Kawasaki Steel Corporation

Takashi Ohtani

Hiroyuki Kaito

Shoji Iwaoka

Yukio Oguchi

Akio Ejima

Shuya Yano

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

An alloy steel having a high chromium content and an extremely low carbon content is produced by soft blowing oxygen gas under vacuum into a molten steel in a ladle containing a high chromium content and a high carbon content while blowing an inert gas of a flowing rate of 1-15 Nl/min per ton of the molten steel into the molten steel until the carbon content in the molten steel becomes 0.025-0.050% by weight. And subsequently only the blowing of the inert gas is conducted into the molten steel under a high vacuum degree of less than 10 torr so that the reaction active area ratio becomes more than 7% to reduce the carbon content in the steel to less than 0.003%.

Method for producing alloy steels having a high chromium content and an

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.

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Ashiya, Japan

Takashi Ohtani