The Research On Solution Treatment And Intergranular Corrosion Resistance Of High-nitrogen Stainless Steel

Nowadays,high nitrogen stainless steel is one of the most ideal materials for corrosion,not only because nitrogen element has low price,but also can replace the most expensive element that nickel,what's more,nitrogen can help to stabilize austenite in steel and improve local corrosion of stainless steel.Solution treatment can make the nitrogen element distribute evenly in stainless steel,thus hinder the occurrence of chromium-depleted zone,and resist the effect of the intergranular corrosion.The high nitrogen austenitic stainless steel was prepared by vacuum induction melting method.The composition,microstructure and structure of the prepared material were examined and tested in 3%Na Cl solution.The polarization curves and impedance spectra in the normal situation and after solid solution treatment were tested.After doing sensitization treatment,we use Electrochemical Potentiokinetic Reactivation and oxalic acid corrosion to test intergranular corrosion resistance of the materials which had finished solution treatment was studied,and use those methods can accurately reflect the effect that the solution treatment on the intergranular corrosion resistance of high nitrogen steel.Under normal conditions,increasing the solution temperature reduces the passivation region,and reduces the resistance of the passivation film.When the corrosion medium changed from acid to alkaline,the film resistance increased,and the stability of passivation became better.The increase of solid solution temperature and holding time resulted in the transformation of the matrix ferrite into a smooth round shape.The electrochemical experiments show that long short holding time.With the increase of temperature,the passive current density decreased,slow corrosion,the corrosion resistance of the film increased,improve sample passivation stability;when the time is too long,the corrosion resistance of the coatings decreased,the corrosion resistance of passivation film uniformity becomes worse,reduce corrosion as a result of poor performance.The samples with good corrosion resistance can be obtained by holding 20 min at 1050?.The H2SO4+Na2S4O6 of EPR solution is suitable for checking the intergranular corrosion sensibility of high nitrogen austenitic stainless steel.The test shows that the holding time is short,the solid solution temperature rises,the R value decreases,the electricity quantity is lower than the Qr/Qa,the holding time is too long,the R value increases,and the quantity of electricity is bigger than the Qr/Qa.In the oxalic acid etching experiment,10% oxalic acid solution was chosen as electrolyte,and the material was eroded by 1A at constant current for 90 s.The conclusion is consistent with that of EPR.The holding time is short,with the solution temperature,grain growth,grain size,resistance to intergranular corrosion resistance;When holding time is too long,precipitates and intergranular corrosion occurs along grain boundaries and intergranular corrosion resistance to poor performance.So,heating at 1050? for 20 min can obtain better specimen.