Differential scanning calorimetry study of the solidification sequence of austenitic stainless steel

The solidification sequence of austenitic stainless steels can be predicted with thermodynamic calculations. Another way is to use models where the value of the Cr-eq./Ni-eq. ratio determines the relationship between the solidification mode and the composition factor. In this study the solidification of AISI 304LN stainless steel at different cooling rates was studied using differential scanning calorimetry (DSC). The samples were linearly heated above the liquidus temperature to 1550 A degrees C at heating rates of 5, 10, and 25 K/min. The solidification (cooling) scans from 1550 A degrees C involved the same selected ramps. After the DSC measurements the samples were metallographically analyzed to reveal the variations in the solidification microstructures. The microhardness of the solidified samples was also measured. It was found that the cooling rate critically influenced the solidification. The solidification behavior, which depends on the cooling rate, determines the evolution of the microstructure. At the slowest cooling rates a relief-cell morphology was observed, and at the fastest cooling rate the formation of dendrites was evident. With an increasing cooling rate the liquidus temperature decreased and the reaction enthalpy increased.