Study On The Erosion Corrosion Resistance Of Hyper Duplex Stainless Steel

As newly developed stainless steels,SAF3207 hyper duplex stainless steels exhibit more excellent corrosion resistance and mechanical property than other stainless steels.They are attractive materials for the application in the field of petroleum chemical industry,bridge construction and deep sea.However,there are limited reports working on the erosion corrosion resisitance of SAF3207 hyper duplex stainless steel.The results in this work are expected to provide reference for these materials for the application in erosion damage conditions.In this work,the effects of velocity,sand content,sulphuric acid concentration and the erosion of time on the slurry erosion corrosion of SAF3207 hyper duplex stainless steel were studied on a home-made erosion tester by means of weight-loss method,electrochemical polarization curves and SEM.And analyzed the failure process,discussed the synergistic mechanism of this material.The results indicate that:In 3.5wt.%NaCl and 5wt.%garnet sand content solution,the self-corrosion potential,the corrosion rate and mass loss rate increased with the increasing of velocity(0-8m/s).And the erosion-corrosion damages of the material increased significantly when the flow velocity exceeded the critical velocity of about 4m/s.In 3.5wt.%NaCl and 6m/s content solution,The mass loss rate rised with the increasing of sand content(0?7wt.%),and it reached its maximum at a sand content of 7wt.%,where the most severe electrochemical corrosion damage ocurred.With more sand content(7-llwt.%),however,the mass loss rate descended and tended to be stable.The corrosion-accelerated erosion was the major contribution of synergy.In 6m/s?3.5wt.%NaCl and 5wt.%garnet sand content solution,with the increasing of sulfuric acid concentration from 0 tolOwt.%,the mass loss rate rised slowly;Then with the increasing of sulfuric acid concentration from 10wt.%to 40wt.%,the mass loss rate rised significantly,and electrochemical corrosion intensified;When the concentration was more than 40wt.%,the concentration change had little effect on Material.The corrosion-accelerated erosion was the major contribution of synergy;H+ was enriched in cracks,then the cracks propagation and connects.Material appeared chunk peelings due to the erosion.In 6m/s?3.5wt.%NaCl and 5wt.%garnet sand content solution,the material corrosion rate increased with the increasing of time(0?6h)and the material mass loss process was divided into incubation,sustained and stationary periods with a maximum mass loss rate of 12.97g·h-1·m-2after eroding for 2.5h.The material mass loss was mostly attributed to the damage of ferrite phrase.The failure modes in the two phases of the material were different in the erosion process:Shallow erosion pits and thin squeeze lips formed in austenite at the beginning.As the erosion corrosion went on,the thin squeeze lips developed into bands with some micro holes and cracks,and finally shear fracture took place along the bands.In ferrite,however,deep pits and thick squeeze lips formed firstly,and then they were deformed into chips by sands with some cracks around,and some of these chips would develop into small holes.With sustained erosion effect,the cracks grew and eventually impel chips to fall off,leaving big holes on the surface.The erosion-accelerated corrosion was the major contribution of synergy in incubation period,and the corrosion-accelerated erosion was the major contribution of synergy in sustained and stationary periods.