Abstract Scope |
Niobium (Nb) is a widely recognized micro-alloying element due to its low cost and low cost and substantial impact on material properties. This study investigates the microstructure, distribution and precipitation behavior of Nb in X70 pipeline steel weld metal using optical microscopy, scanning electron microscopy, and transmission electron microscopy. Two distinct Nb-rich precipitates were observed, formed by different mechanisms in the weld reinforcement region and around inclusions along the prior austenite grain boundaries. Simulations were performed on steel with the same chemical composition to examine the evolution of Nb. The analysis reveals that the distribution of Nb in the weld metal is primarily in the form of solid solution, due to its high partition coefficient and the short thermal history. The results provide insights into the underlying mechanisms of how Nb affects weld metal and its distribution in various forms. |