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
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • 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
  • C21D1/26—Methods of annealing
• • 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
  • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
  • C21D1/60—Aqueous agents
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/005—Heat treatment of ferrous alloys containing Mn
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/008—Heat treatment of ferrous alloys containing Si
• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
• • 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
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • 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
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • 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
  • C21D2211/001—Austenite

Definitions

• the invention relates to an austenitic drill string component, in particular for use in media with high corrosive attack, and a method for its production.
• Austenitic materials are used in deep drilling technology, particularly in oil and gas fields. In these applications, it is essential to determine the borehole trajectory as precisely as possible. This applies especially to drilling operations that are not exclusively vertical or perpendicular, but also those that involve changes in direction. Accurate borehole trajectory determination is crucial for controlling the drilling process. This is typically achieved by determining the drill head's position using magnetic field probes, which utilize the Earth's magnetic field for measurement. For this purpose, certain components of the drill string are made of non-magnetic alloys. This means that sections of the drill string located in close proximity to magnetic field probes must have a relative magnetic permeability ⁇ R ⁇ 0.1.
• Such components include, in particular, the so-called heavy bars or MWD (Measurement While Drilling) and LWD (Logging While Drilling) components, which are positioned above the actual drill head and serve, among other things, to house the corresponding measuring electronics. These applications are characterized by having a diameter greater than 80 mm and being free of precipitates right to the center.
• MWD Measurement While Drilling
• LWD Logging While Drilling
• austenitic drill string components Another requirement for austenitic drill string components is that they must withstand corrosive attack.
• the corrosion-resistant, austenitic steel alloy chosen here is... This is an alloy comprising particularly high contents of manganese, chromium, molybdenum, and nickel.
• nitrogen is present in contents of 0.35 to 1.05 wt.%, which also contributes to corrosion resistance and is a strong austenite former.
• the tendency to form nitrogenous precipitates, especially chromium nitride also increases.
• manganese is used in contents of more than 19 to 30 wt.%. This is intended to ensure that pore-free materials can be produced even when solidifying under atmospheric pressure.
• the manganese is intended to stabilize the austenitic microstructure against the formation of deformation martensite at high degrees of deformation.
• WO 02/02837 A1 It is a corrosion-resistant material known for use in media with high chloride concentrations in oilfield technology. It is a chromium-nickel-molybdenum superaustenite characterized by comparatively low nitrogen contents but very high chromium and nickel contents.
• chromium-nickel-molybdenum steels typically exhibit improved corrosion resistance compared to the previously mentioned chromium-manganese-nitrogen steels.
• chromium-manganese-nitrogen steels are a relatively cost-effective alloy composition that nevertheless offers an excellent combination of strength, toughness, and corrosion resistance.
• the aforementioned chromium-nickel-molybdenum steels achieve significantly higher corrosion resistance than chromium-manganese-nitrogen steels, but are associated with considerably higher costs due to their very high nickel content.
• Superaustenitic alloys typically have molybdenum contents > 4 wt.% and a MARC value > 42 to achieve high corrosion resistance.
• molybdenum increases the tendency for segregation, thus increasing susceptibility to precipitation, particularly of the brittle sigma or chi phases. Consequently, these alloys require homogenization annealing, and at molybdenum contents above 4%, remelting is even necessary to reduce segregation. Even then, the tendency for precipitation is so high that dimensions larger than 250 mm cannot be produced without precipitation due to the reduced cooling rate in the center.
• the materials still have a magnetic permeability of ⁇ R ⁇ 1.01 even after cold forming.
• MARC wt.% Cr + 3.3 wt.% Mo + 20 wt.% N + 20 wt.% C - 0.5 wt.% Mn.
• a MARC value of 20 - 42 indicates a corrosion-resistant, austenitic alloy.
• samples of the austenitic material with dimensions of 25 x 30 x 5 mm are prepared, ground, and cleaned with deionized water and acetone.
• the sample is then placed in a test solution of 1 molar NaCl (corresponding to 58.45 g NaCl diluted with deionized water to 1 liter).
