EP0403332B1 - Resulfurized austenitic stainless steel with improved machinability - Google Patents

Resulfurized austenitic stainless steel with improved machinability Download PDF

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EP0403332B1
EP0403332B1 EP90401511A EP90401511A EP0403332B1 EP 0403332 B1 EP0403332 B1 EP 0403332B1 EP 90401511 A EP90401511 A EP 90401511A EP 90401511 A EP90401511 A EP 90401511A EP 0403332 B1 EP0403332 B1 EP 0403332B1
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inclusions
calcium
stainless steel
equal
fact
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EP0403332A1 (en
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Olivier Bletton
Roger Duet
Marc Henry
Jean-Yves Cogne
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Ugitech SA
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Ugine Savoie 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

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  • the present invention relates to a resulfurized austenitic stainless steel with improved machinability.
  • Such an austenitic steel is known from JP-A-160785.
  • This patent deals with a steel which can be machined and deformed cold and which, in weight composition, in particular, a sulfur content of less than 0.030%, calcium and oxygen contents respectively included in the ranges 10-300 ppm and 30-300 ppm , 0.8 to 5% copper and 0.01 to 0.25% lead.
  • austenitic stainless steels are difficult to machine, largely because of their low thermal conductivity, resulting in poor flow of heat produced at the tip of a cutting tool and rapid deterioration of the 'tool and their high hardening locally inducing high hardness areas.
  • One way to improve machinability is the introduction of the lead element, in particular in a proportion of 0.01 to 0.25%.
  • This element has the disadvantages of being difficult to dissolve homogeneously in a molten bath, and, because of its high density, of having a tendency to accumulate in the bottom of metallurgical vessels. In addition, it forms phases with a low melting point deteriorating the hot deformability.
  • FR-A-2,542,761 which describes a process manufacturing high machinability steel
  • another cause of the difficulty in machining stainless steels is the fact that they contain inclusions of hard oxides such as for example alumina or chromite which damage the cutting tools.
  • One way to reduce the harmfulness of hard oxide inclusions is to introduce into the steel one or more alkaline earth compounds, in order to replace in a good proportion the hard inclusions by inclusions of calcium-based oxides, for example. It is specified on the one hand, that a certain quantity of sulfur combined with hard inclusions reduces its harmfulness, the sulfur content being generally less than 0.5 10 ⁇ 4%, and on the other hand, that a Another way to reduce the harmfulness of inclusions is to reduce their quantity thanks to good deoxidation and good decantation of the molten bath during the production of steel.
  • an austenitic stainless steel which has good aptitude for hot work and whose weight composition is as follows: carbon between 0.03 and 0.15% silicon between 0.10 and 1.00% manganese between 1.00 and 2.00% phosphorus less than 0.20% except between 0.15 and 0.35% nickel between 8.00 and 10.00% chromium between 17.00 and 19.00% calcium between 20.10-4 and 60.10-4 oxygen less than 45.10-4 the rest being iron.
  • the problem which this document proposes to solve is to obtain a steel which has a good aptitude for hot working and which does not exhibit any tearing of the ends when the ingot is rolled in order to prevent the ends from rolling up. around the cylinders.
  • the subject of the present invention is a resulfurized austenitic steel with improved unisability containing on the one hand sulfur for the creation of a manganese and chromium sulfide having lubricating properties and on the other hand a determined proportion oxygen and calcium introduced in the form of lime silicoaluminate, in order to create, in number, specific inclusions improving the machinability.
  • Calcium is introduced, during the preparation, into the molten bath, by addition of silico-calcium under control of the oxygen contents.
  • the austenitic steel comprises sulfur in a proportion of between 0.15 and 0.35%.
  • the value of the ratio of the contents of calcium and oxygen elements is between 0.3 and 0.5.
  • the range of values of the Ca / O ratio is determined by machinability measurements of the various steels having the basic composition of the steel according to the invention and the calcium and oxygen contents are varied.
  • the manganese sulfide and chromium inclusions are coated with a lime silicoaluminate phase of the anorthite and / or pseudowollastonite type to form associated inclusions.
  • the creation of this type of inclusion is made possible by the introduction of calcium compounds into the liquid bath under the control of determined oxygen contents.
  • the associated inclusions have a form factor of between 3 and 6.
  • the form factor is determined by the ratio of the length to the width of the inclusion, the value of the form factor being a criterion for measuring the quality of steel machinability.
  • FIG. 1 represents the CaO-Al2O3-SiO2 ternary composition diagram locating the weight composition of the anorthite of pseudowollastonite and of gehlenite.
  • Figure 2 shows a sectional image of an associated inclusion.
  • FIG. 3 is a diagram representing the values of the machinability criterion VB30 / 0.3 as a function of the variation in oxygen concentration.
  • FIG. 4 is a diagram representing the values of the machinability criterion VB30 / 0.3 as a function of the variation in sulfur concentration.
  • FIG. 5 represents, in an example of steel given for comparison (steel according to the invention without sulfur), a diagram representing the values VB30 / 0.3 as a function of the ratio of the Ca / O contents.
  • the present invention relates to a resulfurized austenitic stainless steel alloy whose machinability is improved by the creation of associated inclusions, lime silicoaluminate / manganese sulfide and chromium.
  • Sulfur generates manganese sulfide inclusions also containing chromium in the steel.
  • the lime silico-aluminate oxides are created during the production of the steel by the introduction of calcium, preferably, in the form of a wire filled with silicocalcium, in the molten bath under control of the oxygen contents.
  • the vast majority of the oxides are linked to the sulphides and, with the inclusion of the sulphides, form associated inclusions, the sulphide being placed inside the oxide inclusions.
  • These sulfides are manganese sulfides, however, also containing chromium.
  • the lime silicoaluminate oxides in their chemical composition are preferably anorthite or pseudowollastonite, (the chemical composition of which is shown in the ternary diagram of FIG. 1), the majority of said oxides being anorthite. These oxides can also contain a little MnO.
  • the lime silicoaluminate oxides formed around the sulphides are malleable, low-melting oxides which can easily deform during rolling.
  • these inclusions play a lubricating role at the interface-steel to be machined-cutting tool, thus leading to reduced wear of cutting tools and better surface appearance of the machined parts.
  • FIG. 2 is a sectional image of a steel according to the invention containing an associated inclusion 2 of lenticular form composed of lime silicoaluminate 3 coating inclusions of sulfide 4 of manganese and chromium.
  • Table 1 gives some results obtained on steels whose basic composition is: C: 0.05%, Si: 0.5%, Mn: 1.8%, Ni: 8.6%, Cr: 17%, Mo: 0.2%, S: 0.3%, but whose calcuim and oxygen contents vary.
  • the average surface and the average form factor (length / width) of the sulfide inclusions and of the associated oxide / sulfide inclusions are given.
  • Steels No. 3 to 7 corresponding to a composition according to the invention.
  • the values of VB30 / 0.3 are higher by about 20%.
  • the mean surface and the mean form factor of the sulphide inclusions of steels No. 1 and No. 2 on the one hand and of steels No. 3 to No. 7 do not differ significantly.
  • the criteria used to compare the steels are on the one hand the time leading to an undercut wear of 0.15 mm under the cutting conditions given above and on the other hand the measurement of wear in skin after 30 minutes of cutting.
  • FIG. 3 presents a diagram giving the variations of the machinability criterion VB30 / 0.3 as a function of the oxygen concentration in a series of measurements corresponding on the one hand to the production of the steels according to the invention and, on the other hand, the development of calcium-free steel.
  • FIG. 4 represents a diagram giving the variations of the machinability criterion VB30 / 0.3 as a function of the sulfur concentration in a series of measurements corresponding on the one hand to the preparation according to the invention and, on the other hand , to the development of calcium-free steel.
  • Figures 3 and 4 show first of all that the evolution of grades of resulfurized austenitic stainless steels towards high oxygen contents or high sulfur contents does not make it possible to improve machinability significantly (criterion VB 30 / 0.3).
  • steels according to the invention constitutes a separate population, on the diagrams of FIGS. 3 and 4, with high machinability criteria.
  • These steels contain little or no sulfur compared to the steel according to the invention.
  • Table III gives the values of VB 30 / 0.3 of several steels as a function of the calcium and oxygen content and of the value of the ratio of element concentrations.
  • TABLE III STEEL N ° Ca (ppm) O (ppm) Ca
  • Steels No. 8 and No. 9 contain little or no calcium and are the reference steels for these measurements.
  • the oxide inclusions are of the polyphase silicate and chromite type.
  • Steel No. 13 has an oxygen content corresponding to that of the composition of the steel according to the invention without sulfur but a calcium content and a lower Ca / O ratio. The machinability is not significantly improved.
  • Steel No. 14 has contents corresponding to those of the composition of the steel according to the invention without sulfur, but a Ca / O ratio below 0.30.
  • the improvement in machinability is appreciable but remains far below that of steels N ° 10 and N ° 11.
  • the present invention relates to a resulfurized austenitic stainless steel whose machinability is improved thanks to the creation of associated inclusions of oxides of lime silico-aluminate / sulfide (Mn, Cr) S type.
  • oxides coating sulfide inclusions are lime silico-aluminates, preferably of the anorthite and pseudowollastonite type, the chemical compositions of which are determined in the ternary diagram CaO-SiO2-Al203 in FIG. 1.
  • These associated inclusions have a surface and a form factor (length / width) important. The high deformability of the inclusions and their lubricating effect at the cutting tool / chip interface allowing improved machinability.

