EP0469115A1 - Agent for improving the resistance to hydrogen cracking of low or medium alloy steels, a method for using said agent, and parts thereby obtained - Google Patents

Agent for improving the resistance to hydrogen cracking of low or medium alloy steels, a method for using said agent, and parts thereby obtained

Info

Publication number
EP0469115A1
EP0469115A1 EP91904295A EP91904295A EP0469115A1 EP 0469115 A1 EP0469115 A1 EP 0469115A1 EP 91904295 A EP91904295 A EP 91904295A EP 91904295 A EP91904295 A EP 91904295A EP 0469115 A1 EP0469115 A1 EP 0469115A1
Authority
EP
European Patent Office
Prior art keywords
cobalt
steels
less
parts
agent
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91904295A
Other languages
German (de)
French (fr)
Inventor
Régis BLONDEAU
Jean Beguinot
Philippe Bourges
Lionel Coudreuse
Gilbert Primon
Jacques Charles
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.)
Creusot Loire SA
Creusot Loire Industrie SA
Original Assignee
Creusot Loire SA
Creusot Loire Industrie SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Creusot Loire SA, Creusot Loire Industrie SA filed Critical Creusot Loire SA
Publication of EP0469115A1 publication Critical patent/EP0469115A1/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
    • 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
    • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt

Definitions

  • Agent for improving the resistance to cracking by hydrogen of low or medium alloyed steels process for using this agent and parts obtained.
  • the present invention relates to an agent for improving the resistance to cracking by hydrogen of boilermaking steels e / or of weakly alloyed construction usable in particular in hydrogenated media such as gases enriched in H2S and for also improving the weldability of these steels and their aptitude for flame cutting or cutting with a plasma torch.
  • European patent EP-0021349 proposes a high yield strength steel containing Cobalt to improve the resistance to hydrogen cracking induced by the presence of H 2 S.
  • this patent relates to steels for thin-walled tubes (at most a few millimeters). This patent indicates that the Cobalt acts by forming a layer enriched with Cobalt on the surface of the steel, slowing down the penetration of hydrogen due to corrosion by H2S.
  • This barrier is all the better formed the faster the austenitization before quenching.
  • the object of the invention is therefore to find a means which makes it possible to improve the resistance to hydrogen embrittlement of steels used in particular in very thick areas and therefore containing segregated zones, while in particular allowing to meet the building codes of pressurized boilers, that hydrogen is introduced into the metal by corrosion in an acid medium, such as wet I ⁇ 2S, or during welding or thermal cutting operations; therefore, the object of the invention is also to improve the weldability and the cutting ability.
  • the object of the invention is an agent intended to improve the resistance to cracking by hydrogen of the steels used in particular in hydrogenated medium, also intended to improve the weldability and 1 • aptitude for cutting by thermal means of these steels in particular when they are intended to produce very thick parts.
  • This agent is Cobalt added in weight contents of between 0.05% and 2%.
  • the invention also relates to low-alloy steels intended in particular for the production of boilers assemblies used in environments enriched in H2S, with improved weldability and cuttability whose chemical composition by weight comprises from 0.05% to 0.6% of Carbon and less than 10% of alloying elements taken in particular from Silicon, Manganese, Nickel, Chromium, Molybdenum and in which 0.05% to 2% by weight of Cobalt has been added, the remainder consisting of iron and residual impurities resulting from the melting of the materials in the preparation.
  • the chemical composition by weight of these steels comprises: - from 0.05% to 0.6% of Carbon
  • carburogenic elements such as Vanadium or Niobium can be added in contents up to 0.2%.
  • steels correspond in particular to steels:
  • class 1 - A 633 all grades defined by the American standard ASTM or the equivalent grades of other standards to which 0.05% to 2% of Cobalt has been added; the use of these steels is imposed by the ASME code for the construction of pressure vessels.
  • the invention also relates to a method of manufacturing blocks, plates, bars, tubes or parts according to which or where a steel is produced in accordance with the invention, this steel is shaped either by molding of parts, or by hot plastic deformation of ingots, slabs, bars, billets or the like for obtaining blocks, plates, bars, tubes or molded parts, said plates, bars, tubes or parts undergo a normalization heat treatment at a temperature higher than AC3 and possibly an income at a temperature below AC ⁇ .
  • the blocks, plates, bars, tubes or parts undergo a quenching treatment followed by tempering.
  • the invention finally relates to any block, plate, bar, tube or part made of steel object of the invention using the method according to the invention, said blocks, plates, bars, tubes or parts having good resistance to cracking by hydrogen, good weldability and good ability to cut by thermal processes.
  • - Fig.2 * is a diagram giving the stress crack limits measured on weld test specimens made with the steels taken as an example
  • Fig.3 is a generalization of the results of Fig.2 obtained for a plurality of steels differentiating in particular by their carbon content.
  • cracking can be induced in weakly or moderately alloyed steels by the presence of hydrogen carried by phenomena of the corrosion type in particular when the steel is in contact with gas. enriched in H2S, which reduces the service life of installations working in such conditions.
  • Hydrogen can also be supplied either by a soldering operation, or by a thermal cutting operation, in particular by conventional flame cutting or using a torch. plasma; a steel sensitive to hydrogen will therefore see its weldability or its cutability, that is to say its aptitude to be welded or cut without the appearance of cracked, reduced.
  • weakly or moderately alloyed steel means all the steels used in particular in boiler making which contain from 0.05% to 0.6% of Carbon and less than 10% of alloying elements taken non-exclusively from the silicon, manganese, nickel, chromium, molybdenum, vanadium.
  • the sensitivity to cracking by hydrogen is linked in particular to the presence of .segregations, that is to say zones whose the chemical composition is richer in Carbon and alloying elements than the average composition of steels.
  • the phenomenon already becomes sensitive when the thickness of a sheet exceeds 5 mm and becomes very sensitive when thicknesses of 100 mm are reached or exceeded.
