Study Of Backing Weld Crack Resistance In One-Side Welding Using Flux-Cored Wires And Ceramic Backings

In ship construction, the one side backing weld using flux-cored wires and ceramic backings has no operational sequences such as,the gouging of the Opposite groove, sanding, segmentation keeling over, etc,which greatly improves shipbuilding efficiency. However, longitudinal cracks often emerge in the center surface of the weld during the fabrication, especially in the splice weld structure of the hull such as inner bottom plates, decks, etc. It had been proved that this crack belonged to the hot crack through the metallographic analysis of specimens with cracks.Welding cracks rarely come into being under the condition of small welding parameters based on experience. So the whole idea of this article is seeking the way and the possibility to having no weld cracks in the backing weld using flux-cored wires and ceramic backings Under the condition of large welding parameters (such as welding current260A, welding voltage28V).The research emphasis was the influence law of welding parameters’impact on the hot crack. The test panels’assembly method was slightly improved by the back rib restraining small size test panels from experience. Penetrant flaw detection agent was used to detect the backing weld surface, and the number of cracks was indicated by surface crack rate. The experiment proved that the biggest technological parameters influencing the crack rate included the welding current, weld restraint intensity and welding speed, etc.Welding consumables, like Ceramic backings, flux-cored wires, etc, have an impact on the chemical composition of the backing weld metal in the welding. It had analysed the chemical composition of ceramic, ceramic slag as well as backing weld surface slag, surfacing slag, and found that the composition of backing weld slag was less affected by ceramic backings, however, there was more elements exchange between the ceramic backing and the backing weld metal. Under the same conditions, it’s not easy to see the crack when the steel backing was used, which just verified inclusions from welding consumables were one of the main factors that caused this hot crack.The crack resistance differences were analyzed and discussed, between solid wires and flux cored wires, and different brands of flux-cored wires.The alkalinity of ceramic backings may influence the crack resistance. Solid wires which whose welding speed was low had smaller crack rate than that of the flux-cored wires, several brands of commercially available flux-cored wires had crack rate differences in large welding parameters, but overall,had no satisfying results of the crack resistance. Ceramic backings with high alkalinity had superior crack resistance.The influnce about elements inclduing S, P, B, Si and rare earth impacting on the hot crack was researched,and several groups of E71T-1system flux-cored wires were prepared to do comparison experiment about the crack resistance, and metallographic analysis about the morphology of each specimen’ welded joint was done. It was found that the boron content affected the hot crack greatly. Austenite grain were made up of many massive ferrites on boundaries and intragranular coarse acicular ferrites in the backing weld center, and most of the hot cracks observed generated in the massive ferrites and extended along the austenite grain boundaries. The larger the grain size of acicular ferrite in the austenite grain was, the greater the tendency of hot cracking appearing was.