EP2617854A1 - Heat-resistant ferrite-type stainless steel plate having excellent oxidation resistance - Google Patents
Heat-resistant ferrite-type stainless steel plate having excellent oxidation resistance Download PDFInfo
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- EP2617854A1 EP2617854A1 EP11825311.1A EP11825311A EP2617854A1 EP 2617854 A1 EP2617854 A1 EP 2617854A1 EP 11825311 A EP11825311 A EP 11825311A EP 2617854 A1 EP2617854 A1 EP 2617854A1
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- Prior art keywords
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- oxidation resistance
- stainless steel
- steel
- resistance
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- 230000003647 oxidation Effects 0.000 title claims abstract description 56
- 238000007254 oxidation reaction Methods 0.000 title claims abstract description 56
- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 29
- 239000010935 stainless steel Substances 0.000 title claims description 9
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 11
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 9
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 8
- 229910052802 copper Inorganic materials 0.000 claims abstract description 7
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 7
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 7
- 229910052799 carbon Inorganic materials 0.000 claims description 10
- 229910052750 molybdenum Inorganic materials 0.000 claims description 9
- 229910052758 niobium Inorganic materials 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 abstract description 2
- 229910000831 Steel Inorganic materials 0.000 description 54
- 239000010959 steel Substances 0.000 description 54
- 230000000694 effects Effects 0.000 description 20
- 230000007797 corrosion Effects 0.000 description 15
- 238000005260 corrosion Methods 0.000 description 15
- 239000004615 ingredient Substances 0.000 description 11
- 238000005096 rolling process Methods 0.000 description 11
- 230000015572 biosynthetic process Effects 0.000 description 7
- 230000000087 stabilizing effect Effects 0.000 description 7
- 238000000137 annealing Methods 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 238000000034 method Methods 0.000 description 6
- 229910000859 α-Fe Inorganic materials 0.000 description 6
- 230000002159 abnormal effect Effects 0.000 description 5
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- 238000005097 cold rolling Methods 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- 238000004901 spalling Methods 0.000 description 4
- 238000009628 steelmaking Methods 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- 238000005098 hot rolling Methods 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 208000025599 Heat Stress disease Diseases 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000005554 pickling Methods 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- 229910052718 tin Inorganic materials 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- 229910001018 Cast iron Inorganic materials 0.000 description 1
- 229910020010 Nb—Si Inorganic materials 0.000 description 1
- 241000272534 Struthio camelus Species 0.000 description 1
- 241000009298 Trigla lyra Species 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000003779 heat-resistant material Substances 0.000 description 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 1
- 238000004881 precipitation hardening Methods 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- 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
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- 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
- C21D8/0273—Final recrystallisation annealing
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
-
- 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
- C22C38/004—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
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
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- 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
Definitions
- the present invention relates to a heat-resistant ferritic stainless steel sheet having excellent oxidation resistance which is optimal in particular for use for exhaust system members which require high temperature strength or oxidation resistance.
- Exhaust manifolds, front pipes, center pipers, and other exhaust system members of automobiles carry high temperature exhaust gas which is exhausted from the engines, so the materials forming the exhaust members are required to have various properties such as oxidation resistance, high temperature strength, and heat fatigue characteristics.
- exhaust manifolds have generally been made using cast iron, but from the viewpoints of stronger exhaust gas controls, improving engine performance, lightening the car body, etc., exhaust manifolds made of a stainless steel have come into use.
- Exhaust gas temperatures differ depending on the car model or engine structure, but 600 to 800°C or so is prevalent. A material which has an excellent high temperature strength and oxidation resistance in an environment where it is used for a long period of time in such a temperature region is demanded.
- an austenitic stainless steel has excellent heat resistance and workability, but has a large heat expansion coefficient, so when applied to a member like an exhaust manifold which is repeatedly subjected to heating and cooling, thermal fatigue breakage easily occurs.
- a ferritic stainless steel has a smaller heat expansion coefficient compared with the austenitic stainless steel, excellent heat fatigue characteristics, and scale spalling resistance. Further, compared with the austenitic stainless steel, since Ni is not contained, and the material cost is not expensive, therefore this is used for general applications. However, the ferritic stainless steel has lower high temperature strength compared with the austenitic stainless steel, so the art has been developed for improving the high temperature strength. For example, there are SUS430J1L (Nb steel), Nb-Si steel, and SUS444 (Nb-Mo steel). Each of these is predicated on addition of Nb. They used solution strengthening or precipitation strengthening by Nb to raise the high temperature strength.
- Nb steel also has problems such as the hardening of the finished sheets, the drop in elongation, and the low r-value which is an indicator of deep drawability. This is because the presence of solute Nb or precipitated Nb enables the hardening at room temperature or the growth of a recrystallized texture to be suppressed, but obstructs the press formability and shape freedom when shaping exhaust parts. Further, Nb is high material cost and raises the manufacturing cost as well. If the steel sheet would secure the high temperature characteristics by added elements other than Nb, it would be possible to keep down the amount of addition of Nb and provide the heat-resistant ferritic stainless steel sheet which has low cost and excellent workability. The Mo which is added to SUS444 results in a high alloy cost, so the problem of a remarkable rise in the part costs also arises.
- PLTs 1 to 6 disclose the art relating to addition of Cu.
- PLT 1 studies the addition of Cu in an amount of 0.5% or less so as to improve the low temperature toughness, but does not add it from the viewpoint of the heat resistance.
- PLT 2 is the art which utilizes its action in improving the corrosion resistance and weathering resistance of steel, but does not add it from the viewpoint of the heat resistance.
- PLTs 3 to 6 disclose the arts which utilize the precipitation hardening by Cu precipitates to improve the high temperature strength at the 600°C or 700 to 800°C temperature region.
