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EP0845544A1 - Steel product made from bainitic steel and process for making the steel product - Google Patents

Steel product made from bainitic steel and process for making the steel product Download PDF

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Publication number
EP0845544A1
EP0845544A1 EP97402787A EP97402787A EP0845544A1 EP 0845544 A1 EP0845544 A1 EP 0845544A1 EP 97402787 A EP97402787 A EP 97402787A EP 97402787 A EP97402787 A EP 97402787A EP 0845544 A1 EP0845544 A1 EP 0845544A1
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EP
European Patent Office
Prior art keywords
steel
steel product
temperature
chemical composition
product
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP97402787A
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German (de)
French (fr)
Other versions
EP0845544B1 (en
Inventor
Jacques Bellus
Gilles Pierson
Claude Pichard
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ascometal SA
Original Assignee
Ascometal SA
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Publication of EP0845544A1 publication Critical patent/EP0845544A1/en
Application granted granted Critical
Publication of EP0845544B1 publication Critical patent/EP0845544B1/en
Anticipated expiration legal-status Critical
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/20—Isothermal quenching, e.g. bainitic hardening
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite

Definitions

  • the present invention relates to a steel product having high mechanical properties, good impact resistance and good machinability, the steel product can be used to manufacture directly by machining mechanical steel parts with high mechanical characteristics and good impact resistance.
  • Step product means a steel product obtained by rolling with hot of a semi-finished product such as an ingot, a bloom, a billet or a slab, possibly having undergone a heat treatment after the hot rolling, and being, for example, in the form of a bar round or square section, of a profile, a wire, a sheet, a plate, or even in the form of a seamless tube.
  • the tempering generates risks of spotting which makes the manufacture of the steel product delicate, this manufacture being all the more delicate as the mechanical characteristics sought are high.
  • the need for income after quenching lengthens the manufacturing process, which increases costs.
  • the relatively high carbon content, necessary to obtain such characteristics mechanical makes machining difficult, in particular because, during tempering, very hard carbides can form.
  • the object of the present invention is to remedy these drawbacks by proposing a means for manufacturing a mechanical mechanical part of which one at least part has both a tensile strength greater than 1000 MPa, very good ductility, good machinability, these properties being obtained without the need for treatment thermal income.
  • the invention relates to a method for manufacturing a steel mechanical part, the mechanical characteristics of which at 20 ° C. are: Rm ⁇ 1000 MPa Rp0.2 / Rm ⁇ 0.78 Z ⁇ 55% Km ⁇ 45 J / cm 2 according to which a steel product according to the invention is supplied and a machining is carried out.
  • This steel is cast in the form of a semi-finished product such as an ingot, a bloom, a billet or a slab which is hot rolled after reheating at a temperature above 1000 ° C and below or equal to 1250 ° C to form an iron and steel product such as a round or square bar, a profile, a plate, a wire, a seamless tube or a sheet metal.
  • the steel product is subjected to a heat treatment to give it a bainitic structure having the desired mechanical characteristics, namely: Rm ⁇ 1000 MPa Rp0.2 / Rm ⁇ 0.78 Z ⁇ 55% Km ⁇ 45 J / cm 2 Km being Mesnager resilience.
  • the mechanical part is then machined in the steel product, and there is no need for additional heat treatment.
  • the second embodiment includes reheating additional but it has the advantage of leading to a greater refinement of the grain, which is favorable in particular to the impact resistance and to the ductility.
  • a mechanical part was made consisting of a solid axis comprising two cylindrical parts of diameter 48 mm and 46 mm, from a steel steel product according to the invention.
  • This steel was hot rolled and then subjected to heat treatment oil quenching followed by tempering.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Coating With Molten Metal (AREA)

Abstract

A steel section comprises by weight 0.06-0.11% carbon, 1-1.7% manganese, 0.15-0.40% silicon, 0.025-0.10% sulphur, up to 0.025% phosphorous, 0-0.25% nickel, 0.5-1.2% chromium, 0.08-0.13% molybdenum, 0-0.25% copper, 0.003-0.035% aluminium, 0-0.035% titanium, 0-0.10% vanadium, 0-0.06% niobium, 0.0008-0.0040% boron and 0.0060-0.011% nitrogen, with optionally up to following levels- 0.010% tellurium, 0.025% selenium, 0.13% bismuth, 0.090% lead and 0.0040% calcium, the remainder being iron and impurities. The sum Mn+Cr+Mo is at least 2.1%, the sum V+Nb+Ti is between 0.015 and 0.13%, Al+Ti is at least 0.020% and the ratio Mn/S is at least 12. The section has a bainitic structure and exhibits following mechanical properties at 20 degrees C- tensile strength at least 1000 MPa, ratio of elastic limit to tensile strength at least 0.78, resilience at least 45 J/cm<2> and contraction of area at least 55%. Also claimed are making such a section and machining it to form a finished article.

Description

La présente invention est relative à un produit sidérurgique ayant des caractéristiques mécaniques élevées, une bonne tenue au choc et une bonne usinabilité, le produit sidérurgique pouvant être utilisé pour fabriquer directement par usinage des pièces mécaniques en acier ayant des caractéristiques mécaniques élevées et une bonne tenue au choc. Par « produit sidérurgique », on entend un produit en acier, obtenu par laminage à chaud d'un demi-produit tel qu'un lingot, un bloom, une billette ou une brame, ayant subi éventuellement un traitement thermique postérieurement au laminage à chaud, et se présentant, par exemple, sous forme d'une barre de section ronde ou carrée, d'un profilé, d'un fil, d'une tôle, d'un plat, ou encore sous forme d'un tube sans soudure.The present invention relates to a steel product having high mechanical properties, good impact resistance and good machinability, the steel product can be used to manufacture directly by machining mechanical steel parts with high mechanical characteristics and good impact resistance. By "Steel product" means a steel product obtained by rolling with hot of a semi-finished product such as an ingot, a bloom, a billet or a slab, possibly having undergone a heat treatment after the hot rolling, and being, for example, in the form of a bar round or square section, of a profile, a wire, a sheet, a plate, or even in the form of a seamless tube.

