Carbide precipitates in Thin Wall Ductile Iron (TWDI) used for automotive applications needs to be eliminated or reduced for improved strength, ductility, crack propagation resistance and good machinability. Ductile i...Carbide precipitates in Thin Wall Ductile Iron (TWDI) used for automotive applications needs to be eliminated or reduced for improved strength, ductility, crack propagation resistance and good machinability. Ductile iron thin section profiles (≤3 mm) present danger of massive carbide precipitations in the as-cast sample. Precipitated carbide phase is brittle and negatively affects the mechanical properties of the iron matrix. The suppression of carbide formation is associated with the nucleating properties of the nodularizer and innoculant alloys. This treatment is vital in ensuring that carbide precipitation, flake graphite structure and non-nodular graphite phases are reduced or completely eliminated in the TWDI castings. Therefore, the temperature and technique of treatment would influence the yield of the process, and ultimately the mechanical properties. In this study, the effect of nodularization and inoculation treatment temperature on the microstructure and mechanical properties of TWDI castings is examined. The results indicate that good nodularity and nodule count with better percent elongations are achieved using low treatment temperatures in descending order of 1490°C, 1470°C and 1450°C, but have negative effect at lower treatment temperature of 1430°C. However, TWDI castings have superior properties in terms of nodule counts and nodularity at 1450°C. Treatment temperature does not produce significant influence on ultimate tensile strength (UTS) and hardness of TWDI castings. TWDI castings show poor nodularity, nodule count and ductility at higher inoculation treatment temperatures of 1550°C, 1530°C and 1510°C.展开更多
It has been shown that it is possible to produce thin wall ductile iron (TWDI) castings of considerable length using an Archimedes spirals with a wall of 1, 2 or 3 mm in thickness. The fluidities for different mouldin...It has been shown that it is possible to produce thin wall ductile iron (TWDI) castings of considerable length using an Archimedes spirals with a wall of 1, 2 or 3 mm in thickness. The fluidities for different moulding materials [(classical mould, chemically bonded silica sand and chemically bonded low-density alumina-silicate ceramic sand (LDASC)], chemical composition, and pouring temperature were estimated. There is a significant temperature drop in thin sections (contrary to typical sections) during the mould filling. A profile of real temperature drop is presented along with theoretical predictions. The high temperature drop of liquid iron results in an increased cooling rate (before the eutectic equilibrium solidification temperature), which in turn affects the solidification and microstructure of TWDI castings. Microstructures were characterized quantitatively using an image analyser. Structure parameters for different wall thicknesses and moulding materials (graphite nodule count, ferrite and cementite fraction) are plotted, which is versus distance from the entrance to the mould cavity. It has been shown that the thin wall castings have a gradient structure. Moreover, a strong influence of LDASC sand (material with low ability to absorb the heat) on the structure parameters of TWDI castings is presented.展开更多
文摘Carbide precipitates in Thin Wall Ductile Iron (TWDI) used for automotive applications needs to be eliminated or reduced for improved strength, ductility, crack propagation resistance and good machinability. Ductile iron thin section profiles (≤3 mm) present danger of massive carbide precipitations in the as-cast sample. Precipitated carbide phase is brittle and negatively affects the mechanical properties of the iron matrix. The suppression of carbide formation is associated with the nucleating properties of the nodularizer and innoculant alloys. This treatment is vital in ensuring that carbide precipitation, flake graphite structure and non-nodular graphite phases are reduced or completely eliminated in the TWDI castings. Therefore, the temperature and technique of treatment would influence the yield of the process, and ultimately the mechanical properties. In this study, the effect of nodularization and inoculation treatment temperature on the microstructure and mechanical properties of TWDI castings is examined. The results indicate that good nodularity and nodule count with better percent elongations are achieved using low treatment temperatures in descending order of 1490°C, 1470°C and 1450°C, but have negative effect at lower treatment temperature of 1430°C. However, TWDI castings have superior properties in terms of nodule counts and nodularity at 1450°C. Treatment temperature does not produce significant influence on ultimate tensile strength (UTS) and hardness of TWDI castings. TWDI castings show poor nodularity, nodule count and ductility at higher inoculation treatment temperatures of 1550°C, 1530°C and 1510°C.
文摘It has been shown that it is possible to produce thin wall ductile iron (TWDI) castings of considerable length using an Archimedes spirals with a wall of 1, 2 or 3 mm in thickness. The fluidities for different moulding materials [(classical mould, chemically bonded silica sand and chemically bonded low-density alumina-silicate ceramic sand (LDASC)], chemical composition, and pouring temperature were estimated. There is a significant temperature drop in thin sections (contrary to typical sections) during the mould filling. A profile of real temperature drop is presented along with theoretical predictions. The high temperature drop of liquid iron results in an increased cooling rate (before the eutectic equilibrium solidification temperature), which in turn affects the solidification and microstructure of TWDI castings. Microstructures were characterized quantitatively using an image analyser. Structure parameters for different wall thicknesses and moulding materials (graphite nodule count, ferrite and cementite fraction) are plotted, which is versus distance from the entrance to the mould cavity. It has been shown that the thin wall castings have a gradient structure. Moreover, a strong influence of LDASC sand (material with low ability to absorb the heat) on the structure parameters of TWDI castings is presented.