- the inventors engaged in studies on steel ingredients not containing Nb, They studied in case of adding Cu and considered the effect of fine dispersion of Cu precipitates and thereby improving the high temperature strength. In addition, they engaged in detailed studies on the all important oxidation resistance in the heat-resistant steel sheet. As a result, examples of the oxidation resistance dropped sharply were found in steel which large amounts of Cu were added, compared with the steel to which Cu was not added, in the region exceeding 900°C. In particular, this trend was seen in the low Cr steel.
- the present invention has an object to improve the oxidation resistance of the Cu steel and to provide the heat-resistant ferritic stainless steel sheet which has excellent oxidation resistance.
- the inventors studied in detail a new ferritic stainless steel which keeps addition of the expensive Nb and Mo to a minimum and utilizes the relative inexpensive Cu to enable suitable use for exhaust parts. As a result, they invented the Cu ferritic stainless steel having excellent heat resistance and filed patent applications for them (Japanese Patent Application No. 2010-055944 and Japanese Patent Application No. 2010-072889 ).
- the inventors further studied in detail the oxidation resistance and discovered the occurrence of the phenomenon of the oxidation resistance rapidly deteriorating in the temperature region of over 900°C in the case of low Cr steel to which Cu is added. Further, they found that this phenomenon is correlated to the formation of a ⁇ -phase directly under the oxide scale. They also found that the formation of a ⁇ -phase causes the oxidation resistance to fall as a general trend. However, they found that even if a ⁇ -phase is formed with a small amount, a sufficient oxidation resistance can be maintained.
- ⁇ 23 % Ni + 9 % Cu + 7 % Mn - 11.5 % Cr - 11.5 % Si - 52 % Al - 49 ⁇ Ti % - 4 ⁇ % C + % N - 23 % V - 12 % Mo - 47 % Nb + 189
- This formula is based on the Castro formula (following formula (2)) for evaluation of the stability of the ⁇ -phase (following formula (2)).
- formula (2) carbon and nitrogen have direct effects on the stabilization of the ⁇ -phase.
- carbon and nitrogen are substantially fixed by Ti as carbonitrides, and do not directly contribute to ⁇ -stability. Further, the effect by Ti is limited to the part of Ti not fixed as carbonitrides. Therefore, based on the above such thinking, formula (2) was modified and the above formula (1) was derived.
- ⁇ p 420 % C + 470 % N + 23 % Ni + 23 % Ni + 9 % Cu + 7 % Mn - 11.5 % Cr - 11.5 % Si - 52 % Al - 49 [ Ti % - 23 % V - 12 % Mo - 47 % Nb + 189
- the above formula (1) is an indicator which shows easily formation of the ⁇ -phase in high purity ferritic stainless steel at 900°C to 1000°C.
- the larger the ⁇ p value the easier it is for the ⁇ -phase to be formed as a general trend.
- the ⁇ -value is a certain value (35) or less, even at 930°C, abnormal oxidation and scale spalling no longer occur and the oxidation resistance is remarkably improved. That is, by mutually adjusting the alloy ingredients according to this formula, it is possible to improve the high temperature strength by the addition of Cu, and obtain the heat-resistant ferritic stainless steel having excellent oxidation resistance.
- the present invention was made based on the above-type stainless e discovery and has as its gist the following:
- the heat-resistant ferritic stainless steel sheet is obtained even if not adding the expensive Nb and Mo.
- C degrades the shapeability and corrosion resistance and causes a drop in the high temperature strength.
- N degrades the shapeability and corrosion resistance and causes a drop in the high temperature strength.
- P is an ingredient which is unavoidably contained in the steel. But if included in over 0.04%, the toughness falls, the upper limit of P was 0.04%.
- S is an ingredient which is unavoidably contained in steel. But in the present invention, when included in over 0.01%, CaS easily forms. So the upper limit was 0.01%. Further, the content of S which is less than 0.0005% would cause an extremely large increase in the steelmaking costs. So the lower limit is 0.0005% preferably.
- Si is an element which improves the oxidation resistance and is a ferrite stabilizing element. Si is essential in the present invention and is positively added. Its effect is exhibited at 0.3% or more. Further, if over 1.5%, the workability remarkably falls and scale spalling is promoted. The upper limit was 1.5%. If considering the balance of the workability and the oxidation resistance, the content of Si which is 0.4% to 1.0% is more preferable.
- Mn is an element which improves the oxidation resistance and in particular is an element which improves the scale spalling resistance, and is an essential element in the present invention. However, it has the effect of increasing the increase in oxidation. If excessively added, abnormal oxidation easily occurs. Further, it is an austenite-forming element, in the present invention, the suitable range was 0.3 to 0.7%. If considering the workability, the content of Mn which is 0.3 to 0.6% is more preferable.
- Cr in the present invention, is an essential element for securing oxidation resistance and corrosion resistance. If Cr is less than 11.0%, the effect does not appear. The lower limit was 11.0%. Further, Cr is a ferrite stabilizing element. If over 17.0%, due to the amount of Cr, the ⁇ -phase stabilizes, and there is no longer a need to mutually adjust the elements. Therefore, the upper limit of the amount of Cr of the present invention was 17.0%. That is, the present invention, the lower the Cr is in the steel, the better effect exhibits. The preferable range is 12.0% to 15.0%.
- Cu is an element which is effective for improving the high temperature strength, in particular the high temperature strength in the medium temperature range of 600 to 800°C or so.
- the precipitation strengthening due to formation of Cu precipitates in this temperature region is the main cause. Furthermore, even if over 900°C, this has a certain extent of strength improving effect. This effect appears at 0.8% or more, so the lower limit was 0.8%. Further, if adding over 1.5%, the oxidation resistance and the workability deteriorate, so the upper limit was 1.5%. If considering the balance of the high temperature strength, oxidation resistance, and workability, the content of Cu which is 1.0 to 1.4% is preferable.
