Key Engineering Materials Vol. 457

Abstract: Using thermal analysis a preliminary study of the evolution of the metallurgical quality was carried out, concluding that it was strongly deteriorated during the Mg treatment, worsened at the pouring furnace. In order to improve the metallurgical quality a new phase of conditioning before the Mg treatment has been implemented. Also a special ladle was designed and built to be able to perform this new process stage in a robust manner. In this way the main objective was reached, increasing the metallurgical quality of the melt inside the treatment ladle and also at the pouring furnace, obtaining at the same time better process stability. The metallurgical quality improvement reflects at the cooling curves (stable solidification patterns), at the microstructure (higher nodule count, better graphite distribution and more ferrite content in the matrix) and at the mechanical properties (less tensile strength, higher elongation, less hardness and higher impact toughness) of the casting parts.

Abstract: Ductile irons with chemical compositions of Fe-3.6%C-2.6%Si-0.50%Cu-0.51%Ni were cast into standard keel blocks. Austenitizing heat treatment was carried out on test pieces at 875°C followed by austempering at 320, 365 and 400°C for times within the austempering processing window in a salt bath furnace. Rotating bending fatigue tests were performed with Roell Amsler UBM 200™ equipment at 3500 rpm at room temperature. Metallography and X-ray diffraction techniques were used to evaluate the fatigue life. Results indicate an increase of 10, 20 and 24% in fatigue life for specimens austempered at temperatures of 320, 365 and 400°C respectively, compared to that of as cast samples. According to the XRD test results; there is an increase in volume fraction of high carbon austenite by increasing the austempering temperature.

Abstract: This paper investigates the effects of graphite added as a conditioner, of Lantanum containing nodulariser and of pouring temperature on the formation of shrinkage porosity in ductile iron casting with an eutectic composition. In this experiment for each heat the cooling curves were recorded by the use of Quick-Cups (thermal analysis cups) and different solidification parameters such as TElow, GRF1, GRF2 and TS were calculated and compared with the porosity which was found from the microstructure examination. The results show that there is a good correlation between the amount of the shrinkage formation and the thermal analysis values. Also this experiment confirm that by using certain treating elements and pouring temperature which was between 1340-1350°C it is possible to eliminate the shrinkage defects in ductile iron castings without using feeders.