PURPOSE: To obtain a seamless steel tube of duplex stainless steel excellent in the outside surface quality of tube without rolling flaw that is harmful to productivity and cost by rolling by Mannesmann process for making tube using a round billet or square bloom which is provided with chrome film.
CONSTITUTION: After applying thermal spraying, plating or the like of chromium on the surface of the round billet or square bloom, they are made into tube according to usual Mannesmann rolling process and its manufacturing conditions. In this way, rug-gedness on the surface of bar for tube is smoothed and also the generation of surface defects in piercing rolling before rolling with an elongator is reduced. Because alpha single phase allay layer which is diffused in the interior of duplex stainless steel at a high temp. and excellent in workability is formed, rolling flaw is difficult to be propagated.
SOGO YASUO
MIZOGUCHI SHIGERU
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