The Research On Forming Performance And Corrosion Resistance Of Cold Rolled Austenitic Stainless Steel Plates

Stainless steels are widely applied in industry production and daily life fields owing to the forming property and the corrosion resistance. In this paper, the forming property and the corrosion resistance of cold-rolled plates of 304 austenitic stainless steels have been researched by means of its microstructure and compared with these of ferritic stainless steels (430, 410S and 409L) and austenitic stainless steels (904L, 316L). As a result, the theory to guide production practice was provided in improving the forming property, the corrosion resistance and the modified process of 304 austenitic stainless steels.First, the features of stain-induced martensite of 304 austenitic stainless steels were studied. The important influence factors of stain-induced martensite of 304 austenitic stainless steels are strain degree, stress condition and material state. As to the state of cold rolling of 304 austenitic stainless steels, the more deformation quantity is, the more martensite quantity was induced under uniaxial tension stress. When the strain was 10-20%, the quantity of martensitic transformation was very little. When the strain was 20%-40%, the quantity of martensitic transformation was more. As to the state of hot rolling of 304 austenitic stainless steels, the stability of martensite was inferior to that under the state of cold rolling because of existence of carbides and inhomogeneity of structure. Under the state of hot rolling, the quantity of martensitic transformation through tensile deformation was more (35%), but under the state of cold rolling, the quantity of martensitic transformation through tensile deformation was little (10%). The bi-directional(tangential and radial) tensile stresses contribute to the transformation from austenite to martensite on cupping of hole expansion test specimen of 304 austenitic stainless steels, and the quantity of induced martensite was more (25%).Second, the forming property of the cold-rolled plate of 304 austenitic stainless steels was studied. 304 stainless steels possess the mechanics performance parameters such as higher n value and uniform elongationδu which are helpful to the forming property. The hole expansion test and cupping test are plastic making process, and therefore related to some basic mechanics performance parameters. Of course, these relationships are not necessarily very simple linear relationships. The relevance between the mechanics performance parameters and cupping test value IE are better than hole expanding rate. The correlation betweenδu (orσs/σb or n) andλ(or IE) seemed better than the correlation between△r (or (γ|-) ) andλ(or IE). Since the grain size of 304 plates is the 7th grade, and 304 plates is the equiaxed grain, it is conducive to the forming property. The dimples of 304 are uniform small size ones. The dimples formed at small carbides in the mid-late of deformation, which benefits the large deformation and forming. The induced martensite of 304 austenitic stainless steels strain can improve the work hardening capacity and strain induced martensite can induce plasticity. As a result, the forming property of 304 austenitic stainless steels is superior to the other 3 types of ferritic stainless steels (410S, 409L, 430).Finally, the corrosion resistance of the cold-rolled plate of 304, 304-20%ε, 304-30%ε, 304-40%, 316 and 904L in oxidative, reducible, alkali and salt solutions were studied, and the pitting corrosion resistance of 304 austenitic stainless steels and their deformation sample was determined by cyclic voltammetry. The polarization curves in different corrosive media were measured, and the corrosion resistance was evaluated by characteristic parameters. There is the obvious passivation region in corrosive media, and the passivation current is regarded as the evaluation standard. The tendency of metal corrosion was judged by self-corrosion potential. When there is not the obvious passivation region in corrosive media, the corrosion resistance should be evaluated by self-corrosion current (logi_corrr). The decrease order of corrosion resistance was 904L, 316L, 304, 304-20%ε, 304-30%εand 304-40%εin oxidative and reducible media, alkali solution and ferric trichloride solution. The higher the breakdown potential (E_b) is, the steadier the metal passivation is and the higher the potential to occur pitting corrosion is in the pitting corrosion experiment. The closer the value between E_b and E_p is, the better the repair capacity of passive film is. The pitting corrosion resistance from high to low was 304, 304-20%ε, 304-30%εand 304-40%εaccording to morphology photos of pitting corrosion and E_b-E_p values.