EP0896072A1 - Austenitic stainless steel with very low nickel content - Google Patents

Austenitic stainless steel with very low nickel content Download PDF

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Publication number
EP0896072A1
EP0896072A1 EP98401734A EP98401734A EP0896072A1 EP 0896072 A1 EP0896072 A1 EP 0896072A1 EP 98401734 A EP98401734 A EP 98401734A EP 98401734 A EP98401734 A EP 98401734A EP 0896072 A1 EP0896072 A1 EP 0896072A1
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Prior art keywords
steel
less
composition
content
steel according
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German (de)
French (fr)
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EP0896072B1 (en
Inventor
Laurent Chesseret
Jean-Michel Hauser
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Ugine SA
Ugitech SA
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Ugine Savoie SA
USINOR SA
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt

Definitions

  • the invention relates to an austenitic stainless steel with a very low nickel content.
  • Austenitic steels are steels generally comprising in their weight composition a nickel content greater than 3%.
  • a steel austenitic N ° 1.4301 of standard NF EN 10 088 (AISI 304) contains more than 8% nickel in its composition.
  • the object of the invention is to produce an austenitic steel called "to very low nickel content ”with particular properties mechanical and welding equivalent, and even superior to those austenitic steels with a high nickel content.
  • the single figure shows necking characteristics in temperature function for different steels.
  • the austenitic steel according to the invention is produced by limiting the nickel content of the composition.
  • the austenitizing effect usually attributed to the nickel element, must necessarily be offset by gamagens such as manganese, copper, nitrogen and carbon and it is necessary to reduce, as far as possible, the contents of alphagenic elements such as chromium, molybdenum and silicon.
  • the steel according to the invention has a ferritic type solidification.
  • the solidifying ferrite regresses to austenite, when the steel cools, following the casting.
  • the ferrite content of the steels according to the invention is less than 5%.
  • the steel according to the invention contains less than 20% of ferrite after reheat for 30 min at 1240 ° C.
  • the steel according to the invention After hot rolling and hyper quenching treatment at 1100 ° C for 30 min, the steel according to the invention has a percentage of ferrite less than 5%. After hot working, annealing, cold working and annealing, a steel with only a few traces of residual ferrite.
  • the measurement of the austenite / ferrite proportion was evaluated by magnetization at saturation or by X-ray diffraction analysis.
  • the carbon is limited to a content of less than 0.1% for avoid sensitization of steel to intergranular corrosion after treatment at temperatures between 550 ° C and 800 ° C. Of preferably the carbon content is less than 0.08% for the same right.
  • Nitrogen and carbon have a similar effect on the mode of solidification, the balance of the ferrite and austenite phases and the stability of austenite for martensite formation, although nitrogen has a slightly more austenitizing character than carbon.
  • Manganese increases the solubility of nitrogen.
  • a content minimum of 5% of this element is necessary to dissolve enough nitrogen and guarantee the steel an austenitic structure.
  • the effect of manganese on the proportion of ferrite is constant for contents between 5% and 9%.
  • the manganese content must also be limited to avoid deteriorate hot ductility.
  • Silicon is deliberately limited to less than 1%, and, from preferably less than 0.7% to avoid the formation of ferrite and to have satisfactory behavior of the steel during pickling.
  • Content minimum of 0.1% is necessary in the elaboration and a content 0.5% minimum is preferable to avoid the formation of oxide of olivine type.
  • olivine type oxides FeO / SiO2 / MnO
  • the hot rolling operation it is formed, if the content in silicon is less than 0.5%, a mixed zone with a metallic matrix containing these oxides in the liquid state, which leads to a bad state of surface on the steel strip, in particular after pickling.
  • the silicon is limited to a content of less than 2%, and, from preferably at 1% because taking into account the other elements of the composition, it does not contribute, when its content is higher, to obtaining an austenitic structure.
  • Nickel is an essential element of austenitic steels in general, and the problem posed of the invention is notably the obtaining of an austenitic steel containing little nickel, expensive element, price very variable, uncontrollable, which, due to price fluctuations, disrupts the proper functioning of the company responsible for developing steel. Nickel also has the disadvantage of increasing sensitivity to stress corrosion of austenitic steels. We have also found that the nickel limitation allowed the development of a new generation of steel with improved properties as will be described below.
  • chromium content is linked to the fact that the steel according to the invention must remain with a ferrite content less than 5% after the hyperhardening treatment. Chromium contents above 19% lead to chromium contents too large ferrite which does not guarantee an elongation in sufficient traction.
  • a content of at least 0.1% nitrogen is requested. Beyond a content of 0.4% nitrogen, it forms within steel, during solidification, bubbles of this so-called gas "Puffs".
  • the required nitrogen content can be high when introduced into the composition of steel, for the improvement of corrosion resistance, molybdenum with contents below 2%. Molybdenum contents greater than 2% require a more than 0.4% nitrogen to avoid the presence of ferrite, which which is not feasible during the production of pressure steel normal.
  • the composition of the steel according to the invention contains boron in a proportion of between 5.10 -4 % and 50.10 -4 %.
  • the addition of boron to the composition consequently improves the hot ductility, in particular between 900 ° C. and 1150 ° C., as materialized by the characteristics of necking in hot traction as a function of the temperature.
  • Above 50.10 -4 % of boron there is too great a reduction in the burn point, that is to say that there is a risk of formation of liquid metal areas upon reheating before rolling.
  • the sulfur is introduced into the steel in a proportion of less than 0.01% to ensure that the steel has satisfactory resistance to pitting corrosion.
  • the sulfur content is less than 20.10 -4 %, which notably improves the hot ductility at 1000 ° C. and beyond.
  • the low sulfur content can be obtained by the controlled use of calcium and aluminum generating final aluminum contents of less than 0.03%, preferably less than 50.10 -4 % or less than 30.10 -4 %% , and calcium contents of 10.10 -4 % and preferably less than 5.10 -4 %, the resulting oxygen content is then generally from 20.10 -4 to 60.10 -4 %.
  • the phosphorus content is limited to 0.05%, as in the most austenitic stainless steels to limit segregation during solidification of welds and phenomena hot tear that can result when cooling these.
  • the steel according to the invention is compared, in the description, to a AISl 304 type steel, called "reference" steel.
  • the composition of steel according to the invention is presented in Tables 1 and 2 of Annex 1 below, pages 14 and 15.
  • compositions of the steel according to the invention are marked with an asterisk.
  • Table 4 presents the measured values of IF 2 , IF 1 , as well as the measured martensite IS rate formed after a deformation of 30% in tension.
  • Hot ductility was measured by tensile tests at hot. The measurements were carried out on a solidification raw steel and on a wrought and annealed steel.
  • Wrought steel is obtained by forging at a temperature of starting at 1250 ° C. The steel is then annealed at a temperature of 1100 ° C for 30 min.
  • the thermal cycle of the tensile test includes a temperature rise to 1240 ° C with a speed of 20 ° C / s, maintaining at the temperature of 1240 ° C for one minute and a descent at a speed of 2 ° C / s to the temperature of deformation.
  • We measure the diametral constriction which corresponds to ratio, expressed in%, of the difference between the initial diameter and final diameter by the initial diameter.
  • the single figure shows necking characteristics in function of the deformation temperature for steels 769- (B) and 771- (C) according to the invention compared to low sulfur steels 774- (D), 768- (A) without boron and with 671 steel called “reference” (AISI 304).
  • the steel 771- (C) having a sulfur content of less than 20.10 -4 % has a better characteristic in hot ductility in the entire temperature range between 900 ° C and 1250 ° C and is close in ductility to reference steel 671.
  • the mechanical properties were evaluated on an annealed wrought steel. The working is carried out by forging from 1250 ° C. The steel is then annealed at a temperature of 1100 ° C. for 30 minutes in a salt bath.
  • the tensile test specimens used are barrel specimens of circular section having a diameter of 5 mm and a length of 50 mm. They are subjected to a traction speed of 20 mm / minute.
  • the steels according to the invention have an elongation of between 55% and 67%.
  • the following table 5 presents the measured characteristics of the steel according to the invention, of low-nickel steels outside the invention and of a reference steel of type AISI 304. Mechanical properties.
  • the rate of martensite after 30% of true deformation in tension was measured (table 4): For the steel according to the invention, it is less than 20%.
  • Steels outside the invention containing more than 0.1% carbon, like 594 and 596 steels, have no characteristics acceptable.
  • the steels according to the invention which contain in their composition less than 0.1% carbon, such as steels 567, 592, 584, are comparable in terms of intergranular corrosion, to steel AISI 304 for test b.
  • the pitting potential is significantly higher on steels whose composition has an aluminum content not exceeding 50.10 -4 % and which also contain less than 10.10 -4 % calcium, less than 60.10 -4 % d 'oxygen and less than 20.10 -4 % sulfur.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
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Abstract

