| The weathering steel material has become the main materials of the bogies of the high-speed train because of its high tensile strength,good plasticity.The most popular were S355J2W and SMA490BW.But the welded joints had some defects such as lack of penetration,low efficiency and large amount of filling.This thesis paper was focused on:(1)With the study on the thermal physical properties of the heat affected zone of S355J2W steel,the results showed that the microstructure of the overheated zone were mainly composed of ferrites,pearlites when the cooling speed was at the 0.05℃/s-0.1℃/s.The microstructure of the overheated zone were mainly composed of ferrites,pearlites,granular bainites and plate strip bainites when the cooling speed was at the 0.1℃/s-1℃/s.The microstructure of the overheated zone were mainly composed of ferrites,pearlites,few granular bainites and a lot of plate strip bainites when the cooling speed was at the 1℃/s-3℃/s.The microstructure of the overheated zone were mainly composed of lower bainites and plate strip bainites when the cooling speed was higher 10℃/s.(2)The tensile strength properties and impact toughness properties of the plasma hybrid MAG welded joints were studied and the fracture was then observed.The results showed that the original mechanical properties of the plasma hybrid welded joints were higher than the original MAG welded joints.(3)The morphology of the plasma hybrid MAG welded joints and original MAG welded joints were studied.The results showed that the grains size of the former was more tiny than the latter.(4)The fatigue properties of S355J2W steel and plasma hybrid MAG welded joints were studied and then the fracture morphology were studied.The results showed that the fatigue properties of plasma hybrid MAG welded joints was 5%higher than the MAG welded joints and the grains size in the weld and in the overheated was more tiny than that in the other zones. |
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