Ferrous Metal Die Casting
Ferrous metal die-casting is a die-casting process developed for ferrous materials such as steel and cast iron. This process transcends traditional die-casting’s reliance on low-melting-point metals. By utilizing specialized mold materials, high-temperature smelting, and high-pressure forming techniques, it enables the efficient and precise manufacture of ferrous metal parts. Due to the high melting point of ferrous metals (iron melts at 1538°C) and their poor fluidity, this process requires significantly more equipment and process than non-ferrous metal die-casting, representing both a technical challenge and a key development direction in the die-casting field.
The core challenge of ferrous metal die-casting lies in the selection and protection of mold materials, which must simultaneously meet the requirements of high-temperature resistance, wear resistance, and thermal shock resistance. Traditional hot-work die steels (such as H13) have extremely short service lives in ferrous metal die-casting (typically less than 500 cycles). Therefore, new materials are needed, such as powder metallurgy high-speed steel (such as ASP-60). These materials contain up to 2.3% carbon and over 20% total alloying elements such as tungsten, molybdenum, and vanadium. They achieve high-temperature hardness exceeding 50 HRC, extending their service life to 5,000-10,000 cycles. The mold surface requires a multi-layer coating: a nitride layer (5-10μm thick) for increased hardness, a TiAlN coating (3-5μm thick) for wear resistance, and an AlCrN coating (2-3μm thick) for oxidation resistance. This ensures the mold maintains stable performance even at temperatures exceeding 1,000°C. Furthermore, the mold cooling system must utilize a combination of forced water and air cooling, with a cooling rate of 50°C/s, to prevent overheating and softening of the cavity.
The melting and filling processes for ferrous metal die-casting are unique. The melting stage requires a vacuum induction furnace to melt iron, carbon, and alloying elements (such as chromium, nickel, and manganese) in a vacuum environment (≤1Pa) to prevent oxidation. The carbon content is controlled at 2.7%-3.8% (gray cast iron) or 3.2%-3.6% (ductile iron) to ensure fluidity. The molten metal temperature must be precisely controlled between 1400°C and 1550°C. Excessively high temperatures can increase mold wear, while excessively low temperatures can lead to insufficient filling. The filling stage utilizes a two-stage injection molding process: the first stage, at a speed of 1-3 m/s, steadily pushes the molten metal into the sprue; the second stage, at a speed of 5-8 m/s, fills the mold cavity under high pressure (150-250 MPa). This specific injection pressure is two to three times that of aluminum alloy die-casting. Since ferrous metals solidify quickly (solidification time is only 1/3 of that of aluminum alloys), the holding time needs to be shortened to 0.5~2 seconds, and the holding pressure is increased to 90% of the injection pressure to prevent shrinkage cavities.
Ferrous metal die-castings possess excellent mechanical properties and performance characteristics. Gray iron die-castings can achieve a tensile strength of 250-350 MPa and a hardness of 200-250 HBW. They also possess excellent wear resistance and shock absorption, making them suitable for manufacturing parts such as machine tool beds and engine blocks. Ductile iron die-castings, spheroidized by adding magnesium or cerium, increase their tensile strength to 400-600 MPa and elongation by 5%-15%. They can replace some forged steel parts, such as automotive rear axle housings and crane hooks. Compared to sand casting, ferrous metal die-castings offer higher dimensional accuracy (IT8-IT10), surface roughness Ra 3.2-6.3 μm, over 50% reduction in machining allowance, and a 3-5-fold increase in production efficiency. Furthermore, die-castings feature a dense microstructure, uniform graphite distribution, and the absence of pinholes and porosity, extending fatigue life by 20%-30%.
The application of ferrous metal die-casting is gradually expanding, primarily in areas requiring high strength and wear resistance. In the machine tool industry, the spindle housing of a grinding machine is made of gray cast iron die-casting, which is 20% lighter than welded structures, reduces vibration amplitude by 15%, and improves machining precision by a level. In the construction machinery sector, the hydraulic pump housing of an excavator is die-cast from ductile iron, capable of withstanding an operating pressure of 30 MPa and boasting a service life 1.5 times that of a cast part. In the automotive industry, commercial vehicle brake drums are integrally formed using ferrous metal die-casting, achieving wall thickness uniformity within ±0.5 mm, increasing heat dissipation efficiency by 10%, and significantly improving braking stability. Although the equipment investment for ferrous metal die-casting is high (two to three times that of aluminum alloy die-casting machines), the overall cost is 15% to 20% lower than sand casting for large-scale production (over 100,000 units per year). In the future, with advances in mold materials and process optimization, ferrous metal die-casting will expand into larger sizes (such as wind turbine equipment bases) and higher precision (such as precision gears), further replacing traditional casting and forging processes.
