EP1739200A1 - Strip made of stainless austenitic steel with bright surface and excellent mechanical properties - Google Patents

Strip made of stainless austenitic steel with bright surface and excellent mechanical properties Download PDF

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Publication number
EP1739200A1
EP1739200A1 EP05291384A EP05291384A EP1739200A1 EP 1739200 A1 EP1739200 A1 EP 1739200A1 EP 05291384 A EP05291384 A EP 05291384A EP 05291384 A EP05291384 A EP 05291384A EP 1739200 A1 EP1739200 A1 EP 1739200A1
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EP
European Patent Office
Prior art keywords
strip
process according
equal
stainless steel
austenitic stainless
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.)
Withdrawn
Application number
EP05291384A
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German (de)
French (fr)
Inventor
François Conrad
Christian Proudhon
Patrick Borgna
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.)
Aperam Stainless France SA
Original Assignee
Ugine et Alz France SA
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 Ugine et Alz France SA filed Critical Ugine et Alz France SA
Priority to EP05291384A priority Critical patent/EP1739200A1/en
Priority to PCT/FR2006/000785 priority patent/WO2007003725A1/en
Priority to JP2008518892A priority patent/JP2009503246A/en
Priority to BRPI0613998-1A priority patent/BRPI0613998B1/en
Priority to AT06743665T priority patent/ATE417135T1/en
Priority to DE602006004213T priority patent/DE602006004213D1/en
Priority to ES06743665T priority patent/ES2317540T3/en
Priority to PT06743665T priority patent/PT1899490E/en
Priority to CNA2006800234667A priority patent/CN101384744A/en
Priority to MX2007015786A priority patent/MX2007015786A/en
Priority to SI200630172T priority patent/SI1899490T1/en
Priority to EP06743665A priority patent/EP1899490B1/en
Priority to RU2008102981/02A priority patent/RU2361929C1/en
Priority to KR1020077030554A priority patent/KR101004597B1/en
Priority to US11/994,275 priority patent/US8268101B2/en
Priority to DK06743665T priority patent/DK1899490T3/en
Publication of EP1739200A1 publication Critical patent/EP1739200A1/en
Priority to ZA200711238A priority patent/ZA200711238B/en
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
    • C25F1/02—Pickling; Descaling
    • C25F1/04—Pickling; Descaling in solution
    • C25F1/06—Iron or steel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/02—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
    • C22C38/44—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

Definitions

  • the present invention relates to an austenitic stainless steel strip, having an elastic limit Rp 0.2 greater than or equal to 600 MPa, an upper tensile load Rm greater than or equal to 800 MPa, an elongation A 80 greater than or equal to 40%, and a glossy surface appearance, of annealing-gloss type.
  • the invention also relates to a continuous manufacturing process for this austenitic stainless steel strip.
  • austenitic stainless steels are used in a wide range of end applications such as for example the manufacture of mechanical parts, cooking utensils, and tubes.
  • the strip of austenitic stainless steel is subjected to a heat treatment and a final etching which, according to the conditions of implementation, gives it either a surface appearance having a high gloss, interesting by example for platerie, an aspect of matte surface interesting for the manufacture of building facades.
  • gloss means a surface having a gloss greater than 50
  • a “matte surface appearance” means a surface having a gloss of less than 20.
  • the gloss corresponds to measuring the reflectivity of the surface and is measured at an angle of 60 °.
  • the austenitic stainless steel strip is cold-rolled beforehand with rolls which impart a glossy surface appearance to the strip.
  • the cold rolled strip is then degreased and rinsed, and then undergoes a heat treatment in a vertical furnace called "bright annealing" in which there is a reducing atmosphere.
  • the strip travels in the oven consisting of an enclosure completely isolated from the outside atmosphere, comprising three zones in which a neutral or reducing gas circulates.
  • This gas is chosen for example, from hydrogen, nitrogen or a mixture of hydrogen and nitrogen (HNX gas), and has a dew point of between -60 and -45 ° C.
  • the strip is first heated in the first zone of the oven at a temperature of between 1050 and 1150 ° C, and at a heating rate of 30 to 60 ° C / sec. Then, it is maintained at this temperature in the second zone of the oven for a time sufficient to allow the recrystallization of the steel and the restoration of the mechanical properties. Finally, it is cooled in the third zone of the oven to a temperature of the order of 150 ° C to prevent re-oxidation of the surface of the strip with the oxygen of the air, when the band leaves the oven enclosure.
  • the glossy surface appearance imparted to the strip during cold rolling is maintained, because the oxide film which formed during the annealing is very thin, of a thickness of the order of 10 angstrom.
  • Another means of manufacturing an austenitic stainless steel strip having a glossy surface appearance is to subject the strip to a final treatment of the annealing-pickling type, which gives it an annealed-stripped surface appearance; to say a matte surface appearance, then to proceed to an operation of either polishing the surface of the strip, or skin-pass of the strip.
  • the procedure is as follows.
  • the previously cold-rolled strip undergoes continuous annealing at a temperature of the order of 1100 ° C, for about 1 min, in an oven where the thermal energy is generated by combustion of hydrocarbons which regulates the air supply to the burner so as to obtain an oxidizing atmosphere.
  • a reducing atmosphere that is to say an atmosphere containing an excess of hydrocarbons, to avoid degradation of the corrosion resistance of the strip by re-carburation of steel by hydrocarbons.
  • the annealed strip then undergoes air cooling and / or forced cooling by spraying water outside the oven.
  • the pickling is generally carried out in several pickling tanks containing acid solutions capable of removing this oxide layer, such as a mixture of nitric acid and hydrofluoric acid.
  • the strip is subjected to either a skin-pass operation or a polishing operation until the desired glossy surface appearance is obtained.
  • the skin-pass is made with so-called mirror-polishing cylinders, ie cylinders having an arithmetic average roughness Ra of between 0.05 and 0.08 ⁇ m which give the steel strip a surface appearance. gloss.
  • the austenitic stainless steel strips obtained according to these two processes have insufficient mechanical characteristics, since their elastic limit Rp 0.2 is between 250 and 350 MPa, and their load at break Rm is between 600 and 700 MPa, for an elongation A 80 of between 50 and 60%.
  • the operation of skin-pass or polishing is an additional step.
  • the polishing operation is a long and delicate operation.
  • the present invention therefore aims to avoid the disadvantages of the processes of the prior art, and to provide a method for conferring on an austenitic stainless steel strip treated in a hydrocarbon combustion furnace, an appearance of glossy surface, an elastic limit Rp 0.2 of 600 MPa and a tensile strength Rm of 800 MPa associated with elongation A 80 greater than or equal to 40%.
  • the strip of steel according to the invention also advantageously has a surface whose arithmetic average roughness is less than or equal to 0.08 ⁇ m, which gives the strip a smooth surface and therefore an even brighter surface appearance.
  • the invention also relates to a continuous manufacturing process for this austenitic stainless steel strip.
  • the remainder of the composition is iron and other elements usually expected to be found as impurities resulting from the processing of stainless steel, in proportions that do not affect the properties sought.
  • the slab After being cast, the slab is hot rolled in a strip train to form a hot rolled strip which is annealed and optionally etched.
  • the hot-rolled strip then undergoes various treatments, so as to obtain a strip having both excellent mechanical characteristics and a glossy surface appearance, without having recourse to either annealing in a bright annealing furnace, or a final polishing of the surface of the strip or a final skin-pass operation.
  • the installation used to manufacture the strip according to the invention comprises a cold rolling device of strips, consisting of a band train comprising working rolls between which scrolls the austenitic stainless steel strip of composition according to the invention.
  • the working rolls have an arithmetic mean roughness Ra of less than or equal to 0.15 ⁇ m, and preferably less than or equal to 0.10 ⁇ m.
  • the diameter of the working rolls of the belt gear is between 50 and 100 mm, to minimize the rolling forces for the high reduction rates, that is to say from 75% reduction.
  • the band train not only reduces the thickness of the band, but also to help crush the asperities from the previously hot rolled strip.
  • the installation comprises a hydrocarbon combustion furnace comprising an open enclosure through which the band passes, and means for introducing a gas mixture of hydrocarbon and air.
  • the open enclosure comprises, in the running direction of the band shown, two successive zones, a first heating zone and a second temperature maintenance.
  • the first heating zone is equipped with powerful heating means (not shown) capable of rapidly heating the strip at a heating rate V1, up to a holding temperature T1.
  • the strip is maintained at this temperature T1 in the second zone, during a holding time M, and then cooled at a speed V2 in a cooling zone located just after the exit of the oven.
  • the installation comprises a pickling device which comprises at least one acid-resistant pickling tank, and containing a pickling solution.
  • the previously hot rolled austenitic steel strip is cold rolled at room temperature, with a reduction ratio of between 55 and 85%.
  • a cold-rolled strip having a thickness of between 0.6 and 2 mm is thus obtained.
  • deformation martensite ⁇ ' is observed by micrography and its volume fraction can be measured by X-ray diffraction or magnetic induction measurement (ferromagnetic phase).
  • a recrystallization annealing should be carried out making it possible to obtain austenite grains whose average size does not exceed 4 ⁇ m.
  • the elastic limit Rp 0.2 is inversely proportional to the square root of the grain size.
  • a fine-grained structure ie a structure in which the average size of the austenite grains does not exceed 4 ⁇ m, is significantly resistant, as will be seen later, to the phenomenon of matting (loss brightness) during cold forming operations, for example by stamping.
  • the reduction ratio is between 70 and 85%, so as to obtain a band having a smooth surface topography, ie an arithmetic average roughness Ra of between 0.07 and 0.12 ⁇ m, free micro-defects of shot blasting craters and / or etched grain boundaries.
  • This also makes it possible to store sufficient plastic deformation energy to promote faster recrystallization at low temperatures.
  • the inventors have demonstrated that when the strip is cold rolled with a sufficiently high reduction ratio, and with work rollers having an arithmetic mean roughness Ra less than or equal to 0.15 ⁇ m, then is subject to partial recrystallization annealing at a temperature of the order of 800 ° C, in a hydrocarbon combustor, to form an oxide layer sufficiently thin to be readily removed by acid stripping, without the grain boundaries are attacked, then the strip has both excellent mechanical characteristics and a glossy, gloss-like surface finish.
  • the average arithmetic roughness Ra transferred to the strip by the working rolls during the operation of Cold rolling is very little degraded. So, to get a band with a shine greater than 50, it is essential that the working rolls have an arithmetic average roughness of less than or equal to 0.15 ⁇ m, and preferably less than 0.10 ⁇ m.
  • the brightness measured in the context of the present invention corresponds to the measurement of the reflectivity of the surface and is measured at an angle of 60 °.
  • the cold-rolled strip is then passed through the open chamber of the hydrocarbon combustion furnace, inside which there is an oxidizing atmosphere with respect to the iron, in order for it to undergo a heat treatment. consisting of a partial recrystallization annealing of the steel, followed by forced cooling.
  • the atmosphere in the furnace is composed of a gaseous mixture of air and at least one hydrocarbon in an air / hydrocarbon volume ratio of between 1.1 and 1.5, the gas mixture comprising in addition 3 to 8 % by volume of oxygen.
  • the furnace atmosphere is preferably a gaseous mixture of air and hydrocarbon in an air / hydrocarbon volume ratio of between 1.1 and 1.5, the gaseous mixture further comprising 3 to 8% by volume of oxygen.
  • the at least one hydrocarbon is chosen from natural gas, butane and methane. Natural gas is preferentially chosen because of its low cost and ease of transportation.
  • the atmosphere in the annealing furnace is too oxidizing and the formed oxide layer is so thick that to eliminate it, aggressive pickling solutions will have to be used. that will attack the grain boundaries. The surface appearance of the strip will then be dull.
  • the air / hydrocarbon volume ratio is less than 1.1, the atmosphere in the annealing furnace is too reducing. Therefore, the re-carburization of the steel by the hydrocarbons can not be avoided, and the corrosion resistance of the steel will be degraded.
  • the heat treatment is adjusted so as to obtain a steel strip whose recrystallized volume fraction is between 60 and 75%. Indeed, if the non-recrystallized volume fraction (measured by micrographic observation and image analysis) is greater than 40%, the microstructure of the steel induces mechanical properties that are too high, and the elongation A 80 of the strip is less than at 40%. On the other hand, if the non-recrystallized volume fraction is less than 25%, the mechanical characteristics such as the elastic limit Rp 0.2 , will be insufficient.
  • the partial recrystallization annealing is carried out at a speed V1 of between 10 and 80 ° C./s, a temperature T of between 800 and 950 ° C. and a holding time M of between 10 and 100 seconds, advantageously between 60 and 80 seconds.
  • the annealing of the strip at a temperature T between 800 and 950 ° C makes it possible to limit the diffusion of chromium at the grain boundaries, and consequently limits the attack of the grain boundaries during the subsequent chemical stripping of the strip, which promotes obtaining a glossy surface appearance.
  • the steel When the temperature T is less than 800 ° C., the steel does not recrystallize sufficiently to obtain the desired mechanical properties. Indeed, the steel has an elastic limit Rp 0.2 greater than 600 MPa but an elongation A 80 less than 40% mediocre, which greatly limits its cold deformation capabilities.
  • the stainless steel can only recrystallize during a very long maintenance time M which is not compatible with the industrial requirements.
  • the austenite grains increase in favor of martensite, and the elastic limit Rp 0.2 is insufficient to give the stainless steel good mechanical properties.
  • the recrystallized volume fraction of the strip will be less than 60%, and the elongation A 80 of the strip is insufficient.
  • the austenitic grains grow in favor of martensite, and the mechanical characteristics, such as the elastic limit Rp 0.2 , become insufficient.
  • the partially recrystallized steel strip then undergoes forced cooling at a speed V 2 of between 10 and 80 ° C / s, for example by blowing air or by blowing air under pressure and spraying water.
  • V 2 a speed of between 10 and 80 ° C / s
  • the yield point Rp 0.2 and the breaking load Rm increase.
  • the strip When the strip is cooled, it is stripped with an acid pickling solution capable of completely removing said oxide layer depending on its thickness and nature, without attacking the grain boundaries of the steel.
  • the strip undergoes a first electrolytic pickling in a bath containing sodium sulphate whose concentration is between 150 and 200 g / l, with a pH of less than 3, and with an amperage of between 5 and 12 kA.
  • austenitic stainless steel strips according to the invention have comparable weldability to standard annealed austenitic stainless steel or standard annealed-pickled stainless steel strips.
  • an austenitic stainless steel strip according to the invention will be compared with, on the one hand, a austenitic stainless steel strip of the standard annealed-pickled type (2D standard), and on the other hand a standard annealing-austenitic stainless steel strip (standard 2RB).
  • Table 1 chemical composition of the stainless steel according to the invention, expressed in% by weight, the balance being iron and unavoidable impurities.
  • AS33 steel is cast to form a slab that is hot rolled to a thickness of 4.5 mm. This slab is then cold-rolled with working rolls having an arithmetic average roughness Ra of 0.1 ⁇ m, with a reduction ratio of 82% so as to obtain in a passage a strip of 0.8 mm thickness.
  • This cold-rolled strip is subjected to a partial recrystallization annealing of the steel in a combustion furnace, heating it with a heating rate of 50 ° C / sec, up to a holding temperature of 820 ° C and during a hold time of 50 seconds.
  • the atmosphere in the furnace is a mixture of air and natural gas comprising an oxygen level of 4% by volume.
  • the volume ratio of air to natural gas is 1.3.
  • the web is then cooled at a cooling rate of 70 ° C / sec to room temperature.
  • the strip undergoes a first electrolytic pickling in a bath containing sodium sulphate whose concentration is 175 g / l, pH 2, with an amperage of 9 kA, and for a duration of 15 s, then a second etching electrochemical in a bath containing nitric acid whose concentration is 100 g / l, pH 2, with an amperage of 9 kA, and for a period of 15 s.
  • the band obtained undergoes no further treatment, nor polishing of the surface, nor skin pass.
  • AS33 steel is cast to form a slab that is hot rolled to a thickness of 4.5 mm. This slab is then laminated to cold with a reduction rate of 82% so as to obtain in one pass a 0.8 mm thick strip.
  • This cold-rolled strip is subjected to a complete recrystallization annealing of the steel, in a combustion furnace, at a temperature of 1120 ° C. for a period of 50 seconds.
  • the atmosphere in the furnace is a mixture of air and natural gas comprising an oxygen level of 4% by volume.
  • the volume ratio of air to natural gas is 1.3.
  • the web is then cooled at a cooling rate of 80 ° C / sec to room temperature.
  • the strip is stripped to completely remove the 0.2 ⁇ m thick formed oxide layer in sodium sulfate and sulfuric acid baths.
  • the band obtained undergoes no further treatment, nor polishing of the surface, nor skin pass.
  • AS33 steel is cast to form a slab that is hot rolled to a thickness of 4.5 mm. This slab is then cold rolled with working rolls which give a glossy surface appearance to the strip, with a reduction rate of 82% so as to obtain in one pass a 0.8 mm thick strip.
  • This cold-rolled strip is subjected to a complete recrystallization annealing of the steel, in a bright-annealing furnace inside which an atmosphere consisting of a gaseous mixture comprising 10% by volume of nitrogen and 90% prevails. in volume of hydrogen and having a dew point of -50 ° C, heating it with a heating rate of 50 ° C / sec, up to a holding temperature of 1100 ° C.
  • the strip is cooled at a cooling rate of 60 ° C / s to room temperature.
  • the band obtained undergoes no further treatment, nor polishing of the surface, nor skin pass.
  • Table 2 shows the mechanical and appearance characteristics of these three types of tape.
  • Elastic limit Rp 0.2 (MPa) 312 308 596 Breaking Load
  • Rm MPa 656 677 796 Lengthening
  • A80 % 59 59 42
  • Grain size ⁇ m 12 to 25 15 to 20 1 to 4
  • Appearance characteristics 2D standard tape 2RB standard tape Strip according to the invention Brightness (60 °, long direction) 21 55 50 Avg. Roughness arithm., Ra ( ⁇ m) 0.12 0.12 0.07 Surface hardness (HV 5 ) 169 172 286
  • the strip according to the invention has, compared to standard 2D and standard 2RB strips, both a glossy surface appearance and good mechanical characteristics. It also has a superficial hardness greater than the two bands of the prior art.
  • Blanks are cut in the steel strip according to the invention, in the standard 2RB band and in the standard 2D band. These blanks are then stamped in a stamping press conventionally comprising a punch, a die and a blank holder, to form buckets.
  • the brightness of the surface is measured both in the bottom of the bucket and on the skirt of the bucket, which estimates an average value of gloss of the stamped part.
  • the loss of gloss is low, and much lower than that observed for the standard 2B and standard 2RB strips.
  • the scratch resistance tests are carried out on the steel strip according to the invention, and the standard strip 2RB according to the ISO 1518 standard using a Clemen machine whose hemispherical steel hardened tip has a hardness of 1500 Hv, and a diameter of 1 mm.
  • the tests consist of applying, with variable loads of 50 g, 200 g and 400 g, the hemispherical tip to the surface of the strip so as to create a scratch.
  • the test results are summarized in Table 4. TABLE 4 Charge (g) Depth of scratch ( ⁇ m) for standard 2RB tape Depth of scratch ( ⁇ m) for the strip according to the invention Relative difference (%) 50 1.08 0.73 32 200 3 1.35 55 400 3.35 2.33 30
  • test results show that the steel strip according to the invention is more resistant to scratching than the standard 2RB strips, an order of magnitude of 40% on average, corresponding to the difference in relative surface hardness of the strip.
  • the intergranular corrosion resistance test is carried out on samples taken from the steel strip according to the invention and from the standard 2D strip.
  • This test is performed according to the NFA 05-159 standard. It involves immersing the sample in a boiling solution of sulfuric acid and copper sulphate for a period of 20 hours. The sample is then bent at 90 ° and the observation of the convex face of the latter, in comparison with a reference sample which has not been immersed in said solution, makes it possible to determine the degree of cracking in the extreme skin.
  • a low resistance to intergranular corrosion is characterized by the presence of numerous cracks on the convex face of the folded sample.
  • the intergranular corrosion resistance tests show that the austenitic stainless steel strip according to the invention is more resistant to intergranular corrosion than the standard 2D strip.

