Influence of Chromium and Molybdenum in Solidification and Shrinkage Defects for High Resistance Grey Iron Alloys

Abstract

This paper presents an evaluation of Cr and Mo influence in solidification and shrinkage defects in grey cast iron. A series of five grey cast irons were produced with different Cr and Mo additions. A test casting was developed by casting process simulation to reproduce defects of an specific cylinder head. Macroshrinkage cavities were detected in the top of the test parts and microshrinkage porosity defects were analyzed in the hot spots. Macroshrinkage volumes were measured by filling the cavities with water. The microshrinkage porosities were evaluated by liquid penetrant examination and image analysis. The solidification sequence and microstructure were evaluated by thermal analysis and metallography. Combinations of 0,4%, 0,6% and 1,00 % of Cr + Mo presented a significant increase in macroshrinkage volumes and combinations of 0,6% and 1,00% of Cr + Mo presented an increase of microshrinkage porosity. In solidification Cr and Mo increased undercooling, austenite pro-eutectic fraction volume, intercellular carbides, reduced the eutectic cell size and fraction volume of graphite.