Abstract
Critical pitting temperature (CPT) is one of the most accepted criteria for alloy classification concerning pitting corrosion. The techniques used nowadays to determine CPT have different parameters for alloys of different material classes, preventing the comparison between stainless steels and nickel based alloys. This study aims to compare the corrosion resistance of nickel based alloys and stainless steels with high corrosion resistance through potentiostatic tests for CPT determination, using a 3M MgCl2 aqueous solution. CPT values were effectively determined for the stainless steels studied but the technique did not have the same efficiency for nickel based alloys due to the occurrence of crevice corrosion, even considering the higher PRE of nickel based alloys.
Highlights
Critical pitting temperature (CPT) is widely used to analyze pitting corrosion resistance of stainless steel and other alloys, following ASTM G481 and ASTM G1502
Inclusion analyses revealed that the materials have type 1 fine series oxides inclusions, following the inclusion classification standards proposed by Jernkontoret[16]
The inclusions were found in small quantity and size for all materials, they probably have small influence on the comparison of the obtained corrosion results for the alloys
Summary
CPT (critical pitting temperature) is widely used to analyze pitting corrosion resistance of stainless steel and other alloys, following ASTM G481 (using immersion tests) and ASTM G1502 (for potentiostatic tests). It is commonly used to compare the performance of materials on a given medium. Another way of analyzing pitting resistance is through the PRE-number, which can be calculated through PRE equation: PRE =% Cr + 3.3% Mo + 16% N. Immersion corrosion methods such as the ones described in ASTM G481 have different tests methodologies for stainless steels or nickel alloys, preventing a direct comparison of CPT results obtained from different materials using immersion tests
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