The absorption rate of recarburizers is influenced by a complex "process system," and optimization needs to start from these aspects and their interactions.
The following are systematic process optimization measures to improve the absorption rate of recarburizers: Optimization of smelting operation process (key)
This is the most crucial and effective aspect for improving the absorption rate.
1. Correct timing of addition ("in-furnace method" is superior to "in-ladle method")
Preferred method: Bottom addition. Before charging, add most of the required recarburizer (approximately 60%-80%) to the bottom of the furnace, covering it with metallic charge (such as pig iron or scrap steel). This avoids direct contact between the recarburizer and the furnace wall, while simultaneously allowing it to be washed and soaked by the high-temperature molten iron, creating the longest dissolution and diffusion time, resulting in the highest and most stable absorption rate.
Secondary method: Mid-process addition. During the smelting process, after some of the iron has melted to form a molten pool, add the remaining recarburizer to the molten pool. At this stage, the molten iron temperature is still relatively low (approximately 1350-1400℃), allowing the recarburizer to be quickly submerged, reducing oxidation and burn-off.
Avoid: Surface application. Directly applying the recarburizer to the surface of the high-temperature molten iron will cause it to burn violently, producing a large amount of smoke and resulting in extremely low absorption (possibly below 50%).
Avoid adding it into the ladle: Adding it during tapping results in large fluctuations in absorption rate and can easily cause temperature drops and uneven composition.
2. Scientific Batching and Calculation. Accurately calculate the amount to be added based on the target carbon content and expected absorption rate (usually estimated at 90%-95% for in-furnace addition). Avoid excessive addition leading to saturation precipitation.
Control the ratio of pig iron to scrap steel, especially ensuring the original carbon content of the scrap steel is clear.
3. Sufficient Stirring. The electromagnetic stirring of the medium-frequency electric furnace itself is sufficient. However, ensure moderate stirring intensity to promote uniform composition and recarburizer dissolution without causing excessive surface turbulence that could expose and oxidize the recarburizer.
For unstirred induction furnaces or the pouring method, appropriate manual stirring is required.
4.Temperature and Time Control
Suitable Melting Temperature: Recarburizers dissolve best within the range of 1450℃ - 1550℃. Too low a temperature results in slow dissolution; too high a temperature (e.g., exceeding 1550℃), while dissolving quickly, exacerbates recarburizer burn-off and iron oxidation, potentially reducing net absorption and increasing energy consumption.
Necessary Holding Time: After adding the recarburizer, a certain holding time (usually 5-10 minutes) is needed for complete dissolution and diffusion. Too short a time results in incomplete carbon dissolution; too long a time is uneconomical and may cause element burn-off.
Summary and Best Practice Recommendations
To systematically improve recarburizer absorption, the following comprehensive measures are recommended:
Procurement Control:** Select granular recarburizers with fixed high carbon content, low sulfur content, and graphitization treatment.
Process Lock-in:** Mandate the use of the "bottom-feeding method," which is the most effective and economical step in improving absorption.
Process Control: Accurately calculate the amount of recarburizer added.
Control the charging sequence: bottom recarburizer → middle layer light/small material → top layer large material.
Control the melting temperature within a reasonable range (e.g., around 1500℃) and ensure sufficient holding time.
Data Monitoring: Record the amount of recarburizer added and the carbon content at the furnace outlet for each furnace, and calculate the actual absorption rate. Through long-term data analysis, find the process parameters most suitable for the company's equipment and raw materials.
Through the above systematic optimization, the absorption rate of recarburizer can typically be stably increased to 90%-95% or even higher, thereby achieving significant cost reduction and efficiency improvement.
