NUMERICAL SIMULATION OF EFFECTS OF THE MINOR ACTIVE-ELEMENT OXYGEN ON THE Marangoni CONVECTION AND THE WELD SHAPE

A mathematical model was developed to calculate the 3D transient temperature, velocity distribution and the evolution of weld pool shape in a stationary gas tungsten arc (GTA) weld pool of 304 stainless steels with different oxygen contents.The results indicate that when the oxygen content increased,the convection pattern in the weld pool changed from a dominant outward convection,outward on pool center together with inward on pool periphery,and finally to a domi- nant inward convection.Accordingly,the weld pool evolves from a shallow wide shape,a spoon-like shape to a deep narrow one.The minor active-element oxygen in the weld pool influences on the temperature coefficient of the surface tension ((?)γ/(?)T) directly,which leads to the significant change of the Marangoni convection pattern and hence the weld shape.When the oxygen content is below 80×10~(-6),an outward Marangoni convection pattern on the weld pool surface occurs,and forms a shallow and wide weld shape.As the oxygen content exceeding 120×10~(-6),the Marangoni convection changes to inward direction and the weld shape varies from a shallow and wide shape to a deep and narrow one.When the oxygen content is between 80×10~(-6) and 120×10~(-6),the weld pool exhibits a spoon-like shape.And as time going,the outward convection region in the weld pool becomes smaller gradually,and the inward convection region becomes larger.The simulation results agree well with the experimental data under Ar-O_2 mixed shielding stationary GTA welding on SUS304 plates.