INTRODUCTION

Contamination of welds and deposited metal with non-metallic inclusions is predetermined, ceteris paribus, by the viscosity and oxidation of the slag system. Moreover, the mechanical properties of the weld are predetermined by the presence of nonmetallic inclusions of both endogenous and exogenous types [1, 2].

To reduce the cost of production and manufacturing of welding and surfacing materials, as well as to reduce the level of pollution from non-metallic inclusions, lighter-melting slag systems have recently been used, including those with the use of technogenic waste from metallurgical production, [3–18].

Previously, various compositions of welding fluxes using ladle electric steel slag were studied in [19–21]: the chemical composition of the samples was studied, wear tests were carried out, and the quantitative composition of non-metallic inclusions was investigated.

The objective of this work is to conduct studies of the dependence of the mechanical properties of the weld on oxygen concentration.

RESEARCH METHODS

The chemical composition of the studied welded samples was determined according to GOST 10543–98 by the X-ray fluorescence method on the XRF-1800 spectrometer and the atomic emission method on the DFS-71 spectrometer. Metallographic studies were carried out according to GOST 1778–70 on microsections without etching using an OLYMPUS GX-51 optical microscope at a magnification of 100. Fractional gas analysis was performed using a LECO TS-600 analyzer. The study of welded samples for impact strength (KCV) at positive and negative temperatures was carried out using a pendulum hammer according to GOST 9454–78.

RESULTS AND COMPREHENSIVE REVIEW

In the present work, further studies of welding and surfacing fluxes containing ladle slag of electric steel production of rail steel of EVRAZ—West Siberian Smelter JSC (EVRAZ ZSMK JSC) were carried out. Based on the results of previous studies [19–21], the best samples of welding flux were selected to study the toughness and total oxygen content in the weld metal. For the manufacture of welding flux, components of the following chemical composition were used:

—ladle slag of electric steel production of rail steel of EVRAZ ZSMK JSC, % (by weight): 1.31 FeO, 0.22 MnO, 36.19 CaO, 36.26 SiO2, 6.17 Al2O3, 11.30 MgO, 0.28 Na2O, 0 K2O, 3.34 F, <0.12 C, 1.26 S, 0.02 P;

—barium-strontium modifier BSK according to TU 1717-001-75073896 – 2005 manufactured by NPK Metallotekhnoprom LLC, % (by weight): 13.0–19.0 BaO, 3.5–7.5 SrO, 17.5–25.5 CaO, 19.8–29.8 SiO2, 0.7–1.1 MgO, 2.5–3.5 K2O, 1.0–2.0 Na2O, 1.5–6.5 Fe2O3, 0–0.4 MnO, 1.9–3.9 Al2O3, 0.7–1.1 TiO2, 16.0–20.0 CO2;

—silicomanganese slag produced by the West Siberian steel plant, % (by weight): 6.91–9.62 Al2O3, 22.85–31.70 CaO, 46.46–48.16 SiO2, 0.27–0.81 FeO, 6.48–7.92 MgO, 8.01–8.43 MnO, 0.28–0.76 F, 0.26–0.36 Na2O, up to 0.62 K2O, 0.15–0.17 S, 0.01 P;

—dust of electrofilters of aluminum production of OK RUSAL (carbon-containing additive), % (by weight): 21.00–46.23 Al2O3, 18–27 F, 8–15 Na2O, 0.4–6.0 K2O, 0.7–2.3 CaO, 0.50–2.48 SiO2, 2.10–3.27 Fe2O3, 12.5–30.2 Ctot, 0.07–0.90 MnO, 0.06–0.90 MgO, 0.09–0.19 S, 0.10–0.18 P.

The composition of welding fluxes is presented in Table 1.

Table 1.   Composition of welding fluxes
Full size table

The manufacturing scheme of welding flux and flux additives is described in earlier studies [19–21]. Welding under fluxes was carried out end-to-end without beveling edges on both sides on samples of size 500 × 75 mm, thickness 16 mm, made of sheet steel of 09G2S grade. The process was carried out by the Sv-08GA wire with diameter of 4 mm using the ASAW1250 welding tractor. Welding mode: current strength (Isv) 680 A, voltage (Ud) 28 V, welding speed (Vsv) 28 m/h.

After welding the samples, the chemical compositions of welding fluxes (Table 2), slag crusts (Table 3), and welded samples (Table 4) were determined.

Table 2.   Chemical composition of the studied fluxes
Full size table
Table 3.   Chemical composition of slag crusts
Full size table
Table 4.   Chemical composition of welded samples
Full size table

Samples were cut from welded samples to study non-metallic inclusions, to determine the oxygen content in the weld metal and to determine the impact strength (KCV) at positive and negative temperatures. Metallographic studies were performed using the OLYMPUS GX-51 optical microscope on microsections without etching at a magnification of 100 (Fig. 1).

Fig. 1. 
figure 1

Non-metallic  inclusions  in  zone  of  welded  samples  1–5  (a–e).

Full size image

Assessment of non-metallic inclusions was carried out according to GOST 1778–70, with results shown in Table 5. Studies of the total oxygen and surface oxygen content were carried out using the LECO ТС–600 analyzer (Table 6, Fig. 2).

Table 5.   Non-metallic inclusions in the welds’ metal
Full size table
Table 6.   Content of oxygen and compounds in welds
Full size table
Fig. 2. 
figure 2

Oxygen content in welds: —1; —2; —3; —4; —5.

Full size image

With the introduction of various flux additives in the ladle electric steel slag, the oxygen concentration in the welds decreases.

The results of studies of impact strength (KCV) at positive and negative temperatures are presented below and in Fig. 3.

Sample

Impact strength, J/cm2

KCV+20°C

KCV–20°C

0

49.0

16.3

1

65.7

27.3

2

65.7

27.0

3

65.7

29.3

4

74.3

27.7

Fig. 3.
figure 3

Change in toughness and total oxygen content in a weld: (1 and 2) change and linear change in impact strength (KCV) at t = 20° C; (3 and 4) change and linear change in the content of total oxygen; (5 and 6) change and linear change in impact strength (KCV) at t = –20° C.

Full size image

In the study of the toughness of welded samples, it was found that with the use of various flux additives, toughness increases at positive and negative temperatures.

CONCLUSIONS

Studies conducted have shown the suitability of using ladle electric steel slag for welding and surfacing of alloyed metal. Moreover, the introduction of various flux additives reduces the concentration of total oxygen in the welds, which, in turn, increases the toughness at positive and negative temperatures. It has been determined that the best, from the point of view of oxygen concentration in the weld metal and impact strength, is the use of silica-manganese slag and a carbon-fluorine additive as flux additives.