DEOXIDIZING NICKEL BASE AND COBALT BASE ALLOYS
United States Patent 3816104
A method of deoxidizing metal while maintaining the carbon content of the metal at a level about equal to or lower than the level prior to deoxidizing. It comprises the steps of introducing hydrocarbon deoxidizer and diluent gas into a vessel containing molten metal, determining the effect of the hydrocarbon deoxidizer and diluent gas upon the carbon content of the metal and controlling the proportion of hydrocarbon deoxidizer to diluent gas so that the average rate of carbon leaving the vessel is about equal to or greater than the average rate of carbon being introduced into the vessel.
US Patent References:
Process for vacuum deoxidation of alloys
Sluis et al. - November 1965 - 3218156
/3725041.html
Ramachandran - April 1973 - 3725041
Process for vacuum deoxidation of alloys
Sluis et al. - November 1965 - 3218156
/3725041.html
Ramachandran - April 1973 - 3725041
Application Number:
05/307661
Publication Date:
06/11/1974
Filing Date:
11/24/1972
View Patent Images:
Export Citation:
Assignee:
Allegheny Ludlum Industries, Inc. (Pittsburgh, PA)
Primary Class:
Other Classes:
75/628, 75/626, 75/385
International Classes:
C21C7/06; C22B9/05; C22B9/00; C22B23/00
Field of Search:
75/82,93,60,59,49 72/82,59,60
Primary Examiner:
Rutledge, Dewayne L.
Assistant Examiner:
Andrews M. J.
Attorney, Agent or Firm:
Gioia, Vincent Dropkin Robert G. F.
Parent Case Data:
This application is a division of copending application Ser. No. 75,738, filed Sept. 25, 1970 now U.S. Pat. No. 3,725,041.
Claims:
I claim
1. A method of deoxidizing molten metal from the group consisting of nickel base and cobalt base alloys and controlling its final oxygen content while maintaining a carbon level about equal to or lower than the carbon level which was present prior to deoxidizing, which comprises the steps of: analyzing molten metal from the group consisting of nickel base and cobalt base alloys to determine its oxygen content; introducing hydrocarbon deoxidizer and diluent gas at an average injection rate of at least 20 cu.ft. per hour into a vessel containing said molten metal at a subatmospheric pressure, said hydrocarbon deoxidizer reacting with oxygen within said metal to form gaseous carbon compounds which exit from said vessel; determining the effect of the hydrocarbon deoxidizer and diluent gas upon the carbon content of said metal; controlling the proportion of hydrocarbon deoxidizer to diluent gas so that the average rate of carbon leaving said vessel is about equal to or greater than the average rate of carbon being introduced into said vessel; and discontinuing said introduction of hydrocarbon deoxidizer and diluent gas into said vessel after a predetermined amount of oxygen has been removed from said metal.
2. A method according to claim 1 wherein said introducing of hydrocarbon deoxidizer and diluent gas into said vessel containing molten metal comprises the step of blowing hydrocarbon deoxidizer and diluent gas into said molten metal.
3. A method according to claim 1 wherein said introducing of hydrocarbon deoxidizer and diluent gas into said vessel containing molten metal comprises the step of blowing hydrocarbon deoxidizer and diluent gas onto said molten metal.
4. A method according to claim 1 wherein said molten metal is a second melt and wherein said determining of the effect of said hydrocarbon deoxidizer and diluent gas upon the carbon content of said melt, comprises the steps of: analyzing a first melt contained within a vessel to determine its carbon content; deoxidizing said first melt with hydrocarbon deoxidizer; calculating the amount of carbon introduced into said vessel containing said first melt; analyzing said deoxidized first melt to determine its carbon content; and calculating the efficiency of said introduced carbon in deoxidizing said first melt.
5. A method according to claim 1 wherein said determining of the effect of said hydrocarbon deoxidizer and diluent gas upon the carbon content of said metal comprises the steps of: calculating the rate at which carbon is introduced into said vessel; and calculating the rate at which carbon leaves said vessel.
