CS267296B1 - A method for determining the effect of Co-Cr-.V-Ee chemical composition on its corrosion stability - Google Patents

Abstract

It solves 3e and a method of determining the influence of the chemical composition of the Co-Cr-.V-Pe weld on its corrosion stability, based on the measurement of the reactivation charge and the regression analysis of the influence of individual elements determined by the chemical analysis of the weld. The determination is carried out by first adjusting the sample surface by a rapid potentiodynamic change of potential with subsequent holding of the potential at the highest value until complete passivation of the surface, after which the reactive charge is measured during slow potentiodynamic reactivation of the sample surface and by regression analysis of its values for welds of different chemical composition, the influence of individual chemical elements of the weld on the magnitude of the reactivation charge is determined.

Description

The invention relates to a method for determining the effect of the chemical composition of a Co-Cr-W-Fe deposit on its corrosion stability, in particular the stability against the corrosive action of deactivation solutions.

Iron, nickel, cobalt, manganese and silicon, as well as chromium, tungsten and molybdenum, dissolve in the carbide precipitate contained in the Co-Cr-W-Fe alloy build-up structure. * Depending on the welding technology and the electrodes or powders used, Corrosion resistance of carbide precipitate and solid solution and on their final chemical composition, influencing the chemical composition of the deposit, or on the ability of these elements to enter the carbide lattice and affect the passive stability of complex carbide and solid solution · Among media capable of causing violation also deactivating solutions used to remove radionuclides from parts made of these alloys in the core of nuclear reactors include the passive or active state. These radionuclides, released into the heat carrier from the structural materials of the active components of the nuclear reactor, must be removed using relatively very aggressive oxidizing agents, which at the same time remove the original oxide layer, which in Co-Cr-W-Fe alloys includes chromium oxide CrgOj. by oxidative treatment of the surface, for example with a solution of -5% HMO 2 + 0.3% KMnO 2, the Cr ₂ O 2 layer is removed, but a layer of Mn O ₂ is formed on the surface. for example with a solution of 0.5% ^H 2 ^C 2 ° 4 · Repeated rinsing of the Co-Cr-W-Fe alloy weld surface by alternating these oxidative and reducing solutions disturb the stability of the passive state of both phases present in its structure · It turned out that the worse is the stability of carbides to the oxidative treatment of the surface, the worse is the stability of the solid solution to possible reactivation during the reduction of the surface treatment. Previous experience

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- 2 simultaneously confirm that the corrosion stability of both of these phases decreases with repeated action of this corrosion mechanism with increasing difference of cobalt, chromium and tungsten contents in the mentioned phases · These different contents of cobalt, chromium and tungsten in the mentioned phases also affect the resulting chemical composition of the weld · Z It follows that monitoring the chemical composition of these phases, depending on the rolling technology and the electrodes or powders used, can be used to optimize the corrosion quality of these welds. A combination of scan transmission electron microscopy with X-ray dispersion analysis can be used for this. However, these methods require the use of very expensive and unique instruments, and the quality of the results is highly dependent on the qualifications and experience of highly specialized workers in the field of electron microscopy and X-ray dispersion analysis.

The disadvantages of the prior art are largely eliminated by the method for determining the influence of the chemical composition of the Co-Cr-W-Fe weld on its corrosion stability by measuring the reactivation charge and regression analysis of the influence of individual elements determined by chemical analysis of the weld according to the invention. The essence of the invention is that the sample surface is treated by a rapid potentiodynamic potential change in the range of -600 to +400 mV (SCE) with a potential increase at a rate of 10 mV.s ^-1 with the following potential endurance at the highest value of complete passivation of the sample surface. then, with slow potentiodynamic reactivation of the sample surface at a rate of 1 mV.s ^5, the reactivation charge is measured and the influence of individual chemical elements of the deposit on the size of the reactivation charge is determined by regression analysis of its values for welds of different chemical composition. Preferably, this evaluation is performed in a sulfuric acid solution with the addition of 0.01% KSCN at a temperature of 18 to 22 ° C.

The method of determining the influence of the chemical composition of the Co-Cr-W-Fe alloy deposit on its corrosion stability carried out according to the invention makes it possible for this type of alloy to reduce the time action potentials in the activity area and to facilitate passivation in the electrolyte, which must be sufficiently aggressive. induction of measurable reactivation for welds performed by different welding technologies from electrodes and powders of different chemical composition · In addition, it allows to assess the possibilities of partial cobalt replacement

267 296 iron in terms of corrosion quality of welds made of low-cobalt alloy Co-Cr-W-Fe. .

The invention is further elucidated by way of example of its specific embodiment with the aid of the accompanying drawings, in which FIGS. thickness of welded layers. Said curves were recorded with a continuous decrease of the potential from the value of +400 mV (SCE) at a speed of 1 mV.s ^-1 using a potentate with a saw generator. The areas under these curves were integrated simultaneously with the recording of these curves by means of an integrator connected to the potentate, and from the measured values of the passed charge the regression analysis evaluated the influence of individual elements determined by chemical analysis of the deposit.

