EP0170546A1 - High-strength nitriding steel with good machinability, useful as construction steel, and process for its manufacture - Google Patents

High-strength nitriding steel with good machinability, useful as construction steel, and process for its manufacture Download PDF

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Publication number
EP0170546A1
EP0170546A1 EP85401162A EP85401162A EP0170546A1 EP 0170546 A1 EP0170546 A1 EP 0170546A1 EP 85401162 A EP85401162 A EP 85401162A EP 85401162 A EP85401162 A EP 85401162A EP 0170546 A1 EP0170546 A1 EP 0170546A1
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Prior art keywords
steel
nitriding
content
weight
chemical composition
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EP85401162A
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German (de)
French (fr)
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EP0170546B1 (en
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Mario Confente
Jean Bellot
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Ascometal SA
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Societe des Acieries de Pompey
Ascometal 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

Definitions

  • the present invention relates to a high strength structural steel having good machinability and a great ability to surface hardening by nitriding, the use of this steel before or after nitriding as a structural steel, as well as a method for manufacturing this steel. .
  • the sulfur content although expected to be 0.02 to 0.10% by weight, is in practice close to 0.080%.
  • This prior steel from the applicant has excellent machinability and average mechanical properties.
  • this steel does not have a capacity for hardening by nitriding, in particular by ion bombardment, while this technique makes it possible to superficially treat completely finished mechanical parts without any resumption of machining.
  • a fine-grained steel, and its preparation process also having improved machining, containing at most 0.70% carbon and preferably 0.13 to 0.70% carbon, maximum 0.45% silicon, 0.015 to 0.1% and preferably 0.03 to 0.06% aluminum.
  • the calcium content preferably varies between 2 and 30 ppm. In the examples given, the carbon content is greater than 0.2
  • these steels in particular by a very low aluminum content as in the preceding steels of the Applicant, do not have a capacity for hardening by nitriding, which limits their use or application as structural steel.
  • the carbon content is in practice at least 0.40 (see talbeau 1, page 3). Also, the silicon content is in practice close to 0.2 to 0.3%. This steel contains neither chromium nor even nickel.
  • the sulfur content is between 0.04 and 0.4. It is therefore highly resulfurized steel.
  • this steel often does not contain aluminum or in very small quantities while the Applicant has discovered that this element is essential to obtain the desired effect of high suitability for nitriding.
  • most of the steels according to this document have a high carbon content greater than 0.20%.
  • AFNOR 40 CAD 6-12 is known for steels with improved machinability containing from 0.36 to 0.40% of carbon, from 0.5 to 0.8% of manganese, from 0.10 to 0.40% silicon, 0.8-1.30% aluminum, uncontrolled sulfur content of up to 0.035%, 1.5-1.8% chromium and 0.20 0.40% molybdenum.
  • This steel which also has a very low aluminum content, is hardly suitable for a nitriding treatment.
  • the steels known in the art do not allow, in the field of mechanical construction, to simultaneously obtain a simplification of the production ranges and the obtaining of high mechanical characteristics on core parts and especially on the surface. However, this implies the use of special steels having a set of very specific properties that no steel known to date exhibits.
  • the present invention solves this new technical problem for the first time.
  • a new family of steels which simultaneously has the properties previously stated thanks to a low carbon content (less than 0.30%, preferably less than 0.20% and more preferably less than 0 , 15%), with simultaneously a relatively high aluminum content (0.20 to 2%, preferably at least 0.5% to 1.5%) with the simultaneous presence of chromium (at least 0.5% ) and manganese (at least 0.5
  • Aluminum, chromium and manganese are the three basic elements for the desired effect of high suitability for nitriding.
  • the present invention provides mechanical steels with low sulfur content or slightly resulfurized, ie 0.01 to 0.1% and preferably from 0.020 to 0.040%.
  • the surface percentage of the clusters of alumina in the cross section of the matrix of the steel according to the invention is generally less than 0.1%.
  • a new steel containing carbon, manganese, silicon, chromium, aluminum, sulfur, phosphorus and optionally nickel, characterized in that it has the following chemical composition (in percentages by weight): preferably preferably ; iron balance and usual unavoidable residual impurities.
  • this new steel can also advantageously contain elements improving the mechanical properties such as Vanadium, Niobium, Titanium, each up to approximately 1%, or preferably in total up to approximately 1%.
  • this new steel has a preferred sulfur content of between 0.020 and 0.040.
  • the preferred carbon content is from 0.05 to 0.20, more preferably is between 0.11 and 0.15.
  • Carbon has a significant effect on the mechanical properties of steel. Above 0.30, the requirements for ductility, toughness and above all weldability are not sufficiently satisfactory.
  • a minimum of 0.05 is required to have a visible effect of carbon.
  • a content of less than 0.20% of carbon is preferred in order to obtain good mechanical properties with excellent ductility, toughness and weldability.
  • the preferred content of 0.11 to 0.15 constitutes a range of values where the best properties are obtained.
  • the manganese content is 0.5 to 2%, preferably 0.7 to 1.8 %.
  • Manganese is present to improve the mechanical properties of steel, in particular thanks to its hardening effect. On the other hand, it is an element favorable to hardening by nitriding. A minimum content of 0.5% of manganese is required to obtain the minimum effect, while above 2%, manganese reduces hot ductility and therefore hot work and causes corrosion of oven refractories. . A maximum content of 1.8% is therefore preferred.
  • An even more preferred manganese content is 0.7 to 0.9%.
  • a preferred content of silicon is from 0.20 to 0.80 and more preferably from 0.5 to 0.80.
  • Silicon is one of the essential elements to improve the mechanical resistance of steel by its hardening effect in solid solution.
  • the phosphorus content is limited to 0.10 and preferably is less than or equal to 0.030 because it is an impurity whose content must be limited to avoid the usual harmful effects well known in the literature.
  • the sulfur content according to the invention is strictly controlled at a low value.
  • Sulfur is one of the essential elements improving the machinability of steel.
  • the minimum sulfur content is 0.010 and the maximum content 0.10%.
  • the maximum sulfur content is less than 0.050 and more preferably between 0.020% and 0.040% so as to obtain the best machinability without harming the other properties.
  • Chromium is an element which brings about an improvement in the mechanical characteristics of steel.
  • chromium has a strong affinity for nitrogen and therefore constitutes a basic element for nitriding.
  • chromium not only limits the total depth of nitriding, but it also forms alphagenic phases which can give rise to difficulties in rolling. 3.90 to 4.30% chromium is preferred.
  • nickel is possible and is preferred to improve the hardenability of the steel, a property which is of great importance in the case of large products.
  • nickel increases the brittle breaking strength (resilience).
  • the nickel content is limited to 2% because beyond that, the nickel modifies the structure of the steel. In addition, nickel is an expensive element.
  • a minimum content of 0.10% is preferred to obtain the desired effect.
  • a more preferred nickel content is at least 0.5% and is more preferably between 0.6 and 0.90%.
  • Aluminum is a basic element for obtaining an excellent suitability of steel for nitriding.
  • a minimum aluminum content for this purpose is 0.20%. Above 2%, aluminum causes significant grain enlargement, the appearance of alphagenic phases, leading to problems of rolling and brittleness of the metal.
  • a preferred aluminum content is at least 0.5% and at most 1.5%. Again, preferably, the aluminum content is between 0.7 and 1 % .
  • Molybdenum is optionally present in the steel according to the invention. Molybdenum is preferably present because it has a significant effect on hardenability and on hardening and resistance to softening of the matrix. A minimum content of 0.10% is required to achieve this effect while its content is limited to 0.50%, since it is an expensive element and that beyond this content, it crystallographic changes occur which influence machinability.
  • Calcium and tellurium are preferred elements carefully controlled to obtain excellent machinability steel. They may therefore be possible.
  • the preferred calcium content is 0.01 to 0.003% (i.e. 10 to 30 ppm).
  • a minimum content of 0.003% tellurium is preferred to improve the machinability of the steel. Beyond 0.010% tellurium, the shape of the sulphide inclusions is modified unfavorably with respect to the properties of steel as already described in the prior application of the aforementioned applicant FR-A-2,395,323.
  • Vanadium is a possible element which is preferably added because it has a carburogenic effect causing a hardening of the matrix. In addition, vanadium limits the softening during the tempering caused by the nitriding treatment. Vanadium also has a favorable effect on hardening by nitriding at the bottom of nitrogen diffusion layers.
  • the vanadium content is limited to 1%, preferably 0.5% and more preferably is between 0.10 and 0.20% in order to obtain these effects without interfering with the crystallographic structure of the steel and therefore with properties, especially on machinability.
  • Leniobium is also a possible element having the same carburogenic effect as vanadium causing a hardening of the matrix while also limiting softening during the income caused by the nitriding treatment. Niobium also has an effect favoring hardening by nitriding at the bottom of nitrogen diffusion layers.
  • niobium has a grain refining effect, in particular of ferrite.
  • the niobium can be present up to 1%, but is preferably limited when it is present to less than 0.5%, being more preferably between 0.1 and 0.2%.
  • Titanium is also a possible element having a carburogenic effect causing a hardening of the matrix such as vanadium or niobium. Titanium also has a grain refining effect like niobium.
  • the titanium content can also reach 1% but a maximum preferred content is 0.5% and more preferably the titanium is limited to 0.1-0.2% when it is present.
  • the total content should not exceed 1% and preferably is limited to 0.5%.
  • vanadium niobium and titanium, it is preferred to use vanadium.
  • the steel according to the invention has the following preferred composition (in percentages by weight): preferably Balance F er and usual unavoidable residual impurities.
  • the mechanical resistance Rm is of the order of 900-1400 MNewton / m 2 depending on the size of the products (round or laminated, forged products) and the cooling conditions after rolling / forging or standardization.
  • the machining performance at low or medium cutting speed (high-speed steel tools) and high speed (carbide tools) is greatly improved in combination by rigorous control of the inclusion of sulphides (globularization by addition of tellurium) and oxide (transformation of alumina strings Al 2 0 3 into polyphase inclusions, alumina substituted in lime xAl 2 O 3 , yCaO + substituted sulphide of the type (Mn, Ca) S .
  • a tellurium / sulfur ratio of between 0.07 and 0.13 is preferred as indicated in the prior application of the applicant FR-A-2,395,323, preferably between 0.09 and 0.11 and also of preferably about 0.10.
  • the steels according to the present invention have a surface hardness and kinetics of nitriding, in particular by ion bombardment, much higher, unexpectedly, than conventional steels for nitriding. treated by quenching and tempering, and in particular those according to standard AFNOR 40 CAD 6-12, as will be demonstrated in the following example.
  • the invention also relates to a process for the preparation of steel according to the invention, characterized in that it comprises the addition in a known manner during the metallurgical process, and the control of the content of the various constituents so as to obtain a steel having the chemical composition previously indicated.
  • this method according to the invention preferably comprises an additional step of stabilization by treatment of the steel, directly on the raw rolling or forging state, or after normalization, at a temperature of between approximately 500 and 620 °. vs.
  • the purpose of this stabilization treatment is to avoid, during the subsequent nitriding treatment, any deformation of the parts by relaxation of the internal stresses.
  • the mechanical resistance Rm is between 800 and 1300 M.Newton / m 2 .
  • the method according to the invention also preferably comprises a usual nitriding step.
  • this nitriding step consists of a nitriding treatment by ion bombardment carried out at a temperature of at least 450 ° C. for one or more days depending on the desired surface hardness, the desired depth of nitriding at the surface or at the core.
  • the invention also relates to a use of this steel as a structural steel.
  • the invention makes it possible to simplify the processing and manufacturing cycle for the user by avoiding the annealing treatment for machining and a quenching and tempering treatment after machining as well as a rectification treatment on the treated state, as shown in Table I below:
  • Ingots of 5 tonnes are processed in an 80-ton electric furnace to be processed by rolling into rounds of diameter 90 to 220 mm, in a conventional manner, to result in a steel according to the invention having the following chemical composition:
  • FIG. 1 represents the Wickers hardness curves obtained under a load of 0.05 kg after a nitriding treatment by conventional sequences of 70 hours. Wickers hardness is shown on the ordinate, while the abscissa indicates the layer depth where the hardness is measured.
  • FIG. 2 represents the hardness curve of the alloy according to the invention with the alloy for nitriding 40CAD 6-12, as a function of the load on the abscissa.
  • FIG. 3 shows by way of indication the evolution of the Wickers hardness over time during the nitriding treatment at 530 ° C.
  • the Wickers hardness is indicated on the ordinate, while the abscissa indicates the depth of the layer where the hardness is measured as in FIG. 1.