6. A method according to claim 5 including the step of analyzing the gases exiting from said vessel.
7. A method according to claim 1 wherein said average injection rate is at least 30 cu.ft. per hour.
8. A method according to claim 1 wherein said hydrocarbon deoxidizer is comprised of methane.
9. A method according to claim 8 wherein said diluent gas is comprised of argon.
10. A method according to claim 1 wherein said hydrocarbon deoxidizer is a liquid and including the steps of atomizing and mixing said liquid hydrocarbon deoxidizer into said diluent gas.
1. A method of deoxidizing molten metal from the group consisting of nickel base and cobalt base alloys and controlling its final oxygen content while maintaining a carbon level about equal to or lower than the carbon level which was present prior to deoxidizing, which comprises the steps of: analyzing molten metal from the group consisting of nickel base and cobalt base alloys to determine its oxygen content; introducing hydrocarbon deoxidizer and diluent gas at an average injection rate of at least 20 cu.ft. per hour into a vessel containing said molten metal at a subatmospheric pressure, said hydrocarbon deoxidizer reacting with oxygen within said metal to form gaseous carbon compounds which exit from said vessel; determining the effect of the hydrocarbon deoxidizer and diluent gas upon the carbon content of said metal; controlling the proportion of hydrocarbon deoxidizer to diluent gas so that the average rate of carbon leaving said vessel is about equal to or greater than the average rate of carbon being introduced into said vessel; and discontinuing said introduction of hydrocarbon deoxidizer and diluent gas into said vessel after a predetermined amount of oxygen has been removed from said metal.
2. A method according to claim 1 wherein said introducing of hydrocarbon deoxidizer and diluent gas into said vessel containing molten metal comprises the step of blowing hydrocarbon deoxidizer and diluent gas into said molten metal.
3. A method according to claim 1 wherein said introducing of hydrocarbon deoxidizer and diluent gas into said vessel containing molten metal comprises the step of blowing hydrocarbon deoxidizer and diluent gas onto said molten metal.
4. A method according to claim 1 wherein said molten metal is a second melt and wherein said determining of the effect of said hydrocarbon deoxidizer and diluent gas upon the carbon content of said melt, comprises the steps of: analyzing a first melt contained within a vessel to determine its carbon content; deoxidizing said first melt with hydrocarbon deoxidizer; calculating the amount of carbon introduced into said vessel containing said first melt; analyzing said deoxidized first melt to determine its carbon content; and calculating the efficiency of said introduced carbon in deoxidizing said first melt.
5. A method according to claim 1 wherein said determining of the effect of said hydrocarbon deoxidizer and diluent gas upon the carbon content of said metal comprises the steps of: calculating the rate at which carbon is introduced into said vessel; and calculating the rate at which carbon leaves said vessel.
6. A method according to claim 5 including the step of analyzing the gases exiting from said vessel.
7. A method according to claim 1 wherein said average injection rate is at least 30 cu.ft. per hour.
8. A method according to claim 1 wherein said hydrocarbon deoxidizer is comprised of methane.
9. A method according to claim 8 wherein said diluent gas is comprised of argon.
10. A method according to claim 1 wherein said hydrocarbon deoxidizer is a liquid and including the steps of atomizing and mixing said liquid hydrocarbon deoxidizer into said diluent gas.
Description:
The present invention relates to a method of deoxidizing molten metal and more particularly to a method of deoxidizing molten metal while maintaining the carbon content of the metal at a level about equal to or lower than the level prior to deoxidizing.
Present day metal-making; e.g., steel-making, processes often involve a deoxidizing treatment. It is highly desirable to lower the oxygen content of a melt since oxygen dissolved in a melt can precipitate as nonmetallic inclusions which adversely affect the properties of the metal.
