What are the advantages of gray iron castings?

What are the advantages of gray iron castings?

Casting gray iron castings offers numerous benefits, primarily in the following areas. Gray iron castings include items such as cast iron flat plates, machine tool castings, ground rails, and machine tool worktables. So, what are the advantages of gray iron castings?

What are the advantages of gray iron castings?

1. High dimensional accuracy and minimal machining waste are achieved through ceramic precision casting for manufacturing both metal and gray iron castings. The machining waste for each part can be as follows: 0.4 mm for cavity surfaces; 1.5 mm for typeface surfaces of lead type, and 3 mm for the main typeface surface.

2. The performance remains consistent in every direction—during forging or rolling, the deformation and elongation of non-metallic inclusions lead to varying mechanical properties across different directions, a phenomenon known as "anisotropy." However, gray cast iron exhibits uniform properties in all directions, which is why it offers numerous advantages.

3. High-temperature hardness tests comparing H-13 die steel produced by segmented rolling versus casting at the Steel Company show that, at the same hardness level, cast steel exhibits slightly lower hardness than forged steel when the working temperature is below 200°C; however, above 200°C, cast steel demonstrates higher hardness compared to forged steel.

4. Notably, as the temperature rises, the advantage of high-temperature hardness becomes even more pronounced. At 650°C, the hardness value of cast steel is 8 HRC higher than that of forgings. Moreover, when gray cast iron castings undergo precision molding, the machining allowance within the casting cavity is minimal, allowing the fine-grained microstructure on the gem surface to exhibit excellent wear resistance.

What are the functions and applications of gray iron castings?

1. The excellent casting properties of gray cast iron—specifically its strength and hardness—are primarily determined by its microstructure. Typically, the electrical resistivity of gray cast iron is three to four times higher than its tensile strength, which is a characteristic feature of this material. However, compared to carbon steel, gray cast iron exhibits lower tensile strength, ductility, toughness, and elastic modulus, as shown in the table. For this reason, gray cast iron is often used for LED components that require high compressive resistance. This is also why the vehicle underbody panels and pillars are widely employed as load-bearing structural supports.

2. The mechanical properties of gray cast iron are enhanced by its relatively large graphite content, which helps reduce shrinkage during casting. This, in turn, simplifies the manufacturing process, minimizes casting stresses, and enables the formation of a dense microstructure. Moreover, since gray cast iron’s chemical composition closely matches its eutectic point, molten iron can be used to cast even highly complex parts with remarkable precision.

3. Lower gap sensitivity and excellent machinability: Since the graphite present in gray cast iron effectively creates numerous tiny gaps, surface defects and gaps become nearly imperceptible. As a result, surface flaws have minimal impact on the fatigue strength of cast iron, though its fatigue strength still remains lower than that of steel. Moreover, the graphite in cast iron acts as both a flake-like material and a natural lubricant, contributing to its superior machinability.

4. Excellent wear resistance and impact strength—graphite itself possesses lubricating properties. When dropped, graphite can effectively adsorb and retain lubricants, imparting superior wear resistance to the castings. Moreover, the presence of highly hard, common crystalline structures within the castings further enhances their wear resistance, making this feature particularly significant for manufacturing piston rings and cylinder liners. Graphite also helps prevent the diffusion of subsequent moving parts. Notably, gray cast iron exhibits a wear resistance 10 times greater than that of steel, making it a popular choice for producing machine bedplates and ironing boards subjected to vibrational stresses.