The paper deals with the formation of coarse nitride non-metallic inclusions in steel. The thermodynamic calculations for the determination of the equilibrium solubility of nitrogen in the steel melt at a given temperature and chemical composition are presented. Some of the negative effects of excessive nitrogen contents, like blow holes, strain aging and, most importantly, nitride non-metallic inclusion formation are discussed. Five types of the coarse nitride non-metallic inclusions that occur in industrial practice are presented: aluminium, boron, niobium, titanium, and zirconium nitrides. Examples of the negative effect of coarse nitrides from case studies are also shown. The basic thermodynamic tools and values of the parameters for calculating the nitride precipitation in the steel melt are given in the paper.

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In this paper two examples of thermodynamic investigation of stainless steels using both, experimental and modeling approach are described. The ferritic-austenitic duplex stainless steel and austenitic stainless steel were investigated using thermal analysis. The complex melting behavior was evident for both alloy systems. Experimentally obtained data were compared with the results of the thermodynamic calculations using the CALPHAD method. The equilibrium thermal events were also described by the calculated heat capacity. In spite of the complexity of both selected real alloy systems a relative good agreement was obtained between the thermodynamic calculations and experimental results