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Abstract

1. A steel containing carbon, silicon, manganese, chromium, aluminium, sulphur and phosphorus, characterized in that it has the following chemical composition in percentage by weight : C/0.05-0.30 Mn/0.50-2.00 Si/0.10-0.80 P/=< 0.100 S/0.01-0.10 Cr/0.50-6.00 Ni/0.10-2.00 Mo/0.10-0.50 Al/0.20-2.00 Ca/0.001-0.010 Te/0.003-0.020 and possibly at least one of the elements selected from the group comprising vanadium, niobium and titanium to about a total of 1% by weight, the residue being iron with the usual inevitable residual impurities.

Description

La présente invention concerne un acier de construction à haute résistance présentant une bonne usinabilité et une grande aptitude au durcissement superficiel par nitruration, l'utilisation de cet acier avant ou après nitruration comme acier de construction, ainsi qu'un procédé de fabrication de cet acier.The present invention relates to a high strength structural steel having good machinability and a great ability to surface hardening by nitriding, the use of this steel before or after nitriding as a structural steel, as well as a method for manufacturing this steel. .

On connait déjà par la demande de brevet français antérieure de la demanderesse FR-A-2 395 323, un acier de construction à grain fin, à usinabilité améliorée présentant une très faible proportion d'aluminium (de 0,01 à 0,05 % en poids) et une teneur en carbone de 0 ,05 à 1,20 % en étant habituellement voisine de 0,40 % dans les exemples.We already know from the prior French patent application of the applicant FR-A-2 395 323, a fine-grained structural steel, with improved machinability having a very low proportion of aluminum (from 0.01 to 0.05% by weight) and a carbon content of 0.05 to 1.20%, being usually close to 0.40% in the examples.

De même, la teneur en soufre, bien que prévue de 0,02 à 0,10% en poids est voisine, en pratique, de 0,080 %.Likewise, the sulfur content, although expected to be 0.02 to 0.10% by weight, is in practice close to 0.080%.

Cet acier antérieur de la demanderesse présente une excellente usinabilité et des propriétés mécaniques moyennes.This prior steel from the applicant has excellent machinability and average mechanical properties.

