| 316LN austenitic stainless steel has now been used in pressure tanks,wastewater pipelines,nuclear industry pipelines and other equipment,and the material is prone to local corrosion in the environment of industrial corrosive media,so it is particularly important to study the corrosion resistance of 316LN.In this dissertation,316LN is used as the research object and 316L is used as the control material.Electrochemical tests,chemical immersion tests,slow strain rate tensile tests,and scanning electron microscopy tests are used to study the local corrosion behavior of the materials in Na Cl and FeCl3solutions.The main conclusions are as follows:(1)In NaCl solution,as the concentration of Cl- increases,the pitting resistance of the two materials decreases.After the temperature is increased to 50°C,the pitting corrosion resistance of the two materials is further reduced,and the pitting corrosion resistance of 316LN is better than that of 316L.(2)After the two materials are immersed in a 6%FeCl3solution at 25?for 7days,most of the pitting pits of 316LN in this environment are mainly single-hole growth,and the pits develop in a typical semi-ellipsoidal shape.The pits on the surface of 316L are very densely distributed,interpenetrating between the pits,and some secondary holes appear inside the pits.After the temperature rises to 50?,the adjacent pits eventually expand laterally into larger pits.In 6%FeCl3solution,the corrosion characteristics of 316LN pits conform to the autocatalytic process model,which can be used to explain the growth mechanism of pits.(3)In an air medium with a strain rate of 1×10-5/s,both materials show mechanical ductile fracture,and the 316LN fracture shows a typical coaxial dimple plastic fracture morphology.In a 3.5%NaCl solution with a strain rate of 1×10-5/s,the plastic loss of the two is smaller,and the stress corrosion resistance of 316LN is better than that of 316L.In the 6%FeCl3solution with a strain rate of 1×10-5/s,the fracture of 316LN fracture along the Y-axis direction is almost 45°,and the surface of the fracture is mainly elongated shear dimple morphology.316LN has significant pitting corrosion in 6%FeCl3at a solution temperature of 50?.The morphology of part of the fracture dimples can still be observed.There are dense pitting pits on the surface.The etch pit can reach more than 30?m,the size of the etch hole is less than 316L,and small cracks with a length of about 100?m are locally generated on the fracture surface.The stress corrosion fracture of 316L in 6%FeCl3solution has a typical equiaxed dimple fracture morphology.Due to the stress corrosion tendency,the fracture dimples are shallow,and some of the fractures have sprouted tiny metastable points due to the action of corrosive media pits.After the temperature rises,the dimples in the fracture are more flat and localized,and the cleavage surface of typical brittle fracture has appeared locally.According to the fracture morphology of 316LN,the"anodic dissolution model"can be used to explain its stress corrosion cracking mechanism. |
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