EP1408132B1 - Acier ferritique inoxydable pour systèmes d'échappement ayant une bonne aptitude de formage, une haute résistance mécanique, une haute tenacité à basse température et une excellent résistance à l'oxydation à haute température - Google Patents

Acier ferritique inoxydable pour systèmes d'échappement ayant une bonne aptitude de formage, une haute résistance mécanique, une haute tenacité à basse température et une excellent résistance à l'oxydation à haute température Download PDF

Info

Publication number
EP1408132B1
EP1408132B1 EP03022874A EP03022874A EP1408132B1 EP 1408132 B1 EP1408132 B1 EP 1408132B1 EP 03022874 A EP03022874 A EP 03022874A EP 03022874 A EP03022874 A EP 03022874A EP 1408132 B1 EP1408132 B1 EP 1408132B1
Authority
EP
European Patent Office
Prior art keywords
temperature
steel sheet
formability
content
low
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.)
Expired - Lifetime
Application number
EP03022874A
Other languages
German (de)
English (en)
Other versions
EP1408132A1 (fr
Inventor
Manabu Oku
Yoshiaki Hori
Yoshitomo c/o Nisshin Steel Co. Ltd. Fujimura
Takeshi Utsunomiya
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 Nisshin Co Ltd
Original Assignee
Nisshin Steel Co Ltd
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 Nisshin Steel Co Ltd filed Critical Nisshin Steel Co Ltd
Publication of EP1408132A1 publication Critical patent/EP1408132A1/fr
Application granted granted Critical
Publication of EP1408132B1 publication Critical patent/EP1408132B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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
    • 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
    • C22C38/18—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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron

