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

Abstract

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 Y2O3 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 Y2O3 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, Y2O3 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.