CS264694B1 - Determination method of the content of sulphur,sulphides and segregation in metal materials - Google Patents

Abstract

Sulfur and sulphide content determination and segregation in metallic materials, in particular of stainless steels that are carried out that the surface of the sample to be measured polarizes potentiokinetically optionally potentiostatically in the area of optimum passivity potentials and on places the determination of current density and potentials the peaks on the polarization curves are determined reducing the passive stability that is proportional sulfur, sulphide and segregation levels.

Description

The present invention relates to the determination of the sulfur, sulfide and segregation levels of metallic materials due to their influence on weldability, hot and cold cracking, and corrosion resistance.

So far, the determination of sulfur, sulfide and segregation in metallic materials has been carried out by methods based on analytical, microanalytical and diffractive methods. Such methods are described, for example, in Boháček, Mayer, Tůma; Carbides and intermetallic phases in steels, Prague SNTL 1969. Assessment by these methods is difficult, time and equipment intensive and does not give any evidence on the effect of sulfur, sulfides and segregation on corrosion characteristics.

These drawbacks of the prior art are largely overcome by the method of determining the sulfur, sulfide and segregation levels in metallic materials based on potential polarization measurements of these materials, in particular stainless steels, according to the invention. The principle of the invention is that the surface of the sample to be measured is polarized potentiokinetically or potentiostatically in the region of optimum passivity potentials - from 0.2 to 0.9 V to the calomel electrode - and by determining the current density and peak potentials on the polarization curves passive state, which is proportional to the contents of sulfur, sulfides and segregation. It is desirable to determine the time dependence of current densities at potentials corresponding to maxima on the polarization curve. It is further preferred that the charges passed through the electrolyte-metal interface are determined within the range of potentials of increased current densities over a specified period of time. In the case of very low levels of sulfur, sulphides and extent of segregation, successive measurements repeated immediately in succession on the same demarcated sample area are preferred. Increasing the sensitivity of the evaluation can be achieved by a measurement procedure based on the transpasive state.

The sulphide content is proportional to the magnitude of the current density expressed as the maximum curve in the potential range of +0.2 to +0.9 V _SCE . The same result can be obtained by recording the passed charge defined by the sulfide dissolution curve.

In any case, the change in passivity induced on the potentiokinetic curve by dissolving sulfides is a deviation from the general state and can be used for at least a semi-quantitative evaluation of the changes. The higher the values can be read from the curve, the higher the sulphide contents in the test metal.

The method of evaluating the reduction of the passive state stability by potentiokinetic or potentiostatic polarization in the area of the potentials of the optimal passive state in relation to the sulfur, sulphide and segregation levels in metallic materials is less time consuming and instrumental than the methods used hitherto. A further advantage of the method according to the invention is that it allows quantitative or at least semi-quantitative evaluation of the sulfur, sulphide and segregation contents and the assessment of the corrosion characteristics of the monitored materials without long-term and energy-intensive immersion corrosion tests.

The measurements according to the invention can be carried out on the potentiostat and the potential for continuous potential change. As a test environment jc possible to use conventional solutions ΙΙ ₂ 8 (= 2 mol of Λ I "with 0.01% KSCN. The speed of the change in potential at around 1 V / 6.6 min. At a measuring range of up to -0.7 + J, 2 V (V _{S (} .,.). The registered dependencies are shown in the examples in Figures 1 to 4.

The sensitivity and accuracy of the measurement based on current densities and charge passed on a sample area of 1 cm ² corresponds to the series changes in the sulfur content and hence the sulphide contents as shown in Example 2, Table 1. Example 1

The sulfur content of two types of stainless steels was determined by the method of the invention and the potentiokinetic polarization curves shown in Figures 1 to 4 were obtained. Figures 1 and 3 show the curves of the original surface samples and Figures 2 and 4 show the curves of the samples after sulfinization, the characteristic current maximum being indicated by an arrow.

Giant. 1

ČSN 41 7021 steel annealed at 800 ° C for 50 hours in an inert atmosphere Fig. 2

ČSN 41 7021 steel annealed at 800 ° C for 50 hours in a hydrogen environment in the presence of 1 mg of sulfur per cm ² of sample area

Giant. 3

ČSN 41 7241 steel annealed at 800 ° C for 50 hours in an inert atmosphere Fig. 4

ČSN 41 7241 steel annealed at 800 ° C for 50 hours in a hydrogen environment in the presence of 1 mg of sulfur per cm ² of sample area.

Example 2

The second example relates to Cr18NilOTi steel in which, with a constant composition with graded sulfur content, the maximum characteristic for the dissolution of titanium sulfides increases. Data from potentiokinetic measurements for the three steels of this composition are shown in Table 1.

Table 1

Steel JtíjS J No _{Ti; S} C. (A cm ² ) (C cm ² ) 1 2.6. 10 * 0.0005 2 2.3. 10 * 0,0025 3 1.1 .10 ~ ⁴ 0.0180 C Mn Si S P Ni Cr Ti

(% wt.)

0.085 0.42 0.31 0.004 0.007 10.0018.00 0.42

0.068 0.48 0.30 0.0150.016 12.05 18.00 0.65

0.035 0.43 0.30 0.125 0.005 10.05 18.05 0.78

The invention can be used to control the quality of stainless steels at manufacturers, processors and users.

Claims (3)

SUBJECT OF THE INVENTION A method for determining the sulfur, sulphide and segregation content of metallic materials on the basis of potential polarization measurements of these materials, in particular stainless steels, characterized in that the surface of the measured sample is polarized potentiinetically or potentiostatically in the region of optimal passivity potentials 0.9 V relative to the calomel electrode, and based on the determination of current density and peak potentials on the polarization curves, a reduction in the stability of the passive state is proportional to the sulfur, sulfide and segregation contents. 2. Method according to claim 1, characterized in that the time dependence of current densities at potentials corresponding to the maxima on the polarization curve is determined. 3. A method according to claim 1 or 2, characterized in that the charge passed through the electrolyte-metal interface is determined within the range of potentials of increased current densities over a specified period of time.