Abstract

Austenitic stainless steel strip comprises (by %.wt): 0.025 = carbon = 0.15; 0.20 =silicon = 1.0; 0.50 = manganese = 2.0; 6.0 = nickel = 12.0; 16.0 = chromium = 20.0; molybdenum = 3.0; 0.030 = nitrogen = 0.16; copper = 0.50; phosphorus = 0.50; sulfur = 0.015; possibly 0.10 = vanadium (V) and 0.03 = niobium (Nb) = 0.50, with 0.10 = Nb + V = 0.50; remainder being iron and production impurities, of which the average grain size of the austenite is less than or equal to 4 mu m and the surface has a brilliance greater than 50. An independent claim is also included for the continuous fabrication of the austenitic stainless steel strip.

Description

La présente invention concerne une bande en acier inoxydable austénitique, présentant une limite élastique Rp0.2 supérieure ou égale à 600 MPa, une charge à la rupture supérieure Rm supérieure ou égale à 800 MPa, un allongement A80 supérieur ou égal à 40 %, et un aspect de surface brillant, de type recuit-brillant. L'invention concerne également un procédé de fabrication en continu de cette bande en acier inoxydable austénitique.The present invention relates to an austenitic stainless steel strip, having an elastic limit Rp 0.2 greater than or equal to 600 MPa, an upper tensile load Rm greater than or equal to 800 MPa, an elongation A 80 greater than or equal to 40%, and a glossy surface appearance, of annealing-gloss type. The invention also relates to a continuous manufacturing process for this austenitic stainless steel strip.

Du fait de leur très bonne capacité de conformation à froid caractérisée par une résistance mécanique et une ductilité élevées, leur bonne soudabilité et leur excellente résistance à la corrosion, les aciers inoxydables austénitiques sont utilisés dans une large gamme d'applications finales telles que par exemple la fabrication de pièces mécaniques, les ustensiles de cuisson, et les tubes.Because of their very good cold forming capacity characterized by high mechanical strength and ductility, good weldability and excellent corrosion resistance, austenitic stainless steels are used in a wide range of end applications such as for example the manufacture of mechanical parts, cooking utensils, and tubes.

Selon l'application à laquelle on destine la bande en acier inoxydable austénitique, on lui fait subir un traitement thermique et un décapage final qui, selon les conditions de mise en oeuvre, lui confère soit un aspect de surface présentant une brillance élevée, intéressant par exemple pour la platerie, soit un aspect de surface mat intéressant pour la fabrication de façades de bâtiment. Dans le cadre de la présente invention, on entend par aspect de surface brillant, une surface présentant une brillance supérieure à 50, et par aspect de surface mat, une surface présentant une brillance inférieure à 20. Selon l'invention, la brillance correspond à la mesure de la réflectivité de la surface et est mesurée selon un angle de 60°.Depending on the application for which the strip of austenitic stainless steel is intended, it is subjected to a heat treatment and a final etching which, according to the conditions of implementation, gives it either a surface appearance having a high gloss, interesting by example for platerie, an aspect of matte surface interesting for the manufacture of building facades. In the context of the present invention, the term "glossy surface appearance" means a surface having a gloss greater than 50, and a "matte surface appearance" means a surface having a gloss of less than 20. According to the invention, the gloss corresponds to measuring the reflectivity of the surface and is measured at an angle of 60 °.

Conventionnellement, pour obtenir un aspect de surface brillant, la bande en acier inoxydable austénitique est préalablement laminée à froid avec des cylindres qui confèrent un aspect de surface brillant à la bande. La bande laminée à froid est ensuite dégraissée et rincée, puis subit un traitement thermique dans un four vertical dit de « recuit brillant » dans lequel règne une atmosphère réductrice. A cet effet, la bande défile dans le four constitué d'une enceinte complètement isolée de l'atmosphère extérieure, comprenant trois zones dans lesquelles circule un gaz neutre ou réducteur. Ce gaz est choisi par exemple parmi l'hydrogène, l'azote ou un mélange d'hydrogène et d'azote (gaz HNX), et présente un point de rosée compris entre -60 et -45°C. La bande est d'abord chauffée dans la première zone du four à une température comprise entre 1050 et 1150°C, et à une vitesse de chauffage de 30 à 60°C/s. Puis, elle est maintenue à cette température dans la deuxième zone du four pendant une durée suffisante pour permettre la recristallisation de l'acier et la restauration des propriétés mécaniques. Enfin, elle est refroidie dans la troisième zone du four jusqu'à une température de l'ordre de 150°C pour éviter toute ré-oxydation de la surface de la bande avec l'oxygène de l'air, lorsque la bande quitte l'enceinte du four.Conventionally, to obtain a glossy surface appearance, the austenitic stainless steel strip is cold-rolled beforehand with rolls which impart a glossy surface appearance to the strip. The cold rolled strip is then degreased and rinsed, and then undergoes a heat treatment in a vertical furnace called "bright annealing" in which there is a reducing atmosphere. For this purpose, the strip travels in the oven consisting of an enclosure completely isolated from the outside atmosphere, comprising three zones in which a neutral or reducing gas circulates. This gas is chosen for example, from hydrogen, nitrogen or a mixture of hydrogen and nitrogen (HNX gas), and has a dew point of between -60 and -45 ° C. The strip is first heated in the first zone of the oven at a temperature of between 1050 and 1150 ° C, and at a heating rate of 30 to 60 ° C / sec. Then, it is maintained at this temperature in the second zone of the oven for a time sufficient to allow the recrystallization of the steel and the restoration of the mechanical properties. Finally, it is cooled in the third zone of the oven to a temperature of the order of 150 ° C to prevent re-oxidation of the surface of the strip with the oxygen of the air, when the band leaves the oven enclosure.

A la sortie du four, l'aspect de surface brillant conféré à la bande lors du laminage à froid est maintenu, car le film d'oxyde qui s'est formé lors du recuit est très mince, d'une épaisseur de l'ordre de 10 angstrom.At the exit of the furnace, the glossy surface appearance imparted to the strip during cold rolling is maintained, because the oxide film which formed during the annealing is very thin, of a thickness of the order of 10 angstrom.

Cependant, notamment en raison de l'utilisation de gaz tel que l'hydrogène et/ou l'azote, et la nécessité de maintenir dans l'enceinte du four une atmosphère contrôlée avec un point de rosée constant, l'utilisation de ce type de four est complexe et onéreuse.However, particularly because of the use of gases such as hydrogen and / or nitrogen, and the need to maintain in the furnace enclosure a controlled atmosphere with a constant dew point, the use of this type oven is complex and expensive.

