Chromium is the most widely used and most commonly used alloy element.
Chromium has a strong affinity for nitrogen, oxygen, carbon and other elements.
In the smelting process, the control of chromium is particularly critical, mainly including the following aspects.
1. Reduce the oxidation loss of chromium
Oxidation is the main form of loss of chromium during the smelting process.
After oxidation, chromium enters the slag layer in the form of Cr2O3.
The oxidation of chromium mainly occurs during the melting period. The chromium-containing charge is heated to high temperature and combines with oxygen to form chromium oxide. At the same time, chromium in the molten pool will also be oxidized.
Therefore, the formation of covering slag early in the melting period is an important measure to reduce chromium oxidation.
If the amount of chromium added is small, the molten steel can be added in the middle and late stages of melting or after pre-deoxidation of the melt, which can also reduce the oxidation loss of chromium.
2. Implement single slag smelting to reduce chromium oxide in the slag
Before charging, add sufficient bottom slag, and then add chromium-containing charge, etc.
After melting, the temperature is raised to adjust the fluidity of the slag.
Use aluminum powder or calcium silicate powder to reduce Cr2O3 in the slag until the green color of the slag is almost gone.
3. Reduce chromium’s absorption of nitrogen from the atmosphere
When smelting ferritic chromium stainless steel, the molten steel should be prevented from absorbing nitrogen from the atmosphere to form Cr2N, which will cause the steel to embrittle.
Nitrogen absorption in chromium-containing liquid steel can be reduced by the following operations.
a. Create a good covering slag layer, isolate the chromium-containing molten pool from contact with the atmosphere, and reduce the amount of nitrogen absorbed by the molten steel.
b. Add the chromium-containing charge during the middle and late stages of melting to reduce the time of contact with the atmosphere.
4. Chromium addition form and recovery rate
Adding method: Chromium is added in the form of metallic chromium, ferrochromium, and chromium-containing return materials. And it can be added during charging or melting. Vacuum microcarbon ferrochrome should be added to the molten steel in batches to reduce nitrogen absorption.
Recovery rate: When smelting new materials, the recovery rate of chromium can reach 92% to 98%, and the higher the chromium content, the higher the recovery rate. When using returned materials for smelting, the chromium recovery rate is 92% to 96%.