Various deoxidizing methods have been employed in the past. One method involves the use of highly reactive elements; e.g., silicon, titanium and/or aluminum, which combine with oxygen in the melt to form oxides that subsequently separate from the melt. Sufficient time must, however, be provided for the oxides and melt to separate. A second method involves the mixing of a predetermined quantity of carbon with the melt and a dynamic hydrogen atmosphere to control carbon boil. This method is effective for lowering the oxygen content but often adversely affects the desired low carbon content. It is disclosed in U.S. Pat. No. 3,188,198 which issued on June 8, 1965. A third method, particularly effective for alloy steels with high carbon contents, involves the lowering of the partial pressure of carbon monoxide in the vessel. A lowering of the partial pressure of carbon monoxide changes equilibrium relationships and shifts the attainable end point carbon to lower levels without necessitating excessive oxidation of metallic components and, thereby, frees carbon to combine with oxygen within the melt. Reduction in the partial pressure can be accomplished by reducing the pressure in the vessel and/or by introducing argon into the vessel. This third method, however, does not measure up to theoretical expectations as the carbon-oxygen reaction fails to proceed to completion. From a thermodynamic point of view, the system acts as if it were under a higher pressure.
Another prior art process of considerable interest is disclosed in an article entitled Deoxidation Techniques for Vacuum-Induction Melting by W. F. Moore. It appeared on pages 918 - 921 in the December 1963 issue of the Journal of Metals. The process described therein employed natural gas which consisted of, by volume, 94.9 percent CH 4 , 3.2 percent C 2 H 6 , 1.0 percent C 3 H 8 , 0.1 percent C 2 H 4 , 0.6 percent CO 2 , 0.1 percent H 2 O and 0.1 percent N 2 + CO, to deoxidize a melt. Results from the process were promising with regard to the degree of deoxidizing but were unfortunately disappointing to processors who require both low carbon and oxygen contents in their steel. The natural gas injected an excess of carbon into the melt and thereby, raised its carbon content.
It would appear that the major shortcoming of the process described in the above referred to Journal of Metals article could be rectified by reducing the amount of natural gas injected into the melt. The most obvious manner of accomplishing this would be to simply reduce the natural gas input flow rate. This however, diminishes the mixing caused by the input of the gas which in turn reduces the degree of reaction between carbon that evolves from the gas and oxygen in the melt.
The present invention provides a method which effectively deoxidizes a melt while controlling the carbon content at a level about equal to or lower than that which was present prior to deoxidizing. It employs at least one hydrocarbon as a deoxidizer and at least one diluent gas. The diluent gas enables the processor to use small amounts of hydrocarbon deoxidizer, thereby precluding excessive injection of carbon into the melt, while maintaining a gaseous injection rate which is sufficient to insure adequate mixing between the hydrocarbon deoxidizer and the melt. Thus, the hydrocarbon deoxidizer input rate can be lowered without reducing the rate of oxygen reaction with carbon, by introducing a diluent gas with the hydrocarbon deoxidizer.
It is accordingly an object of this invention to provide a method of deoxidizing molten metal.
It is an additional object of this invention to provide a method of deoxidizing molten metal while maintaining the carbon content of the metal at a level about equal to or lower than the level prior to deoxidizing.
The present invention comprises the steps of introducing hydrocarbon deoxidizer and diluent gas into a vessel containing molten metal, determining the effect of the hydrocarbon deoxidizer and diluent gas upon the carbon content of the metal and controlling the proportion of hydrocarbon deoxidizer to diluent gas so that the average rate of carbon leaving the vessel is about equal to or greater than the average rate of carbon being introduced into the vessel.
The invention embraces the use of one or more hydrocarbon deoxidizers chosen from a wide spectrum of gaseous and liquid hydrocarbons and hydrocarbon containing substances as well as the use of one or more diluent gases chosen from a wide spectrum of diluent gases. Illustrative hydrocarbons and hydrocarbon containing substances are methane, ethane, propane, ethylene, water gas and natural gas. Illustrative diluent gases are argon, nitrogen, hydrogen and carbon monoxide. Liquid hydrocarbons and hydrocarbon containing substances require the additional step of atomizing the liquid into the diluent gas stream. The hydrocarbon deoxidizer and diluent gas can be blown into or blown onto the top of the melt.
