Analyses of Transient and Tertiary Small Punch Creep Deformation of 316LN Stainless Steel

Abstract

Creep deformation behavior of 316LN stainless steel (SS) under small punch creep (SPC) and uniaxial creep test has been assessed and compared at 923 K (650 °C). The transient and tertiary creep deformation behaviors have been analyzed according to the equation proposed for SPC deflection, \( \delta = \delta_{0} + \delta_{\text{T}} \cdot (1 - {\text{e}}^{ - \kappa \cdot t} ) + \dot{\delta }_{\text{s}} t + \delta_{3} {\text{e}}^{{\left[ {\varphi \left( {t - t_{\text{r}} } \right)} \right]}} \) on the basis of Dobes and Cadek equation for uniaxial creep strain. Trends in the variations of (i) rate of exhaustion of transient creep (κ) with steady-state deflection rate (\( \dot{\delta }_{\text{s}} \)) (ii) ‘κ’ with time to attain steady-state deflection rate, and (iii) initial creep deflection rate with steady-state deflection rate implied that transient SPC deformation obeyed first-order reaction rate theory. The rate of exhaustion of transient creep (r′) values that were determined from uniaxial creep tests were correlated with those obtained from SPC tests. Master curves representing transient creep deformation in both SPC and uniaxial creep tests have been derived and their near coincidence brings unique equivalence between both the test techniques. The relationships between (i) rate of acceleration of tertiary creep (φ) and steady-state deflection rate, (ii) ‘φ’ and time spent in tertiary stage, and (iii) final creep deflection rate and steady-state deflection rate revealed that first-order reaction rate theory governed SPC deformation throughout the tertiary region also. Interrelationship between the transient, secondary, and tertiary creep parameters indicated that the same mechanism prevailed throughout the SPC deformation.