- Ni is an element which improves the corrosion resistance and the high temperature salt damage resistance. Its effect is exhibited with addition of 0.05% or more. However, this is an austenite stabilizing element, so excessive addition would cause the oxidation resistance to drop. Therefore, the upper limit is 1.0%. If considering the workability, addition of a trace amount is preferable, the content of Ni which is 0.05 to 0.50% is more suitable.
- V is added since it is a ferrite stabilizing element. However, if over 0.5%, the hot rolled plate falls in toughness, the upper limit is 0.5%. If considering the steelmaking costs and workability, the content of V which is 0.03% to 0.5% is preferable.
- Al is an element which is added as a deoxidizing element and is also added in accordance with need for improving the oxidation resistance. Further, it is a ferrite stabilizing element and improves the oxidation resistance. Excessive addition causes hardening and a remarkable drop in the uniform elongation and also causes the toughness to remarkably fall, so the upper limit was 0.1%. Furthermore, if considering the formation of surface defects, weldability, and manufacturability, the content of Al which is 0.01 to 0.05% is preferable.
- Ti is an element which bonds with C and N to improve the corrosion resistance, intergranular corrosion resistance, room temperature ductility, and deep drawability.
- the exhaust system members etc. for which the steel sheet of the present invention is used are usually welded structures. So intergranular corrosion resistance is essential.
- the amount of addition of Ti is important. These effects appear at 10(C+N)% or more. The lower limit was 10(C+N)%. Further, on the other hand, if adding over 0.3%, the oxidation resistance falls. The upper limit was 0.3%. If considering the workability and the manufacturability, the content of Ti which is 10(C+N) to 0.25% is preferable.
- Nb is expensive, but is an element which improves the high temperature strength and is a ferrite stabilizing element. When Nb adds even in a trace amount, Nb can improve the heat resistance and oxidation resistance. The effect appears at 0.001% or more. When adding over 0.3%, the effect of improving the high temperature strength becomes smaller. The upper limit was 0.3%.
- Mo is also expensive, but is an element which improves the high temperature strength and is a ferrite stabilizing element. When Mo adds even in a trace amount, Mo can improve the heat resistance and oxidation resistance. The effect appears at 0.01% or more. When adding over 0.5%, the effect of improving the high temperature strength becomes smaller. The upper limit was made 0.5%.
- B is an element which improves the secondary workability at the time of press forming a product. This effect acts from 0.0003%, so the lower limit was 0.0003%. Excessive addition results in hardening and a problem with intergranular corrosion due to the formation of precipitates of Cr and B. Further, the problem of weld cracks also arises. The upper limit was 0.0050%. Furthermore, if considering the manufacturability, the content of B is 0.0003 to 0.0015% preferably.
- Zr is a more powerful carbonitride forming element than Ti. It can fix carbonitrides at a higher temperature, so can be expected to have the effect of lowering the austenite phase stability. However, excessive addition causes a drop in the manufacturability. The upper limit was 1.0%.
- Sn is an element which has a large atomic radius and is effective for solution strengthening at a high temperature. Sn is an element which results in only a little drop in mechanical properties at room temperature, and is added in accordance with need. However, if excessively added, the manufacturability and the weldability fall. The upper limit was 1.0%.
- Co is an element which improves the high temperature strength, but if excessively added, the manufacturability falls.
- the upper limit was 0.5%.
- the method of production of the steel sheet of the present invention is comprised of the steps of steelmaking, hot rolling, pickling, cold rolling, and annealing and pickling.
- the steel which contains the above essential ingredients and ingredients which are added in accordance with need is suitably produced in a converter and then secondarily refined.
- the produced molten steel is made into a slab by a known casting method (continuous casting).
- the slab is heated to a predetermined temperature and is hot rolled by continuous rolling to a predetermined plate thickness.
- the cold rolling of the stainless steel sheet is usually performed by reverse rolling by a Sendzimir rolling mill or one-directional rolling by a tandem rolling mill.
- tandem rolling is superior in productivity compared with Sendzimir rolling and also raises the r-value indicator of workability. It is preferable to perform the cold rolling by a tandem rolling mill which a roll diameter is a 400 mm or more.
- the annealing of the hot rolled plate which is usually performed in the production of ferritic stainless steel sheet is preferably omitted, but the hot rolled plate may also be annealed.
- the other steps of the method of production are not particularly defined.
- the hot rolling conditions, hot rolled plate thickness, cold rolled sheet annealing temperature, atmosphere, etc. may be suitably selected. Further, after the cold rolling and annealing, temper rolling may be performed or a tension leveler may be applied. Furthermore, the final sheet thickness may be suitably selected in accordance with the demanded thickness of the member.
- the steel of each of the compositions of ingredients which are shown in Table 1 was produced and cast into a slab.
- the slab was hot rolled to obtain a 5 mm thick hot rolled coil.
- the hot rolled coil was pickled and was cold rolled down to a 2 mm thickness, then was annealed and pickled to obtain a product sheet.
- the annealing temperature of the cold rolled sheet was made 850 to 1000°C so as to make the grain size number about 6 to 8.
- the annealing time was 120 seconds.
- Nos. 1 to 15 are invention steels
- Nos. 16 to 39 are comparative steels.
- the No. 1A steel and the No. 2A steel are steels of the same ingredients as respectively the No. 1 steel and No.
- the hot rolled plates are annealed at 850 to 1000°C for 120 seconds, then are pickled in the same way as other steels and, furthermore, cold rolled, annealed, and pickled to obtain the final sheets.
- high temperature tensile test pieces were taken, subjected to tensile tests at 800°C and 900°C, and measured for 0.2% yield stress (based on JISG0567).
- 25 MPa at 800°C and 15 MPa at 900°C levels substantially equal to those of 0.4Nb-1Si steel currently most generally used as steel for exhaust manifolds, were used as the passing criteria.
