outokumpu Oy ferritic stainless steel
JP7118015B2 (en) * 2019-01-16 2022-08-15 日鉄ステンレス株式会社 Method for predicting and evaluating the amount of slag spots generated in stainless steel
KR102326044B1 (en) * 2019-12-20 2021-11-15 주식회사 포스코 Ferritic stainless steel with improved magnetization properties and manufacturing method thereof

Family Cites Families (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5188413A (en) 1975-02-01 1976-08-03 Kotaishokuseifueraitosutenresuko
JP2739531B2 (en) * 1991-09-17 1998-04-15 日新製鋼株式会社 Ferritic stainless steel with excellent weld corrosion resistance
JP2880906B2 (en) 1993-05-19 1999-04-12 川崎製鉄株式会社 Ferritic stainless steel with excellent weather resistance and crevice corrosion resistance
JPH08144021A (en) * 1994-11-18 1996-06-04 Sumitomo Metal Ind Ltd Production of ferritic stainless steel and cold rolled sheet therefrom
JPH1012212A (en) * 1996-06-18 1998-01-16 Yuasa Corp Sealed lead acid battery
JPH10102212A (en) * 1996-09-30 1998-04-21 Kawasaki Steel Corp Ferritic stainless steel sheet excellent in penetration at welding
JP3190290B2 (en) * 1997-09-26 2001-07-23 日新製鋼株式会社 Ferritic stainless steel with excellent corrosion resistance at welds
JP4465853B2 (en) * 2000-10-30 2010-05-26 Ｊｆｅスチール株式会社 Ferritic stainless steel cold rolled steel for jar pot containers and ferritic stainless steel containers for jar pots with excellent corrosion resistance and scale adhesion
JP3976660B2 (en) * 2002-10-10 2007-09-19 新日鐵住金ステンレス株式会社 Chromium-containing steel for container material, welding method thereof, and container material
JP4025171B2 (en) * 2002-10-29 2007-12-19 日本冶金工業株式会社 Stainless steel having excellent corrosion resistance, weldability and surface properties and method for producing the same
JP4397772B2 (en) * 2004-09-24 2010-01-13 新日鐵住金ステンレス株式会社 Manufacturing method of ferritic stainless steel sheet with excellent workability
JP4784239B2 (en) * 2005-02-28 2011-10-05 Ｊｆｅスチール株式会社 Ferritic stainless steel filler rod for TIG welding
JP2006241564A (en) 2005-03-07 2006-09-14 Nisshin Steel Co Ltd Ferritic stainless steel for welded structure
JP5119605B2 (en) * 2006-03-31 2013-01-16 Ｊｆｅスチール株式会社 Ferritic stainless steel with excellent corrosion resistance of welds
JP5010323B2 (en) * 2006-04-10 2012-08-29 日新製鋼株式会社 Ferritic stainless steel for hot water container with welded structure, hot water container and manufacturing method thereof
WO2008084838A1 (en) * 2007-01-12 2008-07-17 Jfe Steel Corporation Ferritic stainless steel sheet for water heater excellent in corrosion resistance at welded part and steel sheet toughness
JP5010301B2 (en) * 2007-02-02 2012-08-29 日新製鋼株式会社 Ferritic stainless steel for exhaust gas path member and exhaust gas path member
JP5111910B2 (en) * 2007-03-23 2013-01-09 新日鐵住金ステンレス株式会社 Ferritic stainless steel with low surface defects and excellent weldability and crevice corrosion resistance
JP2009091654A (en) * 2007-09-18 2009-04-30 Jfe Steel Kk Ferritic stainless steel having excellent weldability
JP4651682B2 (en) * 2008-01-28 2011-03-16 新日鐵住金ステンレス株式会社 High purity ferritic stainless steel with excellent corrosion resistance and workability and method for producing the same
JP5305289B2 (en) 2009-01-29 2013-10-02 日本電信電話株式会社 User authentication method, user authentication system, user terminal, user authentication device, user terminal program, and user authentication device program
JP5489759B2 (en) * 2009-02-09 2014-05-14 新日鐵住金ステンレス株式会社 Ferritic stainless steel with few black spots

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
None *

Also Published As

Publication number Publication date
TWI526549B (en) 2016-03-21
JP5793283B2 (en) 2015-10-14
KR20130034042A (en) 2013-04-04
EP2602351A1 (en) 2013-06-12
CN103052731A (en) 2013-04-17
TW201213559A (en) 2012-04-01
WO2012018074A1 (en) 2012-02-09
AU2011286685A1 (en) 2013-02-28
US20130129560A1 (en) 2013-05-23
EP2602351A4 (en) 2017-04-05
JP2012036444A (en) 2012-02-23

