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A Discussion on the Performance and Application Fields of Ductile Iron Automotive Components
Release time：
2025-11-07
Ductile cast iron achieves graphite spheroidization through magnesium/cerium alloy treatment,
A Discussion on the Performance and Application Fields of Ductile Iron Automotive Components
I. Material Properties: Performance Enhancement Achieved Through Graphite Spheroidization
Ductile cast iron achieves graphite spheroidization through magnesium/cerium alloy treatment, transforming the flaky graphite found in conventional cast iron into spherical structures measuring 0.05 to 0.3 mm in diameter. This remarkable microstructural change imparts the material with tensile strength ranging from 500 to 900 MPa, yield strength exceeding 400 MPa, and elongation between 10% and 25%, delivering overall performance comparable to that of medium-carbon alloy steels. Moreover, the spherical graphite particles act as "crack stoppers," effectively inhibiting crack propagation and enabling the material to exhibit exceptional toughness even under impact loading conditions.
In a typical application, QT800-5 grade ductile iron achieves a 30% cost reduction in automotive chassis brackets while still meeting the stringent requirement of 1.2 million fatigue test cycles. Additionally, its density—10% lower than steel—enables a single-wheel hub to be reduced by 0.5 kg in weight. When paired with a crankshaft manufactured using the austempered ductile iron (ADI) process, this material delivers a 10% weight reduction compared to forged steel components, while also boosting fatigue strength by 20%.
II. Heat Treatment Processes: A Precision Approach to Performance Control
1. Austempered Ductile Iron (ADI) Process
By rapidly cooling the austenitized casting into the bainitic transformation range (250–400°C) and holding it there, a microstructure of carbide-free bainite plus retained austenite is formed. This process enables the material to achieve a tensile strength of 1200–1400 MPa, an impact toughness of 25–40 J/cm², and significantly enhances wear resistance—up to 3 times better than that of quenched and tempered steel. In the application of Yuchai's QT800-6 crankshaft, controlling the austenitizing temperature at 920°C ± 5°C and maintaining the isothermal holding time at 120 minutes successfully achieves a bending fatigue strength of 650 MPa, meeting the demanding requirements of heavy-duty engines.
2. Quenching and Tempering Process
By employing quenching at 860–880°C followed by tempering at 550–650°C, a tempered sorbite matrix is achieved. This process ensures that the camshaft surface reaches a hardness of HRC45–50, while maintaining a core toughness with an elongation of 15%. As a result, the component has successfully passed a 200,000-kilometer durability test in a 4-cylinder engine without any failures.
3. Special Surface Treatment
The fillet rolling process induces a plastic deformation layer of 0.2–0.3 mm on the crankshaft surface, which, combined with the phase transformation hardening of residual austenite in the ADI matrix, results in a surface hardness reaching HV600–700 and boosts fatigue strength by 40%. After this treatment, the bending fatigue life of a certain commercial vehicle crankshaft was significantly improved—from 10⁷ cycles to 5 × 10⁷ cycles.
III. Analysis of Typical Application Areas
1. Core Components of the Power System
- Crankshaft: ADI crankshafts already account for 35% of the passenger car market share. After a certain German-brand 2.0T engine adopted an ADI crankshaft, the overall engine weight was reduced by 8 kg, and fuel consumption dropped by 2%.
- Connecting Rods: Isothermal quenching connecting rods achieve a burst pressure resistance of 180 MPa in diesel engines, while reducing costs by 40% compared to forged steel products.
- Cylinder Head: The cylinder head, made of vermicular graphite cast iron with ductile iron bushings, achieves a 30% improvement in thermal conductivity and reduces thermal deformation by 0.02 mm in the V8 engine.
2. Key Components of the Chassis System
- Steering knuckle: A ductile iron steering knuckle achieves a weight reduction of 1.2 kg per unit in SUV models, and when combined with topology optimization design, stiffness is improved by 15%.
- Rear axle housing: The QT600-3 rear axle housing, used in heavy-duty trucks, has successfully passed a 1-million-cycle bench test and offers a 25% cost reduction compared to cast steel products.
- Dual-link rod: ADI dual-link rods achieve a 20% increase in modal frequency and significantly enhance NVH performance in the electric drive systems of new-energy vehicles.
3. Dedicated Application for New Energy
- Motor housing: The ductile iron motor housing achieves a 30% reduction in wall thickness through controlled cooling technology, while still meeting the IP67 protection rating.
- Battery tray: The QT700-2 battery tray absorbed up to 15 kJ of energy in crash tests, offering comparable weight to aluminum alloy products while reducing costs by 50%.
- Gearbox housing: The ADI housing reduces gear meshing noise by 5 dB(A) under high-speed operation at 8,000 rpm.
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