Jp. Bellot et al., Evaporation of Fe and Cr from induction-stirred austenitic stainless steel. Influence of the inert gas pressure, ISIJ INT, 41(7), 2001, pp. 696-705
In Vacuum metallurgy one of the purposes is the reduction (or at least the
accurate prediction) of the evaporation losses. It is well known that the a
ddition of an inert gas in a vacuum furnace increases the recondensation of
the volatile elements and then reduces the evaporation losses. We may defi
ne the pressure P-1/2 required to halve the evaporation rate. The objective
of this study is a theoretical and experimental evaluation of P-1/2 in the
case of an austenitic stainless steel, and the analysis of the parameters
which influence this value.
The experimental programme was carried out on an austenitic stainless steel
to determine the net flux of evaporation from a well-mixed liquid in an am
bient pressure of argon ranging from 0.03 to 133 Pa. P-1/2=30 Pa is estimat
ed from the experimental curve.
The mechanisms of volatilization have been modeled using both a system base
d and a mechanistic approach, and the calculation of the pressure P-1/2 giv
es respectively 45 and 90 Pa. The numerical simulations (mechanistic approa
ch) emphasize the strong expansion of the vapor from the high density regio
ns close to the liquid surface. The macroscopic velocity of the vapor decre
ases as the argon pressure in the chamber increases since the average frequ
ency of collision with the argon atoms increases.
We have set up a sensitivity study in order to analyse the effects of the g
eometry and scale of the furnace and of the liquid temperature on the facto
r P-1/2. Since geometry and temperature vary in large scales for the indust
rial applications, the use of the experimental value P-1/2=30 Pa obtained i
s discussed.