A low nickel content austenitic stainless steel has the composition (by wt.) less than 0.1% C, 0.1-1% (exclusive) Si, 5-9% (exclusive) Mn, 0.1-2% (exclusive) Ni, 13-19% (exclusive) Cr, 1-4% (exclusive) Cu, 0.1-0.40% (exclusive) N, 5 x 10<-4>-50 x 10<-4>% (exclusive) B, less than 0.05% P and less than 0.01% S. Preferably, both the ferrite index (IF1) and the martensite stability index (IS) are less than 20, where IF1 = 0.034 x x<2> + 0.284 x x - 0.347 and IS = 0.0267 x y<2> + 0.4332 x y - 3.1459, in which x = 6.903 x Ä-6.998 + Cr% - 0.972 x (Ni% + 20.04C% + 21.31N% + 0.46Cu% + 0.08Mn%)Ü and y = 250.4 - 205.4C% - 101.4N% - 7.6Mn% - 12.1Ni% - 6.1Cr% - 13.3Cu%.

Description

L'invention concerne un acier inoxydable austénitique comportant une teneur très faible en nickel.The invention relates to an austenitic stainless steel with a very low nickel content.

Les aciers inoxydables sont classés par grandes familles en fonction de leur structure métallurgique. Les aciers austénitiques sont des aciers comportant généralement dans leur composition pondérale une teneur en nickel supérieure à 3%. Par exemple, un acier austénitique N° 1.4301 de la norme NF EN 10 088 (AISI 304) comporte dans sa composition plus de 8% de nickel.Stainless steels are classified by major families in depending on their metallurgical structure. Austenitic steels are steels generally comprising in their weight composition a nickel content greater than 3%. For example, a steel austenitic N ° 1.4301 of standard NF EN 10 088 (AISI 304) contains more than 8% nickel in its composition.

Le coût élevé de l'élément nickel et les variations incontrôlables de son prix orientent les sidérurgistes à mettre au point des aciers austénitiques dont la composition ne comporte pas de nickel ou bien en comporte très peu.The high cost of the nickel element and the uncontrollable variations of its price guide steelmakers to develop steels austenitics whose composition does not contain nickel or has very few.

Le but de l'invention est de réaliser un acier austénitique dit « à très basse teneur en nickel » présentant notamment des propriétés mécaniques et de soudage équivalentes, et même supérieures à celles des aciers austénitiques comportant une teneur élevée en nickel.The object of the invention is to produce an austenitic steel called "to very low nickel content ”with particular properties mechanical and welding equivalent, and even superior to those austenitic steels with a high nickel content.

Les directives internationales orientent vers une baisse du relargage en nickel des matériaux, notamment dans le domaine de l'eau et du contact cutané.International guidelines point to a decline in nickel release of materials, especially in the water sector and skin contact.

L'objet de l'invention est un acier austénitique comportant une teneur très faible en nickel, caractérisé en la composition pondérale suivante :

  • carbone < 0,1%
  • 0,1% < silicium < 1%
  • 5% < manganèse < 9%
  • 0,1%<nickel < 2%
  • 13% < chrome < 19%
  • 1% < cuivre < 4%
  • 0,1% < azote < 0,40%,
  • 5 10-4% < bore < 50.10-4%
  • phosphore < 0,05%,
  • soufre < 0,01%.
    • The object of the invention is an austenitic steel comprising a very low nickel content, characterized in the following weight composition:
  • carbon <0.1%
  • 0.1% <silicon <1%
  • 5% <manganese <9%
  • 0.1% <nickel <2%
  • 13% <chromium <19%
  • 1% <copper <4%
  • 0.1% <nitrogen <0.40%,
  • 5 10 -4 % <boron <50.10 -4 %
  • phosphorus <0.05%,
  • sulfur <0.01%.

