We propose a new approach to automatically reconstruct the orientation map from the ’ map inherited by the bainitic or martensitic ’ phase transformation. Our model comprises two main steps (1) identification of reliable fractions of parent grains – each fraction orientation is determined from neighbouring variants related to a unique orientation with a low tolerance angle; (2) expansion of these fractions by collecting adjacent variants being in orientation relation (OR) with the orientation of the initial fraction - using now a higher tolerance around the strict OR. The code was tested on ’ maps we built from reference maps to control some characteristics of the transformation, i.e. the type of OR used, the spread around OR, the number of inherited variants. The results show that even with a large spread around OR, the shape and orientation of most of the grains are accurately calculated.