Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/006—Continuous casting of metals, i.e. casting in indefinite lengths of tubes
• • 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

Definitions

• the invention relates to a method for producing seamless tubes from austenitic, chromium and nickel-containing steels.
• Austenitic tubes can be manufactured using an inclined rolling process, by extrusion, continuous casting or by welding sheet metal strips.
• the welded pipes are less expensive to manufacture, but due to the weld seam present, they have only a relatively small area of application.
• a mandrel In the cross-rolling process, a mandrel has to be driven through a corresponding blank, an economical application only being given for certain cross sections.
• a heated steel In the production of seamless tubes by means of extrusion, a heated steel is pressed through a die, with the most severe deformations occurring.
• the present invention has set itself the goal of providing a method for producing seamless tubes from an austenitic, chromium and nickel-containing alloy, in which the above-mentioned. Disadvantages are avoided, the advantages of continuous casting should also be combined with those of extrusion.
• the process according to the invention for the production of seamless tubes made of austenitic chromium-nickel-containing steels with continuous casting whereby a molten metal is continuously poured into a cooled mold with a round mold cavity and partially solidified in it, drawn off and the through-hardened strand is cut to length in that the metal melt, which has not yet solidified, is electromagnetically stirred in the direction about the longitudinal axis of the strand and in that the cut-to-length castings are annealed between 1100 and 1250 ° C, preferably between 1150 and 1200 ° C, between 30 minutes and 4 hours, preferably between 1 and 2 Are subjected to hours, whereupon the castings are allowed to cool and mechanically machined to form extrusion billets, whereupon seamless pipes are produced in a manner known per se from the extrusion billets which are in the cast state and have not yet undergone hot deformation.
• the molten metal is moved at least in a part of the mold around the longitudinal axis of the strand, the relative movement between the strand shell and the liquid strand core preferably reaching up to the casting level.
• a particularly advantageous, labor-saving method is obtained if the mechanical machining of the continuous castings into an extrusion die is carried out before the annealing. With this procedure, mechanical machining is particularly easy to carry out, since there is less material toughness before annealing.
• extrusion die which is in the as-cast state, is subjected to extrusion from the incandescent heat, additional manipulation is omitted, and at the same time the energy for reheating does not have to be consumed.
• a steel X10CrNiTi 18 9 was melted in a medium frequency induction crucible furnace and tapped into a pan and brought to a continuous casting plant. From this pan, the alloy was poured into the distributor of the continuous casting plant, the superheating of the metal being 35 ° C. The steel was introduced from the distributor into the continuous casting mold with an inside diameter of 210 mm by means of a pouring tube, after a start-up phase of 0.3 min. was a casting speed of 1.05 m / min. reached. The casting was carried out with a covered casting level, ie under powder.
• a three-pole rotating field device was installed in the system 220 mm below the lower edge of the 650 mm long mold. During the casting, the rotating field was supplied with an output of 72 kVA. On the basis of observations of the casting level or of the casting powder on the casting head, it was found that the liquid strand, up to the casting level in the mold, rotated around the longitudinal axis of the strand.
• a test piece was taken from it for further investigations.
• the strand pieces were annealed in an oven at 1190 ° C., the holding time being 1.6 hours. After the annealing treatment, a test piece was again taken from the strand.
• the comparative investigations showed that after the continuous casting a delta ferrite content of 4.6% was present. Such high delta ferrite contents have an extremely disadvantageous effect on the deformability of the material. After annealing, the delta ferrite content in the strand was below 1%.
• the extrusion die After processing the surface of the continuous casting, sawing and drilling, the extrusion die was heated up inductively and expanded by means of an expanding cap and punch. The expansion process went smoothly, ie the material had good thermoformability properties. In connection after intermediate heating, the extrusion process was carried out (according to the Handbook of Stainless Steels, Mr. Graw Hill Book Comp. 1977, Chapter 23). The pressed raw pipe had a good surface both inside and outside. No difficulties were found during further processing either, since the material was readily deformable.
• the quality of the pipe was also examined by step turning tests. It was found that there were no disturbing elongated non-metallic inclusions in the tube wall, i.e. that the pipe had particularly high quality features.
• Example 2 The procedure was analogous to Example 1, a composite tubular mold with an integrated stirring coil being used and a steel X5CrNi 18 9 being cast.
• the melt overheated to 25 ° C. After a start-up phase of 0.4 min. the casting speed was 1.0 m / min.
• the rotating field power of the electromagnetic agitation was 65 kVA.
• the annealing was carried out at 1150 ° C. and for 2.8 hours.
• the delta ferrite content was 4.8% before the annealing and was below 1% after the annealing. No problems arose during the extrusion process and the pressed tube had a good surface both inside and outside.
• a steel X2CrNiMo 18 10 was processed analogously to the example, the superheating of the melt being 30 ° C. and after a start-up phase of 0.3 min. a casting speed of 1.1 m / min. was observed.
• the rotating field power of the electromagnetic stirring device was 72 kVA.
• the strand Castings were placed immediately after the continuous casting with a strand surface temperature of 715 ° C in an oven and an annealing at 1200 ° C u. Subject for 1, 4 hours. The delta ferrite content was below 1%.
• the extruded casting which was then machined mechanically to form an extrusion die was subjected to the extrusion process according to Example 1, the tube obtained having no surface defects and the extrusion process being uneventful.
• a steel X10CrNiNb 18 9 was processed analogously to Example 1, the mechanical machining of the continuous casting being carried out to form an extrusion die before annealing. Machining was easier than in the previous examples because there were short breaking chips.
• the continuous cast billet was then heated to 1190 ° C. in a rotary hearth furnace and left at this temperature for 2 hours.
• the extrusion process was carried out directly from the heat of the incandescent heat, whereby no difficulties could be ascertained during processing by the extrusion and the raw tube had a good surface both inside and outside.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Extrusion Of Metal (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Articles (AREA)
• Continuous Casting (AREA)

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• 1981
  • 1981-10-08 AT AT0431381A patent/AT383065B/de not_active IP Right Cessation
• 1982
  • 1982-09-07 ES ES515529A patent/ES8308243A1/es not_active Expired
  • 1982-10-04 US US06/432,762 patent/US4432811A/en not_active Expired - Fee Related
  • 1982-10-04 JP JP57173368A patent/JPS5870955A/ja active Pending
  • 1982-10-07 EP EP82890145A patent/EP0077322B1/fr not_active Expired
  • 1982-10-07 DE DE8282890145T patent/DE3270460D1/de not_active Expired

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