Constitutive modelling of stress-relaxation behaviour of tempered martensitic P91 steel using sine hyperbolic rate law

• Published in: Materials chemistry and physics 2018-02, Vol.205, p.442-451
• Main Authors: Christopher, J., Choudhary, B.K.
• Format: Article
• Language: English
• Subjects: Activation; Activation volume; Evolution; Internal stress; Martensitic stainless steels; Mathematical models; P91 steel; Relaxation stress; Residual stress; Steel; Strain; Strain rate; Stress relaxation; Trigonometric functions
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2017.11.053

A constitutive model describing stress-relaxation behaviour of P91 steel at 873 K has been presented. In the model, the equations defining the evolution of internal stress and relaxation stress with time have been coupled with the sine hyperbolic rate law to predict the relaxation stress as a function of hold time as well as the stress dependence of inelastic strain rate. The evolution of internal stress with time has been derived from the power law dependence of internal stress on relaxation stress. The predicted evolution of internal and effective stresses with time exhibited an initial rapid decrease followed by stress plateaus at longer durations. The applicability of the model has been demonstrated for two different strain holds of 1.3 and 2.5% in P91 steel. It has been shown that the present model can be used to predict the evolution of inter-barrier spacing and activation volume with time for both the strain holds at 873 K. Further, the observed increase in activation volume and inter-barrier spacing with hold time in P91 steel has been presented. •A constitutive model has been developed to describe stress-relaxation behaviour.•Interrelationship between internal stress and relaxation stress has been derived.•Model accurately described the relaxation stress vs. hold time data of P91 steel at 873 K.•Model can predict the variations in activation volume and inter-barrier spacing with hold time.