  • Segregation accentuates the sensitivity of steel to hydrogen cracking because these are areas whose behavior during thermal cycles experienced by blocks, plates, bars, tubes or parts, is not the same as the average behavior of steel.
  • the segregated zones can be "hardened” and have a rough martensitic structure of very hard hardening and very sensitive to hydrogen.
  • the segregated areas are harder and more fragile than the mass of the blocks or parts.
  • Cobalt has been found to decrease the harmful effects of these segregated areas. Cobalt acts by two mechanisms: - First of all in the mass of the blocks or parts, it is capable of trapping the hydrogen, which limits the hydrogen capable of reaching the segregated areas. - on the other hand, and above all, Cobalt is an element which reduces the hardenability of the steel; this is what is seen in FIG.
  • Cobalt which, added in contents of between 0.05% and 2% to low and medium alloyed steels, improves the resistance to cracking by hydrogen and consequently, the weldability and the ability to cut by thermal means such as 1'oxycou ⁇ page.
  • the steel taken as an example for Fig.l has the following composition:
  • the difference between the non-cracking constraints for steels with and without Cobalt is approximately 100 MPa when the carbon content is approximately 0.150% and 50 MPa when this content is approximately 0.2%. .
  • Cobalt Since the effect of Cobalt is sensitive to the carbon content, this effect can be improved by introducing into the steel carburogenic elements such as Vanadium and Niobium, in contents less than or equal to 0.2%. Indeed, these elements, by forming carbides decrease the content of "free" Carbon which alone has an unfavorable effect. The Cobalt content can also be increased. Naturally, the addition of Cobalt in no way prevents the use of the means known to those skilled in the art for reducing the sensitivity to cracking by hydrogen. These means being in particular good cleanliness of the steel (non-metallic inclusions reduced to a minimum).
  • the invention also relates to the method which makes it possible to produce blocks, plates, bars, tubes or parts using a steel into which Cobalt has been introduced as an agent reducing the sensitivity to embrittlement by hydrogen.
  • This process consists of:
  • the invention finally relates to any block, plate, bar, tube or part obtained by the process which has just been described using a steel to which Cobalt has been added as an agent reducing the sensitivity to cracking by hydrogen.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Arc Welding In General (AREA)
  • Heat Treatment Of Articles (AREA)

Abstract

L'agent considéré est du Cobalt ajouté en des teneurs comprises entre 0,05 % et 2 % à des aciers contenant de 0,05 % à 0,6 % de Carbone et moins de 10 % d'éléments d'alliage, pris parmi le Silicium, le Manganèse, le Nickel, le Chrome et le Molybdène, pour réaliser des blocs, plaques, barres ou pièces de forte dimension éventuellement normalisés, à résistance à la fissuration par l'hydrogène améliorée et à soudabilité et découpabilité thermique améliorées. L'invention est également relative à un procédé d'utilisation de l'agent et aux pièces ainsi obtenues.The agent considered is cobalt added in contents of between 0.05% and 2% to steels containing from 0.05% to 0.6% of carbon and less than 10% of alloying elements, taken from among Silicon, Manganese, Nickel, Chromium and Molybdenum, to produce blocks, plates, bars or large-sized parts that may be standardized, with improved resistance to hydrogen cracking and improved weldability and thermal cuttability. The invention also relates to a method of using the agent and to the parts thus obtained.

Description

Agent pour améliorer la résistance à la fissuration par l'hydrogène d'aciers faiblement ou moyennement alliés, procédé d'utilisation de cet agent et pièces obtenues.Agent for improving the resistance to cracking by hydrogen of low or medium alloyed steels, process for using this agent and parts obtained.
La présente invention concerne un agent pour améliorer la résistance à la fissuration par l'hydrogène des aciers de chaudronnerie e /ou de construction fai¬ blement alliés utilisables notamment dans des milieux hydrogénés tels que des gaz enrichis en H2S et pour améliorer également la soudabilitê de ces aciers et leur aptitude à l'oxycoupage ou au découpage au chalumeau à plasma.The present invention relates to an agent for improving the resistance to cracking by hydrogen of boilermaking steels e / or of weakly alloyed construction usable in particular in hydrogenated media such as gases enriched in H2S and for also improving the weldability of these steels and their aptitude for flame cutting or cutting with a plasma torch.
Il est bien connu que 1'acier est sensible à la présence d'hydrogène qui peut induire des fissura¬ tions inacceptables. Cet hydrogène peut résulter de l'élaboration de l'acier, être introduit par un méca¬ nisme du type corrosion, en particulier lorsque l'acier est utilisé dans un milieu contenant de IΗ2S, ou encore lors d'opérations de soudage ou de découpage par oxycou- page classique ou au chalumeau à plasma.It is well known that steel is sensitive to the presence of hydrogen which can induce unacceptable cracking. This hydrogen can result from the production of steel, be introduced by a mechanism of the corrosion type, in particular when the steel is used in a medium containing IΗ2S, or also during welding or cutting operations. by conventional oxycoupling or with a plasma torch.
Cette sensibilité de 1'acier est accentuée par la présence de zones ségrégées contenant plus de carbone et d'éléments d'alliage que la composition moyenne. Ces zones ségrégées sont d'autant plus impor¬ tantes que 1'acier est utilisé sous forme de produits massifs par exemple de tôles dont 1'épaisseur va de 5 mm à quelques centaines de millimètres.This sensitivity of steel is accentuated by the presence of segregated zones containing more carbon and alloying elements than the average composition. These segregated areas are all the more important as steel is used in the form of solid products, for example sheets whose thickness ranges from 5 mm to a few hundred millimeters.
