What are the types of iron castings and the role of iron castings

Cast iron is one of the oldest ferrous metals in commercial use. It consists primarily of iron (Fe), carbon (C) and silicon (Si), but may also contain traces of sulfur (S), manganese (Mn) and phosphorus (P). It has a relatively high carbon content of 2% to 5%. It is generally brittle and non-ductile (that is, it cannot be bent, stretched, or hammered into shape) and relatively weak in tension.

Cast iron components break easily with little deformation. However, cast iron has excellent compressive strength and is often used in structures that require this property. The composition, method of manufacture and heat treatment of cast iron are critical in determining its final properties.

In order to achieve the optimum casting for a particular application that meets the component requirements, it is necessary to understand the various types of cast iron. The generic name cast iron has no meaning unless the part is distinguished from steel castings. Therefore, more specific designations should be made.

According to composition and metallographic structure, cast iron can be divided into five categories:

grey cast iron,

ductile iron,

white cast iron,

malleable cast iron,

compacted graphite cast iron,

alloy cast iron.

The composition of cast iron varies significantly depending on the grade of pig iron used in its manufacture. It is controlled to produce various grades with significantly different mechanical properties and weldability.

Due to the relatively high silicon content of cast iron, cast iron itself resists oxidation and corrosion by forming tightly adherent oxides and scales, thereby minimizing further erosion. Iron castings are used in applications where this resistance provides a relatively long service life.

Heat resistance, oxidation resistance and corrosion resistance are significantly enhanced

Use alloy iron. However, since cast iron contains more than 2% carbon, 1%~3% silicon and up to 1% manganese, its weldability is poor. Because cast irons are relatively cheap, easy to cast into complex shapes, and easy to machine, they are an important group of materials.

Unfortunately, most grades are not weldable, and even so-called weldable grades usually require special precautions. One of the reasons for the widespread use of iron castings is their high performance-to-cost ratio.

This high value stems from a number of factors, one of which is the control of the microstructure and properties that can be achieved in the as-cast condition, allowing the production of high proportions of ferritic and pearlitic iron castings without the additional cost of heat treatment. However, producing high-quality castings requires the use of consistent charge materials and consistent and efficient practices for melting, holding, handling, inoculating and cooling in the mold.

Heat treatment is a valuable and versatile tool that extends the consistency and performance range of iron castings beyond the limits of iron castings produced in the as-cast condition. Cast iron has been used in many industrial applications such as the water industry for over 150 years. 

Therefore, in the past a large part of water transmission and distribution pipes were mainly made of cast iron, but with the introduction of new materials, cast iron pipes were gradually phased out. Buried cast iron pipelines deteriorate during service due to the various aggressive environments surrounding the pipeline. 

Cast iron piping deteriorates at different rates depending on a number of factors, including the type of cast iron material, local geology, and operating conditions. 

However, the corrosion rate of buried pipelines is known to decrease over time. This is mainly due to the formation of graphite-containing corrosion products that tightly adhere to the unaffected metal substrate, providing a barrier and limiting the rate at which further corrosion attack can occur.