Definitions

  • This invention relates to a ferritic steel sheet concurrently improved in formability such as deep drawability, stretch formability and the like, high-temperature strength, high-temperature oxidation resistance, and low-temperature toughness, particularly a steel sheet that, being usable in a 800 - 900 °C high-temperature atmosphere, is suitable for utilization in automobile engine exhaust gas passage components.
  • ferritic stainless steels have a smaller thermal expansion coefficient than austenitic stainless steels and are excellent in thermal fatigue property and high-temperature oxidation property, they are used as heat-resistant materials in applications where thermal strain is an issue.
  • Typical applications include automobile engine exhaust gas passage components such as exhaust manifolds, front pipes, catalyst carrier outer cylinders, center pipes, mufflers and tailpipes.
  • SUH409L and SUS430J1L are known as ferritic stainless steels having high heat resistance.
  • SUH409L is commonly used as an exhaust gas passage component material because of its good workability and low-temperature toughness.
  • the level of its heat resistance makes it unsuitable for applications in which the material temperature exceeds 800 °C. It is also lacks sufficient deep drawability for application to components with complicated shapes.
  • SUS430J1L has excellent heat resistance that makes it usable at 900 °C. But it is hard and poor in formability.
  • Patent Reference 1 among the references listed below teaches a ferritic heat-resistant stainless steel with a Cr level of 17.0 - 25.0%. This steel is added with Mo and Cu in combination to improve high-temperature strength and with Mn to suppress scale spalling. Degradation of impact value by Mo is overcome to some degree by combined addition of Cu and Ni. However, the steel's formability is not adequate to cope with the needs of complexly shaped exhaust gas passage components. And its high Cr content makes it disadvantageous from the cost aspect.
  • Patent Reference 2 teaches a 13% Cr ferritic stainless steel that exhibits heat resistance at least as good as an 18% Cr ferritic stainless steel and also has improved high-temperature salt corrosion property.
  • high-temperature strength is increased by ensuring the presence of solid solution Nb
  • high-temperature oxidation property is improved by liberal addition of Mn and Si
  • NaCl-induced hat corrosion resistance is improved by the Si.
  • the steel cannot adequately respond to the recent harsh requirements mentioned earlier.
  • Patent Reference 3 teaches a Nb-containing heat-resistant ferritic stainless steel with a Cr level of 11.0 - 15.5% that is aimed at improving high-temperature oxidation resistance and scale adherence. These properties are markedly improved by strictly constraining Mn/Sn within the range of 0.7 - 1.5.
  • This Patent Reference also teaches improvement of low-temperature toughness and workability by Cu addition. Regarding workability, for example, it presents data showing that no cracking occurred in a 180-degree bending test. In light of the fact that demands regarding the shape of exhaust gas passage components are becoming more and more challenging, however, the materials used in these components have come to require excellent formability that is compatible with various forming methods (discussed later).
  • Patent Reference 3 pays no attention to deep drawability and other drawability-related stretch formability and, as such, cannot be considered capable of responding to today's severe requirements.
  • its Cr content of 11.0% or greater is on the level required in a stainless steel, which is inconsistent with the desire to reduce cost by lowering the Cr content in exhaust gas passage components that do not necessarily require use of stainless steels.
  • Patent Reference 4 teaches a ferritic stainless steel for exhaust manifolds that contains Cr at 11 - 14%. This is a steel enhanced in high-temperature strength by positive addition of Si to a Nb-containing steel. Its high temperature can be considered to be the same as the steel of Patent Reference 3. As it does not give consideration to improving formability and low-temperature toughness beyond the level of the prior art, however, it is incapable of thoroughly responding to the harsh demands placed on steels in recent years. It also needs further reduction in Cr level.
  • Patent Reference 5 teaches a ferritic heat-resistant steel for engine exhaust gas passage components having a Cr content of 8.0 - 10.0%. This is a steel that achieves better heat resistance than SUH409L while also reducing cost through low Cr content. This reference further teaches that Cu is effective for improving both low-temperature toughness and workability. Regarding workability, it was for example found to possess ductility on a par with SUH409L in tensile tests at room temperature. As it is not aimed at improvement of the in-plane anisotropy of ductility or deep drawability, however, it leaves unresolved the problem of imparting formability thoroughly matched to the needs of various forming methods (discussed later). Nor does it offer a method for consistently imparting excellent low-temperature toughness. Patent Reference 5 can therefore not be viewed as sufficiently responding to the recent severe requirements with respect to exhaust gas passage components.
  • Patent References 6 and 7 teach ferritic steels with a Cr content of 10 to less than 15% that improve the corrosion resistance against condensed moisture needed by mufflers and other low-temperature components and also the high-temperature strength needed by exhaust manifolds and other high-temperature components. But they merely assess workability in terms of proof stress, while offering nothing specific with regard to high-temperature oxidation resistance. Patent References 6 and 7 are not directed to the goal of concurrently and consistently improving high-temperature oxidation resistance and formability with good reproducibility, and are silent regarding methods for achieving this objective. From the viewpoint of fabrication into exhaust gas passage components of various complex shapes, therefore, the steels taught by Patent References 6 and 7 cannot be considered steels that fully meet all formability requirements.
  • steel sheet for automobile exhaust gas passage components is now being required to contribute to greater component design freedom by offering excellent formability that enables fabrication into complicated shapes by a diversity of forming methods. But this need should best be met while maintaining high-temperature strength and high-temperature oxidation resistance at 800 - 900 °C on a par with SUS430J1L, and also ensuring excellent low-temperature toughness.
  • Patent References no steel sheet has yet been developed that is concurrently improved to a high degree in all of formability, high-temperature strength, high-temperature oxidation resistance, and low-temperature toughness.
  • An object of the present invention is to provide a new ferritic heat-resistant steel that concurrently offers excellent formability enabling ready application to complexly configured automobile exhaust gas passage components, excellent high-temperature strength and high-temperature oxidation resistance enabling it to withstanding use at 900 °C and excellent low-temperature toughness having an energy transition temperature of minus 50 °C or lower, and that is lowered in cost by reducing Cr content to below 11 mass percent.
  • the present invention was accomplished based on the foregoing findings.