D'autre part, cet acier ne présente pas d'aptitude au durcissement par nitruration, notamment par bombardement ionique, alors que cette technique permet de traiter superficiellement des pièces mécaniques entièrement terminées sans aucune reprise d'usinage. On connait, d'autre part, par la demande de brevet français FR-A-2 212 432 un acier à grain fin, et son procédé de préparation, présentant également un usinage amélioré, contenant au maximum 0,70% de carbone et de préférence 0,13 à 0,70% de carbone, au maximum 0,45% de silicium, 0,015 à 0,1 % et de préférence 0,03 à 0,06 % d'aluminium.On the other hand, this steel does not have a capacity for hardening by nitriding, in particular by ion bombardment, while this technique makes it possible to superficially treat completely finished mechanical parts without any resumption of machining. On the other hand, we know from French patent application FR-A-2 212 432 a fine-grained steel, and its preparation process, also having improved machining, containing at most 0.70% carbon and preferably 0.13 to 0.70% carbon, maximum 0.45% silicon, 0.015 to 0.1% and preferably 0.03 to 0.06% aluminum.

La teneur en calcium varie de préférence entre 2 et 30ppm. Dans les exemples indiqués, la teneur en carbone est supérieure à 0,2The calcium content preferably varies between 2 and 30 ppm. In the examples given, the carbon content is greater than 0.2

De même, ces aciers, notamment par une très faible teneur en aluminium comme dans les aciers précédents de la Demanderesse, ne présentent pas d'aptitude au durcissement par nitruration, ce qui en limite l'utilisation ou application comme acier de construction.Likewise, these steels, in particular by a very low aluminum content as in the preceding steels of the Applicant, do not have a capacity for hardening by nitriding, which limits their use or application as structural steel.

On connait aussi par la demande de brevet français FR-A-2 088 862 un acier de décolletage amélioré provoquant une abrasion minime des outils et de bonnes propriétés mécaniques contenant de 0,08 à 0,60 % de carbone, de 0,15 à 0,60 % de silicium, de 0,030 à 0,15% de soufre,de 20 à 200 ppm de calcium et 0,005 à 0,05 % d'aluminium soluble.We also know from French patent application FR-A-2 088 862 an improved free cutting steel causing minimal abrasion of tools and good mechanical properties containing from 0.08 to 0.60% carbon, from 0.15 to 0.60% silicon, 0.030-0.15% sulfur, 20-200 ppm calcium and 0.005-0.05% soluble aluminum.

D'autre part, et comme pour les autres aciers précédents la teneur en carbone est en pratique au moins de 0,40 (voir talbeau 1, page 3). Egalement, la teneur en silicium est en pratique voisine de 0,2 à 0,3 % . Cet acier ne contient ni chrome ni même du nickel.On the other hand, and as for the other preceding steels, the carbon content is in practice at least 0.40 (see talbeau 1, page 3). Also, the silicon content is in practice close to 0.2 to 0.3%. This steel contains neither chromium nor even nickel.

On connait encore par la demande de brevet français FR-A-2 445 388 un acier de décolletage contenant des particules incluses de sulfure ayant un allongement, une taille, et une distribution déterminés.Also known from French patent application FR-A-2 445 388 is a free-cutting steel containing included sulphide particles having a determined elongation, size and distribution.

La teneur en soufre est comprise entre 0,04 et 0,4 Il s'agit donc d'acier fortement resulfuré.The sulfur content is between 0.04 and 0.4. It is therefore highly resulfurized steel.

La demanderesse a pu observer que des teneurs en soufre supérieures à 0,1 % doivent être proscrites car elles conduisent à une fragilité excessive des couches superficielles élaborées à la surface d'un acier lorsqu'il est soumis au traitement de nitruration.The Applicant has observed that sulfur contents greater than 0.1% must be prohibited since they lead to excessive brittleness of the surface layers produced on the surface of a steel when it is subjected to the nitriding treatment.

Ainsi, les aciers décrits dans ce document comme dans le document précédent, ne présenteront pas d'aptitude au durcissement par nitruration.Thus, the steels described in this document as in the previous document, will not have no suitability for hardening by nitriding.

D'autre part, cet acier ne contient souvent pas d'aluminium ou en quantité très faible alors que la demanderesse a découvert que cet élément est essentiel pour obtenir l'effet recherché de haute aptitude à la nitruration. De même, la plupart des aciers selon ce document ont une teneur élevée en carbone supérieure à 0,20 %.On the other hand, this steel often does not contain aluminum or in very small quantities while the Applicant has discovered that this element is essential to obtain the desired effect of high suitability for nitriding. Likewise, most of the steels according to this document have a high carbon content greater than 0.20%.

Par ailleurs, il est connu par la norme AFNOR 40 CAD 6-12 des aciers à usinabilité améliorée contenant de 0,36 à 0,40 % de carbone, de 0,5 à 0,8 % de manganèse, de 0,10 à 0,40 % de silicium,de 0,8 à 1,30 % d'aluminium, une teneur en soufre non contrôlée pouvant aller jusqu'à 0,035 %, de 1,5 à 1,8 % de chrome et de 0,20 à 0,40 % de molybdène.Furthermore, AFNOR 40 CAD 6-12 is known for steels with improved machinability containing from 0.36 to 0.40% of carbon, from 0.5 to 0.8% of manganese, from 0.10 to 0.40% silicon, 0.8-1.30% aluminum, uncontrolled sulfur content of up to 0.035%, 1.5-1.8% chromium and 0.20 0.40% molybdenum.

Ces aciers, selon cette norme AFNOR, présentent une aptitude à la nitruration, mais sont déficients en ce qui concerne leurs propriétés d'usinabilité et de soudabilité.These steels, according to this AFNOR standard, have a capacity for nitriding, but are deficient with regard to their machinability and weldability properties.

On connait également, par le brevet japonais SUMITOMO 3P-B-12.133/1977, un acier à usinabilité améliorée ayant une teneur en aluminium très faible (0,002 à 0,015 % d'aluminium soluble), une teneur en silicium de 0,05 à 0,40 %, la teneur en carbone étant préférée de 0,45 à 0,8 %. On peut ajouter dans cer acier du chrome, du nickel ou du molybdène à teneur respective de 0,5 à 3,5 % ; 1,0 à 3,5 % et 0,5 à 2 %.We also know, from the Japanese patent SUMITOMO 3P-B-12.133 / 1977, a steel with improved machinability having a very low aluminum content (0.002 to 0.015% of soluble aluminum), a silicon content of 0.05 to 0 , 40%, the carbon content being preferred from 0.45 to 0.8%. Chromium, nickel or molybdenum with a respective content of 0.5 to 3.5% can be added to this steel; 1.0 to 3.5% and 0.5 to 2%.

Cet acier, présentant également une très faible teneur en aluminium, se prête difficilement à un traitement de nitruration.This steel, which also has a very low aluminum content, is hardly suitable for a nitriding treatment.

On connait encore d'autres aciers ayant une résistance mécanique élevée, anayant pas d'aptitude particulière en ce qui concerne l'usinabilité, ni en ce qui concerne la nitruration par les documents suivants :

  • FR-A-2 488 285 ; FR-A-2 529 231 , FR-A-2 516 942 ; FR-A- 2 525 709, FR-A-2 526 122 ; et FR-2 531 998.
Other steels having a high mechanical strength are known, having no particular aptitude as regards machinability, nor as regards nitriding by the following documents:
  • FR-A-2 488 285; FR-A-2,529,231, FR-A-2,516,942; FR-A- 2,525,709, FR-A-2,526,122; and FR-2,531,998.

Les aciers connus de la technique ne permettent pas, dans le domaine de la construction mécanique, d'obtenir simultanément une simplification des gammes de fabrication et l'obtention de caractéristiques mécaniques élevées sur pièces à coeur et surtout en surface. Or, ceci implique l'utilisation d'aciers spéciaux présentant un ensemble de propriétés très spécifiques qu'aucun acier connu à ce jour ne présente.The steels known in the art do not allow, in the field of mechanical construction, to simultaneously obtain a simplification of the production ranges and the obtaining of high mechanical characteristics on core parts and especially on the surface. However, this implies the use of special steels having a set of very specific properties that no steel known to date exhibits.