Pour diminuer cette sensibilité de 1'acier à la fissuration à l'hydrogène, l'homme de métier sait qu'il faut en combinaison ou séparément réduire au maximum les inclusions non métalliques, réduire la teneur en éléments d'alliage aux teneurs minimales nécessaires pour obtenir les caractéristiques mécaniques souhaitées et, de préférence, faire un traitement ther¬ mique de trempe et de revenu pour obtenir une structure martensitique revenue.To reduce this sensitivity of steel to hydrogen cracking, those skilled in the art know that, in combination or separately, it is necessary to reduce non-metallic inclusions as much as possible, reduce the content of alloying elements to the minimum necessary contents. to obtain the desired mechanical characteristics and, preferably, to carry out a thermal treatment of quenching and tempering to obtain a tempered martensitic structure.
Cependant, les codes de construction d'ap¬ pareils à pression, le code ASME par exemple, n'autori- sent pas toujours l'utilisation d'aciers trempés reve¬ nus.However, the building codes of pressure vessels, the ASME code for example, does not allow not always feel the use of bare tempered steels.
Le fait d'abaisser au minimum les teneurs en éléments d'alliage rend souvent difficile l'obtention des caractéristiques mécaniques imposées par les mêmes codes.Lowering the contents of alloying elements to a minimum often makes it difficult to obtain the mechanical characteristics imposed by the same codes.
Le brevet européen EP-0021349 propose un acier à haute limite d'élasticité contenant du Cobalt pour améliorer la résistance à la fissuration par l'hydrogène induite par la présence d'H2S.European patent EP-0021349 proposes a high yield strength steel containing Cobalt to improve the resistance to hydrogen cracking induced by the presence of H 2 S.
Mais ce brevet exige que l'acier soit trempé et revenu.But this patent requires that the steel be quenched and tempered.
De plus, il indique clairement que l'opération de trempe doit être faite après une austénitisation très rapide, à une vitesse de l'ordre de 2°C/S, ce qui limite cet acier à des applications utilisant des produits minces donc exempts de zones ségrégées importantes. En fait, ce brevet concerne des aciers pour tubes à parois minces (au plus quelques millimètres). Ce brevet indique que le Cobalt agirait en formant à la surface de l'acier une couche enrichie en Cobalt, ralentissant la pénétration d'hydrogène du fait de la corrosion par 1'H2S.In addition, it clearly indicates that the quenching operation must be carried out after a very rapid austenitization, at a speed of the order of 2 ° C / S, which limits this steel to applications using thin products therefore free of important segregated areas. In fact, this patent relates to steels for thin-walled tubes (at most a few millimeters). This patent indicates that the Cobalt acts by forming a layer enriched with Cobalt on the surface of the steel, slowing down the penetration of hydrogen due to corrosion by H2S.
Cette barrière est d'autant mieux formée que 1'austénitisation avant trempe est plus rapide.This barrier is all the better formed the faster the austenitization before quenching.
Ce brevet explique également que 1'effet du Cobalt est très faible lorsque la structure est de la ferrite perlite obtenue soit par normalisation soit par laminage contrôlé. Enfin, il ne dit rien de l'influence du Cobalt sur le soudage et sur 1'aptitude au découpage par oxy- coupage ou au plasma.This patent also explains that the effect of Cobalt is very weak when the structure is perlite ferrite obtained either by normalization or by controlled rolling. Finally, he says nothing about the influence of Cobalt on welding and on the ability to cut by oxygen cutting or plasma.
Le problème soulevé précédemment reste donc entier. Le but de l'invention est donc de trouver un moyen permettant d'améliorer la résistance à la fragili¬ sation par l'hydrogène d'aciers utilisés notamment en forte épaisseur et contenant de ce fait des zones ségré- gées, tout en permettant notamment de satisfaire aux codes de construction d'appareils chaudronnés à pres¬ sion, que l'hydrogène soit introduit dans le métal par une corrosion en milieu acide, tel que IΗ2S humide, ou lors d'opérations de soudage ou de découpage par voie thermique; de ce fait, le but de l'invention est égale¬ ment d'améliorer la soudabilité et 1'aptitude au décou¬ page.The problem raised above therefore remains unresolved. The object of the invention is therefore to find a means which makes it possible to improve the resistance to hydrogen embrittlement of steels used in particular in very thick areas and therefore containing segregated zones, while in particular allowing to meet the building codes of pressurized boilers, that hydrogen is introduced into the metal by corrosion in an acid medium, such as wet IΗ2S, or during welding or thermal cutting operations; therefore, the object of the invention is also to improve the weldability and the cutting ability.
L'objet de lîinvention est un agent destiné à améliorer la résistance à la fissuration par l'hydrogène des aciers utilisés notamment en milieu hydrogénés, destiné également a améliorer la soudabilité et 1•ap¬ titude au découpage par des moyens thermiques de ces aciers notamment lorsqu'ils sont destinés à réaliser des pièces de forte épaisseur. Cet agent est du Cobalt ajouté en des teneurs pondérales comprises entre 0,05% et 2%.The object of the invention is an agent intended to improve the resistance to cracking by hydrogen of the steels used in particular in hydrogenated medium, also intended to improve the weldability and 1 • aptitude for cutting by thermal means of these steels in particular when they are intended to produce very thick parts. This agent is Cobalt added in weight contents of between 0.05% and 2%.
L'invention concerne également des aciers faiblement alliés destinés notamment à la réalisation d'ensembles chaudronnés utilisés dans des milieux en- richis en H2S, à soudabilité et découpabilité améliorée dont la composition chimique pondérale comporte de 0,05% à 0,6% de Carbone et moins de 10% d'éléments d'alliage pris notamment parmi le Silicium, le Manganèse, le Nickel, le Chrome, le Molybdène et dans lesquels on a ajouté en outre de 0,05% à 2% en poids de Cobalt, le reste étant constitué par du fer et des impuretés rési¬ duelles résultant de la fusion des matières à 1'élabora¬ tion.The invention also relates to low-alloy steels intended in particular for the production of boilers assemblies used in environments enriched in H2S, with improved weldability and cuttability whose chemical composition by weight comprises from 0.05% to 0.6% of Carbon and less than 10% of alloying elements taken in particular from Silicon, Manganese, Nickel, Chromium, Molybdenum and in which 0.05% to 2% by weight of Cobalt has been added, the remainder consisting of iron and residual impurities resulting from the melting of the materials in the preparation.