• Electrodes and thermometers are installed in the test cell for the measurement. Initially, the test solution is kept at a constant 10°C for 10 minutes. The temperature of the test solution is then increased at 1°C/min. Time, temperature, and current density are continuously measured. The temperature is increased until the measured current density exceeds 100 ⁇ A/cm2 for one minute.
• the CPT (temperature per maximum temperature) is defined as the temperature at which the current density exceeds 100 ⁇ A/cm2 for one minute. If the measured current density exceeds 100 ⁇ A/cm2 for one minute at the start of the experiment, the result is considered to be ⁇ 10°C.
• Austenitic alloys are also known for their use as shipbuilding steels for submarines. These are chromium-nickel-manganese-nitrogen steels, further alloyed with niobium to stabilize the carbon. However, the latter reduces impact toughness. These steels generally contain little manganese and therefore have relatively good corrosion resistance, but they do not achieve the strength and, above all, the toughness of CrMnN alloys used for heavy bars.
• the object of the invention is to create an austenitic drill string component which, with regard to its manganese and nickel content, represents a significantly reduced alloy design. simultaneously exhibits high corrosion resistance, high strength and toughness, as well as good paramagnetic behavior.
• an object of the invention to provide a method for producing an austenitic drill string component which exhibits high strength and toughness and good paramagnetic behavior in addition to increased corrosion resistance.
• the austenitic drill string component should possess a completely austenitic microstructure, in particular without carbides and/or nitrides and/or carbonitrides and/or without deformation martensite, even after cold forming, wherein the magnetic permeability ⁇ R ⁇ 1.01, preferably ⁇ R ⁇ 1.005. Since ferrite or deformation martensite exhibit magnetic behavior, they increase the permeability and are therefore to be avoided in this embodiment.
• the process is called cold forming.
• the yield strength Rp0.2 is greater than 900 MPa, with values greater than 1100 MPa being achieved in practice.
• the impact energy at 20°C is greater than 80 J, with values greater than 130 J being achieved in practice.
• the impact strength is determined by the standard DIN EN ISO 148-1.
• the yield strength R p0,2 is determined by the standard EN-ISO 6892-1.
• austenitic drill string components are not only made from the appropriate alloys, but that appropriate post-treatments are also carried out to ensure that a homogeneous, precipitation-free, high-strength and, in particular, high-impact alloy is present.
• austenitic drill string components with a diameter of 80 mm to 450 mm are selected so that the minimum values of the mechanical properties, in particular the 0.2% yield strength R p0.2 and tensile strength, are sufficient to withstand the dynamically changing loads that occur.
• the individual elements possibly in combination with the other alloying components, are described in more detail below. All information regarding the alloy composition is given in weight percent (wt%). The upper and lower limits of the individual alloying elements can be freely combined within the limits of the invention.
• Carbon (C) is a strong austenite former and has a beneficial effect on high mechanical properties. For this reason, a lower limit of 0.05 wt.%, 0.06 wt.%, 0.07 wt.%, 0.08 wt.%, 0.09 wt.%, or 0.10 wt.% should be defined. To avoid carbide precipitates and embrittlement of the material, an upper limit of 0.30 wt.% should be selected. Preferably, a carbon content between 0.05 and 0.30 wt.% is used.
• Silicon (Si) serves to deoxidize steel. It also increases strength through the formation of solid solutions. To achieve these effects, a lower limit of 0.05 wt.%, 0.06 wt.%, or 0.07 wt.% is required. However, if silicon is added in excessive amounts, there is a risk of intermetallic phase formation. Since silicon is also a ferrite former, the upper limit is defined by a safety margin. Specifically, silicon can be added in amounts of ⁇ 0.50 wt.%, ⁇ 0.45 wt.%, ⁇ 0.40 wt.%, ⁇ 0.35 wt.%, or ⁇ 0.30 wt.%. A particularly preferred range lies between 0.05 and 0.30 wt.%.
• Manganese (Mn) increases nitrogen solubility. It was previously assumed that manganese contents of more than 19.00 wt.%, ideally more than 20 wt.%, were necessary for high nitrogen solubility. Surprisingly, with the present alloy, it has been found that high nitrogen solubility is also achieved with low manganese contents, without... that expensive printing with embroidery becomes necessary.
• the lower limit for manganese is 8.50 wt.%.
