EP1996738B1 - System zur herstellung schweissbarer und rostfreier rohrkonstruktionen mit hoher mechanischer festigkeit und auf diese weise hergestelltes produkt - Google Patents

System zur herstellung schweissbarer und rostfreier rohrkonstruktionen mit hoher mechanischer festigkeit und auf diese weise hergestelltes produkt Download PDF

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EP1996738B1
EP1996738B1 EP07736718.3A EP07736718A EP1996738B1 EP 1996738 B1 EP1996738 B1 EP 1996738B1 EP 07736718 A EP07736718 A EP 07736718A EP 1996738 B1 EP1996738 B1 EP 1996738B1
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Prior art keywords
production
tubular structures
steel
heat treatment
martensitic
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English (en)
French (fr)
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EP1996738A2 (de
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Serena Omodeo Sale'
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Gilcotubi Srl
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Gilcotubi Srl
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    • 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
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
    • 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
    • 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
    • C21D2211/008—Martensite

Definitions

  • the present invention refers to a production system of weldable and stainless tubular structures with high mechanical strength and product obtained therefrom, particularly indicated for making cold-drawn stainless steel tubular elements, workable with different thicknesses and shapes, provided with high performances in terms of mechanical and weldability characteristics for the construction of light and ultralight structural frames destined for a dynamic use, such as for example those for competition vehicles like race cars, high-end bicycles and for aeronautics.
  • the structural frames mentioned above are those for which particular performances are requested, in addition to strength and reliability, of lightness and good behaviour in the presence of dynamic stresses, as is the case of the structures for competition vehicles and for aeronautics.
  • the steel structural frames for dynamic use traditionally consisted of multi-way tubes, made with different steel qualities, welded together or interconnected by metal connection elements.
  • One dynamic frame example is that employed for making bicycles.
  • tubes destined for high-end bicycle frames, requires that they are subjected to particular working (shaping and differentiation of the thicknesses, also along the same tube, by means of broaching and/or coning) so to obtain a weight reduction, while ensuring a good mechanical strength even near the weld, and to increase the consistency of the structure, conferring greater stiffness and not only for aesthetic and design reasons.
  • TIG Tungsten Inert Gas
  • TIG Tungsten Inert Gas
  • An electric arc is used for heating and melting the metal: the electric arc is started between the electrode and the piece to be welded.
  • a protection gas passes through the nozzle, protecting the welding bath and the tungsten electrode.
  • the main object of the protection gas in TIG welding consists of protecting the hot zones and the melted zones of the piece, the weld material and the electrode from the negative influence of the surrounding air.
  • the protection gas influences the characteristics of the arc and the aesthetics of the weld.
  • the TIG welding advantages include the high quality of the joints and the absence of slag and spatter. Another welding method is braze-welding. These techniques require a high degree of precision and involve refined welding methods even if considered of artisan type.
  • the electron beam welding can join two materials even of different nature with high precision, which causes perfect adhesion between them without requiring a weld line. But in addition to requiring a very high initial investment cost, and the use of electricity, the costs exponentially increase in proportion with the size of the object to be welded, resulting hence unacceptably high.
  • the electron beam welding and laser welding are not adapted for joining pieces of a certain size, such as frames, and are so costly and demanding that they require excessive investments to be used in the sector of bicycle frame producers. Moreover, after the welding, the finished frame requires an additional heat treatment with consequent movement costs etc. which considerably increase the production costs.
  • the steel 15CrMoV6 which is nickel-plated rather than painted; the corrosion protection is ensured in this case both outside and inside the tube.
  • the nickel-plating treatment it is necessary to take into account the multiple negative effects which if not well controlled could cause further drawbacks.
  • the negative impact is known which the electroplating activity has on the environment, due to the emission of various toxic substances, like heavy metals, cyanides and strong acids (sulphuric acid, hydrochloric acid) with high environmental impact.