  • the aforesaid object is achieved by a ferritic steel sheet concurrently improved in formability, high-temperature oxidation resistance, high-temperature strength, and low-temperature toughness comprising, in mass percent, C : not more than 0.02%, Si : 0.7 - 1.1%, Mn : not more than 0.8%, Ni : not more than 0.5%, Cr : 8.0 to less than 11.0%, N : not more than 0.02%, Nb : 0.10 - 0.50%, Ti: 0.07- 0.25%, Cu: 0.02- 0.5%, B: 0.0005- 0.02%, V: 0 (no addition) - 0.20%, preferably 0.01 - 0.20%, one or both of Ca and Mg : 0 (no addition) - 0.01% in total, preferably 0.0003 - 0.01% in total, one or more elements among Y and rare earth elements : 0 (no addition) - 0.20% in total, preferably 0.01 - 0.2
  • the steel sheet may further include Mo : not more than 0.50% and Al : not more than 0.10%.
  • Equation (3) Each element symbol in Equations (1) - (3) is replaced by a value representing the content of the element in mass percent. In Equation (3), symbols of elements not contained are replaced by zero.
  • the aforesaid steel sheet may have a metallic structure obtained by cold rolling and annealing a partially recrystallized hot-rolled sheet.
  • a "partially recrystallized hot-rolled sheet” as termed here means a hot-rolled sheet 10 - 90 vol% of whose structure is accounted for by recrystallized grains and the remainder of which is accounted for by un-recrystallized grains. The amount of recrystallized grains present can be ascertained by observing a cross-section of the hot-rolled sheet with an optical microscope.
  • hot-rolled sheet is meant the steel sheet that has been subjected to hot rolling and may have been subjected to heat treatment after hot rolling but has not be subjected to cold rolling. The final metallic structure obtained by conducting cold rolling and annealing is totally recrystallized.
  • the aforesaid steel sheet may have a metallic structure obtained by cold rolling and annealing a tatally recrystallized hot-rolled sheet.
  • a "tatally recrystallized hot-rolled sheet” as termed here means a hot-rolled sheet more than 90 vol% of whose structure is accounted for by recrystallized grains.
  • the steel sheet provided by the present invention is particularly one used as fabricated into an automobile engine exhaust gas passage component.
  • FIG. 1 shows how Ti content and difference between partial and complete recrystallization after hot rolling affected r value (r D ) at 45 degrees to the rolling direction in ferritic steels whose basic composition was 10 Cr- 0.9 Si - 0.3 Nb - 0.1 V - 0.1 Cu.
  • the partially recrystallized hot-rolled sheets were 4.0 mm-thick hot-rolled sheets heat treated at 700 - 1000 °C for 1 minute to have a structure 10 - 90 vol% of which was accounted for by recrystallized grains.
  • the totally recrystallized hot-rolled sheets were 4.0 mm-thick hot-rolled sheets heat treated at about 1050 °C for 1 minute.
  • the hot-rolled sheets were cold rolled to 2.0 mm and totally recrystallized by annealing at 1050 °C, whereafter tensile test pieces were cut from them.
  • the r D value rose sharply when Ti was added to a content of 0.07 mass% or more.
  • the r D value was improved markedly over the full range of Ti content by partially recrystallizing the steel sheets after hot rolling.
  • FIG. 2 shows how Cu content affected energy transition temperature and amount of oxidation increase after 900 °C x 200 hour heating in the atmosphere in ferritic steels whose basic composition was 10 Cr- 0.9 Si-0.3 Nb - 0.1 V - 0.001 B.
  • the specimens used were totally recrystallized steel sheets obtained by cold rolling partially crystallized 4.0 mm-thick hot-rolled sheets to a thickness of 2.0 mm and then finally annealing them at 1050 °C.
  • the energy transition temperature was ascertained by a Charpy impact test. No.
  • FIG. 3 shows how Cr content and Si content affected high-temperature oxidation resistance and formability in ferritic steels whose basic composition was 8 to 14 Cr - 0.5 to 1.0 Si - 0.3 Nb - 0.1 Ti - 0.1 V - 0.1 Cu.
  • the specimens were prepared by the process explained regarding FIG. 2.
  • the 0.2% proof stress at 45 degrees to the rolling direction determined in a room-temperature tensile test was used as an index of formability. When this value exceeded 300 MPa, it was judged that as a material for exhaust gas passage components the steel was basically lacking in formability capable of meeting the needs of various forming methods.
  • FIG. 3 shows how Cr content and Si content affected high-temperature oxidation resistance and formability in ferritic steels whose basic composition was 8 to 14 Cr - 0.5 to 1.0 Si - 0.3 Nb - 0.1 Ti - 0.1 V - 0.1 Cu.
  • the specimens were prepared by the process explained regarding FIG. 2.
  • AM value represents the balance between ferrite phase and austenite phase.
  • high ductility was obtained only in the region of an AM value not more than 70 and degenerated precipitously when AM exceeded 70.
  • Equation (3) 420 C - 11.5 Si + 7 Mn + 23 Ni - 11.5 Cr - 12 Mo + 9 Cu - 49 Ti - 25 ( Nb + V ) - 52 Al + 470 N + 189 ⁇ 70
  • C and N are generally effective for improving creep strength, creep rupture strength and other high-temperature strength properties.
  • low-temperature toughness is degraded by a high content of C and N. This makes it necessary to increase the amount of added Nb and Ti in order to stabilize C and N as carbonitrides. The result is higher cost.
  • an attempt to markedly lower C and N content makes steelmaking more onerous, which also increases cost.
  • Si and Cr are both very effective for improving high-temperature oxidation property but they also harden the steel.
  • the Si and Cr contents need to be controlled to within the range satisfying Equations (1) and (2), as explained earlier with reference to FIG. 3.
  • upper and lower limits of Si and Cr content are further defined from the standpoint of ensuring good corrosion resistance and low-temperature toughness.
  • the minimum required level of corrosion resistance exemplified by SUH409L cannot be achieved when the Si and Cr contents are too small, whereas the low-temperature toughness level of the SUH409L steel cannot be realized when their contents are too high.
  • Si content is therefore defined as 0.7 - 1.1 mass%. A more preferable range of Si content is 0.8 - 1.0 mass%.
  • Cr content is defined as 8.0 to less than 11.0%. A more preferable range of Cr content is 9.0 to less than 11.0% and a still more preferable range of Cr content is 9.0 to less than 10.0%.
  • Mn hardens the steel and degrades its low-temperature toughness and formability when added in excess. Particularly in the composition system of the present invention, excessive addition of Mn is liable to adversely affect high-temperature oxidation resistance by causing generation of austenitic phase during hot use.
  • the upper limit of Mn content is therefore defined as 0.8 mass%.
  • Mn is preferably added to within the content range of 0.2 - 0.8 mass%.
  • Ni is effective for improving low-temperature toughness but hardens the steel and degrades its formability when added in excess. Moreover, in the composition system of the present invention, excessive addition of Ni is, like excessive addition of Mn, liable to degrade high-temperature oxidation resistance by causing generation of austenitic phase during hot use.
  • the upper limit of Ni content is therefore defined as 0.5 mass%.
  • Nb is very effective for improving high-temperature strength. Since Ti is added in the present invention, substantially no Nb is fixed to C and N, so that essentially all added Nb can be considered to work effectively toward enhancing high-temperature strength. This effect manifests itself at a content of not less than 0.10 mass%. On the other hand, excessive Nb addition degrades formability and low-temperature toughness. The Nb content is therefore defined as 0.10 - 0.50 mass%. In order to obtain still higher formability and high-temperature strength, a Nb content in the range of 0.10 - 0.40 mass% is preferable.
