LAUSR

1.1. Solidification Structure Control A typical cast macrostructure of austenitic stainless steel (ASS) alloyed by Cr, Ni, Mo and the other transition metals has a fine surface chilled zone followed by an elongated dendrite zone and centrally located equiaxed crystals. The size and morphology of primary grains are of particular importance for physicochemical and mechanical properties of ASS. The grain size in the columnar and equiaxed zones, their ratio, and a columnar-to-equiaxed transition (CET) are the main parameters which characterize ASS solidification macro-structure. A CET zone in high alloy ASS is considered to be a possible place for element segregation and agglomeration of undesirable structural features (inclusion, micro-porosity etc.). The solidification macrostructure of ASS can be modified in two ways: (i) A fully columnar grain structure can be promoted. The oriented columnar and single grain cast structures of this type are very effective for high temperature applications, such as for directionally solidified aircraft turbine blades.1) Chills are often employed in ASS castings produced in sand molds for this purpose and to control shrinkage porosity. (ii) A fully equiaxed grain structure can be promoted. Grain refining extends the equiaxed zone and can partially or fully suppresses the columnar dendrite zone.2) Control of Columnar to Equiaxed Transition in Solidification Macrostructure of Austenitic Stainless Steel Castings