G. Re

Relationship Between the Electrochemical and Corrosion Behavior and the Structure of Stainless Steels Subjected to Cold Plastic Deformation

The present inves t iga t ion forms pa r t of a sys temat ic s tudy about the influence of cold p las t ic deformat ion on the electrochemical and corrosion b e hav ior of meta l l ic mater ials , wi th the aim of de te rmining and e luc ida t ing such aspects of the i r behavior and corre la t ing them wi th the micros t ruc tura l effects of the deformat ion, these being analyzed by meta l lographic and x r a y techniques and by t ransmiss ion e lec t ron microscopy. In this respect, the influence of cold plast ic deformat ion on the e lectrochemical and corrosion behavior of two stainless steels (AISI 304 L and 316 L) in different aggressive media (wi th and wi thout chlor ide ions) has been s tudied wi th reference to the fol lowing points: (i) de format ion type, i.e., tensi le stress, cold drawing, or cold roll ing, and conditions, i.e., at room t empera tu r e and at --196~ (ii) re la t ive or ien ta t ion of the exposed surface wi th the deformat ion direction, i.e., para l l e l and perpendicu la r ; (iii) texture , defects, and mar tens i t e t ransformat ion. t ion of these mate r ia l s which are of ten used in the w o r k h a r d e n e d state. The corre la t ion be tween the elect rochemical behavior and the s t ruc tura l effects p ro duced by cold plast ic deformat ion, i.e., texture , surface Fig. 1. Test cell (cross section) The s tudy of the influence of cold plast ic de fo rmat ion on the e lect rochemical and corrosion behavior of austenit ic s tainless steels was carr ied out in our In s t i tu te main ly because of the need for a sys temat ic collection of da ta as a basis for a more re l iab le u t i l iza* Electrochemical Society Act ive Member. 1 Present address: Cent ro Informazioni Studi Esperienze ( CISE ), Milano, I taly.

Experimental Evaluation of a Metallurgical Model for Austenitic Stainless Steels Sensitization

Abstract The improved depleted zone theory of intergranular corrosion, developed by Stawstrom and Hillert, has been applied to commercial austenitic stainless steels for predicting carbide precipitation kinetics and time required for the onset and termination of sensitization. There seems to be good agreement between experimental and theoretical results regarding carbide precipitation kinetics, but some discrepancies arise between experimentally determined and theoretically predicted desensitization times. In some cases, the S-H model predicts nonsensitization conditions, while the modified Strauss test shows a sensitized state; this discrepancy makes us question the reliability of the S-H model in predicting sensitization and self-healing times, particularly in the case of LTS and subsequent IGSCC.

Contribution to the Interpretation of Current Maxima in the Passivity Range of Austenitic Stainless Steels

Abstract Passive current density maxima have been observed by various workers during the anodic polarization of different stainless steels in sulfuric acid solutions and have been explained by many theories. This paper describes the precorrosion time and some other pretreatments of the sample surface which change drastically the anodic polarization curve of AISI Type 304 stainless steel in 2N H2SO4, lowering the critical current density and causing two passive maxima. Our results are used in a critical analysis of the conclusions of other authors. The passive current density maxima are attributed to the oxidation of hydrogen formed during precorrosion and absorbed into the alloy and of ions present in the solution and coming from the alloy dissolution.

Localized Corrosion Susceptibility of Work-Hardened Stainless Steels in a Physiological Saline Solution

This paper describes: (1) an electrochemical technique for crevice corrosion testing and (2) the results of a study concerning the susceptibility to crevice and pitting corrosion of work-hardened AISI 316L and 304L stainless steels in a sodium chloride buffered solution simulating the aggressiveness of the human body. In particular, the importance of the deformation degree and the orientation of the specimen surface under study with respect to the deformation direction is shown and discussed in relation to characteristic structural aspects.