  • the use of mineral salts, caustic substances and solvents in rather high quantities are a problem regarding both the waste waters and the waste disposal.
  • the formation of toxic vapours and powders coming from the working produces a considerable impact on the air.
  • the austenitic stainless steels (such as for example AISI 304, AISI 308 etc.) have optimal weldability and stainless characteristics but poor mechanical properties; they are ductile but not hard, and (being monophasic) do not take to hardening: in fact, even with a fast cooling, after heating to temperatures greater than the transformation point (AC3), they do not change structure, remaining austenitic.
  • AC3 transformation point
  • the stainless steels can be hardened with the treatment by mechanical stress (such as drawing, for example).
  • chrome-nickel stainless steels cannot be hardened, the chrome martensitic stainless steels can be hardened.
  • the austenite solubilised during the heat treatment and subjected to quick cooling generates a martensitic structure, attaining high mechanical characteristics.
  • these materials have a low modulus of elasticity and are of considerably more complex working than that required by steel.
  • tubes are made, also drawn but always obtained by means of plate welding (and therefore never by billet extrusion).
  • complex working and heat treatments once made in a specific diameter and thickness (like the materials already described), they can no longer be modified if not at costs which would make the production uneconomical.
  • the consolidation of the frame points close to the weld must be carried out with the application of external reinforcement elements (gaskets).
  • Object of the present invention is substantially that of resolving the problems of the prior art by overcoming the above-described difficulties by means of a production system of weldable and stainless tubular structures with high mechanical strength and product obtained therefrom, capable of making tubes which cannot be attacked by corrosion, provided with high mechanical strength, easily workable for the obtainment of different thicknesses and shapes and easily weldable with limited weakness inductions near the weld.
  • a second object of the present invention is that of making a production system of weldable and stainless tubular structures with high mechanical strength and product obtained therefrom, capable of offering an improved technological response for the construction of light structural frames and welded tubular structures destined for dynamic use, obtained with tubes without welding and therefore structurally homogenous.
  • a third object of the present invention is that of having a production system of weldable and stainless tubular structures with high mechanical strength and product obtained therefrom which is capable of making tubes with high mechanical properties and optimal safety and quality standards, destined to give an improved technological response for making mechanical components subject to dynamic stresses, for use also in extreme conditions in which high performance characteristics are required, in sectors such as aerospace, aeronautics, nuclear, chemical, marine, motor sports and cycling.
  • Another object of the present invention is that of making a production system of weldable and stainless tubular structures with high mechanical strength and product obtained therefrom which has a high index of workability.
  • a further object of the present invention is that of making a production system of weldable and stainless tubular structures with high mechanical strength and product obtained therefrom which permits reducing many of the environmental problems tied to the entire lifecycle of the object: reducing the processes in the production step and consequent consumption of toxic-harmful substances; in the useful lifetime steps of the object ensuring the lengthening of the durability, raising of the safety conditions and eliminating the use of chemical substances for maintenance; and at the end of the useful lifetime, in the discard step, ensuring the total recyclability without any loss of the raw material characteristics (as instead occurs in the recycling of the soft metals).
  • Not the least object of the present invention is that of making a production system of weldable and stainless tubular structures with high mechanical strength and product obtained therefrom which is simply made and has a good functionality.
  • the process of the present invention provides for the use of a steel which can be defined, for its characteristics, as "austenitic-martensitic”; in fact, its specific chemical composition has a carbon content and molybdenum content of an austenitic stainless steel, and a nickel and chromium content of a martensitic stainless steel.
  • the austenitic-martensitic steel according to the invention will have a martensitic percentage which can even arrive at about 95%. For this reason, the process of the invention can also be applied to martensitic steel.
  • One type of steel which is advantageously employed in the process of the invention is that called X4CrNiMo 16-5-1.
  • the production system of weldable and stainless tubular structures with high mechanical strength of the present invention is substantially composed of the following steps:
  • the process can then be completed by conventional passages such as the cutting of the tube thus produced into more easily manageable pieces, quality control and packaging.
