| 摘要 |
<p>1458168 Producing low-nitrogen steel USS ENGS & CONSULTANTS Inc 29 Aug 1975 [30 Aug 1974] 35768/75 Heading C7D In a bottom-blown process for refining molten pig-iron having an initial N content > 0À002%, a stream of free-oxygen-containing gas is introduced into the melt at rate R T in the range 75 to 160 NCF/min/ton where RT = R O + R S , R O being the rate of introduction of O 2 and R S that of the other gases, and RO being # 0À8R T ; thereafter there is introduced at rate # 0À8R T an inert purging gas while the C content of the melt is # 0À3%, until the N content of the melt has been reduced to <80% of the original level, and then oxygen is introduced at rate # 0À8R T until the C content of the melt falls below 0.2%. The process may be used in a Q-BOP type process, wherein O 2 is blown into the bottom of the melt surrounded by a sheath of protective gas, e.g. methane, blown in at rate R p ; in this case RS may be R p + R A where R A is the rate of argon input; this may be substantially zero initially. Then, preferably after the silicon portion of the blow, R O is reduced, preferably to zero while RA is increased to R T ; some O 2 may be present in the Ar, however. When the N 2 content has been suitably reduced, R O is again increased to # 0À8 RT until the C content is reduced as required.</p> |
