Influence Of Environmental Humidity On Properties Of MAG Welded Joint Of SMA490BW Weathering Steel

With the rapid development of the high-speed trains,more strick requirements have been placed on train manufacturing,service and safety and reliability.As a key component of high-speed trains,bogies are the key compinent in determining vehicle safety and speed.In this paper,SMA490BW weathering steel for bogies was taken as the research object.Research the mechanical properties and corrosion behavior of MAG welded joints under40°C,and 50%,60%,70%,80%and 90%relative humidity.Analyzed The effect of ambient humidity on joint performance.The joints welded under different humidity conditions are well formed without obvious external defects.The analysis of the perforation of the joints under five kinds of humidity environments by X-ray inspection shows that the pores slightly increase with the increase of welding humidity.However,the difference is not obvious and its distribution is discrete,and the pore size meets the requirements of ISO5817 Class B weld.Further analysis of the pore morphology of the weld seam revealed that the pore was a small circular pore with small number.The microstructure of the joints under different kinds of humidity environment is similar.The microstructure of the weld zone is mainly coarse columnar pre-eutectoid ferrite,side slab ferrite and acicular ferrite.The grain size of the superheated zone is different,mainly due to the pro-eutectoid ferrite,and a small amount of pearlite and bainite.The normalized zone is composed of fine ferrite and pearlite.The incomplete normalized zone is composite of fine ferrite and part of pearlite.The base metal is fine ferrite and ribbon pearlite.The basic mechanical properties such as tensile,bending,impact and hardness of the joints under different humidity conditions were studied.In the tensile test,the samples of different humidity joints fractured at the base metal,and the tensile strength was about 570MPa.The joints have good bending resistance,and no cracks or cracks appear after bent at180°.The impact toughness of different humidity joints is also consistent,and the impact energy is about 150J.The hardness of the different joints from the base metal to the weld has the same tendency,that is,first increase and then decrease,the maximum hardness is about230 HV in the overheated zone adjacent to the weld;the hardness of the base metal is about180 HV.The residual stress difference of the five joint stability sections is small,the maximum stress is 309 MPa and the minimum is 290 MPa.The fracture toughness and crack propagation mechanical properties of different joints were studied.It was found that the KIC value of fracture toughness of joints under different humidity conditions was about 60MPa·m^1/2 and the crack growth rate was basically the same.Corrosion resistance performance of different weldments was studied.As the relative humidity of the weld increased,the corrosion resistance of the welds decreased slightly and the corrosion rate increased slightly.There is no corrosion caused by pores in the corrosion morphology,and slight differences in corrosion performance may be caused by weld microstructure inhomogeneity.