Kväve i LD-processen

Nitrogen is an element with both positive and negative effects on the properties of carbon steel and it is therefore essential to control the nitrogen content in steel during the manufacturing process, with respect to the requirement of final product characteristics. The ability to control the final nitrogen content are heavily influenced by progress in the LD-process, i.e. the process step where hot metal is converted into crude steel, mainly through the addition of pure oxygen. Both carbon and oxygen have a strong impact on nitrogen solubility in molten steel. A number of planned experiments with sampling under running LD-process and analysis with LECO® were the subject of a survey of the nitrogen cycle, especially with regard to the conversion of steel that is recycled in the process, the so-called liquid return steel.The results of the trials show that the carbon in the charged hot metal controls how long the conversion process will take, which in turn determines how much nitrogen can be degassed. Normally the conversion process provides a highly effective gas development which degasses hot metal with high nitrogen level to crude steel with very low nitrogen level. Reblowing of crude steel which does not meet the specified requirements does not generally lead to higher nitrogen content, except in a few cases where high nitrogen gains has been observed. When charging with low-carbon liquid return steel the result is a faster conversion process with less time for the degassing of nitrogen, resulting in higher nitrogen content in the crude steel. Taking these results into account, it is recommended to control the use of liquid return steel to produce steel with requirements for low nitrogen content.Validerat; 20110923 (anonymous