A semi-solid processing technique combining a cooling plate and various mold materials is developed to produce high quality gray cast iron components. Flow behavior of semi-solid slurry along an inclined cooling plate is studied to establish the effect of plate orientation on the integrity of cast products. The concept of multiple-stage cooling is discussed by considering cooling rates at different stages of processing along the cooling plate and in sand, graphite and metallic molds to show the significance of cooling rate in determining component microstructure. The morphology of microstructure in cast components is discussed and image analysis results presented. A refined microstructure of primary austenite and graphite, and their characteristics associated with the use of different mold materials are reported. Angle of inclination of plate is shown to influence the morphology and quantity of precipitated phases. Finally, the effects of cooling plate and mold material on Vickers hardness and mechanical strength of cast components are discussed.
Semi-solid processed 18% Cr and 27% Cr cast irons were produced by using copper cooling plate and metal mold. A series of experiments were carried out to clarify the effect of heat treatment on microstructure, hardness, wear properties, and corrosion characteristics. The results show that 27% Cr alloys possess better abrasive resistance than 18% Cr alloys due to higher carbide volume under all the conditions when tested by dry sand rubber wheel with silica abrasive. However 18% Cr alloys show higher wear resistance than 27% Cr alloys when using super hard alloy disk against the specimen plate surface. The harder disk indent into the carbides, leads to spalling and pitting, and therefore greater wear rate. For the corrosion test result, 27% Cr alloys have better corrosion resistance than 18% Cr alloys as a result of higher chromium content. A combination of semi-solid processing and heat treatment improves wear resistance and corrosion resistance of chromium cast iron.
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