Effect of Hydrogen on Blowhole Formation in Pure Iron during Solidification

Abstract

The blowhole formation of the Fe-H system during solidification was investigated.
Pure iron was melted in various hydrogen partial pressures and temperatures by means of the levitation method, and cast into a water-cooled copper mold after equilibrated with the atmosphere. The blowholes in specimens were detected by means of specific gravity, radiograph and cross section methods.
The results were as follows:
The blowhole formation was influenced remarkably by hydrogen partial pressure and melt temperature. The results can be reduced to the simple relation between hydrogen concentration and blowhole formation in specimens. That is, the critical hydrogen concentration for the blowhole formation in specimens was found to be about 13cc/100gFe.
In order that a bubble is present stably in molten iron, the hydrogen concentration in molten iron must be at least 25.2cc/100gFe which is the equilibrium value at P_H2=1atm. The above critical hydrogen concentration is lower than this value 25.2 cc/100gFe.
When the increase of hydrogen concentration in front of a solidification interface is considered, the maximum hydrogen concentration can exceed the value 25.2cc/100gFe. The effective distribution coefficient under these experimental conditions was estimated to be higher than the equilibrium one.