  • Ti fixes C and N and is generally known to improve grain boundary corrosion resistance. In this invention, however, it is a very important element for improving formability (particularly deep drawability).
  • the formability improving effect of Ti appears conspicuously at content of not less than 0.07 mass% (see FIG. 1). However, excessive Ti addition degrades toughness and adversely affects product surface properties. Ti content is therefore defined as 0.07 - 0.25 mass%.
  • Ti is preferably added to satisfy Ti ⁇ 6 (C + N). In order to obtain a product with surface properties as good as or better than SUH409L, Ti is preferably added to a content of not more than 0.20 mass%.
  • Mo is effective for increasing high-temperature strength but makes the steel brittle when present at a high content.
  • Mo is very expensive. While adequate heat resistance can be secured without Mo addition by optimizing the contents of other constituent elements, Mo addition is advantageous in that it increases the freedom of composition design.
  • its content is preferably not more than 0.50 mass%.
  • Mo can be added in excess of 0.5 mass% but should not be added in excess of 3.0 mass%, the level beyond which an extreme decline in low-temperature toughness occurs.
  • Cu improves low-temperature toughness. In order to markedly improve low-temperature toughness to the level required in exhaust gas passage components, however, it is important to incorporate not less than 0.02 mass% of Cu in combination with B (discussed later). When the Cu content exceeds 0.5 mass%, however, high-temperature oxidation resistance degenerates sharply (see FIG. 2). Cu content is therefore defined as 0.02 - 0.5 mass% in the present invention.
  • V is a carbonitride-forming element that is effective for improving grain boundary corrosion resistance and the toughness of sites affected by welding heat. Moreover, like Nb, V contributes to high-temperature strength improvement in the solid solution state. This effect is particularly pronounced when V is present together with Nb. In addition, V is thought to be effective for improving high-temperature oxidation resistance. However, a V content in excess of 0.20 mass% degrades workability and low-temperature toughness. When V is added, therefore, its content must be kept to not more than 0.20 mass%. For thoroughly obtaining the foregoing effects of V, it is preferably added in the range of 0.01 - 0.20 mass%.
  • Al is highly effective for improving high-temperature oxidation resistance.
  • the composition according to the present invention is designed to enable excellent high-temperature oxidation resistance even without incorporation of Al. Excessive Al addition degrades formability, weldability and low-temperature toughness. Moreover, deoxidation by Al is not particularly necessary because the present invention calls for addition of Ti and Si. When Al is incorporated, it must be added at no more than 0.10 mass%. When adding Al in a case where formability, weldability and low-temperature toughness are particularly important, the Al content is preferably restricted to not more than 0.07 mass%.
  • B suppresses low-temperature brittleness and secondary work brittleness in a ferritic steel also containing Nb and Ti. This effect was found to be pronounced when B is added in combination with Cu. In order to thoroughly improve low-temperature toughness, B needs to be added at not less than 0.0005 mass%. On the other hand, excessive B addition beyond 0.02 mass% leads to generation of borides that degrade formability and degrade rather than improve low-temperature toughness. In the present invention, B is incorporated at 0.0005 - 0.02 mass% together with Cu at 0.02 - 0.5 mass%.
  • Ca and Mg have strong binding force with S and therefore reduce the amount of MnS generation to improve corrosion resistance.
  • Ca and Mg are elements that in themselves effectively work to improve high-temperature oxidation resistance. When importance is attached to corrosion resistance and high-temperature oxidation resistance, therefore, these elements can be added as required. However, addition in large amounts increases inclusions that degrade low-temperature toughness and formability. When one or both of Ca and Mg are added, therefore, the combined content thereof needs to be held to not more than 0.01 mass%. In order to bring out the effect of Ca and Mg addition strongly, the total of the Ca and Mg contents should preferably made 0.003 - 0.01 mass%.
  • Y and REMs such as La and Ce stabilize the chromium oxide coating that forms on the steel surface and, by enhancing the adherence between the steel matrix and the oxide coating, manifestly improve the high-temperature oxidation resistance of the steel sheet.
  • these elements can be added as required.
  • addition in large amounts not only degrades formability and low-temperature toughness but also promotes generation of inclusions that may become starting points of abnormal oxidation, meaning that high-temperature oxidation resistance is degraded rather than improved. Therefore, when one or more elements selected from among Y and rare earth elements are added, the combined amount thereof must be made not more than 0.20 mass%. For maximizing the effect of Y and REM addition, one or more elements selected from among these elements should preferably be added to a combined total of 0.01 - 0.20 mass%.
  • one or more of Zr, Hf, Ta, W, Re and Co can be included for their ability to improve high-temperature strength. Since excessive addition of these elements hardens the steel, however, they must, when incorporated, be added to a combined content of not more than 3.0 mass%. The preferable amount is not more than 0.5 mass% in total.
  • P, S, O, Zn, Sn, Pb and other common impurity elements is preferably reduced to the lowest level possible in order to ensure good formability and low-temperature toughness.
  • these elements should, at the most lenient, be restricted to P : not more than 0.04 mass%, S : not more than 0.03 mass%, O : not more than 0.02 mass%, Zn : not more than 0.10 mass%, Sn : not more than 0.10 mass%, and Pb: not more than 0.10 mass%.
  • P not more severe restrictions can be imposed in accordance with the product quality desired.
  • Equations (1) - (3) define the composition range required for concurrent improvement of formability and high-temperature oxidation resistance.
  • AM value the value of the left side of Eqution (3)
  • a steel with a low AM value ordinarily contains liberal amounts of ferrite generating elements like Si, Cr, Mo, Ti, Nb, V and Al. When large amounts of these elements are contained, formability and low-temperature toughness degenerate. Studies showed that it is preferable to regulate the constituents so that the AM value is 40 or higher.
  • the r value an index of deep drawability
  • the r value can be markedly improved by the steps of making a hot-rolled sheet 10 - 90 vol% of whose structure is accounted for by recrystallized grains and the remainder of which is accounted for by un-recrystallized grains, cold rolling the hot-rolled sheet, and totally recrystallizing it by annealing (see FIG. 1).
  • the steel sheet having the metallic structure obtained in this manner possesses formability fully capable of responding to the increasingly severe shape requirements of today's exhaust gas passage components.
  • Partial recrystallization of the hot-rolled sheet can be carried out directly during hot rolling process or by heating conducted between hot rolling and cold rolling.
  • Partial recrystallization during hot rolling can, for instance, be conducted by hot rolling in the temperature range of 950 - 1250 °C, coiling, and cooling in the coiled state. Optimum conditions can be selected in accordance with the facility specifications and the hot-rolling pass schedule. Partial recrystallization by heating after hot rolling can be conducted, for example, by heating the steel sheet cooled after hot rolling in the temperature range of 850 - 1000 °C. The heating can be carried out at any stage before cold rolling.