De nombreuses pièces mécaniques sont fabriquées par usinage d'un produit sidérurgique laminé soumis, avant usinage, à un traitement thermique de trempe et revenu destiné à conférer à l'acier les propriétés mécaniques souhaitées. Selon cette technique, pour obtenir de très hautes caractéristiques mécaniques telle qu'une résistance à la traction supérieure à 1000 MPa, on utilise un acier faiblement allié (acier dont la somme des teneurs en éléments d'alliage, en % en poids, est inférieure à 8 %) contenant de 0,25% à 0,45% en poids de carbone, et un ou plusieurs éléments d'alliage tels que le nickel, le chrome et le molybdène. La composition chimique de l'acier est choisie pour qu'il ait une trempabilité suffisante afin que la trempe effectuée sur le produit sidérurgique conduise à une structure martensitique. Cette technique présente plusieurs inconvénients. D'une part la trempe engendre des risques de tapures qui rend délicate la fabrication du produit sidérurgique, cette fabrication étant d'autant plus délicate que les caractéristiques mécaniques recherchées sont élevées. D'autre part, la nécessité d'un revenu effectué après la trempe allonge le processus de fabrication, ce qui augmente les coûts. Enfin, la relativement forte teneur en carbone, nécessaire pour obtenir de telles caractéristiques mécaniques, rend l'usinage difficile, notamment parce que, au cours du revenu, des carbures très durs peuvent se former.Many mechanical parts are manufactured by machining a rolled steel product subjected, before machining, to a heat treatment quenching and tempering intended to give the steel the mechanical properties desired. According to this technique, to obtain very high characteristics mechanical properties such as tensile strength greater than 1000 MPa, uses low-alloy steel (steel whose sum of element contents alloy, in% by weight, is less than 8%) containing from 0.25% to 0.45% in weight of carbon, and one or more alloying elements such as nickel, chromium and molybdenum. The chemical composition of the steel is chosen for it has sufficient hardenability so that the quenching carried out on the product steel industry leads to a martensitic structure. This technique presents several disadvantages. On the one hand the tempering generates risks of spotting which makes the manufacture of the steel product delicate, this manufacture being all the more delicate as the mechanical characteristics sought are high. On the other hand, the need for income after quenching lengthens the manufacturing process, which increases costs. Finally, the relatively high carbon content, necessary to obtain such characteristics mechanical, makes machining difficult, in particular because, during tempering, very hard carbides can form.

On fabrique également des pièces de mécaniques par usinage d'un produit sidérurgique laminé en acier contenant en poids de 0,35 à 0,50% de carbone, de 1,3 à 1,6% de manganèse, de 0,5 à 1,2% de silicium et de 0,08 à 0,15% de vanadium. Dans ce cas, le produit sidérurgique est refroidit lentement après laminage de façon à présenter une structure ferrito-perlitique. Cette technique a l'avantage d'être plus économique que la précédente, mais elle présente plusieurs inconvénients. Tour d'abord il est très difficile d'obtenir de très hautes caractéristiques mécaniques : la résistance Rm est limitée à 1000 MPa et le ratio limite d'élasticité sur résistance à 0,70, et beaucoup plus souvent à 0,65, ce qui réduit les possibilités d'utilisation notamment lorsque la tenue des pièces est calculée par référence à la limite d'élasticité. Par ailleurs la tenue au choc est faible, tout particulièrement lorsque la résistance avoisine 1000 MPa. De plus, la ductilité est faible puisque la striction Z n'excède pas 45% dans les meilleurs des cas. En second lieu les difficultés d'usinage sont similaires à celles de la technique précédente en raison des teneurs en carbone nécessaires pour obtenir des niveaux de résistance voisins de 1000 MPa.We also manufacture mechanical parts by machining a steel rolled steel product containing by weight from 0.35 to 0.50% of carbon, 1.3 to 1.6% manganese, 0.5 to 1.2% silicon and 0.08 to 0.15% vanadium. In this case, the steel product is cooled slowly after rolling so as to present a ferrito-pearlitic structure. This technique has the advantage of being more economical than the previous one, but it has several drawbacks. First turn it is very difficult to get very high mechanical properties: the resistance Rm is limited to 1000 MPa and the yield strength to strength ratio at 0.70, and much more often at 0.65, which reduces the possibilities of use especially when the part strength is calculated by reference to the yield strength. otherwise the impact resistance is low, especially when the resistance is close 1000 MPa. In addition, the ductility is low since the necking Z does not exceed 45% in the best of cases. Second, the machining difficulties are similar to those of the previous technique due to the contents in carbon necessary to obtain resistance levels close to 1000 MPa.

On fabrique aussi des pièces de mécaniques par usinage d'un produit sidérurgique laminé en acier contenant en poids de 0,15 à 0,40% de carbone, plus de 1,9% de manganèse ou plus de 1,5% de chrome (les teneurs en ces éléments pouvant atteindre 4 %), refroidi lentement après laminage pour obtenir une structura bainitique. Cette technique présente l'inconvénient de ne pas permettre d'obtenir de façon fiable et régulière une résistance à la traction supérieure à 1000 MPa. De plus, elle conduit à la formation de bandes dures souvent ségrégées ayant une structure martensitique qui rendent l'usinage difficile.We also manufacture mechanical parts by machining a product steel rolled steel containing by weight from 0.15 to 0.40% of carbon, more than 1.9% manganese or more than 1.5% chromium (the contents in these elements up to 4%), cooled slowly after rolling to obtain a bainitic structure. This technique has the disadvantage of not not provide reliable and regular tensile strength greater than 1000 MPa. In addition, it leads to the formation of hard bands often segregated having a martensitic structure which makes machining difficult.

Le but de la présente invention est de remédier à ces inconvénients en proposant un moyen pour fabriquer une pièce de mécanique en acier dont une partie au moins présente à la fois une résistance à la traction supérieure à 1000 MPa, une très bonne ductilité, une bonne aptitude à l'usinage, ces propriétés étant obtenues sans qu'il soit nécessaire d'effectuer un traitement thermique de revenu.The object of the present invention is to remedy these drawbacks by proposing a means for manufacturing a mechanical mechanical part of which one at least part has both a tensile strength greater than 1000 MPa, very good ductility, good machinability, these properties being obtained without the need for treatment thermal income.

A cet effet, l'invention a pour objet un produit sidérurgique tel que, par exemple, une barre ronde ou carrée, un tube sans soudure, un plat ou une tôle, ayant une structure bainitique, et, à 20°C, une résistance à la traction Rm ≥ 1000 MPa, un rapport limite d'élasticité sur résistance à la traction Rp0,2 / Rm ≥ 0,78, une striction Z ≥ 55 % et une résilience Mesnager Km ≥ 45 J/cm2, ledit produit sidérurgique étant constitué d'un acier dont la composition chimique comprend, en poids: 0,06% ≤ C ≤ 0,11% 0,9% ≤ Mn ≤ 1,7% 0,15% ≤ Si ≤ 0,40% 0,025% ≤ S ≤ 0,10% P ≤ 0,025% 0% ≤ Ni ≤ 0,25% 0,5% ≤ Cr ≤ 1,20% 0,08% ≤ Mo ≤ 0,13% 0% ≤ Cu ≤ 0,25% 0,003% ≤ Al ≤ 0,035% 0% ≤ Ti ≤ 0,035% 0% ≤ V ≤ 0,10% 0% ≤ Nb ≤ 0,06% 0,0008% ≤ B ≤ 0,0040% 0,0060% ≤ N ≤ 0,011% éventuellement un ou plusieurs éléments pris parmi Te jusqu'à 0,010%, Se jusqu'à 0,025%, Bi jusqu'à 0,13%, Pb jusqu'à 0,090%, Ca jusqu'à 0,0040% le reste étant du fer et des impuretés résultant de l'élaboration, la composition chimique satisfaisant en outre les relations : Mn + Cr + Mo ≥ 2,1% 0,015% ≤ V + Nb + Ti ≤ 0,13% Al + Ti ≥ 0,020% Mn/S ≥ 12 To this end, the subject of the invention is a steel product such as, for example, a round or square bar, a seamless tube, a plate or a sheet, having a bainitic structure, and, at 20 ° C., a resistance tensile Rm ≥ 1000 MPa, a yield strength to tensile strength ratio Rp0,2 / Rm ≥ 0.78, a necking Z ≥ 55% and a Mesnager resilience Km ≥ 45 J / cm 2 , said steel product consisting of a steel the chemical composition of which comprises, by weight: 0.06% ≤ C ≤ 0.11% 0.9% ≤ Mn ≤ 1.7% 0.15% ≤ If ≤ 0.40% 0.025% ≤ S ≤ 0.10% P ≤ 0.025% 0% ≤ Ni ≤ 0.25% 0.5% ≤ Cr ≤ 1.20% 0.08% ≤ Mo ≤ 0.13% 0% ≤ Cu ≤ 0.25% 0.003% ≤ Al ≤ 0.035% 0% ≤ Ti ≤ 0.035% 0% ≤ V ≤ 0.10% 0% ≤ Nb ≤ 0.06% 0.0008% ≤ B ≤ 0.0040% 0.0060% ≤ N ≤ 0.011% possibly one or more elements taken from Te up to 0.010%, Se up to 0.025%, Bi up to 0.13%, Pb up to 0.090%, Ca up to 0.0040% the rest being iron and impurities resulting from the preparation, the chemical composition further satisfying the relationships: Mn + Cr + Mo ≥ 2.1% 0.015% ≤ V + Nb + Ti ≤ 0.13% Al + Ti ≥ 0.020% Mn / S ≥ 12

