Effect of cold rolling and annealing on microstructure and properties of a new resource-saving duplex stainless steel Fe-19Cr-0.6Al-12Mn

An Fe-19Cr-0.6Al-12Mn duplex stainless steel with an optimized alloy composition of Ni replaced by Mn and Cr partially replaced by Al was developed to avoid the edge cracking, which is a common defect in the hot rolling of traditional two-phase stainless steels. The newly developed duplex stainless steel could be hot-rolled in the single-phase ferrite (alpha) region by controlling rolling temperature and the single-phase ferrite microstructure was retained on water cooling. To obtain the two-phase stainless steel product with ferrite and austenite (gamma) microstructure, cold rolling and annealing were carried out, and appropriate cold rolling reduction and annealing process parameters were determined. The significant impact of annealing on microstructure, mechanical properties and pitting resistance of the experimental steel was studied. It was observed that with the increase in cold rolling reduction, the number of gamma nucleation points was dramatically increased leading to the precipitation of more gamma at alpha grain boundaries after annealing. During annealing at 800 degrees C and with the increase in annealing time, the austenite fraction was increased with a lower rate and remained almost constant when the annealing time was greater than 4 h. With the increase in annealing temperature, the austenite fraction decreased gradually in the temperature range of 750-860 degrees C. Good combination of strength, ductility and excellent pitting resistance was obtained by cold rolling to 80% reduction and annealing at 800 degrees C for 4 h. Grain refinement and the existence of sigma 3 boundaries played a vital role in improving the pitting resistance of the experimental steel. With good combination of strength, ductility and corrosion resistance, the newly developed duplex stainless steel is expected to be a new resource-saving dual-phase stainless steel.