Influence of Hydrogen on the Graphitization of the Pearite-Cementite in Gray Cast Iron

Abstract

It is generally recognized that the abnormal expansion at Ar₁ transformation of gray cast iron is due to the graphitization of the pearite-cementite. In the following experiments, the present authors tried to confirm quantitatively the effect of hydrogen to retard the graphitizaton of the pearite-cementite in cast iron by using the above-mentioned fact.
Gray cast iron specimens, 8 mm in diameter, and 80 mm in length, were prepared from the gray cast iron castings of the size, 30 mm×30 mm×130 mm, which were made by casting the melt with varied perecnt of silicon in green sand mould. In order to measure the expansion at their Ar₁ transformation, the dilatometric experiments were carried out. Soon after they were heated in air and in hydrogen, respectively, up to the temperature 50° above their Ac₁ point, they were cooled. The heating and cooling rate were 10°/min, and the rate of flow of the purified hydrogen in the dilatometer was 50 cc per minute. The microstracture of the specimens was also studied.
At the present stage of experiment, the effect of hydrogen to retard the graphitization of the pearite-cementite was found to be very strong and almost corresponded indegree to the effect of 2.5∼3.0 pct. silicon in favour of the graphitization in question. It was also found that A₁ transformation temperature of the specimens was almost independent of the atmospheres in which they were heated.