The effect of the hydrocarbon deoxidizer upon the carbon content of a melt can be determined from the initial and final melt analysis of a previously deoxidized melt. A comparison of the initial and final analysis along with the input rate and analysis of the hydrocarbon deoxidizer and/or diluent gas (diluent gas is not necessary here as this is not necessarily a heat requiring a low carbon level) introduced into the vessel sets forth the information necessary to determine the efficiency at which carbon, from the deoxidizer, combined with oxygen. The efficiency at which carbon and oxygen combined tells a processor what the proportion of hydrocarbon deoxidizer to diluent gas should be for subsequent heats, of similar chemistry, which are to be deoxidized under similar conditions, e.g., similar gaseous injection rates. For example, a heat deoxidized with 80 percent hydrocarbon deoxidizer and 20 percent diluent gas and having a 50 percent carbon-oxygen reaction efficiency indicates that subsequent heats should use 40 percent or less hydrocarbon deoxidizer and 60 percent or more diluent gas if the heats are of similar chemistry and are to be similarly deoxidized.
Although the above described procedure for determining the effect of the hydrocarbon deoxodizer is far better than adequate, it does have a shortcoming. The end-point control may not be too precise due to heat variations in analysis, temperature and efficiency of gas blowing.
An alternative process for determining the effect of the hydrocarbon deoxidizer overcomes the shortcoming of the above described procedure. It involves calculating the rate at which carbon is introduced to the vessel and the rate at which it leaves the vessel. The carbon input rate can be calculated from the analysis and input rate of hydrocarbon deoxidizer and diluent gas. The carbon output rate can be calculated from the output rate and analysis of the gases exiting the vessel (a monitoring system can be used to analyze the exiting gases). The calculations enable a processor to control the carbon content of the melt by adjusting the rate at which carbon is introduced to the vessel.
The following paragraphs are exemplary of the type of reactions which occur during the deoxidizing method of this invention and of method for calculating both the carbon input and output. Methane, CH 4 , has been chosen as the hydrocarbon deoxidizer for purposes of illustration.
The major reactions which occur during deoxidation with methane are:
CH 4 (gas) + O = CO (gas) + 2H 2 (gas)
CH 4 (gas) + MO = M + CO (gas) + 2H 2 (gas)
The deoxidizing reactions can be carried out at pressures which are at, below or above atmospheric pressure.
The reaction which leads to carburization of the bath is:
CH 4 (gas) = C + 2H 2 (gas)
An additional carburization reaction which can occur to an intolerable degree when there is an excessive amount of hydrocarbon deoxidizer is:
CH 4 (gas) = C + 2H 2 (gas)
The hydrocarbon deoxidizer cracks and deposits carbon (soot) in the cooler parts of the vessel.
The carbon input and input rate can be obtained from the following equations: ##SPC1##
The carbon output and output rate can be obtained from the following equations: ##SPC2##
No numerical value can be set for the ratio of hydrocarbon deoxidizer to diluent gas as it can change throughout the deoxidizing treatment. At times, it is even desirable to complete the final stages of deoxidation with an inert gas and without any hydrocarbon deoxidizer. The inert gas will lower the partial pressure of carbon monoxide, change equilibrium relationships and shift the attainable end point carbon to lower levels without necessitating excessive oxidation of metallic components, thereby freeing carbon to combine with oxygen within the melt. It will additionally cause a mixing of the melt which will promote the carbon-oxygen reaction. As a general rule the hydrocarbon deoxidizer and the diluent gas are injected into the vessel at an average gaseous injection rate of at least 20 cu.ft. per hour. A preferred average gaseous injection rate is at least 30 cu.ft. per hour. Lower injection rates are, however, embraced within this invention. A precise value can not be set for the minimum rate as it fluctuates with process variables, such as the depth of the molten metal.
The invention can additionally encompass controlling of the final oxygen content. This entails knowledge of the oxygen content prior to or at some stage during deoxidation and calculating of the amount of oxygen leaving the system. Oxygen in the melt can be measured by an EMF cell or by chemical analysis. The amount of oxygen leaving the system can be calculated from an analysis of the gases exiting from the system and from the following equations: ##SPC3##
Knowing the measured oxygen in the melt and the rate at which oxygen is leaving the system enables a processor to determine the amount of oxygen remaining in the melt.
