EP3259378B1 - Method for producing a strand from stainless steel - Google Patents

Method for producing a strand from stainless steel Download PDF

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Publication number
EP3259378B1
EP3259378B1 EP16704447.8A EP16704447A EP3259378B1 EP 3259378 B1 EP3259378 B1 EP 3259378B1 EP 16704447 A EP16704447 A EP 16704447A EP 3259378 B1 EP3259378 B1 EP 3259378B1
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EP
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Prior art keywords
billet
stainless steel
strand
gas atmosphere
protective gas
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German (de)
French (fr)
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EP3259378A1 (en
Inventor
Thomas FROBÖSE
Udo RAUFFMANN
Christofer HEDVAL
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Alleima GmbH
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Sandvik Materials Technology Deutschland GmbH
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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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C23/00—Extruding metal; Impact extrusion
    • B21C23/02—Making uncoated products
    • B21C23/04—Making uncoated products by direct extrusion
    • B21C23/08—Making wire, bars, tubes
    • B21C23/085—Making tubes
    • 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
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C21D9/14—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes wear-resistant or pressure-resistant 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr

Definitions

  • the present invention relates to a method for producing a strand of austenitic stainless steel by cold-forming a shell to form the work-hardened strand and then annealing the strand.
  • Strand-shaped stainless steel products i.e. in particular profiles, rods and tubes, are often produced by cold forming a semi-finished product, referred to in this application as a hollow, into the actual strand.
  • the shell In addition to a change in its dimensions, the shell also experiences strain hardening during cold forming.
  • Cold forming gives the stainless steel strand properties that cannot be achieved through hot forming.
  • strands with high tensile strengths can be produced by cold forming, which cannot or can only be achieved with difficulty in any other way.
  • the elongation of cold-formed strands made of stainless steel is rather low compared to strands made by other forming processes.
  • a method for cold forming a strand is known, the strand being annealed at a temperature of 450 ° C. after the cold forming.
  • the metastable austenitic stainless steel wire for a spring with high strength and high rigidity contains components that are 0.03 to 0.14% C, 0.1 to 4.0% Si, 1.0 to 8.0% Mn, 1 , 0 to 5.0% NiCr and 0.05 to 0.30% N and the remainder contain Fe with the inevitable impurities, the value of Md30 expressed by the specified formula being -10 to 40 ° C.
  • a pipe made of a duplex stainless steel is known with a tensile strength (YS LT ) of 689.1 to 1000.5 MPa in the pipe axis direction, the tensile strength (Y-SLT), the compressive strength (YS LC ) in the pipe axis direction, the tensile strength (YS CT ) in the circumferential direction of the pipe and the compressive strength (YScc) in the circumferential direction of the pipe made of the duplex stainless steel satisfy equations (1) to (4): (1) 0.09 YS LC / YS LT 1.11; (2) 0.90 YS cc / YS CT 1.11; (3) 0.90 YS cc / YS LT 1.11; and (4) 0.90 YS CT / YS LT 1.11.
  • At least one of the aforementioned objects is achieved by a method according to claim 1.
  • this information relates to the surface temperature of the work-hardened strand itself.
  • Cold forming processes in the sense of the present application are all forming processes in which the shell, i.e. the semi-finished product, is formed at temperatures that are below the recrystallization temperature of the austenitic stainless steel used.
  • cold forming takes place in particular by cold pilger rolling or cold drawing.
  • an extended hollow, raw-like shell as a semi-finished product is cold-reduced by compressive stresses in the completely cooled state.
  • the shell is formed into a tube with a defined, reduced outer diameter and a defined wall thickness or thickness.
  • the hollow shell is pushed over a calibrated rolling mandrel, i.e. the inner diameter of the finished pipe, and encompassed from the outside by two calibrated rollers, i.e., the outer diameter of the finished pipe defining, and rolled out in the longitudinal direction over the rolling mandrel.
  • a calibrated rolling mandrel i.e. the inner diameter of the finished pipe
  • two calibrated rollers i.e., the outer diameter of the finished pipe defining, and rolled out in the longitudinal direction over the rolling mandrel.
  • the billet is fed step-by-step in the direction of the rolling mandrel or over it.
  • the rollers are rotated over the mandrel and thus moved over the billet and roll out the billet.
  • the rolls release the shell and this is advanced by a further step in the direction of the tool, ie the roll mandrel or the rolls.
  • the billet is advanced over the mandrel with the aid of a translationally driven clamping slide, which executes a translational movement in a direction parallel to the axis of the rolling mandrel and transfers this to the billet.
  • the billet is also rotated around its longitudinal axis in order to enable the billet to be rolled out evenly.
