| A special device for the formation tenuous cast iron welding rod is designed and manufactured according to suction casting principle. With this device, the filling capacity of liquid metal increases remarkably under the double roles of melt's gravity and vacuum suction and two kinds of welding rods with the size of F5mm×400mm and F3mm×400mm are produced under a vacuum level at 15KPa and pouring temperature at the range from 1300℃to 1400℃conditions. Statistic analyses show that the technological yield rate of F5mm welding rod is up to 80% and the technological yield rate of F3mm welding rod is lower relatively. The main proportion of F3mm welding rod belongs to two length scales: L<250mm and L=400mm with the proportion of 38.10% and 27.34%, separately. If acceptance standard is L≥300mm, then the percent pass would reach to 51.51%.The welding performance of micro-alloyed cast iron rod is studied by oxygen-acetylene flame welding and the homogeneous welding joints are obtained. The joint consists of weld, bonding zone and heat affected zone. The weld has well fused with base metal, and the heat-affected zone is wider. There is no chill microstructure in fusion zone. With the increase of Bi content in welding rod, the graphitized ability increases. When the content of Bi reaches to 100ppm, the weld matrix is pure ferrite with lower hardness. The hardness of weld is merely 222HB, while the fusion zone is 235HB. When the Bi content reaches to 120ppm, the weld hardness is increased slightly. The effect of Ti on joint properties is complex. When Ti content is low, the weld graphitization decrease sharply with the increase of Ti content. When the Ti content in rod is 0.1%, the weld hardness is 262HB and the hardness of fusion zone is 278HB, and graphitization in weld is increasing gradually with increasing the Ti content. When the Ti content reaches to 0.3%, ferrite percentage in weld reaches to maximum and the weld hardness is 223HB, the hardness of fusion zone is 239HB. The hardness of welding zone will increase once more while Ti content reached to 0.4%. The strength of HT150 cast iron joint is more than 163.3MPa.Micro-alloyed cast iron homogeneous electrode is manufactured by coating graphitizated coat on welding rod. The welding properties of electrode is studied via the technology of backing welding with low-current and then continuous welding with high-current. The results show that the ability of weld graphitization increase with the elevation of preheating temperature. When the preheating temperature reaches to 200℃, the microstructure of weld consists of pearlite, ferrite, fine flaky graphite and rosette graphite, the percentage of ferrite reached 23.66%, the microstructure of fusion zone consists of pearlite, small shiver ferrite and undercooled graphite. The hardness of weld and bonding zone is 176HB and 198HB, separately. The machining properties of welding zone is excellent, the joint has excellent properties and the strength of weld metal can reach to 451 MPa.
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