Mechanical properties of CMT-WAAM 2209 duplex stainless steel at elevated temperatures in a fire

Abstract

To investigate the mechanical properties at elevated temperatures of Cold Metal Transfer-Wire Arc Additive Manufacturing (CMT-WAAM) 2209 duplex stainless steel, 63 tensile specimens were tested under steady-state elevated temperatures simulating conditions in a fire, which were achieved using an electric heating furnace. The tensile specimens were cut from the CMT-WAAM plates using ER2209 duplex stainless steel wire with a diameter of 1 mm. The tests covered three loading directions (0°, 45°, and 90°) and seven different temperature levels (300 °C to 900 °C). Combining Digital Image Correlation (DIC) technology, stress-strain curves at elevated temperatures were captured for all specimens, from which in-fire key mechanical properties were extracted and compared against mechanical properties at ambient temperature. Microstructural analysis was also conducted to investigate the evolution and fracture mechanisms at elevated temperatures. Results demonstrated that increasing temperature significantly enhanced ductility but reduced the strength of the material. The residual mechanical properties at elevated temperatures were analyzed, and existing reduction factors of traditional duplex stainless steels were evaluated based on the test data. It was found that existing prediction expressions were not suitable for CMT-WAAM 2209 duplex stainless steel at elevated temperatures. A new constitutive model was proposed to accurately predict the in-fire stress-strain response of the printed material. The results of this study provide engineers with references for assessing the in-fire residual strength of CMT-WAAM 2209 duplex stainless steel and guide fire-resistant design.