Reduction of Tungsten from Its Oxide in Surfacing by Means of Powder-Core Wire

The influence of introducing tungsten and tungsten concentrate in powder-core wire on the structure, microhardness of the structural components, hardness, and wear of the applied metal layer is studied. For surfacing, tungsten-bearing powder wire (types H and E in the IIW classification) is produced in the laboratory. The fillers employed are KR-1 silicon powder (State Standard GOST 2169–69); MR-0 manganese powder (State Standard GOST 6008–82); PKhA-1M chromium powder (Technical Specifications TU 14-1-1474–75); VEL-1 vanadium (Technical Specifications TU 48-0533–71); PNK-1L5 nickel (State Standard GOST 9722–97); PAP-1 aluminum (State Standard GOST 5494–95); PVT tungsten (Technical Specifications TU 48-19-72–92); and PZhV-1 iron powder (State Standard GOST 0489–96). In some wire, tungsten powder is replaced by KSh-4 tungsten concentrate (State Standard GOST 213–83), produced by OAO GK AIR. The carbon-bearing reducing agent employed is gas-purification dust from aluminum production. Its composition is as follows: 21.00–43.27 wt % Al₂O₃, 18–27 wt % F, 8–13 wt % Na₂O, 0.4–6.0 wt % K₂O, 0.7–2.1 wt % CaO, 0.50–2.48 wt % SiO₂, 2.1–2.3 wt % Fe₂O₃; 12.5–28.2 wt % C_tot; 0.03–0.90 wt % MnO, 0.04–0.90 wt % MgO, 0.09–0.46 wt % S, and 0.10–0.18 wt % P. The wire (diameter 5 mm) is produced on laboratory equipment. An ASAW 1250 system is used for surfacing, in the following conditions: I_s = 400–450 A; U_arc = 32–36 V; V_s = 24–30 m/h. In surfacing, five metal layers are applied, under a layer of AN-26S flux and flux based on slag from silicomanganese production. The chemical composition of the applied metal is determined, and metallographic data are obtained: the size of the former austenite grain, the size of the martensite needles, and the content of nonmetallic inclusions are determined. Wear tests are conducted, and the hardness and microhardness are measured. The use of tungsten concentrate instead of tungsten powder in surfacing is shown to be possible in principle. The degree of tungsten extraction is calculated. For type-H wire, the replacement of tungsten powder by tungsten concentrate does not increase the content of nonmetallic inclusions in the metal layers applied; the primary austenite grain size is decreased. For type-E wire, the use of tungsten concentrate tends to decrease the primary austenite grain size and the size of the martensite needles and also increases the microhardness of martensite within the applied layer. The replacement of tungsten powder by tungsten concentrate in class-H wire considerably increases the hardness and wear resistance of the applied layer.