Effect of Heat Input on Microstructure and Properties of Weld Metal in Submerged-Arc Welded Bridge Steel
Q340qEHW steel was subjected to high heat input(50 to 150 kJ/cm)submerged-arc welding by using ER55HW welding wire which matched Q345qE to Q420qE bridge steels.The microstructure and properties of the weld metal were analyzed via metallographic microscope,scanning electron microscope,transmission electron microscope,energy spectrum analysis,and impact test.The results showed that(a)as the heat input increased from 50 to 150 kJ/cm,the proportion of acicular ferrite in the weld metal decreased from 85％to 59％,the proportion of large-sized M-A components increased from 28.8％to 38.9％,and the proportion of M-A components in the weld also increased from 0.363％to 0.975％,the number of inclusions in the weld metal decreased,and their proportion decreased from 0.41％to 0.25％;and(b)with the increase in heat input,the fiber ratio of the impact fracture of the weld metal showed a degressive trend,and the impact absorbed energy at-40 ℃ decreased from 117 J at 50 kJ/cm to 59 J at 150 kJ/cm;the dimples in the fiber zone exhibited an increase in size and a change from circular to elliptical form,uneven size distribution and an increase in the size of dissociation in the radiation zone.
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