Microstructure evolution and mechanical properties of two kinds of weathering steel welded joints

Abstract

The microstructural evolution and mechanical properties of welded joints for Q450NQR1 and Q450AWR5 alloys were investigated. The inhomogeneous microstructures of Q450NQR1 and Q450AWR5 welded joints can result in heterogeneous mechanical responses. Microhardness distributions of the two welded joints are not uniform with the highest hardness value in the FZ, followed by the HAZ, and the lowest hardness value in the BM. The tensile strength of Q450AWR5 welded joints is slightly higher than the Q450NQR1 welded joints. The tensile fracture occurred in the BM of both welded joints, probably due to the strengthening effect of bainite with high dislocation density and lattice distortion. The fatigue life is dominated by the welded defects inside the welded joint. The location of fatigue failure occurs mainly near the fusion zone and is limited by the welded defects, independent of the microstructure.

Comparison in microstructure, mechanical properties, and fatigue behavior of 9Cr3W3Co turbine rotor steel and its welded joint

“…The local lattice distortions were assessed using the grain orientation spread (GOS) as depicted in Figure 12A–D. Higher GOS values indicate greater strain accumulation and more lattice distortion, resulting in higher deformation degree 53 . Thus, Figure 12A–D illustrates the distribution of strains within different sub‐regions.…”

“…Higher GOS values indicate greater strain accumulation and more lattice distortion, resulting in higher deformation degree. 53 Thus, Figure 12A-D illustrates the distribution of strains within different sub-regions. It is evident that the BM exhibits more severe strain accumulation compared to WNZ, making it susceptible to fatigue crack initiation due to high GOS values.…”