- the ingredient elements are in the ranges of the present invention, but the ⁇ -values are over 35, so abnormal oxidation occurs at 930°C and the oxidation resistances are inferior.
- the Nos. 18 and 19 steels respectively have C and N outside the upper limit and are inferior in high temperature strength, oxidation resistance, and workability.
- the No. 20 steel has insufficient Si and is inferior in oxidation resistance.
- the No. 21 steel has Si added in excess and is inferior in workability.
- the No. 22 has little addition of Mn and is inferior in oxidation resistance.
- the No. 23 steel has Mn added in excess and is inferior in oxidation resistance and workability.
- the No. 24 has P added in excess, is inferior in toughness, and exhibited fine cracks in the hot rolled plate at the stage of production of steel sheets.
- the No. 25 steel has S added in excess and was confirmed to have the formation of CaS - the cause of deterioration of the corrosion resistance.
- the No. 26 steel has a small amount of Cr, and is low in high temperature strength and is inferior in oxidation resistance.
- the No. 27 steel has a small amount of addition of Cu and is inferior in high temperature strength.
- the No. 28 steel has Cu added in excess and is inferior in workability.
- the No. 29 steel has Ni added in excess and is inferior in workability.
- the No. 30 steel has V added in excess and is inferior in workability.
- the No. 31 steel has Al added in excess and is inferior in workability.
- the No. 25 steel has S added in excess and was confirmed to have the formation of CaS - the cause of deterioration of the corrosion resistance.
- the No. 26 steel has a small amount of Cr
- the 32 steel has a small amount of addition of Ti and is inferior in intergranular corrosion resistance.
- the No. 33 steel has Ti added in excess and is inferior in workability.
- the No. 34 steel has Nb added in excess and is inferior in workability.
- the No. 35 steel has Mo added in excess and is inferior in workability.
- the No. 36 steel has B added in excess, is inferior in workability, and is inferior in intergranular corrosion resistance.
- the Nos. 37, 38, and 39 steels respectively have Zr, Sn, and Co added in excess. But it is found that these steels are inferior in workability, exhibit fine cracks in the hot rolled plates when producing steel sheet, and are inferior in manufacturability.
- the present invention it is possible to provide the heat-resistant stainless steel sheet having excellent oxidation resistance even without adding large amounts of expensive alloy elements such as Nb or Mo.
- the part costs are reduced and the weight can be lightened by application to exhaust members.
- the social contribution, including protection of the environments, is extremely great.
Abstract
Description
- The present invention relates to a heat-resistant ferritic stainless steel sheet having excellent oxidation resistance which is optimal in particular for use for exhaust system members which require high temperature strength or oxidation resistance.
- Exhaust manifolds, front pipes, center pipers, and other exhaust system members of automobiles carry high temperature exhaust gas which is exhausted from the engines, so the materials forming the exhaust members are required to have various properties such as oxidation resistance, high temperature strength, and heat fatigue characteristics.
- In the past, in automobile exhaust members, exhaust manifolds have generally been made using cast iron, but from the viewpoints of stronger exhaust gas controls, improving engine performance, lightening the car body, etc., exhaust manifolds made of a stainless steel have come into use. Exhaust gas temperatures differ depending on the car model or engine structure, but 600 to 800°C or so is prevalent. A material which has an excellent high temperature strength and oxidation resistance in an environment where it is used for a long period of time in such a temperature region is demanded.
- In the stainless steel, an austenitic stainless steel has excellent heat resistance and workability, but has a large heat expansion coefficient, so when applied to a member like an exhaust manifold which is repeatedly subjected to heating and cooling, thermal fatigue breakage easily occurs.
- On the other hand, a ferritic stainless steel has a smaller heat expansion coefficient compared with the austenitic stainless steel, excellent heat fatigue characteristics, and scale spalling resistance. Further, compared with the austenitic stainless steel, since Ni is not contained, and the material cost is not expensive, therefore this is used for general applications. However, the ferritic stainless steel has lower high temperature strength compared with the austenitic stainless steel, so the art has been developed for improving the high temperature strength. For example, there are SUS430J1L (Nb steel), Nb-Si steel, and SUS444 (Nb-Mo steel). Each of these is predicated on addition of Nb. They used solution strengthening or precipitation strengthening by Nb to raise the high temperature strength.
- In this regard, Nb steel also has problems such as the hardening of the finished sheets, the drop in elongation, and the low r-value which is an indicator of deep drawability. This is because the presence of solute Nb or precipitated Nb enables the hardening at room temperature or the growth of a recrystallized texture to be suppressed, but obstructs the press formability and shape freedom when shaping exhaust parts. Further, Nb is high material cost and raises the manufacturing cost as well. If the steel sheet would secure the high temperature characteristics by added elements other than Nb, it would be possible to keep down the amount of addition of Nb and provide the heat-resistant ferritic stainless steel sheet which has low cost and excellent workability. The Mo which is added to SUS444 results in a high alloy cost, so the problem of a remarkable rise in the part costs also arises.
- PLTs 1 to 6 disclose the art relating to addition of Cu. PLT 1 studies the addition of Cu in an amount of 0.5% or less so as to improve the low temperature toughness, but does not add it from the viewpoint of the heat resistance. PLT 2 is the art which utilizes its action in improving the corrosion resistance and weathering resistance of steel, but does not add it from the viewpoint of the heat resistance. PLTs 3 to 6 disclose the arts which utilize the precipitation hardening by Cu precipitates to improve the high temperature strength at the 600°C or 700 to 800°C temperature region.
-
- PLT 1: Japanese Unexamined Patent Publication No.
2006-37176 A2 - PLT 2: Japanese Patent No.
3446667 B2 - PLT 3:
WO2003/004714 Al - PLT 4: Japanese Patent No.
