A discussion on evaluation criteria for crevice corrosion of various stainless steels

In this study,crevice corrosion performances of a newly developed LDSS 2002 and three commercial stainless steels(AISI 304,AISI 316L and DSS 2205)were investigated and discussed.Crevice repassivation potential(ER,CREV),which was measured by the potentiodynamic-galvanostatic-potentiodynamic(PDGS-PD)test,was applicable to crevice corrosion evaluation of 304 and 316 L stainless steels.However,much lower(ER,CREV values were obtained for DSS 2205 and LDSS 2002.These abnormal(ER,CREV values for duplex stainless steels may be related to the selective attack of the less corrosion-resistant phase,the lower corrosion potential in the crevice-like solution,and more crevice corrosion sites in the PD-GS-PD test.A critical chloride concentration of crevice corrosion(CCCCREV)measurement was introduced for crevice corrosion evaluation of various stainless steels.The derived CCCCREVwas proved to be a valid criterion for crevice corrosion evaluation of both the austenitic and duplex stainless steels.An order of crevice corrosion resistance of AISI 304≈LDSS 2002相似文献   

Influence of nitrogen addition on the crevice corrosion resistance of nitrogen-bearing austenitic stainless steels

Crevice corrosion studies were carried out on nitrogen-bearing types 304, 316 and 317 austenitic stainless steels (SS) by a potentiodynamic anodic polarisation method in an acidic chloride medium. A special all-glass crevice assembly was used for providing reproducible crevice effects on the surface of the test specimen. The results indicated that the increase in nitrogen content improved the crevice corrosion resistance of the alloys by decreasing the active dissolution, and increasing both passive film stability and the potential at which crevice attack was stable. This was very significant for 304 and 316 SS alloys in comparison with 317 SS alloys. The combined influence of nitrogen and molybdenum was found to be very significant in providing high crevice corrosion resistance for 317 SS alloys. Optical microscopic observation revealed severe crevice attack on types 304 and 316 SS alloys compared to mild crevice attack on type 317 alloys. Based on the results of the present investigation a possible mechanism by which nitrogen addition improved the crevice corrosion resistance is discussed.     

Intergranular corrosion resistance of nanostructured austenitic stainless steel

Nanostructured metals and alloys possess very high strength but exhibit limited plasticity. Enhancement of the strength/ductility balance is of prime importance to achieve wide industrial applications. However, post-deformation heat treatment, which is usually used to improve plasticity, can lead to a decrease in other properties. In the case of austenitic stainless steels, heat treatment in the range from 480 to 815 °C can increase their susceptibility to intergranular corrosion. The aim of the work reported in this paper was to determine if nanostructured austenitic stainless steel is susceptible to intergranular corrosion if heat treated for 1 h at 700 °C. Samples of 316LVM austenitic stainless steel were hydrostatically extruded, in a multi-step process with the total true strain of 1.84 to produce a uniform microstructure consisting of nanotwins. These nanotwins averaged 21 nm in width and 197 nm in length. Subsequent annealing at 700 °C produced a recrystallised structure of 68-nm-diameter nanograins. The heat treatment improved the ductility from 7.8 to 9.2 % while maintaining the ultimate tensile strength at the high level of 1485 MPa. Corrosion tests were performed in an aqueous solution consisting of 450 ml concentrated HNO₃ and 9 g NaF/dm³ (according to ASTM A262-77a). The evaluation of the corrosion resistance was based on transmission and scanning electron microscopic observation of the microstructure and chemical analyses. The results revealed that both the as-received and HE-processed samples are slightly susceptible to the intergranular corrosion after annealing at 700 °C for 1 h.     

Intergranular corrosion of welds in type 405 stainless steel

A low chromium ferritic stainless steel (Type 405) with different heat treatments and weld configurations, has been investigated for susceptibility to intergranular corrosion by chemical and electrochemical potentiodynamic reactivation (EPR) tests, and the results were evaluated by weight losses, dye penetration, metallographic techniques, and the ratio of the reactivating and activating currents. Welds are susceptible to attack, particularly in the heat-affected zone. Applied stress in a U-bend increases significantly the attack on welds, and annealing eliminates the effects of stress. Results on the susceptibility of unwelded specimens in the form of flat plates and U-bends after various heat treatments are also presented and discussed.     

Chemiluminescent investigations of corrosion of stainless steels

Chemiluminescent systems of luminol are used to design and improve methods for the direct express evaluation of the content of chromium and nickel in corrosive media of stainless steels. By these methods, we can determine nanogram amounts of chromium and nickel in the presence of greater amounts of iron and other components of corrosive media. The methods were approved while testing corrosion of 40KhN steel in a 3% NaCl aqueous solution. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv; Franko State University, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 6, pp. 15–20, November–December, 1997.     

A multiphysics model for studying transient crevice corrosion of stainless steel

The transient crevice corrosion behavior of 304 stainless steel in NaCl solution has been investigated by a multiphysics coupling model.The model considers local electrochemical reactions,transport of diffe rent species,and homogeneous reactions.The moving mesh method is used to obtain the geometrical change of the crevice wall with time due to corrosion.The level set method is employed to quantitatively describe the influence of the precipitation process on electrochemical reactions.The transient crevice corrosion morphology,potential and current distributions,and pH and chloride ion concentration distributions are obtained by simulation.The effect of crevice geometry factors on the corrosion process is also discussed.The simulation results are in good agreement with the experiments,showing that the model has high reliability.     

