Process for subsequent treatment of extruded tubes of stainless or high alloy nickel steel produced by a powder-metallurgic method

摘要

Procedure for after-treatment of powder-metallurgically produced, extrusion pressed pipe of stainless steel or high-alloy nickel steel whereby the pressed pieces are first produced in a process through which a capsule of thin sheet metal is filled with powder, consisting primarily of spherical grain that is produced by atomizing the desired raw material. The powder-filled capsule is then tightly sealed and cold isostatic pressing is used to increase the density to at least 80-93 percent of the theoretical density. The pressed pieces thus obtained are extrusion pressed into pipe at a temperature of 1200 degrees C using glass as a lubricant. The extrusion pressed, encapsulated pipes are then given a first treatment with a hydrated sulphuric acid to remove any glass remaining on the surface. The pipes are then cold worked through drawing or pilgrim-step rolling and are subsequently annealed in an oxidizing atmosphere until the capsule is oxidized to such a degree that mild mordanting can generate a capsule-free surface.IMAGE