HIGH-STRENGTH HIGH TOUGHNESS COMPACTED GRAPHITE CAST-IRON

In the present paper, heat treatments were used to obtain upper and lower bainitic compacted graphite cast irons. The effects of the percentage of compacted graphite, the matrix structure, and the specimen thickness on the mechanical properties, fracture toughness, and fatigue crack growth rate of the irons were evaluated. Optical microscopy scanning electron microscopy, and X-ray diffraction were used to correlate the microstructural features with the observed properties. It was found that austempering not only greatly increases the strength of the compacted graphite irons, it also enhances the plane strain fracture toughness values by similar to 15-60% of that of the as cast (ferritic-pearlitic) material. The crack growth rate was also reduced by toughness than 30%. Plane stress fracture toughness values were found to increase with decreasing specimen thickness for all matrixes and percentages of compacted graphite. (C) 1995 The Institute of Materials.