In ferrous metallurgy, there is often a need for express analysis of carbon content in liquid melt. Thermal analysis allows determining the carbon content directly at the melting site without the help of a chemical laboratory. This method is fast and economical.

How does thermal analysis work? This method is based on the analysis of the dynamics of temperature change of a cooling melt. In particular, to determine the carbon content, it is necessary to register the liquidus and solidus temperatures of the melt. The liquidus temperature is the temperature at which the appearance of the solid phase begins in the absolutely liquid phase (the crystallization process begins), and the solidus temperature is the temperature at which the liquid phase completely turns into a solid (the crystallization process ends). The liquidus and solidus temperatures, in particular, directly depend on the carbon content in the melt, i.e., in other words, a certain carbon content corresponds to a certain liquidus and solidus temperature. Knowing the liquidus and solidus temperatures (as well as other critical points), you can determine the carbon content.

So, how do you determine the liquidus and solidus temperatures when the liquid melt cools? During the cooling process, the melt gradually approaches the liquidus point. As soon as it reaches this temperature, the crystallization process begins in the melt, which is accompanied by the release of heat. As a result, the cooling rate of the melt decreases. When this sign appears, the liquidus temperature is recorded. As soon as the crystallization process ends, the heat release as a result of this process stops, and the cooling rate of the melt increases. When the speed increases, the solidus temperature is recorded. Thus, by analyzing the cooling dynamics of the melt, it is possible to obtain reliable results on the liquidus and solidus temperature values. And based on the values of these temperatures, it is possible to draw a conclusion about the contents of the melt.

What tools are needed to conduct an express analysis of the carbon content in the melt using the thermal analysis method? Currently, the following set of tools is used in the metallurgical industry:

- secondary instrument;
- crystallization cups or immersion probes;
- stand for installing cups or a rod for immersion probes;
- compensation cable.

Let's consider the application of this complex in more detail. In order to be able to analyze the dynamics of melt crystallization, it is first necessary to select a portion of this melt from the industrial unit in which the melting is taking place. In modern metallurgy, two options have become widespread:

1. Taking the melt with a ladle, which is then poured into a crystallization cup;

2. Immersing a probe into the melt, into which liquid metal flows, followed by extraction.

Both the cup and the immersion probe use a thermocouple (type B, S, or R) to continuously measure the temperature of the cooling melt. The thermocouple is a thin wire of two junctions, placed in a U-shaped quartz glass, the ends of which are welded to a connector for connection.

If a crystallization cup is used, this cup is pre-installed on a stand, connecting it to a connector, which in turn is connected to a secondary instrument with compensation wires, which registers changes in the EMF generated by the thermocouple when the melt cools, and with further analysis of the dynamics of the obtained data.

When using an immersion probe, a rod is used, onto which this probe is put on and connected to it using a contact block. In turn, the rod itself is connected to the secondary instrument using a compensation cable. This is where the difference from using these two options ends.

The workflow is as follows:

1. Metal sampling (into a cup or a probe);

2. Its cooling;

3. Registration of temperature change;

4. Analysis of the obtained dynamics;

5. Output of results (on the secondary instrument).

Our company manufactures both EVRAZKARB crystallization cups (analogous to Heraeus Electro-Nite's "Econ-O-Carb" cups for steel and "QuiK-Cup" cups for cast iron), as well as EVRAZKARB probes for determining carbon content in steel (analogous to Heraeus Electro-Nite's "QuiK-Carb" and "TapTip" probes).

Heraeus Electro-Nite instruments such as "Multi-Lab Quik-Lance", "Carbon-Lab E", and "Quik-Lab E" can be used as the secondary instrument."