  • the feed steps are usually smaller than the total stroke of the roll stand between the two reversal points.
  • a strand-shaped billet is pulled through a drawing die, which has an inner diameter that is smaller than the outer diameter of the billet, and thus reshaped and re-dimensioned.
  • drawing tubes between the so-called hollow draw, in which the deformation is only reduced with a previously described drawing die (also referred to as a drawing ring, draw hollow or drawing die), and the so-called core draw or rod draw, in which the The inner diameter and the wall thickness of the drawn tube can be defined by a drawing core arranged in the interior of the shell.
  • the tensile strength in the sense of the present application is understood to mean the stress that is calculated in the tensile test from the maximum tensile force achieved immediately before the sample breaks, based on the original cross-section of the sample.
  • the dimension of tensile strength is force per area.
  • Elongation in the context of the present application is understood to mean the permanent elongation of a strand, which is pulled under the action of force until it breaks, based on the initial measuring length.
  • This elongation is also referred to as elongation at break or yield point.
  • the elongation at break is calculated as the quotient of the remaining change in length after the break divided by the initial length before the force was applied. This gives a dimensionless quantity and is often given as a percentage.
  • a particularly advantageous improvement in tensile strength while maintaining a high degree of elongation compared to a cold forming process, which completely dispenses with annealing after cold forming, is achieved in a range from 410 ° C. to 450 ° C., preferably in a range from 435 ° C. to 445 ° C and particularly preferably at 440 ° C.
  • this protective gas atmosphere advantageously has argon, preferably an argon content of more than 95% by volume.
  • the oxygen content of the protective gas atmosphere during annealing is less than 50 ppm, preferably less than 15 ppm and particularly preferably less than 10 ppm. Then oxidation processes on the surface of the strand are negligible.
  • the dew point of the protective gas atmosphere at atmospheric pressure (1013 mbar) is at a temperature of -40 ° C. or less, preferably -50 ° C. or less.
  • an austenitic stainless steel is understood to mean a face-centered cubic mixed crystal of an iron alloy, in particular a y mixed crystal.
  • a strand in the sense of the present application is in the form of a tube.
  • the method according to the invention is used to manufacture a pipe.
  • Tubes with a high tensile strength and, at the same time, high elongation are required above all in the field of medical implants, but also as high-pressure lines for a wide variety of applications.
  • the work-hardened strand is a tube with an inner diameter and an outer diameter, the inner diameter being half the outer diameter or less, preferably one third of the outer diameter or less.
  • FIG. 10 shows a flow diagram of the method for producing an austenitic stainless steel pipe according to an embodiment of the present invention.
  • the hollow was first cold reduced by cold pilger rollers to a finished dimensioned stainless steel pipe.
  • the tube rolled in this way has an elongation A (H) of 25.0% and a tensile strength Rp 0.2 of 762 N / mm 2 .
  • This cold consist tube was then annealed under a protective gas atmosphere with an argon content of more than 95% by volume at a temperature of 440 ° C.
  • the oxygen content in the protective gas atmosphere was less than 10 ppm.
  • the annealed tube has an elongation A (H) of 15.1% after annealing.
  • the tensile strength Rp 0.2 is 812 N / mm 2 .
  • a tube made of austenitic stainless steel is provided as a shell as the starting material.
  • stainless steel contains carbon with a proportion of not more than 0.06% by weight, manganese with a proportion of not more than 1.8% by weight, silicon with a proportion of not more than 0, 7% by weight, nickel with a proportion of 11% by weight, chromium with a proportion of 17% by weight and molybdenum with a proportion of 2.3% by weight.
  • This shell is then cold-formed by cold pilger rolling in step 2 into a finished dimensioned tube.
  • the finished tube is then annealed in step 3 under a protective gas atmosphere with an argon content of more than 95% by volume and an oxygen content in the protective gas atmosphere of less than 10 ppm at a temperature of 440 ° C.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
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Description

Die vorliegende Erfindung betrifft ein Verfahren zum Herstellen eines Strangs aus austenitischem Edelstahl durch Kaltfumformen einer Luppe zu dem kaltverfestigten Strang und nachfolgend Glühen des Strangs.The present invention relates to a method for producing a strand of austenitic stainless steel by cold-forming a shell to form the work-hardened strand and then annealing the strand.

Strangförmige Edelstahlprodukte, d.h. insbesondere Profile, Stäbe und Rohre werden häufig durch Kaltumformen eines in dieser Anmeldung als Luppe bezeichneten Halbzeugs zu dem eigentlichen Strang hergestellt.Strand-shaped stainless steel products, i.e. in particular profiles, rods and tubes, are often produced by cold forming a semi-finished product, referred to in this application as a hollow, into the actual strand.