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Abstract

Resulphurized austenitic stainless steel with improved machinability, characterized in that its weight composition is the following: carbon lower than or equal to 0.15% silicon lower than or equal to 2% manganese lower than or equal to 2% molybdenum lower than or equal to 3% nickel between 7 and 12% chromium between 15 and 25% sulphur between 0.10 and 0.40% calcium higher than or equal to 30x10-4% oxygen higher than or equal to 70x10-4% the ratio of the calcium content and of the oxygen content Ca/O being between 0.2 and 0.6.

Description

La présente invention concerne un acier inoxydable austénitique resulfuré à usinabilité améliorée.The present invention relates to a resulfurized austenitic stainless steel with improved machinability.

Un tel acier austénitique est connu dans le JP-A-160785. Ce brevet traite d'un acier usinable et déformable à froid et ayant, en composition pondérale, notamment, une teneur en soufre inférieure à 0,030%, des teneurs en calcium et oxygène respectivement comprises dans les intervalles 10-300 ppm et 30-300 ppm, de 0,8 à 5% de cuivre et de 0,01 à 0,25% de plomb.Such an austenitic steel is known from JP-A-160785. This patent deals with a steel which can be machined and deformed cold and which, in weight composition, in particular, a sulfur content of less than 0.030%, calcium and oxygen contents respectively included in the ranges 10-300 ppm and 30-300 ppm , 0.8 to 5% copper and 0.01 to 0.25% lead.

Dans cet acier inoxydable austénitique, on introduit de l'oxygène et du calcium, ce qui permet de transformer des inclusions dures en inclusions à base d'oxyde de calcium. L'amélioration de l'usinabilité est générée par l'introduction, dans la composition, d'une quantité variable de plomb.In this austenitic stainless steel, oxygen and calcium are introduced, which makes it possible to transform hard inclusions into inclusions based on calcium oxide. The improvement in machinability is generated by the introduction into the composition of a variable amount of lead.

Il est bien connu que les aciers inoxydables austénitiques sont difficiles à usiner, en grande partie à cause de leur faible conductibilité thermique, d'où un mauvais écoulement de la chaleur produite à la pointe d'un outil de coupe et une détérioration rapide de l'outil et de leur forte écrouissabilité induisant localement des zones de dureté élevée.It is well known that austenitic stainless steels are difficult to machine, largely because of their low thermal conductivity, resulting in poor flow of heat produced at the tip of a cutting tool and rapid deterioration of the 'tool and their high hardening locally inducing high hardness areas.

Un moyen d'améliorer l'usinabilité est l'introduction de l'élément plomb notamment dans une proportion de 0,01 à 0,25%. Cet élément à les inconvénients d'être difficile à dissoudre de façon homogène en bain fondu, et, en raison de sa densité élevée, d'avoir tendance à s'accumuler dans le fond des récipients métallurgiques. De plus il forme des phases à bas point de fusion détériorant la déformabilité à chaud.One way to improve machinability is the introduction of the lead element, in particular in a proportion of 0.01 to 0.25%. This element has the disadvantages of being difficult to dissolve homogeneously in a molten bath, and, because of its high density, of having a tendency to accumulate in the bottom of metallurgical vessels. In addition, it forms phases with a low melting point deteriorating the hot deformability.