  • the hot-rolled sheet partially recrystallized by one of the foregoing methods is then totally recrystallized by annealing.
  • the cold rolling is conducted at a reduction in the range of, for example, 30 - 90%.
  • the final sheet thickness is adjusted to, for example, about 0.4 - 1.2 mm.
  • the annealing temperature is preferably in the range of, for instance, 950 - 1150 °C.
  • the ferritic steel sheet obtained is excellent in formability and low-temperature toughness and these properties are retained even after fabrication into welded steel tube.
  • the totally recrystallized hot-rolled sheet can be obtained by subjecting the hot-rolled sheet into a heat treatment at the temperatures between 950 and 1100 °C
  • Ferritic steels having the chemical compositions shown in Tables 1 and 2 were made using a high-frequency vacuum melting furnace and cast into 30-Kg ingots. The ingots were hot-forged and then hot-rolled into 4.0 mm hot-rolled sheets. The hot rolling was conducted at a hot-rolling temperature of 700 - 1250 °C and a draft (rolling reduction) per pass of about 30%. Each hot-rolled sheet was water cooled and then held at 900 - 1000 °C for 1 minute. The cross-sectional metallic structure of the hot-rolled sheet was observed with an optical microscope. Recrystallized grains were found to account for 10 - 90 vol.% of every specimen, the balance being un-recrystallized structure. It was thus ascertained that partial recrystallization had been achieved.
  • the partially recrystallized hot-rolled sheets were cold rolled to a thickness of 2 mm and thereafter totally recrystallized by annealing for 1 minute at 1050 °C to afford cold-rolled annealed sheets.
  • Nos. 1-21 in Table 1 are ferritic steels satisfying the chemical composition defined by the present invention.
  • Nos. 22 - 31 in Table 2 are comparative steels not meeting compositional requirements of the present invention.
  • No. 22 corresponds to SUH409Land No. 23 to SUS430J1L.
  • a test piece cut from each cold-rolled annealed sheet was subjected to a tensile test, a Charpy impact test, a high-temperature tensile test, and a high-temperature oxidation test.
  • Formability was evaluated based on the 0.2% strength, breaking extension and plastic strain ratio determined by the tensile test.
  • No. 13B test pieces (prescribed by JIS Z 2201) cut from each steel sheet specimen in directions parallel, 45 degrees and 90 degrees to the rolling direction were used as the tensile test pieces.
  • 0.2% strength and breaking extension were determined by subjecting the test piece taken 45 degrees with respect to the rolling direction to the tests prescribed by JIS Z 2241.
  • Plastic strain ratio was determined in accordance with JIS Z 2254 using the test pieces taken in all three of the aforesaid directions.
  • the Charpy impact test was conducted by the method explained with reference to FIG. 2.
  • the energy transition temperature was determined and used as an index of low-temperature toughness.
  • the high-temperature tensile test was conducted in accordance with JIS G 0657 using the tensile test piece taken at 45 degrees.
  • the 0.2% strength at 900 °C was determined and used as an index of high-temperature strength.
  • the high-temperature oxidation test was conducted in accordance with JIS Z 2281 by determining the amount of oxidation increase after heating at 900 °C for 200 hours in the atmosphere. The result was used as an index of high-temperature oxidation resistance.
  • the steels Nos. 1 - 21, examples of the present invention all had softness (0.2% proof stress) falling about midway between SUH409L (No. 22) and SUS430J1L (No. 23) and ductility (elongation) similar to SUH409L. They were superior to SUH409L and SUS430J1L in deep drawability, i.e., in average plastic strain ratio r AV and in-plane plastic anisotropy ⁇ r. Their low-temperature toughness (energy transition temperature) performance was also excellent, matching that of SUH409L.
  • the invention steels were clearly superior to SUH409L and substantially matched the performance of SUS430J1L in 900 °C heat resistance (high-temperature strength and high-temperature oxidation resistance).
  • the steels of the present invention achieved excellent formability while also thoroughly maintaining high-temperature strength, high-temperature oxidation resistance and low-temperature toughness.
  • steel No. 22 a comparative example steel equivalent to SUH409L, was inferior in heat resistance, and No. 23, equivalent to SUS430J1L, was hard and insufficient in formability.
  • Steels Nos. 24 and 25 are types that have actually been used in automobile engine exhaust gas passage components. However, No. 24 was inferior in formability and low-temperature toughness owing to the fact that, inter alia, it was not added with Ti and had Si and Cr contents falling outside the ranges of the present invention, while No. 25 was poor in formability, low-temperature toughness and high-temperature oxidation resistance because it was high in C and Nb and had Si and Cr contents falling outside the ranges of the present invention. Steel No.
  • the steels shown in Tables 1 and 2 as from No.1 to No.10 and from No.22 to 26 were hot-rolled and then subjected to the heat treatment at temperatures between 950 and 1100 °C for 1 minute, thereby to obtain the hot rolled sheet having totally recrystallized structure.
  • the sheets obtained were cold rolled into 2.0 mm and thereafter totally recrystallized by annealed at 1050 °C for 1 minute to afford cold rolled annealed sheets.
  • Example 2 a piece cut from each cold-rolled annealed sheet was subjected to the test to evaluate 0.2% strength, breaking extension, plastic strain ratio and in-plane anisotropy. Further, in order to evaluate a surface appearance after formed, a piece cut from each cold-rolled annealed sheet was imposed 20 % of plastic strain in direction parallel to the rolling direction and subjected to the test to evaluate the surface roughness of the test piece surface in direction perpendicular to the rolling direction by using a contact-type surface roughness meter, the surface roughness being 10 points average roughness Rz in accordance with JIS B 0660. For comparative, the surface roughness was tested as same above for the test pieces shown in Table 3 which were derived from the partially recrystallized hot-rolled sheets and the results was shown in Table 4 as Comparative value of surface roughness.
  • the present invention enables concurrent improvement of formability, high-temperature strength, high-temperature oxidation resistance and low-temperature toughness in a ferritic heat-resistant steel sheet.
  • the ferritic steel sheet of the present invention is particularly notable in that it offers excellent formability, specifically deep drawability and isotropy thereof, capable of responding to the needs of a diversity of forming methods.
  • the steel sheet of the present invention is endowed with new capabilities not envisioned by conventional ferritic heat-resistant steel sheets. It also offers high-temperature strength, high-temperature oxidation resistance and low-temperature toughness that achieve a performance level equal to or better than the steel sheets currently used in exhaust gas passage components.
  • the present invention concurrently achieves excellent performance on all of these points at a Cr content of not more than 11%.
  • the present invention enables application of ferritic heat-resistant steel to complicatedly shaped exhaust gas passage components, helps to expand the degree of freedom in designing such components, and makes a marked contribution to cost reduction.