Example

Tests were performed with Co-Cr-W-Fe, which depending on those electrodes or powders and the following chemical composition:

samples of nine alloy welds on the welding technology, using welded layers had

Table 1

Designation hm% C Mn Yes Cr What Fe W Ni Mo C 2 1.02 1.39- 0.81 26.63 50.38 14.67 3.86 - - E 1 1.38 0.22 1.52 27.07 59.25 6.47 4.93 - - E 2 1.26 0.26 1.30 24.29 55.67 9.79 7.44 - * · G 1 1, 88 0.22 1.42 0.22 59.96 5.39 4.29 G 2 1.51 0.19 1.28 27.36 61.04 6.06 4.29 - - P 2 ' 0.89 0.15 1.82 29.27 49.46 9.55 4.40 4.46 - V 1 ' 1.36 0.28 0.57 28.54 9.01 55.87 4.04 - 0.32 V 2 1.45 0.26 0.63 30.46 9.72 52.84 4.34 - 0.29 S 3 1.53 0.16 1.03 24.75 60.35 5.23 6.80 - · *

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Samples of bimetal welds ♦ stainless steel 03Crl7Ni12Mo2 had the shape of cylinders of 0 20 mm and a height of 10 mm, of which the thickness of the weld made of Co-Cr-W-Fe alloy, made by different welding technology from electrodes or powders of different chemical composition, was 2 to 3 mm After normal preparation of the weld surface and delimitation of the working area with 0.16 cm 3 of asphalt topcoat, carried out under a microscope, these samples were immersed in a solution of 2MH ₂ SO 4 with the addition of 0.01 wt.% KSCN. Immediately afterwards, they underwent a rapid potentiodynamic change from the hydrogen excretion region to the passivity region, ie, the potential range -600 to +400 mV (SCE), with the potential increase at TO mV.s ~ ¹ · · With a potential endurance of +400 mV SCE) the complete passivation was then checked by observing the change in charge values registered by the integrator connected to the recorder. of reactivation charge measured for samples of welds C 2 - S 3 (see table · 1), Using these values and data on the chemical composition of welds, the influence of individual elements on the value of this charge was evaluated by regression analysis with the following result

C _& = 1.2426% C - 0.1197% Mn - 0.1282 «Si - 0.0125% Cr - 0.0193% Co - 0.0068% Fe + 0.1185 + 0.0063% Ni -. 1, 3327 Sío _t

For comparison, Table 3 shows the mass changes during repassivation, measured on samples taken from C 2, E 2, G 2, P 2 and V 2 welds, for which the decontamination regime was modeled in 30 minute cycles of 5% HNOj + 3 solution change. % KMnO 2 solution with 0.5% H ₂ C ₂ O ₄ at 90 ° C. These mass changes during the first cycle reflect the rate of repassivation in a reducing solution of 0.5% ^K 2 ^C 2 ° 4 after etching the surface of the welds in an oxidizing solution of 5% HNO3 + KMnO2 and confirm comparability with data on the effect of chemical composition of Co-Cr alloy welds. -W-Fe on the corrosion stability of its structural phases, evaluated by measuring the parameter C _and for welds of different chemical composition and performing a regression analysis of the influence of individual elements, determined by chemical analysis of these welds.

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Table 2 02 E1 E2 G1 G2 P2 V1 V2 S3 Ca (C / cin ² ) 0.048 0.55 0.803 1.1 0.635 0.0175 0.726 0.891 1.106 Table 3 02 E2 G2 P2 V2 g.m * 0.895 5,474 4.65 0.054 6.913

In addition to determining the effect of the chemical composition of the Co-Cr-W-Fe alloy weld on the corrosion stability of its structural phases, the invention can be used to quickly detect the possibility of partial replacement of cobalt with iron in terms of maintaining corrosion quality of the Co-Cr-W-Fe alloy. . This procedure can be used to obtain the information necessary for the optimization of the rolling technology and the starting electrodes or powders of the Co-Cr-W-Fe alloy for the parts coming into contact with the inactivation solutions.

Claims (1)

Method for determining the influence of the chemical composition of Co-Cr-W-Fe on its corrosion stability based on the measurement of the reactivation charge and regression analysis of the influence of individual elements determined by chemical analysis of the weld, characterized in that the sample surface is adjusted by rapid potentiodynamic change in potential up to +400 mV (SCE) at an increase in potential at a rate of 10 s followed by the endurance of the potential at the highest value until complete passivation of the sample surface, after which the activation charge is measured by slow potentiodynamic reactivation of the sample surface at 1 mV.s for welds of different chemical composition, the influence of individual chemical elements of the weld on the size of the reactivation charge is determined «