Stress corrosion of stainless steels in aerated steam

The possibility of electrochemical phenomena and metal stress corrosion taking place in aerated steam was investigated. The temperature range in which stress corrosion in this medium is most intense was determined, the effect of the composition of corrosive media on the resistance of stainless steel to stress corrosion was investigated, and the influence of an inhibitor (octadecylamine) was studied.     

Intergranular crack paths during fatigue in interstitial-free steels

Interstitial-free (IF) steels are known to exhibit intergranular (IG) faceting during fatigue under certain conditions. The presence of IG facets is often ascribed to either environmental effects or to grain boundary embrittlement. In many cases this attribution to environment or embrittlement is erroneous with the IG faceting actually arising from the intrinsic slip characteristics of body-centred cubic (bcc) alloys. This paper summarises the background to slip-induced intergranular fatigue and explores two issues of importance to users of IF steels; alloy conditions in which IG fatigue occurs and whether the fatigue performance in the presence of an IG crack path is lower than similar IF steels which exhibit a transgranular crack path. To explore this latter issue fatigue performance is presented as a function of yield strength.     

Studying localized corrosion in stainless steels with surface-sensitive methods

Different surface-sensitive techniques have been used to investigate localized corrosion of stainless steels in environments containing thiosulfate, chlorides, and sulfates. Pitting was induced in laboratory by using a scratch technique and electrochemical polarization. The diameter of the pits was less than 0.2mm. The morphology of the pits and the composition of the corrosion product in the pits were studied. The pits on surfaces were investigated directly after the electrochemical tests, on cross sections, and on replicas. The surface-sensitive techniques used provided consistent results with valuable complementary information. The corrosion product in the pits contained high amounts of chromium, and sulfur as sulfides and sulfates. The pit deposit in the molybdenum-alloyed stainless steel contained additionally a high amount of molybdenum. Indications of a very thin chlorine-rich layer next to the parent metal was detected.     

In vitro corrosion resistance of Lotus-type porous Ni-free stainless steels

The corrosion behavior of three kinds of austenitic high nitrogen Lotus-type porous Ni-free stainless steels was examined in acellular simulated body fluid solutions and compared with type AISI 316L stainless steel. The corrosion resistance was evaluated by electrochemical techniques, the analysis of released metal ions was performed by inductively coupled plasma mass spectrometry (ICP-MS) and the cytotoxicity was investigated in a culture of murine osteoblasts cells. Total immunity to localized corrosion in simulated body fluid (SBF) solutions was exhibited by Lotus-type porous Ni-free stainless steels, while Lotus-type porous AISI 316L showed very low pitting corrosion resistance evidenced by pitting corrosion at a very low breakdown potential. Additionally, Lotus-type porous Ni-free stainless steels showed a quite low metal ion release in SBF solutions. Furthermore, cell culture studies showed that the fabricated materials were non-cytotoxic to mouse osteoblasts cell line. On the basis of these results, it can be concluded that the investigated alloys are biocompatible and corrosion resistant and a promising material for biomedical applications.     

On the stress corrosion cracking mechanisms of austenitic stainless steels

In this paper, experimental results on stress corrosion cracking in austenitic stainless steels are described. Crack growth data in sodium chloride solution for AISI 304 steel obtained for different metallurgical conditions, acoustic emission data recorded during crack growth and fractographic observations have been discussed with a view to identifying the operating mechanism. Some of the experimental observations such as crack propagation occurring in discontinuous jumps of the order of a few microns, lowering of the threshold stress intensity andJ-integral values on sensitization and cold working, typical transgranular fractographic features, transition in mode of fracture from transgranular to intergranular in sensitized conditions and activation energies of the order of 50 to 65 kJ/mol can all be accounted by hydrogen embrittlement mechanism. Hydrogen generated at the crack tip by corrosion reaction diffuses ahead of the crack tip under hydrostatic stress and influences the deformation process at the crack tip and also leads to the brittle component of the crack advance in jumps.     

Passivation and stress corrosion cracking tendency of manganese stainless steels

Stress corrosion cracking (SCC) behaviour of three grades of nickel-substituted manganese stainless steels have been studied at room temperature in 1M HCl under constant load at different applied potentials. Repassivation studies have also been carried out using a scratching electrode technique. Selective dissolution and film formation similar to that of films formed on alpha brass in ammoniacal solutions, were found to induce SCC in manganese stainless steels. With decrease in nickel content, these alloys were found to be highly susceptible to SCC.     

Intergranular corrosion behavior and mechanism of the stabilized ultra-pure 430LX ferritic stainless steel

Intergranular corrosion (IGC) behavior of the stabilized ultra-pure 430LX ferritic stainless steel (FSS) was investigated by using double loop electrochemical potentiokinetic reactivation (DL-EPR) and oxalic acid etch tests to measure the susceptibility of specimens given a two-step heat treatment. The results reveal that IGC occurs in the specimens aged at the temperature range of 600–750 °C for a short time. The aging time that is required to cause IGC decreases with the increase of aging temperature. A longer aging treatment can reduce the susceptibility to IGC. The microstructural observation shows that M₂₃C₆ precipitates form along the grain boundaries, leading to the formation of Cr-depleted zones. The presence of Cr-depleted zones results in the susceptibility to IGC. However, the atoms of stabilizing elements replace chromium atoms to form MC precipitates after long-time aging treatment, resulting in the chromium replenishment of Cr-depleted zones and the reduction of the susceptibility to IGC.