Claims (8)

  1. Tôle d'acier ferritique améliorée simultanément en ce qui concerne sa capacité de formage, sa résistance à l'oxydation à haute température, sa dureté à haute température, et sa ténacité à basse température comprenant, en pourcents en poids :
    C : pas plus de 0,02 %,
    Si : 0,7 à 1,1 %,
    Mn : pas plus de 0,8 %,
    Ni : pas plus de 0,5 %
    Cr : 8,0 à moins de 11,0 %,
    N : pas plus de 0,02 %,
    Nb : de 0,10 à 0,50 %,
    Ti : 0,07 à 0,25 %,
    Cu : 0,02 à 0,5 %
    B : 0,0005 à 0,02 %,
    V : 0 (pas d'adition) à 0,20 %,
    un ou plusieurs de Ca et Mg : 0 (pas d'adition) à 0,01 % au total,
    un ou plusieurs éléments choisis parmi Y et des éléments de terre rare : 0 (pas d'adition) à 0,20 % au total,
    le reste en fer et en impuretés inévitables,
    et ayant une composition chimique satisfaisant les équations (1) à (3) " ( 1 ) " 3  Cr + 40  Si ≥ 61
    Figure imgb0019
     " ( 2 ) " Cr + 10  Si ≤ 21
    Figure imgb0020
     " ( 3 ) . " 420  C - 11.5  Si + 7  Mn + 23  Ni - 11.5  Cr - 12  Mo + 9  Cu - 49  Ti -            25 ( Nb + V ) - 52  Al + 470  N + 189 ≤ 70
    Figure imgb0021
     cet acier comprenant optionnellement en pourcent en poids :
    Mo : pas plus de 0,50 %, et
    Al : pas plus de 0,10 %
  2. Tôle d'acier selon la revendication 1, dans laquelle le contenu en V est de 0,01 à 0,20 %.
  3. Tôle d'acier selon la revendication 1 ou 2, dans laquelle le contenu d'un ou plusieurs de Ca et Mg est de 0,0003 à 0,01 % au total.
  4. Tôle d'acier selon l'une quelconque des revendications précédentes, dans laquelle le contenu d'un ou plusieurs éléments parmi Y et des éléments de terre rare est de 0,01 à 0,20 % au total.
  5. Tôle d'acier selon l'une quelconque des revendications précédentes, comprenant en outre, à la place d'une partie du fer, en pourcent en poids, un ou plusieurs de Zr, Hf, Ta, W, Re et Co qui, quand ils sont incorporés, ont un contenu combiné non supérieur à 3,0 % en poids, de préférence non supérieur à 0,5 % en poids au total.
  6. Tôle d'acier selon l'une quelconque des revendications de 1 à 5, ayant une structure métallique obtenue par laminage à froid et recuit d'une tôle laminée à froid partiellement recristallisée.
  7. Tôle d'acier selon l'une quelconque des revendications de 1 à 5, ayant une structure métallique obtenue par laminage à froid et recuit d'une tôle laminée à chaud totalement recristallisée.
  8. Tôle d'acier selon l'une quelconque des revendications de 1 à 7, utilisée telle que fabriquée dans un composant de passage de gaz d'échappement de moteur automobile.
EP03022874A 2002-10-08 2003-10-08 Acier ferritique inoxydable pour systèmes d'échappement ayant une bonne aptitude de formage, une haute résistance mécanique, une haute tenacité à basse température et une excellent résistance à l'oxydation à haute température Expired - Lifetime EP1408132B1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP2002294433 2002-10-08
JP2002294433 2002-10-08
JP2003319733A JP4185425B2 (ja) 2002-10-08 2003-09-11 成形性と高温強度・耐高温酸化性・低温靱性とを同時改善したフェライト系鋼板
JP2003319733 2003-09-11

