Abstract: Various conventional problems produced by the reason that the coil preparatory line and the reversing cold rolling line are independent of each other are to be solved by unifying the both lines without reducing efficiency of rolling operation. A reversing rolling apparatus according to the present invention includes a first and a second coiling-uncoiling units supported by a common frame, disposed between a reversing rolling mill for cold rolling steel strips and a joining unit for joining the trailing end portion of a preceding steel strip un-coiled by a uncoiling unit to the leading end portion of a following steel strip directly or via a dummy strip, or for joining dummy strips to end portions of a steel strip so that positions of both the coiling-uncoiling units are to be switchable.

Abstract: A box annealing furnace for annealing a metal sheet includes an oxygen removal unit for removing oxygen from the atmosphere in a box annealing furnace, with a gas circulation system for withdrawing atmosphere from the box annealing furnace during annealing, treating the gas, and for refeeding the deoxidized gas to the box annealing furnace. The box annealing furnace may also include a moisture removal unit for removing moisture from the gas. The oxygen removal unit and the moisture removal unit can reliably remove oxygen and moisture from the gas and suppress the formation, during annealing, of oxide film on a ferrous metal sheet.

Abstract: An anti-oxidation agent for preventing oxidation of a stainless steel strip during continuous annealing comprising a colloidal inorganic substance which can be crystallized at a temperature not higher than 1300.degree. C. at least one compound having a melting point not higher than 1300.degree. C., selected from the group consisting of silicates, borates and phosphates, a dispersion agent, and the balance substantially water. The anti-oxidation agent is applied to the surface of the stainless steel strip. During the annealing, the anti-oxidation agent enhances the heat absorption so that the stainless steel strip temperature is elevated to the annealing temperature in a short time. The anti-oxidation agent on the strip surface forms a film of a fine structure which keeps the strip surface away from oxidizing components of the annealing atmosphere so as to suppress generation of oxide scale. The film is easily separated due to thermal contraction in the course of the cooling after the annealing.

Abstract: A descaling method for removing oxide scale from a hot-rolled stainless steel strip. A solution of an alkaline earth metal chloride is applied to the surface of the oxide scale layer formed on the hot-rolled stainless steel strip, and the solution is allowed to penetrate into the oxide scale layer. In a subsequent annealing, the solution is heated and dehydrated to become solid matter and the dehydrated matter is melted and diffused into the oxide scale layer to soften the oxide scale layer. The oxide scale layer is then removed by a simple mechanical descaling by, for example, grinding brushes with or without a subsequent chemical descaling by a weak acid solution.

Abstract: A method for blowing a gas from below into a molten steel in a refining vessel, which comprises: using a refining vessel including at least one gas blowing aperture provided in the bottom wall thereof and a frustoconical plug matching with said aperture, releasably inserted into said gas blowing aperture, which has a small-diameter bore having a diameter within the range of from 0.5 to 6.

Abstract: 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.

Abstract: 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%.

Abstract: 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:[C].ltoreq.[C] 0.3, when 0.8.ltoreq.[C].ltoreq.1.0% (1)[c].ltoreq.55/70[c]--6/70, when 1.0.ltoreq.[C].ltoreq.2.5% (2).

Abstract: 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.