The following examples are illustrative of the invention. They are directed to steel embodiments which comprise the bulk of the invention's utility. The invention is however, applicable to a wide range of metals which include both nickel and cobalt base alloys.
Three stainless steel heats (A, B and C) having the carbon, oxygen and nitrogen analysis shown below in Table I were deoxidized.
TABLE I ______________________________________ uz,4/16 Analysis (ppm) Heat C O N ______________________________________ A 71 187 18 B 190 388 140 C 240 161 145 ______________________________________
Heats A and B were deoxidized for 30 minutes with pure methane and heat C was deoxidized for 30 minutes with a gaseous mixture comprised of 2 percent methane and 98 percent argon (diluent gas). The average input rate for both the pure methane used in conjection with heats A and B and for the methane-argon mixture of heat C was 36 cu.ft. per hour.
The carbon, oxygen and nitrogen analysis for the deoxidized heats is shown below in Table II. ______________________________________ uz,4/16 Analysis (ppm) Heat C O N ______________________________________ A 164 115 13 B 440 86 84 C 10 32 43 ______________________________________
A study of the results reveals that the carbon content of heats A and B increased despite the fact that their oxygen contents decreased whereas the carbon and oxygen contents of heat C substantially decreased. Heats A and B were not deoxidized in accordance with this invention as they involved the injection of pure methane into the melt. On the other hand, heat C was deoxidized in accordance with the method of this invention as it involved the injection of methane and diluent gas.
It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific examples thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the specific examples of the invention described herein.
Present day metal-making; e.g., steel-making, processes often involve a deoxidizing treatment. It is highly desirable to lower the oxygen content of a melt since oxygen dissolved in a melt can precipitate as nonmetallic inclusions which adversely affect the properties of the metal.
Various deoxidizing methods have been employed in the past. One method involves the use of highly reactive elements; e.g., silicon, titanium and/or aluminum, which combine with oxygen in the melt to form oxides that subsequently separate from the melt. Sufficient time must, however, be provided for the oxides and melt to separate. A second method involves the mixing of a predetermined quantity of carbon with the melt and a dynamic hydrogen atmosphere to control carbon boil. This method is effective for lowering the oxygen content but often adversely affects the desired low carbon content. It is disclosed in U.S. Pat. No. 3,188,198 which issued on June 8, 1965. A third method, particularly effective for alloy steels with high carbon contents, involves the lowering of the partial pressure of carbon monoxide in the vessel. A lowering of the partial pressure of carbon monoxide changes equilibrium relationships and shifts the attainable end point carbon to lower levels without necessitating excessive oxidation of metallic components and, thereby, frees carbon to combine with oxygen within the melt. Reduction in the partial pressure can be accomplished by reducing the pressure in the vessel and/or by introducing argon into the vessel. This third method, however, does not measure up to theoretical expectations as the carbon-oxygen reaction fails to proceed to completion. From a thermodynamic point of view, the system acts as if it were under a higher pressure.
Another prior art process of considerable interest is disclosed in an article entitled Deoxidation Techniques for Vacuum-Induction Melting by W. F. Moore. It appeared on pages 918 - 921 in the December 1963 issue of the Journal of Metals. The process described therein employed natural gas which consisted of, by volume, 94.9 percent CH 4 , 3.2 percent C 2 H 6 , 1.0 percent C 3 H 8 , 0.1 percent C 2 H 4 , 0.6 percent CO 2 , 0.1 percent H 2 O and 0.1 percent N 2 + CO, to deoxidize a melt. Results from the process were promising with regard to the degree of deoxidizing but were unfortunately disappointing to processors who require both low carbon and oxygen contents in their steel. The natural gas injected an excess of carbon into the melt and thereby, raised its carbon content.