    • Les autres caractéristiques de l'invention sont :

    • la composition satisfait à la relation définissant un indice ferritique IF1: IF1 = 0,034x2 + 0,284 x - 0,347 < 20 avec x = 6,903.[ - 6,998 + Cr% - 0,972.( Ni% + 21,31 N% + 20,04.C% + 0,46.Cu% + 0,08.Mn% )]
    • la composition satisfait à la relation suivante utilisant un indice de stabilité martensitique IS : IS = 0,0267.x2 + 0,4332 x - 3,1459 < 20 avec : x= 250,4 - 205,4.C% - 101,4.N% - 7,6.Mn% - 12,1.Ni% - 6,1.Cr% - 13,3.Cu%.
    • l'acier comporte dans sa composition moins de 1% de nickel.
    • de 15% à 17% de chrome.
    • moins de 0,08% de carbone.
    • de 0,5% à 0,7% de silicium.
    • moins de 2% de molybdène.
    • moins de 0,0020% de soufre.
    • l'acier comporte en outre dans sa composition moins de 0,030% d'aluminium, de préférence moins de 50.10-4% d'aluminium et moins de 20.10-4% de calcium et de préférence moins de 5.10-4% de calcium.
    The other characteristics of the invention are:
    • the composition satisfies the relation defining a ferritic index IF 1 : IF 1 = 0.034x 2 + 0.284 x - 0.347 <20 with x = 6.903. [- 6.998 + Cr% - 0.972. (Ni% + 21.31 N% + 20.04 C% + 0.46.Cu% + 0.08.Mn%)]
    • the composition satisfies the following relation using an IS martensitic stability index: IS = 0.0267.x 2 + 0.4332 x - 3.1459 <20 with: x = 250.4 - 205.4.C% - 101.4.N% - 7.6.Mn% - 12.1.Ni% - 6.1.Cr% - 13.3.Cu%.
    • steel contains less than 1% nickel in its composition.
    • from 15% to 17% chromium.
    • less than 0.08% carbon.
    • 0.5% to 0.7% silicon.
    • less than 2% molybdenum.
    • less than 0.0020% sulfur.
    • the steel further comprises in its composition less than 0.030% aluminum, preferably less than 50.10 -4 % aluminum and less than 20.10 -4 % calcium and preferably less than 5.10 -4 % calcium.

    La description qui suit, complétée par la figure annexée, le tout donné à titre d'exemple non limitatif, fera mieux comprendre l'invention.The following description, supplemented by the appended figure, all given as a non-limiting example, will make it easier to understand the invention.

    La figure unique présente des caractéristiques de striction en fonction de la température pour différents aciers.The single figure shows necking characteristics in temperature function for different steels.

    L'acier austénitique selon l'invention est élaboré en limitant la teneur en nickel de la composition. L'effet austénitisant, habituellement attribué à l'élément nickel, doit nécessairement être compensé par des éléments gamagènes comme le manganèse, le cuivre, l'azote et le carbone et il est nécessaire de réduire, dans la mesure du possible, les teneurs en éléments alphagènes tels que le chrome, le molybdène et le silicium.The austenitic steel according to the invention is produced by limiting the nickel content of the composition. The austenitizing effect, usually attributed to the nickel element, must necessarily be offset by gamagens such as manganese, copper, nitrogen and carbon and it is necessary to reduce, as far as possible, the contents of alphagenic elements such as chromium, molybdenum and silicon.

    L'acier selon l'invention a une solidification de type ferritique. La ferrite de solidification régresse en austénite, lors du refroidissement de l'acier, à la suite de la coulée. Au stade de la coulée, l'acier étant refroidi, la teneur en ferrite résiduelle en pourcentage volumique est approximativement donnée par l'indice suivant établi expérimentalement : IF2 = 0,1106.x2 + 0,0331.x + 0,403 avec x = 2,52.[ -7,65 + Cr% + 0,03.Mn% - 0,864.( Ni% + 16,10.C% + 19,53.N% + 0,35.Cu% )] The steel according to the invention has a ferritic type solidification. The solidifying ferrite regresses to austenite, when the steel cools, following the casting. At the casting stage, the steel being cooled, the residual ferrite content in percentage by volume is approximately given by the following index established experimentally: IF 2 = 0.1106.x 2 + 0.0331.x + 0.403 with x = 2.52. [-7.65 + Cr% + 0.03.Mn% - 0.864. (Ni% + 16.10.C% + 19.53.N% + 0.35.Cu%)]

    A ce stade, la teneur en ferrite des aciers selon l'invention est inférieure à 5%.At this stage, the ferrite content of the steels according to the invention is less than 5%.

    L'acier est ensuite réchauffé pour laminage à chaud à 1240°C pendant 30 mn. On constate que la teneur en ferrite est alors représentée par la relation : IF1 = 0,034.x2 + 0,284.x - 0,347 avec x = 6,903.[ - 6,998 + Cr% - 0,972.( Ni% + 21,31.N% + 20,04.C% + 0,46.Cu% + 0,08.Mn% )] The steel is then reheated for hot rolling at 1240 ° C for 30 min. It can be seen that the ferrite content is then represented by the relation: IF 1 = 0.034.x 2 + 0.284.x - 0.347 with x = 6.903. [- 6.998 + Cr% - 0.972. (Ni% + 21.31.N% + 20.04. C% + 0.46.Cu% + 0.08.Mn%)]

    L'acier selon l'invention contient moins de 20% de ferrite après réchauffage de 30 mn à 1240°C.The steel according to the invention contains less than 20% of ferrite after reheat for 30 min at 1240 ° C.

    Après laminage à chaud et traitement hypertrempe à 1100°C pendant 30 mn, l'acier selon l'invention présente un pourcentage de ferrite inférieur à 5%. On obtient après corroyage à chaud, recuit, corroyage à froid et recuit, un acier ne comportant que quelques traces de ferrite résiduelle.After hot rolling and hyper quenching treatment at 1100 ° C for 30 min, the steel according to the invention has a percentage of ferrite less than 5%. After hot working, annealing, cold working and annealing, a steel with only a few traces of residual ferrite.

    La mesure de la proportion austénite/ferrite a été évaluée par aimantation à saturation ou par analyse par diffraction des rayons X. The measurement of the austenite / ferrite proportion was evaluated by magnetization at saturation or by X-ray diffraction analysis.

    Du point de vue du rôle des éléments contenus dans la composition, le carbone est limité a une teneur inférieure à 0,1% pour éviter une sensibilisation de l'acier à la corrosion intergranulaire après traitement à des températures comprises entre 550°C et 800°C. De préférence, la teneur en carbone est inférieure à 0,08% pour la même raison.From the point of view of the role of the elements contained in the composition, the carbon is limited to a content of less than 0.1% for avoid sensitization of steel to intergranular corrosion after treatment at temperatures between 550 ° C and 800 ° C. Of preferably the carbon content is less than 0.08% for the same right.

    L'azote et le carbone ont un effet semblable sur le mode de solidification, l'équilibre des phases ferrite et austénite et la stabilité de l'austénite vis-à-vis de la formation de martensite, bien que l'azote ait un caractère légèrement plus austénitisant que le carbone.Nitrogen and carbon have a similar effect on the mode of solidification, the balance of the ferrite and austenite phases and the stability of austenite for martensite formation, although nitrogen has a slightly more austenitizing character than carbon.

