Effect of cold rolling reduction on the precipitation behavior of σ phase in 2906 duplex stainless steel

Abstract

The effect of cold rolling reduction on the precipitation of σ phase at 800 °C in the 2906 DSS was investigated. The results show that the precipitation rate of the σ phase is improved with the increase of rolling reduction, and the maximum volume fraction is limited to 15%–20% due to the exhaust of ferrite. Improving the rolling reduction could promote the diffusion of Cr, Ni, Mo departing from ferrite and Ni, Mo departing from austenite during the following aging process. The contents of Cr, Ni and Mo increased suddenly and then keep stable in the σ phase, which preferentially nucleated around the narrow ferrite regions. The increase of cold rolling reduction is favorable for σ phase precipitation due to the promoted diffusion of Cr, Ni and Mo elements, as well as the decrease in thickness of ferrite/austenite lamellar interface. The σ phase/austenite interface is incoherent without orientation relationship between the σ phase and austenite, the orientation relationship between ferrite and austenite illustrates (02-2)γ//(-13-2)α and (33-1)γ//(-33-2)α, and the σ phase becomes coarsen and continuous along the ferrite/austenite interface.

Keywords

• Duplex stainless steel
• σ phase
• Precipitation behavior
• In-situ TEM