Neben einer Änderung ihrer Abmessungen erfährt die Luppe bei einer Kaltumformung auch eine Kaltverfestigung.In addition to a change in its dimensions, the shell also experiences strain hardening during cold forming.

Durch die Kaltumformung erhält der Strang aus Edelstahl daher Eigenschaften, welche sich durch ein Warmumformen nicht erzielen lassen. Insbesondere können durch Kaltumformen Stränge mit hohen Zugfestigkeiten hergestellt werden, so wie sie auf andere Weise nicht oder nur schwer erreichbar sind. Dem gegenüber ist die Dehnung von kaltumgeformten Strängen aus Edelstahl verglichen mit durch andere Umformverfahren hergestellten Strängen eher gering.Cold forming gives the stainless steel strand properties that cannot be achieved through hot forming. In particular, strands with high tensile strengths can be produced by cold forming, which cannot or can only be achieved with difficulty in any other way. In contrast, the elongation of cold-formed strands made of stainless steel is rather low compared to strands made by other forming processes.

Aus der WO 2014/034522 A1 ist ein Verfahren zum Kaltumformen eines Strangs bekannt, wobei der Strang nach dem Kaltumformen bei einer Temperatur von 450 °C geglüht wird.From the WO 2014/034522 A1 a method for cold forming a strand is known, the strand being annealed at a temperature of 450 ° C. after the cold forming.

Aus der JP 2005 298932 A ist ein Verfahren zum Herstellen eines hochfesten Edelstahldrahtes bekannt, dessen Steifigkeit erheblich verbessert ist und dessen Steifigkeit der von Pianodraht aus Kohlenstoffdraht entspricht. Der metastabile austenitische Edelstahldraht für eine Feder mit hoher Festigkeit und hoher Steifigkeit enthält Komponenten, die nach Masse 0,03 bis 0,14 % C, 0,1 bis 4,0 % Si, 1,0 bis 8,0 % Mn, 1,0 bis 5,0 % NiCr und 0,05 bis 0,30 % N und der Rest Fe enthalten mit den unvermeidlichen Verunreinigungen, wobei der durch die spezifizierte Formel ausgedrückte Wert von Md30 -10 bis 40 °C beträgt.From the JP 2005 298932 A a method for producing a high-strength stainless steel wire is known, the rigidity of which is considerably improved and the rigidity of which corresponds to that of piano wire made of carbon wire. The metastable austenitic stainless steel wire for a spring with high strength and high rigidity contains components that are 0.03 to 0.14% C, 0.1 to 4.0% Si, 1.0 to 8.0% Mn, 1 , 0 to 5.0% NiCr and 0.05 to 0.30% N and the remainder contain Fe with the inevitable impurities, the value of Md30 expressed by the specified formula being -10 to 40 ° C.

Aus der WO 2014/034522 A1 ist ein Rohr aus einem Duplexedelstahl bekannt mit einer Zugfestigkeit (YSLT) von 689,1 bis 1000,5 MPa in der Rohrachsenrichtung, wobei die Zugfestigkeit (Y-SLT), die Kompressionsfestigkeit (YSLC) in der Rohrachsenrichtung, die Zugfestigkeit (YSCT) in der Umfangsrichtung des Rohres und die Kompressionsfestigkeit (YScc) in der Umfangsrichtung des Rohres aus dem Duplexedelstahl die Gleichungen (1) bis (4) erfüllt: (1) 0,09 ≤ YSLC/YSLT ≤ 1,11; (2) 0,90 ≤ YScc/YSCT ≤ 1,11; (3) 0,90 ≤ YScc/YSLT ≤ 1,11; und (4) 0,90 ≤ YSCT/YSLT ≤ 1,11. Daher ist es Aufgabe der vorliegenden Erfindung, ein Verfahren zum Herstellen eines Strangs aus austenitischem Edelstahl bereitzustellen, welches es ermöglicht, Stränge aus austenitischem Edelstahl zu fertigen, die sowohl eine hohe Zugfestigkeit als auch eine hohe Dehnung aufweisen. Zudem ist es Aufgabe der vorliegenden Erfindung, einen Strang aus austenitischem Edelstahl bereitzustellen, welcher sowohl eine hohe Zugfestigkeit als auch eine hohe Dehnung aufweist.From the WO 2014/034522 A1 a pipe made of a duplex stainless steel is known with a tensile strength (YS LT ) of 689.1 to 1000.5 MPa in the pipe axis direction, the tensile strength (Y-SLT), the compressive strength (YS LC ) in the pipe axis direction, the tensile strength (YS CT ) in the circumferential direction of the pipe and the compressive strength (YScc) in the circumferential direction of the pipe made of the duplex stainless steel satisfy equations (1) to (4): (1) 0.09 YS LC / YS LT 1.11; (2) 0.90 YS cc / YS CT 1.11; (3) 0.90 YS cc / YS LT 1.11; and (4) 0.90 YS CT / YS LT 1.11. It is therefore the object of the present invention to provide a method for producing a strand of austenitic stainless steel which makes it possible to produce strands of austenitic stainless steel which have both high tensile strength and high elongation. In addition, it is an object of the present invention to provide a strand made of austenitic stainless steel which has both high tensile strength and high elongation.

