Mitsuharu Takita

Mould filling behaviour and solidification structure of semi-solid gray iron

The stirring strength, cooling rate and solidified fraction in co-existing liquid/solid phases are important factors influencing mould filling behaviour of semi-solid metal slurry. In the present study the investigation is carried out on semi-solid processing of gray iron to clarify the effects of these factors. The results indicate that the apparent viscosity and primary particle morphology have pronounced effects on the filling ability of semi-solid slurry. The particle segregation in the solidified sample is observed between the upper and lower part of the sample and is shown to decrease with the increase of stirring in semi-solid state. Finally, raising the die temperature improves the mould filling ability while the primary particle size becomes larger.

Casting of semi-solid cast iron slurry using combination of cooling slope and pressurisation

Abstract A system developed at Nagoya University combining a cooling slope, gravity pouring and pressurisation was utilised to cast components from hypoeutectic cast iron in the semi-solid state. Investigation of resulting microstructure and attendant defects was carried out, which revealed significant improvements in primary particle size refinement and globularity in components produced through semi-solid casting (SSC) when compared with normal gravity die casting (GDC) of super-heated melt. Sub-surface anomalies such as chilling tendency and skin-deep shrinkage cavities were unavoidable in components cast under pressure in a metallic mould at room temperature but, increasing the mould preheat temperature reduced the anomalies whereas increased pressurisation improved melt feeding and drastically reduced porosity attributed to gas entrapment and solidification shrinkage.

Effect of heat treatment on microstructure, wear properties and corrosion characteristics of semi-solid processed high chromium cast iron

Semi-solid processed high chromium cast irons were produced using a copper cooling plate and metal mould. 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 semi-solid processing by heat treatment improves wear resistance and corrosion resistance of high chromium cast iron. IJCMR/480

Mechanical properties and microstructure of semi-solid processed cast iron

Attempts to develop appropriate semi-solid processing techniques to manufacture iron castings have not been successful despite extensive laboratory studies done in the past. This research aimed at producing equiaxed primary phase structure in gray cast iron slurry using a cooling plate under a mechanism explained by the crystal separation theory, and casting the slurry into moulds made from different materials to form cylindrical components. A boron nitride coating was applied onto the surface of the cooling plate to improve melt-flow and prevent the melt from sticking along the flow path. Primary particle size, number, volume fraction and hardness for cast components were investigated with respect to radial and longitudinal position along sectioned surfaces. Results on size, shape and grain count of graphite precipitated in the matrix are also discussed, comparing resulting component microstructure with that of castings made through conventional sand casting. Pouring of melt onto the cooling plate was done at a temperature a little higher than liquidus to initiate nucleation of primary phase along the flow path. The casting technique enhanced nucleation rate, leading to finer and higher volume fraction of the primary particles before the slurry flowed into the mould. The nature of flow along the cooling plate ensured that agglomeration of primary particles was minimized, resulting in highly globular grains hence better mechanical properties.

Inclusion removal using ceramic foam filters and filter size estimation

It is well known that inclusion removal processes play a key role in casting quality control and the use of ceramic foam filters has grown substantially over the past few years. In this study specific weight separation and the deep bed mechanism have been studied and are discussed in detail. Mathematical models for pressure head drop and filter sizing have been established and tested experimentally. The effective combination of these models with the design of the gating system provides the basic idea for optimization of the inclusion removal process during casting.

Microstructure and Properties of Cast Iron with Semi-Solid Process Using Cooling Plate Technique

Semi-solid metal processing with the cooling plate technique is one of the key technologies for producing advanced materials. The multitude of cast iron families with their wide range of mechanical properties, and relatively low costs combined with the advantage of semi-solid processing allow production of high quality cast components from cast iron. The effect of semi-solid processing using the cooling plate technique on the microstructure and the properties of cast iron is studied. The investigated material is hypo-eutectic, hyper-eutectic gray iron, compacted graphite and ductile cast iron. The results indicated that the microstructure (primary austenite and graphite) becomes finer and more globular by increasing the fraction of solid. The tensile strength of semi-solid processed cast iron is relatively high compared with ordinary cast iron. The values of both the tensile strength and the elongation depend on the fraction of solid. The total fracture strength is observed to depend on the graphite morphology as well as the matrix contribution that mainly depends on fraction of solid. The wear resistance and damping capacity of cast iron were investigated as a function of the relative amount of primary fraction of solid.

Effect of flow behaviour on the removal of inclusions by filter

Filtration offers foundries a means of cost-effective production of high-grade castings, and so the use of ceramic foam filters has grown rapidly over the past few years. In this paper the removal of inclusions by a foam filter is investigated using casting experiments and numerical flow analysis. Three different patterns for setting the ceramic foam filter in the gating system are studied focusing on removal of inclusions from iron castings. The results of the flow analysis correspond well with the experimental results for the ductile iron castings.