Dans le FR-A-2.542.761 qui décrit un procédé de fabrication d'acier à haute usinabilité, il est précisé qu'une autre cause de la difficulté d'usiner les aciers inoxydables est le fait qu'ils contiennent des inclusions d'oxydes durs comme par exemple de l'alumine ou de la chromite qui détériorent les outils de coupe.In FR-A-2,542,761 which describes a process manufacturing high machinability steel, it is specified that another cause of the difficulty in machining stainless steels is the fact that they contain inclusions of hard oxides such as for example alumina or chromite which damage the cutting tools.

Un moyen de réduire la nocivité des inclusions d'oxydes durs est d'introduire dans l'acier un ou plusieurs composés alcalinoterreux, afin de remplacer dans une bonne proportion les inclusions dures par des inclusions d'oxydes à base de calcium, par exemple. Il est précisé d'une part, qu'une certaine quantité de soufre combiné à des inclusions dures en réduit la nocivité, la teneur en soufre étant généralement inférieure à 0,5 10⁻⁴ %, et d'autre part, qu'un autre moyen de réduire la nocivité des inclusions est de réduire leur quantité grâce à une bonne désoxydation et une bonne décantation du bain fondu lors de la réalisation de l'acier.One way to reduce the harmfulness of hard oxide inclusions is to introduce into the steel one or more alkaline earth compounds, in order to replace in a good proportion the hard inclusions by inclusions of calcium-based oxides, for example. It is specified on the one hand, that a certain quantity of sulfur combined with hard inclusions reduces its harmfulness, the sulfur content being generally less than 0.5 10⁻⁴%, and on the other hand, that a Another way to reduce the harmfulness of inclusions is to reduce their quantity thanks to good deoxidation and good decantation of the molten bath during the production of steel.

Dans les documents mentionnés ci-dessus, l'amélioration de l'usinabilité de l'acier est réalisée :

  • par introduction de plomb en tant que lubrifiant,
  • par introduction d'oxygène ou de calcium pour réduire les inclusions dures en inclusions à base de composés alcalinoterreux.
  • en réduisant le nombre d'inclusions dures par désoxydation du bain fondu, lors de l'élaboration.
In the documents mentioned above, the machinability of the steel is improved:
  • by introducing lead as a lubricant,
  • by introducing oxygen or calcium to reduce hard inclusions to inclusions based on alkaline earth compounds.
  • by reducing the number of hard inclusions by deoxidation of the molten bath, during the preparation.

On connaît également dans le brevet JP-A-56.090.959 un acier inoxydable austénitique qui présente une bonne aptitude au travail à chaud et dont la composition pondérale est la suivante :
   carbone entre 0,03 et 0,15%
   silicium entre 0,10 et 1,00%
   manganèse entre 1,00 et 2,00%
   phosphore moins de 0,20%
   saufre entre 0,15 et 0,35%
   nickel entre 8,00 et 10,00%
   chrome entre 17,00 et 19,00%
   calcium entre 20.10-4 et 60.10-4
   oxygène moins de 45.10-4
   le reste étant constitué par du fer.Also known from patent JP-A-56,090,959 is an austenitic stainless steel which has good aptitude for hot work and whose weight composition is as follows:
carbon between 0.03 and 0.15%
silicon between 0.10 and 1.00%
manganese between 1.00 and 2.00%
phosphorus less than 0.20%
except between 0.15 and 0.35%
nickel between 8.00 and 10.00%
chromium between 17.00 and 19.00%
calcium between 20.10-4 and 60.10-4
oxygen less than 45.10-4
the rest being iron.

Le problème que se propose de résoudre ce document est d'obtenir un acier qui présente une bonne aptitude au travail à chaud et qui ne présente pas de déchirement d'extrémité au moment du laminage du lingot afin d'éviter que les extrémités s'enroulent autour des cylindres.The problem which this document proposes to solve is to obtain a steel which has a good aptitude for hot working and which does not exhibit any tearing of the ends when the ingot is rolled in order to prevent the ends from rolling up. around the cylinders.

La présente invention a pour objet un acier austénitique resulfuré à unisabilité améliorée contenant d'une part, du soufre pour la création d'un sulfure de manganèse et chrome ayant des propriétés lubrifiantes et, d'autre part, une proportion déterminée d'oxygène et de calcium introduite sous forme de silicoaluminate de chaux, afin de créer, en nombre, des inclusions spécifiques améliorant l'usinabilité.The subject of the present invention is a resulfurized austenitic steel with improved unisability containing on the one hand sulfur for the creation of a manganese and chromium sulfide having lubricating properties and on the other hand a determined proportion oxygen and calcium introduced in the form of lime silicoaluminate, in order to create, in number, specific inclusions improving the machinability.

L'acier inoxydable austénitique se caractérise par la composition suivante exprimée en pourcentages pondéraux :

  • Carbone inférieur ou égal à 0,15%
  • Silicium inférieur ou égal à 2%
  • Manganèse inférieur ou égal à 2%
  • Molybdène inférieur ou égal à 3%
  • Nickel compris entre 7 et 12%
  • Chrome compris entre 15 et 25%
  • Soufre compris entre 0,10 et 0,40%
  • Calcium supérieur ou égal à 30 10⁻⁴%
  • Oxygène supérieur ou égal à 70 10⁻⁴%
  • Le rapport de la teneur en calcium et en oxygène Ca/O étant compris entre 0,2 et 0,6,
Austenitic stainless steel is characterized by the following composition expressed in weight percentages:
  • Carbon less than or equal to 0.15%
  • Silicon less than or equal to 2%
  • Manganese less than or equal to 2%
  • Molybdenum less than or equal to 3%
  • Nickel between 7 and 12%
  • Chrome between 15 and 25%
  • Sulfur between 0.10 and 0.40%
  • Calcium greater than or equal to 30 10⁻⁴%
  • Oxygen greater than or equal to 70 10⁻⁴%
  • The ratio of the calcium and oxygen Ca / O content being between 0.2 and 0.6,

le reste étant du fer et en ce qu'il contient des inclusions de silicoaluminate de chaux de type anorthite et/ou pseudowollastonite.the rest being iron and in that it contains inclusions of lime silicoaluminate of the anorthite and / or pseudowollastonite type.

