1. Electric Arc Furnace (EAF) or Basic Oxygen Furnace (BOF) Steelmaking with Secondary Refining
Process Requirements:
Low-impurity steelmaking:
Sulfur (S) ≤ 0.025% – Achieved via desulfurization (CaO injection).
Phosphorus (P) ≤ 0.025% – Controlled through slag refining.
Microalloying:
Niobium (Nb), Vanadium (V), Titanium (Ti) additions for grain refinement.
Boron (B) in trace amounts for hardenability control.
Secondary refining:
Ladle furnace (LF) treatment for precise chemistry adjustment.
Vacuum degassing (RH or VD) to reduce hydrogen content (<2 ppm).
ABS Compliance:
Chemical composition must meet ABS Grade E limits (C ≤ 0.18%, CEV ≤ 0.43).
2. Continuous Casting with Electromagnetic Stirring (EMS) for Homogeneity
Process Requirements:
Electromagnetic stirring (EMS) in the mold and secondary cooling zone to:
Reduce centerline segregation of alloying elements.
Minimize internal cracks and porosity.
Controlled casting speed:
1.0–1.4 m/min for slabs (200–300mm thickness).
Soft reduction technology:
Applied at the final solidification stage to eliminate shrinkage cavities.
ABS Compliance:
Macro-etch testing (ASTM E381) required to verify internal soundness.
3. Thermo-Mechanical Controlled Rolling (TMCP) for Grain Refinement
Process Requirements:
Two-stage rolling:
Roughing stage (1050–1100°C): Breaks down cast structure.
Finishing stage (800–880°C): Recrystallization-controlled rolling.
Accelerated cooling (ADCOS® or similar):
Water cooling rate: 10–25°C/s to achieve fine bainitic/martensitic microstructure.
Coiling temperature control:
500–600°C for optimal toughness.
ABS Compliance:
Charpy impact testing (-40°C) must exceed 34J.
4. Heat Treatment (Normalizing or Quenching & Tempering for Thick Plates)
Process Requirements (for plates >40mm):
Normalizing:
Heating to 900–950°C, air cooling for uniform grain structure.
Quenching & tempering (Q&T):
Water quenching (880–920°C) → Tempering (580–650°C).
Online heat treatment monitoring:
Infrared thermography for temperature uniformity (±15°C tolerance).
ABS Compliance:
Hardness testing (HV10 ≤ 350) required after tempering.
5. Final Inspection & Non-Destructive Testing (NDT) per ABS Rules
Process Requirements:
Ultrasonic testing (UT):
100% automated scanning for plates ≥15mm (per ABS Ch.2, Sec.3).
Mechanical testing:
Tensile, Charpy impact, bend tests per heat/batch.
Surface quality checks:
Visual inspection (VT), magnetic particle testing (MT) for defects.
ABS Compliance:
Mill certificate must include:
Chemical composition, mechanical properties, NDT reports.
