Effect of short duration solution treatment at temperatures below 1000 °C on σ‐phase precipitation in a super duplex stainless steel alloy

Abstract

AbstractSuper duplex stainless steel alloys are characterized by a high content of chromium, nickel, molybdenum and nitrogen. In these steels, the main role of chromium, nickel and molybdenum alloying elements is to increase corrosion resistance. Increased mechanical properties are obtained by adding nitrogen, which promotes structural hardening. The microstructure of super duplex stainless steels consists of a mixture of ferrite and austenite phases, while other phases are also formed, such as: sigma, chi, chromium nitride, carbides and secondary austenite. All secondary phases are considered deleterious phases due to their negative effect on corrosion resistance and mechanical properties. The precipitation formation mechanism of the sigma phase assumes depletion of chromium and molybdenum from the matrix, worsening the alloy properties. The aim of the present work is to show the microstructural changes occurring during a short duration (10 minutes) solution treating of an UNS S32760/1.4501/F55 alloy, three temperatures being considered: 800 °C, 900 °C and 1000 °C. Scanning electron microscopy (energy dispersive spectroscopy and electron backscattered diffraction) was used for quantifying the alloying elements distribution, to distinguish between the observed phases, and to better understand the evolution of each phase.