Le calcium est introduit, Lors de l'élaboration, dans le bain fondu, par addition de silico-calcium sous contrôle des teneurs en oxygène.Calcium is introduced, during the preparation, into the molten bath, by addition of silico-calcium under control of the oxygen contents.

Dans une composition préférentielle de l' invention, l'acier austénitique comprend du soufre dans une proportion comprise entre 0,15 et 0,35%. Le saufre forme avec le manganèse et dans une plus faible proportion, avec le chrome, un sulfure de manganèse et chrome (Mn, Cr) S qui génère-sous forme d'inclusions une lubrification à chaud de l'outil de coupe lors de l'usinage de l'acier.In a preferred composition of the invention, the austenitic steel comprises sulfur in a proportion of between 0.15 and 0.35%. Horses form with manganese and, to a lesser extent, with chromium, a manganese sulphide and chromium (Mn, Cr) S which generates -in the form of inclusions a hot lubrication of the cutting tool during the machining of steel.

Dans une autre forme de l'invention, la valeur du rapport des teneurs en éléments calcium et oxygène est comprise entre 0,3 et 0,5.In another form of the invention, the value of the ratio of the contents of calcium and oxygen elements is between 0.3 and 0.5.

L'intervalle des valeurs du rapport Ca/O est déterminé par des mesures d'usinabilité des différents aciers ayant la composition de base de l'acier selon l'invention et dont on fait varier les teneurs en calcium et oxygène.The range of values of the Ca / O ratio is determined by machinability measurements of the various steels having the basic composition of the steel according to the invention and the calcium and oxygen contents are varied.

Particulièrement les inclusions de sulfure de manganèse et chrome sont enrobées d'une phase de silicoaluminate de chaux de type anorthite et/ou pseudowollastonite pour former des inclusions associées. La création de ce type d'inclusion est rendue possible grâce à l'introduction de composés de calcium, dans le bain liquide sous contrôle de teneurs déterminées en oxygène.In particular, the manganese sulfide and chromium inclusions are coated with a lime silicoaluminate phase of the anorthite and / or pseudowollastonite type to form associated inclusions. The creation of this type of inclusion is made possible by the introduction of calcium compounds into the liquid bath under the control of determined oxygen contents.

De plus, les inclusions associées ont un facteur de forme compris entre 3 et 6. Le facteur de forme est déterminé par le rapport de la longueur sur la largeur de l'inclusion, la valeur du facteur de forme étant un critère de mesure de la qualité de l'usinabilité de l'acier.In addition, the associated inclusions have a form factor of between 3 and 6. The form factor is determined by the ratio of the length to the width of the inclusion, the value of the form factor being a criterion for measuring the quality of steel machinability.

Les essais décrits ci-dessous et les figures annexées feront mieux comprendre l'invention.The tests described below and the appended figures will make the invention better understood.

La figure 1 représente le diagramme de composition ternaire CaO-Al₂O₃-SiO₂ situant la composition pondérale de l'anorthite de la pseudowollastonite et de gehlenite.FIG. 1 represents the CaO-Al₂O₃-SiO₂ ternary composition diagram locating the weight composition of the anorthite of pseudowollastonite and of gehlenite.

La figure 2 représente une image en coupe d'une inclusion associée.Figure 2 shows a sectional image of an associated inclusion.

La figure 3 est un diagramme représentant les valeurs du critère d'usinabilité VB30/0,3 en fonction de la variation de concentration d'oxygène.FIG. 3 is a diagram representing the values of the machinability criterion VB30 / 0.3 as a function of the variation in oxygen concentration.

La figure 4 est un diagramme représentant les valeurs du critère d'usinabilité VB30/0,3 en fonction de la variation de concentration de soufre.FIG. 4 is a diagram representing the values of the machinability criterion VB30 / 0.3 as a function of the variation in sulfur concentration.

La figure 5 représente, dans un exemple d'acier donné à titre de comparaison (acier selon l'invention sans soufre), un diagramme représentant les valeurs VB30/0,3 en fonction du rapport des teneurs Ca/O.FIG. 5 represents, in an example of steel given for comparison (steel according to the invention without sulfur), a diagram representing the values VB30 / 0.3 as a function of the ratio of the Ca / O contents.

La présente invention concerne un alliage d'acier inoxydable austénitique resulfuré dont l'usinabilité est améliorée par la création d'inclusions associées, silicoaluminate de chaux/sulfure de manganèse et chrome.The present invention relates to a resulfurized austenitic stainless steel alloy whose machinability is improved by the creation of associated inclusions, lime silicoaluminate / manganese sulfide and chromium.

L'alliage comprend, en poids :

  • Carbone inférieur ou égal à 0,15%
  • Silicium inférieur ou égal à 2%
  • Manganèse inférieur ou égal à 2%
  • Molybdène inférieur ou égal à 3%
  • Nickel compris entre 7 et 12%
  • Chrome compris entre 15 et 25%
  • soufre compris entre 0,10 et 0,40%
  • oxygène supérieur ou égal à 70 ppm
  • Calcium supérieur ou égal à 30 ppm.
The alloy includes, by weight:
  • Carbon less than or equal to 0.15%
  • Silicon less than or equal to 2%
  • Manganese less than or equal to 2%
  • Molybdenum less than or equal to 3%
  • Nickel between 7 and 12%
  • Chrome between 15 and 25%
  • sulfur between 0.10 and 0.40%
  • oxygen greater than or equal to 70 ppm
  • Calcium greater than or equal to 30 ppm.

Le rôle bénéfique du soufre sur l'usinabilité est bien connu. Le soufre engendre dans l'acier des inclusions de sulfure de manganèse contenant également du chrome.The beneficial role of sulfur on machinability is well known. Sulfur generates manganese sulfide inclusions also containing chromium in the steel.

L'addition de soufre, ou encore par exemple du sélénium, permet d'améliorer l'usinabilité des aciers inoxydables austénitiques mais au détriment d'autres propriétés comme par exemple une diminution de la résistance à la corrosion et de la déformabilité à chaud et à froid.The addition of sulfur, or even, for example, selenium, makes it possible to improve the machinability of austenitic stainless steels but to the detriment of other properties such as, for example, a reduction in corrosion resistance and in hot and deformability. cold.