De préférence, la dimension caractéristique du produit sidérurgique est comprise entre 10 mm et 50 mm.Preferably, the characteristic dimension of the steel product is between 10 mm and 50 mm.

L'invention concerne également un procédé de fabrication du produit sidérurgique conforme à l'invention selon lequel :

  • on se procure un demi produit en acier ayant la composition chomique indiquée ci-dessus, par exemple un lingot, une brame, un bloom ou une billette,
  • on chauffe le demi produit jusqu'à une température supérieure à 1000°C et on le lamine pour former un produit sidérurgique,
  • directement après laminage, on refroidit le produit sidérurgique à une vitesse de refroidissement moyenne supérieure ou égale à 0,5 °C/s jusqu'à une température inférieure ou égale à Ms - 350°, Ms étant la température maximale de début de transformation martensitique de l'acier,
  • on réchauffe le produit sidérurgique jusqu'à une température supérieure à Ac3 et comprise de préférence entre 910 °C et 980 °C,
  • et on le refroidit à une vitesse de refroidissement moyenne comprise entre 17 °C/s et 150 °C/s jusqu'à une température inférieure ou égale à Bs - 450°, puis on le laisse refroidir jusqu'à la température ambiante.
The invention also relates to a process for manufacturing the steel product according to the invention, according to which:
  • a semi-finished steel product is obtained having the chemical composition indicated above, for example an ingot, a slab, a bloom or a billet,
  • the semi-finished product is heated to a temperature above 1000 ° C. and is laminated to form a steel product,
  • directly after rolling, the steel product is cooled at an average cooling rate greater than or equal to 0.5 ° C / s to a temperature less than or equal to Ms - 350 °, Ms being the maximum temperature at the start of martensitic transformation steel,
  • the steel product is heated to a temperature above Ac 3 and preferably between 910 ° C and 980 ° C,
  • and it is cooled at an average cooling rate of between 17 ° C / s and 150 ° C / s to a temperature less than or equal to Bs - 450 °, then it is allowed to cool to room temperature.

Le produit sidérurgique peut, également, être fabriqué par un procédé selon lequel :

  • on se procure un demi produit en acier dont la composition chimique est indiquée ci-dessus, par exemple un lingot, une brame, un bloom ou une billette,
  • on chauffe le demi produit jusqu'à une température supérieure à 1000°C et on le lamine pour former un produit sidérurgique qu'on laisse refroidir naturellement jusqu'à une température comprise entre 920 °C et 980 °C,
  • et on refroidit le produit sidérurgique à une vitesse de refroidissement moyenne comprise entre 17 °C/s et 150 °C/s jusqu'à une température inférieure ou égale à Bs - 400°, Bs étant la température de début de transformation bainitique de l'acier à la vitesse de refroidissement effective, puis on le laisse refroidir jusqu'à la température ambiante.
The steel product can also be produced by a process according to which:
  • a semi-finished steel product is obtained, the chemical composition of which is indicated above, for example an ingot, a slab, a bloom or a billet,
  • the semi-finished product is heated to a temperature above 1000 ° C. and it is laminated to form a steel product which is allowed to cool naturally to a temperature between 920 ° C. and 980 ° C.,
  • and the steel product is cooled at an average cooling rate of between 17 ° C / s and 150 ° C / s to a temperature less than or equal to Bs - 400 °, Bs being the bainitic transformation start temperature of l steel at the effective cooling rate, then allowed to cool to room temperature.

L'invention concerne enfin, un procédé de fabrication d'une pièce de mécanique en acier dont les caractéristiques mécaniques à 20 °C sont : Rm ≥ 1000 MPa Rp0,2 / Rm ≥ 0,78 Z ≥ 55% Km ≥ 45 J/cm2 selon lequel on approvisionne un produit sidérurgique selon l'invention et on effectue un usinage.Finally, the invention relates to a method for manufacturing a steel mechanical part, the mechanical characteristics of which at 20 ° C. are: Rm ≥ 1000 MPa Rp0.2 / Rm ≥ 0.78 Z ≥ 55% Km ≥ 45 J / cm 2 according to which a steel product according to the invention is supplied and a machining is carried out.

L'invention va maintenant être exposée de façon plus précise mais non limitative et illustrée par les exemples qui suivent.The invention will now be explained in more detail but not limiting and illustrated by the examples which follow.

Pour fabriquer de façon fiable et sans trop de difficultés d'usinage une pièce de mécanique en acier dont les caractéristiques mécaniques à 20°C sont : Rm ≥ 1000 MPa Rp0,2 / Rm ≥ 0,78 Z ≥ 55% Km ≥ 45 J/cm2 on utilise un acier au quel on confère une structure bainitique et dont la composition chimique comprend, en poids :