  • the first step of the process is the obtainment of the "preform", which is the raw material from which one starts for carrying out the process according to the present invention.
  • the preform is a tube which is hot-worked (at about 1300°C) : it can be rolled with the wheels which form it or extruded with a press.
  • the characteristics of the preform are typical of a working carried out at high temperature: oxidised surfaces, coarse tolerances, large thicknesses with respect to the diameter, possibility of having only standard dimensions.
  • the preform is composed of material at the hardened and tempered state, whose high mechanical strength would not permit its drawing.
  • it is necessary to subject it to an annealing process in one step if in a static furnace (or shaft furnace, load furnace etc.) or in several steps if in continuous or muffle furnaces, with the goal of passing it through the drawing machine and thus reduce its diameter and thickness.
  • controlled atmosphere it is intended an atmosphere of inert gases (such as nitrogen, helium, argon, etc.) or a vacuum atmosphere.
  • a particularly advantageous controlled atmosphere in the scope of the present invention is a gaseous mixture composed of about 50% nitrogen and about 50% reducing gas, in which the reducing gas is for example a gas containing hydrogen such as that obtainable by steam reforming.
  • the heat treatment is a preparation treatment of the material for the subsequent steps and workings.
  • the annealing step provides for a first heating step from ambient temperature to the annealing temperature, a treatment step at the annealing temperature and a cooling step.
  • the preheating from ambient temperature to the annealing temperature is carried out in times of generally less than 1 hour.
  • the annealing treatment is carried out at a temperature which varies between 600°C and 750°C, preferably between 650°C and 700°C. In particularly preferred embodiment of the invention, the annealing treatment is carried out at a temperature of about 680°C.
  • the annealing treatment will be extended for a time of at least 1 hour, more preferably less than 3 hours. In a particularly preferred embodiment of the invention, the annealing treatment will be extended for about 1 hour and 20 minutes.
  • the combination of treatment temperature and time is essential in order to obtain a material having the desired characteristics, i.e. high weldability together with optimal mechanical properties. In general, it can be affirmed that the treatment temperature is inversely proportional to the treatment time: if one operates at a temperature close to the lower limit of the above-outlined range, it will therefore be necessary to prolong the treatment times.
  • the cooling of the annealed tube is an extremely important operation.
  • a slow cooling in a controlled atmosphere is essential.
  • cooling times are provided for between 2 and 4 hours.
  • the material in order to verify that the material has the required characteristics and specifications for the subsequent steps, it is subjected to a mechanical test which permits establishing if the mechanical characteristics of the material are suitable for subjecting the tube to drawing and metallography for evaluating if the structure of the material comes within already established parameters, so to be able to proceed with the drawing; otherwise, the material will have to undergo an annealing treatment to soften it so it can be worked.
  • a mechanical test which permits establishing if the mechanical characteristics of the material are suitable for subjecting the tube to drawing and metallography for evaluating if the structure of the material comes within already established parameters, so to be able to proceed with the drawing; otherwise, the material will have to undergo an annealing treatment to soften it so it can be worked.
  • the step in question consists of the immersion of the tube in a first tub containing a suitable acid (of nitric-hydrofluoric type) for a predetermined time (on the order of 40 minutes), rinsing in water in a second tub and a subsequent immersion in a bath of an oxalate salt for a pre-established time (on the order of 20 minutes) and a final immersion in a stearic ester (preferably in 3% by weight concentration) which serves for lubricating the outer surface of the tube.
  • a suitable acid of nitric-hydrofluoric type
  • the oxalate concentration will generally be in the range of 8 - 16% by weight.
  • Drawing is a mechanical working which permanently deforms the materials, in the present case steel. It is executed cold and therefore at ambient temperature by means of a machine (the drawing machine) which forces the material, drawing it by one end, to pass through the drawing equipment which determines its final configuration.
  • the drawing equipment in the case of tubes, can be made to work both on the tube exterior and interior.