La présente invention a donc pour but de résoudre le nouveau problème technique consistant à créer une nouvelle famille d'aciers qui présenterait à la fois :

  • a) une résistance à l'état traité par normalisation et revenu comparable à celle atteinte sur acier au carbone et allié après trempe et revenu ;
  • b) une bonne usinabilité, permettant une mise en oeuvre suffisamment aisée par usinage dans cet état ;
  • c) une bonne soudabilité, permettant l'assemblage par soudage
  • d) une grande aptitude au durcissement par nitruration notamment par bombardement ionique, technique permettant de traiter superficiellement sous vide partiel et à des températures relativement basses, de l'ordre d'au moins 450°C des pièces mécaniques entièrement terminées sans aucune reprise d'usinage.
The present invention therefore aims to solve the new technical problem of creating a new family of steels which would present both:
  • a) a resistance in the treated state by normalization and tempering comparable to that reached on carbon and alloy steel after quenching and tempering;
  • b) good machinability, allowing a sufficiently easy implementation by machining in this state;
  • c) good weldability, allowing assembly by welding
  • d) a high aptitude for hardening by nitriding, in particular by ion bombardment, a technique making it possible to surface treatment under partial vacuum and at relatively low temperatures, of the order of at least 450 ° C. of the fully finished mechanical parts without any recovery of machining.

La présente invention permet de résoudre ce nouveau problème technique pour la première fois.The present invention solves this new technical problem for the first time.

Selon l'invention, on fournit ainsi une nouvelle famille d'aciers présentant simultanément les propriétés précédemment énoncées grâce à une faible teneur en carbone (inférieure à 0,30 %, de préférence inférieure à 0,20 % et encore de préférence inférieure à 0,15 %), avec simultanément une teneur relativement élevée en aluminium (0,20 à 2 %, de préférence au moins 0,5 % à 1,5 % ) avec la présence simultanée de chrome (d'au moins 0,5 %) et de manganèse (d'au moins 0,5According to the invention, a new family of steels is thus provided which simultaneously has the properties previously stated thanks to a low carbon content (less than 0.30%, preferably less than 0.20% and more preferably less than 0 , 15%), with simultaneously a relatively high aluminum content (0.20 to 2%, preferably at least 0.5% to 1.5%) with the simultaneous presence of chromium (at least 0.5% ) and manganese (at least 0.5

L'aluminium, le chrome et le manganèse sont les trois éléments de base pour l'effet recherché de haute aptitude à la nitruration.Aluminum, chromium and manganese are the three basic elements for the desired effect of high suitability for nitriding.

D'autre part, la présente invention fournit des aciers de construction mécanique à basse teneur ensoufre ou faiblement resulfurés,soit 0,01 à 0,1 % et de préférence de 0,020 à 0,040 %.On the other hand, the present invention provides mechanical steels with low sulfur content or slightly resulfurized, ie 0.01 to 0.1% and preferably from 0.020 to 0.040%.

On observera que le pourcentage surfacique des amas d'alumine dans la section transversale de la matrice de l'acier selon l'invention est généralement inférieur à 0,1 %.It will be observed that the surface percentage of the clusters of alumina in the cross section of the matrix of the steel according to the invention is generally less than 0.1%.

Ainsi, selon un premier aspect de la présente invention, on fournit un nouvel acier contenant du carbone, du manganèse, du silicium, du chrome, de l'aluminium, du soufre, du phosphore et éventuellement du nickel, caractérisé en ce qu'il a la composition chimique suivante (en pourcentages en poids) :

Figure imgb0001
Figure imgb0002
de préférence
Figure imgb0003
de préférence
Figure imgb0004
; solde fer et impuretés résiduelles inévitables habituelles.Thus, according to a first aspect of the present invention, a new steel is provided containing carbon, manganese, silicon, chromium, aluminum, sulfur, phosphorus and optionally nickel, characterized in that it has the following chemical composition (in percentages by weight):
Figure imgb0001
Figure imgb0002
preferably
Figure imgb0003
 preferably
Figure imgb0004
 ; iron balance and usual unavoidable residual impurities.

Selon l'invention, ce nouvel acier peut également contenir avantageusement des éléments améliorant les propriétés mécaniques comme le Vanadium, le Niobium, le Titane, chacun jusqu'à environ 1 %, ou de préférence au total jusqu'à environ 1 %.According to the invention, this new steel can also advantageously contain elements improving the mechanical properties such as Vanadium, Niobium, Titanium, each up to approximately 1%, or preferably in total up to approximately 1%.

Selon une autre caractéristique de l'invention, ce nouvel acier présente une teneur préférée en soufre comprise entre 0,020 et 0,040.According to another characteristic of the invention, this new steel has a preferred sulfur content of between 0.020 and 0.040.

D'autre part, la teneur préférée en carbone est de 0,05 à 0,20, encore de préférence est comprise entre 0,11 et 0,15.On the other hand, the preferred carbon content is from 0.05 to 0.20, more preferably is between 0.11 and 0.15.

Le carbone a un effet important sur les propriétés mécaniques de l'acier. Au-delà de 0,30, les exigences de ductilité, ténacité et surtout soudabilité ne sont pas suffisamment satisfaisantes.Carbon has a significant effect on the mechanical properties of steel. Above 0.30, the requirements for ductility, toughness and above all weldability are not sufficiently satisfactory.

Un minimum de 0,05 est exigé pour avoir un effet visible du carbone. On préfère une teneur inférieure à 0,20 % de carbone pour obtenir de bonnes propriétés mécaniques avec une ductilité, une ténacité et une soudabilité excellentes. La teneur préférée de 0,11 à 0,15 constitue une plage de valeurs où les meilleures propriétés sont obtenues.A minimum of 0.05 is required to have a visible effect of carbon. A content of less than 0.20% of carbon is preferred in order to obtain good mechanical properties with excellent ductility, toughness and weldability. The preferred content of 0.11 to 0.15 constitutes a range of values where the best properties are obtained.

La teneur en manganèse est de 0,5 à 2 %, de préférence de 0,7 à 1,8 %. Le manganèse est présent pour améliorer les propriétés mécaniques de l'acier, en particulier grâce à son effet durcissant. D'autre part, il s'agit d'un élément favorable au durcissement par nitruration. Il faut une teneur minimum de 0,5 % de manganèse pour obtenir l'effet minimum, tandis qu'au-delà de 2 %, le manganèse diminue la ductilité à chaud et donc le travail à chaud et provoque la corrosion des réfractaires du four. On préfère donc une teneur maximum de 1,8 %.The manganese content is 0.5 to 2%, preferably 0.7 to 1.8 %. Manganese is present to improve the mechanical properties of steel, in particular thanks to its hardening effect. On the other hand, it is an element favorable to hardening by nitriding. A minimum content of 0.5% of manganese is required to obtain the minimum effect, while above 2%, manganese reduces hot ductility and therefore hot work and causes corrosion of oven refractories. . A maximum content of 1.8% is therefore preferred.

Une teneur encore préférée de manganèse est de 0,7 à 0,9 %.An even more preferred manganese content is 0.7 to 0.9%.

Une teneur préférée de silicium est de 0,20 à 0,80 et encore de préférence de 0 ,5 à 0,80.A preferred content of silicon is from 0.20 to 0.80 and more preferably from 0.5 to 0.80.

