MEASUREMENTS OF NITROGEN SOLUBILITY IN IRON AND IRON-NICKEL ALLOYS, USING A NEW TEMPERATURE-GRADIENT METHOD

Gas solubility measurements in metals are usually done isothermally and separately for the solid and liquid states. The knowledge of gas solubility at phase changes, especially in the melting range, is of interest for foundrymen or welders, as defects (segregation, gas pores, inclusions) may occur due to the change of solubility. Therefore, a method has been developed in which a finely grained sample is exposed to a temperature gradient in a long ceramic tube until equilibrium with the gas phase with regard to local temperature is reached. The chilled sample is subdivided into small samples which can be analysed for gas content. The method is demonstrated for the determination of nitrogen solubility in iron and some iron-nickel alloys, where results for the austenite and δ-ferrite phases are presented.