Zumindest eine der vorgenannten Aufgaben wird durch ein Verfahren nach Anspruch 1 erreicht.At least one of the aforementioned objects is achieved by a method according to claim 1.

Ein kaltverfestigter Strang aus austenitischem Edelstahl, welcher auf diese Weise hergestellt wird, verfügt überraschenderweise über eine hohe Dehnung, wobei gleichzeitig die hohe durch das Kaltumformen erzielte Zugfestigkeit erhalten bleibt oder sogar noch verbessert wird.A work-hardened strand made of austenitic stainless steel, which is produced in this way, surprisingly has a high degree of elongation, while at the same time the high tensile strength achieved by cold forming is maintained or even improved.

Dies ist insofern überraschend, da ein Glühen eines Strangs aus Edelstahl im Stand der Technik immer zum sogenannten Weichglühen bzw. Rekristalisationsglühen verwendet wird, d.h. um die Zugfestigkeit, zumeist zu Gunsten einer Bearbeitbarkeit des Strangs in einem weiteren Kaltumformschritt, herabzusetzen.This is surprising insofar as annealing a strand made of stainless steel is always used in the prior art for so-called soft annealing or recrystallization annealing, i.e. to reduce the tensile strength, mostly in favor of the machinability of the strand in a further cold forming step.

Wenn im Sinne der vorliegenden Anmeldung Temperaturen des Strangs während dem Glühen beschrieben werden, so bezieht sich diese Angabe auf die Oberflächentemperatur des kaltverfestigten Strangs selbst.If, for the purposes of the present application, temperatures of the strand during annealing are described, this information relates to the surface temperature of the work-hardened strand itself.

Kaltumformverfahren im Sinne der vorliegenden Anmeldung sind alle Umformverfahren, bei welchen die Luppe, d.h. das Halbzeug, bei Temperaturen umgeformt wird, die unterhalb der Rekristalisationstemperatur des verwendeten austenitischen Edelstahls liegen.Cold forming processes in the sense of the present application are all forming processes in which the shell, i.e. the semi-finished product, is formed at temperatures that are below the recrystallization temperature of the austenitic stainless steel used.

Im Sinne der vorliegenden Anmeldung erfolgt das Kaltumformen insbesondere durch Kaltpilgerwalzen oder Kaltziehen.In the context of the present application, cold forming takes place in particular by cold pilger rolling or cold drawing.

Insbesondere zum Herstellen von präzisen Rohren aus austenitischem Edelstahl wird eine ausgedehnte hohle, rohartige Luppe als Halbzeug im vollständig erkalteten Zustand durch Druckspannungen kaltreduziert. Dabei wird die Luppe zu einem Rohr mit definiertem, reduziertem Außendurchmesser und einer definierten Wanddicke bzw. -stärke umgeformt.In particular for the production of precise tubes from austenitic stainless steel, an extended hollow, raw-like shell as a semi-finished product is cold-reduced by compressive stresses in the completely cooled state. The shell is formed into a tube with a defined, reduced outer diameter and a defined wall thickness or thickness.

Dazu wird beim Kaltpilgerwalzen (auch als Kaltpilgern bezeichnet) die Luppe über einen kalibrierten, d.h. den Innendurchmesser des fertigen Rohrs aufweisenden Walzdorn geschoben und dabei von außen von zwei kalibrierten, d.h. den Außendurchmesser des fertigen Rohrs definierenden Walzen umfasst und in Längsrichtung über den Walzdorn ausgewalzt.For this purpose, in cold pilger rolling (also known as cold pilgrimage), the hollow shell is pushed over a calibrated rolling mandrel, i.e. the inner diameter of the finished pipe, and encompassed from the outside by two calibrated rollers, i.e., the outer diameter of the finished pipe defining, and rolled out in the longitudinal direction over the rolling mandrel.