En outre, dans le cas d'un traitement de recuit brillant de la bande en acier inoxydable austénitique sous atmosphère gazeuse comprenant de l'hydrogène, les propriétés mécaniques de l'acier sont dégradées car l'hydrogène favorise l'apparition de fissures dans certaines zones des pièces obtenues par emboutissage de la bande. Cette fragilisation à l'hydrogène est d'autant plus sévère que la température de recuit est élevée et la teneur en hydrogène du mélange HNX est grande.In addition, in the case of a bright annealing treatment of the austenitic stainless steel strip under gaseous atmosphere comprising hydrogen, the mechanical properties of the steel are degraded because the hydrogen promotes the appearance of cracks in certain areas of the pieces obtained by stamping the band. This embrittlement with hydrogen is all the more severe as the annealing temperature is high and the hydrogen content of the HNX mixture is large.

Un autre moyen de fabrication d'une bande en acier inoxydable austénitique présentant un aspect de surface brillant, consiste à faire subir à la bande un traitement final de type recuit-décapage, qui lui confère un aspect de surface recuit-décapé, c'est à dire un aspect de surface mat, puis à procéder à une opération soit de polissage de la surface de la bande, soit de skin-pass de la bande.Another means of manufacturing an austenitic stainless steel strip having a glossy surface appearance is to subject the strip to a final treatment of the annealing-pickling type, which gives it an annealed-stripped surface appearance; to say a matte surface appearance, then to proceed to an operation of either polishing the surface of the strip, or skin-pass of the strip.

Pour obtenir une bande en acier inoxydable austénitique présentant un aspect de surface de type recuit-décapé, on procède comme suit. La bande préalablement laminée à froid subit un recuit continu à une température de l'ordre de 1100°C, pendant environ 1 min, dans un four où l'énergie thermique est générée par combustion d'hydrocarbures dont on règle l'arrivée d'air au brûleur de manière à obtenir une atmosphère oxydante. En effet, il est exclu de soumettre la bande à une atmosphère réductrice, c'est à dire une atmosphère contenant un excès d'hydrocarbures, pour éviter la dégradation de la tenue à la corrosion de la bande par re-carburation de l'acier par les hydrocarbures. La bande recuite subit ensuite un refroidissement à l'air et/ou un refroidissement forcé par aspersion d'eau en dehors du four. Enfin, elle est soumise à un décapage apte à éliminer la couche d'oxyde épaisse, de l'ordre de 0,1 à 0,3 µm, qui s'est formée à la surface de la bande lors du recuit dans le four. Le décapage est généralement réalisé dans plusieurs bacs de décapage contenant des solutions acides capables d'éliminer cette couche d'oxyde, comme par exemple un mélange d'acide nitrique et d'acide fluorhydrique.In order to obtain an austenitic stainless steel strip having an annealed-stripped surface appearance, the procedure is as follows. The previously cold-rolled strip undergoes continuous annealing at a temperature of the order of 1100 ° C, for about 1 min, in an oven where the thermal energy is generated by combustion of hydrocarbons which regulates the air supply to the burner so as to obtain an oxidizing atmosphere. Indeed, it is excluded to subject the strip to a reducing atmosphere, that is to say an atmosphere containing an excess of hydrocarbons, to avoid degradation of the corrosion resistance of the strip by re-carburation of steel by hydrocarbons. The annealed strip then undergoes air cooling and / or forced cooling by spraying water outside the oven. Finally, it is subjected to etching capable of removing the thick oxide layer, of the order of 0.1 to 0.3 μm, which formed on the surface of the strip during annealing in the oven. The pickling is generally carried out in several pickling tanks containing acid solutions capable of removing this oxide layer, such as a mixture of nitric acid and hydrofluoric acid.

Enfin, on soumet la bande soit à une opération de skin-pass, soit à une opération de polissage jusqu'à l'obtention de l'aspect de surface brillant souhaité. Le skin-pass est réalisé avec des cylindres de travail dit poli-miroir, c'est à dire des cylindres présentant une rugosité moyenne arithmétique Ra comprise entre 0,05 et 0,08 µm qui confèrent à la bande en acier un aspect de surface brillant.Finally, the strip is subjected to either a skin-pass operation or a polishing operation until the desired glossy surface appearance is obtained. The skin-pass is made with so-called mirror-polishing cylinders, ie cylinders having an arithmetic average roughness Ra of between 0.05 and 0.08 μm which give the steel strip a surface appearance. gloss.

Cependant, les bandes en acier inoxydable austénitique obtenues selon ces deux procédés présentent des caractéristiques mécaniques insuffisantes, puisque leur limite élastique Rp0,2 est comprise entre 250 et 350 MPa, et leur charge à la rupture Rm est comprise entre 600 et 700 MPa, pour un allongement A80 compris entre 50 et 60 %. Enfin, l'opération de skin-pass ou de polissage constitue une étape supplémentaire. En outre, l'opération de polissage est une opération longue et délicate.However, the austenitic stainless steel strips obtained according to these two processes have insufficient mechanical characteristics, since their elastic limit Rp 0.2 is between 250 and 350 MPa, and their load at break Rm is between 600 and 700 MPa, for an elongation A 80 of between 50 and 60%. Finally, the operation of skin-pass or polishing is an additional step. In addition, the polishing operation is a long and delicate operation.

La présente invention a donc pour but d'éviter les inconvénients des procédés de l'art antérieur, et de mettre à disposition un procédé permettant de conférer à une bande en acier inoxydable austénitique traitée dans un four à combustion d'hydrocarbures, un aspect de surface brillant, une limite élastique Rp0,2 de 600 MPa et une charge à la rupture Rm de 800 MPa associées à un allongement A80 supérieur ou égal à 40 %.The present invention therefore aims to avoid the disadvantages of the processes of the prior art, and to provide a method for conferring on an austenitic stainless steel strip treated in a hydrocarbon combustion furnace, an appearance of glossy surface, an elastic limit Rp 0.2 of 600 MPa and a tensile strength Rm of 800 MPa associated with elongation A 80 greater than or equal to 40%.

A cet effet, l'invention a pour objet une bande en acier inoxydable austénitique, présentant une limite élastique Rp0,2 supérieure ou égale à 600 MPa, une charge à la rupture Rm supérieure ou égale à 800 MPa, un allongement A80 supérieur ou égale à 40 %, dont la composition comprend en % en poids :

  • 0,025 ≤ C ≤ 0,15 %
  • 0,20 ≤ Si ≤ 1,0 %
  • 0,50 ≤ Mn ≤ 2,0 %
  • 6,0 ≤ Ni ≤ 12,0 %
  • 16,0 ≤ Cr ≤ 20,0 %
  • Mo ≤ 3,0%
  • 0,030 ≤ N ≤ 0,160 %
  • Cu ≤ 0,50 %
  • P ≤ 0,50 %
  • S ≤ 0,015 %
  • Eventuellement 0,10 ≤ V ≤ 0,50 %, et 0,03 ≤ Nb ≤ 0,50% avec 0,10 ≤ Nb + V ≤ 0,50%
le complément étant du fer et d'éventuelles impuretés résultant de l'élaboration, dont la taille moyenne des grains d'austénite est inférieure ou égale à 4 µm, et la surface présente une brillance supérieure à 50.For this purpose, the subject of the invention is an austenitic stainless steel strip having an elastic limit Rp 0.2 greater than or equal to 600 MPa, a tensile strength Rm of greater than or equal to 800 MPa, and a higher elongation A 80. or equal to 40%, whose composition comprises in% by weight:
  • 0.025 ≤ C ≤ 0.15%
  • 0.20 ≤ If ≤ 1.0%
  • 0.50 ≤ Mn ≤ 2.0%
  • 6.0 ≤ Ni ≤ 12.0%
  • 16.0 ≤ Cr ≤ 20.0%
  • Mo ≤ 3.0%
  • 0.030 ≤ N ≤ 0.160%
  • Cu ≤ 0.50%
  • P ≤ 0.50%
  • S ≤ 0.015%
  • Optionally 0.10 ≤ V ≤ 0.50%, and 0.03 ≤ Nb ≤ 0.50% with 0.10 ≤ Nb + V ≤ 0.50%
the balance being iron and any impurities resulting from the preparation, the average size of the austenite grains is less than or equal to 4 microns, and the surface has a gloss greater than 50.

La bande en acier selon l'invention bande présente en outre avantageusement une surface dont la rugosité moyenne arithmétique est inférieure ou égale à 0,08 µm, ce qui confère à la bande une surface lisse et donc un aspect de surface encore plus brillant.The strip of steel according to the invention also advantageously has a surface whose arithmetic average roughness is less than or equal to 0.08 μm, which gives the strip a smooth surface and therefore an even brighter surface appearance.

L'invention a également pour objet un procédé de fabrication en continu de cette bande en acier inoxydable austénitique.The invention also relates to a continuous manufacturing process for this austenitic stainless steel strip.

Les caractéristiques et avantages de la présente invention apparaîtront mieux au cours de la description qui va suivre, donnée à titre d'exemple non limitatif.The features and advantages of the present invention will appear better in the following description given by way of non-limiting example.

Pour obtenir une bande d'acier inoxydable austénitique selon l'invention, il faut d'abord élaborer, puis couler sous forme d'une brame un acier inoxydable austénitique qui comprend les éléments suivants :

