Detailed Explanation of Steel Rail Steelmaking
Date: 2025/6/9
Category: Metallurgical encyclopedia terms
Views: 330
1. Hot Metal Desulfurization Pretreatment
Sulfur in steel negatively impacts rail mechanical performance, requiring hot metal pretreatment to control sulfur content. Research demonstrates that when sulfur content exceeds 0.02%, surface quality defects in continuous casting slabs double compared to levels below 0.019%. Therefore, sulfur must be maintained below 0.02%, and reduced to under 0.01% for high-performance steel grades. Hot metal desulfurization is an essential process for premium rail production, primarily utilizing the KR stirring method and injection method. Desulfurizing agents include calcium/magnesium-based materials such as calcium carbide (CaC₂), lime (CaO), and metallic magnesium (Mg).
Although phosphorus is also detrimental to steel (causing cold brittleness), approximately 80% can be removed during converter refining. Consequently, hot metal pretreatment in rail production focuses solely on sulfur removal, with no need for dephosphorization.
2.Basic Oxygen Steelmaking (BOS)
In China's steel rail production, combined top-bottom blowing converters (top oxygen injection + bottom argon stirring) are widely adopted. To ensure high-quality molten steel, the Basic Oxygen Steelmaking (BOS) process strictly controls five critical stages:
（1）Charging：Adjust scrap-to-hot metal ratio based on silicon content in hot metal.
（2）Slag Formation: Adjust limestone dosage to ensure proper alkalinity, with corrections from previous slag conditions, carbon content, and temperature.
（3）Blowing Phase:
Early Stage: Silicon/manganese oxidation and peak dephosphorization efficiency.
Mid-Stage: Slag optimization, accelerated decarbonization, and uniform temperature rise (avoiding splashing).
Final Stage: Adjust slag composition and prepare for tapping.
（4）Post-Blowing Treatment：Fine-tune tapping temperature (1,640–1,660°C) based on ladle condition and nozzle size.
（5）Tapping & Deoxidation：Full argon stirring during tapping; strict slag retention; aluminum-free deoxidation using Si-Ca-Ba as final deoxidizer.
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3.Secondary Refining
Steel rail refining typically employs LF refining furnaces and VD/RH degassing units.
The LF refining furnace utilizes slag washing principles, where solid synthetic slag is added to the ladle. Through arc heating and oxygen blowing agitation, it facilitates desulfurization, deoxidation, and composition adjustment of molten steel.
VD/RH degassing units apply vacuum conditions to remove gases (decarburization, deoxygenation, dehydrogenation) and phosphorus from molten steel, reducing oxygen and hydrogen content to (2-3)×10^-4%. With auxiliary argon blowing, phosphorus removal reactions, or extended vacuum deoxygenation, hydrogen levels can be further reduced to 1×10^-4%.
