US 4,364,162 AGranted

Process for the after-treatment of powder-metallurgically produced extruded tubes

AssigneeGranges Nyby AB

InventorsPeter Nilsson, Christer Aslund

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Abstract

A process for the after-treatment of powder-metallurgically produced extruded tubes of stainless steel or highly alloyed nickel steels, pressings initially being produced by introducing into a capsule of thin sheet steel a powder consisting predominantly of spherical particles which have been produced from the required starting material by sputtering and, after the capsule has been closed, the density of the powder is increased to at least about 80% to about 93% of the theoretical density by cold isostatic pressing and the pressings obtained are then extruded into tubes at temperatures around 1200.degree. C. using glass as the lubricant and the extruded tubes still surrounded by the capsule are initially treated with aqueous sulphuric acid to remove the glass still present on their surface, subsequently cold-worked by drawing or reciprocating rolling and, after cold-working, are annealed in an oxidising atmosphere until the capsule has been converted into scale to such an extent that a surface free from capsule residues is obtained after pickling with mild pickles.

Claims14

Dependent claims

A process for the after-treatment of encapsulated powder-metallurgically produced extruded tubes of stainless steel or highly alloyed nickel steels produced, from pressings comprising a tubular capsule of thin, preferably 1 to 2 mm thick, low-carbon sheet steel preferably having a carbon content of less than 0.015% containing a powder of metal or metal alloys or mixtures thereof which after the capsule has been closed, has had its density increased to at least about 80% to about 93% of the theoretical density by isostatic cold pressing under a pressure of at least about 4000 bars, and then has been extruded at high temperatures, preferably around 1200.degree. C., using glass as a lubricant, into tubes having a dense structure, comprising the steps of:

(a) removing glass present on the surface of the encapsulated extended tubes by means of aqueous sulphuric acid;
(b) subsequently cold-working the encapsulated tubes by one of cold drawing and reciprocating rolling;
(c) after step (b), annealing the encapsulated tubes in an oxidizing atmosphere in a manner converting the capsule to scale;
and
(d) pickling said tubes in a mild pickling liquid in a manner removing said scale.

2 more elements

Dependencies are inferred from the claim text.