1971 Volume 40 Issue 8 Pages 748-754
The reason why most of the coated electrodes can give a sound weld metal.even under water but low hydrogen type electrode and semi-automatic CO2 welding are apt to produce blowholes in an underwater weld metal is investigated in this report by oscillograms, chemical analysis of gases in blowhole and the configuration, the microstructure and the hardness of deposited bead made under water as compared with those in air.
Results are as follows;
1) Arc of ilmenite, high titania, lime titania, high iron oxide-iron powder and high cellulose type electrodes is stable and their droplet transfer in arc is spray type, while underwater arc of low hydrogen type electrode and semi-automatic CO2 welding has a considerably long arc-disappearing time on oscillogram and it seems difficult to reignite arc.
2) Main component of blowhole gas in an underwater deposit is hydrogen, which is very different from the case of usual welding in air.
3) Microstructure of the heat affected zone of an underwater weld of mild steel is bainitic-martensitic and its hardness is very high.
4) The cause of blowhole formation by low hydrogen electrode and CO2 welding is probably attributed to their insufficient reignition of arc on a cold base metal under water, which makes solidification rate of weld metal so extraordinarily fast that a large amount of hydrogen produced by arc under water can not escape from molten metal.