Regulation of Nitrogen Content in High Alloyed Stainless Steels during the AOD Process

Abstract: As a final step in the argon oxygen decarburisation (AOD) process, argon- and nitrogen gas is blown through the melt. To regulate the nitrogen content in the steel melt during this step a reliable model is needed. With data from 31 heats of the duplex stainless steel SAF2507 collected at Sandvik Materials Technology (SMT), different models are investigated. This is done by looking at the partial pressure of the nitrogen gas and the nitrogen content achieved during each heat. By calculating the nitrogen solubility in the steel melt with different models and then using Sieverts’s law, a partial pressure for the nitrogen gas is obtained for each heat and compared with the data. With adjustments done for a model obtained from J. Kijac et al., more reliable results are attained than by the model used today at SMT. It should be kept in mind that this model is based on the theory with diluted solution and is therefore not optimal for high alloyed steels, and it is suggested to develop a model from a software based on real solution such as Thermo-Calc.