| The stainless steel sheet has been widely used in the field of bio-pharmaceuticals, medical equipment, micro-electronics and machining due to properties of the high corrosion resistance, nonmagnetic and high-temperature strength. In any structure application of those materials, its weldability is of most importance as welding is wildly used for joining it. Compared with the traditional welding process which can result the defect of burn through and deformation, the impulse microbeam plasma welding has a series of advantage, like a low heat input and energy concentration, which is a suitable way for the bonding of stainless steel sheet. However, due to the complex of the process parameters of the impulse microbeam plasma welding, it has an important academic theory and engineering practical significance to use the numerical simulation technique to research the influence of weld thermal cycle on the formation and the microstructure of the welding joint.In current paper, that 84 groups pulse current parameters were applied to research the thermal cycle influence on the 0.1 mm thick of stainless steel welding joint in the ANSYS FLUENT finite element software. The results showed that the thermal cycles present a dynamic characteristic on the condition of pulse electric flow, and the highest temperature of the welding joint center of the last pulse cycle is different and appear the dynamic change trend. The speed of cooling and heating did not show a linear change. While in the process of heating and cooling, there would be a short process of temperature down and rise respectively. The pulse frequency and pulse ratio also has the influence on the highest temperature of the welding joint center point and cooling rate.Using 84 groups pulse current parameters to weld the 0.1 mm thick of SUS321 stainless steel and five types of welding joint can be fabricated. Then based on the result of the numerical simulation technique to research the formation mechanism of the welding joint. The result shows that the change of pulse current parameters cause the change of the welding thermal cycle characteristic parameters, and the different thermal cycle can cause the different geometrical shape.The microstructure of welded joint of SUS321 stainless steel was analyzed in this paper. Spectrophotometer, scanning electron microscopy and X-ray diffraction were conducted for the welding seam structure, the results show that the isometric crystal distribute in the welding line and the columnar crystal list on the side of the welding line. Two mainly phases(austenite and ferrite) can be confirmed in the welding joint. And the ferrite exists in the boundary of austenite grain as the shape of vermicular and bone structure. Finally making a research on the influence of the pulse current parameters to the microstructure and the micro-hardness of the smooth continuous welding joint. The result shows that with the decrease of pulse peak current, the width of the weld molten pool is decrease, and the columnar crystal is at the both side of the welding line and the center of the welding joint is filled with the isometric crystal. The quantity of the isometric crystal and fine grain are increasing with the decrease of the pulse peak current. And while the quantity of the columnar crystal on the side of the welding line is decrease and the crystal orientation is complex with the decrease of the pulse peak current. With the decrease of the peak current, the micro-hardness of the welding joint present a rising trend. When the pulse frequency increased from 5Hz to 100 Hz, the welding grain become more and more fine and uniform and the welding joint micro-hardness is increased. |
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