Corrosion Behaviors Of Super Austenite Stainless Steel AL-6XN In Simulated Seawater

The so called“small reactor”is a kind of small size,cost-effective,safe and new reactor,which is considered as the new direction of the future nuclear power development.The national development and reform commission has put the development of offshore floating reactors into the13^th Five Year Plan.Super austenitic stainless steel AL-6XN has perform corrosion resistance in sea water during the last years,which means that AL-6XN has the protential of acting as structure material in offshore floating reactors.In this paper,the author has taken use of electrochemical method,DCPD method and slow strain rate tensile test in the study of electrochemical resistance,corrosion fatigue resistance and SCC resistance of AL-6XN in simulated sea water,thus to give a comprehensive evaluation of the corrosion resistance of AL-6XN in sea water.In terms of electrochemical corrosion performance,Tafel curve,linear polarization,cyclic polarization,Eis impedance test and Mott-schottky curve were adopted on AL-6XN with different cold-worked degree in simulatied sea water of different temperature.The study found that when the temperature of sea water increased,the corrosion potential of AL-6XN droped,the corrosion current density increased,the linear polarization resistance decreased,the density of current carrier on the passive film increased.The influence of cold work on corrosion performance of AL-6XN was related to temperature.In high temperature which means80?,the corrosion current density decreased,the linear polarization resistance increased and the corrosion potential droped after cold-worked.It's double passivation layer in surface of cold-worked AL-6XN in 80?sea water,while single-layer structure was found in the surface of AL-6XN base metal.In 80?sea water,cold work leaded to a decrease of the density of current carrier on the passive film.All the corrosion potential tested in various temperatures of AL-6XN with different cold-worked degrees was higher than that of nuclear grade 304ss in the same environment.In terms of corrosion fatigue performance,DCPD method was adopted to study the effects of environment,material state and loading parameters on corrosion fatigue crack growth rate of AL-6XN in simulated sea water.The study found that corrosion accelerated the corrosion fatigue CGR of AL-6XN remarkably and the accelerating effect got more obvious with the increase of load ratio.The change of temperature in the range of 30?to80?had little impact on CGR.The cold-worked AL-6XN cracked faster in comparision with the base metal while all AL-6XN specimen with different cold-worked degrees cracked slower than the nuclear grade 304ss,which means AL-6XN has better corrosion fatigue resistance than 304ss.When K_max was constant,the CGR grew faster not only with the decrease of load ratio but also with the decrease of frequency,which means the corrosion effect get stronger when the fatigue gets lower.The corrosion fatigue crack growth threshold?K_th of AL-6XN base metal in simulated sea water in 80?was 3.96 MPa·m^0.5,which was in good agreement with Priddle model.It's transgranular cracking of AL-6XN fatigue crack and the cold-worked specimen had finer main crack with more secondary cracks.In terms of SCC performance,slow strain rate tensile?SSRT?tests were applied in this work both in simulated sea water and in argon atmosphere.The study found that the tensile strength and elongation decreased in simulated sea water compared with that in argon atmosphere while the yield strength kept stable.The SCC sensitivity of AL-6XN in sea water was relatively low which was 4.54%and 6.82%in 30?and 80?respectively.The slower rate of strain,stress corrosion cracking effect more significantly;Cold work can raise the stress corrosion cracking sensitivity of AL-6XN,and also induse a significant decrease in the plasticity.The results in this paper can provide theoretical basis and data support in evaluating the possibility of AL-6XN as a candidate structure material of offshore floating reactors.In addition,the data about pitting,corrosion fatigue and SCC in this paper could be used in service performance assessment and service life prediction of AL-6XN in seawater environment such as the third loop industrial cooling piping,which is of great significance in industrial applications.