Similar Documents

Publication Publication Date Title
EP2602351B1 (en) Ferritic stainless steel
EP2395121B1 (en) Ferrite stainless steel with low black spot generation
EP3438310B1 (en) Ferritic stainless steel sheet used for tig welding
EP3029170B1 (en) Ferrite-martensite dual-phase stainless steel, and method for producing same
EP2787097B1 (en) Ferritic stainless steel
KR20090087072A (en) Ferritic stainless steel sheet for water heater excellent in corrosion resistance at welded part and steel sheet toughness
EP2799577B1 (en) Ferritic stainless steel
WO2014119189A1 (en) Coated electrode
EP3647452A1 (en) Steel sheet having excellent resistance to liquid metal embrittlement cracks and method for manufacturing same
US8900380B2 (en) Low-chromium stainless steel excellent in corrosion resistance of weld
TW201207128A (en) Structural stainless steel sheet having excellent corrosion resistance at weld and method for manufacturing same
EP3901292A1 (en) Cr-based stainless steel having excellent hydrogen embrittlement resistance
JP3247244B2 (en) Fe-Cr-Ni alloy with excellent corrosion resistance and workability
US7429302B2 (en) Stainless steel sheet for welded structural components and method for making the same
JP6354772B2 (en) Ferritic stainless steel
JP5012194B2 (en) Ferritic stainless steel sheet for water heater with high welded joint strength and manufacturing method thereof
WO2021201122A1 (en) Welded structure and storage tank
JP6262893B1 (en) Ferritic stainless steel and welded structures
JPH0641697A (en) Fe-cr alloy excellent in corrosion resistance

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 20130305

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

DAX Request for extension of the european patent (deleted)
RA4 Supplementary search report drawn up and despatched (corrected)

Effective date: 20170306

RIC1 Information provided on ipc code assigned before grant

Ipc: C22C 38/24 20060101ALI20170228BHEP

Ipc: C22C 38/06 20060101ALI20170228BHEP

Ipc: C22C 38/40 20060101ALI20170228BHEP

Ipc: C22C 38/28 20060101ALI20170228BHEP

Ipc: C22C 38/20 20060101ALI20170228BHEP

Ipc: C22C 38/26 20060101ALI20170228BHEP

Ipc: C21D 8/02 20060101ALI20170228BHEP

Ipc: C22C 38/00 20060101AFI20170228BHEP

Ipc: F28F 21/08 20060101ALI20170228BHEP

Ipc: C22C 38/22 20060101ALI20170228BHEP

Ipc: C21D 6/00 20060101ALI20170228BHEP

Ipc: C22C 38/02 20060101ALI20170228BHEP

Ipc: C22C 38/04 20060101ALI20170228BHEP

Ipc: C22C 38/42 20060101ALI20170228BHEP

REG Reference to a national code

Ref country code: DE

Ref legal event code: R079

Ref document number: 602011062497

Country of ref document: DE

Free format text: PREVIOUS MAIN CLASS: C22C0038280000

Ipc: C22C0038000000

GRAP Despatch of communication of intention to grant a patent

Free format text: ORIGINAL CODE: EPIDOSNIGR1

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: GRANT OF PATENT IS INTENDED

RIC1 Information provided on ipc code assigned before grant

Ipc: C22C 38/26 20060101ALI20190208BHEP

Ipc: C22C 38/24 20060101ALI20190208BHEP

Ipc: C22C 38/28 20060101ALI20190208BHEP

Ipc: C21D 8/02 20060101ALI20190208BHEP

Ipc: C22C 38/22 20060101ALI20190208BHEP

Ipc: C22C 38/40 20060101ALI20190208BHEP

Ipc: C21D 6/00 20060101ALI20190208BHEP

Ipc: C22C 38/04 20060101ALI20190208BHEP

Ipc: C22C 38/42 20060101ALI20190208BHEP

Ipc: C22C 38/00 20060101AFI20190208BHEP

Ipc: C22C 38/02 20060101ALI20190208BHEP

Ipc: C22C 38/06 20060101ALI20190208BHEP

Ipc: C22C 38/20 20060101ALI20190208BHEP

Ipc: F28F 21/08 20060101ALI20190208BHEP

INTG Intention to grant announced

Effective date: 20190226

GRAS Grant fee paid

Free format text: ORIGINAL CODE: EPIDOSNIGR3

GRAJ Information related to disapproval of communication of intention to grant by the applicant or resumption of examination proceedings by the epo deleted