Publications (2)

Publication Number Publication Date
EP1408132A1 EP1408132A1 (fr) 2004-04-14
EP1408132B1 true EP1408132B1 (fr) 2006-02-08

Family

ID=32032946

Family Applications (1)

Application Number Title Priority Date Filing Date
EP03022874A Expired - Lifetime EP1408132B1 (fr) 2002-10-08 2003-10-08 Acier ferritique inoxydable pour systèmes d'échappement ayant une bonne aptitude de formage, une haute résistance mécanique, une haute tenacité à basse température et une excellent résistance à l'oxydation à haute température

Country Status (6)

Country Link
US (2) US20040065390A1 (fr)
EP (1) EP1408132B1 (fr)
JP (1) JP4185425B2 (fr)
KR (1) KR101092244B1 (fr)
DE (1) DE60303472T2 (fr)
ES (1) ES2256640T3 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104372262A (zh) * 2014-11-10 2015-02-25 苏州蔻美新材料有限公司 一种医疗器械用不锈钢及其制备方法
RU2627533C1 (ru) * 2016-06-16 2017-08-08 Юлия Алексеевна Щепочкина Коррозионно-стойкая сталь

Families Citing this family (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP5349153B2 (ja) * 2009-06-15 2013-11-20 日新製鋼株式会社 ろう付け用フェライト系ステンレス鋼材および熱交換器部材
WO2011013193A1 (fr) * 2009-07-27 2011-02-03 日新製鋼株式会社 Acier inoxydable ferritique pour refroidisseur rge et refroidisseur rge
CN103938094B (zh) * 2014-04-28 2016-08-24 宝山钢铁股份有限公司 一种超高强度高韧性石油套管及其制造方法
CN104313484B (zh) * 2014-11-07 2016-05-11 江苏天舜金属材料集团有限公司 高强度抗震耐腐蚀钢筋用钢及其热处理工艺
CN105543691A (zh) * 2015-12-31 2016-05-04 芜湖恒耀汽车零部件有限公司 一种汽车排气管专用合金材料及其制备方法
CN106286885A (zh) * 2016-08-30 2017-01-04 宁波长壁流体动力科技有限公司 一种用于换向阀的主阀芯
CN106382403A (zh) * 2016-08-30 2017-02-08 宁波长壁流体动力科技有限公司 一种换向阀中的主阀芯
CN106435391B (zh) * 2016-11-14 2018-06-19 国家电网公司 镍钨钛合金高阻尼电阻
CN106756482A (zh) * 2016-12-12 2017-05-31 山东钢铁股份有限公司 一种厨具用深冲冷轧钢板及其制造方法
JP7246145B2 (ja) * 2018-07-13 2023-03-27 日鉄ステンレス株式会社 フェライト系ステンレス鋼
KR102173277B1 (ko) * 2018-11-06 2020-11-03 주식회사 포스코 저온 충격인성이 우수한 열연 강판 및 그 제조방법
CN113337771B (zh) * 2021-05-20 2022-11-22 包头钢铁（集团）有限责任公司 一种ld-lf-cc工艺下稳定稀土收得率的方法

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS59123745A (ja) * 1982-12-29 1984-07-17 Nisshin Steel Co Ltd 耐食性合金
US5304259A (en) * 1990-12-28 1994-04-19 Nisshin Steel Co., Ltd. Chromium containing high strength steel sheet excellent in corrosion resistance and workability
ES2184767T3 (es) * 1993-04-27 2003-04-16 Nisshin Steel Co Ltd Acero inoxidable ferritico excelente por su resistencia a la oxidacion a alta temperatura y a la adherencia de la capa de oxido.
JP2772237B2 (ja) * 1994-03-29 1998-07-02 川崎製鉄株式会社 面内異方性が小さいフェライト系ステンレス鋼帯の製造方法
JP3067577B2 (ja) * 1995-03-20 2000-07-17 住友金属工業株式会社 耐酸化性と高温強度に優れたフェライト系ステンレス鋼
JPH08260110A (ja) * 1995-03-23 1996-10-08 Nisshin Steel Co Ltd 耐高温酸化性およびスケール密着性に優れたフエライト系ステンレス鋼の薄板または薄肉管
JP3064871B2 (ja) * 1995-06-22 2000-07-12 川崎製鉄株式会社 成形加工後の耐肌あれ性および高温疲労特性に優れるフェライト系ステンレス熱延鋼板
JPH10147848A (ja) * 1996-11-19 1998-06-02 Nisshin Steel Co Ltd 高温強度及び高温酸化特性に優れたエンジン排ガス経路部材用フェライト系高Ｃｒ鋼
TW480288B (en) 1999-12-03 2002-03-21 Kawasaki Steel Co Ferritic stainless steel plate and method
KR100762151B1 (ko) * 2001-10-31 2007-10-01 제이에프이 스틸 가부시키가이샤 딥드로잉성 및 내이차가공취성이 우수한 페라이트계스테인리스강판 및 그 제조방법

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104372262A (zh) * 2014-11-10 2015-02-25 苏州蔻美新材料有限公司 一种医疗器械用不锈钢及其制备方法
RU2627533C1 (ru) * 2016-06-16 2017-08-08 Юлия Алексеевна Щепочкина Коррозионно-стойкая сталь

Also Published As

Publication number Publication date
ES2256640T3 (es) 2006-07-16
KR20040032049A (ko) 2004-04-14
EP1408132A1 (fr) 2004-04-14
KR101092244B1 (ko) 2011-12-12
JP4185425B2 (ja) 2008-11-26
US20040065390A1 (en) 2004-04-08
US20060237102A1 (en) 2006-10-26
DE60303472T2 (de) 2006-09-28
JP2004149916A (ja) 2004-05-27
DE60303472D1 (de) 2006-04-20

