Effect of volume fraction of phases and precipitates on the mechanical behavior of UNS S31803 duplex stainless steel

Mechanical properties of a grade UNS S31803 duplex stainless steel were studied. Samples were annealed at three different temperatures, 1060 degrees C, 1200 degrees C, and 1300 degrees C, to change the alpha/gamma proportion, to precipitate undesirable phases (for example, alpha', sigma and chromium nitrides), and to study the effect of the microstructure on the mechanical behavior. Specimens with a thickness of 1.8 mm were prepared according to ASTM standards and tested at room temperature. Tensile tests were conducted using displacement control at a rate of 5 mm/min. Force-controlled constant amplitude axial fatigue tests were conducted at a frequency of 30 Hz and an R stress ratio of 0.1. Microstructural analyses, performed by optical microscopy and scanning electron microscopy, showed the following modifications to the microstructure: changes in the phase volume fractions, the phase grain growths, and the morphology of the gamma-phase and the precipitation of chromium nitrides in the alpha-phase. The mechanical properties of the steel were significantly changed due to the changed microstructure. The results demonstrate the sensitivity of the steel to the annealing temperature. (C) 2015 Elsevier Ltd. All rights reserved.