Production of Steel Rails via Bloom Continuous Casting
Date: 2025/6/10
Category: Metallurgical encyclopedia terms
Views: 506
1. Advantages of Steel Rail Production via Bloom Continuous Casting
(1)Significant Improvement in Metal Yield: The metal yield of rail production via continuous casting blooms reaches 93%, an 11% increase compared to ingot casting (82%), with simultaneous reductions in process steps, energy consumption, and productivity gains.
(2)Enhanced Surface Quality: Continuously cast blooms reduce surface defects in rails by 55% versus ingot-rolled rails.
(3)Homogenized Internal Structure: Continuously cast blooms exhibit more uniform and dense microstructures, with 45% fewer inclusions and lighter segregation compared to ingot casting.
(4)Superior Mechanical Properties: Tests by the American Railway Association (ARA) confirm that continuously cast blooms produce rails with higher tensile strength, yield strength, elongation, and reduction of area than ingot-cast rails, albeit with slightly lower hardness.
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2.Control of Center Segregation in Continuous Casting Process of Rail Steel
（1）Optimization of Bloom Cross-Section:
Aspect ratio range: 1.15–1.45 (preferably ≥1.28). Increasing aspect ratio reduces thermal gradient and promotes equiaxed crystal growth.
Rolling reduction ratio must exceed 10 to concentrate center segregation in the rail web (avoiding head/foot) and eliminate micro-porosity.
（2）Electromagnetic Stirring (EMS):
Suppresses columnar crystal growth, increases equiaxed crystal ratio, and homogenizes segregated elements (e.g., C, Mn), effectively mitigating center segregation.
（3）Precision Superheat Control:
ΔT >25°C: Dominant columnar crystals with severe segregation.
ΔT <25°C: Expanded equiaxed zone with reduced segregation.
ΔT <10°C: Negligible segregation.
Recommended superheat for rail steel: 10–15°C.
（4）Final-Stage Soft Reduction：
Applies micro-compression at the solidification end to compensate shrinkage, blocking backflow of solute-rich liquid. Proven to significantly reduce segregation, shrinkage cavities, and cracks in high-carbon/alloy steels.
（5）Low Casting Speed Requirement：
Strict casting speed limit <6.0 m/min to prevent bulging and interfacial cracks (due to high carbon sensitivity and low high-temperature tensile strength).
（6） Controlled Cooling Intensity:
Cooling water flow rate limited to 0.2–0.5 L/kg to minimize thermal stress-induced internal cracks (critical for low thermal conductivity below 1000°C).
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3.Cleanliness Control in Continuous Casting Process of Rail Steel
(1)Control of Inclusions and Oxygen Content
Total oxygen content in steel must be controlled below 0.002% (20 ppm).
Inclusions should be spherical composite particles with sizes <13 μm. Avoid Al₂O₃ formation.
Key measures:
Implement proper deoxidation practices (e.g., Si-Mn deoxidation with calcium treatment).
Adopt full-process protective casting (argon shielding from ladle to mold).
Apply tundish metallurgy (weir-dam systems + ceramic filters).
(2)Control of Hydrogen Content
To prevent hydrogen-induced flakes (white spots):
Thoroughly bake metallurgical equipment and refractory materials (moisture <0.5%).
Perform vacuum degassing (e.g., RH or VD treatment) to reduce hydrogen to <0.00015% (1.5 ppm).
Enforce slow cooling of continuously cast blooms (rate <15°C/h below 600°C).