  • de 0,06 % à 0,11 % de carbone pour obtenir une structure bainitique ayant les caractéristiques mécaniques requises, et exempte de gros carbures défavorables à l'usinabilité ;
  • de 0,9% à 1,7%, et de préférence plus de 1 %, de manganèse, pour obtenir une bonne coulabilité et une bonne santé interne notamment en coulée continue, pour fixer le soufre ajouté pour améliorer l'usinabilité et pour augmenter la trempabilité, le rapport Mn/S étant supérieur ou égal à 12 ;
  • de 0,15% à 0,40% de silicium pour obtenir une désoxydation suffisante, notamment lorsque la teneur en aluminium est faible ;
  • de 0,025% à 0,10% de soufre pour améliorer l'usinabilité ;
  • moins de 0,025% de phosphore pour ne pas détériorer la résilience ;
  • moins de 0,25% de nickel pour éviter la formation de martensite, cet élément est considéré comme un résiduel apporté par les matières premières au cours de l'élaboration de l'acier, sa teneur peut, éventuellement, être égale à 0% ;
  • moins de 0,25 % de cuivre afin d'éviter de diminuer la tenue au choc et la ductilité, cet élément est considéré comme un résiduel apporté par les matières premières lors de l'élaboration, sa teneur peut, éventuellement, être égale à 0% ;
  • de 0,5% à 1,20% de chrome pour augmenter la trempabilité sans durcir excessivement la bainite pour ne pas détériorer l'usinabilité ;
  • de 0,08% à 0,13% de molybdène pour augmenter la trempabilité en synergie avec le bore, et, en particulier, augmenter le domaine d'existence de la structure bainitique ;
  • de 0% à 0,035% de titane, de 0% à 0,10% de vanadium et de 0% à 0,06% de niobium, la somme des teneurs en ces trois éléments étant comprise entre 0,015% et 0,13% afin d'obtenir une structure entièrement bainitique dans toute la masse du produit sidérurgique ;
  • de 0,003% à 0,035% d'aluminium, la somme Al + Ti étant supérieure à 0,02% afin d'obtenir un grain suffisamment fin pour obtenir la résilience souhaitée ;
  • de 0,0008% à 0,0040% de bore pour augmenter la trempabilité et éviter la formation de ferrite ;
  • de 0,0060 à 0,011% d'azote pour former des nitrures d'aluminium, de titane ou de vanadium, sans former des nitrures de bore ;
  • éventuellement un ou plusieurs éléments pris parmi Te jusqu'à 0,010%, Se jusqu'à 0,025%, Bi jusqu'à 0,13%, Pb jusqu'à 0,090%, Ca jusqu'à 0,0040% pour améliorer l'usinabilité ;
le reste étant du fer et des impuretés résultant de l'élaboration.To reliably manufacture and without too many machining difficulties a mechanical steel part whose mechanical characteristics at 20 ° C are: Rm ≥ 1000 MPa Rp0.2 / Rm ≥ 0.78 Z ≥ 55% Km ≥ 45 J / cm 2 a steel is used which is given a bainitic structure and the chemical composition of which comprises, by weight:
  • from 0.06% to 0.11% carbon to obtain a bainitic structure having the required mechanical characteristics, and free of large carbides unfavorable to machinability;
  • from 0.9% to 1.7%, and preferably more than 1%, of manganese, to obtain good flowability and good internal health, especially in continuous casting, to fix the added sulfur to improve machinability and to increase the hardenability, the Mn / S ratio being greater than or equal to 12;
  • from 0.15% to 0.40% of silicon to obtain sufficient deoxidation, in particular when the aluminum content is low;
  • from 0.025% to 0.10% sulfur to improve machinability;
  • less than 0.025% phosphorus so as not to deteriorate the resilience;
  • less than 0.25% of nickel to avoid the formation of martensite, this element is considered to be a residual provided by the raw materials during the production of the steel, its content may possibly be equal to 0%;
  • less than 0.25% of copper in order to avoid reducing the impact strength and ductility, this element is considered to be a residual provided by the raw materials during production, its content may possibly be equal to 0 %;
  • from 0.5% to 1.20% chromium to increase the hardenability without excessively hardening the bainite so as not to deteriorate the machinability;
  • from 0.08% to 0.13% of molybdenum to increase the quenchability in synergy with boron, and, in particular, to increase the domain of existence of the bainitic structure;
  • from 0% to 0.035% of titanium, from 0% to 0.10% of vanadium and from 0% to 0.06% of niobium, the sum of the contents of these three elements being between 0.015% and 0.13% so to obtain a fully bainitic structure throughout the mass of the steel product;
  • from 0.003% to 0.035% aluminum, the sum Al + Ti being greater than 0.02% in order to obtain a grain which is sufficiently fine to obtain the desired resilience;
  • from 0.0008% to 0.0040% boron to increase the hardenability and avoid the formation of ferrite;
  • from 0.0060 to 0.011% nitrogen to form aluminum, titanium or vanadium nitrides, without forming boron nitrides;
  • possibly one or more elements taken from Te up to 0.010%, Se up to 0.025%, Bi up to 0.13%, Pb up to 0.090%, Ca up to 0.0040% to improve machinability ;
the remainder being iron and impurities resulting from processing.

En outre, et afin de garantir une résistance à la traction supérieure à 1000 MPa, la composition chimique doit satisfaire la relation : Mn + Cr + Mo ≥ 2,1% In addition, and in order to guarantee a tensile strength greater than 1000 MPa, the chemical composition must satisfy the relationship: Mn + Cr + Mo ≥ 2.1%

Cet acier est coulé sous forme d'un demi produit tel qu'un lingot, un bloom, une billette ou une brame qui est laminé à chaud après réchauffage à une température supérieure à 1000°C et inférieure ou égale à 1250 °C pour former un produit sidérurgique tel qu'une barre de section ronde ou carrée, un profilé, un plat, un fil, un tube sans soudure ou une tôle. En fin de laminage, le produit sidérurgique est soumis à un traitement thermique pour lui conférer une structure bainitique ayant les caractéristiques mécaniques souhaitées, à savoir : Rm ≥ 1000 MPa Rp0,2 / Rm ≥ 0,78 Z ≥ 55 % Km ≥ 45 J/cm2 Km étant la résilience Mesnager.This steel is cast in the form of a semi-finished product such as an ingot, a bloom, a billet or a slab which is hot rolled after reheating at a temperature above 1000 ° C and below or equal to 1250 ° C to form an iron and steel product such as a round or square bar, a profile, a plate, a wire, a seamless tube or a sheet metal. At the end of rolling, the steel product is subjected to a heat treatment to give it a bainitic structure having the desired mechanical characteristics, namely: Rm ≥ 1000 MPa Rp0.2 / Rm ≥ 0.78 Z ≥ 55% Km ≥ 45 J / cm 2 Km being Mesnager resilience.

La pièce de mécanique est alors usinée dans le produit sidérurgique, et il n'est pas besoin de faire un traitement thermique supplémentaire.The mechanical part is then machined in the steel product, and there is no need for additional heat treatment.

Le traitement thermique effectué en fin de laminage peut être réalisé, au moins, de deux façons distinctes :

  • soit, en fin de laminage, on laisse le produit sidérurgique refroidir naturellement jusqu'à une température comprise entre 920 °C et 980 °C et on le refroidit à une vitesse de refroidissement moyenne comprise entre 17 °C/s et 150 °C/s jusqu'à une température inférieure ou égale à Bs - 400°, Bs étant la température de début de transformation bainitique de l'acier à la vitesse de refroidissement effective, puis on le laisse refroidir jusqu'à la température ambiante,
  • soit, en fin de laminage, on refroidit le produit sidérurgique à une vitesse de refroidissement moyenne supérieure ou égale à 0,5 °C/s jusqu'à une température inférieure ou égale à Ms - 350°, on réchauffe alors le produit sidérurgique jusqu'à une température supérieure à Ac3, et, de préférence, comprise entre 910 °C et 980 °C, et on le refroidit à une vitesse de refroidissement moyenne comprise entre 17 °C/s et 150 °C/s jusqu'à une température inférieure ou égale à Bs - 450°, puis on le laisse refroidir jusqu'à la température ambiante.
The heat treatment carried out at the end of rolling can be carried out, at least, in two distinct ways:
  • or, at the end of rolling, the steel product is allowed to cool naturally to a temperature between 920 ° C and 980 ° C and it is cooled at an average cooling rate between 17 ° C / s and 150 ° C / s up to a temperature less than or equal to Bs - 400 °, Bs being the temperature at the start of bainitic transformation of the steel at the effective cooling rate, then it is allowed to cool to room temperature,
  • or, at the end of rolling, the steel product is cooled at an average cooling rate greater than or equal to 0.5 ° C / s to a temperature less than or equal to Ms - 350 °, the steel product is then heated to '' at a temperature higher than Ac 3 , and preferably between 910 ° C and 980 ° C, and it is cooled at an average cooling rate between 17 ° C / s and 150 ° C / s to a temperature less than or equal to Bs - 450 °, then it is allowed to cool down to room temperature.