De façon préférentielle, la composition chimi- que pondérale de ces aciers comprend : - de 0,05% à 0,6% de CarbonePreferably, the chemical composition by weight of these steels comprises: - from 0.05% to 0.6% of Carbon
- moins de 1% de Silicium- less than 1% of Silicon
- moins de 2% de Manganèse- less than 2% of Manganese
- moins de 6% de Nickel - moins de 6% de Chrome- less than 6% of Nickel - less than 6% of Chromium
- moins de 2% de Molybdène- less than 2% of Molybdenum
- de 0,05% à 2% de Cobalt- from 0.05% to 2% of Cobalt
De préférence, on peut ajouter des éléments carburigènes tels que le Vanadium ou le Niobium en des teneurs pouvant atteindre 0,2%.Preferably, carburogenic elements such as Vanadium or Niobium can be added in contents up to 0.2%.
Ces aciers correspondent notamment aux aciers:These steels correspond in particular to steels:
- A 516 tous grades- A 516 all grades
- A 515 tous grades- A 515 all grades
- A 537 classe 1 - A 633 tous grades définis par la norme américaine ASTM ou les nuances équivalentes des autres normes auxquels on a ajouté de 0,05% à 2% de Cobalt; l'utilisation de ces aciers est imposée par le code ASME de construction d'appareils à pression.- A 537 class 1 - A 633 all grades defined by the American standard ASTM or the equivalent grades of other standards to which 0.05% to 2% of Cobalt has been added; the use of these steels is imposed by the ASME code for the construction of pressure vessels.
L'invention concerne également un procédé de fabrication de blocs, plaques, barres, tubes ou pièces selon lequel ou élabore un acier conforme à 1'invention, on met en forme cet acier soit par moulage de pièces, soit par déformation plastique à chaud de lingots, brames, barres, billettes ou analogue pour obtenir des blocs, des plaques, des barres, des tubes ou des pièces moulées, lesdits plaques, barres, tubes ou pièces subis¬ sent un traitement thermique de normalisation à une température supérieure à AC3 et éventuellement un revenu à une température inférieure à AC^.The invention also relates to a method of manufacturing blocks, plates, bars, tubes or parts according to which or where a steel is produced in accordance with the invention, this steel is shaped either by molding of parts, or by hot plastic deformation of ingots, slabs, bars, billets or the like for obtaining blocks, plates, bars, tubes or molded parts, said plates, bars, tubes or parts undergo a normalization heat treatment at a temperature higher than AC3 and possibly an income at a temperature below AC ^.
Dans un autre mode de réalisation, les blocs, plaques, barres, tubes ou pièces subissent un traitement de trempe suivi d'un revenu. L'invention concerne enfin tout bloc, plaque, barre, tube ou pièce réalisé en acier objet de l'inven¬ tion à l'aide du procédé selon l'invention, lesdits blocs, plaques, barres, tubes ou pièces présentant une bonne résistance à la fissuration par l'hydrogène, une bonne soudabilité et une bonne aptitude au découpage par des procédés thermiques.In another embodiment, the blocks, plates, bars, tubes or parts undergo a quenching treatment followed by tempering. The invention finally relates to any block, plate, bar, tube or part made of steel object of the invention using the method according to the invention, said blocks, plates, bars, tubes or parts having good resistance to cracking by hydrogen, good weldability and good ability to cut by thermal processes.
La plus p'etite dimension de ces blocs, pla¬ ques, barres, tubes ou pièces étant supérieure ou égale à 5 mm, et dans certains modes de réalisation, cette plus petite dimension est supérieure ou égale à 200 mm.The smallest dimension of these blocks, plates, bars, tubes or parts being greater than or equal to 5 mm, and in certain embodiments, this smaller dimension is greater than or equal to 200 mm.
L'invention sera mieux comprise à l'aide de la description qui va suivre, donnée uniquement à titre d'exemple et faite en se référant aux dessins annexés, sur lesquels : - la Fig.l représente' des diagrammes de trans¬ formation en refroidissement continu (TRC) pour deux aciers pris en exemple;The invention will be better understood with the aid of the description which follows, given solely by way of example and made with reference to the appended drawings, in which: - Fig.l represents' diagrams of transformation into continuous cooling (TRC) for two example steels;
- la Fig.2*est un diagramme donnant les con¬ traintes limites de fissuration mesurées sur des éprou- vettes d'essai de soudure réalisées avec les aciers pris en exemple;- Fig.2 * is a diagram giving the stress crack limits measured on weld test specimens made with the steels taken as an example;
- la Fig.3 est une généralisation des résul¬ tats de la Fig.2 obtenue pour une pluralité d'aciers se différenciant en particulier pair leur teneur en carbone. Comme il a été indiqué plus haut, des fis¬ sures peuvent être induites dans les aciers faiblement ou moyennement alliés par la présence d'hydrogène ap¬ porté par des phénomènes du type corrosion en particu¬ lier lorsque 1'acier est au contact de gaz enrichis en H2S, ce qui réduit la tenue en service des installations travaillant dans de telles conditions. L'hydrogène peut être également apporté soit par une opération de souda¬ ge, soit par une opération de -découpe thermique, notam¬ ment par oxycoupage classique ou à 1'aide d'un chalumeau à plasma; un acier sensible à l'hydrogène verra donc sa soudabilité ou sa découpabilité, c'est à dire son ap¬ titude à être soudé ou découpé sans apparition de fis¬ sures, diminuées. Par acier faiblement ou moyennement alliés, on entend tous les aciers utilisés notamment en chaudron¬ nerie qui contiennent de 0,05% à 0,6% de Carbone et moins de 10% d'éléments d'alliage pris de façon non exclusive parmi le silicium, le manganèse, le nickel, le chrome, le molybdène, le vanadium.- Fig.3 is a generalization of the results of Fig.2 obtained for a plurality of steels differentiating in particular by their carbon content. As indicated above, cracking can be induced in weakly or moderately alloyed steels by the presence of hydrogen carried by phenomena of the corrosion type in particular when the steel is in contact with gas. enriched in H2S, which reduces the service life of installations working in such conditions. Hydrogen can also be supplied either by a soldering operation, or by a thermal cutting operation, in particular by conventional flame cutting or using a torch. plasma; a steel sensitive to hydrogen will therefore see its weldability or its cutability, that is to say its aptitude to be welded or cut without the appearance of cracked, reduced. The term “weakly or moderately alloyed steel” means all the steels used in particular in boiler making which contain from 0.05% to 0.6% of Carbon and less than 10% of alloying elements taken non-exclusively from the silicon, manganese, nickel, chromium, molybdenum, vanadium.
