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

Technical Paper

Abstract

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.

Keywords

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

List of symbols

ɛe

Elastic strain

ɛi

Inelastic strain

ɛt

Total strain

\(\dot{\varepsilon }\)

Minimum or steady state creep rate

σ

Applied stress

σi

Internal stress

σ0

Initial stress

σH

Threshold stress

σT

Transition stress

A

Constant in power law equation

n

Power law stress exponent

T

Test temperature

tr

Time to rupture

ΔG0

Activation energy for creep deformation under a stress-free state

C

Monkman–Grant constant

α

Slope of Monkman–Grant relation

σr

Rupture stress

σc

Creep stress

Ω

Temperature dependent constant

k

Boltzmann constant

K

Ratio of threshold stress and transition stress

s and υ

Parameters associated with Dimelfi equation

C1

Larsen–Miller parameter constant

D′

Strain rate constant

M

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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