Austenite grain growth modelling in weld heat affected zone of Nb/Ti microalloyed linepipe steel

A model to predict the austenite grain size in an Nb/Ti microalloyed steel weld heat affected zone (HAZ) was developed. The present work investigates grain growth behaviour under the influence of pinning carbonitrides. The steel has been subjected to austenitising heat treatments to selected peak temperatures at various heating rates that are typical for thermal cycles in the HAZ. The effect of temperature and heating rate on the grain size is studied. A model is proposed for the dissolution of NbCN precipitates. This model has been coupled to an austenite grain growth model in the presence of pinning particles. This coupling leads to accurate prediction of the austenite grain size along the heating path simulating selected thermal profiles of the HAZ.