Microstructure and impact toughness at different positions of weld metal in thick plate of 2.25Cr-1Mo-0.25V steel

XU Xiaolong; DOU Guishan; YAO Jun; YANG Fei; JIANG Yong; CAO Rui

doi:10.16579/j.issn.1001.9669.2026.07.012

Abstract：[Objective]Low impact energy occurring in multi-layer and multi-pass weld metal of 2.25Cr-1Mo-0.25V steel is a critical concern in the petrochemical industry.Investigating the microstructure in different regions of thick-plate multi-layer multi-pass weld metal and its influence on impact toughness is of great significance for improving the safe service performance of welded structures.[Methods]Firstly,optical microscopy and scanning electron microscopy were adopted to characterize the microstructure at different positions of the weld metal.Afterwards,Charpy impact tests and microhardness tests were carried out to examine the stability of mechanical properties of the weld metal.[Results]The results reveal that the microstructure of weld metal at all tested positions consists of ferrite,carbides,Martensite-Austenite constituents and non-metallic inclusions.Nevertheless,the minimum impact energy of 31 J is obtained at the middle position(1/2 thickness from the top surface),and the microhardness at this position is lower than that at the position 1/4 thickness from the top surface.The degradation of impact toughness mainly originates from the microstructural inhomogeneity in this region,manifested as coarse grains and large-sized non-metallic inclusions.These factors collectively reduce the plastic deformation capacity and degree of deformation of local areas,weakening the resistance to crack nucleation and propagation.Cleavage cracks tend to initiate at an early stage and propagate rapidly,resulting in a short steady-state propagation zone of ductile cracks.Consequently,the combined effect of coarse grains and large non-metallic inclusions drastically deteriorates the impact toughness of the local middle region of the weld.