Comparison of Results of Accelerated and Conventional Creep Tests of Dissimilar Weld Joint of Steels FB2 and F

Abstract

The recently developed simulative accelerated creep testing (ACT) on a Gleeble thermal mechanical simulator allows the microstructural transformation of creep-resisting materials in a relatively short time (less than 100 hours) to a state resembling that of multiyear application under creep conditions. This contribution deals with the comparison of long-term conventional creep testing (CCT) with ACT on a dissimilar weld joint prepared from steels COST FB2 (X13CrMoCoVNbN 9-1-1) and COST F (X14CrMoVNbN 10-1). Creep tests to rupture were carried out at temperatures from 550 °C to 650 °C in a stress range from 70 MPa to 220 MPa. Creep rupture strength was evaluated using the Larson-Miller parameter. Evolution of the microstructure, changes of precipitates and dislocation of the substructure in different zones of the weld joint (Fig. 1) were correlated with the position of fracture and the creep strength. The fine grained part of the heat affected zone of steel COST F was found to be a critical zone of creep damage. ACT of samples machined from various positions in the weldment was performed at 600°C under 100 MPa. Changes in the hardness and the microstructures of the samples, which underwent both types of creep tests, were compared. The results of both creep testing methods are compared from a point of view of the potential for utilization of ACT in industry. It seems that microstructural processes taking place during creep exposures are accelerated by ACT, however, further experiments have to be performed to improve the accuracy of fracture prediction and verification if long-term CCT is to be replaced by ACT.