Während des Kaltpilgerns erfährt die Luppe einen schrittweisen Vorschub in Richtung auf den Walzdorn hin bzw. über diesen hinweg. Zwischen zwei Vorschubschritten werden die Walzen drehend über den Dorn und damit die Luppe bewegt und walzen die Luppe aus. An jedem Umkehrpunkt des Walzgerüsts mit den daran drehend befestigten Walzen geben die Walzen die Luppe frei und diese wird um einen weiteren Schritt in Richtung auf das Werkzeug, d.h. den Walzdorn bzw. die Walzen, hin vorgeschoben.During the cold pilgrimage, the billet is fed step-by-step in the direction of the rolling mandrel or over it. Between two feed steps, the rollers are rotated over the mandrel and thus moved over the billet and roll out the billet. At each reversal point of the roll stand with the rolls attached to it rotating, the rolls release the shell and this is advanced by a further step in the direction of the tool, ie the roll mandrel or the rolls.

Der Vorschub der Luppe über den Dorn erfolgt mit Hilfe eines translatorisch angetriebenen Vorschubspannschlittens, welcher eine Translationsbewegung in einer Richtung parallel zur Achse des Walzdorns ausführt und diese auf die Luppe überträgt.The billet is advanced over the mandrel with the aid of a translationally driven clamping slide, which executes a translational movement in a direction parallel to the axis of the rolling mandrel and transfers this to the billet.

Während dem Vorschub wird zudem die Luppe um ihre Längsachse gedreht, um ein gleichmäßiges Auswalzen der Luppe zu ermöglichen. Durch mehrfaches Überwalzen jedes Rohrabschnitts werden eine gleichmäßige Wanddicke und Rundheit des Rohrs sowie gleichmäßige Innen- und Außendurchmesser erreicht. Daher sind in der Regel die Vorschubschritte kleiner als der Gesamthub des Walzgerüsts zwischen den beiden Umkehrpunkten.During the feed, the billet is also rotated around its longitudinal axis in order to enable the billet to be rolled out evenly. By rolling over each pipe section several times, a uniform wall thickness and roundness of the pipe as well as uniform inner and outer diameters are achieved. Therefore, the feed steps are usually smaller than the total stroke of the roll stand between the two reversal points.

Im Gegensatz dazu wird beim Kaltziehen als einem weiteren hier beispielhaft zu betrachtenden Kaltumformverfahren eine strangförmige Luppe durch eine Ziehmatrize, welche einen Innendurchmesser aufweist, der geringer ist als der Außendurchmesser der Luppe, hindurchgezogen und damit umgeformt und neu dimensioniert.In contrast to this, in cold drawing, another cold forming process to be considered here as an example, a strand-shaped billet is pulled through a drawing die, which has an inner diameter that is smaller than the outer diameter of the billet, and thus reshaped and re-dimensioned.

In Abhängigkeit von dem verwendeten Werkzeug unterscheidet man beim Ziehen von Rohren den sogenannten Hohlzug, bei welchem die Umformung lediglich mit einer zuvor beschriebenen Ziehmatrize (auch als Ziehring, Ziehhohl oder Ziehstein bezeichnet) reduziert wird, und den sogenannten Kernzug oder Stangenzug, bei welchem auch der Innendurchmesser sowie die Wanddicke des gezogenen Rohrs durch einen im Inneren der Luppe angeordneten Ziehkern definiert werden.Depending on the tool used, a distinction is made when drawing tubes between the so-called hollow draw, in which the deformation is only reduced with a previously described drawing die (also referred to as a drawing ring, draw hollow or drawing die), and the so-called core draw or rod draw, in which the The inner diameter and the wall thickness of the drawn tube can be defined by a drawing core arranged in the interior of the shell.

Unter der Zugfestigkeit im Sinne der vorliegenden Anmeldung wird die Spannung verstanden, die im Zugversuch aus der maximal erreichten Zugkraft unmittelbar vor dem Bruch der Probe bezogen auf den ursprünglichen Querschnitt der Probe errechnet wird. Die Dimension der Zugfestigkeit ist Kraft pro Fläche.The tensile strength in the sense of the present application is understood to mean the stress that is calculated in the tensile test from the maximum tensile force achieved immediately before the sample breaks, based on the original cross-section of the sample. The dimension of tensile strength is force per area.

Unter Dehnung im Sinne der vorliegenden Anmeldung wird die bleibende Verlängerung eines Strangs, welcher unter Krafteinwirkung bis zum Bruch gezogen wird, bezogen auf die Anfangsmesslänge verstanden. Diese Dehnung wird auch als Bruchdehnung oder Dehngrenze bezeichnet. Berechnet wird die Bruchdehnung als Quotient aus der verbleibenden Längenänderung nach dem Bruch geteilt durch die Anfangslänge vor der Krafteinwirkung. Diese ergibt eine dimensionslose Größe und wird häufig als Prozentwert angegeben.Elongation in the context of the present application is understood to mean the permanent elongation of a strand, which is pulled under the action of force until it breaks, based on the initial measuring length. This elongation is also referred to as elongation at break or yield point. The elongation at break is calculated as the quotient of the remaining change in length after the break divided by the initial length before the force was applied. This gives a dimensionless quantity and is often given as a percentage.

