| 摘要 |
PURPOSE:To improve the accuracy in hitting of the content of nitrogen in steel and to eliminate influence upon the controlling of other components such as Mn by estimating the content of nitrogen during tapping of steel from a converter from the content of free oxygen detected when the converter is blown out, and adding a specific nitrogen source at proper timings. CONSTITUTION:Steel is beforehand refined in a converter at the content of nitrogen therein slightly lower than a desired content, and when the converter is blown out, the content of free oxygen in molten steel is directly detected. The relation between the content of free oxygen and the content of nitrogen in such molten steel is as shown in the figure, from which the content of nitrogen of the molten steel in the blowing-out time can be estimated. The difference from a required content of nitrogen is determined from the estimated value, and a required amt. of a nitrogen source is added into a ladle during tapping. The basic flux consisting essentially of >=20% CaO and 10-50% N2 (generally called lime nitrogen) is used for the nitrogen source. Such flux is added during the time since tapping until the steel is received in the ladle to 1/2 its capacity. If it is added later than this time, the flux is difficult to be included in the molten metal and is extremely unstable because the nitrogen source is light, thus affecting the yield of nitrogen. |