    Le manganèse accroít la solubilité de l'azote. Une teneur minimale de 5% de cet élément est nécessaire pour dissoudre assez d'azote et garantir à l'acier une structure austénitique. La limite supérieure de 9% de la teneur en manganèse dans la composition de l'acier de l'invention et liée à l'utilisation, dans l'élaboration de l'acier selon l'invention, de ferro-manganèse carburé, de préférence à du ferro-manganèse affiné. L'effet du manganèse sur la proportion en ferrite est constant pour des teneurs comprises entre 5% et 9%. En outre, on doit également limiter la teneur en manganèse pour éviter de détériorer la ductilité à chaud.Manganese increases the solubility of nitrogen. A content minimum of 5% of this element is necessary to dissolve enough nitrogen and guarantee the steel an austenitic structure. The limit 9% higher than the manganese content in the composition of the steel of the invention and related to the use, in the production of steel according to the invention, carburized ferro-manganese, preferably refined ferro-manganese. The effect of manganese on the proportion of ferrite is constant for contents between 5% and 9%. In in addition, the manganese content must also be limited to avoid deteriorate hot ductility.

    Le silicium est volontairement limité à moins de 1%, et, de préférence à moins de 0,7% pour éviter la formation de ferrite et pour avoir un comportement satisfaisant de l'acier au décapage. La teneur minimale de 0,1% est nécessaire dans l'élaboration et une teneur minimale de 0,5% est préférable pour éviter la formation d'oxyde de type olivine. En effet, lors de la transformation de l'acier par laminage à chaud, il se forme sur un acier selon l'invention et ne comportant qu'une faible teneur en silicium, par exemple moins de 0,5%, des oxydes du type olivine (FeO/SiO2 /MnO) à bas point de fusion.Silicon is deliberately limited to less than 1%, and, from preferably less than 0.7% to avoid the formation of ferrite and to have satisfactory behavior of the steel during pickling. Content minimum of 0.1% is necessary in the elaboration and a content 0.5% minimum is preferable to avoid the formation of oxide of olivine type. Indeed, during the transformation of steel by rolling when hot, it forms on a steel according to the invention and does not comprise that a low silicon content, for example less than 0.5%, olivine type oxides (FeO / SiO2 / MnO) with low melting point.

    Pendant l'opération de laminage à chaud, il se forme, si la teneur en silicium est inférieure à 0,5%, une zone mixte à matrice métallique contenant ces oxydes à l'état liquide, ce qui entraíne un mauvais état de surface sur la bande d'acier notamment après décapage.During the hot rolling operation, it is formed, if the content in silicon is less than 0.5%, a mixed zone with a metallic matrix containing these oxides in the liquid state, which leads to a bad state of surface on the steel strip, in particular after pickling.

    Pour éviter la formation de ces oxydes, à bas point de fusion, on a constaté qu'il fallait enrichir la composition de l'acier en silicium au delà de 0,5%. On forme alors des oxydes à point de fusion plus élevé qui ne posent plus de problème d'état de surface lors du laminage à chaud.To avoid the formation of these oxides, at a low melting point, we found that the composition of silicon steel had to be enriched above 0.5%. Oxides with a higher melting point are then formed. which no longer pose a surface finish problem during rolling at hot.

    Le silicium est limité à une teneur inférieure à 2%, et, de préférence à 1% car compte tenu des autres éléments de la composition, il ne contribue pas, lorsque sa teneur est plus élevée, à l'obtention d'une structure austénitique.The silicon is limited to a content of less than 2%, and, from preferably at 1% because taking into account the other elements of the composition, it does not contribute, when its content is higher, to obtaining an austenitic structure.

    Le nickel est un élément essentiel des aciers austénitiques en général, et le problème posé de l'invention est notamment l'obtention d'un acier austénitique contenant peu de nickel, élément cher, de prix très variable, incontrôlable, qui, du fait des fluctuations de prix, perturbe le bon fonctionnement de l'entreprise chargée de l'élaboration de l'acier. Le nickel a aussi l'inconvénient d'augmenter la sensibilité à la corrosion sous tension des aciers austénitiques. Nous avons également constaté que la limitation en nickel permettait l'élaboration d'une nouvelle génération d'acier comportant des propriétés améliorées comme il sera décrit ci-dessous.Nickel is an essential element of austenitic steels in general, and the problem posed of the invention is notably the obtaining of an austenitic steel containing little nickel, expensive element, price very variable, uncontrollable, which, due to price fluctuations, disrupts the proper functioning of the company responsible for developing steel. Nickel also has the disadvantage of increasing sensitivity to stress corrosion of austenitic steels. We have also found that the nickel limitation allowed the development of a new generation of steel with improved properties as will be described below.

    Une teneur en chrome supérieure à 13%, et, de préférence à 15%, est nécessaire pour garantir une résistance à la corrosion de l'acier inoxydable.A chromium content greater than 13%, and preferably at 15%, is necessary to guarantee corrosion resistance of stainless steel.

    La limite de la teneur en chrome à 19%, et de préférence à 17%, est liée au fait que l'acier selon l'invention doit rester avec une teneur en ferrite inférieure à 5% après le traitement d'hypertrempe. Des teneurs en chrome supérieures à 19% entraínent des teneurs en ferrite trop importantes qui ne garantissent pas un allongement en traction suffisant. The limit of chromium content to 19%, and preferably to 17%, is linked to the fact that the steel according to the invention must remain with a ferrite content less than 5% after the hyperhardening treatment. Chromium contents above 19% lead to chromium contents too large ferrite which does not guarantee an elongation in sufficient traction.

    Pour garantir une structure de type austénitique du fait de la réduction de la teneur en nickel, il faut un minimum de 1% de cuivre. Au delà d'une teneur de 4% de cuivre, la forgeabilité de l'acier se détériore fortement et la transformation à chaud dudit acier devient difficile. Le cuivre a un effet austénitisant égal à environ 40% de celui du nickel.To guarantee an austenitic structure due to the reduction in nickel content, a minimum of 1% copper is required. Beyond a content of 4% of copper, the forgeability of the steel strongly deteriorates and the hot transformation of said steel becomes difficult. Copper has an austenitizing effect equal to about 40% of that nickel.

    Pour garantir également la structure de type austénitique de l'acier selon l'invention, une teneur d'au moins 0,1% d'azote est demandée. Au delà d'une teneur de 0,4% d'azote, il se forme au sein de l'acier, pendant la solidification, des bulles de ce gaz dites « soufflures ».To also guarantee the austenitic type structure of the steel according to the invention, a content of at least 0.1% nitrogen is requested. Beyond a content of 0.4% nitrogen, it forms within steel, during solidification, bubbles of this so-called gas "Puffs".