Free format text: ORIGINAL CODE: EPIDOSDIGR1

GRAL Information related to payment of fee for publishing/printing deleted

Free format text: ORIGINAL CODE: EPIDOSDIGR3

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: REQUEST FOR EXAMINATION WAS MADE

GRAR Information related to intention to grant a patent recorded

Free format text: ORIGINAL CODE: EPIDOSNIGR71

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: GRANT OF PATENT IS INTENDED

INTC Intention to grant announced (deleted)
GRAA (expected) grant

Free format text: ORIGINAL CODE: 0009210

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE PATENT HAS BEEN GRANTED

INTG Intention to grant announced

Effective date: 20190730

AK Designated contracting states

Kind code of ref document: B1

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

REG Reference to a national code

Ref country code: GB

Ref legal event code: FG4D

REG Reference to a national code

Ref country code: CH

Ref legal event code: EP

Ref country code: AT

Ref legal event code: REF

Ref document number: 1186239

Country of ref document: AT

Kind code of ref document: T

Effective date: 20191015

REG Reference to a national code

Ref country code: DE

Ref legal event code: R096

Ref document number: 602011062497

Country of ref document: DE

REG Reference to a national code

Ref country code: IE

Ref legal event code: FG4D

REG Reference to a national code

Ref country code: SE

Ref legal event code: TRGR

REG Reference to a national code

Ref country code: NL

Ref legal event code: MP

Effective date: 20191002

REG Reference to a national code

Ref country code: LT

Ref legal event code: MG4D

REG Reference to a national code

Ref country code: AT

Ref legal event code: MK05

Ref document number: 1186239

Country of ref document: AT

Kind code of ref document: T

Effective date: 20191002

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: PT

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200203

Ref country code: BG

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200102

Ref country code: GR

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200103

Ref country code: PL

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: NO

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200102

Ref country code: LV

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: ES

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: NL

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: LT

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: AT

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: CZ

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: IS

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200224

Ref country code: HR

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: RS

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: AL

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

REG Reference to a national code

Ref country code: DE

Ref legal event code: R097

Ref document number: 602011062497

Country of ref document: DE

PG2D Information on lapse in contracting state deleted

Ref country code: IS

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: DK

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: EE

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: RO

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: IS

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20200202

PLBE No opposition filed within time limit

Free format text: ORIGINAL CODE: 0009261

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: NO OPPOSITION FILED WITHIN TIME LIMIT

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: SM

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: SK

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

26N No opposition filed

Effective date: 20200703

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: SI

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: MC

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

REG Reference to a national code

Ref country code: CH

Ref legal event code: PL

GBPC Gb: european patent ceased through non-payment of renewal fee

Effective date: 20200804

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: CH

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20200831

Ref country code: LI

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20200831

Ref country code: LU

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20200804

REG Reference to a national code

Ref country code: BE

Ref legal event code: MM

Effective date: 20200831

REG Reference to a national code

Ref country code: FI

Ref legal event code: PCE

Owner name: NIPPON STEEL STAINLESS STEEL CORPORATION

REG Reference to a national code

Ref country code: DE

Ref legal event code: R081

Ref document number: 602011062497

Country of ref document: DE

Owner name: NIPPON STEEL STAINLESS STEEL CORPORATION, JP

Free format text: FORMER OWNER: NIPPON STEEL & SUMIKIN STAINLESS STEEL CORPORATION, TOKYO, JP

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: BE

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20200831

Ref country code: IE

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20200804

Ref country code: GB

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20200804

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: TR

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: MT

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

Ref country code: CY

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: MK

Free format text: LAPSE BECAUSE OF FAILURE TO SUBMIT A TRANSLATION OF THE DESCRIPTION OR TO PAY THE FEE WITHIN THE PRESCRIBED TIME-LIMIT

Effective date: 20191002

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: IT

Payment date: 20230811

Year of fee payment: 13

Ref country code: FI

Payment date: 20230808

Year of fee payment: 13

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: SE

Payment date: 20230815

Year of fee payment: 13

Ref country code: FR

Payment date: 20230811

Year of fee payment: 13

Ref country code: DE

Payment date: 20230830

Year of fee payment: 13