  • the steel drawn by one end takes the form of the equipment in which it is drawn and made to pass through.
  • the drawing step of the invention several passages are executed in order to obtain the desired thicknesses of the tubes, since at each passage one succeeds to obtain a thickness reduction of about 20%.
  • the drawing speed also depends on the material thickness: in fact, if one starts with 5 mm - 1.75 mm thicknesses, the drawing speed is moderate while with smaller thicknesses it is lower.
  • the material is preferably subjected to a subsequent heat treatment with a passage in a furnace, since otherwise the material would break with the risk of inclusions.
  • a subsequent heat treatment with a passage in a furnace, since otherwise the material would break with the risk of inclusions.
  • Such heat treatment called normalisation, is particularly advised once thin thicknesses of the tube have been reached (thicknesses less than 2 mm for a tube diameter of about 5 cm).
  • the material before entering the furnace, is subjected to a cleaning operation for removing the lubricating residues.
  • the cleaning is carried out by immersion in tubs containing a solution of surface-active substances and carbonate salts.
  • the normalisation is normally conducted at a temperature in the range of 950°C - 1150°C for a time greater than 10 minutes and less than 1 hour.
  • the material is generally subjected to different steps of drawing, cleaning, normalisation by furnace heat treatment and chemical preparation of the surfaces until the desired thickness is obtained.
  • the material is subjected to the step of final heat treatment which gives the mechanical characteristics to the material (mechanical strength, yield and elongation).
  • the final heat treatment of normalisation and stress relieving occurs - always in controlled atmosphere - with temperatures and stay times set as a function both of the geometry of the finished tube and the final mechanical and desired microstructural characteristics.
  • the normalisation will be carried out at temperatures in the range of 950°C - 1150 °C for a time greater than 10 minutes and less than 1 hour. It should be taken into consideration that for tube thicknesses greater than 2 mm longer treatment times could be necessary than for lesser thicknesses.
  • the cooling modes are very important in order to determine a high quality product.
  • Such heat treatment process is very different from the traditional heat treatments with cooling in oil carried out in traditional chamber or muffle furnaces.
  • the incandescent steel 900°C
  • the oil's capacity to exchange heat is very high (the oil does not evaporate at 900°C) and there is therefore a drastic cooling.
  • the surface of the tubes is in contact with oil and there is a "contamination" which causes oxidation, so that the tubes would require a tempering heat treatment which cannot be achieved on tubes with small thicknesses (less than 1 mm) since they would irreparably deform.
  • a step of rapid cooling is preferably carried out which operates by means of forced cooling on the controlled atmosphere around the tube (in detail, the tube is not in contact with the cooling water) and a step of gradual cooling until the tube is brought to ambient temperature.
  • a refrigerated controlled atmosphere is used, for example by placing, inside the cooling zone downstream of the furnace, a cold-water jacket or tubing near the working tubes.
  • the heating of the material serves so to be able to bring the steel to have a specific starting structure, chosen as a function of the desired end product.
  • the stay time serves to ensure a certain homogeneity: i.e. since the entire volume of the steel is homogeneous and has the same structure.
  • the cooling serves to obtain specific structures and hence mechanical characteristics: as a function of the cooling speed, one can obtain different structures.
  • the production system according to the present invention provides for the step of straightening the tube, to which the step of pickling and/or passivation follows.
  • the tube is treated so to induce a compact chromium oxide patina onto the steel, which ensures its resistance to corrosion.
  • the methods used are conventional and consist of an acid treatment with acid baths like those described above (pickling), followed by washing and by subsequent immersion in a less aggressive acid bath (for example, diluted nitric acid) to induce a passivation speed.
  • the tube is subjected to the step of cutting, in which it is brought to the desired length as a function of the subsequent structural needs and is then packaged for storage and sale.
  • the cutting can also be advantageously carried out before the pickling and passivation step.
