Study on fracture properties of duplex stainless steel and its weld based on micromechanical models

Abstract

The application of stainless steel in structures is increasing recently, but few related seismic studies have been conducted. The purpose of this paper is to study the ductile fracture behavior, especially under Ultra-low-cycle fatigue (ULCF) of duplex stainless steel and its weld based on micromechanical fracture models. A total of 148 specimens covering multiple geometries were manufactured from duplex stainless steel base metal, heat-affected zone, and weld metal. To investigate the mechanical properties of these materials and calibrate the parameters of constitutive models, monotonic and cyclic tests of smooth round bars were conducted. Moreover, monotonic and cyclic tests of notched round bars were performed, followed by the finite element method analyses to calibrate the fracture models including void growth model (VGM), the stress modified critical strain (SMCS) model, and the cyclic void growth model (CVGM). VGM and SMCS were verified to be effective for these materials to predict ductile fracture under monotonic loading, but CVGM cannot calculate the accurate damage under different cyclic test conditions. Then the CVGM was modified by a novel damage variable. Desirable fitting results were obtained by adopting this damage variable. While duplex stainless steel base metal exhibits excellent ductility, that of the welds is much lower with large dispersion. The reason for the low toughness of welds was found to be related to the unbalanced microstructure formed in welding. The study contributes to developing fracture prediction models of duplex stainless steel, and benefits the research on the seismic behavior of duplex stainless steel structures.