3468156 B2 - PLT 5: Japanese Patent No.
3397167 B2 - PLT 6: Japanese Unexamined Patent Publication No.
2008-240143 Al - The inventors engaged in studies on steel ingredients not containing Nb, They studied in case of adding Cu and considered the effect of fine dispersion of Cu precipitates and thereby improving the high temperature strength. In addition, they engaged in detailed studies on the all important oxidation resistance in the heat-resistant steel sheet. As a result, examples of the oxidation resistance dropped sharply were found in steel which large amounts of Cu were added, compared with the steel to which Cu was not added, in the region exceeding 900°C. In particular, this trend was seen in the low Cr steel.
- In exhaust system members, there is a possibility of the exhaust gas temperature rising despite of the non-steady state. It is preferable to be able to maintain a stable oxidation resistance even over 900°C. Further, it can be used as a member which high strength is not required.
- From the above description, the present invention has an object to improve the oxidation resistance of the Cu steel and to provide the heat-resistant ferritic stainless steel sheet which has excellent oxidation resistance.
- In the present invention, for the purpose of providing a low cost heat-resistant material, the inventors studied in detail a new ferritic stainless steel which keeps addition of the expensive Nb and Mo to a minimum and utilizes the relative inexpensive Cu to enable suitable use for exhaust parts. As a result, they invented the Cu ferritic stainless steel having excellent heat resistance and filed patent applications for them (Japanese Patent Application No.
2010-055944 2010-072889 - In the present invention, the inventors further studied in detail the oxidation resistance and discovered the occurrence of the phenomenon of the oxidation resistance rapidly deteriorating in the temperature region of over 900°C in the case of low Cr steel to which Cu is added. Further, they found that this phenomenon is correlated to the formation of a γ-phase directly under the oxide scale. They also found that the formation of a γ-phase causes the oxidation resistance to fall as a general trend. However, they found that even if a γ-phase is formed with a small amount, a sufficient oxidation resistance can be maintained. The inventors studied the addition of various alloy ingredients based on these new findings and discovered that a correlation is seen between the γ-value which is defined by the following formula (1) and the oxidation resistance:
- This formula is based on the Castro formula (following formula (2)) for evaluation of the stability of the γ-phase (following formula (2)). In formula (2), carbon and nitrogen have direct effects on the stabilization of the γ-phase. On the other hand, in the high purity ferritic stainless steel which is covered by the present invention, at 1000°C or less, carbon and nitrogen are substantially fixed by Ti as carbonitrides, and do not directly contribute to γ-stability. Further, the effect by Ti is limited to the part of Ti not fixed as carbonitrides. Therefore, based on the above such thinking, formula (2) was modified and the above formula (1) was derived.
- The above formula (1) is an indicator which shows easily formation of the γ-phase in high purity ferritic stainless steel at 900°C to 1000°C. The larger the γp value, the easier it is for the γ-phase to be formed as a general trend. In accordance with this formula (1), if the γ-value is a certain value (35) or less, even at 930°C, abnormal oxidation and scale spalling no longer occur and the oxidation resistance is remarkably improved. That is, by mutually adjusting the alloy ingredients according to this formula, it is possible to improve the high temperature strength by the addition of Cu, and obtain the heat-resistant ferritic stainless steel having excellent oxidation resistance.
- The present invention was made based on the above-type stainless e discovery and has as its gist the following:
- (1) A ferritic stainless steel sheet having excellent heat resistant and oxidation resistance comprising: by mass%, C: 0.015% or less, N: 0.020% or less, P: 0.04% or less, S: 0.01% or less, Si: 0.3 to 1.5%, Mn: 0.3 to 0.7%, Cr: 11.0 to 17.0%, Cu: 0.8 to 1.5%, Ni: 0.05 to 1.0%, V: 0.5% or less, Al: 0.01 to 0.1%, and Ti: 10(C+N) to 0.3%; the amounts of the elements being mutually adjusted such that the γ-value which is defined by the following formula (1), becomes 35 or less, and has a balance of Fe and unavoidable impurities:
- (2) Furthermore, the ferritic stainless steel sheet having excellent heat-resistance and oxidation resistance as set forth in (1), wherein the stainless steel sheet further comprises, by mass%, at least one or more of Nb: 0.001 to 0.3%, Mo: 0.01 to 0.5%, and B: 0.0003 to 0.0050%.
- (3) Furthermore, the ferritic stainless steel sheet having excellent heat-resistance and oxidation resistance as set forth in (1) or (2), wherein the stainless steel sheet further comprises, by mass%, at least one or more of Zr: 1.0% or less, Sn: 1.0% or less, and Co: 0.5% or less.
- According to the present invention, the heat-resistant ferritic stainless steel sheet is obtained even if not adding the expensive Nb and Mo. By applying this in particular to the exhaust system members of automobiles, boilers, etc. a great effect can be obtained in protecting the environments and lowering the costs of parts.
- Here, absence of defined lower limits means inclusion of up to the level of unavoidable impurities. The reasons for limitation of the present invention will be explained as below. "%" means mass%.
- C degrades the shapeability and corrosion resistance and causes a drop in the high temperature strength. The smaller the content, the higher temperature strength is obtained. Therefore the content of C was 0.015% or less. Furthermore, excessive reduction would increase the refining costs. Considering oxidation resistance, the content of C is 0.002 to 0.010% preferably.
- N, like C, degrades the shapeability and corrosion resistance and causes a drop in the high temperature strength. The smaller the content, the higher temperature strength is obtained. Therefore the content of N was 0.020% or less. Furthermore, excessive reduction would increase the refining costs. Considering oxidation resistance, the content of N is 0.002 to 0.015% preferably.
- P is an ingredient which is unavoidably contained in the steel. But if included in over 0.04%, the toughness falls, the upper limit of P was 0.04%.
