ESTIMATION OF A REGION WITH SOLIDIFICATIO N STRUCTURE REFINED BY REDUCTION IN SEMISOLID STATE THROUGH SOLIDIFICATION AND STRAIN ANALYSIS OFA CAST

It is well known that solidification structure is made finer by reduct ion in semisolid state. The object of this research is to clarify the condition of occurrence of such a process quantitatively and to make i t possible to estimate the size of the refined region in cast products . We made experiments in which cast pieces were reduced in semisolid s tate. We also analysed the distribution of temperature, fraction of so lid and strain in the thickness direction of cast pieces. The results obtained from these experiments and/or analyses are as follows. (1) Th e solidification structure of the region refined by reduction is equia xed and transformed into globular austenite, while that of the other p art, columnar dendritic or equiaxed with regular size, is transformed into columnar austenite. (2) The portion of refined region becomes lar ger as average fraction of solid and/or reduction ratio increase. Prec isely, the condition of refining is expressed with the following equat ion in terms of local solid fraction and local compressive strain. f(s ) less than or equal to 0.75 epsilon(0.132) (3) By use of the above qu antitative relations for refining, it becomes possible to estimate the fined region in cast pieces.