Abstract
The effects of mold materials and melt compositions on the hydrogen absorption of melts during mold filling were investigated as related to the pinhole defects of gray cast iron castings. Pinhole defects were observed to occur easily in castings when approximately 0.02mass% aluminum was added to the melt. The number of pinholes in the castings increased with the moisture content in the green sand mold and the contents of sulfur and manganese in the melt. On the other hand, pinholes were reduced by increasing the addition of coal powder to the green sand mold. That is to say, the pinhole defects correlate with the amount of hydrogen absorption of the melt during mold filling. In the present experiment, the contents of the hydrogen absorption of melts at the end of mold filling were in the range of 0.5ppm to 1.5ppm. The amount of hydrogen absorption further increased approximately to a maximum of 3ppm in the 40seconds from the end of mold filling to the start of solidification. Many pinholes occurred under the surfaces of the castings when the total amount of hydrogen in the melt exceeded 5ppm.
