Structure and Impact Property of Cast Steel

Abstract

Impact tests were carried out using cast steels with different carbon and silicon contents. Time-load curves were measured at the same time. Cracks and fractured surfaces were observed by an optical and a scanning electron microscopes. Observations of macro and micro-structures and a measurement of austenite grain size in different quench temperature were also carried out. The results obtained are as follows:(1) Impact values of the cast steels increase with decreases of carbon and silicon contents and they show a maximum when C+1/4 Si is about 0.2-0.3%. The impact value is the greatest near the chilled surface and decreases near the sand mould and at the center of the cast steel piece in this order.(2) From the time-load curves, it can be seen that the fracture mode is brittle. More than 60% of the impact energy at room temperature is consumed in the initiation of crack and the energy for propagation is small.(3) Most of the fractured surfaces consist of cleavage facets. The size of cleavage facet is equal to the ferrite length and they vary inversely as the impact value.(4) It is often recognized that the crack propagates along a ferrite platelet.(5) The austenite grain size becomes coarser during cooling and it is influencedby the quench temperature above 1200°C.