Carbide Extraction From the Weldox Steel

Table 1: Chemical composition of the investigated steels.

Table 2: The composition of electrolyte–solutions applied for the anodic dissolution of the investigated steels by PN 64/H-04510.

Figure 1: Diagram of an electrolyzer for the anodic solution of Weldox steels: 1-Haber-Lugin capillary with a reference electrode, 2-auxiliary electrode (cathode), 3-holder of the tested electrode, 4-sample (anode), 5- diaphragm made of sinter glass.

Figure 2: Potentiodynamic curves of the anodic polarization for Weldox 1300 steel obtained by the method of linear voltamperometry for various electrolytic solutions.

Figure 3: Chronoamperometric curves of the anodic polarization for Weldox 1300 steel in various electrolytic solutions.

Figure 4: Chronopotentiometric curves of the anodic polarization for Weldox 1300 steel in various electrolytic solutions.

Investigations were carried out on high-resistant microalloyed constructional Weldox steels, resulting from industrial smelting in the Swedish firm SSAB (Oxelösund). The chemical composition of the investigated steels is to be seen in Table 1. The material was supplied in the form of steel sheets, with a thickness of 20 mm (Weldox 900) and 10 mm (Weldox 1300). These sheets were sampled for anodic dissolution (Ø7 mm and Ø15 mm and the length 40 mm) and measurements of their hardness and for metallographic investigations. The hardness of steel Weldox 900 in the delivered state amounts to about 34 HRC, and that of Weldox 1300 to about 48 HRC. Metallographic observations have revealed in these steels a fine dispersive structure of tempered martensite with various morphologies.
Electrochemical investigations comprised the determination of the active potential of dissolution of the investigated steels in various chemical reagents (Table 2) and anodic dissolution both by means of the chronopotentiometric method (at a constant current) and the chronoamperometric method (at a constant potential. The dissolution of electrochemically active phases in a given electrolyte solution was controlled potentiostatically by keeping the given potential versus the reference electrode (saturated calomel electrode, SCE). For this purpose curves of anodic polarization I=f(E) were plotted determining the dependence of the rate of dissolution on the assumed potential, and the ranges of active dissolution and anodic passivation of the metal were found. The dependence permitted to determine the potentional, at which the ratio of the dissolution rate of the matrix versus the precipitation reaches the highest values.
The anodic polarization curves of the investigated steels were determined potentialdynamically making use of a glass electrolyzer (Fig. 1) and a PGP 201 potentiostat from the firm Radiometric Copenhagen which is a part of the system VoltaLab21 cooperating with the personal computer. The curves of anodic polarization determined for various solutions are to be seen in Fig. 2. Chronoamperometric and chronopotentiometric curves of the anodic dissolution of Weldox 1300 steel in the investigated solutions have been presented in Figs. 3. and 4.
X-ray investigations of electrolytic extractions were run by means of an X-ray diffractometer type XRD 7, produced by Seifert-FPM, applying the radiation of an anode CoKalpha and a Fe - filter. Electrolytic extractions, deposited on a filter paper were analyzed within the range of angles 2theta from 1 deg 2theta. The step-scanning method was used at a step value of 0.1 deg 2heta and a time of measurements amounting to 7 seconds in one measurement position. The obtained diffraction patterns were analyzed applying the program Diffract AT Search/Match.

Reference: W. Ozgowicz, A. Kurc, G. Nawrat, Identification of precipitations in anodically dissolved high-strength microalloyed Weldox steels, Archives of Materials Science and Engineering, Volume 31, Issue 2, June 2008, pp. 96-97.

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