Malgré l'effet défavorable d'une réduction de la résistance à la corrosion engendré par le soufre, les essais sur l'usinabilité des aciers austénitiques se sont orientés vers l'introduction, dans un acier resulfuré, d'oxydes silicoaluminates de chaux. Ces oxydes ne détériorent pas la résistance à la corrosion.Despite the unfavorable effect of a reduction in the resistance to corrosion caused by sulfur, tests on the machinability of austenitic steels have been directed towards the introduction, into resulfurized steel, of lime silicoaluminate oxides. These oxides do not deteriorate the corrosion resistance.

Le oxydes silico-aluminates de chaux sont créés lors de l'élaboration de l'acier grâce à l'introduction de calcium, préférentiellement ,sous forme de fil fourré de silicocalcium, dans le bain fondu sous contrôle des teneurs en oxygène.The lime silico-aluminate oxides are created during the production of the steel by the introduction of calcium, preferably, in the form of a wire filled with silicocalcium, in the molten bath under control of the oxygen contents.

Selon l'invention, les oxydes sont en grande majorité liés aux sulfures et forment avec les inclusion de sulfures, des inclusions associées, le sulfure se plaçant à l'intérieur des inclusions d'oxyde. Ces sulfures sont des sulfures de manganèse contenant toutefois également du chrome.According to the invention, the vast majority of the oxides are linked to the sulphides and, with the inclusion of the sulphides, form associated inclusions, the sulphide being placed inside the oxide inclusions. These sulfides are manganese sulfides, however, also containing chromium.

Les oxydes silicoaluminates de chaux dans leur composition chimique sont préférentiellement de l'anorthite ou de la pseudowollastonite, (dont la composition chimique est représentée sur le diagramme ternaire de la figure 1), la majorité desdits oxydes étant de l'anorthite. Ces oxydes peuvent de plus contenir un peu de MnO.The lime silicoaluminate oxides in their chemical composition are preferably anorthite or pseudowollastonite, (the chemical composition of which is shown in the ternary diagram of FIG. 1), the majority of said oxides being anorthite. These oxides can also contain a little MnO.

Les oxydes silicoaluminates de chaux formés autour des sulfures sont des oxydes malléables, à bas point de fusion qui peuvent se déformer facilement lors du laminage. Pendant l'usinage de l'acier, du fait des températures de coupe élevées, ces inclusions jouent un rôle lubrifiant à l'interface-acier à usiner-outil de coupe, conduisant ainsi à une usure réduire des outils de coupe et à un meilleur aspect de surface des pièces usinées.The lime silicoaluminate oxides formed around the sulphides are malleable, low-melting oxides which can easily deform during rolling. During the machining of steel, due to the high cutting temperatures, these inclusions play a lubricating role at the interface-steel to be machined-cutting tool, thus leading to reduced wear of cutting tools and better surface appearance of the machined parts.

Les recherches réalisées ont permis de conduire à la définition d'une composition d'acier de haute usinabilité à partir d'une base dont la composition a été donnée ci-dessus et ayant essentiellement :

  • une teneur en soufre de 0,15 à 0,35%.
  • une teneur en calcium supérieure ou égale à 30 ppm sur produit fini,
  • une teneur en oxygène supérieure ou égale à 70 ppm sur produit fini,
  • un rapport des teneurs en élément Ca/O compris entre 0,3 et 0,5. Il en découle :
  • la présence d'inclusions oxydes de silico-aluminates de chaux préférentiellement d'anorthite (majoritaire) ou de pseudowollastonite (minoritaire) enrobant généralement des sulfures de manganèse et chrome.
The research carried out led to the definition of a composition of high machinability steel from a base whose composition was given above and having essentially:
  • a sulfur content of 0.15 to 0.35%.
  • a calcium content greater than or equal to 30 ppm on the finished product,
  • an oxygen content greater than or equal to 70 ppm on the finished product,
  • a Ca / O element content ratio of between 0.3 and 0.5. It follows:
  • the presence of inclusions of silico-aluminate oxides of lime preferably of anorthite (majority) or of pseudowollastonite (minority) generally coating manganese and chromium sulphides.

La figure 2 est une image en coupe d'un acier selon l'invention contenant une inclusion 2 associée de forme lenticulaire composée de silicoaluminate de chaux 3 enrobant des inclusions de sulfure 4 de manganèse et chrome.FIG. 2 is a sectional image of a steel according to the invention containing an associated inclusion 2 of lenticular form composed of lime silicoaluminate 3 coating inclusions of sulfide 4 of manganese and chromium.

De manière nette, il n'y a pas formation de sulfure de calcium, sulfure reconnu comme nocif, pour l'usinabilité des aciers et la résistance à la corrosion.Clearly, there is no formation of calcium sulphide, sulphide recognized as harmful, for the machinability of steels and corrosion resistance.

Les essais suivants illustrent de façon comparative les qualités d'usinabilité de l'acier selon l'invention.The following tests illustrate in a comparative manner the qualities of machinability of the steel according to the invention.

Des essais de tournage avec outil en carbure (de référence P20 ISO) ont été réalisés. Pour une profondeur de passe de 1,5 mm, une avance de 0,25 mm/tour, plusieurs vitesses de coupe sont fixées. Pour chaque vitesse de coupe, l'outil est démonté toutes les 4 mn pour mesure de l'usure en dépouille. Ainsi, pour plusieurs vitesses V1, V2, V3..., une courbe donnant l'usure en dépouille de l'outil en fonction du temps ce l'usinage est tracée. La vitesse de coupe, conduisant à une usure en dépouille de 0,3 mm en 30 mn, peut ainsi être déterminée pour chaque élaboration, et être prise en référence sous le critère VB30/0,3.Turning tests with a carbide tool (P20 ISO reference) were carried out. For a cutting depth of 1.5 mm, an advance of 0.25 mm / revolution, several cutting speeds are fixed. For each cutting speed, the tool is disassembled every 4 min to measure the undercut wear. Thus, for several speeds V1, V2, V3 ..., a curve giving the wear and tear of the tool as a function of time, this machining is plotted. Cutting speed, leading to a wear and tear of 0.3 mm in 30 min, can thus be determined for each preparation, and be taken as a reference under the criterion VB30 / 0.3.

