EFFECT OF GAS INLET POSITIONS ON PLASMA CARBURIZING OF AISI-1020 STEEL

Samples of 1020 grade steel were carburized for 30 min at 1000 degrees C in a d.c. plasma system enclosed in a tube furnace. A gas mixture c onsisting of methane (CH,) and hydrogen was bled into the system using one of two inlet positions located at the top and the bottom of the r eactor. The latter position was close to the vacuum pump outlet. It wa s found that the carburizing results obtained with each gas inlet posi tion differ significantly even though all other parameters (temperatur e, pressure, current density, flow rate and treatment time) were ident ical. The carburizing results are discussed in view of different mass transfer rates of carbon species in the plasma in the two different po sitions. It is concluded that when the gas inlet is located at the bot tom of the reactor a large proportion of the methane molecules are not reaching the plasma reaction zone efficiently as their concentration in the stream is depleted faster than with flow from the opposite posi tion, and this affects the active carburizing capacity of the plasma.