Cast Iron Materials for Automobile Engine Blocks

I. Current Usage Status of Pig Iron in Automobile Engine Blocks

(I) Influence of Pig Iron Elements on Engine Blocks

The proportion of elements in pig iron directly determines the performance of engine blocks. 

Carbon (C), the main component, ranges from 2.11% to 4.3%. When present as graphite, it enhances molten iron fluidity for casting complex structures, though excessive carbon reduces material strength.

Silicon (Si) promotes graphitization, reduces white - mouth tendency, and improves toughness/machinability while aiding heat dissipation. 

Manganese (Mn) neutralizes sulfur (forming MnS) to enhance strength and wear resistance. 

Harmful elements like sulfur (reducing fluidity and causing hot cracking) and phosphorus (brittleness) must be strictly controlled (typically ≤ 0.08%).

(II) Current Application of Gray Iron and Ductile Iron in Engine Blocks

Gray iron and ductile iron remain the dominant materials in engine block manufacturing. Gray iron, with excellent castability, machinability, and cost - efficiency, accounts for over 60% of mid - to low - end vehicle applications. 

Ductile iron, valued for higher strength and toughness, has seen its market share rise to ~30% in high - performance/large - horsepower engines and lightweight designs, with the remainder occupied by aluminum alloys.

II. Gray Iron for Engine Blocks

(I) Advantages

Excellent Castability: Molten gray iron flows readily to fill complex molds, minimizing casting defects and enabling precise formation of internal channels (e.g., water/oil passages).

Superior Machinability: Flake graphite acts as a natural lubricant during cutting, reducing tool wear and lowering machining costs by 15% - 20%.

Vibration Damping & Wear Resistance: Flake graphite absorbs operational vibrations, while its structure ensures long - term wear resistance, extending block service life to over 250,000 km.

Cost Efficiency: Mature production processes and abundant raw materials make gray iron blocks 15% - 20% cheaper than alternative materials.

Thermal Conductivity: High thermal conductivity (45 - 55 W/(m·K)) dissipates engine heat to maintain optimal operating temperatures.

(II) Disadvantages

1. Limited Mechanical Strength: Tensile strength (150 - 350 MPa) falls short of high - performance engines requiring resistance to 15 MPa 爆发 pressures and cyclic stresses.

   
   

2. High Density: Unsuitable for lightweight designs, as it increases vehicle weight and fuel consumption.

III. Ductile Iron for Engine Blocks

(I) Advantages

1. High Strength & Toughness: Spherical graphite minimizes matrix disruption, yielding tensile strength (400 - 900 MPa) and elongation (2% - 18%) ideal for high - load engines (e.g., performance SUVs).

2. Fatigue Resistance: Withstands cyclic stresses from frequent starts/stops, reducing fatigue crack risks during 1,000+ hour bench tests.

3. Lightweight Potential: Despite similar density to gray iron, high strength allows structural optimization for 10% weight reduction in EV range extenders.

4. Thermal Performance: Adequate thermal conductivity (35 - 45 W/(m·K)) supports engine heat management.

(II) Disadvantages

1. Higher Costs: Nodulization treatment (using Mg - based inoculants) and strict process control raise costs by 20% - 30% compared to gray iron.

2. Complex Casting: Nodulization decay requires pouring within 30 minutes, increasing defect rates and production complexity.

IV. Pig Iron vs. Aluminum: Which Is Better for Engine Blocks?

Aluminum alloys (1/3 the density of cast iron) excel in lightweight EV and fuel - efficient designs but lack hardness/wear resistance (requiring surface treatments) and lose strength at high temperatures. 

Conversely, pig iron dominates traditional engines due to its proven durability, cost - effectiveness, and heat resistance—critical for large - displacement/high - torque applications. Selection depends on engine performance, cost, and end - use requirements.

V. Tiegu’s Pig Iron Solutions for Engine Blocks

(I) Product Models & Specifications

• Gray Iron HT250: Tensile ≥ 250 MPa, HB 170 - 241, C: 3.2% - 3.6%, Si: 1.8% - 2.2% (suitable for mid - range vehicles).

• Ductile Iron QT500 - 7: Tensile ≥ 500 MPa, Elongation ≥ 7%, HB 170 - 230 (ideal for high - performance engines).
  All products meet strict impurity standards (S/P ≤ 0.08%).

(II) Application Cases

• A leading automaker uses HT250 for 3,000 tons/year of passenger car blocks, achieving <2% defect rates and 15% machining efficiency gains.

• A powertrain supplier employs QT500 - 7 for SUV blocks, passing 1,000 - hour high - pressure tests with no cracks/deformations.

VI. Conclusion