In Situ Observation of CGHAZ Microstructure Evolution of Hot‐Rolled Ship Plate Steel Containing 0.012 Yttrium under High‐Heat‐Input Welding

The laser scanning confocal microscope is used to simulate the microstructural evolution of a coarse‐grained zone composed of hot‐rolled ship steel with yttrium under high‐energy input welding. The results demonstrate that Y 2 O 3 near the austenite grain boundary can effectively block the overall migration of the austenite grain boundary during the application of the welding heating process. Additionally, the presence of Y 2 O 3 in the austenite grain can promote the formation of new grain and subgrain boundaries, thereby refining the austenite grain. During the postweld cooling process, the undercooling degree is high under a lower heat input, and the phase variation occurs along the direction at a large angle to the proto‐austenite boundary. Thus, a large amount of acicular ferrite (AF) is formed perpendicular to the proto‐austenite boundary. Based on the first principle, Y 2 O 3 can be used as the nucleation site for AF phase transformation to promote the formation of a fine interlocking structure. However, its impact is limited because the cooling rate significantly affects the microstructure evolution of the coarse‐grain zone of the weld during welding with a high heat input.