Research On Double-wire Saw Technology And Microstructure Behavior Of The Welded Joint Of 10Ni3CrMoV Steel

Double-wire submerged arc welding is one of the high efficient welding technologies in shipbuilding for its high efficiency, saving energy and high quality. Compared to single wire submerged arc welding, the Double-wire submerged arc welding has more adjustable parameters. Therefore, it is necessary to study these adjustable parameters which have great effect on the welded joint.Studies of the arrangement mode of the double-wire, the distance between the double wires and the welding speed have been conducted. Best appearance of the welding bead and the cross-section shape can be formed by setting the arrangement mode of the double-wire as tandem mode. When the distance between the double wires is between 20~40mm and the welding speeding is between 60~80cm/min,a good welding joint and cross-section shape have been formed. When the distance between the double wires is between 40~60mm, and the welding speeding is between 60~80cm/min, a good welding joint and cross-section shape have also been formed. When the distance between the double wires is between 60~100mm with a welding speeding less than 60cm/min, a not bad formed welding joint will be obtained. the plate tensile tests and -50℃charpy impact tests have been conducted on the welded joints. According to the results, the lowest impact value have been obtained in the fusion-line in the condition of big distance between double wires and high welding speed, the lowest value is 59J.the weld seams and the heat affected zones have obtained the similar microstructures. The weld seam is mainly consisted of acicular ferrite, granular bainite and little proeutectoid ferrite. And coarse grain zone is mainly consisted of granular bainite and ferrite.The thermal cycle of the double-wire submerged arc welding have been measured. When the distance between double wires is less than 20mm, the two wires are in a shared welding pool, and there is only one peak temperature on thermal cycle curve. When the distance between double wires is between 20~40mm with slower welding speed, and there is only one peak temperature, with faster welding speed, there are two peak temperature. When the distance between double wires is between 40~100mm, and the thermal cycle curve obviously have two peak temperatures.Based on the measured double-wires thermal cycle, thermal simulation tests have been conducted. And the impact test results show that the specimens undergoing the thermal cycle measured when the distance between double wires is 20mm in the processing of double-wire SAW, and the peak temperature is more than 1100℃, have obtained poor impact toughness. When the peak temperature is between AC3~1100℃, the specimens have obtained good impact toughness. It has also been founded that the peak temperature has great effect on the embitterment than the t8/5 does. The impact toughness value of the specimens undergoing the thermal cycle measured when the distance between double wires is 40mm in the processing of double-wire SAW varies from high to low when the trailing peak temperatures are 780℃, 1049℃and 1327℃in the condition of the leading peak temperature is 1327℃. It has been obtained that the trailing peak temperature is important factor on the embrittlement occurring in the simulated HAZ.The embrittlement phenomena of simulated double-wire welding HAZ have been studied in the aspects of grain coarsening, brittle precipitates, brittle transformed structure and large heat input. And according to the above aspects, the main reasons of embrittlement phenomena occurring under the lower temperature have been analyzed. large heat input have been found as the main reason for forming the grain coarsening of the simulated HAZ and brittle transformed structure .