A process for the production of steel powders including the steps of: providing molten iron from a blast furnace, refining the molten iron in a converter to form molten steel including up to 600 ppm C, up to 120 ppm S, up to 125 ppm P, up to 50 ppm N and up to 1200 ppm O, pouring the molten steel in a plurality of induction furnaces, adding, in each of the plurality of induction furnaces, at least one ferroalloy to adjust the steel composition, pouring the molten steel at the desired composition of each induction furnace in a dedicated reservoir connected to at least one gas atomizer, feeding the at least one gas atomizer of each reservoir in molten steel from each reservoir under pressure and gas atomizing the molten steel to form the steel powder at the desired composition.

A process for the production of steel powders including the steps of: providing molten iron from a blast furnace, refining the molten iron in a converter to form molten steel including up to 600 ppm C, up to 120 ppm S, up to 125 ppm P, up to 50 ppm N and up to 1200 ppm O, pouring the molten steel in a plurality of induction furnaces, adding, in each of the plurality of induction furnaces, at least one ferroalloy to adjust the steel composition, pouring the molten steel at the desired composition of each induction furnace in a dedicated reservoir connected to at least one gas atomizer, feeding the at least one gas atomizer of each reservoir in molten steel from each reservoir under pressure and gas atomizing the molten steel to form the steel powder at the desired composition.

A steel sheet according to the present invention includes a predetermined chemical composition, in which amounts of each elements by mass % in the chemical composition satisfy both of expression 0.3000{Ca/40.88+(REM/140)/2}/(S/32.07) and expression Ca0.00580.0050C, and a number density of carbonitrides including Ti which exists independently and has a long side of 5 m or more is limited to 5 pieces/mm.sup.2 or less.

A steel sheet according to the present invention includes a predetermined chemical composition, in which amounts of each elements by mass % in the chemical composition satisfy both of expression 0.3000{Ca/40.88+(REM/140)/2}/(S/32.07) and expression Ca0.00580.0050C, and a number density of carbonitrides including Ti which exists independently and has a long side of 5 m or more is limited to 5 pieces/mm.sup.2 or less.

A process for the production of steel powders including the steps of: providing molten iron from a blast furnace, refining the molten iron in a converter to form molten steel, refining the molten steel in a vacuum arc degasser to obtain a refined molten steel comprising from 20 to less than 600 ppm C, from 15 to less than 120 ppm S, up to 125 ppm P, up to 80 ppm N and up to 30 ppm O, pouring in a plurality of induction furnaces, adding at least one ferroalloy, pouring the molten steel of each induction furnace in a dedicated reservoir connected to at least one gas atomizer, feeding the at least one gas atomizer of each reservoir in molten steel from each reservoir under pressure and gas atomizing the molten steel to form the steel powder at the desired composition.

A process for the production of steel powders including the steps of: providing molten iron from a blast furnace, refining the molten iron in a converter to form molten steel, refining the molten steel in a vacuum arc degasser to obtain a refined molten steel comprising from 20 to less than 600 ppm C, from 15 to less than 120 ppm S, up to 125 ppm P, up to 80 ppm N and up to 30 ppm O, pouring in a plurality of induction furnaces, adding at least one ferroalloy, pouring the molten steel of each induction furnace in a dedicated reservoir connected to at least one gas atomizer, feeding the at least one gas atomizer of each reservoir in molten steel from each reservoir under pressure and gas atomizing the molten steel to form the steel powder at the desired composition.

A method for dephosphorization of molten iron includes, while blowing a hydrogen gas, a hydrocarbon gas, or a mixture of these gases into molten iron held in a vessel, supplying a slag-forming agent and an oxygen source to perform a dephosphorization treatment of the molten iron and obtain dephosphorized molten iron, and after the dephosphorization treatment, separating slag floating on a surface of the dephosphorized molten iron from the dephosphorized molten iron. In this method for dephosphorization of molten iron, before the dephosphorization treatment, when obtaining molten iron by melting a cold iron source in a melting furnace and discharging the molten iron from the melting furnace into the vessel, one or both of the following are performed: separating generated slag from the molten iron before the discharge; and separating slag that has flowed into the vessel along with the molten iron from the molten iron.

Embodiments include a method of making steel with low carbon content which includes preparing a heat of molten steel composition in a steelmaking furnace to a tapping temperature ranging from 2912 to 3060 degrees F. and tapping into a ladle the molten steel composition having an oxygen level is about 700 to 1000 ppm. The molten steel composition is then transported to a ladle metallurgy furnace, where the molten steel composition is further heated and one or more elements are added to the molten steel composition. The molten steel composition is then transported from the ladle metallurgy furnace to a vacuum tank degasser. The molten steel composition is then decarburized and one or more elements are added to the molten steel composition at the vacuum tank degasser for deoxidization and desulphurization. The molten steel composition is then transported to a ladle metallurgy furnace to further adjust chemistry and temperature.

Embodiments include a method of making steel with low carbon content which includes preparing a heat of molten steel composition in a steelmaking furnace to a tapping temperature ranging from 2912 to 3060 degrees F. and tapping into a ladle the molten steel composition having an oxygen level is about 700 to 1000 ppm. The molten steel composition is then transported to a ladle metallurgy furnace, where the molten steel composition is further heated and one or more elements are added to the molten steel composition. The molten steel composition is then transported from the ladle metallurgy furnace to a vacuum tank degasser. The molten steel composition is then decarburized and one or more elements are added to the molten steel composition at the vacuum tank degasser for deoxidization and desulphurization. The molten steel composition is then transported to a ladle metallurgy furnace to further adjust chemistry and temperature.

A molten steel refining method includes throwing a powder to molten steel while heating the powder with a flame formed by combustion of a hydrocarbon gas at the leading end of a top blowing lance. The lance height of the top blowing lance (the distance between the static bath surface of the molten steel and the leading end of the lance) is controlled to 1.0 to 7.0 m, and the dynamic pressure P of a jet flow ejected from the top blowing lance calculated from equation (1) below is controlled to 20.0 kPa or more and 100.0 kPa or less. P=.sub.g U.sup.2/2 . . . (1) wherein P is the dynamic pressure (kPa) of the jet flow at an exit of the top blowing lance, .sub.g the density (kg/Nm.sup.3) of the jet flow, and U the velocity (m/sec) of the jet flow at the exit of the top blowing lance.