DISSOLUTION AND COARSENING OF LARGE NIOBIUM CARBONITRIDES IN A MICROALLOYED STEEL

Observations and measurements of the kinetics of coarsening and dissolution of large cuboidal niobium carbonitrides during solution treatments of a high nitrogen niobium microalloyed steel are reported. At temperatures between 1473 and 1573 K a competitive coarsening and dissolution process was established where the larger niobium carbonitrides grew at the expense of the smaller, or employing niobium and nitrogen which remained in solid solution. In this temperature range growth or dissolution rates and critical sizes could be determined from the analysis of the evolution of particle size distribution. At higher temperatures (1623-1723 K), only a dissolution process existed, where the dissolution rates as a function of particle size was found to increase with increasing temperature.