The early stages of the formation of acicular ferrite in a low carbon steel weld were studied by serial sectioning and computer-aided three dimensional (3D) visualization. The specimens were taken from the weld of low carbon steel, containing 0.08% C, 0.9% Si, 1.57% Mn and 0.032% O, and were austenitized and isothermally reacted at 600 and 570°C for less than 10 s. Very thin and long plates were formed initially and thickening occurred probably after lengthening was hampered due to impingement on prior austenite grain boundaries and/or pre-formed ferrite plates. Multi-variant ferrite plates were nucleated at inclusions and grew radially in the directions close to <110>γ with habit planes near {111}γ thus forming a characteristic "Widmanstätten star" noted earlier in a medium carbon steel on polished surfaces.