Le silicium est l'un des éléments esentiels pour améliorer la résistance mécanique de l'acier par son effet durcissant en solution solide.Silicon is one of the essential elements to improve the mechanical resistance of steel by its hardening effect in solid solution.

D'autre part, il s'agit d'un élément augmentant l'aptitude à la nitruration de l'acier.On the other hand, it is an element increasing the ability to nitride the steel.

Ces objectifs sont de préférence atteints lorsque le silicium est présent dans les teneurs préférées mentionnées ci-dessus.These objectives are preferably achieved when the silicon is present in the preferred contents mentioned above.

La teneur en phosphore est limitée à 0,10 et de préférence est inférieure ou égale à 0,030 car il s'agit d'une impureté dont la teneur doit être limitée pour éviter les effets néfastes habituels bien connus dans la littérature.The phosphorus content is limited to 0.10 and preferably is less than or equal to 0.030 because it is an impurity whose content must be limited to avoid the usual harmful effects well known in the literature.

La teneur en soufre est selon l'invention strictement contrôlée à une valeur faible. Le soufre constitue un des éléments essentiels améliorant l'usinabilité de l'acier.The sulfur content according to the invention is strictly controlled at a low value. Sulfur is one of the essential elements improving the machinability of steel.

Pour cet effet, la teneur minimum en soufre est de 0,010 et la teneur maximale de 0,10 %.For this purpose, the minimum sulfur content is 0.010 and the maximum content 0.10%.

De préférence, la teneur maximale en soufre est infé- ri-erre à 0,050 et encore de préférence comprise entre 0,020 % et 0,040 % de manière à obtenir la meilleure usinabilité sans nuire aux autres propriétés.Preferably, the maximum sulfur content is less than 0.050 and more preferably between 0.020% and 0.040% so as to obtain the best machinability without harming the other properties.

Il est à noter que lorsque la teneur en soufre est trop élevée, en particulier lorsque cette teneur est supérieure à 0,10, l'état des inclusions de sulfures est moins bon, ce qui diminue les propriétés mécaniques de l'acier.It should be noted that when the sulfur content is too high, in particular when this content is greater than 0.10, the state of the sulfide inclusions is less good, which decreases the mechanical properties of the steel.

Le chrome est un élément qui apporte une amélioration des caractéristiques mécaniques de l'acier. En outre, le chrome présente une forte affinité pour l'azote et constitue donc un élément de base pour la nitruration.Chromium is an element which brings about an improvement in the mechanical characteristics of steel. In addition, chromium has a strong affinity for nitrogen and therefore constitutes a basic element for nitriding.

A cet effet, une teneur minimale de 0,5 % est exigée pour obtenir lors de la nitruration un durcissement suffisant de la zone de diffusion.To this end, a minimum content of 0.5% is required to obtain sufficient hardening of the diffusion zone during nitriding.

D'autre part, une teneur d'environ 4 % est souhaitée pour obtenir une grande profondeur de nitruration.On the other hand, a content of about 4% is desired to obtain a great depth of nitriding.

Au delà de 6 % le chrome limite non seulement la profondeur totale de nitruration mais il forme de plus des phases alphagènes pouvant donner naissance à des difficultés de laminage. On préfère 3,90 à 4,30 % de chrome.Above 6% chromium not only limits the total depth of nitriding, but it also forms alphagenic phases which can give rise to difficulties in rolling. 3.90 to 4.30% chromium is preferred.

La présence du nickel est éventuelle et est préférée pour améliorer la trempabilité de l'acier, propriété qui est d'une grande importance dans le cas de produits de grande dimension. En outre, le nickel augmente la résistance à la rupture fragile (résilience).The presence of nickel is possible and is preferred to improve the hardenability of the steel, a property which is of great importance in the case of large products. In addition, nickel increases the brittle breaking strength (resilience).

La teneur en nickel est limitée à 2 % car au delà, le nickel modifie la structure de l'acier. En outre, le nickel est un élément coûteux.The nickel content is limited to 2% because beyond that, the nickel modifies the structure of the steel. In addition, nickel is an expensive element.

On préfère une teneur minimale de 0,10 % pour obtenir l'effet reherché. Une teneur davantage préférée en nickel est d'au moins 0,5 % et est encore de préférence comprise entre 0,6 et 0,90 %.A minimum content of 0.10% is preferred to obtain the desired effect. A more preferred nickel content is at least 0.5% and is more preferably between 0.6 and 0.90%.

L'aluminium est un élément de base pour obtenir une aptitude excellente de l'acier à la nitruration.Aluminum is a basic element for obtaining an excellent suitability of steel for nitriding.

L'aluminium conduit lors de la nitruration à une forte élévation de la dureté superficielle ainsi qu'à une augmentation importante de la longueur du palier de dureté.Aluminum leads during nitriding to a strong increase in surface hardness as well as to a significant increase in the length of the hardness level.

Une teneur minimale à cet effet de l'aluminium est de 0,20 %. Au delà de 2 %, l'aluminium provoque un grossissement des grains important, l'apparition de phases alphagènes, aboutissant à des problèmes de laminage et de fragilité du métal.A minimum aluminum content for this purpose is 0.20%. Above 2%, aluminum causes significant grain enlargement, the appearance of alphagenic phases, leading to problems of rolling and brittleness of the metal.

Une teneur préférée en aluminium est d'au moins 0,5 % et au maximum de 1,5 %. Encore, de préférence, la teneur en aluminium est comprise entre 0,7 et 1 %.A preferred aluminum content is at least 0.5% and at most 1.5%. Again, preferably, the aluminum content is between 0.7 and 1 % .

Le molybdène est éventuellement présent dans l'acier selon l'invention. Le molybdène est de préférence présent car il a un effet important sur-la trempabilité et sur le durcissement et la résistance à l'adoucissement de la matrice. Une teneur minimale de 0,10 % est exigée pour obtenir cet effet tandis que sa teneur est limitée à 0,50 %, étant donné qu'il s'agit d'un élément coûteux et qu'au-delà de cette teneur, il se produit des modifications cristallographiques ayant une influence sur l'usinabilité.Molybdenum is optionally present in the steel according to the invention. Molybdenum is preferably present because it has a significant effect on hardenability and on hardening and resistance to softening of the matrix. A minimum content of 0.10% is required to achieve this effect while its content is limited to 0.50%, since it is an expensive element and that beyond this content, it crystallographic changes occur which influence machinability.

Le calcium et le tellure sont des éléments préférés soigneusement contrôlés pour obtenir une excellente usinabilité de l'acier. Ils peuvent donc être éventuels.Calcium and tellurium are preferred elements carefully controlled to obtain excellent machinability steel. They may therefore be possible.

Lors de leur emploi, une teneur minimum de 0,001 % de calcium est exigée à cet effet,au-delà de 0,010 % de calcium, on provoque l'apparition de grosses inclusions d'oxydes du type calcique préjudiciables aux propriétés d'emploi.During their use, a minimum content of 0.001% of calcium is required for this purpose, beyond 0.010% of calcium, it causes the appearance of large inclusions of oxides of the calcium type detrimental to the properties of use.

La teneur préférée en calcium est de 0,01 à 0,003 % (soit 10 à 30 ppm).The preferred calcium content is 0.01 to 0.003% (i.e. 10 to 30 ppm).

