The dynamic strain aging behavior during tensile tests of Inconel 690 alloy has been investigated in temperature ranged 25-700℃ under strain rate ranged $10^{-5}-10^{-3}s^{-1}$. Characteristic serrations in stress-strain curves were observed in temperature between 200 and 600℃, and negative strain rate sensitivities were observed in temperature between 300 and 500℃. Four different types of serrations, identified as A1, A2, B, C type serrations, were observed depending on the temperature, strain rate and strain. A1 type serration, a periodic rise and drop of stress with small amplitude, was observed in temperature ranged 200-245℃. A2 type serration, a rise of stress followed by a drop of stress, was observed at higher temperature ranged 245-400℃. B type serration, a successive oscillation of stress, was observed in temperature ranged 245-500℃. C type serration, characterized as abrupt irregular stress drops, was observed at 600℃. The strain exponent and activation energy were calculated for A1, A2 and B type serration from measurement of the critical strains for the onset of serrations. The critical strain $ε_c$ and its dependence on strain rate ε and temperature Τ can be analysed by Van den Beukel's equation, $ε_c^{m+β}$ = Kεexp(Q/RT), where K is constant, m and β are the exponents related with the strain dependence of vacancy concentration ($C_v$ ∝ $ε^m$) and the strain dependence of mobile dislocation density ($ρ_m$ ∝ $ε^β$), Q is the activation energy for the onset of serration. The sum of strain exponents, m+β, in the critical strain-strain rate relation was calculated as 2.47, 1.06 and 1.01 for A1, A2 and B type serration, respectively. Therefore, it was analysed that A1 type serration was controlled by substitutional atoms and A2, B serrations were controlled by interstitial atoms. The activation energies for the onset of serration were calculated as 122, 72 and 132kJ/mol for A1, A2 and B type serration, respectively, from the analysis of the critical strains for the onset of serrations. The rate controlling mechanism for dynamic strain aging is suggested as the migration of substitutional atoms for A1 type serration, the carbon diffusion through dislocation core for A2 type serration and the carbon diffusion through lattice for B type serration.
