Quality Control Techniques in Ductile Iron Casting Production Using Medium-Frequency Furnaces

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This article presents optimized quality control strategies for producing ductile iron casting rollers through medium-frequency induction furnace processes. Key improvements focus on metallurgical control, process parameter optimization, and defect mitigation in large-diameter industrial rollers.

1. Chemical Composition Design

The chemical composition significantly impacts graphite nodularization and matrix structure. For rollers exceeding 600mm diameter, the carbon equivalent (CE) should be maintained at:

$$ CE = C + \frac{1}{3}(Si + P) = 3.8\%-3.9\% $$

Typical composition control ranges are shown in Table 1.

Table 1. Chemical Composition Control of Ductile Iron Rollers
Layer C Si Mn P S Ni Cr Mo V Mg
Outer 2.6-2.7 0.45-0.55 0.85-0.95 ≤0.05 ≤0.02 1.25-1.35 17.7-17.9 1.25-1.35 0.2-0.3 –
Core 3.0-3.3 2.0-2.2 0.4-0.6 ≤0.08 ≤0.03 0.3-0.5 ≤0.25 – – ≥0.04

2. Process Parameter Optimization

The temperature control model follows the Arrhenius equation for reaction kinetics:

$$ k = A \cdot e^{-\frac{E_a}{RT}} $$

Where:

  • k = Reaction rate constant
  • A = Pre-exponential factor
  • Ea = Activation energy (250 kJ/mol for SiO2 reduction)
  • R = Universal gas constant
  • T = Absolute temperature (K)

Key process parameters include:

Table 2. Critical Process Parameters
Melt Charge Ratio 25-35% Pig Iron + 55-65% Returns + 5-15% Steel Scrap
Pouring Temperature 1,360-1,380°C
Holding Time ≤15min post-treatment
Cooling Rate 20-25°C/hr through 650-450°C range

3. Nodularization and Inoculation

The magnesium recovery rate during treatment follows:

$$ Mg_{rec} = \frac{Mg_{final} – Mg_{initial}}{Mg_{added}} \times 100\% $$

Typical treatment materials include:

  • NiMg alloy (5kg/t)
  • RESiFe (10kg/t)
  • SiZr composite (3kg/t)

4. Quality Improvement Results

Process optimization achieved significant improvements:

Table 3. Quality Improvement Metrics
Parameter Pre-Optimization Post-Optimization
Nodularity 70% 95%
Tensile Strength 400 MPa 520 MPa
Hardness (HSD) 70-72 76-78
Service Life 3,000-4,000t 3,200-4,800t

5. Defect Control Mechanism

The shrinkage porosity index (SPI) can be calculated as:

$$ SPI = \frac{C + Si}{3} – \frac{Mn + Cr + Mo}{5} $$

Maintaining SPI between 0.8-1.2 ensures proper feeding characteristics in ductile iron casting.

6. Economic Considerations

The cost-benefit ratio (CBR) for process improvements is:

$$ CBR = \frac{\Delta L \cdot P – C_{imp}}{C_{imp}} $$

Where:

  • ΔL = Service life improvement (1,200t)
  • P = Value per ton throughput ($50/t)
  • Cimp = Implementation cost ($15,000)

These quality control techniques demonstrate that optimized ductile iron casting processes can significantly enhance mechanical properties and service performance while maintaining economic viability. Proper implementation of metallurgical controls, precise temperature management, and systematic process optimization are critical for producing high-performance industrial rollers.

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