Une teneur minimale de 0,003 % de tellure est préférée pour améliorer l'usinabilité de l'acier. Au-delà de 0,010 % de tellure, on modifie la forme des inclusions de sulfures de façon défavorable vis-à-vis des propriétés de l'acier comme déjàdécrit dans la demande antérieure de la demanderesse précitée FR-A-2 395 323.A minimum content of 0.003% tellurium is preferred to improve the machinability of the steel. Beyond 0.010% tellurium, the shape of the sulphide inclusions is modified unfavorably with respect to the properties of steel as already described in the prior application of the aforementioned applicant FR-A-2,395,323.

Le vanadium est un élément éventuel qui est de préférence ajouté car il présente un effet carburigène provoquant un durcissement de la matrice. En outre, le vanadium limite l'adoucissement au cours du revenu provoqué par le traitement de nitruration. Le vanadium a aussi un effet favorable sur le durcissement par nitruration en fond de couches de diffusion de l'azote.Vanadium is a possible element which is preferably added because it has a carburogenic effect causing a hardening of the matrix. In addition, vanadium limits the softening during the tempering caused by the nitriding treatment. Vanadium also has a favorable effect on hardening by nitriding at the bottom of nitrogen diffusion layers.

La teneur en vanadium est limitée à 1 %, de préférence 0,5 % et encore de préférence est comprise entre 0,10 et 0,20 % afin d'obtenir ces effets sans interférer sur la structure cristallographique de l'acier et donc sur les propriétés, notamment sur l'usinabilité.The vanadium content is limited to 1%, preferably 0.5% and more preferably is between 0.10 and 0.20% in order to obtain these effects without interfering with the crystallographic structure of the steel and therefore with properties, especially on machinability.

Leniobium est également un élément éventuel ayant le même effet carburigène que le vanadium provoquant un durcissement de la matrice en limitant aussi l'adoucissement au cours du revenu provoqué par le traitement de nitruration. Le niobium a également un effet favorisant le durcissement par nitruration en fond de couches de diffusion de l'azote.Leniobium is also a possible element having the same carburogenic effect as vanadium causing a hardening of the matrix while also limiting softening during the income caused by the nitriding treatment. Niobium also has an effect favoring hardening by nitriding at the bottom of nitrogen diffusion layers.

En outre, le niobium a un effet d'affineur de grain, notamment de ferrite.In addition, niobium has a grain refining effect, in particular of ferrite.

Le niobium peut être présent jusqu'à 1 %, mais de préférence est limité lorsqu'il est présent à moins de 0,5 % en étant encore de préférence compris entre 0,1 et 0,2 %.The niobium can be present up to 1%, but is preferably limited when it is present to less than 0.5%, being more preferably between 0.1 and 0.2%.

Le titane est également un élément éventuel ayant un effet carburigène provoquant un durcissement de la matrice comme le vanadium ou le niobium. Le titane présente également un effet affineur de grain comme le niobium. La teneur en titane peut également atteindre 1 % mais une teneur préférée maximum est de 0,5 % et encore de préférence le titane est limité à 0,1-0,2 % lorsqu'il est présent.Titanium is also a possible element having a carburogenic effect causing a hardening of the matrix such as vanadium or niobium. Titanium also has a grain refining effect like niobium. The titanium content can also reach 1% but a maximum preferred content is 0.5% and more preferably the titanium is limited to 0.1-0.2% when it is present.

Enfin, lorsque l'on combine ces éléments, la teneur totale ne doit pas dépasser 1 % et de préférence est limitée à 0,5 %.Finally, when these elements are combined, the total content should not exceed 1% and preferably is limited to 0.5%.

Parmi le vanadium, le niobium et le titane, on préfère utiliser le vanadium.Among vanadium, niobium and titanium, it is preferred to use vanadium.

Ainsi, l'acier selon l'invention présente la composition préférée suivante (en pourcentages en poids) :

Figure imgb0005
de préférence
Figure imgb0006
Figure imgb0007
Solde Fer et impuretés résiduelles inévitables habituelles.Thus, the steel according to the invention has the following preferred composition (in percentages by weight):
Figure imgb0005
 preferably
Figure imgb0006
Figure imgb0007
 Balance F er and usual unavoidable residual impurities.

Les caractéristiques mécaniques de cet acier sont excellentes ainsi que son usinabilité et son aptitude à la nitruration.The mechanical characteristics of this steel are excellent as well as its machinability and its ability to nitriding.

A l'état brut de laminage ou de forgeage, ou à l'état normalisé, la résistance mécanique Rm est de l'ordre de 900-1400 MNewton/m2 suivant la dimension des produits (ronds ou laminés, produits forgés) et les conditions de refroidissement après laminage/forgeage ou normalisation.In the raw rolling or forging state, or in the standardized state, the mechanical resistance Rm is of the order of 900-1400 MNewton / m 2 depending on the size of the products (round or laminated, forged products) and the cooling conditions after rolling / forging or standardization.

En ce qui concerne l'usinabilité, à ce niveau de résistance, les performances d'usinage à vitesse de coupe basse ou moyenne (outils en acier rapide) et haute vitesse (outils carbure) sont très largement améliorées en combinaison par un contrôle rigoureux des inclusions de sulfures (globularisation par addition de tellure) et d'oxyde (transformation des chapelets d'alumine Al203 en inclusions polyphasées, alumine substituée en chaux xAl2O3, yCaO + sulfure substitué du type (Mn,Ca)S.With regard to machinability, at this level of resistance, the machining performance at low or medium cutting speed (high-speed steel tools) and high speed (carbide tools) is greatly improved in combination by rigorous control of the inclusion of sulphides (globularization by addition of tellurium) and oxide (transformation of alumina strings Al 2 0 3 into polyphase inclusions, alumina substituted in lime xAl 2 O 3 , yCaO + substituted sulphide of the type (Mn, Ca) S .

A ce sujet, on préfère un rapport tellure/soufre compris entre 0,07 et 0,13 comme indiqué dans la demande antérieure de la demanderesse FR-A-2 395 323, de préférence entre 0,09 et 0,11 et encore de préférence à environ 0,10.In this regard, a tellurium / sulfur ratio of between 0.07 and 0.13 is preferred as indicated in the prior application of the applicant FR-A-2,395,323, preferably between 0.09 and 0.11 and also of preferably about 0.10.

D'autre part, et de manière également essentielle, les aciers selon la présente invention ont une dureté superficielle et une cinétique de nitruration, notamment par bombardement ionique, beaucoup plus élevées, de manière inattendue, que les aciers conventionnels pour nitruration traités par trempe et revenu, et notamment ceux selon la norme AFNOR 40 CAD 6-12, comme cela sera démontré dans l'exemple suivant.On the other hand, and equally essential, the steels according to the present invention have a surface hardness and kinetics of nitriding, in particular by ion bombardment, much higher, unexpectedly, than conventional steels for nitriding. treated by quenching and tempering, and in particular those according to standard AFNOR 40 CAD 6-12, as will be demonstrated in the following example.

L'invention concerne également un procédé de préparation de l'acier selon l'invention, caractérisé en ce qu'il comprend l'addition de manière connue lors du processus métallurgique, et le contrôle de la teneur des divers constituants de manière à obtenir un acier ayant la composition chimique précédemment indiquée.The invention also relates to a process for the preparation of steel according to the invention, characterized in that it comprises the addition in a known manner during the metallurgical process, and the control of the content of the various constituents so as to obtain a steel having the chemical composition previously indicated.

En outre, ce procédé selon l'invention comprend de préférence une étape supplémentaire de stabilisation par traitement de l'acier, directement sur l'état brut de laminage ou de forgeage, ou après normalisation, à une température comprise entre environ 500 et 620°C.In addition, this method according to the invention preferably comprises an additional step of stabilization by treatment of the steel, directly on the raw rolling or forging state, or after normalization, at a temperature of between approximately 500 and 620 °. vs.