  • du carbone à une teneur comprise entre 0,025 et 0,15 % en poids. Le carbone favorise la formation d'austénite, et contrôle la quantité et la dureté de la martensite de déformation. En outre, sa mise en solution solide durcit l'acier et augmente sa résistance mécanique. Si la teneur en carbone est inférieure à 0,025 %, l'acier devient instable et il se forme beaucoup de martensite, avec comme conséquence un allongement A80 insuffisant. En revanche, si la teneur en carbone est supérieure à 0,15 %, l'acier devient stable, la formation de martensite de déformation est insuffisante et l'acier ne possède plus assez d'énergie pour recristalliser. Par conséquent, la température de recuit minimum pour déclencher la recristallisation est élevée et la taille des grains d'austénite devient trop importante pour atteindre des caractéristiques mécaniques élevées. De plus, des teneurs en carbone encore supérieures favorisent la formation de carbures de chrome aux joints de grain lors des traitements thermiques ultérieurs et augmentent ainsi les risques de corrosion inter-granulaire.
  • du silicium à une teneur comprise entre 0,20 et 1,0 % en poids. Le silicium est utilisé à titre de désoxydant de l'acier liquide, et il participe au durcissement en solution solide. On limite sa teneur à 1,0 % en poids, car il a tendance à perturber le procédé de fabrication de la bande d'acier en posant des problèmes de ségrégation pendant la coulée en brame de l'acier.
  • du manganèse à une teneur comprise entre 0,50 et 2,0 % en poids. Le manganèse favorise la formation d'austénite. Si la teneur en manganèse est supérieure à 2,0 %, l'austénite étant trop stable, la formation de martensite de déformation est insuffisante et cela ne permet pas d'atteindre les niveaux de limite d'élasticité requis. Cependant, si la teneur en manganèse est inférieure à 0,50 %, la désoxydation de l'acier est insuffisante.
  • du chrome à une teneur comprise entre 16,0 et 20,0 %. Le chrome favorise la formation de martensite de déformation, et est un élément essentiel pour conférer à l'acier une bonne résistance à la corrosion. Si la teneur en chrome est supérieure à 20,0 %, on génère trop de martensite de déformation, ce qui oblige à augmenter la teneur des éléments favorisant la formation d'austénite comme le carbone, l'azote, le nickel et le manganèse. Si la teneur en chrome est inférieure à 16,0 %, la résistance à la corrosion de l'acier est insuffisante.
  • du nickel à une teneur comprise entre 6,0 et 12,0 %. Le nickel stabilise l'austénite et favorise la re-passivation. Si la teneur en nickel est inférieure à 6,0 %, la résistance à la corrosion de l'acier est insuffisante. Si la teneur en nickel est supérieure à 12,0 %, l'austénite se sur-stabilise, on ne forme plus suffisamment de martensite de déformation, et les caractéristiques mécaniques de l'acier sont insuffisantes.
  • du molybdène à une teneur inférieure ou égale à 3,0 %. Le molybdène favorise la formation de martensite de déformation et, augmente la résistance à la corrosion, surtout s'il est combiné avec l'azote. Au-delà d'une teneur de 3,0 %, la résistance à la corrosion de l'acier ne sera pas améliorée.
  • de l'azote à une teneur comprise entre 0,030 et 0,160 %. L'azote favorise la formation de l'austénite, retarde la précipitation des carbures, stabilise l'austénite, et améliore la formabilité. En outre, il joue un rôle dans l'ajustement de la taille des grains dans la structure. Cependant, s'il est ajouté à une teneur supérieure à 0,160 %, il risque de détériorer la ductilité à chaud de l'acier.
  • du cuivre à une teneur inférieure ou égale à 0,50 %. Le cuivre favorise la formation d'austénite et contribue à la résistance contre la corrosion. Cependant, au-delà d'une teneur de 0,50 %, la proportion de cuivre qui n'est pas en solution solide dans l'austénite augmente et la formabilité à chaud de l'acier est dégradée.
  • du phosphore à une teneur inférieure ou égale à 0,50 %. Le phosphore est un élément ségrégeant. Il favorise le durcissement en solution solide de l'acier, cependant sa teneur doit être limitée à 0,50 % car il augmente la fragilité de l'acier et son aptitude au soudage.
  • du soufre à une teneur inférieure ou égale à 0,015 %. Le soufre est également un élément ségrégeant dont la teneur doit être limitée afin d'éviter les fissure lors du laminage à chaud.
En outre, la composition peut éventuellement comprendre:
  • du vanadium à une teneur comprise entre 0,10 et 0,50 %. Le vanadium favorise la soudabilité de l'acier, et freine la croissance des grains d'austénite dans la zone affectée par la chaleur. Au-delà de 0,50 %, le vanadium ne contribue pas à l'amélioration de la soudabilité, et en dessous de 0,10 %, la soudabilité de l'acier est insuffisante.
  • du niobium à une teneur comprise entre 0,03 et 0,50 %. Le niobium favorise la soudabilité de l'acier, cependant au-delà de 0,50 %, il dégrade la formabilité à chaud de la bande d'acier.
  • avec une teneur totale en niobium et vanadium comprise entre 0,10 et 0,50 % pour garantir la soudabilité de l'acier sans effet néfaste sur la ductilité à chaud.
To obtain an austenitic stainless steel strip according to the invention, it is first necessary to form and then cast in the form of a slab an austenitic stainless steel which comprises the following elements:
  • carbon at a content of between 0.025 and 0.15% by weight. Carbon promotes the formation of austenite, and controls the amount and hardness of deformation martensite. In addition, its solid solution solution hardens the steel and increases its mechanical strength. If the carbon content is less than 0.025%, the steel becomes unstable and much martensite is formed, resulting in an elongation A 80 insufficient. On the other hand, if the carbon content is greater than 0.15%, the steel becomes stable, the formation of deformation martensite is insufficient and the steel no longer has enough energy to recrystallize. As a result, the minimum annealing temperature for initiating recrystallization is high and the size of the austenite grains becomes too large to achieve high mechanical characteristics. In addition, even higher carbon contents favor the formation of chromium carbides at the grain boundaries during subsequent heat treatments and thus increase the risk of intergranular corrosion.
  • silicon at a content of between 0.20 and 1.0% by weight. Silicon is used as the deoxidizer of liquid steel, and it participates in hardening in solid solution. Its content is limited to 1.0% by weight because it has a tendency to disturb the manufacturing process of the steel strip by posing problems of segregation during slab casting of the steel.
  • manganese at a level of between 0.50 and 2.0% by weight. Manganese promotes the formation of austenite. If the manganese content is greater than 2.0%, the austenite being too stable, the formation of deformation martensite is insufficient and this does not allow to reach the required levels of elastic limit. However, if the manganese content is less than 0.50%, the deoxidation of the steel is insufficient.
  • chromium at a level of between 16.0 and 20.0%. Chromium promotes the formation of deformation martensite, and is an essential element in giving steel good corrosion resistance. If the chromium content is greater than 20.0%, too much deformation martensite is generated, which makes it necessary to increase the content of the elements favoring the formation of austenite such as carbon, nitrogen, nickel and manganese. If the chromium content is less than 16.0%, the corrosion resistance of the steel is insufficient.
  • nickel at a level of between 6.0 and 12.0%. Nickel stabilizes the austenite and promotes re-passivation. If the nickel content is less than 6.0%, the corrosion resistance of the steel is insufficient. If the nickel content is greater than 12.0%, the austenite over-stabilizes, there is not enough deformation martensite, and the mechanical characteristics of the steel are insufficient.
  • molybdenum at a content of not more than 3.0%. Molybdenum promotes the formation of deformation martensite and increases corrosion resistance, especially when combined with nitrogen. Beyond a content of 3.0%, the corrosion resistance of the steel will not be improved.
  • nitrogen at a content of between 0.030 and 0.160%. Nitrogen promotes the formation of austenite, delays the precipitation of carbides, stabilizes austenite, and improves formability. In addition, it plays a role in the adjustment of grain size in the structure. However, if it is added at a level greater than 0.160%, it may deteriorate the hot ductility of the steel.
  • copper at a level not exceeding 0.50%. Copper promotes the formation of austenite and contributes to resistance against corrosion. However, beyond a content of 0.50%, the proportion of copper that is not in solid solution in the austenite increases and the hot formability of the steel is degraded.
  • phosphorus at a level not exceeding 0.50%. Phosphorus is a segregating element. It promotes solid solution hardening of steel, however its content must be limited to 0.50% because it increases the fragility of steel and its weldability.
  • sulfur at a level of less than or equal to 0.015%. Sulfur is also a segregating element whose content must be limited in order to avoid cracking during hot rolling.
In addition, the composition may optionally include:
  • vanadium at a content of between 0.10 and 0.50%. Vanadium promotes the weldability of steel, and inhibits the growth of austenite grains in the heat affected zone. Above 0.50%, vanadium does not contribute to the improvement of the weldability, and below 0.10%, the weldability of the steel is insufficient.
  • niobium at a level of between 0.03 and 0.50%. Niobium promotes the weldability of steel, however beyond 0.50%, it degrades the hot formability of the steel strip.
  • with a total niobium and vanadium content of between 0.10 and 0.50% to ensure the weldability of the steel with no adverse effect on hot ductility.

Le reste de la composition est constitué de fer et d'autres éléments que l'on s'attend habituellement à trouver en tant qu'impuretés résultant de l'élaboration de l'acier inoxydable, dans des proportions qui n'influent pas sur les propriétés recherchées.The remainder of the composition is iron and other elements usually expected to be found as impurities resulting from the processing of stainless steel, in proportions that do not affect the properties sought.

Après avoir été coulée, la brame est laminée à chaud dans un train à bandes pour former une bande laminée à chaud qui est recuite et, éventuellement décapée.After being cast, the slab is hot rolled in a strip train to form a hot rolled strip which is annealed and optionally etched.

La bande laminée à chaud subit ensuite divers traitements, de manière à obtenir une bande présentant à la fois d'excellentes caractéristiques mécaniques et un aspect de surface brillant, et cela sans avoir recours ni à un recuit dans un four de recuit-brillant, ni à un polissage final de la surface de la bande ou à une opération de skin-pass finale.The hot-rolled strip then undergoes various treatments, so as to obtain a strip having both excellent mechanical characteristics and a glossy surface appearance, without having recourse to either annealing in a bright annealing furnace, or a final polishing of the surface of the strip or a final skin-pass operation.

L'installation utilisée pour fabriquer la bande selon l'invention comprend un dispositif de laminage à froid de bandes, constituée d'un train à bandes comprenant des cylindres de travail entre lesquels défile la bande en acier inoxydable austénitique de composition selon l'invention. Les cylindres de travail présente une rugosité moyenne arithmétique Ra inférieure ou égale à 0,15 µm, et de préférence inférieure ou égale à 0,10 µm. Le diamètre des cylindres de travail du train à bandes est compris entre 50 et 100 mm, pour minimiser les efforts de laminage pour les taux de réduction élevés, c'est à dire à partir de 75% de réduction. Le train à bandes permet non seulement de réduire l'épaisseur de la bande, mais également de favoriser l'écrasement des aspérités issues de la bande préalablement laminée à chaud.The installation used to manufacture the strip according to the invention comprises a cold rolling device of strips, consisting of a band train comprising working rolls between which scrolls the austenitic stainless steel strip of composition according to the invention. The working rolls have an arithmetic mean roughness Ra of less than or equal to 0.15 μm, and preferably less than or equal to 0.10 μm. The diameter of the working rolls of the belt gear is between 50 and 100 mm, to minimize the rolling forces for the high reduction rates, that is to say from 75% reduction. The band train not only reduces the thickness of the band, but also to help crush the asperities from the previously hot rolled strip.

Successivement au dispositif de laminage à froid, l'installation comprend un four à combustion d'hydrocarbure comportant une enceinte ouverte au travers de laquelle la bande défile, et des moyens d'introduction d'un mélange gazeux d'hydrocarbure et d'air. L'enceinte ouverte comporte, dans le sens de défilement de la bande représenté, deux zones successives, une première zone de chauffage et une deuxième de maintien en température.Successively to the cold rolling device, the installation comprises a hydrocarbon combustion furnace comprising an open enclosure through which the band passes, and means for introducing a gas mixture of hydrocarbon and air. The open enclosure comprises, in the running direction of the band shown, two successive zones, a first heating zone and a second temperature maintenance.

La première zone de chauffage est équipée de moyens de chauffage puissants (non représentés) aptes à chauffer rapidement la bande à une vitesse de chauffage V1, jusqu'à une température de maintien T1. La bande est maintenue à cette température T1 dans la deuxième zone, pendant un temps de maintien M, puis est refroidie à une vitesse V2 dans une zone de refroidissement située juste après la sortie du four.The first heating zone is equipped with powerful heating means (not shown) capable of rapidly heating the strip at a heating rate V1, up to a holding temperature T1. The strip is maintained at this temperature T1 in the second zone, during a holding time M, and then cooled at a speed V2 in a cooling zone located just after the exit of the oven.

Enfin, après la zone de refroidissement, l'installation comprend un dispositif de décapage qui comporte au moins un bac de décapage résistant aux acides, et contenant une solution de décapage.Finally, after the cooling zone, the installation comprises a pickling device which comprises at least one acid-resistant pickling tank, and containing a pickling solution.

Selon l'invention, la bande en acier austénitique préalablement laminée à chaud est laminée à froid, à température ambiante, avec un taux de réduction compris entre 55 et 85 %. On obtient ainsi une bande laminée à froid présentant une épaisseur comprise entre 0,6 et 2 mm.According to the invention, the previously hot rolled austenitic steel strip is cold rolled at room temperature, with a reduction ratio of between 55 and 85%. A cold-rolled strip having a thickness of between 0.6 and 2 mm is thus obtained.

Lors de l'opération de laminage à froid à un taux de réduction compris entre 55 et 85 %, il se forme entre 50 et 90 % en volume de martensite de déformation α'. La martensite de déformation α' est observée par micrographie et sa fraction volumique peut être mesurée par diffraction des rayons X ou mesure d'induction magnétique (phase ferromagnétique).During the cold rolling operation at a reduction rate of between 55 and 85%, it forms between 50 and 90% by volume of deformation martensite α '. The deformation martensite α 'is observed by micrography and its volume fraction can be measured by X-ray diffraction or magnetic induction measurement (ferromagnetic phase).

Lorsque le taux de réduction est inférieur à 55%, les taux de martensite de déformation α' et de dislocation sont insuffisants pour conférer à l'acier inoxydable selon l'invention les caractéristiques mécaniques requises. En effet, pour des taux de réduction trop bas, l'énergie de déformation stockée en volume ne permet pas une recristallisation homogène de l'acier pour obtenir des grains austénitiques ayant une taille moyenne inférieure ou égale à 4 µm.When the reduction rate is less than 55%, deformation martensite α 'and dislocation rates are insufficient to give the stainless steel according to the invention the required mechanical characteristics. Indeed, for rates of reduction too low, the deformation energy stored in volume does not allow a homogeneous recrystallization of the steel to obtain austenitic grains having a mean size less than or equal to 4 microns.

Pour obtenir une limite élastique Rp0,2 élevée, il convient de réaliser un recuit de recristallisation permettant d'obtenir des grains d'austénite dont la taille moyenne n'excède pas 4 µm. En effet, il est connu que selon la loi de Hall-Petch, la limite élastique Rp0.2 est inversement proportionnelle à la racine carré de la taille de grain. En outre, une structure à grains fins, c'est à dire une structure dans laquelle la taille moyenne des grains d'austénite n'excède pas 4 µm, résiste de manière significative, comme on le verra ultérieurement, au phénomène de matification (perte de brillance) lors des opérations de mise en forme à froid, par exemple par emboutissage.To obtain a high elastic limit Rp 0.2 , a recrystallization annealing should be carried out making it possible to obtain austenite grains whose average size does not exceed 4 μm. Indeed, it is known that according to the Hall-Petch law, the elastic limit Rp 0.2 is inversely proportional to the square root of the grain size. In addition, a fine-grained structure, ie a structure in which the average size of the austenite grains does not exceed 4 μm, is significantly resistant, as will be seen later, to the phenomenon of matting (loss brightness) during cold forming operations, for example by stamping.

En outre, d'un point de vue brillance de surface après laminage à froid, des taux de réduction inférieurs à 55% ne permettent pas de réparer l'aspect de surface de la bande préalablement laminée à chaud, et il persiste en conséquence des cratères de grenaillage ou des restes d'attaques inter-granulaires issus des opérations de décalaminage mécanique et chimique préalables au laminage à froid et postérieures au laminage à chaud. Un taux de réduction supérieur à 55% permet de diminuer la densité de micro-défauts de type cratères de grenaillage et/ou joints de grain et ainsi d'obtenir un aspect surface présentant une brillance homogène et élevée après laminage à froid.In addition, from a surface gloss point of view after cold rolling, reduction rates of less than 55% do not make it possible to repair the surface appearance of the previously hot-rolled strip, and consequently craters persist. shot peening or remnants of intergranular attack from mechanical and chemical descaling operations prior to cold rolling and subsequent to hot rolling. A reduction rate greater than 55% makes it possible to reduce the density of micro-defects of the shot peening crater type and / or grain boundaries and thus to obtain a surface appearance having a uniform and high gloss after cold rolling.

