Analysis of different acicular ferrite microstructures in low-carbon steels by electron backscattered diffraction. Study of their toughness behavior

Acicular ferrite formation, promoted by the intragranular nucleation of ferrite plates, is well known to be beneficial for achieving a good combination of mechanical properties. However, the set of microstructures that can be obtained during the subsequent development of the transformation from the primary plates generated at particles can be quite complex and depends on a certain number of variables: steel composition, temperature range, prior austenite grain size, and particle density. In the present work, acicular ferrite microstructures have been produced by isothermal treatments in three different steels with different active particle types and densities. The morphology of the obtained intragranular microstructures has been found to depend on the steel composition, the prior austenite grain size, and the density of particles able to promote intragranular nucleation. Electron backscattered diffraction (EBSD) techniques have been used to define the microstructural unit controlling toughness in these types of microstructures.