A titre indicatif cela recouvre les aciers dont la composition chimique pondérale se trouve à 1'intérieur du domaine suivant :As an indication, this covers steels whose chemical composition by weight is within the following range:
- de 0,05% à 0,6% de Carbone - moins de 1% de Silicium- from 0.05% to 0.6% of Carbon - less than 1% of Silicon
- moins de 2% de Manganèse- less than 2% of Manganese
- moins de 6% de Nickel- less than 6% of Nickel
- moins de 6% de Chrome- less than 6% of Chrome
- moins de 2% de Molybdène Et en particulier, cela recouvre les aciers imposés par les codes de construction pour les appareils à pression tels que le code ASME ou les codes analogues.- less than 2% of Molybdenum And in particular, this covers the steels imposed by the building codes for pressure vessels such as the ASME code or similar codes.
Ces codes font en particulier référence à la norme américaine ASTM qui définit notamment les aciers : - A 516 tous gradesThese codes refer in particular to the American standard ASTM which notably defines steels: - A 516 all grades
- A 515 tous grades- A 515 all grades
- A 537 classe 1- A 537 class 1
- A 633 tous grades- A 633 all grades
Ces aciers, ainsi que les aciers équivalents des autres normes existant dans le monde sont concernés par 1'invention.These steels, as well as equivalent steels of other standards existing in the world, are concerned by the invention.
Pour tous ces aciers, la sensiblité à la fisssuration par l'hydrogène est liée en particulier à la présence de .ségrégations, c'est à dire des zones dont la composition chimique est plus riche en Carbone et en éléments d'alliage que la composition moyenne des aciers.For all these steels, the sensitivity to cracking by hydrogen is linked in particular to the presence of .segregations, that is to say zones whose the chemical composition is richer in Carbon and alloying elements than the average composition of steels.
L'homme de métier sait que ces ségrégations sont d'autant plus importantes que le bloc d'acier ou la pièce est massif, par exemple qu'une tôle est épaisse, qu'une barre a un grand diamètre, etc..Those skilled in the art know that these segregations are all the more important when the steel block or the part is solid, for example that a sheet is thick, that a bar has a large diameter, etc.
A titre indicatif, le phénomène devient déjà sensible lorsque 1'épaisseur d'une tôle dépasse 5 mm et devient très sensible lorsque l'on atteint ou dépasse des épaisseurs de 100 mm.By way of indication, the phenomenon already becomes sensitive when the thickness of a sheet exceeds 5 mm and becomes very sensitive when thicknesses of 100 mm are reached or exceeded.
Les ségrégations accentuent la sensibilité de l'acier à la fissuration par l'hydrogène parce que ce sont des zones dont le comportement au cours des cycles thermiques que subissent les blocs, plaques, barres, tubes ou pièces, n'est pas le même que le comportement moyen de 1'acier.Segregation accentuates the sensitivity of steel to hydrogen cracking because these are areas whose behavior during thermal cycles experienced by blocks, plates, bars, tubes or parts, is not the same as the average behavior of steel.
A titre d'exemple, lors du refroidissement qui suit un traitement de normalisation, alors que la masse de la pièce a une structure du type ferrite-perlite, les zones ségrégées peuvent être "trempées" et avoir une structure martensitique brute de trempe très dure et très sensible à 1'hydrogène.For example, during the cooling which follows a normalization treatment, while the mass of the part has a structure of the ferrite-perlite type, the segregated zones can be "hardened" and have a rough martensitic structure of very hard hardening and very sensitive to hydrogen.
De même, aia cours d'opérations de soudage ou dOxycoupage, au voisinage des joints soudés ou des coupes, l'acier subit un cycle thermique qui peut con¬ duire a des structures martensitiques dures et sensibles à l'hydrogène.Likewise, during welding or oxygen cutting operations, in the vicinity of welded joints or cuts, the steel undergoes a thermal cycle which can lead to hard martensitic structures which are sensitive to hydrogen.
De même, après une trempe et un revenu, les zones ségrégées sont plus dures et plus fragiles que la masse des blocs ou pièces.Similarly, after quenching and tempering, the segregated areas are harder and more fragile than the mass of the blocks or parts.
