Decarburization of Steel to Ultra-low-carbon Levels by Vacuum Levitation.

Vacuum levitation experiments were carried out on approximately I g steel samples initially containing from 35 to 2 OOO ppm (mass) carbon, from 40 to 3 300 ppm (mass) sulphur and from 200 to 800 ppm (mass) oxygen at temperatures in the range 1 550 to 1 850'C and at vacuums of 20 and 40 Pa.1)It was found that the rate of decarburization was proportional to the carbon content of the samples.The overall carbon mass transfer coef- ficient was approximately I .6 x l0~5 m/s and was seen to increase slightly with decreasing chamber pressure.Chemical reaction control was not suggested since the decarburization rate was insensitive to initial sulphur content and the variation associated with levitation temperature due to variation in the initial sample mass, * The value used for the chamber pressure is greater than the measuredpressure and since it is believed that there may have been a localised higher pressure region inside the glass tube due to the evaporation of iron.In practice, the actual pressure in the vicinity of the droplet was likely somewhere betweenthese two extremes and hencethe effect of pressure would not havebeenquite as great as the mathematical analysis suggests 1 ol