42 巻 (1973) 6 号 p. 544-553
In submerged arc welding of high tensile strength steels, it is positively demanded to produce weld metal having low crack sensitivity, especially hydrogen induced crack sensitivity.
Agglomerated flux has many advantages, such as generation of more shield gas, high basicity and so on, but it has disadvantage of having a hygroscopic character.
Meanwhile, it is generally believed that fused flux decreases the hydrogen content in weld metal on account of its unhygroscopicity.
This is, however, not true because fused flux contains much hydrogen in flux itself in the form of OH radical, which is derived from the atmosphere of its manufacturing process.
This investigation shows clearly that highly basic agglomerated flux, which generates plenty of CO2 gas in welding, can minimize hydrogen content of the weld metal.
The effects of basicity, CO2 gas, absorbed moisture and dissolved hydrogen in flux on hydrogen content of the weld metal are quantitatively determined by a model of hydrogen dissolution mechanism proposed in this paper.
The main results obtained are summarized as follows;
1) With an increasing basicity of the flux, the diffusible hydrogen in deposited metal decreases and the hydrogen dissolved into slag increases.
2) The diffusible hydrogen in deposited meatl steeply decreases with an increasing carbonate in flux.
3) Agglomerated flux has hygroscopicity, but that is lower than that of the low hydrogen type electrode coating.
4) Absorbed moisture of agglomerated flux completely evaporates at temperatures up to about 200°C.
5) In the case of the agglomerated flux about 20% of the air which has existed in the consumed particles of the flux enter the arc cavity and its ratio decreases to one third through generation of CO2 gas.
6) Only 0.015-0.020% of absorbed moisture in the flux enters the arc cavity, and its ratio decreases to one tenth when the flux generates CO2 gas.
7) Partial pressure of CO2 gas generated from the flux in the welding accounts for two thirds of total pressure in the acr acvity.
8) In the case of the fused flux, main source of the diffusible hydrogen in deposited metal is the hydrogen contained in flux itself in the form of OH radical.