A physico-chemical study has been made on the chemical reaction between molten slag and metal in welding process by the arc welding electrode containing Fe-Mn in its coating as deoxidizer, and the following results were obtained.
(1) Equilibrium index K'
Mn{(% MnO)/[%Mn]⋅(%FeO)} is independent of slag-basicity, and its value is 3.08
(2) Equilibrium index K'
O{[%O]/(%FeO)} is also independent of slag-basicity, and its value is 0.00973.
(3) Equilibrium index K'
Si{[%Si]⋅(%FeO)/(%SiO
2)} increases with decreasing slag-basicity, and the relation between K'
Si and basicity B
L is represented by the following equation;
logK'
Si=-0.4080B
L-0.668
(4) Activity coefficient of SiO
2 in weld slag "ySiO
2" increases with decreasing slag-basicity, where YSiO
2→1 when slag-basicity B
L→0, and it is a function of only B
L, represented by the following equation ; log ySiO
2=-0.408B
L(5) Oxygen content in weld metal has not only relations with Si content in weld metal, but also slag-basicity and SiO
2 content in weld slag, and the following equation was obtained for oxygen content in weld metal; log[%O]=-0.204B
L-0.5log[%Si]+0.5log(%SiO
2)-2.346
(6) The expression of slag-basicity proposed by K. Mori is the most suitable for weld slag.
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