Hiroyuki Ike

Composite reinforcement of the surface of cast iron by WC powder inserts

Inserts represent a convenient means of improving the properties of cast materials by the use of other materials, such as steel, iron, and ceramics. These reinforcement materials are generally used in the form of blocks or plates. The use of hard powders as reinforcement materials for inserts is also the topic of much research. The purpose of the present research is to investigate the reinforcement of gray cast iron locally by inserting tungsten carbide (WC) powders. Three WC powders were used for the inserts, having average grain diameters of 1 μm, 6 μm and 60 μm, respectively. The experiment on the inserts was carried out by firstly inserting WC powders only and then by mixing some alloy powders into the WC powders separately, such as electrolytic chromium, Fe-Mo alloy, and Fe-P alloy. The mold for the insert, which makes five cylindrical specimens, is made by the carbon dioxide process, and each of the specimens measures 30 mm diameter by 50 mm long. WC powders were mixed with a sodium silicate of 0.7 mass% as a binder and then filled into a bottom-mold about 5 mm thick. Gray cast iron (FC150) was used as a parent material for the insert. It was melted with a high frequency induction furnace and poured into the mold at 1623 K. The results confirmed that an approximately uniform inserted layer formed at the bottom of specimens regardless of the particle size of the WC. In the inserted layer, the dispersion form of the WC particles depended on particle size. Here, the matrix structure of the inserted layer remains the same as gray cast iron when only WC powders were inserted. In contrast, when adding chromium powders or Fe-Mo alloy powders to the WC powders, the matrix structure transformed to white cast iron. The hardness of the gray cast iron increases from about 200HV0.3 to about 400HV0.3 with the insert. When adding further alloying elements, the hardness increased further than when inserting WC powders only. Specifically, addition of chromium into WC powders under 6 μm in size increased the hardness to 700HV0.3 or above.

Bending Strength of Cast Materials Reinforced with Hard Particles

Particle reinforcement via the insertion of hard particles is a promising process in materials reinforcing. Particle-reinforced spheroidal graphite martensitic cast iron (SGMC), in which mixed particles of cermet and cemented carbide are dispersed, was achieved by an insertion process. A four-point bending strength test was applied to evaluate the particle composite material. An evaporative pattern process was used on the bending-test specimen to form a composite layer in the central part. Using a combination of three sizes of cermet particles and two sizes of cemented-carbide particles, the bending strength was found to increase with each small-particle combination. The Weibull coefficient m of the four-point bending strength of the particle-reinforced composite material (PRCM) ranged from 4 to 13, and m was large in the specimen with large bending strength.