• the upper limit for manganese is 13.00 wt.%. This is a remarkably low value compared to high-nitrogen materials according to the prior art.
• a manganese content between 8.50 and 13.00 wt.% is provided. A particularly preferred range lies between 9.50 and 13.00 wt.%.
• the addition of copper (Cu) proves advantageous for resistance in sulfuric acid.
• copper values > 0.50 wt.% increase the tendency for chromium nitride precipitation, which in turn negatively affects corrosion properties. Therefore, the upper limit is set at 0.50 wt.%, 0.15 wt.%, or 0.10 wt.%.
• the copper content can also be chosen so that it is below the detection limit, meaning no deliberate addition of copper.
• Chromium (Cr) increases the corrosion resistance of the alloy and is also essential for maintaining nitrogen solubility. For improved corrosion resistance, chromium contents of 17.00 wt.% or more are necessary. According to the invention, at least 18.00 wt.% and at most 22.50 wt.% chromium are present. This optimally influences the resistance to pitting and stress corrosion cracking.
• the lower limit for chromium is 18.00 wt.%, 18.50 wt.%, 19.00 wt.%, 19.50 wt.%, or 20.00 wt.%.
• the upper limit for chromium can be 22.50 wt.% or 22.00 wt.%.
• a chromium content between 18.00 and 22.50 wt.% is provided. A particularly preferred range lies between 20.00 and 22.00 wt.%.
• Molybdenum (Mo) contributes significantly to corrosion resistance in general and pitting corrosion resistance in particular.
• a lower limit of 0.50 wt.%, 0.60 wt.%, 0.70 wt.%, 0.80 wt.%, 0.90 wt.%, 1.00 wt.%, 1.10 wt.%, 1.20 wt.%, 1.30 wt.%, 1.40 wt.%, or 1.50 wt.% is required.
• molybdenum contents > 5.00 wt.% necessitate electroslag remelting (ESR) or pressure electroslag remelting. (DESU) is absolutely necessary to prevent segregation.
• a maximum of 5.00 wt.%, 4.50 wt.%, or 4.00 wt.% molybdenum is added.
• a molybdenum content between 0.50 and 5.00 wt.% is used.
• a particularly preferred range is between 1.50 and 4.00 wt.%.
• Tungsten (W) has the same properties as molybdenum, thus contributing to increased corrosion resistance and strength.
• the upper limit for the tungsten content can be 3.00 wt.%, 2.00 wt.%, or 1.00 wt.%. Due to the additional alloying of molybdenum, a lower limit for the tungsten content is not required.
• Nickel (Ni) improves stress corrosion cracking resistance in chloride-containing media. Nickel is also an austenite-stabilizing element. To utilize the positive effects of nickel, a lower limit of 0.50 wt.%, 1.00 wt.%, 1.50 wt.%, 2.00 wt.%, or 2.10 wt.% is required. With increasing nickel content, the driving force for precipitation formation also increases. At the given carbon and nitrogen levels, this would lead to undesirable carbide, nitride, and/or carbonitride precipitation. For this reason, the upper limit for nickel is chosen to be 6.00 wt.%, 5.50 wt.%, 5.00 wt.%, or 4.50 wt.%. Preferably, a nickel content between 0.50 and 6.00 wt.% or 1.50 and 5.50 wt.% is provided. A particularly preferred range lies between 2.00 and 5.50 wt.%.
• Co Co
• the upper limit for cobalt is 0.50 wt%, 0.40 wt%, 0.30 wt%, 0.20 wt%, or 0.10 wt%.
• the cobalt content can also be chosen so that it is below the detection limit (i.e., no deliberate addition of cobalt).
• Nitrogen is added to ensure high strength. Furthermore, nitrogen contributes to corrosion resistance and is a strong austenite former. Therefore, nitrogen contents higher than 0.40 wt%, and especially higher than 0.45 wt%, are advantageous. However, to avoid nitrogenous precipitates, particularly chromium nitride, the upper limit of the The nitrogen content is limited to 0.80 wt.%, 0.75 wt.%, or 0.70 wt.%. It has been shown that, despite the very low manganese content compared to known alloys, these high nitrogen contents can be achieved in the alloy without pressure nitrogenation. A nitrogen content between 0.40 and 0.80 wt.% is preferred. A particularly preferred range is between 0.45 and 0.70 wt.%.
