Effect Of Double Wire Welding Parameters On The Micro-structure And Properties Of Hsla Welds

Twin wire submerged arc welding for its high efficiency, energy saving, high quality characteristics has become one of the high efficient welding method of ship construction. Compared with the wire submerged arc welding, twin wire submerged arc welding has more adjustable welding process parameters. It is necessary to study the double wire submerged arc welding process parameters which have great influence on the joint performance.In this paper, engineering testing was executed on 20 mm 10Ni3Cr Mo V steel by using twin-wire submerged arc welding. The main study of the effect of double wire submerged arc welding process of twin wire spacing, welding speed and current on the weld cross-section morphology, weld forming, chemical composition, micro-structure and properties of welded joints. Double wire spacing between 20 ~ 30 mm, can obtain good welding weld joint forming speed change between40 ~ 80cm/min. When the double wire spacing is too small(below 10mm), Double wire become co pool and the interference caused particularly strong. Under this large heat input the leading and tracking wire is easy to be bonded together, so the forming is the worst and cannot be normally completion of welding; When the wire spacing above 40 mm, "Dragon Valley" will be formed In the weld center which makes the weld shape variation. The wire spacing between 20 ~ 30 mm, when the welding speed is below 40cm/min, which makes the weld surface spread a little too open, the weld width become larged but the reinforcement deficiency for its slow welding speed. When the welding speed exceeds 80 cm/min, the molten can not completely spread out which made poor weld seam and protruding ridge will be formed in the central of the weld joint.The optical microscopy, scanning electron microscopy and electron back scattering were used to analysis the micro-structure and the chemical composition of the joint. During double-pass welding, the first CGHAZ is modified with the second pass thermal cycles which forming discontinues zones. The reheated CGHAZ regions was divided into three parts: Super-critically Reheated CGHAZ(TP2>Ac3),Inter-critically Reheated CGHAZ(Ac3>TP2>Ac1),sub-critically Reheated CGHAZ(TP2<Ac1).The results showed that the Inter-critically Reheated CGHAZ will formed of low toughness but also formation of low toughness than in coarse grain zone. It is generally recognized that the MA island structure was the main reason for the decrease in toughness in heat affected zone, some austenite islands organizations Turn into carbon rich region and then in the cooling process will be transformed into MA organization.The study showed that the O content increased with the welding current but inversely proportional to the welding speed.The original austenite grain width results indicated that The original austenite grain width is inversely proportional to welding speed, but will be increased with the welding current(the increase of heat input).