Influence of Solution Annealing Temperature on the Microstructure, Mechanical Properties, and Corrosion Resistance of a Lean Duplex Stainless Steel Fe-0.02C-20Cr-6Mn-1Ni-0.2N-0.35Si

The influence of solution annealing temperature on the microstructure, mechanical properties and corrosion resistance of a lean duplex stainless steel Fe-0.02C-20Cr-6Mn-1Ni-0.2N-0.35Si is investigated. It is found that the austenite content first increased and then decreased with the increasing solution annealing temperature. Moreover, the alloying elements distribution changed due to the increase in solution annealing temperature, which resulted in a change of the austenite deformation mechanism. The austenite deformation was mainly controlled by the transformation-induced plasticity (TRIP) at the solution annealing temperatures of 900-1100 °C. In this range, due to the low stability of the austenite, it is easier to transform to martensite, resulting in higher tensile strength and yield strength. When the solution annealing temperature was in the range of 1150-1200 °C, the deformation of austenite was mainly controlled by the twinning-induced plasticity (TWIP). Under these conditions, austenite stability was increased and martensite transformation was limited, resulting in a decrease in yield strength and tensile strength. Due to the TRIP/TWIP effect, the elongation of the steel was over 65%. Compared with TRIP, TWIP had a better effect on improving plasticity, but the strain hardening ability was lower, so the elongation reached 72.2% at a solution annealing temperature of 1150 °C. In the ferrite, the dislocation slip was the main deformation mechanism. With the increase of the solution annealing temperature, the distribution of alloying elements in the two phases was more and more balanced, the proportion of the two phases was close to 1:1 and the corrosion resistance was gradually improved. The corrosion performance was best at a solution annealing temperature of 1150 °C. In addition, the ferrite was preferentially corroded, which was related to the relatively low PREN value of ferrite and the high solubility of N in the austenite.