SU911240A1 - Method of determination of ferro-nickel alloy tendency to inter-crystallite corrosion - Google Patents

Description

The invention relates to the testing of materials and can be used in determining the susceptibility of iron-nickel alloys to intergranular corrosion.,

A method is known for determining the propensity of iron-nickel alloys for intergranular corrosion, which consists in keeping the spal sample in acidic sodium chloride on the basis of chlorine content for 30 min, at a constant potential of 0.1 V relative to the chlorine-silver electrode and the anodic current is recorded, the change of which is judged on the propensity of the alloy to cross-scale corrosion.

The disadvantages of this method are low accuracy, since the current value ambiguously characterizes the appearance of intergranular corrosion, and the magnitude of the potential may be insufficient to detect the tendency of the alloy to intergranular corrosion, and the longer duration of the determination.

The purpose of the invention is to improve the accuracy and performance of the determination.

In order to achieve this goal, the method for determining the propensity of iron-nickel alloys to intergranular corrosion is that the alloy sample is kept in an acidic solution of sodium chloride at a constant potential relative to the silver chloride electrode and the anodic current is measured, and the change intergranular corrosion, using a solution based on hydrochloric acid, the exposure time is set to 6-10 minutes, and the potential is chosen + 0.75 + 0.85 V.

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The determination of the propensity of iron-nickel alloys for intergranular corrosion by the proposed method is based on the fact that in alloys prone to intergranular corrosion, grain boundaries due to chromium depletion have a less resistant passive film and are subject to sustained activation in solutions containing active halogen ions. Chromium depletion of the alloy grain boundaries occurs as a result of the precipitation of chromium carbides and chromium-rich phases, and the dependence of g on the content of carbon and heat treatment in the alloy. The criterion for susceptibility to intercrystalline corrosion is a steady increase in anodic current throughout the test at a potential from + Q, T5 to + 0.85 V, which lies in the area of pittin formation. The increase in current at a potential of +0.75 0/85 V is caused by the formation and development of pits, the appearance of dix at the grain boundaries. In this case, in the case of an alloy less prone to intergranular corrosion, the current grows less intensively than for a more prone one. On an alloy not prone to intergranular corrosion, the growth of anode current, noted only in the first 1-2 minutes, is associated with the local activation of defective surface areas of Persian, edge corners. Further, as the defective areas are etched, the anode current decreases (the curve in time thus passes through a maximum) and continues to decrease until the test. The method is carried out as follows. As a working electrolyte, a solution of H7t- / NaCL + l% HCfi is used. at. room temperature 20-25 0 The tests are carried out on sample plates of size (2-5) x (13-20) x (20-80 mm. Samples are immersed in the solution without additional isolation, the working surface is 310 cm. Before immersion in the electrolyte, the samples are cleaned on a grinding machine or manually, washed with water, dried with filter paper and no longer loaded into a three-electrode cell with an electrolyte solution, an auxiliary platinum electrode and an silver electrode. A potential of +0.75 +0.85 V relative to a chlorine-silver electrode and a current-time curve is taken within 6-10 minutes. The slope of an alloy sample to intergranular corrosion is judged by the continuous increase in anodic current during this time. +0.8 V and a time of 6 minutes are optimal for removing the current-time curve. At potentials of + 0.75 V, the tendency to intergranular corrosion in alloys weakly inclined to intercrystalline corrosion may not appear; at Potentials of + 0.85V, it is possible to sustain splgvvov activation, not prone to intergranular corrosion. At time b min, the differences between alloys prone to and not prone to intergranular corrosion may still not be apparent. A time 10 min is impractical because it does not change the test score. The method allows quickly and with high accuracy to investigate iron-nickel alloys for susceptibility to intergranular corrosion, does not require additional calculations, since the evaluation criterion is visual, and the electrolyte used is not very dangerous. invention The method of determining the tendency of iron-nickel alloys to intergranular. corrosion, which means that the sample of the alloy is kept in an acidic solution of sodium chloride at a constant potential relative to the chlorine-silver electrode, and an anodic current is recorded, by changing which the tendency of the alloy to intercrystalline corrosion, which is taller, is recorded: In order to improve the accuracy and performance of the determinations, a solution based on hydrochloric acid is used, the dwell time is set to 6-10 minutes, and the potential is chosen to be +0.75 +0.85 volts. Sources of information taken into account during the examination 1. Protection of metals, 1979, 15, No. 3, p. 303-308 (prototype).

Claims (1)

Claim A method for determining the tendency of iron-nickel alloys to intercrystal. cast corrosion, which consists in the fact that the alloy sample is kept in an acidic solution of sodium chloride at a constant potential relative to the silver chloride electrode and the anode current is recorded, the change in which determines the tendency of the alloy to intergranular corrosion, which is such that, in order to increase the accuracy and the performance of the determination, use a solution based on hydrochloric acid, the exposure time is set to 6-10 minutes, and the potential is chosen +0.75 +0.85 volts.