On a constaté que le Cobalt diminuait les effets néfastes de ces zones ségrégées. Le Cobalt agis¬ sant par deux mécanismes : - tout d'abord dans la masse des blocs ou pièces, il est susceptible de piéger l'hydrogène, ce qui limite 1'hydrogène susceptible d'atteindre les zones ségrégées. - d'autre part, et surtout, le Cobalt est un élément qui diminue la trempabilité de l'acier; c'est ce que l'on voit à la figure 1 dans laquelle la courbe 1 correspond à un acier sans Cobalt et la courbe 2, au même acier auquel on a ajouté 0,15% de Cobalt; la trem- pabilité de 1'acier sans Cobalt correspond à une vitesse critique de trempe de 3 x 10^°C/h alors que pour l'acier au Cobalt, cette vitesse critique est supérieure à 10^°C/h; l'acier au Cobalt est donc beaucoup moins trempant que l'acier sans Cobalt; du fait de cette moindre trempabilité et de la ségrégation du Cobalt, les zones ségrégées seront moins facilement trempées dans l'acier au Cobalt que dans l'acier sans Cobalt, ce qui diminue la sensibilité de 1'acier à la fissuration par 1'hydrogène. L'invention consiste donc en un agent, leCobalt has been found to decrease the harmful effects of these segregated areas. Cobalt acts by two mechanisms: - First of all in the mass of the blocks or parts, it is capable of trapping the hydrogen, which limits the hydrogen capable of reaching the segregated areas. - on the other hand, and above all, Cobalt is an element which reduces the hardenability of the steel; this is what is seen in FIG. 1 in which curve 1 corresponds to a steel without Cobalt and curve 2, to the same steel to which 0.15% of Cobalt has been added; the hardness of steel without Cobalt corresponds to a critical quenching speed of 3 x 10 ^ ° C / h while for Cobalt steel, this critical speed is greater than 10 ^ ° C / h; Cobalt steel is therefore much less quenching than steel without Cobalt; due to this lower quenchability and the segregation of Cobalt, the segregated zones will be less easily quenched in Cobalt steel than in steel without Cobalt, which reduces the sensitivity of steel to cracking by hydrogen. . The invention therefore consists of an agent, the
Cobalt, qui, ajouté en des teneurs comprises entre 0,05% et 2% aux aciers faiblement et moyennement alliés, améliore la résistance à la fissuration par 1'hydrogène et par voie de conséquence, la soudabilité et l'aptitude à la coupe par des moyens thermiques tels que 1'oxycou¬ page. Cet agent agissant :Cobalt, which, added in contents of between 0.05% and 2% to low and medium alloyed steels, improves the resistance to cracking by hydrogen and consequently, the weldability and the ability to cut by thermal means such as 1'oxycou¬ page. This acting agent:
- d'une part en piégeant une partie de 1'hy¬ drogène ;on the one hand by trapping part of the hydrogen;
- d'autre part, en diminuant la trempabilité des zones ségrégées.- on the other hand, by reducing the hardenability of the segregated areas.
L'acier pris en exemple pour la Fig.l a la composition suivante :The steel taken as an example for Fig.l has the following composition:
- 0,2% de Carbone- 0.2% Carbon
- 1,1% de Manganèse - 0,3% de Silicium - 0,25% de Nickel- 1.1% Manganese - 0.3% Silicon - 0.25% Nickel
- 0,15% de Chrome- 0.15% chromium
- 0,05% de Molybdène et 0% de Cobalt dans un cas (courbe 1 de la Fig.l) et 0,15% de Cobalt dans l'autre cas (courbe 2 de la Fig.l). Différents essais comparatifs peuvent être envisagés pour mettre en évidence l'effet du cobalt. On a choisi l'essai de fissuration sur implants, méthode bien connue de l'homme de métier, notamment pour quali- fier la résistance à la fissuration à froid par l'hydro¬ gène, lors des opérations de soudage.- 0.05% of Molybdenum and 0% of Cobalt in one case (curve 1 of Fig.l) and 0.15% of Cobalt in the other case (curve 2 of Fig.l). Different comparative tests can be envisaged to demonstrate the effect of cobalt. The cracking test on implants was chosen, a method well known to those skilled in the art, in particular for qualifying the resistance to cold cracking by hydrogen during welding operations.
Mais cet essai peut permettre également d'éva¬ luer 1'effet du cobalt dans le cas d'opérations d'oxy¬ coupage sur des aciers ou d'aciers subissant une cor- rosion en milieu hydrogéné.However, this test can also make it possible to assess the effect of cobalt in the case of oxy-cutting operations on steels or steels undergoing corrosion in hydrogenated medium.
A cet effet, des simulations sur implants destinées à évaluer la contrainte limite de non-fissura¬ tion ont été réalisées sur deux aciers de compositions analytiques comparables dont 1'une ne comporte pas de cobalt et dont l'autre comporte 0,15% de cobalt. Les résultats sont indiqués à la Fig.2 qui montre que, pour des éprouvettes prises en long comme en travers dans des plaques, la contrainte limite de non fissuration est de:To this end, simulations on implants intended to evaluate the limit stress of non-cracking were carried out on two steels of comparable analytical compositions, one of which does not contain cobalt and the other of which contains 0.15% of cobalt. The results are indicated in Fig. 2 which shows that, for specimens taken lengthwise as well as crosswise in plates, the limiting stress of non-cracking is:
- 100 MPa pour l'acier sans Cobalt - 150 MPa pour l'acier avec du Cobalt- 100 MPa for steel without Cobalt - 150 MPa for steel with Cobalt
Ce qui démontre l'effet favorable du Cobalt. Ce résultat a été confirmé par des essais réalisés sur huit aciers :This demonstrates the favorable effect of Cobalt. This result was confirmed by tests carried out on eight steels:
- deux contenant environ 0,150% de Carbone et 0% de Co - deux contenant environ 0,150% de Carbone et 0,15% de- two containing approximately 0.150% of Carbon and 0% of Co - two containing approximately 0.150% of Carbon and 0.15% of
Co \Co \
- deux contenant enviϋron 0,200% de Carbone et 0% de Co- two containing about 0.200% of Carbon and 0% of Co
- deux contenant environ 0,2% de Carbone et 0,15% de Co- two containing about 0.2% Carbon and 0.15% Co
Les résultats sont indiqués à la Fig.3 et montrent que les aciers au Cobalt ont une contrainte limite de non fissuration plus élevée que les aciers sans Cobalt.The results are shown in Fig. 3 and show that Cobalt steels have a stress higher non-cracking limit than steels without Cobalt.