• the ratio according to formula A ensures a completely austenitic microstructure and sufficient strength.
• the manganese content is reduced to improve pitting corrosion resistance.
• reducing the manganese content also results in a reduction of the austenite stabilizers. This is compensated for by increasing the carbon content.
• the carbon as an interstitially dissolved element, ensures the required strength and also increases the solubility of nitrogen in the austenite.
• the ratio of (C + N) in the range of 0.60 to 0.90 is particularly advantageous: 0.60 ⁇ (C + N) ⁇ 0.90.
• the ratio according to formula B is particularly advantageous for this drill string component, as it has a positive effect on the precipitation behavior.
• thermokinetics of precipitation formation is surprisingly positively influenced.
• precipitation can occur, potentially forming M23C6 and/or M2N .
• the metal-to-carbon ratio is approximately 4:1, while in the nitride M2N , the metal-to-nitrogen ratio is 2 :1.
• the carbide tends to have a higher precipitation potential, but due to the abundance of dissolved nitrogen atoms, the precipitation processes inhibit each other, and precipitation is delayed. Water quenching is required after the final hot forming step or an optional solution annealing. This ensures that the drill string component is produced without precipitation.
• Precipitation-free in this context means that no precipitates such as carbides, carbonitrides, or nitrides are present.
• the ratio of (C / N) is particularly advantageous in the ranges 0.10 to 0.48: 0.10 ⁇ (C / N) ⁇ 0.48.
• boron, aluminum and sulfur may be included as additional alloying elements.
• the alloying elements vanadium and titanium are not necessarily present in the steel alloy in question. Although these elements have a positive effect on the solubility of nitrogen. This contributes to ensuring high nitrogen solubility even in their absence.
• Niobium should not be included in the alloy, as concentrations above 0.015 wt.% can lead to the precipitation of niobium carbides or niobium carbonitrides. For austenitic alloys used in particularly corrosive environments, these precipitates have a detrimental effect; the preferential precipitation at grain boundaries reduces impact toughness. Niobium is typically used only for carbon bonding, which is undesirable in this alloy embodiment. Niobium contents up to 0.03 wt.% are still tolerable, but should not exceed the content of unavoidable impurities.
• the invention thus relates to an austenitic drill string component comprising (all values in wt.%) the following elements: Carbon (C) 0.05 - 0.30 Silicon (Si) 0.05 - 0.50 Manganese (Mn) 8.50 - 13.00 Phosphorus (P) ⁇ 0.05 Sulfur (S) ⁇ 0.005 Chromium (Cr) 18.00 - 22.50 Molybdenum (Mo) 0.50 - 5.00 Nickel (Ni) 0.50 - 6.00 Vanadium (V) ⁇ 0.50 Wolfram (W) ⁇ 3.00 Copper (Cu) ⁇ 0.50 Cobalt (Co) ⁇ 0.50 Titanium (Ti) ⁇ 0.50 Aluminum (Al) ⁇ 0.50 Niobium (Nb) ⁇ 0.03 Boron (B) ⁇ 0.01 Nitrogen (N) 0.40 - 0.80
• Residual iron and unavoidable impurities whereby the following applies: 0,55 ⁇ C + N ⁇ 0,95 0,07 ⁇ C/N ⁇ 0,50 and where formula A is given in wt.% and formula B is dimensionless.
• drill string component is completely austenitic after cold forming, i.e., free of deformation martensite and/or carbides and/or carbonitrides and/or nitrides.
• the chromium content is 19.5 - 22.5 wt.%, particularly preferably 20 - 22.5 wt.%.
• CPT Critical Pitting Temperature
• nickel content should be 0.50 - 5.5 wt.%, preferably 1.5 - 5.5 wt.%.
• nickel content should be 2.0 - 5.5 wt.%.
• the austenitic alloy is obtained through secondary metallurgical treatment of the melt, casting into blocks, immediately followed by hot forging, cold forging and, if necessary, further mechanical processing.