    La teneur en azote nécessaire peut être élevée lorsque l'on introduit dans la composition de l'acier, pour l'amélioration de la résistance à la corrosion, du molybdène avec des teneurs inférieures à 2%. Des teneurs en molybdène supérieures à 2% nécessitent un apport supérieur à 0,4% en azote pour éviter la présence de ferrite, ce qui n'est pas réalisable lors d'une élaboration de l'acier à la pression normale.The required nitrogen content can be high when introduced into the composition of steel, for the improvement of corrosion resistance, molybdenum with contents below 2%. Molybdenum contents greater than 2% require a more than 0.4% nitrogen to avoid the presence of ferrite, which which is not feasible during the production of pressure steel normal.

    La composition de l'acier selon l'invention contient du bore dans une proportion comprise entre 5.10-4% et 50.10-4%. L'apport du bore dans la composition améliore de façon conséquente la ductilité à chaud, notamment entre 900°C et 1150°C, comme matérialisé par les caractéristiques en striction en traction à chaud en fonction de la température. Au delà de 50.10-4% de bore, il se produit un abaissement trop important du point de brûlure, c'est-à-dire qu'il y a un risque de formation de plages de métal liquide au réchauffage avant laminage.The composition of the steel according to the invention contains boron in a proportion of between 5.10 -4 % and 50.10 -4 %. The addition of boron to the composition consequently improves the hot ductility, in particular between 900 ° C. and 1150 ° C., as materialized by the characteristics of necking in hot traction as a function of the temperature. Above 50.10 -4 % of boron, there is too great a reduction in the burn point, that is to say that there is a risk of formation of liquid metal areas upon reheating before rolling.

    Le soufre est introduit dans l'acier dans une proportion inférieure à 0,01% pour assurer à l'acier une tenue satisfaisante à la corrosion par piqûre.
    De préférence, la teneur en soufre est inférieure à 20.10-4%, ce qui améliore notablement la ductilité à chaud à 1000°C et au delà.    The sulfur is introduced into the steel in a proportion of less than 0.01% to ensure that the steel has satisfactory resistance to pitting corrosion.
    Preferably, the sulfur content is less than 20.10 -4 %, which notably improves the hot ductility at 1000 ° C. and beyond.

    La basse teneur en soufre peut être obtenue par l'utilisation contrôlée de calcium et d'aluminium générant des teneurs finales en aluminium de moins de 0,03%, de préférence de moins de 50.10-4% ou moins de 30.10-4% %, et des teneurs en calcium de 10.10-4% et de préférence de moins de 5.10-4%, la teneur en oxygène qui en résulte est alors généralement de 20.10-4 à 60.10-4%.The low sulfur content can be obtained by the controlled use of calcium and aluminum generating final aluminum contents of less than 0.03%, preferably less than 50.10 -4 % or less than 30.10 -4 %% , and calcium contents of 10.10 -4 % and preferably less than 5.10 -4 %, the resulting oxygen content is then generally from 20.10 -4 to 60.10 -4 %.

    La teneur en phosphore est limitée à 0,05%, comme dans la plupart des aciers inoxydables austénitiques pour limiter les ségrégations lors de la solidification des soudures et les phénomènes de déchirure à chaud qui peuvent en résulter lors du refroidissement de celles-ci.The phosphorus content is limited to 0.05%, as in the most austenitic stainless steels to limit segregation during solidification of welds and phenomena hot tear that can result when cooling these.

    L'acier selon l'invention est comparé, dans la description, à un acier de type AISl 304 dit de «référence ». La composition de l'acier selon l'invention est présentée dans les tableaux 1 et 2 de l'annexe 1 ci-après, pages 14 et 15.The steel according to the invention is compared, in the description, to a AISl 304 type steel, called "reference" steel. The composition of steel according to the invention is presented in Tables 1 and 2 of Annex 1 below, pages 14 and 15.

    Dans la description, les compositions de l'acier selon l'invention sont marquées d'un astérisque.In the description, the compositions of the steel according to the invention are marked with an asterisk.

    Le tableau 3 suivant présente pour différents aciers, les valeurs des indices IF1, IF2 et IS calculées. Acier IF1 IF2 IS. *567 5,1 6,3 5,1 *569 0,9 3,6 15,1 570 43,6 25,7 15,1 571 25,1 18,3 5,6 572 19,0 12,1 75,9 *574 2,7 5,7 2,8 *577 13,1 12,8 - 4,9 578 2,9 4,9 32,4 *579 - 0,9 2,4 1,5 *580 8,6 9,0 3,7 *583 - 0,2 4,4 4,1 *584 5,7 7,5 4,3 *585 - 0,6 2,4 1,7 *587 0,9 0,5 - 1,9 *588 11,8 11,8 - 2,1 *590 7,5 9,5 4,0 *592 - 0,8 2,2 - 2,6 *594 1,5 0,5 - 4,4 *596 - 0,7 2,5 - 4,8 *653 6,5 7,9 4,2 *654 6,3 7,9 4,3 662 24,2 17,6 7,6 667 40,4 24,5 13,7 *720 0,3 4,1 - 4,8 *723 3,5 6,0 7,1 768 0,2 3,6 3,4 *769 0,8 4,1 5,8 *771 2,6 5,5 5,1 774 - 0,4 3,0 0,3 *775 1,6 4,5 5,8 *783 1,0 4,3 4,9 The following table 3 presents for different steels, the values of the indices IF 1 , IF 2 and IS calculated. Steel IF 1 IF 2 IS. * 567 5.1 6.3 5.1 * 569 0.9 3.6 15.1 570 43.6 25.7 15.1 571 25.1 18.3 5.6 572 19.0 12.1 75.9 * 574 2.7 5.7 2.8 * 577 13.1 12.8 - 4.9 578 2.9 4.9 32.4 * 579 - 0.9 2.4 1.5 * 580 8.6 9.0 3.7 * 583 - 0.2 4.4 4.1 * 584 5.7 7.5 4.3 * 585 - 0.6 2.4 1.7 * 587 0.9 0.5 - 1.9 * 588 11.8 11.8 - 2.1 * 590 7.5 9.5 4.0 * 592 - 0.8 2.2 - 2.6 * 594 1.5 0.5 - 4.4 * 596 - 0.7 2.5 - 4.8 * 653 6.5 7.9 4.2 * 654 6.3 7.9 4.3 662 24.2 17.6 7.6 667 40.4 24.5 13.7 * 720 0.3 4.1 - 4.8 * 723 3.5 6.0 7.1 768 0.2 3.6 3.4 * 769 0.8 4.1 5.8 * 771 2.6 5.5 5.1 774 - 0.4 3.0 0.3 * 775 1.6 4.5 5.8 * 783 1.0 4.3 4.9

