Experiences and Techniques for Cleaning the Cold-Keeping Phenomenon in Ductile Iron Castings

Ductile iron castings require a flat and smooth surface. Today, we’ll discuss the requirements our foundry has for ductile iron castings.

For ductile iron parts, we must first familiarize ourselves with the tools used for repairing—such as sandpaper, brushes, spray paint, or bucket paint. When selecting paint, be sure to choose either rust-proof paint or polyester topcoat, and ensure that the ductile iron parts are brushed at least twice as often. Additionally, any rust spots on areas where corrosion has occurred must be thoroughly cleaned with sandpaper.

The painting stage using pigments must be applied evenly. Allow the paint to dry completely before applying another coat. During the final coating stage, use a polyurethane-based topcoat, ensuring the surface remains smooth and flawless.

If the ductile iron parts are severely aged, you should consider replacing them with new ones. To minimize paint chipping on ductile iron components, it’s important to pay attention to their maintenance and care—only then can you achieve better performance and longevity.

Experiences and Techniques for Cleaning Cold-Keeping Phenomena in Ductile Iron Castings

During the casting stage of ductile iron parts, the molten steel flowing toward the same target material from two different sources exhibits excellent fusion, resulting in indentations and rounded edges on the stainless steel castings. Much of this phenomenon is caused by the surface tension of the stainless steel castings. If you want to clean it, you should approach it from more angles.

When casting, it's important to improve control over the steel melt's texture, enhance its fluidity, and then optimize the casting temperature for maximum efficiency. Additionally, a carefully timed acceleration of the pouring process can also subtly influence the effectiveness of the cooling phase. During the setup stage, ensure thorough attention is paid to enhancing the permeability of the mold, as this will help minimize defects in ductile iron castings.

A strong brand helps our foundry thrive, but quality assurance is the standard that ensures our survival. Only by doing things right will more people come to appreciate and recognize you. Henan Chemical Machinery Manufacturing Co., Ltd. specializes in producing a wide range of large-scale castings, pressure vessels, carbonization towers, chemical pumps and valves—and we guarantee quality every step of the way. You’ll get exceptional value for your money, making our products truly worth every penny.

Heat Treatment of Ductile Iron

Ductile iron has minimal splitting action on the matrix, so its mechanical properties primarily depend on the matrix structure. Consequently, heat treatment can significantly enhance the mechanical performance of ductile iron.

① Annealing

Stress-relief annealing: The casting stress in ductile iron is approximately twice that of gray iron. For ductile iron parts that will no longer undergo additional heat treatment, stress-relief annealing is essential. The purpose of graphitizing annealing is to decompose the free cementite present in the as-cast microstructure and the eutectoid cementite within the pearlite, resulting in ductile iron with a high-ductility ferrite matrix. This process also helps eliminate casting stresses, thereby enhancing the material's mechanical properties and machinability.

② Normalization

The purpose of normalizing is to obtain a matrix microstructure dominated by pearlite, refine the grain size of stainless steel strips, and enhance the strength, hardness, and wear resistance of ductile iron. Normalizing can be divided into high-temperature normalizing and low-temperature normalizing. For high-temperature normalizing, especially in the case of thick-walled castings, air cooling or even spray quenching should be employed to ensure the formation of pearlitic ductile iron. Low-temperature normalizing involves heating the casting to 840–860°C, holding it for 1–4 hours, and then allowing it to cool naturally in the furnace, resulting in a pearlitic-ferritic matrix in the ductile iron.