Three-dimensional Morphology of Acicular Ferrite in a Low Carbon Steel Weld

摘要

Three-dimensional (3D) morphology of acicular ferrite in a low carbon steel weld was studied by means of serial sectioning and computer-aided reconstruction techniques. The welding was conducted with SM 490 as a base metal and a welding wire of Si-Mn steel containing titanium under a shielding gas 100% CO_2. The specimens taken from the weld deposit were austenitized at 1350℃ for 150s, cooled to 570℃, and isothermally reacted for less than 5s. The sizes of individual ferrite plates were measured from 3D reconstructed images for the specimens. The length ranged from several to a few tens of microns, the width and thickness was normally less than 6 μm and 3 μm, respectively. The morphology of ferrite varied from lath to plate, although it scattered widely in one specimen. The shape of acicular ferrite does not appear to be needle-like as the use of the term "acicular" would imply.