Le premier mode de réalisation à l'avantage de ne pas comporter de réchauffage après laminage.The first embodiment has the advantage of not comprising any reheating after rolling.

Le deuxième mode de réalisation comporte un réchauffage supplémentaire mais il a l'avantage d'entraíner un affinage plus important du grain, ce qui est favorable notamment à la tenue au choc et à la ductilité.The second embodiment includes reheating additional but it has the advantage of leading to a greater refinement of the grain, which is favorable in particular to the impact resistance and to the ductility.

Enfin, pour que la structure soit entièrement bainitique de façon à obtenir avec fiabilité l'ensemble des caractéristiques mécaniques, il est préférable que la dimension caractéristique du produit sidérurgique, c'est à dire la dimension qui détermine la répartition des vitesses de refroidissement dans la masse, soit comprise entre 10 mm et 50 mm. Cette dimension caractéristique est, par exemple, pour une barre ronde, le diamètre ; pour une barre de section carrée, la longueur d'un côté du carré ; pour une tôle ou un plat, l'épaisseur. Finally, so that the structure is entirely bainitic so as to reliably obtain all the mechanical characteristics, it is preferable than the characteristic dimension of the steel product, i.e. the dimension that determines the distribution of cooling rates in the mass, between 10 mm and 50 mm. This characteristic dimension is, for example, for a round bar, the diameter; for a section bar square, the length of one side of the square; for a plate or a dish, the thickness.

A titre de premier exemple, on a fabriqué une pièce mécanique consistant en un axe plein comportant deux parties cylindriques de diamètre 48 mm et 46 mm, à partir d'un produit sidérurgique en acier acier conforme à l'invention. Le produit sidérurgique était une barre laminée ronde et la composition chimique de l'acier comprenait, en poids : C = 0,061% Mn = 1,57% Si = 0,28% S = 0,025% P = 0,004% Ni = 0,11% Cr = 0,80% Mo = 0,12% Cu = 0,21% Al = 0,025% Ti = 0,016% V = 0,08% Nb = 0,01% B = 0,0040% N = 0,0080% remplissant donc les conditions : Mn + Cr + Mo = 2,50% ≥ 2,1% V + Nb + Ti = 0,11 soit ≥ 0,015% et ≤ 0,13% Al + Ti = 0,041%, soit ≥ 0,020% Mn/S = 62 ≥ 12 As a first example, a mechanical part was made consisting of a solid axis comprising two cylindrical parts of diameter 48 mm and 46 mm, from a steel steel product according to the invention. The steel product was a round rolled bar and the chemical composition of the steel included, by weight: C = 0.061% Mn = 1.57% If = 0.28% S = 0.025% P = 0.004% Ni = 0.11% Cr = 0.80% Mo = 0.12% Cu = 0.21% Al = 0.025% Ti = 0.016% V = 0.08% Nb = 0.01% B = 0.0040% N = 0.0080% thus fulfilling the conditions: Mn + Cr + Mo = 2.50% ≥ 2.1% V + Nb + Ti = 0.11 or ≥ 0.015% and ≤ 0.13% Al + Ti = 0.041%, i.e. ≥ 0.020% Mn / S = 62 ≥ 12

Pour fabriquer le produit sidérurgique, on a laminé l'acier sous forme d'une barre ronde de 49 mm de diamètre, après l'avoir réchauffé à 1180 °C. La température de fin de laminage était de 1020°C. On a laissé la barre refroidir à l'air jusqu'à 950 °C, puis on l'a refroidie jusqu'à 32 °C (soit, Bs-584°C) à la vitesse de refroidissement moyenne de 19°C/s.To manufacture the steel product, the steel was rolled in the form a round bar 49 mm in diameter, after having heated it to 1180 ° C. The end of rolling temperature was 1020 ° C. We let the bar cool down to air to 950 ° C, then cooled to 32 ° C (i.e., Bs-584 ° C) at average cooling rate of 19 ° C / s.

La structure était entièrement bainitique et homogène sur toute la section. Les caractéristiques mécaniques déterminées sur l'axe mécanique étaient à 20°C : Rm = 1047 MPa Rp0,2/Rm = 0,792 Z = 71% Km = 176J/cm2 The structure was entirely bainitic and homogeneous over the entire section. The mechanical characteristics determined on the mechanical axis were at 20 ° C: Rm = 1047 MPa Rp0.2 / Rm = 0.792 Z = 71% Km = 176J / cm 2

Puis, pour fabriquer la pièce, on a éffectué un usinage par enlèvement de copeaux à l'aide d'un outil comportant une plaquette carbure revêtue de Ti(C,N) + Al2O3, jusqu'à 48 mm pour la partie principale et 46 mm pour la partie restante, n'a pas présenté de difficultés particulières.Then, to manufacture the part, machining was carried out by removing chips using a tool comprising a carbide plate coated with Ti (C, N) + Al 2 O 3 , up to 48 mm for the part main and 46 mm for the remaining part, did not present any particular difficulties.

A titre de deuxième exemple, on a fabriqué une pièce de forme généralement plate, d'épaisseur 25 mm, destinée à être fixée par boulonnage et, de ce fait, nécessitant le perçage de trous. La pièce a été fabriquée à partir d'un produit sidérurgique en un acier selon l'invention dont la composition chimique comprenait, en poids : C = 0,083% Mn = 1,341% Si = 0,29% S = 0,081% P = 0,010% Ni = 0,14% Cr = 0,808% Mo = 0,105% Cu = 0,182% Al = 0,028% Ti = 0,015% V = 0,081% Nb = 0,030% B = 0,0021% N = 0,011% remplissant donc les conditions : Mn + Cr + Mo = 2,25% ≥ 2,1% V + Nb + Ti = 0,126, soit ≥ 0,015% et ≤ 0,13% Al + Ti = 0,043%, soit ≥ 0,020% Mn/S = 16,5 ≥ 12 As a second example, a generally flat part, 25 mm thick, was produced, intended to be fixed by bolting and, therefore, requiring the drilling of holes. The part was made from a steel product from a steel according to the invention, the chemical composition of which included, by weight: C = 0.083% Mn = 1.341% If = 0.29% S = 0.081% P = 0.010% Ni = 0.14% Cr = 0.808% Mo = 0.105% Cu = 0.182% Al = 0.028% Ti = 0.015% V = 0.081% Nb = 0.030% B = 0.0021% N = 0.011% thus fulfilling the conditions: Mn + Cr + Mo = 2.25% ≥ 2.1% V + Nb + Ti = 0.126, i.e. ≥ 0.015% and ≤ 0.13% Al + Ti = 0.043%, i.e. ≥ 0.020% Mn / S = 16.5 ≥ 12