    Le tableau 4 présente les valeurs mesurées de IF2, IF1, ainsi que le taux de martensite IS mesuré formé après une déformation de 30% en traction. ACIER IF2 IF1 % de ferrite après Hypertrempe % de martensite après traction. *567 2,7 9,9 0,2 2,6 *569 0,7 0,3 0,2 13,3 570 17,1 42,8 0,2 - 571 9,9 25,5 10,9 - 572 6,7 21,0 4,4 75,8 *574 0,9 1,4 0,2 1,2 *577 4,9 12,0 4,6 1,2 578 0,7 1,3 0,3 37,8 *579 0,2 0,2 0,2 0,4 *580 3,4 9,0 0,6 2,6 *583 0,8 0,8 0,2 0,1 *584 2,0 6,8 0,3 1,5 *585 0,3 0,2 0,2 0,3 *587 0,2 0,2 0,2 0,9 *588 3,9 12,9 2,9 - *590 2,2 7,0 0,2 2,4 *592 0,4 0,2 0,2 0,4 *594 0,2 0,2 0,2 0,2 *596 0,3 0,2 0,2 0,2 *671 3,3 3,7 0,2 7,0 Table 4 presents the measured values of IF 2 , IF 1 , as well as the measured martensite IS rate formed after a deformation of 30% in tension. STEEL IF2 IF1 % ferrite after Hyper quenching % martensite after traction. * 567 2.7 9.9 0.2 2.6 * 569 0.7 0.3 0.2 13.3 570 17.1 42.8 0.2 - 571 9.9 25.5 10.9 - 572 6.7 21.0 4.4 75.8 * 574 0.9 1.4 0.2 1.2 * 577 4.9 12.0 4.6 1.2 578 0.7 1.3 0.3 37.8 * 579 0.2 0.2 0.2 0.4 * 580 3.4 9.0 0.6 2.6 * 583 0.8 0.8 0.2 0.1 * 584 2.0 6.8 0.3 1.5 * 585 0.3 0.2 0.2 0.3 * 587 0.2 0.2 0.2 0.9 * 588 3.9 12.9 2.9 - * 590 2.2 7.0 0.2 2.4 * 592 0.4 0.2 0.2 0.4 * 594 0.2 0.2 0.2 0.2 * 596 0.3 0.2 0.2 0.2 * 671 3.3 3.7 0.2 7.0

    - Propriété à chaud de l'acier selon l'invention.- Hot property of the steel according to the invention.

    La ductilité à chaud a été mesurée par des tests de traction à chaud. Les mesures ont été réalisées sur un acier brut de solidification et sur un acier corroyé et recuit.Hot ductility was measured by tensile tests at hot. The measurements were carried out on a solidification raw steel and on a wrought and annealed steel.

    L'acier corroyé est obtenu par forgeage à une température de départ de 1250°C. L'acier subit ensuite un recuit à une température de 1100°C pendant 30 mn. Le cycle thermique du test de traction comprend une montée en température à 1240°C avec une vitesse de 20°C/s, un maintien à la température de 1240°C pendant une minute et une descente à une vitesse de 2°C/s jusqu'à la température de déformation. On mesure la striction diamétrale qui correspond au rapport, exprimé en %, de la différence entre diamètre initial et diamètre final par le diamètre initial.Wrought steel is obtained by forging at a temperature of starting at 1250 ° C. The steel is then annealed at a temperature of 1100 ° C for 30 min. The thermal cycle of the tensile test includes a temperature rise to 1240 ° C with a speed of 20 ° C / s, maintaining at the temperature of 1240 ° C for one minute and a descent at a speed of 2 ° C / s to the temperature of deformation. We measure the diametral constriction which corresponds to ratio, expressed in%, of the difference between the initial diameter and final diameter by the initial diameter.

    La figure unique présente des caractéristiques de striction en fonction de la température de déformation pour les aciers 769-(B) et 771-(C) selon l'invention comparés aux aciers 774-(D) bas soufre, 768-(A) sans bore et à l'acier 671 dit «de référence » (AISI 304).The single figure shows necking characteristics in function of the deformation temperature for steels 769- (B) and 771- (C) according to the invention compared to low sulfur steels 774- (D), 768- (A) without boron and with 671 steel called "reference" (AISI 304).

    L'acier 768-(A) à 30 10-4% de soufre sans bore présente une ductilité à chaud nettement plus faible que l'acier de référence. Il en est de même pour l'acier 774-(D) à 9.10-4% de soufre sans bore. L'addition de bore améliore, comme présenté sur la figure, la ductilité entre 900°C et 1050°C.Steel 768- (A) 30 10-4% sulfur without boron has a significantly lower hot ductility than the reference steel. It The same is true for 774- (D) steel with 9.10-4% sulfur without boron. The addition of boron improves, as shown in the figure, the ductility between 900 ° C and 1050 ° C.

    On remarque, en outre, qu'en présence de bore, l'acier 771-(C) ayant une teneur en soufre inférieure à 20.10-4% présente une meilleure caractéristique en ductilité à chaud dans tout le domaine de température compris entre 900°C et 1250°C et se rapproche en ductilité de l'acier de référence 671.It is further noted that in the presence of boron, the steel 771- (C) having a sulfur content of less than 20.10 -4 % has a better characteristic in hot ductility in the entire temperature range between 900 ° C and 1250 ° C and is close in ductility to reference steel 671.

    - Propriétés mécaniques, à température ambiante de l'acier selon l'invention.- Mechanical properties, at room temperature of steel according to the invention.