Erstaunlich ist, dass in dem angegebenen Temperaturbereich von 400° C bis 460° C die Verfestigung des Strangs durch das Kaltumformen, d.h. die erzielte hohe Zugfestigkeit, durch das Glühen noch gesteigert wird, während gleichzeitig die Dehnung nicht nennenswert reduziert wird.It is astonishing that in the specified temperature range of 400 ° C to 460 ° C the solidification of the strand by the cold forming, ie the high tensile strength achieved, is increased by the annealing, while at the same time the elongation is not significantly reduced.

Eine makroskopische oder mikroskopische Veränderung von Strängen, welche von der Anmelderin nach dem Kaltumformen in diesem Temperaturbereich geglüht wurden, ist nicht feststellbar.A macroscopic or microscopic change in strands which were annealed by the applicant after cold forming in this temperature range cannot be ascertained.

Eine insbesondere vorteilhafte Verbesserung der Zugfestigkeit bei Gleichzeitiger Beibehaltung einer hohen Dehnung gegenüber einem Kaltumformverfahren, welches auf ein Glühen nach dem Kaltumformen vollständig verzichtet, wird in einem Bereich von 410° C bis 450° C, vorzugsweise in einem Bereich von 435° C bis 445° C und besonders bevorzugt bei 440° C erreicht."A particularly advantageous improvement in tensile strength while maintaining a high degree of elongation compared to a cold forming process, which completely dispenses with annealing after cold forming, is achieved in a range from 410 ° C. to 450 ° C., preferably in a range from 435 ° C. to 445 ° C and particularly preferably at 440 ° C. "

Um die Oxidation des Edelstahlmaterials beim Glühen minimal zu gestalten, erfolgt das Glühen in einer Schutzgasatmosphäre, welche den Strang während dem Glühen umgibt. Diese Schutzgasatmosphäre weist vorteilhafterweise in einer Ausführungsform Argon auf, vorzugsweise einen Anteil an Argon von mehr als 95 Vol.-%.In order to minimize the oxidation of the stainless steel material during annealing, the annealing takes place in a protective gas atmosphere, which surrounds the strand during annealing. In one embodiment, this protective gas atmosphere advantageously has argon, preferably an argon content of more than 95% by volume.

In einer Ausführungsform der Erfindung beträgt der Sauerstoffgehalt der Schutzgasatmosphäre beim Glühen weniger als 50 ppm, vorzugsweise weniger als 15 ppm und besonders bevorzugt weniger als 10 ppm. Dann sind Oxidationsprozesse zu der Oberfläche des Strangs zu vernachlässigen.In one embodiment of the invention, the oxygen content of the protective gas atmosphere during annealing is less than 50 ppm, preferably less than 15 ppm and particularly preferably less than 10 ppm. Then oxidation processes on the surface of the strand are negligible.

In einer Ausführungsform der Erfindung liegt der Taupunkt der Schutzgasatmosphäre bei Atmosphärendruck (1013 mbar) bei einer Temperatur von -40° C oder weniger, vorzugsweise von -50° C oder weniger.In one embodiment of the invention, the dew point of the protective gas atmosphere at atmospheric pressure (1013 mbar) is at a temperature of -40 ° C. or less, preferably -50 ° C. or less.

Während davon auszugehen ist, dass der beschriebene Effekt des Glühens bei den erfindungsgemäßen Temperaturen bei allen Edelstahlmaterialien eintritt, konnte er von den Erfindern insbesondere für austenitische Edelstähle explizit nachgewiesen werden.While it can be assumed that the described annealing effect occurs with all stainless steel materials at the temperatures according to the invention, the inventors were able to explicitly demonstrate it, in particular for austenitic stainless steels.

Dabei wird im Sinne der vorliegenden Anmeldung unter einem austenitischen Edelstahl ein kubisch-flächenzentrierter Mischkristall einer Eisenlegierung, insbesondere ein y-Mischkristall, verstanden.In the context of the present application, an austenitic stainless steel is understood to mean a face-centered cubic mixed crystal of an iron alloy, in particular a y mixed crystal.

Ein Strang im Sinne der vorliegenden Anmeldung ist in Form eines Rohres.A strand in the sense of the present application is in the form of a tube.

