Features of Structure and Solidification of Extended Double Ingots for Hollow Forgings. Part 1

Results are provided for a study of features of the structure of extended double hot-topped ingots. In the upper half of a test ingot, there is significant development of defects of shrinkage origin (closed secondary shrinkage cavities and zone of axial porosity), and they are significantly developed over the height and insignificantly over the diameter. Defects of shrinkage origin are concentrated within the upper half of an ingot body. It is established that within a double ingot nonmetallic inclusion distribution and cast structure parameters differ from the distribution for an ingot of normal geometry. Comparison of mathematical modeling data with results of studying ingot structure shows that a higher temperature in a narrow axial part of an actual ingot slows down solidification. This leads to an increase in dendrite parameter, a reduction in dendrite structure density, an increase in porosity, the amount of readily melting sulfide and complex oxysulfide nonmetallic inclusions, and also formation of a closed secondary shrinkage cavities. This position of defects of shrinkage and liquation origin facilitates their removal during ingot forging, and provides the possibility of obtaining hollow forgings from them. In test ingot forgings, there is a fourfold reduction in their chemical inhomogeneity and an increase in mechanical property stability over an object’s length. Use of extended double ingots for preparing hollow billets makes it possible to increase output of finished metal in a forging by 8%.