Droplet transfer characteristics and mechanical properties of deposited metal as welded matching with cryogenic temperature steel for nickel based consumables

The ENiCrMo-6 electrode for cryogenic temperature application was developed which was made of nickel alloy core wires obtained by duplex refining of vacuum melting and electroslag remelting, and specially designed coatings with high basicity allowing the formation of gradient composite slag. Mechanical property tests were carried out on the deposited metal and the welding joint of 9Ni steel welded by ENiCrMo-6 electrode. With the aid of Acuteye high speed photograph technology, the characteristics of the droplet transfer and the molten metal flow have been studied, and the microstructure of the composite slag layer has been observed by JSM-6360LV scanning electron microscope. The weld and heat affected zone are observed and analyzed to investigate the low-temperature fracture behavior from different perspectives. The results show that large shaped molten droplets of nickel alloy and the poor fluidity result in difficulties in weld formation, while special designed coatings is an effective solution, which allows the formation of a gradient composite slag layer to accelerate the forming of weld. To ensure joint ductility in cryogenic conditions, it is critical to avoid the coarsening of austenite columnar grains and reduce the ductility loss in weld metal as welded. The experiment results has proved that when welding 9Ni steel with ENiCrMo-6 electrode, the effect of overheat on lath martensite or reversed austenite in the as-welded heat affect zone is insignificant. Generally, overheat will not largely reduce the number of reversed austenite or retained austenite within the lath martensites, which guaranteed the ductility of joint under cryogenic condition.