Effects of hot-working parameters on microstructural evolution of high nitrogen austenitic stainless steel

The microstructural evolution of high nitrogen austenitic stainless steel under various deformation conditions was characterized by isothermal compression test. Special attention was paid to the variation of microhardness and its relationship with grain size was also derived. Results indicated that two kinds of strengthening mechanism acted during the whole temperature range. When the temperature is between 950 °C and 1150 °C, grain refinement plays a dominant role. But at temperatures lower than 900 °C, no recrystallization occurs and substructure (dislocations and twins) contributes massively to the strength. Furthermore, it was found that the peak precipitation of grain boundary carbides which are seriously detrimental to toughness appeared at 850 °C. Therefore, an optimizing processing route could be recommended to achieve a good combination of high strength and good toughness. Firstly, the hot-rolling at 950–1100 °C should have large stain to gain refined grains, and accelerated cooling is applied from 950 to 750 °C in order to avoid carbide precipitation along grain boundary. Lastly, at temperatures lower than 750 °C warm-rolling with medium stain can get substructure strengthening effects.

► The microhardness of high nitrogen steel increases with decreasing deformation temperature and increasing strain. ► At higher temperatures refinement of recrystallized grains leads to increased microhardness. ► Peak precipitation of M23C6 harmful to the toughness occurs at 850 °C. ► Substructure, i.e. dislocation and twins is the main reason for high microhardness when deformed lower than 850 °C. ► And the deformation in the no -recrystallization region can contribute greatly to the strength.