Similar Documents

Publication Publication Date Title
US20060237102A1 (en) Ferritic steel sheet concurrently improved in formability, high-temperature strength, high temperature oxidation resistance, and low temperature toughness
JP4197492B2 (ja) 排ガス流路部材用フェライト系ステンレス鋼
JP4702493B1 (ja) 耐熱性に優れるフェライト系ステンレス鋼
KR100799240B1 (ko) 가공성이 우수한 페라이트계 스테인레스 강판 및 그것의제조 방법
TWI465587B (zh) 耐氧化性優異之肥粒鐵系不鏽鋼
JP5396752B2 (ja) 靭性に優れたフェライト系ステンレス鋼およびその製造方法
JP5540637B2 (ja) 耐熱性に優れるフェライト系ステンレス鋼
WO2012036313A1 (fr) Plaque en acier inoxydable thermorésistant de type ferrite présentant une excellente résistance à l'oxydation
JP2017179398A (ja) 排気マニホールド用フェライト系ステンレス鋼板および排気マニホールド
JP5208450B2 (ja) 熱疲労特性に優れたＣｒ含有鋼
WO2020090936A1 (fr) Tôle d'acier inoxydable austénitique
JP3269799B2 (ja) 加工性、耐粒界腐食性および高温強度に優れるエンジン排気部材用フェライト系ステンレス鋼
JP2001303204A (ja) 耐熱性フェライト系ステンレス鋼とその鋼板
JPH07145453A (ja) 自動車排気マニホールド用フェライト系ステンレス鋼
JP7278079B2 (ja) ステンレス冷延鋼板、ステンレス熱延鋼板及びステンレス熱延鋼板の製造方法
JP4116134B2 (ja) 耐高温へたり性に優れるオーステナイト系ステンレス鋼およびその製造方法
WO1994025636A1 (fr) Acier inoxydable ferritique presentant d'excellentes caracteristiques de resistance a l'oxydation a temperature elevee et d'adhesion de couche d'oxyde
JP5239642B2 (ja) 熱疲労特性、高温疲労特性および耐酸化性に優れるフェライト系ステンレス鋼
JP6678217B2 (ja) ステンレス鋼
JP2005200746A (ja) 自動車排気系部材用フェライト系ステンレス鋼
JP4562281B2 (ja) 加工性に優れたフェライト系ステンレス鋼板及びその製造方法
JP4940844B2 (ja) 高温強度および靱性に優れたＣｒ含有鋼管の製造方法、およびＣｒ含有鋼管
JP5810722B2 (ja) 熱疲労特性と加工性に優れたフェライト系ステンレス鋼
JP2004010967A (ja) 二次加工性に優れたフェライト系ステンレス鋼管
JPH0641691A (ja) 自動車エギゾーストマニホールド用鋼

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

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LI LU MC NL PT RO SE SI SK TR

AX Request for extension of the european patent

Extension state: AL LT LV MK

17P Request for examination filed

Effective date: 20041012

17Q First examination report despatched

Effective date: 20041108

AKX Designation fees paid

Designated state(s): DE ES FR SE

GRAP Despatch of communication of intention to grant a patent

Free format text: ORIGINAL CODE: EPIDOSNIGR1

GRAS Grant fee paid

Free format text: ORIGINAL CODE: EPIDOSNIGR3

GRAA (expected) grant

Free format text: ORIGINAL CODE: 0009210

AK Designated contracting states

Kind code of ref document: B1

Designated state(s): DE ES FR SE

REF Corresponds to:

Ref document number: 60303472

Country of ref document: DE

Date of ref document: 20060420

Kind code of ref document: P

REG Reference to a national code

Ref country code: SE

Ref legal event code: TRGR

REG Reference to a national code

Ref country code: ES

Ref legal event code: FG2A

Ref document number: 2256640

Country of ref document: ES

Kind code of ref document: T3

ET Fr: translation filed
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

26N No opposition filed

Effective date: 20061109

REG Reference to a national code

Ref country code: FR

Ref legal event code: PLFP

Year of fee payment: 13

REG Reference to a national code

Ref country code: FR

Ref legal event code: PLFP

Year of fee payment: 14

REG Reference to a national code

Ref country code: FR

Ref legal event code: PLFP

Year of fee payment: 15

REG Reference to a national code

Ref country code: FR

Ref legal event code: PLFP

Year of fee payment: 16

REG Reference to a national code

Ref country code: ES

Ref legal event code: PC2A

Owner name: NIPPON STEEL STAINLESS STEEL CORPORATION

Effective date: 20220526

REG Reference to a national code

Ref country code: DE

Ref legal event code: R081

Ref document number: 60303472

Country of ref document: DE

Owner name: NIPPON STEEL STAINLESS STEEL CORPORATION, JP

Free format text: FORMER OWNER: NISSHIN STEEL CO., LTD., TOKIO/TOKYO, JP

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

Ref country code: FR

Payment date: 20221028

Year of fee payment: 20

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

Ref country code: SE

Payment date: 20221019

Year of fee payment: 20

Ref country code: ES

Payment date: 20221222

Year of fee payment: 20

Ref country code: DE

Payment date: 20221019

Year of fee payment: 20

REG Reference to a national code

Ref country code: DE

Ref legal event code: R071

Ref document number: 60303472

Country of ref document: DE

REG Reference to a national code

Ref country code: ES

Ref legal event code: FD2A

Effective date: 20231026

REG Reference to a national code

Ref country code: SE

Ref legal event code: EUG

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

Ref country code: ES

Free format text: LAPSE BECAUSE OF EXPIRATION OF PROTECTION

Effective date: 20231009

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

Ref country code: ES

Free format text: LAPSE BECAUSE OF EXPIRATION OF PROTECTION

Effective date: 20231009