Hot-Rolled Steel Strip Production
Raw Materials and Heating Process
What are the critical quality inspection points for slabs before furnace entry?
Dimensional Tolerances: Verify thickness (±5mm) and width (±3mm) for rolling compatibility.
Surface Defects: Check for cracks, inclusions, and scabs to prevent defect propagation.
Material ID: Match slab identification with the production plan to avoid grade mixing.
Cleanliness: Remove rust and debris for uniform heating.
Curvature: Check for slab bending to prevent furnace jamming.
What does "three-stage heating" in the furnace refer to?
Preheating Section: Uses flue gas waste heat to bring slabs to 800-900°C.
Heating Section: Rapidly increases temperature to 1100-1200°C.
Soaking Section: Maintains temperature for 20-30 minutes to eliminate internal temperature differences.
What are the hazards of decarburization and how is it controlled?
Hazards: Reduces surface hardness and wear resistance, compromising mechanical properties.
Control: Keep oxygen content $\le 3\%$, maintain a reducing atmosphere ($CO_2/CO \approx 1$), and shorten high-temperature soaking time.
What are the advantages of oxygen-enriched combustion?
Thermal Efficiency: Increases furnace temperature by 50-100°C and shortens heating time by 15-20%.
Sustainability: Reduces fuel consumption (10-15%) and lowers $CO_2$ and $NO_x$ emissions.
What are the core functions of the rough rolling mill?
Reduces slab thickness from 200-300mm to 30-60mm.
Removes primary scale and adjusts width via the vertical roll mill (tolerance ±2mm).
Corrects external defects like camber and bending.
Why is "continuous rolling tension" critical in finish rolling?
Maintains stable strip travel to prevent deviation or “cobbles” (piling).
Reduces thickness fluctuations and suppresses vibration to protect the rolls.
How do work rolls and backup rolls interact?
- Work Rolls: Directly contact the strip; made of wear-resistant high-chromium alloy.
- Backup Rolls: Bear the rolling force; made of high-strength forged alloy steel.
- Ratio: Backup rolls are usually 3-4 times larger in diameter to minimize work roll deflection.
What is the Automatic Gauge Control (AGC) system?
time monitoring and dynamic roll gap adjustment, ensuring strip thickness tolerances stay within ±0.05mm.
What are the objectives of the laminar flow cooling system?
Microstructure Control: Precisely manages the cooling rate to optimize grain size.
Uniformity: Ensures even transverse cooling to prevent internal stress and warping.
Why use "fast cooling front, slow cooling rear" logic?
Front Section: Rapidly suppresses austenite grain growth.
Rear Section: Prevents martensite formation (brittleness) and balances internal stress.
How does coiling temperature affect performance?
Too High: Leads to coarse grains and decreased strength.
Too Low: Increases hardness and makes subsequent processing difficult.
Target: Low-carbon steel is typically coiled at 600-650°C.
How is "Tower-Shaped" coil defect prevented?
Maintain winding tension fluctuations $\le 5\%$.
Ensure lateral deviation $\le 2mm$ through the centering system.
Regularly inspect the mandrel for deformation.
How is "Oxide Scale Indentation" prevented?
Optimize high-pressure descaling (pressure $\ge 18MPa$).
Maintain descaling nozzle angles at 30-45°.
Control furnace temperature to keep scale thickness $\le 0.5mm$.
What are the maintenance keys for the hydraulic system?
Maintain oil levels above 2/3 and temperatures between 30-55°C.
Ensure filtration accuracy $\le 10\mu m$ and replace filters every 3 months.
Maintain oil cleanliness at NAS Level $\le 8$.
How can energy consumption be optimized?
Implement waste heat recovery for combustion air (15-20% fuel savings).
Use variable frequency motors for load-based speed adjustment.
Optimize the heating curve to reduce high-temperature holding time.