- S is an ingredient which is unavoidably contained in steel. But in the present invention, when included in over 0.01%, CaS easily forms. So the upper limit was 0.01%. Further, the content of S which is less than 0.0005% would cause an extremely large increase in the steelmaking costs. So the lower limit is 0.0005% preferably.
- Si is an element which improves the oxidation resistance and is a ferrite stabilizing element. Si is essential in the present invention and is positively added. Its effect is exhibited at 0.3% or more. Further, if over 1.5%, the workability remarkably falls and scale spalling is promoted. The upper limit was 1.5%. If considering the balance of the workability and the oxidation resistance, the content of Si which is 0.4% to 1.0% is more preferable.
- Mn is an element which improves the oxidation resistance and in particular is an element which improves the scale spalling resistance, and is an essential element in the present invention. However, it has the effect of increasing the increase in oxidation. If excessively added, abnormal oxidation easily occurs. Further, it is an austenite-forming element, in the present invention, the suitable range was 0.3 to 0.7%. If considering the workability, the content of Mn which is 0.3 to 0.6% is more preferable.
- Cr, in the present invention, is an essential element for securing oxidation resistance and corrosion resistance. If Cr is less than 11.0%, the effect does not appear. The lower limit was 11.0%. Further, Cr is a ferrite stabilizing element. If over 17.0%, due to the amount of Cr, the α-phase stabilizes, and there is no longer a need to mutually adjust the elements. Therefore, the upper limit of the amount of Cr of the present invention was 17.0%. That is, the present invention, the lower the Cr is in the steel, the better effect exhibits. The preferable range is 12.0% to 15.0%.
- Cu is an element which is effective for improving the high temperature strength, in particular the high temperature strength in the medium temperature range of 600 to 800°C or so. The precipitation strengthening due to formation of Cu precipitates in this temperature region is the main cause. Furthermore, even if over 900°C, this has a certain extent of strength improving effect. This effect appears at 0.8% or more, so the lower limit was 0.8%. Further, if adding over 1.5%, the oxidation resistance and the workability deteriorate, so the upper limit was 1.5%. If considering the balance of the high temperature strength, oxidation resistance, and workability, the content of Cu which is 1.0 to 1.4% is preferable.
- Ni is an element which improves the corrosion resistance and the high temperature salt damage resistance. Its effect is exhibited with addition of 0.05% or more. However, this is an austenite stabilizing element, so excessive addition would cause the oxidation resistance to drop. Therefore, the upper limit is 1.0%. If considering the workability, addition of a trace amount is preferable, the content of Ni which is 0.05 to 0.50% is more suitable.
- V is added since it is a ferrite stabilizing element. However, if over 0.5%, the hot rolled plate falls in toughness, the upper limit is 0.5%. If considering the steelmaking costs and workability, the content of V which is 0.03% to 0.5% is preferable.
- Al is an element which is added as a deoxidizing element and is also added in accordance with need for improving the oxidation resistance. Further, it is a ferrite stabilizing element and improves the oxidation resistance. Excessive addition causes hardening and a remarkable drop in the uniform elongation and also causes the toughness to remarkably fall, so the upper limit was 0.1%. Furthermore, if considering the formation of surface defects, weldability, and manufacturability, the content of Al which is 0.01 to 0.05% is preferable.
- Ti is an element which bonds with C and N to improve the corrosion resistance, intergranular corrosion resistance, room temperature ductility, and deep drawability. In particular, the exhaust system members etc. for which the steel sheet of the present invention is used, are usually welded structures. So intergranular corrosion resistance is essential. The amount of addition of Ti is important. These effects appear at 10(C+N)% or more. The lower limit was 10(C+N)%. Further, on the other hand, if adding over 0.3%, the oxidation resistance falls. The upper limit was 0.3%. If considering the workability and the manufacturability, the content of Ti which is 10(C+N) to 0.25% is preferable.
- To improve the oxidation resistance in the ranges of these alloy elements, it is necessary to mutually adjust the elements so that the γ-value given by the following formula (1) becomes 35 or less. If over 35, a γ-phase is easily formed under the scale at a high temperature region of over 900°C and abnormal oxidation easily occurs, so this is not preferable., Note that the effect of unavoidable impurities is considered to be zero. The grounds for deriving the formula (1) are as follows:
- In the present invention, the following elements may also be added in accordance with the desired properties.
- Nb is expensive, but is an element which improves the high temperature strength and is a ferrite stabilizing element. When Nb adds even in a trace amount, Nb can improve the heat resistance and oxidation resistance. The effect appears at 0.001% or more. When adding over 0.3%, the effect of improving the high temperature strength becomes smaller. The upper limit was 0.3%.
- Mo is also expensive, but is an element which improves the high temperature strength and is a ferrite stabilizing element. When Mo adds even in a trace amount, Mo can improve the heat resistance and oxidation resistance. The effect appears at 0.01% or more. When adding over 0.5%, the effect of improving the high temperature strength becomes smaller. The upper limit was made 0.5%.
- B is an element which improves the secondary workability at the time of press forming a product. This effect acts from 0.0003%, so the lower limit was 0.0003%. Excessive addition results in hardening and a problem with intergranular corrosion due to the formation of precipitates of Cr and B. Further, the problem of weld cracks also arises. The upper limit was 0.0050%. Furthermore, if considering the manufacturability, the content of B is 0.0003 to 0.0015% preferably.
- Zr is a more powerful carbonitride forming element than Ti. It can fix carbonitrides at a higher temperature, so can be expected to have the effect of lowering the austenite phase stability. However, excessive addition causes a drop in the manufacturability. The upper limit was 1.0%.
- Sn is an element which has a large atomic radius and is effective for solution strengthening at a high temperature. Sn is an element which results in only a little drop in mechanical properties at room temperature, and is added in accordance with need. However, if excessively added, the manufacturability and the weldability fall. The upper limit was 1.0%.