It would appear that the major shortcoming of the process described in the above referred to Journal of Metals article could be rectified by reducing the amount of natural gas injected into the melt. The most obvious manner of accomplishing this would be to simply reduce the natural gas input flow rate. This however, diminishes the mixing caused by the input of the gas which in turn reduces the degree of reaction between carbon that evolves from the gas and oxygen in the melt.
The present invention provides a method which effectively deoxidizes a melt while controlling the carbon content at a level about equal to or lower than that which was present prior to deoxidizing. It employs at least one hydrocarbon as a deoxidizer and at least one diluent gas. The diluent gas enables the processor to use small amounts of hydrocarbon deoxidizer, thereby precluding excessive injection of carbon into the melt, while maintaining a gaseous injection rate which is sufficient to insure adequate mixing between the hydrocarbon deoxidizer and the melt. Thus, the hydrocarbon deoxidizer input rate can be lowered without reducing the rate of oxygen reaction with carbon, by introducing a diluent gas with the hydrocarbon deoxidizer.
It is accordingly an object of this invention to provide a method of deoxidizing molten metal.
It is an additional object of this invention to provide a method of deoxidizing molten metal while maintaining the carbon content of the metal at a level about equal to or lower than the level prior to deoxidizing.
The present invention comprises the steps of introducing hydrocarbon deoxidizer and diluent gas into a vessel containing molten metal, determining the effect of the hydrocarbon deoxidizer and diluent gas upon the carbon content of the metal and controlling the proportion of hydrocarbon deoxidizer to diluent gas so that the average rate of carbon leaving the vessel is about equal to or greater than the average rate of carbon being introduced into the vessel.
The invention embraces the use of one or more hydrocarbon deoxidizers chosen from a wide spectrum of gaseous and liquid hydrocarbons and hydrocarbon containing substances as well as the use of one or more diluent gases chosen from a wide spectrum of diluent gases. Illustrative hydrocarbons and hydrocarbon containing substances are methane, ethane, propane, ethylene, water gas and natural gas. Illustrative diluent gases are argon, nitrogen, hydrogen and carbon monoxide. Liquid hydrocarbons and hydrocarbon containing substances require the additional step of atomizing the liquid into the diluent gas stream. The hydrocarbon deoxidizer and diluent gas can be blown into or blown onto the top of the melt.
The effect of the hydrocarbon deoxidizer upon the carbon content of a melt can be determined from the initial and final melt analysis of a previously deoxidized melt. A comparison of the initial and final analysis along with the input rate and analysis of the hydrocarbon deoxidizer and/or diluent gas (diluent gas is not necessary here as this is not necessarily a heat requiring a low carbon level) introduced into the vessel sets forth the information necessary to determine the efficiency at which carbon, from the deoxidizer, combined with oxygen. The efficiency at which carbon and oxygen combined tells a processor what the proportion of hydrocarbon deoxidizer to diluent gas should be for subsequent heats, of similar chemistry, which are to be deoxidized under similar conditions, e.g., similar gaseous injection rates. For example, a heat deoxidized with 80 percent hydrocarbon deoxidizer and 20 percent diluent gas and having a 50 percent carbon-oxygen reaction efficiency indicates that subsequent heats should use 40 percent or less hydrocarbon deoxidizer and 60 percent or more diluent gas if the heats are of similar chemistry and are to be similarly deoxidized.
Although the above described procedure for determining the effect of the hydrocarbon deoxodizer is far better than adequate, it does have a shortcoming. The end-point control may not be too precise due to heat variations in analysis, temperature and efficiency of gas blowing.
An alternative process for determining the effect of the hydrocarbon deoxidizer overcomes the shortcoming of the above described procedure. It involves calculating the rate at which carbon is introduced to the vessel and the rate at which it leaves the vessel. The carbon input rate can be calculated from the analysis and input rate of hydrocarbon deoxidizer and diluent gas. The carbon output rate can be calculated from the output rate and analysis of the gases exiting the vessel (a monitoring system can be used to analyze the exiting gases). The calculations enable a processor to control the carbon content of the melt by adjusting the rate at which carbon is introduced to the vessel.