L'acier a été laminé à chaud pour obtenir un plat et la température de fin de laminage était de 1010 °C, puis il a été refroidit à partir de 980 °C jusqu'à 58° C, soit Ms - 405°C, à la vitesse moyenne de refroidissement de 0,75 °C/s, avant d'être réchauffé à la température de 940 °C, soit Ac3 + 72 °C, puis refroidit jusqu'à 28 °C, soit Bs - 601 °C, à la vitesse moyenne de refroidissement de 39 °C/s.The steel was hot rolled to obtain a dish and the end of rolling temperature was 1010 ° C., then it was cooled from 980 ° C. to 58 ° C., ie Ms - 405 ° C., at the average cooling rate of 0.75 ° C / s, before being reheated to the temperature of 940 ° C, i.e. Ac 3 + 72 ° C, then cooled to 28 ° C, i.e. Bs - 601 ° C, at the average cooling rate of 39 ° C / s.

Les caractéristiques mécaniques obtenues à 20 °C étaient les suivantes : Rm = 1087 MPa Rp0,2 / Rm = 0,804 Z = 59 % KMésnager = 74 J/cm2 et la structure était bainitique.The mechanical characteristics obtained at 20 ° C were as follows: Rm = 1087 MPa Rp 0.2 / Rm = 0.804 Z = 59% K Housewife = 74 J / cm 2 and the structure was bainitic.

Le plat a été usiné sans difficultés par découpage pour mise à longueur, puis usiné, sans difficultés également, pour percer des trous de fixation de diamètre 10 mm avec un foret de diamètre 10 mm comportant des plaquettes en acier rapide allié HSCO 6-5-2-5 revêtu de TiN.The dish was machined without difficulty by cutting to length, then machined, also without difficulty, to drill fixing holes for 10 mm diameter with a 10 mm diameter drill with inserts made of HSCO 6-5-2-5 high-alloy steel coated with TiN.

La facilité d'usinage a été évaluée en mesurant les efforts spécifiques de coupe axiaux ka et les couples spécifiques de coupe tangentiels kt observés avec la pièce qui vient d'être décrite, et en les comparant aux mêmes grandeurs, mesurées dans les mêmes conditions d'usinage, sur une pièce identique, mais réalisée en acier selon l'art antérieur et dont la composition chimique comprenait, en poids : C = 0,42 % Mn = 1,03 % Si = 0,17 % Ni = 0,22 % Cr = 1,09 % Mo = 0,3 % Cu = 0,25 % Al = 0,023 % N = 0,01 % P = 0,018 % The ease of machining has been evaluated by measuring the specific axial cutting forces k a and the specific tangential cutting torques k t observed with the part which has just been described, and by comparing them to the same quantities, measured in the same machining conditions, on an identical part, but made of steel according to the prior art and whose chemical composition included, by weight: C = 0.42% Mn = 1.03% If = 0.17% Ni = 0.22% Cr = 1.09% Mo = 0.3% Cu = 0.25% Al = 0.023% N = 0.01% P = 0.018%

Cet acier a été laminé à chaud, puis soumis à un traitement thermique de trempe à l'huile suivi d'un revenu. Les températures d'austénitisation et de revenu ont dû être ajustées, la première à 875 °C et la seconde à 590 °C, pour obtenir la même dureté qu'avec l'acier selon l'invention, à savoir 330 HB.This steel was hot rolled and then subjected to heat treatment oil quenching followed by tempering. The austenitization and had to be adjusted, the first to 875 ° C and the second to 590 ° C, to obtain the same hardness as with the steel according to the invention, namely 330 HB.

En prenant comme base 100 les valeurs de ka et kt obtenues avec l'acier selon l'art antérieur, les valeurs obtenues avec l'acier selon l'invention ont été ka = 90, soit un gain de 10 %, et kt = 76, soit un gain de 24 %.Taking as a base 100 the values of k a and k t obtained with the steel according to the prior art, the values obtained with the steel according to the invention were k a = 90, ie a gain of 10%, and k t = 76, a gain of 24%.

Ces résultats montrent que l'acier et le procédé selon l'invention permettent de fabriquer des produit sidérurgiques facilement usinables pouvant être utilisés pour fabriquer directement par usinage des pièces à hautes caractéristiques. Ces pièces peuvent être pleines ou creuses puisque le procédé s'applique aussi bien à la fabrication de barres pleines que de tubes. Les pièces peuvent présenter les caractéristiques mécaniques élevées en tous leurs points.These results show that the steel and the process according to the invention make it possible to manufacture easily machinable steel products which can be used to directly manufacture by machining parts with high characteristics. These parts can be solid or hollow since the process applies to both the production of solid bars and tubes. The parts can have high mechanical characteristics in all their points.

Claims (5)