- Co is an element which improves the high temperature strength, but if excessively added, the manufacturability falls. The upper limit was 0.5%.
- Next, the method of production will be explained. The method of production of the steel sheet of the present invention is comprised of the steps of steelmaking, hot rolling, pickling, cold rolling, and annealing and pickling. In the steelmaking, the steel which contains the above essential ingredients and ingredients which are added in accordance with need is suitably produced in a converter and then secondarily refined. The produced molten steel is made into a slab by a known casting method (continuous casting). The slab is heated to a predetermined temperature and is hot rolled by continuous rolling to a predetermined plate thickness. Regarding the cold rolling conditions, the cold rolling of the stainless steel sheet is usually performed by reverse rolling by a Sendzimir rolling mill or one-directional rolling by a tandem rolling mill. In the present invention, any rolling method may be employed, but tandem rolling is superior in productivity compared with Sendzimir rolling and also raises the r-value indicator of workability. It is preferable to perform the cold rolling by a tandem rolling mill which a roll diameter is a 400 mm or more.
- From the viewpoint of the productivity, the annealing of the hot rolled plate which is usually performed in the production of ferritic stainless steel sheet is preferably omitted, but the hot rolled plate may also be annealed.
- The other steps of the method of production are not particularly defined. The hot rolling conditions, hot rolled plate thickness, cold rolled sheet annealing temperature, atmosphere, etc. may be suitably selected. Further, after the cold rolling and annealing, temper rolling may be performed or a tension leveler may be applied. Furthermore, the final sheet thickness may be suitably selected in accordance with the demanded thickness of the member.
- The steel of each of the compositions of ingredients which are shown in Table 1 was produced and cast into a slab. The slab was hot rolled to obtain a 5 mm thick hot rolled coil. After that, the hot rolled coil was pickled and was cold rolled down to a 2 mm thickness, then was annealed and pickled to obtain a product sheet. The annealing temperature of the cold rolled sheet was made 850 to 1000°C so as to make the grain size number about 6 to 8. The annealing time was 120 seconds. In the table, Nos. 1 to 15 are invention steels, while Nos. 16 to 39 are comparative steels. Further, the No. 1A steel and the No. 2A steel are steels of the same ingredients as respectively the No. 1 steel and No. 2 steel but where after the hot rolling, the hot rolled plates are annealed at 850 to 1000°C for 120 seconds, then are pickled in the same way as other steels and, furthermore, cold rolled, annealed, and pickled to obtain the final sheets. From the obtained final sheets, high temperature tensile test pieces were taken, subjected to tensile tests at 800°C and 900°C, and measured for 0.2% yield stress (based on JISG0567). Here, 25 MPa at 800°C and 15 MPa at 900°C, levels substantially equal to those of 0.4Nb-1Si steel currently most generally used as steel for exhaust manifolds, were used as the passing criteria.
- Furthermore, as a test of the oxidation resistance, continuous oxidation tests were run in the air at 900°C and 930°C for 200 hours and the presence of any abnormal oxidation was evaluated (based on JISZ2281). In addition, for the workability at room temperature, JIS No. 13B test pieces were fabricated and subjected to tensile tests in the rolling direction to measure the elongation at break. Here too, 32%, a level substantially equal to that of existing 0.4Nb-1Si steel, was used as the passing criteria.
- Furthermore, to clarify the intergranular corrosion resistance of the weld zone, toe welding was performed using the TIG welding method, then a Strauss test was performed and the presence of intergranular corrosion was studied.
-
- As clear from Table 1, it is found that steels having compositions of ingredients defined by the present invention have no problem at all in high temperature strength, oxidation resistance, room temperature elongation, and intergranular corrosion resistance and exhibit excellent properties.
- As opposed to these, in the comparative steels of Nos. 16 and 17, the ingredient elements are in the ranges of the present invention, but the γ-values are over 35, so abnormal oxidation occurs at 930°C and the oxidation resistances are inferior. The Nos. 18 and 19 steels respectively have C and N outside the upper limit and are inferior in high temperature strength, oxidation resistance, and workability. The No. 20 steel has insufficient Si and is inferior in oxidation resistance. The No. 21 steel has Si added in excess and is inferior in workability. The No. 22 has little addition of Mn and is inferior in oxidation resistance. The No. 23 steel has Mn added in excess and is inferior in oxidation resistance and workability. The No. 24 has P added in excess, is inferior in toughness, and exhibited fine cracks in the hot rolled plate at the stage of production of steel sheets. The No. 25 steel has S added in excess and was confirmed to have the formation of CaS - the cause of deterioration of the corrosion resistance. The No. 26 steel has a small amount of Cr, and is low in high temperature strength and is inferior in oxidation resistance. The No. 27 steel has a small amount of addition of Cu and is inferior in high temperature strength. The No. 28 steel has Cu added in excess and is inferior in workability. The No. 29 steel has Ni added in excess and is inferior in workability. The No. 30 steel has V added in excess and is inferior in workability. The No. 31 steel has Al added in excess and is inferior in workability. The No. 32 steel has a small amount of addition of Ti and is inferior in intergranular corrosion resistance. The No. 33 steel has Ti added in excess and is inferior in workability. The No. 34 steel has Nb added in excess and is inferior in workability. The No. 35 steel has Mo added in excess and is inferior in workability. The No. 36 steel has B added in excess, is inferior in workability, and is inferior in intergranular corrosion resistance. The Nos. 37, 38, and 39 steels respectively have Zr, Sn, and Co added in excess. But it is found that these steels are inferior in workability, exhibit fine cracks in the hot rolled plates when producing steel sheet, and are inferior in manufacturability.