Das erfindungsgemäße Verfahren dient der Herstellung eines Rohrs. Rohre mit einer hohen Zugfestigkeit bei gleichzeitig hoher Dehnung werden vor allem auf dem Gebiet medizinischer Implantate aber auch als Hochdruckleitungen für die unterschiedlichsten Anwendungszwecke benötigt.The method according to the invention is used to manufacture a pipe. Tubes with a high tensile strength and, at the same time, high elongation are required above all in the field of medical implants, but also as high-pressure lines for a wide variety of applications.

Während man aber zunächst davon ausgehen könnte, dass der beschriebene Effekt des Glühens bei den erfindungsgemäßen Temperaturen nur bei dünnwandigen kaltverfestigten Edelstahlrohren eintritt, hat sich überraschenderweise gezeigt, dass dieser auch bei stabförmigen kaltverfestigten Strängen mit einem massiven Querschnitt und insbesondere auch bei dickwandigen Rohren auftritt. Solche dickwandigen Rohre werden in der Hochdrucktechnik zur Fluidführung benötigt. Bei einem rohrförmigen Strang weisen die Luppe und der fertige Strang einen Innendurchmesser und einen Außendurchmesser auf. Rohre, bei denen der Innendurchmesser die Hälfte des Außendurchmessers oder weniger, vorzugsweise ein Drittel des Außendurchmessers oder weniger, beträgt, gelten als hochdruckfest und werden im Sinne der vorliegenden Anmeldung als Hochdruckrohre bezeichnet.While one could initially assume that the annealing effect described at the temperatures according to the invention only occurs with thin-walled, cold-worked stainless steel tubes, it has surprisingly been shown that this also occurs with rod-shaped, cold-worked strands with a massive cross-section and, in particular, with thick-walled tubes. Such thick-walled tubes are required in high-pressure technology for guiding fluids. In the case of a tubular strand, the billet and the finished strand have an inside diameter and an outside diameter. Pipes in which the inside diameter is half the outside diameter or less, preferably a third of the outside diameter or less, are considered to be high-pressure-resistant and are referred to as high-pressure pipes in the context of the present application.

Erfindungsgemäß ist der kaltverfestigte Strang ein Rohr mit einem Innendurchmesser und einem Außendurchmesser, wobei der Innendurchmesser die Hälfte des Außendurchmessers oder weniger, vorzugsweise ein Drittel des Außendurchmessers oder weniger beträgt.According to the invention, the work-hardened strand is a tube with an inner diameter and an outer diameter, the inner diameter being half the outer diameter or less, preferably one third of the outer diameter or less.

Weitere Vorteile, Merkmale und Anwendungsmöglichkeiten der vorliegenden Erfindung werden anhand der folgenden Beschreibung eines Beispiels deutlich.Further advantages, features and possible applications of the present invention will become clear from the following description of an example.

Figur 1 zeigt ein Flussdiagramm des Verfahrens zum Herstellen eines austenitischen Edelstahlrohrs gemäß einer Ausführungsform der vorliegenden Erfindung. Figure 1 FIG. 10 shows a flow diagram of the method for producing an austenitic stainless steel pipe according to an embodiment of the present invention.

In einem Versuch wurde ein Rohr als Luppe aus einem austenitischen Edelstahl gemäß DIN1.44/41, das Kohlenstoff mit einem Anteil von nicht mehr als 0,06 Gew.-%, Mangan mit einem Anteil von nicht mehr als 1,8 Gew.-%, Silizium mit einem Anteil von nicht mehr als 0,7 Gew.-%, Nickel mit einem Anteil von 11 Gew.-%, Chrom mit einem Anteil von 17 Gew.-% und Molybdän mit einem Anteil von 2,3 Gew.-% aufweist mit einem Rest Eisen und unvermeidbaren Verunreinigungen hergestellt.In an experiment, a tube made of an austenitic stainless steel according to DIN 1.44 / 41, the carbon with a proportion of not more than 0.06 wt .-%, manganese with a proportion of not more than 1.8 wt .-% %, Silicon with a proportion of not more than 0.7% by weight, Nickel with a proportion of 11% by weight, chromium with a proportion of 17% by weight and molybdenum with a proportion of 2.3% by weight, with the remainder being made of iron and unavoidable impurities.

Die Luppe wurde zunächst durch Kaltpilgerwalzen zu einem fertig dimensionierten Edelstahlrohr kalt reduziert.The hollow was first cold reduced by cold pilger rollers to a finished dimensioned stainless steel pipe.

Das so gewalzte Rohr hat eine Dehnung A(H) von 25,0 % und eine Zugfestigkeit Rp 0,2 von 762 N/mm2.The tube rolled in this way has an elongation A (H) of 25.0% and a tensile strength Rp 0.2 of 762 N / mm 2 .

