Study on Solidification of Heavy Steel Ingots

Abstract

Solidification processes of heavy steel ingots are analogized by using computer, and internal structure is discussed in connection with distribution of chemical elements, equi-solidus line, freezing rate (velocity of averaged advancing solidus line) and staying time (staying time between liquidus and solidus temperature). The results are as follows:
1) An intimate relation is seen among the internal structures, freezing rate and its distribution.
2) Inverse V segregation appeared mainly in the zone with positive acceleration of freezing rate. This means that the segregation take place in granular crystal zone as well as in equi-axial crystal zone.
3) The pouring temperature appears to have a great influence on internal structures. In discussing the internal structures, therefore, a good care must be paid on the difference between the pouring temperature of liquid steel and the solidus temperature which is subject to the chemical composition.
4) The internal structures along an equi-time solidus line differ in top side and bottom side. There are branched columnar crystals in the top part, equi-axial crystals in the middle part and granular crystals on the bottom parts of 20t ingot along the 2 hr-solidus line after pouring.
5) The last solidifying zone (V segregation zone) shows the gourd-like-shape, which is obviously affected by the electric arc hot-topping, and then fine equi-axial crystals or granular crystals are formed at the bottom.