• the invention further relates to a method for producing an austenitic drill string component, wherein an alloy comprising the following components (all values in wt.%): Carbon (C) 0.05 - 0.30 Silicon (Si) 0.05 - 0.50 Manganese (Mn) 8.50 - 13.00 Phosphorus (P) ⁇ 0.05 Sulfur (S) ⁇ 0.005 Chromium (Cr) 18.00 - 22.50 Molybdenum (Mo) 0.50 - 5.00 Nickel (Ni) 0.50 - 6.00 Vanadium (V) ⁇ 0.50 Wolfram (W) ⁇ 3.00 Copper (Cu) ⁇ 0.50 Cobalt (Co) ⁇ 0.50 Titanium (Ti) ⁇ 0.50 Aluminum (Al) ⁇ 0.50 Niobium (Nb) ⁇ 0.03 Boron (B) ⁇ 0.01 Nitrogen (N) 0.40 - 0.80
• Residual iron and unavoidable impurities whereby the following applies: 0,55 ⁇ C + N ⁇ 0,95 0,07 ⁇ C/N ⁇ 0,50 and where formula A is given in wt.% and formula B is dimensionless, is melted and subsequently treated by secondary metallurgy, the alloy thus obtained is cast into blocks and allowed to solidify, with remelting if necessary, The material is then heated and immediately hot-formed by forging, with water quenching following the last hot-forming step, and the forgings are subjected to further cold forming and subsequent mechanical processing after cooling.
• Further training involves hot forming in several stages, during which the block is reheated, and after the last hot forming stage, solution annealing at 1050 to 1200°C for a duration of 0.5 to 12 hours, if necessary. Water quenching follows the last hot forming stage and/or solution annealing.
• the cold-formed, austenitic drill string component has a final diameter of 80 to 450 mm.
• the first column of the table in Figure 1 Figure 1 shows the elemental composition of the austenitic drill string component according to the invention, which is characterized by increased corrosion resistance, high strength and toughness, and good paramagnetic behavior. These latter positive properties are achievable if the contents of the respective elements are within the limit ranges specified in the second column and satisfy formulas A (0.55 ⁇ (C + N) ⁇ 0.95) and B (0.07 ⁇ (C / N) ⁇ 0.50), although not all alloying elements are necessarily present.
• nitrogen values above 0.40 wt.% can be achieved despite the low contents of nitrogen solubility-promoting elements, such as manganese, without a special nitrogenization process such as pressure electroslag remelting (DESU) or melting in a vacuum melting furnace under a nitrogen atmosphere.
• nitrogen solubility-promoting elements such as manganese
• FIG. 2 The figure shows a highly schematic representation of a possible process for manufacturing the drill string component according to the invention.
• the material In the vacuum induction melting unit (VID), the material is simultaneously melted and undergoes secondary metallurgical treatment.
• the melt can be melted in the electric arc furnace (EAF) and subsequently undergo secondary metallurgical treatment in the AOD (argon oxygen decarburization) converter.
• EAF electric arc furnace
• AOD argon oxygen decarburization
• the molten metal is treated.
• the molten metal is poured into molds (ingots) and solidifies there into blocks.
• the solidified blocks are hot-formed.
• "Immediately" in the context of the invention means that no additional remelting process, such as electroslag remelting (ESR) or pressure electroslag remelting (PER), is necessary.
• ESR electroslag remelting
• PER pressure electroslag remelting
• the advantage of the drill string component according to the invention is that homogenization annealing or remelting is not necessary.
• the hot forming process then proceeds in several stages. After the final stage, solution annealing at 1050–1200°C for 0.5–12 hours can be performed if required. Water quenching follows either the final stage or the solution annealing. This special process step allows critical temperature ranges to be traversed more quickly and prevents the formation of grain boundary precipitates and/or carbides and/or nitrides and/or carbonitrides. Further cold forming steps, such as forging on a long forging machine, are then carried out to determine the final properties, with the diameter of the final products ranging from 80 to 450 mm.
• mechanical processing takes place, which can be, for example, turning or peeling.
• the present austenitic drill string component can be found not only via the described and especially in Figure 2
• the alloy can be produced not only by a schematically depicted manufacturing route, but also by a powder metallurgical production route, whereby the advantageous properties of the alloy can also be achieved.