L'écart entre les contraintes de non fissura¬ tion pour les aciers avec et sans Cobalt est d'environ 100 MPa lorsque la teneur en Carbone est d'environ 0,150% et de 50 MPa lorsque cette teneur est d'environ 0,2%.The difference between the non-cracking constraints for steels with and without Cobalt is approximately 100 MPa when the carbon content is approximately 0.150% and 50 MPa when this content is approximately 0.2%. .
Là encore, l'effet du Cobalt est démontré puisque ce critère de contrainte limite de non fissura- tion intervient aussi bien pour la fissuration par 1'hydrogène induite par une corrosion ou lors d'un oxycoupage que pour celle qui est induite lors d'un soudage et il est à noter que tous les résultats présen¬ tés ont été obtenus sur des échantillons obtenus après normalisation donc, ayant une structure ferrite-perlite hors des zones ségrégées.Here again, the effect of Cobalt is demonstrated since this criterion of limiting stress of non-cracking intervenes as well for the cracking by hydrogen induced by corrosion or during an oxygen cutting as for that which is induced during welding and it should be noted that all the results presented were obtained on samples obtained after normalization therefore, having a ferrite-perlite structure outside of the segregated zones.
L'effet du Cobalt étant sensible à la teneur en Carbone, on peut améliorer cet effet en introduisant dans 1'acier des éléments carburigènes tels que le Vanadium et le Niobium, en des teneurs inférieures ou égales à 0,2%. En effet, ces éléments, en formant des carbures diminuent la teneur en Carbone "libre" qui seul a un effet défavorable. On peut également augmenter la teneur en Cobalt. Naturellement, l'addition de Cobalt n'empêche en rien de mettre en oeuvre les moyens connus de 1'homme de métier pour diminuer la sensibilité à la fissuration par l'hydrogène. Ces moyens étant en particulier une bonne propreté de 1'acier (inclusions non métalliques réduites au minimum).Since the effect of Cobalt is sensitive to the carbon content, this effect can be improved by introducing into the steel carburogenic elements such as Vanadium and Niobium, in contents less than or equal to 0.2%. Indeed, these elements, by forming carbides decrease the content of "free" Carbon which alone has an unfavorable effect. The Cobalt content can also be increased. Naturally, the addition of Cobalt in no way prevents the use of the means known to those skilled in the art for reducing the sensitivity to cracking by hydrogen. These means being in particular good cleanliness of the steel (non-metallic inclusions reduced to a minimum).
L'invention concerne également le procédé qui permet de réaliser des blocs, plaques, barres, tubes ou pièces en utilisant un acier dans lequel on a introduit du Cobalt en tant qu'agent réduisant la sensibilité à la fragilisation par l'hydrogène. Ce procédé consiste à :The invention also relates to the method which makes it possible to produce blocks, plates, bars, tubes or parts using a steel into which Cobalt has been introduced as an agent reducing the sensitivity to embrittlement by hydrogen. This process consists of:
- élaborer l'acier selon les régies de l'art- elaborate steel according to the rules of art
- ajouter du Cobalt en la teneur souhaitée- add Cobalt in the desired content
- couler l'acier pour le solidifier selon les régies de 1'art.- pour the steel to solidify it according to the rules of art.
. soit sous forme de demi-produits tels que lingots, brames, blooms, billettes.. either in the form of semi-finished products such as ingots, slabs, blooms, billets.
. soit sous forme de pièces moulées.. either in the form of molded parts.
- lorsqu'il s'agit de demi produit, de les mettre en forme par déformation plastique à chaud par forgeage, laminage ou tout autre moyen équivalent.- in the case of semi-finished products, to shape them by hot plastic deformation by forging, rolling or any other equivalent means.
- à effectuer un traitement thermique selon les régies de 1'art pour obtenir les caractéristiques mécaniques souhaitées; ce traitement thermique peut être une normalisation par réchauffage au-dessus de AC3 ou une trempe, ces traitements étant éventuellement suivi d'un revenu à une température inférieure à AC^ ou un detensionnement par un maintien à une température de l'ordre de 200°C. L'invention- concerne enfin tout bloc, plaque, barre, tube ou pièce obtenus par le procédé qui vient d'être décrit en utilisant un acier auquel on a ajouté du Cobalt en tant qu'agent réduisant la sensibilité à la fissuration par l'hydrogène. - to carry out a heat treatment according to the rules of the art to obtain the desired mechanical characteristics; this heat treatment can be normalization by reheating above AC3 or quenching, these treatments possibly being followed by tempering at a temperature below AC ^ or stress relieving by maintaining at a temperature of the order of 200 ° vs. The invention finally relates to any block, plate, bar, tube or part obtained by the process which has just been described using a steel to which Cobalt has been added as an agent reducing the sensitivity to cracking by hydrogen.

Claims

REVENDICATIONS
1. Agent pour améliorer la résistance à la fissuration par l'hydrogène des aciers faiblement ou moyennement alliés utilisés notamment pour réaliser des appareils chaudronnés travaillant dans des milieux hydrogénés tels que du gaz enrichi en H2S et pour amé¬ liorer également la soudabilité et 1'aptitude au décou¬ page par des moyens thermiques de ces aciers en par¬ ticulier lorsqu'ils sont utilisés sous forme de pièces de forte épaisseur, caractérisé en ce que cet agent est du Cobalt ajouté en des teneurs pondérales comprises entre 0,05% et 2%.1. Agent for improving the resistance to cracking by hydrogen of weakly or moderately alloyed steels used in particular to produce boiled apparatus working in hydrogenated media such as gas enriched in H 2 S and to also improve weldability and 1'écou¬ page by thermal means of these steels in particular when¬ when used in the form of thick pieces, characterized in that this agent is Cobalt added in weight contents between 0.05 % and 2%.
