Fabrication And Extrusion Of Semi-solid Slurry Of Hypoeutectic High Chromium Cast Iron

The slope plate cooling method was applied to the fabricate the semi-solid slurry of the hypoeutectic high chromium cast iron, the Spheroidizing and fining mechanism of the hypoeutectic high chromium cast iron primary austenite was also discussed. The influences of casting temperature, slope angle and slot radius on the shapes and sizes of primary austenite was studied. The mechanical property of the hypoeutectic high chromium cast iron extrusion samples was analyzed after extruded by semi-solid rheocasting forming.The dendritic crystal grains of primary austenite were spheroidized and fined significantly after the alloy slurry flowed through the cooling slope plate. When the molten alloy was chilling by the slope plate during flowing process, the crystal nucleus would be formed continuously in a nonuniform way and grew up into dendritic shape. When the plate length increased to some extend, the probability of austenite crystal nucleus forming and growth reduced. On the other hand, the dendrites of austenite were broken and crushed into some short dendrites and sphere crystal due to the physical effects like collision, friction, swilling and cutting between the dendrites.When the casting temperature was low, the austenite grew slowly, which was round and fine. With the increasing of casting temperature, the dendrites grew fast, which could spheroidize and fine partial austenite with worse circularity and bigger size. When the temperature increased in a further step, for the cooling rate of the molten was proper, it was easy to form the dendrites with big head and small root, which would be fused, crushed, broken into rounder and finer austenite. With the temperature increased again, the molten temperature increased, the solid phase fraction decreased and so did the viscidity, however the inner physical effect and the cooling speed of molten reduced, which could form the dendrites with similar size on its head and root that could not be broken easily. Once the angle of the slope plate increased, the speed of the molten on the plate also increased, the cutting effect of the slope plate and the inner physical effect of the molten were strengthened, which helped spheroidizing and fining the austenite more. When the angel increased in a further step, the speed of the molten on the plate also increased, the time ofslope plate cutting and inner physical effect became short, which meant that the dendrites was not easy to crush and break, and the circularity became worse and the size was bigger. When the slot radius increased, the contact area between molten and slope plate increased, the flowing layer became thinner, heat dissipation was fast, the super cooling degree increased, the dendrites growth speed reduced and the austenite circularity increased and the size became smaller. The research indicated that with the condition of 1390°C~1400°C casting temperature, 500mm slope plate length, 30° slope angle and 400mm section slot radius, the austenite is roundest and smallest.The slurry was extruded by above parameters and the mechanical property of the extrusion sample was tested. The research indicated that, compared with the liquid sand-type casting, the rheocasting sample has higher density and better mechanical property.