Nitrogen Trapping to Chromium in α Iron Studied by Internal Friction and Magnetic After-effect Techniques

摘要

The effect of chromium on the behaviour of nitrogen in α iron has been studied by anelastic and magnetic relaxation measurements on dilute Fe-Cr-N alloys. The presence of chromium is known to give rise to an additional contribution to the Snoek relaxation at a higher temperature than the ordinary Snoek peak. When specimens quenched from a solution-treatment temperature are subjected to isothermal ageing at room temperature, the high temperature component develops while the ordinary component decays. This observation can be explained in terms of redistribution of nitrogen atoms: almost random distribution established at the solution-treatment temperature changes into a metastable distribution, in which a substantial number of nitrogen atoms are bound to chromium atoms. The binding energy of a Cr-N pair has been estimated independently from two experiments: 20 ± 2kJ/mol from the kinetics of the redistribution and 15kJ/mol from the characteristics of the Snoek relaxation profile, which are in reasonable agreement with each other.