2. Aciers faiblement ou moyennement alliés à résistance à la fissuration par l'hydrogène et découpa- bilité par des moyens thermiques et soudabilité amélio¬ rés contenant en leur composition pondérale de 0,05% à 0,6% de Carbone et moins de 10% d'éléments d'alliage pris notamment parmi le Silicium, le Manganèse, le Nickel, le Chrome, le Molybdène, caractérisés en ce qu'ils comprennent en outre de 0,05% à 2% de Cobalt, le reste étant constitué par du fer et des impuretés rési¬ duelles résultant de la fusion des matières nécessaires à l'élaboration.2. Low or medium alloyed steels with resistance to cracking by hydrogen and separability by thermal means and improved weldability containing in their weight composition from 0.05% to 0.6% of Carbon and less than 10 % of alloying elements taken in particular from Silicon, Manganese, Nickel, Chromium, Molybdenum, characterized in that they also comprise from 0.05% to 2% of Cobalt, the rest being constituted by iron and residual impurities resulting from the fusion of the materials necessary for the preparation.
3. Aciers selon la revendication 2, carac- térisés en ce qu'ils contiennent en outre dans leur composition pondérale de base des éléments carburigènes pris notamment parmi le niobium et le vanadium en des teneurs inférieures à 0,2%.3. Steels according to claim 2, characterized in that they additionally contain, in their basic weight composition, carburogenic elements taken in particular from niobium and vanadium in contents of less than 0.2%.
4. Aciers selon l'une quelconque des reven- dications 2 et 3, caractérisés en ce que leur composi¬ tion chimique pondérale contient :4. Steels according to any one of claims 2 and 3, characterized in that their chemical composition by weight contains:
- de 0,05% à 0,6% de Carbone- from 0.05% to 0.6% of Carbon
- moins de 1% de Silicium- less than 1% of Silicon
- moins de 2% de Manganèse - moins de 6% de Nickel - moins de 6% de Chrome- less than 2% Manganese - less than 6% Nickel - less than 6% of Chrome
- moins de 2% de Molybdène- less than 2% of Molybdenum
- de 0,05% à 2% de Cobalt- from 0.05% to 2% of Cobalt
5. Aciers du type : - A 516 tous grades5. Steels of the type: - A 516 all grades
- A 515 tous grades- A 515 all grades
- A 537 classe 1- A 537 class 1
- A 633 tous grades définis par la norme américaine ASTM ou les nuances analogues définies par les autres normes et dont l'uti¬ lisation est imposée notamment par le code de construc¬ tion ASME pour les appareils à pression, caractérisés en ce qu'ils contiennent en outre de 0,05% à 2% de Cobalt.- A 633 all grades defined by the American ASTM standard or similar grades defined by the other standards and the use of which is imposed in particular by the ASME construction code for pressure vessels, characterized in that they additionally contain from 0.05% to 2% of Cobalt.
6. Procédé de fabrication de blocs, plaques, barres, tubes ou pièces réalisés en un acier selon l'une quelconque des revendications 2 à 5, caractérisé en ce qu'au cours de l'élaboration on ajoute de 0,05% à 2% en poids de Cobalt, et en ce qu'après solidification sous forme de lingots, brames, barres, billettes ou analogue et mise en forme par déformation plastique à chaud de ces demi-produits ou après solidification sous forme de pièces moulées, lesdits blocs, plaques, barres, tubes ou pièces subissent un traitement thermique de normalisa¬ tion à une température supérieure à AC3 et éventuelle- ment un traitement thermique complémentaire tel qu'un revenu à une température inférieure à AC^.6. A method of manufacturing blocks, plates, bars, tubes or parts made of steel according to any one of claims 2 to 5, characterized in that during the development is added from 0.05% to 2 % by weight of Cobalt, and in that after solidification in the form of ingots, slabs, bars, billets or the like and shaping by hot plastic deformation of these semi-finished products or after solidification in the form of molded parts, said blocks , plates, bars, tubes or parts undergo a normalization heat treatment at a temperature above AC3 and optionally an additional heat treatment such as tempering at a temperature below AC ^.
7. Blocs, plaques, barres, tubes ou pièces réalisés à 1'aide du procédé selon la revendication 6 en utilisant un acier selon l'une quelconque des revendica- tions 2 à 5 et présentant une bonne decoupabilité par des moyens thermiques, une soudabilité améliorée et une résistance à la fissuration par l'hydrogène améliorée.7. Blocks, plates, bars, tubes or parts produced using the method according to claim 6 using a steel according to any one of claims 2 to 5 and having good cutability by thermal means, weldability and improved resistance to hydrogen cracking.
8. Blocs, plaques, tubes ou pièces selon la revendication 7, caractérisés en ce que leur plus petite dimension est supérieure ou égale à 5 mm. 8. Blocks, plates, tubes or parts according to claim 7, characterized in that their smallest dimension is greater than or equal to 5 mm.
9. Blocs, plaques, barres, tubes ou pièces selon la revendication 8, caractérisés en ce que leur plus petite dimension est supérieure ou égale à 100 mm. 9. Blocks, plates, bars, tubes or parts according to claim 8, characterized in that their smallest dimension is greater than or equal to 100 mm.
EP91904295A 1990-02-14 1991-02-11 Agent for improving the resistance to hydrogen cracking of low or medium alloy steels, a method for using said agent, and parts thereby obtained Withdrawn EP0469115A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9001758A FR2658207B1 (en) 1990-02-14 1990-02-14 LOW ALLOY BOILER AND / OR CONSTRUCTION STEEL FOR USE IN PARTICULAR IN HYDROGEN MEDIA.
FR9001758 1990-02-14

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FR626814A (en) * 1926-12-28 1927-09-20 Composite molten steel
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GB734676A (en) * 1950-11-03 1955-08-03 Nyby Bruk Ab Heat resisting alloy steel and method for its heat treatment
US2631096A (en) * 1951-02-01 1953-03-10 United States Steel Corp High-temperature steel
US3155500A (en) * 1959-05-29 1964-11-03 Wilson Brothers Alloy steels
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