High Temperature, Low Cycle Fatigue Characterisation of P91 Weld and Heat Affected Zone Material

Abstract

The high temperature low cycle fatigue behaviour of P91 weld metal (WM) and weld joints (cross-weld) is presented. Strain-controlled tests have been carried out at 400 °C and 500 °C. The cyclic behaviour of the weld material (WM) and cross-weld (CW) specimens are compared with previously published base material (BM) tests. The weld material is shown to give a significantly harder and stiffer stress-strain response than both the base material and the cross-weld material. The cross-weld tests exhibited a cyclic stress-strain response which was similar to that of the base material. All specimen types exhibited cyclic softening but the rate of softening exhibited by the CW specimens was lower than that of the base and all-weld tests. Finite element models of the base metal, weld metal and CW test specimens are developed and employed for identification of the cyclic viscoplasticity material parameters. HAZ cracking was the primary mode of failure for the cross-weld tests.