Investigation On Corrosion Behavior Of Annealing-treated Economical 19 Cr Duplex Stainless

Economic duplex stainless steel has been widely applied in petrochemical and transportation industries with low cost and good corrosion resistance.The solid solution 19 Cr economic duplex stainless steel after cold rolling has fine structure and good strength-toughness after tempering.In this paper,the corrosion resistance of coldrolled 19 Cr economic duplex stainless steel was evaluated after tempering at 850-1050 °C on strength evaluation.The effects of tempered structure evolution on materials were investigated by using transmission electron microscope(TEM),scanning electron microscope(SEM),differential scanning calorimetry(DSC),Thermo-Calc thermodynamic equilibrium phase diagram calculation,electrochemical experiment.The corrosion resistance and semiconductor characteristics were discussed in 3.5% Na Cl solution.The mainly contents can be concluded as follows:(1)The evolution of the structure after tempering has a significant impact on the pitting corrosion performance of the material.The pitting corrosion resistance of the material will increase,then will decrease with the tempering treatment at 850-1050 °C.The disappearance of the martensite phase in tempering treatment will improves the corrosion resistance.The satellite-shaped pits were produced by the remaining martensite phase which caused with short tempering time in the austenite phase.The coarsening of grains and the imbalance of phase ratio in the structure will lead to the corrosion resistance decreased with the tempering time increased.The pitting corrosion pits of the sample after tempering mostly occur in the ferrite phase or phases boundary.(2)The corrosion rate of the tempered sample was speed up by erosion.The highspeed agitation of erosion will dissolved oxygen to accelerate the material exchange between the cathode and anode.The sand will increase the damage rate of the passive film and accelerate the material corrosion.The coordinated corrosion of erosion behavior increases the proportion of weight loss when the concentration of sand increases.For the tempered at 950 °C for 30 s,the proportion of concentration weight loss increases rapidly from 4.6% to 54.8% when the sand concentration rises from 20%to 30%.The erosion behavior will not affect the corrosion resistance of the material.Although the tempering time of 15 min had the highest weight loss ratio of 55.04%,but which had the lowest weight loss among the three samples.(3)Tempering will affect the corrosion resistance by changing the donor or acceptor density in the passivation film,but without changing the type of semiconductor of the passivation film.The semiconductor characteristics of the passive film grown in the 3.5% Nac Cl solution of duplex stainless steel are mainly controlled by Fe and Cr elements.When the scanning potential is-0.6V-0.3V,the samples are characterized by n-type semiconductors.When the scanning potential is 0.3V-1 V,the samples show p-type semiconductor characteristics.The experimental results show the sample when the film-forming potential of 0.3V-1 V,tempering temperature of 950 °C,holding time of 15 minutes,exhibit the best corrosion resistance.