Solidification Structure and Segregation in Austenitic Stainless Steel Containing Phosphorus

Abstract

This paper describes an experimental study made of the solidification structure and the segregation in austenitic stainless steels containing phosphorus.
Small melts were unidirectionally solidified to simplify the freezing process. The cooling curves were also obtained in 300kg ingots to compare the solidification structure with unidirectionally solidified ingots.
The results obtained are as follows:
1) The secondary dendrite-arm spacing in the columnar crystal zone in the unidirectionally solidified ingots was influenced by the average cooling rate during solidification and phosphorus content. The ralation between the secondary dendrite-arm spacing and the average cooling rate in the above mentioned ingots was applicable to the 300kg ingots.
2) The primary dendrite-arm spacing in the columnar crystal zone was also influenced by the average cooling rate. but the result obtained from the unidirectionally solidified ingots was not applicable to the 300kg ingots.
3) Microsegregations around the primary and the secondary dendrite arms in the unidirectionally solidified ingots were determined by an electron probe microanalysis. The degress of microsegregation of phosphorus, chromium, and molybdenum increased with a decrease of the cooling rate.
4) An inverse segregation was found in a 300kg ingot. It should have resulted from the solidification shrinkage in a wide mushy zone formed in the ingot.