Abstract
An investigation has been done on the microstructures of white cast iron solidified unidirectionally. The mould was made from exothermic material of tapered thickness to control solidification, the bottom of which was provided with a water-cooled copper chill plate. The solidification velocity in the mould was inversely proportional to the square root of the time elapsed after pouring. The primary dendrite of austenite, the primary plate of cementite and the ledeburite eutectic solidified unidirectionally, while the primary graphite and the austenite-graphite eutectic did not. In pure iron-carbon alloy the ledeburite structure was lamellar, while in the case of cast iron containing chromium it was rod-like. In the latter case, it might be observed to be changeable from rod-like according to the section. As the ledeburite eutectic cells developed from the plate-like cementite crystals, the form of the cells was also flat. The thickness of the cells was in inverse proportion to the square root of the solidification velocity, and the arm space of primary austenite dendrites increased with decreasing of the solidification velocity. In the alloys containing silicon, small flaky graphites were readily separated at the boundaries of the ledeburite eutectic cells by annealing after solidification.
