Aging Precipitation Behavior And Its Effect On Properties Of TRIP Cr19 Duplex Stainless Steel

At present,the third generation of energy-saving duplex stainless steel has replaced most of the traditional austenitic stainless steel due to its superior performance and low cost,and is widely used in many fields such as petrochemical,construction,automobile,navigation and rail transportation.In addition,Mn-N instead of Ni can make steel undergo phase transformation induced plasticity（TRIP effect）in the tensile process,which further improves the strength and elongation.However,if the heat treatment process is improper or such steel is prone to failure under high temperature conditions,causing major accidents.Therefore,it is of great significance to study the microscopic mechanism of such steel during aging treatment and its influence on mechanical properties and corrosion resistance for practical engineering applications.In this paper,a kind of energy-saving duplex stainless steel with TRIP effect was taken as the research object to study the phase precipitation behavior at different aging temperatures,and the influence of precipitation on TRIP effect,mechanical properties and corrosion resistance was discussed.The main results are as follows:（1）The experimental steel was aged at 700,800 and 900°C for 10min,30min,1h,3h,5h,7h and 12h,respectively.The morphology,type and content of precipitates after aging were analyzed by OM,SEM,EDS and XRD.The precipitation kinetics at different aging temperatures was established based on the Avrami model.The results showed that the precipitated phases after aging at 700,800 and 900°C were Cr₂₃C₆,Cr₂N and Cr₂N,respectively.The content continued to increase with aging,and reached saturation at 7h,30min and 1h,respectively.（2）Through the tensile and microhardness tests on the aged specimens,the effects of precipitation on the mechanical properties,TRIP effect and hardness were summarized by SEM,XRD and EBSD,and the martensitic transformation kinetics under various conditions was established.The results show that martensite transformation follows two mechanisms:γ→α’andγ→ε→α’.The precipitation of Cr₂₃C₆and Cr₂N enhances the phase transformation by hindering dislocation slip and reducing austenite stability.The combined effect of Cr₂₃C₆and Cr₂N makes the elongation decrease obviously,which has little effect on the hardness of austenite phase,but makes the hardness of ferrite phase decrease slightly.（3）The corrosion resistance of the specimens after aging treatment was analyzed by weight loss method,surface observation method and electrochemical method.The results show that the precipitation of Cr₂₃C₆or Cr₂N leads to the appearance of Cr-poor zone,which is easy to cause pitting after Cl^-corrosion and reduces the overall pitting resistance.