Microstructural evolution roadmap in heat-affected zones of EH36 shipbuilding steel has been investigated at different welding heat inputs. Quantified results show that resultant microstructures transform from fine bainite accompanied by acicular ferrite at low heat input, to coarse bainite at medium heat input, and to polygonal ferrite and pearlite at high heat input. In addition, it is found that heat input does not have significant influence over the characteristics of potent inclusions promoting acicular ferrite nucleation.