The Research Of Stress Corrosion Crack Behavior For 310S Austenitic Stainless Steel In H₂S/CO₂ Environment

In China,the corrosion problem of high content of H₂S-CO₂-Cl^-in acid oil and gas field is very serious.People are looking forward to find a stainless steel which have good corrosion resistance and low price.Austenitic stainless steel has excellent chemical stability,stable mechanical properties,but there is a serious problem of stress corrosion cracking.In this paper,310S austenitic stainless steel with cold rolling,solid solution and aging was selected as the object of experimental study.Metallographical study,stress corrosion behavior and electrochemical properties were researched to explore the factors that affect the SCC behavior of 310S and its mechanism.Firstly,we observed the microstructure of the materials.We found that the microstructure of soluted 310S is austenite.The grain size is uneven,the density of dislocation is low.The microstrcture of cold-rolled 310S is still pure austenite,no martensite was found.At the nanometer scale,a large number of slip bands and twins are distributed inside the matrix,and a large number of dislocations are distributed around the slip bands.A large number of precipitates gathered at the grain boundary of aged 310S.the situation is same in the grain.After analyzing we make sure that it is M₂₃C₆.Then we made a electrochemical test to the samples with loading and without loading.The results show that cold rolling can improve the corrosion resistance of 310S stainless steel,and the aging treatment will reduce the corrosion resistance of stainless steel.In addition,the presence of stress can reduce the corrosion resistance of the material.By more analysis,it was found that the reduction of the total impedance mainly comes from the reduction of the resistance for passivation film.Therefore,it can be inferred that the composition,thickness or compactness of the 310S passivation film is changed after loading,then the corrosion resistance of the material is reduced.Finally,stress corrosion experiments were carried out.In the four-point bending test,only the cold-rolled specimen was broken,and many cracks were not observed on the surface of the sample.The cracked form was transgranular fracture.In the SSRT experiment,the cold-rolled 310S has the biggest tend of SCC.The aging sample is more prone to cracking than the soluted sample.The analysis shows that the cleavage form is quasi-cleavage or cleavage.the 310S sample stretched in the H₂SO₄ environment is seriously corroded,the hydrogen permeation specimen has a plastic deformation.From the tensile curve,their strength and elongation are reduced but higher than the sample in the H₂S-CO₂ environment.In the H₂S-CO₂ environment,there are many cracks in the side of the specimen,and there is obvious local corrosion around the crack.the local surface fall off.In some crack tip that has not cracked yet also occurred local corrosion.In the hydrogen permeation TEM experiment,it was found that the H entering the 310S promoted the movement of the dislocation,which was more likely to cause the increase and piled of the dislocation and finally lead to the stress concentration.