| When the bullet's copper-rotating band was claded by means of tungsten inert gas (TIG) welding, the phenomenon of infiltrated cracks and cladding layer hardened because iron return was usually appeared. In this paper, the pure iron(carbon content less than 0.04%) was selected to produce rotating band as the cladding materials instead of copper. The code-wire TIG welding, new design hot-wire TIG welding and vibration TIG welding were adopted to clad the pure iron to the bullet's steel surface. In the experiment, the base metal included 20#, 45# and 50# steel. Compared the technology of pure iron cladding, the relationship between welding joints'appearance, interface morphology, microstructure of surfacing and different welding methods was studied. The hardness value and distribution and the shear strength of the cladding layer was measured. Finally, the bullet was emitted to confirm the effect of pure iron rotating band.By means of the code-wire welding , the available welding parameters of 30mm diameter bullet's pure iron rotating band was obtained: welding current 180-220A, cladding speed 1.3-1.5m/min, rotation period 100-110s,argon flow 10L/min. The new design hot-wire welding technology of double-TIG power source can largely increase the cladding speed and reduce the welding current of welding gun. The vibration welding can reduce the welding current, increase the cladding speed and improve the microstructure of cladding layer.The macro photos of pure iron welding joints showed that, with the increase of welding current, the width of cladding layer increased and the height reduced, the Heat Affected Zone(HAZ) becomed larger. Water cooling can effectively reduce the size of HAZ.Analyzed the interface of joint by means of optical microscope and scanning electron microscopy(SEM), the result showed that, with the increase of welding current, the melting of the base metal increased, more carbon entered into the weld pool through the interface. The hot-wire welding made the grain of coarse grain zone where near the interface seriously grow up, some of the them melted. The concordia grain on the interface was large. The vibration welding made the grain on the interface more small. Analyzed the microstructure of pure iron cladding layer, the result showed that, when the current of code-wire welding less than 180A, the microstructure of pure iron cladiing layer on the 20# steel was ferrite most of all. When the current becomed 220A, granular bainite appear in the cladding layer. The microstructure of cladding layer by hot-wire welding composed by cylindrical ferrite which was perpendicular to the fusion line, massive ferrite, granular pearlite and a small amount of bainite. The microstructure of cladding layer by vibration welding was ferrite for the most part. When the base metal was different, with the increase of carbon content in the base metal, pearlite and bainite type organization would appear in the puer iron cladding layer.According to the mechanical property of cladding layer, methods like water cooling and choosing low-carbon materials and reducing welding currents can offer benefits to lower the hardness of pure iron cladding layer. Despite this, another method like vibration welding can reduce this kind of layer's average hardness of 20# steel substance to 160HV. By lowering 15HV or so, the level of this method is nearer the level of method using mechanical pressing technology, when compared with the other two methods. As for the welding joints produced from the three welding methods, through shearing experiments, it showed that the ways for fractures to be slit are the same on the rotating band layer between the cladding layer of pure iron and copper. Moreover, the value of intensity on the connecting interface was much higher than its original intensity of bullet's cladding layer. Through the results of bullet's emitting experiments, it was identified that pure iron is another kind of feasible alternatives for copper as the bullets'cladding materials. |
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