  • the previous operations are all carried out with a controlled atmosphere to prevent the oxygen from coming into contact with the tube surfaces, since at high temperatures the oxidation process is very reactive and amplified.
  • the present invention thus attains the aimed objects.
  • tubular structures of the invention permits obtaining a tubular element with high mechanical properties and high quality and safety standards, destined to give the best technological response for making mechanical components subjected to dynamic stress, for uses even in extreme conditions, in which considerable performance characteristics are required in sectors such as aerospace, aeronautics, nuclear, marine, chemical, motor sports and cycling.
  • tubular structures of the invention permits obtaining:
  • the system according to the present invention permits maintaining high weldability characteristics (as shown in figures 3, 4 , 5, 6 and 7 ) and, specifically, due to the particular chemical composition of the material which ensures high weldability, microcracks are not caused in the welding process, as illustrated in figure 5.
  • Figure 5 shows an enlargement of the HAZ (Heat Altered Zone) surrounding the weld line in which the metallurgic transformation of martensite is clearly shown to be very limited, while presenting this area with a martensitic structure and a second "mixed" structure zone ( figure 4 ), formed by the welding heat.
  • HAZ Heat Altered Zone
  • break points are determined at the welds (or near these), since greater material vulnerability is created due to the formation of microcracks, which create weak points.
  • the weld quality obtained in the tubes described here simplifies the working process and also introduces new opportunities, permitting using the process of shaping with differentiated thicknesses according to new criteria, process destined to give different levels of desired stiffness (specific stiffness) in different points of the elements assembled together in order to improve the geometric stability of the frame while further reducing the weight.
  • the high modulus of elasticity of 211,000 Mpa - twice the value of that of a titanium tube and three times that of aluminium - permits making extremely light frames with a high degree of stiffness.
  • the optimal expansion coefficient - in the field 20 ⁇ 100°C ⁇ 0.00001 mm - ensures optimal geometric and dimensional stability of the structure during the useful lifetime.
  • the steel obtained with the present system is stainless and weldable with extremely reduced thicknesses, since the steel of the weld and that in the surrounding areas has the mechanical characteristics of the rest of the structure as it is heated during welding and then quickly cooled.
  • the steel obtained with the production system according to the present invention can be worked with already existing machines and tools and with known technologies, permitting considerable savings in the tubular structure production costs.
  • the production system is quite versatile and is capable of offering a production with decidedly innovative and reliable characteristics, given that the tubular element is obtained by a billet-extruded material, it is hence without welding and is cold-drawn. Moreover, the tubular element puts together the high technical performances of the martensitic steels with the high weldability characteristics of the austenitic steels, and is therefore optimally weldable with TIG and MIG technologies of known type and without elaborate processes as occurs in the prior art to obtain welds with high strength and seal characteristics.
  • the obtained tubular element has high strength characteristics (1.000 ⁇ 1.300 MPa), high modulus of elasticity (211,000 MPa, twice that of a titanium tube and three times that of an aluminium tube), an optimal dimensional stability (20 ⁇ 100°C - 0.0001 mm) and therefore geometric stability ensured over the time of use, it is easily workable obtaining the most varied shapes and thicknesses and has an excellent surface finish, in addition to the fact that, being highly stainless, it is free from degradation and wear over time.

