Stress Corrosion Experimental Research For The Effects Of Welding Heat Input On Q345R Steel Welded Joints In Wet Hydrogen Sulfide Solution

Q345R are widely used in the manufacture of low-pressure vessel due to the good mechanical properties and process performance. Since fusion welding is the main mode of the Q345R welding, heat input will change as long as the welding parameters change during the welding process, and it will affect the microstructure and performance. Higher heat input could lead to deterioration of the microstructure, and increase the sensitivity to the stress corrosion of the weld joints.In this paper, welding speed and welding current were fixed, and welding voltage was changed in order to get different heat input. Then, an optical microscope was applied to analysis the microstructure of the Q345R steel welded joints, and slow strain rate testing(SSRT) was employed to study how the heat input effect the stress corrosion susceptibility of the Q345R steel welded joints when the steel was in hydrogen sulfide solution. The main work and the results are as follow.(1) In this work, welding voltages were selected as40V,45V and50V. The microstructure of the Q345R steel welded joints showed that the HAZ microstructures of the samples were composed of the coarse westergren and pearlite at three different welding voltages. However, HAZ microstructures were coarsening with the welding heat input increasing. The microstructure of the weld zone was composed of eutectoid ferrite and pearlite when welding voltage was40V and45V. When welding voltages were50V, the welded joints were overheated, the microstructure of the weld zone was composed of eutectoid ferrite, acicular ferrite and bainite.(2) The slow strain rate testing result shows that, when the concentration hydrogen sulfide solution was0.1mol/L,0.05mol/L and O.Olmol/L, the fracture morphology of all the samples was cleavage, and the fracture mode is brittle fracture; The stress corrosion sensitivity indexs of all the samples were above35%,and all the samples have a strong stress corrosion tendency. And when the welding voltages were the same, the stress corrosion susceptibility index sample F(A) and F(δ) increased as the solubility of hydrogen sulfide increased. (3) when the concentration hydrogen sulfide solution was O.lmol/L and0.05mol/L, the stress corrosion susceptibility indexs of all the samples were large, but with few difference; when the concentration hydrogen sulfide solution was0.01mol/L, as the welding voltage was increased from40V to45V, the stress corrosion susceptibility index increased because of the microstructures coarsening; When the welding voltage reached50V, the welded joints were overheated, and acicular ferrite appeared in the weld zone. Meanwhile, eutectoid ferrite became coarse. Under the combined effects of the both, the stress corrosion susceptibility index was slightly increased compared to the samples when the welding voltage was40V, but with few difference.