Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%

Definitions

• the N07718 alloy with which good mechanical characteristics can be achieved without compromising the grain boundary with elevated precipitations of detrimental phases, can be used at moderate temperatures and not in the presence of elemental sulphur; - the N07716 alloy, aged so as to obtain high mechanical characteristics, has micro-structures with grain boundaries decorated by significant phase precipitations which affect the behaviour of this alloy in laboratory tests of intergranular corrosion and which, therefore, hamper its use in the HPHT (High Pressure High Temperature) sphere and in those environments in which the presence of nascent hydrogen is possible, making products in this alloy incredibly fragile.
• HPHT High Pressure High Temperature
• the present invention lies thus in the above context, proposing to provide a method of manufacture and nickel-based alloys able to overcome the drawbacks spoken of in relation to the prior art.
• Such objectives are achieved by a manufacturing method of a nickel-based alloy comprising the steps of: i) forging and solution treating a metal mass;
• step ii) subjecting the product of step i) to a first ageing step at a higher temperature
• step iv) subjecting the product of step iii) to a second ageing step at a lower temperature
• step iv) cooling, preferably in air, the product of step iv) to obtain the nickel-based alloy.
• the hardening metal phases ( ⁇ ' and ⁇ ") precipitate eminently in steps ii) and iv) , and the ageing steps have been selected in such a way as to have the maximum precipitation rate of said phases.
• the hardening metal phases may continue to precipitate but no longer at an optimal rate while the carbide phases (also referred to as “carbides” in this description) , and optionally the undesired intermetallic phases, may have high precipitation rates during this process.
• the nickel-based alloy comprises hardening phases ⁇ ' and ⁇ " precipitated in an essentially non-intergranular position, and carbides precipitated in a discontinuous manner at least along the boundary of the aforesaid grains.
• the Fe may be present in a percentage of about 5-15_or about 5-12.
• the metal mass may consist exclusively of the elements mentioned above, i.e. could consist of C, Si, Mn, Cr, Ni, Mo, S, P, Cu, Co, Al, Ti, Nb, Fe in the indicated percentages.
• step i) comprises sub- steps of forging the metal mass at a temperature of approximately 1000-1160°C and then solution treating said mass at a temperature of approximately 1030-1080°C.
• the sub-step of solution treating could be followed by a cooling step in water before step ii) , or by a rapid cooling of an equivalent type .
• step iii) by itself already constitutes a product of industrial interest and with its own market.
• this method could comprise a step of separating the product of step iii) , and a step of transforming a first part of the separated product into a first finished product, e.g. with lower performances, and/or a step of storing said separated product .
• step v) not all the forged and solution treated metal mass starting the process needs necessarily to lead to the product of step v) , but a part thereof could be withdrawn at the end of step iii) , and be transformed as indicated above, or even simply stored.
• the step iii) product could be characterised by a yield strength, measured at ambient temperature, equal to or greater than approximately 827 MPa .
• the method may comprise a step of sending to step iv) (and subsequently to step v) ) a second part of the aforesaid separated product at step iii) , to obtain a second product, e.g. of higher performances, made of the nickel-based alloy.
• step iv) the separated and/or stored product may be subjected to step iv) at a different time from step iii), for example as a result of an order for the nickel-based alloy.
• the nickel-based alloy is characterised by a yield strength, measured at ambient temperature, equal to or greater than about 950-970 MPa, preferably greater than or equal to 970 MPa.
• a yield strength measured at ambient temperature, equal to or greater than about 950-970 MPa, preferably greater than or equal to 970 MPa.
• step ii) said step is specifically used in order to minimise the precipitation of carbides and other unwanted phases at the grain boundaries.
• step ii) could be conducted at a temperature (defined as "higher”) of about 720-780°C for about 3-8 hours, or for about 3-6 hours.
• step iv) could be conducted at a temperature (defined as "lower”) of about 600-640°C for about 4-10 hours.
• cooling steps iii) and/or v) could be performed in air at room temperature, preferably up to about an ambient temperature of the respective products.
• ambient temperature a temperature external to the strongly heated ambient in which the ageing steps ii) and iv) are conducted.
• ambient temperature could refer to the temperature outside the furnace used to perform the aforesaid ageing heat treatments, more precisely at the cooling planes situated inside the production plant.
• the ambient temperature could be the temperature of the production plant, changing greatly depending on the season of the year in which the production takes place and/or on the latitude of the production site in which the aforesaid method takes place .
• step ii) subjecting the product of step i) to a first ageing step at a higher temperature
• step iii) cooling the product of step ii) in air; iv) subjecting the product of step iii) to a second ageing step at a lower temperature;
• step iv) cooling, preferably in air, the product of step iv) to obtain a nickel-based alloy.
• the nickel- based alloy comprises metal hardening phases precipitated uniformly throughout its grains.
• the nickel-based alloy comprises hardening phases ⁇ ' and ⁇ " precipitated in an essentially non-intergranular position, and carbides precipitated in a discontinuous manner at least along the boundary of said grains.
• step iii) and iv) interspersed by step iii) promote the precipitation of the hardening phases ⁇ ' and ⁇ " in a uniform and preferably fine manner, minimising the precipitation carbides and unwanted intermetallic phases at the grain boundary.
• Said alloy is characterised in that it comprises hardening phases ⁇ ' and ⁇ " precipitated essentially in a non-intergranular position, advantageously evenly and preferably finely, and carbides precipitated discontinuously at least at the boundary of said grains.
