| Semi-solid billets of hypoeutectic high chromium cast iron prepared by inclined cooling plate method were reheated, then thixotropic extruding filled. The influences of holding time and reheating temperature on microstructure of semi-solid billets and as-cast billets during reheating were investigated. The influences of holding time and reheating temperature on the filling property and microstructure and mechanical property of filled parts were studied.Semi-solid billets during the semi-solid interval, pro-eutectic austenite grains circulated from the spheroidizing to the merge growing process, and the cycle time was prolonged gradually, and the final period of exacerbation was more prominent than prior period. With the reheating temperature up, the speed of the spheroidizing and the merge growing of grains changed from quick to slow, and exacerbation changed small gradually. When the reheating temperature is enough excessive, the coarsing of grains was serious, and sample oxidized serious and flowed.As-cast billets possess dendritic structure, when the reheating temperature was lower, even if prolonged the holding time, the dendritic structure was also hard to spheroidized. Increasing the reheating temperature and prolonging the holding time, the dendritic structure just began to burn out and spheroidized, but the spheroidized effect was not ideal, meanwhile the coarsing of grains was serious.Semi-solid billets have better filling property than as-cast billets, and as-cast billets are difficult to filling. When the reheating temperature is low, billets can not filling wholly. Increasing the reheating temperature, when the holding time is short, and billets are difficult to filling wholly. Prolonging the holding time, reheating of billets is more homogeneous, billets can filled wholly with better surface quality. When the reheating temperature is too higher, although billets can filling wholly, the surface quality of filling parts is lower.The internal soundness of rheologic filled parts is unsound, and has much central shrinkage cavity in the middle of filled parts. The thixotropic filled parts have better internal soundness, but some filled parts have shrinkage porosity and crack upside the parts.The microstructure of thixotropic filled parts has much refinement than before filled parts, because grains were crushed. Axial direction of parts from top to down, the size of grains become fine gradually, and the grains in the upper position of sample has much dendritic, and the roundness of grains in the middle of parts was high, and grains distributed evenly. Cross direction of parts from margin to center, grains grow in some sort, but the change was not obvious. Prolonging the holding time, the microstructure of filled parts was a little increase.The thixotropic filled parts have high mechanical property than rheologic filled parts, and filled parts have higher density and fine grains. |