- As clear from the above explanation, according to the present invention, it is possible to provide the heat-resistant stainless steel sheet having excellent oxidation resistance even without adding large amounts of expensive alloy elements such as Nb or Mo. In particular, the part costs are reduced and the weight can be lightened by application to exhaust members. The social contribution, including protection of the environments, is extremely great.
Claims (3)
- ferritic stainless steel sheet having excellent heat resistant and oxidation resistance comprising: by mass%,
C: 0.015% or less,
N: 0.020% or less,
P: 0.04% or less,
S: 0.01% or less,
Si: 0.3 to 1.5%,
Mn: 0.3 to 0.7%,
Cr: 11.0 to 17.0%,
Cu: 0.8 to 1.5%,
Ni: 0.05 to 1.0%,
V: 0.5% or less,
Al: 0.01 to 0.1%, and
Ti: 10(C+N) to 0.3%;
the amounts of the elements being mutually adjusted such that the γ-value which is defined by the following formula (1), becomes 35 or less, and
has a balance of Fe and unavoidable impurities: - The ferritic stainless steel sheet having excellent heat-resistance and oxidation resistance as set forth in claim 1, wherein said stainless steel sheet further comprises, by mass%, at least one or more of
Nb: 0.001 to 0.3%,
Mo: 0.01 to 0.5%, and
B: 0.0003 to 0.0050%. - The ferritic stainless steel sheet having excellent heat-resistance and oxidation resistance as set forth in claim 1 or 2, wherein said stainless steel sheet further comprises, by mass%, at least one or more of
Zr: 1.0% or less,
Sn: 1.0% or less, and
Co: 0.5% or less.
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JP3446667B2 (en) | 1999-07-07 | 2003-09-16 | 住友金属工業株式会社 | Ferritic stainless steel, ferritic stainless steel ingot excellent in workability and toughness, and method for producing the same |
EP1413640B1 (en) * | 2001-07-05 | 2005-05-25 | Nisshin Steel Co., Ltd. | Ferritic stainless steel for member of exhaust gas flow passage |
JP2006037176A (en) | 2004-07-28 | 2006-02-09 | Nisshin Steel Co Ltd | Ferritic stainless steel for exhaust manifold |
JP4468137B2 (en) * | 2004-10-20 | 2010-05-26 | 日新製鋼株式会社 | Ferritic stainless steel material and automotive exhaust gas path member with excellent thermal fatigue characteristics |
CN101437974B (en) * | 2006-05-09 | 2011-07-13 | 新日铁住金不锈钢株式会社 | Stainless steel excellent in corrosion resistance, ferritic stainless steel excellent in resistance to crevice corrosion and formability, and ferritic stainless steel excellent inresistance to crevice |
JP4948998B2 (en) * | 2006-12-07 | 2012-06-06 | 日新製鋼株式会社 | Ferritic stainless steel and welded steel pipe for automotive exhaust gas flow path members |
JP5297630B2 (en) * | 2007-02-26 | 2013-09-25 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel plate with excellent heat resistance |
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 |
JP5274074B2 (en) * | 2008-03-28 | 2013-08-28 | 新日鐵住金ステンレス株式会社 | Heat-resistant ferritic stainless steel sheet with excellent oxidation resistance |
JP2010055944A (en) | 2008-08-28 | 2010-03-11 | Jsr Corp | Conductive laminate film, and touch panel using the same |
JP4950970B2 (en) | 2008-09-18 | 2012-06-13 | 日本放送協会 | Image feature extraction device |
KR102065814B1 (en) * | 2010-09-16 | 2020-01-13 | 닛테츠 스테인레스 가부시키가이샤 | Heat-resistant ferrite-type stainless steel plate having excellent oxidation resistance |
-
2011
- 2011-09-15 KR KR1020157034409A patent/KR102065814B1/en active IP Right Grant
- 2011-09-15 CN CN201180044131.4A patent/CN103097564B/en active Active
- 2011-09-15 US US13/817,997 patent/US20130149187A1/en not_active Abandoned
- 2011-09-15 KR KR1020157028102A patent/KR20150119496A/en not_active Application Discontinuation
- 2011-09-15 KR KR1020137005982A patent/KR20130060290A/en not_active Application Discontinuation
- 2011-09-15 EP EP11825311.1A patent/EP2617854B1/en active Active
- 2011-09-15 JP JP2012534083A patent/JP5709875B2/en active Active
- 2011-09-15 WO PCT/JP2011/071765 patent/WO2012036313A1/en active Application Filing
- 2011-09-15 KR KR1020187003512A patent/KR20180017220A/en active Search and Examination
Non-Patent Citations (1)
Title |
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See references of WO2012036313A1 * |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2014036091A1 (en) * | 2012-08-31 | 2014-03-06 | Ak Steel Properties, Inc. | Ferritic stainless steel with excellent oxidation resistance, good high temperature strength, and good formability |
EP3249067A4 (en) * | 2015-01-19 | 2018-07-04 | Nippon Steel & Sumikin Stainless Steel Corporation | Ferritic stainless steel for exhaust system member having excellent corrosion resistance after heating |
Also Published As
Publication number | Publication date |
---|---|
KR20150140423A (en) | 2015-12-15 |
KR20180017220A (en) | 2018-02-20 |
KR102065814B1 (en) | 2020-01-13 |
CN103097564A (en) | 2013-05-08 |
EP2617854B1 (en) | 2019-09-11 |
EP2617854A4 (en) | 2018-01-10 |
KR20130060290A (en) | 2013-06-07 |
JPWO2012036313A1 (en) | 2014-02-03 |
CN103097564B (en) | 2015-11-25 |
US20130149187A1 (en) | 2013-06-13 |
KR20150119496A (en) | 2015-10-23 |
WO2012036313A1 (en) | 2012-03-22 |
JP5709875B2 (en) | 2015-04-30 |
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