Kawasaki Steel Corporation

Akio Ejima

Yukio Oguchi

Hiroyuki Kaito

Shoji Iwaoka

Takashi Ohtani

Shuya Yano

Takaaki Toyooka

Yoshitomi Onoda

Eiichi Yokoyama

In a method of forming an electric welded steel tube, wherein a hot-rolled sheet is formed into a cylindrical shape, with the central portion thereof being lowered as the forming progresses, and thereafter, subjected to reduction in the circumferential direction of the tube by means of tandem type fin-pass rolls to be finished into the tube, the proper forming condition ranges capable of eliminating occurrence of edge waves in the tube seam edge portion and/or of cambers in the longitudinal direction of the tube by three forming conditions factors including the downhill value D.sub.H (downhill coefficient .eta.) of the hot-rolled sheet, the fin-pass total reduction R of the tandem type fin-pass rolls and the distribution of the fin-pass reduction (the distribution ratio .delta. of the first fin-pass reduction).

Method of forming electric welded steel tube

High chromium steels having extremely low carbon and nitrogen contents are produced by blowing more than 15 up to 40 Nl/min per ton of molten steel of an inert gas into a high chromium steel containing 0.8 to 2.5% of C and 10 to 35% of Cr in a ladle under a reduced pressure from bottom of a ladle and concurrently blowing oxygen gas to the molten steel surface to form 1 to 100 kg per ton of the molten steel of a slag containing not less than 20% of SiO.sub.2 and not more than 25% of Cr.sub.2 O.sub.3 at the end of oxygen blowing, terminating the oxygen blowing when the carbon concentration in the molten steel becomes not more than 0.020%, and subsequently blowing 6 to 40 Nl/min per ton of molten steel of an inert gas under a high vacuum of not more than 10 torr.

Method for producing high chromium steels having extremely low carbon

A method of denitriding a high chromium molten steel with a minimum chromium loss is disclosed. A high chromium molten steel containing 0.8-2.5% of C and 10-35% of Cr is denitrided to a final nitrogen content of not more than 40 ppm in a ladle under vacuum by flowing an inert gas into molten steel at a flow rate of not less than 15 Nl/min per ton of molten steel and at the same time blowing oxygen gas against molten steel until carbon content [C] in molten steel satisfies the following equations (1) and (2) in accordance with the carbon content prior to decarburization [C] of molten steel:

Method of denitriding a high chromium molten steel with a minimum

A method of producing alloy steels having an extremely low carbon content of not higher than 30 ppm is disclosed. The alloy steels can be obtained by vacuum treating a preliminarily decarburized molten steel in the presence of a proper amount of a slag containing specifically limited amounts of chromic oxide and silicon oxide under an inert gas atmosphere by means of a commonly used degassing apparatus.

Growing community of inventors

Chiba, Japan

Akio Ejima