Evaluation of susceptibility to stress corrosion cracking (SCC) in sodium chloride solution of weldments of cold rolled type 316 stainless steel

This article does not have an abstract

Evaluation of the stress corrosion resistance of cold rolled aisi type 316 stainless steel using constant load and slow strain rate tests

The effect of cold rolling (5 to 15% reduction in thickness) of an AISI Type 316 stainless steel on stress corrosion cracking (SCC) has been studied in boiling magnesium chloride of 45% concentration (boiling point = 428 K) using both constant load and slow strain rate methods. The constant load test results indicated increasing SCC susceptibility with increasing degree of prior deformation, whereas the ranking by the slow strain rate technique was in the reverse order. The reasons for this discrepancy have been discussed. A modified procedure of slow strain rate testing, involving the interruption of the test after a chosen duration of time and measuring average crack growth is suggested as an alternative

Morphological differentiation observed in manganese oxidizing bacterial colonies

Bacteria play a vital role in bringing about Mn(II) oxidation in the natural environment. A study was conducted to identify the potential threat offered by these bacteria in bringing about biomineralisation of manganese dioxide on titanium surfaces exposed to seawater. During the study it was observed that the bacteria such as Pseudomonas and Bacillus formed brown colonies on agar plates amended with Mn2+ indicating their ability to oxidize Mn(II). These colonies showed distinct morphologies when grown on plates containing Mn(II) while they formed normal colonies in the absence of Mn.(II).Hence it is possible that these morphologically distinct structures produced by the bacterial colonies assist these bacteria to perform this function of Mn-oxidation

Corrosion of Zircaloy-4 and its welds in nitric acid medium

Zirconium and its alloys are considered as candidate materials for various applications in spent nuclear fuel reprocessing plants involving nitric acid of various concentrations at different temperatures. In the present work an attempt was made to study the corrosion behaviour of Zircaloy-4 (Zr-with Sn-1.5%, Fe-0.22%, Cr-0.1%) in wrought and welded forms in comparison with other candidate materials like commercially pure Titanium (CP-Ti), Ti-5%Ta and Ti-5%Ta-2%Nb. Manual TIG welding and electron beam welding was carried out with Zircaloy-4 pipes of 5 mm thick and 120 mm diameter, and radiography was made for choosing defect-free regions for making samples for corrosion investigations. Three phase corrosion testing in liquid, vapour and condensate regions was conducted in boiling 11.5 M nitric acid medium using a specially designed experimental set up. The results indicated that Zircaloy-4 exhibit superior corrosion resistance in both wrought and welded conditions in comparison with other materials. The electron beam welded samples did not show any deterioration and performed similar to wrought alloy. The detailed results of microstructure, microhardness, corrosion rate, morphology of attack and nature of surface film formed are presented in this paper. The results of the present investigation indicated that Zircaloy-4 could be a candidate material for nitric acid medium of high concentration and temperature in reprocessing plants and other industries

Influence of laser surface alloying with chromium and nickel on corrosion resistance of type 304L stainless steel

The influence of laser surface alloying (LSA) with Cr and Cr + Ni on the corrosion behaviour of type 304L stainless steel (SS) was investigated using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) in chloride (0.5M NaCI) and acidic (1 N H2SO4) media. Surface alloying was carried out by laser cladding type 304L SS substrate with premixed powders of AISI type 316L SS and the desired alloying elements. The results indicated that Cr surface alloyed specimen exhibited a duplex (γ+α) microstructure with Cr content of ~24 wt-%, whereas Cr+Ni surface alloyed specimen was associated with austenitic microstructure with Cr and Ni contents of ~22 wt-% each. The potentiodynamic polarisation results in chloride solution indicated that LSA with Cr+Ni considerably enhanced the pitting corrosion resistance compared with LSA with Cr alone. In acidic media, such beneficial effects were not observed. Electrochemical impedance spectroscopy results showed an increase in semicircle arc for both chloride and acidic media for both Cr and Cr+Ni clad samples indicating improvement in the oxide film stability compared with untreated specimen. The polarisation resistance was higher and capacitance values of the laser clad specimen were lower than those in the untreated specimen. The microstructural changes and compositional variations produced by LSA are correlated to the corrosion behaviour

Biomineralisation of manganese on titanium surfaces exposed to seawater

A 2-year long study was carried out to isolate and characterise various bacterial species present in the biofilm formed on titanium surfaces exposed to seawater and to assess the manganese oxidizing potential of the marine isolates. The amount of manganese present in the biofilm was also measured using atomic absorption spectrometry (AAS). The results showed that titanium was susceptible to biofouling. More than 50% of the culturable marine bacterial isolates were capable of bringing about oxidation of Mn(II). All these manganese oxidizing bacteria were heterotrophic. Autotrophic manganese oxidizing bacteria such as Leptothrix was not isolated in the present study. The AAS results confirmed that the manganese content in the biofilms increased with increasing exposure time. Hence, the study indicates that the titanium surfaces when exposed to seawater were colonised by a large number of heterotrophic bacteria, which have the ability of bringing about biomineralisation of manganese