1961 Volume 47 Issue 5 Pages 715-720
The growing interest in vacuum melting for production of alloys has promoted investigation of the variables in the process. One of the advantage of vacuum melting is the opportunity for reduction of oxygen content of the melt by the use of hydrogen or carbon, and reaction products of those are gas phases. This investigation dealt with the carbon-and hydrogen refining phases of the process in vacuum induction melting of iron-base and nickelbase alloys containing 0-20% chromium which are major composition of heat-resisting steel. Attainable limit of gas content in vacuum melting has also been investigated with standard commercial alloys, AISI type 304 and Inconel.
Electrolytic materials weighting about 2 to 5kg were melted in an Al203 crucible by using a laboratory-scale vacuum induction apparatus.
In the case of carbon reduction, 0-0.30% of granular graphite was added into the melt after the charge had been completely melted down, and the melt which was kept in vacuum during an hour for boiling and degassing.
In the case of hydrogen reduction, the melt was impinged for an hour with a stream of dry hydrogen, the dew point of which was varied in a range from -30°C to-70°C. During deoxidation processes of both cases, the molten metal was kept at 1570-1620°C.
Results were as follows:
1. Attainable oxygen level in nickel-base alloy was considered to be lower than in ironbase alloy in any reduction practice. The amount of oxygen attainable after reduction practice was increased by addition of chromium.
2. The oxygen and the nitrogen of standard commercial alloys finally attained by carbon treatment were respectively below 0.0010% and 0.0030% which were some tenths of hose by the conventional method.
3. Deoxidation by dry hydrogen was incapable for reducing oxygen content in the alloys and metals except in pure nickel regardless of the dew point of hydrogen used.
4. The oxygen and nitrogen values obtained experimentally were extremely higher than the equilibrium values theoritically calculated. Therefore it may be presumed that, regarding the degassing by vacuum induction melting, the process of CO gas bubble formation and crucible reaction should be studied in conjunction with a study of the phenomenon from the kinetic point of view.