Abstract
The vacuum casting is no cure-all, but has a number of advantages. Following a through twenty months experience, the following benefits were recognized.
(1) 60% of hydrogen in steel and 30% of oxygen were removed, but nitrogen content would not vary appreciably.
(2) The vacuum pouring gave higher properties in directions transverse to the direction of work. It was noted that there was little or no change in tensile and yield strength, an improvement was indicated in elongation and reduction of area on the vacuum steel. Generally properties of the vacuum steel had less variances than those of air ingots.
(3) Ultrasonic test had proved no internal defects.
(4) Microscopic study and sand analysis indicated the reduction of non-metallic inclusions by 30%. But porous or spongy surface by the spraying resulted in increase of sand marks in gurface.
(5) The segregation was not materially affected.
The dendritic structure had less growth by the vacuum casting; and a ghost with microcracks was dissolved.
(6) The vacuum pouring had resulted in elimination of the secondary cavity with a greater certainty.
(7) The vacuum steel had indicated a freedom from flakes.
(8) The heat treatment cycles would be reduced from a half to one third.
