Chapter 4 Raw Materials for Induction Melting

The raw materials used for steelmaking in an induction furnace include steel scrap, pure metals and ferroalloys, oxidizers and deoxidizers, carburizers and sulfurizing agents, and slag-forming materials.

Because an induction furnace has relatively limited refining ability and less operational flexibility, its requirements for raw materials are much stricter than those of an electric arc furnace. During induction furnace melting, the raw materials should meet the following requirements.

1. Accurate Chemical Composition

The chemical composition of raw materials must be accurate, because accurate composition is the basis for charge calculation.

All incoming raw materials should be sampled and analyzed according to the methods specified in the relevant standards. Even if the materials come with a certificate of conformity from the manufacturer, they still need to be analyzed. This is because manufacturers usually produce in large batches, and the sample may not fully represent the actual batch of raw materials received. In addition, analysis helps prevent possible errors.

Based on the analysis results, the materials should first be used on a trial basis. Only after confirming that there are no problems should they be put into large-scale use.

2. Clean, Free of Oil, and Low in Rust

Oil contamination and rust on furnace charge materials are sources of gases in molten steel, especially hydrogen.

The main component of iron rust is Fe2O3·2H2O. At high temperature, it undergoes the following reaction:

Fe2O3·2H2O = Fe2O3 + 2H2O↑

The water vapor above the molten steel surface then reacts with the molten steel as follows:

H2O(g) + [Fe] = H2(g) + [FeO]
H2(g) = 2[H]

As a result, the hydrogen content [H] in the molten steel increases. Similarly, moisture contained in slag materials or other raw materials can also cause similar reactions, increasing the hydrogen content in the molten steel.

Oil contamination is mainly composed of hydrocarbons. After burning and decomposition at high temperature, it can also generate hydrogen, which increases the [H] content in the molten steel.

Therefore, raw materials containing oil, rust, or moisture should be properly treated before use. Oil and moisture can be removed by baking. Rust can be removed by shot blasting or drum treatment.

3. Suitable Charge Size

To improve melting speed, suitable raw materials should be selected according to the furnace power frequency, especially the size of steel charge materials.

The relationship between power frequency and the optimal size of steel charge materials can be found in Table 1-1.