Cependant, lorsque le taux de laminage à froid est supérieur à 85 %, on inflige des contraintes trop importantes sur les cylindres de travail, et il n'est plus possible de laminer la bande. De plus, le risque d'apparition de micro-défauts de type « griffes de chaleur » dus à des contraintes de cisaillement à l'interface cylindre/bande laminée à froid trop élevées, devient trop important.However, when the cold rolling rate is greater than 85%, excessive stresses are imposed on the work rolls, and it is no longer possible to roll the strip. In addition, the risk of micro-defects appearing of the type "heat claws" due to shear stresses at the interface cylinder / strip cold rolled too high, becomes too important.

De préférence, le taux de réduction est compris entre 70 et 85 %, de manière à obtenir une bande présentant une topographie de surface lisse, c'est à dire une rugosité moyenne arithmétique Ra comprise entre 0,07 et 0,12 µm, exempte de micro-défauts de type cratères de grenaillage et/ou joints de grain attaqués chimiquement. Cela permet en outre de stocker une énergie de déformation plastique suffisante pour favoriser une recristallisation plus rapide à basse température.Preferably, the reduction ratio is between 70 and 85%, so as to obtain a band having a smooth surface topography, ie an arithmetic average roughness Ra of between 0.07 and 0.12 μm, free micro-defects of shot blasting craters and / or etched grain boundaries. This also makes it possible to store sufficient plastic deformation energy to promote faster recrystallization at low temperatures.

Les demandeurs tiennent à souligner que l'obtention d'un aspect de surface brillant non pas par un procédé de recuit brillant classique, mais par un procédé de recuit oxydant suivi d'un décapage était contraire aux attentes initiales des inventeurs, qui prévoyaient, selon leur théorie, d'obtenir une bande présentant un aspect de surface mat à faible brillance caractéristique des aciers recuits dans un four à combustion d'hydrocarbure. En effet, les inventeurs pensaient, que selon leur théorie, la limitation de la croissance de la taille de grain en volume, obtenue par recristallisation contrôlée d'un acier inoxydable austénitique, tout en augmentant la densité surfacique des joints de grains attaqués chimiquement, favoriserait la réflexion diffuse de la lumière à la surface et donc l'obtention d'une surface mate et non brillante.Applicants wish to emphasize that obtaining a glossy surface appearance not by a conventional bright annealing process, but by an oxidative annealing process followed by stripping was contrary to the initial expectations of the inventors, which provided, according to their theory, to obtain a strip having a matt low gloss surface appearance characteristic of steels annealed in a hydrocarbon combustion furnace. Indeed, the inventors thought that, according to their theory, the limitation of the growth of the grain size in volume, obtained by controlled recrystallization of austenitic stainless steel, while increasing the surface density of chemically etched grain boundaries, would favor the diffuse reflection of the light on the surface and thus obtaining a matt and non-glossy surface.

Or, les inventeurs ont mis en évidence, que lorsque la bande est laminée à froid avec un taux de réduction suffisamment élevé, et avec des cylindres de travail présentant une rugosité moyenne arithmétique Ra inférieure ou égale à 0,15 µm, puis est soumise à un recuit de recristallisation partiel à une température de l'ordre de 800°C, dans un four à combustion d'hydrocarbure, pour former une couche d'oxyde suffisamment mince pour être facilement éliminée par un décapage acide, sans que les joints de grains soient attaqués, alors la bande présente à la fois d'excellentes caractéristiques mécaniques et un aspect de surface brillant, de type recuit-brillant.However, the inventors have demonstrated that when the strip is cold rolled with a sufficiently high reduction ratio, and with work rollers having an arithmetic mean roughness Ra less than or equal to 0.15 μm, then is subject to partial recrystallization annealing at a temperature of the order of 800 ° C, in a hydrocarbon combustor, to form an oxide layer sufficiently thin to be readily removed by acid stripping, without the grain boundaries are attacked, then the strip has both excellent mechanical characteristics and a glossy, gloss-like surface finish.

Dans les conditions de l'invention, c'est à dire en l'absence de l'attaque des joints de grain de l'acier, la rugosité moyenne arithmétique Ra transférée à la bande par les cylindres de travail lors de l'opération de laminage à froid est très peu dégradée. Ainsi, pour obtenir une bande ayant une brillance supérieure à 50, il est essentiel que les cylindres de travail présentent une rugosité moyenne arithmétique inférieure ou égale à 0,15 µm, et de préférence inférieure à 0,10 µm. La brillance mesurée dans le cadre de la présente invention, correspond à la mesure de la réflectivité de la surface et est mesurée selon un angle de 60°.Under the conditions of the invention, that is to say in the absence of the attack of the grain boundaries of the steel, the average arithmetic roughness Ra transferred to the strip by the working rolls during the operation of Cold rolling is very little degraded. So, to get a band with a shine greater than 50, it is essential that the working rolls have an arithmetic average roughness of less than or equal to 0.15 μm, and preferably less than 0.10 μm. The brightness measured in the context of the present invention corresponds to the measurement of the reflectivity of the surface and is measured at an angle of 60 °.

Selon l'invention, on fait ensuite défiler la bande laminée à froid dans l'enceinte ouverte du four à combustion d'hydrocarbure, à l'intérieur de laquelle règne une atmosphère oxydante vis à vis du fer, pour lui faire subir un traitement thermique consistant en un recuit de recristallisation partiel de l'acier, suivi par un refroidissement forcé.According to the invention, the cold-rolled strip is then passed through the open chamber of the hydrocarbon combustion furnace, inside which there is an oxidizing atmosphere with respect to the iron, in order for it to undergo a heat treatment. consisting of a partial recrystallization annealing of the steel, followed by forced cooling.

L'atmosphère régnant dans le four est composée d'un mélange gazeux d'air et d'au moins un hydrocarbure dans un rapport volumique air/hydrocarbure compris entre 1,1 et 1,5, le mélange gazeux comprenant en outre 3 à 8% en volume d'oxygène. L'atmosphère du four est préférentiellement un mélange gazeux d'air et d'hydrocarbure dans un rapport volumique air/hydrocarbure compris entre 1,1 et 1,5, le mélange gazeux comprenant en outre 3 à 8% en volume d'oxygène.The atmosphere in the furnace is composed of a gaseous mixture of air and at least one hydrocarbon in an air / hydrocarbon volume ratio of between 1.1 and 1.5, the gas mixture comprising in addition 3 to 8 % by volume of oxygen. The furnace atmosphere is preferably a gaseous mixture of air and hydrocarbon in an air / hydrocarbon volume ratio of between 1.1 and 1.5, the gaseous mixture further comprising 3 to 8% by volume of oxygen.

L'au moins un hydrocarbure est choisi parmi le gaz naturel, le butane et le méthane. Le gaz naturel est préférentiellement choisi en raison de son faible coût, et de sa facilité de transport.The at least one hydrocarbon is chosen from natural gas, butane and methane. Natural gas is preferentially chosen because of its low cost and ease of transportation.

Si le rapport volumique air/hydrocarbure est supérieur à 1,5, l'atmosphère régnant dans le four de recuit est trop oxydante et la couche d'oxyde formée est tellement épaisse que pour l'éliminer, il faudra utiliser des solutions de décapage agressives qui vont attaquer les joints de grain. L'aspect de surface de la bande sera alors mat.If the air / hydrocarbon volume ratio is greater than 1.5, the atmosphere in the annealing furnace is too oxidizing and the formed oxide layer is so thick that to eliminate it, aggressive pickling solutions will have to be used. that will attack the grain boundaries. The surface appearance of the strip will then be dull.

Cependant, si le rapport volumique air/hydrocarbure est inférieur à 1,1, l'atmosphère régnant dans le four de recuit est trop réductrice. Par conséquent, la re-carburation de l'acier par les hydrocarbures ne pourra pas être évitée, et la tenue à la corrosion de l'acier sera dégradée.However, if the air / hydrocarbon volume ratio is less than 1.1, the atmosphere in the annealing furnace is too reducing. Therefore, the re-carburization of the steel by the hydrocarbons can not be avoided, and the corrosion resistance of the steel will be degraded.

Pour obtenir une bande dont la surface présente un aspect brillant, on doit veiller à régler les conditions du traitement thermique de manière à obtenir une bande couverte par une couche d'oxyde, dont l'épaisseur est inférieure à 0,10 µm. En effet, si l'épaisseur d'oxyde est supérieure ou égale à 0,10 µm, il faudra, pour retirer cette couche d'oxyde épaisse, mettre en oeuvre des acides de décapage agressifs qui vont attaquer les joints de grain, et cela conférera un aspect de surface mat à la bande.To obtain a strip whose surface has a glossy appearance, care must be taken to adjust the conditions of the heat treatment so as to obtain a strip covered by an oxide layer, the thickness of which is less than 0.10 μm. Indeed, if the oxide thickness is greater than or equal to 0.10 μm, it In order to remove this thick oxide layer, it will be necessary to use aggressive pickling acids that will attack the grain boundaries, and this will impart a matte surface appearance to the strip.

Pour obtenir les caractéristiques mécaniques requises, on ajuste le traitement thermique de manière à obtenir une bande en acier dont la fraction volumique recristallisée est comprise entre 60 et 75 %. En effet, si la fraction volumique non recristallisée (mesurée par observation micrographique et analyse d'image) est supérieure à 40 %, la microstructure de l'acier induit des propriétés mécaniques trop élevées, et l'allongement A80 de la bande est inférieur à 40 %. En revanche, si la fraction volumique non recristallisée est inférieure à 25 %, les caractéristiques mécaniques comme la limite élastique Rp0,2, seront insuffisantes.To obtain the required mechanical characteristics, the heat treatment is adjusted so as to obtain a steel strip whose recrystallized volume fraction is between 60 and 75%. Indeed, if the non-recrystallized volume fraction (measured by micrographic observation and image analysis) is greater than 40%, the microstructure of the steel induces mechanical properties that are too high, and the elongation A 80 of the strip is less than at 40%. On the other hand, if the non-recrystallized volume fraction is less than 25%, the mechanical characteristics such as the elastic limit Rp 0.2 , will be insufficient.

De préférence, le recuit de recristallisation partiel est réalisé à une vitesse V1 comprise entre 10 et 80°C/s, une température T comprise entre 800 et 950°C et un temps de maintien M compris entre 10 et 100 secondes, avantageusement entre 60 et 80 secondes.Preferably, the partial recrystallization annealing is carried out at a speed V1 of between 10 and 80 ° C./s, a temperature T of between 800 and 950 ° C. and a holding time M of between 10 and 100 seconds, advantageously between 60 and 80 seconds.

Le recuit de la bande à une température T comprise entre 800 et 950°C permet de limiter la diffusion du chrome aux joints de grain, et par conséquent limite l'attaque des joints de grains lors du décapage chimique ultérieur de la bande, ce qui favorise l'obtention d'un aspect de surface brillant.The annealing of the strip at a temperature T between 800 and 950 ° C makes it possible to limit the diffusion of chromium at the grain boundaries, and consequently limits the attack of the grain boundaries during the subsequent chemical stripping of the strip, which promotes obtaining a glossy surface appearance.

Lorsque la température T est inférieure à 800°C, l'acier ne recristallise pas suffisamment pour obtenir les propriétés mécaniques recherchées. En effet, l'acier présente une limite élastique Rp0,2 supérieure à 600 Mpa mais un allongement A80 inférieur à 40% médiocre, ce qui limite fortement ses capacités de déformation à froid.When the temperature T is less than 800 ° C., the steel does not recrystallize sufficiently to obtain the desired mechanical properties. Indeed, the steel has an elastic limit Rp 0.2 greater than 600 MPa but an elongation A 80 less than 40% mediocre, which greatly limits its cold deformation capabilities.

Lorsque la température T est supérieure à 950°C, non seulement la limite élastique Rp0.2 de la bande est insuffisante en raison du grossissement des grains d'austénite au profit de la martensite qui disparaît complètement, mais aussi, la brillance de la surface de la bande diminue car la couche d'oxyde devient importante.When the temperature T is greater than 950 ° C, not only the elastic limit Rp 0.2 of the band is insufficient because of the magnification of the austenite grains in favor of martensite which disappears completely, but also, the brightness of the surface of the band decreases because the oxide layer becomes important.

Lorsque la vitesse de chauffage V1 de la bande est inférieure à 10°C/s, l'acier inoxydable ne peut recristalliser que pendant un temps de maintien M très long qui n'est pas compatible avec les exigences industrielles. D'autre part, les grains d'austénite grossissent au profit de la martensite, et la limite élastique Rp0.2 est insuffisante pour conférer à l'acier inoxydable de bonnes propriétés mécaniques.When the heating rate V1 of the strip is less than 10 ° C./s, the stainless steel can only recrystallize during a very long maintenance time M which is not compatible with the industrial requirements. Else on the other hand, the austenite grains increase in favor of martensite, and the elastic limit Rp 0.2 is insufficient to give the stainless steel good mechanical properties.

En dessous d'un temps de maintien M à la température T inférieure à 10 secondes, la fraction volumique recristallisée de la bande sera inférieure à 60 %, et l'allongement A80 de la bande est insuffisant. En revanche, au-delà de 100 secondes, les grains austénitiques grossissent au profit de la martensite, et les caractéristiques mécaniques, telle que la limite élastique Rp0.2, deviennent insuffisantes.Below a holding time M at the temperature T less than 10 seconds, the recrystallized volume fraction of the strip will be less than 60%, and the elongation A 80 of the strip is insufficient. On the other hand, beyond 100 seconds, the austenitic grains grow in favor of martensite, and the mechanical characteristics, such as the elastic limit Rp 0.2 , become insufficient.