Le tableau 1 ci-dessous donne quelques résultats obtenus sur des aciers dont la composition de base est : C : 0,05%, Si : 0,5%, Mn : 1,8%, Ni : 8,6%, Cr : 17%, Mo : 0,2%, S : 0,3%, mais dont les teneurs en calcuim et oxygène varient. De plus, pour chaque élaboration, la surface moyenne et le facteur de forme moyen (longueur/largeur) des inclusions de sulfure et des inclusions associées oxyde/sulfure sont donnés. TABLEAU I ACIER N° CA (ppm) O (ppm) Ca|O VB 30/0,3 (m/mn) SURFACE INCLUSIONS ASSOCIEES (mm)² FACTEUR DE FORME INCLUSIONS ASSOCIEES SURFACE SULFURE (mm)² FACTEUR DE FORME SULFURES 1 5 94 0,05 245 2,4 1,8 39,3 3,1 2 5 70 0,07 250 2,1 2,1 31,1 3,2 3 45 120 0,38 300 24,9 4,5 31,4 3,1 4 43 105 0,41 295 41,9 5 21,7 2,8 5 40 96 0,42 303 39,8 5,4 31,4 3,1 6 47 102 0,46 300 39,2 4,8 27,4 3,4 7 35 73 0,48 308 45,5 5,6 35,3 3,7 Table 1 below gives some results obtained on steels whose basic composition is: C: 0.05%, Si: 0.5%, Mn: 1.8%, Ni: 8.6%, Cr: 17%, Mo: 0.2%, S: 0.3%, but whose calcuim and oxygen contents vary. In addition, for each preparation, the average surface and the average form factor (length / width) of the sulfide inclusions and of the associated oxide / sulfide inclusions are given. TABLE I STEEL N ° CA (ppm) O (ppm) Ca | O VB 30 / 0.3 (m / min) SURFACE ASSOCIATED INCLUSIONS (mm) ² FORM FACTOR RELATED INCLUSIONS SULFURIZED SURFACE (mm) ² SULFIDE FORM FACTOR 1 5 94 0.05 245 2.4 1.8 39.3 3.1 2 5 70 0.07 250 2.1 2.1 31.1 3.2 3 45 120 0.38 300 24.9 4.5 31.4 3.1 4 43 105 0.41 295 41.9 5 21.7 2.8 5 40 96 0.42 303 39.8 5.4 31.4 3.1 6 47 102 0.46 300 39.2 4.8 27.4 3.4 7 35 73 0.48 308 45.5 5.6 35.3 3.7

Les aciers N° 1 et N° 2 constituent des références et ne contiennent pas de silicoaluminate de chaux.Steels N ° 1 and N ° 2 constitute references and do not contain lime silicoaluminate.

Les inclusions associées sont très peu nombreuses, très petites et peu déformées.The associated inclusions are very few, very small and slightly deformed.

Les aciers N° 3 à 7 correspondant à une composition selon l'invention. Les valeurs de VB30/0,3, sont plus élevées d'environ 20%. La surface moyenne et le facteur de forme moyen des inclusions de sulfure des aciers N° 1 et N° 2 d'une part et des aciers N° 3 à N° 7 ne diffèrent pas significativement.Steels No. 3 to 7 corresponding to a composition according to the invention. The values of VB30 / 0.3 are higher by about 20%. The mean surface and the mean form factor of the sulphide inclusions of steels No. 1 and No. 2 on the one hand and of steels No. 3 to No. 7 do not differ significantly.

Par contre, les inclusions associées des aciers selon l'invention (N° 3 à 7) ont une surface beaucoup plus grande et sont beaucoup plus déformées donc beaucoup plus déformables.On the other hand, the associated inclusions of the steels according to the invention (Nos. 3 to 7) have a much larger surface and are much more deformed therefore much more deformable.

Ainsi, ces inclusions associées de silico-aluminates de chaux enrobant les inclusions de sulfure de manganèse et de chrome sont à l'origine de l'élévation importante de la valeur du critère d'usinabilité VB 30/0,3.Thus, these associated inclusions of lime silico-aluminates coating the inclusions of manganese sulfide and chromium are at the origin of the significant increase in the value of the machinability criterion VB 30 / 0.3.

De même, des essais de tournage avec outil en carbure revêtu TiN ont été réalisés. Ces outils sont de plus en plus utilisés par les usineurs. Pour une avance de 0,25 mm/tour, une passe de 1,5 mm et une vitesse de 340 m/mn, il a été mesuré l'usure en dépouille de l'outil en fonction du temps. Le tableau II ci-dessous donne quelques valeurs obtenues sur les aciers N° 1, 4, 5 et 6 du tableau précédent. TABLEAU II ACIER N° Ca (ppm) O (ppm) Ca/O Temps pour usure 0,15 mm (mn) Usure au bout de 30 mn de coupe (mm) 1 5 94 0,05 5 0,27 4 43 105 0,41 22 0,16 5 40 96 0,42 24 0,16 6 47 102 0,46 24 0,17 Similarly, turning tests with a TiN-coated carbide tool were carried out. These tools are increasingly used by machinists. For a feed of 0.25 mm / revolution, a pass of 1.5 mm and a speed of 340 m / min, the wear and tear of the tool was measured as a function of time. Table II below gives some values obtained on steels N ° 1, 4, 5 and 6 from the previous table. TABLE II STEEL N ° Ca (ppm) O (ppm) Ca / O Time for wear 0.15 mm (min) Wear after 30 min of cutting (mm) 1 5 94 0.05 5 0.27 4 43 105 0.41 22 0.16 5 40 96 0.42 24 0.16 6 47 102 0.46 24 0.17

Dans ces essais, les critères retenues pour comparer les aciers sont d'une part le temps conduisant à une usure en dépouille de 0,15 mm dans les conditions de coupe données ci-dessus et d'autre part la mesure de l'usure en dépouille après 30 mn de coupe.In these tests, the criteria used to compare the steels are on the one hand the time leading to an undercut wear of 0.15 mm under the cutting conditions given above and on the other hand the measurement of wear in skin after 30 minutes of cutting.

Ainsi, par rapport à l'acier de référence N° 1 ne correspondant pas à une composition selon l'invention, les essais réalisés sur les aciers N° 4, 5 et 6 montrent que le temps de coupe avant usure de 0,15 mm est multiplié d'un facteur 4 et que l'usure, mesurée sur l'outil après 30 mn de coupe, est réduite de 60% environ.Thus, compared with reference steel No. 1 not corresponding to a composition according to the invention, the tests carried out on steels No. 4, 5 and 6 show that the cutting time before wear of 0.15 mm is multiplied by a factor of 4 and the wear, measured on the tool after 30 minutes of cutting, is reduced by around 60%.

