the first phase of the preferred method takes place in the basic oxygen furnace after being charged with the necessary starting materials , typically on the order of about 75 % molten iron and 25 % scrap . the ratio is determined by a heat and mass balance for a given charge . in order to provide the nitrogen gas necessary to achieve the required chemistry , a high pressure nitrogen gas line was tapped into the main oxygen line of each oxygen lance at a bof converter . the nitrogen line is tapped into the oxygen line between the lance and the oxygen flow regulating equipment so that the oxygen source and nitrogen source can be regulated independently . to compensate for the thermal effects of the nitrogen gas the target temperature of the blow may be increased above the normal target temperature for a given charge . for example , the target temperature can be increased by 40 ° f . so that instead of entering a target temperature of 2950 ° f . for the blow , one would input a target temperature of 2990 ° f . otherwise , the oxygen blowing sequence is commenced in the normal fashion known to those of ordinary skill in the art for bof processing . the aim in this phase is to reduce the carbon content to between about 0 . 02 and 0 . 03 %, preferably about 0 . 028 %, in order to allow for the greatest possible nitrogen uptake during a period of the blow where minimal co gas is being generated . the target temperature , oxygen volume and duration of the blow will vary from charge to charge . the appropriate calculations for the blow parameters are well known to those of ordinary skill in the art . as the oxygen blowing sequence in the bof approaches completion , and the carbon content of the steel is being reduced , nitrogen is added to the oxygen line . ideally , the nitrogen flow is commenced at the point in the blow where about 65 % of the predicted oxygen volume has been blown . at this point the oxygen flow rate is approximately 19 , 000 standard cubic feet per minute ( scfm ). the nitrogen is introduced at a flow rate of approximately 3000 scfm . the resultant mixture of oxygen and nitrogen is blown through the oxygen lance into the bath for the balance of the required oxygen blow and causes the nitrogen content of the bath to increase , while allowing the carbon to continue to decrease . the introduction of nitrogen to the oxygen stream does not effect the total amount of oxygen required to reach the endpoint calculated by the heat and mass balance . the nitrogen gas content in the stream from the oxygen lance is about 5 - 20 % by weight based on the weight of oxygen and nitrogen in the stream . preferably , the nitrogen content is about 10 %. if the nitrogen content is too low , insufficient nitrogen will be dissolved in the steel to prevent hydrogen defects in the enameled product . if the nitrogen content is too high , there will not be enough oxygen in the stream to ignite and react with the charge and sufficiently reduce the carbon content . at turndown , the dissolved nitrogen content is measured before proceeding to the second phase of the inventive method . based on the measured nitrogen content it may be necessary to take corrective action to ensure that the final nitrogen content is at least between 0 . 01 to 0 . 015 % prior to proceeding to the degasser . if the nitrogen content is below 0 . 01 % the melt is re - blown with the combined nitrogen and oxygen stream . if the nitrogen content is between about 0 . 010 and 0 . 015 %, it is desirable to add nitrided manganese or similar nitrogen containing alloy during tap . in the case of the typical charge about 1500 pounds of nitrided manganese should be added . if the nitrogen content is over about 0 . 015 %, the melt can proceed to the degasser without modification . however , it may in some cases be desirable to combine several nitrogen adding techniques to further increase the nitrogen content even prior to the termination of the initial blowing sequence . for example , nitrogen containing alloys such as nitrided manganese can be added to the melt and / or nitrogen gas can be introduced to the melt through tuyeres in the bof to augment the nitrogen supply . in addition to bringing the nitrogen content of the heat to about 0 . 