La bande d'acier partiellement recristallisé subit ensuite un refroidissement forcé à une vitesse V2 comprise entre 10 et 80°C/s, par exemple par insufflation d'air ou par insufflation d'air sous pression et pulvérisation d'eau. Lorsque la vitesse de refroidissement V2 est supérieure à 10 °C/s, la limite élastique Rp0,2 et la charge à la rupture Rm augmentent.The partially recrystallized steel strip then undergoes forced cooling at a speed V 2 of between 10 and 80 ° C / s, for example by blowing air or by blowing air under pressure and spraying water. When the cooling rate V2 is greater than 10 ° C / s, the yield point Rp 0.2 and the breaking load Rm increase.

Lorsque la bande est refroidie, elle subit un décapage à l'aide d'une solution de décapage acide capable d'éliminer complètement ladite couche d'oxyde en fonction de son épaisseur et de sa nature, sans attaquer les joints de grains de l'acier.When the strip is cooled, it is stripped with an acid pickling solution capable of completely removing said oxide layer depending on its thickness and nature, without attacking the grain boundaries of the steel.

Par exemple, la bande subit un premier décapage électrolytique dans un bain contenant du sulfate de sodium dont la concentration est comprise entre 150 et 200 g/l, de pH inférieur à 3, et avec un ampérage compris entre 5 et 12 kA.For example, the strip undergoes a first electrolytic pickling in a bath containing sodium sulphate whose concentration is between 150 and 200 g / l, with a pH of less than 3, and with an amperage of between 5 and 12 kA.

Elle subit ensuite un second décapage électrochimique dans un bain contenant de l'acide nitrique dont la concentration est comprise entre 80 et 120 g/l, le pH inférieur à 3, et avec un ampérage compris entre 5 et 12 kA.It then undergoes a second electrochemical etching in a bath containing nitric acid whose concentration is between 80 and 120 g / l, the pH below 3, and with an amperage of between 5 and 12 kA.

La bande selon l'invention présente en outre les avantages suivants:

  • Une meilleure résistance de la brillance après déformation que les bandes en acier inoxydable austénitique ayant subi un recuit dans un four de recuit-brillant (standard 2RB). En effet, la perte de la brillance de la bande selon l'invention n'est que de 30 % après emboutissage, alors qu'elle est de 80 % pour la bande recuit-brillant standard.
  • Une meilleure résistance contre la corrosion inter-granulaire que les bandes en acier inoxydable austénitique ayant subi un traitement de type recuit-décapé standard (standard 2D).
  • Une meilleure résistance contre les rayures que les bandes en acier inoxydable austénitique recuit-brillant standard (standard 2RB).
  • Une dureté Vickers HV5, mesurée par indentation, supérieure à celle des bandes en acier inoxydable austénitique ayant subi un traitement de type recuit-décapé standard (standard 2D), et à celle des bandes en acier inoxydable austénitique recuit-brillant standard (standard 2RB).
The band according to the invention also has the following advantages:
  • Better gloss resistance after deformation than the austenitic stainless steel strips annealed in a bright annealing furnace (standard 2RB). Indeed, the loss of the brightness of the strip according to the invention is only 30% after stamping, while it is 80% for the standard annealed-gloss tape.
  • Better resistance against intergranular corrosion than austenitic stainless steel strips having undergone a standard annealing-pickling treatment (2D standard).
  • Better scratch resistance than standard austenitic annealed-gloss stainless steel strips (standard 2RB).
  • Vickers HV 5 hardness, measured by indentation, higher than that of austenitic stainless steel strips having undergone a standard annealing-pickling treatment (standard 2D), and that of standard annealed austenitic-bright stainless steel strips (standard 2RB ).

Par ailleurs, les bandes en acier inoxydables austénitiques selon l'invention présentent une aptitude au soudage comparable aux bandes en acier inoxydable austénitique recuit-brillant standard ou recuit-décapé standard.Furthermore, the austenitic stainless steel strips according to the invention have comparable weldability to standard annealed austenitic stainless steel or standard annealed-pickled stainless steel strips.

L'invention va à présent être illustrée par des exemples donnés à titre indicatif, et non limitatif.The invention will now be illustrated by examples given for information only, and not limiting.

Dans un premier temps, on va comparer les caractéristiques mécaniques et la brillance d'une bande en acier inoxydable austénitique selon l'invention avec d'une part une bande en acier inoxydable austénitique de type recuit-décapé standard (standard 2D), et d'autre part une bande en acier inoxydable austénitique de type recuit-brillant standard (standard 2RB).In a first step, the mechanical characteristics and the brightness of an austenitic stainless steel strip according to the invention will be compared with, on the one hand, a austenitic stainless steel strip of the standard annealed-pickled type (2D standard), and on the other hand a standard annealing-austenitic stainless steel strip (standard 2RB).

Puis, on comparera l'aptitude à l'emboutissage de ces trois types de bande, leur perte de brillance après emboutissage, leur résistance à la rayure, et enfin leur résistance à la corrosion inter-granulaire.Then, the drawability of these three types of tape, their loss of gloss after stamping, their scratch resistance, and finally their resistance to intergranular corrosion will be compared.

Pour cela, on va d'abord fabriquer à partir d'une même nuance d'acier inoxydable austénitique AS33, dont la composition chimique est donnée dans le tableau 1 ci-dessous, une bande en acier selon l'invention, une bande standard 2D et une bande standard 2RB.For this, we will first manufacture from the same grade of austenitic stainless steel AS33, the chemical composition of which is given in Table 1 below, a steel strip according to the invention, a standard 2D strip. and a standard 2RB band.

Tableau 1 : composition chimique de l'acier inoxydable selon l'invention, exprimée en % en poids, le complément étant du fer et des impuretés inévitables. TABLEAU 1 C Si Mn Ni Cr Mo N Cu P S V Nb 0,055 0,51 1,25 8,03 18,1 0,15 0,045 0,41 0,03 0,002 0,11 0,03 Table 1: chemical composition of the stainless steel according to the invention, expressed in% by weight, the balance being iron and unavoidable impurities. TABLE 1 VS Yes mn Or Cr MB NOT Cu P S V Nb 0,055 0.51 1.25 8.03 18.1 0.15 0,045 0.41 0.03 0,002 0.11 0.03

1- Fabrication de la bande selon l'invention 1- Fabrication of the strip according to the invention

L'acier AS33 est coulé pour former une brame qui est laminée à chaud jusqu'à atteindre une épaisseur de 4,5 mm. Cette brame est ensuite laminée à froid avec des cylindres de travail présentant une rugosité moyenne arithmétique Ra de 0,1 µm, avec un taux de réduction de 82 % de manière à obtenir en un passage une bande de 0,8 mm d'épaisseur.AS33 steel is cast to form a slab that is hot rolled to a thickness of 4.5 mm. This slab is then cold-rolled with working rolls having an arithmetic average roughness Ra of 0.1 μm, with a reduction ratio of 82% so as to obtain in a passage a strip of 0.8 mm thickness.

Cette bande laminée à froid est soumise à un recuit de recristallisation partiel de l'acier dans un four à combustion, en la chauffant avec une vitesse de chauffage de 50°C/s, jusqu'à une température de maintien de 820°C et pendant un temps de maintien de 50 secondes. L'atmosphère régnant dans le four est un mélange d'air et de gaz naturel comprenant un taux d'oxygène de 4% en volume. Le rapport volumique air/gaz naturel est de 1,3.This cold-rolled strip is subjected to a partial recrystallization annealing of the steel in a combustion furnace, heating it with a heating rate of 50 ° C / sec, up to a holding temperature of 820 ° C and during a hold time of 50 seconds. The atmosphere in the furnace is a mixture of air and natural gas comprising an oxygen level of 4% by volume. The volume ratio of air to natural gas is 1.3.

La bande est ensuite refroidie à une vitesse de refroidissement de 70°C/s jusqu'à la température ambiante.The web is then cooled at a cooling rate of 70 ° C / sec to room temperature.

Après refroidissement, une couche d'oxyde de 0,08 µm d'épaisseur s'est formée à la surface de la bande.After cooling, an oxide layer 0.08 μm thick formed on the surface of the strip.

Enfin, la bande subit un premier décapage électrolytique dans un bain contenant du sulfate de sodium dont la concentration est de 175 g/l, de pH 2, avec un ampérage de 9 kA, et pendant une durée de 15 s, puis un second décapage électrochimique dans un bain contenant de l'acide nitrique dont la concentration est de 100 g/l, de pH 2, avec un ampérage de 9 kA, et pendant une durée de 15 s.Finally, the strip undergoes a first electrolytic pickling in a bath containing sodium sulphate whose concentration is 175 g / l, pH 2, with an amperage of 9 kA, and for a duration of 15 s, then a second etching electrochemical in a bath containing nitric acid whose concentration is 100 g / l, pH 2, with an amperage of 9 kA, and for a period of 15 s.

La bande obtenue ne subit aucun autre traitement ultérieur, ni polissage de la surface, ni skin-pass.The band obtained undergoes no further treatment, nor polishing of the surface, nor skin pass.

2- Fabrication de la bande standard 2D d'aspect de surface mat 2- Fabrication of the standard 2D strip of matt surface appearance

L'acier AS33 est coulé pour former une brame qui est laminée à chaud jusqu'à atteindre une épaisseur de 4,5 mm. Cette brame est ensuite laminée à froid avec un taux de réduction de 82 % de manière à obtenir en un passage une bande de 0,8 mm d'épaisseur.AS33 steel is cast to form a slab that is hot rolled to a thickness of 4.5 mm. This slab is then laminated to cold with a reduction rate of 82% so as to obtain in one pass a 0.8 mm thick strip.

Cette bande laminée à froid est soumise à un recuit de recristallisation complet de l'acier, dans un four à combustion, à une température de 1120 °C, pendant un temps de 50 secondes. L'atmosphère régnant dans le four est un mélange d'air et de gaz naturel comprenant un taux d'oxygène de 4% en volume. Le rapport volumique air/gaz naturel est de 1,3.This cold-rolled strip is subjected to a complete recrystallization annealing of the steel, in a combustion furnace, at a temperature of 1120 ° C. for a period of 50 seconds. The atmosphere in the furnace is a mixture of air and natural gas comprising an oxygen level of 4% by volume. The volume ratio of air to natural gas is 1.3.

La bande est ensuite refroidie à une vitesse de refroidissement de 80 °C/s, jusqu'à la température ambiante.The web is then cooled at a cooling rate of 80 ° C / sec to room temperature.

Enfin, la bande subit un décapage pour éliminer complètement la couche d'oxyde formée d'épaisseur de 0,2 µm, dans des bains de sulfate de sodium et d'acide sulfurique.Finally, the strip is stripped to completely remove the 0.2 μm thick formed oxide layer in sodium sulfate and sulfuric acid baths.

La bande obtenue ne subit aucun autre traitement ultérieur, ni polissage de la surface, ni skin-pass.The band obtained undergoes no further treatment, nor polishing of the surface, nor skin pass.

3- Fabrication de la bande standard 2RB 3- Manufacture of the standard 2RB tape

L'acier AS33 est coulé pour former une brame qui est laminée à chaud jusqu'à atteindre une épaisseur de 4,5 mm. Cette brame est ensuite laminée à froid avec des cylindres de travail qui confèrent un aspect de surface brillant à la bande, avec un taux de réduction de 82 % de manière à obtenir en un passage une bande de 0,8 mm d'épaisseur.AS33 steel is cast to form a slab that is hot rolled to a thickness of 4.5 mm. This slab is then cold rolled with working rolls which give a glossy surface appearance to the strip, with a reduction rate of 82% so as to obtain in one pass a 0.8 mm thick strip.

Cette bande laminée à froid est soumise à un recuit de recristallisation complet de l'acier, dans un four de recuit-brillant à l'intérieur duquel règne une atmosphère composée d'un mélange gazeux comprenant 10% en volume d'azote et 90% en volume d'hydrogène et présentant un point de rosée de - 50 °C, en la chauffant avec une vitesse de chauffage de 50°C/s, jusqu'à une température de maintien de 1100°C.This cold-rolled strip is subjected to a complete recrystallization annealing of the steel, in a bright-annealing furnace inside which an atmosphere consisting of a gaseous mixture comprising 10% by volume of nitrogen and 90% prevails. in volume of hydrogen and having a dew point of -50 ° C, heating it with a heating rate of 50 ° C / sec, up to a holding temperature of 1100 ° C.

Enfin, la bande est refroidie à une vitesse de refroidissement de 60°C/s jusqu'à la température ambiante.Finally, the strip is cooled at a cooling rate of 60 ° C / s to room temperature.

La bande obtenue ne subit aucun autre traitement ultérieur, ni polissage de la surface, ni skin-pass.The band obtained undergoes no further treatment, nor polishing of the surface, nor skin pass.