• FIG. 3 Three different variants of the drill string components and compositions according to the invention are shown, which satisfy formulas A and B.
• two reference examples (D and E) are shown, which do not satisfy both formulas A and B and also other than the intended composition, and another reference example F which fulfills formulas A and B, but whose chromium and nickel content falls outside the specified chemical analysis.
• All six alloys investigated were produced using the same process. All alloys were melted in a vacuum induction melting unit (VID) and subjected to secondary metallurgical treatment. The molten metal was then poured into molds (ingots) where it solidified into ingots. These ingots were subsequently hot-formed in several stages on the P52 forging press. All alloys were then subjected to solution annealing at 1100°C for 8 hours. This was followed by water quenching and an initial characterization of their properties. Cold forming then took place on the long forging press. All alloys were cold-formed to a final diameter of 200 mm, with a cold forming degree of 15% for all alloys. A final characterization of the properties was then performed. To characterize the mechanical properties, samples were taken every 25 mm below the outer surface.
• VIP vacuum induction melting unit
• FIG 4 An isothermal phase diagram for alloy B (calculated with the program ThermCalc 2024a, database TCFE 12 at 1100°C) is shown.
• the phase diagram consists of the phase components austenite (face-centered cubic, FCC), ferrite (body-centered cubic, BCC), M23C6 , M77C3 , and M25N , and a gas phase (gas).
• the ratio (C / N) is plotted on the secondary axis.
• the aim of the alloys according to the invention is to be in the stable austenite phase.
• alloys Compared to alloy B (2.14 wt% Ni), both alloys have a considerably higher nickel content (alloy A: 5.45 wt% Ni, alloy C: 4.09 wt% Ni). Due to the austenite-stabilizing effect of nickel, these alloys also exhibit pure austenite at 1100°C. In alloys D and E, the BCC phase and the undesired carbide precipitates are present in the calculated phase diagram. A comparison between alloy F and alloy B is not valid due to the nickel content of 8.0 wt% in alloy F. The high nickel content increases the driving force for precipitation formation so strongly that carbide precipitates occur.
• the microstructure including individual phases, can be examined using a scanning electron microscope (SEM) at 20,000x magnification.
• SEM scanning electron microscope
• a sample (10 x 10 mm) is cut from the formed block with a diameter of 80–450 mm, preferably directly. from the center, as the center of the deformed block is of particular interest for characterization.
• the samples are then ground and polished. Additional etching allows for better identification of the phases.
• the phases to be determined are austenite, ferrite, deformation-induced martensite, carbides, nitrides, and carbonitrides.
• alloys A to C consistently shows an austenitic matrix. They are free of carbides, carbonitrides, nitrides, and/or deformation martensite. Alloy D deviates significantly from formulas A and B, with a (C + N) ratio of 0.52 wt.%, which is below the intended limit of 0.55 to 0.95 wt.%. Furthermore, the (C / N) ratio of 0.70 also deviates considerably from the intended limit of 0.07 ⁇ (C / N) ⁇ 0.50. These deviations, combined with the 200 mm diameter, lead to the formation of carbide inclusions in the alloy. This makes the alloy very poorly suited for corrosion resistance in aggressive media. In alloy E, the (C / N) ratio was increased even further to investigate its effects. This resulted in even worse corrosion behavior and a significantly higher carbide content in the microstructure.
• the invention is advantageous in that the austenitic drill string component with good corrosion resistance has been created with very low manganese and nickel content.
• the austenitic drill string component with good corrosion resistance has been created with very low manganese and nickel content.
• carbon and nitrogen according to the ratios described by formulas A and B it has been possible to produce a completely austenitic alloy without inclusions, such as carbides or carbonitrides.
• Nitride or deformation methylenesite can be manufactured that exhibits both high strength and good paramagnetic behavior; even after cold forming, a perfectly austenitic microstructure with a magnetic permeability of ⁇ r ⁇ 1.005 is present. Additionally, corrosion resistance, measured by the critical pitting temperature, has been improved.

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• 2024
  • 2024-12-19 EP EP24221698.4A patent/EP4764005A1/fr active Pending
• 2025
  • 2025-12-18 WO PCT/EP2025/088008 patent/WO2026132230A1/fr active Pending

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