Abstract: A mushy zone is formed in
the lower part of an ingot by the showering of crystallites from
the top and the free dendritic arms fused and broken from the
dendrites growing on the side mold wall. The zone obstructs the
inclusions to buoy up. In addition, the inclusions buoying to
the upper part of the ingot can be carried down to the bottom by
natural convective flow and trapped by the mushy zone. On the
other hand, an equiaxed crystal zone in the bottom of the steel
ingot results from the crystals coming from the sides and the
growth of crystals caused by heat transfer. An interval from the
beginning of pouring to the time when the velocity of convective
flow becomes too low to carry any inclusions larger than
tolerant ones down to the bottom is defined as critical time.
Then, the size of bottom cone of inclusions is equal to that of
equiaxed crystal zone formed in the critical time. In this paper,
the method for determining critical time was proposed, and the
numerical simulation on the formation of bottom equiaxed crystal
zone was carried out. A 27Cr2Mo1V steel ingot of 68 tons in
weight was studied. From the results of numerical simulation,
the weight ratio of cut tail end to ingot body was 8.11%. This
result corresponds with the weight ratio of 8.8% in production
practice of the same ingot approximately.
Key words:
Chrome-molybdenum steel Steel ingot
casting Inclusion Numerical simulation
|