On Estimation of Creep Constitutive Equation for Welded Joint by High-Temperature Indentation Creep Testing Method

Abstract

The stress and strain fields formed in the heat-affected zone (HAZ) of the weldment involved in pipes in thermal power plant have recently attracted attention as key plant management issue. The microstructure in the HAZ changes locally as a result of the thermal history imposed by the welding procedure. Hence, these changes manifest in time-dependent deformation, unlike those of the base material. In this study, the creep parameter involved in the constitutive equations of Norton’s law was identified for the base metal, HAZ, and weld metal in the weldment of a high-Cr ferritic heat-resistance steel by conducting a high temperature indentation creep test, which is useful for the in-situ identification of the creep parameter of aged components on site. The steel, which was treated here, is known to be a candidate material for the steam generating tube of the supercritical boiler. Finite element (FE) analysis was used to analyze some important engineering problems, such as the welded plate and tube subjected to creep loading by using the estimated creep parameter. As a result, the FE analysis results from the welded plate revealed that the creep strain localized at the HAZ relaxed as the angle between the weld line and loading direction increased, which indicated that the groove shape of the weld part should be sharp. From the results of the welded tube, the maximum stress component is occurred at the interface between base metal and HAZ and hydrostatic stress is also occurred at the interface in the HAZ at a deep position far from the surface of the pipe, which means that the creep void initiates in the HAZ and then grows near the interface between HAZ and base metal.