Welcome to the world of automotive cast iron components, where strength, durability, and innovation converge. In the realm of automobiles, various types of cast iron parts have emerged to meet the ever-growing demands of the industry. From the classic gray cast iron cylinder body to the cutting-edge vermicular graphite cast iron and isothermally quenched ductile iron, each type plays a crucial role in enhancing performance and pushing the boundaries of automotive engineering.
Auto Casting Guide: 5 Types Of Cast Iron Parts
In this auto casting guide, we dive into the requirements and advancements of five key types of cast iron parts essential for automobiles. From the renowned gray cast iron that withstands high engine power to the resilient ductile iron used in crankshafts and axle housings, we explore the fascinating world of these materials. We also delve into the rising prominence of vermicular graphite cast iron and isothermally quenched ductile iron, which offer exceptional strength, weight reduction, and improved performance.
1. Gray Cast Iron
The representative gray cast iron component in automobiles is the cylinder body, which has a development direction of thin-walled high strength. There are two main ways to achieve this: one is the low-carbon equivalent process, which mainly improves the strength of gray cast iron by reducing its C and Si content. Its main advantages are: easy to achieve and high reliability by changing the burden after the furnace; Low cost with no or minimal use of alloy elements; The requirements for furnace pretreatment and operation are relatively loose. Its disadvantages are also obvious: low carbon equivalent, poor casting performance, easy to cause shrinkage (porosity) waste and increase casting stress; The processing performance and cross-sectional uniformity of castings are poor, and the thermal conductivity of castings is affected.
The second is high carbon equivalent and alloying process: mainly to maintain the C and Si content of gray cast iron at a high level; The casting performance is good, and the tendency to form shrinkage (porosity) waste is small; The processing performance and thermal conductivity of castings are good. The disadvantage is that a large amount of alloying elements are added, resulting in higher casting costs. Poor treatment may also affect the workability and leakage of the casting; The requirements for furnace pretreatment are relatively strict. With the increase of engine power, the performance requirements for gray cast iron have further improved. Some cylinder blocks of domestic and foreign engines have been manufactured using HT300 or even HT350. FAW Casting Company has steadily adopted HT300 to produce 6DL and Deutz engine cylinder blocks, while also reserving production technology for HT350. In order to meet the needs of high-speed cutting of car cylinder bodies, measures such as optimizing melting process, materials, and alloying technology have been taken to successfully solve the problems of high performance and high-speed cutting of cylinder body materials.
2. Ductile Iron Castings
The representative components of ductile iron in automobiles are crankshaft, camshaft, middle and rear axle housing, various brackets, housings, and other components. At present, the development of as cast high-strength pearlite matrix ductile iron (QT700-2, QT800-2, QT800-5) and as cast high toughness ferrite ductile iron (QT400-18, QT400-15, QT600-10) is being carried out. Mainly obtained by optimizing the smelting process, strictly controlling the S, P content and trace element content in the original molten iron, selecting suitable spheroidizing agents, inoculants, alloy elements and addition methods, and strictly following the flow inoculation process.
3. Vermicular Graphite Cast Iron
Vermicular graphite cast iron has been widely used in automotive castings such as exhaust pipes and high horsepower engine cylinder heads. Using vermicular graphite cast iron to manufacture medium and high-power engine cylinder heads can reduce the weight of the cylinder head through design, and also improve the performance of the cylinder head and increase the power of the engine. At present, the application of vermicular graphite cast iron in high-power engine cylinder blocks is increasing, which can reduce thin-walled thickness, eliminate reinforcing ribs, and reduce weight by about 25%. It has been successfully applied in high-power engine cylinder blocks of foreign companies such as Ford and Audi, and there are also reports of successful applications in domestic FAW and Jinan Heavy Duty Truck. The application of vermicular graphite cast iron is mainly limited by the difficulty of stable control in its production process.
SinterCast is a Swedish joint-stock company specializing in research and production equipment manufacturing of vermicular graphite cast iron technology. Its products (SinterCast vermicular iron production control system) are applied in three continents (America, Europe, and Asia) around the world, providing technical support for vermicular graphite cast iron production to 8 of the world’s 10 largest automobile manufacturers. Approximately 20000 cylinder or cylinder head products worldwide are manufactured using vermicular graphite cast iron every month. SinterCast claims that over 95% of the world’s vermicular graphite cast iron products are produced by its control systems.
4. Isothermally Quenched Ductile Iron
Isothermally quenched ductile iron (ADI) Isothermally quenched ductile iron has comprehensive mechanical properties of high strength, plasticity, and toughness, which can be generally divided into two categories: high-strength type with a strength of 1200-1600 N/mm2 and high-strength type with a elongation of about 10% with a strength of 900-1200 N/mm2. Due to its excellent material properties, ADI products have achieved rapid development in developed countries in Europe and America, and have been successfully applied in truck chassis, engines, and car crankshafts. In recent years, the application of ADI in small cars has been increasing in the European market, accounting for 32% of the entire ADI market. In the US market, heavy and light truck ADI components account for 51% of the total ADI market.
Dongfeng Automobile Co., Ltd. has developed a suspension system for military off-road vehicle chassis, with 17 suspension parts changed from cast steel to ADI. The total weight of this series of parts has been reduced from 630.62Kg to 380.66kg, with a weight reduction rate of 39.6%. The rear steel plate spring bracket of FAW Group’s heavy-duty vehicles, as well as the gear housing cover (claw) and gear housing of military vehicles, have been replaced with ADI. At present, heat treatment bases for isothermal quenching have been built in cities such as Changchun and Suzhou in China.
5. Development of Special Cast Iron
With the improvement of engine performance, the heat resistance requirements of some castings such as exhaust pipes are becoming increasingly high, and high silicon molybdenum ductile iron, medium silicon molybdenum vermicular iron, and high nickel ductile iron continue to appear. The joint venture of FAW Group has mass applied high silicon molybdenum ductile iron exhaust pipes to the Deutz engine, and some turbocharged engines of FAW Volkswagen have mass applied high nickel ductile iron exhaust pipes. In some domestic brand engines of FAW, these three types of cast iron have also begun to be applied.