Long-Term Stress Relaxation Properties of 1Cr-0.5Mo-0.25V Steel

Abstract

In order to clarify the long-term stress relaxation behaviour, the stress relaxation tests up to one year have been carried out on a batch of domestic 1Cr-0.5Mo-0.25V high temperature bolted steel used for a steam turbine at the test temperatures of 450°C, 500°C and 550°C for the total strains of 0.10%, 0.15%, 0.20% and 0.25%.
The influence of the total strain on the residual stress was discussed, and the relationship between creep and stress relaxation was analysed using the creep constitutive equations based on strain hardening, time hardening, exponential and hyperbolic-sine laws.
The results obtained are summarized as follows:
(1) The influence of the total strain on the residual stress tended to decrease with increasing test temperature and test period. Within the range of present test temperatures, there was little influence of the total strain on the residual stress when the total strain was raised over 0.15% and time was prolonged over 1000hrs.
(2) The estimated stress relaxation curves obtained from the creep data at the transient stage by applying the strain hardening theory almost agreed with the observed ones. However, the estimated residual stresses were slightly weaker than the observed ones at every temperature and every value of the total strains.