Abstract: P91 is a new kind of heat-resistant high-tensile steel. It is widely used in kinds of heat-resistant pipes in big thermal power plants, mainly produced by hot plastic deformation unlike common welding steel pipes, and investigations in its high-temperature mechanical properties are very significant. Lots of experiments on the thermo-mechanical simulator Gleeble 1500D are operated, and the true strain-true stress curves under different deforming conditions are obtained. Dynamic recrystallization during deformation is observed as the experimental curves show, and as the deformation temperature rises or the strain rate decreases, dynamic recrystallization happens at an earlier critical strain and drags the flow stress down more notably. By the analysis of the flow stresses in different conditions with Origin 7.0, the relationship among flow stress, temperature and strain rate known as Zener-Hollomon parameter is found, the math model of P91’s flow stresses at high temperature is established.

Key words: Dynamic recrystallization, Flow stress, P91, Zener-Hollomon parameter