Abstract
The rates of absorption of nitrogen in liquid iron and liquid iron alloys were measured for inductively melted iron under pure nitrogen at 1600°C.
The experimental data show a linear correlation, which gives the apparent mass transfer coefficient, k′, when the variable, log [(Cs-Co)/(Cs-C)] is plotted vs F·t/V.
The experimental values of the apparent mass transfer coefficient obtained for lower oxygen melts are as follows:
k′=34-35×10-3 cm·sec-1 for 0.005-0.006% O
k′=27-29×10-3cm·sec-1 for 0.008-0.013% O
At present, it appears that the transfer of nitrogen across the gas/metal interface is controlled by the transport in the metal. Some models of gas absorption in liquid, such as the film theory, the penetration theory and the surface renewal theory, were taken into account to explain the present results.
The effects of several alloying elements on the absorption rates were also measured. It is to be noted that carbon, chromium and manganese have practically little influence, silicon, however, has somewhat remarkable influence in the lower concentrations. Namely, mass transfer coefficient increases gradually as silicon increases and reaches the limiting value of 5×10-2 cm·sec-1 at about 2% Si. It seems reasonable to consider that silicon reduces oxygen poison effect which is caused by absorption of dissolved oxygen on the metal surface, even in low oxygen level (0.002% O).
Transfer of nitrogen from gas into liquid iron may also be chemically controlled when the liquid iron contains some surface active agents. The role of surface active agents such as oxygen and sulphur will be discussed in the next paper.