• the latter alloy could be obtained using the method according to any of the embodiments illustrated above.
• preferred or advantageous variants of said alloy could comprise any manufacturing step deductible from the aforesaid description.
• the alloy of the present invention is preferably usable for making equipment and pipes for the chemical or petrol industries.
• Example 1 Means for implementing the method.
• the metal mass which the invention relates to is preferably melted in an electric arc furnace, refined in A.O.D. (Argon Oxygen Decarburization) so as to obtain an intense desulphurisation, thorough deoxidisation and a very restricted analytical range of compositions to ensure repeatability of the mechanical and corrosion properties .
• A.O.D. Aral Oxygen Decarburization
• the refining process could be completed by at least one of the following operations:
• V.A.R. / E.S.R. Vauum Arch Remelting / Electro Slag Remelting
• the ingots obtained after V.A.R. or E.S.R. remelting may be subjected to appropriate homogenisation heat treatment and then transformed into blooms through use of a forging press, for example having two integrated, fully automated manipulators programmable both for the entity and deformation rate for each cycle.
• the blooms, after intermediate grinding, could be transformed into billets/bars through the use of a hydraulic press with four synchronised hammers, for example with dual manipulator and/or new concept RCD (Round Continuous Deforming) rolling mill. These last two systems could also be automated and programmable.
• the heat-processing plants, designed ad hoc for long products in particular having a extension length substantially greater than the width or thickness, such as pipes or bars) , make it possible to work within narrow temperature ranges so as to have a good control of the grain uniformity and avoid the precipitation of deleterious phases especially for resistance corrosion in the environments in which the products, made from the alloy according to the invention, are intended for use.
• Example 2 Comparison of the nickel-based alloy of the invention with traditional alloys currently used.
• the nickel-based alloy of the present invention after heat transformation in the temperature range 1000-1160 °C and solution treatment in the range 1030-1080°C, typically has the mechanical features shown in Figure 1.
• the nickel-based alloy of the present invention (called "AF.955"), after solution treatment as in the above paragraph, if aged in the temperature range 720- 780 °C for 3-8 hours and air cooled (or equivalent cooling, or in case of faster cooling) typically has the mechanical features specified in Figure 2 and the resistance data to intergranular corrosion and pitting referred to in Figures 6-7-8.
• the alloy after a second ageing at 600°-640°C for a time ranging from 4-10 hours, followed by air cooling, presents the mechanical characteristics specified in Figure 3, and the resistance to intergranular corrosion and pitting referred to Figures 6-7-8.
• Figures 4-5 shows the chemical composition and characteristic mechanical properties of the alloys most commonly used in the numerous environments encountered in the oil and natural gas extraction industry.
• the 3 grades (Gr. 3) differ from the 3HS grades (Gr.3HS) only in the methods (temperatures/times) of the thermal ageing treatment.
• the 3 grades (Gr.3) relate to a nickel- based alloy subjected to a single ageing step and subsequent cooling as per steps ii) and iii) mentioned above.
• the 3HS grades (Gr.3HS) relate to an alloy which has also undergone the second steps of ageing and cooling - namely also steps iv) and v) .
• Figures 6-7-8-9-10 provide information on the resistance capacity of the materials in the laboratory corrosion tests compared to the alloy of the invention.
• Figures 11A-11B show the metallography of the alloy AF.955 (at 100X and 500X magnifications) before step ii) , namely at the end of forging and solution treating of the metal mass only.
• Figures 11C-11D show the metallography - again at the aforesaid magnifications - of the aforesaid step iii) product, i.e. following the first ageing and subsequent air cooling step.
• Figures 11E-11F lastly show metallographies corresponding to the previous ones, relative to the alloy AF.955 at the end of step v) .
• Figures 12A-12F and Figures 13A-13F show a metallography respectively of the alloy N07718 and of the alloy N07716 corresponding to the aforementioned Figures (after solution treating, 12A-12B for the alloy N07718 and 13A-13B for the alloy N07716; after a first type of ageing for each alloy Gr. 3 (12C-12D and 13C-13D) and after a second ageing for Gr.3HS for each alloy (12E-12F and 13E-13F) .
• the method and nickel alloys of the present invention make it possible to brilliantly resolve the drawbacks spoken of in relation to the prior art.
• the method and the nickel alloys of the present invention are substantially free of intergranular metal phase precipitates, in particular of carbides, so that the corrosion phenomenon at the grain boundary is dramatically reduced, if not substantially absent compared to the prior art.
• the alloy of the present invention has greater mechanical and traction resistance properties, and in particular lengthening and pinch point data, than the metal alloys it was compared to, a considerable resistance to corrosion under stress and very low hydrogen embrittlement with elongation at rupture characteristics still high enough to guarantee safe use of the alloy in environments in which nascent hydrogen may develop.
• step iii) product proves to be optimal for certain industrial applications.

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• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Metallurgy (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Crystallography & Structural Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Forging (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Powder Metallurgy (AREA)

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• 2013
  • 2013-12-05 IT IT000061A patent/ITVA20130061A1/it unknown
• 2014
  • 2014-12-05 AU AU2014358718A patent/AU2014358718B2/en active Active
  • 2014-12-05 JP JP2016557205A patent/JP6571103B2/ja active Active
  • 2014-12-05 EP EP14830602.0A patent/EP3077558B1/en active Active
  • 2014-12-05 US US15/101,747 patent/US20180171456A1/en not_active Abandoned
  • 2014-12-05 WO PCT/IB2014/066645 patent/WO2015083133A1/en active Application Filing
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