The following paragraphs are exemplary of the type of reactions which occur during the deoxidizing method of this invention and of method for calculating both the carbon input and output. Methane, CH 4 , has been chosen as the hydrocarbon deoxidizer for purposes of illustration.
The major reactions which occur during deoxidation with methane are:
CH 4 (gas) + O = CO (gas) + 2H 2 (gas)
CH 4 (gas) + MO = M + CO (gas) + 2H 2 (gas)
The deoxidizing reactions can be carried out at pressures which are at, below or above atmospheric pressure.
The reaction which leads to carburization of the bath is:
CH 4 (gas) = C + 2H 2 (gas)
An additional carburization reaction which can occur to an intolerable degree when there is an excessive amount of hydrocarbon deoxidizer is:
CH 4 (gas) = C + 2H 2 (gas)
The hydrocarbon deoxidizer cracks and deposits carbon (soot) in the cooler parts of the vessel.
The carbon input and input rate can be obtained from the following equations: ##SPC1##
The carbon output and output rate can be obtained from the following equations: ##SPC2##
No numerical value can be set for the ratio of hydrocarbon deoxidizer to diluent gas as it can change throughout the deoxidizing treatment. At times, it is even desirable to complete the final stages of deoxidation with an inert gas and without any hydrocarbon deoxidizer. The inert gas will lower the partial pressure of carbon monoxide, change equilibrium relationships and shift the attainable end point carbon to lower levels without necessitating excessive oxidation of metallic components, thereby freeing carbon to combine with oxygen within the melt. It will additionally cause a mixing of the melt which will promote the carbon-oxygen reaction. As a general rule the hydrocarbon deoxidizer and the diluent gas are injected into the vessel at an average gaseous injection rate of at least 20 cu.ft. per hour. A preferred average gaseous injection rate is at least 30 cu.ft. per hour. Lower injection rates are, however, embraced within this invention. A precise value can not be set for the minimum rate as it fluctuates with process variables, such as the depth of the molten metal.
The invention can additionally encompass controlling of the final oxygen content. This entails knowledge of the oxygen content prior to or at some stage during deoxidation and calculating of the amount of oxygen leaving the system. Oxygen in the melt can be measured by an EMF cell or by chemical analysis. The amount of oxygen leaving the system can be calculated from an analysis of the gases exiting from the system and from the following equations: ##SPC3##
Knowing the measured oxygen in the melt and the rate at which oxygen is leaving the system enables a processor to determine the amount of oxygen remaining in the melt.
The following examples are illustrative of the invention. They are directed to steel embodiments which comprise the bulk of the invention's utility. The invention is however, applicable to a wide range of metals which include both nickel and cobalt base alloys.
Three stainless steel heats (A, B and C) having the carbon, oxygen and nitrogen analysis shown below in Table I were deoxidized.
TABLE I ______________________________________ uz,4/16 Analysis (ppm) Heat C O N ______________________________________ A 71 187 18 B 190 388 140 C 240 161 145 ______________________________________
Heats A and B were deoxidized for 30 minutes with pure methane and heat C was deoxidized for 30 minutes with a gaseous mixture comprised of 2 percent methane and 98 percent argon (diluent gas). The average input rate for both the pure methane used in conjection with heats A and B and for the methane-argon mixture of heat C was 36 cu.ft. per hour.
The carbon, oxygen and nitrogen analysis for the deoxidized heats is shown below in Table II. ______________________________________ uz,4/16 Analysis (ppm) Heat C O N ______________________________________ A 164 115 13 B 440 86 84 C 10 32 43 ______________________________________
A study of the results reveals that the carbon content of heats A and B increased despite the fact that their oxygen contents decreased whereas the carbon and oxygen contents of heat C substantially decreased. Heats A and B were not deoxidized in accordance with this invention as they involved the injection of pure methane into the melt. On the other hand, heat C was deoxidized in accordance with the method of this invention as it involved the injection of methane and diluent gas.
It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific examples thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the specific examples of the invention described herein.