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Claims (12)

  1. Verfahren zur Herstellung von schweißbaren und rostfreien rohrförmigen Strukturen mit hoher mechanischer Festigkeit, welches nacheinander die folgenden Schritte aufweist:
    - Glühwärmebehandlung einer Rohr-Vorform in martensitischem oder austenitsich-martensitischem Stahl, welche einen ersten Schritt aufweist, von Umgebungstemperatur auf die Glühtemperatur zu erhitzen, einen Schritt der Glühbehandlung bei einer Temperatur von etwa 680°C, die sich für eine Zeit von wenigstens 1 Stunde und bevorzugt weniger als 3 Stunden erstreckt, und einen Schritt des Kühlens;
    - chemisches Präparieren der Oberflächen zum Schmieren der Kontaktoberflächen des Rohrs mit dem Streckgerät;
    - zumindest einen Streckdurchgang zum permanenten Verformen des Materials; und
    - eine finale Wärmebehandlung zum Reformieren der Struktur des Stahls, der verformt worden war, und zum Bestimmen der gewünschten finalen Charakteristiken, die bei einer Temperatur im Bereich von 950°C-1150°C und über eine Zeit länger als 10 Minuten und kürzer als 1 Stunde durchgeführt wird;
    wobei der finalen Wärmebehandlung ein rascher Abkühlschritt und ein langsamer Abkühlschritt folgt, wobei der rasche Abkühlschritt mittels des Kontakts der rohrförmigen Struktur mit einer gekühlten kontrollierten Gasatmosphäre durchgeführt wird und für die Temperaturabsenkung der rohrförmigen Struktur von etwa 920°C (Temperatur am Ofenauslass) bis etwa 450°C in einer Zeit im Bereich von 30 Sekunden bis 2 Minuten, bevorzugt etwa 1 Minute, sorgt; und
    wobei der Stahl martensitischer oder austenitsich-martensitischer Stahl ist und X4Cr-Ni-Mo 16-5-1 ist.
  2. Das Verfahren zur Herstellung rohrförmiger Strukturen nach Anspruch 1, das zumindest zwei Streckdurchgänge aufweist, bis die vorbestimmte Dicke erreicht ist.
  3. Das Verfahren zur Herstellung rohrförmiger Strukturen nach Anspruch 1 oder 2, wobei in jedem Streckdurchgang die Dicke um etwa 20% reduziert wird.
  4. Das Verfahren zur Herstellung rohrförmiger Strukturen nach Anspruch 1 bis 3, das nach jedem des zumindest einen Streckdurchgangs einen Schritt zur Normalisierungswärmebehandlung der rohrförmigen Struktur aufweist.
  5. Das Verfahren zur Herstellung rohrförmiger Strukturen nach Anspruch 4, wobei der Schritt zur Normalisierungswärmebehandlung bei einer Temperatur im Bereich von 950°C-1150°C und für eine Zeit länger als 10 Minuten und bevorzugt kürzer als 1 Stunde durchgeführt wird.
  6. Das Verfahren zur Herstellung rohrförmiger Strukturen nach Anspruch 1, wobei der Schritt des Erwärmens von Umgebungstemperatur auf die Glühtemperatur in einer Zeit weniger als oder gleich 1 Stunde durchgeführt wird.
  7. Das Verfahren zur Herstellung rohrförmiger Strukturen nach Anspruch 1 bis 6, wobei der Kühlschritt in einer Zeit im Bereich von 2-4 Stunden durchgeführt wird.
  8. Das Verfahren zur Herstellung rohrförmiger Strukturen nach einem der Ansprüche 1 bis 7, wobei der chemische Präparationsschritt der Oberflächen aufweist: Eintauchen der rohrförmigen Struktur in ein eine Säure enthaltendes Gefäß für eine vorbestimmte Zeit, bevorzugt in der Größenordnung von 40 Minuten, Spülen von Wasser in einem zweiten Gefäß und anschließendes Eintauchen in ein Bad eines Oxalat-Salzes für eine vorbestimmte Zeit, bevorzugt in der Größenordnung von 20 Minuten, und letztendliches Eintauchen in einen Stearin-Ester, bevorzugt in einer Konzentration von 3 Gewichts-%, zum Schmieren der Außenoberfläche der rohrförmigen Struktur, wobei für die Säurebehandlung 140 kg/m3 von 56%iger Salpetersäure und 40 kg/m3 von 38-40%iger Fluor-Wasserstoff-Säure verwendet werden, und wobei, für die Behandlung mit Oxalat, die Oxalat-Konzentration allgemein im Bereich von 8-16 Gewichts-% liegen wird.
