Thermodynamic Calculation and Experimental Investigation of Second Phase Particles in Low Carbon Nb Microalloyed Steels

摘要

Many experimental methods such as transmission electron microscopy (TEM) and X-ray energy dispersive spectroscopy were used to study the precipitates of low carbon steel with niobium addition, the austenite/carbonitride equilibrium in Fe—Nb—C—N system was performed in this paper. The equilibrium volume fraction, chemical driving force of carbonitride precipitation fraction of each element in austenite, and carbonitride at different temperature were calculated. The results show that the equilibrium mole fraction of carbonitride increases, mole fraction of each element dissolved in austenite are basically precipitated fully at low temperature, the chemical driving force is 2.072 x 10~3 J.mol~(-1) at 1050°C. it is found that Nb(CN) precipitated on grain boundaries by using TEM. The volume fraction of Nb(CN) precipitates increased with the temperature decrease, which is in good agreement with the value calculated by the model.