Effects Of Solution Temperature And Alloy Composition On The Duplex Stainless Steel Corrosion Resistance

In this paper,the effect of main factors(content of alloy composition,solution temperature) on pitting corrosion and crevice corrosion performance was studied. The orthogonal experimental design with four factors and three levels were carried out and optimised designation of composition and of solution treatment were gained based on the criterion of pitting corrosion and crevice corrosion performance.The addition elements are Cr,Ni,Mn,Mo,Cu,N,Si and so on.Of which,Ni, Mn,N elements play an important role to stabilize and expand the austenite phase region,at the same time,Mo,Cr elements and so on may form a stable ferrite phase.Since the ratio of alloying elements are controlled appropriately,the steel microstructure and phase composition are ensured uniform and balanced.The steel at room temperature are composited of austenitic,ferritic,mesophase,as well as the metal inclusions.Pitting corrosion is a form of localized corrosion which is caused by a very small positive battery cathode and the anode area is high concentrated,and the appearance is concealed and devastating.The pitting corrosion results show that the steel of 25Cr-8Ni-3Mo-4Cu-N has small weight loss rate which is 2.0g/(m~2·h),but the steel of 25Cr7Ni5Mo2Cu-N and 25Cr-7Ni4-Mo-4Cu-N have high weight loss rate which are 15.7 g/(m~2·h)和12.7g/(m~2·h).At the same time,the steel surface of 25Cr-6Ni-3Mo-2Cu-N and 25Cr-8Ni-3Mo-4Cu-N have not obviously corroded.But different types of corrosion pits respectively appear on the steel surface of 25-Cr-7Ni-3Mo-3Cu-N,25Cr-7Ni-4Mo-4Cu-N and 25Cr-7Ni-5Mo-2Cu-N.These pits size are from several microns to tens of microns.The steel of 25Cr-8Ni-4Mo2Cu-N,25Cr-8Ni-5Mo-3Cu-N and 25Cr-6Ni-5Mo-4Cu-N have corrosion products covered in pit.The steel of 25Cr-6Ni-4Mo-3Cu-N has cracking surface and its grain boundary are looming.Pitting potential is an important parameters to determine the pitting resistance performance of metal.Different composition of alloying elements and different solution temperature may lead to different pitting potential of metallic materials. The electrochemical test results show that the steel of 25Cr-8Ni-3Mo-4Cu-N and 25Cr-8Ni-4Mo-2Cu-N have high pitting potential and low pitting current,and it proved that they have better pitting resistance performance.In contrast,the steel of 25Cr-7Ni-5Mo-2Cu-N and 25Cr-7Ni-5Mo-2Cu-N have low pitting potential and high pitting current,and it prove that they have poor pitting resistance performance.The crevice corrosion results shows that the steel of 25Cr-7Ni-3Mo-3Cu-N,25Cr-8Ni-3Mo-4Cu-N and 25Cr-8Ni-5Mo-3Cu-N has small weight loss rate which is 0.1g/(m~2·h),0.1 g/(m~2·h) and 0.27 g/(m~2·h),but the steel of 25Cr7Ni-4Mo-4Cu-N and 25Cr-6Ni4-Mo-3Cu-N have high weight loss rate which are 5.87 g/(m~2·h)和3.46 g/(m~2·h).At the same time,the steel surface of 25Cr-7Ni-3Mo-3Cu-N,25Cr-8Ni-3Mo-4Cu-N,25Cr-8Ni-5Mo-3Cu-N and 25Cr-7Ni-5Mo-2Cu-N have not obviously corroded.But the steel of 25-Cr-6Ni-3Mo-2Cu-N cockle slightly.The steel of 25Cr-8Ni-4Mo2Cu-N has corrosion pits on its surface,and the steel of 25Cr-6Ni-4Mo-3Cu-N has corrosion products covered in pit.The steel surface of 25Cr-7Ni-4Mo-4Cu-N and 25Cr-6Ni-5Mo-4Cu-N have a large area exposed,their corrosion are serious and irregular.