A treatment method of molten steel capable of preventing metal components in molten steel from being reoxidized by reacting with oxides in molten slag, inhibiting occurrence of inclusions, and reducing nitrogen in the molten steel. The treatment method of molten steel in which a potential difference is applied between the molten steel and the molten slag by using a direct-current power supply and through two electrodes which are a negative electrode being an electrode in contact with the molten steel and a positive electrode being another electrode in contact with only the molten slag is characterized by including: a deoxidation step of deoxidizing the molten steel by adding a deoxidizing agent to the molten steel; and a step of applying the potential difference after the deoxidation step. Also, a steel production method by which the obtained molten steel is cast after components thereof are adjusted.

Disclosed is a method for preparing a titanium-containing ultra-low-carbon steel, comprising molten iron pretreatment, converter primary smelting, vacuum refining, continuous casting, hot rolling, pickling, and cold rolling. After vacuum refining decarbonization is finished, the content of free oxygen in molten steel is 100-350 ppm; after Al is then added for deoxidation treatment, the circulation time of the molten steel is greater than or equal to 3 min; after other alloys and rare earth elements are then added to the molten steel to adjust the components of the molten steel to the specifications of a finished product, the circulation time of the molten steel is greater than or equal to 2 min; and finally, an oxide Re.sub.2O.sub.3.Math.Al.sub.2O.sub.3 is generated in the molten steel, and the vacuum refining is finished. The method can effectively improve the properties of a deoxidation inclusion in steel, solve the problem of smooth running of casting of the molten steel, reduce the incidence of cold rolling defects caused by Al.sub.2O.sub.3, and improve the product quality of the titanium-containing ultra-low-carbon steel.

A molten steel denitrification method including CaO-and-Al.sub.2O.sub.3-containing slag is formed by adding a metal-Al-containing substance to molten steel to deoxidize and turn the molten steel into Al-containing molten steel and adding a CaO-containing substance to the molten steel, and then an oxygen-containing gas is blown from above the slag to perform a denitrification treatment. T.Math.Fe in the slag after the denitrification treatment is set to 3.0 mass % or lower. It is preferable that, in the denitrification treatment, the oxygen-containing gas be supplied such that a ratio L.sub.s/L.sub.s0 between a thickness L.sub.s0 of the slag and a depth L.sub.s of a depression in the slag resulting from blowing of the oxygen-containing gas becomes 0.9 or lower. The obtained molten steel is cast after its components are adjusted. The method allows an extremely low nitrogen concentration range to be stably reached in a short time.

A method for secondarily refining molten steel s by which a low nitrogen concentration range can be stably reached at high speed without causing operational problems, and a method of producing steel are proposed. In the method for secondarily refining molten steel, CaO-and-Al.sub.2O.sub.3-containing slag is formed by a combination of an Al addition step of adding a metal-Al-containing substance to molten steel to turn the molten steel into Al-containing molten steel and a CaO addition step of adding a CaO-containing substance to the molten steel, and then an oxygen blowing process including a denitrification process is performed by blowing oxygen-containing gas so as to pierce the slag to reach the Al-containing molten steel, in which an Al concentration [Al].sub.i (mass %) in the molten steel immediately before the oxygen blowing process is equal to or higher than a value [Al].sub.e calculated by Formula (A) based on a stirring power density ? (W/t) during formation of the slag, and an Al concentration [Al].sub.f upon completion of the oxygen blowing process is 0.03 mass % or higher. In the method of producing steel, the obtained molten steel is cast after adjusting the composition.

[Al].sub.e=?0.072?In(?)+0.5822 . . . (A)

A method wherein a denitrification treatment allows an extremely low nitrogen concentration range to be stably and quickly reached, so denitrification and/or desulfurization of molten steel can be efficiently performed. Wherein CaO-and-Al.sub.2O.sub.3-containing slag is formed on top of molten steel charged in a vessel and an oxygen-containing gas is blown from above, while the slag and the molten steel are brought into contact with each other to remove nitrogen in the molten steel. An Al concentration in the steel is kept at or higher than a value determined by Formula (1) according to a stirring power density, and the gas is blown so a ratio between a thickness L.sub.s0 of the slag and a depth L.sub.s of a depression in the slag resulting from blowing of the gas meets L.sub.s/L.sub.s0?1:

Al concentration (mass %) in molten steel=?0.072?ln(stirring power density (W/t))+0.5822(1)

A non-oriented electrical steel sheet with fine magnetic performance, and a calcium treatment method therefor, including an RH (Ruhrstahl-Heraeus) refinement step. The RH refinement step sequentially comprises a decarbonization step, an aluminum deoxidation step, and a step of adding calcium alloy. In the step of adding calcium alloy, time when the calcium alloy is added satisfies the following condition: time interval between Al and Ca/total time after Al=0.2-0.8. In this method, production cost is reduced, the production process is simple, a normal processing cycle of RH refinement is not affected, the device is convenient in operation and is controllable, and foreign substances are controllable in both shape and quantities. The non-oriented electrical steel sheet prepared according to the present invention has fine magnetic performance, and the method can be used for mass production of the non-oriented electrical steel sheet with fine magnetic performance.

There is a hot-rolled steel according to one aspect of the invention including predetermined chemical compositions including 0.0001 to 0.0050 mass % of Bi, in which 90 area % or more of a metallographic structure is configured with a ferrite and a pearlite, and an average number density of Mn sulfides extending along a rolling direction and having an aspect ratio exceeding 10 and equal to or smaller than 30, which is measured on a cross section parallel to the rolling direction, is 50 to 200 number/mm.sup.2.

The invention relates to interstitial free (IF) steel production using scrap and its production method.

In particular, the invention relates to IF steel with improved formability and strength properties and its production method, which is produced using scrap to eliminate the dependence on raw iron ore in IF steel production by using recyclable and reusable resources.

The present invention relates to IF steel and its production method, which is produced using 50-100% scrap, which eliminates dependence on raw iron ore in IF steel production by utilizing recyclable, reusable resources.

A control process of inclusions in ultra-clean rare earth steel, wherein the content of rare earth elements REM in the ultra-clean rare earth steel, the total oxygen content T[O]m, the total sulfur content T[S]m in the steel, and the total oxygen content T[O]r in a rare earth metal or alloy added to the steel are controlled to satisfy the following formula: ?500<REM?(m*T[O]m+n*T[O]r+k*T[S]m)<?30, where REM is the content of rare earth elements in the steel, in ppm; T[O]m is the total oxygen content in the steel, in ppm; T[O]r is the total oxygen content in a rare earth metal or alloy added to the steel, in ppm; T[S]m is the total sulfur content in the steel, in ppm; m is a first correction coefficient, with a value of 2-4.5;n is a second correction coefficient; and k is a third correction coefficient.

Stabilized volatile briquettes and processes and apparatuses for making and using the same are provided. The stabilized volatile briquette includes a volatile material and a thermoplastic binder material such that the thermoplastic binder material binds the volatile material together to define a briquette that is stable. The process includes mixing a volatile waste material and a thermoplastic binder material to form a briquette mixture, shearing the briquette mixture, extruding the briquette mixture to form a thermoplastic briquette extrusion, and hardening the thermoplastic briquette extrusion to form a stabilized volatile briquette. The apparatus includes an extruder, a heating portion operably connected to the extruder, and a heated die operably connected to the heating portion such that the extruder, the heating portion, and the heated die are configured to gradually heat a thermoplastic binder material such that the thermoplastic binder material binds a provided volatile material together.