Ce traitement de stabilisation a pour but d'éviter, au cours de traitement ultérieur de nitruration, toute déformation des pièces par relaxation des contraintes internes. Dans cet état, la résstance mécanique Rm est comprise entre 800 et 1300 M.Newton/m2.The purpose of this stabilization treatment is to avoid, during the subsequent nitriding treatment, any deformation of the parts by relaxation of the internal stresses. In this state, the mechanical resistance Rm is between 800 and 1300 M.Newton / m 2 .

Le procédé selon l'invention comprend en outre de préférence une étape de nitruration habituelle. De préférence, cette étape de nitruration consiste en un traitement de nitruration par bombardement ionique effectué à une température d'au moins 450°C pendant un ou plusieurs jours selon la dureté superficielle désirée, la profondeur de nitruration désirée en surface ou à coeur.The method according to the invention also preferably comprises a usual nitriding step. Preferably, this nitriding step consists of a nitriding treatment by ion bombardment carried out at a temperature of at least 450 ° C. for one or more days depending on the desired surface hardness, the desired depth of nitriding at the surface or at the core.

L'invention concerne également une utilisation de cet acier comme acier de construction.The invention also relates to a use of this steel as a structural steel.

L'invention permet de simplifier le cycle de traitement et de fabrication chez l'utilisateur en évitant le traitement de recuit pour usinage et un traitement de trempe et de revenu après usinage ainsi qu'un traitement de rectification sur l'état traité, comme cela ressort du tableau I suivant :The invention makes it possible to simplify the processing and manufacturing cycle for the user by avoiding the annealing treatment for machining and a quenching and tempering treatment after machining as well as a rectification treatment on the treated state, as shown in Table I below:

Figure imgb0008
L'invention sera maintenant décrite en référence à un exemple de réalisation comprenant une comparaison avec un acier antérieurement connu selon la norme AFNOR 40 CAD 6-12. Cet exemple est naturellement donné à titre d'illustration et ne saurait en aucune façon limiter la portée de l'invention. Dans cet exemple, tous les pourcentages sont donnés en poids sauf indication contraire, le solde étant le fer.
Figure imgb0008
 The invention will now be described with reference to an exemplary embodiment comprising a comparison with a steel previously known according to the AFNOR 40 CAD 6-12 standard. This example is naturally given by way of illustration and cannot in any way limit the scope of the invention. In this example, all the percentages are given by weight unless otherwise indicated, the balance being iron.

ExempleExample

On élabore dans un four électrique de 80 tonnes des lingots de 5 tonnes à transformer par laminage en ronds de diamètre 90 à 220 mm, de manière classique, pour aboutir à un acier selon l'invention ayant la composition chimique suivante :

Figure imgb0009
Figure imgb0010
 Ingots of 5 tonnes are processed in an 80-ton electric furnace to be processed by rolling into rounds of diameter 90 to 220 mm, in a conventional manner, to result in a steel according to the invention having the following chemical composition:
Figure imgb0009
Figure imgb0010

On élabore de la même manière un acier de comparaison standard selon la norme AFNOR CAD 6-12, ci-après dénommé acier 40 CAD 6-12 ayant la composition chimique suivante :

  • C : 0,39 ; Mn : 0,59 ; Si : 0,32 ; P : 0,018 ; S : 0,024 Cr : 1,63 ; Mo : 0,29 ; Al : 1,00 ;
A standard comparison steel is produced in the same way according to the AFNOR CAD 6-12 standard, hereinafter called 40 CAD 6-12 steel having the following chemical composition:
  • C: 0.39; Mn: 0.59; If: 0.32; P: 0.018; S: 0.024 Cr: 1.63; Mo: 0.29; Al: 1.00;

Dans ces deux aciers, le solde est naturellement du fer avec les impuretés inévitables habituelles.In these two steels, the balance is naturally iron with the usual unavoidable impurities.

Les caractéristiques mécaniques comparées de ces deux aciers sur des lingots de 5 tonnes transformés par laminage en ronds de diamètre 100 mm sont répertoriées au tableau II suivant, ces caractéristiques étant mesurées à coeur :The comparative mechanical characteristics of these two steels on 5-ton ingots processed by rolling in rounds with a diameter of 100 mm are listed in Table II below, these characteristics being measured at heart:

Figure imgb0011
On a également comparé la dureté superficielle et la cinétique de nitruration, notamment par bombardement ionique, entre l'acier selon l'invention et l'acier conventionnel pour nitruration traité par trempe et revenu précité 40CAD 6-12.
Figure imgb0011
 The surface hardness and the kinetics of nitriding, in particular by ion bombardment, were also compared between the steel according to the invention and the conventional steel for nitriding treated by quenching and above-mentioned tempering 40CAD 6-12.

La figure 1 annexée représente les courbes de dureté Wickers obtenues sous une charge de 0,05 kg après un traitement de nitruration par séquences classiques de 70 heures. La dureté Wickers est représentée en ordonnée, tandis qu'en abscisse on a indiqué la profondeur de couche où est mesurée la dureté.The appended FIG. 1 represents the Wickers hardness curves obtained under a load of 0.05 kg after a nitriding treatment by conventional sequences of 70 hours. Wickers hardness is shown on the ordinate, while the abscissa indicates the layer depth where the hardness is measured.

Il est à noter une augmentation remarquable de dureté obtenue par l'acier selon l'invention, qui est tout à fait inattendue pour un homme du métier.It should be noted a remarkable increase in hardness obtained by the steel according to the invention, which is completely unexpected for a person skilled in the art.

De même, la figure 2 représente la courbe de dureté de l'alliage selon l'invention avec l'alliage pour nitruration 40CAD 6-12, en fonction de la charge en abscisse.Likewise, FIG. 2 represents the hardness curve of the alloy according to the invention with the alloy for nitriding 40CAD 6-12, as a function of the load on the abscissa.

D'autre part, la figure 3 représente à titre indicatif l'évolution de la dureté Wickers au cours du temps lors du traitement de nitruration à 530°C. La dureté Wickers est indiquée en ordonnée, tandis qu'en abscisse on indique la profondeur de la couche où est mesurée la dureté comme pour la figure 1.On the other hand, FIG. 3 shows by way of indication the evolution of the Wickers hardness over time during the nitriding treatment at 530 ° C. The Wickers hardness is indicated on the ordinate, while the abscissa indicates the depth of the layer where the hardness is measured as in FIG. 1.

On peut indiquer que la dureté superficielle après nitruration par bombardement ionique effectuée à 530°C pendant 64 heures, d'un acier selon l'invention, conduit, pour une configuration y aux performances suivantes :

  • - dureté superficielle : 1400-1600 HV0,1
  • - profondeur de nitruration à HV0,05 ≥ 1000 : 400 pm
  • - profondeur de nitruration à HV0,05 ≥ HV coeur + 100):500 µm
It may be indicated that the surface hardness after nitriding by ion bombardment carried out at 530 ° C. for 64 hours, of a steel according to the invention, leads, for a configuration y, to the following performances:
  • - surface hardness: 1400-1600 HV 0.1
  • - nitriding depth at HV 0.05 ≥ 1000: 400 pm
  • - nitriding depth at HV 0.05 ≥ HV core + 100): 500 µm

Claims (12)

