A Study of the Strain Ageing in Fe-C and Fe-N Alloys by Internal Friction

Abstract

We have studied the process of the strain ageing and the reversion of the meta-stable phase precipitated from the super-saturated solid solution by the internal friction method.
The degree of strain ageing was accelerated and the ageing curve shifted to the side of short ageing time by the increase of strain.
From changes of the exponent (n) determined on the basis of the equation, W=1−exp[−(t⁄τ)ⁿ], the process of the strain ageing was able to separate into two stages.
The non-reversional internal friction obtained from the reversion treatment increased with the increase of strain.
The meta-stable phase precipitated in the 2nd stage of strain ageing was completely resolved by an up-quenching treatment.
All changes of the internal friction was separated into two stages by the level of the up-quenched internal friction value. The changes of the internal friction in each stage was normalized, and the ageing exponents (n₁,n₂) and the time constants (τ₁,τ₂) were determined respectively. This technique of the two stage separation of the strain ageing curve based on the reversion treatment seemed to be more reasonable compared to the other conventional methods.
A relationship of ρ\fallingdotseq6.31×10⁸×ε^1.88 was obtained between the quantity of the strain (ε) and the dislocation density (ρ).
The atmosphere density calculated from both the non-reversional internal friction and the dislocation density was about 1∼3 atoms per atom plane threading the edge dislocation line.
The binding energy between the dislocation and the N atom of 0.4 eV was determined from the experiments in the decay of atmosphere.