On a regroupé dans le tableau 2, les caractéristiques mécaniques et d'aspect de ces trois types de bande. TABLEAU 2 Caractéristiques mécaniques Bande standard 2D Bande standard 2RB Bande selon l'invention Limite élastique, Rp 0,2 (MPa) 312 308 596 Charge à la rupture, Rm (MPa) 656 677 796 Allongement, A80 (%) 59 59 42 Taille des grains (µm) 12 à 25 15 à 20 1 à 4 Caractéristiques d'aspect Bande standard 2D Bande standard 2RB Bande selon l'invention Brillance (60°, sens long) 21 55 50 Rugosité moy. arithm., Ra (µm) 0,12 0,12 0,07 Dureté superficielle (HV5) 169 172 286 Table 2 shows the mechanical and appearance characteristics of these three types of tape. TABLE 2 Mechanical characteristics 2D standard tape 2RB standard tape Strip according to the invention Elastic limit, Rp 0.2 (MPa) 312 308 596 Breaking Load, Rm (MPa) 656 677 796 Lengthening, A80 (%) 59 59 42 Grain size (μm) 12 to 25 15 to 20 1 to 4 Appearance characteristics 2D standard tape 2RB standard tape Strip according to the invention Brightness (60 °, long direction) 21 55 50 Avg. Roughness arithm., Ra (μm) 0.12 0.12 0.07 Surface hardness (HV 5 ) 169 172 286

La bande selon l'invention présente par rapport aux bandes standard 2D et standard 2RB, à la fois un aspect de surface brillant, et de bonnes caractéristiques mécaniques. Elle présente en outre, une dureté superficielle supérieure aux deux bandes de l'art antérieur.The strip according to the invention has, compared to standard 2D and standard 2RB strips, both a glossy surface appearance and good mechanical characteristics. It also has a superficial hardness greater than the two bands of the prior art.

4- Aptitude à l'emboutissage, et conséquences sur la brillance 4- Stamping ability, and consequences on gloss

Des flans sont découpés dans la bande en acier selon l'invention, dans la bande standard 2RB et dans la bande standard 2D. Ces flans sont ensuite emboutis dans une presse d'emboutissage comprenant classiquement un poinçon, une matrice et un serre-flan, pour former des godets.Blanks are cut in the steel strip according to the invention, in the standard 2RB band and in the standard 2D band. These blanks are then stamped in a stamping press conventionally comprising a punch, a die and a blank holder, to form buckets.

Après opération de mise en forme par emboutissage, la brillance de la surface est mesurée à la fois dans le fond du godet et sur la jupe du godet, ce qui permet d'estimer une valeur moyenne de brillance de la pièce emboutie.After stamp forming operation, the brightness of the surface is measured both in the bottom of the bucket and on the skirt of the bucket, which estimates an average value of gloss of the stamped part.

Les résultats sont regroupés dans le tableau 3. TABLEAU 3 Bande standard 2D Bande standard 2RB Bande selon l'invention Brillance de la bande 21 55 50 Brillance dans le fond du godet 7 7 34 Brillance sur la jupe du godet 10 13 35 Brillance moyenne du godet 8,5 10 34,5 Perte relative de brillance après emboutissage (%) 52 81 30 The results are summarized in Table 3. TABLE 3 2D standard tape 2RB standard tape Strip according to the invention Brightness of the band 21 55 50 Brightness in the bottom of the bucket 7 7 34 Shine on the skirt of the bucket 10 13 35 Average brightness of the bucket 8.5 10 34.5 Relative loss of gloss after stamping (%) 52 81 30

Par rapport à la valeur de la brillance du produit à plat, on observe classiquement une perte de brillance des pièces mises en forme à froid. Les essais réalisés sur les différents types de bandes étudiés montrent que la bande en acier inoxydable austénitique selon l'invention résiste mieux à la matification de surface par déformation que les bandes standard 2D et standard 2RB.Compared with the value of the gloss of the flat product, a loss of gloss of the cold-formed parts is conventionally observed. The tests carried out on the different types of strips studied show that the austenitic stainless steel strip according to the invention is more resistant to surface matting by deformation than the standard 2D and standard 2RB strips.

Après emboutissage de la bande en acier selon l'invention, la perte de brillance est faible, et largement inférieure à ce qu'on observe pour les bandes standard 2B et standard 2RB.After stamping the steel strip according to the invention, the loss of gloss is low, and much lower than that observed for the standard 2B and standard 2RB strips.

5- Résistance à la rayure 5- Resistance to scratching

Les tests de résistance à la rayure sont réalisés sur la bande en acier selon l'invention, et la bande standard 2RB selon la norme ISO 1518 en utilisant une machine Clemen dont la pointe hémisphérique en acier trempé a une dureté de 1500 Hv, et un diamètre de 1 mm. Les tests consistent à appliquer, avec des charges variables de 50 g, 200 g et 400 g, la pointe hémisphérique à la surface de la bande de manière à créer une rayure. Les résultats des tests sont regroupés dans le tableau 4. TABLEAU 4 Charge (g) Profondeur de la rayure (µm) pour la bande standard 2RB Profondeur de la rayure (µm) pour la bande selon l'invention Différence relative (%) 50 1,08 0,73 32 200 3 1,35 55 400 3,35 2,33 30 The scratch resistance tests are carried out on the steel strip according to the invention, and the standard strip 2RB according to the ISO 1518 standard using a Clemen machine whose hemispherical steel hardened tip has a hardness of 1500 Hv, and a diameter of 1 mm. The tests consist of applying, with variable loads of 50 g, 200 g and 400 g, the hemispherical tip to the surface of the strip so as to create a scratch. The test results are summarized in Table 4. TABLE 4 Charge (g) Depth of scratch (μm) for standard 2RB tape Depth of scratch (μm) for the strip according to the invention Relative difference (%) 50 1.08 0.73 32 200 3 1.35 55 400 3.35 2.33 30

Les résultats des tests montrent que la bande en acier selon l'invention résiste mieux à la rayure que les bandes standard 2RB, d'un ordre de grandeur de 40 % en moyenne, correspondant à la différence de dureté superficielle relative de la bande.The test results show that the steel strip according to the invention is more resistant to scratching than the standard 2RB strips, an order of magnitude of 40% on average, corresponding to the difference in relative surface hardness of the strip.

6- Résistance à la corrosion inter-qranulaire 6- Resistance to inter-rectangular corrosion

Le test de résistance à la corrosion inter-granulaire est réalisé sur des échantillons prélevés dans la bande en acier selon l'invention et dans la bande standard 2D.The intergranular corrosion resistance test is carried out on samples taken from the steel strip according to the invention and from the standard 2D strip.

Ce test est réalisé selon la norme NFA 05-159. Il consiste à immerger l'échantillon dans une solution bouillante d'acide sulfurique et de sulfate de cuivre pendant une durée de 20 heures. L'échantillon est ensuite plié à 90° et l'observation de la face convexe de ce dernier, en comparaison avec un échantillon de référence n'ayant pas été immergé dans ladite solution, permet de déterminer le degré de fissuration en extrême peau. Une faible résistance à la corrosion inter-granulaire se caractérise par la présence de nombreuses fissures sur la face convexe de l'échantillon plié. Les tests de résistance à la corrosion inter-granulaire montrent que la bande en acier inoxydable austénitique selon l'invention résiste mieux à la corrosion inter-granulaire que la bande standard 2D.This test is performed according to the NFA 05-159 standard. It involves immersing the sample in a boiling solution of sulfuric acid and copper sulphate for a period of 20 hours. The sample is then bent at 90 ° and the observation of the convex face of the latter, in comparison with a reference sample which has not been immersed in said solution, makes it possible to determine the degree of cracking in the extreme skin. A low resistance to intergranular corrosion is characterized by the presence of numerous cracks on the convex face of the folded sample. The intergranular corrosion resistance tests show that the austenitic stainless steel strip according to the invention is more resistant to intergranular corrosion than the standard 2D strip.

Claims (15)

Bande en acier inoxydable austénitique, présentant une limite élastique Rp0,2 supérieure ou égale à 600 MPa, une charge à la rupture Rm supérieure ou égale à 800 MPa, un allongement A80 supérieur ou égal à 40 %, dont la composition comprend en % en poids: 0,025 ≤ C ≤ 0,15 % 0,20 ≤ Si ≤ 1,0 % 0,50 ≤ Mn ≤ 2,0 % 6,0 ≤ Ni ≤ 12,0 % 16,0 ≤ Cr ≤ 20,0 % Mo ≤ 3,0% 0.030 ≤ N ≤ 0,16 % Cu ≤ 0,50 % P ≤ 0.50 % S ≤ 0,015 % éventuellement 0,10 ≤ V ≤ 0,50 %, et 0,03 ≤ Nb ≤ 0,50%, avec 0,10 ≤ Nb + V ≤ 0,50 % le complément étant du fer et d'éventuelles impuretés résultant de l'élaboration, dont la taille moyenne des grains d'austénite est inférieure ou égale à 4 µm, et la surface présente une brillance supérieure à 50.Austenitic stainless steel strip, having an elastic limit Rp 0.2 greater than or equal to 600 MPa, a tensile strength Rm greater than or equal to 800 MPa, an elongation A 80 of greater than or equal to 40%, whose composition comprises % in weight: 0.025 ≤ C ≤ 0.15% 0.20 ≤ If ≤ 1.0% 0.50 ≤ Mn ≤ 2.0% 6.0 ≤ Ni ≤ 12.0% 16.0 ≤ Cr ≤ 20.0% Mo ≤ 3.0% 0.030 ≤ N ≤ 0.16% Cu ≤ 0.50% P ≤ 0.50% S ≤ 0.015% optionally 0.10 ≤ V ≤ 0.50%, and 0.03 ≤ Nb ≤ 0.50%, with 0.10 ≤ Nb + V ≤ 0.50% the balance being iron and any impurities resulting from the preparation, the average size of the austenite grains is less than or equal to 4 microns, and the surface has a gloss greater than 50. Bande en acier inoxydable austénitique selon la revendication 1, caractérisée en ce qu'elle présente une surface dont la rugosité moyenne arithmétique Ra est inférieure ou égale à 0,08 µm.Austenitic stainless steel strip according to claim 1, characterized in that it has a surface whose arithmetic mean roughness Ra is less than or equal to 0.08 μm. Procédé de fabrication en continu d'une bande en acier inoxydable austénitique selon l'une des revendications 1 ou 2 comprenant les étapes consistant à : - laminer à froid une bande en acier inoxydable austénitique comprenant, en % en poids : 0,025 ≤ C ≤ 0,15 % 0,20 ≤ Si ≤ 1,0 % 0,50 ≤ Mn ≤ 2,0 % 6,0 ≤ Ni ≤ 12,0 % 16,0 ≤ Cr ≤ 20,0 % Mo ≤ 3,0% 0,030 ≤ N ≤ 0,16% Cu ≤ 0.50% P ≤ 0,50 % S ≤ 0,015% éventuellement 0,10 ≤ V ≤ 0,50 %, et 0,03 ≤ Nb ≤ 0,50%, avec 0,10 ≤ Nb + V ≤ 0,50 % le complément étant du fer et d'éventuelles impuretés résultant de l'élaboration, le laminage à froid étant réalisé avec des cylindres de travail présentant une rugosité moyenne arithmétique Ra inférieure ou égale à 0,15 µm, - faire subir un traitement thermique à la bande laminée à froid, dans un four de recuit à l'intérieur duquel règne une atmosphère oxydante vis à vis du fer, pour obtenir une bande couverte d'une couche d'oxyde, ledit traitement thermique étant ajusté de manière à effectuer une recristallisation partielle de l'acier pour obtenir une bande dont la fraction volumique recristallisée est comprise entre 60 et 75 % et, - à décaper la bande ayant subi le traitement thermique, à l'aide d'au moins une solution de décapage acide capable d'éliminer complètement ladite couche d'oxyde en fonction de son épaisseur et de sa nature, sans attaquer les joints de grains de l'acier. A method of continuously manufacturing an austenitic stainless steel strip according to one of claims 1 or 2 comprising the steps of: cold rolling an austenitic stainless steel strip comprising, in% by weight: 0.025 ≤ C ≤ 0.15% 0.20 ≤ If ≤ 1.0% 0.50 ≤ Mn ≤ 2.0% 6.0 ≤ Ni ≤ 12.0% 16.0 ≤ Cr ≤ 20.0% Mo ≤ 3.0% 0.030 ≤ N ≤ 0.16% Cu ≤ 0.50% P ≤ 0.50% S ≤ 0.015% possibly 0.10 ≤ V ≤ 0.50%, and 0.03 ≤ Nb ≤ 0.50%, with 0.10 ≤ Nb + V ≤ 0.50% the balance being iron and any impurities resulting from the preparation, the cold rolling being carried out with working cylinders having an arithmetic average roughness Ra less than or equal to 0.15 μm, heat treating the cold-rolled strip in an annealing furnace inside which an oxidizing atmosphere with respect to the iron prevails, to obtain a strip covered with an oxide layer, said heat treatment being adjusted to effect a partial recrystallization of the steel to obtain a band whose recrystallized volume fraction is between 60 and 75% and - stripping the strip having undergone the heat treatment, using at least one acid pickling solution capable of completely removing said oxide layer depending on its thickness and its nature, without attacking the grain boundaries steel. Procédé selon la revendication 3, caractérisé en ce que la rugosité moyenne arithmétique Ra des cylindres de travail est inférieure ou égale à 0,10 µm.Process according to Claim 3, characterized in that the arithmetic average roughness Ra of the working rolls is less than or equal to 0.10 μm. Procédé selon l'une des revendications 3 ou 4, caractérisé en ce que la bande est laminée à froid avec un taux de réduction compris entre 55 et 85%.Method according to one of claims 3 or 4, characterized in that the strip is cold rolled with a reduction ratio between 55 and 85%. Procédé selon la revendication 5, caractérisé en ce que le taux de réduction est compris entre 70 et 85 %.Process according to Claim 5, characterized in that the reduction ratio is between 70 and 85%. Procédé selon l'une quelconques des revendications 2 à 6, caractérisé en ce que l'atmosphère du four est un mélange gazeux d'air et d'au moins un hydrocarbure dans un rapport volumique air/hydrocarbure compris entre 1,1 et 1,5, ledit mélange gazeux comprenant en outre 3 à 8 % en volume d'oxygène.Process according to any one of Claims 2 to 6, characterized in that the furnace atmosphere is a gaseous mixture of air and at least one hydrocarbon in an air / hydrocarbon volume ratio of between 1.1 and 1.5, said gaseous mixture further comprising 3 to 8% by volume of oxygen. Procédé selon la revendication 7, caractérisé en ce que le rapport volume air/hydrocarbure est compris entre 1,1 et 1,3.Process according to Claim 7, characterized in that the air / hydrocarbon volume ratio is between 1.1 and 1.3. Procédé selon l'une des revendications 7 ou 8, caractérisé en ce que l'au moins un hydrocarbure est choisi parmi le gaz naturel, le butane et le méthane.Process according to one of Claims 7 or 8, characterized in that the at least one hydrocarbon is chosen from natural gas, butane and methane. Procédé selon l'une quelconque des revendications 3 à 9, caractérisé en ce que le traitement thermique comprend une phase de chauffage à une vitesse de chauffage V1, une phase de maintien à une température T et pendant un temps de maintien M, suivi d'une phase de refroidissement à une vitesse de refroidissement V2.Process according to any one of Claims 3 to 9, characterized in that the heat treatment comprises a heating phase at a heating rate V1, a holding phase at a temperature T and during a holding time M, followed by a cooling phase at a cooling rate V2. Procédé selon la revendication 10, caractérisé en ce que la température T est comprise entre 800 et 950°C.Process according to Claim 10, characterized in that the temperature T is between 800 and 950 ° C. Procédé selon la revendication 10, caractérisé en ce que la vitesse V1 est comprise entre 10 et 80°C/s.Process according to Claim 10, characterized in that the velocity V1 is between 10 and 80 ° C / s. Procédé selon la revendication 10, caractérisé en ce que le temps de maintien M est compris entre 10 s et 100 s.Process according to Claim 10, characterized in that the holding time M is between 10 s and 100 s. Procédé selon la revendication 10, caractérisé en ce que la vitesse V2 est comprise entre 10 et 80°C/s.Process according to Claim 10, characterized in that the velocity V2 is between 10 and 80 ° C / s. Procédé selon l'une quelconque des revendications 3 à 14, caractérisé en ce que la bande partiellement recuite subit un premier décapage électrolytique dans un bain contenant du sulfate de sodium dont la concentration est comprise entre 150 et 200 g/l, de pH inférieur à 3, et avec un ampérage compris entre 5 et 12 kA, suivi d'un second décapage électrochimique dans un bain contenant de l'acide nitrique dont la concentration est comprise entre 80 et 120 g/l, le pH inférieur à 3 , et avec un ampérage compris entre 5 et 12 kA.Process according to any one of Claims 3 to 14, characterized in that the partially annealed strip undergoes a first electrolytic pickling in a bath containing sodium sulphate, the concentration of which is between 150 and 200 g / l, with a pH of less than 3, and with an amperage between 5 and 12 kA, followed by a second electrochemical pickling in a bath containing nitric acid whose concentration is between 80 and 120 g / l, the pH below 3, and with an amperage between 5 and 12 kA.
EP05291384A 2005-06-28 2005-06-28 Strip made of stainless austenitic steel with bright surface and excellent mechanical properties Withdrawn EP1739200A1 (en)

