DEVELOPMENT AND INVESTIGATION OF CERAMIC FLUXES FOR HIGH-HARDNESS WEAR-RESISTANT SURFACING NOT REQUIRING HEAT TREATMENT

Yu. A. Evtyushkin

(Submitted by the scientific seminar of the Department of Equipment and Technology of Welding Production)

The properties of deposited metal are determined mainly by its chemical composition and heat treatment. The chemical composition of the deposited metal is varied within the required limits by introducing various alloying elements. The cheapest and most accessible of these are carbon, manganese, silicon, chromium, and titanium. They make it possible to obtain a definite set of mechanical properties and wear resistance of the metal under abrasion.

To obtain the required chemical composition of the deposited metal, alloying through the filler wire, flux, and base metal is used.

The chemical composition of the deposited metal can be selected using structural diagrams (Fig. 1). Then, with the aid of recovery coefficients, the chemical composition of the electrode wire and flux is calculated. In the present case we use a ceramic flux, since it has a greater alloying capacity than a fused flux.

The recovery coefficient of an alloying element may be represented by the following expression:

\[ X_{\text{rec. el.}} = \frac{[\mathrm{E}]_{\text{w}}} {\alpha[\mathrm{E}]_{\text{b.m.}} + (1-\alpha-\gamma)[\mathrm{E}]_{\text{e.w.}} + \gamma[\mathrm{E}]_{\phi}}, \]

where

\[ X_{\text{rec. el.}} \]
— the total recovery coefficient of the element;

\[ [\mathrm{E}]_{\text{w}} \]
— the amount of the element in the deposited metal;

\[ [\mathrm{E}]_{\text{b.m.}}, [\mathrm{E}]_{\text{e.w.}}, [\mathrm{E}]_{\phi} \]
— the amount of this element, respectively, in the base metal, the electrode wire, and the metallic addition to the ceramic flux;

\[ \alpha,\ (1-\alpha),\ \gamma \]
— the fractions participating in the formation of the weld metal, respectively, of the base metal, the electrode wire, and the metallic addition in the flux.

The total fractional participation of all constituents of the weld metal is equal to unity. In this case the fraction of base metal in the first layer of surfacing \((\alpha)\), depending on the surfacing conditions, is \(0.2 \div 0.3\).

According to the experiments of K. V. Lyubarskii [1], the participation share of the metallic addition of the flux in the weld composition \((\gamma)\) is determined by its amount in the flux. The dependence of \((\gamma)\) on the total content of the metallic addition in the flux is evident from the graph (Fig. 2). From the graph it is seen that this dependence can be expressed by the formula

Fig. 1. Structural diagram

Visible labels in Fig. 1: vertical axis, “Chromium content, %”; horizontal axis, “Carbon content, %”; “carbide-formation boundary”; phase-field labels include \(M\), \(M'\), \(M+M'\), \(M+M'+\Phi\), \(\Phi+M'\), \(\Phi+P+M'\), \(\Phi+P+M\), \(P+M+M'\), \(P\), \(\Phi+P+M'\), \(\Phi+P\).

Fig. 2. Graph of the dependence of the value \(\gamma\) on the total content of metallic addition in the flux

Visible labels in Fig. 2: vertical axis, \(\gamma\); horizontal axis, “metallic addition in flux,” \(\%\).

\[ \gamma = K(\% \cdot Me) \simeq 0.3(\%\,Me), \]

where

\(Me\) is the content of the metallic addition in the flux.

Example of calculating ceramic fluxes.

According to the requirement imposed on the deposited metal by service conditions, its hardness must be \(45 \div 50\) HRC. This hardness is provided by a ferrite-carbide mixture in the form of troostite. According to the diagram, this structure can be obtained in steel with a carbon content of \(0.2\%\) and chromium content of \(4\%\).

To ensure the chemical composition of the deposited metal, we calculate the chemical composition of the ceramic flux. The coefficient of transfer of chromium from a ceramic flux on a calcium-fluoride base is \(0.85\), and for carbon \(0.46\) [2]. Since alloying is carried out by the flux, the calculation formula takes the form:

\[ X_{\text{ass., el.}}=\frac{[\mathrm{E}]_{\mathrm{w}}}{\gamma \cdot [\mathrm{E}]_{\partial}}. \]

We determine the value of the coefficient from the graph (Fig. 2) for \(25\%\) metallic addition in the flux

\[ \gamma = 0.7. \]

We find the required chromium content in the metallic addition.

\[ [\mathrm{E}]_{\partial}=\frac{[\mathrm{E}]_{\mathrm{w}}}{\gamma \cdot X_{\text{ass., el.}}}, \]

then

\[ [\mathrm{E}]_{\partial.\mathrm{Cr}}=\frac{4\%}{0.7\cdot 0.85}=6.6\%. \]

The required content of ferrochrome in the flux, if it contains \(56\%\) chromium, is equal to \(12\%\).

To determine the chemical composition of the flux, a series of ceramic fluxes was prepared. The most suitable proved to be a flux of the following composition:

When alloying the deposited metal with Sv-10Kh5M wire, the following flux was used:

The results of the experiments are as follows. For fluxes No. 1 and No. 2.

Fig. 3, 4. Curves of hardness variation of the deposited and base metals

Fig. 5. Microstructure of the deposited metal under flux No. 1

Fig. 6. Microstructure of the deposited metal under flux No. 2

The change in hardness is shown in Figs. 3, 4. The microstructure of the deposited metal under these fluxes is shown respectively in Figs. 5, 6 and is a mixture consisting of pearlite with sorbite, pearlite with troostite, and bainite.

Conclusions

1. The presented method for calculating fluxes makes it possible to obtain the chemical composition of the deposited metal with sufficient accuracy.

2. Flux No. 1 makes it possible to perform wear-resistant surfacing with ordinary welding wire when alloyed electrode wire is unavailable.

3. Flux No. 2 is a protective flux; therefore, wear-resistant surfacing can be performed only with alloyed electrode wire.

4. Final conclusions can be obtained after production tests.

References

1. K. V. Lyubavskii. Metallurgy of Welding Steels by Surfacing. 1961.

2. G. L. Petrov, A. S. Tumarev. Theory of Welding Processes. Moscow, 1967.