Extruded stainless steel tubes prodn. by powder metallurgy - by cold pressing, extruding, washing off glass lubricant using sulphuric acid, cold working and heating to red heat

摘要

The parent patent described the prodn. of extruded stainless steel tubes by a powder metallurgical process in which the stainless steel powder was isostatically cold pressed in a thin-walled, pref. low alloy carbon steel capsule and then extruded, pref. at 1200 degrees C using a glass lubricant to give a dense product. In the present invention, the product (still encapsulated) is treated with aq. sulphuric acid soln. to remove glass residues, cold worked by drawing or pilger rolling, and then heated to red heat in an oxidising atmos. HF-HNO3 acid baths are not required since the H2SO4 acid soln. removes the glass residues and the cold working reduces the thickness of the capsule residue so that it can be removed by the oxidn. step. By leaving the capsule residues on the product, cold working is improved since simple oils (instead of highly chlorinated oils) can be used as lubricants and continuous advancement of the zone of deformation is facilitated. The surface quality of the finished product is also improved.