Study on Metallurgical Reactions in Arc Welding (Report 2)

Rates of Deoxidations in Arc Melting

Abstract

The rates of the Si and Si-Mn deoxidations in arc melting were studied in order to investigate their behaviour in deoxidation reactions in arc welding. The temperature of the melting pool ranges between the melting point of iron and about 2000°C. However, according to our previous paper on deoxidation equilibriums in arc melting, it was shown that deoxidation reaction in arc melting could be treated as a reaction at some mean temperature.
On this basis, the rates of the Si and Si-Mn deoxidations were measured using the apparatus and melting procedure which were almost identical to the ones reported in the previous paper. The results of the analysis of the experiments were as follows:
(1) Rate of deoxidation is shown by the following equation:
d[%O]/dt=I/V k₀([%O]-[%O]_e)
where [%O] is oxygen content at time t; [%O]_e is oxygen content at apparent equilibrium; I is current; V is volume of molten pool. The rate constant, k₀, is independent of the melting condition (pressure of Ar Atmosphere, current and voltage), but depends upon the content of elements (Si, Mn, O) in the specimen and also the appartus used.
(2) The above equation was compared with the reaction model, which assumes that the separation process of the deoxidation product is the rate determining step and also that the rate depends upon the strength of the stirring in the pool. Then, it is probable that the strength of the stirring (stirring speed at the place where the deoxidation product is separated) is proportional to the current. However, this conclusion has to be further investigated.
(3) In the Si deoxidation process, the rate constant, k₀, is constant in low Si range (Si<0.4%), but increases as the content of Si increases in high Si range (Si>0.4%). In the Si-Mn deoxidation, k₀ increases as the content of Si decreases and the content of Mn increases. In addition, k₀ increases as the oxygen content in the specimen increases.