Produit sidérurgique caractérisé en ce qu'il a une structure bainitique, en ce que ses caractéristiques mécaniques à 20 °C sont : Rm ≥ 1000 MPa Rp0,2 / Rm ≥ 0,78 Z ≥ 55% Km ≥ 45 J/cm2 et en ce qu'il est constitué d'un acier dont la composition chimique comprend, en poids : 0,06% ≤ C ≤ 0,11% 1% ≤ Mn ≤ 1,7% 0,15% ≤ Si ≤ 0,40% 0,025% ≤ S ≤ 0,10% P ≤ 0,025% 0% ≤ Ni ≤ 0,25% 0,5% ≤ Cr ≤ 1,20% 0,08% ≤ Mo ≤ 0,13% 0% ≤ Cu ≤ 0,25% 0,003% ≤ Al ≤ 0,035% 0% ≤ Ti ≤ 0,035% 0% ≤ V ≤ 0,10% 0% ≤ Nb ≤ 0,06% 0,0008% ≤ B ≤ 0,0040% 0,0060% ≤ N ≤ 0,011% éventuellement un ou plusieurs éléments pris parmi Te jusqu'à 0,010%, Se jusqu'à 0,025%, Bi jusqu'à 0,13%, Pb jusqu'à 0,090%, Ca jusqu'à 0,0040% le reste étant du fer et des impuretés résultant de l'élaboration, la composition chimique satisfaisant en outre les relations : Mn + Cr + Mo ≥ 2,1% 0,015% ≤ V + Nb + Ti ≤ 0,13% Al + Ti ≥ 0,020% Mn/S ≥ 12 Steel product characterized in that it has a bainitic structure, in that its mechanical characteristics at 20 ° C are: Rm ≥ 1000 MPa Rp0.2 / Rm ≥ 0.78 Z ≥ 55% Km ≥ 45 J / cm 2 and in that it consists of a steel whose chemical composition comprises, by weight: 0.06% ≤ C ≤ 0.11% 1% ≤ Mn ≤ 1.7% 0.15% ≤ If ≤ 0.40% 0.025% ≤ S ≤ 0.10% P ≤ 0.025% 0% ≤ Ni ≤ 0.25% 0.5% ≤ Cr ≤ 1.20% 0.08% ≤ Mo ≤ 0.13% 0% ≤ Cu ≤ 0.25% 0.003% ≤ Al ≤ 0.035% 0% ≤ Ti ≤ 0.035% 0% ≤ V ≤ 0.10% 0% ≤ Nb ≤ 0.06% 0.0008% ≤ B ≤ 0.0040% 0.0060% ≤ N ≤ 0.011% possibly one or more elements taken from Te up to 0.010%, Se up to 0.025%, Bi up to 0.13%, Pb up to 0.090%, Ca up to 0.0040% the rest being iron and impurities resulting from the preparation, the chemical composition further satisfying the relationships: Mn + Cr + Mo ≥ 2.1% 0.015% ≤ V + Nb + Ti ≤ 0.13% Al + Ti ≥ 0.020% Mn / S ≥ 12 Produit sidérurgique selon la revendication 1 caractérisé en ce que sa dimension caractéristique est comprise entre 10 mm et 50 mm. Steel product according to claim 1 characterized in that its characteristic dimension is between 10 mm and 50 mm. Procédé pour la fabrication d'un produit sidérurgique selon la revendication 1 ou la revendication 2 caractérisé en ce que : on se procure un demi produit en acier dont la composition chimique comprend, en poids : 0,06% ≤ C ≤ 0,11% 1% ≤ Mn ≤ 1,7% 0,15% ≤ Si ≤ 0,40% 0,025% ≤ S ≤ 0,10% P ≤ 0,025% 0% ≤ Ni ≤ 0,25% 0,5% ≤ Cr ≤ 1,20% 0,08% ≤ Mo ≤ 0,13% 0% ≤ Cu ≤ 0,25% 0,003% ≤ Al ≤ 0,035% 0% ≤ Ti ≤ 0,035% 0% ≤ V ≤ 0,10% 0% ≤ Nb ≤ 0,06% 0,0008% ≤ B ≤ 0,0040% 0,0060% ≤ N ≤ 0,011% éventuellement un ou plusieurs éléments pris parmi Te jusqu'à 0,010%, Se jusqu'à 0,025%, Bi jusqu'à 0,13%, Pb jusqu'à 0,090%, Ca jusqu'à 0,0040% le reste étant du fer et des impuretés résultant de l'élaboration, la composition chimique satisfaisant en outre les relations : Mn + Cr + Mo ≥ 2,1% 0,015% ≤ V + Nb + Ti ≤ 0,13% Al + Ti ≥ 0,020% Mn/S ≥ 12, on chauffe le demi produit jusqu'à une température supérieure à 1000°C et on le lamine pour former un produit sidérurgique, directement après laminage, on refroidit le produit sidérurgique à une vitesse de refroidissement moyenne supérieure ou égale à 0,5 °C/s jusqu'à une température inférieure ou égale à Ms - 350°, Ms étant la température maximale de début de transformation martensitique de l'acier, on réchauffe le produit sidérurgique jusqu'à une température supérieure à Ac3 et comprise entre 910 °C et 980 °C, et on le refroidit à une vitesse de refroidissement moyenne comprise entre 17 °C/s et 150 °C/s jusqu'à une température inférieure ou égale à Bs - 450°, puis on le laisse refroidir jusqu'à la température ambiante. Process for the production of a steel product according to claim 1 or claim 2 characterized in that: a semi-finished steel product is obtained, the chemical composition of which comprises, by weight: 0.06% ≤ C ≤ 0.11% 1% ≤ Mn ≤ 1.7% 0.15% ≤ If ≤ 0.40% 0.025% ≤ S ≤ 0.10% P ≤ 0.025% 0% ≤ Ni ≤ 0.25% 0.5% ≤ Cr ≤ 1.20% 0.08% ≤ Mo ≤ 0.13% 0% ≤ Cu ≤ 0.25% 0.003% ≤ Al ≤ 0.035% 0% ≤ Ti ≤ 0.035% 0% ≤ V ≤ 0.10% 0% ≤ Nb ≤ 0.06% 0.0008% ≤ B ≤ 0.0040% 0.0060% ≤ N ≤ 0.011% possibly one or more elements taken from Te up to 0.010%, Se up to 0.025%, Bi up to 0.13%, Pb up to 0.090%, Ca up to 0.0040% the rest being iron and impurities resulting from the preparation, the chemical composition further satisfying the relationships: Mn + Cr + Mo ≥ 2.1% 0.015% ≤ V + Nb + Ti ≤ 0.13% Al + Ti ≥ 0.020% Mn / S ≥ 12, the semi-finished product is heated to a temperature above 1000 ° C. and is laminated to form a steel product, directly after rolling, the steel product is cooled at an average cooling rate greater than or equal to 0.5 ° C / s to a temperature less than or equal to Ms - 350 °, Ms being the maximum temperature at the start of martensitic transformation steel, the steel product is heated to a temperature above Ac 3 and between 910 ° C and 980 ° C, and it is cooled at an average cooling rate of between 17 ° C / s and 150 ° C / s to a temperature less than or equal to Bs - 450 °, then it is allowed to cool to room temperature. Procédé pour la fabrication d'un produit sidérurgique selon la revendication 1 ou la revendication 2 caractérisé en ce que : on se procure un demi produit en acier dont la composition chimique comprend, en poids : 0,06% ≤ C ≤ 0,11% 1% ≤ Mn ≤1,7% 0,15% ≤ Si ≤ 0,40% 0,025% ≤ S ≤ 0,10% P ≤ 0,025% 0% ≤ Ni ≤ 0,25% 0,5% ≤ Cr ≤ 1,20% 0,08% ≤ Mo ≤ 0,13% 0% ≤ Cu ≤ 0,25% 0,003% ≤ Al ≤ 0,035% 0% ≤ Ti ≤ 0,035% 0% ≤ V ≤ 0,10% 0% ≤ Nb ≤ 0,06% 0,0008% ≤ B ≤ 0,0040% 0,0060% ≤ N ≤ 0,011% éventuellement un ou plusieurs éléments pris parmi Te jusqu'à 0,010%, Se jusqu'à 0,025%, Bi jusqu'à 0,13%, Pb jusqu'à 0,090%, Ca jusqu'à 0,0040% le reste étant du fer et des impuretés résultant de l'élaboration, la composition chimique satisfaisant en outre les relations : Mn + Cr + Mo ≥ 2,1% 0,015% ≤ V + Nb + Ti ≤ 0,13% Al + Ti ≥ 0,020% Mn/S ≥ 12 on chauffe le demi produit jusqu'à une température supérieure à 1000°C et on le lamine pour former un produit sidérurgique qu'on laisse refroidir naturellement jusqu'à une température comprise entre 920 °C et 980 °C, et on refroidit le produit sidérurgique à une vitesse de refroidissement moyenne comprise entre 17 °C/s et 150 °C/s jusqu'à une température inférieure ou égale à Bs - 400°, Bs étant la température de début de transformation bainitique de l'acier à la vitesse de refroidissement effective, puis on le laisse refroidir jusqu'à la température ambiante. Process for the production of a steel product according to claim 1 or claim 2 characterized in that: a semi-finished steel product is obtained, the chemical composition of which comprises, by weight: 0.06% ≤ C ≤ 0.11% 1% ≤ Mn ≤1.7% 0.15% ≤ If ≤ 0.40% 0.025% ≤ S ≤ 0.10% P ≤ 0.025% 0% ≤ Ni ≤ 0.25% 0.5% ≤ Cr ≤ 1.20% 0.08% ≤ Mo ≤ 0.13% 0% ≤ Cu ≤ 0.25% 0.003% ≤ Al ≤ 0.035% 0% ≤ Ti ≤ 0.035% 0% ≤ V ≤ 0.10% 0% ≤ Nb ≤ 0.06% 0.0008% ≤ B ≤ 0.0040% 0.0060% ≤ N ≤ 0.011% possibly one or more elements taken from Te up to 0.010%, Se up to 0.025%, Bi up to 0.13%, Pb up to 0.090%, Ca up to 0.0040% the rest being iron and impurities resulting from the preparation, the chemical composition further satisfying the relationships: Mn + Cr + Mo ≥ 2.1% 0.015% ≤ V + Nb + Ti ≤ 0.13% Al + Ti ≥ 0.020% Mn / S ≥ 12 the semi-finished product is heated to a temperature above 1000 ° C. and it is laminated to form a steel product which is allowed to cool naturally to a temperature between 920 ° C. and 980 ° C., and the steel product is cooled at an average cooling rate of between 17 ° C / s and 150 ° C / s to a temperature less than or equal to Bs - 400 °, Bs being the bainitic transformation start temperature of l steel at the effective cooling rate, then allowed to cool to room temperature. Procédé de fabrication d'une pièce de mécanique en acier dont les caractéristiques mécaniques à 20 °C sont : Rm ≥ 1000 MPa Rp0,2 / Rm ≥ 0,78 Z ≥ 55 % Km ≥ 45 J/cm2 caractérisé en ce qu'on se procure un produit sidérurgique selon la revendication 1 et en ce qu'on effectue un usinage.Method for manufacturing a steel mechanical part, the mechanical characteristics of which at 20 ° C are: Rm ≥ 1000 MPa Rp0.2 / Rm ≥ 0.78 Z ≥ 55% Km ≥ 45 J / cm 2 characterized in that a steel product is obtained according to claim 1 and in that a machining is carried out.
EP97402787A 1996-11-26 1997-11-20 Steel product made from bainitic steel and process for making the steel product Expired - Lifetime EP0845544B1 (en)

