Influence of cooling rate upon weld metal microstructural evolution behaviors of EH36 shipbuilding steel

Microstructural evolution features have been systematically investigated for the weld metal of EH36 shipbuilding steel under an in situ confocal scanning laser microscope. The influence of cooling rate on microstructural changes during the transformation from austenite to ferrite has been clarified. It is found that ferrite side plates form preceding to acicular ferrites, although the starting temperature of respective component decreases as the cooling rate is raised. In particular, the growth rate of acicular ferrite is measured to increase significantly, rising from 30.4 mu m/s at a cooling rate of 3 K/s to 109.0 mu m/s at 15 K/s, driven primarily by an ever-increasing degree of undercooling. These findings highlight the critical role of cooling rate in dictating the sequence and growth rate of microstructural transformations, which is crucial for optimizing welding processes to obtain desired microstructures while avoiding the formation of deleterious components.