Critical Assessment of Short-Term Stress-Relaxation Studies for the Prediction of Creep Properties of P91 Steel

Technical Paper


An attempt has been made to interrelate the predicted creep-rupture properties using stress relaxation tests (SRT) with those obtained from uniaxial monotonic creep tests in P91 steel. Stress-relaxation tests were performed at specified total strain levels of 1.3 and 2.5% for fixed duration of 24 h at 873 K. The results from SRT have been used to predict the rupture life using Monkman–Grant relation and Gill–Goldhoff correlation for the steel. Further, the observed stress-relaxation behaviour has been described appropriately using an analytical model with suitable parameter values related to activation volume and activation energy.


Stress relaxation Monkman–Grant relation Gill–Goldhoff correlation Activation volume Activation energy 

List of symbols


Elastic strain


Inelastic strain


Total strain

\(\dot{\varepsilon }\)

Minimum or steady state creep rate


Applied stress


Internal stress


Initial stress


Threshold stress


Transition stress


Constant in power law equation


Power law stress exponent


Test temperature


Time to rupture


Activation energy for creep deformation under a stress-free state


Monkman–Grant constant


Slope of Monkman–Grant relation


Rupture stress


Creep stress


Temperature dependent constant


Boltzmann constant


Ratio of threshold stress and transition stress

s and υ

Parameters associated with Dimelfi equation


Larsen–Miller parameter constant


Strain rate constant


Effective modulus of the specimen and the machine system


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Copyright information

© The Indian Institute of Metals - IIM 2017

Authors and Affiliations

  1. 1.Deformation and Damage Modeling Section, Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic ResearchHBNIKalpakkamIndia

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