    Les propriétés mécaniques ont été évaluées sur un acier corroyé recuit. Le corroyage est effectué par forgeage à partir de 1250°C. L'acier subit ensuite un recuit à une température de 1100°C pendant 30 mn en bain de sel. Les éprouvettes de test de traction utilisées sont des éprouvettes de fût de section circulaire ayant un diamètre de 5 mm et une longueur de 50 mm. Elles sont soumises à une vitesse de traction de 20 mm/minute. Les aciers selon l'invention présentent un allongement compris entre 55% et 67%. A titre de comparaison, le tableau 5 suivant présente les caractéristiques mesurées de l'acier selon l'invention, d'aciers à basse teneur en nickel hors invention et d'un acier de référence de type AISI 304. Propriété mécaniques. Coulée RPO.2 (Mpa) Rm (Mpa) A% d(ln(σ) / d(ln(ε) *567 282 623 66.0 0.479 *569 309 747 62.7 0.615 570 393 657 54.8 0.319 571 376 703 57.5 0.395 572 294 1010 33.7 *574 323 679 66.0 0.483 *577 348 688 59.4 0.395 578 331 800 55.9 0.59 *579 343 690 62.5 0.438 *580 330 681 61.9 0.42 *583 345 651 58.8 0.378 *584 325 686 64.2 0.454 *585 342 679 61.3 0.403 *587 287 528 62.0 0.434 *588 365 705 57.6 0.357 *590 380 757 62.9 0.457 *592 330 660 60.6 0.397 *594 266 599 58.5 0.387 *596 316 660 63.7 *654 341 700 65.0 0.467 662 375 830 42.4 667 375 700 61.4 0.423 671 232 606 67.0 0.587 AISI 304 230 606 67 - The mechanical properties were evaluated on an annealed wrought steel. The working is carried out by forging from 1250 ° C. The steel is then annealed at a temperature of 1100 ° C. for 30 minutes in a salt bath. The tensile test specimens used are barrel specimens of circular section having a diameter of 5 mm and a length of 50 mm. They are subjected to a traction speed of 20 mm / minute. The steels according to the invention have an elongation of between 55% and 67%. By way of comparison, the following table 5 presents the measured characteristics of the steel according to the invention, of low-nickel steels outside the invention and of a reference steel of type AISI 304. Mechanical properties. Casting RPO.2 (Mpa) Rm (Mpa) AT% d (ln (σ) / d (ln (ε) * 567 282 623 66.0 0.479 * 569 309 747 62.7 0.615 570 393 657 54.8 0.319 571 376 703 57.5 0.395 572 294 1010 33.7 * 574 323 679 66.0 0.483 * 577 348 688 59.4 0.395 578 331 800 55.9 0.59 * 579 343 690 62.5 0.438 * 580 330 681 61.9 0.42 * 583 345 651 58.8 0.378 * 584 325 686 64.2 0.454 * 585 342 679 61.3 0.403 * 587 287 528 62.0 0.434 * 588 365 705 57.6 0.357 * 590 380 757 62.9 0.457 * 592 330 660 60.6 0.397 * 594 266 599 58.5 0.387 * 596 316 660 63.7 * 654 341 700 65.0 0.467 662 375 830 42.4 667 375 700 61.4 0.423 671 232 606 67.0 0.587 AISI 304 230 606 67 -

    Le taux de martensite après 30% de déformation vraie en traction a été mesuré ( tableau 4) : Pour l'acier selon l'invention, il est inférieur à 20%.The rate of martensite after 30% of true deformation in tension was measured (table 4): For the steel according to the invention, it is less than 20%.

    Aucune trace de martensite ε n'a été observée sur les éprouvettes de l'acier selon l'invention déformées à rupture. Les aciers selon l'invention dont l'indice IS est inférieur à 20 et dont l'indice IF1 est inférieur à 20 présentent un allongement en traction supérieur à 55% après transformation telle que définie ci-dessus. Un tel allongement est nécessaire pour obtenir une ductilité à froid adéquate.No trace of martensite ε was observed on the test pieces of the steel according to the invention deformed to rupture. The steels according to the invention whose IS index is less than 20 and whose IF 1 index is less than 20 have a tensile elongation greater than 55% after transformation as defined above. Such an elongation is necessary to obtain an adequate cold ductility.

    -Résistance à la corrosion.-Corrosion resistance.

    Dans le domaine de la corrosion intergranulaire, un test suivant la norme ASTM 262 E a été effectué sur des aciers comportant des teneurs en carbone et azote variables. Les aciers sur lesquels le test est pratiqué sont des aciers mis sous forme d'une bande laminée à chaud de 3 mm d'épaisseur et recuite à 1100°C ( hypertrempe ). In the area of intergranular corrosion, a following test ASTM 262 E was carried out on steels containing variable carbon and nitrogen contents. The steels on which the test is practiced are steels formed in the form of a strip rolled to hot 3 mm thick and annealed at 1100 ° C (hyper quenching).

    Les aciers subissent ensuite un des deux traitements de sensibilisation qui suivent:

  • a) un recuit à 700°C pendant 30 mn suivi d'une trempe à l'eau ou,
  • b) un recuit à 650°C pendant 10 mn suivi d'une trempe à l'eau. Les résultats du test sont présentés sur le tableau 6 suivant : a b Acier 700°C/30 mn + trempe à l'eau 650°C/30 mn + trempe à l'eau Perte de masse (mg) fissures µm Test Perte de masse (mg) fissures µm Test 721 4,6 0 Bon 2,7 - Bon 567 4,8 20 Bon - - Bon 592 4,95 65 Bon - - Bon 584 27,7 2500 Mauvais 3,3 0 Bon 594 70,6 2500 Mauvais 5,4 22 Mauvais 596 68,9 2500 Mauvais 9,4 1250 Mauvais
    • The steels then undergo one of the following two sensitization treatments:
  • a) annealing at 700 ° C for 30 min followed by quenching with water or,
  • b) annealing at 650 ° C for 10 min followed by quenching with water. The results of the test are presented in the following table 6: at b Steel 700 ° C / 30 min + water quenching 650 ° C / 30 min + water quenching Weight loss (mg) µm cracks Test Weight loss (mg) µm cracks Test 721 4.6 0 Well 2.7 - Well 567 4.8 20 Well - - Well 592 4.95 65 Well - - Well 584 27.7 2500 Bad 3.3 0 Well 594 70.6 2500 Bad 5.4 22 Bad 596 68.9 2500 Bad 9.4 1250 Bad

    • Les aciers hors invention, comportant plus de 0,1% de carbone, comme les aciers 594 et 596, ne présentent pas de caractéristiques acceptables.Steels outside the invention, containing more than 0.1% carbon, like 594 and 596 steels, have no characteristics acceptable.

    Les aciers selon l'invention qui contiennent dans leur composition moins de 0,1% de carbone, comme les aciers 567, 592, 584, sont comparables en terme de corrosion intergranulaire, à l'acier AISI 304 pour le test b.The steels according to the invention which contain in their composition less than 0.1% carbon, such as steels 567, 592, 584, are comparable in terms of intergranular corrosion, to steel AISI 304 for test b.

    Seuls, les aciers selon l'invention contenant dans leur composition moins de 0,080% de carbone sont comparables à l'acier AISI 304 pour le test a. La teneur de carbone selon l'invention est donc limitée à moins de 0,1%, et, de préférence limitée à moins de 0,08%.Only the steels according to the invention containing in their composition less than 0.080% carbon are comparable to steel AISI 304 for the test a. The carbon content according to the invention is therefore limited to less than 0.1%, and preferably limited to less than 0.08%.