Nachfolgend wurde dieses kaltgepilgerte Rohr unter einer Schutzgasatmosphäre mit einem Anteil an Argon von mehr als 95 Vol.-% bei einer Temperatur von 440° C geglüht. Dabei war der Sauerstoffgehalt in der Schutzgasatmosphäre geringer als 10 ppm.This cold pilgrim tube was then annealed under a protective gas atmosphere with an argon content of more than 95% by volume at a temperature of 440 ° C. The oxygen content in the protective gas atmosphere was less than 10 ppm.

Das geglühte Rohr weist nach dem Glühen eine Dehnung A(H) von 15,1 % auf. Die Zugfestigkeit Rp 0,2 beträgt 812 N/mm2.The annealed tube has an elongation A (H) of 15.1% after annealing. The tensile strength Rp 0.2 is 812 N / mm 2 .

Zur Erläuterung wird nun anhand des Flussdiagramms aus Figur 1 das Verfahren zur Herstellung eines Edelstahlrohrs gemäß der vorliegenden Erfindung noch einmal kurz zusammengefasst.For the purpose of explanation, the flowchart will now be used Figure 1 the method for producing a stainless steel pipe according to the present invention once again briefly summarized.

Zunächst wird in Schritt 1 als Ausgangsmaterial ein Rohr aus austenitischem Edelstahl als Luppe bereitgestellt. Der Edelstahl enthält neben Eisen und unvermeidbaren Verunreinigungen Kohlenstoff mit einem Anteil von nicht mehr als 0,06 Gew.-%, Mangan mit einem Anteil von nicht mehr als 1,8 Gew.-%, Silizium mit einem Anteil von nicht mehr als 0,7 Gew.-%, Nickel mit einem Anteil von 11 Gew.-%, Chrom mit einem Anteil von 17 Gew.-% und Molybdän mit einem Anteil von 2,3 Gew.-%. Diese Luppe wird dann durch Kaltpilgerwalzen in Schritt 2 zum fertig dimensionierten Rohr kaltumgeformt.First, in step 1, a tube made of austenitic stainless steel is provided as a shell as the starting material. In addition to iron and unavoidable impurities, stainless steel contains carbon with a proportion of not more than 0.06% by weight, manganese with a proportion of not more than 1.8% by weight, silicon with a proportion of not more than 0, 7% by weight, nickel with a proportion of 11% by weight, chromium with a proportion of 17% by weight and molybdenum with a proportion of 2.3% by weight. This shell is then cold-formed by cold pilger rolling in step 2 into a finished dimensioned tube.

Das fertige Rohr wird sodann in Schritt 3 unter einer Schutzgasatmosphäre mit einem Anteil an Argon von mehr als 95 Vol.-% und einem Sauerstoffgehalt in der Schutzgasatmosphäre von weniger als 10 ppm bei einer Temperatur von 440° C geglüht.The finished tube is then annealed in step 3 under a protective gas atmosphere with an argon content of more than 95% by volume and an oxygen content in the protective gas atmosphere of less than 10 ppm at a temperature of 440 ° C.

Claims (8)

  1. A method of manufacturing a billet of stainless steel comprising:
    cold forming a bloom to give the strain-hardened billet; and
    subsequent annealing of the billet,
    wherein upon annealing of the billet the billet is heated to a temperature in a range of from 400° C to 460° C,
    characterised in that
    the strain-hardened billet is surrounded by a protective gas atmosphere during heating,
    wherein the method further has the step of cooling the billet after heating, wherein the billet during cooling is surrounded by the protective gas atmosphere,
    wherein the bloom and the billet are in the form of a tube with an inside diameter and an outside diameter,
    wherein a tube is formed by the cold forming operation, the inside diameter of which is half of the outside diameter or less,
    wherein the material of the bloom is an austenitic stainless steel.
  2. A method according to claim 1 characterised in that the billet is heated to a temperature in a range of from 410° C to 450° C, preferably in a range of from 435° C to 445° C and particularly preferably to 440° C
  3. A method according to one of the preceding claims characterised in that the protective gas atmosphere comprises argon, preferably with a proportion of argon of more than 95% by volume.
  4. A method according to one of the preceding claims characterised in that the protective gas atmosphere has an oxygen content of less than 50 ppm, preferably less than 15 ppm and particularly preferably less than 10 ppm.
  5. A method according to one of the preceding claims characterised in that the dew point of the protective gas atmosphere at atmospheric pressure is at a temperature of -40° C or lower, preferably 50° C or lower.
  6. A method according to one of the preceding claims characterised in that the inside diameter is a third of the outside diameter or less.
  7. A method according to one of the preceding claims characterised in that the cold forming operation is carried out by cold pilger rolling.
  8. A method according to one of the preceding claims characterised in that the stainless steel is an austenitic stainless steel according to DIN 1.44/41.
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