  9. Das Verfahren zur Herstellung rohrförmiger Strukturen nach einem der Ansprüche 1 bis 8, wobei die rohrförmige Struktur vor dem finalen Wärmebehandlungsschritt einer Reinigungsoperation unterzogen wird, um die Schmiermittelreste zu entfernen, wobei der Reinigungsschritt durch Eintauchen in eine Lösung von oberflächenaktiven Substanzen und Karbonatsalzen ausgeführt wird.
  10. Das Verfahren zur Herstellung rohrförmiger Strukturen nach einem der Ansprüche 1 bis 9, wobei die Wärmebehandlungen zum Glühen, Normalisieren und die finale Wärmebehandlung in Öfen mit kontrollierter Atmosphäre ausgeführt werden, um zu vermeiden, dass das Material Oberflächenveränderungen, sowohl extern als auch intern, unterliegt, um die etwaige Oxidation und die Dekarbonisierung zu verhindern, wobei die kontrollierte Atmosphäre ein Gasgemisch ist, bestehend aus etwa 50% Stickstoff und etwa 50% reduzierendem Gas, wobei das reduzierende Gas bevorzugt ein Wasserstoff enthaltendes Gas ist, wie etwa jenes, das durch Dampfreformieren erhältlich ist.
  11. Das Verfahren zur Herstellung rohrförmiger Strukturen nach einem der Ansprüche 1 bis 10, wobei die Vorform ein rohes Rohr ist, das durch Heißbearbeitung aus einem Barren oder einer anderen Quelle von martensitischem oder austenitsich-martensitischem Stahl erhalten wird, bevorzugt durch Extrusion, und wobei die rohrförmigen Strukturen, nach dem finalen Wärmebehandlungsschritt, einem Beiz- und/oder Passivierungsschritt unterzogen werden.
  12. Rohrförmige Struktur aus martensitischem oder austenitsich-martensitischem Stahl, der schweißbar mit hoher mechanischer Festigkeit ist, erhalten mittels des Verfahrens nach einem der Ansprüche 1 bis 11, wobei der Stahl X4Cr-Ni-Mo 16-5-1 ist und eine Zugfestigkeit > 1100 N/mm2 hat.
EP07736718.3A 2006-03-23 2007-03-23 System zur herstellung schweissbarer und rostfreier rohrkonstruktionen mit hoher mechanischer festigkeit und auf diese weise hergestelltes produkt Active EP1996738B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IT000021A ITMN20060021A1 (it) 2006-03-23 2006-03-23 Sistema di produzione di strutture tubolari inossidabili e saldabili con alta resistenza meccanica e relativo prodotto ottenuto
PCT/IT2007/000214 WO2007108038A2 (en) 2006-03-23 2007-03-23 Production system of weldable and stainless tubular structures with high mechanical strength and product obtained therefrom

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JP4858659B2 (ja) * 2010-01-28 2012-01-18 住友金属工業株式会社 原子力プラント用金属管の熱処理方法、およびそれに用いるバッチ式真空熱処理炉、並びにそれにより処理された原子力プラント用金属管
US20110209802A1 (en) * 2010-03-01 2011-09-01 Chih-Feng Ho Method for processing steel tubes and the likes
DE102013104806A1 (de) * 2013-05-08 2014-11-13 Sandvik Materials Technology Deutschland Gmbh Bandofen
CN108544186A (zh) * 2018-03-28 2018-09-18 徐州东鑫铸造有限公司 一种螺丝生产工艺
CN113681242A (zh) * 2021-08-31 2021-11-23 浙江圣洁钛业科技有限公司 一种高性能不锈钢管的加工工艺

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US20090277543A1 (en) 2009-11-12
EP1996738A2 (de) 2008-12-03
WO2007108038A3 (en) 2007-11-22
JP2009530499A (ja) 2009-08-27
ITMN20060021A1 (it) 2007-09-24
WO2007108038A2 (en) 2007-09-27
WO2007108038A8 (en) 2007-12-21

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