Nitrogen control in argon oxygen refining of molten metal

Claim 2

The process of claim 2 wherein the molten metal is selected from the group consisting of carbon steel, stainless steel, ferrous alloys and nickel based alloys.

Claim 3

The process of claim 2 wherein the first period of said decarburization is terminated after 50-70 percent of the oxygen calculated as necessary for the decarburization step has been injected.

Claim 4

The process of claim 2 wherein following the decarburization step, nitrogen alone is injected into the melt for a sufficient time to increase the nitrogen content of the refined molten steel to any desired level up to within about 90 percent of its equilibrium value.

Claim 5

The process of claim 2 wherein the decarburizatiOn step is followed by reduction and finishing steps, and wherein nitrogen alone is injected into the melt during or after the finishing steps to increase the nitrogen content of the refined melt to the desired level up to within about 90 percent of its equilibrium value.

Claim 6

In a process for refining molten metal comprising the step of decarburizing a mass of molten metal by injecting into said mass from underneath the surface thereof, oxygen and at least one inert gas selected from the group consisting of helium, neon, argon xenon and nitrogen, the improvement comprising: producing a refined molten metal mass having a predetermined nitrogen content within the range of from about 10 ppm to about 90 percent of the equilibrium level, by (a) injecting a gas mixture consisting essentially of oxygen and nitrogen throughout a first period of the decarburization step, wherein the percentage of nitrogen in said gas mixture is maintained such that the partial pressure of the nitrogen in the ambient atmosphere in contact with the melt is greater than the partial pressure of nitrogen in equilibrium with the predetermined nitrogen content sought for the refined melt, thereby causing the nitrogen content of the melt at the end of said first period of the decarburization step to be greater than the predetermined nitrogen content sought for the refined melt, and thereafter (b) adding an inert gas other than nitrogen to said oxygen-nitrogen gas mixture during the remainder of said decarburization step and continuing the injection of said other inert gas until the nitrogen content of the melt is reduced to said predetermined value.

Claim 7

The process of claim 7 wherein said other inert gas is argon.

Claim 8

The process of claim 8 wherein the molten metal is selected from the group consisting of carbon steel, stainless steel, ferrous alloys and nickel based alloys.

Claim 9

The process of claim 8 wherein the first period of said decarburization is terminated after 50-70 percent of the oxygen calculated as necessary for the decarburization step has been injected.

Claim 10

The process of claim 8 wherein following the decarburization step, nitrogen alone is injected into the melt for a sufficient time to increase the nitrogen content of the refined molten steel to any desired level up to within about 90 percent of its equilibrium value.

Claim 11

The process of claim 8 wherein the decarburization step is followed by reduction and finishing steps, and wherein nitrogen alone is injected into the melt during or after the finishing steps to increase the nitrogen content of the refined melt to the desired level up to within about 90 percent of its equilibrium value.

Claim 12

In a process for refining molten metal comprising the step of decarburizing said molten metal by injecting into said molten metal from underneath the surface thereof, oxygen and at least one inert gas selected from the group consisting of helium, neon, argon, xenon and nitrogen, the improvement comprising: producing a refined molten metal charge having a predetermined nitrogen content within the range of from about 10 ppm to about 90 percent of the equilibrium level, by injecting a three component gas mixture of oxygen, nitrogen and another of said inert gases, throughout at least a first period of the decarburization step, and wherein the percentage of nitrogen in the said mixture is maintained such that the partial pressure of the nitrogen in the gaseous atmosphere in contact with the melt is equal to the partial pressure of nitrogen in equilibrium with the predetermined nitrogen content sought in the refined melt divided by X where X 0.7 to 1.0.

Claim 13

The process of claim 13 wherein said three component gas mixture is injected throughout the entire decarburization step.

Claim 14

The process of claim 14 wherein said other inert gas is argon.

Claim 15

The process of claim 15 wherein the molten metal is selected from the group consisting of carbon steel, stainless steel, ferrous alloys and nickel based alloys.

Claim 16

The process of claim 15 wherein the first period of said decarburization is terminated after 50-70 percent of the oxygen calculated as necessary for the decarburization step has been injected.

Claim 17

The process of claim 15 wherein following the decarburization step, nitrogen alone is injected into the melt for a sufficient time to increase the nitrogen content of the refined molten steel to any desired level up to within about 90 percent of its equilibrium value.

Claim 18

The process of claim 15 wherein the decarburization step is followed by reduction and finishing steps, and wherein nitrogen alone is injected into the melt during or after the finishing steps to increase the nitrogen content of the refined melt to the desired level up to within about 90 percent of its equilibrium value.

Claim 19

The process of claim 13 wherein subsequent to termination of said first period of the decarburization step, the nitrogen flow is reduced to zero.

Claim 20

The process of claim 20 wherein said other inert gas is argon.

Claim 21

The process of claim 21 wherein the molten metal is selected from the group consisting of carbon steel, stainless steel, ferrous alloys and nickel based alloys.

Claim 22

The process of claim 21 wherein the first period of said decarburization is terminated after 50-70 percent of the oxygen calculated as necessary for the decarburization step has been injected.

Claim 23

The process of claim 21 wherein following the decarburization step, nitrogen alone is injected into the melt for a sufficient time to increase the nitrogen content of the refined molten steel to any desired level up to within about 90 percent of its equilibrium value.

Claim 24

The process of claim 21 wherein the decarburization step is followed by reduction and finishing steps, and wherein nitrogen alone is injected into the melt during or after the finishing steps to increase the nitrogen content of the refined melt to the desired level up to within about 90 percent of its equilibrium value.