Thermodynamic analysis of the precipitation of carbonitrides in microalloyed steels

The production of mass-products of microalloyed steels with a high strength requires a proper adjustment of the thermomechanical processing and the kinetics of the precipitation of the MX-type (M -microalloying element, X -metalloid) phases in austenite.The understanding of the effect of carbonitrides on the processes of hot-working and cooling from the finishing deformation temperature requires the knowledge of the mechanism of their formation and their stability in austenite.The research was carried out on newly manufactured Ti-V and Ti-Nb-V steels for forged machine parts with thermomechanical processing.The analysis of the precipitation of the carbonitrides with the stoichiometric compositions of TixV1-xCyN1-y and TixNbvV1-x-vCyN1-y was based on the Hillert-Staffanson model improved by Adrian.The effect of the austenitizing temperature in the range from 900 °C to 1200 °C on the grain size of the original austenite was investigated to verify the results of the calculation.The result provides the basis for a suitable design of the manufacturing process of the thermomechanical treatment to obtain high-strength forged elements of microalloyed steels.