RevendicationsClaims 1. Acier contenant du carbone, du silicium, du manganèse, du chrome, de l'aluminium, du soufre, du phosphore et éventuellement du nickel, caractérisé en ce qu'il présente la composition chimique suivante, en pourcentages en poids :
Figure imgb0012
Figure imgb0013
de préférence
Figure imgb0014
de préférence
Figure imgb0015
Le solde étant du fer avec les impuretés résiduelles inévitables habituelles.1. Steel containing carbon, silicon, manganese, chromium, aluminum, sulfur, phosphorus and optionally nickel, characterized in that it has the following chemical composition, in percentages by weight:
Figure imgb0012
Figure imgb0013
preferably
Figure imgb0014
 preferably
Figure imgb0015
 The balance being iron with the usual unavoidable residual impurities. 2. Acier selon la revendication 1, caractérisé en ce qu'il présente la composition chimique suivante, en pourcentages en poids :
Figure imgb0016
Figure imgb0017
Figure imgb0018
Le solde étant du fer avec les impuretés résiduelles inévitables habituelles.2. Steel according to claim 1, characterized in that it has the following chemical composition, in percentages by weight:
Figure imgb0016
Figure imgb0017
Figure imgb0018
The balance being iron with the usual unavoidable residual impurities. 3. Acier selon la revendication 1 ou 2, caractérisé en ce qu'il contient en outre l'un des éléments choisis dans le groupe consistant en du vanadium, du niobium et du titane jusqu'à environ 1 % en poids.3. Steel according to claim 1 or 2, characterized in that it also contains one of the elements chosen from the group consisting of vanadium, niobium and titanium up to approximately 1% by weight. 4. Acier selon l'une des revendications 1 à 3, caractérisé en ce que sa teneur en carbone est inférieure à 0,20 % ; avantageusement sa teneur en silicium est comprise entre 0,30 et 0,80 et encore de préférence entre 0,5 et 0,80 tandis que sa teneur en soufre est inférieure à 0,050.4. Steel according to one of claims 1 to 3, characterized in that its carbon content is less than 0.20%; advantageously its silicon content is between 0.30 and 0.80 and more preferably between 0.5 and 0.80 while its sulfur content is less than 0.050. 5. Acier selon l'une quelconque des revendications 1 à 4 caractérisé en ce qu'il présente la composition chimique suivante (en pourcentages en poids) :
Figure imgb0019
Figure imgb0020
Figure imgb0021
Le solde étant du fer avec les quantités résiduelles inévitables habituelles.5. Steel according to any one of claims 1 to 4 characterized in that it has the following chemical composition (in percentages by weight):
Figure imgb0019
Figure imgb0020
Figure imgb0021
The balance is iron with the usual unavoidable residual amounts. 6. Acier selon l'une des revendications 1 à 4 précitées, caractérisé en ce qu'il présente la composition chimique suivante (en pourcentages en poids) : C . 0,135 ; Mn : 0,81 ; Si : 0,508 ; P : 0,016 ; S : 0,016; Ni : 0,73 ; Cr : 4,01 ; Mo : 0,204 ;Al : 1,02 ; Ti : 0,009; Te : 0,007 ; Ca : 0,003. 6. Steel according to one of the aforementioned claims 1 to 4, characterized in that it has the following chemical composition (in percentages by weight): VS . 0.135; Mn: 0.81; If: 0.508; P: 0.016; S: 0.016; Ni: 0.73; Cr: 4.01; Mo: 0.204; Al: 1.02; Ti: 0.009; Te: 0.007; Ca: 0.003. 7. Procédé de préparation d'un acier, caractérisé en ce qu'il comprend l'addition de manière connue lors du processus métallurgique et le contrôle de la teneur des divers constituants de manière à obtenir la composition de l'acier telle que définie selon l'une quelconque des revendications 1 à 6.7. A method of preparing a steel, characterized in that it comprises the addition in a known manner during the metallurgical process and the control of the content of the various constituents so as to obtain the composition of the steel as defined according to any one of claims 1 to 6. 8. Procédé selon la revendication 7, caractérisé en ce qu'il comprend en outre une étape de stabilisation comprenant un traitement de l'acier, directement sur l'état brut de laminage ou de forgeage, ou après normalisation, à une température comprise entre 500 et 620°C.8. Method according to claim 7, characterized in that it further comprises a stabilization step comprising a treatment of the steel, directly on the raw state of rolling or forging, or after normalization, at a temperature between 500 and 620 ° C. 9. Procédé selon la revendication 7 ou 8, caractérisé en ce qu'il comprend une étape de nitruration de l'acier, de préférence par bombardement ionique.9. Method according to claim 7 or 8, characterized in that it comprises a step of nitriding the steel, preferably by ion bombardment. 10. Utilisation de l'acier tel que défini selon l'une quelconque des revendications 1 à 6 comme acier de construction à haute résistance présentant une bonne usinabilité et une grande aptitude au durcissement superficiel par nitruration.10. Use of steel as defined in any one of claims 1 to 6 as high strength structural steel having good machinability and a great ability to surface hardening by nitriding. 11. Utilisation selon la revendication 10, caractérisé en ce que l'acier a subi un traitement de nitruration et présente une dureté superficielle de 1400 à 1600 HV0,01, une profondeur de nitruration à HV0,05 ≥ 1000 : 400 µm et une profondeur de nitruration à HV0,05 ≥ (HV coeur+100): 500 pm11. Use according to claim 10, characterized in that the steel has undergone a nitriding treatment and has a surface hardness of 1400 to 1600 HV 0.01 , a nitriding depth at HV 0.05 ≥ 1000: 400 µm and a nitriding depth at HV 0.05 ≥ (HV core + 100): 500 pm
EP85401162A 1984-06-13 1985-06-12 High-strength nitriding steel with good machinability, useful as construction steel, and process for its manufacture Expired EP0170546B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT85401162T ATE38531T1 (en) 1984-06-13 1985-06-12 HIGH STRENGTH NITRIDING STEEL WITH GOOD MACHINABILITY, USABLE AS STRUCTURAL STEEL AND PROCESS FOR ITS PRODUCTION.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8409251A FR2566000B1 (en) 1984-06-13 1984-06-13 HIGH STRENGTH CONSTRUCTION STEEL HAVING GOOD MACHINABILITY AND HIGH ABILITY FOR SURFACE CURING BY NITRURATION, USE OF THIS STEEL BEFORE OR AFTER NITRURATION AS A CONSTRUCTION STEEL AND PROCESS FOR THE MANUFACTURE OF THIS STEEL
FR8409251 1984-06-13

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EP0170546A1 true EP0170546A1 (en) 1986-02-05
EP0170546B1 EP0170546B1 (en) 1988-11-09

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0875590A1 (en) * 1997-04-29 1998-11-04 Ovako Steel AB Nitriding steel

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2881869B2 (en) * 1989-12-06 1999-04-12 大同特殊鋼株式会社 Steel for plastic molds with excellent weldability

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1597415A (en) * 1968-06-26 1970-06-29
FR2445388A1 (en) * 1978-12-25 1980-07-25 Daido Steel Co Ltd Free cutting steel for use on automatic lathes - contains manganese, sulphur and tellurium, where manganese sulphide inclusions have specific size and shape

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1597415A (en) * 1968-06-26 1970-06-29
FR2445388A1 (en) * 1978-12-25 1980-07-25 Daido Steel Co Ltd Free cutting steel for use on automatic lathes - contains manganese, sulphur and tellurium, where manganese sulphide inclusions have specific size and shape

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0875590A1 (en) * 1997-04-29 1998-11-04 Ovako Steel AB Nitriding steel

Also Published As

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DE170546T1 (en) 1986-09-25
FR2566000B1 (en) 1988-09-16
ATE38531T1 (en) 1988-11-15
DE3566127D1 (en) 1988-12-15
FR2566000A1 (en) 1985-12-20
EP0170546B1 (en) 1988-11-09

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