ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Regular Article
Control of Columnar to Equiaxed Transition in Solidification Macrostructure of Austenitic Stainless Steel Castings
Simon Naumovich LekakhRon O’malleyMark EmmendorferBrenton Hrebec
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2017 Volume 57 Issue 5 Pages 824-832

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Abstract

Solidification macrostructure is of great importance for the properties and the quality of castings made from austenitic grade stainless steels (ASS) because there are limited options to change as-cast macrostructure in the solid condition. A typical cast macrostructure of ASS has a fine surface chilled zone followed by an elongated dendrite zone, columnar to equiaxed transition (CET) zone, and centrally located equiaxed crystals. Several castings from ASS were produced to determine the effects of casting geometry, chilling, and grain refinement on CET. The transient thermal field in solidified heavy castings was simulated and used to determine an isotherm velocity (V) and the thermal gradient (G) in mushy zone at 50% solid fraction. The critical value of the parameter Gn/V was determined from the macrostructure of the cylindrical casting. Using this value, the location of CET was predicted in the heavy rectangular casting and this prediction was in agreement with experimental macrostructure. Two methods of controlling casting macrostructure by using a chilled mold to stimulate extensive columnar zone and by using melt grain refinement to produce fine equiaxed crystals were experimentally verified and simulated.

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© 2017 by The Iron and Steel Institute of Japan
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