The purpose of this master thesis is to determine the fracture and impact toughness of EN-GJS-400-18LT ductile iron at different temperatures and compare it to S235JR+AR hot-rolled structural steel. Several Y-block ductile iron castings were made in order to make specimens for determining the fracture and impact toughness and samples for metallographic examination. We made specimens for impact and fracture toughness as well as metallographic samples out of 25 mm thick hot rolled steel plate. Microstructure examination was performed by light microscopy, while chemical analysis was performed by optical emission spectroscopy. Impact toughness was determined with the use of the Charpy method at room temperature, 0 °C, -20 °C and -40°C. At the same temperatures, J-integral values as well as crack tip opening displacement – CTOD and fracture toughness were determined by three-point bending test. Microfractography was performed by using scanning electron microscope.
EN-GJS-400-18LT has a ferritic – perlitic microstructure with carbon in form of graphite nodules embedded in the matrix. Hot rolled S235JR+AR steel has a ferritic – perlitic microstructure with crystal grains extended and orientated in the direction of rolling. It turned out that the impact toughness of steel at room temperature is greatly higher than that of ductile iron, but it decreases sharply with decreasing temperature. At -40 °C the impact toughness of both materials is practically the same. Fracture toughness of ductile iron is higher at all temperatures tested than fracture toughness of steel and it actually rises a bit with decreasing temperature.
|
