Properties of gray cast iron

Casting performance: it refers to some technological properties of whether the metal or alloy is suitable for casting, mainly including fluidity, mold filling capacity, shrinkage (capacity of volume shrinkage during casting solidification), uneven chemical composition (segregation), gettering (ability to absorb gas during melting and pouring), etc. Because the chemical composition of gray cast iron is close to the eutectic point, the molten iron has good fluidity and can cast very complex castings. In addition, due to the large specific volume of graphite, the shrinkage of the casting during solidification is reduced, which can simplify the process, reduce the stress of the casting and obtain a dense structure.

Notch sensitivity: it refers to the reduction of nominal “strength” of metal materials (now also including plastic alloys and polymer materials such as PBT and PBT / PC alloys) due to local stress concentration caused by notches (sharp changes in sections such as notches, sharp corners, grooves and cross holes); The “strength” mentioned here can be tensile strength, flexural strength, impact toughness or fatigue strength. The existence of graphite in gray cast iron splits the continuity of metal matrix, which is equivalent to a large number of small gaps in the matrix. Therefore, compared with carbon steel with the same metal matrix, gray cast iron has low sensitivity to surface gaps. However, the existence of graphite makes the tensile strength and fatigue strength of gray cast iron lower than that of carbon steel.

Cutting performance: the degree of difficulty in cutting metal materials is called cutting performance. The cutting performance of metal materials is generally determined by the surface roughness of the material after cutting and the remaining life of the tool. The difficulty of material cutting mainly depends on the chemical composition, microstructure, hardness, plasticity and so on. Because the graphite in gray cast iron has the function of chip breaking, and the graphite in gray cast iron also has the function of lubrication and drag reduction for cutting tools, gray cast iron has better cutting performance than carbon steel.

Mechanical properties: the tensile strength, plasticity, toughness and elastic modulus of gray cast iron are lower than those of carbon steel, but the compressive strength of gray cast iron is three or four times higher than that of tensile strength. Therefore, instead of using gray cast iron as tensile parts, it is better to do pressure parts, which is why gray cast iron is widely used as pressure parts of machine tool bed and pillar.