Cette amélioration est liée aux inclusions associées décrites, et introduites dans l'acier selon l'invention.This improvement is linked to the associated inclusions described, and introduced into the steel according to the invention.

La figure 3 présente un diagramme donnant les variations du critère d'usinabilité VB30/0,3 en fonction de la concentration en oxygène dans une série de mesures correspondant d'une part à l'élaboration des aciers selon l'invention et, d'autre part, à l'élaboration de l'acier sans calcium.FIG. 3 presents a diagram giving the variations of the machinability criterion VB30 / 0.3 as a function of the oxygen concentration in a series of measurements corresponding on the one hand to the production of the steels according to the invention and, on the other hand, the development of calcium-free steel.

La Figure 4 représente un diagramme donnant les variations du critère d'usinabilité VB30/0,3 en fonction de la concentration en soufre dans une série de mesures correspondant d'une part à l'élaboration selon l'invention et, d'autre part, à l'élaboration de l'acier sans calcium.FIG. 4 represents a diagram giving the variations of the machinability criterion VB30 / 0.3 as a function of the sulfur concentration in a series of measurements corresponding on the one hand to the preparation according to the invention and, on the other hand , to the development of calcium-free steel.

Les figures 3 et 4 montrent tout d'abord que l'évolution de nuances d'aciers inoxydables austénitiques resulfurés vers des teneurs en oxygène élevées ou des teneurs en soufre élevées ne permet pas d'améliorer l'usinabilité de façon significative (critère VB 30/0,3). Par contre, les aciers selon l'invention constituent une population à part, sur les diagrammes des figures 3 et 4, avec des critères d'usinabilité élevés.Figures 3 and 4 show first of all that the evolution of grades of resulfurized austenitic stainless steels towards high oxygen contents or high sulfur contents does not make it possible to improve machinability significantly (criterion VB 30 / 0.3). On the other hand, steels according to the invention constitutes a separate population, on the diagrams of FIGS. 3 and 4, with high machinability criteria.

A titre de comparaison, il a été réalisé les mêmes essais d'usinabilité en utilisant le critère d'usinabilité VB 30/0,3 sur des aciers austénitiques dont la composition de base est la suivante :
C : 0,06%, Si : 0,45%, Mn : 0,6%, Ni : 8,6%, Cr : 18%, Mo : 0.2%, S : 0.02%.By way of comparison, the same machinability tests were carried out using the machinability criterion VB 30 / 0.3 on austenitic steels whose basic composition is as follows:
C: 0.06%, Si: 0.45%, Mn: 0.6%, Ni: 8.6%, Cr: 18%, Mo: 0.2%, S: 0.02%.

Ces aciers ne contiennent pas ou très peu de soufre comparativement à l'acier selon l'invention.These steels contain little or no sulfur compared to the steel according to the invention.

Les essais ont porté sur la variation du calcium et de l'oxygène, en utilisant le même mode opératoire d'introduction du silicoaluminate de chaux que dans l'élaboration des aciers selon l'invention.The tests focused on the variation of calcium and oxygen, using the same procedure for introducing lime silicoaluminate as in the preparation of the steels according to the invention.

Le tableau III ci-dessous donne les valeurs de VB 30/0,3 de plusieurs aciers en fonction de la teneur en calcium et oxygène et de la valeur du rapport des concentrations en élément. TABLEAU III ACIER N° Ca (ppm) O (ppm) Ca|O VB 30|0,3 (m/mn) 8 2 57 0,04 168 9 6 123 0,05 160 10 32 79 0,4 200 11 43 118 0,36 200 12 26 47 0,55 155 13 17 117 0,15 172 14 32 129 0,25 180 Table III below gives the values of VB 30 / 0.3 of several steels as a function of the calcium and oxygen content and of the value of the ratio of element concentrations. TABLE III STEEL N ° Ca (ppm) O (ppm) Ca | O VB 30 | 0.3 (m / min) 8 2 57 0.04 168 9 6 123 0.05 160 10 32 79 0.4 200 11 43 118 0.36 200 12 26 47 0.55 155 13 17 117 0.15 172 14 32 129 0.25 180

Les aciers N° 8 et N° 9 ne comportent pas ou très peu de calcium et sont les aciers de références pour ces mesures. Les inclusions d'oxydes sont du type silicate polyphasé et chromite.Steels No. 8 and No. 9 contain little or no calcium and are the reference steels for these measurements. The oxide inclusions are of the polyphase silicate and chromite type.

L'évolution vers des teneurs en oxygène élevées seules n'entraîne pas d'amélioration de l'usinabilité (comparaison des valeurs de VB 30/0,3 entre les aciers N° 8 et 9).The evolution towards high oxygen contents alone does not lead to an improvement in the machinability (comparison of the values of VB 30 / 0.3 between steels N ° 8 and 9).

Les aciers n° 10 et N° 11 ayant :

  • une teneur en calcium supérieure à 30 ppm sur produit fini,
  • une teneur en oxygène supérieure à 70 ppm sur produit fini,
  • un rapport des teneurs en élément Ca/O compris entre 0,30 et 0,50 ont seulement des inclusions d'oxydes de type anorthite. On remarque, à l'usinage, une augmentation des valeurs du critère d'usinabilité VB 30/0,3 comme représentée en exemple sur la figure 5.
Steels No. 10 and No. 11 having:
  • a calcium content greater than 30 ppm on the finished product,
  • an oxygen content greater than 70 ppm on the finished product,
  • a Ca / O element content ratio of between 0.30 and 0.50 has only oxides of the anorthite type. Note, during machining, an increase in the values of the machinability criterion VB 30 / 0.3 as shown in example in FIG. 5.

L'acier N° 12 a des teneurs en calcium et oxygène faibles et un rapport Ca/O très élevé. L'usinabilité reste médiocre. Les inclusions analysées chimiquement sont de type gehlenite (Figure 1).Steel No. 12 has low calcium and oxygen contents and a very high Ca / O ratio. Machinability remains poor. The inclusions analyzed chemically are of the gehlenite type (Figure 1).

L'acier N° 13 a une teneur en oxygène correspondant à celle de la composition de l'acier selon l'invention sans soufre mais une teneur en calcium et un rapport Ca/O plus faible. L'usinabilité n'est pas améliorée significativement.Steel No. 13 has an oxygen content corresponding to that of the composition of the steel according to the invention without sulfur but a calcium content and a lower Ca / O ratio. The machinability is not significantly improved.