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EP05291384A EP1739200A1 (en) 2005-06-28 2005-06-28 Strip made of stainless austenitic steel with bright surface and excellent mechanical properties
MX2007015786A MX2007015786A (en) 2005-06-28 2006-04-06 Austenitic stainless steel strip having a bright surface finish and excellent mechanical properties.
SI200630172T SI1899490T1 (en) 2005-06-28 2006-04-06 Austenitic stainless steel strip having a bright surface finish and excellent mechanical properties
BRPI0613998-1A BRPI0613998B1 (en) 2005-06-28 2006-04-06 Austenitic Stainless Steel Strip Fabrication Process
AT06743665T ATE417135T1 (en) 2005-06-28 2006-04-06 AUSTENITIC STAINLESS STEEL BAND WITH SHINY SURFACE FINISH AND EXCELLENT MECHANICAL PROPERTIES
DE602006004213T DE602006004213D1 (en) 2005-06-28 2006-04-06 BAND OF AUSTENITIC STAINLESS STEEL WITH SHINY SURFACE FINISH AND EXCELLENT MECHANICAL CHARACTERISTICS
ES06743665T ES2317540T3 (en) 2005-06-28 2006-04-06 SUBSTANTIOUS STAINLESS STEEL BAND THAT PRESENTS A GLOSSY SURFACE ASPECT AND EXCELLENT FEATURES.
PT06743665T PT1899490E (en) 2005-06-28 2006-04-06 Austenitic stainless steel strip having a bright surface finish and excellent mechanical properties
CNA2006800234667A CN101384744A (en) 2005-06-28 2006-04-06 Strip made of stainless austenitic steel with bright surface and excellent mechanical properties
PCT/FR2006/000785 WO2007003725A1 (en) 2005-06-28 2006-04-06 Austenitic stainless steel strip having a bright surface finish and excellent mechanical properties
JP2008518892A JP2009503246A (en) 2005-06-28 2006-04-06 Austenitic stainless steel strip with bright surface finish and excellent mechanical properties
EP06743665A EP1899490B1 (en) 2005-06-28 2006-04-06 Austenitic stainless steel strip having a bright surface finish and excellent mechanical properties
RU2008102981/02A RU2361929C1 (en) 2005-06-28 2006-04-06 Strip made of austenitic stainless steel, allowing bright surface and superb mechanical properties
KR1020077030554A KR101004597B1 (en) 2005-06-28 2006-04-06 Austenitic stainless steel strip having a bright surface finish and excellent mechanical properties
US11/994,275 US8268101B2 (en) 2005-06-28 2006-04-06 Austenitic stainless steel strip having a bright surface finish and excellent mechanical properties
DK06743665T DK1899490T3 (en) 2005-06-28 2006-04-06 Austenitic stainless steel strip with shiny surface finish and excellent mechanical properties
ZA200711238A ZA200711238B (en) 2005-06-28 2007-12-07 Austenitic stainless steel strip having a bright surface finish and excellent mechanical properties

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CN (1) CN101384744A (en)
AT (1) ATE417135T1 (en)
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DE (1) DE602006004213D1 (en)
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2072631A1 (en) * 2007-12-20 2009-06-24 Ugine & Alz France Austenitic stainless steel sheet and method for obtaining this sheet

Families Citing this family (27)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP5464511B2 (en) * 2009-05-14 2014-04-09 独立行政法人物質・材料研究機構 Manufacturing method of orifice plate for liquid injection
CN101633999B (en) * 2009-05-26 2011-06-01 山西太钢不锈钢股份有限公司 Austenitic stainless steel, steel tube thereof and manufacturing method thereof
WO2013019109A1 (en) * 2011-07-29 2013-02-07 Fps Food Processing Systems B.V. Device for treating and processing food products and food components
US10329649B2 (en) * 2012-01-20 2019-06-25 Solu Stainless Oy Austenitic stainless steel product and a method for manufacturing same
UA111115C2 (en) 2012-04-02 2016-03-25 Ейкей Стіл Пропертіс, Інк. cost effective ferritic stainless steel
ES2596681T3 (en) * 2012-09-28 2017-01-11 Thyssenkrupp Steel Europe Ag Procedure for the manufacture of a flat steel product with high reflection capacity, flat steel product and mirror element for solar concentrators
CN103972566A (en) * 2014-04-03 2014-08-06 上海华篷防爆科技有限公司 Solid hydrogen power generating device provided with fluorine polymer electrolyte membrane
CN104152814A (en) * 2014-05-28 2014-11-19 无锡兴澄华新钢材有限公司 Explosion-proof austenitic stainless steel mesh
FR3027032B1 (en) * 2014-10-08 2021-06-18 Air Liquide ALLOY MICROSTRUCTURE FOR REFORMING TUBE
AT516464B1 (en) * 2014-11-03 2018-02-15 Berndorf Band Gmbh Metallic strips and their manufacturing processes
AT516453B1 (en) * 2014-11-03 2018-02-15 Berndorf Band Gmbh Metallic strips and their manufacturing processes
JP6505415B2 (en) * 2014-11-04 2019-04-24 日本冶金工業株式会社 Surface treatment method of Fe-Cr-Ni alloy material excellent in workability and corrosion resistance
KR20170056047A (en) * 2015-11-12 2017-05-23 주식회사 포스코 Austenitic stainless steel having exceelent orange peel resistance and method of manufacturing the same
CN107036902B (en) * 2016-11-15 2019-05-24 武汉科技大学 A kind of force application apparatus for strand-anneal(ing) experiment
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0525548A (en) * 1990-12-05 1993-02-02 Nippon Steel Corp Production of cr-ni stainless steel sheet excellent in material and surface quality
US5830291A (en) * 1996-04-19 1998-11-03 J&L Specialty Steel, Inc. Method for producing bright stainless steel
JPH1180906A (en) * 1997-09-03 1999-03-26 Nisshin Steel Co Ltd High strength stainless steel strip increased in yield stress, and its production
JP2004137538A (en) * 2002-10-17 2004-05-13 Sumitomo Metal Ind Ltd Austenitic stainless steel strip and method for manufacturing the same

Family Cites Families (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1471880A (en) * 1973-10-26 1977-04-27 Air Prod & Chem Furnace atmosphere for the heat treatment of ferrous metal
FR2668584B1 (en) * 1990-10-26 1994-03-18 Lair Liquide PROCESS FOR DEVELOPING A HEAT TREATMENT ATMOSPHERE AND HEAT TREATMENT PLANT.
JPH05317910A (en) * 1992-03-12 1993-12-03 Sumitomo Metal Ind Ltd Manufacture of metal strip with high glossiness
JP3534886B2 (en) * 1995-03-24 2004-06-07 日新製鋼株式会社 Austenitic stainless steel sheet excellent in pocket wave resistance and method for producing the same
JPH09184012A (en) * 1995-12-28 1997-07-15 Kawasaki Steel Corp Production of austenitic stainless steel sheet excellent in surface brightness characteristic abd corrosion resistance
TW330214B (en) 1996-03-22 1998-04-21 Kawasaki Steel Co Austenitic stainless stee with excellent corrosion resistance and glossiness
JPH11158699A (en) * 1997-11-25 1999-06-15 Hitachi Ltd Method for descaling stainless steel strip and its continuous production device
WO1999048628A1 (en) * 1998-03-24 1999-09-30 Kawasaki Steel Corporation Method of manufacturing high-gloss stainless cold rolled steel strip
JP2002194506A (en) * 2000-12-25 2002-07-10 Sumitomo Metal Ind Ltd Stainless steel sheet and production method for the same
FR2864108B1 (en) * 2003-12-22 2006-01-27 Ugine Et Alz France STAINLESS STEEL SHEET HAVING HIGH RESISTANCE AND LENGTH ELONGATION, AND METHOD OF MANUFACTURE
JP2005213640A (en) * 2004-02-02 2005-08-11 Kobe Steel Ltd High-strength cold rolled steel sheet excellent in ductility and stretch-flanging property and manufacturing method for the same

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0525548A (en) * 1990-12-05 1993-02-02 Nippon Steel Corp Production of cr-ni stainless steel sheet excellent in material and surface quality
US5830291A (en) * 1996-04-19 1998-11-03 J&L Specialty Steel, Inc. Method for producing bright stainless steel
US5830291C1 (en) * 1996-04-19 2001-05-22 J & L Specialty Steel Inc Method for producing bright stainless steel
JPH1180906A (en) * 1997-09-03 1999-03-26 Nisshin Steel Co Ltd High strength stainless steel strip increased in yield stress, and its production
JP2004137538A (en) * 2002-10-17 2004-05-13 Sumitomo Metal Ind Ltd Austenitic stainless steel strip and method for manufacturing the same

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
"ASM Handbook Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys", 1990, ASM INTERNATIONAL, USA, XP002351204 *
PATENT ABSTRACTS OF JAPAN vol. 017, no. 309 (C - 1070) 14 June 1993 (1993-06-14) *
PATENT ABSTRACTS OF JAPAN vol. 1999, no. 08 30 June 1999 (1999-06-30) *
PATENT ABSTRACTS OF JAPAN vol. 2003, no. 12 5 December 2003 (2003-12-05) *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2072631A1 (en) * 2007-12-20 2009-06-24 Ugine & Alz France Austenitic stainless steel sheet and method for obtaining this sheet
WO2009101285A1 (en) * 2007-12-20 2009-08-20 Arcelormittal-Stainless France Austenitic stainless steel sheet and method for making said sheet

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US20090202380A1 (en) 2009-08-13
DE602006004213D1 (en) 2009-01-22

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