    On a réalisé, dans un four électrique et à l'AOD des aciers selon les compositions de l'annexe 3, à teneurs en aluminium, calcium, oxygène, soufre variables, ces teneurs ayant été mesurées par des méthodes particulièrement précises comme, la spectrométrie d'absorption atomique pour le calcium, la spectrométrie par décharge luminescente pour l'aluminium; à partir des produits corroyés, on a réalisé des tests de corrosion par piqûre en NaCl 0,02 M à 23°C et pH égal à 6,6 dont les résultats sont reportés sur le tableau 7. Le potentiel E1 correspond à la probabilité de 1 piqûre par cm2.Steels were produced in an electric furnace and at AOD according to the compositions of Annex 3, with varying aluminum, calcium, oxygen and sulfur contents, these contents having been measured by particularly precise methods such as spectrometry atomic absorption for calcium, glow discharge spectrometry for aluminum; from the wrought products, pitting corrosion tests were carried out in 0.02 M NaCl at 23 ° C and pH equal to 6.6, the results of which are given in Table 7. The potential E1 corresponds to the probability of 1 bite per cm 2 .

    On constate que le potentiel de piqûre est notablement plus élevé sur les aciers dont la composition présente une teneur en aluminium ne dépassant pas 50.10-4% et qui contiennent en outre moins de 10.10-4% de calcium, moins de 60.10-4% d'oxygène et moins de 20.10-4% de soufre.We note that the pitting potential is significantly higher on steels whose composition has an aluminum content not exceeding 50.10 -4 % and which also contain less than 10.10 -4 % calcium, less than 60.10 -4 % d 'oxygen and less than 20.10 -4 % sulfur.

    On a pu observer en outre, par microscopie électronique à balayage que les aciers A et B contenant dans leur composition, respectivement, 110.10-4% d'aluminium et 115.10-4% comportent des inclusions de type aluminate de chaux et alumine-magnésie entourées de sulfures de calcium dont les tailles peuvent atteindre plusieurs micromètres. Aucun sulfure de calcium n'a été trouvé sur les aciers C et D contenant moins de 30.10-4% d'aluminium et moins de 10.10-4% de calcium. Acier Potentiel de piqûre E1 (mV/ECS) A 280 B 305 C 450 D 475

    Figure 00140001
    Figure 00150001
    It has also been observed, by scanning electron microscopy, that the steels A and B containing in their composition, respectively, 110 × 10 -4 % aluminum and 115 × 10 -4 % include inclusions of the lime aluminate and alumina-magnesia type surrounded of calcium sulphides whose sizes can reach several micrometers. No calcium sulfide was found on steels C and D containing less than 30.10 -4 % aluminum and less than 10.10 -4 % calcium. Steel Puncture potential E1 (mV / DHW) AT 280 B 305 VS 450 D 475
    Figure 00140001
    Figure 00150001

    Claims (10)

    Acier inoxydable austénitique comportant une teneur très faible en nickel, caractérisé en la composition pondérale suivante : carbone < 0,1% 0,1% < silicium < 1% 5% < manganèse < 9% 0,1 < nickel < 2% 13% < chrome < 19% 1% < cuivre < 4% 0,1% < azote < 0,40% 510-4% < bore < 50.10-4% phosphore < 0,05%, soufre < 0,01 %. Austenitic stainless steel with a very low nickel content, characterized by the following composition by weight: carbon <0.1% 0.1% <silicon <1% 5% <manganese <9% 0.1 <nickel <2% 13% <chromium <19% 1% <copper <4% 0.1% <nitrogen <0.40% 510-4% <boron <50.10 -4 % phosphorus <0.05%, sulfur <0.01%. Acier austénitique selon la revendication 1, caractérisé en ce que la composition satisfait à la relation utilisant un indice ferritique IF1 : IF1 = 0,034x2 + 0,284 x - 0,347 < 20 avec x = 6,903.[ - 6,998 + Cr% - 0,972.( Ni% + 20,04.C% + 21,31.N% + 0,46.Cu% + 0,08.Mn% )]. Austenitic steel according to claim 1, characterized in that the composition satisfies the relationship using a ferritic index IF 1 : IF 1 = 0.034x 2 + 0.284 x - 0.347 <20 with x = 6.903. [- 6.998 + Cr% - 0.972. (Ni% + 20.04C% + 21.31.N% + 0.46.Cu% + 0.08.Mn%)]. Acier austénitique selon la revendication 1, caractérisé en ce que la composition satisfait à la relation suivante utilisant un indice de stabilité martensitique IS: IS = 0,0267.x2 + 0,4332 x - 3,1459 < 20 avec, x= 250,4 - 205,4.C% - 101,4.N% - 7,6.Mn% - 12,1.Ni% - 6,1.Cr% - 13,3.Cu%. Austenitic steel according to claim 1, characterized in that the composition satisfies the following relationship using a martensitic stability index IS: IS = 0.0267.x 2 + 0.4332 x - 3.1459 <20 with, x = 250.4 - 205.4.C% - 101.4.N% - 7.6.Mn% - 12.1.Ni% - 6.1.Cr% - 13.3.Cu%. Acier austénitique selon les revendications 1 à 3, caractérisé en ce qu'il comporte dans sa composition moins de 1% de nickel. Austenitic steel according to claims 1 to 3, characterized in that it contains less than 1% nickel in its composition. Acier austénitique selon les revendications 1 à 3, caractérisé en ce qu'il comporte dans sa composition de 15% à 17% de chrome.Austenitic steel according to claims 1 to 3, characterized in that it comprises in its composition from 15% to 17% of chromium. Acier austénitique selon les revendications 1 à 3, caractérisé en ce qu'il comporte dans sa composition moins de 0,08% de carbone.Austenitic steel according to claims 1 to 3, characterized in that it contains less than 0.08% carbon in its composition. Acier austénitique selon les revendications 1 à 3, caractérisé en ce qu'il comporte dans sa composition de 0,5% à 0,7% de silicium.Austenitic steel according to claims 1 to 3, characterized in that it comprises in its composition from 0.5% to 0.7% of silicon. Acier austénitique selon les revendications 1 à 3, caractérisé en ce qu'il comporte en outre dans sa composition moins de 2% de molybdène.Austenitic steel according to claims 1 to 3, characterized in that it further comprises in its composition less than 2% of molybdenum. Acier austénitique selon les revendications 1 à 3, caractérisé en ce qu'il comporte en outre dans sa composition moins de 0,0020% de soufre.Austenitic steel according to claims 1 to 3, characterized in that it further comprises in its composition less than 0.0020% sulfur. Acier austénitique selon les revendications 1 à 3, caractérisé en ce qu'il comporte en outre dans sa composition moins de 0,030% d'aluminium, de préférence moins de 50.10-4% d'aluminium et moins de 20.10-4% de calcium et de préférence moins de 5.10-4% de calcium.Austenitic steel according to claims 1 to 3, characterized in that it further comprises in its composition less than 0.030% aluminum, preferably less than 50.10 -4 % aluminum and less than 20.10 -4 % calcium and preferably less than 5.10 -4 % calcium.
    EP98401734A 1997-07-29 1998-07-09 Austenitic stainless steel with very low nickel content Expired - Lifetime EP0896072B1 (en)

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