Microstructures And Mechanical Properties Of The Welded Joints In Bogie Frame

Bogie frame, being the key component on locomotive and rolling stocks, bears working loads that from other installation parts and various forces namely tractive force, brake force and inertia force when it is operating. A higher materials quality of bogie frame and the performances of the corresponding welded joints are desired with the rising of dynamic load when running speed of locomotives heightened continually. Therefore, optimizing welding technology and improving welding quality will be of great application value and significance.In this paper, by using ER50-6 and SM-70 welding wire and under differ processing parameters, Q345E steel has been welded. Then, tensile, bending, impact and pulsating tensile fatigue tests were carried out referred to the correlate standards. The microstructures and fracture morphologies were observed using optical and electronic microscopies as well.The results showed that Q345E steel when welded by using welding wire of ER50-6 and SM-70 with low current, the microstructure in welded metal mainly contains proeutectoid ferrites appeared along the grain boundaries, pearlites and acicular ferrites appeared within the grains; in overheated zone mainly contains block or columnar ferrites along boundaries, pearlites and bainites within the grains; in normalized zone mainly contains small and homogeneous ferrites and pearlites. Welding joints have favorable mechanical properties include good tensile and low temperature impact toughness. Q345E steel when welded using welding wire of SM-70 with high current, Widmanstaten structures appeared within the welded metal and overheated zone, which do harmful to low-temperature impact properties, but do not effect on tensile properties.The results about fatigue-testing shows that the processing parameter of bevel and reserved definite gap can improve fatigue performance of cruciform joint; TIG refusion and sanding treatments only can amend stress state at toe zone, which would be ineffect if the fatigue crack initiates at the root. Fatigue strength of abutment is better than that of cruciform joint.