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FR9614434A FR2756298B1 (en) 1996-11-26 1996-11-26 STEEL AND METHOD FOR THE MANUFACTURE OF A MECHANICAL PART HAVING A BATH STRUCTURE

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2802607A1 (en) 1999-12-15 2001-06-22 Inst Francais Du Petrole FLEXIBLE DRIVING HAVING LOW CARBON STEEL ARMORS
EP1138796A1 (en) * 2000-03-29 2001-10-04 Usinor High strength hot rolled steel with high yield strength for use in the car industry
US6818072B2 (en) * 2001-07-19 2004-11-16 Mitsubishi Heavy Industries, Ltd. High-strength heat-resistant steel, process for producing the same, and process for producing high-strength heat-resistant pipe
EP2103704A1 (en) 2008-03-10 2009-09-23 Swiss Steel AG Hot-rolled long product and method for its manufacture
FR2958660A1 (en) * 2010-04-07 2011-10-14 Ascometal Sa STEEL FOR MECHANICAL PIECES WITH HIGH CHARACTERISTICS AND METHOD FOR MANUFACTURING THE SAME.
EP2453027A1 (en) 2010-11-10 2012-05-16 Swiss Steel AG Thermoformed product and method for producing same
CN1860249B (en) * 2003-09-30 2012-09-19 新日本制铁株式会社 High-yield-ratio high-strength thin steel sheet and high-yield-ratio high-strength hot-dip galvanized thin steel sheet excelling in weldability and ductility as well as high-yield-ratio high-strength alloyed hot-dip galvanized thin steel sheet and manufacture method thereof
WO2013117953A1 (en) * 2012-02-10 2013-08-15 Ascometal Process for making a steel part, and steel part so obtained

Families Citing this family (1)

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Publication number Priority date Publication date Assignee Title
US20160138142A1 (en) 2014-11-18 2016-05-19 Air Liquide Large Industries U.S. Lp Materials of construction for use in high pressure hydrogen storage in a salt cavern

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Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2802607A1 (en) 1999-12-15 2001-06-22 Inst Francais Du Petrole FLEXIBLE DRIVING HAVING LOW CARBON STEEL ARMORS
EP1138796A1 (en) * 2000-03-29 2001-10-04 Usinor High strength hot rolled steel with high yield strength for use in the car industry
FR2807068A1 (en) * 2000-03-29 2001-10-05 Usinor HOT ROLLED STEEL HAVING A VERY HIGH LIMIT OF ELASTICITY AND MECHANICAL STRENGTH USED ESPECIALLY FOR THE PRODUCTION OF PARTS OF MOTOR VEHICLES
US6818072B2 (en) * 2001-07-19 2004-11-16 Mitsubishi Heavy Industries, Ltd. High-strength heat-resistant steel, process for producing the same, and process for producing high-strength heat-resistant pipe
CN1860249B (en) * 2003-09-30 2012-09-19 新日本制铁株式会社 High-yield-ratio high-strength thin steel sheet and high-yield-ratio high-strength hot-dip galvanized thin steel sheet excelling in weldability and ductility as well as high-yield-ratio high-strength alloyed hot-dip galvanized thin steel sheet and manufacture method thereof
EP2103704A1 (en) 2008-03-10 2009-09-23 Swiss Steel AG Hot-rolled long product and method for its manufacture
CN102985569A (en) * 2010-04-07 2013-03-20 阿斯科麦托有限公司 Mechanical part made of steel having high properties and process for manufacturing same
FR2958660A1 (en) * 2010-04-07 2011-10-14 Ascometal Sa STEEL FOR MECHANICAL PIECES WITH HIGH CHARACTERISTICS AND METHOD FOR MANUFACTURING THE SAME.
WO2011124851A3 (en) * 2010-04-07 2015-06-25 Ascometal Mechanical part made of steel having high properties and process for manufacturing same
CN102985569B (en) * 2010-04-07 2015-08-05 阿斯科麦托有限公司 Mechanical part be made up of the steel of high characteristic and preparation method thereof
EP2453026A1 (en) 2010-11-10 2012-05-16 Swiss Steel AG Thermoformed steel product and method for producing same
EP2453027A1 (en) 2010-11-10 2012-05-16 Swiss Steel AG Thermoformed product and method for producing same
WO2013117953A1 (en) * 2012-02-10 2013-08-15 Ascometal Process for making a steel part, and steel part so obtained

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ATE230443T1 (en) 2003-01-15
NO975392L (en) 1998-05-27
DE69718132T2 (en) 2003-10-09
DE69718132D1 (en) 2003-02-06
FR2756298A1 (en) 1998-05-29
ES2190514T3 (en) 2003-08-01
NO975392D0 (en) 1997-11-24
FR2756298B1 (en) 1998-12-24

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