L'acier N° 14 a des teneurs correspondant à celles de la composition de l'acier selon l'invention sans soufre, mais un rapport Ca/O en dessous de 0,30. L'amélioration de l'usinabilité est sensible mais reste très en-dessous de celle des aciers N° 10 et N° 11.Steel No. 14 has contents corresponding to those of the composition of the steel according to the invention without sulfur, but a Ca / O ratio below 0.30. The improvement in machinability is appreciable but remains far below that of steels N ° 10 and N ° 11.

La comparaison des valeurs VB 30/0,3 des tableaux I et III montre l'importance de l'effet des inclusions d'anorthite seules et de l'effet des inclusions contenues dans l'acier resulfuré selon l'invention.The comparison of the VB 30 / 0.3 values in Tables I and III shows the importance of the effect of the anorthite inclusions alone and of the effect of the inclusions contained in the resulfurized steel according to the invention.

La présente invention a pour objet un acier inoxydable austénitique resulfuré dont l'usinabilité est améliorée grâce à la création d'inclusions associées oxydes de type silico-aluminate de chaux/sulfure (Mn, Cr)S.The present invention relates to a resulfurized austenitic stainless steel whose machinability is improved thanks to the creation of associated inclusions of oxides of lime silico-aluminate / sulfide (Mn, Cr) S type.

Les caractéristiques permettant d'obtenir une usinabilité améliorée sont :

  • une teneur en soufre compris entre 0,10 et 0,40% et de préférence entre 0,15 et 0,35%
  • une teneur en calcium supérieure ou égale à 30 ppm,
  • une teneur en oxygène supérieure ou égale à 70 ppm,
  • un rapport de la teneur en calcium et en oxygène Ca/O compris entre 0,2 et 0,6 et préférentiellement entre 0,3 et 0,5.
The characteristics enabling improved machinability are:
  • a sulfur content of between 0.10 and 0.40% and preferably between 0.15 and 0.35%
  • a calcium content greater than or equal to 30 ppm,
  • an oxygen content greater than or equal to 70 ppm,
  • a ratio of the calcium and oxygen Ca / O content of between 0.2 and 0.6 and preferably between 0.3 and 0.5.

Ces résultats entraînent la présence d'inclusions associées et déformées d'oxydes enrobant des inclusions de sulfure. Les oxydes sont des silico-aluminates de chaux, préférentiellement de type anorthite et pseudowollastonite dont les compositions chimiques sont déterminées dans le diagramme ternaire CaO-SiO2-Al203 de la figure 1. Ces inclusions associées ont une surface et un facteur de forme (longueur/largeur) importants. La déformabilité élevée des inclusions et leur effet lubrifiant à l'interface outil de coupe/copeau permettant une amélioration de l'usinabilité.These results lead to the presence of associated and deformed inclusions of oxides coating sulfide inclusions. The oxides are lime silico-aluminates, preferably of the anorthite and pseudowollastonite type, the chemical compositions of which are determined in the ternary diagram CaO-SiO2-Al203 in FIG. 1. These associated inclusions have a surface and a form factor (length / width) important. The high deformability of the inclusions and their lubricating effect at the cutting tool / chip interface allowing improved machinability.

Claims (7)

  1. Austenitic stainless steel resulphurated with enhanced machinability, characterised by the fact that its composition by weight is as follows:
    - carbon less than or equal to 0.15%
    - silicon less than or equal to 2%
    - manganese less than or equal to 2%
    - molybdenum less than or equal to 3%
    - nickel between 7 and 12%
    - chromium between 15 and 25%
    - sulphur between 0.10 and 0.40%
    - calcium more than 30 10⁻⁴%
    - oxygen more than 70 10⁻⁴%
    - the ratio between the calcium content and the oxygen content Ca/O falls between 0.2 and 0.6, the remainder being iron, and as applicable
    containing inclusions of silico-aluminate of lime of the anorthite and/or pseudo-wollastonite type.
  2. Stainless steel as per claim 1, characterised by the fact that it contains sulphur in a proportion ranging from 0.15 to 0.35%.
  3. Stainless steel as per claims 1 and 2, characterised by the fact that it contains inclusions of manganese and chromium sulphide (Mn, Cr)S.
  4. Stainless steel as per claim 1, characterised by the fact that the value of the ratio of its content of the elements calcium and oxygen falls between 0.3 and 0.5.
  5. Stainless steel as per claims 1 to 4, characterised by the fact that the inclusions of manganese and chromium sulphide are coated with a phase of silico-aluminate of lime, of the anorthrite and/or pseudo-wollastonite type, to form associated inclusions.
  6. Stainless steel as per claim 5, characterised by the fact that the associated inclusions are generated by the addition of calcium introduced into the bath whilst fusion is taking place, in the form of wire lined with silico-calcium.
  7. Stainless steel as per claim 5, characterised by the fact that the inclusions have a mould factor which falls between 3 and 6.
EP90401511A 1989-06-16 1990-06-05 Resulfurized austenitic stainless steel with improved machinability Expired - Lifetime EP0403332B1 (en)

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JPS5690959A (en) * 1979-12-24 1981-07-23 Sanyo Tokushu Seikou Kk Austenitic s free-cutting stainless steel

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
T0624/91 *

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FI902985A0 (en) 1990-06-14
FI98533B (en) 1997-03-27
NO902659L (en) 1990-12-17
CA2019105C (en) 2000-04-25
ATE127163T1 (en) 1995-09-15
US5089224A (en) 1992-02-18
FR2648477B1 (en) 1993-04-30
EG19821A (en) 1996-02-29
GR3018176T3 (en) 1996-02-29
FR2648477A1 (en) 1990-12-21
DD298434A5 (en) 1992-02-20
NO902659D0 (en) 1990-06-14
DE69021941T2 (en) 1996-03-07
IL94622A (en) 1995-07-31
DE69021941D1 (en) 1995-10-05
DK0403332T3 (en) 1995-11-20
IL94622A0 (en) 1991-04-15
ES2076346T3 (en) 1995-11-01
FI98533C (en) 1997-07-10
NO177392B (en) 1995-05-29
NO177392C (en) 1995-09-06
CA2019105A1 (en) 1990-12-16
TR26587A (en) 1995-03-15
EP0403332A1 (en) 1990-12-19

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