01 % or greater , the use of this technique typically allows the resultant chemistry of the heat , after tap , to be such that the oxygen content of the bath exceeds the carbon content by more than 150 ppm . additionally , the carbon content of the heat , after tap , can be restricted to below 300 ppm . this provides good chemistry for the second decarburization phase . the combination of low carbon , high nitrogen and adequate oxygen to carbon ratio is important to the production of ultra - low carbon enameling grade steel . at the completion of the first phase of the inventive process , the steel comes out of the bof at about 0 . 03 % carbon . in the second phase the carbon content is taken down to the 0 . 0025 to 0 . 005 % ultra low carbon range in the vacuum degasser . by implementation of the second phase of the inventive method , the average nitrogen content can be maintained at values above about 0 . 012 %. in the vacuum degasser , processing to ultra low carbon levels proceeds as normal for vacuum circulation decarburization processing with the exception that the lift gas injected into the vacuum circulation process ( vcp ) vessel through the inert gas tuyeres is varied according to the nitrogen content of the incoming melt . if the nitrogen content of the incoming melt is less than about 0 . 016 %, the lift gas through the tuyeres is comprised entirely of nitrogen gas . if the nitrogen content of the incoming melt is between about 0 . 016 and 0 . 020 %, the lift gas may comprise a mixture of nitrogen and argon or other inert gas . if the incoming nitrogen content is above about 0 . 020 %, it may not be necessary to introduce any nitrogen in the vcp and the lift gas can be entirely comprised of argon or other inert gas . as the decarburization process proceeds , the nitrogen content of the heat is reduced into the desired product range of 0 . 010 - 0 . 015 %, as will be seen from the following non - limiting example . a basic oxygen furnace was charged with 558 , 000 lbs . molten iron , 68 , 000 lbs . scrap , 14 , 000 lbs . burnt lime and 8 , 000 lbs . dolomitic lime . the aim turndown temperature was 2950 ° f . at 0 . 030 % carbon . the calculated oxygen volume was 473 , 000 scf . the blowing sequence began at 14 : 44 at an oxygen flow rate of 23 , 000 scfm and oxygen pressure of 190 psig . after 300 , 000 scf of oxygen had blown , nitrogen enrichment of the oxygen was commenced . approximately 2500 scfm of nitrogen gas at 400 psig . was added to the oxygen line , and the total combined nitrogen and oxygen flow was held at 25 , 000 scfm at a line pressure of 198 psig . this gas mixture was blown until the total of 450 , 000 scf of oxygen was blown , at which time the nitrogen was turned off . the oxygen blow was terminated at 474 , 000 scf oxygen at 15 : 06 . the actual blowing temperature reached 2963 ° f . the chemistry of the melt at tap was 0 . 024 % carbon , 0 . 016 % nitrogen and 537 ppm oxygen . no additions were made at tap . the melt was moved to the ladle metallurgy facility heating station where 6000 kwh of electrical energy were added to the heat while it was held for vacuum processing . during the hold time 40 lbs . of antimony was added to provide a product containing 0 . 005 to 0 . 010 % antimony . a small aluminum addition of 272 lbs . was also made to balance the 0 . 021 % carbon and 533 ppm oxygen ( measured at the heating station ). the melt was maintained at the heating station for approximately one hour . after leaving the heating station the heat arrived at the vacuum circulation process ( vcp ) degassing unit . the oxygen value upon arrival at the vcp was measured at 462 ppm . degassing commenced at 17 : 56 and the decarburization cycle proceeded until 18 : 07 . the vessel pressure obtained was 3 . 4 torr . based on the incoming nitrogen value , an all argon lift gas was used . alloy additions at the vcp were 600 lbs . aluminum , 600 lbs . ferrotitanium , 500 lbs . ferrocolumbium and 300 lbs . low carbon manganese . after degassing the heat was at 2895 ° f . the chemistry of the heat was 0 . 0018 % carbon , 0 . 011 % nitrogen , 0 . 058 % columbium , 0 . 074 % titanium , 0 . 060 % aluminum , about 0 . 007 % antimony and 0 . 12 % manganese . many modifications and variations of the invention will be apparent to those of ordinary skill in the art in light of the foregoing disclosure . therefore , it is to be understood that , within the scope of the appended claims , the invention can be practiced otherwise than has been specifically shown and described .